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    INTERNATIONAL PROGRAMME ON CHEMICAL SAFETY



    ENVIRONMENTAL HEALTH CRITERIA 154





    ACETONITRILE





    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.

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

    First draft prepared by Dr K. Hashimoto (Kanazawa University, Japan),
    Dr. K. Morimoto (National Institute of Hygienic Sciences, Japan) and
    Dr. S. Dobson (Institute of Terrestrial Ecology, Monks Wood
    Experimental Station, United Kingdom)

    World Health Orgnization
    Geneva, 1993


         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
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    toxicology. Other activities carried out by the IPCS include the
    development of know-how for coping 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

    Acetonitrile.

        (Environmental health criteria ; 154)

        1.Acetonitriles - adverse effects  2.Acetonitriles - toxicity
        3.Environmental exposure     I.Series

        ISBN 92 4 157154 3        (NLM Classification: QV 633)
        ISSN 0250-863X

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    CONTENTS

    ENVIRONMENTAL HEALTH CRITERIA FOR ACETONITRILE

    1. SUMMARY

         1.1. Properties, uses and analytical methods
         1.2. Environmental levels and sources of human exposure
         1.3. Environmental distribution and transformation
         1.4. Environmental effects
         1.5. Absorption, distribution, biotransformation and
               elimination
         1.6. Effects on laboratory mammals
         1.7. Effects on humans

    2. IDENTITY, PHYSICAL AND CHEMICAL PROPERTIES, AND
         ANALYTICAL METHODS

         2.1. Identity
         2.2. Physical and chemical properties
               2.2.1. Physical properties
               2.2.2. Chemical properties
         2.3. Conversion factors
         2.4. Analytical methods
               2.4.1. Determination of acetonitrile in ambient air
                       2.4.1.1  Sampling methods
                       2.4.1.2  Measurement of acetonitrile in
                                collected air samples
               2.4.2. Monitoring methods for the determination of
                       acetonitrile and its metabolites in
                       biological materials
                       2.4.2.1  Acetonitrile in urine
                       2.4.2.2  Acetonitrile in serum
                       2.4.2.3  Acetonitrile metabolites in tissues
                                and biological fluids

    3. SOURCES OF HUMAN AND ENVIRONMENTAL EXPOSURE

         3.1. Natural occurrence
         3.2. Anthropogenic sources
               3.2.1. Production levels and processes
               3.2.2. Uses

    4. ENVIRONMENTAL TRANSPORT, DISTRIBUTION AND TRANSFORMATION

         4.1. Transport and distribution between media
               4.1.1. Water
         4.2. Transformation
               4.2.1. Biodegradation
                       4.2.1.1  Water and sewage sludge
                       4.2.1.2  Soil
               4.2.2. Abiotic degradation
                       4.2.2.1  Water
                       4.2.2.2  Air

    5. ENVIRONMENTAL LEVELS AND HUMAN EXPOSURE

         5.1. Environmental levels
               5.1.1. Air
               5.1.2. Water and bottom sediment
               5.1.3. Food
               5.1.4. Tobacco smoke
               5.1.5. Other sources of exposure
         5.2. Occupational exposure
         5.3. Acetonitrile in various solvent products

    6. KINETICS AND METABOLISM IN LABORATORY ANIMALS AND HUMANS

         6.1. Absorption
               6.1.1. Human studies
               6.1.2. Experimental animal studies
                       6.1.2.1  Intake through inhalation
                       6.1.2.2  Dermal absorption
                       6.1.2.3  Intake via the gastrointestinal tract
         6.2. Distribution
               6.2.1. Human studies
               6.2.2. Experimental animal studies
         6.3. Biotransformation and elimination
               6.3.1. Human studies
               6.3.2. Experimental animal studies and
                        in vitro studies
                       6.3.2.1  Cyanide liberation from acetonitrile
                       6.3.2.2  The oxidative pathway of acetonitrile
                                metabolism
         6.4. Biological monitoring of acetonitrile uptake

    7. EFFECTS ON LABORATORY MAMMALS; IN VITRO TEST SYSTEMS

         7.1. Acute toxicity
               7.1.1. Single exposure
               7.1.2. Clinical observations
                       7.1.2.1  Effect on skin
                       7.1.2.2  Effect on the eyes
                       7.1.2.3  Effect on respiration
                       7.1.2.4  Effect on adrenals
                       7.1.2.5  Effect on the gastrointestinal tract
               7.1.3. Biochemical changes and mechanisms of
                       acetonitrile toxicity
                       7.1.3.1  Effect on cytochrome oxidase
                       7.1.3.2  Effect on glutathione
               7.1.4. Antidotes to acetonitrile
         7.2. Subchronic toxicity
               7.2.1. Inhalation exposure
               7.2.2. Subcutaneous administration
         7.3. Teratogenicity and embryotoxicity
         7.4. Mutagenicity
               7.4.1. Bacterial systems
               7.4.2. Yeast assays
               7.4.3.  Drosophila melanogaster
               7.4.4. Mammalian  in vivo assays
               7.4.5. Chromosome aberrations and sister chromatid
                       exchange
         7.5. Carcinogenicity
         7.6. Cytotoxicity testing

    8. EFFECTS ON HUMANS

         8.1. Acute toxicity
               8.1.1. Inhalation exposure
               8.1.2. Dermal exposure
               8.1.3. Oral exposure
         8.2. Chronic toxicity
         8.3. Mutagenicity and carcinogenicity
         8.4. Occupational exposure to cyanide
         8.5. Chronic poisoning by cyanides
               8.5.1. Ingestion

    9. EFFECTS ON OTHER ORGANISMS IN THE LABORATORY AND FIELD

         9.1. Microorganisms
         9.2. Aquatic organisms

    10. EVALUATION OF HUMAN HEALTH RISKS AND EFFECTS ON THE ENVIRONMENT

         10.1. Evaluation of human health risks
         10.2. Evaluation of effects on the environment

    11. RECOMMENDATIONS FOR THE PROTECTION OF HUMAN HEALTH

    12. FURTHER RESEARCH

    13. PREVIOUS EVALUATIONS BY INTERNATIONAL BODIES

    REFERENCES

    RESUME

    RESUMEN
    

    WHO TASK GROUP ON ENVIRONMENTAL HEALTH
    CRITERIA FOR ACETONITRILE

     Members

    Dr  R. Bruce, System Toxicants Assessment Branch, Office of Research
        and Development, Environmental Criteria and Assessment Office,
        US Environmental Protection Agency, Cincinnati, Ohio, USA
         (Joint Rapporteur)

    Dr  R.J. Bull, College of Pharmacy, Washington State University,
        Pullman, Washington, USA

    Dr  S. Dobson, Institute of Terrestrial Ecology, Monks Wood
        Experimental Station, Huntingdon, United Kingdom
         (Vice-Chairman)

    Dr  K. Hashimoto, Department of Hygiene, School of Medicine,   
        Kanazawa University, Kanazawa, Japan

    Dr  P. Lauriola, Local Hygiene Unit, Office of Public Hygiene,   
        Modena, Italy

    Dr  M. Lotti, Institute of Occupational Medicine, University of   
        Padua, Padua, Italy  (Chairman)

    Dr  K. Morimoto, Division of Biological Chemistry and Biologicals,
        National Institute of Hygienic Sciences, Tokyo, Japan  (Joint
         Rapporteur)

    Dr  Y.F. Panga, Department of Standard Setting, Chinese Academy of
        Preventive Medicine, Beijing, China

    Dr  S.A. Soliman, Department of Pesticide Chemistry, College of   
        Agriculture and Veterinary Medicine, King Saud University,
        Al-Qasseem, Bureidah, Saudi Arabia

     Secretariat

    Dr  B.H. Chen, International Programme on Chemical Safety,
        World Health Organization, Geneva, Switzerland  (Secretary)

    Dr  E. Smith, International Programme on Chemical Safety,
        World Health Organization, Geneva, Switzerland

                 

    a  Invited but unable to attend.

    NOTE TO READERS OF THE CRITERIA MONOGRAPHS

        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 kindly
    requested to communicate any errors that may have occurred to the
    Director of the International Programme on Chemical Safety, World
    Health Organization, Geneva, Switzerland, in order that they may be
    included in corrigenda.

                                   *  *  *

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

                                   *  *  *

        This publication was made possible by grant number
    5 U01 ES02617-14 from the National Institute of Environmental Health
    Sciences, National Institutes of Health, USA.

    WHO TASK GROUP ON ENVIRONMENTAL HEALTH
    CRITERIA FOR ACETONITRILE

        A WHO Task Group on Environmental Health Criteria for
    Acetonitrile met in Modena, Italy, from 24 to 28 November 1992.
    Mr Giorgio Baldini, the President of the Province of Modena, opened
    the meeting and greeted the participants on behalf of the Province
    of Modena.  Dr B.H. Chen of the International Programme on Chemical
    Safety (IPCS) welcomed the participants on behalf of the Director,
    IPCS, and the three IPCS cooperating organizations (UNEP/ILO/WHO). 
    The Task Group reviewed and revised the draft criteria monograph and
    made an evaluation of the risks for human health and the environment
    from exposure to acetonitrile.

        The first draft of this monograph was prepared by Dr K.
    Hashimoto, Kanazawa University, Japan, Dr K. Morimoto, National
    Institute of Hygienic Sciences, Japan, and Dr S. Dobson, Institute
    of Terrestrial Ecology, Monks Wood Experimental Station, United
    Kingdom.  The second draft was prepared by Dr K. Morimoto
    incorporating comments received following the circulation of the
    first draft to the IPCS Contact Points for Environmental Health
    Criteria monographs.  Dr M. Lotti (Institute of Occupational
    Medicine, University of Padua, Italy) made a considerable
    contribution to the preparation of the final text.

        Dr B.H. Chen and Dr P.G. Jenkins, both members of the IPCS
    Central Unit, were responsible for the overall scientific content
    and technical editing, respectively.  The efforts of all who helped
    in the preparation and finalization of the document are gratefully
    acknowledged.

                                   *  *  *

        Financial support for this Task Group meeting was provided by
    the Province of Modena, Communes of Mirandola and Medolla, Local
    Hygiene Units N. 16 of Modena and N. 15 of Mirandola, Association of
    Business and Industries of the Province of Modena and ENICHEM
    (National Organization of Industrialization for Chemistry) in Italy.

    ABBREVIATIONS

    CLD      chemiluminescence nitrogen detector
    GC       gas chromatography
    HPLC     high performance liquid chromatography
    NPD      nitrogen-phosphorus selective detector
    TCD      thermal conductivity detection
    TEA      thermal energy analyser

    1.  SUMMARY

    1.1  Properties, uses and analytical methods

        Acetonitrile (CH3CN) is a by-product of acrylonitrile
    manufacture.  It may also be formed by the combustion of wood and
    vegetation.  It is a liquid with an ether-like odour.  Acetonitrile
    is a volatile, highly polar  solvent used to extract fatty acids and
    animal and vegetable oils. It is used in the petrochemical industry
    in extractive distillation based on its selective miscibility with
    organic compounds.  It is used as a solvent for spinning synthetic
    fibres and in casting and moulding plastics.  In laboratories, it is
    widely used in high-performance liquid chromatographic (HPLC)
    analysis and as a solvent for DNA synthesis and peptide sequencing.

        The most widely used analytical technique for acetonitrile is
    gas chromatography.

    1.2  Environmental levels and sources of human exposure

        Very few data on acetonitrile levels in the environment are
    available.  Worldwide, acetonitrile concentrations in air of 200 to
    42 000 ng/m3 have been reported.  Slightly higher values were
    obtained for urban than rural air in one study.  Single measurements
    before and after burning of bush and straw showed a 10-fold increase
    in acetonitrile air concentration.

        Acetonitrile was not detected in 72 water samples from Japan but
    was found in 11 out of 60 aquatic sediment samples at
    concentrations between 0.02 and 0.54 mg/kg.  Acetonitrile has not
    been detected in food.

        Tobacco smoke contains acetonitrile and burning polyurethane
    foam releases acetonitrile and hydrogen cyanide.

        Whilst production of acrylonitrile offers the greatest potential
    for exposure, this is carried out in a closed system.  Practical
    uses of acetonitrile lead to greater exposure.

    1.3  Environmental distribution and transformation

        Acetonitrile volatilizes from water and would also volatilize
    from soil surfaces.  It is readily biodegraded by several strains of
    bacteria common in sewage sludge, natural waters and soil. 
    Acclimatization of bacteria to acetonitrile or petroleum wastes
    increases the rate of degradation.  Anaerobic degradation appears to
    be limited or absent.

        Hydrolysis of acrylonitrile in water is extremely slow.  There
    is no significant photodegradation in either water or the
    atmosphere.  Reaction with ozone is slow as is reaction with singlet
    oxygen.  The major mechanism for removal of acetonitrile from the
    troposphere is reaction with hydroxyl radicals;  residence times
    have been estimated at between 20 and 200 days.

        Acetonitrile does reach the stratosphere where it is
    characteristically associated in positive ion clusters in the upper
    regions.

    1.4  Environmental effects

        Acetonitrile has low toxicity to microorganisms (bacteria,
    cyanobacteria, green algae and protozoans) with thresholds at
    500 mg/litre or more.  Freshwater invertebrates and fish acute
    LC50s are 700 mg/litre or more.  Acute tests have been conducted
    under static conditions without analytical confirmation of
    concentrations.  Similar results obtained from 24- and 96-h tests
    suggest volatilization of acetonitrile.

    1.5  Absorption, distribution, biotransformation and elimination

        Acetonitrile is readily absorbed from the gastrointestinal
    tract, through the skin and the lungs.  All three routes of exposure
    have been reported to lead to systemic effects.

        Postmortem examination of tissues from poisoned humans has
    revealed that acetonitrile distributes throughout the body.  This is
    supported by animal studies in which acetonitrile distribution has
    been found to be fairly uniform throughout the body.  There are no
    indications of accumulation in animal tissues following
    repeated administrations of acetonitrile.

        There are substantial data to suggest that most of the systemic
    toxic effects of acetonitrile are mediated through its metabolism to
    cyanide, which is catalysed by the cytochrome P-450 monooxygenase
    system.  Cyanide is subsequently conjugated with thiosulfate to form
    thiocyanate which is eliminated in the urine.  Peak concentrations
    of cyanide in the blood of rats following administration of near
    lethal doses of acetonitrile approximate to the concentrations
    observed following the administration of an LD50 dose of potassium
    cyanide.  However, the peak concentration of cyanide after
    administration of acetonitrile is delayed by up to several hours as
    compared to other nitriles.  Moreover, the more rapid rate at which
    cyanide is produced in the mouse appears to account for the much
    greater sensitivity of this species to the toxic effects of
    acetonitrile.  Cyanide and thiocyanate have been identified in human
    tissues after exposure to acetonitrile.  A portion of the
    acetonitrile dose is also eliminated unchanged in expired air and in
    urine.

    1.6  Effects on laboratory mammals

        Acetonitrile induces toxic effects similar to those observed in
    acute cyanide poisoning, although the onset of symptoms is some-what
    delayed compared to inorganic cyanides or other saturated nitriles. 
    The 8-h inhalation LC50 in male rats is 13 740 mg/m3 (7500 ppm). 
    The oral LD50 in the rat varies from 1.7 to 8.5 g/kg depending on
    the conditions of the experiment.  Mice and guinea-pigs appear to be
    more sensitive, with an oral LD50 in the range of 0.2-0.4 g/kg. 
    The main symptoms in animals appear to be prostration followed by
    seizures.

        Dermal application of acetonitrile causes systemic toxicity in
    animals and has been implicated in the death of one child.  The
    percutaneous LD50 in rabbits is 1.25 ml/kg.

        Subchronic exposure of animals to acetonitrile produces effects
    similar to those seen after acute exposures.

        Acetonitrile is not mutagenic in assays using  Salmonella
     typhimurium, both with and without metabolic activation.  It
    induces aneuploidy in a diploid yeast strain at very high
    concentrations. No animal studies on chronic or carcinogenic effects
    of acetonitrile have been reported.

    1.7  Effects on humans

        The levels causing toxicity in man are unknown but are
    probably in excess of 840 mg/m3 (500 ppm) in air.  Symptoms and
    signs of acute acetonitrile intoxication include chest pain,
    tightness in the chest, nausea, emesis, tachycardia, hypotension,
    short and shallow respiration, headache, restlessness,
    semiconsciousness, and seizures.  Other non-specific symptoms may be
    due to the irritant effects of the compound.  The systemic effects
    appear to be largely attributable to the conversion of acetonitrile
    to cyanide.  Blood cyanide and thiocyanate levels are elevated
    during acute intoxication.  Two fatalities after exposure to
    acetonitrile vapour in the workplace and one fatal case of a child
    ingesting an acetonitrile-containing cosmetic have been reported. 
    Elevated tissue cyanide concentrations were found in postmortem
    examin-ation of these cases.

        No epidemiological study of cancer incidence relating to
    acetonitrile exposure has been reported.

        Acetonitrile can cause severe eye burns.  Skin contact with
    liquid acetonitrile should be avoided.  An employee's exposure to
    acetonitrile in any 8-h shift has been recommended in many
    countries not to exceed a time-weighted average of 70 mg/m3 air
    (40 ppm).

    2.  IDENTITY, PHYSICAL AND CHEMICAL PROPERTIES, AND
        ANALYTICAL METHODS

    2.1  Identity

    Chemical formula:            CH3CN

    Chemical structure:

    CHEMICAL STRUCTURE 1

    Relative molecular mass:     41.05 

    CAS chemical name:           acetonitrile

    CAS registry number:         75-05-8

    Synonyms:                    cyanomethane, ethanenitrile, nitrile of
                                 acetic acid, methyl cyanide, ethyl
                                 nitrile, methanecarbonitrile

         Specifications for commercial acetonitrile are given in
    Table 1.  The principal organic impurity in commercial acetonitrile
    is propionitrile, although small amounts of allyl alcohol may also
    be present (Grayson, 1985).

    2.2  Physical and chemical properties

    2.2.1  Physical properties

         Acetonitrile is a volatile, colourless liquid with a sweet,
    ether-like odour (Grayson, 1985).  It is infinitely soluble in water
    and readily miscible with ethanol, ether, acetone, chloroform,
    carbon tetrachloride and ethylene chloride (Clayton & Clayton,
    1982).  It is immiscible with many saturated hydrocarbons (petroleum
    fractions) (Budavari, 1989).

         Important physical constants and properties of acetonitrile are
    summarized in Table 2.

    Table 1.  Commercial acetonitrile specificationsa

                                                                 

    Specific gravity (at 20 C)                       0.783-0.787

    Distillation range (C)
     initial point, minimum                               80.5
     end point, maximum                                   82.5

    Purity (minimum), % by weight                         99.0

    Acidity (as acetic acid, maximum % by weight)          0.05

    Copper (maximum), ppm                                  0.5

    Iron (maximum), ppm                                    0.5

    Water (maximum), % by weight                           0.3

    Colour (maximum), Pt-Co                                15
                                                                 

    a  From: Grayson (1985)

    2.2.2  Chemical properties

         Although acetonitrile is one of the most stable nitriles, it
    undergoes typical nitrile reactions and is used to produce many
    types of nitrogen-containing compounds.  It can be trimerized to
     S-trimethyltriazine and has been telomerized with ethylene and
    copolymerized with alpha-epoxides (Grayson, 1985).

         Acetonitrile produces hydrogen cyanide when heated to
    decomposition or when reacted with acids or oxidizing agents
    (Reynolds, 1982).

    2.3  Conversion factors

    1 ppm   = 1.68 mg/m3 (25 C, 760 mmHg)

    1 mg/m3 = 0.595 ppm (25 C, 760 mmHg)    (Clayton & Clayton, 1982)

        Table 2.  Physical properties of acetonitrile

                                                                                  

    Properties                 Value                   Reference

                                                                                  

    Appearance                 colourless liquid       Budavari (1989)

    Odour                      ether-like              Budavari (1989)

    Boiling point              81.6 C (760 mmHg)      Budavari (1989)

    Freezing point             -45.7 C                Grayson (1985)
                               -44 to -41 C           Verschueren (1983)

    Specific gravity           0.78745 (15/4 C)       Grayson (1985)
                               0.7138 (30/4 C)        Grayson (1985)

    Vapour density             1.42 (air = 1)          Clayton & Clayton (1982)

    Refractive index (ND)      1.34604 (15 C)         Clayton & Clayton (1982)
                               1.33934 (30 C)         Clayton & Clayton (1982)

    Solubility in water        infinitely soluble      Clayton & Clayton (1982)

    Vapour pressure
        at (15.5 C)           7.32 kPa (54.9 mmHg)    US EPA (1984)
        at (20.0 C)           (74.0 mmHg)             Verschueren (1983)
        at (30.0 C)           (115.0 mmHg)            Verschueren (1983)

    Water azeotrope            boiling point 76 C
                               water content 16%       US EPA (1984)

    Log P (octanol/water       -0.38                   Leo  et al. (1971)
     partition coefficient     -0.34                   Verschueren (1983)
                                                                                  

    Table 2 (contd)

                                                                                  

    Properties                 Value                   Reference

                                                                                  

    Flash point                5.6 C (open cup)       Reynolds (1982)
                               12.8 C (closed cup)    Reynolds (1982)

    Ignition temperature       524 C                  Sax & Lewis (1989)

    Explosive limits           lower 4.4               Grayson (1985)
     in air (% by volume)            3.05              Prager (1985)
                               upper 16.0              Grayson (1985)
                                     17.0              Prager (1985)
                                                                                  
    
    2.4  Analytical methods

    2.4.1  Determination of acetonitrile in ambient air

    2.4.1.1  Sampling methods

         The use of absorption tubes to trap acetonitrile from ambient
    air with subsequent thermal or liquid desorption prior to gas
    chromatographic (GC) analysis has been reported in many references. 
    The National Institute of Occupational Safety and Health (NIOSH,
    1977, 1984) recommended the use of a glass tube (9 cm long and 6 mm
    internal diameter) containing two sections of 20-40 mesh activated
    (600 C) coconut charcoal (front = 400 mg and back = 200 mg)
    separated by 3 mm section urethane foam and held in place with plugs
    of silanized glass wool.  The tube is then flame-sealed at both ends
    until it is used for air sampling.  Other sampling tubes containing
    different sorbents (i.e. porous polymer beads) have also been
    recommended (Campbell & Moore, 1979; Berg  et al., 1980; Rigby,
    1981; Kashihira, 1983; Kashihira  et al., 1984; Wood, 1985; Cobb
     et al., 1986).

    2.4.1.2  Measurement of acetonitrile in collected air samples

         Several methods have been used to measure acetonitrile in
    environmental samples.  Most of the reported methods are based on
    the use of GC.

    a)  Gas chromatography

         GC is frequently used for determining acetonitrile using
    different kinds of detectors in conjunction with the charcoal or
    porous polymer beads sampling technique.  A number of detectors have
    been recommended.  Until recently, almost all of the
    published work involved the use of flame ionization detection (FID). 
    However, it was found that FID did not respond to acetonitrile in a
    repeatable way even with the use of internal standards (Joshipura
     et al., 1983).

         Attention has therefore turned to the use of thermal
    conductivity detection (TCD) (Joshipura  et al., 1983) and to
    nitrogen-phosphorus selective detector, NPD (Cooper  et al., 1986). 
    Rounbehler  et al. (1982) described a modification for the thermal
    energy analyser (TEA), a highly sensitive nitrosyl-specific GC
    chemiluminescence detector, which allows it to be used as a highly
    selective one in detecting nitrogen-containing compounds.  They
    concluded that the modified TEA was as sensitive as the alkali-bead
    flame ionization detection (AFID) but had a much higher selectivity
    toward nitrogen-containing compounds.  Using the TEA, these
    investigators were not able to detect any acetonitrile in bacon or
    beer. Kashihira  et al. (1984) used a chemiluminescence nitrogen
    detector GC (CLD-GC) method to measure acetonitrile and

    acrylonitrile in air.  The method was able to detect as little as
    20 ng of acetonitrile per injection.

         Cooper  et al. (1986) developed a very sensitive method of
    measuring nitrogen-containing hazardous pollutants in complex
    matrices by GC with NPD and were able to detect 1.5 pg acetonitrile.

         Table 3 summarizes the different types of detectors used in GC
    analysis of acetonitrile along with the conditions employed and
    their corresponding detectability.

    b)  High-performance liquid chromatography (HPLC)

         The use of HPLC to determine trace amount of acetonitrile in
    environmental samples has not been reported.

    c)  Microwave spectrometry

         Kadaba  et al. (1978) analysed toxic constituents including
    acetonitrile in tobacco smoke by microwave spectroscopy and were
    able to measure acetonitrile down to 2 ppm.

    2.4.2  Monitoring methods for the determination of acetonitrile and
           its metabolites in biological materials

    2.4.2.1  Acetonitrile in urine

         Mckee  et al. (1962) determined acetonitrile in urine samples
    obtained from 20 male nonsmokers and 40 male smokers by a
    modification of the method reported by Rhoades (1958, 1960) for the
    analysis of coffee volatiles.  The modification permitted the
    stripping of urinary volatiles at 37 C and at reduced pressure. 
    The stripped volatiles were collected in a liquid nitrogen trap,
    vapourized, and analysed by GC with a thermal conductivity detector.
    The column, which was packed with 15% Carbowax 1500 and silicone oil
    200 (ratio 2:1) on 40-60 mesh Chromosorb P, was operated at 40 C. 
    The carrier gas was helium at a pressure of 4 pounds per square
    inch.  Acetonitrile concentrations as low as 2.9 g/litre could be
    measured in urine using this method.


        Table 3.  Gas chromatographic conditions for acetonitrile determination

                                                                                                                            

    Packing               Conditions                            Detection    Reported level of    References
                                                                             detectability
                                                                                                                            

    Porapak               250 x 0.25 cm, 160 C injector           FID       10 ppm in            Thomson (1969)
                          150 C helium, 70 ml/min                           acrylonitrile

    Porapak Q             122 x 0.63 cm, 180 C injector           FID       10 mg/m3 in air      NIOSH (1977)
                          270 C nitrogen, 50 ml/min                         (6 ppm)

    Porapak Q             305 x 0.32 cm, 200 C injector           FID       0.01 ppm in air      Campbell & Moore (1979)
                          200 C nitrogen, 20 ml/min

    0.1% SP 1000          200 x 0.19 cm, 35-235 C injector        FID       0.07 ppm in air      Berg et al. (1980)
    on Carbopack C        125 C nitrogen, 21 ml/min

    20% Carbowax          180 x 0.2 cm, 90-145 C injector         TEA       0.041 ppm            Rounbehler et al. (1982)
    20 M                  120 C

    Chromosorb 103        90 x 0.3 cm, 85 C injector              CLD       1 ppb in air         Kashihira et al. (1984)
                          150 C helium, 60 ml/min

    Porapak Q             508 x 0.32 cm, 170 C injector           FID       0.2 ppm in air       Wood (1985)
                          200 C nitrogen, 30 ml/min

    20% SP-1200W/0.1%     305 x 0.32 cm, 180 C injector           NPD       1.5 ppb              Cooper et al. (1986)
    Carbowax 1500         190 C nitrogen, 30 ml/min or
                          helium, 35 ml/min
                                                                                                                            

    FID = Flame ionization detection; CLD = Chemiluminescent nitrogen detection; NPD =
    Nitrogen-phosphorous detection; TEA = Thermal energy analyser
    

    2.4.2.2  Acetonitrile in serum

         Freeman & Hayes (1985a) determined serum acetonitrile
    concentrations in rats dosed orally with acetone, acetonitrile, and
    a mixture of acetone and acetonitrile by GC equipped with FID.  The
    analysis was performed isothermally (150 C) at a helium flow rate
    of 30 ml/min using a 2 mm x 1.22 m Chromosob 104 column (100/120
    mesh) with a 15-cm precolumn.  Propionitrile was added to the serum
    samples as an internal standard prior to injection, and the samples
    were injected directly into the column.  Under the conditions of
    this study, the retention times of acetone, acetonitrile and
    propionitrile were 2.05, 3.65 and 6.20 min, respectively.  The limit
    of detection was not reported.  However, it was reported that the
    serum acetonitrile concentrations of animals in the control group
    were all below 1 mg/litre.

    2.4.2.3  Acetonitrile metabolites in tissues and biological fluids

    a)  Cyanide

         Since hydrogen cyanide is a reactive and volatile nucleophile,
    a variety of problems are encountered in its assay in biological
    materials due to tissue binding or diffusibility (Troup &
    Ballantyne, 1987).  To reduce artefacts due to simple evaporative
    losses, cyanide should be extracted under alkaline conditions.

         Amdur (1959) determined the cyanide level in the blood of 16
    workers, who were accidentally exposed to acetonitrile, by the
    method of Feldstein & Klendshoj (1954), which uses a Conway
    microdiffusion approach (Conway, 1950).  The sensitivity of this
    method is as low as 0.1 g cyanide in a 1 ml sample.  Willhite &
    Smith (1981) measured cyanide concentrations in the liver and brain
    of mice challenged by acetonitrile using the method of Bruce  et al.
    (1955), which is capable of determining 0.05 g cyanide in a 1 ml
    sample.  Haguenoer  et al. (1975a,b) determined free cyanide in the
    tissues and urine of rats using the pyridine-benzidine method
    described by Aldridge (1944); the sensitivity of this method was
    0.7 g hydrogen cyanide in a 1 ml sample.  Ahmed & Farooqui (1982)
    determined the tissue and blood cyanide levels in rats by the Conway
    diffusion method described by Pettigrew & Fell (1973).  Willhite
    (1983) determined tissue cyanide level in hamsters by the procedure
    of Bruce  et al. (1955).  A combination of the aeration procedure
    of Bruce  et al. (1955) with the colorimetric method of Epstein
    (1947), which can determine 0.2 g of cyanide in a 1 ml sample, has
    been used to determine the cyanide level in brain (Tanii &
    Hashimoto, 1984a) and in liver microsomes of mice (Tanii &
    Hashimoto, 1984b).  The aeration apparatus consists of three serial
    tubes containing 25 ml 20% NaOH, 5 ml 20% trichloroacetic acid and
    0.5 ml 0.1 N NaOH.  An aliquot of samples is added to the tube
    containing trichloroacetic acid, which is then aerated at a flow
    rate of 600 ml/min, passing from the tube containing 20% NaOH for

    10 min toward the tube containing 0.1 N NaOH.  An aliquot from the
    tube containing 0.1N NaOH is then removed, neutralized with acetic
    acid and subjected to analysis for cyanide.  Under these conditions,
    the recovery of known amounts of cyanide is 97-100%.  Freeman &
    Hayes (1985a) determined cyanide in the blood of rats  by a
    microdiffusion method modified from Feldstein & Klendshoj (1954). 
    Samples were analysed colorimetrically at 586 nm using
    pyridine-barbituric acid reagent as described by Blanke (1976). 
    Cyanide concentrations as low as 0.1 mg/litre could be reproducibly
    detected by these methods.  Zamecnik & Tam (1987) reported an
    improved GC method for cyanide analysis in blood with acetonitrile
    as an internal standard.  GC with NPD was used with a 180 x 0.2 cm
    column packed with 100/120 mesh Porapak Q.  Other conditions were:
    temperature, column 120 C, detector 250 C, and a helium gas flow
    rate of 20 ml/min.  The blood samples containing cyanide were
    pipetted into disposable vials.  Samples were then sealed and
    glacial acetic acid was injected into the vials.  These were then
    vortexed and allowed to equilibrate for 30 min at room temperature. 
    The head space was injected into the gas chromatograph.  The typical
    retention times for the cyanide and acetonitrile peaks were 0.6 min
    and 2.5 min, respectively.  The sensitivity for cyanide was
    0.05 ppm.  Three procedures for the determination of cyanide in
    biological fluids have been reported with full detail (Rieders &
    Valentour, 1975).  The first procedure is qualitative, the second
    colorimetric (chloramine-T and barbituric acid and pyridine), and
    the third depends on GC using electron capture detection.

         Table 4 summarizes the methods which have been used for cyanide
    analysis in biological samples.

    b)  Thiocyanate

         Pozzani  et al. (1959a) determined urinary thiocyanate levels
    in various animals by means of the colorimetric method of Chesley
    (1941).  Using this method, 25-180 mg thiocyanate/litre urine could
    be measured with a  4% error.  Silver  et al. (1982) determined
    thiocyanate in the urine of rats dosed with acetonitrile. 
    Thiocyanate was first isolated from urine by separation on an ion
    exchange column (10 x 1 cm) of Amberlite CG-400 as described by
    Kanai & Hashimoto (1965) and then measured colorimetrically
    according to the method of Epstein (1947).  Willhite (1983)
    determined the tissue thiocyanate levels in hamsters using the
    method described by Bruce  et al. (1955).


        Table 4.  Analysis of cyanide in biological materials

                                                                                                                                         

                                    Analytical methods                                            Application

    Principle                  Detectability        References                   Biological materials        References
                                 (g/ml)
                                                                                                                                         

    Conway diffusion method         0.1        Feldstein & Klendshoj (1954)      human blood                 Amdur (1959)

                                    0.1        Pettigrew & Fell (1973)           rat tissues and blood       Ahmed & Farooqui (1982)

                                    0.1        Feldstein & Klendshoj (1954);     rat blood                   Freeman & Hayes (1985a)
                                               Blanke (1976)

    Benzidine and pyridine          0.1        Aldridge (1944)                   rat tissues and             Haguenoer et al.
    methods, colorimetry                                                         urine                       (1975a,b)

    Aeration procedure and          0.2        Bruce et al. (1955);              mouse brain                 Tanii & Hashimoto
    colorimetry                                Epstein (1947)                                                (1984a,b)

                                    0.05       Bruce et al. (1955)               mouse liver and brain       Willhite & Smith (1981)

                                    0.05       Bruce et al. (1955)               hamster tissues             Willhite (1983)

    GC, nitrogen-phosphorus         0.05               -                         blood                       Zamecnik & Tam (1987)
    detector
                                                                                                                                         
    

         Pereira  et al. (1984) used the method of Contessa & Santi
    (1973) to determine thiocyanate levels in urine samples collected
    from rats treated with different nitriles.  The method was able to
    detect thiocyanate concentrations as low as 100 g in a 0.2 ml urine
    sample.

         Table 5 summarizes the methods reported for analysis of
    thiocyanate in biological samples.


        Table 5.  Analysis of thiocyanate in biological materials

                                                                                                                                         

                                    Analytical methods                                            Application

    Principle                  Detectability        References                   Biological materials        References
                                 (g/ml)
                                                                                                                                         

    Colorimetry                    25          Chesley (1941)                    animal urine                Pozzani (1959a)

                                    0.6        Bruce et al. (1955)               hamster tissues             Willhite (1983)

    Ion exchange separation         0.5        Kanai & Hashimoto (1965);         rat urine                   Silver et al. (1982)
    and colorimetry                            Epstein (1947)
                                                                                                                                         
    

    3.  SOURCES OF HUMAN AND ENVIRONMENTAL EXPOSURE

    3.1  Natural occurrence

         Acetonitrile may be formed by combustion of wood, straw and
    other vegetation.  However, the rate of formation and the
    contribution to atmospheric acetonitrile has not been quantified
    (Becker & Ionescu, 1982).

    3.2  Anthropogenic sources

    3.2.1  Production levels and processes

         Acetonitrile is a by-product of acrylonitrile synthesis.  This
    process is known as the SOHIO (Standard Oil Company of Ohio) process
    and involves a high temperature catalytic reaction between propylene
    and ammonia.  The SOHIO process is the principal route to both
    acrylonitrile and acetonitrile, produced in the ratio of 0.035 kg
    acetonitrile/kg acrylonitrile (Lowenheim & Moran, 1975).

         Acetonitrile can be synthesized by several other routes.  Good
    yields are obtained by dehydration of an acetic acid and ammonia
    mixture, acetamide or ammonium acetate.

               CH3COOH + NH3 -> CH3CN + 2H2O
               CH3CONH2 -> CH3CN + H2O
               CH3CO2NH4 -> CH3CN + 2H20

         A 90% yield of acetonitrile is obtained by the reaction of
    ethanol and ammonia in the presence of catalyst such as Ag, Cu,
    MoO3, and ZnS at moderate temperatures.  Acetonitrile is also
    produced by the reaction of cyanogen chloride with methane, ketones,
    ethanol, alkylene epoxides, and paraffins or olefins.

         The principal organic impurity in commercial acetonitrile is
    propionitrile, together with a small amount of allyl alcohol (US
    EPA, 1992).

         Reported production of acetonitrile in the USA during the
    period 1980-83 (US EPA, 1985) was:

            Year             Production (millions of kg)
                                                        

            1980                        10.1
            1981                         9.5
            1982                         9.4
            1983                        11.4

    3.2.2  Uses

         Being a volatile highly polar solvent, acetonitrile finds its
    greatest use as an extracting fluid for fatty acids and animal and
    vegetable oils.

         Acetonitrile has been widely used as an extractive distillation
    solvent in the petrochemical industry for separating olefin-diolefin
    mixtures and for C4-hydrocarbons.  When acetonitrile is used in this
    way, recycling is effected by water dilution of the extract and
    condensate with subsequent phase separation, after which the
    acetonitrile is azeotroped from the aqueous phase.

         Acetonitrile has been used as a solvent for polymer spinning
    and casting because of the combination of high solubility and
    desirable intermediate volatility.  It is also used as a solvent for
    isolating components from crude products such as crude wool resin. 
    Acetonitrile is used as a common laboratory solvent for
    recrystallizing various chemicals and is widely used as a solvent in
    HPLC analysis.  Acetonitrile is also used in biotechnology research
    as a solvent in the synthesis of DNA and peptide sequencing (Borman,
    1990).

         Acetonitrile can be used to remove tars, phenols and colouring
    matter from petroleum hydrocarbons that are not soluble in
    acetonitrile.

         Acetonitrile is also used as a starting material for the
    synthesis of many chemicals such as acetophenone, alpha-naphthyl
    acetic acid, thiamine and acetomidine (Hawley, 1971).

         The use patterns of acetonitrile are summarized in Table 6.

    Table 6.  Main use patterns of acetonitrilea

                                                                

    Extraction of fatty acids and animal and vegetable oils

    Extraction of unsaturated petroleum hydrocarbons

    Solvent for polymer spinning and casting

    Moulding of plastics

    Removal of tars, phenols and colouring matter from petroleum
    hydrocarbons

    Purification of wool resin

    Recrystallization of steroids

    Starting material for synthesis of chemicals

    Solvent in DNA synthesis and peptide sequencing

    Medium for promoting reactions

    Solvent in non-aqueous titrations

    Non-aqueous solvent for inorganic salts

    High-pressure liquid chromatographic analysis

    Catalyst and component of transition-metal complex catalysts

    Extraction and refining of copper

    Stabilizer for chlorinated solvents

    Perfume manufacture

    Pharmaceutical solvents
                                                                

    a  From: Veatch  et al. (1964); NIOSH (1978); Toxic Substances
       Control Act (1979); Smiley (1983); Borman (1990)

    4.  ENVIRONMENTAL TRANSPORT, DISTRIBUTION AND TRANSFORMATION

    4.1  Transport and distribution between media

    4.1.1  Water

         Hine & Mookerjee (1975) reported that the ratio of
    concentration in the water phase to the gas phase of a dilute
    aqueous solution of acetonitrile at equilibrium at 25 C is 891:1. 
    The inverse of this ratio (1.1 x 10-3) is the unit-less Henry's
    Law constant.  Conversion to units, using an RT value of 2.4 x
    10-2-m3 atm/mol (where R is the gas constant and T is the
    temperature in K), yields a Henry's Law constant of
    2.6 x 10-5-m3 atm/mol.  This value of Henry's Law constant
    indicates that the volatilization of acetonitrile is probably
    significant for most environmental bodies of water (Lymann  et al.,
    1982).  The concentration of acetonitrile in river water decreased
    to 5% of the original level after 72 h in a study carried out under
    stable conditions (Chen  et al., 1981).

    4.2  Transformation

    4.2.1  Biodegradation

    4.2.1.1  Water and sewage sludge

         Ludzack  et al. (1958, 1959) measured the biodegradation of
    acetonitrile in Ohio River water and in aged sewage by measuring
    CO2 production.  Degradation in the river water occurred at a
    faster rate than in the sewage; the 12-day biological oxygen demand
    (BOD) was 40% in river water but only 20% in the sewage.
    Acclimatization of microorganisms was examined by reculturing, and
    the degradation was found to occur 5 times more rapidly using
    acclimatized microorganisms.  The effect of temperature on
    biodegradation was also studied; degradation at 5 C took 2.5-5
    times longer than at 20 C.  Ludzack  et al. (1961) examined the
    degradation of acetonitrile by activated sludge in a continuous feed
    test at 22-25 C; 82-94% BOD was removed during 4 weeks of test
    operation.  Anaerobic digestion does not appear to be an effective
    means of removing the compound from waste water (Ludzack  et al.,
    1961).

         Using the Japanese MITI (Ministry of International Trade and
    Industry) test, Sasaki (1978) reported that acetonitrile is "readily
    biodegradable", meaning that oxygen consumption is > 30% in 2
    weeks.  Thom & Agg (1975) reported that acetonitrile should be
    degradable by biological sewage treatment with appropriate
    acclimatization.  Mimura  et al. (1969) isolated the bacterium
     Corynebacterium nitrilophius from activated sludge and found that
    this microorganism was capable of assimilating acetonitrile.  Kelly
     et al. (1967) found virtually no degradation of acetonitrile using
    a nitrogenase from  Azotobacter chroococcum.

         Goud  et al. (1985) isolated bacteria of several genera from
    various points in an effluent treatment plant at a petrochemical
    installation.   Azobacter spp and, more particularly,  Pseudomonas
    spp were able to degrade acetonitrile, added to the culture medium
    at 1% as sole carbon source.   Aeromonas spp and  Bacillus spp,
    however, were unable to degrade acetonitrile.  The authors pointed
    out that many of the bacterial species tested are common in the
    environment, and that regular exposure to petrochemicals selects
    strains that are able to degrade such compounds.

         Chapatwala  et al. (1992) investigated mixed cultures of
    bacteria isolated from an area contaminated with organic cyanide and
    polychlorinated biphenyls and found that they readily utilized
    acetonitrile as sole carbon and nitrogen source.  Nearly 70% of
    14C-labelled acetonitrile was recovered as CO2, the remainder
    being incorporated into bacterial growth.  The mixed culture lost
    its capacity to degrade biphenyl when repeatedly recultured with
    acetonitrile, indicating more ready degradation of the nitrile.

         Ludzack  et al. (1961) observed high levels of nitrates in
    effluents from activated sludge degrading acetonitrile.  Firmin &
    Gray (1976) used a species of  Pseudomonas capable of utilizing
    acetonitrile as sole carbon source to show that acetonitrile
    undergoes direct enzymatic hydrolysis.  These authors postulated the
    following metabolic pathway based on their results with [2-14C]
    acetonitrile: acetonitrile -> acetamide -> acetate -> tricarboxylic
    acid cycle intermediates (citrate, succinate, fumarate, malate,
    glutamate, etc.).

    4.2.1.2  Soil

         DiGeronimo & Antoine (1976) isolated  Nocardia rhodochrus
    Ll100-21 from barnyard soil and demonstrated that the
    microorganism was capable of using acetonitrile as a source of
    carbon and nitrogen.  A decrease in acetonitrile content within the
    culture medium was correlated with an increase in acetamide and
    acetic acid levels; ammonia was also detected.  Under the test
    conditions, the initial concentration of acetonitrile was reduced by
    14% in 3 h and by 52% in 8 h.  Crude cell-free extracts were also
    found to degrade acetonitrile by an enzymatic hydrolysis
    mechanism that was reported to be inducible.  Kuwahara  et al.
    (1980) found that  Aeromonas species BN 7013 could be grown
    using acetonitrile as a nitrogen source; the microorganism was
    isolated from soil.  Harper (1977) isolated a strain of the fungus
     Fusarium solani from soil and found that cell-free extracts,
    containing the nitrilase enzyme, were capable of hydrolysing
    acetonitrile enzymatically.

    4.2.2  Abiotic degradation

    4.2.2.1  Water

         Brown  et al. (1975) reported that the hydrolysis rate
    constant for acetonitrile in an aqueous solution of pH 10 is 1.195 x
    10-8 M-1 sec-1.  Assuming a constant pH of 10, the half-life
    for this process would be > 18 000 years.

         Anbar & Neta (1967) reported that the rate constant for the
    reaction of acetonitrile with hydroxyl radicals in aqueous solution
    at pH 9 and room temperature is 2.1 x 106 M-1 sec-1; assuming
    an environmental hydroxyl radical concentration at 10-17 M, a
    half-life of 1042 years can be calculated.  Dorfman & Adams (1973)
    reported a similar hydroxyl radical rate constant of 3.5 x 106
    M-1 sec-1.

         The absorption maximum for acetonitrile in the UV range is
    < 160 nm (Silverstein & Bassler, 1967); therefore, the direct
    photolysis of acetonitrile in the aquatic environment is not
    expected to occur.

    4.2.2.2  Air

         Harris  et al. (1981) found in laboratory studies that the
    rate of reaction of acetonitrile with ozone was relatively slow, the
    rate constant being < 1.5 x 10-19 cm3 molecule-1 sec-1. 
    Assuming a typical atmosphere concentration of 1012 ozone
    molecules/cm3, a half-life of > 54 days can be calculated from
    this rate constant.

         The reaction rate constant between singlet oxygen and
    acetonitrile is reported to be 2.4 x 10-16 cm3 molecule-1
    sec-1 (Graedel, 1978); this predicts an atmospheric half-life of >
    5000 years for acetonitrile.

         Dimitriades & Joshi (1977) reported on the reactivity of
    acetonitrile as measured in an US EPA smog chamber with 22
    blacklights, 7 sunlamps, 4 ppm acetonitrile and 0.2 ppm NOx. 
    Acetonitrile was found to be unreactive with respect to ozone yield. 
    The average rate of disappearance of acetonitrile was found to be
    0.02% per hour, i.e. 100 times slower than that measured for
    propane.  Kagiya  et al. (1975) measured the photochemical
    decomposition rate of acetonitrile (300-2000 ppm) in air saturated
    with water in a reaction cell irradiated with a mercury lamp.  No
    degradation was observed, however, when chlorine gas (2000 ppm) was
    added to the cell, the decomposition rate being 1.32% per second. 
    Reaction between chlorine radicals and acetonitrile in the
    atmosphere is not thought to be significant in relation to hydroxyl
    radical reaction (Arijs  et al., 1983).

         The absorption maximum for acetonitrile in the UV range is
    < 160 nm (Silverstein & Bassler, 1967).  Therefore, the direct
    photolysis of acetonitrile in the ambient atmosphere is not expected
    to occur.

         The major mechanism for removal of acetonitrile from the
    troposphere is reaction with hydroxyl radicals.  The rate constant
    for the gas-phase reaction of acetonitrile with hydroxyl radicals
    has been experimentally determined by Harris  et al. (1981) to be
    0.494 x 10-13 cm3 molecule-1 sec-1 at 24.2 C; in the
    temperature range 298-424 K (25-151 C), the rate constant was
    described by the equation k = 5.86 x 10-13 exp (-1500 cal
    mole-1/RT).  From this rate constant data, Harris  et al. (1981)
    calculated the tropospheric destruction rate of acetonitrile at
    25 C to be approximately 5 x 10-7 sec-1 for a mean
    concentration of 107 hydroxyl radicals/cm3 in a moderately
    polluted troposphere; this rate yielded a tropospheric lifetime of
    approximately 20 days.  In a more average atmosphere of 106
    hydroxyl radicals/cm3, the lifetime will be 10 times longer. 
    Guesten  et al. (1981) reported the rate constant for the reaction
    between hydroxyl radicals and acetonitrile in the gas phase to be
    approximately 0.2 x 10-13 cm3 molecule-1 sec-1 at room
    temperature, which agrees reasonably well with the findings of
    Harris  et al. (1981).  The Arrhenius activation energy of
    approximately 1500 cal mole-1, as determined by Harris  et al.
    (1981), indicates that the reaction proceeds largely or entirely by
    abstraction of a hydrogen atom.

         Acetonitrile does reach the upper atmosphere.  It is
    characteristically associated in positive ion clusters of the form
    H+(CH3CN)m (H2O)n.  These ions do not occur in the
    ionosphere but become important at 35 km altitude.  At lower
    altitudes still (about 12 km), acetone ions become evident (Arijs
     et al., 1983; Huertas & Marenco, 1986).

    5.  ENVIRONMENTAL LEVELS AND HUMAN EXPOSURE

    5.1  Environmental levels

    5.1.1  Air

         Becker & Ionescu (1982) monitored air near to the ground in
    both urban and rural areas and detected acetonitrile at
    concentrations of 3360 to 11 960 g/m3 (2-7 ppb by volume) using
    GC/MS.  There was some indication that results from city centre
    samples were higher than general rural samples; acetonitrile at
    concentrations of 7.4  2.4 ppb was reported for the city centre in
    Wuppertal, Germany.  Given the small number of samples, however, a
    comparison of the sites is difficult.  A rural site was sampled in
    the air before and after burning of bush and grass by farm workers
    and results showed an increase in acetonitrile concentration from
    4.0 to 34.9 ppb.  This seems to be the only reported demonstration
    of non-anthropogenic sources of atmospheric acetonitrile. 
    Acetonitrile has also been reported to be present in the upper
    stratosphere (Arijs  et al., 1983).  It was detected at
    concentrations of 210 to 42 000 ng/m3 in the Environmental Survey
    of Chemicals in Japan (Office of Health Studies, Environment Agency,
    1990).

         In the USA, two samplings of air over a period of 24 h in a
    rural area gave daily mean levels of 0.048 ppb by volume.  A single
    sampling of urban air was below the detection limit of the
    analytical method (US EPA, 1988).

    5.1.2  Water and bottom sediment

         Acetonitrile was not detected in water but was detected in
    bottom sediment in the Environmental Survey of Chemicals in Japan
    (Office of Health Studies, Environment Agency, 1990).  The sampling
    was conducted in all 47 prefectures of Japan, but no information is
    available concerning the nature of the sampling sites.  It is not
    known, therefore, whether the high ends of the ranges in air and
    aquatic sediment were associated with industrial production and
    release (Table 7).

    5.1.3  Food

         No report has been published showing contamination of food by
    acetonitrile.

    Table 7.  Environmental levels in Japan of acetonitrile in 1987a

                                                                 
               Concentration       Frequency of   Detection limit
                                   detectionb
                                                                 

    Water      not detected            0/72       3 g/litre

    Sediment   0.021 to 0.54 mg/kg    11/60       0.021 mg/kg

    Air        210 to 42 000 ng/m3    44/70       200 ng/m3
                                                                 

    a  From: Office of Health Studies (1990)
    b  Number of detections/number of samples

    5.1.4  Tobacco smoke

         The absorption of acetonitrile from smoke has been confirmed by
    GC/MS analysis of a composite sample of the urine of 40 smokers
    (Mckee  et al., 1962).  The average acetonitrile level was
    117.6 g/litre urine, while the average level for 20 nonsmokers was
    2.9 g/litre urine.

    5.1.5  Other sources of exposure

         Nitrogen-containing products such as hydrogen cyanide,
    acetonitrile and acrylonitrile, and some other toxic gases have been
    detected from the thermal decomposition of flexible polyurethane
    foams (Woolley, 1972).  The yield of hydrogen cyanide and
    acetonitrile, respectively, from 10 mg foam was 26.4 and 21.4 g at
    800 C, where a volatile yellow smoke was produced, and 522 and
    30.5 g at 1000 C, where the yellow smoke was decomposed.

    5.2  Occupational exposure

         Synthesis of acetonitrile is usually carried out in a closed
    system.  Therefore, occupational exposure would only be accidental. 
    NIOSH estimated that 23 000 workers may be exposed to acetonitrile
    in the USA.  Since much of the acetonitrile produced has noncaptive
    uses, the general population may also be exposed (NIOSH, 1979).

         The occupational exposure limit for acetonitrile in various
    countries is shown in Table 8.

    Table 8.  Occupational exposure limits for various countriesa

                                                              

    Country                TWA              STEL
                                                  
                      (ppm)  (mg/m3)    (ppm)  (mg/m3)
                                                              

    Australia           40      70        60      105

    Belgium             40      67        60      101

    Denmark             40      70         -       -

    Finland             40      70        60      105

    France              40      70         -       -

    Germany             40      70         -       -

    Hungary              -      50         -      100

    Switzerland         40      70        80      140

    United Kingdom      40      70        60      105

    USA

      (ACGIH)           40      67        60      101
      (NIOSH/OSHA)      40      70        60      101

    USSR                 -       -         -       10
                                                              

    a  From: ILO (1991)

    5.3  Acetonitrile in various solvent products

         After a nationwide survey in Japan of organic solvent
    components in various solvent products, acetonitrile was not
    detected in either thinners (321 samples) or miscellaneous solvents
    (56 samples), but was detected in 1% of the degreasers (145 samples)
    (Inoue  et al., 1983).

    6.  KINETICS AND METABOLISM IN LABORATORY ANIMALS AND HUMANS

    6.1  Absorption

    6.1.1  Human studies

         Acetonitrile is well absorbed by inhalation.  There is little
    information on absorption of inhaled acetonitrile in humans.

         Studies on smokers showed that 91  4% of the acetonitrile
    inhaled in cigarette smoke was retained (Dalhamn  et al., 1968a). 
    A significant portion of this could have been retained in the mouth,
    as 74% of the acetonitrile was retained as a result of holding smoke
    in the mouth for 2 sec (Dalhamn  et al., 1968b).

         There are no absorption studies concerning dermal or oral
    exposure.  However, human poisoning cases indicate that acetonitrile
    is well absorbed by both routes.

    6.1.2  Experimental animal studies

    6.1.2.1  Intake through inhalation

         Although there is information that acetonitrile is easily
    absorbed from the lungs of animals exposed to acetonitrile vapour,
    no quantitative analytical data is available on the pulmonary
    absorption of acetonitrile.

    6.1.2.2  Dermal absorption

         Pozzani  et al. (1959a) studied the skin penetration of
    undiluted or diluted acetonitrile under polyethylene sheeting in
    rabbits (the site of application was not reported).  The dermal
    LD50 value was decreased when application was made as a 75% (by
    volume) aqueous solution, i.e. from 1.25 (0.84 to 1.85) ml/kg in the
    case of the undiluted compound to 0.5 (0.37 to 0.67) ml/kg in the
    case of the diluted aqueous solution.  These LD50 values are
    similar or even lower than those obtained after oral administration
    in other animal species, indicating effective skin absorption of
    acetonitrile.

    6.1.2.3  Intake via the gastrointestinal tract

         Although there is information that acetonitrile is easily
    absorbed from the gastrointestinal tract, no quantitative analytical
    data are available.

    6.2  Distribution

    6.2.1  Human studies

         A postmortem investigation on a man accidentally exposed to
    acetonitrile suggested that acetonitrile absorbed through inhalation
    or skin contact is distributed in the body as shown in Table 21
    (section 8.1.1).

    6.2.2  Experimental animal studies

         Ahmed  et al. (1992) studied by means of whole body
    auto-radiography the distribution of radioactivity derived from
    2-14C-acetonitrile in the body of ICR mice at time points between
    5 min and 48 h after administration of a single intravenous dose. 
    Irreversible association of label was determined in co-precipitated
    protein and nucleic acids and extracted lipid.  No attempt was made
    to distinguish between metabolically incorporated or adducted label. 
    The highest concentrations of non-volatile radioactive compounds
    were generally found in the liver, kidney and the contents of the
    upper gastrointestinal tract.  A significant fraction (40-50%) of
    the radioactivity found in liver at 24 and 48 h was bound to the
    macromolecular fractions of the tissues.  The radioactivity contents
    of other organs were, in large part (40-50% of total), present in
    the lipid fraction of the tissue.

    6.3  Biotransformation and elimination

    6.3.1  Human studies

         There is no specific human study describing acetonitrile
    biotransformation and elimination.  However, accidental poisoning
    cases indicate that acetonitrile is biotransformed to cyanide and
    thiocyanate, which are then excreted from urine (see section 9).

    6.3.2  Experimental animal studies and  in vitro studies

    6.3.2.1  Cyanide liberation from acetonitrile

         The release of cyanide from acetonitrile and its subsequent
    metabolism to thiocyanate have been studied under a number of
    experimental conditions and in several animal species.

         Biotransformation of acetonitrile to cyanide and thiocyanate
    has been demonstrated in a variety of  in vitro preparations. 
    Liver slices obtained from male golden hamsters show an increasing
    generation of cyanide and thiocyanate as the concentration of
    acetonitrile increases (Willhite, 1983).  Release of cyanide from
    acetonitrile is also catalysed by liver microsomes of hamster in a
    concentration-dependent manner (Willhite, 1983).  Production of
    cyanide from acetonitrile has been demonstrated in isolated

    hepatocytes from female SD rats; the Km and Vmax values (mean 
    SD) were 3.4  0.8 mM and 1.1  0.1 nmol cyanide/106 cells per
    10 min, respectively (Freeman & Hayes, 1987).  The release of
    hydrogen cyanide from acetonitrile has also been demonstrated in
    mouse liver microsomes, both with and without NADPH (Ohkawa  et al.,
    1972).  The Km and Vmax values obtained from male ddY mouse
    microsomes were 4.19 mM and 14.3 ng cyanide formed in 15 min per mg
    protein, respectively (Tanii & Hashimoto, 1984a).

         Dahl & Waruszewski (1989) studied the metabolism of
    aceto-nitrile to cyanide in rat nasal and liver tissues and found
    that the maximum rates of cyanide production from acetonitrile by
    nasal maxilloturbinate and ethmoturbinate microsomes and liver
    microsomes were 0, 0.9  0.2 and 0.098  0.008 nmol cyanide/mg
    protein per min, respectively.

          In vivo metabolism of acetonitrile to cyanide and thiocyanate
    was first demonstrated by Pozzani  et al. (1959a).  Studies were
    conducted in rats, monkeys and dogs under a number of experimental
    conditions.  Fifteen male and fifteen female rats were exposed to
    acetonitrile vapour (166, 330, and 655 ppm) 7 h/day, 5 days/week for
    90 days.  During the 5-day sampling period (inhalation days 59 to
    63), thiocyanate concentrations in urine ranged from 27 to 79 and 29
    to 60 mg/100 ml for the 166 and 330 ppm exposure groups,
    respectively.  Thiocyanate was not completely eliminated between
    daily exposures, but was almost completely excreted during the
    2.5-day rest period over weekends.  The excretion of thiocyanate in
    the higher exposure group was not reported.

         The concentrations of thiocyanate in the urine of three dogs
    exposed to 350 ppm acetonitrile in air increased from 69 to
    252 mg/litre over the same 5-day inhalation period as described
    above for rats.  Unlike the rats, dogs continued to eliminate
    thiocyanate beyond the 2.5-day rest period over the weekend.  When
    three monkeys were exposed to 350 ppm acetonitrile in the same
    manner as the dogs, the urinary thiocyanate concentration ranged
    from 60 to 114 mg/litre.  Thiocyanate was also excreted after the
    2.5-day rest period.

         Rhesus monkeys were injected intravenously either with
    acetonitrile (0.1 ml/kg) or with thiocyanate (1.55 ml/kg of a 10%
    solution in saline).  The percentages of the dose excreted as
    thiocyanate were 12% and 55%, respectively.  It seems therefore that
    more than 12% of the injected acetonitrile was converted into
    thiocyanate (Pozzani  et al., 1959a).

         After a single intraperitoneal administration of acetonitrile
    (780 mg/kg) in rats, all animals died in 3 to 12 h, and acetonitrile
    was found to be distributed in various organs (Dequidt & Haguenoer,
    1972).  The free cyanide varied from 170 g/kg in the liver to

    3.5 mg/kg in the spleen.  Concentrations of combined cyanide in the
    liver, spleen, stomach and skin were 3.6, 13.5, 17.6 and 10.5 mg/kg
    tissue, respectively.

         Haguenoer  et al. (1975a,b) studied the pharmacokinetics of
    acetonitrile in male Wistar rats after a single intraperitoneal
    acetonitrile injection or inhalation exposure.  Rats given 2340 or
    1500 mg/kg died within 3 to 28 h after the intraperitoneal
    injection, but rats given 600 mg/kg survived with no apparent
    symptoms.  After administration of 2340 mg/kg, concentrations of
    acetonitrile and free and combined cyanide in various organs ranged
    from 900 to 1700 mg/kg, 200 to 3500 g/kg, and 3.5 to 17 mg/kg
    tissue, respectively.  Mean total urinary acetonitrile and free and
    combined cyanide (essentially all thiocyanate) excreted during the
    11 days following an intraperitoneal injection of 600 mg/kg were 28,
    0.2 and 12 mg, respectively.  These values were equivalent to 3,
    0.035 and 2.3% of the acetonitrile dose, respectively.  Urinary
    acetonitrile was detectable for 4 days after dosing, whereas free
    and combined cyanide were detectable until 11 days, at which time
    the animals were sacrificed.  Rats inhaling 25 000 ppm died within
    30 min from the beginning of exposure.  The concentration of
    acetonitrile in muscle and kidney ranged from about 1.4 to 24 mg/kg,
    and that of free cyanide in liver and spleen from 0.3 to 4 mg/kg
    tissue.  When three rats were exposed to 2800 ppm (2 h/day for
    3-5 days) the concentrations of acetonitrile and free cyanide in
    various tissues at the time of death were 1000-2900 mg/kg and
    0.5-10 mg/kg tissue, respectively.

         The liver and brain cyanide levels of male CD-1 mice (n = 9-10)
    that died 2.5 h after intraperitoneal administration of 175 mg
    acetonitrile/kg were found to be 47.8  36.1 and 13.4  4.8 mol/kg,
    respectively (Willhite & Smith, 1981).  Sprague-Dawley rats
    administered an oral LD50 of acetonitrile (2460 mg/kg) were found
    to have cyanide levels of 16  6 mg/kg in liver, 102  39 mg/kg in
    kidney and 28  5 mg/kg in brain (Ahmed & Farrooqui, 1982).

         Freeman & Hayes (1985a) found that the peak blood cyanide
    concentration (5.2  0.5 mg/litre) was achieved 35 h after oral
    administration of 1470 mg/kg to female SD rats.  Silver  et al.
    (1982) reported that urinary thiocyanate excretion for a 24-h period
    following oral or intraperitoneal adminstration of acetonitrile
    (30.8 mg/kg) in SD rats was 11.8  2.5 and 4.4  0.5% of the dose,
    respectively.  Inhalation studies on male and female Wistar rats
    exposed to 166 and 330 ppm (660 ppm was fatal) indicated that the
    amount of thiocyanate in urine was not proportional to the
    concentration of acetonitrile inhaled (Pozzani  et al., 1959a).

         Table 9 shows that acetonitrile is converted to cyanide at a
    slower rate than other nitriles.  In fact, one hour after
    acetonitrile administration the blood level of cyanide was much
    lower than those after acute toxic doses of other nitriles. Peak

    concentrations of blood cyanide were found 7.5 h after acetonitrile
    dosing and were comparable to those of other nitriles measured one
    hour after dosing.

         Brain cyanide concentration one hour after acetonitrile dosing
    was also lower than those after exposure to potassium cyanide (KCN)
    or other nitriles.  Urinary excretion of thiocyanate after exposure
    to various nitriles indicated that for acetonitrile the percentage
    of the dose excreted was lower than for other nitriles, even though
    the absolute given amount of acetonitrile, based on its oral LD50
    value, was much higher.  These data, taken together, indicate that
    the toxicity of acetonitrile is lower than those of cyanide and
    other nitriles, as shown by oral LD50 values in Table 9.  The
    reason for this is most probably the slower transformation of
    acetonitrile to cyanide and consequently the more efficient
    detoxification via thiocyanate excretion.

         The relevance of acetonitrile pharmacokinetics is further
    illustrated by examining the relationship between symptoms produced
    by acetonitrile one hour after exposure and the amounts of cyanide,
    as well as the effect on cytochrome  c oxidase in the brain
    (Table 10).  Animals treated with acetonitrile were asymptomatic at
    this time, but animals treated with other nitriles or KCN at LD50
    doses were symptomatic.  In fact, the inhibition of brain cytochrome
     c oxidase paralleled brain cyanide concentrations.  In the case of
    acetonitrile, the brain cyanide concentration was too low to affect
    cytochrome  c oxidase activity and therefore to cause symptoms.

         In conclusion, the data reported in Tables 9 and 10 indicate
    that the apparent lack of relationship, assessed shortly after
    dosing, between acetonitrile toxicity and cyanide production is due
    to the slow transformation of acetonitrile to cyanide.

         There is sufficient evidence from all animal species studied
    that the toxicity of acetonitrile is due to cyanide.  Interspecies
    variations, as shown in Tables 11 and 12, are probably related to
    the relative speed of cyanide formation from acetonitrile (data of
    Willhite & Smith, 1981 in mice versus the data of Ahmed & Farooqui,
    1982 in rats).


        Table 9.  Metabolism of nitriles to cyanide in relation to their lethal effects

                                                                                                                     

    Compound                       Cyanide concentration              Urinary thiocyanate           Oral LD50
                                  (1 h after an oral LD50)                 excretion           (mg/kg body weight)c
                             Blood (mg/litre)a     Brain (mg/kg)c        (% dose/24 h)d
                                                                                                                     

    Potassium cyanide              6.3                748  200            not measured                  10

    Acetonitrile                   0.3b                28  5               11.8  2.5                 2460

    Propionitrile                  4.0                508  84              65.1  2.9                   40

    Butyronitrile                  3.8                437  106             64.9  3.5                   50

    Malononitrile                  6.5                649  209            not measured                  60

    Isobutyronitrile          not measured          not measured            74.0  2.6                  160

    Acrylonitrile                  4.1                 395-106              37.3  1.9                   90
                                                                                                                     

    a  Estimated from: Ahmed & Farooqui (1982)
    b  7.5 h after oral administration (1470 mg/kg body weight), the blood cyanide level was found to
       be 7.3 mg/litre (Estimated from: Freeman & Hayes, 1985a)
    c  Ahmed & Farooqui (1982) 1 h after oral LD50
    d  Silver et al. (1982)
    

    6.3.2.2  The oxidative pathway of acetonitrile metabolism

         Following the observation of acetonitrile metabolism to cyanide
    and thiocyanate by Pozzani  et al. (1959a), many authors reported
    the same results in humans as well as in experimental animals both
     in vitro and  in vivo (Amdur, 1959; Ohkawa  et al., 1972;
    Willhite & Smith, 1981; Ahmed & Farooqui, 1982; Silver  et al.,
    1982; Willhite, 1983; Pereira  et al., 1984; Tanii & Hashimoto,
    1984a,b, 1986; Freeman & Hayes, 1985a,b; Ahmed  et al., 1992). 
    They all suggested a metabolic pathway in which acetonitrile is
    bio-transformed by cytochrome P-450 monooxygenase system initially
    to cyanohydrin, which then spontaneously decomposes to hydrogen
    cyanide and formaldehyde as shown in Fig. 1. Formaldehyde has not
    been identified in all of these studies, but this could be due to
    its high reactivity and rapid conversion into a simple metabolite
    (CO2).

         Acetone, an inducer of cytochrome P-450 isozyme LM3a (Koop &
    Casazza, 1985; Johannsen  et al., 1986), has been demonstrated to
    stimulate the metabolism of acetonitrile to cyanide  in vivo in
    rabbits (Freeman & Hayes, 1985a).  In an  in vitro  study, liver
    microsomes were isolated and pooled 24 h after pretreatment of
    female Sprague-Dawley rats with acetone. Microsomal metabolism of
    acetonitrile to cyanide was found to be NADPH-dependent and
    heat-inactivated tissue was unable to catalyse this reaction
    (Freeman & Hayes, 1985b).  The metabolism of some nitriles,
    including acetonitrile to cyanide by mouse hepatic microsome system,
    has been shown to be NADPH-dependent and enhanced by pretreatment
    with ethanol (Tanni & Hashimoto, 1986).  Ohkawa  et al. (1972)
    found that the amount of hydrogen cyanide released in mouse liver
    microsomal preparations was increased greatly by the addition of
    NADPH.  It is known that treatment of rats with cobalt-heme
    effectively depletes liver cytochrome P-450 concentrations (Drummond
    & Kappas, 1982).  Freeman & Hayes (1987) demonstrated a marked
    decrease in acetonitrile metabolism in isolated hepatocytes prepared
    from rats pretreated subcutaneously with cobalt-heme (90 mol/kg)
    48 h before killing.  However, the rate of acetonitrile
    biotransformation into cyanide by liver microsomal preparation
    obtained from cobalt-heme-treated rats was 13% of controls, while
    the total cytochrome P-450 content was reduced by only 41% compared
    to the controls.


        Table 10.  Biochemical and clinical effects in Sprague-Dawley male rats dosed with cyanide and nitrilesa

                                                                                                                     

    Compound                 Brain cyanide     Brain cytochrome c        CNS          Convulsionb     Respiratory
                             concentration     oxidase activity       depressionb                       failureb
                                (mg/kg)        (% of control)
                                                                                                                     

    Control                       0                  100                  no              no               no

    Potassium cyanide         748  200               29                   4               4                4

    Acetonitrile               28  5                 92                  no              no               no

    Propionitrile             508  54                47                   3               1                1

    Butyronitrile             437  106               41                   2               1                1

    Malononitrile             649  209               73                   3               3                2
                                                                                                                     

    a  Measured 1 h after an LD50; data from: Ahmed & Farooqui (1982)
    b  Physiological changes were graded on a scale of 1 (lowest) to 4 (highest)
    

            NADPH, O2            spontaneous

    CH3CN   ------->   HOCH2CN   -------> [HCHO] + CN-       (1)

            mixed-function
            oxidases


            rhodanese

    CN-     ------->   SCN-                                  (2)

            S2O3


                      [HCHO] has not been identified
                      CN- and SCN- have been identified both
                       in vitro and  in vivo

    Fig. 1.  Oxidation (1) and conjugation (2) reactions in acetonitrile
             metabolism

         Treatment of rats with inducers of P-450 IIE1, such as
    pyrazole, 4-methylpyrazole and ethanol, resulted in a 4- to 5-fold
    increase in cyanide production from acetonitrile by isolated
    microsomes (Feierman & Cederbaum, 1989).  Phenobarbital treatment
    had a small stimulatory effect, whereas 3-methylcholan-threne
    treatment decreased microsomal oxidation of acetonitrile.  Cyanide
    production was inhibited by carbon monoxide, ethanol, 2-butanol,
    dimethyl sulfoxide (DMSO) and 4-methylpyrazole  in vitro. 
    Oxidation of acetonitrile to cyanide by microsomes from rats treated
    with pyrazole or 4-methylpyrazole was nearly completely inhibited by
    an antibody (IgG) against P-450 3a.

         These results imply a role for P-450 in the oxidation of
    acetonitrile to cyanide and suggest that P-450 IIE1 may be the
    specific catalyst for this oxidation.  Acetonitrile oxidation was
    not affected by hydroxyl radical scavengers or by desferrioxamine.

         The results of human and animal studies indicate that cyanide
    formed  in vivo is subsequently conjugated with thiosulfate to form
    thiocyanate, which is then eliminated in urine.  This conjugation is
    catalysed by the enzyme rhodanese (thiosulfate cyanide sulfur
    transferase: EC 2.8.1.1) (Pozzani  et al., 1959a; Takizaw &
    Nakayama, 1979; Silver  et al., 1982; Willhite, 1983; Pereira
     et al., 1984).

         Acetone inhibits acetonitrile metabolism when the two compounds
    are administered simultaneously.  Blood cyanide concentrations were
    maximally elevated 9 to 15 h after female SD rats were dosed with
    acetonitrile alone at 1470 mg/kg.  In rats dosed concomitantly with

    acetonitrile (1470 mg/kg) and acetone (1960 mg/kg), blood cyanide
    concentrations measured 0 to 24 h after dosing were much lower than
    those in rats given the same dose of acetonitrile alone.  Blood
    cyanide levels, however, reached peak concentration 39 to 48 h after
    dosing with the two compounds and were 50% higher than those
    measured in rats treated with acetonitrile only (Freeman & Hayes,
    1985a). 

         From these time courses of blood cyanide it was postulated that
    acetone has a biphasic effect on acetonitrile metabolism, causing an
    initial inhibition and a subsequent stimulation of cyanide
    generation from acetonitrile.  Freeman & Hayes (1985b) also found
    that the  in vitro metabolism of acetonitrile to cyanide by either
    hepatic microsomal preparations or by isolated liver cells
    (hepatocytes) from rats pretreated with acetone (2.5 ml/kg) was
    significantly increased (2 fold).  However, when acetone was
    incubated with hepatocytes, it inhibited acetonitrile metabolism
    without affecting cell viability.

         Ethanol has also been shown to affect the  in vitro metabolism
    of some nitriles, including acetonitrile (Tanii & Hashimoto, 1986). 
    A 1.8-fold increase in cyanide liberation from acetonitrile was
    observed in hepatic microsomes from male ddY mice pretreated with
    ethanol (4.0 g/kg) 13 h prior to the study.

         Freeman & Hayes (1988) further investigated the metabolism of
    acetonitrile  in vitro and the effects of acetone and other
    compounds.  They suggested that the conversion of acetonitrile to
    cyanide is mediated by specific acetone-inducible isoforms of
    cytochrome P-450 and cytochrome P-450j (LM3, LMeb).  Acetone,
    dimethylsulfoxide and ethanol competitively inhibited this
    conversion.  Aniline HCl has been shown to reduce acetonitrile
    metabolism.

    6.4  Biological monitoring of acetonitrile uptake

         Workers accidentally exposed to acetonitrile vapour showed
    increased serum cyanide and thiocyanate levels but the exposure
    concentrations were unknown (Amdur, 1959).  In three human
    volunteers exposed at different times to concentrations of up to
    160 ppm for 4 h (Pozzani, 1959a), no significant changes in urinary
    blood cyanide and thiocyanate levels were observed compared to those
    measured prior to exposure.  In experimental animal studies using
    various routes of exposure, blood cyanide and thiocyanate levels
    showed increases but they were not proportional to the exposures
    (Pozzani, 1959a).  It should be noted that there is a delay of
    several hours in the formation of cyanide following exposure to
    acetonitrile, and the timing of blood sampling is therefore
    critical.

         From these data it is not possible to derive biological indices
    for exposure monitoring.

    7.  EFFECTS ON LABORATORY MAMMALS;  IN VITRO TEST SYSTEMS

    7.1  Acute toxicity

    7.1.1  Single exposure

         The LD50 values for acetonitrile in mammals are summarized in
    Table 11; they range between 175 and 5620 mg/kg body weight.  The
    mouse and the guinea-pig seem to be the most sensitive species.  No
    consistent effects of sex, administration route or vehicle were
    observed.  An experiment using four different age groups of rats
    showed that new-born rats (24 to 48 h old, 5-8 g) are the most
    sensitive.  Significant differences in LD50 values were found
    between 14-day-old and adult rats, but not between young adults
    (80-160 g body weight) and older adults (300-470 g body weight)
    (Kimura  et al., 1971).

         The acute inhalation toxicity of acetonitrile in various animal
    species is shown in Table 12. The LC50 values range between about
    2700 ppm for a 1-h inhalation or 2300 ppm for a 2-h inhalation in
    mice and 16 000 ppm for a 4-h inhalation or 12 000 ppm for an 8-h
    inhalation in rats.  Mice appear to be the most sensitive species to
    acetonitrile inhalation.  In Nelson rats, the LC50 value for an
    8-h inhalation was significantly lower in males (7551 ppm with 5975
    to 9542 confidence interval) than in females (12 435 ppm with 11 036
    to 14 011 confidence interval), while that for a 4-h inhalation was
    the same in both sexes (16 000 ppm with 13 070 to 19 636 confidence
    interval) (Pozzani  et al., 1959a).

         Pozzani  et al. (1959b) studied the relationship between the
    observed and predicted LD50 of acetonitrile given in combination
    with other chemicals to rats exposed orally or by inhalation. 
    Predictions were made using the method of Finney (1952).  The
    mixture of acetonitrile and acetone seemed to show effects that were
    greater than additive.  Results are summarized in Table 13.

    7.1.2  Clinical observations

         Signs and symptoms of acute acetonitrile intoxication are
    similar in different animal species.  Verbrugge (1899) described
    signs of acute acetonitrile toxicity in rabbits.  One to three hours
    after a subcutaneous acetonitrile injection of 90 to 150 mg/kg,
    rabbits showed rapid and irregular respiration, immobilization and
    convulsions, and two out of seven animals died.  Monkeys exposed to
    2510 ppm acetonitrile vapour appeared normal after the first day of
    inhalation but showed poor coordination followed by prostration and
    laboured breathing during the second day.  Death occurred a few
    hours later (Pozzani  et al., 1959a).  Mice exposed to
    concentrations of acetonitrile ranging from 500 to 5000 ppm (the
    LC50 for a 60-min exposure was 2693 ppm) displayed dyspnoea,
    tachypnoea, gasping, tremors, convulsions and corneal opacity
    30-300 min after the beginning of the exposure.  Exposure of mice to

    5000 ppm acetonitrile for 60 min killed all the animals within 2 h. 
    The syndrome of acute acetonitrile toxicity was indistinguishable
    from that observed after exposure to cyanide or other nitriles
    (Willhite, 1981; Willhite & Smith, 1981).

         In a study by Willhite (1983), pregnant hamsters were exposed
    to acetonitrile concentrations from 3800 to 8000 ppm for one hour. 
    The number of hamsters showing tremors, hypersalivation, ataxia,
    hypothermia, lethargy and coma increased with increasing dose. 
    Hamsters died about 3 h after exposure to 5000 ppm acetonitrile and
    within 90 min after exposure to 8000 ppm acetonitrile.

         In a study by Johansen  et al. (1986), all of five pregnant
    rats treated with acetonitrile at doses of 750 mg/kg or more per day
    by gavage on gestation days 6-15 died, whereas only three out of
    five animals treated with 375 mg/kg per day died.  Four out of six
    rats treated with 275 mg/kg had reduced body weight at parturition,
    while two others died.

         Ahmed & Farooqui (1982) measured cyanide levels one hour after
    administration of LD50 doses of several saturated and unsaturated
    nitriles to male SD rats.  Few symptoms were noted with acetonitrile
    in this study because little cyanide was released within the first
    hour following treatment.  The tissue concentrations of cyanide
    after lethal doses of propionitrile, butyronitrile and malononitrile
    were very similar and approximately those observed with a lethal
    dose of KCN.

         In female SD rats given an oral dose of acetonitrile
    (1770 mg/kg), acute toxic effects appeared after 30 h (Freeman &
    Hayes, 1985a).

    7.1.2.1  Effect on skin

         The skin irritation of acetonitrile in Sherman rats was
    reported by Smyth & Carpenter (1948) to be comparable to that of
    acetone, although no precise description of the technique used for
    testing skin irritation was provided.

    7.1.2.2  Effect on the eyes

         Eye injury caused by acetonitrile, reported by Smyth &
    Carpenter (1948), is of intermediate intensity and similar to that
    produced by acetone (Carpenter & Smyth, 1946).  Corneal opacity has
    been observed after either inhalation or intraperitoneal
    administration of acetonitrile in male mice (Willhite, 1981;
    Willhite & Smith 1981).  Pregnant hamsters exposed to 8000 ppm
    acetonitrile via inhalation for 60 min showed eye irritation
    (Willhite, 1983).


        Table 11.  LD50 values of acetonitrile for various species and different routes of administration

                                                                                                                                              

    Species (strain)            Sex       Observation     Route                LD50 (mg/kg or       Vehicle       References
                                         period (days)                       ml/kg body weightb
                                                                                                                                              

    Mouse (Kunming)             male          -a          gavage                 453 mg/kg          water         Chen et al. (1981)
    Mouse                                      1          intraperitoneal        520.79 mg/kg                     Yoshikawa (1968)
    Mouse                                      -          intraperitoneal        0.25 ml/kg         saline        Pozzani et al. (1959a)
    Mouse (NMRI)                               7          intraperitoneal        400 mg/kg          water         Zeller et al. (1969)
    Mouse (CD-1)                male           7          intraperitoneal        175 mg/kg          water         Willhite & Smith (1981)
    Mouse (ddY)                 male           7          oral                   269 mg/kg          water         Tanii & Hashimoto (1984a)

    Rat (Sherman)                              -          oral                   3800 mg/kg         -a            Smyth & Carpenter (1948)
    Rat (Wistar) or albino      male           -          gavage                 1.68 ml/kg         undiluted     Pozzani et al. (1959a)
    Rat (Wistar) or albino      male           -          gavage                 2460 mg/kg         water         Pozzani et al. (1959a)
    Rat (Wistar) or albino      male           -          intravenous            1.68 ml/kg         undiluted     Pozzani et al. (1959a)
    Rat (Wistar) or albino      female         -          gavage                 2230 mg/kg         1% Tgc        Pozzani et al. (1959a)
    Rat (Wistar) or albino      female         -          gavage                 1730 mg/kg         corn oil      Pozzani et al. (1959a)
    Rat (Wistar) or albino      female         -          gavage                 8.56 ml/kg         undiluted     Pozzani et al. (1959a)
    Rat (Wistar) or albino      female         -          intraperitoneal        7.96 ml/kg         undiluted     Pozzani et al. (1959a)
    Rat (Wistar) or albino      female         -          intraperitoneal        5620 mg/kg         saline        Pozzani et al. (1959a)
    Rat (Wistar) or albino      female         -          intraperitoneal        0.85 ml/kg         undiluted     Pozzani et al. (1959a)
    Rat (Wistar) or albino      female         -          intravenous            1.68 ml/kg         undiluted     Pozzani et al. (1959a)
    Rat (SD)                                   -          oral                   3200 mg/kg         water         Zeller et al. (1969)
    Rat (SD) 14-day old         male           -          oral                   0.2 ml/kg          undiluted     Kimura et al. (1971)
    Rat (SD) young adult        male           -          oral                   3.9 ml/kg          undiluted     Kimura et al. (1971)
    Rat (SD) older adult        male           -          oral                   4.4 ml/kg          undiluted     Kimura et al. (1971)
    Rat (SD)                    female         3          oral                   4050 mg/kg         undiluted     Freeman & Hayes (1985a)
                                                                                                                                              

    Table 11 (contd).

                                                                                                                                              

    Species (strain)            Sex       Observation     Route                LD50 (mg/kg or       Vehicle       References
                                         period (days)                       ml/kg body weightb
                                                                                                                                              

    Guinea-pig                  male           -          gavage                 0.177 ml/kg        undiluted     Pozzani et al. (1959a)

    Rabbit                                     -          skin                   5.0 ml/kg          undiluted     Smyth & Carpenter (1948)
    Rabbit                      male           -          skin                   1.25 ml/kg         undiluted     Pozzani et al. (1959a)
    Rabbit                      male           -          skin                   0.50 ml/kg         water         Pozzani et al. (1959a)
                                                                                                                                              

    a  - = not reported
    b  1 ml acetonitrile = 783-787 mg at 20 C
    c  Tg = Tergitol 7 in water
    

        Table 12.  Acute inhalation toxicity of acetonitrilea

                                                                                  

    Species (strain)      Sex         Concentration    Exposure      Mortality
                                          (ppm)        time (h)      measuresb
                                                                                  

    Mouse (Kunming)                        2300            2         LC50
    Mouse (Kunming)                        5700            2         LC50
    Mouse (CD-1)          male             2700            1         LC50
                          male             5000            1         10/10

    Rat (Nelson)          male             7551            8         LC50
                          female         12 435            8         LC50
                          male           16 000            4         LC50
                          female         16 000            4         LC50
    Rat (Wistar)                         12 000            2         MLC

    Guinea-pig            male +           5655            4         LC50
                          female
    Guinea-pig                             7400            2         MLC

    Rabbit                male             2800            4         LC50
    Rabbit                                 4500            2         MLC

    Dog                   male           32 000            4         1/1
                          male           16 000            4         3/3
                          male             8000            4         0/1
                          male             2000            4         0/2
                                                                                  

    a  From: Willhite (1981), Pozzani  et al. (1959a,b), Wang  et al. (1964)
    b  MLC = minimum lethal concentration

    Table 13.  Predicted and observed LC50 and LD50 values of acetonitrile in
               combination with other solvents in rata

                                                                                     

                                    4-h inhalation (g/m3)          Oral (ml/kg)

                                    PLC50          OLC50        PLD50         OLD50
                                                                                     

    Acetonitrile                      -            26.9          -             8.27

    Acetonitrile + n-hexane         45.6           74.1          -              -  

    Acetonitrile + acetone          39.7           14.6         9.99           2.75

    Acetonitrile + ethyl            32.4           51.4         9.40           14.1
     acetate

    Acetonitrile + carbon           31.5           45.5         4.35           6.77
     tetrachloride

    Acetonitrile + toluene          22.3           44.4         8.68           3.73
                                                                                     

    a  From: Pozzani  et al. (1959b)
       PLC50 or PLD50 = predicted LC50 or LD50
       OLC50 or OLD50 = observed LC50 or LD50
    
    7.1.2.3  Effect on respiration

         Animals exposed to acetonitrile via different routes of dosing
    always showed respiratory symptoms: rapid and irregular respiration
    after subcutaneous administration in rabbits (Verbrugge, 1899),
    laboured or difficult breathing after inhalation exposure in monkeys
    (Pozzani  et al., 1959a) or rats (Haguenoer  et al., 1975b), and
    intense dyspnoea after either inhalation or intraperitoneal
    administration in mice (Willhite, 1981; Willhite & Smith, 1981). 
    Histopathological investigations of rat lungs after acetonitrile
    inhalation showed haemorrhage and congestion (Haguenoer  et al.,
    1975b).  After inhaling 660 ppm acetonitrile for 2 h, two monkeys
    showed focal areas of emphysema and atelectasis, with occasional
    proliferation of alveolar septa (Pozzani  et al., 1959a).

    7.1.2.4  Effect on adrenals

         Szabo  et al. (1982) studied structure-activity relationships
    of 56 chemicals, including acetonitrile, with respect to their
    potential for causing adrenocortical necrosis in rats.  The dose was
    selected on the basis of preliminary experiments and was aimed to
    lead to 70 to 100% mortality in 4 to 5 days.  The compounds were
    given 3 times per day for 4 days, and surviving animals were
    sacrificed on the 5th day.  Acetonitrile, along with 13 other
    compounds out of 56 test chemicals, did not show any
    adrenocorticolytic effect in rats.

    7.1.2.5  Effect on the gastrointestinal tract

         Rats that inhaled acetonitrile at a concentration of 2800 ppm
    (2 h/day for 2 days) showed temporary diarrhoea (Haguenoer  et al.,
    1975b).

         Acetonitrile did not produce duodenal ulcers in female SD rats
    after oral or subcutaneous administration 3 times per day for 4
    days, the total dose being 432 mmol/kg (Szabo  et al., 1982).

    7.1.3  Biochemical changes and mechanisms of acetonitrile toxicity

    7.1.3.1  Effect on cytochrome oxidase

         An  in vitro study carried out by Willhite & Smith (1981)
    showed that high concentrations of acetonitrile (up to 0.47 M) did
    not inhibit cytochrome  c oxidase activity.  Ahmed & Farooqui
    (1982) investigated the ability of acetonitrile and other nitriles
    to inhibit cytochrome  c oxidase one hour after they were
    administered at the LD50 to male SD rats.  There was no direct
    evidence for the inhibition of cytochrome oxidase after the
    administration of acetonitrile.  However, very little increase in
    tissue or blood cyanide concentrations was observed one hour after
    dosing with acetonitrile.  Symptoms had not occurred within this
    time period, and the evidence from other studies indicates that peak

    cyanide levels are achieved much later than one hour (in 9-15 h)
    (Freeman & Hayes, 1985a).  The need to consider the different
    pharmacokinetic and metabolic factors involved in making such
    comparisons was emphasized by Willhite & Smith (1981).

    7.1.3.2  Effect on glutathione

         Levels of glutathione (GSH) in liver, kidney and brain were
    unaffected one hour after oral administration of acetonitrile (at
    the LD50 level) in male SD rats (Ahmed & Farooqui, 1982).  Aitio &
    Bend (1979) studied the  in vitro effect of 12 organic solvents,
    including acetonitrile, on the activity of rat liver soluble
    glutathione S-transferase.  They demonstrated that in the presence
    of 630 mM acetonitrile, the conjugation of styrene oxide,
    benzo[ a]pyrene-4,5-oxide and 1,2-dichloro-4-nitrobenzene by GSH
    was reduced to 79.0  5.2, 92.6  3.0 and 59.2  1.4%,
    respectively, of the control values.

    7.1.4  Antidotes to acetonitrile

         Multiple intraperitoneal administrations of 1 g sodium
    thiosulfate per kg at the rate of one injection every 100 min over a
    10-h period or two intraperitoneal injections of 75 mg sodium
    nitrite per kg significantly reduced mortality in CD-1 mice exposed
    to 3800 or 5000 ppm acetonitrile by inhalation for 60 min (Willhite,
    1981).  Treatment of animals with thiosulfate at a dose rate of
    1 g/kg every 100 min for an 8-h period was effective in providing
    significant protection against the lethal effect of an
    intraperitoneal injection of acetonitrile (575 mg/kg) in male CD-1
    mice (Willhite & Smith, 1981).  An intraperitoneal injection of
    sodium thiosulfate (300 mg/kg) 20 min prior to inhalation of
    8000 ppm acetonitrile in pregnant hamsters abolished the overt signs
    of acetonitrile poisoning and reduced mortality from 3 out of 12
    hamsters to zero (Willhite, 1983).  Repeated intraperitoneal
    administrations (6 injections in 10 h) of sodium thiosulfate
    (1 g/kg), which started at the onset of acute toxicity about 30 h
    after oral administration of acetone (1960 mg/kg) and acetonitrile
    (1770 mg/kg) given simultaneously, provided significant protection
    against mortality in female SD rats (Freeman & Hayes, 1985a).

         Two intraperitoneal injections of 75 mg sodium nitrite did not
    provide CD-1 mice with any significant protection against the lethal
    effect of acetonitrile (575 mg/kg) (Willhite & Smith, 1981).

    7.2  Subchronic toxicity

    7.2.1  Inhalation exposure

         In a rat study, the body weight gain and organ weights of male
    and female rats which inhaled 166, 330 or 655 ppm acetonitrile
    (7 h/day, 5 days/week, for a total of 90 days) did not differ

    significantly from those of the controls (Pozzani  et al., 1959a). 
    Histopathological examination showed that of the 28 rats that
    inhaled 166 ppm, one had histiocyte clumps in the alveoli and
    another had atelectasis.  Of 26 rats that inhaled 330 ppm, three
    showed bronchitis, pneumonia, atelectasis and histiocyte clumps in
    the alveoli.  After the inhalation of 655 ppm acetonitrile vapour,
    10 out of 27 animals showed alveolar capillary congestion and/or
    focal oedema in the lung, often accompanied by bronchial
    inflammation, desquamation and hypersecretion.  Tubular cloudy
    swelling of the kidneys in eight rats and swelling of the livers of
    seven rats were observed.  These effects were statistically
    significant (lungs, P < 0.001; kidney, P < 0.005; liver,
    P < 0.04) compared with control animals.  No lesions were found in
    the adrenals, pancreas, spleen, testes or trachea.  Focal cerebral
    haemorrhage was observed in one of the five brains examined.

         Wang  et al. (1964) reported that there was no change of
    iodine levels in the thyroid of Wistar rats exposed to 80 or 400 mg
    acetonitrile/m3 (4 h/day, 6 days/week) for 10 weeks. Degenerative
    changes in the epithelial cells of thyroid follicles were observed
    in rabbits exposed to 400 mg/m3 (4 h/day, 6 days/week) for 16
    weeks.

         In an inhalation study (7 h/day) on four Rhesus monkeys, one
    female monkey was exposed to 2510 ppm, two females to 660 ppm and
    one male to 330 ppm (Pozzani  et al., 1959a).  The monkey exposed
    to 2510 ppm appeared normal during the first inhalation day but on
    the second day showed incoordination and laboured breathing and died
    a few hours later.  In the two monkeys exposed to 600 ppm there was
    also incoordination from the second week.  One monkey died on day 23
    and the other on day 51.  The monkey exposed to 330 ppm showed
    overextension reflexes and hyperexcitability towards the end of the
    99-day inhalation period and was sacrificed then.  At autopsy, the
    monkey exposed to 2510 ppm had engorgement of the dural capillaries,
    and the animals exposed to 660 and 330 ppm showed focal dural or
    subdural haemorrhage in the parietal and/or occipital tissues
    adjacent to the superior sagittal sinus.  The monkey exposed to
    2510 ppm had pleural effusion, and those exposed to 660 ppm had
    focal areas of emphysema and atelectasis with occasional
    proliferation of alveolar septa, and cloudy swelling of the proximal
    and convoluted tubules of the kidneys.  The monkey exposed to
    330 ppm had pneumonitis as shown by diffuse proliferation of
    alveolar septa, monocytic infiltration and pleural adhesions.

         In another inhalation study (Pozzani  et al., 1959a), three
    male Rhesus monkeys were exposed to 350 ppm acetonitrile (7 h/day,
    5 days/week) for 91 days, and at the end of the study the animals
    were sacrificed.  At autopsy, haemorrhages of the superior and
    inferior sagittal sinuses were found in the brains of all three
    monkeys.  Small discrete caseous nodules were seen in the lungs of

    two monkeys and one monkey had a pale liver.  Histological
    investigations of the lung showed focal emphysema, diffuse
    proliferation of alveolar septa, and focal accumulations of
    pigment-bearing macrophages.  In two of the monkeys there was cloudy
    swelling of the proximal tubules of the kidney.

         One female and two male dogs inhaled 350 ppm acetonitrile
    (7 h/day, 5 days/week) for 91 days.  The haematocrit and haemoglobin
    values of the three dogs were depressed by the fifth week of
    inhalation, but with the exception of one dog, there was a return to
    pre-inhalation values toward the end of the 91-day inhalation
    period.  No significant deviation of the erythrocyte counts was seen
    in any dogs.  Histopathological examination of these dogs showed
    some focal emphysema and proliferation of alveolar septa.

         Roloff  et al. (1985) exposed groups of male and female rats
    (strain unspecified) to acetonitrile vapour (0, 1038, 3104 and
    10 485 mg/m3) for one month (6 h/day, 5 days/week).  Death and
    reduced body weight gains were observed at the highest exposure
    level.  Respiratory and/or ocular irritation were noted in animals
    exposed to 3104 and 10 485 mg/m3.

         In a 13-week inhalation study of acetonitrile (100, 200 and
    400 ppm) in 25 male mice and male rats, there were no effects on
    body weight or on testicular weight and sperm motility (Morrissey
     et al., 1988).

         In a 13-week inhalation study on acetonitrile in mice and rats,
    ten mice (B6C3F1) and ten rats (F-344/N) of each sex were exposed
    to acetonitrile vapour at 0, 100, 200, 400, 800 and 1600 ppm
    (6 h/day, excluding weekends and holidays) for 13 weeks (Battelle,
    Pacific Northwest Laboratories, 1986a,b).  At 400 ppm one female
    mouse, at 800 ppm one male and four female mice, and at 1600 ppm ten
    female and ten male mice were found dead during the study.  The
    majority of the mortality occurred after two weeks of exposure. 
    Clinical signs observed were hypoactivity and a hunched rigid
    posture.  Body weight gains were comparable to control values for
    all surviving mice.  An increase in absolute and relative liver
    weight was attributed to acetonitrile exposure.  The maximum
    tolerated concentration determined by this 13-week subchronic study
    was 200 ppm.  Significant changes were observed in the liver and
    stomach of male mice exposed to 400 ppm of acetonitrile and female
    mice exposed to 200 ppm or more.  At 800 ppm one male rat and at
    1600 ppm six male and three female rats were either moribund (and so
    sacrificed) or found dead during the study.  The clinical signs
    observed were hypoactive, abnormal posture, ataxia, bloody crusts on
    nose and/or mouth and a rough haircoat.  The moribund, sacrificed
    rats exhibited tonic/clonic convulsions. Reductions in body weight
    gain were observed in rats exposed to 1600 ppm.  Minimum to mild
    lesions were found in the lungs and brain of some rats exposed to
    800 ppm (Table 14).

         In a 92-day study, reported as an abstract, acetonitrile was
    administered by inhalation to B6C3F1 mice and Fischer-344 rats at
    concentrations of (25, 50, 100, 200 and 400 ppm) for a total of 65
    days (Hazleton, 1990b).  In mice, one male in each of the 50, 200
    and 400 ppm groups died.  There was an increase in body weight gain
    in all males exposed to 50, 100, 200 and 400 ppm acetonitrile and in
    the females of the 200 and 400 ppm groups.  Body weight gain was
    decreased by comparison with controls in the 25, 50 and 100 ppm
    female groups.  Liver/body weight ratio was increased in males at
    400 ppm group and in females at 100, 200 and 400 ppm groups. 
    Liver/brain weight ratio was increased in males at the 400 ppm and
    in female at 100 and 400 ppm groups.  There was slight cytoplasmic
    vacuolization of hepatocytes in both males and females in the 200
    and 400 ppm groups. Mean haemato-crit and erythrocyte counts were
    marginally reduced in females at 200 and 400 ppm group. In females
    of the 200 and 400 ppm groups haematocrit, haemoglobin, red and
    white blood cell counts, and serum IgG were all depressed.  In rats,
    one male in the 400 ppm group died during the study.  There was
    slight cytoplasmic vacuolization of hepatocytes in females at
    400 ppm.  Marginal decreases in mean leucocyte counts were reported
    in males at 100 and 200 ppm and in both males and females at
    400 ppm.

    7.2.2  Subcutaneous administration

         Marine  et al. (1932a) gave daily subcutaneous injections of
    0.1 ml acetonitrile to 4-month-old rabbits for 21 days.  Two groups
    of four male rabbits developed pronounced (more than twice normal
    size) thyroid hyperplasia whereas one group of four females showed
    no effect.  Allyl-benzyl and phenyl nitriles produced less
    pronounced hyperplasia or no effect on thyroids at up to 4 times the
    dose of acetonitrile.  A further study (Marine  et al., 1932b)
    suggested that young rabbits were more susceptible than adults and
    that the effect varied with the strain.

    7.3  Teratogenicity and embryotoxicity

         In a study by Berteau  et al. (1982), mated rats were
    administered daily aqueous solutions of acetonitrile by gavage
    (125, 190 and 275 mg/kg) on gestation days 6-19.  Although maternal
    body weights were reduced and death occurred in the high-dose group,
    no other maternal effects were noted in any treated group. 
    Embryotoxic effects, as shown by increases in early resorptions and
    postimplantation losses, were also noted in the high-dose group. 
    However, no teratogenic responses were observed at any dose level.


        Table 14.  Subchronic inhalation toxicity of acetonitrile in mice and rats

                                                                                                                                              

    Spe