IPCS INCHEM Home




    INTERNATIONAL PROGRAMME ON CHEMICAL SAFETY

    WORLD HEALTH ORGANIZATION





    SAFETY EVALUATION OF CERTAIN FOOD
    ADDITIVES AND CONTAMINANTS



    WHO FOOD ADDITIVES SERIES: 44





    Prepared by the Fifty-third meeting of the Joint FAO/WHO
    Expert Committee on Food Additives (JECFA)





    World Health Organization, Geneva, 2000
    IPCS - International Programme on Chemical Safety


    SIMPLE ALIPHATIC AND AROMATIC SULFIDES AND THIOLS

    First draft prepared by Dr A. Mattia1 and Professor A.G. Renwick2

    1Division of Product Policy, Office of Premarket Approval, Center for
    Food Safety and Applied Nutrition, US Food and Drug Administration,
    Washington DC, United States; 2Clinical Pharmacology Group,
    University of Southampton, Southampton, United Kingdom

    Evaluation
         Introduction
         Estimated daily intake
         Metabolic considerations
         Application of the Procedure for the Safety Evaluation of 
         Flavouring Agents
         Consideration of combined intakes
         Conclusions
    Relevant background information
         Explanation
         Additional considerations on intake
         Biological data
              Absorption, distribution, metabolism, and excretion
                   Simple sulfides (thioethers)
                   Acyclic sulfides with oxidized side-chains
                   Cyclic sulfides
                   Simple thiols
                   Thiols with oxidized side-chains
                   Dithiols
                   Simple disulfides
                   Disulfides with oxidized side-chains
                   Trisulfides
                   Heterocyclic disulfides
                   Thioesters
                   Sulfoxides
              Toxicological studies
                   Acute toxicity
                   Short-term studies of toxicity
                   Ninety-day studies of toxicity
                   Long-term studies of toxicity and carcinogenicity
                   Genotoxicity
                   Developmental toxicity
                   Chemoprevention
              Observations in humans
    References

    1.  EVALUATION

    1.1  Introduction

         The Committee evaluated a group of 137 flavouring agents that
    includes aliphatic and aromatic sulfides and thiols, with and without
    an additional oxygenated functional group (see Table 1), using the
    Procedure for the Safety Assessment of Flavouring Agents (Figure 1, p.
    122). The Committee has not previously evaluated any member of the
    group.

    1.2  Estimated daily intake

         The total annual volume of the 137 sulfides and thiols in this
    group is approximately 6000 kg in Europe and 5300 kg in the United
    States. Approximately 51% and 52%, respectively, of the total annual
    volume in Europe and in the United States is accounted for by methyl
    sulfide (No. 452). The estimated daily intake, modified for use to
    calculate the intake of flavouring agents and for 'eaters only' (see
    introduction to this section), of methyl sulfide is 10 g/kg bw in
    Europe and 9 g/kg bw in the United States; the intake of the
    remaining substances in this group is lower. The estimated modified
    daily intake of methyl 3-methylthiopropionate (No. 472) in Europe and
    of bis(methylthio)methane (No. 533) in the United States is 2 g/kg
    bw. The estimated modified intake of four substances in Europe,
    3(methylthio)propional-dehyde (No. 466), ethyl 3-methyl-thiopropionate
    (No. 476), methyl mercaptan (No. 508), and allyl disulfide (No. 572),
    and two substances in the United States, benzenethiol (No. 525) and
    3-methyl-1,2,4-trithiane (No. 574), is estimated to be 0.0003-0.2
    g/kg bw per day. The values for the intake of each substance in the
    group in Europe and in the United States are reported in Table 1.

         Sulfides and thiols have been detected in a variety of foods,
    including onion, garlic, beer, cabbage, tea, and coffee. Of the
    substances in this group, 106 have been reported to occur naturally in
    foods. Quantitative data on the natural occurrence of 19 substances in
    the group demonstrate that they are consumed predominantly from
    traditional foods, with the exception of methyl 3-methylthiopropionate
    (No. 472) and ethyl 3-methylthiopropionate (No. 476).

         One-hundred-and-six of the 137 sulfur-containing substances in
    this group of flavours have been detected as natural components of
    traditional foods (Maarse et al., 1994; see Table 2). Quantitative
    data on the natural occurrence of 19 of these substances have been
    reported which indicate that the intake of 17 of them is predominantly
    from food (i.e. a consumption ratio >1; Stofberg & Kirschman, 1985;
    Stofberg & Grundschober, 1987). The exceptions are methyl
    3-methylthiopropionate (No. 472) (consumption ratio = 0.0006 in Europe
    and 0.1 in the United States) and ethyl 3-methylthiopropionate (No.
    476) (consumption ratio = 0.05 in Europe and 1 in the United States)
    suggesting that the intake of these two substances is greater from
    their use as flavours than from their consumption in food.

    1.3  Metabolic considerations

         The large group of 137 flavouring agents considered at this
    meeting was divided into 12 subgroups on the basis of the position of
    the sulfur atom, to facilitate the assessment of their metabolism and
    the data on toxicity. The subgroups are:

    (i)       simple sulfides (thioethers), in which the sulfur is located
              between two unoxidized alkyl or aryl side-chains (Nos
              452-455, 457-460, and 533);

    (ii)      acyclic sulfides with oxidized side-chains, in which an
              alcohol, aldehyde, ketone, ester, carboxylic acid, or phenol
              group is present (Nos 461-463, 465-481, 495-497, 500-503,
              and 505);

    (iii)     cyclic sulfides (Nos 456, 464, 498, 499, 534, 543, 550, and
              562);

    (iv)      simple thiols with unoxidized aliphatic or aromatic
              side-chains (Nos 508-531);

    (v)       thiols with oxidized side chains, in which an alcohol,
              aldehyde, ketone, ester, or carboxylic acid group is present
              (Nos 544-549, 551-561, and 563);

    (vi)      dithiols (Nos 532 and 535-542);

    (vii)     simple disulfides (Nos 564-572 and 575-579);

    (viii)    disulfides with oxidized side chains (Nos 580 and 581);

    (ix)      trisulfides and polysulfides (Nos 582-588);

    (x)       heterocyclic disulfides (Nos 573 and 574);

    (xi)      thioesters (Nos 482-494, 504, and 506a and b); and

    (xii)     sulfoxides (No. 507).

         All of the sulfur substances considered are of low relative
    molecular mass and are sufficiently lipophilic to be absorbed from the
    intestine. These flavouring agents would be metabolized through many
    different pathways. As metabolism would usually result in increased
    polarity and greater likelihood of excretion, they would not be
    expected to accumulate in the body. Many substances, such as thiols
    and disulfides, would be able to form disulfide bonds with endogenous
    thiols. Disulfides formed with cysteine could be excreted in the urine
    as the xenobiotic cysteine disulfide, whereas formation of disulfides
    with endogenous macromolecules would delay elimination and could
    result in effects such as enzyme inhibition.


        Table 1. Summary of results of safety evaluations of aliphatic and aromatic sulfides and thiols
                                                                                                                                               

    Substance                         JECFA  CAS No.      Step B3     Step B4. Adequate                         Step B5       Conclusion
    and structure                     No.                 Does        margin of safety                          Does intake   based on
                                                          intake      for substance or                          exceed        current
                                                          exceed      related substance?                        1.5 g/day?   intake
                                                          threshold
                                                          for human
                                                          intake?
                                                                                                                                               

    Subgroup (i): Simple sulfides (thioethers)
    Structural class I

    Methyl sulfide                    452    75-18-3      No          Yes. A NOEL of 250                        N/R           No safety
                                                                      mg/kg bw per day was                                    concern
                                                                      reported in a 14-week 
                                                                      study in rats treated 
                                                                      with methyl sulfide at
                                                                      multiple doses.
    CHEMICAL STRUCTURE 1

    Methyl ethyl                      453    624-89-5     No          Yes. A NOEL of 250 mg/kg bw               N/R           No safety
    sulfide                                                           per day was reported in                                 concern
                                                                      a 14-week study in rats 
                                                                      treated with methyl sulfide
                                                                      at multiple doses.
    CHEMICAL STRUCTURE 2

    Diethyl sulfide                   454    352-93-2     No          Yes. A NOEL of 250 mg/kg bw               N/R           No safety 
                                                                      per day was reported in a                               concern
                                                                      14-week study in rats treated
                                                                      with methyl sulfide at multiple
                                                                      doses.
    CHEMICAL STRUCTURE 3

    Table 1. (continued)
                                                                                                                                               

    Substance                         JECFA  CAS No.      Step B3     Step B4. Adequate                         Step B5       Conclusion
    and structure                     No.                 Does        margin of safety                          Does intake   based on
                                                          intake      for substance or                          exceed        current
                                                          exceed      related substance?                        1.5 g/day?   intake
                                                          threshold
                                                          for human
                                                          intake?
                                                                                                                                               
    Butyl sulfide                     455    544-40-1     No          Yes. A NOEL of 250 mg/kg bw per           N/R           No safety
                                                                      day was reported in a 14-week                           concern
                                                                      study in rats treated with 
                                                                      methyl sulfide at multiple doses.
    CHEMICAL STRUCTURE 4

    (1-Butenyl-1)                     457    32951-19-2   No          Yes. A NOEL of 250 mg/kg bw per           N/R           No safety
    methyl sulfide                                                    day was reported in a 14-week                           concern
                                                                      study in rats treated with methyl
                                                                      sulfide at multiple doses.
    CHEMICAL STRUCTURE 5

    Bis(methylthio)methane            533    1618-26-4    No          Yes. A NOEL of 250 mg/kg bw per           N/R           No safety 
                                                                      day was reported in a 14-week                           concern
                                                                      study in rats treated with methyl
                                                                      sulfide (No. 452) at multiple
                                                                      doses
    CHEMICAL STRUCTURE 6

    Table 1. (continued)
                                                                                                                                               

    Substance                         JECFA  CAS No.      Step B3     Step B4. Adequate                         Step B5       Conclusion
    and structure                     No.                 Does        margin of safety                          Does intake   based on
                                                          intake      for substance or                          exceed        current
                                                          exceed      related substance?                        1.5 g/day?   intake
                                                          threshold
                                                          for human
                                                          intake?
                                                                                                                                               
    Structural class II

    Allyl sulfide                     458    592-88-1     No          No. Allyl mercaptan is not predicted      Yes           No safety
                                                                      to be a metabolite of allyl sufide.                     concern
    CHEMICAL STRUCTURE 7

    Methyl phenyl sulfide             459    100-68-5     No          No                                        Yes           No safety
                                                                                                                              concern
    CHEMICAL STRUCTURE 8

    Benzyl methyl sulfide             460    766-92-7     No          No                                        Yes           No safety
                                                                                                                              concern
    CHEMICAL STRUCTURE 9

    Table 1. (continued)
                                                                                                                                               

    Substance                         JECFA  CAS No.      Step B3     Step B4. Adequate                         Step B5       Conclusion
    and structure                     No.                 Does        margin of safety                          Does intake   based on
                                                          intake      for substance or                          exceed        current
                                                          exceed      related substance?                        1.5 g/day?   intake
                                                          threshold
                                                          for human
                                                          intake?
                                                                                                                                               
    Subgroup (ii): Acyclic sulfides with oxidized side-chains

    Structural class I

    3-(Methylthio)propanol            461    505-10-2     No          Yes. A NOEL of 1.4 mg/kg bw per           N/R           No safety
                                                                      day was reported in a 90-day syudy                      concern
                                                                      in rats given
                                                                      2-(methylthiomethyl)-3-phenyl-propenal
                                                                      (No. 505) only at that dose. Data
                                                                      for methyl sulfide (No. 452) are
                                                                      relevant to compounds with a simple
                                                                      oxidized side-chain.
    CHEMICAL STRUCTURE 10

    4-(Methylthio)butanol             462    999999-26-9  No          Yes. A NOEL of 1.4 mg/kg bw was           N/R           No safety
                                                                      in a reported 90-day syudy                              concern
                                                                      in rats given
                                                                      2-(methylthiomethyl)-3-phenyl-propenal
                                                                      (No. 505) only at that dose. Data for 
                                                                      methyl sulfide (No. 452) are relevant
                                                                      to compounds with a simple oxidized
                                                                      side-chain.
    CHEMICAL STRUCTURE 11

    Table 1. (continued)
                                                                                                                                               

    Substance                         JECFA  CAS No.      Step B3     Step B4. Adequate                         Step B5       Conclusion
    and structure                     No.                 Does        margin of safety                          Does intake   based on
                                                          intake      for substance or                          exceed        current
                                                          exceed      related substance?                        1.5 g/day?   intake
                                                          threshold
                                                          for human
                                                          intake?
                                                                                                                                               
    3-(Methylthio)-1-hexanol          463    51755-66-9   No          Yes. A NOEL of 1.4 mg/kg bw was reported  N/R           No safety
                                                                      in a 90-day syudy in rats given                         concern
                                                                      2-(methylthiomethyl)-3-phenyl-propenal
                                                                      (No. 505) only at that dose.
                                                                      Data for methyl sulfide (No. 452) are
                                                                      relevant to compounds with a simple
                                                                      oxidized side-chain.
    CHEMICAL STRUCTURE 12

    2-Methylthioacetaldehyde          465    23328-62-3   No          Yes. A NOEL of 1.4 mg/kg bw was reported  N/R           No safety 
                                                                      in a 90-day syudy in rats given                         concern
                                                                      2-(methylthiomethyl)-3-phenyl-propenal
                                                                      (No. 505) only at that dose.
                                                                      Data for methyl sulfide (No. 452) are
                                                                      relevant to compounds with a simple
                                                                      oxidized side-chain.
    CHEMICAL STRUCTURE 13

    Table 1. (continued)
                                                                                                                                               

    Substance                         JECFA  CAS No.      Step B3     Step B4. Adequate                         Step B5       Conclusion
    and structure                     No.                 Does        margin of safety                          Does intake   based on
                                                          intake      for substance or                          exceed        current
                                                          exceed      related substance?                        1.5 g/day?   intake
                                                          threshold
                                                          for human
                                                          intake?
                                                                                                                                               

    3-(Methylthio)                    466    3268-49-3    No          Yes. A NOEL of 1.4 mg/kg bw per day was   N/R           No safety 
    propionaldehyde                                                   reported in a 90-day study in rats                      concern
                                                                      treated with
                                                                      2-(methylthiomethyl)-3-phenylpropenal
                                                                      (No. 505) only at that dose. Data for
                                                                      methyl sulfide (No. 452) are relevant 
                                                                      to compounds with a simple oxidized
                                                                      side-chain.
    CHEMICAL STRUCTURE 14

    3-(Methylthio)butanal             467    16630-52-7   No          Yes. A NOEL of 1.4 mg/kg bw per day was   N/R           No safety
                                                                      reported in a 90-day study in rats                      concern
                                                                      treated with
                                                                      2-(methylthiomethyl)-3-phenylpropenal
                                                                      (No. 505) only at that dose. Data for
                                                                      methyl sulfide (No. 452) are relevant
                                                                      to compounds with a simple oxidized
                                                                      side-chain.
    CHEMICAL STRUCTURE 15

    Table 1. (continued)
                                                                                                                                               

    Substance                         JECFA  CAS No.      Step B3     Step B4. Adequate                         Step B5       Conclusion
    and structure                     No.                 Does        margin of safety                          Does intake   based on
                                                          intake      for substance or                          exceed        current
                                                          exceed      related substance?                        1.5 g/day?   intake
                                                          threshold
                                                          for human
                                                          intake?
                                                                                                                                               

    4-(Methylthio)butanal             468    42919-64-2   No          Yes. A NOEL of 1.4 mg/kg bw per day       N/R           No safety
                                                                      was reported in a 90-day study in rats                  concern
                                                                      treated with 
                                                                      2-(methylthiomethyl)-3-phenylpropenal
                                                                      (No. 505) only at that dose. Data for
                                                                      methyl sulfide (No. 452) are relevant
                                                                      to compounds with a simple oxidized
                                                                      side-chain.
    CHEMICAL STRUCTURE 16

    3-Methylthiohexanal               469    38433-74-8   No          Yes. A NOEL of 1.4 mg/kg bw per day       N/R           No safety 
                                                                      was reported in a 90-day study in rats                  concern
                                                                      treated with 
                                                                      2-(methylthiomethyl)-3-phenylpropenal
                                                                      (No. 505) only at that dose. Data for
                                                                      methyl sulfide (No. 452) are relevant
                                                                      to compounds with a simple oxidized
                                                                      side-chain.
    CHEMICAL STRUCTURE 17

    Table 1. (continued)
                                                                                                                                               

    Substance                         JECFA  CAS No.      Step B3     Step B4. Adequate                         Step B5       Conclusion
    and structure                     No.                 Does        margin of safety                          Does intake   based on
                                                          intake      for substance or                          exceed        current
                                                          exceed      related substance?                        1.5 g/day?   intake
                                                          threshold
                                                          for human
                                                          intake?
                                                                                                                                               

    2-(Methylthio)                    470    40878-72-6   No          No                                        No            No safety 
    methyl-2-butenal                                                                                                          concern

    CHEMICAL STRUCTURE 18

    2,8-Dithianon-4-ene-4-carbox-     471    59902-01-1   No          No                                        No            No safety
    aldehyde                                                                                                                  concern

    CHEMICAL STRUCTURE 19

    Table 1. (continued)
                                                                                                                                               

    Substance                         JECFA  CAS No.      Step B3     Step B4. Adequate                         Step B5       Conclusion
    and structure                     No.                 Does        margin of safety                          Does intake   based on
                                                          intake      for substance or                          exceed        current
                                                          exceed      related substance?                        1.5 g/day?   intake
                                                          threshold
                                                          for human
                                                          intake?
                                                                                                                                               

    Methyl 3-methylthiopropionate     472    13532-18-8   No          Yes. A NOEL of 1.4 mg/kg bw per day       N/R           No safety
                                                                      was reported in a 90-day study in                       concern
                                                                      rats treated with 
                                                                      2-(methylthiomethyl)-3-phenylpropenal
                                                                      (No. 505) only at that dose. Data for
                                                                      methyl sulfide (No. 452) are relevant
                                                                      to compounds with a simple oxidized 
                                                                      side-chain. The simple side-chain acid
                                                                      and ester would be predicted to be of
                                                                      low toxicity.
    CHEMICAL STRUCTURE 20

    Table 1. (continued)
                                                                                                                                               

    Substance                         JECFA  CAS No.      Step B3     Step B4. Adequate                         Step B5       Conclusion
    and structure                     No.                 Does        margin of safety                          Does intake   based on
                                                          intake      for substance or                          exceed        current
                                                          exceed      related substance?                        1.5 g/day?   intake
                                                          threshold
                                                          for human
                                                          intake?
                                                                                                                                               
    Methylthiomethyl butyrate         473    74758-93-3   No          Yes. A NOEL of 1.4 mg/kg bw per day       N/R           No safety
                                                                      was reported in a 90-day study in                       concern
                                                                      rats treated with 
                                                                      2-(methylthiomethyl)-3-phenylpropenal
                                                                      (No. 505) only at that dose. Data for
                                                                      methyl sulfide (No. 452) are relevant
                                                                      to compounds with a simple oxidized
                                                                      side-chain.
    CHEMICAL STRUCTURE 21

    Methyl 4-(methylthio)butyrate     474    53053-51-3   No          Yes. A NOEL of 1.4 mg/kg bw per day       N/R           No safety 
                                                                      was reported in a 90-day study in rats                  concern
                                                                      treated with 
                                                                      2-(methylthiomethyl)-3-phenylpropenal 
                                                                      (No. 505) only at that dose. Data for 
                                                                      methyl sulfide (No. 452) are relevant 
                                                                      to compounds with a simple oxidized
                                                                      side-chain.
    CHEMICAL STRUCTURE 22

    Table 1. (continued)
                                                                                                                                               

    Substance                         JECFA  CAS No.      Step B3     Step B4. Adequate                         Step B5       Conclusion
    and structure                     No.                 Does        margin of safety                          Does intake   based on
                                                          intake      for substance or                          exceed        current
                                                          exceed      related substance?                        1.5 g/day?   intake
                                                          threshold
                                                          for human
                                                          intake?
                                                                                                                                               
    Ethyl 2-(methylthio)acetate       475    4455-13-4    No          Yes. A NOEL of 1.4 mg/kg bw per day       N/R           No safety 
                                                                      was reported in a 90-day study in                       concern
                                                                      rats treated with 
                                                                      2-(methylthiomethyl)-3-phenylpropenal 
                                                                      (No. 505) only at that dose. Data for
                                                                      methyl sulfide (No. 452) are relevant 
                                                                      to compounds with a simple oxidized
                                                                      side-chain.
    CHEMICAL STRUCTURE 23

    Ethyl 3-methylthiopropionate      476    133327-56-5  No          Yes. A NOEL of 1.4 mg/kg bw per day       N/R           No safety 
                                                                      was reported in a 90-day study in                       concern
                                                                      rats treated with 
                                                                      2-(methylthiomethyl)-3-phenylpropenal 
                                                                      (No. 505) only at that dose. Data for 
                                                                      methyl sulfide (No. 452) are relevant 
                                                                      to compounds with a simple oxidized
                                                                      side-chain.
    CHEMICAL STRUCTURE 24

    Table 1. (continued)
                                                                                                                                               

    Substance                         JECFA  CAS No.      Step B3     Step B4. Adequate                         Step B5       Conclusion
    and structure                     No.                 Does        margin of safety                          Does intake   based on
                                                          intake      for substance or                          exceed        current
                                                          exceed      related substance?                        1.5 g/day?   intake
                                                          threshold
                                                          for human
                                                          intake?
                                                                                                                                               
    Ethyl 4-(methylthio)butyrate      477    22014-48-8   No          Yes. A NOEL of 1.4 mg/kg bw per day       N/R           No safety 
                                                                      was reported in a 90-day study in                       concern
                                                                      rats treated with 
                                                                      2-(methylthiomethyl)-3-phenylpropenal 
                                                                      (No. 505) only at that dose. Data for 
                                                                      methyl sulfide (No. 452) are relevant 
                                                                      to compounds with a simple oxidized
                                                                      side-chain.
    CHEMICAL STRUCTURE 25

    3-(Methylthio)propyl acetate      478    16630-55-0   No          Yes. A NOEL of 1.4 mg/kg bw per day       N/R           No safety 
                                                                      was reported in a 90-day study in                       concern
                                                                      rats treated with 
                                                                      2-(methylthiomethyl)-3-phenylpropenal
                                                                      (No. 505) only at that dose. Data
                                                                      for methyl sulfide (No. 452) are
                                                                      relevant to compounds with a simple
                                                                      oxidized side-chain.
    CHEMICAL STRUCTURE 26

    Table 1. (continued)
                                                                                                                                               

    Substance                         JECFA  CAS No.      Step B3     Step B4. Adequate                         Step B5       Conclusion
    and structure                     No.                 Does        margin of safety                          Does intake   based on
                                                          intake      for substance or                          exceed        current
                                                          exceed      related substance?                        1.5 g/day?   intake
                                                          threshold
                                                          for human
                                                          intake?
                                                                                                                                               
    Methylthiomethyl hexanoate        479    74758-91-1   No          Yes. A NOEL of 1.4 mg/kg bw per day       N/R           No safety 
                                                                      was reported in a 90-day study in                       concern
                                                                      rats treated with 
                                                                      2-(methylthiomethyl)-3-phenylpropenal
                                                                      (No. 505) only at that dose. Data for
                                                                      methyl sulfide (No. 452) are relevant 
                                                                      to compounds with a simple oxidized
                                                                      side-chain.
    CHEMICAL STRUCTURE 27


    Ethyl 3-(methylthio)butyrate      480    Pending      No          Yes. A NOEL of 1.4 mg/kg bw per day       N/R           No safety 
                                                                      was reported in a 90-day syudy in                       concern
                                                                      rats treated with 
                                                                      2-(methylthiomethyl)-3-phenylpropenal
                                                                      (No. 505) only at that dose. Data for
                                                                      methyl sulfide (No. 452) are relevant
                                                                      to compounds with a simple oxidized
                                                                      side-chain.
    CHEMICAL STRUCTURE 28

    Table 1. (continued)
                                                                                                                                               

    Substance                         JECFA  CAS No.      Step B3     Step B4. Adequate                         Step B5       Conclusion
    and structure                     No.                 Does        margin of safety                          Does intake   based on
                                                          intake      for substance or                          exceed        current
                                                          exceed      related substance?                        1.5 g/day?   intake
                                                          threshold
                                                          for human
                                                          intake?
                                                                                                                                               
    3-(Methylthio)hexyl acetate       481    51755-85-2   No          Yes. A NOEL of 1.4 mg/kg bw per day       N/R           No safety 
                                                                      was reported in a 90-day study in                       concern
                                                                      rats treated with 
                                                                      2-(methylthiomethyl)-3-phenylpropenal
                                                                      (No. 505) only at that dose. Data for
                                                                      methyl sulfide (No. 452) are relevant
                                                                      to compounds with a simple oxidized
                                                                      side-chain.
    CHEMICAL STRUCTURE 29


    1-Methylthio-2-propanone          495    14109-72-9   No          Yes. A NOEL of 1.4 mg/kg bw per day       N/R           No safety 
                                                                      was reported in a 90-day study                          concern
                                                                      in rats given 
                                                                      2-(methylthiomethyl)-3-phenyl-propenal
                                                                      (No. 505) only at that dose. Data for
                                                                      methyl sulfide (No. 452) are relevant
                                                                      to compounds with a simple oxidized
                                                                      side-chain.
    CHEMICAL STRUCTURE 30

    Table 1. (continued)
                                                                                                                                               

    Substance                         JECFA  CAS No.      Step B3     Step B4. Adequate                         Step B5       Conclusion
    and structure                     No.                 Does        margin of safety                          Does intake   based on
                                                          intake      for substance or                          exceed        current
                                                          exceed      related substance?                        1.5 g/day?   intake
                                                          threshold
                                                          for human
                                                          intake?
                                                                                                                                               
    1-(Methylthio)-2-butanone         496    13678-58-5   No          Yes. A NOEL of 1.4 mg/kg bw per day       N/R           No safety 
                                                                      was reported in a 90-day study in                       concern
                                                                      rats treated with 
                                                                      2-(methylthiomethyl)-3-phenylpropenal 
                                                                      (No. 505) only at that dose. Data for 
                                                                      methyl sulfide (No. 452) are relevant 
                                                                      to compounds with a simple oxidized
                                                                      side-chain.
    CHEMICAL STRUCTURE 31

    4-(Methylthio)-2-butanone         497    34047-39-7   No          Yes. A NOEL of 1.4 mg/kg bw per day       N/R           No safety 
                                                                      was reported in a 90-day study in                       concern
                                                                      rats treated with 
                                                                      2-(methylthiomethyl)-3-phenylpropenal 
                                                                      (No. 505) only at that dose. Data for
                                                                      methyl sulfide (No. 452) are relevant
                                                                      to compounds with a simple oxidized
                                                                      side-chain.
    CHEMICAL STRUCTURE 32

    Table 1. (continued)
                                                                                                                                               

    Substance                         JECFA  CAS No.      Step B3     Step B4. Adequate                         Step B5       Conclusion
    and structure                     No.                 Does        margin of safety                          Does intake   based on
                                                          intake      for substance or                          exceed        current
                                                          exceed      related substance?                        1.5 g/day?   intake
                                                          threshold
                                                          for human
                                                          intake?
                                                                                                                                               
    4-(Methylthio)-4-methyl-2-        500    23550-40-5   No          Yes. A NOEL of 1.4 mg/kg bw per day       N/R           No safety 
    pentanone                                                         was reported in a 90-day study in                       concern
                                                                      rats treated with 
                                                                      2-(methylthiomethyl)-3-phenylpropenal
                                                                      (No. 505) only at that dose. Data for
                                                                      methyl sulfide (No. 452) are relevant
                                                                      to compounds with a simple oxidized
                                                                      side-chain.
    CHEMICAL STRUCTURE 33

    Di(butan-3-one-1-yl) sulfide      502    40790-04-3   No          Yes. A NOEL of 1.4 mg/kg bw per day       N/R           No safety 
                                                                      was reported in a 90-day study in                       concern
                                                                      rats treated with 
                                                                      2-(methylthiomethyl)-3-phenylpropenal
                                                                      (No. 505) only at that dose. Data for
                                                                      methyl sulfide (No. 452) are relevant
                                                                      to compounds with a simple oxidized
                                                                      side-chain. 
    CHEMICAL STRUCTURE 34

    Table 1. (continued)
                                                                                                                                               

    Substance                         JECFA  CAS No.      Step B3     Step B4. Adequate                         Step B5       Conclusion
    and structure                     No.                 Does        margin of safety                          Does intake   based on
                                                          intake      for substance or                          exceed        current
                                                          exceed      related substance?                        1.5 g/day?   intake
                                                          threshold
                                                          for human
                                                          intake?
                                                                                                                                               
    Structural class II

    ortho-(Methylthio)phenol          503    1073-29-6    No          Yes. A NOEL of 1.4 mg/kg bw per day       N/R           No safety 
                                                                      was reported in a 90-day study in                       concern
                                                                      rats treated with 
                                                                      2-(methylthiomethyl)-3-phenylpropenal
                                                                      (No. 505) only at that dose. Data for 
                                                                      methyl sulfide (No. 452) are relevant
                                                                      to compounds with a simple oxidized
                                                                      side-chain.
    CHEMICAL STRUCTURE 35


    Table 1. (continued)
                                                                                                                                               

    Substance                         JECFA  CAS No.      Step B3     Step B4. Adequate                         Step B5       Conclusion
    and structure                     No.                 Does        margin of safety                          Does intake   based on
                                                          intake      for substance or                          exceed        current
                                                          exceed      related substance?                        1.5 g/day?   intake
                                                          threshold
                                                          for human
                                                          intake?
                                                                                                                                               
    Structural class III

    4-(Methylthio)-2-oxobutanoic      501    51828-97-8   No          Yes. A NOEL of 1.4 mg/kg bw per day       N/R           No safety
    acid, sodium salt                                                 was reported in a 90-day study in                       concern
                                                                      rats treated with 
                                                                      2-(methylthiomethyl)-3-phenylpropenal
                                                                      (No. 505) only at that dose. Data for
                                                                      methyl sulfide (No. 452) are relevant
                                                                      to compounds with a simple oxidized
                                                                      side-chain.
    CHEMICAL STRUCTURE 36

    2-(Methylthiomethyl)-3-phenyl     505    65887-08-3   No          Yes. A NOEL of 1.4 mg/kg bw per day       N/R           No safety
    - propenal                                                        was reported in a 90-day study in                       concern
                                                                      rats treated with this substance only
                                                                      at that dose. Data for methyl sulfide
                                                                      (No. 452) are relevant to compounds
                                                                      with a simple oxidized side-chain.
    CHEMICAL STRUCTURE 37

    Table 1. (continued)
                                                                                                                                               

    Substance                         JECFA  CAS No.      Step B3     Step B4. Adequate                         Step B5       Conclusion
    and structure                     No.                 Does        margin of safety                          Does intake   based on
                                                          intake      for substance or                          exceed        current
                                                          exceed      related substance?                        1.5 g/day?   intake
                                                          threshold
                                                          for human
                                                          intake?
                                                                                                                                               
    Subgroup (iii): Cyclic sulfides

    Structural class I

    2,5-Dimethyl-2,5-dihydroxy-1,4-   562    55704-78-4   No          Yes. A NOEL of 3.1 mg/kg bw per day       N/R           No safety 
    dithiane                                                          was reported in a 90-day study in rats                  concern
                                                                      treated with this substance only at
                                                                      that dose.
    CHEMICAL STRUCTURE 38

    2,5-Dihydroxy-1,4-dithiane        550    40018-26-6   No          Yes. A NOEL of 3.1 mg/kg bw per day       N/R           No safety 
                                                                      was reported in a 90-day study in                       concern
                                                                      rats treated with 
                                                                      2,5-dimethyl-2,5-dihydroxy-1,4-dithiane
                                                                      (No. 562) only at that dose.
    CHEMICAL STRUCTURE 39

    Table 1. (continued)
                                                                                                                                               

    Substance                         JECFA  CAS No.      Step B3     Step B4. Adequate                         Step B5       Conclusion
    and structure                     No.                 Does        margin of safety                          Does intake   based on
                                                          intake      for substance or                          exceed        current
                                                          exceed      related substance?                        1.5 g/day?   intake
                                                          threshold
                                                          for human
                                                          intake?
                                                                                                                                               
    Structural class II

    2-Methyl-4-propyl-1,3-oxathiane   464    67715-80-4   No          Yes. A NOEL of 0.44 mg/kg bw per day      N/R           No safety 
                                                                      was reported in a 90-day study in rats                  concern
                                                                      treated with this substance only at 
                                                                      that dose.
    CHEMICAL STRUCTURE 40

    4,5-Dihydro-3-(2H)-thiophenone    498    1003-04-9    No          Yes. A NOEL of 9.2 mg/kg bw per day       N/R           No safety 
                                                                      was reported in a 90-day study in rats                  concern
                                                                      treated with this substance only at
                                                                      that dose.
    CHEMICAL STRUCTURE 41

    Table 1. (continued)
                                                                                                                                               

    Substance                         JECFA  CAS No.      Step B3     Step B4. Adequate                         Step B5       Conclusion
    and structure                     No.                 Does        margin of safety                          Does intake   based on
                                                          intake      for substance or                          exceed        current
                                                          exceed      related substance?                        1.5 g/day?   intake
                                                          threshold
                                                          for human
                                                          intake?
                                                                                                                                               

    2-Methyltetrahydrothiophen-3-one  499    13679-85-1   No          Yes. A NOEL of 9.2 mg/kg bw per day       N/R           No safety 
                                                                      was reported in a 90-day study in                       concern
                                                                      rats treated with 
                                                                      4,5-dihydro-3-(2H)-thiophenone (No. 498)
                                                                      only at that dose.
    CHEMICAL STRUCTURE 42

    1,4-Dithiane                      456    505-29-3     No          Yes. NOELs of 0.44, 7, and 0.2 mg/kg      N/R           No safety 
                                                                      bw per day were reported in 90-day                      concern
                                                                      studies in rats treated with 
                                                                      2-methyl-4-propyl-1,3-oxathiane 
                                                                      (No. 464), 2-methyl-1,3-dithiolane
                                                                      (No. 534), and tri-thioacetone
                                                                      (No. 543), respectively, only at those
                                                                      doses.
    CHEMICAL STRUCTURE 43

    Table 1. (continued)
                                                                                                                                               

    Substance                         JECFA  CAS No.      Step B3     Step B4. Adequate                         Step B5       Conclusion
    and structure                     No.                 Does        margin of safety                          Does intake   based on
                                                          intake      for substance or                          exceed        current
                                                          exceed      related substance?                        1.5 g/day?   intake
                                                          threshold
                                                          for human
                                                          intake?
                                                                                                                                               

    2-Methyl-1,3-dithiolane           534    5616-51-3    No          Yes. A NOEL of 7 mg/kg bw per day         N/R           No safety
                                                                      was reported in a 90-day study in rats                  concern
                                                                      treated with this substance only at
                                                                      that dose.
    CHEMICAL STRUCTURE 44

    Trithioacetone                    543    828-26-2     No          Yes. A NOEL of 0.2 mg/kg bw per day       N/R           No safety
                                                                      was reported in a 90-day study in rats                  concern
                                                                      treated with this substance only at
                                                                      that dose.
    CHEMICAL STRUCTURE 45

    Subgroup (iv): Thiols

    Structural class I

    Methyl mercaptan                  508    74-93-1      No          Yes. A NOEL of 0.56 mg/kg bw per day      N/R           No safety 
                                                                      was reported in a 90-day study in rats                  concern
                                                                      treated with cyclopentanethiol 
                                                                      (No. 516) only at that dose.
    CHEMICAL STRUCTURE 46

    Table 1. (continued)
                                                                                                                                               

    Substance                         JECFA  CAS No.      Step B3     Step B4. Adequate                         Step B5       Conclusion
    and structure                     No.                 Does        margin of safety                          Does intake   based on
                                                          intake      for substance or                          exceed        current
                                                          exceed      related substance?                        1.5 g/day?   intake
                                                          threshold
                                                          for human
                                                          intake?
                                                                                                                                               
    Propanethiol                      509    107-03-9     No          Yes. A NOEL of 0.56 mg/kg bw per day      N/R           No safety 
                                                                      was reported in a 90-day study in rats                  concern
                                                                      treated with cyclopentanethiol
                                                                      (No. 516) only at that dose.
    CHEMICAL STRUCTURE 47

    2-Propanethiol                    510    75-33-2      No          Yes. A NOEL of 0.56 mg/kg bw per day      N/R           No safety 
                                                                      was reported in a 90-day study in rats                  concern
                                                                      treated with cyclopentanethiol 
                                                                      (No. 516) only at that dose.
    CHEMICAL STRUCTURE 48

    1-Butanethiol                     511    109-79-5     No          Yes. A NOEL of 0.56 mg/kg bw per day      N/R           No safety 
                                                                      was reported in a 90-day study in rats                  concern
                                                                      treated with cyclopentanethiol 
                                                                      (No. 516) only at that dose.
    CHEMICAL STRUCTURE 49

    Table 1. (continued)
                                                                                                                                               

    Substance                         JECFA  CAS No.      Step B3     Step B4. Adequate                         Step B5       Conclusion
    and structure                     No.                 Does        margin of safety                          Does intake   based on
                                                          intake      for substance or                          exceed        current
                                                          exceed      related substance?                        1.5 g/day?   intake
                                                          threshold
                                                          for human
                                                          intake?
                                                                                                                                               
    2-Methyl-1-propanethiol           512    513-44-0     No          Yes. A NOEL of 0.56 mg/kg bw per day      N/R           No safety 
                                                                      was reported in a 90-day study in rats                  concern
                                                                      treated with cyclopentanethiol
                                                                      (No. 516) only at that dose.
    CHEMICAL STRUCTURE 50

    3-Methylbutanethiol               513    541-31-1     No          Yes. A NOEL of 0.56 mg/kg bw per day      NR            No safety 
                                                                      was reported in a 90-day study in rats                  concern
                                                                      treated with cyclopentanethiol 
                                                                      (No. 516) only at that dose.
    CHEMICAL STRUCTURE 51

    2-Pentanethiol                    514    2084-19-7    No          Yes. A NOEL of 0.56 mg/kg bw per day      N/R           No safety 
                                                                      was reported in a 90-day study in rats                  concern
                                                                      treated with cyclopentanethiol
                                                                      (No. 516) only at that dose.
    CHEMICAL STRUCTURE 52

    Table 1. (continued)
                                                                                                                                               

    Substance                         JECFA  CAS No.      Step B3     Step B4. Adequate                         Step B5       Conclusion
    and structure                     No.                 Does        margin of safety                          Does intake   based on
                                                          intake      for substance or                          exceed        current
                                                          exceed      related substance?                        1.5 g/day?   intake
                                                          threshold
                                                          for human
                                                          intake?
                                                                                                                                               
    2-Methyl-1-butanethiol            515    1878-18-8    No          Yes. A NOEL of 0.56 mg/kg bw per day      N/R           No safety 
                                                                      was reported in a 90-day study in rats                  concern
                                                                      treated with cyclopentanethiol
                                                                      (No. 516) only at that dose.
    CHEMICAL STRUCTURE 53

    3-Methyl-2-butanethiol            517    2084-18-6    No          Yes. A NOEL of 0.56 mg/kg bw per day      N/R           No safety 
                                                                      was reported in a 90-day study in rats                  concern
                                                                      treated with cyclopentanethiol
                                                                      (No. 516) only at that dose.
    CHEMICAL STRUCTURE 54

    1-Hexanethiol                     518    111-31-9     No          Yes. A NOEL of 0.56 mg/kg bw per day      N/R           No safety 
                                                                      was reported in a 90-day study in rats                  concern
                                                                      treated with cyclopentanethiol 
                                                                      (No. 516) only at that dose.
    CHEMICAL STRUCTURE 55

    Table 1. (continued)
                                                                                                                                               

    Substance                         JECFA  CAS No.      Step B3     Step B4. Adequate                         Step B5       Conclusion
    and structure                     No.                 Does        margin of safety                          Does intake   based on
                                                          intake      for substance or                          exceed        current
                                                          exceed      related substance?                        1.5 g/day?   intake
                                                          threshold
                                                          for human
                                                          intake?
                                                                                                                                               
    32-Ethylhexanethiol               519    7341-17-5    No          Yes. A NOEL of 0.56 mg/kg bw per day      N/R           No safety 
                                                                      was reported in a 90-day study in rats                  concern
                                                                      treated with cyclopentanethiol 
                                                                      (No. 516) only at that dose.
    CHEMICAL STRUCTURE 56

    Prenythiol                        522    5287-45-6    No          Yes. A NOEL of 0.56 mg/kg bw per day      N/R           No safety 
                                                                      was reported in a 90-day study in rats                  concern
                                                                      treated with cyclopentanethiol 
                                                                      (No. 516) only at that dose; see diallyl 
                                                                      trisulfide (No. 587, subgroup ix), which 
                                                                      is predicted to be metabolized to allyl 
                                                                      disulfide and allyl thiol.
    CHEMICAL STRUCTURE 57

    Table 1. (continued)
                                                                                                                                               

    Substance                         JECFA  CAS No.      Step B3     Step B4. Adequate                         Step B5       Conclusion
    and structure                     No.                 Does        margin of safety                          Does intake   based on
                                                          intake      for substance or                          exceed        current
                                                          exceed      related substance?                        1.5 g/day?   intake
                                                          threshold
                                                          for human
                                                          intake?
                                                                                                                                               
    Thiogeraniol                      524    39067-80-6   No          Yes. A NOEL of 0.56 mg/kg bw  per day     N/R           No safety 
                                                                      was reported in a 90-day study in rats                  concern
                                                                      treated with cyclopentanethiol 
                                                                      (No. 516) only at that dose; see 
                                                                      diallyl trisulfide (No. 587, subgroup 
                                                                      ix), which is predicted to be 
                                                                      metabolized to allyl disulfide and 
                                                                      allyl thiol.
    CHEMICAL STRUCTURE 58

    Structural class II

    Cyclopentanethiol                 516    1679-07-8    No          Yes. A NOEL of 0.56 mg/kg bw per day      N/R           No safety 
                                                                      was reported in a 90-day study in rats                  concern
                                                                      treated with this substance only at 
                                                                      that dose.
    CHEMICAL STRUCTURE 59

    Table 1. (continued)
                                                                                                                                               

    Substance                         JECFA  CAS No.      Step B3     Step B4. Adequate                         Step B5       Conclusion
    and structure                     No.                 Does        margin of safety                          Does intake   based on
                                                          intake      for substance or                          exceed        current
                                                          exceed      related substance?                        1.5 g/day?   intake
                                                          threshold
                                                          for human
                                                          intake?
                                                                                                                                               
    2,3- or 10-Mercaptopinane         520    23832-18-0   No          Yes.  A NOEL of 0.06 mg/kg bw per day     N/R           No safety 
                                                                      was reported in a 90-day study in rats                  concern
                                                                      treated with this substance only at 
                                                                      that dose. NOELs of 0.56, 0.52, 0.43, 
                                                                      and 3.4 mg/kg bw per day were reported 
                                                                      in 90-day studies in rats treated with 
                                                                      cyclo-pentanethiol (No. 516),
                                                                      ortho-toluenethiol (No. 528),
                                                                      2,6-dimethylthiophenol (No. 530), and
                                                                      2-naphthalenethiol (No. 531), 
                                                                      respectively, only at those doses.
    CHEMICAL STRUCTURE 60

    Allyl mercaptan                   521    870-23-5     No          Yes. A NOEL of 0.56 mg/kg bw per day      N/R           No safety 
                                                                      was reported in a 90-day study in rats                  concern
                                                                      treated with cyclopentanethiol 
                                                                      (No. 516) only at that dose.
    CHEMICAL STRUCTURE 61

    Table 1. (continued)
                                                                                                                                               

    Substance                         JECFA  CAS No.      Step B3     Step B4. Adequate                         Step B5       Conclusion
    and structure                     No.                 Does        margin of safety                          Does intake   based on
                                                          intake      for substance or                          exceed        current
                                                          exceed      related substance?                        1.5 g/day?   intake
                                                          threshold
                                                          for human
                                                          intake?
                                                                                                                                               
    1-para-Menthene-8-thiol           523    71159-90-5   No          Yes. A NOEL of 0.56 mg/kg bw per day      N/R           No safety 
                                                                      was reported in a 90-day study in rats                  concern
                                                                      treated with cyclopentanethiol 
                                                                      (No. 516) only at that dose.
    CHEMICAL STRUCTURE 62

    Benzenethiol                      525    108-98-5     No          Yes. NOELs of 0.52, 0.43, and 3.4         N/R           No safety 
                                                                      mg/kg bw per day were reported in                       concern
                                                                      90-day studies in rats treated with 
                                                                      ortho-toluenethiol (No. 528), 
                                                                      2,6-dimethyl-thiophenol (No. 530), and
                                                                      2-naphthal-enethiol (No. 531), 
                                                                      respectively, only at those doses.
    CHEMICAL STRUCTURE 63

    Table 1. (continued)
                                                                                                                                               

    Substance                         JECFA  CAS No.      Step B3     Step B4. Adequate                         Step B5       Conclusion
    and structure                     No.                 Does        margin of safety                          Does intake   based on
                                                          intake      for substance or                          exceed        current
                                                          exceed      related substance?                        1.5 g/day?   intake
                                                          threshold
                                                          for human
                                                          intake?
                                                                                                                                               
    Benzyl mercaptan                  526    100-53-8     No          Yes. NOELs of 0.52, 0.43, and 3.4         N/R           No safety 
                                                                      mg/kg bw per day were reported in                       concern
                                                                      90-day studies in rats treated with 
                                                                      ortho-toluenethiol (No. 528),
                                                                      2,6-dimethyl-thiophenol (No. 530), and 
                                                                      2-naphthal-enethiol (No. 531),
                                                                      respectively, only at those doses.
    CHEMICAL STRUCTURE 64

    Phenethyl mercaptan               527    4410-99-5    No          Yes. NOELs of 0.52, 0.43, and 3.4         N/R           No safety 
                                                                      mg/kg bw per day were reported in                       concern
                                                                      90-day studies in rats treated with 
                                                                      ortho-toluenethiol (No. 528), 
                                                                      2,6-dimethyl-thiophenol (No. 530), and 
                                                                      2-naphthal-enethiol (No. 531), 
                                                                      respectively, only at those doses.
    CHEMICAL STRUCTURE 65

    Table 1. (continued)
                                                                                                                                               

    Substance                         JECFA  CAS No.      Step B3     Step B4. Adequate                         Step B5       Conclusion
    and structure                     No.                 Does        margin of safety                          Does intake   based on
                                                          intake      for substance or                          exceed        current
                                                          exceed      related substance?                        1.5 g/day?   intake
                                                          threshold
                                                          for human
                                                          intake?
                                                                                                                                               
    ortho-Toluenethiol                528    137-06-4     No          Yes. A NOEL of 0.52 mg/kg bw per day      N/R           No safety 
                                                                      was reported in a 90-day study in rats                  concern
                                                                      treated with this substance only at 
                                                                      that dose.
    CHEMICAL STRUCTURE 66

    2,6-Dimethylthiophenol            530    118-72-9     No          Yes. A NOEL of 0.43 mg/kg bw per day      N/R           No safety 
                                                                      was reported in a 90-day study in rats                  concern
                                                                      treated with this substance only at 
                                                                      that dose.
    CHEMICAL STRUCTURE 67

    2-Naphthalenethiol                531    91-60-1      No          Yes. A NOEL of 3.4 mg/kg bw per day       N/R           No safety 
                                                                      was reported in a 90-day study in                       concern
                                                                      rats treated with this substance
                                                                      only at that dose.
    CHEMICAL STRUCTURE 68

    Table 1. (continued)
                                                                                                                                               

    Substance                         JECFA  CAS No.      Step B3     Step B4. Adequate                         Step B5       Conclusion
    and structure                     No.                 Does        margin of safety                          Does intake   based on
                                                          intake      for substance or                          exceed        current
                                                          exceed      related substance?                        1.5 g/day?   intake
                                                          threshold
                                                          for human
                                                          intake?
                                                                                                                                               
    Structural class III

    2-Ethylthiophenol                 529    4500-58-7    No          Yes. NOELs of 0.52, 0.43, and 3.4         N/R           No safety 
                                                                      mg/kg bw per day were reported in                       concern
                                                                      90-day studies in rats treated with 
                                                                      ortho-toluenethiol (No. 528), 
                                                                      2,6-dimethyl-thiophenol (No. 530), 
                                                                      and 2-naphthal-enethiol (No. 531),
                                                                      respectively, only at those doses.
    CHEMICAL STRUCTURE 69

    Table 1. (continued)
                                                                                                                                               

    Substance                         JECFA  CAS No.      Step B3     Step B4. Adequate                         Step B5       Conclusion
    and structure                     No.                 Does        margin of safety                          Does intake   based on
                                                          intake      for substance or                          exceed        current
                                                          exceed      related substance?                        1.5 g/day?   intake
                                                          threshold
                                                          for human
                                                          intake?
                                                                                                                                               
    Subgroup (v): Thiols with oxidized side-chains

    Structural class I

    2-Mercaptopropionic acid          551    79-42-5      No          Yes. NOELs of 1,9, 2.8, and 1.9 mg/kg     N/R           No safety 
                                                                      bw per day were reported in 90-day                      concern
                                                                      studies in rats treated with 
                                                                      2-mercapto-3-butanol (No. 546),
                                                                      alpha-methyl-beta-hydroxypropyl
                                                                      alpha-methyl-beta-mercaptopropyl sulfide
                                                                      (No. 547), and 3-mercapto-2-pentanone
                                                                      (No. 560), respectively, only at those
                                                                      doses.
    CHEMICAL STRUCTURE 70


    Table 1. (continued)
                                                                                                                                               

    Substance                         JECFA  CAS No.      Step B3     Step B4. Adequate                         Step B5       Conclusion
    and structure                     No.                 Does        margin of safety                          Does intake   based on
                                                          intake      for substance or                          exceed        current
                                                          exceed      related substance?                        1.5 g/day?   intake
                                                          threshold
                                                          for human
                                                          intake?
                                                                                                                                               

    Ethyl 2-mercaptopropionate        552    19788-49-9   No          Yes. NOELs of 1,9, 2.8, and 1.9 mg/kg     N/R           No safety 
                                                                      bw per day were reported in 90-day                      concern
                                                                      studies in rats treated with
                                                                      2-mercapto-3-butanol (No. 546),
                                                                      alpha-methyl-beta-hydroxypropyl
                                                                      alpha-methyl-beta-mercaptopropyl sulfide
                                                                      (No. 547), and 3-mercapto-2-pentanone
                                                                      (No. 560), respectively, only at those
                                                                      doses.
    CHEMICAL STRUCTURE 71

    Ethyl 3-mercaptopropionate        553    5466-06-8    No          Yes. NOELs of 1,9, 2.8, and 1.9 mg/kg     N/R           No safety 
                                                                      bw per day were reported in 90-day                      concern
                                                                      studies in rats treated with 
                                                                      2-mercapto-3-butanol (No. 546), 
                                                                      alpha-methyl-beta-hydroxypropyl
                                                                      alpha-methyl-beta-mercaptopropyl sulfide
                                                                      (No. 547), and 3-mercapto-2-pentanone 
                                                                      (No. 560), respectively, only at those
                                                                      doses.
    CHEMICAL STRUCTURE 72

    Table 1. (continued)
                                                                                                                                               

    Substance                         JECFA  CAS No.      Step B3     Step B4. Adequate                         Step B5       Conclusion
    and structure                     No.                 Does        margin of safety                          Does intake   based on
                                                          intake      for substance or                          exceed        current
                                                          exceed      related substance?                        1.5 g/day?   intake
                                                          threshold
                                                          for human
                                                          intake?
                                                                                                                                               
    3-Mercaptohexyl acetate           554    136954-20-6  No          Yes. NOELs of 1,9, 2.8, and 1.9 mg/kg     N/R           No safety 
                                                                      bw per day were reported in 90-day                      concern
                                                                      studies in rats treated with 
                                                                      2-mercapto-3-butanol (No. 546),
                                                                      alpha-methyl-beta-hydroxypropyl
                                                                      alpha-methyl-beta-mercaptopropyl sulfide
                                                                      (No. 547), and 3-mercapto-2-pentanone 
                                                                      (No. 560), respectively, only at those
                                                                      doses.
    CHEMICAL STRUCTURE 73

    3-Mercaptohexyl butyrate          555    136954-21-7  No          Yes. NOELs of 1,9, 2.8, and 1.9 mg/kg     N/R           No safety 
                                                                      bw per day were reported in 90-day                      concern
                                                                      studies in rats treated with 
                                                                      2-mercapto-3-butanol (No. 546), 
                                                                      alpha-methyl-beta-hydroxypropyl
                                                                      alpha-methyl-beta-mercaptopropyl sulfide
                                                                      (No. 547), and 3-mercapto-2-pentanone 
                                                                      (No. 560), respectively, only at those
                                                                      doses.
    CHEMICAL STRUCTURE 74

    Table 1. (continued)
                                                                                                                                               

    Substance                         JECFA  CAS No.      Step B3     Step B4. Adequate                         Step B5       Conclusion
    and structure                     No.                 Does        margin of safety                          Does intake   based on
                                                          intake      for substance or                          exceed        current
                                                          exceed      related substance?                        1.5 g/day?   intake
                                                          threshold
                                                          for human
                                                          intake?
                                                                                                                                               
    3-Mercaptohexyl hexanoate         556    136954-22-8  No          Yes. NOELs of 1,9, 2.8, and 1.9 mg/kg     N/R           No safety 
                                                                      bw per day were reported in 90-day                      concern
                                                                      studies in rats treated with 
                                                                      2-mercapto-3-butanol (No. 546), 
                                                                      alpha-methyl-beta-hydroxypropyl
                                                                      alpha-methyl-beta-mercaptopropyl sulfide
                                                                      (No. 547), and 3-mercapto-2-pentanone
                                                                      (No. 560), respectively, only at those
                                                                      doses.
    CHEMICAL STRUCTURE 75

    1-Mercapto-2-propanone            557    24653-75-6   No          Yes. NOELs of 1,9, 2.8, and 1.9 mg/kg     N/R           No safety 
                                                                      bw per day were reported in 90-day                      concern
                                                                      studies in rats treated with 
                                                                      2-mercapto-3-butanol (No. 546), 
                                                                      alpha-methyl-beta-hydroxypropyl
                                                                      alpha-methyl-beta-mercaptopropyl sulfide 
                                                                      (No. 547), and 3-mercapto-2-pentanone 
                                                                      (No. 560), respectively, only at those
                                                                      doses.
    CHEMICAL STRUCTURE 76

    Table 1. (continued)
                                                                                                                                               

    Substance                         JECFA  CAS No.      Step B3     Step B4. Adequate                         Step B5       Conclusion
    and structure                     No.                 Does        margin of safety                          Does intake   based on
                                                          intake      for substance or                          exceed        current
                                                          exceed      related substance?                        1.5 g/day?   intake
                                                          threshold
                                                          for human
                                                          intake?
                                                                                                                                               
    3-Mercapto-2-butanone             558    40789-98-8   No          Yes. NOELs of 1,9, 2.8, and 1.9 mg/kg     N/R           No safety 
                                                                      bw per day were reported in 90-day                      concern
                                                                      studies in rats treated with 
                                                                      2-mercapto-3-butanol (No. 546),
                                                                      alpha-methyl-beta-hydroxypropyl
                                                                      alpha-methyl-beta-mercaptopropyl sulfide
                                                                      (No. 547), and 3-mercapto-2-pentanone
                                                                      (No. 560), respectively, only at those
                                                                      doses.
    CHEMICAL STRUCTURE 77

    2-Keto-4-butanethiol              559    34619-12-0   No          Yes. NOELs of 1,9, 2.8, and 1.9 mg/kg     N/R           No safety 
                                                                      bw per day were reported in 90-day                      concern
                                                                      studies in rats treated with 
                                                                      2-mercapto-3-butanol (No. 546), 
                                                                      alpha-methyl-beta-hydroxypropyl
                                                                      alpha-methyl-beta-mercaptopropyl sulfide 
                                                                      (No. 547), and 3-mercapto-2-pentanone 
                                                                      (No. 560), respectively, only at those
                                                                      doses.
    CHEMICAL STRUCTURE 78

    Table 1. (continued)
                                                                                                                                               

    Substance                         JECFA  CAS No.      Step B3     Step B4. Adequate                         Step B5       Conclusion
    and structure                     No.                 Does        margin of safety                          Does intake   based on
                                                          intake      for substance or                          exceed        current
                                                          exceed      related substance?                        1.5 g/day?   intake
                                                          threshold
                                                          for human
                                                          intake?
                                                                                                                                               
    3-Mercapto-2-pentanone            560    67633-97-0   No          Yes. A NOEL of 1.9 mg/kg bw per day       N/R           No safety 
                                                                      was reported in a 90-day study in rats                  concern
                                                                      given this substance only at that dose.
    CHEMICAL STRUCTURE 79

    3-Mercapto-3-methyl-1-butanol     544    34300-94-2   No          Yes. NOELs of 1,9, 2.8, and 1.9 mg/kg     N/R           No safety 
                                                                      bw per day were reported in 90-day                      concern
                                                                      studies in rats treated with 
                                                                      2-mercapto-3-butanol (No. 546),
                                                                      alpha-methyl-beta-hydroxypropyl 
                                                                      alpha-methyl-beta-mercaptopropyl sulfide 
                                                                      (No. 547), and 3-mercapto-2-pentanone 
                                                                      (No. 560), respectively, only at those
                                                                      doses.
    CHEMICAL STRUCTURE 80

    Table 1. (continued)
                                                                                                                                               

    Substance                         JECFA  CAS No.      Step B3     Step B4. Adequate                         Step B5       Conclusion
    and structure                     No.                 Does        margin of safety                          Does intake   based on
                                                          intake      for substance or                          exceed        current
                                                          exceed      related substance?                        1.5 g/day?   intake
                                                          threshold
                                                          for human
                                                          intake?
                                                                                                                                               
    3-Mercaptohexanol                 545    51755-83-0   No          Yes. NOELs of 1,9, 2.8, and 1.9 mg/kg     N/R           No safety 
                                                                      bw per day were reported in 90-day                      concern
                                                                      studies in rats treated with 
                                                                      2-mercapto-3-butanol (No. 546),
                                                                      alpha-methyl-beta-hydroxypropyl
                                                                      alpha-methyl-beta-mercaptopropyl sulfide 
                                                                      (No. 547), and 3-mercapto-2-pentanone 
                                                                      (No. 560), respectively, only at those
                                                                      doses.
    CHEMICAL STRUCTURE 81

    Table 1. (continued)
                                                                                                                                               

    Substance                         JECFA  CAS No.      Step B3     Step B4. Adequate                         Step B5       Conclusion
    and structure                     No.                 Does        margin of safety                          Does intake   based on
                                                          intake      for substance or                          exceed        current
                                                          exceed      related substance?                        1.5 g/day?   intake
                                                          threshold
                                                          for human
                                                          intake?
                                                                                                                                               
    2-Mercapto-3-butanol              546    37887-04-0   No          Yes. A NOEL of 1.9 mg/kg bw per day       N/R           No safety 
                                                                      was reported in a 90-day study in rats                  concern
                                                                      given this substance only at that dose.
    CHEMICAL STRUCTURE 82

    alpha-methyl-beta-hydroxypropyl   547    54957-02-7   No          Yes. A NOEL of 2.8 mg/kg bw per day       N/R           No safety 
    alpha-methyl-beta-mercaptopropyl                                  was reported in a 90-day study in rats                  concern
    sulfide                                                           given this substance only at that dose.

    CHEMICAL STRUCTURE 83

    4-Methyoxy-2-methyl-2-butane-     548    94087-83-9   No          Yes. NOELs of 1,9, 2.8, and 1.9 mg/kg     N/R           No safety 
                                                                      bw per day were reported in 90-day                      concern
                                                                      studies in rats treated with
                                                                      2-mercapto-3-butanol (No. 546),
                                                                      alpha-methyl-beta-hydroxypropyl
                                                                      alpha-methyl-beta-mercaptopropyl sulfide
                                                                      (No. 547), and 3-mercapto-2-pentanone
                                                                      (No. 560), respectively, only at those
                                                                      doses.
    CHEMICAL STRUCTURE 84

    Table 1. (continued)
                                                                                                                                               

    Substance                         JECFA  CAS No.      Step B3     Step B4. Adequate                         Step B5       Conclusion
    and structure                     No.                 Does        margin of safety                          Does intake   based on
                                                          intake      for substance or                          exceed        current
                                                          exceed      related substance?                        1.5 g/day?   intake
                                                          threshold
                                                          for human
                                                          intake?
                                                                                                                                               
    3-Methyl-3-mercaptobutyl formate  549    50746-10-6   No          Yes. NOELs of 1,9, 2.8, and 1.9 mg/kg     N/R           No safety 
                                                                      bw per day were reported in 90-day                      concern
                                                                      studies in rats treated with 
                                                                      2-mercapto-3-butanol (No. 546),
                                                                      alpha-methyl-beta-hydroxypropyl 
                                                                      alpha-methyl-beta-mercaptopropyl sulfide 
                                                                      (No. 547), and 3-mercapto-2-pentanone 
                                                                      (No. 560), respectively, only at those
                                                                      doses.
    CHEMICAL STRUCTURE 85

    Table 1. (continued)
                                                                                                                                               

    Substance                         JECFA  CAS No.      Step B3     Step B4. Adequate                         Step B5       Conclusion
    and structure                     No.                 Does        margin of safety                          Does intake   based on
                                                          intake      for substance or                          exceed        current
                                                          exceed      related substance?                        1.5 g/day?   intake
                                                          threshold
                                                          for human
                                                          intake?
                                                                                                                                               
    Structural class II

    para-Mentha-8-thiol-3-one         561    38462-22-5   No          Yes. NOELs of 1,9, 2.8, and 1.9 mg/kg     N/R           No safety 
                                                                      bw per day were reported in 90-day                      concern
                                                                      studies in rats treated with 
                                                                      2-mercapto-3-butanol (No. 546),
                                                                      alpha-methyl-beta-hydroxypropyl
                                                                      alpha-methyl-beta-mercaptopropyl sulfide 
                                                                      (No. 547), and 3-mercapto-2-pentanone 
                                                                      (No. 560), respectively, only at those doses.
    CHEMICAL STRUCTURE 86

    Table 1. (continued)
                                                                                                                                               

    Substance                         JECFA  CAS No.      Step B3     Step B4. Adequate                         Step B5       Conclusion
    and structure                     No.                 Does        margin of safety                          Does intake   based on
                                                          intake      for substance or                          exceed        current
                                                          exceed      related substance?                        1.5 g/day?   intake
                                                          threshold
                                                          for human
                                                          intake?
                                                                                                                                               
    Structural class III

    Sodium 3-mercapto-oxo-propionate  563    10255-67-1   No          Yes. NOELs of 1,9, 2.8, and  1.9 mg/kg    N/R           No safety 
                                                                      bw per day were reported in 90-day                      concern
                                                                      studies in rats treated with 
                                                                      2-mercapto-3-butanol (No. 546),
                                                                      alpha-methyl-beta-hydroxypropyl
                                                                      alpha-methyl-beta-mercaptopropyl sulfide  
                                                                      (No. 547), and 3-mercapto-2-pentanone     
                                                                      (No. 560), respectively, only at those    
                                                                      doses. See subgroup (i), No. 452 for the  
                                                                      sulfur moiety; the oxopropionate moiety   
                                                                      would be predicted to be of low
                                                                      toxicity.
    CHEMICAL STRUCTURE 87

    Table 1. (continued)
                                                                                                                                               

    Substance                         JECFA  CAS No.      Step B3     Step B4. Adequate                         Step B5       Conclusion
    and structure                     No.                 Does        margin of safety                          Does intake   based on
                                                          intake      for substance or                          exceed        current
                                                          exceed      related substance?                        1.5 g/day?   intake
                                                          threshold
                                                          for human
                                                          intake?
                                                                                                                                               
    Subgroup (vi): Dithiols

    Structural class I

    1,2-Ethanedithiol                 532    540-63-6     No          Yes. NOELs of 0.7 mg/kg bw per day        N/R           No safety 
                                                                      were reported in 90-day studies in rats                 concern
                                                                      treated with 2,3-butanedithiol 
                                                                      (No. 539) and 1,8-octanedithiol 
                                                                      (No. 541) only at that dose.
    CHEMICAL STRUCTURE 88

    1,3-Propanedithiol                535    109-80-8     No          Yes. NOELs of 0.7 mg/kg bw per day        N/R           No safety 
                                                                      were reported in 90-day studies in rats                 concern
                                                                      treated with 2,3-butanedithiol (No. 539)
                                                                      and 1,8-octanedithiol (No. 541) only at
                                                                      that dose.
    CHEMICAL STRUCTURE 89

    Table 1. (continued)
                                                                                                                                               

    Substance                         JECFA  CAS No.      Step B3     Step B4. Adequate                         Step B5       Conclusion
    and structure                     No.                 Does        margin of safety                          Does intake   based on
                                                          intake      for substance or                          exceed        current
                                                          exceed      related substance?                        1.5 g/day?   intake
                                                          threshold
                                                          for human
                                                          intake?
                                                                                                                                               
    1,2-Propanedithiol                536    814-67-5     No          Yes. NOELs of 0.7 mg/kg bw per day        N/R           No safety 
                                                                      were reported in 90-day studies in rats                 concern
                                                                      treated with 2,3-butanedithiol (No. 539)
                                                                      and 1,8-octanedithiol (No. 541) only at
                                                                      that dose.
    CHEMICAL STRUCTURE 90

    1,2-Butanedithiol                 537    16128-68-0   No          Yes. NOELs of 0.7 mg/kg bw per day        N/R           No safety 
                                                                      were reported in 90-day studies in rats                 concern
                                                                      treated with 2,3-butanedithiol (No. 539)
                                                                      and 1,8-octanedithiol (No. 541) only at
                                                                      that dose.
    CHEMICAL STRUCTURE 91

    1,3-Butanedithiol                 538    24330-52-7   No          Yes. NOELs of 0.7 mg/kg bw per day        N/R           No safety 
                                                                      were reported in 90-day studies in rats                 concern
                                                                      treated with 2,3-butanedithiol (No. 539)
                                                                      and 1,8-octanedithiol (No. 541) only at
                                                                      that dose.
    CHEMICAL STRUCTURE 92

    Table 1. (continued)
                                                                                                                                               

    Substance                         JECFA  CAS No.      Step B3     Step B4. Adequate                         Step B5       Conclusion
    and structure                     No.                 Does        margin of safety                          Does intake   based on
                                                          intake      for substance or                          exceed        current
                                                          exceed      related substance?                        1.5 g/day?   intake
                                                          threshold
                                                          for human
                                                          intake?
                                                                                                                                               
    2,3-Butanedithiol                 539    4532-64-3    No          Yes. A NOEL of 0.7 mg/kg bw per day       N/R           No safety
                                                                      was reported in a 90-day study in rats                  concern
                                                                      given this substance only at that dose.
    CHEMICAL STRUCTURE 93

    1,6-Hexanedithiol                 540    1191-43-1    No          Yes. NOELs of 0.7 mg/kg bw per day        N/R           No safety
                                                                      were reported in 90-day studies in rats                 concern
                                                                      treated with 2,3-butanedithiol (No. 539)
                                                                      and 1,8-octanedithiol (No. 541) only at
                                                                      that dose.
    CHEMICAL STRUCTURE 94

    1,8-Octanedithiol                 541    1191-62-4    No          Yes. A NOEL of 0.7 mg/kg bw per day       N/R           No safety
                                                                      was reported in a 90-day study in rats                  concern
                                                                      given this substance only at that dose.
    CHEMICAL STRUCTURE 95

    Table 1. (continued)
                                                                                                                                               

    Substance                         JECFA  CAS No.      Step B3     Step B4. Adequate                         Step B5       Conclusion
    and structure                     No.                 Does        margin of safety                          Does intake   based on
                                                          intake      for substance or                          exceed        current
                                                          exceed      related substance?                        1.5 g/day?   intake
                                                          threshold
                                                          for human
                                                          intake?
                                                                                                                                               
    1,9-Nonanedithiol                 542    3489-28-9    No          Yes. NOELs of 0.7 mg/kg bw per day        N/R           No safety
                                                                      were reported in 90-day studies in rats                 concern
                                                                      treated with 2,3-butanedithiol (No. 539)
                                                                      and 1,8-octanedithiol (No. 541) only at
                                                                      that dose.
    CHEMICAL STRUCTURE 96

    Subgroup (vii): Simple disulfides

    Structural class I

    Dimethyl disulfide                564    624-92-0     No          Yes. A NOEL of 7.3 mg/kg bw per day       N/R           No safety
                                                                      was reported in a 90-day study in rats                  concern
                                                                      treated with propyl disulfide (No. 566)
                                                                      at two doses.
    CHEMICAL STRUCTURE 97

    Table 1. (continued)
                                                                                                                                               

    Substance                         JECFA  CAS No.      Step B3     Step B4. Adequate                         Step B5       Conclusion
    and structure                     No.                 Does        margin of safety                          Does intake   based on
                                                          intake      for substance or                          exceed        current
                                                          exceed      related substance?                        1.5 g/day?   intake
                                                          threshold
                                                          for human
                                                          intake?
                                                                                                                                               
    Methyl propyl disulfide           565    2179-60-4    No          Yes. A NOEL of 7.3 mg/kg bw per day       N/R           No safety 
                                                                      was reported in a 90-day study in rats                  concern
                                                                      treated with propyl disulfide (No. 566)
                                                                      at two doses.
    CHEMICAL STRUCTURE 98

    Propyl disulfide                  566    629-19-6     No          Yes. A NOEL of 7.3 mg/kg bw per day       N/R           No safety
                                                                      was reported in a 90-day study in rats                  concern
                                                                      treated with this substance at two
                                                                      doses.
    CHEMICAL STRUCTURE 99

    Diisopropyl disulfide             567    4253-89-8    No          Yes. NOELs of 7.3 and 0.23 mg/kg bw       N/R           No safety 
                                                                      per day were reported in 90-day studies                 concern
                                                                      in rats treated with propyl disulfide 
                                                                      and dicyclohexyl disulfide at two and 
                                                                      single doses, respectively.
    CHEMICAL STRUCTURE 100

    Table 1. (continued)
                                                                                                                                               

    Substance                         JECFA  CAS No.      Step B3     Step B4. Adequate                         Step B5       Conclusion
    and structure                     No.                 Does        margin of safety                          Does intake   based on
                                                          intake      for substance or                          exceed        current
                                                          exceed      related substance?                        1.5 g/day?   intake
                                                          threshold
                                                          for human
                                                          intake?
                                                                                                                                               
    Methyl 1-propenyl disulfide       569    5905-47-5    No          Yes. A NOEL of 7.3 mg/kg bw per day       N/R           No safety 
                                                                      was reported in a 90-day study in rats                  concern
                                                                      treated with propyl disulfide (No. 566) 
                                                                      at two doses.
    CHEMICAL STRUCTURE 101

    Propenyl propyl disulfide         570    5905-46-4    -           Yes. A NOEL of 7.3 mg/kg bw per day       N/R           No safety 
                                                                      was reported in a 90-day study in rats                  concern
                                                                      treated with propyl disulfide (No. 566) 
                                                                      at two doses.
    CHEMICAL STRUCTURE 102

    Methyl 3-methyl-1-butenyl         571    Pending      -           Yes. A NOEL of 7.3 mg/kg bw per day       N/R           No safety 
    disulfide                                                         was reported in a 90-day study in rats                  concern
                                                                      treated with propyl disulfide (No. 566) 
                                                                      at two doses.
    CHEMICAL STRUCTURE 103

    Table 1. (continued)
                                                                                                                                               

    Substance                         JECFA  CAS No.      Step B3     Step B4. Adequate                         Step B5       Conclusion
    and structure                     No.                 Does        margin of safety                          Does intake   based on
                                                          intake      for substance or                          exceed        current
                                                          exceed      related substance?                        1.5 g/day?   intake
                                                          threshold
                                                          for human
                                                          intake?
                                                                                                                                               
    Structural class II

    Allyl methyl disulfide            568    2179-58-0    No          Yes. A NOEL of 4.6 mg/kg bw per day       N/R           No safety 
                                                                      was reported in a 90-day study in rats                  concern
                                                                      treated with diallyl trisulfide 
                                                                      (No. 587, group ix) at a single dose for
                                                                      90 days; this substance is predicted to 
                                                                      be metabolized to allyl mercaptan.
    CHEMICAL STRUCTURE 104

    Allyl disulfide                   572    2179-57-9    No          Yes. A NOEL of 4.6 mg/kg bw per day       N/R           No safety 
                                                                      was reported in a 90-day study in rats                  concern
                                                                      treated with diallyl trisulfide 
                                                                      (No. 587, group ix) at a single dose for 
                                                                      90 days; this substance is predicted to 
                                                                      be metabolized to allyl mercaptan.
    CHEMICAL STRUCTURE 105

    Table 1. (continued)
                                                                                                                                               

    Substance                         JECFA  CAS No.      Step B3     Step B4. Adequate                         Step B5       Conclusion
    and structure                     No.                 Does        margin of safety                          Does intake   based on
                                                          intake      for substance or                          exceed        current
                                                          exceed      related substance?                        1.5 g/day?   intake
                                                          threshold
                                                          for human
                                                          intake?
                                                                                                                                               
    Dicyclohexyl disulfide            575    2550-40-5    No          Yes. A NOEL of 0.23 mg/kg bw per day      N/R           No safety 
                                                                      was reported in a 90-day study in rats                  concern
                                                                      treated with this substance only at 
                                                                      that dose.
    CHEMICAL STRUCTURE 106

    Methyl phenyl disulfide           576    14173-25-2   No          Yes. A NOEL of 3.4 mg/kg bw per day       N/R           No safety 
                                                                      was reported in a 90-day study in rats                  concern
                                                                      treated with 2-naphthalenethiol 
                                                                      (No. 531, group iv) at a single dose for
                                                                      90 days; this substance is predicted to 
                                                                      be reduced rapidly to thiophenol.
    CHEMICAL STRUCTURE 107

    Table 1. (continued)
                                                                                                                                               

    Substance                         JECFA  CAS No.      Step B3     Step B4. Adequate                         Step B5       Conclusion
    and structure                     No.                 Does        margin of safety                          Does intake   based on
                                                          intake      for substance or                          exceed        current
                                                          exceed      related substance?                        1.5 g/day?   intake
                                                          threshold
                                                          for human
                                                          intake?
                                                                                                                                               
    Methyl benzyl disulfide           577    699-10-5     No          Yes. A NOEL of 1.2 mg/kg bw per day       N/R           No safety
                                                                      was reported in a 90-day study in rats                  concern
                                                                      treated with this substance only at
                                                                      that dose.
    CHEMICAL STRUCTURE 108

    Benzyl disulfide                  579    150-60-7     No          Yes. A NOEL of 1.2 mg/kg bw per day       N/R           No safety 
                                                                      was reported in a 90-day study in rats                  concern
                                                                      treated with methyl benzyl disulfide 
                                                                      (No. 579) only at that dose
    CHEMICAL STRUCTURE 109

    Structural class III

    Phenyl disulfide                  578    882-33-7     No          Yes. A NOEL of 3.4 mg/kg bw per day       N/R           No safety 
                                                                      was reported in a 90-day study in rats                  concern
                                                                      treated with 2-naphthalenethiol 
                                                                      (No. 531, group iv) at a single dose for  
                                                                      90 days; this substance is predicted to
                                                                      be reduced rapidly to thiophenol.
    CHEMICAL STRUCTURE 110

    Table 1. (continued)
                                                                                                                                               

    Substance                         JECFA  CAS No.      Step B3     Step B4. Adequate                         Step B5       Conclusion
    and structure                     No.                 Does        margin of safety                          Does intake   based on
                                                          intake      for substance or                          exceed        current
                                                          exceed      related substance?                        1.5 g/day?   intake
                                                          threshold
                                                          for human
                                                          intake?
                                                                                                                                               
    Subgroup (viii): Disulfides with oxidized side-chains

    Structural class I

    2-Methyl-2-(methyldithio)         580    67952-60-7   No          Yes. NOELs of 7.3, 0.23, 1.2,and 1.9      N/R           No safety 
    -propanal                                                         mg/kg bw per day were reported in                       concern
                                                                      90-day studies in rats treated with 
                                                                      propyl disulfide (No. 566), dicyclohexyl  
                                                                      disulfide (No. 575), methyl benzyl 
                                                                      disulfide (No. 577), and
                                                                      3-mercapto-2-pentanone (No. 560), 
                                                                      respectively, only at those doses. 
                                                                      See cyclopentanethiol (No. 516, 
                                                                      sub-group iv) for the thiol products
                                                                      of reduction.
    CHEMICAL STRUCTURE 111

    Table 1. (continued)
                                                                                                                                               

    Substance                         JECFA  CAS No.      Step B3     Step B4. Adequate                         Step B5       Conclusion
    and structure                     No.                 Does        margin of safety                          Does intake   based on
                                                          intake      for substance or                          exceed        current
                                                          exceed      related substance?                        1.5 g/day?   intake
                                                          threshold
                                                          for human
                                                          intake?
                                                                                                                                               
    Ethyl 2-(methyldithio)propionate  581    23747-43-5   No          Yes. NOELs of 7.3, 0.23, 1.2,and 1.9      N/R           No safety 
                                                                      mg/kg bw per day were reported in                       concern
                                                                      90-day studies in rats treated with 
                                                                      propyl disulfide (No. 566), dicyclohexyl  
                                                                      disulfide (No. 575), methyl benzyl 
                                                                      disulfide (No. 577), and 
                                                                      3-mercapto-2-pentanone (No. 560), 
                                                                      respectively, only at those doses.
                                                                      See cyclopentanethiol (No. 516, 
                                                                      sub-group iv) for the thiol products of   
                                                                      reduction.
    CHEMICAL STRUCTURE 112

    Table 1. (continued)
                                                                                                                                               

    Substance                         JECFA  CAS No.      Step B3     Step B4. Adequate                         Step B5       Conclusion
    and structure                     No.                 Does        margin of safety                          Does intake   based on
                                                          intake      for substance or                          exceed        current
                                                          exceed      related substance?                        1.5 g/day?   intake
                                                          threshold
                                                          for human
                                                          intake?
                                                                                                                                               
    Subgroup (ix): Trisulfides

    Structural class I

    Dimethyl trisulfide               582    3658-80-8    No          Yes. A NOEL of 4.8 mg/kg bw per day       N/R           No safety 
                                                                      was reported in a 90-day study in rats                  concern
                                                                      treated with dipropyl trisulfide 
                                                                      (No. 585) only at that dose 
    CHEMICAL STRUCTURE 113

    Methyl ethyl trisulfide           583    31499-71-5   No          Yes. A NOEL of 4.8 mg/kg bw per day       N/R           No safety 
                                                                      was reported in a 90-day study in rats                  concern
                                                                      treated with dipropyl trisulfide 
                                                                      (No. 585) only at that dose 
    CHEMICAL STRUCTURE 114

    Table 1. (continued)
                                                                                                                                               

    Substance                         JECFA  CAS No.      Step B3     Step B4. Adequate                         Step B5       Conclusion
    and structure                     No.                 Does        margin of safety                          Does intake   based on
                                                          intake      for substance or                          exceed        current
                                                          exceed      related substance?                        1.5 g/day?   intake
                                                          threshold
                                                          for human
                                                          intake?
                                                                                                                                               
    Methyl propyl trisulfide          584    17619-36-2   No          Yes. A NOEL of 4.8 mg/kg bw per day       N/R           No safety 
                                                                      was reported in a 90-day study in rats                  concern
                                                                      treated with dipropyl trisulfide 
                                                                      (No. 585) only at that dose 
    CHEMICAL STRUCTURE 115

    Dipropyl trisulfide               585    6028-61-1    No          Yes. A NOEL of 4.8 mg/kg bw per day       N/R           No safety 
                                                                      was reported in a 90-day study in rats                  concern
                                                                      treated with this substance only at 
                                                                      that dose.
    CHEMICAL STRUCTURE 116

    Table 1. (continued)
                                                                                                                                               

    Substance                         JECFA  CAS No.      Step B3     Step B4. Adequate                         Step B5       Conclusion
    and structure                     No.                 Does        margin of safety                          Does intake   based on
                                                          intake      for substance or                          exceed        current
                                                          exceed      related substance?                        1.5 g/day?   intake
                                                          threshold
                                                          for human
                                                          intake?
                                                                                                                                               
    Structural class II

    Allyl methyl trisulfide           586    34135-85-8   No          Yes. A NOEL of 4.6 mg/kg bw per day       N/R           No safety 
                                                                      was reported in a 90-day study in rats                  concern
                                                                      treated with diallyl trisulfide 
                                                                      (No. 587) only at that dose.
    CHEMICAL STRUCTURE 117

    Diallyl trisulfide                587    2050-87-5    No          Yes. A NOEL of 4.6 mg/kg bw per day       N/R           No safety 
                                                                      was reported in a 90-day study in rats                  concern
                                                                      treated with this substance only at 
                                                                      that dose.
    CHEMICAL STRUCTURE 118

    Diallyl polysulfide               588    72869-75-1   No          Yes. A NOEL of 4.6 mg/kg bw per day       N/R           No safety 
                                                                      was reported in a 90-day study in rats                  concern
                                                                      treated with diallyl trisulfide 
                                                                      (No. 587) only at that dose.
    CHEMICAL STRUCTURE 119

    Table 1. (continued)
                                                                                                                                               

    Substance                         JECFA  CAS No.      Step B3     Step B4. Adequate                         Step B5       Conclusion
    and structure                     No.                 Does        margin of safety                          Does intake   based on
                                                          intake      for substance or                          exceed        current
                                                          exceed      related substance?                        1.5 g/day?   intake
                                                          threshold
                                                          for human
                                                          intake?
                                                                                                                                               
    Subgroup (x): Heterocyclic disulfides

    Structural class II

    3,5-Dimethyl-1,2,4-trithiolane    573    23654-92-4   No          Yes. A NOEL of 1.9 mg/kg bw per day       N/R           No safety 
                                                                      was reported in a 90-day study in rats                  concern
                                                                      treated with this substance only at 
                                                                      that dose.
    CHEMICAL STRUCTURE 120

    3-Methyl-1,2,4-trithiane          574    43040-01-3   No          Yes. NOELs of 1.9 and 0.3 mg/kg bw        N/R           No safety 
                                                                      per day were reported in 90-day studies                 concern
                                                                      in rats treated with 
                                                                      3,5-dimethyl-1,2,4-tri-thiolane 
                                                                      (No. 573) and this substance,
                                                                      respectively, only at those doses.
    CHEMICAL STRUCTURE 121

    Table 1. (continued)
                                                                                                                                               

    Substance                         JECFA  CAS No.      Step B3     Step B4. Adequate                         Step B5       Conclusion
    and structure                     No.                 Does        margin of safety                          Does intake   based on
                                                          intake      for substance or                          exceed        current
                                                          exceed      related substance?                        1.5 g/day?   intake
                                                          threshold
                                                          for human
                                                          intake?
                                                                                                                                               
    Subgroup (xi): Thioesters

    Structural class I

    S-Methyl thioacetate              482    1534-08-3    No          Yes. A NOEL of 6.5 mg/kg bw per day       N/R           No safety 
                                                                      was reported in a 90-day study in rats                  concern
                                                                      treated with ethyl thioacetate 
                                                                      (No. 483) only at that dose, and a NOEL 
                                                                      of 1000 mg/kg bw per day was reported 
                                                                      in a 90-day study in rats treated with 
                                                                      methyl thio-butyrate (No. 484) at
                                                                      multiple doses.
    CHEMICAL STRUCTURE 122

    Ethyl thioacetate                 483    625-60-5     No          Yes. A NOEL of 6.5 mg/kg bw per day       N/R           No safety
                                                                      was reported in a 90-day study in rats                  concern
                                                                      treated with this substance only at 
                                                                      that dose.
    CHEMICAL STRUCTURE 123

    Table 1. (continued)
                                                                                                                                               

    Substance                         JECFA  CAS No.      Step B3     Step B4. Adequate                         Step B5       Conclusion
    and structure                     No.                 Does        margin of safety                          Does intake   based on
                                                          intake      for substance or                          exceed        current
                                                          exceed      related substance?                        1.5 g/day?   intake
                                                          threshold
                                                          for human
                                                          intake?
                                                                                                                                               
    Methyl thiobutyrate               484    2432-51-1    No          Yes. A NOEL of 1000 mg/kg bw per day      N/R           No safety
                                                                      was reported in a 90-day study in rats                  concern
                                                                      treated with this substance only at 
                                                                      that dose.
    CHEMICAL STRUCTURE 124

    Propyl thioacetate                485    2307-10-0    No          Yes. A NOEL of 6.5 mg/kg bw per day       N/R           No safety 
                                                                      was reported in a 90-day study in rats                  concern
                                                                      treated with ethyl thioacetate (No. 483)  
                                                                      only at that dose, and a NOEL of 1000 
                                                                      mg/kg bw per day was reported in a 
                                                                      90-day study in rats treated with methyl 
                                                                      thio-butyrate (No. 484) at multiple
                                                                      doses.
    CHEMICAL STRUCTURE 125

    Table 1. (continued)
                                                                                                                                               

    Substance                         JECFA  CAS No.      Step B3     Step B4. Adequate                         Step B5       Conclusion
    and structure                     No.                 Does        margin of safety                          Does intake   based on
                                                          intake      for substance or                          exceed        current
                                                          exceed      related substance?                        1.5 g/day?   intake
                                                          threshold
                                                          for human
                                                          intake?
                                                                                                                                               
    Methyl 2-methylthiobutyrate       486    42075-45-6   No          Yes. A NOEL of 6.5 mg/kg bw per day       N/R           No safety 
                                                                      was reported in a 90-day study in rats                  concern
                                                                      treated with ethyl thioacetate (No. 483)  
                                                                      only at that dose, and a NOEL of 1000 
                                                                      mg/kg bw per day was reported in a 
                                                                      90-day study in rats treated with methyl 
                                                                      thio-butyrate (No. 484) at multiple
                                                                      doses.
    CHEMICAL STRUCTURE 126

    SS-Methyl 3-methylbutanethioate   487    23747-45-7   No          Yes. A NOEL of 6.5 mg/kg bw per day       N/R           No safety 
                                                                      was reported in a 90-day study in rats                  concern
                                                                      treated with ethyl thioacetate (No. 483)  
                                                                      only at that dose, and a NOEL of 1000 
                                                                      mg/kg bw per day was reported in a 
                                                                      90-day study in rats treated with methyl 
                                                                      thio-butyrate (No. 484) at multiple
                                                                      doses.
    CHEMICAL STRUCTURE 127

    Table 1. (continued)
                                                                                                                                               

    Substance                         JECFA  CAS No.      Step B3     Step B4. Adequate                         Step B5       Conclusion
    and structure                     No.                 Does        margin of safety                          Does intake   based on
                                                          intake      for substance or                          exceed        current
                                                          exceed      related substance?                        1.5 g/day?   intake
                                                          threshold
                                                          for human
                                                          intake?
                                                                                                                                               
    S-Methyl 4-methylpentanethioate   488    61122-71-2   No          Yes. A NOEL of 6.5 mg/kg bw per day       N/R           No safety 
                                                                      was reported in a 90-day study in rats                  concern
                                                                      treated with ethyl thioacetate (No. 483) 
                                                                      only at that dose, and a NOEL of 1000 
                                                                      mg/kg bw per day was reported in a 
                                                                      90-day study in rats treated with methyl 
                                                                      thio-butyrate (No. 484) at multiple
                                                                      doses.
    CHEMICAL STRUCTURE 128

    S-Methyl hexanethioate            489    20756-86-9   No          Yes. A NOEL of 6.5 mg/kg bw per day       N/R           No safety 
                                                                      was reported in a 90-day study in rats                  concern
                                                                      treated with ethyl thioacetate (No. 483) 
                                                                      only at that dose, and a NOEL of 1000 
                                                                      mg/kg bw per day was reported in a 
                                                                      90-day study in rats treated with methyl 
                                                                      thio-butyrate (No. 484) at multiple
                                                                      doses.
    CHEMICAL STRUCTURE 129

    Table 1. (continued)
                                                                                                                                               

    Substance                         JECFA  CAS No.      Step B3     Step B4. Adequate                         Step B5       Conclusion
    and structure                     No.                 Does        margin of safety                          Does intake   based on
                                                          intake      for substance or                          exceed        current
                                                          exceed      related substance?                        1.5 g/day?   intake
                                                          threshold
                                                          for human
                                                          intake?
                                                                                                                                               
    Allyl thiopropionate              490    41820-22-8   No          Yes. A NOEL of 6.5 mg/kg bw per day       N/R           No safety 
                                                                      was reported in a 90-day study in rats                  concern
                                                                      treated with ethyl thioacetate (No. 483) 
                                                                      only at that dose, and a NOEL of 1000 
                                                                      mg/kg bw per day was reported in a 
                                                                      90-day study in rats treated with methyl 
                                                                      thio-butyrate (No. 484) at multiple
                                                                      doses. See diallyl trisulfide 
                                                                      (No. 587, subgroup ix), which is 
                                                                      predicted to be metabolized to allyl 
                                                                      thiol (allyl mercaptan) via diallyl
                                                                      disulfide.
    CHEMICAL STRUCTURE 130

    Table 1. (continued)
                                                                                                                                               

    Substance                         JECFA  CAS No.      Step B3     Step B4. Adequate                         Step B5       Conclusion
    and structure                     No.                 Does        margin of safety                          Does intake   based on
                                                          intake      for substance or                          exceed        current
                                                          exceed      related substance?                        1.5 g/day?   intake
                                                          threshold
                                                          for human
                                                          intake?
                                                                                                                                               
    Prenyl thioacetate                491    33049-93-3   No          Yes. A NOEL of 6.5 mg/kg bw per day       N/R           No safety 
                                                                      was reported in a 90-day study in rats                  concern
                                                                      treated with ethyl thioacetate (No. 483) 
                                                                      only at that dose, and a NOEL of 1000 
                                                                      mg/kg bw per day was reported in a 
                                                                      90-day study in rats treated with methyl 
                                                                      thio-butyrate (No. 484) at multiple 
                                                                      doses. See diallyl trisulfide (No. 587, 
                                                                      subgroup ix), which is predicted to be 
                                                                      metabolized to allyl thiol (allyl 
                                                                      mercaptan) via diallyl disulfide.
    CHEMICAL STRUCTURE 131

    Table 1. (continued)
                                                                                                                                               

    Substance                         JECFA  CAS No.      Step B3     Step B4. Adequate                         Step B5       Conclusion
    and structure                     No.                 Does        margin of safety                          Does intake   based on
                                                          intake      for substance or                          exceed        current
                                                          exceed      related substance?                        1.5 g/day?   intake
                                                          threshold
                                                          for human
                                                          intake?
                                                                                                                                               
    Methylthio 2-(acetyloxy)          492    74586-09-7   No          Yes. A NOEL of 6.5 mg/kg bw per day       N/R           No safety 
                                                                      was reported in a 90-day study in rats                  concern
                                                                      treated with ethyl thioacetate (No. 483)
                                                                      only at that dose, and a NOEL of 1000 
                                                                      mg/kg bw per day was reported in a 
                                                                      90-day study in rats treated with methyl 
                                                                      thio-butyrate (No. 484) at multiple 
                                                                      doses.
    CHEMICAL STRUCTURE 132

    Methylthio 2-(propionyloxy)       493    999999-90-9  No          Yes. A NOEL of 6.5 mg/kg bw per day       N/R           No safety 
                                                                      was reported in a 90-day study in rats                  concern
                                                                      treated with ethyl thioacetate (No. 483)
                                                                      only at that dose, and a NOEL of 1000 
                                                                      mg/kg bw per day was reported in a 
                                                                      90-day study in rats treated with methyl  
                                                                      thio-butyrate (No. 484) at multiple
                                                                      doses.
    CHEMICAL STRUCTURE 133

    Table 1. (continued)
                                                                                                                                               

    Substance                         JECFA  CAS No.      Step B3     Step B4. Adequate                         Step B5       Conclusion
    and structure                     No.                 Does        margin of safety                          Does intake   based on
                                                          intake      for substance or                          exceed        current
                                                          exceed      related substance?                        1.5 g/day?   intake
                                                          threshold
                                                          for human
                                                          intake?
                                                                                                                                               
    3-Acetylmercaptohexyl acetate     494    136954-25-1  No          Yes. A NOEL of 6.5 mg/kg bw per day       N/R           No safety 
                                                                      was reported in a 90-day study in rats                  concern
                                                                      treated with ethyl thioacetate (No. 483) 
                                                                      only at that dose, and a NOEL of 1000 
                                                                      mg/kg bw per day was reported in a 
                                                                      90-day study in rats treated with methyl 
                                                                      thio-butyrate (No. 484) at multiple
                                                                      doses.
    CHEMICAL STRUCTURE 134

    Subgroup (xi), Structural class II

    S-Methyl benzothioate             504    5925-68-8    No          Yes. A NOEL of 6.5 mg/kg bw per day       N/R           No safety 
                                                                      was reported in a 90-day study in rats                  concern
                                                                      treated with ethyl thioacetate (No. 483)  
                                                                      only at that dose, and a NOEL of 1000 
                                                                      mg/kg bw per day was reported in a 
                                                                      90-day study in rats treated with methyl 
                                                                      thio-butyrate (No. 484) at multiple
                                                                      doses.
    CHEMICAL STRUCTURE 135

    Table 1. (continued)
                                                                                                                                               

    Substance                         JECFA  CAS No.      Step B3     Step B4. Adequate                         Step B5       Conclusion
    and structure                     No.                 Does        margin of safety                          Does intake   based on
                                                          intake      for substance or                          exceed        current
                                                          exceed      related substance?                        1.5 g/day?   intake
                                                          threshold
                                                          for human
                                                          intake?
                                                                                                                                               
    s- and                            506a   cis,         No          Yes. A NOEL of 6.5 mg/kg bw per day       N/R           No safety 
    trans-Menthone-8-thioacetate      and    57129-12-1               was reported in a 90-day study in rats                  concern
                                      506b   trans,                   treated with ethyl thioacetate (No. 483)                
                                             57074-34-7               only at that dose, and a NOEL of 1000 
                                                                      mg/kg bw per day was reported in a 
                                                                      90-day study in rats treated with methyl
                                                                      thio-butyrate (No. 484) at multiple
                                                                      doses.
    CHEMICAL STRUCTURE 136

    Table 1. (continued)
                                                                                                                                               

    Substance                         JECFA  CAS No.      Step B3     Step B4. Adequate                         Step B5       Conclusion
    and structure                     No.                 Does        margin of safety                          Does intake   based on
                                                          intake      for substance or                          exceed        current
                                                          exceed      related substance?                        1.5 g/day?   intake
                                                          threshold
                                                          for human
                                                          intake?
                                                                                                                                               
    Subgroup (xii), Structural class III: Sulfoxides

    Methylsulfinylmethane (DMSO)      507    67-68-5      No          Yes. A NOEL of 3000 mg/kg bw per day      N/R           No safety 
                                                                      was reported in monkeys given this                      concern
                                                                      substance at multiple doses for 74-87 
                                                                      weeks; similar results in rats, dogs, 
                                                                      and humans.
    CHEMICAL STRUCTURE 137

                                                                                                                                               
    N/R, not relevant to the evaluation; ND, no data reported; bw, body weight

    a None of the substances in this group are predicted to be metabolized to innocuous products. They were placed in subgroups
      (i)-(xii) on the basis of the position of the sulfur atom.

    b The thresholds for human intake are 1800 g/day for class I, 540 g/day for class II, and 90 g/day for class III.


    Table 2. Annual volume and intake of aliphatic and aromatic sulfides and thiols used as
    flavouring substances in Europe and the United States
                                                                                                  

    Substance (No.)                    Most recent     Intakeb                    Annual volume in
                                       annual volume                            naturally 
                                       (kg)a           g/day       g/kg bw      occurring
                                                                    per day       foods (kg)c
                                                                                                  

    Methyl sulfide (452)

         Europe                        3100            590          10
         United States                 2800            530          9             57 000

    Methyl ethyl sulfide (453)

         Europe                        NR              NA           NA
         United States (A)             9               2            0.03          +

    Diethyl sulfide (454)

         Europe                        NR              NA           NA
         United States (A)             68              13           0.22          +

    Butyl sulfide (455)                                                           

         Europe                        19              4            0.1
         United States                 0.5             0.1          0.002         +

    1,4-Dithiane (456)                 

         Europe                        NR              NA           NA
         United States (A)             0.45            0.1          0.001         +

    (1-Butenyl-1) methyl sulfide (457)

         Europe                        NR              NA           NA
         United States (A)             0.45            0.1          0.001         +

    Table 2. (cont'd)
                                                                                                  

    Substance (No.)                    Most recent     Intakeb                    Annual volume in
                                       annual volume                            naturally 
                                       (kg)a           g/day       g/kg bw      occurring
                                                                    per day       foods (kg)c
                                                                                                  
    Allyl sulfide (458)

         Europe                        NR              NA           NA
         United States                 2               0.4          0.01          +

    Methyl phenyl sulfide (459)

         Europe                        NR              NA           NA
         United States (A)             2               0.4          0.01          +

    Benzyl methyl sulfide (460)

         Europe                        1.1             0.2          0.003
         United States (1982)          0.1             0.02         0.0003        +

    3-(Methylthio)propanol (461)

         Europe                        23              4            0.1
         United States                 4               1            0.01          +

    4-(Methylthio)butanol (462)

         Europe                        0.1             0.02         0.0003
         United States                 0.5             0.1          0.002         +

    3-(Methylthio)-1-hexanol (463)

         Europe                        26              5            0.1
         United States                 0.5             0.1          0.002         +

    2-Methyl-4-propyl-1,3-oxathiane (464)

         Europe                        11              2            0.03
         United States (A)             5               1            0.02          +

    Table 2. (cont'd)
                                                                                                  

    Substance (No.)                    Most recent     Intakeb                    Annual volume in
                                       annual volume                            naturally 
                                       (kg)a           g/day       g/kg bw      occurring
                                                                    per day       foods (kg)c
                                                                                                  
    2-Methylthioacetaldehyde (465)

         Europe                        NR              NA           NA
         United States (1970)          3               1            0.01          +

    3-(Methylthio)propionaldehyde (466)

         Europe                        230             45           1             
         United States                 130             25           0.4           637

    3-(Methylthio)butanal (467)

         Europe                        0.7             0.1          0.002
         United States                 0.5             0.1          0.002         +

    4-(Methylthio)butanal (468)

         Europe                        NR              NA           NA
         United States                 0.1             0.02         0.0003        -

    3-Methylthiohexanal (469)

         Europe                        NR              NA           NA
         United States (A)             4.5             1            0.01          +

    2-(Methylthio)methyl-2-butenal (470)

         Europe                        0.2             0.04         0.001
         United States (1982)          0.5             0.1          0.002         +

    Table 2. (cont'd)
                                                                                                  

    Substance (No.)                    Most recent     Intakeb                    Annual volume in
                                       annual volume                            naturally 
                                       (kg)a           g/day       g/kg bw      occurring
                                                                    per day       foods (kg)c
                                                                                                  
    2,8-Dithianon-4-en-4-carboxaldehyde (471)

         Europe                        0.1             0.01         0.0002
         United States                 0.5             0.0:         0.002         +

    Methyl 3-methylthiopropionate (472)

         Europe                        770             146          2             
         United States                 46              9            0.1           5

    Methylthiomethyl butyrate (473)

         Europe                        NR              NA           NA
         United States (A)             0.45            0.1          0.001         +

    Methyl 4-(methylthio)butyrate (474)

         Europe                        0.5             0.1          0.002
         United States                 0.5             0.1          0.002         -

    Ethyl 2-(methylthio)acetate (475)

         Europe                        NR              NA           NA
         United States (A)             0.45            0.1          0.001         +

    Ethyl 3-methylthiopropionate (476)

         Europe                        200             37           1             
         United States                 9               2            0.03          9

    Table 2. (cont'd)
                                                                                                  

    Substance (No.)                    Most recent     Intakeb                    Annual volume in
                                       annual volume                            naturally 
                                       (kg)a           g/day       g/kg bw      occurring
                                                                    per day       foods (kg)c
                                                                                                  
    Ethyl 4-(methylthio)butyrate (477)

         Europe                        NR              NA           NA
         United States (A)             11              2            0.03          -

    3-(Methylthio)propyl acetate (478)

         Europe                        NR              NA           NA
         United States (A)             59              11           0.2           +

    Methylthiomethyl hexanoate (479)

         Europe                        NR              NA           NA
         United States (A)             0.45            0.1          0.001         +

    Ethyl 3-(methylthio)butyrate (480)

         Europe                        NR              NA           NA
         United States (A)             0.45            0.1          0.001         +

    3-(Methylthio)hexyl acetate (481)

         Europe                        0.4             0.1          0.001
         United States (A)             45              9            0.1           +

    S-Methyl thioacetate (482)

         Europe                        NR              NA           NA
         United States (A)             0.01            0.002        0.00003       2 

    Table 2. (cont'd)
                                                                                                  

    Substance (No.)                    Most recent     Intakeb                    Annual volume in
                                       annual volume                            naturally 
                                       (kg)a           g/day       g/kg bw      occurring
                                                                    per day       foods (kg)c
                                                                                                  
    Ethyl thioacetate (483)

         Europe                        0.1             0.02         0.0003        
         United States                 0.1             0.02         0.0003        56

    Methyl thiobutyrate (484)

         Europe                        24              5            0.1
         United States                 27              5            0.1           +

    Propyl thioacetate (485)

         Europe                        2.2             0.4          0.01
         United States                 0.1             0.02         0.0003        +

    Methyl 2-methylthiobutyrate (486)

         Europe                        0.8             0.2          0.003
         United States                 0.5             0.01         0.002         +

    S-Methyl 3-methylbutanethioate (487)

         Europe                        NR              NA           NA
         United States (A)             1               0.19         0.003         +

    S-Methyl 4-methylpentanethioate (488)

         Europe                        NR              NA           NA
         United States (A)             0.0045          0.001        0.00001       +

    Table 2. (cont'd)
                                                                                                  

    Substance (No.)                    Most recent     Intakeb                    Annual volume in
                                       annual volume                            naturally 
                                       (kg)a           g/day       g/kg bw      occurring
                                                                    per day       foods (kg)c
                                                                                                  
    S-Methyl hexanethioate (489)

         Europe                        NR              NA           NA
         United States (A)             0.45            0.1          0.001         3

    Allyl thiopropionate (490)

         Europe                        NR              NA           NA
         United States                 0.5             0.1          0.002         -

    Prenyl thioacetate (491)

         Europe                        NR              NA           NA
         United States (A)             1               0.19         0.003         +

    Methyl 2-(acetyloxy) propionate (492)

         Europe                        NR              NA           NA
         United States (A)             45              9            0.1           -

    Methylthio 2-(propionyloxy) propionate (493)

         Europe                        NR              NA           NA
         United States (A)             45              9            0.1           -

    3-Acetylmercaptohexyl acetate (494)

         Europe                        NR              NA           NA
         United States (A)             2.2             0.4          0.01          +

    Table 2. (cont'd)
                                                                                                  

    Substance (No.)                    Most recent     Intakeb                    Annual volume in
                                       annual volume                            naturally 
                                       (kg)a           g/day       g/kg bw      occurring
                                                                    per day       foods (kg)c
                                                                                                  
    1-Methylthio-2-propanone (495)

         Europe                        NR              NA           NA
         United States (A)             1               0.2          0.003         -

    1-(Methylthio)-2-butanone (496)

         Europe                        0.03            0.01         0.0001
         United States (1982)          0.1             0.02         0.0003        +

    4-(Methylthio)-2-butanone (497)

         Europe                        0.1             0.02         0.0003
         United States                 2               0.4          0.01          +

    4,5-Dihydro-3(2H)-thiophenone (498)

         Europe                        3.6             1            0.01
         United States                 13              2            0.04          +

    2-Methyltetrahydrothiophen-3-one (499)

         Europe                        100             19           0.3           
         United States (A)             0.5             0.1          0.002         5036

    4-(Methylthio)-4-methyl-2-pentanone (500)

         Europe                        0.2             0.04         0.0006
         United States                 0.5             0.1          0.002         -

    Table 2. (cont'd)
                                                                                                  

    Substance (No.)                    Most recent     Intakeb                    Annual volume in
                                       annual volume                            naturally 
                                       (kg)a           g/day       g/kg bw      occurring
                                                                    per day       foods (kg)c
                                                                                                  
    4-(Methylthio)-2-oxobutanoic acid, sodium salt (501)

         Europe                        NR              NA           NA
         United States (A)             1               0.2          0.003         +

    Di(butan-3-one-1-yl) sulfide (502)

         Europe                        NR              NA           NA
         United States (1982)          0.1             0.02         0.0003        -


    ortho-(Methylthio)phenol (503)

         Europe                        5               1            0.02
         United States (1970)          5               1            0.02          +

    S-Methyl benzothioate (504)

         Europe                        NR              NA           NA
         United States (A)             0.0045          0.001        0.00001       +

    2-(Methylthiomethyl)-3-phenylpropenal (505)

         Europe                        NR              NA           NA
         United States                 10              2            0.03          -

    cis- and trans-Menthone-8-thioacetate (506)

         Europe                        NR              NA           NA
         United States (A)             2.3             0.4          0.01          +

    Table 2. (cont'd)
                                                                                                  

    Substance (No.)                    Most recent     Intakeb                    Annual volume in
                                       annual volume                            naturally 
                                       (kg)a           g/day       g/kg bw      occurring
                                                                    per day       foods (kg)c
                                                                                                  
    Methylsulfinylmethane (507)

         Europe                        NR              NA           NA
         United States (A)             0.0045          0.001        0.00001       45 000 

    Methyl mercaptan (508)

         Europe                        440             83           1
         United States                 0.9             0.2          0.003         +

    Propanethiol (509)

         Europe                        18              3            0.1           
         United States                 38              7            0.1           360

    2-Propanethiol (510)

         Europe                        NR              NA           NA
         United States (A)             0.022           0.004        0.0001        +

    1-Butanethiol (511)

         Europe                        3.2             0.5          0.01
         United States                 0.2             0.04         0.001         +

    2-Methyl-1-propanethiol (512)

         Europe                        NR              NA           NA
         United States (A)             6.8             1.3          0.021         +

    Table 2. (cont'd)
                                                                                                  

    Substance (No.)                    Most recent     Intakeb                    Annual volume in
                                       annual volume                            naturally 
                                       (kg)a           g/day       g/kg bw      occurring
                                                                    per day       foods (kg)c
                                                                                                  
    3-Methylbutanethiol (513)

         Europe                        NR              NA           NA
         United States (A)             0.045           0.01         0.0001        23

    2-Pentanethiol (514)

         Europe                        12              2            0.04
         United States (A)             11              2            0.03          +

    2-Methyl-1-butanethiol (515)

         Europe                        2.5             0.5          0.01
         United States (1982)          0.1             0.02         0.0003        +

    Cyclopentanethiol (516)

         Europe                        NR              NA           NA
         United States (A)             4.5             1            0.01          -

    3-Methyl-2-butanethiol (517)

         Europe                        0.1             0.02         0.0003
         United States                 0.1             0.02         0.0003        +

    1-Hexanethiol (518)

         Europe                        NR              NA           NA
         United States (A)             0.045           0.01         0.0001        +

    Table 2. (cont'd)
                                                                                                  

    Substance (No.)                    Most recent     Intakeb                    Annual volume in
                                       annual volume                            naturally 
                                       (kg)a           g/day       g/kg bw      occurring
                                                                    per day       foods (kg)c
                                                                                                  

    2-Ethylhexanethiol (519)

         Europe                        NR              NA           NA
         United States (A)             0.045           0.01         0.0001        +

    2,3, or 10-Mercatopinane (520)

         Europe                        0.3             0.1          0.001
         United States                 50              10           0.2           -

    Allyl mercaptan (521)

         Europe                        1.3             0.2          0.003         
         United States                 8               2            0.03          480

    Prenythiol (522)

         Europe                        NR              NA           NA
         United States (A)             1               0.2          0.003         +

    1-para-Menthene-8-thiol (523)

         Europe                        2.8             1            0.01
         United States (A)             4.5             1            0.01          +

    Thiogeraniol (524)

         Europe                        9               2            0.03
         United States                 0.1             0.02         0.0003        -

    Table 2. (cont'd)
                                                                                                  

    Substance (No.)                    Most recent     Intakeb                    Annual volume in
                                       annual volume                            naturally 
                                       (kg)a           g/day       g/kg bw      occurring
                                                                    per day       foods (kg)c
                                                                                                  
    Benzenethiol (525)

         Europe                        6               1            0.02
         United States                 160             30           1             +

    Benzyl mercaptan (526)

         Europe                        10              2            0.03
         United States                 2               0.4          0.01          +

    Phenethyl mercaptan (527)

         Europe                        NR              NA           NA
         United States (A)             1               0.2          0.003         +

    ortho-Toluenethiol (528)

         Europe                        140             27           0.4
         United States                 0.9             0.2          0.003         +

    2-Ethylthiophenol (529)

         Europe                        0.001           0.0002       0.0
         United States                 0.5             0.10         0.002         -

    2,6-Dimethylthiophenol (530)

         Europe                        11              2            0.03
         United States                 0.1             0.02         0.0003        +

    Table 2. (cont'd)
                                                                                                  

    Substance (No.)                    Most recent     Intakeb                    Annual volume in
                                       annual volume                            naturally 
                                       (kg)a           g/day       g/kg bw      occurring
                                                                    per day       foods (kg)c
                                                                                                  
    2-Naphthalenethiol (531)

         Europe                        NR              NA           NA
         United States (A)             0.34            0.1          0.001         +

    1,2-Ethanedithiol (532)

         Europe                        0.01            0.002        0.00003
         United States (A)             4.5             0.9          0.01          +

    Bis(methylthio)methane (533)

         Europe                        NR              NA           NA
         United States (A)             500             94           2             +

    2-Methyl-1,3-dithiolane (534)

         Europe                        0.5             0.1          0.002
         United States (A)             23              4            0.1           +

    1,3-Propanedithiol (535)

         Europe                        7               1            0.02
         United States (A)             4.5             0.9          0.01          +

    1,2-Propanedithiol (536)

         Europe                        NR              NA           NA
         United States (A)             4.5             0.9          0.01          -

    Table 2. (cont'd)
                                                                                                  

    Substance (No.)                    Most recent     Intakeb                    Annual volume in
                                       annual volume                            naturally 
                                       (kg)a           g/day       g/kg bw      occurring
                                                                    per day       foods (kg)c
                                                                                                  

    1,2-Butanedithiol (537)

         Europe                        NR              NA           NA
         United States                 0.9             0.2          0.003         -

    1,3-Butanedithiol (538)

         Europe                        NR              NA           NA
         United States (A)             4.5             0.9          0.01          -

    2,3-Butanedithiol (539)

         Europe                        0.4             0.1          0.001
         United States                 0.9             0.2          0.003         -

    1,6-Hexanedithiol (540)

         Europe                        13              2.5          0.04
         United States                 0.5             0.1          0.002         +

    1,8-Octanedithiol (541)

         Europe                        17              3            0.1
         United States (A)             4.5             0.9          0.01          -

    1,9-Nonanedithiol (542)

         Europe                        0.01            0.002        0.00003
         United States (A)             4.5             0.9          0.01          -

    Table 2. (cont'd)
                                                                                                  

    Substance (No.)                    Most recent     Intakeb                    Annual volume in
                                       annual volume                            naturally 
                                       (kg)a           g/day       g/kg bw      occurring
                                                                    per day       foods (kg)c
                                                                                                  
    Trithioacetone (543)

         Europe                        12              2            0.04
         United States                 2               0.4          0.01          +

    3-Mercapto-3-methyl-1-butanol (544)

         Europe                        NR              NA           NA
         United States (A)             10              1.9          0.03          +

    3-Mercaptohexanol (545)

         Europe                        NR              NA           NA
         United States (A)             4.5             1            0.01          +

    2-Mercapto-3-butanol (546)

         Europe                        33              6            0.1
         United States                 0.5             0.1          0.002         -

    alpha-Methyl--hydroxypropyl alpha-methyl--mercaptopropyl sulfide (547)

         Europe                        NR              NA           NA
         United States                 4               1            0.01          -

    4-Methyoxy-2-methyl-2-butanethiol (548)

         Europe                        NR              NA           NA
         United States (A)             4               0.8          0.01          +

    Table 2. (cont'd)
                                                                                                  

    Substance (No.)                    Most recent     Intakeb                    Annual volume in
                                       annual volume                            naturally 
                                       (kg)a           g/day       g/kg bw      occurring
                                                                    per day       foods (kg)c
                                                                                                  
    3-Mercapto-3-methylbutyl formate (549)

         Europe                        NR              NA           NA
         United States (A)             0.5             0.1          0.002         +

    2,5-Dihydroxy-1,4-dithiane (550)

         Europe                        NR              NA           NA
         United States (A)             0.45            0.1          0.001         -

    2-Mercaptopropionic acid (551)

         Europe                        17              3            0.1
         United States                 440             84           1             -

    Ethyl 2-mercaptopropionate (552)

         Europe                        3.2             0.5          0.01
         United States                 2               0.4          0.01          +

    Ethyl 3-mercaptopropionate (553)

         Europe                        0.6             0.1          0.002
         United States (A)             230             43           1             +

    3-Mercaptohexyl acetate (554)

         Europe                        NR              NA           NA
         United States (A)             1               0.2          0.003         +

    Table 2. (cont'd)
                                                                                                  

    Substance (No.)                    Most recent     Intakeb                    Annual volume in
                                       annual volume                            naturally 
                                       (kg)a           g/day       g/kg bw      occurring
                                                                    per day       foods (kg)c
                                                                                                  
    3-Mercaptohexyl butyrate (555)

         Europe                        NR              NA           NA
         United States (A)             1               0.2          0.003         +

    3-Mercaptohexyl hexanoate (556)

         Europe                        NR              NA           NA
         United States (A)             1               0.2          0.003         +

    1-Mercapto-2-propanone (557)

         Europe                        NR              NA           NA
         United States (A)             0.45            0.09         0.001         +

    3-Mercapto-2-butanone (558)

         Europe                        26              5            0.1
         United States (1982)          0.2             0.04         0.001         +

    2-Keto-4-butanethiol (559)

         Europe                        NR              NA           NA
         United States                 0.5             0.1          0.002         -

    3-Mercapto-2-pentanone (560)

         Europe                        NR              NA           NA
         United States                 0.5             0.1          0.002         -

    Table 2. (cont'd)
                                                                                                  

    Substance (No.)                    Most recent     Intakeb                    Annual volume in
                                       annual volume                            naturally 
                                       (kg)a           g/day       g/kg bw      occurring
                                                                    per day       foods (kg)c
                                                                                                  

    para-Mentha-8-thiol-3-one (561)

         Europe                        86              16           0.3
         United States                 9               2            0.03          +

    2,5-Dimethyl-2,5-dihydroxy-1,4-dithiane (562)

         Europe                        1.2             0.2          0.004
         United States                 0.9             0.2          0.003         -

    Sodium 3-mercaptooxopropionate (563)

         Europe                        NR              NA           NA
         United States (A)             1               0.2          0.003         -

    Dimethyl disulfide (564)

         Europe                        57              11           0.2           
         United States                 13              2            0.04          1 400

    Methyl propyl disulfide (565)

         Europe                        32              6            0.10          
         United States                 0.1             0.02         0.0003        13 000

    Propyl disulfide (566)

         Europe                        28              5            0.1           
         United States                 0.5             0.1          0.002         14 000

    Table 2. (cont'd)
                                                                                                  

    Substance (No.)                    Most recent     Intakeb                    Annual volume in
                                       annual volume                            naturally 
                                       (kg)a           g/day       g/kg bw      occurring
                                                                    per day       foods (kg)c
                                                                                                  
    Diisopropyl disulfide (567)

         Europe                        NR              NA           NA
         United States (A)             41              8            0.1           +

    Allyl methyl disulfide (568)

         Europe                        0.01            0.002        0.00003
         United States (1982)          0.1             0.02         0.0003        +

    Methyl 1-propenyl disulfide (569)

         Europe                        NR              NA           NA
         United States (1982)          4               1            0.01          1 

    Propenyl propyl disulfide (570)

         Europe                        NR              NA           NA
         United States (1970)          40              8            0.1           +

    Methyl 3-methyl-1-butenyl disulfide (571)

         Europe                        NR              NA           NA
         United States (A)             0.45            0.1          0.001         +

    Allyl disulfide (572)

         Europe                        480             92           2
         United States                 44              8            0.1           +

    Table 2. (cont'd)
                                                                                                  

    Substance (No.)                    Most recent     Intakeb                    Annual volume in
                                       annual volume                            naturally 
                                       (kg)a           g/day       g/kg bw      occurring
                                                                    per day       foods (kg)c
                                                                                                  

    3,5-Dimethyl-1,2,4-trithiolane (573)

         Europe                        0.2             0.04         0.001
         United States (1982)          0.5             0.0:         0.002         +

    3-Methyl-1,2,4-trithiane (574)

         Europe                        0.6             0.1          0.002
         United States (A)             230             43           1             +

    Dicyclohexyl disulfide (575)

         Europe                        0.1             0.02         0.0003
         United States                 0.9             0.2          0.003         -

    Methyl phenyl disulfide (576)

         Europe                        NR              NA           NA
         United States (A)             1               0.2          0.003         +

    Methyl benzyl disulfide (577)

         Europe                        0.1             0.02         0.0003
         United States                 0.5             0.1          0.002         +

    Table 2. (cont'd)
                                                                                                  

    Substance (No.)                    Most recent     Intakeb                    Annual volume in
                                       annual volume                            naturally 
                                       (kg)a           g/day       g/kg bw      occurring
                                                                    per day       foods (kg)c
                                                                                                  

    Phenyl disulfide (578)

         Europe                        NR              NA           NA
         United States (1982)          0.2             0.04         0.001         -

    Benzyl disulfide (579)

         Europe                        0.1             0.01         0.0002
         United States (1982)          0.5             0.1          0.002         +

    2-Methyl-2-(methyldithio) propanal (580)

         Europe                        NR              NA           NA
         United States (A)             9               2            0.03          +

    Ethyl 2-(methyldithio)propionate (581)

         Europe                        NR              NA           NA
         United States (A)             0.45            0.1          0.001         +

    Dimethyl trisulfide (582)

         Europe                        9               2            0.03          
         United States                 0.1             0.02         0.0003        3 000

    Methyl ethyl trisulfide (583)

         Europe                        NR              NA           NA
         United States (A)             3               1            0.01          +

    Table 2. (cont'd)
                                                                                                  

    Substance (No.)                    Most recent     Intakeb                    Annual volume in
                                       annual volume                            naturally 
                                       (kg)a           g/day       g/kg bw      occurring
                                                                    per day       foods (kg)c
                                                                                                  
    Methyl propyl trisulfide (584)

         Europe                        1.7             0.3          0.01          
         United States                 0.4             0.1          0.001         13  000

    Dipropyl trisulfide (585)

         Europe                        60              11           0.2           
         United States                 5               1            0.02          16 000

    Allyl methyl trisulfide (586)

         Europe                        NR              NA           NA
         United States (A)             4.5             0.9          0.01          +

    Diallyl trisulfide (587)

         Europe                        29              6            0.1
         United States (1970)          0.1             0.02         0.0003        +

    Diallyl polysulfide (588)

         Europe                        10              2            0.03
         United States                 0.1             0.02         0.0003        -


    TOTAL

         Europe                        6 100
         United States                 5 300

                                                                                                  

    A, volume anticipated on the basis of recent estimates (communication from the Flavor and Extract
    Manufacturers' Association to the Committee); NR, not reported; NA, not applicable; +, reported
    to occur naturally in foods (CIVO-TNO, 1994), but quantitative data were not available; -, not
    reported to occur naturally in foods

    a    Volumes reported in a survey in Europe (International Organization of the Flavor
    Industry, 1995) and in a survey in the United States (National Academy of Sciences, 1989).
    Most of the data for the United States are for 1987 (and there is no entry); when data
    for 1987 were not available, data for 1982 or 1970 were used, as indicated.

    b    Per capita intake (mg/day) calculated as follows:
    [(annual usage, kg)  (1  109 mg/kg) / (population  0.6   365 days)], where population
    (10% 'eaters only') = 32  106 for Europe and 24  106 for the USA; 0.6 represents the
    assumption that only 60% of the annual usage of the flavour was reported in the survey.
    Intake (mg/kg bw per day) calculated as follows: [(mg/day)/body weight], where body weight = 60 kg.

    c    From Stofberg & Kirschman (1985); Stofberg & Grundschober (1987)
    

         Potential toxicity can be deduced by comparison with structural
    analogues on the basis of metabolic similarities. In the absence of
    information on the toxicity of structural analogues, however, it is
    not possible to conclude  a priori that the substances are
    metabolized to innocuous products.

    (i)  Simple sulfides (thioethers)

         Once alkyl and aromatic thioethers, commonly called 'sulfides',
    enter the systemic circulation, they are rapidly oxidized to
    sulfoxides and, depending on the structure of the thioether, may be
    further oxidized to sulfones. Sulfoxides and sulfones are major
    urinary metabolites of simple sulfides. Aliphatic thioethers (Nos
    452-455, 457, 458, and 533) and thioethers containing an aromatic
    nucleus (Nos 459 and 460) yield mixtures of sulfoxide and sulfone
    metabolites. Enzymes of the cytochrome P450 superfamily and
    flavin-containing monooxygenases catalyse the oxidation of thioethers
    to sulfoxides. Oxidation of sulfoxides to the corresponding sulfones
    occurs both in tissues and in aerobic microorganisms and is an
    irreversible metabolic reaction in mammals. Sulfoxides can also be
    metabolized back to the thioether by aldehyde oxidase, thioredoxin and
    its reductase, and the gut microflora in the anaerobic environment of
    the lower bowel.

         The methyl aromatic thioethers (Nos 459 and 460) are predicted to
    be major metabolites of the corresponding aromatic thiols (Nos 525 and
    526, subgroup iv) and would be oxidized to sulfoxides and sulfones,
    which would be excreted.

    (ii)  Acyclic sulfides with oxidized side-chains

         The presence of other functional groups, such as alcohol (Nos
    461-463), aldehyde (Nos 465-471 and 505), ester (Nos 472-481), acid
    (No. 501), -ketone (Nos 495-497, 500, and 502), and phenol (No. 503),
    provides centres of greater polarity and additional sites for the
    biotransformation of thioethers. The presence of these polar groups
    would also result in increased renal excretion. The biotransformations
    of such oxygenated, carbon-containing, functional groups are well
    characterized and have been described for groups of flavouring agents
    previously evaluated by the Committee. Concurrent metabolism of
    various substrates at both sulfur and oxygenated functional groups has
    been reported, and sulfoxide formation usually predominates as the
    major metabolic pathway of detoxification. Experiments  in vitro
    suggest that hydrolysis of carboxyl esters occurs in the presence of
    thioether (sulfide) groups. In consequence, thioethers with oxidized
    side-chains would be expected to be eliminated more rapidly than
    simple sulfides.

    (iii)  Cyclic sulfides

         Oxidation of unsubstituted and methyl-substituted cyclic
    thioethers by the cytochrome P450 superfamily produces the
    corresponding sulfoxides. The mono-sulfoxides are predicted to be the

    main urinary metabolites of simple cyclic sulfides (Nos 456, 534, and
    543). The metabolism of cyclic sulfides containing oxidized carbon
    atoms (Nos 464, 498, 499, 550, and 562) has not been studied but would
    be predicted to involve extensive  S-oxidation and possibly oxidation
    or conjugation of alcohol groups. The polarity of the hydroxy
    thioethers (Nos 550 and 562) may allow their elimination unchanged.

    (iv)  Simple thiols

         The simple thiol flavouring agents considered are alkyl and
    alicyclic thiols (Nos 508-524, 526, and 527) and aromatic thiols
    (thiophenols; Nos 525 and 528-531). These substances may be
    metabolized along several pathways. Simple aliphatic and aromatic
    thiols undergo  S-methylation in mammals to produce the corresponding
    methyl thioether or sulfide. Methylation is catalysed by thiopurine
    methyltransferase in the cytoplasm and thiol methyltransferase in
    microsomes, and both reactions require  S-adenosyl-l-methionine as a
    methyl group donor. Thiopurine methyltransferase is present in human
    liver, kidney, and erythrocytes; preferential substrates for this
    enzyme include aromatic and heterocyclic thiols.  S-Methylation of
    aliphatic thiols is catalysed by microsomal thiol methyltransferase,
    and the resulting methyl thioether (sulfide) metabolite would undergo
     S-oxidation to give the methyl sulfoxide and methyl sulfone
    analogues as urinary products.

         Thiols may react with glutathione and other endogenous thiol
    substances to form mixed disulfides. Both microsomal and cytoplasmlic
    thioltransferases have been reported to catalyse the formation of
    mixed disulfides. The resulting mixed disulfides can undergo reduction
    back to thiols, oxidative desulfuration, or oxidation to a sulfonic
    acid via the intermediate thiosulfinate and sulfinic acids. The
    principal form in the circulation would probably be a mixed disulfide
    formed with albumin.

          S-Glucuronidation of aromatic thiols has been reported, and
    this may be a pathway for the metabolism of aromatic thiols
    (thiophenols) (Nos 525 and 528-531) and simple aromatic disulfides
    (Nos 576 and 578; subgroup vii) after their reduction (see below).
    Glucuronyl transferases behave similarly towards hydroxyl and
    sulfydryl groups, and the two activities have the same subcellular
    location and optimal pH.

         Thiols may be oxidized to form sulfenic acids (RSOH), which are
    unstable and readily undergo further oxidation to sulfinic (RSO2H)
    and sulfonic (RSO3H) acids or combine with nucleophiles. The sulfonic
    acid group is a highly polar centre and makes molelcules highly
    soluble in water. In general, sulfonic acids are stable to metabolism.

         Alkyl thiols of low relative molecular mass undergo oxidative
    desulfuration  in vivo to yield CO2 and SO4=. This reaction has
    been shown, for example, for methanethiol (methyl mercaptan; No. 508).
    Whereas the carbon atom from thiols may be used in the biosynthesis of
    amino acids, the sulfur atom is not used significantly in the
    synthesis of sulfur-containing amino acids.

    (v)  Thiols with oxidized side chains

         Although alkyl thiols with oxidized side-chains (Nos 544-549,
    551-561, and 563) comprise a significant proportion of the flavouring
    agents evaluated, their metabolic fate has not been studied. Their
    metabolism is predicted to involve a combination of the pathways
    described above for simple thiols and further oxidation or conjugation
    of the oxidized side-chain. The class III compound, sodium
    3-mercapto-oxopropionate (No. 563), would be expected to be eliminated
    very rapidly by metabolism at both the thiol and keto-acid groups.

    (vi)  Dithiols

         The metabolism of the simple aliphatic dithiols evaluated (Nos
    532 and 535-542) is predicted to involve the pathways described above
    for simple thiols. Urinary metabolites could result from methylation,
     S-oxidation of one S atom to yield a polar sulfonate, and the
    formation of mixed disulfides of low relative molecular mass such as
    cysteine, an endogenous thiol. The longer, linear dithiols (Nos 535
    and 540-542) could form intramolecular disulfide bonds, with
    interconversion between dithiol and cyclic disulfide forms.

    (vii)  Simple disulfides

         The reduction of xenobiotic disulfides is believed to be
    extensive, and the reaction may be catalysed enzymatically by
    thioltransferases and chemically by exchange with glutathione,
    thioredoxin, cysteine, and other endogenous thiols. Reduction of the
    non-cyclic disulfides considered in the group of flavours (Nos 564-572
    and 575-579) would result in the formation of thiols of low relative
    molecular mass, which would then be metabolized by the various
    pathways described above for simple thiols.

    (viii)  Disulfides with oxidized side-chains

         As discussed above for subgroups (ii) and (iii), additional sites
    of carbon oxidation would result in greater polarity and further
    oxidation or conjugation of the flavouring agents evaluated (Nos 580
    and 581). However, as disulfide bonds in substances in subgroup (v)
    are susceptible to reductive cleavage, this would be expected to be
    the initial metabolic reaction, and the polarity of the side-chains
    would primarily affect elimination of the thiol fragments.

    (ix)  Trisulfides and polysulfides

         The trisulfide of glutathione is labile and readily converted to
    the disulfide, the sulfur being released as hydrogen sulfide.
    Trisulfides and polysulfides are predicted to be converted rapidly to
    the corresponding disulfides, which would then be reduced to thiols,
    which themselves would follow the pathways described above for thiols.
    The potential toxicity of trisulfides (Nos 582-587) and polysulfides
    (No. 588) is probably related to their metabolic lability and to the
    nature of the eventual thiol (e.g. allyl thiol).

    (x)  Heterocyclic disulfides: The heterocyclic disulfides (Nos 573 and
    574) are five-and six-carbon rings which also contain a cyclic
    thioether bond. Lipoic acid, an endogenous substance, is a
    five-membered cyclic disulfide which undergoes rapid redox cycling
    between ring disulfide and open dithiol forms. The principal metabolic
    pathways are predicted to be disulfide reduction with ring opening to
    produce a dithiol, and S-oxidation of the cyclic thioether.

    (xi)  Thioesters

         Thioester groups (-S-CO-) are present in a number of the
    flavouring agents evaluated (Nos 482-494, 504, and 506). Hydrolysis of
    esters has been considered previously by the Committee, but that of
    thioesters has not. Thioesters are hydrolysed by lipase and esterases,
    and the rate of hydrolysis increases as the length of the C-chain of
    the carboxylic acid fragment increases, and decreases as oxygenation
    of the carbon chain in the thiol moiety increases.

         Hydrolysis could result in a thioic acid and an alcohol or a
    carboxylic acid and a thiol (the metabolic fates of which have been
    outlined above). Data for dithioic acids and esters indicate that the
    esters of monothioic acids would be poor substrates for oxidation, but
    the monothioic acid released by hydrolysis would be oxidized to the
    dioxo acid. Other possibilities for elimination  in vivo include renal
    excretion of thiocarboxylic acid. The substances evaluated (with the
    exceptions of prenyl thioacetate (No. 491) and allyl thiopropionate
    (No. 490)) are simple linear alkyl compounds, branched-chain alkyl
    compounds, or their side-chain hydroxyester analogues, so that
    comparison of the toxicity of the different substances is reasonable.

    (xii)  Sulfoxides

         The metabolism of sulfoxides by oxidation and reduction is
    described above under 'Thioethers'. The only sulfoxide flavouring
    agent evaluated was methylsulfinylmethane (dimethyl sulfoxide, DMSO;
    No. 507), for which data were available on both metabolism and
    toxicity in experimental animals and humans. DMSO is readily absorbed
    and excreted in urine as the parent sulfoxide and dimethyl sulfone.

    1.4  Application of the Procedure for the Safety
         Evaluation of Flavouring Agents

    Step 1.   In applying the Procedure for the Safety Evaluation of
              Flavouring Agents to the above-mentioned aliphatic and
              aromatic sulfides and thiols, the Committee assigned 97 of
              the 137 substances (Nos 452-455, 457, 461-463, 465-497, 500,
              502, 508-515, 517-519, 522, 524, 532, 533, 535-542, 544-560,
              562, 564-567, 569-571, and 580-585), which may or may not
              contain an additional oxygenated functional group, to
              structural class I. The Committee assigned 34 of the 137
              substances to structural class II because they are aromatic
              sulfides or thiols (Nos 459, 460, 503, 504, 525-528, 530,
              531, 576, 577, and 579), alicyclic (Nos 506, 516, 520, 523,
              561, and 575) or heterocyclic substances (Nos 456, 464, 498,
              499, 534, 543, 573, and 574), or allyl mercaptan or sulfides
              (Nos 458, 521, 568, 572, and 586-588), which are common
              components of food. The aromatic thiols or thioethers that
              are not common compo-nents of food (Nos 505, 529, and 578)
              were assigned to structural class III. The remaining three
              substances were also assigned to structural class III by
              virtue of the fact that they are aliphatic thiols or
              thioethers containing more than three functional groups (Nos
              501 and 563) or do not contain divalent sulfur (No. 507). 

    Step 2.   None of the substances in this group can be predicted to be
              metabolized to innocuous products. The evaluation of these
              substan-ces therefore proceeded via the right-hand side of
              the decision tree.

    Step B3.  The estimated daily  per capita intake in Europe and in the
              United States for each of the substances in the overall
              group of 137 flavouring agents is below the threshold for
              human intake for the structural class in which the substance
              falls. The thresholds are 1800 g/person per day for class
              I, 540 g/person per day for class II, and 90 g/person per
              day for class III.

    Step B4.  The Committee considered the results of 90-day studies of
              toxicity in rodents for 27 substances in this group of
              flavouring agents. The Committee noted that the single or
              multiple doses of flavouring agents tested in a number of
              studies had no effect in rats and that the NOELs were
              consequently derived from studies that did not show toxic
              effects. The results of long-term studies in multiple
              species were considered for one substance, DMSO (No. 507).
              To facilitate comparisons of the toxicity of structurally
              related substances, the agents were considered in subgroups
              (i)- (xii) on the basis of the position of the sulfur atom
              (see Tables 1 and 3). Toxicity was compared within and
              across subgroups with no restriction on the basis of
              structural class assignment (Step 1). 

              (i)  Simple sulfides (thioethers): This subgroup comprises
              nine flavouring agents that are simple thioethers. The NOEL
              for methyl sulfide (No. 452) in a 14-week study in rats
              treated with multiple doses by gavage was 250 mg/kg bw per
              day. This NOEL provides an adequate basis for evaluation of
              five structurally and metabolically related substances (Nos
              453, 454, 455, 457, and 533); however, the NOEL for methyl
              sulfide was considered inappropriate for evaluation of allyl
              sulfide (No. 458) and two aromatic thioethers, methyl phenyl
              sulfide and benzyl methyl sulfide (Nos 459 and 460,
              respectively), and the evaluation of these three substances
              therefore proceeded to step B5.

              (ii)  Acyclic sulfides with oxidized side-chains: This
              subgroup comprises 28 flavouring agents that are acyclic
              thioethers with oxidized side-chains. The NOEL in a 90-day
              study in rats treated with a single dose of
              2-(methylthiomethyl)-3-phenylpropenal (No. 505) was 1.4
              mg/kg bw per day. This substance is an aromatic compound
              with a sulfide group in an unsaturated side-chain; it was
              assigned to structural class III, because it is not a common
              component of food. Data for methyl sulfide (No. 452) were
              also considered relevant for assessing the toxicity of
              sulfide substances with oxidized side-chains (Nos 461-463,
              465-469, 472-481, 495-497, and 500-503). Although
              2-(methylthiomethyl)-3-phenylpropenal (No. 505) is not an
              aryl thioether, the safety margin between its NOEL and the
              intake of ortho-(methylthio)phenol pentanone (No. 503) was
              considered to be adequate. The NOEL for
              2-(methylthiomethyl)-3-phenylpropenal (No. 505) does not
              provide a high margin of safety (i.e. > 1000) for methyl
              3-methylthiopropionate (No. 472) at the current estimated
              level of intake; however, the simple side-chain acid and
              ester would have little toxic potential, and the NOEL for
              methyl sulfide (No. 452) provides an adequate margin of
              safety. The NOELs for 2-(methylthio-methyl)-3-phenylpropenal
              (No. 505) and methyl sulfide (No. 452, subgroup (i)) were
              considered inappropriate for evaluation of the toxicity of
              two alpha,beta-unsaturated carbonyls (Nos 470 and 471)
              because they are potentially more reactive and toxic, and
              the evaluation of these substances therefore proceeded to
              step B5.

              (iii)  Cyclic sulfides: This subgroup comprises eight
              substances that are cyclic thioethers. NOELs of 0.44 mg/kg
              bw per day for 2-methyl-4-propyl-1,3-oxathiane (No. 464),
              9.2 mg/kg bw per day for 4,5-dihydro-3(2 H)-thiophenone
              (No. 498), 7 mg/kg bw per day for 2-methyl-1,3-dithiolane
              (No. 534), 0.2 mg/kg bw per day for trithioace-tone (No.
              543), and 3.1 mg/kg bw per day for

              2,5-dimethyl-2,5-dihydroxy-1,4-dithiane (No. 562) were
              reported. These values provide an adequate margin of safety
              for evaluation of the toxicity of substances No. 456, 499,
              and 550.

        Table 3. Comparison of the toxicity and intake data used in the safety evaluations of
    137 simple aliphatic and aromatic sulfides and thiols, by subgroupa
                                                                                            

    Subgroup                      Adequate NOEL     Adequate NOEL         No adequate NOEL
                                  for substanceb    for structurally      for substance or
                                                    related substanceb    related substance,
                                                                          but intake 
                                                                          < 1.5 g/dayc
                                                                                            

    (i)      Simple sulfides      No. 452           Nos 453-455,          Nos 458-460
             (thioethers)                           457, 533

    (ii)     Acyclic thioethers   No. 505           Nos 461-463,          Nos 470, 471
             with oxidized                          465-469, 472-481,
             side-chains                            495-497, 500-503

    (iii)    Cyclic sulfides      Nos 464, 498,     Nos 456, 499,         N/R
                                  534, 543, 562     550

    (iv)     Thiols               Nos 516, 520,     Nos 508-515,          N/R
                                  528, 530, 531     517-519, 521-527,
                                                    529

    (v)      Thiols with          Nos 546, 547,     Nos 544, 545, 548,    N/R
             oxidized             560               549, 551-559, 561,
             side-chains                            563

    (vi)     Dithiols             Nos 539, 541      Nos 532, 535-538,     N/R
                                                    540, 542

    (vii)    Simple disulfides    Nos 566, 575,     Nos 564, 565,         N/R
                                  577               567-572, 576, 578,
                                                    579

    (viii)   Disulfides with      None              Nos 580, 581          N/R
             oxidized 
             side-chains

    (ix)     Trisulfides and      Nos 585, 587      Nos 582-584, 586,     N/R
             polysulfides                           588

    (x)      Heterocyclic         No. 573           No. 574               N/R
             disulfides

    Table 3. (continued)

                                                                                            

    Subgroup                      Adequate NOEL     Adequate NOEL         No adequate NOEL
                                  for substanceb    for structurally      for substance or
                                                    related substanceb    related substance,
                                                                          but intake 
                                                                          < 1.5 g/dayc
                                                                                            

    (xi)     Thioesters           Nos 483, 484      Nos 482, 485-494,     N/R
                                                    504, 506

    (xii)    Sulfoxides           No. 507           N/R                   N/R
                                                                                            

    N/R, not relevant to the evaluation
    a  See Table 1 for further details of the evaluations.
    b  See Figure 1, step B4 and pp. 121-123 for further information. 
    c  See Figure 1, step B5 and pp. 121-123 for further information.
    
              (iv)  Simple thiols: This subgroup comprises 24 flavouring
              agents that are simple thiols. NOELs of 0.56 mg/kg bw per
              day for cyclopentanethiol (No. 516), 0.06 mg/kg bw per day
              for 2,3-and 10-mercaptopinane (No. 520), 0.52 mg/kg bw per
              day for  ortho-toluenethiol (No. 528), 0.43 mg/kg bw per
              day for 2,6-dimethyl-thiophenol (No. 530), and 3.4 mg/kg bw
              per day for 2-naphthalenethiol (No. 531) were reported.
              These values provide adequate margins of safety for the
              individual substances and for the other structurally related
              thiols in the group in relation to current estimates of
              intake, with the exception of 2,3 and 10-mercaptopinane (No.
              520). A margin of safety of about 300 (based on an estimated
              modified  per capita intake of 0.2 g/kg bw per day in the
              United States) was obtained from the results of a 90-day
              study in which only a single dose of 0.06 mg/kg bw per day
              was tested. This substance was therefore also evaluated by
              comparison with other substances in this subgroup (Nos 516,
              528, 530, and 531) for which there was an adequate margin of
              safety. The Committee noted that Nos 521-524 are unsaturated
              thiols. Of these, allyl mercaptan (allyl thiol; No. 521)
              would be expected to be more toxic than others that have
              double bonds in different positions (by analogy to their
              oxygenated analogues). Although data were not available on
              allyl mercaptan (No. 521), the NOEL of diallyl trisulfide
              (No. 587), which would be converted to allyl mercaptan after
              reduction to allyl disulfide, was 4.6 mg/kg bw per day in a
              90-day study in rats. This NOEL was considered to provide an
              adequate safety margin for Nos 521-524.

              (v)  Thiols with oxidized side-chains: This subgroup
              comprises thiols with oxygenated side-chains. The NOELs
              available for three of the substances in class I (1.9 mg/kg
              bw per day for 2-mercapto-3-butanol (No. 546), 2.8 mg/kg bw
              per day for alpha-methyl-beta-hydroxypropyl
              alpha-methyl-beta-mercaptopropyl sulfide (No. 547), and 1.9
              mg/kg bw per day for 3-mercapto-2-pentanone (No. 560)) were
              considered to provide adequate safety margins for the
              flavouring agents in this subgroup, including the one
              substance in structural class III, 3-mercapto-oxopropionate
              (No. 563). Although the last compound has more than three
              functional groups, the oxopropionate moiety would have
              little toxic potential, and the NOELs for Nos 546, 547, and
              560 were considered to provide an adequate margin of safety.

              (vi)  Dithiols: This subgroup comprises flavouring agents
              that are dithiols. The NOEL for 2,3-butanedithiol (No. 539)
              and 1,6-hexane-dithiol (No. 540) was 0.7 mg/kg bw per day,
              which provides adequate margins of safety for all of the
              substances in the subgroup.

              (vii)  Simple disulfides: This subgroup comprises 14
              flavouring agents that are disulfides. The major metabolites
              of these unsaturated disulfides would be thiols. The NOELs
              were 7.7 mg/kg bw per day for propyl disulfide (No. 566),
              0.23 mg/kg bw per day for dicyclohexyl disulfide (No. 575),
              and 1.2 mg/kg bw per day for methyl benzyl disulfide (No.
              577). These values provide adequate margins of safety for
              each substance tested and for four structurally related
              substances, Nos 564, 565, 567, and 579, at currently
              estimated levels of intake. The substances in this subgroup
              for which NOELs are available do not include unsaturated or
              aryl disulfides. The aryl disulfides, methyl phenyl
              disulfide and phenyl disulfide (Nos 576 and 578,
              respectively), would be rapidly reduced to thiophenol, and
              the NOEL of 3.4 mg/kg bw per day for 2-naphtha-lenethiol
              (No. 531, subgroup iv) was considered to provide an adequate
              safety margin for these agents. The Committee was aware that
              propenyl disulfides can cause haemolytic anaemia in certain
              species after short-term exposure. This effect would be of
              concern to susceptible individuals. Substances Nos 568 and
              572 would be metabolized to allyl mercaptan (No. 521;
              subgroup iv). The Committee noted that the NOEL for diallyl
              trisulfide (No. 587; subgroup ix) in a 90-day study in rats
              given a single dose was 4.6 mg/kg bw per day, and that this
              would provide an adequate safety margin for the allyl thiol
              produced on reduction of substances Nos 568 and 572.
              Di(1-propenyl) disulfide was about four times more potent
              than allyl disulfide (No. 572) and about 20 times more
              potent than propyl disulfide (No. 566). The intakes of the

              related propenyl and butenyl flavours Nos 569, 570, and 571
              gave safety margins of > 50 000 in comparison with the NOEL
              for propyl disulfide (No. 566), and this was considered to
              be adequate to allow for the differences in potency.

              (viii)  Disulfides with oxidized side-chains: This subgroup
              consists of two disulfides with oxidized side-chains,
              2-methyl-2-(methyldithio)-propanal (No. 580) and ethyl
              2-(methyldithio)propionate (No. 581). The toxicity of these
              agents has not been studied, but the Committee considered
              these substances by analogy to disulfides (subgroup vii) and
              concluded that adequate margins of safety were available,
              given their greater polarity and the presence of thiols with
              and without oxidized side-chains, i.e. subgroups (iv) and
              (v).

              (ix)  Trisulfides and polysulfides: This subgroup consists
              of six trisulfides and one polysulfide. NOELs of 4.8 mg/kg
              bw per day for dipropyl trisulfide (No. 585) and 4.6 g/kg bw
              per day for diallyl trisulfide (No. 587) were reported,
              which gave adequate margins of safety for all substances in
              this subgroup.

              (x)  Heterocyclic disulfides: This subgroup comprises two
              flavouring agents that are heterocyclic disulfides. The NOEL
              of 1.9 mg/kg bw per day for 3,5-dimethyl-1,2,4-trithiolane
              (No. 573) provides an adequate margin of safety for this
              substance at current levels of use. 3-Methyl-1,2,4-trithiane
              (No. 574) was reported to have no effect at the single dose
              of 0.3 mg/kg bw per day tested in a 90-day study; this dose
              provides a margin of safety of only 100 at the estimated
              modified  per capita intake level of 1 g/kg bw per day in
              the United States. However, the NOEL for the closely related
              compound 3,5-dimethyl-1,2,4-trithiolane provides an adequate
              margin of safety (> 1000).

              (xi)  Thioesters: This subgroup consists of 15 thioesters.
              The NOELs of 6.5 mg/kg bw per day for ethylthioacetate (No.
              483) and 1000 mg/kg bw per day for methylthiobutyrate (No.
              484) give an adequate margin of safety for all other esters
              in this group. The conclusion that the current intake levels
              of allyl thiopropionate and prenyl thioacetate are safe is
              supported by the NOEL of 4.6 mg/kg bw per day for the
              unsaturated diallyl trisulfide (No. 587), which would be
              reduced to allyl disulfide and then allyl sulfide.

              (xii)  Sulfoxides: This subgroup consists of only one
              substance, DMSO (No. 507). The NOEL in monkeys given DMSO by
              gavage for 74-87 weeks was 3000 mg/kg bw per day. This NOEL
              and other data provide an adequate margin of safety for the
              use of DMSO as a flavouring agent at the estimated modified
              daily  per capita intake of 0.001 g/day in the United
              States.

    Step B5.  Five substances, allyl sulfide (No. 458), methyl phenyl
              sulfide (No. 459), benzyl methyl sulfide (No. 460),
              2-(methylthio)methyl-2-butenal (No. 470), and
              2,8-dithianon-4-ene-carboxaldehyde (No. 471), were evaluated
              at this step of the Procedure. The modified daily  per
               capita intake of all five substances is less than 1.5 g
              in Europe and in the United States. Applying the criteria
              for Step B5 outlined in Annex 5 of the evaluations published
              after its forty-ninth meeting Annex 1, reference 132), the
              Committee concluded that use of these substances at their
              current levels of intake poses no safety concern.

         In summary, for 100 agents in subgroups (iii) to (xii), a NOEL
    was available for the substance, a closely related substance, or a
    predicted major metabolite that provided an adequate margin of safety
    (> 1000). For 6/9 of the agents in subgroup (i) and 26/28 in subgroup
    (ii), a NOEL for the substance or a closely related substance was
    available that provided an adequate margin of safety (i.e. > 1000).
    Therefore, the Committee determined at Step B4 of the Procedure that
    the safety of these 132 substances would be expected to be of no
    concern when they are used at their currently estimated level of daily
    intake. The evaluation of the remaining five substances (Nos 458, 459,
    and 460 in subgroup (i) and Nos 470 and 471 in subgroup (ii))
    proceeded to Step B5 of the Procedure. The comparisons of toxicity and
    the intake considerations for each subgroup that were used to apply
    Steps B4 and B5 of the Procedure to the evaluation of individual
    substances in this group of flavouring agents are summarized in Table
    3 and given in more detail in Table 1.

    1.5  Consideration of combined intakes

         In the unlikely event that all 137 aliphatic and aromatic
    sulfides and thiols in the overall group or in subgroups were to be
    consumed simultaneously on a daily basis, the estimated combined
    intake would not exceed the human intake threshold for class I
    substances. The powerful aroma of these substances limits the level of
    their use in foods.

    1.6  Conclusions

         The Committee concluded that the 137 flavouring agents comprising
    aromatic sulfides and thiols evaluated at the present meeting could
    not be predicted to be metabolized to innocuous products. According to
    the Procedure, data on toxicity were needed to evaluate the safety of
    this group of flavouring agents. The primary data that were used in
    the evaluations consisted of 27 90-day studies in rodents with 25 of
    the substances and long-term studies in multiple species for one
    substance (DMSO). Most of these studies were conducted at a single
    dose or multiple doses, which had no effects. The Committee noted that
    the NOELs were thus derived from studies in which no toxic effects
    were seen.

         On the basis of the available data on the toxicity of
    representative substances in each subgroup and on their metabolism,
    the Committee determined that the safety of 132 of the flavouring
    agents poses no concern when they are consumed at their current levels
    of intake. The safety of the remaining five substances was considered
    to pose no concern when they are consumed at levels of intake < 1.5
    g/day.

         Other data on toxicity, including the results of short-term tests
    for toxicity and studies of teratogenicity and genotoxicity, were
    consistent with the results of the safety evaluation.

    2.  RELEVANT BACKGROUND INFORMATION

    2.1  Explanation

         The 137 compounds evaluated have a diverse array of chemical
    structures, each of which contains a sulfur atom attached to a carbon,
    hydrogen, oxygen, or second sulfur atom. The substances were separated
    into 12 subgroups on the basis of the position of the sulfur atom, as
    indicated in section 1.3 above. The key data on metabolism and
    toxicity relevant to the safety evaluation are presented below by
    subgroup. Information on intake, special studies, and observations in
    humans are also discussed.

    2.2  Additional considerations on intake

         Thiols (i.e. mercaptans), thioethers, and their oxygenated
    derivatives are known for their powerful aromas. They provide cooked,
    browned, and roasted flavours when added as flavouring substances.
    Their strong organoleptic properties make a significant contribution
    to the taste and smell of various foods even when they are added at
    low concentrations. The thresholds of odour detection for aromatic and
    aliphatic thiols and thioethers range from 0.08 g/m3 for amyl
    mercaptan (not in any subgroup) to 0.03 mg/m3 for benzyl mercaptan
    (No. 526); the odour threshold for methyl sulfide (No. 452), the
    thioether with the highest annual volume of use as a flavouring
    substance, is about 1 g/m3, and that for the corresponding thiol,
    methyl mercaptan (No. 508), is 2 g/m3 (Farr & Kirwin, 1994). In
    tests for sensory tolerance, most of the panelists reported that
    atmospheres containing thiols, thioesters, or thioethers at
    concentrations > 1 mg/m3 are intolerable (Flavor and Extract
    Manufacturers' Association, 1996).

         A direct result of the extremely low odour threshold of thiols
    and thioethers is that their use in food is self-limiting, because
    high concentrations would result in foods that are repulsive. The
    levels of use in the vast majority of food categories are much less
    than 1 mg/m3. In foods in which substantial evaporation of the sulfur
    derivative occurs during processing, such as hard candies and baked

    goods, the concentration is usually < 10 mg/m3. The low levels of
    use in food are reflected in the low reported annual volumes of use of
    thiols and thioethers as flavouring substances.

    2.3  Biological data

    2.3.1  Absorption, distribution, metabolism, and excretion

         Simple, non-polar thioether, disulfide, and thiol flavouring
    substances would be absorbed rapidly from the gastrointestinal tract
    intact and excreted in urine, probably as metabolites, and in some
    cases in the expired air as the parent compound. Essentially complete
    absorption has been reported for methyl sulfide (No. 452) (Williams et
    al., 1966) and dipropyl sulfide (Nickson & Mitchell, 1994). The
    presence of other functional groups, such as an alcohol (e.g. Nos
    461-463), aldehyde (e.g. Nos 465-471, 505), ester (e.g. Nos 472-481
    and 492-494), acid (e.g. No. 501), alpha-ketone (or thioester) (e.g.
    Nos 482-494, 504, and 506), beta-ketone (e.g. Nos 495-500, and 502),
    or phenol (e.g. No. 503), provides a centre of greater polarity which
    could slow the rate of absorption and would provide other sites for
    oxidative metabolism (see below). The metabolism of sulfur centres is
    shown in Figure 1. All the sulfur compounds considered at this meeting
    are of low relative molecular mass and of sufficient lipophilicity to
    be absorbed from the intestine. Some functional groups such as
    aldehydes, esters, and thioesters probably undergo presystemic
    metabolism in the gut lumen, gut wall, or liver.

         (i)  Simple sulfides (thioethers)

         Thioethers are commonly called 'sulfides', as if the hydrogen
    atoms of hydrogen sulfide were replaced by alkyl or aryl substituents.
    Flavours are usually given such trivial names, which are simplified
    even further when the two substituents are the same; for instance,
    dimethyl thioether is called 'methyl sulfide'. The presence of a lone
    pair of electrons on a divalent sulfur allows rapid oxidation of the
    sulfide to a sulfoxide, which occurs both as part of metabolism and
    also before ingestion or absorption under aerobic conditions. For
    example, allyl sulfide (No. 458), a volatile constituent of onions and
    garlic, is oxidized rapidly in air to the corresponding sulfoxide,
    which is partly respon-sible for the lachrymatory effects of these
    foods (Brodnitz & Pascale, 1971).

         In many natural and pharmaceutical compounds, one or more oxygen
    atoms is linked to the sulfur centre of an organic molecule, and the
    chemical and biological properties of the compound depend on the
    nature of the substituents on the sulfur and oxygen atoms. The
    oxidation state of sulfur is of major importance in determining the
    polarity of the compound and hence its interaction with biological
    systems. Once alkyl and aromatic sulfides enter the systemic
    circulation, they are oxidized rapidly to sulfoxides and, depending on
    the structure of the sulfide, may be further oxidized to the sulfone.

    Aliphatic sulfides generally yield mixtures of sulfone and sulfoxide
    metabolites; the relative amounts excreted depend on the polarity of
    the sulfide (Damani, 1987). Methyl sulfide (No. 452) administered to
    rabbits is excreted in the urine as DMSO and dimethyl sulfone
    (Williams et al., 1966), whereas the sulfone is the main urinary
    metabolite of diethyl sulfide (No. 454) (Hoodi & Damani, 1984).

         Dipropyl sulfide, a volatile component of onions and garlic, is
    metabolized mainly to the corresponding sulfoxide with small amounts
    of the sulfone and trace amounts of inorganic sulfate. Individual
    studies on the sulfoxide and sulfone indicate that these metabolites
    are relatively stable under physiological conditions (Nickson &
    Mitchell, 1994; Nickson et al., 1995). Male Wistar rats eliminated 93%
    of a single oral dose of [35S]-dipropyl sulfide over three days, with
    66% in the urine and lesser amounts in exhaled air (18%), faeces
    (4.6%), and the carcass (1.5%). The sulfoxide was the only compound
    detected in plasma. About 25% of the radiolabel was recovered in urine
    on day 1 and 39% on day 2, and approximately 25% of the radiolabel was
    eliminated in bile over 48 h as the sulfoxide (20%) and sulfone (5%).
    Enterohepatic recirculation was probably responsible for the delayed
    urinary excretion and the plasma profiles, which showed a slow
    increase with peaks at 12-15 h. Urinary metabolites collected during
    the first 24 h included the sulfoxide (92%), sulfone (5%), and sulfate
    (3%); on days 2 and 3, the sulfoxide accounted for > 98% of daily
    urinary metabolites (Nickson & Mitchell, 1994). Methyl phenyl sulfide
    administered per se orally to rats or produced by methylation of
    benzenethiol (No. 525) was eliminated in the urine as methyl phenyl
    sulfone and hydroxylated sulfones (McBain & Menn, 1969).

         The major enzyme systems involved in xenobiotic oxidation are the
    cytochrome P450 superfamily (CYP-450) (Souhaili-El Amri et al., 1987)
    and the flavin-containing monooxygenases (FMO) (Levi & Hodgson, 1988;
    Ziegler, 1989; Hodgson & Levi, 1992). The oxidation of thioethers to
    sulfoxides is catalysed by these two enzyme systems (Renwick, 1989).
    Simple aliphatic (e.g. diethyl sulfide), alicyclic (e.g. thiolane),
    and aromatic (e.g. ethyl  para-tolyl sulfide) sulfides are oxidized
    primarily by FMO and to a lesser extent, by CYP-450. The oxidation of
    diethyl sulfide and thiolane in rats is catalysed almost exclusively
    by FMO (Hoodi & Damani, 1984; Damani, 1987). 4-Chlorophenyl methyl
    sulfide was oxidized by FMO and CYP-450 to the sulfoxide and sulfone
    derivatives  in vitro (Nnane & Damani, 1995), and diphenyl sulfoxide
    was oxidized to the corresponding sulfone in perfused guinea-pig liver
    (Yoshihara & Tatsumi, 1990).

         Enzyme-catalysed thioether oxidation may be stereoselective, FMO
    and CYP-450 selecting different enantiomers (Cashman & Williams,
    1990). The stereochemistry of sulfoxidation by the isoenzymes of FMO
    has been studied in humans (Rettie et al., 1994). When methyl
     para-tolyl sulfide was incubated with human fetal liver and human
    kidney microsomes in which CYP-450 activity had been eliminated, the
    resulting sulfoxide showed an enantiomeric excess (> 86%) of the

    FIGURE 2


    R-isomer. Decreasing stereoselectivity was seen as the size of the
    alkyl group (ethyl, propyl, or isopropyl) (Sadeque et al., 1992) or
    the pH (8.5-10) increased (Rettie et al., 1990). Oxidation of propyl
    and butyl  para-tolyl sulfide by the predominant human liver FMO
    isozyme, FMO3, resulted in greater formation of the R-enantiomer
    (73-88%), whereas oxidation of the methyl or ethyl derivative by human
    FMO5 resulted in a > 90% preference for formation of the
    S-stereoisomer of the sulfoxide (Sadeque et al., 1995). The influence
    of the stereochemistry of sulfoxides on the biological and
    toxicological properties of sulfides has not been evaluated.

         On the basis of numerous examples of successive oxidation of
    sulfides to sulfoxides and sulfones by FMO and CYP-450 enzymes in a
    variety of test systems (Cashman & Williams, 1990; Cashman et al.,
    1990; Rettie et al., 1990; Yoshihara & Tatsumi, 1990; Sadeque et al.,
    1992; Cashman et al., 1995a,b; Elfarra et al., 1995; Nnane & Damani,
    1995; Sadeque et al., 1995), the oxidation pathway appears to be a
    major route for the metabolism of thioethers in humans (Ziegler, 1980;
    Nickson & Mitchell, 1994).

         The sulfoxide group is part of an interconvertible redox series
    involving the sulfide (or thioether), sulfoxide, and sulfone. The
    sulfoxide group is present in numerous molecules, which show a
    diversity of biological activity; examples include pharmaceuticals
    such as sulindac and flosequinan, veterinary drugs such as
    albendazole, and numerous pesticides. Oxidation of a sulfoxide yields
    a sulfone, which is commonly found as a metabolite of sulfoxides but
    is less important as an active chemical entity. Oxidation of
    sulfoxides to the corresponding sulfones occurs in both tissues and
    aerobic microorganisms. The oxidation of the sulfoxide drug sulindac
    to its inactive sulfone is a major metabolic pathway in humans (Strong
    et al., 1985). The enzymes involved have not been studied extensively
    in mammalian tissues (Levi & Hodgson, 1988) or microbes (Davis &
    Guenthner, 1985). Oxidation of the sulfoxide to the sulfone is an
    irreversible reaction which is probably catalysed by CYP-450 (Damani,
    1987). The relative amounts of sulfoxide and sulfone excreted depend
    on the stability and hydrophilicity of the sulfoxide (Damani, 1987).

         After administration of [35S]-dipropyl sulfoxide to rats,
    essentially all of the administered radiolabel was recovered over the
    following three days, in the urine (80%), exhaled air (1.4%), faeces
    (5.0%), and the carcass (13.0%) (Nickson & Mitchell, 1994). The
    profile of urinary metabolites was the same after administration of
    the sulfoxide or the sulfide (see above); the principal quantitative
    difference was that more sulfone was excreted in urine and bile after
    sulfoxide administration. Dipropyl sulfone is physiologically stable
    in rats  in vitro and is excreted unchanged in urine (83%) and bile
    (Nickson et al., 1995). More than 98% was excreted unchanged in the
    urine with trace amounts of inorganic sulfate. No reduction of the
    sulfone group or oxidation of the hydrocarbon chain was observed.

    As the sulfoxide may also be reduced back to the thioether, it is not
    always possible to determine if the activity of a chemical in vivo
    resides in the parent compound or in one of the inter-convertible
    redox forms.

         The three important sites of sulfoxide reduction  in vivo are
    liver, kidney, and gut microflora. The tissue enzymes that can reduce
    sulfoxides  in vitro are primarily aldehyde oxidase (Tatsumi et al.,
    1982, 1983; Yoshihara & Tatsumi, 1985a,b) and thioredoxin and its
    reductase (Anders et al., 1980, 1981). Studies with tissue homogenates
    containing various cofactors and inhibitors have shown that the main
    enzyme involved in the liver is aldehyde oxidase, whereas thioredoxin
    is important in the kidney (Lee & Renwick, 1995a). The former enzyme
    was active mainly under anaerobic conditions, while sulfoxide
    reduction by thioredoxin occurred under both aerobic and anaerobic
    conditions. The possible role of aldehyde oxidase under normal and
    hypoxic conditions was shown in isolated perfused guinea-pig liver;
    CYP-P450-catalysed oxidation of both diphenylsulfide and
    diphenylsulfoxide to the sulfone predominated under aerobic conditions
    (Yoshihara & Tatsumi, 1990), whereas oxidation of diphenylsulfoxide to
    the sulfone was decreased under hypoxic conditions and trace amounts
    of diphenylsulfide were formed. Infusion of the sulfoxide with
    2-hydroxypyrimidine and benzaldehyde, which are electron donors for
    aldehyde oxidase, resulted in increased reduction. The importance of
    the kidney and thioredoxin  in vivo under normal oxygen conditions is
    indicated by the fact that patients with end-stage renal disease show
    decreased reduction of sulindac in comparison with controls (Gibson et
    al., 1987).

         The gut microflora in the anaerobic environment of the lower
    bowel can be an important and sometimes the sole site of reduction of
    sulfoxides. Studies in germ-free animals or animals treated with
    antibiotics to suppress the gut microflora and in patients indicated
    that the gut bacteria were the main, or possibly the sole, site of
    sulfoxide reduction of the drug sulfinpyrazone  in vivo (Renwick et
    al., 1982; Strong et al., 1984a,b, 1986). The intestinal bacteria can
    also reduce sulindac  in vitro (Strong et al., 1985), and the
    thioether is a major circulating metabolite  in vivo. The
    contribution of the intestinal microflora to the reduction of sulindac
    in humans was demonstrated by a study in normal subjects and patients
    who had undergone an ileostomy. The tissues produced an initial peak
    0-12 h after dosing, corresponding to 45% of the total thioether, and
    the intestinal bacteria produced a second peak at 12-72 h,
    corresponding to 55% of the total thioether (Strong et al., 1985).
    Studies with over 200 isolated strains of bacteria from human faeces
    (Strong et al., 1987) showed significant sulfoxide reduction by many
    aerobic organisms such as  Escherichia coli under anaerobic
    conditions. Few strict anaerobes showed high reducing activity  in
    vitro, but they are probably essential  in vivo in providing the
    anaerobic environment in which the aerobes can express their sulfoxide
    reductase activity (Strong et al., 1987). Recent studies with

    xenobiotics as substrates have indicated the presence of a number of
    soluble enzymes in  E. coli that are capable of sulfoxide reduction
    (Lee & Renwick, 1995b).

         The enzymes involved in the reduction of the sulfoxide group
    present in DMSO or of the sulfoxide metabolites of the thioethers are
    likely to be the hepatic and renal systems discussed above. In order
    for the gut flora to be involved in the metabolism of the flavouring
    substances, the sulfur derivatives must either be incompletely
    absorbed or reach the lower gut as biliary metabolites (Renwick &
    George, 1989). The significant biliary excretion of the sulfoxide
    metabolite after administration of dipropyl sulfide (see above) raises
    the possibility of reduction by the intestinal microflora, followed by
    reabsorption and subsequent reoxidation.

         (ii)  Acyclic sulfides with oxidized side-chains

         Oxidized side-chains provide additional sites for the
    biotransformation of sulfides, and, as they are polar groups, they
    would increase renal excretion. When the thioether contains an
    additional oxygenated functional group on a carbon atom (i.e. alcohol,
    aldehyde, acid, or ketone),  C-oxidation competes with sulfoxidation.
    The biotransformation of such oxygenated carbon-containing functional
    groups is well characterized and may have been considered in groups of
    flavouring substances previously evaluated by the Committee.
    Concurrent metabolism via both sulfur and oxygenated functional groups
    has been reported for various substrates (El Fatih et al., 1988;
    Gachon et al., 1988; Feng & Solsten, 1991; Wilson et al., 1991; Black
    et al., 1993). In the presence of oxygenated functional groups,
    sulfoxide formation is usually the major metabolic detoxication
    pathway. The main urinary metabolites seen after intraperitoneal
    administration of thiodiglycol [(HOCH2CH2)2S] to male rats were the
    corresponding sulfoxide (90%) and acid thioether
     S-(2-hydroxyethylthio)acetic acid (10%). The corresponding sulfone and
    combined  C-and  S-oxidation product  S-(2-hydroxyethylsulfinyl)acetic
    acid were minor metabolites (Black et al., 1993). Phenacyl phenyl
    sulfide is oxidized to the sulfoxide  in vitro by FMO but split by
    CYP-450 to give thiophenol (Oae et al., 1985). The corresponding
    sulfoxides are the principal urinary metabolites of aliphatic
    methylthiocarboxylic acids (Alterman et al., 1995), of the mucolytic
    drug  S-carboxymethyl-L-cysteine ( S-containing amino acid), of the
    histamine antagonist cimetidine ( S-containing amidine) in humans
    (Mitchell et al., 1982), and of other thioether drugs (Renwick, 1996).

         Experiments  in vitro suggest that carboxyl ester hydrolysis
    occurs in the presence of thioether groups. The thioether
    3-(methylthio)hexyl acetate (No. 481) was partially (9%) hydrolysed in
    simulated gastric juice containing pepsin (pH = 1.1; 37-38 C) after 4
    h and completely hydrolysed in simulated intestinal fluid containing
    pancreatin (Flavor & Extract Manufacturers' Association, 1991).

         Thioethers with a polar anionic group such as carboxylic acid one
    or more carbon atoms away for the sulfur are inhibitors of rather than
    substrates for FMO (Taylor & Ziegler, 1987) and would probably be
    eliminated without  S-oxidation.

         (iii)  Cyclic sulfides

         There are few published data on the fate of simple cyclic
    thioethers.  S-Oxidation is likely to be a major pathway  in vivo,
    and oxidation  in vitro results in a chiral sulfoxide when the ring
    is asymmetric. Oxidation of unsubstituted and methyl-substituted
    cyclic sulfides by a phenobarbital-type CYP-450 yielded the
    corresponding sulfoxides, but further oxidation of sulfoxides to
    sulfones was not detected (Takata et al., 1983).

         The metabolism of the cyclic sulfides with oxidized carbon atoms
    (Nos 464, 498, 499, 550, and 562) has not been studied but would be
    predicted to comprise extensive  S-oxidation and possibly oxidation
    or conjugation of alcohol groups.

         Substituted 1,3-dithiolane derivatives undergo stereoselective
     S-oxidation to the sulfoxide as a major metabolic pathway (Grosa et
    al., 1991) with slower oxidation to the cyclic sulfone ( S,S-dioxide)
    (Cashman & Olsen, 1990). The reactions are catalysed by both FMO and
    CYP-450 (CYP2B); oxidation at both sulfur atoms was not reported. The
    cyclic mono-sulfoxides of substances Nos 456, 534, and 543 are
    predicted to be the main urinary metabolites, while steric hindrance
    and the higher polarity of the hydroxy thioethers (Nos 550 and 562)
    may allow their elimination unchanged.

         (iv)  Simple thiols

         A large number of the flavouring agents in this group are either
    alkyl or alicyclic thiols (Nos 511-524, 526, 527, and 530), arylthiols
    (thiophenols) (Nos 525, 528, 529, and 531-534), dithiols (Nos
    535-542), or alkylthiols with oxidized side-chains (Nos 544-547, 549,
    551-561, and 563). The thiol group is weakly acidic, and endogenous
    thiols have important nucleophilic functions  in vivo.

         Whereas alcohols are oxidized to give carbonyl compounds
    (aldehydes, ketones, and carboxylic acids), thiols are not readily
    oxidized to the corres-ponding thiocarbonyls. The availability of
    sulfur d-orbitals allows valencies of 4 and 6, so that oxidation of
    the thiol group can lead to sulfenic acids (RSOH), sulfinic acids
    (RSO2H), or sulfonic acids (RSO3H), as well as disulfides (RSSR').

         The metabolic pathways of thiols include oxidation to unstable
    sulfenic acids (RSOH), which may be oxidized to the corresponding
    sulfinic (RSO2H) and sulfonic acids (RSO3H); methylation to yield
    methyl sulfides, which can be oxidized to methyl sulfoxides and
    sulfones; reaction with endogenous thiols such as glutathione to form

    mixed disulfides; conjugation with glucuronic acid; and oxidation of
    the alpha-carbon resulting in desulfuration and formation of an
    aldehyde intermediate (McBain & Menn, 1969; Dutton & Illing, 1972;
    Maiorino et al., 1988; Richardson et al., 1991; Renwick, 1996).

         Sulfenic acids are formed by mild oxidation of thiols but are
    unstable and readily undergo further oxidation to sulfinic and
    sulfonic acids or combine with nucleophiles. Reactions of sulfenic
    acids include dimerization with elimination of water to produce
    R-SO-S-R and oxidation to the corresponding polar sulfinic (RSO2H)
    and sulfonic (RSO3H) acids. Oxidation of the thiol group of cysteine
    in proteins can give stabilized sulfenic acid groups which are
    critical to the active site of enzymes; redox cycling between thiol
    and sulfenic acid in the active site may be essential for the
    catalytic activity of a number of bacterial redox enzymes. The
    sulfinic acid group is an intermediate redox state between sulfenic
    and sulfonic acids. Endogenous sulfinic acids include cysteine
    sulfinic acid, which is released during neuronal stimulation (Klancnik
    et al., 1992) and may be involved in synaptic transmission in the
    hippocampus. Cysteine and homocysteine sulfinic acids are excitatory
    and cytotoxic acidic amino acids (Frandsen et al., 1993). The sulfonic
    acid group is a highly polar centre and makes the molecule very
    soluble in water. In general, sulfonic acids are stable to metabolism,
    and desulfonation was not found  in vivo with simple alkyl
    sulfo-nates (Taylor et al., 1978) or with branched-chain sulfonates
    (Michael, 1968).

         Simple aliphatic and aromatic thiols undergo S-methylation in
    mammals to produce the corresponding methyl thioether or sulfide,
    which may be successively oxidized to the corresponding sulfoxides and
    sulfones. Methylation is catalysed by thiopurine methyltransferase in
    the cytoplasm and by thiol methyltransferase in microsomes, both of
    which require  S-adenosyl-L-methionine as a methyl group donor.
    Thiopurine methyltransferase is present in human liver, kidney, and
    erythrocytes (Woodson et al., 1982; Szumlanski et al., 1988), and
    preferential substrates for this enzyme include aromatic and
    heterocyclic thiols (Woodson & Weinshilboum, 1983; Woodson et al.,
    1983). The apparent  Km values of thiophenols (Ames et al., 1986)
    are at least two orders of magnitude lower than those of aliphatic
    substrates (Woodson & Weinshilboum, 1983). The activity of thiopurine
    methyltransferase in humans shows genetic polymorphism, 89% of
    subjects showing high activity, 11% showing intermediate activity, and
    0.3% showing no activity (Weinshilboum & Sladek, 1980). Studies of
    families indicate that the polymorphism is due to a single genetic
    locus with two alleles,  TPMTH for high activity and  TPMTL for low
    activity (Keith et al., 1983). The frequencies of the  TPMTH and
     TPMTL genes are 94% and 6%, respectively, resulting in the trimodal
    frequency distribution of thiopurine methyltransferase activity in the
    general population. The impact of such differences in 'methylator
    status' on the metabolism of thiol-containing flavouring substances is
    unknown but is likely to be small because of the presence of

    alternative  S-oxidation and conjugation pathways.  S-Methylation of
    aliphatic thiols is catalysed by microsomal thiol methyltrans-ferase,
    and thiol substances such as 2-mercaptoethanol, methylmercaptan, and
    2-mercaptopropionic acid are substrates for this enzyme (Bremer &
    Greenberg, 1961), but the endogenous sulfur amino acid derivatives
    homocysteine and glutathione are not. Microsomal thiol
    methyltransferase and cytoplasmic thiopurine methyltransferase
    activities are regulated independently in humans (Keith et al., 1983),
    and therefore S-methylation by thiol methyltrans-ferase may occur in
    individuals with low or negligible thiopurine methyltrans-ferase
    activity.

         Examples of  S-methylation  in vivo include both aliphatic and
    aromatic substrates. Methyl ethyl sulfide (No. 453), which was
    detected in the urine of guinea-pigs and mice given an oral dose of
    diethyl disulfide (Snow, 1957), was presumably formed by reductive
    cleavage to ethanethiol and subsequent methylation (Snow, 1957); minor
    urinary metabolites were the sulfoxide and sulfone (Parkinson, 1996).
    The sulfoxide and sulfone derivative of benzyl methyl sulfide (No.
    460) were excreted in the urine of rats given an oral dose of
     S-benzyl- N-malonyl-L-cysteine, presumably via methylation and
    oxidation of the intermediate benzyl mercaptan (No. 525) (Richardson
    et al., 1991). The urine of rats given an oral dose of [35S]phenyl
    mercaptan contained S-methylated metabolites such as phenyl methyl
    sulfone and  ortho-and  para-hydroxylated phenyl methyl sulfone
    (McBain & Menn, 1969).

         Thiols may react with glutathione and other endogenous thiol
    compounds to form mixed disulfides, and both membrane-bound and
    cytosolic thioltrans-ferases have been reported to catalyse their
    formation. The resulting mixed disulfides can undergo reduction back
    to thiols, oxidative desulfuration, or oxidation to a sulfonic acid
    via the intermediate thiosulfinate and sulfinic acids (see above).
    Thus, the disulfide represents a reversible metabolic 'reservoir' of
    the xenobiotic thiol compound. The principal form in the circulation
    would probably be a mixed disulfide with albumin. The mixed disulfides
    formed from conjugation of a thiol with glutathione or cysteine are
    not substrates for cysteine conjugate C-S lyase. C-S lyase is found in
    the liver, kidney, and intestinal microflora and catalyses the
    reduction of the C-S bonds of cysteine conjugates, which are formed
    between organic compounds and glutathione and then undergo a series of
    hydrolysis steps. The thiol product is usually methylated to form a
    thioether, which may then be oxidized to sulfoxide and sulfone
    analogues; compounds that undergo this metabolic pathway include
    bromo-benzene, paracetamol (acetominophen), propachlor (a herbicide),
    and chlorinated biphenyls. With some organic compounds, conjugation
    with glutathione followed by hydrolysis and C-S lyase results in a
    novel, unstable thiol; for example, some halogenated substrates and
    S-phenyl-L-cysteine formed from conjugation of bromobenzene yield
    unstable thiols which are toxic to the kidney (Tateishi et al., 1978;
    Shaw & Blagbrough, 1989; Tateishi & Tomisawa, 1989).

          S-Glucuronidation of aromatic thiols has been reported, and
    this is a possible pathway for the aromatic thiols (thio-phenols) (Nos
    525 and 528-531) and aromatic disulfides (Nos 576-578) after their
    reduction. This reaction produced thiophenol glucuronide via
    conjugation to glutathione, with subse-quent C-S lyase action on the
    intermediate cysteine conjugate to yield thiophenol. The metabolism of
    benzothiazole-2-sulfonamide was the first of a S-glucuronide to be
    fully elucidated. Three metabolites were detected in the urine of
    treated rats, benzothiazole-2-thioglucuronide, benzothiazole-2-thiol,
    and benzothiazole-1-mercapturate (see Buckberry & Teesdale-Spittle,
    1996); the thiol group is introduced into position 2 by displacement
    of the sulfonamide by glutathione. Glucuronyl transferases behave in a
    similar way towards hydroxyls and sulfydryls, and the two activities
    have the same subcellular location and optimal pH (Dutton & Illing,
    1972).

         Thiols of low relative molecular mass undergo oxidative
    desulfuration  in vivo to yield CO2 and SO4=. For example, 40% of
    14C-labelled methyl mercaptan (No. 508) administered to rats was
    eliminated as CO2, 6.4% was exhaled as unchanged compound within 6 h,
    and only 2.3% was excreted in the urine. 14C also was detected in
    the beta-carbon of serine and in the methyl groups of methionine,
    choline, and creatine (Canellakis & Tarver, 1953), and formalde-hyde
    has been shown to be an intermediate in the oxidation of methanethiol
     in vitro (Mazel et al., 1964). Whereas the carbon atom from a thiol
    may be used in the biosynthesis of amino acids, the sulfur atom is not
    used significantly in the synthesis of sulfur-containing amino acids:
    31% of 35S-labelled methyl mercaptan was excreted in the urine as
    sulfate ion (Mazel et al., 1964).

         (v)  Thiols with oxidized side-chains

         Although these compounds comprise a significant proportion of the
    flavouring agents in this group, their metabolite fate has not been
    studied specifically. The metabolism is predicted to be a combination
    of the pathways described above for simple thiols, combined with
    further oxidation or conjugation of the oxidized side-chain.

         (vi)  Dithiols

         The metabolism of the simple aliphatic dithiols in this group is
    predicted to involve the pathways described above for thiols,
    particularly oxidation of sulfur and alpha-carbon atoms and formation 
    of disulfides by reaction with endogenous thiols such as glutathione.
     S-Oxidation of one S-atom could yield a polar thiol-sulfonate. Data
    for 2,3-dimercapto-1-propanesulfonate (Maiorino et al., 1996) indicate
    that a thiol-sulfonate would be excreted in the urine as such and also
    as disulfides formed with endogenous thiols of low relative molecular
    mass such as cysteine. The longer, linear dithiols (Nos 535, 538, and
    540-542) may form an intramolecular disulfide bond and exist in
    equilibrium between dithiol and cyclic disulfide.

         (vii)  Simple disulfides

         Disulfide bonds are important elements in protein folding and
    structure (Waring, 1996), and redox interconversion between disulfide
    and dithiol is important in the regulation of the activity of some
    enzymes. Interconversion is catalysed by a number of enzymes; for
    example, glutathione reductase reduces the dimeric disulfide to two
    molecules of the monomeric thiol glutathione. The reduction of
    xenobiotic disulfides is believed to be extensive and may be catalysed
    enzymatically by glutathione reductase (Waring, 1996) or
    thioltrans-ferases (Wells et al., 1993) as well as chemically by
    exchange with glutathione, thioredoxin, cysteine, and other endogenous
    thiols. The non-cyclic disulfides in this group of flavours would be
    metabolized to form low-relative-molecular-mass thiols, which would
    then follow the pathways described above for thiols.

         (viii)  Disulfides with oxidized side-chains

         As discussed above for groups (ii) and (iii), the additional
    sites of carbon oxidation would result in greater polarity and the
    potential for further oxidation or conjugation. Because of the
    instability of disulfide bonds to reductive cleavage, this would be
    expected to be the initial metabolic reaction, and the polarity of the
    side-chains would mainly affect the elimination of thiol fragments.

         (ix)  Trisulfides

         The trisulfide of glutathione is labile and readily converted to
    the disulfide, the sulfur being released as hydrogen sulfide (Moutiez
    et al., 1994). The metabolic lability of trisulfides is associated
    with biological activity, such as inhibition of CYP-450 (Ogasawara et
    al., 1998) and enhancement by diallyl trisulfide (No. 587) of
    unscheduled DNA synthesis produced in rat hepatocytes by known
    mutagens (Deng et al., 1994). The toxicity of trisulfides (Nos
    582-587) and polysulfides (No. 588) is probably related to their
    metabolic lability and the nature of the eventual thiol, such as allyl
    thiol.

         (x)  Heterocyclic disulfides

         The heterocyclic disulfides (Nos 573 and 574) are five-and
    six-membered rings which also contain a cyclic thioether bond. Lipoic
    acid is a five-membered cyclic disulfide, and rapid redox cycling
    between ring disulfide and open dithiol is important in its metabolic
    role  in vivo. The five-membered disulfide (No. 573) would be
    predicted to undergo more rapid reductive ring opening to a dithiol
    than the six-membered compound (No. 574). The principal metabolic
    pathways are predicted to be disulfide reduction to produce a dithiol
    and S-oxidation of the thioether.

         (xi)  Thioesters

         The thioester group (-S-CO-) is present in a number of the
    flavouring substances in this group (Nos 482-494, 504, and 506). The
    hydrolysis of other esters has been considered previously by the
    Committee. Esters are hydrolysed by lipase and esterases (Kurooka et
    al., 1976), and the rate of hydrolysis increases as the length of the
    C-chain of the carboxylic acid fragment increases (Greenzaid & Jencks,
    1971) and decreases as oxygenation of the carbon chain in the thiol
    moiety increases (Kurooka et al., 1976).

         Dithionic acids are oxidized by FMO to the dioxo analogue with
    the monothioc acid as an intermediate (Taylor & Ziegler, 1987), but
    simple esters of dithioic acids are poor substrates for oxidation. The
    esters of monothioic acids are also probably poor substrates for
    oxidation, but the monothioic acid released by hydrolysis would be
    oxidized to the dioxo-acid. Another possibility for elimination  in
     vivo is renal excretion of the thiocarboxylic acid. With the
    exceptions of prenyl thioacetate (No. 491) and methylthio
    2-(acetyloxy)propio-nate (No. 492), the compounds evaluated are simple
    linear alkyl compounds, branched alkyl compounds, or their side-chain
    hydroxy-ester analogues, so that their toxicity can reasonably be
    compared.

         (xii)  Sulfoxides

         The metabolism of sulfoxides by oxidation and reduction is
    described above for thioethers. The only sulfoxide flavouring agent is
    DMSO (No. 507). The absorption, metabolism, and excretion of DMSO were
    studied in rhesus monkeys given a daily oral dose of 3 g/kg bw for 14
    days. DMSO was absorbed rapidly, reached a peak serum concentration
    after about 4 h, and was cleared from the blood within 72 h of the end
    of treatment. Dimethyl sulfone was detected in the blood 2 h after
    treatment, reached a steady-state concentration after four days, and
    was cleared from the blood 120 h after the end of treatment. Urinary
    excretion of DMSO and dimethyl sulfone accounted for approximately 60%
    and 16%, respectively, of the total ingested dose. Neither DMSO nor
    dimethyl sulfone was detected in the faeces (Layman & Jacob, 1985).

         The fate of DMSO in humans is similar to that in monkeys, but the
    elimination is slower. When an oral dose of 1 g/kg bw was given to six
    subjects, peak serum concentrations were observed approximately 4 h
    after administration. The peak concentration of dimethyl sulfone was
    slightly higher than that of DMSO and occurred after 72-96 h.
    Approximately 51% of the dose was excreted in the urine unchanged over
    the first 120 h, and up to 22% was excreted as dimethyl sulfone.
    Repeated daily oral administration of DMSO at 0.5 g/kg bw per day for
    14 days to one adult resulted in peak serum concentrations of DMSO
    within eight days (Hucker et al., 1967).

    2.3.2  Toxicological studies

         The available data on the toxicity of sulfides, thiols, and
    oxygenated functional derivatives in the group of 137
    sulfur-containing flavouring substances are presented below. Although
    the studies of acute and short-term toxicity were of limited use for
    evaluating the safety of these substances, because of their short
    duration, they are included for completeness. Studies related to
    chemoprevention are also described.

    2.3.2.1  Acute toxicity

         Oral LD50 values have been reported for 52 of the 137 sulfur
    compounds. The values ranged from 11 to 28 000 mg/kg bw in male and
    female rats (Fairchild & Stokinger, 1958; Brown et al., 1963; Elf
    Atochem, 1963; Harper & Ginn, 1964; Sommer & Tauberger, 1964; Willson
    et al., 1965; Koptyaev, 1967; Fishman et al., 1969; McBain & Menn,
    1969; Fogelman et al., 1970; Oser, 1970; deGroot et al., 1974;
    Christias, 1975; Moreno, 1975; British Industrial Biological Research
    Association, 1976; Griffiths et al., 1979; Mondino & Peano, 1979;
    Opdyke, 1979; Moran et al., 1980; Moreno, 1980; Panasevich et al.,
    1980; Butterworth & Mason, 1981; Mondino et al., 1981; Peano et al.,
    1981; Mondino & Peano, 1982; Piccirillo & Lunchicki, 1982; Elf
    Atochem, 1985; Schafer & Bowles, 1985; Collinson, 1989; Watanabe &
    Kinosaki, 1989a,b; Phillips Petroleum Co., 1990a,b,c; Rush, 1991; Elf
    Atochem, 1992; Farr & Kirwin, 1994; Sanders, 1997). In male and female
    mice, the values ranged from 61 to > 5000 mg/kg bw (Koptyaev, 1967;
    Oser, 1970; Shellen-berger, 1971a,b; Selyuzhitskii, 1972; Fogelman &
    DeProspo, 1973a,b; Fogelman & Suppers, 1973; Fogelman & DeProspo,
    1974; Fogelman & Suppers, 1974a,b; Bailey, 1976a,b,c; Gallo et al.,
    1976; Griffiths & Babish, 1978; Moran et al., 1980; Butterworth &
    Mason, 1981; Schafer & Bowles, 1985).

    2.3.2.2  Short-term studies of toxicity

          2,8-Dithianon-4-ene-4-carboxaldehyde (No. 471)

         Five male and five female rats (strain not specified) received
    0.33 or 3.3 mg/kg bw per day of 2,8-dithianon-4-ene-4-carboxaldehyde
    (No. 471) by gavage on six days a week for two weeks. Individual body
    weights and feed and water consumption were recorded at one and two
    weeks. Haemoglobin levels determined on day 14 were normal. At
    necropsy on day 14, the liver and kidney were weighed and examined
    macro-and microscopically. No treat-ment-related effects were reported
    (de Groot et al., 1974).

          Methylthio 2-(acetyloxy)propionate (No. 492) and
          methylthio 2-(propionyloxy)propionate (No. 493)

         Groups of five Fischer 344 rats of each sex were given either
    methylthio 2-(acetyloxy)propionate (No. 492) or methylthio
    2-(propionyloxy)propionate (No. 493) in the diet for 14 days at a dose
    of approximately 500 mg/kg bw per day. Control animals received a
    basal diet. The animals were observed and tested daily for clinical
    signs of toxicity. Body weights were measured on days 1, 6, and 14,
    and feed consumption was measured on days 7 and 14. At necropsy,
    organs were weighed and the liver and kidneys were examined
    histologically.

         Neither test material produced any abnormal clinical or
    microscopic changes. The potential treatment-related effects included
    depressed feed consumption, decreased body-weight gains of treated
    males, and depressed relative kidney weights in treated females. The
    depressed feed consumption and decreased body-weight gains observed in
    treated males were probably due to the strong odour of the test
    compounds, which decreased the palatability of the diets. The
    biological significance, if any, of the decreased relative kidney
    weights in the females (7 and 6%, respectively, with methylthio
    2-(acetyloxy)-propionate and methylthio 2-(propionyloxy)propionate) is
    questionable because the change was small and there were no
    histological changes (Hermansky & Weaver, 1990).

          Prenyl thioacetate (No. 491), prenylthiol (No. 522),
          3-mercaptohexanol (No. 545), 3-methyl-3-mercaptobutyl formate
          (No. 549), 3-mercaptohexyl acetate (No. 554), 3-mercaptohexyl
          butyrate (No. 555), and 3-mercaptohexyl hexanoate (No. 556)

         A series of 14-day studies were performed with prenyl thioacetate
    (No. 491), prenylthiol (No. 522), 3-mercaptohexanol (No. 545),
    3-methyl-3-mercaptobutyl formate (No. 549), 3-mercaptohexyl acetate
    (No. 554), 3-mercaptohexyl butyrate (No. 555), and 3-mercaptohexyl
    hexanoate (No. 556). Each substance was provided in the diets of 10
    Sprague-Dawley rats of each sex at a target dose of 10 mg/kg bw per
    day. Weekly measurements of body weight and feed consumption indicated
    that the average daily intakes were 10-13 mg/kg bw per day. Control
    animals received chow alone for the same period. The animals were
    observed for gross signs of toxicity and deaths at least once daily
    for the duration of the study. Body weights and feed consumption were
    measured on days 8 and 15. Gross necropsies were performed on all
    rats, and the kidneys and liver were removed for histopathological
    examination at the time of autopsy. Body-weight gain, organ-to-body
    weight ratios, and the weights of the kidney and liver of test and
    control animals were not significantly different in any of the seven
    studies. Gross necropsy and histopathological examination of kidney
    and liver tissues revealed no lesions related to administration of the
    test substances (Wnorowski, 1996a-e, 1997a,b].

         Prenyl thioacetate (No. 491) and prenylthiol (No. 522),
    respectively, are in the thioester and simple thiol subgroups of the
    larger group of sulfur-containing flavouring substances; the other
    five substances (Nos 545, 549, and 554-556) are thiols with oxidized
    side-chains.

          Allyl disulfide (No. 572), propyl disulfide (No. 566), and
          phenyl disulfide (No. 578)

         In two separate, but similarly conducted studies, allyl disulfide
    (No. 572) was administered at a concentration of 250 or 1000 mol/kg
    (36 or 150 mg/kg bw per day); propyl disulfide (No. 566) at 250, 1000,
    or 5000 mol/kg (38, 150, or 750 mg/kg bw per day); and phenyl
    disulfide (No. 578) at 500 mol/kg (110 mg/kg bw per day), as
    solutions in peanut oil or Tween 80, to groups of six or seven female
    Sprague-Dawley rats. The doses were given by oral intubation for six
    consecutive days. Control groups of 12 or 14 rats received the vehicle
    alone. The animals were killed on day 7 of the experiment, and blood
    was collected from the posterior vena cava. At necropsy, splenic
    weights were recorded and expressed as a percentage of body weight,
    and splenic darkening was assessed visually on an arbitrary scale of
    0-5. Blood was examined for various parameters. Sections of splenic
    sinusoidal engorgement, focal hepatic erythropoiesis, and iron
    deposition in the spleen, liver, and kidneys were also scored on a
    scale of 0-5. The number and size of Heinz bodies were measured to
    estimate any decrease in the optical density of red cell lysates.

         The results for animals given the lower dose of allyl disulfide
    and the two lower doses of propyl disulfide were similar to those of
    controls, whereas those given the higher doses of allyl and propyl
    disulfide had enlargement and darkening of the spleen, increased iron
    concentrations in the spleen, liver, and kidneys, and decreased packed
    cell volume and haemoglobin concentra-tions associated with Heinz body
    formation. No degenerative changes were seen in the spleen, liver, or
    kidneys, but destruction of erthrocytes was indicated by deposition of
    iron in these organs. Similar findings were made in rats given phenyl
    disulfide.

         The haemolysis observed was attributed to oxidative stress due to
    'active oxygen' species formed by intra-erythrocytic redox cycling of
    disulfides. Thiol-disulfide exchange with glutathione results in
    reduction of disulfides to their corresponding thiols. Although
    generally recognized as antioxidants, thiols act as pro-oxidants after
    one-electron oxidation to a thyil radical. In erythrocytes, such
    oxidation is mediated by oxyhaemoglobin and results in the formation
    of methaemoglobin, hydrogen peroxide, and a thiolate anion. The
    hydrogen peroxide and the more active oxygen species formed from the
    thyil radical are responsible for initiating the cellular damage that
    leads to haemolysis. Although human erythrocytes are usually resistant
    to oxidative damage, certain individuals are susceptible because of
    hereditary deficiencies (Munday et al., 1990; Munday & Manns, 1994).

    2.3.2.3  Ninety-day studies of toxicity

         Ninety-day studies were available for 26 of the flavouring
    substances (Table 4). To facilitate comparisons of the toxicity of
    structurally related substances, the studies are grouped according to
    the 12 subgroups. A 90-day study was available for one or more
    substance in each subgroup except that of disulfides with oxidized
    side-chains. Most of the studies were performed at only one dose that
    produced no adverse effects.

         (i)  Simple sulfides (thioethers)
              Methyl sulfide (No. 452)

         Four groups of 15 male and 15 female weanling SPF rats of the
    Wistar strain were given methyl sulfide by oral intubation at
    concentrations of 0 (control), 2.5, 25, or 250 mg/kg bw per day for 14
    weeks. Two further groups of five animals of each sex were given 0.25
    or 250 mg/kg bw per day for two or six weeks, respectively. The
    animals were weighed on day 0 and then weekly throughout the study.
    Feed and water consumption were measured for 24 h before the day of
    weighing. Urine was collected during weeks 2, 6, and 14 and examined
    for appearance, microscopic constituents, and content of glucose,
    ketones, bile salts, and blood. The specific gravity and volume of
    urine produced over 6 h were also noted. At the end of the appropriate
    period of dosing, the rats were killed and blood was taken for
    haematological examination. Gross abnormalities were noted and organs
    weighed, and histological examinations were performed. No adverse
    effect occurred with any treatment (Butterworth et al., 1975). The
    dose of 250 mg/kg bw per day that had no effect is at least 10 000
    times the per capita intakes of 10 and 9 mg/kg bw per day due to use
    of methyl sulfide as a flavouring substance in Europe and the United
    States, respectively.

         In a study designed to investigate the mechanism of lenticular
    changes caused by DMSO (No. 507), 10 eight-week-old New Zealand
    rabbits were given 2000 mg/kg bw per day methyl sulfide (No. 452) in
    drinking-water for 13 weeks. Control animals received drinking-water
    only. Photographs were taken each week of the animals' lens to
    evaluate the occurrence of changes. At termination, the kidney, liver,
    spleen, heart, lung, adrenals, and lens were weighed and examined for
    gross physical abnormalities. Treated animals had a 50% increase in
    lung weight, with pulmonary congestion and some haemorrhagic spots.
    The kidneys showed signs of pyelonephritis. There was no evidence of
    lenticular changes (Wood et al., 1971).

         (ii) Acyclic sulfides with oxidized side-chains
              2-(Methylthiomethyl)-3-phenylpropenal (No. 505)

         In a standardized protocol (referred to below as such for other
    compounds), groups of 15 male and 15 female weanling Sprague-Dawley
    rats were given a single dose of 0 or 1.4 mg/kg bw per day of

    2-(methylthiomethyl)-3-phenylpropenal (No. 505) dissolved in acetone
    and blended into a basal laboratory diet for 92 days. The rats were
    housed individually and given feed and tap water  ad libitum. The
    acetone was fully evaporated before presentation of the diet to the
    animals. Samples of each diet were taken weekly to assess the
    stability and concentration of the test material. Appearance,
    behaviour, appetite, elimination, gross signs of toxic effects, and
    deaths were recorded daily, and body weights and feed consumption were
    measured weekly. Haematological examinations, blood chemical
    determinations, and urine analyses were performed during weeks 6 and
    12 on eight males and eight females from each group. At necropsy, the
    weights of the liver, kidneys, thyroid, spleen, and adrenal glands
    were recorded. At termination, the weights of the thyroid, liver,
    kidneys, spleen, and adrenal glands were recorded. Tissues from 26
    sites and all grossly observable abnormal sites were preserved in
    formalin for histopathological examination.

         The body weights of females were reduced throughout the study,
    and both males and females had decreased feed consumption, but these
    findings did not appear to be biologically significant. No significant
    differences were seen between treated and control animals with respect
    to haematological, blood chemical, or urinary parameters. The absolute
    and relative organ weights of the treated and control animals were
    similar and there was no evidence of gross or histological changes
    (Cox et al., 1979).

         The dose of 2-(methylthiomethyl)-3-phenylpropenal that showed no
    effects (i.e. 1.4 mg/kg bw per day) is more than 10 000 times the
    estimated per capita intake of 0.03 g/kg bw per day of this
    flavouring substance in the United States.

         (iii)  Cyclic sulfides
                2-Methyl-4-propyl-1,3-oxathiane (No. 464)

         Groups of 16 male and 16 female weanling Wistar rats were given
    2-methyl-4-propyl-1,3-oxathiane (No. 464) by oral intubation at a
    daily dose of 0.44 mg/kg bw for 90 days or corn oil alone. The rats
    were weighed on the first day of treatment and thereafter at regular
    intervals throughout the study. Feed intake was recorded at three-or
    four-day intervals. Blood was collected from half the rats in the
    study at six weeks and from all rats at 12 weeks and was examined for
    haemoglobin concentration, packed cell volume, and erythrocyte and
    leukocyte counts. Urea concentration was measured. At necropsy, organs
    were weighed and gross and histological examinations performed.

         A slight increase in body-weight gain was seen in treated males,
    which was associated with increased feed intake thought to result from
    alteration of feeding behaviour due to intubation of highly flavoured
    solutions. Isolated differences from controls were seen in
    haematological parameters, organ weights, and histological appearance,
    but none was statistically significant and were considered not to


        Table 4. Results of short-term studies of toxicity and long-term studies of toxicity and carcinogenicity on aliphatic and aromatic sulfides
    and thiols
                                                                                                                                               

    No.    Substance                               Species     Sex     No. test      Route       Duration     NOEL          Reference
                                                                       groupsa/no.                            (mg/kg bw)
                                                                       per test
                                                                       groupb
                                                                                                                                               

    452    Methyl sulfide                          Rat         MF      3/30          Gavage      14 weeks     250c          Butterworth
                                                                                                                            et al. (1975)
                                                   Rabbit      MF      1/10          Oral        13 weeks     < 2000        Wood et al. (1971)
    464    2-Methyl-4-propyl-1,3-oxathiane         Rat         MF      1/32          Gavage      13 weeks     0.44c         British Industrial 
                                                                                                                            Biological Research
                                                                                                                            Association (1976)
    471    2,8-Dithianon-4-en-4-carboxaldehyde     Rat         MF      2/10          Gavage      2 weeks      ND            de Groot
                                                                                                                            et al. (1974)
    483    Ethyl thioacetate                       Rat         MF      1/46          Oral        13 weeks     6.5c          Shellenberger (1970)
    484    Methyl thiobutyrate                     Rat         M       3/10          Oral        13 weeks     1000c,d       Wheldon et al. (1970)
    491    Prenyl thioacetate                      Rat         MF      1/20          Diet        2 weeks      ND            Wnorowski (1997a)
    498    4,5-Dihydro-3(2H)-thiophenone           Rat         MF      1/30          Oral        92 days      9.2c          Morgareidge (1970)
    505    2-(Methylthiomethyl)-3-phenylpropenal   Rat         MF      1/30          Oral        92 days      1.4c          Cox et al. (1979)

    507    Methylsulfinylmethane                   Rat                 4/20          Oral        13 weeks     2200          Sommer & Tauberger
                                                                                                                            (1964)
                                                   Rat         MF      3/100         Gavage      18 months    < 1100        Noel et al. (1975)
                                                   Dog         MF      3/10          Gavage      18 weeks     1100
                                                                                                 or 2 years
                                                   Monkey      MF      3/4           Gavage      74-87 weeks  3000          Vogin et al. (1970)
    516    Cyclopentanethiol                       Rat         MF      1/30          Oral        92 days      0.56c         Morgareidge &
                                                                                                                            Oser (1970a)
    520    2,3- or 10-Mercaptopinane               Rat         MF      1/30          Oral        92 days      0.06c         Oser (1966)
    522    Prenylthiol                             Rat         MF      1/20          Diet        2 weeks      ND            Wnorowski (1997b)
    528    ortho-Toluenethiol                      Rat         MF      1/20-32       Diet        90 days      0.52c         Posternak 
                                                                                                                            et al. (1969)

    Table 4. (contd)
                                                                                                                                               

    No.    Substance                               Species     Sex     No. test      Route       Duration     NOEL          Reference
                                                                       groupsa/no.                            (mg/kg bw)
                                                                       per test
                                                                       groupb
                                                                                                                                               
    530    2,6-Dimethylthiophenol                  Rat         MF      1/64          Gavage      13 weeks     0.43c         Peano et al. (1981)
    531    2-Naphthalenethiol                      Rat         MF      1/30          Oral        92 days      3.4c          Morgareidge (1971a)
    534    2-Methyl-1,3-dithiolane                 Rat         MF      1/32          Gavage      91 days      7.0c          Griffiths
                                                                                                                            et al. (1979)
    539    2,3-Butanedithiol                       Rat         MF      1/30          Oral        92 days      0.7c          Morgareidge
                                                                                                                            et al. (1974a)
    541    1,8-Octanedithiol                       Rat         MF      1/30          Oral        92 days      0.7c          Morgareidge
                                                                                                                            et al. (1974c)

    543    Trithioacetone                          Rat         MF      1/30          Oral        92 days      0.2c          Cox et al. (1973a)
    545    3-Mercaptohexanol                       Rat         MF      1/20          Diet        2 weeks      ND            Wnorowski (1996a)
    546    2-Mercapto-3-butanol                    Rat         MF      1/30          Oral        92 days      1.9c          Cox et al. (1974a)
    547    a-Methyl-b-hydroxypropyl                Rat         MF      1/30          Oral        92 days      2.8c          Morgareidge
           a-methyl-b-mercaptopropyl                                                                                        et al. (1974c)
           sulfide

    549    3-Mercapto-3-methylbutyl                Rat         MF      1/20          Diet        2 weeks      ND            Wnorowski (1996a)
           formate
    554    3-Mercaptohexyl acetate                 Rat         MF      1/20          Diet        2 weeks      ND            Wnorowski (1996b)
    555    3-Mercaptohexyl butyrate                Rat         MF      1/20          Diet        2 weeks      ND            Wnorowski (1996c)
    556    3-Mercaptohexyl hexanoate               Rat         MF      1/20          Diet        2 weeks      ND            Wnorowski (1996d)
    560    3-Mercapto-2-pentanone                  Rat         MF      1/30          Oral        92 days      1.9c          Morgareidge (1971b)
    562    2,5-Dimethyl-2,5-dihydroxy              Rat         MF      1/30          Diet        92 days      3.1c          Cox et al. (1973b)
           -1,4-dithiane
    566    Propyl disulfide                        Rat         F       1/6           Gavage      6 days       ND            Munday & Manns (1994)
                                                   Rat         M       1/10-16       Diet        90 days      7.3c          Posternak
                                                                                                                            et al. (1969)
                                                               F       1/10-16       Diet        90 days      8.2c
    572    Allyl disulfide                         Rat         F       2/6           Gavage      6 days       36c           Munday & Manns (1994)

    Table 4. (contd)
                                                                                                                                               

    No.    Substance                               Species     Sex     No. test      Route       Duration     NOEL          Reference
                                                                       groupsa/no.                            (mg/kg bw)
                                                                       per test
                                                                       groupb
                                                                                                                                               
    573    3,5-Dimethyl-1,2,4-trithiolane          Rat,        MF      1/32          Gavage      90 days      1.9c          British Industrial
                                                                                                                            Biological Research
                                                                                                                            Association (1976)
    574    3-Methyl-1,2,4-trithiane                Rat         MF      1/32          Oral        13 weeks     0.3c          Mondino (1981)
    575    Dicyclohexyl disulfide                  Rat         MF      1/30          Oral        92 days      0.23c         Cox et al. (1974b)
    577    Methyl benzyl disulfide                 Rat         MF      1/30          Oral        92 days      1.2c          Gallo et al. (1976)
    578    Phenyl disulfide                        Rat         F       1/6           Gavage      6 days       ND            Munday et al. (1990)
    585    Dipropyl trisulfide                     Rat         MF      1/30          Oral        92 days      4.8c          Morgareidge
                                                                                                                            & Oser (1970b)
    587    Diallyl trisulfide                      Rat         MF      1/30          Oral        92 days      4.6c          Morgareidge
                                                                                                                            & Oser (1970c)
                                                                                                                                               

    M, male; F, female; ND, not determined

    a  No. of test groups does not include controls
    b  No. per test group comprises males and females
    c  Study performed with either a single dose or multiple doses that had no effect; the value is therefore the highest dose tested.
    d  Dose increased from 500 to 1000 mg after six weeks
    

    represent adverse effects (British Industrial Biological Research
    Association, 1976). The dose of 0.44 mg/kg bw per day of
    2-methyl-4-propyl-1,3-oxathiane that showed no effects is more than 10
    000 times the estimated per capita intakes of 0.03 mg/kg bw per day in
    Europe and 0.02 mg/kg bw per day in the United States.

          4,5-Dihydro-3(2H)-thiophenone (No. 498)

         4,5-Dihydro-3(2H)-thiophenone (No. 498) was tested in a
    standardized study (see above) at a single dose of 9.16 mg/kg bw per
    day. No effects were observed (Morgareidge, 1970). This dose is 100
    000 times greater than the estimated per capita intakes of 0.01 g/kg
    bw per day in Europe and 0.04 g/kg bw per day in the United States.

          2-Methyl-1,3-dithiolane (No. 534)

         A group of 16 male and 16 female Sprague-Dawley rats received an
    aqueous propylglycol solution (0.2% w/w) containing 7 mg/kg bw of
    2-methyl-1,3-dithiolane (No. 534) daily by oral intubation for 91
    days. Control animals received 0.02% propylene glycol only. The rats
    were observed routinely for body weight and feed consumption.
    Haematological and blood chemical parameters were determined in weeks
    4 and 13. No difference was seen between control and treated groups in
    body-weight gain or feed consumption. A slight, nonsignificant
    reduction in haemoglobin concentration was seen in treated females.
    Gross and histological examinations at termination showed no
    dose-related effects, and organ weights were normal (Griffiths et al.,
    1979). The dose of 7 mg/kg bw per day is greater than 1 000 000 times
    the estimated per capita intake of 0.002 mg/kg bw per day of
    2-methyl-1,3-dithiolane in Europe and 10 000 times that of 0.1 mg/kg
    bw per day in the United States.

          Trithioacetone (No. 543)

         Trithioacetone (No. 543) was tested in a standardized study (see
    above) at a single dose of 0.205 mg/kg bw per day. No effects were
    observed (Cox et al., 1973a). This dose is 10 000 greater than the
    estimated intakes of 0.04 g/kg bw per day in Europe and 0.01 g/kg bw
    per day in the United States.

          2,5-Dimethyl-2,5-dihydroxy-1,4-dithiane (No. 562)

         2,5-Dimethyl-2,5-dihydroxy-1,4-dithiane (No. 562) was tested in a
    standar-dized study (see above) at a single dose of 3.1 mg/kg bw per
    day. No effects were observed (Cox et al., 1973b). This dose is 1 000
    000 greater than the estimated per capita intakes of 0.004 g/kg bw
    per day in Europe and 0.003 g/kg bw per day in the United States.

         (iv)  Simple thiols
               Cyclopentanethiol (No. 516)

         Cyclopentanethiol (No. 516) was tested in a standardized study
    (see above) at a single dose of 0.56 mg/kg bw per day. No effects were
    observed (Morgareidge & Oser, 1970a). This dose is 10 000 times
    greater than the estimated per capita intake of 0.01 g/kg bw per day
    in the United States.

          2,3-or 10-Mercaptopinane (No. 520)

         2,3-or 10-Mercaptopinane (No. 520) was tested in a standardized
    study (see above) at a single dose of 0.06 mg/kg bw per day, No
    effects were observed (Oser, 1966). This dose is 10 000 times greater
    than the estimated per capita intake of 0.001 g/kg bw per day in
    Europe and 100 times that of 0.2 g/kg bw per day in the United
    States.

         ortho- Toluenethiol (No. 528)

         Groups of 10-16 male and 10-16 female rats were given 0.52 mg/kg
    bw per day of  ortho-toluenethiol (No. 528) in the diet for 90 days.
    Control animals received untreated diet. Feed consumption and body
    weights were recorded weekly. Haematological examinations and blood
    urea determinations were conducted on half the animals at seven weeks
    and on all animals at 13 weeks. At necropsy, organs were weighed and
    examined grossly and histologically. No adverse effects were observed
    (Posternak et al., 1969). The dose that had no effect is greater than
    1000 times the estimated per capita intake of 0.4 mg/kg bw per day in
    Europe and 100 000 times that of 0.003 mg/kg bw per day in the United
    States.

          2,6-Dimethylthiophenol (No. 530)

         2,6-Dimethylthiophenol (No. 530) was administered in corn oil by
    gavage to 32 male and 32 female Sprague-Dawley rats at a concentration
    calculated to result in an average intake of 0.43 mg/kg bw per day for
    13 weeks. Control animals received only corn oil. Body weights and
    feed intake were measured weekly, and haematological and blood
    chemical parameters were measured at weeks 4 and 13. Organs were
    weighted and gross and histological examinations were performed at the
    time of autopsy. No significant difference was seen between treated
    and control animals (Peano et al., 1981). The dose that had no effect
    is greater then 10 000 times the estimated per capita intake of 0.03
    mg/kg bw per day in Europe and greater than 1 000 000 times that of
    0.0003 mg/kg bw per day in the United States.

          2-Naphthalenethiol (No. 531)

         2-Naphthalenethiol (No. 531) was tested in a standardized study
    (see above) at a single dose of 3.4 mg/kg bw per day. No effects were
    observed (Morgareidge, 1971a). The dose that had no effect is 1 000
    000 times greater than the estimated per capita intake of 0.001 g/kg
    bw per day in the United States.

         (v)  Thiols with oxidized side-chains
              2-Mercapto-3-butanol (No. 546)

         2-Mercapto-3-butanol (No. 546) was tested in a standardized study
    (see above). No effects were observed (Cox et al., 1974a). The dose of
    1.9 mg/kg bw per day that had no effect is 1000 times greater than the
    estimated per capita intake of 0.1 g/kg bw per day in Europe and
    10 000 times that of 0.002 g/kg bw per day in the United States.

          alpha-Methyl-beta-hydroxypropyl
          alpha-methyl-beta-mercaptopropyl
          sulfide (No. 547)

         alpha-Methyl-beta-hydroxypropyl alpha-methyl-beta-mercaptopropyl
    sulfide (No. 547) was tested in a standardized study (see above) at a
    single dose of 2.815 mg/kg bw per day. No effects were observed
    (Morgareidge et al., 1974b). This dose is 100 000 times greater than
    the estimated per capita intake of 0.01 g/kg bw in the United States.

          3-Mercapto-2-pentanone (No. 560)

         3-Mercapto-2-pentanone (No. 560) was tested in a standardized
    study (see above) at a single dose of 1.89 mg/kg bw per day. No
    effects were observed (Morgareidge, 1971b). This dose is 100 000 times
    greater than the estimated per capita intake of 0.002 g/kg bw per day
    in the United States.

         (vi)  Dithiols

                2,3-Butanedithiol (No. 539) and 1,8-octanedithiol (No. 541)

         2,3-Butanedithiol (No. 539) and 1,8-octanedithiol (No. 541) were
    tested in standardized studies (see above) at single doses of 0.703
    and 0.705 mg/kg bw per day, respectively. No effects were observed
    (Morgareidge et al., 1974a,c). The dose of 2,3-butanedithiol that had
    no effect is 100 000 times greater than the estimated per capita
    intakes of 0.001 g/kg bw per day in Europe and 0.003 g/kg bw per day
    in the United States. The dose of 1,8-octanedithiol that had no effect
    is 1000 times greater than the estimated per capita intake of 0.1
    g/kg bw per day in Europe and 10 000 times that of 0.01 g/kg bw per
    day in the United States.

         (vii)  Simple disulfides

                 Propyl disulfide (No. 566)

         Three groups of 10-16 male and 10-16 female rats were given 7.3
    or 8.2 mg/kg bw per day of propyl disulfide (No. 566) in the diet for
    90 days. Control animals received untreated diet. feed consumption and
    body weights were recorded weekly, and haematological examinations and
    blood urea determinations were conducted on half the animals at seven
    weeks and on all animals at 13 weeks. At necropsy, organs were weighed
    and examined grossly and histologically. No adverse effects were
    observed (Posternak et al., 1969). The doses that had no effects are
    10 000 times greater than the estimated per capita intake of 0.1 mg/kg
    bw per day in Europe and 1 000 000 times that of 0.002 mg/kg bw per
    day in the United States.

          Dicyclohexyl disulfide (No. 575)

         Dicyclohexyl disulfide (No. 575) was tested in a standardized
    study (see above) at a single dose of 0.23 mg/kg bw per day. No
    effects were observed (Cox et al., 1974b). The dose that had no effect
    is 100 000 times greater than the estimated per capita intake of
    0.0003 g/kg bw per day in Europe and 10 000 that of 0.003 g/kg bw
    per day in the United States.

          Methyl benzyl disulfide (No. 577)

         Methyl benzyl disulfide (No. 577) was tested in a standardized
    study (see above) at a single dose of 1.2 mg/kg bw per day, No effects
    were observed (Gallo et al., 1976). The dose that had no effect is 1
    000 000 times greater than the estimated per capita intake of 0.0003
    g/kg bw per day in Europe and 100 000 that of 0.002 g/kg bw per day
    in the United States.

         (viii)  Disulfides with oxidized side-chains

         No studies on the two substances in this group were available,
    but their toxicity can be compared by analogy to that of the
    disulfides.

         (ix)  Trisulfides

                Dipropyl trisulfide (No. 585)

         Dipropyl trisulfide (No. 585) was tested in a standardized study
    (see above) at a single dose of 4.8 mg/kg bw per day, No effects were
    observed (Morgareidge & Oser, 1970b). The dose that had no effect is
    10 000 times greater than the estimated per capita intake of 0.2 g/kg
    bw per day in Europe and 100 000 that of 0.02 g/kg bw per day in the
    United States.

          Diallyl trisulfide (No. 587)

         Diallyl trisulfide (No. 587) was tested in a standardized study
    (see above) at a single dose of 4.6 mg/kg bw per day, No effects were
    observed (Morgareidge & Oser, 1970c). The dose that had no effect is
    10 000 times greater than the estimated per capita intake of 0.1 g/kg
    bw per day in Europe and 100 000 that of 0.0003 g/kg bw per day in
    the United States.

         (x)  Heterocyclic disulfides

               3,5-Dimethyl-1,2,4-trithiolane (No. 573)

         Groups of 16 male and 16 female weanling Wistar rats were given
    3,5-dimethyl-1,2,4-trithiolane (No. 573) by oral intubation at a daily
    dose of 1.9 mg/kg bw for 90 days or corn oil alone. The rats were
    weighed on the first day of treatment and thereafter at regular
    intervals throughout the study. Feed intake was recorded at three- or
    four-day intervals. Blood was collected from half the rats at six
    weeks and from all rats at 12 weeks and was examined for haemoglobin
    concentration, packed cell volume, and numbers of erythrocyte and
    leukocytes. The urea concentration was measured. At necropsy, organs
    were weighed and gross and histological examinations were performed.

         A slight increase in body-weight gain was seen in treated males,
    which was associated with increased feed intake thought to result from
    alteration of feeding behaviour due to intubation of highly flavoured
    solutions. Isolated differences from controls were seen in
    haematological parameters, organ weights, and histological appearance,
    but none was statistically significant and they were considered not to
    represent adverse effects (British Industrial Biological Research
    Association, 1976). The dose that had no effect is 100 000 times
    greater than the estimated per capita intakes of 0.001 mg/kg bw per
    day in Europe and 0.002 mg/kg bw per day in the United States.

          3-Methyl-1,2,4-trithiane (No. 574)

         3-Methyl-1,2,4-trithiane (No. 574) was administered orally to 16
    male and 16 female rats (strain not specified) at a dose of 0.3 mg/kg
    bw per day for 13 weeks. Body weights and feed intake were measured
    weekly. Haematological parameters and blood urea were determined at
    weeks 4 and 13. At necropsy, organs were weighed and examined
    histologically. No adverse effects were observed (Mondino, 1981). The
    dose that had no effect is 100 000 and 100 times greater than the
    estimated per capita intakes of 0.002 mg/kg bw per day in Europe and
    1 mg/kg bw per day in the United States.

         (xi)  Thioesters

                Ethyl thioacetate (No. 483)

         Groups of 23 male and 23 female rats were given ethyl thioacetate
    (No. 483) at a dose of 6.5 mg/kg bw per day in the diet, while a
    control group received basal diet alone. The animals were observed
    daily for appearance, physiological responses, behaviour, any
    pharmacological or toxicological responses, and deaths. Body weights
    and feed consumption were recorded weekly. During weeks 6 and 13,
    urine was obtained from eight males and eight females for estimation
    of pH and specific gravity, for microscopic examination of sediment,
    and for qualitative estimates of albumin, glucose, occult blood,
    ketones, and bilirubin. Eight animals of each sex were killed after
    six weeks, and blood was taken for haematological testing. The
    remaining animals were necropsied at 13 weeks and their tissues
    examined for gross pathological changes. Organs were weighed and
    tissues retained for histological evaluations. The growth, feed
    consumption, and feed utilization of the test animals were similar to
    those of controls throughout the study, and blood biochemical and
    haematological indices were normal. Likewise, there were no
    significant differences in the average absolute or relative organ
    weights. All rats appeared normal throughout the study, and no gross
    pathological lesions were seen in any tissue (Shellenberger, 1970).
    The dose that had no effect is 1 000 000 times greater than the
    estimated per capita intake of 0.0003 mg/kg bw per day in both Europe
    and the United States.

          Methyl thiobutyrate (No. 484)

         Three groups of 10 male rats were fed 20, 200, or 500 mg/kg bw
    per day of methyl thiobutyrate (No. 484) for 13 weeks, the dose given
    to the third group being increased from 500 to 1000 mg/kg bw per day
    after six weeks. A control group received only the basal diet. Feed
    consumption and body weights were recorded weekly. A slight decrease
    in weight gain was observed in treated rats as compared with controls,
    which was attributed to decreased feed intake associated with
    unpalatability. At necropsy, haematological examinations showed normal
    values, and no differences in relative or absolute organ weights or
    gross or histological appearance was seen between test and control
    animals (Wheldon et al., 1970). The dose of 1000 mg/kg bw per day
    which had no effect is 1 000 000 times greater than the estimated per
    capita intake of 0.1 mg/kg bw per day in both Europe and the United
    States.

         (xii)  Sulfoxides

         No 90-day study was available for this group of compounds, but
    methylsulfinylmethane (DMSO; No. 507) has been tested in long-term
    studies of toxicity and carcinogenicity in rats, dogs, and monkeys
    (see below) and has also been given to humans (see below).

    2.3.2.4  Long-term studies of toxicity and carcinogenicity

         Long-term studies of toxicity and carcinogenicity in rats, dogs,
    and monkeys were available only for DMSO (No. 507) (Table 4).

         Groups of 50 male and 50 female Sprague-Dawley rats and groups of
    five male and five female pure-bred Pembrokeshire Corgi dogs were
    given a 50% aqueous solution containing undiluted DMSO at 1100, 3300,
    or 9900 mg/kg bw per day by gavage on five days per week. A control
    group received 1 L/kg bw per day of distilled water. The rats were
    treated for 18 months and the dogs for either 18 weeks or two years.
    All animals were observed daily for clinical signs, and body weight
    and feed consumption were measured weekly. Haematological assessments,
    biochemical measurements, and urinary analyses were performed after 4,
    12, 20, 32, 51, 60, and 72 weeks for the rats and after 1, 3, 4.5, 6,
    9, 12, 18, and 24 months for the dogs. Routine ophthalmo-scopic
    examinations were also performed. At termination, detailed macroscopic
    and histopathological examinations were performed.

         A dose-related decrease in weight gain was observed in rats at
    all doses, except in males receiving the lowest dose. The decrease in
    weight gain was not accompanied by a decrease in feed intake. Male
    rats at the high dose also showed a slight reduction in haemoglobin
    and packed-cell volume. Examination of the eyes revealed no changes in
    the retina or vitreous humour. No adverse effects on body weight or
    feed intake were seen in the dogs. Persistent diuresis was observed in
    those receiving the intermediate and high doses, but there was no
    renal damage. Increased packed-cell volume and haemoglobin levels were
    observed at the highest dose, although the erthrocytes had normal
    haemoglobin concentrations and were of normal size. The most
    significant observation in dogs was lenticular changes, comprising
    changes in the refractive index of the central portion of the lens,
    transitory, dense, white equatorial lens opacity, the appearance of
    persistent opalescence in the central region of the lens, and changes
    in the vitreous humour. Biochemical analyses of the lenses of affected
    animals revealed an increase in insoluble protein and reductions in
    soluble protein, glutathione, and water. These changes were observed
    during the fifth month in dogs receiving the highest dose and during
    the ninth to tenth months in those at the intermediate dose. Nuclear
    refractive changes were observed after six months in dogs at the low
    dose, but none of these animals had opalescence. Those animals that
    were withdrawn from the study at 18 weeks showed partial regression of
    the lenticular changes at the end of the two-year period, and the
    lenses of dogs that received the intermediate dose had apparently
    reverted to a normal state. No abnormalities other than those in the
    eye were detected on macroscopic or histopathological examination
    (Noel et al., 1975).

         Four groups of rhesus monkeys received doses equivalent to 0,
    990, 3000, or 9000 mg/kg bw per day of a 90% solution of DMSO by
    gastric intubation or dermal application for 74-87 weeks. Three
    females and one male received only water by oral intubation, and two
    males and one female received only water dermally and served as
    controls. Two animals of each sex were treated with 990 and 2970 mg/kg
    bw per day, and three animals of each sex received 8910 mg/kg bw per
    day by each route of administration. The topical administration
    consisted of direct application to the entire abdominal skin. Physical
    signs, behaviour, and survival were recorded daily. Body weights,
    water consumption, blood pressure, heart rate, respiratory rate,
    neurological reflexes, and complete haematological  ophthalmological 
    and urinary analyses were performed during weeks 1, 4, 7, 12, 24, 37,
    51, and 73. At termination, gross and histomorphological examinations
    were made.

         All animals treated topically showed scaling and flaking on the
    area of application but no other adverse behavioural or physical
    signs. Animals given the highest dose orally died between weeks 15 and
    53 of the study. No other treatment-related changes were found in the
    monkeys treated orally, in physical examinations, in haematological,
    ophthalmological, urinary, or biochemical parameters, or in absolute
    or relative organ weights. Histologically, atelectasis and emphysema
    were the only pathological changes observed, and were seen only at the
    highest dose. Some regurgitation and/or tracheal inspiration of DMSO,
    which is a highly volatile, irritating substance, may have occurred
    (Vogin et al., 1970).

    2.3.2.5  Genotoxicity

         Studies of mutagenicity and genotoxicity were available for 14
    mono-, di-, and trisulfides, thiols, and related oxygenated
    derivatives in this group and three structurally related substances
    (Table 5). The compounds were tested for mutagenicity  in vitro at
    concentrations up to 300 000 mg/plate. No effect was found in
     Salmonella typhimurium strains TA97, TA98, TA100, TA102, TA1535,
    TA1537, TA1538, or TA2637 with or without metabolic activation (Lavoie
    et al., 1979; Eder et al., 1980, 1982; Wild et al., 1983; Aeschbacher
    et al., 1989; Watanabe & Morimoto, 1989a,b; Phillips Petroleum Co.,
    1990a; Zeiger et al., 1992; Hakura et al., 1993; Wang et al., 1994;
    Karekar et al., 1996; Brams et al., 1997). The only positive results
    found were with 1,2-ethanedithiol (No. 532) and DMSO (No. 507). The
    latter is widely used as a solvent in assays for genotoxicity  in
     vitro.

         In a test for reverse mutation in nine strains of  S.
    typhimurium and  Escherichia coli strains WP2 and WP2uvrA, modified
    by the use of preincubation, DMSO was mutagenic in  S. typhimurium
    TA1537 and TA2637 and in  E. coli WP2uvrA at concentrations of
    0.2-0.4 ml/plate, with and without metabolic activation (Hakura et
    al., 1993). These are relatively high concentrations, some being
    cytolethal, and no mutagenic activity was observed at concentrations
    used routinely in this assay.

         The ability of 1,2-ethanedithiol (No. 532) to induce specific
    locus mutations at the  Tk locus in cultured L5178Y Tk+/- mouse
    lymphoma cells was evaluated in the presence and absence of a
    metabolic activation system prepared from Aroclor-induced rat liver.
    When unactivated cultures were treated with concentrations of 13-150
    g/ml, total cell survival was only 0.9-32%. A dose-related increase
    in mutant frequency was seen relative to control cultures in the
    solvent, DMSO. In cultures with metabolic activation, no evidence of
    mutagenicity was seen at concentrations of 0.07-1 g/ml. The survival
    rate in these cultures (3-49%) was greater than that in cultures
    without activation. Concentrations of 16 and 50 g/ml of
    1,2-ethanedithiol were reported to induce a significant
    ( p < 0.002), concentration-related increase in the frequency of
    sister chromatid exchange in Chinese hamster ovary cells in the
    absence of metabolic activation, and concentrations of 1.6 and 5 g/ml
    induced a significant ( p < 0.004) increase in the frequency of
    sister chromatid exchange in the presence of metabolic activation. No
    cytotoxicity was observed at concentra-tions up to 5 g/ml (Phillips
    Petroleum Co., 1990a).

         The validity of the L5178YTk+/- mouse lymphoma cell assay has
    been evaluated in relation to potentially acidifying substances of low
    relative molecular mass by Brusick (1986) and Heck et al. (1989).
    Those authors concluded that the assay was not valid, since positive
    results can be induced by changes in the pH and osmolality of the
    culture medium. The results of assays for sister chromatid exchange
    may also be artefacts resulting from lysosome breakdown secondary to
    cytotoxicity. Cytotoxic concentrations of substances may also cause
    release of DNase which induces chromosomal aberrations and DNA
    double-strand breaks (Zajac-Kaye & Ts'o, 1984; Bradley et al., 1987).
    Cells with double-strand breaks that survive could be subject to a
    variety of genotoxic consequences, including chromosomal breaks and
    rearrangements. As cytotoxicity and lysosomal breakdown were not
    evaluated in the study of sister chromatid exchange with
    1,2-ethandithiol, the results are difficult to interpret.

         Groups of male ICR mice were given two doses 48 h apart of a
    mixture containing allyl sulfide (No. 458), allyl disulfide (No. 572),
    or diallyl trisulfide (No. 587) in corn oil at doses of 10 or 20 mg/ml
    by gavage. The doses were estimated to provide 0.33 or 0.67 mmol/kg bw
    or 50 or 100 mg/kg bw on the basis of the composition of the mixture.
    No increase in the frequency of mirconucleated polychromatic
    erythrocytes was seen in bone-marrow cells (Marks et al., 1992).

         The results of these assays  in vivo and  in vitro indicate
    that aliphatic and aromatic thiols and sulfides are not genotoxic.

    2.3.2.6  Developmental toxicity

         Studies on teratogenicity were available only for 1-butanethiol
    (No. 511) and benzenethiol (No. 525).


        Table 5. Studies of genotoxicity with aliphatic and aromatic sulfides and thiols
                                                                                                                                               

    No.  Substance                    End-point               Test system                  Concentration       Results     Reference
                                                                                                                                               

    458  Allyl sulfide                Reverse mutation        S. typhimurium TA100         0.004-0.44 g/ml    Negativea   Eder et al. (1982)
    458  Allyl sulfide                Micronucleus formation  Mouse                        38-77 mg/kg bw      Negative    Marks et al. (1992)
    492  Methylthio 2-(acetyloxy)     Reverse mutation        S. typhimurium TA100, TA98,  0.156-5 mg/plate    Negativea   Watanabe & 
         propionate                                           TA1535, TA1537                                               Morimoto (1989a)
    493  Methylthio 2-(propionyloxy)  Reverse mutation        S. typhimurium TA98, TA100,  0.156-5 mg/plate    Negativea   Watanabe & 
         propionate                                           TA1535, TA1537                                               Morimoto (1989b)
    507  DMSOc                        Reverse mutation        S. typhimurium TA97, TA98,   0.005-10 mol/      Negativea   Karekar et al. 
                                                              TA100, TA102                 plate                           (1996)
    507  DMSO                         Reverse mutation        S. typhimurium TA98, TA100   12.5-200 g/plate   Negativea   Wang et al. (1994)
    507  DMSO                         Reverse mutation        S. typhimurium TA97, TA98,   100 000-300 000     Negativea   Brams et al. (1987)
                                                              TA100                        g/plate
    507  DMSO                         Reverse mutation        S. typhimurium TA97, TA98,   100-10 000 g/      Negativea   Zeiger et al. (1992)
                                                              TA100, TA1535, TA1537        plate
    507  DMSO                         Reverse mutation        S. typhimurium TA97, TA98,   0.1-0.4 ml/plate    Negativea   Hakura et al. (1993)
                                                              TA100, TA102, TA104,
                                                              TA1535, TA1538
    507  DMSO                         Reverse mutation        S. typhimurium TA1537,       0.1-0.4 ml/plate    Positived   Hakura et al. (1993)
                                                              TA2637
    521  Allyl mercaptan              Reverse mutation        S. typhimurium TA100         0.005-1.4 g/ml     Negativea   Eder et al. (1980)
    525  Benzenethiol                 Reverse mutation        S. typhimurium TA98, TA100   25-500 g/plate     Negative    Lavoie et al. (1979)
    526  Benzyl mercaptan             Reverse mutation        S. typhimurium TA98, TA100,  < 3.6 mg/plate      Negativea   Wild et al. (1983)
                                                              TA1535, TA1537, TA1538
    532  1,2-Ethanedithiol            Reverse mutation        S. typhimurium TA98, TA100,  5000 g/plate       Negativea   Phillips Petroleum 
                                                              TA1535, TA1537, TA1538                                       Co. (1990a)
    532  1,2-Ethanedithiol            Sister chromatid        Chinese hamster ovary cells  16 g/mle           Positivef   Phillips Petroleum
                                      exchange                                             1.6 g/mlg          Positive    Co. (1990a)
    532  1,2-Ethanedithiol            Forward mutation        L5178Y mouse lymphoma        150 g/mle          Positivef   Phillips Petroleum
                                                              cells, Tk locus              1 g/mlg            Negative    Co. (1990a)
    551  2-Mercaptopropionic          Reverse mutation        S. typhimurium TA98, TA100,  < 3.6 mg/plate      Negativea   Wild et al. (1983)
         acid                                                 TA1535, TA1537, TA1538

    Table 5 (contd)
                                                                                                                                               

    No.  Substance                    End-point               Test system                  Concentration       Results     Reference
                                                                                                                                               

    564  Dimethyl disulfide           Reverse mutation        S. typhimurium TA98, TA100,  0.011-1.1 mmol      Negativea   Aeschbacher et al. 
                                                              TA102                                                        (1989)
    572  Allyl disulfide              Reverse mutation        S. typhimurium TA100         0.0015-0.15 g/ml   Negativea   Eder et al. (1980)
    572  Allyl disulfide              Micronucleus formation  Mouse                        48-98 mg/kg bw      Negativeb   Marks et al. (1992)
    578  Phenyl disulfide             Reverse mutation        S. typhimurium TA98, TA100,  < 3.6 mg/plate      Negativea   Wild et al. (1983)
                                                              TA1535, TA1537, TA1538 
    579  Benzyl disulfide             Reverse mutation        S. typhimurium TA98, TA100,  < 3.6 mg/plate      Negativea   Wild et al. (1983)
                                                              TA1535, TA1537, TA1538
    587  Diallyl trisulfide           Micronucleus formation  Mouse                        59-120 mg/kg bw     Negativeb   Marks et al. (1992)

    Related substances
         tert-Dodecyl                 Reverse mutation        S. typhimurium TA98, TA100,  0.018-10 000 g/    Negativea   Zeiger et al. (1987)
         mercaptan                                            TA1535, TA1537               plate
         Dimethyl sulfone             Reverse mutation        S. typhimurium TA98, TA100,  0.003-0.3 mmol      Negativea   Aeschbacher et al. 
                                                              TA102                                                        (1989)
         n-Butyl sulfone              Disc method             E. coli Sd-4-73              Not specified       Negative    Szybalski, (1958)
    100  2-Mercaptopropionic          Basc mutation           Drosophila                   10 mmol/L           Negative    Wild et al. (1983)
         acid
                                                                                                                                               
    a With and without metabolic activation
    b Mixture of allyl sulfide, allyl disulfide, and allyl trisulfide in a ratio of 68:20:12
    c Tested as solvent control
    d At doses that caused lethality; negative results at doses used routinely in this test
    e Without metabolic activation
    f Positive results in tests for sister chromatid exchange may be a result of lysosome breakdown, and positive results in mouse lymphoma
      cells may be due to pH and osmolality of culture medium
    g With metabolic activation
    

          1-Butanethiol (No. 511)

         Pregnant COBS CD rats were exposed to 1-butanethiol by whole-body
    inhalation for 6 h per day on days 6-19 of gestation at doses of 10,
    68, or 152 mg/kg of diet. The control group was exposed to filtered
    air only. The fetuses were removed from all rats on gestation day 20.
    The animals were examined for gross physical changes, viable fetuses,
    fetal body weights, maternal body-weight changes, and
    post-implantation losses or total implantations. 1-Butanethiol had no
    effect at the lowest dose, but significant differences in fetal body
    weights were seen at 68 and 152 mg/kg of diet (Thomas et al., 1987). 

          Benzenethiol (No. 525)

         Groups of 15-26 New Zealand white rabbits were given benzenethiol
    in corn oil orally at doses of 10, 30, or 40 mg/kg bw per day on days
    6-19 of gestation. Maternal body weight and feed and water consumption
    were recorded. On gestation day 30, the animals were killed and
    maternal organs and fetuses were weighed. The fetuses were also
    examined for external, visceral, and skeletal malformations. There was
    no effect at 10 mg/kg bw per day, but significant differences in
    maternal body weights were seen at 30 and 40 mg/kg bw per day.

         In the same study, groups of 25 rats were given 20, 35, or 50
    mg/kg bw per day orally on days 6-15 of gestation and were killed on
    gestation day 20. They were examined for the same parameters as the
    rabbits. Decreased mater-nal body weight was seen at all doses, and
    fetal body weights were decreased at 35 and 50 mg/kg bw per day. At 50
    mg/kg bw, the relative maternal liver weights were increased and
    increased post-implantation losses occurred, with a slight but
    nonsignificant decrease in the live litter size (George et al., 1995).

    2.3.2.7  Chemoprevention

         Several organosulfur compounds inhibit carcinogenesis by
    increasing the metabolism, detoxification, and elimination of
    carcinogens by phase I and II enzymes. For example, the effect of
    oltipraz in inhibiting colon tumorigenicity is associated with
    increased activity of glutathione S-transferase, NAD(P)H quinone
    reductase, and UDP-glucuronosyl transferase in the colon (Reddy et
    al., 1993). This effect may partly explain the cancer-inhibiting
    effect of foods like garlic that contain organosulfur compounds.

          Allyl sulfide (No. 458)

         Seven-week-old female A/J mice were given allyl sulfide at a dose
    of 200 mg/kg bw per day in the diet for three days. Two hours after
    treatment, the animals were given either a single dose of 100 mg/kg bw
    of the carcinogen 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone and
    kept for 16 weeks for determination of lung tumour production or
    killed immediately for preparation of lung and liver microsomes.

    Administration of the test material before carcinogen treatment
    significantly decreased the lung tumour incidence (by 38%) and tumour
    multiplicity (by 0.6) (Hong et al., 1994).

          Allyl mercaptan (No. 521)

         Groups of male weanling rats were given free access to a purified
    diet for two weeks and then given the same diet containing 0.2% allyl
    mercaptan dissolved in corn oil, corresponding to a calculated (Food
    and Drug Administration, 1993) daily intake of allyl mercaptan of 200
    mg/kg bw. After two weeks, the rats were injected intraperitoneally
    with a single dose of 2 mg/kg bw aflatoxin B1, 910 mg/kg bw
     N-nitrosodimethylamine, or 50 mg/kg bw  N-methyl- N-nitrosourea
    and killed 4 h later. Hepatic DNA damage was evaluated as
    single-strand breaks by the alkaline elution technique, and the amount
    of DNA eluted was determined by a microfluorimetric procedure. Allyl
    mercaptan significantly reduced (by 64%) the incidence of DNA
    single-strand breaks induced by aflatoxin B1 and reduced that induced
    by  N-nitrosodimethylamine by 39%. It had no effect on the incidence
    of breaks induced by  N-methyl- N-nitrosourea (LeBon et al., 1997).

          Propyl disulfide (No. 566)

         Cultures of the adult human tumour cell lines HCT-15 (colon),
    A549 (lung), and SKMEL-2 (skin) were plated for 24 h and then propyl
    disulfide was added at a dose of 100 mmol for up to 48 h. The cells
    were harvested and intracellular free calcium and apoptotic cells were
    determined. There was no effect on apoptosis, but a 12% increase in
    the intracellular concentration of calcium was observed (Sundaram &
    Milner, 1996).

          Allyl disulfide (No. 572)

         Cultures of the adult human tumour cell lines HCT-15 (colon),
    A549 (lung), and SKMEL-2 (skin) were plated for 24 h and then allyl
    disulfide was added at a dose of 100 or 500 mmol for up to 48 h. The
    cells were harvested and intracellular free calcium, apoptotic cells,
    and DNA fragmentation were determined. The proliferation of the HCT-15
    and SKMEL-2 cell lines was depressed by 90% and that of the A549 line
    by 75%, and the intracellular calcium concentration was increased by
    41%. Morphological changes characteristic of apoptosis were observed
    in treated cells, and a fivefold increase in DNA fragmentation was
    seen (Sundaram & Milner, 1996).

         Groups of 12 male Fischer 344 rats received diallyl disulfide at
    a concentra-tion of 0, 100, or 200 mg/kg of diet. After two weeks, the
    animals received azoxymethane, a known carcinogen, subcutaneously once
    a week for two weeks at a dose of 15 mg/kg bw per week. Treatment
    continued for 52 weeks, at which time the animals were killed. Body
    weights were recorded every two weeks for the first 10 weeks and then
    every four to six weeks. At autopsy, the animals were dissected in

    order to detect microscopic tumours, and their location, number, and
    size were recorded. Colon tumors with a diameter > 0.5 cm were cut
    into two halves: one portion was used to measure enzyme activity and
    the other for histopathology. Animals fed 200 mg/kg of diet showed a
    slight but significant decrease in body weight. Neither the incidence
    nor the multiplicity of colon adenomas differed between the control
    and experimental groups, but both doses significantly reduced the
    incidence and multiplicity of invasive colon adenocarcinomas. The
    activities of glutathione S-transferase, NAD(P)H quinone reductase,
    and UDP-glucuronosyl transferase in the liver, colonic mucosa, and
    tumours were also significantly increased in the treated animals
    (Reddy et al., 1993).

    2.3.3  Observations in humans

          Methylsulfinylmethane (DMSO; No. 507)

         In clinical trials to determine the therapeutic effects of DMSO,
    8900 mg/kg bw of 90% DMSO were applied to the entire trunk of 20 men
    either twice daily for three weeks or once daily for 26 weeks.
    Haematological examinations, blood chemical determinations, and urine
    analyses performed at the beginning and end of the three-week study
    revealed no significant changes. In the 26-week study, similar
    examinations were performed at 0, 2, 4, 8, 12, 16, and 24 weeks, in
    addition to thymol turbidity testing and sodium sulfobromophthalein
    determinations. Except for the appearance of cutaneous signs such as
    erythema, scaling, contact urticaria, and stinging or burning
    sensations, DMSO was tolerated well by all but two individuals, who
    developed systemic symptoms including a scaling rash, severe abdominal
    pain, slight nausea, and chest pains during the second week of
    treatment. One of these men did not continue the study; the other
    continued treatment, and the symptoms eventually abated. Clinical and
    laboratory investigations showed no evidence of adverse effects
    (Kligman, 1965).

         Two drops of aqueous solutions of increasing concentrations of
    DMSO were instilled into the lower conjunctival sac of groups of 10
    adult men, each eye being used only once without washing. No adverse
    effects were seen until a concentration of 50% was reached, when the
    men complained of transient burning. With 90% DMSO, all the men noted
    temporary stinging and burning. The external eye was completely normal
    24 h after treatment. The author concluded that DMSO is absorbed so
    rapidly through the conjunctival mucosa that any irritation would not
    be manifested (Kligman, 1965).

         While studies by oral administration are most appropriate for
    evaluating the safety of flavouring substances, the results of studies
    of dermal absorption may be considered useful in their absence for
    substances such as DMSO, which are readily absorbed into the systemic
    circulation. The lack of treatment-related adverse effects (other than
    irritation) in rhesus monkeys after both oral and dermal treatment
    with DMSO (Vogin et al., 1970; see above) demonstrates that the

    toxicity of DMSO is independent of route of administration. Therefore,
    the lack of toxic effects other than irritation in studies in humans
    treated dermally or in the eye (Kligman, 1965) suggests that oral oral
    intake of DMSO used as a flavouring substance would not be toxic.

    3.  REFERENCES

    Aeschbacher, H.U., Wolleb, U., Loliger, J., Spadone, J.C. & Liardon R.
    (1989) Contribution of coffee aroma constituents to the mutagenicity
    of coffee.  Food Chem. Toxicol., 27, 227-232.

    Alterman, M.A., Chaurassia, C.S., Lu, P. & Hanzlik R.P. (1995)
    Metabolism of 10-methoxydecanoic acid (1) and 10-(methylthio)decanoic
    acid(2), (omega-1)-oxa and -thia analogs of lauric acid.  Int. Soc.
     Study Xenobiotics, 8, 118.

    Ames, M.M., Selassie, C.D., Woodson, L.C., Van Loon, J.A., Hansch, C.
    & Weinshilboum, R.M. (1986) Thiopurine methyltransferase:
    Structure-activity relationships for benzoic acid inhibitors and
    thiophenol substrates.  J. Med. Chem., 29, 345-358.

    Anders, M.W., Ratnayake, J.H., Hanna, P.E. & Fucus, J.A. (1980)
    Involvement of thioredoxin in sulfoxide reduction by mammalian
    tissues.  Biochem. Biophys. Res. Commun., 97, 846-851.

    Anders, M.W., Ratnayake, J.H., Hanna, P.E. & Fucus, J.A. (1981)
    Thioredoxin-dependent sulfoxide reduction by rat renal cytosol.
     Biochem. Drug Metab. Disposition, 9, 307-310.

    Bailey, D.E. (1976a) Acute oral toxicity (LD50) studies in mice with
    1,8-octanedithiol. Unpublished study submitted to the Flavor and
    Extract Manufacturers' Association by Food and Drug Research
    Laboratories, Inc.

    Bailey, D.E. (1976b) Acute oral toxicity of 1,2-propanedithiol in
    mice. Unpublished study submitted to the Flavor and Extract
    Manufacturers' Association by Food and Drug Research Laboratories,
    Inc.

    Bailey, D.E. (1976c) Acute oral toxicity (LD50) studies in mice with
    compound 75-31065 (methyl benzyl disulfide). Unpublished study
    submitted to the Flavor and Extract Manufacturers' Association by Food
    and Drug Research Laboratories, Inc.

    Black, R.M., Brewster, K., Clarke, R.J., Hambrook, J.L., Harrison,
    J.M. & Howells, D.J. (1993) Metabolism of thiodiglycol
    (2,2'-thiobis-ethanol): Isolation and identification of urinary
    metabolites following intraperitoneal administration to rat.
     Xenobiotica, 23, 473-481.

    Bradley, M.O., Taylor, V.L., Armstrong, M.J. & Galloway, S.M. (1987)
    Relationship among cytotoxicity, lysosomal breakdown, chromosome
    aberrations, and DNA double-strand breaks.  Mutat. Res., 189, 69-79.

    Brams, A., Buchet, J.P., Crutzen-Fayt, M.C., DeMeester, C., Lauwerys,
    R. & Leonard, A. (1987) A comparative study, with 40 chemicals, of the
    efficiency of the Salmonella assay and the SOS Chromotest (kit
    procedure).  Toxicol. Lett., 38, 123-133.

    Bremer, J. & Greenberg, D.M. (1961) Enzymic methylation of foreign
    sulfhydryl compounds.  Biochim. Biophys. Acta, 46, 217-224.

    British Industrial Biological Research Association (1976) Short-term
    toxicity of samples TT171, TT172, TT173, and TT174 in rats.
    Unpublished study submitted to the Flavor and Extract Manufacturers'
    Association.

    Brodnitz, M.H. & Pascale, J.V. (1971) Thiopropanol S-oxide: A
    lachrymatory factor in onions.  J. Agric. Food Chem., 19, 269.

    Brown, V.K., Robinson, J. & Stevenson, D.E. (1963) A note on the
    toxicity and solvent properties of dimethyl sulfoxide.  J. Pharm.
     Pharmacol., 15, 688-692.

    Brusick, D. (1986) Genotoxic effects in cultured mammalian cells
    produced by low pH treatment conditions and increased ion
    concentrations.  Environ. Mutag., 8, 879-886.

    Buckberry, L.D. & Teesdale-Spittle, P.H. (1996) Sulfur-hydrogen
    compounds. In: Mitchell, S., ed.,  Biological Interactions of Sulfur
     Compounds, London: Taylor & Francis Ltd, pp. 113-144-76.

    Butterworth, K.R. & Mason, P.L. (1981) Acute toxicity of thioguaiacol
    and of versalide in rodents.  Food Chem. Toxicol., 19, 753-755.

    Butterworth, K.R., Carpanini, F.M.B., Gaunt, I.F., Hardy, J., Kiss,
    I.S. & Gangolli, S.D. (1975) Short-term toxicity of dimethyl sulfide
    in rat.  Food Cosmet. Toxicol., 13, 15-22.

    Canellakis, E.S. & Tarver, H. (1953) The metabolism of methyl
    mercaptan in the intact animal.  Arch. Biochem. Biophys., 42,
    446-455.

    Cashman, J.R. & Olsen, L.D. (1990) Stereoselective S-oxygenation of
    2-aryl-1,3-dithiolanes by the flavin-containing and cytocrome P-450
    monooxygenases.  Mol. Pharmacol., 38, 573-585.

    Cashman, J.R. & Williams, D.E. (1990) Enantioselective S-oxygenation
    of 2-aryl-1,3-dithiolanes by rabbit lung enzyme preparations.
     Mol. Pharmacol., 37, 333.

    Cashman, J.R., Olsen, L.D. & Bornheim, L.M. (1990) Enantioselective
    S-oxygenation by flavin containing cytochrome P-450 mono-oxygenases.
     Chem. Res. Toxicol., 3, 344.

    Cashman, J.R., Yang, Z.C., Yang, L. & Wrighton, S.A. (1995a)
    Stereo-and regioselective N-and S-oxygenation of tertiary amines and
    sulfides in adult human liver microsomes.  Int. Soc. Study
     Xenobiotics, 8, 34.

    Cashman, J.R., Park, S.B., Yang, Z.C., Washington, C.B., Gomez, D.Y.,
    Giacomini, K. & Brett, C.M. (1995b) Chemical, enzymatic and human
    enantioselective S-oxygenation of cimetidine.  Int. Soc. Study
     Xenobiotics, 8, 133.

    Christias, C. (1975) Specific inhibition of sclerotium formation by
    2-mercaptoethanol and related sulfhydryl compounds in  Sclerotium
     rolfsii.  Can. J. Microbiol., 21, 1541-1547.

    Collinson, V.A. (1989) ST 15 C 88 Acute oral toxicity study in the
    rat. Unpublished study No. A/0/13008 from Toxicol Laboratories Ltd,
    United Kingdom.

    Cox, G.E., Bailey, D.E. & Morgareidge, K. (1973a) 90-Day feeding
    studies in rats with trithioacetone. Unpublished report submitted to
    the Flavor and Extract Manufacturers' Association by Food and Drug
    Research Laboratories, Inc.

    Cox, G.E., Bailey, D.E. & Morgareidge, K. (1973b) 90-Day feeding
    studies in rats with compound ES-307/308 (14705). Unpublished report
    submitted to the Flavor and Extract Manufacturers' Association by Food
    and Drug Research Laboratories, Inc.

    Cox, G.E., Bailey, D.E. & Morgareidge, K. (1974a) 90-Day feeding study
    in rats with compound 14935 (2-mercapto-3-butanol). Unpublished report
    submitted to the Flavor and Extract Manufacturers' Association by Food
    and Drug Research Laboratories, Inc.

    Cox, G.E., Bailey, D.E. & Morgareidge, K. (1974b) 90-Day feeding
    studies in rats with compound 31098. Unpublished report submitted to
    the Flavor and Extract Manufacturers' Association by Food and Drug
    Research Laboratories, Inc.

    Cox, G.E., Rucci, G. & Babish, J.G. (1979) 90-Day subacute dietary
    toxicity study of IFF code No. 78-002-2 in Sprague-Dawley rats.
    Unpublished report submitted to the Flavor and Extract Manufacturers'
    Association by Food and Drug Research Laboratories, Inc.

    Damani, L.A. (1987) Metabolism of sulphur-containing drugs. In:
    Benford, D.J., Bridges, J.W. & Gibson, G.G., eds,
     Drug Metabolism--From Molecules to Man, London: Taylor & Francis,
    pp. 581-603.

    Davis, P.J. & Guenthner, L.E. (1985) Sulindac oxidation/reduction by
    microbial cultures; microbial models for mammalian metabolism.
     Xenobiotica, 15, 845-857.

    Deng, D.J., Mueller, K., Kasper, P. & Mueller, L. (1994) Effect of
    diallyl trisulfide on induction of UDS by mutagenic drugs in primary
    rat hepatocytes.  Biomed. Environ. Sci., 7, 85-90.

    Dutton, G.J. & Illing, H.P.A. (1972) Mechanism of biosynthesis of
    thio-beta-D-glucosides.  Biochem. J., 129, 539-550.

    Eder, E., Neudecker, T., Lutz, D. & Henschler, D. (1980) Mutagenic
    potential of allyl and allylic compounds. Structure-activity
    relationship as determined by alkylating and direct in vitro mutagenic
    properties.  Biochem. Pharmacol., 29, 993-998.

    Eder, E., Henschler, D. & Neudecker, T. (1982) Mutagenic properties of
    allylic and alpha, beta-unsaturated compounds: Consideration of
    alkylating mechanisms.  Xenobiotica, 12, 831-848.

    Elfarra, A.A., Duescher, R.J., Sausen, P.J., Lawton, M.P. & Philpot,
    R.M. (1995) Potential role of the flavin-containing monooxygenases in
    the metabolism of endogenous compounds.  Int. Soc. Study Xenobiotics,
    8, 9.

    El Fatih, Karim, I.A., Millership, J.S., Temple, D.J. & Woolfson, A.D.
    (1988) An investigation of the metabolism of
    S-carboxymethyl-L-cysteine in man using a novel HPLC-ECD method.
     Eur.  J. Drug. Metab. Pharmacokinet., 13, 253.

    Elf Atochem (1963) Unpublished study from Pharmacology Research Inc.

    Elf Atochem (1985) Unpublished study from Product Safety Labs.

    Elf Atochem (1992) Unpublished study from Centre International de
    Toxicologie.

    Fairchild, E.J. & Stokinger, H.E. (1958) Toxicologic studies on
    organic sulfur compounds. 1. Acute toxicity of some aliphatic and
    aromatic thiols (mercaptans).  Am. Ind. Hyg. Assoc. J., 19, 171-189.

    Farr, C.H. & Kirwin, C.J. (1994) Organic sulfur compounds. In:
    Clayton, D.G. & Clayton, F.E., eds,  Patty's Industrial Hygiene
     and Toxicology, 4th Ed., Vol. 2, New York: John Wiley & Sons, pp.
    4311-4372.

    Feng, P.C.C. & Solsten, R.T. (1991) In vitro transformation of
    dithiopyr by rat liver enzymes: Conversion of methylthioesters to
    acids by oxygenases.  Xenobiotica, 21, 1265.

    Fenwick, G.R. & Hanley, A.B. (1985) The genus  Allium, part 2.  CRC
     Crit. Rev. Food Sci. Nutr., 22, 273-377.

    Fishman, F.G., Jenkins, L.J., Jr, Coon, R.A. & Jones, R.A. (1969)
    Effects of acute and repeated inhalation of dimethyl sulfoxide in
    rats.  Toxicol. Appl. Pharmacol., 15, 74-82.

    Flavor and Extract Manufacturers' Association (1991)  In vitro
    hydrolysis of 3-methylthiohexy acetate. Unpublished report No. 183/91.

    Flavor and Extract Manufacturers' Association (1996) Sensory tolerance
    test protocol. Unpublished report.

    Fogelman, R.W. & DeProspo, J. (1973a) Acute oral toxicity in mice with
    ES-307/308. Unpublished report submitted to the Flavor and Extract
    Manufacturers' Association by Affiliated Medical Research Institute.

    Fogelman, R.W. & DeProspo, J. (1973b) Acute oral toxicity in mice with
    SB-11-2876 (trithioacetate). Unpublished report submitted to the
    Flavor and Extract Manufacturers' Association by Affiliated Medical
    Research Institute.

    Fogelman, R.W. & DeProspo, J. (1974) Acute oral toxicity in mice with
    1,2-ethanedithiol. Unpublished report submitted to the Flavor and
    Extract Manufacturers' Association by Affiliated Medical Research
    Institute.

    Fogelman, R.W. & Suppers, L. (1973) Acute oral toxicity in mice with
    1,8-octanedithiol. Unpublished report submitted to the Flavor and
    Extract Manufacturers' Association by Affiliated Medical Research
    Institute.

    Fogelman, R.W. & Suppers, L. (1974a) Acute oral toxicity in mice with
    1,8-octanedithiol. Unpublished report submitted to the Flavor and
    Extract Manufacturers' Association by Affiliated Medical Research
    Institute.

    Fogelman, R.W. & Suppers, L. (1974b) Acute oral toxicity in mice with
    1,2-propanedithiol. Unpublished report submitted to the Flavor and
    Extract Manufacturers' Association by Affiliated Medical Research
    Institute.

    Fogelman, R.W., Bukva, N.F. & Margolin, S. (1970) Acute oral toxicity
    of 2-4252. Unpublished study submitted by Affiliated Medical
    Enterprises, Inc. Princeton, NJ, USA.

    Food and Drug Administration (1993)  Priority-based Assessment of
    Food  Additives (PAFA) Database, Waskington DC: Center for Food
    Safety and Applied Nutrition, p. 58.

    Frandsen, A., Schousboe, A. & Griffiths, R. (1993) Cytotoxic actions
    and effects on intracellular Ca2+ and cGMP concentrations of
    sulphur-containing excitatory amino acids in cultured cerebral
    cortical neurons.  J. Neurosci. Res., 34, 331-339.

    Gachon, F., Nicolas, C., Maurizis, C., Verny, M., Chabard, J.L.,
    Faurie, M. & Gaillard, G. (1988) Disposition and metabolism of
    letosteine in rats.  Drug Metab. Disposition, 16, 853.

    Gallo, M.A., Cox, G.E. & Babish, J.G. (1976) 90-Day feeding studies in
    rats with compound 75-31065 (methyl benzyl disulfide). Unpublished
    report to the Flavor and Extract Manufacturers' Association by Food
    and Drug Research Laboratories, Inc..

    George, J.D., Price, C.J., Navarro, H.A., Barr, M.C., Myers, C.B.,
    Hunter, E.S., Schwetz, B.A. & Shelby, M.D. (1995) Developmental
    toxicity of thiophenol (thio) in rats and rabbits.  Toxicologist, 15,
    160.

    Gibson, T.P., Dobrinska, M.R., Lin, J.H., Entwistle, L.A. & Davies,
    R.O. (1987) Biotransformation of sulindac in end-stage renal disease.
     Clin. Pharmacol. Ther., 42, 82-88.

    Greenzaid, P. & Jencks, W.P. (1971) Pig liver esterase. Reactions with
    alcohols, structure-reactivity correlations, and the acyl-enzyme
    intermediate.  Biochemistry, 10, 1210.

    Griffiths, P.J. & Babish, J.G. (1978) Acute oral toxicity (LD50) of
    DSE 3303S (15277) in albino mice (BLU: Ha(ICR)). Unpublished report
    No. B-3 to the Flavor and Extract Manufacturers' Association from Food
    and Drug Research Laboratories, Inc. 

    Griffiths, P.J., Giessinger, M. & Fouillet, X. (1979) Report on acute
    oral toxicity (LD/50) and three-month toxicity of TT 184. Unpublished
    report to the Flavor and Extract Manufacturers' Association from
    Battelle Geneva Research Centres.

    de Groot, A.P., Spanjers, M.T. & van der Heijden, C.A. (1974) Acute
    and sub-acute oral toxicity studies in rats with five flavour
    compounds. Unpublished report submitted to the Flavor and Extract
    Manufacturers' Association.

    Grosa, G., Caputo, O., Cerutti, M., Biglino, G., Franzone, J.S.%
    Cravanzola, C. (1991) Metabolism of
    7-(1,3-dithiolan-2-ylmethyl)1,3-dimethylxanthine by rat liver
    microsomes: Diastereoselective metabolism of the 1,3-dithiolane ring.
     Drug Metab. Disposition, 19, 454-457.

    Hakura, A., Mochida, H. & Yamatsu, K. (1993) Dimethyl sulfoxide (DMSO)
    is mutagenic for bacterial mutagenicity tester strains.  Mutat. Res.,
    303, 127-133.

    Harper, K.H. & Gin, H.B. (1964) The acute oral toxicity to rats of
    T59. Unpublished report.

    Heck, J.D., Vollmuth, T.A., Cifone, M.A., Jagannath, D.R., Myhr, B. &
    Curren, R.D. (1989) An evaluation of food flavoring ingredients in a
    genetic toxicity screening battery.  Toxicologist, 9, 257.

    Hermansky, S.J. & Weaver, E.C. (1990) Fourteen-day dietary minimum
    toxicity screen (MTS) with acetyl lactic, thiomethyl ester and
    propiodyl lactic, thiomethyl ester in Fischer 344 rats. Unpublished
    report 53-553 to the Flavor and Extract Manufacturers' Association
    from Bushy Run Research Center, Pennsylvania, USA.

    Hodgson, E. & Levi, P.A. (1992) The role of the flavin-containing
    monooxygenases (EC 1.14.13.8) in the metabolism and mode of action of
    agricultural chemicals.  Xenobiotica, 22, 1175-1183.

    Hong, J.Y., Lin, M.C., Wang, Z.Y., Wang, E.J. & Yang, C.S. (1994)
    Inhibition of chemical toxicity and carcinogenesis by diallyl sulfide
    and diallyl sulfone. In: Huang, M.-T., Osawa, T., Ho, C.-T. & Rosen,
    R.T., eds,  Food Phytochemicals for Cancer prevention I, Fruits and
     Vegetables (ACS Symposium Series 546), Washington DC: American
    Chemical Society, pp. 97-101.

    Hoodi, A.A. & Damani, L.A. (1984) Cytochrome P-450 and non-P-450
    sulphoxidations.  J. Pharm. Pharmacol., 36, 62P.

    Hucker, H.B., Miller, J.K., Hochberg, A., Brobyn, R.D., Riordan, F.H.
    & Calesnick, B. (1967) Studies on the absorption, excretion, and
    metabolism of dimethyl sulfoxide (DMSO) in man.  J. Pharmacol. Exp.
     Ther., 155, 309-317.

    International Organization of the Flavor Industry (1995) European
    inquiry on volume of use. Private communication to the Flavor and
    Extract Manufacturers' Association.

    Karekar, V.R., Mujumdar, A.M., Joshi, S.S., Dhuley, J., Shinde, S.L. &
    Ghaskadbi, S. (1996) Assessment of genotoxic effect of piperine using
     Salmonella typhimurium and somatic and germ cells of Swiss albino
    mice.  Arzneimittel-Forsch., 46, 972-975.

    Keith, R.A., Abraham, R.T., Pazmino, P. & Weinshilboum, R.M. (1983)
    Correlation of low and high affinity thiol methyltransferase and
    phenol methyltransferase activities in human erythrocyte membranes.
     Clin. Chim. Acta, 131, 257-272.

    Klancnik, J.M., Cuenod, M., Gahwiler, B.H., Jiang, Z.P. & Do, K.Q.
    (1992) Release of endogenous amino acids, including homocysteic acid
    and cysteine sulphinic acid, from rat hippocampal slices evoked by
    electrical stimulation of Schaffer collateral-commissural fibres.
     Neuroscience, 49, 557-570.

    Kligman, A.M. (1965) Dimethyl sulfoxide--Part 2.  J. Am. Med. Assoc.,
    193, 151-156.

    Koptyaev, V.G. (1967) Experimental determination of maximum
    permissible concentration of dimethyl sulfide in water bodies.  Hyg.
     Sanit., 32, 315-320.

    Kurooka, S., Hashimoto, M., Tomita, M., Maki, A. & Yoshimura, Y.
    (1976) Relationship between the structure of S-acyl thiol compounds
    and their rates of hydrolysis by pancreatic lipase and hepatic
    carboxylic esterase.  J. Biochem., 79, 533-541.

    Lavoie, E., Tulley, L., Fow, E. & Hoffmann, D. (1979) Mutagenicity of
    aminophenyl and nitrophenyl ethers, sulfides, and disulfides.  Mutat.
     Res., 67, 123-131.

    Layman, D.L. & Jacob, S.W. (1985) The absorption, metabolism, and
    excretion of dimethyl sulfoxide by rhesus monkeys.  Life Sci., 37,
    2431-2437.

    LeBon, A.M., Roy, C., Dupont, C. & Suschete, M. (1997)  In vivo
    antigenotoxic effects of dietary allyl sulfides in the rat.  Cancer
     Lett., 114, 131-134.

    Lee, S.C. & Renwick, A.G. (1995a) Sulphoxide reduction by rat
    intestinal flora and by  Escherichia coli in vitro. Biochem.
     Pharmacol., 49, 1567-1576.

    Lee, S.C. & Renwick, A.G. (1995b) Sulphoxide reduction by rat and
    rabbit tissues  in vitro. Biochem. Pharmacol., 49, 1557-1565. 

    Levi, P.E. & Hodgson, E. (1988) Stereospecificity in the oxidation of
    phorate and phorate sulphoxide by purified FAD-containing
    mono-oxygenase and cytochrome P-450 isozymes.  Xenobiotica, 18,
    29-39.

    Maarse, H., Visscher, C.A., Willemsens, L.C., Nijssen, L.M. & Boelens,
    M.H., eds (1994)  Volatile Components in Food, 6th Ed., Suppl. 5,
    Zeist, TNO Nutrition and Food Research.

    Maiorino, R.M., Bruce, D.C. & Aposhian, H.V. (1988) Determination and
    metabolism of dithiol chelating agents. VI. Isolation and
    identification of the mixed disulfides of meso-2,3-dimercaptosuccinic
    acid with L-cysteine in human urine.  Toxicol. Appl. Pharmacol., 97,
    338.

    Maiorino, R.M., Xu, Z.F. & Aposhian, H.V. (1996) Determination and
    metabolism of dithiol chelating agents. XXII. In humans, sodium
    1,3-dimercapto-1-propanesulfonate is bound to plasma albumin via mixed
    disulfide formation and is found in the urine as cyclic polymeric
    disulfides.  J. Pharmacol. Exp. Ther., 277, 375-384.

    Marks, H.S., Anderson, J.L. & Stoewsand, G.S. (1992) Inhibition of
    benzo[a]pyrene-induced bone marrow micronuclei formation by diallyl
    thioethers in mice.  J. Toxicol. Environ. Health, 37, 1-9

    Mazel, P., Henderson, J.F. & Axelrod, J. (1964) S-Demethylation by
    microsomal enzymes.  J. Pharmacol. Exp. Ther., 143, 1-6.

    McBain, D.A. & Menn, J.J. (1969) S-Methylation, oxidation,
    hydroxylation, and conjugation of thiophenol in the rat.  Biochem.
     Pharmacol., 18, 2282-2285.

    Michael, W.R. 1968) Metabolism of linear alkylate sulfonate and alkyl
    benzene sulfonate in albino rats.  Toxicol. Appl. Pharmacol., 12,
    473-485.

    Mitchell, S.C., Idle, J.R. & Smith, R.L. (1982) The metabolism of
    [14C] cimetidine in man.  Xenobiotica, 12, 283.

    Mondino, A. (1981) Thirteen week repeated dose study of the test
    article TT 191 (3-methyl-1,2,4-trithiane) orally administered to
    Sprague Dawley Charles River CD (SD) BR rats. Unpublished study from
    Instituto di richierche biomedicine 'Antoine Marxer' SpA.

    Mondino, A. & Peano, S. (1979) Acute oral toxicity of
    2,6-dimethylthiophenol. Unpublished report to the Flavor and Extract
    Manufacturers' Association.

    Mondino, A. & Peano, S. (1982) Acute toxicity study, TT 201 and TT202.
    Unpublished report from Instituto di richierche biomedicine 'Antoine
    Marxer' SpA.

    Mondino, A., Peano, S. & Berruto, P. (1981) Acute toxicity study,
    TT191. Unpublished report from Instituto di richierche biomedicine
    'Antoine Marxer' SpA.

    Moran, E.J., Easterday, O.D. & Oser, B.L. (1980) Acute oral toxicity
    of selected flavor chemicals. Drug Chem. Toxicol., 3, 249-258.

    Moreno, O.M. (1975) Acute toxicity studies on rats, rabbits, and
    guinea pigs. Unpublished report to RIFM.

    Moreno, O.M. (1980) Acute toxicity studies. Unpublished report to
    RIFM.

    Morgareidge, K. (1970) 90-Day feeding study in rats with
    tetrahydrothiophene-3-one (31015). Unpublished study submitted to the
    Flavor and Extract Manufacturers' Association.

    Morgareidge K. (1971a) 90-Day feeding study with 2-naphthalenethiol in
    rats. Unpublished study submitted to the Flavor and Extract
    Manufacturers' Association.

    Morgareidge, K. (1971b) 90-Day feeding study with
    2-keto-3-pentanethiol in rats. Unpubli-shed study submitted to the
    Flavor and Extract Manufacturers' Association.

    Morgareidge, K. & Oser, B.L. (1970a) 90-Day feeding studies in rats
    with cyclopentane-thiol. Unpublished study submitted to the Flavor and
    Extract Manufacturers' Association.

    Morgareidge, K. & Oser, B.L. (1970b) 90-Day feeding studies in rats
    with dipropyltrisulfide (30204). Unpublished study submitted to the
    Flavor and Extract Manufacturers' Association.

    Morgareidge, K. & Oser, B.L. (1970c) 90-Day feeding studies in rats
    with diallyltrisulfide. Unpublished study submitted by Food and Drug
    Research Laboratories, Inc. to the Flavor and Extract Manufacturers'
    Association.

    Morgareidge, K., Bailey, D.E. & Cox, G.E. (1974a) 90-Day feeding study
    on 2,3-butanedithiol in rats. Unpublished study submitted to the
    Flavor and Extract Manufac-turers' Association.

    Morgareidge, K., Bailey, D.E. & Cox, G.E. (1974b) 90-Day feeding study
    in rats with compound 14966. Unpublished study submitted to the Flavor
    and Extract Manufac-turers' Association.

    Morgareidge, K., Bailey, D.E. & Cox, G.E. (1974c) 90-Day feeding study
    of 1,8-octane-dithiol in rats. Unpublished study submitted to the
    Flavor and Extract Manufacturers' Association.

    Moutiez, M., Aumercier, M., Tessier, E., Parmentier, B., Tartar, A. &
    Sergheraert, C. (1994) Reduction of a trisulfide derivative of
    glutathione by glutathione reductases.  Biochem. Biophys. Res.
    Commun., 202, 1380-1386.

    Munday, R. & Manns, E. (1994) Comparative toxicity of prop(en)yl
    disulfides derived from Alliaceae. Possible involvement of 1-propenyl
    disulfides in onion-induced hemolytic anemia.  J. Agric. Food Chem.,
    42, 959-962.

    Munday, R., Manns, E. & Fowke, E.A. (1990) Steric effects on the
    haemolytic activity of aromatic disulphides in rats.  Food Chem.
     Toxicol., 28, 561-566.

    National Academy of Sciences (1970)  Evaluating the Safety of Food
     Chemicals, Washington DC.

    National Academy of Sciences (1982)  Evaluating the Safety of Food
     Chemicals, Washington DC.

    National Academy of Sciences (1987)  Evaluating the Safety of Food
     Chemicals, Washington DC.

    Nickson, R.M. & Mitchell, S.C. (1994) Fate of dipropyl sulfide and
    dipropyl sulfoxide in rat.  Xenobiotica, 24, 157-168.

    Nickson, R.M., Mitchell, S.C. & Zhang, A.Q. (1995) Fate of dipropyl
    sulfone in rat.  Xenobiotica, 25, 1391-1398.

    Nnane, P. & Damani, L.A. (1995) The involvement of rat liver CYP2B1
    and CYP2D1 in the microsomal sulphoxidation of 4-chlorophenyl methyl
    sulphide.  Int. Soc. Study Xenobiotics, 8, 110.

    Noel, P.R.B., Barnett, K.C., Davies, R.E., Jolly, D.W., Leahy, J.S.,
    Mawdesley-Thomas, L.E., Shillam, K.W.G., Squires, P.F., Street, A.E.,
    Tucker, W.C. & Worden, A.N. (1975) The toxicity of dimethyl sulphoxide
    (DMSO) for the dog, pig, rat, and rabbit.  Toxicologist, 3, 143-169.

    Oae, S., Mikami, A., Matsura, T., Ogawa-Asada, K., Watanabe, Y.,
    Fujimori, K. & Iyanagi, T. (1985) Comparison of sulfite oxygenation
    mechanism for liver microsomal FAD-containing monooxygenase with that
    for cytochrome P-450.  Biochem Biophys. Res. Commun., 131, 567-573.

    Ogasawara, Y., Isoda, S. & Tanabe, S. (1998) A labile sulfur in
    trisulfide affects cytochrome P-450 dependent lipid peroxidation in
    rat liver microsomes.  Toxicol. Lett., 99, 191-198.

    Opdyke, D.L.J. (1979) Monographs on fragrance raw materials.  Food
     Cosmet. Toxicol., 17, 769.

    Oser, B.L. (1966) Feeding studies with pinanyl mercaptan (PK) in rats.
    Unpublished study submitted to the Flavor and Extract Manufacturers'
    Association.

    Oser, B.L. (1970) The acute oral toxicity to mice of ten compounds.
    Unpublished study submitted to the Flavor and Extract Manufacturers'
    Association.

    Panasevich, R.E., Mallory, V.T. & Matthews, R.J. (1980) Dose-related
    finding and single dose oral study of ethyl 4-(methylthio)butyrate.
    Unpublished study submitted to the Flavor and Extract Manufacturers'
    Association.

    Parkinson, A. (1996) Biotransformation of xenobiotics. In: Klaassen,
    C.D., ed.,  Casarret and Doull's Toxicology: The Basic Science of
     Poisons, 5th Ed., New York, McGraw-Hill Co., pp. 113-118. 

    Peano, S., Roffino, A., Milone, M.F., Orlando, L. & Berruto, G. (1981)
    Thirteen week repeated dose study with 2,6-dimethylthiophenol orally
    administered to Sprague-Dawley Charles River CD (SD) BR rats.
    Unpublished study submitted to the Flavor and Extract Manufacturers'
    Association by Instituto di richierche biomedicine 'Antoine Marxer'
    SpA.

    Phillips Petroleum Co. (1990a) Toxicity study
    summary--1,2-Ethanedithiol (TOX071). 

    Phillips Petroleum Co. (1990b) Toxicity study summary--Isopropyl
    mercaptan (TOX083).

    Phillips Petroleum Co. (1990c) Toxicity study summary--Tertiary butyl
    mercaptan (TOX1-6).

    Piccirillo, V.J. & Lunchicki, C. (1982) Acute oral toxicity (LD50)
    study in the rat with methyl-2-methylthiobutyrate. Unpublished report
    submitted to the Flavor and Extract Manufacturers' Association.

    Posternak, J.M., Linder, A. & Vodoz, C.A. (1969) Summaries of
    toxicological data. Toxicological tests on flavoring matters.  Food
     Cosmet. Toxicol., 7, 405-407.

    Reddy, B.S., Rao, C.V., Rivenson, A. & Kelloff, G. (1993)
    Chemoprevention of colon carcinogenesis by organosulfur compounds.
     Cancer Res., 53, 3493-3498.

    Renwick, A.G. (1989) Sulphoxides and sulphones. In: Damani, L.A., ed.,
     Sulphur-containing Drugs and Related Organic Compounds. Chemistry,
     Biochemistry and Toxicology (Ellis Horwood Series in Biochemical
    Pharmacology), Vol. 1, Part B, New York: John Wiley & Sons, pp.
    133-154.

    Renwick, A.G. (1996) Sulfur-oxygen compounds. In: Mitchell, S., ed.,
     Biological Interactions of Sulfur Compounds, London: Taylor &
    Francis, pp. 42-76.

    Renwick, A.G. & George, C.F. (1989) Metabolism of xenobiotics in the
    gastro-intestinal tract. In: Hudson, D.H., Caldwell, J. & Paulson,
    G.D., eds,  Intermediary Xenobiotic Metabolism in Animals:
     Methodology, Mechanisms and Significance, London, Taylor & Francis,
    pp. 13-40.

    Renwick, A.G., Evans, S.P., Sweatman, T.W., Cumberland, J. & George,
    C.F. (1982) The role of the gut flora in the reduction of
    sulphinpyrazone in the rat.  Biochem. Pharmacol., 31, 2649.

    Rettie, A.E., Bogucki, B.D., Lim, I. & Meier, G.P. (1990)
    Stereoselective sulfoxidation of a series of alkyl p-tolyl sulfides by
    microsomal and purified flavin-containing monooxygenases.
     Mol. Pharmacol., 37, 643.

    Rettie, A.E., Lawton, M.P., Jaffer, A., Sadeque, M. & Meier, G.P.
    (1994) Prochiral sulfoxidation as a probe for multiple forms of the
    microsomal flavin-containing monooxygenase: Studies with rabbit FMO1,
    FMO2, FMO3, and FMO5 expressed in  Escherichia coli. Arch. Biochem.
     Biophys., 311, 369.

    Richardson, K.A., Edward, V.T., Jones, B.C. & Hutson, D.H. (1991)
    Metabolism in the rat of a model xenobiotic plant metabolite
    S-benzyl-N-malonyl-L-cysteine.  Xenobiotica, 21, 371.

    Rush, R.E. (1991) 14-Day dietary toxicity study in rats with
    3-(methylthio)hexyl acetate (MTHA). Unpublished report No. 3141.5 from
    Springborn Laboratories, Inc. to the Flavor and Extract Manufacturers'
    Association.

    Sadeque, A.J.M., Eddy, A.C., Meierand, G.P. & Rettie, A.E. (1992)
    Stereoselective sulfoxidation by human flavin-containing
    monooxygenase.  Drug Metab. Disposition, 20, 832.

    Sadeque, A.J.M., Philpot, R.M. & Rettie, A.E. (1995) Chiral
    sulfoxidation by human liver FMO3 and FMO5.  Int. Soc. Study
     Xenobiotics, 8.

    Sanders, A. (1997) Acute oral toxicity (limit test) in the rat.
    Unpublished SPL project No. 012/234 submitted to the Flavor and
    Extract Manufacturers' Association.

    Schafer, E.W. & Bowles, W.A., Jr (1985) Acute oral toxicity and
    repellency of 933 chemicals to house and deer mice.  Arch. Environ.
     Contam. Toxicol., 14, 111-129.

    Selyuzhitskii, G.V. (1972) Experimental data on substantiation of the
    maximum allowable concentraion of methyl mercaptan, dimethyl sulfide
    and dimethyl disulfide in the air of the working area of pulp paper
    plants.  Gig. Tr. Prof. Zabol., 16, 46-47.

    Shaw, P.N. & Blagbrough, I.S. (1989) Cysteine conjugate beta-lyase,
    II: Isolation, properties and structure-activity relationships. In:
    Damani, L.A., ed.,  Sulphur-containing Drugs and Related Organic
     Compounds, Vol. 2, Part B, Chichester: Ellis Horwood Ltd, pp.
    135-156. 
    Shellenberger, T.E. (1970) Subacute toxicity evaluation of ethyl
    thioacetate in rats. Final report. Unpublished report GSRI Project
    NC-373 from Gulf South Research Institute submitted to the Flavor and
    Extract Manufacturers' Association.

    Shellenberger, T.E. (1971a) Acute toxicological evaluations of
    2-naphthalenethiol in mice. Unpublished report GSRI Project NC-398
    from Gulf South Research Institute submitted to the Flavor and Extract
    Manufacturers' Association.

    Shellenberger, T.E. (1971b) Acute toxicological evaluations of
    chemicals with mice--2-Keto-3-pentanethiol. Unpublished study from
    Gulf South Research Institute.

    Snow, G.A. (1957) The metabolism of compounds related to ethanethiol.
     J. Biochem., 65, 77-82.

    Sommer, S. & Tauberger, G. (1964) Toxicologic investigations of
    dimethyl sulfoxide.  Arnzeimittel. Forsch., 14, 1050-1053.

    Souhaili-El Amri, H., Fargetton, X., Delatour, P. & Batt, A.M. (1987)
    Sulphoxidation of albendazole by the FAD-containing and cytochrome
    P-450 dependent mono-oxygenase from pig liver microsomes.
     Xenobiotica, 17, 1159-1168.

    Stofberg, J. & Grundschober, F. (1987) Consumption ratio and food
    predominance of flavoring materials.  Perfumer Flavorist, 12, 27.

    Stofberg, J. & Kirschman, J.C. (1985) The consumption ratio of
    flavouring materials: A mechanism for setting priorities for safety
    evaluation.  Food Chem. Toxicol., 23, 857-860.

    Strong, H.A., Renwick, A.G. & George, C.F. (1984a) The site of
    reduction of sulphinpyrazone in the rabbit.  Xenobiotica, 14,
    815-826.

    Strong, H.A., Oates, J., Sembi, J., Renwick, A.G. & George, C.F.
    (1984b) Role of the gut flora in the reduction of sulphinpyrazone in
    humans.  J. Pharmacol. Exp. Ther., 230, 726-732.

    Strong, H.A., Warner, J., Renwick, A.G. & George, C.F. (1985) Sulindac
    metabolism: The importance of an intact colon.  Clin. Pharmacol.
    Ther., 38, 387-393.

    Strong, H.A., Angus, R., Oates, J., Sembi, J., Howarth, P., Renwick,
    A.G. & George, C.F. (1986) Effects of ischaemic heart disease, Crohn's
    disease and anti-microbial therapy on the pharmacokinetics of
    sulphinpyrazone.  Clin. Pharmacokinet., 11, 402-411. 

    Strong, H.A., Renwick, A.G., George, C.F., Liu, Y.F. & Hill, M.J.
    (1987) The reduction of sulphinpyrazone and sulindac by intestinal
    bacteria.  Xenobiotica, 17, 685-696.

    Sundaram, S.G. & Milner, J.A. (1996) Diallyl disulfide induces
    apoptosis of human colon tumor cells.  Carcinogenesis, 17, 669-673.

    Szumlanski, C.L., Scott, M.C. & Weinshilboum, R.M. (1988) Thiopurine
    methyltransferase pharmacogenetics: Human liver enzyme activity.
     Clin.  Pharmacol. Ther., 43, 134.

    Szybalski, W. (1958) Special microbiological systems. II. Observations
    on chemical mutagenesis in microorganisms.  Ann. N.Y. Acad. Sci., 76,
    475-489.

    Takata, T., Yamazaki, M., Fujimori, K., Kim, H.Y., Iyanagi, T. & Oae,
    S. (1983) Enzymatic oxygenation of sulfides with cytochrome P-450 from
    rabbit liver: Stereochemistry of sulfoxide formation.  Bull. Chem.
    Soc.  Jpn., 55, 2300-2310.

    Tateishi, M. & Tomisawa, H. (1989) Cysteine conjugate beta-lyase. I:
    Toxic thiol production. In: Damani, L.A., ed.,  Sulphur-containing
     Drugs and Related Organic Compounds, Vol. 2, Part B, Chichester:
    Ellis Horwood Ltd, pp. 121-134.

    Tateishi, M., Suzuki, S. & Shimizu, H. (1978) Cysteine conjugate
    beta-lyase in rat liver.  J. Biol. Chem., 253, 8854.

    Tatsumi, K., Kitamura, S. & Yamada, H. (1982) Involvement of liver
    aldehyde oxidase in sulfoxide reduction.  Chem. Pharm. Bull., 30,
    4585-4588.

    Tatsumi, K., Kitamura, S. & Yamada, H. (1983) Sulfoxide reductase
    activity of liver aldehyde oxidase.  Biochim. Biophys. Acta, 747,
    86-92.

    Taylor, K.L. & Ziegler, D.M. (1987) Studies on substrate specificity
    of the hog liver flavin-containing monooxygenase. Anionic organic
    sulfur compounds.  Biochem. Pharmacol., 36, 141-146.

    Taylor, A.J., Olavesen, A.H., Black, J.G. & Howes, D. (1978) The
    metabolism of the surfactants dodecylsulfonate and hexadecylsulfonate
    in the rat.  Toxicol. Appl. Pharmacol., 45, 105-117.

    Thomas, W.C., Seckar, J.A., Johnson, J.T., Ulrich, C.E, Klonne, D.R.,
    Schardein, J.L. & Kirwin, C.J. (1987) Inhalation teratology studies of
    n-butyl mercaptan in rats and mice.  Fundam. Appl. Toxicol., 8,
    170-178.

    Vogin, E.E., Carson, S., Cannon, G., Linegar, C.R. & Rubin, L.F.
    (1970) Chronic toxicity of DMSO in primates.  Toxicol. Appl.
     Pharmacol., 16, 606-612.

    Wang, C.J., Lin, Y.L. & Lin, J.K. (1994) Mutagenicity and cytotoxicity
    of nitropyrrole compounds derived from the reaction of 2-acetyl
    pyrrole with nitrate.  Food Chem. Toxicol., 32, 839-844.

    Waring, R.H. (1996) Sulfur-sulfur compounds. In: Mitchell, S., ed.,
     Biological Interactions of Sulfur Compounds, London: Taylor &
    Francis, pp. 145-173.

    Watanabe, S. & Kinosaki, A. (1989a) Acute oral toxicity in the rat
    with acetyllactic acid thiomethyl ester. Unpublished report submitted
    to the Flavor and Extract Manufacturers' Association.

    Watanabe, S. & Kinosaki, A. (1989b) Acute oral toxicity in the rat
    with propionyl lactic acid thiomethyl ester. Unpublished report
    submitted to the Flavor and Extract Manufacturers' Association.

    Watanabe, S. & Morimoto, Y. (1989a) Mutagenicity study of acetyl
    lactic acid thiomethyl ester in  Salmonella typhimurium and
     Escherichia  coli. Unpublished study submitted to the Flavor and
    Extract Manufacturers' Association.

    Watanabe, S. & Morimoto, Y. (1989b) Mutagenicity study of propionyl
    lactic acid thiomethyl ester in  Salmonella typhimurium and
     Escherichia  coli. Unpublished study submitted to the Flavor and
    Extract Manufacturers' Association.

    Weinshilboum, R.M. & Sladek, S.L. (1980) Mercaptopurine
    pharmacogenetics: Monogenic inheritance of erythrocyte thiopurine
    methyltransferase activity.  Am. J. Hum. Genet., 32, 651-662.

    Wells, W.W., Yang, Y., Diets, T.L. & Gan, Z.R. (1993)
    Thioltransferases.  Adv. Enzymol. Relat. Areas Mol. Biol., 66,
    149-201.

    Wheldon, G.H., Amyes, S.J., Street, A.E., Hague, P.H. &
    Mawdesley-Thomas, L.E. (1970) Toxicity of Wa 4295, Sa 927, Stl 3048,
    and Wa 3328 in dietary administration to rats over a period of 13
    weeks. Unpublished report from Huntington Research Centre to the
    Flavor and Extract Manufacturers' Association.

    Wild, D., King, M.T., Gocke, E. & Eckhardt, K. (1983) Study of
    artificial flavouring substances for mutagenicity in the
     Salmonella/microsome,  basc and micronucleus tests.  Food Chem.
     Toxicol., 21, 707-719.

    Williams, K.I.H., Burstein, S.H. & Layne, D.S. (1966) Metabolism of
    dimethyl sulfide, dimethyl sulfoxide, and dimethyl sulfone in the
    rabbit.  Arch. Biochem. Biophys., 117, 84-87.

    Willson, J.E., Brown, D.E. & Timmens, E.K. (1965) A toxicologic study
    of dimethyl sulfoxide.  Toxicol. Appl. Pharmacol., 7, 104-122.

    Wilson, K., Chissick, H., Fowler, A.M., Frearson, F.J., Gittins, M. &
    Swinbourne, F.J. (1991) Metabolism of benzothiazole I. Identification
    of ring-cleavage products.  Xenobiotica, 21, 1179.

    Wnorowski, G. (1996a) 14-Day dietary toxicity study: Rats. Unpublished
    study No. 4442 from Product Safety Laboratories to the Flavor and
    Extract Manufacturers' Association.

    Wnorowski, G. (1996b) 14-Day dietary toxicity study: Rats. Unpublished
    study No. 4453 from Product Safety Laboratories to the Flavor and
    Extract Manufacturers' Association.

    Wnorowski, G. (1996c) 14-Day dietary toxicity study: Rats. Unpublished
    study No. 4456 from Product Safety Laboratories to the Flavor and
    Extract Manufacturers' Association.

    Wnorowski, G. (1996d) 14-Day dietary toxicity study: Rats. Unpublished
    study No. 4454 from Product Safety Laboratories to the Flavor and
    Extract Manufacturers' Association. 

    Wnorowski, G. (1996e) 14-Day dietary toxicity study: Rats. Unpublished
    study No. 4457 from Product Safety Laboratories to the Flavor and
    Extract Manufacturers' Association.

    Wnorowski, G. (1997a) 14-Day repeat dose oral toxicity study: Rats.
    Unpublished study No. 5211 from Product Safety Laboratories to the
    Flavor and Extract Manufacturers' Association.

    Wnorowski, G. (1997b) 14-Day dietary toxicity study: Rats. Unpublished
    study No. 5210 from Product Safety Laboratories to the Flavor and
    Extract Manufacturers' Association.

    Wood, D.C., Wirth, N.V., Weber, F.S. & Palmquist, M.A. (1971)
    Mechanism considerations of dimethyl sulfoxide (DMSO)-lenticular
    changes in rabbits.  J. Pharmacol. Exp. Ther., 177, 528-535.

    Woodson, L.C. & Weinshilboum, R.M. (1983) Human kidney thiopurine
    methyltransferase: Purification and biochemical properties.  Biochem.
     Pharmacol., 32, 819-826.

    Woodson, L.C., Dunnette, J.H. & Weinshilboum, R.M. (1982)
    Pharmacogenetics of human thiopurine methyltransferase:
    Kidney-erythrocyte correlation and immunotitra-tion studies.
     J. Pharmacol. Exp. Ther., 222, 174-181.

    Woodson, L.C., Ames, M.M, Selassie, C.D., Hansch, C. & Weinshilboum,
    R.M. (1983) Thiopurine methyltransferase: Aromatic thiol substrates
    and inhibition by benzoic acid derivatives.  Mol. Pharmacol., 24,
    471-478.

    Yoshihara, S. & Tatsumi, K. (1985a) Sulfoxide reduction catalysed by
    guinea pig liver aldehyde oxidase in combination with one electron
    reducing flavoenzymes.  J. Pharmacobio-Dyn., 8, 996-1005.

    Yoshihara, S. & Tatsumi, K. (1985b) Guinea pig liver aldehyde oxidase
    as a sulfoxide reductase: Its purification and characterisation.
     Arch.  Biochem. Biophys., 242, 213-224. 

    Yoshihara, S. & Tatsumi, K. (1990) Metabolism of diphenyl sulphoxide
    in perfused guinea pig liver.  Drug Metab. Disposition, 18, 876.

    Zajac-Kaye, M. & Ts'o, P.O.P. (1984) DNAase I encapsulation in
    liposomes can induce neoplastic transformation of Syrian hamster
    embryo cells in culture.  Cell, 39, 427-437.

    Zeiger, E., Anderson, B., Haworth, S., Lawlor, T., Mortelmans, K. &
    Speck, W. (1987) Salmonella mutagenicity test: III. Results from the
    testing of 255 chemicals.  Environ. Mutag., 9 (Suppl. 9), 1-110.

    Zeiger, E., Anderson, B., Haworth, S., Lawlor, T. & Mortelmans, K.
    (1992)  Salmonella mutagenicity tests. V. Results from the testing of
    311 chemicals.  Environ. Mol. Mutag., 19 (Suppl.21), 2-141.

    Ziegler, D.M. (1980) Microsomal flavin-coenzyme monooxygenase:
    Oxygenation of nucleophilic nitrogen and sulfur compounds. In: Jakoby,
    W.B., ed.,  Enzymatic Basis of Detoxification, Vol. 2, Chichester:
    Ellis Horwood, pp. 201-227.

    Ziegler, D.M. (1989) S-Oxygenases. I. Chemistry and biochemistry. In:
    Damani, L.A., ed.,  Sulphur-containing Drugs and Related Organic
     Compounds, Vol. 2, Part A, Chichester: Ellis Horwood, pp. 53-66.
    


    See Also:
       Toxicological Abbreviations
       Simple aliphatic and aromatic sulfides and thiols (WHO Food Additives Series 52)