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    FERBAM

    First draft prepared by
    J.-J. Larsen,
    Institute of Toxicology, National Food Agency,
    Ministry of Health, Soborg, Denmark

    Explanation
    Evaluation for acceptable daily intake
       Biochemical aspects
          Absorption, distribution, and excretion
          Biotransformation
       Toxicological studies
          Acute toxicity
          Short-term toxicity
          Long-term toxicity and carcinogenicity
          Reproductive toxicity
          Genotoxicity
          Special studies: Dermal and ocular irritation and dermal
            sensitization
    Comments
    Toxicological evaluation
    References

    Explanation

         Ferbam was evaluated for toxicological effects by the Joint
    Meeting in 1965, 1967, 1970, 1974, 1977, and 1980 (Annex 1, references
    4, 8, 14, 22, 28, and 34). A temporary ADI of 0-0.025 mg/kg bw for
    ferbam or ferbam in combination with other dimethyldithiocarbamates
    was allocated in 1967, on the basis of a one-year study in dogs. This
    temporary ADI was lowered to 0-0.005 mg/kg bw in 1974, and a full
    group ADI of 0-0.02 mg/kg bw for ferbam and ziram was allocated in
    1977, which was confirmed in 1980. Since 1980, new studies have become
    available. This monograph summarizes the data received since the
    previous evaluation and includes relevant summaries from the previous
    monograph and monograph addenda on ziram (Annex I, references 4, 9,
    15, 23, 29, and 35).

    Evaluation for acceptable daily intake

    1.  Biochemical aspects

    (a)  Absorption, distribution, and excretion

         Ferbam does not appear to be stored in the tissues of rats or
    dogs, but feeding of ferbam to rats increased the skeletal stores of
    iron (Annex 1, reference 4).

         The disposition and metabolism of ferbam were studied in rats.
    Male rats weighing 125-275 g, pregnant rats on day 16 of gestation,
    and lactating rats six days  post partum were given single oral doses
    of 500 mg/kg bw spiked with 24 Ci of either 35S- or 14C-labelled
    compound. The ferbam was suspended in 0.5% carboxymethyl cellulose.
    After dosing, each male rat was placed in a metabolism cage for
    examination of faeces, urine, and expired air. At termination of the
    experiment, the rat was sacrificed for analysis of radiolabel. Bile
    was collected from some of the male rats. Five pups per lactating
    mother were left for nursing, and the dams and pups were sacrificed
    24 h after dosing. About 40-70% of the dose of labelled ferbam was
    absorbed through the gastrointestinal tract within the first 24 h. In
    rats receiving 35S-ferbam, 23% of the radiolabel was found in urine,
    18% in expired air, and 1% in bile; only small amounts were found
    in tissues, including blood, kidneys, muscle, and brain. In rats
    receiving 14C-ferbam, 43% of the radiolabel was found in urine and
    1.4% in bile, whereas only 0.6% was recovered in expired air. The
    other tissues contained only small amounts of radiolabel. In the
    pregnant rats, a small but significant amount of radiolabel readily
    crossed the placenta into the fetus. In lactating rats, radiolabel was
    secreted into the milk, absorbed by the pups, and excreted in the
    pups' urine (Lee  et al., 1975).

    (b)  Biotransformation

         In rats given ferbam orally at a dose of 500 mg/kg bw, the main
    product in the expired air was carbon disulfide; the main products in
    the urine were inorganic sulfate, a salt of dimethylamine, and the
    glucuronide conjugate of dimethyldithiocarbamate (Figure 1). No
    unchanged ferbam was found in the urine (Lee  et al., 1975).

    2.  Toxicological studies

         Ferbam and ziram share the same core molecule, dimethyldithio-
    carbamate, and differ in the metal ion and the number of dimethyl-
    dithiocarbamate molecules. Ferbam contains three dimethyldithio-
    carbamates and a ferric ion, while ziram contains two dimethyl-
    dithiocarbamates and a zinc ion. The metabolism of ziram and ferbam in
    mammalian systems is similar. In aqueous acid media, such as found in
    the stomach, ziram and ferbam dissociate to dimethyldithiocarbamic
    acid or carbon disulfide and dimethyl amine. The difference between
    the two compounds is that ziram yields zinc ion while ferbam yields
    ferric ion. Zinc and iron are both essential nutrients in mammals;
    however, the amount of iron required for normal homeostasis and the
    body's ability to handle excess iron are much greater than for zinc.
    The greater toxicity of ziram, in comparison with ferbam, is thought
    to result from the inability of organisms to handle excess amounts of
    zinc. Extrapolation of data on the toxicity of ferbam to relate to
    ziram is therefore justified.

    FIGURE 4

    (a)  Acute toxicity

         The acute toxicity of ferbam is summarized in Table 1.

    (b)  Short-term toxicity

    Rats

         Groups of 10 male and 10 female weanling NR strain rats were
    fed ferbam (purity unspecified) at concentrations of 0, 100, 500,
    2500, or 5000 ppm (equivalent to 0, 10, 50, 250, or 500 mg/kg bw per
    day) for one month. At doses > 500 ppm, growth depression was
    found, and at 5000 ppm the mortality rate was increased. No significant
    histopathological changes were seen in any of the animals. The NOAEL
    was 100 ppm, equivalent to 10 mg/kg bw per day, on the basis of growth
    depression at doses > 500 ppm (Annex 1, reference 4).

         Groups of 10 male and 10 female NR strain rats were fed ferbam
    (purity unspecified) at concentrations of 0 or 2500 ppm (equivalent to
    0 or 250 mg/kg bw per day) for one month. Post-mortem examination
    revealed no thyroid abnormalities (Annex I, reference 4).

    Dogs

         One dog (strain unspecified) was given ferbam (purity unspecified)
    and ziram together for one month, each at a dose of 5 mg/kg bw per day.
    The only adverse effect was slight anaemia. Another dog remained
    healthy, except for slight anaemia, when given ferbam alone at a dose
    of 25 mg/kg bw per day for one month or at 50 mg/kg bw per day for one
    week. An attempt to raise the dose to 100 mg/kg bw per day immediately
    provoked severe vomiting and malaise (Annex I, reference 4).

         Groups of two adult dogs (strain unspecified) received ferbam
    (purity unspecified) at doses of 0.5, 5, or 25 mg/kg bw per day for
    one year. Convulsions occurred in animals at 25 mg/kg bw per day.
    Urine analysis, blood picture, organ weights, and histological
    examination (including the thyroid) showed no abnormalities. The NOAEL
    was 5 mg/kg bw per day, on the basis of convulsions at 25 mg/kg bw per
    day (Annex I, reference 4).

        Table 1.  Acute toxicity of ferbam in experimental animals

                                                                                                             

    Species         Sex             Route         Purity      LD50 (mg/kg bw)          Reference
                                                   (%)      or LC50 (mg/litre)
                                                                                                             

    Mouse      Male            Oral                 NR             1000           Annex 1, reference 4
    Mouse      Female          Intraperitoneal      NR             3000           Annex 1, reference 4
    Rat        Male            Oral                 NR           11 000           Annex 1, reference 4
    Rat        Female          Intraperitoneal      NR             2700           Annex 1, reference 4
    Rat        Male, female    Inhalation          91.8            0.40           Hardy & Jackson (1988)
    Rat        Male, female    Inhalation          91.8            0.28           McDonald (1988)
    Rabbit     Male, female    Dermal              91.8          > 4000           Reijnders (1987b)
                                                                                                             

    NR, not reported
        (c)  Long-term toxicity and carcinogenicity

    Rats

         Groups of 25 male and 25 female rats (strain unspecified) were
    fed ferbam (purity unspecified) at concentrations of 0, 25, 250, or
    2500 ppm (equivalent to 1.3, 12.5, or 125 mg/kg bw per day) for two
    years. In animals at the highest dose, the growth rate was depressed,
    the life-span was shortened, neurological changes and cystic brain
    lesions were seen, and the testes were atrophied. The thyroid glands
    were normal in all groups, and there was no increase in tumour
    incidence. The NOAEL was 250 ppm, equivalent to 12.5 mg/kg bw per day,
    on the basis of the changes at 125 mg/kg bw per day (Annex I,
    reference 4).

    (d)  Reproductive toxicity

    Mice

         Groups of six (C3H  C57B1/6)F1 mice, 11-15 weeks old, received
    ferbam (purity, 99.8%) at doses of 0, 250, 500, or 1000 mg/kg bw per
    day orally or 0, 125, 250, or 500 mg/kg bw per day intraperitoneally
    for five days. After 35 days, toxicity to the testis was evaluated by
    measuring the testicular weight, sperm counts, and the percentage of
    abnormal sperm. Neither testicular weights nor sperm counts were
    affected. The frequency of abnormal sperm in the control mice ranged
    from 1.6 to 2.4%. The NOAEL was 500 mg/kg bw per day, on the basis of
    a statistically significant increase in sperm abnormalities (6.3%)
    after oral administration of ferbam at 1000 mg/kg bw per day. No
    effects were seen after intraperitoneal administration, indicating
    that active metabolites were responsible for the effects (Quinto
     et al., 1989).

    Rats

         Groups of 16 male and 16 female rats (strain unspecified) were
    fed ferbam (purity unspecified) at concentrations of 0 or 250 ppm
    (equivalent to 0 or 25 mg/kg bw per day) in a three-generation study
    with two litters per generation. The treated animals were maintained
    for three months after weaning before the first mating. No effect was
    seen on fertility, gestation, viability, lactation, or litter size,
    and no gross or histological abnormalities in comparison with controls
    were found in animals from the second litter of the third filial
    generation selected for examination (Annex I, reference 9).

    (e)  Genotoxicity

         The only results for genotoxicity that have been reported are
    those of an Ames test for reverse mutation in  Salmonella typhimurium
    strains TA98, TA100, TA1535, TA1537, and TA1538 with a preparation
    of ferbam of unspecified purity at doses up to 1500 g/plate. No
    mutagenicity was seen (De Lorenzo  et al., 1978).

    (f)  Special studies: Dermal and ocular irritation and dermal
         sensitization

         The dermal irritancy of ferbam was tested in New Zealand white
    rabbits by removing the hair from the dorsal flanks and 24 h later
    applying a 6-cm2 gauze patch spread evenly with 0.5 g ferbam (purity,
    91.8%) moistened with 0.5 ml water to the left flank of each of six
    animals; the right flank was covered with the same dressing without
    the test substance. The test sites were covered with permeable tape
    and wrapped in flexible bandage. The sites were exposed for 4 h, after
    which the remaining test substance was removed. The treated skin was
    examined for erythema and oedema after 1 h and on days 1, 2, and 3.
    The only dermal reaction seen was very slight erythema in one animal
    1 h after removal of the dressings, which disappeared within 24 h. The
    primary dermal irritation index was 0.02, indicating that ferbam is
    slightly irritating to the skin; however, the occurrence of only a
    brief reaction in one animal led the authors to conclude that it is
    practically non-irritating (Weterings & Daamen, 1987a).

         To test the ocular irritancy of ferbam, the eyes of six female
    New Zealand white rabbits were examined, and then the conjunctival sac
    of the left eye was installed with 21 mg of ferbam (purity, 91.8%),
    equivalent to 0.1 ml, using a spatula. The ocular lesions were graded
    and scored 1, 24, 48, and 72 h and 7 and 10 days after instillation.
    Immediately after scoring, 24 and 72 h after treatment, a solution of
    2% fluorescein in water was applied to both eyes to examine the
    potential for corneal injury. Ferbam affected only the conjunctivae:
    very slight conjunctival redness was seen in all six animals, with a
    short increase to diffuse redness in two animals on day 3. The redness
    had disappeared by day 10. Five of the six animals showed obvious
    chemosis, and the sixth slight chemosis, which had dosappeared by day
    7 in all animals. On the basis of a Draize score of 6.3 (24 h), the
    authors concluded that ferbam is mildly irritating to the eye
    (Weterings & Daamen, 1987b).

         The dermal sensitizing potential of ferbam (purity, 91.8%) was
    examined in 35 adult female Dunkin-Hartley guinea-pigs. After
    induction by epicutaneous applications of the test substance (25% w/w
    in 1% aqueous methylcellulose) and challenge with a series of
    concentrations of ferbam (25, 10, and 5% w/w in 1% aqueous methyl-
    cellulose), one of the experimental animals showed a positive reaction
    to all three concentrations, indicating a sensitization rate of 5%
    (grade 2). Ferbam was thus considered to have weak sensitizing
    properties (Weterings & Daamen, 1987c).

    Comments

         Ferbam is well absorbed after oral administration to rats and is
    extensively metabolized. Most of the administered radiolabel was found
    in the urine, expired air, and bile. In pregnant rats, a small but
    significant amount crossed the placenta into the fetus. In lactating
    rats, the radiolabel was secreted into the milk, absorbed by the pups,
    and excreted in the pups' urine. In expired air, the main product was
    carbon disulfide; in the urine, the main products were inorganic
    sulfate, a salt of dimethylamine, and the glucuronide conjugate of
    dimethyldithiocarbamic acid.

         Ferbam has low acute toxicity and has been classified by WHO as
    unlikely to present an acute hazard in normal use (WHO, 1996).

         In two four-week studies, rats were fed diets providing ferbam at
    concentrations of 0, 100, 500, 2500, or 5000 ppm or 0 or 2500 ppm. The
    NOAEL was 100 ppm, equivalent to 10 mg/kg bw per day, on the basis
    of growth depression at doses > 500 ppm. Post-mortem examination
    revealed no thyroid abnormalities. In another four-week study in which
    one dog was given ferbam and ziram together, each at a dose of 5 mg/kg
    bw per day; the only adverse effect was slight anaemia. Another dog
    remained healthy, except for slight anaemia, when given ferbam alone
    at a dose of 25 mg/kg bw per day for one month or 50 mg/kg bw per day
    for one week. An attempt to raise the dose to 100 mg/kg bw per day
    immediately provoked severe vomiting and malaise.

         In a study in which dogs were treated with ferbam at doses of
    0.5, 5, or 25 mg/kg bw per day for one year, the NOAEL was 5 mg/kg bw
    per day, on the basis of convulsions at 25 mg/kg bw per day.

         In a two-year study of toxicity and carcinogenicity in rats
    treated at dietary concentrations of 0, 25, 250, or 2500 ppm, the
    NOAEL was 250 ppm, equivalent to 12 mg/kg bw per day, on the basis
    of depressed growth rate, shortened life span, neurological
    changes, cystic brain lesions, and testicular atrophy at 2500 ppm.
    Carcinogenicity was not demonstrated.

         Sperm quality was investigated in mice given oral doses of
    0, 250, 500, or 1000 mg/kg bw per day for five consecutive days. The
    NOAEL was 500 mg/kg bw per day, on the basis of an increased frequency
    of sperm abnormalities at 1000 mg/kg bw per day.

         In a three-generation study of reproductive toxicity in rats fed
    dietary concentrations of 0 or 250 ppm, the NOAEL was 250 ppm,
    equivalent to 12 mg/kg bw per day.

         Few data were available on genotoxicity. Ferbam did not induce
    reverse mutation in bacteria.

         Ferbam was slightly irritating to the skin and mildly irritating
    to the eyes of rabbits. It has weak skin sensitizing properties in
    guinea-pigs.

         The Meeting concluded that the toxicological data specifically
    generated for ferbam were inadequate to estimate an ADI; however,
    because of the similarity of the chemical structure of ferbam to
    that of ziram and the comparable toxicological profile of the two
    compounds, ferbam was included in the group ADI of 0-0.003 mg/kg bw
    for ferbam and ziram, which is derived from the information available
    on ziram.

    Toxicological evaluation

    Levels that cause no toxicological effect

         Mouse:    500 mg/kg bw per day (study of sperm quality)

         Rat:      100 ppm, equivalent to 10 mg/kg bw per day (one-month
                   study of toxicity)

                   250 ppm, equivalent to 12 mg/kg bw per day (two-year
                   study of toxicity and carcinogenicity)

                   250 ppm, equivalent to 12 mg/kg bw per day (study of
                   reproductive toxicity)

         Dog:      5 mg/kg bw per day (one-year study of toxicity)

    Estimate of acceptable daily intake for humans

         0-0.003 mg/kg bw (fgroup ADI for ferbam and ziram)

    Studies that would provide information useful for continued evaluation
    of the compound

         1.   Studies on dissociation in aqueous solutions

         2.   Observations in humans

        Toxicological criteria for estimating guidance values for dietary and non-dietary exposure to ferbam

                                                                                                                                      

           Exposure                   Relevant route, study type, species                          Results, remarks
                                                                                                                                      

    Short-term (1-7 days)       Oral, toxicity, mouse                                 LD50 = 1000 mg/kg bw
                                Oral, toxicity, rat                                   LD50 = 11 000 mg/kg bw
                                Inhalation, toxicity, rat                             LC50 = 0.3 mg/litre
                                Dermal, irritation, rabbit                            Slightly irritating
                                Ocular, irritation, rabbit                            Mildly irritating
                                Dermal, sensitization, guinea-pig                     Weakly sensitizing
                                Repeated oral, 5 days, testicular toxicity, mouse     NOAEL = 500 mg/kg bw per day, increased sperm
                                                                                      abnormalities

    Medium-term (1-26 weeks)    Repeated oral, 4 weeks, toxicity, rat                 NOAEL = 10 mg/kg bw per day, reduced body
                                                                                      weight
                                Repeated oral, reproductive toxicity, rat             NOAEL = 12 mg/kg bw per day, reproductive
                                                                                      toxicity

    Long-term (> 1 year)        Repeated oral, 104 weeks, toxicity and                NOAEL = 12 mg/kg bw per day, reduced body
                                carcinogenicity, rat                                  weight, shortened life-span, neurological
                                                                                      changes, cystic brain lesions, and atrophied
                                                                                      testis. No carcinogenicity
                                Repeated oral, 1 year, toxicity, dog                  NOAEL = 5 mg/kg bw per day, convulsions
                                                                                                                                      
        References

    DeLorenzo, F.D., Staiano, N., Lorenzo, S. & Cortese, R. (1978)
    Mutagenicity of diallate, sulfallate, and triallate and relationship
    between structure and mutagenic effects of carbamates used widely in
    agriculture.  Cancer Res., 38, 13-15.

    Hardy, C.J. & Jackson, G.C. (1988) Ferbam technical, acute inhalation
    toxicity in rats, 4-hour exposure. Unpublished report No. UCB
    285/88179 from Huntingdon Research Centre Ltd, Huntingdon, Cambs,
    United Kingdom. Submitted to WHO by UCB Chemicals, Brussels, Belgium.

    Lee, C.-C., Russell, J.Q., Minor, J.L., Kowalski, J.J., Sanyer, J.L.,
    Kintner, L.D., Hodgson, J.R., Short, R.D., Peters, P.J., Dilley, J.V.,
    Murrill, E.A., Holton, D.O. & Ellis, H.V. (1975) Toxicological
    evaluation of ferric dimethyldithiocarbamate (ferbam) and dithio-
    carbamate (thiram) with acute toxicity of manganese and zinc ethylene-
    bisdithiocarbamates (maneb and zineb). Unpublished report No. 3612-B
    from National Institute of Environmental Health Sciences, Research
    Triangle Park, NC, USA. Submitted to WHO by UCB Chemicals, Brussels,
    Belgium.

    McDonald, P. (1988) Ferbam technical, acute inhalation toxicity
    study in rats. Unpublished report No. 5115 from Inveresk Research
    International, Musselburgh, Scotland. Submitted to WHO by UCB
    Chemicals, Brussels, Belgium.

    Reijnders, J.B.J. (1987a) Evaluation of the acute oral toxicity of
    ferbam technical in the rat. Unpublished report No. Notox 0740/930
    from Notox CV, 's-Hertogenbosch, Netherlands. Submitted to WHO by UCB
    Chemicals, Brussels, Belgium.

    Reijnders, J.B.J. (1987b) Evaluation of the acute dermal toxicity of
    ferbam technical in the rabbit. Unpublished report No. Notox 0740/931
    from Notox CV, 's-Hertogenbosch, Netherlands. Submitted to WHO by UCB
    Chemicals, Brussels, Belgium.

    Quinto, I., Marinis, E.D., Mallardo, M., Arcucci, A., Morte, R.D. &
    Staiano, N. (1989) Effect of DNOC, ferbam and imidan exposure on mouse
    sperm morphology.  Mutat. Res., 224, 405-408.

    Weterings, P.J.J.M. & Daamen, P.A.M. (1987a) Assessment of primary
    skin irritation/corrosion by ferbam technical in the rabbit.
    Unpublished report No. Notox 0740/932 from Notox CV, 's-Hertogenbosch,
    Netherlands. Submitted to WHO by UCB Chemicals, Brussels, Belgium.

    Weterings, P.J.J.M. & Daamen, P.A.M (1987b) Assessment of the
    primary eye irritation/corrosion by ferbam technical in the rabbit.
    Unpublished report No. Notox 0740/933 from Notox CV, 's-Hertogenbosch,
    Netherlands. Submitted to WHO by UCB Chemicals, Brussels, Belgium.

    Weterings, P.J.J.M. & Daamen, P.A.M. (1987c) Assessment of the skin
    sensitization potential of ferbam technical in the guinea-pig (split
    adjuvant test). Unpublished-report No. Notox 0740/934 from Notox CV,
    's-Hertogenbosch, Netherlands. Submitted to WHO by UCB Chemicals,
    Brussels, Belgium.

    WHO (1996)  The WHO Recommended Classification of Pesticides by Hazard
     and Guidelines to Classification 1996-1997 (WHO/PCS/96.3), International
    Programme on Chemical Safety, Geneva.
    


    See Also:
       Toxicological Abbreviations
       Ferbam (ICSC)
       Ferbam (FAO Meeting Report PL/1965/10/1)
       Ferbam (FAO/PL:1967/M/11/1)
       Ferbam (IARC Summary & Evaluation, Volume 12, 1976)