This report contains the collective views of an international group of
    experts and does not necessarily represent the decisions or the stated
    policy of the United Nations Environment Programme, the International
    Labour Organisation, or the World Health Organization.

    First draft prepared at the National Institute of Health Sciences,
    Tokyo, Japan, and the Institute of Terrestrial Ecology, Monk's Wood,
    United Kingdom

    Published under the joint sponsorship of the United Nations
    Environment Programme, the International Labour Organisation, and the
    World Health Organization

    World Health Organization
    Geneva, 1995

         The International Programme on Chemical Safety (IPCS) is a joint
    venture of the United Nations Environment Programme, the International
    Labour Organisation, and the World Health Organization. The main
    objective of the IPCS is to carry out and disseminate evaluations of
    the effects of chemicals on human health and the quality of the
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    with chemical accidents, coordination of laboratory testing and
    epidemiological studies, and promotion of research on the mechanisms
    of the biological action of chemicals.

    WHO Library Cataloguing in Publication Data

    Linear Alkylbenzene Sulfonates and Related Compounds.

    (Environmental health criteria ; 174)

    1.Cyclohexanones  2.Environmental exposure
    3.Occupational exposure  4.Solvents   I.Series

    ISBN 92 4 157174 8                 (NLM Classification: QV 633)
    ISSN 0250-863X

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        1.1. Summary and evaluation
              1.1.1. Physical and chemical properties
              1.1.2. Production and use
              1.1.3. Environmental transport, distribution
                      and transformation
              1.1.4. Environmental levels and human exposure
              1.1.5. Kinetics and metabolism in laboratory animals
                      and humans
              1.1.6. Effects on laboratory mammals and  in vitro
                      test systems
              1.1.7. Effect on humans
              1.1.8. Effects on other organisms in the laboratory
                      and field
        1.2. Conclusions
              1.2.1. General population
              1.2.2. Occupational exposure
              1.2.3. The environment
        1.3. Recommendations
              1.3.1. Protection of human health and the environment
              1.3.2. Further research


        2.1. Identity
        2.2. Physical and chemical properties
        2.3. Conversion factors
        2.4. Analytical methods



        4.1. Environmental distribution
        4.2. Biotransformation and environmental fate
              4.2.1. Atmospheric fate
              4.2.2. Aquatic fate
              4.2.3. Terrestrial fate
              4.2.4. Biodegradation
              4.2.5. Bioaccumulation


        5.1. Environmental levels
              5.1.1. Air
              5.1.2. Water
              5.1.3. Soil and sediment
              5.1.4. Terrestrial organisms
              5.1.5. Aquatic organisms
        5.2. General population exposure
        5.3. Occupational exposure


        6.1. Human
        6.2. Laboratory mammals


        7.1. Acute toxicity
              7.1.1. Oral
              7.1.2. Dermal
              7.1.3. Inhalation
        7.2. Skin, eye and respiratory irritation, sensitization
              7.2.1. Skin irritation
              7.2.2. Eye irritation
              7.2.3. Respiratory irritation
              7.2.4. Sensitization
        7.3. Subchronic toxicity
              7.3.1. Inhalation
              7.3.2. Oral
              7.3.3. Dermal
        7.4. Mutagenicity
              7.4.1. Gene mutation in bacteria (Ames tests)
              7.4.2. Gene mutation in mammalian cells
              7.4.3. Chromosome aberrations and sister chromatid
               Chromosome aberrations
               Sister chromatid exchange
              7.4.4. Micronucleus test
              7.4.5. Primary DNA damage
               Bacterial tests
               Unscheduled DNA synthesis
               DNA binding
              7.4.6. Morphological transformation

        7.5. Chronic toxicity and carcinogenicity
        7.6. Mechanisms of toxicity
        7.7. Appraisal for mutagenicity/carcinogenicity
        7.8. Reproduction, embryotoxicity, teratogenicity
        7.9. Neurotoxicity
        7.10. Other special studies


        8.1. Acute
        8.2. Sub-chronic
        8.3. Irritation and sensitization
              8.3.1. Eye and respiratory irritation
        8.4. Chronic toxicity and carcinogenicity


        9.1. Microorganisms
        9.2. Aquatic organisms
        9.3. Terrestrial organisms





         Every effort has been made to present information in the criteria
    monographs as accurately as possible without unduly delaying their
    publication.  In the interest of all users of the Environmental Health
    Criteria monographs, readers are requested to communicate any errors
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    on Chemical Safety, World Health Organization, Geneva, Switzerland, in
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                                    *     *     *

         A detailed data profile and a legal file can be obtained from the
    International Register of Potentially Toxic Chemicals, Case postale
    356, 1219 Châtelaine, Geneva, Switzerland (Telephone No. 9799111).

                                    *     *     *

         This publication was made possible by grant number 5 U01
    ES02617-15 from the National Institute of Environmental Health
    Sciences, National Institutes of Health, USA, and by financial support
    from the European Commission.

    Environmental Health Criteria



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    FIGURE 1

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    Dr L.A. Albert, Xalapa, Veracruz, Mexico  (Vice-Chairman)

    Dr G.J. van Esch, Bilthoven, Netherlands

    Dr S.K. Kashyap, National Institute of Occupational Health Ahmedabad,

    Mr H. Malcolm, Institute of Terrestrial Ecology, Monks Wood
       Experimental Station Huntingdon, United Kingdom (part-time)

    Dr K. Peltonen, Institute of Occupational Health, Helsinki, Finland

    Professor Wai-On Phoon, Worksafe Australia, and Department of
       Occupational Health, University of Sydney, Sydney, Australia

    Mr D.J. Reisman, US Environmental Protection Agency, Cincinnati, USA

    Dr E. Soderlund, National Institute of Public Health, Oslo, Norway


    Dr H. Certa, Hüls AG, Marl, Germany


    Dr K.W. Jager, International Programme on Chemical Safety, World
       Health Organization, Geneva, Switzerland  (Secretary)

    Mr J. Wilbourn, International Agency for Research on Cancer (IARC),
       Lyon, France


         A WHO Task Group on Environmental Health Criteria for Isophorone
    met at the World Health Organization, Geneva, from 12 to 16 December
    1994.  Dr K.W. Jager of the IPCS, welcomed the participants on behalf
    of Dr M. Mercier, Director IPCS, and the three IPCS cooperating
    organizations (UNEP/ILO/WHO).  The Task Group reviewed and revised the
    draft monograph and made an evaluation of the risks for human health
    and the environment from exposure to isophorone.

         The first draft of the monograph was prepared by Dr H.J. Wiegand
    (Hüls), Dr J.F. Regnier (Atochem) and Dr P.L. Mason (British
    Petroleum), and appeared as ECETOC-JACC Report No. 10.  The second
    draft, incorporating comments received following circulation of the
    first draft to the IPCS contact points for Environmental Health
    Criteria, was prepared by the IPCS Secretariat.

         Dr K.W. Jager and Dr P.G. Jenkins, both of the IPCS Central Unit,
    were responsible for the scientific content of the monograph and the
    technical editing, respectively.

         The fact that industry made available to the IPCS and the Task
    Group their proprietary toxicological information on isophorone is
    gratefully acknowledged.  This allowed the Task Group to make its
    evaluation on a more complete data base.

         The effort of all who helped in the preparation and the
    finalization of the document is gratefully acknowledged.


    1.1  Summary and evaluatione

    1.1.1  Physical and chemical properties

         Isophorone is a colourless liquid with a peppermint-like odour. 
    It is soluble in water (12 g/litre) and miscible with most organic
    solvents.  Its freezing point is -8.1°C and its boiling point 215°C. 
    Its vapour pressure at 20°C is in the order of 40 Pa, and its vapour
    density (air = 1) is 4.7.  It is a stable substance.

         Commercial samples of technical grade isophorone contain 1-3% of
    the isomer ß-isophorone (3,5,5-trimethyl-3-cyclohexene-1-one); the sum
    of alpha and isomers exceeds 99%.

    1.1.2  Production and use

         Isophorone is widely used as a solvent for a number of synthetic
    resins and polymers, as well as in special application paints and
    printing inks.  It is also a chemical intermediate and a solvent in
    certain pesticide formulations.

         Its worldwide production was estimated to be in the order of
    92 000 tonnes per year in 1988.

    1.1.3  Environmental transport, distribution and transformation

         Isophorone may enter the environment from numerous industries,
    waste and wastewater disposal and its use as a solvent and a pesticide
    carrier.  Following release to water or soil, environmental
    concentrations will decrease as a result of volatilization and
    biodegradation.  Isophorone in the atmosphere is removed by
    photochemical processes with an estimated half-life of about 30 min
    (based on a mathematical model). In a Die-away test, isophorone was
    biodegraded to the extent of approximately 70% within 14 days and 95%
    within 28 days.  The results of biodegradation studies are variable
    and limited.  Water solubility, soil adsorption coefficients and
    polarity indicate that significant adsorption by suspended solids and
    sediments is unlikely to occur.

         Although isophorone has been found in fish tissues, the data and
    the physical and chemical properties suggest that significant
    bioconcentration is unlikely.  A half-life of one day has been
    measured in a single fish species.

    1.1.4  Environmental levels and human exposure

         Isophorone has not been measured in ambient air.  An isophorone
    concentration in coal fly ash of 490 µg/kg has been reported. 
    Isophorone has been identified in surface waters (0.6 to 3 µg/litre),
    groundwater (10 µg/litre), urban run-off (10 µg/litre) and landfill
    leachate (29 µg/litre).

         Isophorone has been found in industrial wastewater at a
    concentration of 100 µg/litre.  After classical secondary treatment,
    the concentration of isophorone in the effluent was 10 µg/litre.

         Isophorone has been identified in lake sediments (0.6 to 12 µg/kg
    dry weight) and in the tissues of several species of fish at
    concentrations up to 3.61 mg/kg wet weight.

         Isophorone was not detected in the edible parts of bean plants,
    rice or sugar beet following application as a pesticide carrier.

    1.1.5  Kinetics and metabolism in laboratory animals and humans

         Distribution studies in rats using 14C-isophorone showed that
    93% of orally administered radioactivity appeared mainly in urine and
    expired air within 24 h.  The tissues retaining the highest
    concentration after this period were the liver, kidney and preputial

         The metabolites from oral administration of isophorone identified
    in rabbits' urine resulted from oxidation of the 3-methyl group,
    reduction of the keto group and hydrogenation of the double bond of
    the cyclohexene ring, and were eliminated as such or as glucuronide
    derivatives in the case of the alcohols.

         Percutaneous LD50 values indicate that isophorone is rapidly
    absorbed through the skin.

    1.1.6  Effects on laboratory mammals and in vitro test systems

         The acute toxicity of isophorone is low, with oral LD50 values
    being > 1500 mg/kg in the rat, > 2200 mg/kg in the mouse and
    > 2000 mg/kg in the rabbit.  Dermal LD50 values were 1700 mg/kg in
    the rat and > 1200 mg/kg in the rabbit.  Acute effects from dermal
    exposure in rats and rabbits ranged from mild erythema to scabs. 
    Conjunctivitis and corneal damage have been reported following direct
    application to the eye or exposure to high concentrations of
    isophorone.  No skin sensitization was reported in guinea-pigs using
    the Magnusson-Kligman test.

         In acute and short-term oral studies on rodents at high doses
    (> 1000 mg/kg), degenerative effects were seen in the liver as well
    as CNS depression and some deaths. In 90-day studies, a NOEL in rats

    and mice of 500 mg/kg body weight per day was determined.  In a 90-day
    oral study in beagle dogs (with limited numbers), no effects were seen
    at doses of up to 150 mg/kg body weight per day.

         In the acute and short-term inhalation experiments which were
    reviewed, eye and respiratory irritation, haematological effects and
    decreased body weights were noted.  Since the study designs were
    inadequate, no NOEL could be determined and no inference regarding
    human health can be made.

         Isophorone does not induce gene mutations in bacteria,
    chromosomal aberrations  in vitro, DNA repair in primary rat
    hepatocytes, or bone-marrow micronuclei in mice. Positive effects were
    observed only in the absence of an exogenous metabolic system in
    L5178Y TK +/- mouse lymphoma mutagenesis assays as well as in a sister
    chromatid exchange assay.  Isophorone induced morphological
    transformation  in vitro in the absence of an exogenous metabolism
    system.  It did not induce sex-linked recessive lethal mutations in
     Drosophila.  The weight of evidence of all mutagenicity data
    supports the contention that isophorone is not a potent DNA-reactive
    compound. In an  in vivo assay, no DNA binding was observed in the
    liver and kidneys (organs affected in the carcinogenicity bioassays).

         In long-term oral toxicity studies in mice and rats, male rats
    showed several lesions of the kidney, including nephropathy, tubular
    cell hyperplasia and low incidence of tubular cell adenomas and
    adenocarcinomas.  The role of alpha2u-globulin accumulation in the
    etiology of these lesions has been recognized. Since significant
    amounts of alpha2u-globulin have not been detected in humans this
    mechanism of carcinogenesis appears not to be relevant to humans. 
    Preputial gland carcinomas were observed in five high-dose male rats,
    and two clitoral gland adenomas were seen in low-dose female rats
    following exposure to isophorone.  These tumours may also be related
    to alpha2u-globulin accumulation.  Isophorone exposure was
    associated with some neoplastic lesions of the liver, and the
    integumentary and lymphoreticular systems of male mice, as well as
    non-neoplastic liver and adrenal cortex lesions, but this was not
    observed in dosed female mice.

         In the only available long-term inhalation study in rats and
    rabbits, irritation to eye and nasal mucosa, and lung and liver
    changes, were observed at approx. 1427 mg/m3 (approx. 250 ppm). 
    However, it may have been due to limitations in the study.

         Very limited studies in rats and mice indicate that isophorone
    does not affect fertility nor does it cause developmental toxicity in
    experimental animals.

         The fact that central nervous system depression occurs in
    experimental animals could indicate a possible neurotoxic effect. 
    Isophorone also elicited a positive effect in the behavioural despair
    swimming test.

    1.1.7  Effect on humans

         The odour of isophorone can be detected at a concentration as low
    as 1.14 mg/m3 (0.2 ppm).  Eye, nose and throat irritation has been
    reported at concentrations below 28.55 mg/m3 (5 ppm); above
    1142 mg/m3 (200 ppm) nausea, headache, dizziness, faintness and
    inebriation have been reported.

    1.1.8  Effects on other organisms in the laboratory and field

         No data on terrestrial animals were available.

         Acute LC50 values are available for several freshwater and
    marine species.  The 96-h EC50 values (based on cell count and
    chlorophyll) range from 105 to 126 mg/litre.  48-h LC50 values for
     Daphnia magna range from 117 to 120 mg/litre, and 96-h LC50 values
    for freshwater fish range from 145 to 255 mg/litre.

         The 96-h LC50 values for marine invertebrates range from 12.9
    to 430 mg/litre, while the 96-h LC50 for a single marine fish
    species was between 170 and 300 mg/litre.  Data from studies with
    measured exposure concentrations did not differ from studies with
    nominal concentrations.  NOEL values for  Pimephales promelas tested
    in different laboratories ranged from 14 to 45.4 mg/litre.

         The available data suggest that isophorone has a low toxicity to
    aquatic organisms.

    1.2  Conclusions

    1.2.1  General population

         Isophorone is used as a solvent for resins, polymers and
    pesticides formulations.  Dermal and inhalation exposure may occur,
    but will most likely be minimal.  Data show that isophorone can occur
    in µg/litre (kg) concentrations in drinking-water and fish.  In view
    of low toxicity in experimental studies and low levels of exposure
    from environmental sources, the risk to the general population appears
    to be minimal.

    1.2.2  Occupational exposure

         In the absence of adequate engineering controls and industrial
    hygiene measures, occupational exposure to isophorone may exceed
    acceptable levels and cause eye, skin and respiratory irritation.  At

    higher concentrations other health effects may occur.  No studies on
    long-term health effects in workers were available for review by the
    Task Group.

    1.2.3  The environment

         Isophorone may be released into the environment following its use
    as a pesticide carrier and its ubiquitous use as a solvent.  Low
    concentrations have been identified in several environmental
    compartments, although it has a low environmental persistence due to
    biodegradation, volatilization and photochemical oxidation processes. 
    The available data suggest that isophorone has low toxicity to aquatic

    1.3  Recommendations

    1.3.1  Protection of human health and the environment

         Care should be taken to prevent contamination of groundwater and

         Workers manufacturing or using isophorone should be protected
    from exposure by means of adequate engineering controls and
    appropriate industrial hygiene measures.  Their occupational exposure
    should be kept within acceptable levels and monitored regularly.

    1.3.2  Further research

    a)   Health surveillance of exposed workers should be conducted.

    b)   Actual levels of isophorone in the waters surrounding industrial
         areas should be determined.

    c)   Adequate short-term/long-term inhalation studies in experimental
         animals should be conducted in order to determine safe levels of
         occupational exposure.

    d)   Information on anaerobic biodegradation of isophorone is needed,
         especially as it has been identified in landfill leachate.


    2.1  Identity

    Common name:             Isophorone

    Synonyms:                2-cyclohexen-1-one, 3,5,5,-trimethyl;
                             alpha-isophorone; isoacetophorone; isoforone;
                             izoforon; 1,5,5-trimethyl-3-oxo-cyclohexene

    Empirical formula:       C9H14O

    Chemical structure:      CHEMICAL STRUCTURE 1

    Relative molecular
      mass:                  138.2

    CAS registry
      number:                78-59-1

    RTECs registry
      number:                GW7700000

    EEC No:                  606-012-00-8

    EINECS No:               1011260

    2.2  Physical and chemical properties

         Isophorone is a colourless liquid.  Its odour has been described
    as being similar to peppermint and camphor.  It is soluble in water
    and is miscible in all proportions with aliphatic and aromatic
    hydrocarbons, alcohols, ethers, esters, ketones and chlorinated
    hydrocarbons.  Its physical and chemical data are summarized in Table

         A typical commercial sample of isophorone may contain 1-3% of the
    isomer ß-isophorone (3,5,5-trimethyl-3-cyclohexene-1-one) with the sum
    of alpha- and ß-isomers exceeding 99% (Hüls, 1981; Atochem, 1986).

         Isophorone is stable and may be stored in steel or aluminium
    containers.  Prolonged periods of storage may lead to slight

    2.3  Conversion factors

         The following conversion factors have been calculated for 22°C
    and 1013 hPa:

         1 ppm     = 5.71 mg/m3
         1 mg/m3   = 0.175 ppm

    2.4  Analytical methods

         The purity of technical isophorone may be determined by capillary
    gas chromatography (GC) with a flame ionization detector (FID). 
    Recommended conditions are shown in Table 2.

         Earlier methods for determining isophorone in air were based on
    adsorption on charcoal (White et al., 1970; US NIOSH, 1977).  However,
    it has been found that isophorone adsorbed on charcoal decomposes
    during storage.  More recent methods involve adsorption on polymers
    such as XAD resins (Levin & Carleborg, 1987) or Tenax-GC (Brown &
    Purnell, 1979), followed by desorption and analysis by capillary GC
    with FID.

         The analysis of isophorone present in wastewater samples and fish
    tissues may be achieved by solvent extraction, clean up by gel
    permeation chromatography and analysis by GC/MS, in both the electron
    impact and chemical ionization modes (Jungclaus et al., 1976; US EPA,
    1979; Sheldon & Hites, 1979).

        Table 1.  Physical and chemical data of isophorone
                                            Value               Reference

    Specific gravity (20°C/4°C)             0.922               Bartholomé et al. (1977)

    Boiling point at 1013 hPa               215°C               Bartholomé et al. (1977)

    Freezing point                          -8.1°C              Cheminfo (1988)

    Refractive index (n20D)                 1.4775              Bartholomé et al. (1977)

    Viscosity at 20°C                       2.6 mPa             Hüls (1981)

    Coefficient of cubical expansion        0.00085°C-1         BP (1988b)
     at 20°C                                0.00078°C-1         Atochem (1986)

    Surface tension at 20°C                 30 mN/m             BP (1988b)

    Vapour pressure                         40 Pa (20°C)        Bartholomé et al. (1977)
                                            34.7 Pa (25°C)      BIBRA (1991)

    Vapour density (air = 1)                4.7                 Cheminfo (1988)

    Concentration in saturated air
     at 20°C and 1013 hPa                   1941 mg/m3          Cheminfo (1988)

    Solubility at 20°C

    - Isophorone in water                   12.0 g/litre        Lyman et al. (1982)
                                            17.5 g/litrea

    - Water in isophorone                   53 g/litrea

    Log Kow (20°C)                          1.67 (measured)     Veith et al. (1978)
                                            1.7 (estimated)     Callahan et al. (1979)

    Table 1 (cont'd)
                                            Value               Reference

    Solubility parameters (Hansen)

     delta                                  19.2 (J/cm3)1/2     Hüls (1981)
     deltaD                                 16.6 (J/cm3)1/2     Hüls (1981)
     deltaP                                 8.2 (J/cm3)1/2      Hüls (1981)
     deltaH                                 7.4 (J/cm3)1/2      Hüls (1981)

    Hydrogen bonding parameter,
     gamma                                  14.9                Hüls (1981)

    Flash point, closed cup                 85°C                Cheminfo (1988)

    Explosion limits in air                 0.8-3.8 vol-%       Bartholomé et al. (1977)

    Ignition temperature                    470°C               Bartholomé et al. (1977)
                                            455°C               BIBRA (1991)

    Heat of evaporation at 215°C            349.2 kJ/kg         Bartholomé et al. (1977)

    Heat of combustion
     at 20°C                                38 100 kJ/kg        Bartholomé et al. (1977)

    Relative permittivity at 20°C           19.9                Hüls (1981)

    Specific resistivity                    1 × 107 ohm × cm    Atochem (1986)

    a    Communication from Hüls AG, Marl, Germany, 1989.

        Table 2.  Gas chromatographic conditions for the analysis of technical isophorone
    Column                     Fused silica capillarya     Macroboreb

    Coating                    OV-1701                     CP Wax 52CB

    Dimensions                 60 m/0.25 mm                25 m/0.53 mm

    Injector temperature       240°C                       250°C

    Temperature-programme      6 min 70°C to               10 min 105°C to 120°C
                               220°C at 4°/min             at 6°/min
                                                           2 min 120°C to 150°C
                                                           at 10 °/min

    From: a Hüls (1988c); b Atochem (1988)

         Isophorone has tentatively been identified as a component of the
    essential oil of  Thymus cariensis (Baser et al., 1992).

         Isophorone is produced commercially by catalytic condensation of
    acetone at elevated temperature and pressure and is purified by
    distillation. Worldwide annual production capacity was estimated to be
    92 000 tonnes in 1988 (Personal communication from Hüls AG, Marl,
    Germany, 1989, to the IPCS).

         Isophorone is a solvent for a number of natural and synthetic
    resins and polymers such as polyvinyl chlorides and acetates,
    cellulose derivatives, epoxy and alkyd resins and polyacrylates.  It
    is therefore used as a high boiling solvent in industrial air drying
    and stoving paints, nitro emulsion leather finishes and the
    manufacture of vinyl resin based printing inks for plastic surfaces. 
    Isophorone is also used as a solvent for some pesticide formulations,
    especially for emulsifiable concentrates of anilides and carbamates.

         Isophorone is used as a chemical intermediate for the synthesis
    of a variety of organic chemicals (Hüls, 1981; Thier & Xu, 1990).

         Coal-burning power plants may be a source of atmospheric
    isophorone as it was detected in the fly ash from an electrostatic
    precipitator (Harrison et al., 1985).  It has also been found in the
    breathing zones and area samples of work sites (US NIOSH, 1980, 1984)
    and in wastewater from industrial processes (Jungclaus et al., 1976). 
    Thus, some manufacturing processes may be an environmental source of


    4.1  Environmental distribution

         In view of its widespread use as a solvent for polymers, resins,
    waxes, oils and pesticides, there is a possibility of a wide
    distribution into the environment.  Isophorone has been detected in
    river, surface, and groundwaters and in finished drinking-water (Thier
    & Xu, 1990) (see section 5.1.2.), in effluents from latex and chemical
    plants (Shackelford & Keith, 1976), in wastewater from a tyre
    manufacturing plant (Jungclaus et al., 1976), and in air during
    manufacturing operations (US NIOSH, 1980, 1984).  The detection of
    isophorone in coal fly ash suggests that it may also be found in
    ambient air.

    4.2  Biotransformation and environmental fate

    4.2.1  Atmospheric fate

         By virtue of its vapour pressure of 40 Pa at 20°C, atmospheric
    isophorone will exist mainly in the vapour state (ECETOC, 1988).  The
    Graphical Exposure Modelling System (GEMS) predicts that the half-life
    for reaction with both ambient ozone and photo-chemically generated
    hydroxyl radicals will be approximately 30 min. This estimate assumes
    a concentration of 8 × 105 molecules per cm3 and a reaction rate
    constant of 8.14 × 10-11 cm3 molecule-1 sec-1 at 25°C for
    hydroxyl radicals and 1.0 × 1012 molecules per cm3 with a reaction
    rate constant of 5 × 10-16 cm3 molecule-1 sec-1 at 25°C for
    ozone (US EPA, 1986).

    4.2.2  Aquatic fate

         From an estimated Henry's Law constant of 5.8 × 10-6 atm m3
    mole-1, based upon a water solubility of 12 g/litre at 20°C and a
    vapour pressure of 40 Pa at 20°C, the volatilization half-life in a
    model river flowing at 1 m/sec was calculated to be 7.5 days (Lyman et
    al., 1982).  Based on a water solubility of 17.5 g/litre the
    volatilization half-life would be 11 days (Personal communication from
    Hüls AG, Marl, Germany, 1989, to the IPCS).

         The oxidation of isophorone by alkylperoxy radicals or singlet
    oxygen in water is unlikely to be significant in the environment
    (Mabey, 1981).  Although dimerization has been reported in water
    irradiated at wave-lengths > 200 nm and in organic solvents at
    > 300 nm, such products are also considered unlikely at the levels
    existing in the environment (Callahan et al., 1979).

         Evidence that isophorone is photo-oxidized is provided by Borup &
    Middlebrooks (1986).  Treatment with hydrogen peroxide (250 mg/litre)
    followed by UV radiation reduced an isophorone concentration of
    62 mg/litre to < 0.05 mg/litre in 60 min.

         Isophorone has been shown to be converted to a compound(s)
    mutagenic to  Salmonella typhimurium TA100 by aqueous chlorination
    under conditions of pH and reactant concentrations that may be
    relevant to wastewater and drinking-water chlorination (Cheh, 1986).

    4.2.3  Terrestrial fate

         Loss from soil, as in the case of surface water, will be by
    volatilization and biodegradation.  In view of the vapour pressure and
    Henry's Law constant, volatilization from both wet and dry soil
    surfaces would be slow.

         Based on a log Kow of 2.22 and assuming a water solubility of
    12 g/litre at 20°C, a soil adsorption coefficient (Koc) of 25 has
    been estimated (Lyman et al., 1982).  These values suggest that
    isophorone would be mobile in soil and that adsorption on suspended
    solids and sediment in water would be insignificant (Swann et al.,

    4.2.4  Biodegradation

         Tabak et al. (1981a,b) reported that isophorone (concentrations
    of 5 and 10 mg/litre) was rapidly degraded over 7 days by adapted
    microorganisms based on an aerobic-static culture procedure
    incorporating settled domestic wastewater as the microbial inoculum.

         Aerobic incubation of 100 mg/litre with activated sludge
    (30 mg/litre) for 2 weeks resulted in < 30% degradation (Kawasaki,
    1980; Sasaki, 1980).  Price et al. (1974) reported the removal (using
    a BOD procedure) of 9 and 42% isophorone from salt and fresh water,
    respectively, following incubation for 20 days with a settled non-
    adapted domestic wastewater inoculum.

         The losses of isophorone from wastewater treated using a
    trickling filter, activated sludge, aerated lagoon and facultative
    lagoon were 19, 98, 24 and 30%, respectively (Hannah et al., 1986). 
    Intermediate degradation products of isophorone identified by Mikami
    et al. (1981) after incubation with  Aspergillus niger were 3,5,5-
    trimethyl-2-cyclohexene-1,4-dione; 3,5,5-trimethylcyclo-hexane-1,4-
    dione; (S)-4-hydroxy-3,5,5-trimethyl-2-cyclohexene-1-one; and

         In a Die-away test, the breakdown of isophorone after 14 days was
    approximately 70%, whereas 95% was broken down within 28 days
    (Schöberl, 1992).

    4.2.5  Bioaccumulation

         Barrows et al. (1980) reported a measured bioconcentration factor
    of 7 for the bluegill sunfish  (Lepomis macrochirus) exposed for 14
    days to a mean concentration of 92.4 (± 10.5) µg/litre.  The half-life
    of isophorone in the tissues of this species was 1 day.  The
    bioconcentration factor was expressed as the quotient of the mean
    measured residues of the compound in fish tissues (whole body) during
    the equilibrium period divided by the mean measured concentration of
    the compound in water.  The half-life of the compound in tissues was
    the time in days required for mean measured residue concentration in
    tissues to be reduced to half that which was measured during the
    equilibrium period in the uptake phase (Barrows et al., 1980).  Thus,
    it is assumed that isophorone will not bioconcentrate in aquatic


    5.1  Environmental levels

    5.1.1  Air

         Harrison et al. (1985) identified isophorone at a level of
    490 µg/kg by GC/MS in electrostatically precipitated coal fly ash,
    suggesting that coal-fired power stations may be a source of emission
    to the atmosphere.

    5.1.2  Water

         The available data on isophorone concentrations in water are
    presented in Table 3.

         Isophorone was detected in 1% of 795 surface water samples
    (Hauser & Bromberg, 1982).  Concentrations of up to 3 µg/litre were
    reported in the Delaware river (Sheldon & Hites, 1979) and a
    concentration of 10 µg/litre was measured in urban run-off in
    Washington, DC, USA (Cole et al., 1984).

         The US Environmental Protection Agency has identified isophorone
    in finished drinking-water at concentrations ranging from 0.02 to
    9.5 µg/litre (US EPA, 1980).  A maximum concentration of 10 µg/litre
    has been reported in groundwater in the Netherlands (Zoeteman et al.,
    1981); the specific sources of this contamination were not identified.

         Isophorone was not detected in 36 water samples during the 1981
    Environmental Survey of Chemicals in Japan (Japan Environment Agency,

    5.1.3  Soil and sediment

         Isophorone was identified in sediment and soil taken from Love
    Canal, New York, USA (Hauser & Bromberg, 1982) and in sediment taken
    from Lake Pontchartrain, Louisiana, USA (McFall et al., 1985).  The
    concentrations in the latter were 0.9-12 µg/kg dry weight.

         Isophorone was detected in 18 out of 36 bottom sediments, at
    concentrations ranging from 0.6 to 6.6 µg/kg dry weight, in the 1981
    Environmental Survey of Chemicals in Japan (Japan Environment Agency,

    5.1.4  Terrestrial organisms  Plants

         To estimate the decline of isophorone concentration in plants
    treated with pesticides containing isophorone as a carrier,
    14C-isophorone was sprayed on bean plants and rice at a rate

        Table 3.  Isophorone concentrations in water
    Media                 Location                    Number      Analytical   Range          Samples with   Reference
                                                      of samples  method       (µg/litre)     detectable
                                                                               residues (%)

    Surface water         Delaware River, USA                     GC-MS        0.6-3                         Hites (1979)
                          Delaware River, USA                     GC-MS        3                             Sheldon & Hites (1979)

    Drinking-water        USA                                                  0.02-9.5                      US EPA (1980)
                          Philadelphia, USA             12        GC-MS                          17          Suffet et al. (1980)

    Ground water          Netherlands                                          10                            Zoeteman et al. (1981)

    Industrial effluent   manufacturing effluent                  GC-MS        40                            Jungclaus et al. (1976)
                          industrial effluent                     GC-MS        100                           Hites (1979)
                          treated effluent                        GC-MS        10                            Hites (1979)

    Urban run-off         Washington, DC, USA           86                     10                 4          Cole et al. (1984)

    Leachate              hazardous waste landfill       8        GC-MS        29                12.5        Ghassemi et al. (1984)

    equivalent to 7.5 kg/ha.  Samples of the plants were taken
    periodically and assayed for total radioactivity.  No attempt was made
    to characterize metabolites or degradation products.  In bean plants
    total residues declined rapidly from 16 mg/kg one hour after
    application to below 0.1 mg/kg on day 42.  Beans harvested on day 56
    did not contain detectable radioactivity.  Residues in rice plants
    declined from 7.3 mg/kg one hour after application to 3.1 mg/kg on day
    35 and 0.12 mg/kg on day 128.  Immature rice heads did not contain
    radioactivity on days 110 and 128.  The relatively slow decay in rice
    plants was considered by the authors to be due to unfavourable growing
    conditions in this particular study (Rohm & Haas, 1972).

         In a similar study, sugar beet was sprayed at the 2-leaf stage
    with a herbicide containing 14C-isophorone.  Total radioactivity
    found on day 30 was reported to be 10% of the initial value.  On day
    90, residues in the plants were below 0.01 mg/kg except in dry leaves
    where 0.07 mg/kg were found.  The results suggested some uptake of
    radiolabel from the soil from day 60 onwards; this was considered
    likely to be due to the uptake of small carbon fragments or 14CO2
    resulting from degradation of isophorone in the soil (Schering, 1974).  Animals

         No data are available.

    5.1.5  Aquatic organisms

         Isophorone was found in three samples of commercial mussels
     (Mytilus edulis) collected near Holbaek, Denmark, but no
    concentrations were reported (Rasmussen et al., 1993).

         Isophorone was detected in fish sampled from several tributary
    rivers of Lake Michigan, Canada.  Composite samples of several fish
    carcasses were analysed using GC-MS, and the following concentration
    ranges (mg/kg wet weight) were reported: common carp, < 0.02-3.13;
    smallmouth bass, 0.74-3.61; largemouth bass, 0.72; small bass,
    0.74-3.61; pumpkinseed, 0.4; bowfin, < 0.02-0.76; northern pike,
    < 0.02-0.48; rock bass, < 0.02-1.44; and lake trout, 2.38. 
    Isophorone was not detected in the channel catfish sample (Camanzo et
    al., 1987).

    5.2  General population exposure

         No data were available.

    5.3  Occupational exposure

         In the USA, the ACGIH (1986) have adopted a short-term (15 min)
    ceiling value of 28 mg/m3 (5 ppm) and the NIOSH recommended a 10-h
    TWA exposure limit of 23 mg/m3 (4 ppm) based primarily on
    unpublished reports, supplied to the TLV committee, of fatigue and

    malaise in workers exposed to concentrations of 28-46 mg/m3
    (5-8 ppm) for 1 month.  On lowering the concentration to between 5.7
    and 22.8 mg/m3 (1 and 4 ppm) no further complaints were received
    (ACGIH, 1986).  Exposure to isophorone has been determined in a screen
    printing plant, where several environmental conditions favoured
    evaporation of this solvent and where working conditions increased the
    risk of employee exposure.  The highest exposures in screen printers
    were reported to be 131 ± 31 mg/m3 (23 ± 5.4 ppm) (50-90 min TWA) in
    the breathing zone of printing press workers.  Other workers also
    received significant exposures: paint mixers, 102 ± 31 mg/m3
    (17.8 ± 5.5 ppm); manual drying, 86 ± 23 mg/m3 (15 ± 4.1 ppm);
    automatic drying, 54 ± 19 mg/m3 (9.5 ± 3.3 ppm); and screen washer,
    47 ± 32 mg/m3 (8.3 ± 5.6 ppm) (Samimi, 1982).

         A NIOSH health hazard evaluation (US NIOSH, 1980) conducted at a
    screen printing process in 1980 found workshift (6´ h) average
    exposures of printers to isophorone of 4 and 80 mg/m3 (0.7 and
    14 ppm).  Symptoms of respiratory tract and eye irritation reported by
    workers were attributed to the antistatic agent containing principally

         A NIOSH evaluation (US NIOSH, 1984) conducted at another screen
    printing operation in 1984 found no detectable (< 2.8 mg/m3,
    0.5 ppm) exposure to isophorone.

         Isophorone has been found in 6 out of 29 samples of printer's
    inks from different European manufacturers.  The method of analysis
    was headspace gas chromatography and mass spectrometry.  All of the
    samples in the present study were for serigraphy on electric and
    electronic articles (Rastogi, 1991).


    6.1  Human

         No data are available.

    6.2  Laboratory mammals

         Isophorone is absorbed by oral, dermal and inhalation routes.

         Following a single oral administration of isophorone to rats
    (4 g/kg) and rabbits (1 g/kg), the substance was distributed rapidly
    in the body and detected in the stomach, pancreas, adrenals, spleen
    and liver.  Following inhalation (2284 mg/m3, 400 ppm for 4 h)
    isophorone was detected in the kidney, adrenals, liver, pancreas and
    brain of rats (Dutertre-Catella, 1976).

         Strasser et al. (1988) studied the distribution of isophorone in
    male rats following administration by gavage of a single dose
    (3.6 mmol/kg) of 14C-isophorone (in corn oil) containing 177 µCi/kg. 
    Determination of radiolabel distribution of 14C-isophorone 24 h
    after dosing showed that 93% of the label had been excreted in the
    urine, faeces and expired air (approximate ratio 1200:1:67).  The
    remainder of the radiolabel was concentrated in the liver, kidney and
    preputial glands, which contained 3.7, 1.1 and 0.7%, respectively, of
    the original dose.  The high concentration of radiolabel in the
    preputial gland may have been due to the high concentrations of
    alpha2u-globulin to which it could bind (see also section 7.6).

         Following oral administration of isophorone to rats and rabbits,
    the substance was partly eliminated unchanged in expired air and
    urine; the remainder was metabolized (see Fig. 1) to:

    a)   5,5-dimethyl-cyclohex-1-en-3-one-1-carboxylic acid (i), derived
         from isophorone by methyl-oxidation;

    b)   isophorol (3,5,5-trimethyl-cyclohex-2-en-1-ol) (ii), formed by  
         the reduction of the ketonic group to a secondary alcohol and  
         eliminated as a glucuronide; and

    c)   dihydroisophorone (3,5,5-trimethyl-cyclohexanone) (iii),
         proceeding from the hydrogenation of the cyclohexene ring, and
         small quantities of  cis- and  trans-3,5,5-trimethyl-
         cyclohexanol-1 (iv), likely to have been formed from

         The amounts of the identified metabolites as a proportion of the
    administered dose were not reported (Truhaut et al., 1970; Dutertre-
    Catella et al., 1978).

         A single oral isophorone dose of 500 mg/kg to male SD rats has
    been reported to cause significant depletion of hepatic, testicular
    and epididymal glutathione.  Evidence was subsequently presented for
    enhanced ethyl methane sulfonate (EMS)-induced alkylation of DNA taken
    from epididymal spermatozoa (Gandy et al., 1990).  Although individual
    compounds were not identified, the data suggest glutathione may play a
    significant role in the elimination of isophorone and its metabolites.

         Quantitative data regarding the excretion of isophorone are not
    available. In the study of Dutertre-Catella et al. (1978), unchanged
    isophorone, isophorol (ii), dihydroisophorone (iii), 3-carboxy-5,5-
    dimethyl-2-cyclohexene-1-one (i), and  cis- and  trans-3,5,5-
    trimethyl-cyclohexanols (iv) were detected in the urine of rats and
    rabbits 24 h after an oral dose of isophorone.  The expired air
    contained unchanged isophorone 6 h after dosing.

    FIGURE 2


    7.1  Acute toxicity

         The acute LD50 values for various routes of exposure are
    presented in Table 4.

        Table 4.  Acute LD50 values for technical (commercial) grade isophorone
    Route     Species     Sex                    LD50        Reference

    Oral      rat         male and female        1500        Schering (1968)
                          female                 2104        Smyth et al. (1969)
                          male                   2700        Dutertre-Catella (1976)
                          female                 2100        Dutertre-Catella (1976)

              mouse       male and female        2200        Dutertre-Catella (1976)

              rabbit      male and female        2000        Dutertre-Catella (1976)
                          female                 2000        Smyth et al. (1969)

    Dermal    rat         male and female        1700        Schering (1968)

              rabbit      male and female        1200        Dutertre-Catella (1976)

    7.1.1  Oral

         Median lethal doses for isophorone in laboratory mammals ranging
    from 1500 to 2700 mg/kg body weight have been reported.  The signs of
    toxicity were similar to those of solvents and narcotics, prostration
    being followed rapidly by coma.  Deaths occurred within 24 h,
    otherwise recovery was complete.  Degenerative changes in the liver
    were reported in animals that died (Dutertre-Catella, 1976).  ß-Isophorone

         An oral LD50 of 2950 mg/kg in rats has been reported for
    ß-isophorone (purity 97.5%, containing 2.5% alpha-isophorone).  The
    predominant systemic effect was non-specific CNS depression shortly
    after dosing.  Cirrhosis-like changes on the surface of the liver and
    severe irritation of the stomach were observed in the animals that
    died following dosing (Hüls, 1988d).

    7.1.2  Dermal

         Dermal LD50 values indicate that isophorone is rapidly absorbed
    through the skin under occlusion.  During the first 6 h of occluded
    application an increase in respiratory rate, followed by prostration
    and narcosis, was reported in rabbits exposed to 500-1000 mg/kg. 
    Occluded skin contact for 24 h resulted in erythema, followed after
    several days by scarring.  Skin damage was still evident after 14
    days.  In this study, 10-25 ml isophorone was applied to skin as
    compared to 0.5 ml in the skin irritation test (see section 7.2.1)
    (Dutertre-Catella, 1976).

    7.1.3  Inhalation

         Rats and guinea-pigs were exposed to atmospheres containing
    isophorone concentrations of 1713 or 4282 mg/m3 (300 or 750 ppm) for
    24 h, of 5025 mg/m3 (880 ppm) for 12 h, or of 7823 to 26 266 mg/m3
    (1370 to 4600 ppm) for 8 h.  In both animal species, in the order of
    development, eye and respiratory irritation, lachrymation, ataxia,
    dyspnoea, diarrhoea, light narcosis and death were observed. 
    Postmortem examination of rats dying after exposure to isophorone
    showed haemorrhage in the lungs, congestion of the stomach and liver,
    peritoneal effusion and discoloration of the kidney and spleen (Smyth
    & Seaton, 1940).  However, it would appear that some of the
    atmospheric concentrations could not have been achieved with pure
    isophorone, and therefore the results reported in the study are of
    little relevance (Rowe & Wolf, 1963).

         Groups of six rabbits and rats were exposed to isophorone for
    5 h.  The observation period was 2 weeks.  At a concentration of
    39.9 g/m3 (7000 ppm), 10% of the rats and 30% of the rabbits died. 
    No LC50 value could be established from this study (Dutertre-
    Catella, 1976).

    7.2  Skin, eye and respiratory irritation, sensitization

    7.2.1  Skin irritation

         The skin irritation of isophorone was studied by Truhaut et al.
    (1972).  A single application of 0.5 ml isophorone under an occlusive
    patch for a period of 24 h on the shaved or scarified skin of six
    rabbits produced a light erythema which disappeared rapidly after
    exposure.  Microscopical examination did not show any
    histopathological changes.

         In the rabbit, occlusive and semi-occlusive contact with 0.5 ml
    neat isophorone for 1 or 4 h was non-irritating (Potokar et al.,
    1985).  ß-Isophorone

         A single application of 0.5 ml ß-isophorone (containing 2.5%
    alpha-isophorone) under a semi-occlusive patch over a period of 4 h on
    the shaved skin of three rabbits produced moderate erythema and
    swelling (Hüls, 1988e).

    7.2.2  Eye irritation

         A single instillation of 0.1 ml isophorone in the eyes of six
    rabbits caused opacity in four animals, which in some instances
    covered the entire area of the cornea, inflammation of the conjunctiva
    and purulent discharge.  In a supplementary experiment in which the
    rabbits' eyes were washed with 20 ml of warm water 2-4 seconds after
    the introduction of 0.1 ml isophorone, considerable recovery from
    these effects occurred over 7 days (Dutertre-Catella, 1976).

         Grant (1974) reported that application of one drop of isophorone
    to rabbit cornea caused mild transient injury, graded 4 on a scale of
    1 to 10 after 24 h.  Pronounced irritation of eyes and nose occurred
    in rats and guinea-pigs exposed to atmospheres containing isophorone
    (see section 7.1.3) (Smyth & Seaton, 1940; Smyth et al., 1942).  ß-Isophorone

         A single instillation of 0.1 ml in the eyes of three rabbits
    produced moderate conjunctival and corneal opacities.  Iridial changes
    were also reported in two animals.  Although the corneal and iridial
    changes had resolved by 7 days, minor conjunctival irritation was
    still in evidence (Hüls, 1988f).

    7.2.3  Respiratory irritation

         In a study of sensory irritation, De Ceaurriz et al. (1981)
    estimated the concentration of various chemicals causing a 50%
    decrease in respiratory rate (measured using individual
    plethysmographs) in mice (RD50).  The RD50 for isophorone was
    158.7 mg/m3 (27.8 ppm) for a 5-min exposure.  For comparison, the
    RD50 values for toluene diisocyanate and acetone were 0.24 and
    23 480 ppm, respectively.

         Exposure of rats to airborne concentrations of 383-514 mg/m3
    (67 or 90 ppm) for a single 4-h period produced statistically
    significant reductions in circulating leukocytes.  This leukopenia was
    considered to be due to the stress-induced release of cortico-steroids
    resulting from sensory irritation (Brondeau et al., 1990).

    7.2.4  Sensitization

         Isophorone, administered at a concentration of 10% intradermally
    (in maize germ oil) and 100% topically to female guinea-pigs in the
    Magnusson-Kligman test, showed no sensitizing potential (Hüls, 1988a).

    7.3  Subchronic toxicity

    7.3.1  Inhalation

         The effects of repeated whole body exposure to isophorone vapour
    were reported by Smyth et al. (1942).  Groups of male Wistar rats and
    guinea-pigs of both sexes, 16-20 animals per group, were exposed to
    isophorone concentrations up to approximately 2855 mg/m3 (500 ppm)
    8 h/day, 5 days/week, for 6 weeks.  As in the Smyth & Seaton (1940)
    study (section 7.1.3), the air concentrations of isophorone could not
    have been attained under conditions employed by Smyth et al. (1942). 
    In the presentation of these results no distinction was made between
    the two species and no control data were presented.  Growth
    retardation was noted in all animals exposed to higher concentrations. 
    Postmortem examination of animals dying after exposure revealed
    severely injured kidneys and lungs.  The kidneys of surviving animals
    were congested with dilation of Bowman's capsules and cloudy swelling
    of tubular cells.  The lungs and liver were also reported to be
    congested with desquamation of the bronchial epithelium in the lungs
    and cloudy swelling in the liver cells.

         Dutertre-Catella (1976) exposed groups of 10 male and 10 female
    rats to atmospheres reported to contain 2855 mg/m3 8 h/day, 5
    days/week for 6 and 4 months, respectively. Two males and one female
    exposed to isophorone died; there were no deaths in the control
    animals.  The only reported effects were irritation of the eyes and

         Groups of 10 male and 10 female young adult Charles River CD rats
    were exposed to isophorone at air concentrations of 0 or 250 mg/m3,
    6 h/day, 5 days/week, for 4 weeks.  Results of daily spectroscopic
    determinations indicated that the average daily exposure was
    208 mg/m3.  Body weight measurements and haematological studies were
    made before exposure and after 4 weeks.  The rats were killed and
    gross necropsy was performed.  Organ weights were determined for
    lungs, liver, kidneys, adrenals and spleen.  Histological examination
    of those tissues were performed in three males and three females per
    group.  The following effects were observed: transient nasal bleeding,
    increased percentages of lymphocytes, decreased percentages of
    neutrophils and increased haemoglobin concentration in males and
    females and significantly lower terminal body weights and
    significantly decreased absolute and relative liver weights of exposed
    males, compared with controls (Littlefield, 1968).

    7.3.2  Oral

         Four groups of 20 male and 20 female albino rats were fed diets
    containing 0, 750, 1500 or 3000 mg isophorone/kg (0, 37.5, 75 or
    150 mg/kg body weight) for 90 days.  Isophorone in corn oil (ratio
    1:2) was blended with the diet; fresh diets were prepared each week.
    Haematology, serum chemistry and urine analyses were carried out on
    five animals of each sex from each group at week 4 and at termination. 
    Comprehensive histopathological examination was confined to five
    animals of each sex from the control and high dose groups.  The liver
    and kidney from five animals of the intermediate dose levels were also
    examined histopathologically.  Under the conditions of this study, no
    effects on the general appearance of the test animals, on their
    behaviour, on body weight gain or on food consumption were observed at
    a dietary level of 1500 mg/kg or less.  Isophorone did not alter the
    composition of the formed elements of the blood, nor did it interfere
    with the general metabolism or with liver and kidney function.  No
    detectable gross or microscopic pathological changes were noted in any
    of the animals examined after 28 or 90 days of feeding.  Organ/body
    weight ratios for vital organs were not changed.  The only adverse
    finding reported was a reduction in body weight gain in the male rats
    receiving the highest dose (Affiliated Medical Enterprises, 1972a).

         As part of a preliminary investigation prior to an NTP
    carcinogenicity study, five rats (F-344) and five mice (B6C3F1) of
    each sex were given by gavage 12 oral doses of up to 2000 mg
    isophorone/kg body weight administered in corn oil over a 16-day
    period (US NTP, 1986). Lethargy was reported in all rats following
    dosing while in mice uncertain locomotion was reported among animals 
    receiving 1000 mg/kg.  All mice and 50% of the rats receiving
    2000 mg/kg died.  The weight gain of animals surviving 2000 mg/kg and
    all animals receiving 1000 mg/kg was reduced.  As part of the same
    programme, 10 rats and mice of each sex were given by gavage daily
    doses of 0, 62.5, 125, 250, 500 or 1000 mg isophorone/kg body weight
    for 90 days (US NTP, 1986).  The rats were drowsy and lethargic
    following administration. At the highest dose level, one female rat
    and three female mice died.  No macroscopic or microscopic changes
    were observed in the organs examined from either study.  A subsequent
    histopathological review of the kidney, which included re-sectioning
    and additional staining, also failed to reveal any treatment-related
    effects.  The no-observed-effect level in this study was considered to
    be 500 mg/kg body weight per day.

         Groups of four male and four female beagle dogs were given 90
    daily oral doses of isophorone in gelatin capsules at dosage rates of
    35, 75 or 150 mg/kg per day.  Comprehensive haematology, clinical
    chemistry and urine analyses were carried out initially and at 1, 2
    and 3 months.  Apart from a mild intermittent incidence of soft stools
    in animals of the high-dose group, there was no observable effect as
    demonstrated by the data on general appearance and conditions as well
    as those from haematological or biochemical investigations.  At

    autopsy, no changes in the organ/body weight ratios and no
    histopathological changes were observed.  No toxic effect was found at
    any of the dose levels used.  It was concluded that the no-observed-
    effect level for isophorone in the dog was 150 mg/kg per day
    (Affiliated Medical Enterprises, 1972b).

    7.3.3  Dermal

         The daily occluded application on shaved and abraded skin of 0.1
    or 0.2 ml of isophorone to rats for 8 weeks produced erythema and
    scabs at the site of application (Dutertre-Catella, 1976).  The only
    apparent systemic effect reported was an 8% reduction in mean weight
    gain in the females compared with controls; the dose levels at which
    this occurred were not given.

    7.4  Mutagenicity

         The results of mutagenicity tests are summarized in Table 5.

    7.4.1  Gene mutation in bacteria (Ames tests)

         The mutagenic potential of isophorone was examined using
     Salmonella typhimurium strains TA1535, TA1537, TA1538, TA98 and
    TA100, following a preincubation protocol. The test substance
    concentrations used were between 10 and 5000 µg per plate.  There was
    no increase in the number of revertants at any of the concentrations
    tested with and without rat liver S9 fraction (Hüls, 1988b).

         Two further studies were conducted on  Salmonella typhimurium
    TA1535, TA1537 and TA1538 strains (1 to 1000 µg/plate) (Atochem,
    1978a) and TA98, TA100, TA1535 and TA1537 strains (100 to
    10 000 µg/plate) (US NTP, 1986).  No evidence of mutagenic potential
    was provided in the presence or absence of rat or hamster liver S9

          Salmonella strains TA1535, TA1537, TA97, TA98 and TA100 were
    used to test isophorone (up to 10 000 µg/plate) with and without
    Aroclor 1254-induced rat and hamster metabolic activation systems
    (male Sprague-Dawley rats and male Syrian hamsters).  When negative
    results were obtained in the initial assay, the chemicals were
    retested in all strains with and without activation.  Isophorone
    showed no mutagenic activity (Mortelmans et al., 1986).  Dihydroisophorone

         The mutagenic potential of dihydroisophorone (iii in Fig. 1, see
    section 6.2), a metabolite of isophorone, was examined using
     Salmonella typhimurium strains TA1535, TA1537, TA1538, TA98 and
    TA100 at concentrations of 25 to 2500 µg per plate.  There was no
    increase in the number of revertants at the concentrations tested,
    either with or without rat liver S9 fraction (BP, 1988a).

        Table 5.  Isophorone genotoxicity tests
                        Test system                   Results        Reference

    Gene                Ames test (with and           negative       Atochem (1978a); US NTP
     mutation           without S9)                                  (1986); Mortelmans et
                                                                     al. (1986); Hüls (1988b)

                        mouse lymphoma assay          positive       US NTP (1986)
                        (without S9)
                        (with and without S9)         negative       Microbiological Associates
                        (with and without S9)         positive       McGregor et al. (1988)
                        (with and without S9)         negative       O'Donoghue et al. (1988)
                                                      positive       Mitchell (1993)

                        sex-linked recessive          negative       Foureman et al. (1994)
                        lethal in Drosophila

    Chromosome          CHO cells (in vitro)          negative       US NTP (1986)
     aberrations        (with and without S9)         negative       Gulati et al. (1989)

    Micronucleus        mouse (in vivo)               negative       Atochem (1978b); Microbio-
     test                                                            logical Associates (1984b);
                                                                     O'Donoghue et al. (1988)

    Sister              CHO cells (in vitro)
     chromatid          (without S9)                  positive       US NTP (1986)
     exchanges          (with S9)                     negative       US NTP (1986)
                        (without S9)                  positive       Gulati et al. (1989)

    Direct DNA          unscheduled DNA               negative       Microbiological Associates
     damage             synthesis (primary rat                       (1984c); O'Donoghue et al.
                        hepatocyte culture)                          (1988)

    DNA binding         liver and kidney DNA          negative       Thier et al. (1990);
     in vivo            (mouse and rat)                              Thier & Xu (1990)

    Morphological       BALB/c-3T3 cells              positive       Matthews et al. (1993)
     transformation     (without S9)

    7.4.2  Gene mutation in mammalian cells

         Isophorone was tested in the L5178Y TK +/- mouse lymphoma
    mutagenesis assay (MLA) in the presence and absence of rat liver S9
    fraction.  The experiment was performed only once and all doses were
    tested in duplicate.  In the absence of S9, isophorone concentrations
    of 0.13 to 1.3 ml/litre produced total growth of 111% to 12% compared
    to the control.  In the presence of S9, isophorone concentrations of
    0.067 to 0.89 ml/litre produced total growth of 86 to 9% compared to
    the control.  None of these cultures exhibited mutation frequencies
    which were significantly greater than the mean mutation frequency of
    the solvent control (Microbiological Associates, 1984a; O'Donoghue et
    al., 1988).  The authors pointed out that while the results of the MLA
    without metabolic activation were negative in the present study, these
    assays were positive in the NTP study and thus were not reproducible
    between laboratories.  In contrast to O'Donoghue et al. (1988),
    McGregor et al. (1988) reported isophorone to be positive in the MLA
    both with and without rat liver S9 mix (from male Fischer-344 rats). 
    Isophorone was toxic to the cultures only at doses of 600 ml/litre or
    more.  The authors viewed the experiment with reservations since the
    cloning efficiency was low.

         Another MLA study employing concentrations of 400 to
    1200 mg/litre was carried out in the absence of rat liver S9 fraction. 
    Duplicate experiments produced gradations of total growth relative to
    control values of 112 or 118% for the low concentrations to 7 or 14%
    for the high concentrations.  Dose-related increases in mutation
    frequencies compared with control were observed; at the highest dose
    level the increase was 4-fold (US NTP, 1986).

         Mitchell (1993) compared the induction of mutation frequencies by
    the  in situ variant (ISV) approach with the standard MLA. 
    Isophorone was one of the compounds tested, and showed a higher
    induced mutation frequency with the ISV approach than in the standard

         Isophorone was tested for its ability to induce sex-linked
    recessive lethal mutations in post-meiotic and meiotic germ cells of
    male  Drosophila melanogaster.  No induction was observed at 2000 ppm
    by feeding or at 15 000 ppm by injection (Foureman et al., 1994).

    7.4.3  Chromosome aberrations and sister chromatid exchange  Chromosome aberrations

         Isophorone was tested in an  in vitro cytogenetic assay using
    Chinese hamster ovary (CHO) cell cultures.  Treatments were performed
    both in the absence and presence of rat liver S9 fraction.  Under the
    conditions of this test, isophorone did not induce chromosomal
    aberrations (ABS) at concentrations up to 1600 or 1500 mg/litre,
    respectively (US NTP, 1986).

         Twenty-seven chemicals (including isophorone), previously tested
    in rodent carcinogenicity assays were tested for induction of ABS in
    CHO cells as part of a more extensive analysis of the correlation
    between results of  in vitro genetic toxicity assays and
    carcinogenicity bioassays.  Chemicals were tested up to toxic doses
    both with and without exogenous metabolic activation.  A liver
    fraction (S9) prepared from Aroclor 1254-induced male Sprague-Dawley
    rats was used to provide exogenous metabolic activation.  No ABS were
    observed in CHO cells following incubation with isophorone in either
    the presence or the absence of S9 (Gulati et al., 1989).  Sister chromatid exchange

         The ability of isophorone to induce sister chromatid exchange
    (SCE) was studied in CHO cells, in the presence and absence of rat
    liver S9 fraction at concentrations up to 1000 mg isophorone/litre. 
    Without S9, isophorone induced a small but dose-related increase in
    the frequencies of SCE.  No effect was observed in the presence of S9
    (US NTP, 1986).

         A significant increase in SCE frequency with isophorone was
    observed only in the absence of S9, at doses of 500-1000 mg/litre
    (Gulati et al., 1989 - see also section  At these high dose
    levels, isophorone is extremely cytostatic; therefore, the increase in
    SCE frequency was observed only after delayed harvest (6-13 h
    additional culture time).

    7.4.4  Micronucleus test

         Isophorone doses of 450, 900 and 1800 mg/kg body weight were
    administered by gavage to CFLP mice of both sexes in two equal doses
    separated by an interval of 24 h.  Six hours after the last treatment
    the mean micronucleated cell counts and the bone marrow cytotoxicity
    were similar in all test groups and controls (Atochem, 1978b).

         Male and female CD-1 mice were treated by intraperitoneal
    injection of isophorone (0.54 ml/kg body weight).  There was no
    evidence of micronuclei or cytotoxicity in bone marrow samples
    collected 12, 24 and 48 h after administration (Microbiological
    Associates, 1984b; O'Donoghue et al., 1988).

    7.4.5  Primary DNA damage  Bacterial tests

         In the  Bacillus subtilis (strain H17) rec-assay, isophorone
    showed DNA-damaging potential without metabolic activation and a
    reverse effect with activation (Matsui et al., 1989).

         Isophorone did not induce the SOS function responses in the umu
    test using  Salmonella typhimurium strain TA1535/pSK1002 (Ono et al.,
    1991).  Unscheduled DNA synthesis

         Isophorone was tested at dose levels ranging from 0.005 to
    0.40 ml/litre using primary rat cultures of hepatocytes.  There was no
    increase in the mean nuclear grain count compared to the controls or
    in the incidence of cells undergoing repair at any dose level
    (Microbiological Associates, 1984c; O'Donoghue et al., 1988).  DNA binding

         A DNA-binding study was performed with radiolabelled 1,3,5-
    14C-isophorone (Thier et al., 1990; Thier & Xu, 1990).  Male and
    female F-344 rats and male and female B6C3F1 mice received doses
    (500 mg/kg body weight) of unlabelled isophorone containing 0.4 mCi
    (per rat) and 0.8 mCi (per mouse) labelled isophorone in neutral oil
    by gavage.  No binding of the radioactivity to liver or kidney DNA was
    observed in either species.

    7.4.6  Morphological transformation

         Isophorone was positive in a standard transformation assay using
    BALB/c-3T3 cells without exogenous activation at concentrations of
    1.07 g/litre (7.76 mmol/litre) (Matthews et al., 1993).

    7.5  Chronic toxicity and carcinogenicity

         In 18-month inhalation studies, groups of 10 rats and 2 rabbits
    of each sex were exposed to atmospheres containing 1413 mg
    isophorone/m3 (250 ppm) for 6 h/day, 5 days/week.  Slight
    conjunctivitis and irritation of the nasal mucosa with a bloody
    discharge were observed.  In the lungs of the animals, frequent
    haemorrhages were found with oedema in the alveoli.  Vacuolization was
    found in the liver of the treated animals (Dutertre-Catella, 1976).

         Toxicological and carcinogenesis studies of isophorone (more than
    94% pure) were conducted by administering 0, 250 or 500 mg
    isophorone/kg body weight per day by gavage in corn oil to groups of
    50 F-344/N rats and 50 B6C3F1 mice of each sex, 5 days per week for
    103 weeks.  Throughout the 2-year study, the mean body weights of the
    high-dose male rats were on average 5% less than those of the vehicle
    controls.  During the second year, the mean body weights of the female
    high-dose rats were on average 8% less than those of the vehicle
    controls, and the high-dose female mice were 5% lower.  The survival
    of high-dose male rats was significantly lower than that of the
    vehicle controls after week 96 (final survival: vehicle control,
    33/50; low dose, 33/50; high dose, 14/50).  The survival of dosed

    female rats was poor (30/50; 23/50; 20/50), due in part to 20 gavage-
    related accidental deaths of dosed animals.  The survival of male mice
    was also low (16/50; 16/50; 19/50), but there was a significant trend
    toward increased survival of dosed female mice relative to that of the
    vehicle controls (26/50; 35/50; 34/50).  Dosed male rats showed a
    variety of proliferative lesions of the kidney (tubular cell
    hyperplasia: 0/50; 1/50; 4/50; tubular cell adenoma: 0/50; 0/50; 2/50;
    tubular cell adenocarcinoma: 0/50; 3/50; 1/50; epithelial hyperplasia
    of the renal pelvis: 0/50; 5/50; 5/50).  Dosed male rats also
    exhibited increased mineralization of the medullary collecting ducts
    (1/50; 31/50; 20/50), and low-dose male rats showed a more severe
    nephropathy than is commonly seen in ageing F-344/N rats. Carcinomas
    of the preputial gland were increased in high-dose male rats (0/50;
    0/50; 5/50).  With the exception of a moderate increase in nephropathy
    (21/50; 39/50; 32/50), female rats did not show chemically related
    increased incidences of neoplastic or non-neoplastic lesions.  In
    high-dose male mice, isophorone exposure was associated with increased
    incidences of hepatocellular adenomas and carcinomas (18/48; 13/50;
    29/50) and of mesenchymal tumours of the integumentary system
    (fibroma, fibrosarcoma, neurofibrosarcoma or sarcoma: 6/48; 8/50;
    14/50).  An increased incidence of lymphomas or leukaemias was noted
    in low-dose male mice (8/48; 18/50; 5/50).  Coagulative necrosis
    (3/48; 10/50; 11/50) and hepatocytomegaly (23/48; 39/50; 37/50) were
    observed more frequently in the livers of dosed male mice than in
    vehicle controls.  No compound-related neoplastic or non-neoplastic
    lesions associated with isophorone exposure were seen in female mice. 
    Under the conditions of these 2-year gavage studies, there was some
    evidence of carcinogenicity of isophorone in male F-344/N rats as
    shown by the occurrence of renal tubular cell adenomas and
    adenocarcinomas in animals given 250 or 500 mg/kg per day; carcinomas
    of the preputial gland were also observed at increased incidence in
    male rats given 500 mg/kg.  There was no evidence of carcinogenicity
    in female F-344/N rats given 250 or 500 mg/kg per day. For male
    B6C3F1 mice, there was equivocal evidence of carcinogenicity of
    isophorone as shown by an increased incidence of hepatocellular
    adenomas or carcinomas (combined) and of mesenchymal tumours in the
    integumentary system in animals given 500 mg/kg per day and by an
    increase in malignant lymphomas in animals given 250 mg/kg per day. 
    There was no evidence of carcinogenicity of isophorone in female
    B6C3F1 mice given 250 or 500 mg/kg per day (US NTP, 1986).

         In the above NTP study, preputial gland carcinomas were observed
    in five high-dose male rats.  The apparent absence of this tumour in
    vehicle controls or in the low-dose group, and the very low incidence
    (12/1094, i.e. 1%) in corn oil vehicle controls in previous 2-year
    studies, suggest that this may be a chemical-related effect.  No
    preputial gland tumours were observed in male mice, but two
    histogenetically related clitoral gland adenomas were seen in low-dose
    female rats, providing some support for an association of isophorone
    exposure with this tumour type (Bucher et al., 1986).

    7.6  Mechanisms of toxicity

         Swenberg et al. (1992) and US EPA (1991a,b) reviewed the
    mechanisms involved in alpha2u-globulin nephropathy and renal
    carcinogenesis of several chemicals in various animal, biochemical and
    molecular modelling systems.  All of the data are consistent with the
    hypothesis that reversible binding of chemicals or their metabolites
    to this abundant protein is causally related to the induction of
    disease.  Alpha2u-globulin, found mainly in male rats, is
    synthesized by the liver and subsequently transported to the kidney. 
    It is normally present in the cytoplasm of the proximal convoluted
    tubules of untreated animals in the form of hyaline droplets, visible
    by light microscopy.  Xenobiotics, or their metabolites, are bound to
    the alpha2u-globulin in the liver of animals; this conjugate is even
    more difficult to hydrolyse than the alpha2u-globulin itself and
    induces the formation of the hyaline droplets which accumulate in the
    tubules (Swenberg et al., 1989).  Accumulation of the chemical/
    alpha2u-globulin complex causes lysomal protein overload and
    necrosis of the cells with subsequent cellular regeneration.  Thus
    cellular proliferation may contribute to the development of renal

         In order to determine whether isophorone and other compounds that
    cause alpha2u-globulin to accumulate have the same binding
    characteristics, binding studies were conducted with kidney cytosol
    preparations from male Fischer-344 rats.  The inhibition constant
    value (Ki) for isophorone was in the range of 10-6 to
    10-7 mol/litre, while those for  d-limonene, 1,4-dichlorobenzene
    and 2,5-dichlorophenol were higher (around 10-4 mol/litre).  This
    suggests that other factors besides binding are involved in the
    accumulation of alpha2u-globulin.  Results so far indicate that
    binding is dependent on both hydrophobic interactions and hydrogen
    bonding (Borghoff et al., 1991).

         Investigations (Charbonneau et al., 1988; Strasser et al., 1988)
    have shown that isophorone, isophorol and dihydroisophorone bind to
    alpha2u-globulin, resulting in an increased accumulation of hyaline
    droplets in renal tubular cells.  These findings suggest the same
    sequence of events may be responsible for the small increase in the
    incidence of renal tubular neoplasias seen in male rats.
    alpha2u-Globulin was not detected at significant levels in plasma
    and urine of female rats or either sex of mice and humans (Swenberg et
    al., 1989; Olson et al., 1990).  In addition, other laboratory
    rodents, dogs and primates do not develop hydrocarbon-related
    nephropathy (Swenberg et al., 1989).  For these reasons, it was
    concluded that the low increase in the incidence of tubular adenomas
    and adenocarcinomas observed in male rats following isophorone
    administration was attributable to the accumulation of
    alpha2u-globulin and was sex- and species-specific (Charbonneau &
    Swenberg, 1988; Strasser et al., 1988; Swenberg et al., 1989). 
    Further evidence to support this view was gained by a study of

    Dietrich & Swenberg (1991) using male animals of the NCI Black Reiter
    (NBR) strain, which does not synthesize alpha2u-globulin.  It was
    shown that an oral dose (gavage) of 1000 mg isophorone/kg on four
    consecutive days failed to produce the early features of the
    alpha2u-globulin-related nephropathy syndrome (i.e. hyaline droplets
    or alpha2u-globulin) in this strain.

         In terms of human risk assessment, renal tubule tumours produced
    in male rats in association with chemicals inducing alpha2u-globulin
    accumulation should be distinguished from renal tubule tumours of
    other origin (Borghoff et al., 1990; Swenberg, 1991; US EPA, 1991a,b). 
    It has been recognized that the induction of such tumours does not
    necessarily indicate a potential carcinogenic hazard to humans.  The
    significance of this information with respect to the etiology of
    pathological changes is uncertain at present.

         Studies have shown that high levels of alpha2u-globulin and its
    messenger RNA (mRNA) are present in the preputial gland of both male
    and female rats.  The preputial gland in both sexes contained about 3
    times more alpha2u-globulin mRNA and about 300 times more
    alpha2u-globulin than the male rat liver (Murty et al., 1987).  It
    was claimed that this high content of alpha2u-globulin was primarily
    due to the cellular and ductal accumulation of the protein in the
    preputial gland but did not reflect a difference in the rate of
    transcription of the alpha2u-globulin gene.  The high amount of
    radiolabel derived from 14C-isophorone found in the preputial gland
    of the male rats following single gavage dosing with 5 ml/kg (Strasser
    et al., 1988) may therefore be related to its high content of

    7.7  Appraisal for mutagenicity/carcinogenicity

         Isophorone does not induce gene mutations in bacteria,
    chromosomal aberrations  in vitro, bone-marrow micronuclei in mice or
    DNA repair in primary cultures of rat hepatocytes.  No DNA binding  in
     vivo was observed in a DNA binding study using 1,3,5-
    14C-isophorone.  In one study in the absence and in another study in
    the absence and presence of metabolic activation, weak mutagenic
    responses were obtained in three out of five L5178Y TK +/- mouse
    lymphoma mutagenesis assays and a small increase of sister chromatid
    exchange (SCE) was found only without metabolic activation in CHO
    cells.  Another study with SCE showed no increases in chromosomal
    aberrations (for details see section 7.4).  Isophorone was negative in
    a test for sex-linked recessive lethal mutations in  Drosophila.  It
    induced morphological transformation in mouse cells without

         The weight of the evidence of all mutagenicity data supports the
    contention that isophorone is not a potent DNA reactive compound. 
    There was no DNA binding in the liver and kidneys (sites affected in
    the carcinogenicity bioassays).

         The available data on  in vitro mutagenicity and related end-
    points do not suggest that isophorone is genotoxic.

         When tested in a two-year carcinogenicity bioassay, isophorone
    produced a variety of lesions of the kidneys, such as severe
    nephropathy and tubular cell hyperplasia.  A low but statistically
    significant increase in the frequency of renal tubular cell adenomas
    and adenocarcinomas was found in male F-344 rats dosed at levels of
    250 and 500 mg/kg per day (see section 7.5).

         An increase in the number of carcinomas of the preputial gland
    was found only in male rats given 500 mg/kg per day.  In high-dose
    male B6C3F1 mice hepatocellular adenomas and carcinomas were
    observed.  No compound related neoplastic lesions were seen in female
    rats (for details, see section 7.5).

         The induction of these two types of tumours in male rats may be
    associated with nephropathy, epithelial hyperplasia and
    alpha2u-globulin formation and accumulation of the isophorone/
    alpha2u-globulin complex, causing lysomal protein overload and
    necrosis of the kidney cells with subsequent cellular regeneration
    (for details see section 7.6).

    7.8  Reproduction, embryotoxicity, teratogenicity

         The teratogenicity of isophorone to rats and mice was studied by
    Traul et al. (1984).  Groups of 22 confirmed mated females of each
    species were exposed 6 h/day on days 6-15 of gestation to atmospheres
    containing 0, 143, 285 or 656 mg/m3 (0, 25, 50 or 115 ppm)
    isophorone.  At the highest atmospheric concentration there was
    evidence of maternal toxicity which showed as reduced food
    consumption, alopecia and cervical or anogenital staining in the rats
    and reduced body weights in the mice.  Comprehensive uterine and fetal
    examinations did not show any significant differences between animals
    exposed to isophorone and their respective controls.  From the results
    of this study, it can be concluded that no teratogenic or fetotoxic
    effect was observed with 656 mg/m3 in F-344 rats and CD-1 mice.

         In a study by Dutertre-Catella (1976), groups of 10 rats of each
    sex, exposed 6 h/day, 5 days/week to 2855 mg/m3 (500 ppm) isophorone
    for 3 months, were mated to exposed animals or to controls.  All
    females were reported to have delivered 7-10 pups.  Anatomo-
    pathological examination did not show any abnormalities.  However,
    only one isophorone concentration was used, the group size was small,
    and no information was provided on reproductive success and maternal

    7.9  Neurotoxicity

         Central nervous system depression is a characteristic feature of
    isophorone intoxication in experimental animals (Smyth & Seaton, 1940;
    Dutertre-Catella, 1976; De Ceaurriz et al., 1981).

         Isophorone and a number of aliphatic ketones have been studied
    using the mouse behavioural despair swimming test (De Ceaurriz et al.,
    1984).  This test, which was developed for screening antidepressant
    drugs, is based on the duration of the periods of immobility exhibited
    by mice when placed in water.  Mice were exposed to isophorone at
    atmospheric concentrations of 508-782 mg/m3 (89-137 ppm) for 4 h. 
    The ID50 (an estimated concentration producing a 50% reduction in
    the immobility time) for animals thus exposed was 628 mg/m3
    (110 ppm).

    7.10  Other special studies

         One of the current research approaches for assessing cytotoxicity
    is to monitor the respiratory activity of the mitochondrion, a
    sensitive, nonspecific subcellular target site.  Detected changes in
    mitochondrial function after the addition of a test chemical could be
    correlated to toxic effects.  In this case, rat (male, Charles River)
    liver mitochondria were used, and isophorone was shown to induce no
    observable effects on rat liver mitochondria respiratory activity over
    the tested concentration range of 0.273-113.8 mg/litre
    (1.98-825 µmol/litre) (Haubenstricker et al., 1990a).

         Isophorone was tested for its ability to perturb glutathione
    (GSH) levels in the testes and epididymides, as well as liver,
    following single acute dosages to rats.  Groups of four mature male
    Sprague-Dawley rats were administered isophorone intraperitoneally
    (2 ml/kg).  Concurrent control groups were maintained for all time
    points examined to account for possible circadian fluctuation of GSH
    throughout the day.  Animals were sacrificed at 1, 2, 4, 8 or 16 h
    after administration of the test compound.  Liver, testes and
    epididymides were excised for determination of total GSH content by
    spectrophotometry.  Isophorone (500 mg/kg) significantly reduced GSH
    in the liver and in both reproductive organs examined.  The ability of
    isophorone to enhance the covalent binding of tritiated ethyl
    methanesulfonate (3H-EMS) to spermatocytes was assessed. 
    Perturbation of reproductive tract GSH by isophorone treatment
    significantly enhanced the extent of 3H-EMS-induced binding to sperm
    heads.  The authors postulate that chemical-induced lowering of GSH in
    the male reproductive tract may be a mechanism for potentiation of
    chemical-induced germ-cell mutations (Gandy et al., 1990).


    8.1  Acute

         Groups of 11 or 12 subjects exposed for a few minutes to
    atmospheric isophorone concentrations of 228 mg/m3 (40 ppm) or more
    experienced irritation of the eyes, nose and throat.  A few complaints
    of nausea, headache, dizziness, faintness, inebriation and a feeling
    of suffocation occurred at concentrations 1142 mg/m3 (> 200 ppm). 
    The symptoms of irritation and narcosis were said to be less intensive
    following exposure to concentrations below 1142 mg/m3 (Smyth &
    Seaton 1940).  However, this study has been criticized because of
    uncertain actual concentrations and the use of impure substances (Rowe
    & Wolf, 1963).

    8.2  Sub-chronic

         Complaints of fatigue and malaise were reported among workers
    exposed for 1 month to atmospheres containing 28.5 to 48 mg
    isophorone/m3 (5 to 8 ppm) (Communication from Ware, GD, to
    Chairman, TLV Committee, 1973).  No further complaints were received
    following a reduction of the concentration to between 5.7 and
    22.8 mg/m3 (1 and 4 ppm).  On the basis of these data, the American
    Conference of Governmental Industrial Hygienists (ACGIH, 1986)
    recommended a ceiling limit (15 min) of 29 mg/m3 (5 ppm) for

    8.3  Irritation and sensitization

         No report on skin irritation or skin sensitization has been

    8.3.1  Eye and respiratory irritation

         Smyth & Seaton (1940) reported eye, nose and throat irritation
    following exposure to isophorone levels of 228 mg/m3 (40 ppm) or

         Silverman et al. (1946) estimated the sensory threshold of a
    number of ketones including isophorone.  An average of 12 subjects of
    both sexes were used for each solvent exposure.  The time of exposure
    was 15 min.  Irritation of the eyes, nose and throat was experienced
    at 142.7 mg/m3 (25 ppm) isophorone; the highest concentration
    considered acceptable by the majority of subjects for an 8-h exposure
    was 57.1 mg/m3 (10 ppm).

         A NIOSH health hazard evaluation (US NIOSH, 1980) conducted at a
    screen printing process in 1980 found that the workshift (6´ h)
    average exposures of printers to isophorone were 4 and 80 mg/m3

    (0.7 and 14 ppm).  Symptoms of respiratory tract and eye irritation
    reported by workers were attributed to the antistatic agent containing
    principally isophorone.

         Amoore & Hautala (1983) reported an air odour threshold for
    isophorone of 1.14 mg/m3 (0.2 ppm).  The "odour safety factor",
    which was defined as the threshold limit value 28.5 mg/m3 (5 ppm)
    divided by the odour threshold, was 25.  From the magnitude of this
    value the authors predicted that 50% of exposed persons would perceive
    sensory warning of the TLV (28.5 mg/m3, 5 ppm).

    8.4  Chronic toxicity and carcinogenicity

         No long-term surveys have been carried out on occupationally
    exposed workers or other potentially exposed populations.


    9.1  Microorganisms

         Yoshioka et al. (1985) studied the acute toxicity of isophorone
    in  Tetrahymena pyriformis.  The EC50 after a 24-h exposure was
    420 mg/litre.  Yoshioka et al. (1986) found that the EC50 in the
    Activated Sludge Respiration Inhibition Test was 100 mg/litre.

         In a 2-day laboratory test with the marine red alga  Champia
     parvula, 38.3 mg isophorone/litre caused 50% reduction in cystocarp
    formation.  Above 138.5 mg/litre no cystocarps were formed, indicating
    absence of sexual reproduction.  In a 2-week laboratory test,
    107.3 mg/litre completely inhibited cystocarp formation (Thursby &
    Steele, 1986).

         Isophorone was tested in air-saturated media with  Saccharomyces
     cerevisiae at concentrations of 0.272 to 113.7 mg/litre
    (1.97-824 µmol/litre).  These produced no detectable effect on the
    rate of yeast respiration as measured with a dissolved oxygen
    electrode (Haubenstricker et al., 1990b).

    9.2  Aquatic organisms

         The acute toxicity of isophorone to fish, crustaceans and algae
    is summarized in Table 6.  With the exception of  Mysidopsis bahia
    (US EPA, 1978) all acute LC50 values were above 100 mg/litre,
    indicating a relatively low aquatic toxicity.  This was consistent
    with the results of a subacute (14 day) study with the marine red alga
     Champia parvula.  The toxicity of isophorone was determined by means
    of various biological end-points, namely vegetative growth, formation
    of tetrasporangia (asexual reproduction) and production of cystocarps
    (sexual reproduction).  Depending on the toxicological end-point, the
    lowest concentration resulting in a significant difference from
    controls ranged between 50 and 138 mg/litre (Thursby et al., 1985).

         In addition to the results of acute toxicity tests shown in Table
    6, an early life stage toxicity test was conducted with the freshwater
    fathead minnow  Pimephales promelas (Cairns & Nebeker, 1982) using
    concentrations of 11, 19, 30, 56 and 112 mg isophorone/litre. 
    Survival was affected at a concentration of 112 mg/litre, but not at
    56 mg/litre or less; fork length was affected at 30 mg/litre but not
    at 19 mg/litre or less; body weight gain was decreased at 19 mg/litre
    or more but not at 11 mg/litre.  The authors calculated a no-observed-
    effect concentration of 14 mg/litre.  Using the same test with the
    same species, Lemke et al. (1983) found a no-observed-effect level of
    19.5 mg/litre, and in an interlaboratory (6 laboratories) comparison
    no-observed-effect levels of up to 45.4 mg/litre were found (Lemke,

    9.3  Terrestrial organisms

         No data are available concerning the effects of isophorone on
    terrestrial organisms.

        Table 6.  Acute toxicity of technical isophorone to aquatic species
    Test species                  Parameter                Duration       Static/flowa        Resultsb            Reference
                                                           (h)                                (mg/litre)


    Bluegill sunfish              LC50                     96             static              220 (n)             US EPA (1978)
     (Lepomis macrochirus)        LC50                     24             static              240 (n)             Buccafusco et al. (1981)

    Fathead minnow                LC50                     96             flow                145-255 (m)         Cairns & Nebeker (1982)
     (Pimephales promelas)        LC50                     96                                 228                 Geiger et al. (1990)

    Golden orfe                   LC50                     72                                 204                 Scheubel & Scholz (1989)
     (Leuciscus idus melanotus)

    Sheepshead minnow             LC50                     96                                 140                 Ward et al. (1981)
     (Cyprinodon variegatus)      LC50                     96             static              > 170, < 300 (n)    Heitmuller et al. (1981)


    Brine shrimp                  LC50                     24                                 430                 Price et al. (1974)
     (Artemia salina)

    Mysid shrimp                  LC50                     96             static              12.9                US EPA (1978)
     (Mysidopsis bahia)

    Water flea                    immobilization: EC50     24             static              430 (n)             LeBlanc (1980)
     (Daphnia magna)              Immobilization: EC50     24             static              254-277             Scholz (1988a)
                                  immobilization: EC50     48             static              120 (n)             LeBlanc (1980)
                                  immobilization: EC50     48             static              117                 US EPA (1978)


    Selenastrum capricornutum     cell count: EC50         96             static              122                 US EPA (1978)
                                  chlorophyll: EC50        96             static              126                 US EPA (1978)

    Table 6 (cont'd)
    Test species                  Parameter                Duration       Static/flowa        Resultsb            Reference
                                                           (h)                                (mg/litre)

    Skeletonema costatum          cell count: EC50         96             static              105                 US EPA (1978)
                                  chlorophyll: EC50        96             static              110                 US EPA (1978)

    Scenedesmus subspicatus       cell count: EC50         72                                 475-476             Scholz (1988b)
                                  chlorophyll: EC50        72                                 524-527             Scholz (1988c)

    Red alga                      reproduction EC50        24                                 38.3                Thursby & Steele (1986)
     (Champia parvula)

    a  static = static exposure; flow = flow-through exposure
    b  n = nominal exposure concentration; m = measured exposure concentration


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    1.  Résumé et évaluation

    1.1  Propriétés physiques et chimiques

         L'isophorone est un liquide incolore d'odeur mentholée.  Elle est
    soluble dans l'eau (12 g/litre) et miscible à la plupart des solvants
    organiques.  Son point de congélation est de -8,1°C et son point
    d'ébullition de 215°C.  San tension de vapeur à 20°C est de l'ordre
    40 Pa et sa densité de vapeur par rapport à l'air est de 4,7.  C'est
    une substance stable.

         L'isophorone de qualité technique  vendue dans le commerce
    contient 1 à 3% d'isomère ß-(3,5,5-triméthyl-3-cyclohexène-1-one); la
    somme des isomères alpha et ß-dépasse 99%.

    1.2  Production et usage

         L'isophorone est largement utilisée comme solvant pour un grand
    nombre de résines et de polymères de synthèse ainsi que dans certaines
    peintures spéciales et certaines encres d'imprimerie.  Elle joue le
    rôle de produit intermédiaire en synthèse et on l'utilise comme
    solvant dans certaines formulations de pesticides.

         On estime qu'en 1988, la production mondiale d'isophorone était
    de l'ordre de 92 000 tonnes par an.

    1.3  Transport, distribution et transformation dans l'environnement

         L'isophorone peut pénétrer dans l'environnement du fait de son
    utilisation par de nombreuses industries, lors du rejet de déchets ou
    d'eaux usées et par suite de son utilisation comme solvant, notamment
    dans les formulations de pesticides.  Une fois libérée dans l'eau ou
    le sol, sa volatilisation et sa biodégradation entraînent une baisse
    de la concentration.  L'isophorone présente dans l'atmosphère en est
    éliminée par des processus photochimiques avec une demi-vie estimative
    d'environ 30 minutes (selon un modèle mathématique).  On a constaté
    que la biodécomposition de l'isophorone atteignait environ 70% dans
    les 14 jours et 95% dans les 28 jours.  Les résultats des études de
    biodécomposition sont variables et limités.  D'après la solubilité
    dans l'eau, les coefficients d'adsorption au sol et la polarité de ce
    composé, il paraît improbable qu'il soit adsorbé en quantité notable
    sur les matières solides en suspension et les sédiments.

         Bien qu'on ait trouvé de l'isophorone dans des tissus pisciaires,
    les données concernant ce composé et notamment ses propriétés
    physiques et chimiques, incitent à penser qu'il a peu de chances de
    subir une bioconcentration.  On a mesuré une demi-vie d'un jour chez
    une espèce de poisson.

    1.4  Concentrations dans l'environnement et exposition humaine

         On n'a pas procédé au dosage de l'isophorone dans l'air ambiant. 
    On a fait état d'une concentration d'isophorone dans des cendres
    volantes de houille égale à 490 µg/kg.  On a également mis en évidence
    la présence d'isophorone dans des eaux de surface (0,6 à 3 µg/litre),
    des eaux souterraines (10 µg/litre), des eaux de ruissellement
    urbaines (10 µg/litre) et des eaux de lessivage de décharge
    (29 µg/litre).

         De l'isophorone a été trouvée à la concentration de 100 µg/litre
    dans des eaux usées industrielles.  Après un traitement secondaire
    classique, la concentration d'isophorone dans l'effluent était tombée
    à 10 µg/litre.

         La présence d'isophorone a été observée dans des sédiments
    lacustres (0,6 à 12 µg/kg de poids sec) ainsi que dans les tissus de
    plusieurs espèces de poisson à des concentrations allant jusqu'à
    3,61 µg/kg de poids frais.

         On n'a pas constaté la présence d'isophorone dans les parties
    comestibles de plants de haricots, de riz ou dans des betteraves à
    sucre, après application sous la forme de véhicule pour pesticide.

    1.5  Cinétique et métabolisme chez les animaux de laboratoire et

         Des études de distribution effectuées sur des rats au moyen de
    14C-isophorone ont montré que 93% de la radioactivité administrée
    par voie orale, réapparaissaient principalement dans les urines et
    l'air expiré au bout de 24 heures.  Les organes dans lesquels
    subsistait au bout de cette période la plus forte concentration
    d'isophorone étaient le foie, les reins et les glandes préputiales.

         Après administration par voie orale d'isophorone à des lapins, on
    a retrouvé dans l'urine de ces derniers des métabolites résultant
    d'une oxydation du groupe méthyle en position 3, de la réduction du
    groupe carbonyle et de l'hydrogénation de la double liaison du cycle
    cyclohexénique; ces métabolites ont été éliminés tels quels ou sous
    forme de glucuronides dans le cas des alcools.

         Les valeurs de la DL50 percutanée indiquent que l'isophorone
    passe rapidement à travers la peau.

    1.6  Effets sur les mammifères de laboratoire et les systèmes
         d'épreuves in vitro

         La toxicité aiguë de l'isophorone est faible, les valeurs de
    DL50 par voie orale étant > 1500 mg/kg chez le rat, à > 2200 mg/kg
    chez la souris et à > 2000 mg/kg chez le lapin.  On a obtenu pour la
    DL50 par voie percutanée des valeurs de 1700 mg/kg chez le rat et de

    > 1200 mg/kg chez le lapin.  Au niveau cutané les effets aigus d'une
    exposition vont, chez le rat et le lapin, d'un léger érythème à la
    formation de croûtes.  On a signalé une conjonctivite et des lésions
    cornéennes après instillation directe dans l'oeil ou exposition à de
    fortes concentrations d'isophorone.  Le test de Magnusson-Kligman
    pratiqué sur des cobayes n'a pas permis de mettre en évidence un effet
    de sensibilisation cutanée.

         Les études de toxicité aiguë et celles au cours desquelles on a
    administré de l'isophorone par voie orale pendant de brèves périodes à
    des rongeurs ont montré qu'à fortes doses (> 1000 mg/kg), ce
    composé provoquait des effets dégénératifs au niveau du foie ainsi
    qu'une dépression du système nerveux central et une certaine
    mortalité.  Lors d'études de 90 jours, on a évalué à 500 mg/kg de
    poids corporel, la dose quotidienne sans effets observables pour le
    rat et la souris.  Une autre étude de 90 jours, au cours de laquelle
    on a administré de l'isophorone par voie orale à des chiens beagle (en
    nombre limité), n'a révélé aucun effet à des doses quotidiennes allant
    jusqu'à 150 mg/kg de poids corporel.

         Lors d'études de toxicité aiguë au cours desquelles on a fait
    inhaler pendant de brèves périodes de l'isophorone aux animaux de
    laboratoire, on a observé une irritation oculaire et respiratoire, des
    effets hématologiques et une diminution du poids corporel.  Etant
    donné que la conception de ces études laissait à désirer, il n'a pas
    été possible de déterminer la dose sans effets observables et on ne
    peut en tirer aucune conclusion en ce qui concerne la santé humaine.

         L'isophorone ne provoque pas de mutations géniques chez les
    bactéries ni d'aberrations chromosomiques  in vitro; on n'observe pas
    non plus de réparation de l'ADN dans des cultures primaires
    d'hépatocytes de rat, ni la présence de micro-noyaux dans des cellules
    de moelle osseuse de souris.  Des effets positifs ont été observés,
    lors d'essais de mutagénèse, sur des cellules de lymphomes murins
    L5178Y TK +/-, mais uniquement en l'absence d'un système métabolique
    exogène.  Le même phénomène a été observé en ce qui concerne les
    échanges de chromatides soeurs.  L'isophorone a produit une
    transformation morphologique  in vitro, mais là encore, en l'absence
    de système métabolique exogène.  En revanche, elle n'a pas produit de
    mutations létales récessives liées au sexe chez la drosophile.  Les
    données de mutagénicité ont un poids expérimental suffisant pour qu'on
    puisse soutenir que l'isophorone n'est pas un composé qui réagit
    énergiquement avec l'ADN.  D'ailleurs, lors d'une épreuve  in vivo,
    on n'a pas observé de lésion de l'ADN dans des cellules hépatiques et
    rénales (alors que ces organes sont ceux où l'on observe des lésions
    dans les épreuves de cancérogénicité).

         Les études toxicologiques au cours desquelles on a administré
    pendant une longue période de l'isophorone par voie orale à des souris
    et à des rats ont révélé la présence de plusieurs lésions rénales
    prolifératives chez les rats males, comprenant une néphropathie, une

    hyperplasie tubulaire et une faible incidence des adénomes affectant
    les tubules et des adénocarcinomes.  Il est admis que l'accumulation
    d'alpha2u-globuline joue un rôle dans l'étiologie de ces lésions. 
    Etant donné que l'on n'a pas décelé chez l'homme la présence
    d'alpha2u-globuline en quantités appréciables, il ne semble pas que
    ce type de cancérogénèse soit à envisager dans l'espèce humaine.  Chez
    cinq rats males soumis à des fortes doses d'isophorone, on a observé
    des carcinomes de la glande préputiale, et deux adénomes de la glande
    clitoridienne ont été observés chez les rattes soumises à de faibles
    doses d'isophorone.  Là encore, il est possible que l'accumulation
    d'alpha2u-globuline soit en cause.  On a également attribué à
    l'isophorone la présence d'un certain nombre de lésions néoplasiques
    du foie, des téguments et du système lymphoréticulaire, observées chez
    les rats males, de même d'ailleurs que des lésions bénignes du foie et
    du cortex surrénalien, lésions qui n'ont cependant pas été observées
    chez les souris femelles.

         La seule étude d'inhalation à long terme dont on connaisse les
    résultats chez le rat et le lapin, a permis d'observer une irritation
    de la muqueuse oculaire et de la muqueuse nasale et des altérations au
    niveau pulmonaire et hépatique, à une dose de approx.1427 mg/m3
    (environ 250 ppm).  Toutefois ces résultats peuvent s'expliquer par le
    fait que les études en question n'offraient pas toutes les garanties
    de rigueur.

         Des études très limitées effectuées sur des rats et des souris
    indiquent que l'isophorone n'affecte pas la fécondité ni le
    développement chez les animaux de laboratoire.

         Le fait qu'une dépression du système nerveux central se produise
    chez les animaux de laboratoire par suite d'exposition à de
    l'isophorone, pourrait être le signe d'un effet neurotoxique.  Lors
    d'une épreuve comportementale de nage désespérée, l'isophorone a
    également produit un effet positif.

    1.7  Effets sur l'homme

         On peut déceler une odeur d'isophorone à une concentration ne
    dépassant pas 1,14 mg/m3 (0,2 ppm).  A des concentrations
    inférieures à 28,55 mg/m3 (5 ppm), on a signalé une irritation des
    yeux, du nez et de la gorge; au-delà de 1142 mg/m3 (200 ppm) on a
    fait état de nausées, de maux de tête, d'étourdissements, de faiblesse
    et de sensation ébrieuse.

    1.8  Effets sur les autres êtres vivants au laboratoire et dans leur
         milieu naturel

         En ce qui concerne les effets aigus sur un certain nombre
    d'espèces marines ou dulçaquicoles, on possède plusieurs valeurs de la
    CL50.  Les valeurs de CE50 à 96 heures (basées sur la numération
    cellulaire et la chlorophylle) s'échelonnent de 105 à 126 mg/litre.

    Pour  Daphnia magna, les valeurs de la CL50 à 48 heures vont de 177
    à 120 mg/litre et pour les poissons d'eau douce; celles de la CL50 à
    96 heures s'étagent de 145 à 255 mg/litre.

         Les valeurs de la CL50 à 96 heurs pour les invertébrés marins
    vont de 12,9 à 430 mg/litre et pour une espèce de poisson de mer,
    cette valeur se situe entre 170 et 300 mg/litre.  Les données fournies
    par les études au cours desquelles on a utilisé des concentrations
    mesurées ne diffèrent pas de celles où ce sont les concentrations
    nominales dont on s'est servi.  Les épreuves effectuées par différents
    laboratoire sur  Pimephales promelas ont fait ressortir, pour la dose
    sans effets nocifs observables, des valeurs allant de 14 à
    45,4 mg/litre.

         Les données disponibles incitent à penser que l'isophorone n'est
    que faiblement toxique pour les organismes aquatiques.

    2.  Conclusions

    2.1  Population générale

         L'isophorone est utilisée comme solvant pour les résines, les
    polymères et certaines formulations de pesticides.  Il peut y avoir
    exposition par voie cutanée ou respiratoire, mais il y a de grandes
    chances pour qu'elle reste minime.  Les données disponibles montrent
    que l'isophorone peut être présente à des concentrations de l'ordre du
    µg/litre (ou par kg) dans l'eau de boisson et dans le poisson.  Les
    études expérimentales ayant montré que ce composé était faiblement
    toxique et du fait que l'exposition aux sources d'isophorone présentes
    dans l'environnement est peu importante, on peut considérer que le
    risque pour la population générale est minime.

    2.2  Exposition professionnelle

         Faute de contrôles techniques suffisants et de mesures d'hygiène
    industrielle convenables, il est possible que l'exposition
    professionnelle à l'isophorone dépasse les limites acceptables et
    provoque une irritation oculaire, cutanée ou respiratoire.  A plus
    fortes concentrations, d'autres effets nocifs peuvent se produire.  Le
    groupe de travail ne disposait pas d'études sur les effets à long
    terme de ce composé chez les ouvriers.

    2.3  Environnement

         Il est possible que l'isophorone soit libérée dans
    l'environnement lorsqu'on l'utilise comme véhicule de pesticides et du
    fait de son emploi généralisé comme solvant.  On en a trouvé de
    faibles concentrations dans plusieurs compartiments du milieu, mais sa
    persistance est faible par suite des processus de biodécomposition,

    volatilisation et oxydation photochimique qu'elle subit.  D'après les
    données disponibles, il semble que l'isophorone soit peu toxique pour
    les organismes aquatiques.

    3.  Recommandations

    3.1  Protection de la santé humaine et de l'environnement

         Des précautions sont à prendre pour éviter la pollution des eaux
    souterraines et de l'air.

         Les travailleurs qui sont employés à la production d'isophorone
    doivent se prémunir contre l'exposition à ce composé grâce à des
    mesures de contrôle technique suffisantes et à des précautions
    d'hygiène industrielle appropriées.  L'exposition professionnelle doit
    rester dans des limites acceptables et être régulièrement contrôlée.

    3.2  Recherches futures

    a)   Surveillance médicale des travailleurs exposés.

    b)   Détermination de la concentration effective d'isophorone dans les
         eaux à l'entour des zones industrielles.

    c)   Etudes d'inhalation satisfaisantes à court et à long terme sur
         des animaux de laboratoire afin de déterminer les limites de
         sécurité pour l'exposition professionnelle.

    d)   Nécessité d'obtenir des données sur la biodécomposition anaérobie
         de l'isophorone, notamment du fait qu'on en a observé la présence
         dans les lixiviats de décharges.


    1.  Resumen y evaluación

    1.1  Propiedades físicas y químicas

         La isoforona es un líquido incoloro con un olor parecido al de la
    menta.  Es soluble en agua (12 g/litro) y se mezcla con la mayoría de
    disolventes orgánicos.  Su punto de congelación es -8,1°C y su punto
    de ebullición 215°C.  Su presión en vapor a 20°C es del orden de
    40 Pa, y su densidad en vapor (aire = 1) es 4,7.  Es una sustancia

         Las muestras comerciales de isoforona de calidad técnica
    contienen 1-3% del isómero ß-isoforona (3,5,5-trimetil-3-ciclo-
    hexeno-1-1); la suma de isómeros alpha y supera el 99%.

    1.2  Producción y utilización

         La isoforona se utiliza mucho como disolvente para cierto número
    de resinas y polímeros sintéticos, así como en pinturas y tintas de
    imprenta para aplicaciones especiales.  Es también un producto químico
    intermedio y un disolvente en determinadas formulaciones de

         Se ha estimado que en 1988 su producción mundial fue del orden de
    92 000 toneladas.

    1.3  Transporte, distribución y transformación en el medio ambiente

         La isoforona puede introducirse en el medio ambiente teniendo
    como procedencia numerosas industrias, la evacuación de desechos y de
    aguas residuales y a raíz de su utilización como disolvente y como
    portador de plaguicida.  Tras su descarga en el agua o el suelo, la
    concentración ambiental disminuye a consecuencia de la volatilización
    y la biodegradación.  La isoforona de la atmósfera se elimina por
    procesos fotoquímicos con una semivida estimada de unos 30 minutos
    (sobre la base de un modelo matemático).  En una prueba de estimación,
    la isoforona se biodegradó hasta aproximadamente un 70% en 14 días y
    un 95% en 28 días.  Los resultados de los estudios de biodegradación
    son variables y limitados.  Los coeficientes de solubilidad en agua y
    de adsorción en el suelo y la polaridad indican que es improbable que
    tenga lugar una adsorción significativa por sólidos en suspensión y

         Aunque se ha hallado isoforona en tejidos de peces, los datos y
    las propiedades fisicas y químicas parecen indicar que es improbable
    una bioconcentración significativa.  Se ha medido una semivida de un
    día en una única especie de peces.

    1.4  Niveles ambientales y exposición humana

         No se ha medido isoforona en el aire ambiente.  Se ha notificado
    una concentración de isoforona en ceniza volátil de carbón de
    490 µg/kg.  Se ha identificado isoforona en aguas superficiales (0,6 a
    3 µg/litro), en aguas subterráneas (10 µg/litro), en aguas de
    escorrentía urbanas (10 µg/litro) y en lixiviado de terraplenados
    (29 µg/litros).

         Se ha hallado isoforona en aguas residuales industriales en una
    concentración de 100 µg/litro.  Tras un tratamiento secundario
    clásico, la concentración de isoforona en el efluente fue de
    10 µg/litro.

         Se ha identificado isoforona en sedimentos lacustres (0,6 a
    12 µg/kg de peso en seco) y en los tejidos de varias especies de peces
    en concentraciones de hasta 3,61 mg/kg de peso en húmedo.

         No se detectó isoforona en las partes comestibles de las plantas
    del frijol, del arroz o de la remolacha azucarera tras la aplicación
    de un portador de plaguicida.

    1.5  Cinética y metabolismo en animales de laboratorio y en el ser

         Los estudios de distribución en ratas utilizando 14C-isoforona
    mostraron que el 93% de la radiactividad administrada por vía oral
    aparecía principalmente en la orina y el aire espirado en 24 horas. 
    Los tejidos que retuvieron la mayor concentración tras ese periodo
    fueron el hígado, los riñones y las glándulas prepuciales.

         Los metabolitos tras administración oral de isoforona
    identificados en la orina de conejos fueron resultado de la oxidación
    del grupo 3-metilo, la reducción del grupo keto y la hidrogenación del
    enlace doble del anillo de ciclohexeno, y se eliminaron como tales o
    como derivados de glucuronida en el caso de los alcoholes.

         Los valores de la DL50 percutáneas indican que la isoforona se
    absorbe rápidamente a través de la piel.

    1.6  Efectos en mamíferos de laboratorio y en sistemas de prueba in

         La toxicidad aguda de la isoforona es baja, con valores de DL50
    oral > 1500 mg/kg en la rata, > de 2200 mg/kg en el ratón y
    > 2000 mg/kg en el conejo.  Los valores de la DL50 cutáneas fueron
    1700 mg/kg en la rata y > 1200 mg/kg en el conejo.  Los efectos
    agudos por exposición cutánea en ratas y conejos oscilaron entre
    eritema leve y escaras.  Se han notificado casos de conjuntivitis y

    lesión corneana tras la aplicación directa al ojo o la exposición a
    concentraciones elevadas de isoforona, pero ningún caso de
    sensibilización de la piel en cobayos utilizando la prueba Magnusson-

         En estudios de administración por vía oral sobre efectos agudos y
    a corto plazo a roedores en dosis altas (> 1000 mg/kg) se
    observaron efectos degenerativos en el hígado, así como depresión del
    sistema nervioso central y algunas defunciones.  En estudios de 90
    días, se determinó un NOEL en ratas y ratones de 500 mg/kg de peso
    corporal por día.  En un estudio de administración por vía oral de 90
    días a perros pachón (en número limitado) no se apreciaron efectos en
    dosis de hasta 150 mg/kg de peso corporal por día.

         En los experimentos examinados de inhalación aguda y a corto
    plazo, se observaron irritación ocular y respiratoria, efectos
    hematológicos y reducción del peso corporal.  Como el diseño de los
    estudios era inadecuado, no pudo determinarse NOEL y no puede hacerse
    ninguna deducción con respecto a la salud humana.

         La isoforona no induce mutaciones genéticas en bacterias,
    aberraciones cromosómicas  in vitro, reparación del ADN en los
    hepatocitos primarios de la rata, ni micronúcleos de médula ósea en
    los ratones.  Se observaron efectos positivos únicamente en ausencia
    de un sistema metabólico exógeno en valoraciones L5178Y TK+/- de los
    mutagénesis de linfoma del ratón, así como en una valoración de
    intercambio de cromátides hermanos.  La isoforona indujo
    transformación morfológica  in vitro en ausencia de un sistema
    metabólico exógeno.  No indujo mutaciones recesivas letales ligadas al
    sexo en  Drosophila.  El peso probatorio de conjunto de datos sobre
    mutagenicidad avala la tesis de que la isoforona no es un potente
    compuesto ADN-reactivo.  En una valoración  in vivo no se observó
    enlace con el ADN en el hígado y los riñones (órganos afectados en las
    biovaloraciones de carcinogenicidad).

         En estudios de toxicidad por administración oral a largo plazo en
    ratones y ratas, las ratas macho mostraron varias lesiones del riñón,
    incluidas nefropatía, hiperplasia de las células tubulares y una baja
    incidencia de adenomas y adenocarcinomas de ese tipo de células.  Se
    ha reconocido el papel que desempeña la acumulación de
    alpha2u-globulina en la etiología de estas lesiones.  Como no se han
    detectado cantidades significativas de alpha2u-globulina en el
    hombre, este mecanismo de carcinogénesis no parece ser importante en
    la especie humana. Se observaron carcinomas de la glándula prepucial
    en cinco ratas macho sometidas a dosis elevadas y dos adenomas de la
    glándula clitorídea en ratas hembra expuestas a bajas dosis de
    isoforona.  Estos tumores pueden estar relacionados también con la
    acumulación de alpha2u-globulina.  La exposición a la isoforona se
    asoció con algunas lesiones neoplásicas del hígado, y de los sistemas
    integumentario y linforreticular de los ratones macho, así como con

    lesiones no neoplásicas del hígado y de la corteza suprarrenal, pero
    esto no se observó en los ratones hembra a los que se administraron
    estas dosis.

         En el único estudio a largo plazo disponible sobre inhalación en
    ratas y conejos, se observaron irritación de los ojos y de la mucosa
    nasal, así como cambios pulmonares y hepáticos, a dosis de
    approx.1427 mg/m3 (approx. 250 ppm).  Sin embargo, estos resultados
    pueden haberse debido a las limitaciones del estudio.

         Estudios muy limitados en ratas y ratones indican que la
    isoforona no afecta a la fecundidad ni produce toxicidad para el
    desarrollo en los animales de experimentación.

         El hecho de que en los animales de experimentación se produzca
    depresión del sistema nervioso central podría indicar un posible
    efecto neurotóxico.  La isoforona también produjo un efecto positivo
    en la prueba de comportamiento de natación desesperada.

    1.7  Efectos en el ser humano

         El olor de la isoforona puede detectarse a concentraciones de
    sólo 1,14 mg/m3 (0,2 ppm).  Se ha observado irritación de los ojos,
    la nariz y la garganta a concentraciones inferiores a 28,55 mg/m3
    (5 ppm); y por encima de 1142 mg/m3 (200 ppm), náuseas, cefalea,
    vértigo, desmayo y embriaguez.

    1.8  Efectos en otros organismos en laboratorio y sobre el terreno

         No se dispuso de datos sobre animales terrestres.

         Se dispone de valores de LC50 agudos en varias especies de agua
    dulce y marinas.  Los valores EC50 en 96 horas (basados en recuento
    celular y clorofila) oscilan entre 105 y 126 mg/litro.  Los valores
    LC50 en 48 horas para Daphnia magna oscilan entre 117 y
    120 mg/litro, y los valores LC50 en 96 horas para peces de agua
    dulce, entre 145 y 255 mg/litro.

         Los valores de la LC50 en 96 horas para animales invertebrados
    marinos oscilan entre 12,9 y 430 mg/litro, y el valor de la LC50 en
    96 horas para una única especie de pez marino, entre 170 y
    300 mg/litro.  Los datos de estudios a concentraciones de exposición
    medida no fueron diferentes de los obtenidos en estudios a
    concentraciones nominales.  Los valores NOEL para Pimephales promelas
    sometidos a prueba en diferentes laboratorios oscilaron entre 14 y
    45,4 mg/litro.

         Los datos disponibles parecen indicar que la isoforona tiene una
    baja toxicidad para los organismos acuáticos.

    2.  Conclusiones

    2.1  Población general

         La isoforona se utiliza como disolvente para formulaciones de
    resinas, polímeros y plaguicidas.  Puede producirse una exposición
    cutánea y por inhalación, pero lo más probable es que sea
    insignificante.  Los datos muestran que la isoforona puede aparecer en
    concentraciones de µg/litro (kg) en el agua de bebida y en los peces. 
    En vista de la baja toxicidad en los estudios experimentales y de los
    bajos niveles de exposición a partir de fuentes ambientales, parece
    ser mínimo el riesgo para la población general.

    2.2  Exposición ocupacional

         A falta de controles técnicos adecuados y de medidas de higiene
    industrial, la exposición ocupacional a la isoforona puede superar los
    niveles aceptables y producir irritación ocular, cutánea y
    respiratoria.  En concentraciones superiores pueden producirse otros
    efectos sobre la salud.  El Grupo Especial no dispuso de estudios
    sobre los efectos a largo plazo en la salud de los trabajadores.

    2.3  El medio ambiente

         La isoforona puede pasar al medio ambiente tras su utilización
    como portador de plaguicida y su uso generalizado como disolvente.  Se
    han identificado concentraciones bajas en varios compartimientos
    ambientales, aunque tiene una baja persistencia ambiental a causa de
    los procesos de biodegradación, volatilización y oxidación
    fotoquímica.  Los datos disponibles parecen indicar que la isoforona
    tiene una baja toxicidad para los organismos acuáticos.

    3.  Recomendaciones

    3.1  Protección de la salud humana y del medio ambiente

         Hay que tener cuidado en prevenir la contaminación de las aguas
    subterráneas y del aire.

         Los trabajadores que fabrican o utilizan isoforona deben
    protegerse de la exposición a ésta por medio de controles técnicos y
    medidas de higiene industrial adecuados.  Su exposición ocupacional
    debe mantenerse dentro de niveles aceptables y vigilarse de forma

    3.2  Investigaciones ulteriores

    a)   Debe procederse a la vigilancia sanitaria de los trabajadores

    b)   Deben determinarse los niveles efectivos de isoforona en las
         aguas que rodean a las zonas industriales.

    c)   Deben realizarse estudios adecuados a corto y largo plazo sobre
         inhalación en animales de experimentación para determinar los
         niveles inocuos de exposición ocupacional.

    d)   Es necesaria información sobre la biodegradación anaerobia de la
         isoforona, especialmente por haberse identificado en la
         lixiviación de terraplenados.

    See Also:
       Toxicological Abbreviations
       Isophorone (HSG 91, 1995)
       Isophorone (ICSC)
       ISOPHORONE (JECFA Evaluation)