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

    First draft prepared by Dr. R.B. Williams,
    United States Environmental Protection Agency

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

    World Health Organization
    Geneva, 1992

        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

    WHO Library Cataloguing in Publication Data


        (Environmental health criteria; 138)

        1. Environmental exposure   2. Propane - analogs & derivatives
        3. Propane - toxicity    I. Series

        ISBN 92 4 157138 1         (NLM Classification QV 633)
        ISSN 0250-863X

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    1. SUMMARY

         1.1. Properties and analytical methods
         1.2. Uses and sources of exposure
               1.2.1. Production
               1.2.2. Uses and loss to the environment
         1.3. Environmental transport and distribution
         1.4. Environmental levels and human exposure
         1.5. Kinetics and metabolism
         1.6. Effects on laboratory mammals and  in vitro
         1.7. Effects on humans
         1.8. Effects on other organisms in the laboratory
               and field


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


         3.1. Natural occurrence
         3.2. Anthropogenic sources
               3.2.1. Production levels and processes
               3.2.2. Uses
         3.3. Release into the environment


         4.1. Transport in the environment
         4.2. Biotic and abiotic transformation


         5.1. Environmental levels and general population
         5.2. Potential occupational exposure


         6.1. Absorption
         6.2. Distribution
         6.3. Metabolic transformation
         6.4. Elimination and excretion
         6.5. Retention and turnover


         7.1. Single exposure
         7.2. Short-term and long-term repeated exposure
         7.3. Reproduction, embryotoxicity, and teratogenicity
         7.4. Mutagenicity and related end-points
               7.4.1. Prokaryotes and yeast
               7.4.2. Eukaryotes
         7.5. Carcinogenicity
         7.6. Pharmacological effects


         8.1. General population exposure
         8.2. Occupational exposure
               8.2.1. Acute toxicity
               8.2.2. Effects of long-term exposure



         10.1. Human health risks
         10.2. Effects on the environment



         12.1. Environment
         12.2. Epidemiology
         12.3. Toxicokinetics
         12.4. Carcinogenesis







    Dr D. Anderson, British Industrial Biological Research
        Association, Carshalton, Surrey, United Kingdom

    Dr U. Andrae, Institute for Toxicology, Research Centre for
        Environment and Health, Neuherberg, Munich, Germany

    Dr B. Baranski, Hofer Institute of Occupational Medicine,
        Lodz, Poland

    Dr S. Dobson, Institute of Terrestral Ecology, Monks Wood
        Experimental Station, Abbots Ripton, Huntingdon, United

    Dr E.S. Fiala, Naylor Dana Institute for Disease Prevention,
        American Health Foundation, Valhalla, New York, USA

    Dr P. Lundberg, Department of Toxicology, National Institute
        of Occupational Health, Solna, Sweden

    Dr M.H. Noweir, Industrial Engineering Department, College of
        Engineering, King Abdul Aziz University, Jeddah, Saudi

    Dr C.N. Ong, Department of Community, Occupational and
        Family Medicine, National University of Singapore, Singapore
         (Joint Rapporteur)

    Dr R.B. Williams, Exploratory Research, US Environmental
        Protection Agency, Washington DC, USA  (Joint Rapporteur)


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

    Dr P.G. Jenkins, International Programme on Chemical Safety,
        World Health Organization, Geneva, Switzerland

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


        Every effort has been made to present information in the
    criteria documents as accurately as possible without unduly delaying
    their publication. In the interest of all users of the Environmental
    Health Criteria documents, 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, Palais
    des Nations, 1211 Geneva 10, Switzerland (Telephone No. 7988400 or


        A WHO Task Group on Environmental Health Criteria for
    2-Nitropropane met in Geneva from 4 to 8 November 1991. Dr B.H.
    Chen, 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 document and
    made an evaluation of the risks for human health and the environment
    from exposure to 2-nitro-propane.

        The first draft of this monograph was prepared by Dr R.B.
    Williams of the US Environmental Protection Agency. The second draft
    was also prepared by Dr R.B. Williams incorporating comments
    received following the circulation of the first draft to the IPCS
    Contact Points for Environmental Health Criteria documents.

        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.


    DDT         dichlorodiphenyltrichloroethane
    DMSO        dimethyl sulfoxide
    SCE         sister chromatid exchange
    SGPT        serum glutamic pyruvic transaminase
    STEL        short-term exposure limit
    TWA         time-weighted average


    1.1  Properties and analytical methods

        2-Nitropropane (2-NP) is a colourless, oily liquid with a mild
    odour. It is flammable, only moderately volatile, and stable under
    ordinary conditions. It is only slightly soluble in water but
    miscible with many organic liquids, and it is an excellent solvent
    for many types of organic compounds. Adequate analytical methods
    exist for the identification and measurement of 2-NP at
    environmental concentrations. Current methods use gas chromatography
    and a flame ionization or electron capture detector or,
    alternatively, high-performance liquid chromatography with an
    ultraviolet detector. For measurement in air, 2-NP must first be
    trapped and concentrated in a solid sorbent.

    1.2  Uses and sources of exposure

    1.2.1  Production

        Current world production figures are not available. In 1977
    production in the USA was approximately 13 600 tonnes. 2-NP is
    currently manufactured by two USA companies and one French company.
    It is produced naturally in trace amounts in the combustion of
    tobacco and other nitrate-rich organic matter, but there is no
    evidence that it is produced by any biological processes.

    1.2.2  Uses and loss to the environment

        2-NP is used as a solvent, principally in blends, and has many
    industrial applications as a solvent for printing inks, paints,
    varnishes, adhesives and other coatings such as beverage container
    linings. It has also been used as a solvent to separate closely
    related substances such as fatty acids, as an intermediate in
    chemical syntheses, and as a fuel additive. Losses to the
    environment are mainly to the air and are due principally to solvent
    evaporation from coated surfaces.

    1.3  Environmental transport and distribution

        2-NP appears to be highly mobile in the natural environment.
    Since it is slightly water soluble, slightly adsorbed by sediment,
    slightly bioaccumulated, and evaporates readily into the atmosphere,
    it will be distributed in both air and water and not accumulated in
    any individual environmental compartment. Ultraviolet
    photoabsorption by 2-NP is within the range of wavelengths occurring
    naturally in the environment, and it is thus likely that 2-NP
    undergoes slow photolysis in the atmosphere. Slow biological
    conversion of 2-NP to less toxic compounds also appears likely in
    both aquatic and terrestrial environments.

    1.4  Environmental levels and human exposure

        General population exposure to 2-NP appears to be very low and
    is derived from cigarette smoke (1.1 to 1.2 µg/cigarette), from
    residues in coatings such as beverage can coatings, adhesives and
    print, and from vegetable oils fractionated with 2-NP. Industrial
    exposure worldwide is unknown, but in the USA appears to be limited
    to 0.02-0.19% of the workforce. Significant exposure (exposure to
    9.1 mg/m3 (2.5 ppm) or more) in the USA may be limited to about
    4000 workers (approximately 0.005% of the workforce). Occupational
    exposure limits in the air vary among different countries and range
    from 3.6 mg/m3 (1 ppm) (TWA) to 146 mg/m3 (40 ppm) (STEL).
    Manufacture of 2-NP is an enclosed process and usually involves
    little employee exposure, but some workers in industries such as
    painting, printing, and solvent extraction have in the past been
    exposed to levels much greater than occupational exposure limits.
    Concentrations as high as 6 g/m3 (1640 ppm) in air were recorded
    in a drum-filling operation.

    1.5  Kinetics and metabolism

        Human uptake of 2-NP occurs mainly through the lungs. In
    experimental animals, 2-NP has been shown to be rapidly absorbed not
    only via the lungs but also from the peritoneal cavity and the
    gastrointestinal tract. There is no satisfactory information on
    absorption via the skin. Information on distribution in rats is
    somewhat contradictory. 2-NP is rapidly metabolized, mainly to
    acetone and nitrite. Some isopropyl alcohol may also be formed.
    Following intraperitoneal injection, 2-NP and its carbon-containing
    metabolites are concentrated initially in fat and subsequently in
    bone marrow as well as in the adrenal glands and other internal
    organs. Following inhalation, 2-NP and its carbon-containing
    metabolites are concentrated in the liver and kidney, with
    relatively little in fat. Several different enzyme systems may be
    involved and there are species differences concerning rates and
    pathways. 2-NP and its carbon-containing metabolites are rapidly
    lost from the body by metabolic transformation, exhalation, and
    excretion in the urine and faeces. Satisfactory information on the
    distribution and excretion of nitro moiety metabolites is lacking.

    1.6  Effects on laboratory mammals and  in vitro systems

        2-NP has moderate acute toxicity for mammals. Males are more
    sensitive than females, at least among rats, and sensitivity differs
    widely among the species that have been tested. The LC50
    (concentration causing 50% mortality within 14 days) for rats
    following a 6-h exposure was 1.5 g/m3 (400 ppm) for males and
    2.6 g/m3 (720 ppm) for females. Lethality appeared to be
    associated mainly with the narcotic effects, but mammals exposed to
    concentrations of at least 8.4 g/m3 (2300 ppm) for one hour or
    longer displayed severe pathological changes including
    hepatocellular damage, pulmonary oedema, and haemorrhage.

        There is clear evidence that 2-NP is carcinogenic in rats.
    Long-term inhalation exposure of rats to 0.36 g/m3 (100 ppm) for
    18 months (7 h/day, 5 days/week) induced destructive changes in the
    liver, including hepatocellular carcinomas in some males. A
    concentration of 0.75 g/m3 (207 ppm) induced more severe damage,
    including a high incidence of hepatocellular carcinomas, more
    quickly. Moderate-chronic oral dosage also induced excess
    hepatocellular carcinomas in rats. However, long-term inhalation
    exposure of rats to 91 or 98.3 mg/m3 (25 or 27 ppm) produced no
    detectable injury. Exposure of mice and rabbits to concentrations of
    2-NP that induced hepatocellular carcinomas in rats had little or no
    effect, but these studies were too limited to completely rule out
    2-NP carcinogenicity in these two species. 2-NP slightly retarded
    fetal development of rats, but there is a paucity of data on
    embryotoxicity, teratogenicity, and reproductive toxicity. 2-NP was
    found to be strongly genotoxic in rat hepatocytes both  in vitro
    and  in vivo, but no significant genotoxicity was observed in other
    organs of the rat or in cell lines of extrahepatic origin without
    exogenous metabolic activation. 2NP has been shown to be mutagenic
    in bacteria both in the presence and absence of exogenous metabolic

    1.7  Effects on humans

        Human exposure to high concentrations of 2-NP is largely or
    entirely occupationally related. High concentrations (actual values
    are unknown but in one case they were estimated to be 2184 mg/m3
    (600 ppm)) are acutely toxic and have produced industrial
    fatalities. Initial symptoms included headache, nausea, drowsiness,
    vomiting, diarrhoea, and pain. Victims often showed temporary
    improvement, but in some cases death occurred 4 to 26 days after
    exposure. Hepatic failure was the primary cause of death, and lung
    oedema, gastrointestinal bleeding, and respiratory and kidney
    failure were contributing factors. Occupational exposure to
    estimated levels of 73 to 164 mg/m3 (20 to 45 ppm) induced nausea
    and loss of appetite, which persisted for several hours after
    leaving the workplace, whereas occupational exposure to estimated
    levels of 36.4 to 109 mg/m3 (10 to 30 ppm) (< 4 h/day for
    < 3 days/week) produced no noticeable ill effects.

        Although available data are inadequate, there is no indication
    that chronic occupational exposure to 2-NP at concentrations usually
    encountered in the workplace induces hepatic or other neoplasms, or
    other long-term adverse effects.

    1.8  Effects on other organisms in the laboratory and field

        The few studies performed on microorganisms, invertebrates, and
    fish indicate low toxicity of 2-NP for non-mammalian organisms.


    2.1  Identity

    Chemical structure:            NO2
                            H3C  -  C  -  CH3

    Empirical formula:      C3H7NO2

    Synonyms:               Dimethylnitromethane, isonitropropane,
                            nitroisopropane, 2-NP

    Trade names:            NiPar S-20 (solvent), NiPar S-30 (solvent, a
                            mixture of 1- and 2-nitro-propane)

    CAS registry number:    79-46-9

    RTECS number:           TZ 5250000

    Relative molecular
    mass:                   89.09

    2.2  Physical and chemical properties

        2-Nitropropane (2-NP) is an important synthetic organic
    chemical. Its physical properties have been described by Angus
    Chemical Co. (1985), Baker & Bollmeier, (1981), Woo et al. (1985),
    and Weast (1986) and are summarized in Table 1. It is a colourless,
    oily liquid with a mild odour and remains liquid over a relatively
    broad temperature range, i.e. -93 to 120 °C. 2-NP is flammable, and
    although only moderately volatile, its vapour forms flammable or
    explosive mixtures with air. It is stable under ordinary
    circumstances, but may undergo explosive decomposition under
    conditions of extreme shock combined with heavy confinement and
    elevated temperature. 2-NP is only slightly soluble in water (17
    ml/litre at 20 °C) and water is even less soluble in 2-NP (5 ml/l at
    20 °C). With increasing temperature, solubility of both 2-NP in
    water and water in 2-NP increases, and an azeotrope containing 29.4%
    water ultimately is formed. Its boiling point is 88.6 °C. 2-NP is,
    however, miscible with many organic compounds including chloroform,
    aromatic hydrocarbons, alcohols, esters, ketones, ethers, and higher
    aliphatic carboxylic acids. Alkanes and cycloalkanes have more
    limited solubility in 2-NP (Baker & Bollmeier, 1981). Azeotropes are
    formed with some organic liquids.

    Table 1.  Physical properties of 2-nitropropane


    Appearance                      colourless, oily    Stokinger (1982)

    Relative molecular mass         89.09               Stokinger (1982)
                                                        Weast (1986)
                                                        Windholz (1983)

    Specific gravity                0.988               Baker & Bollmeier (1981)
    (liquid density)                                    Stokinger (1982)
    (at 20 °/4 °C)

    Vapour density (air = 1.00)     3.06                Stokinger (1982)

    Vapour pressure (20 °C)         1.72 MPa            Stokinger (1982)
                                    (12.9 torr)

    Boiling point                   120.3 °C            Baker & Bollmeier (1981)
                                                        Stokinger (1982)
                                                        Windholz (1983)

    Melting point                   -93 °C              Weast (1986)

    Water solubility (20 °C)        17 ml/l             Baker & Bollmeier (1981)
                                                        Stokinger (1982)
                                                        Windholz (1983)

    Refractive index (20 °C)        1.3944              Baker & Bollmeier (1981)
                                                        Weast (1986)

    Flash point (open cup)          38 °C               Stokinger (1982)

    Lower inflammability limit      2.6 volume %        National Fire Protection
                                    in air              Association (1968)

    Partition coefficients
     water/air                      128                 Filser & Baumann (1988)
     olive oil/air                  710                 Filser & Baumann (1988)
      in vivo whole body             175                 Filser & Baumann (1988)
        2-NP, like other nitroparaffins, undergoes a variety of chemical
    reactions. The chemistry of nitroparaffins has been the subject of a
    number of reviews and symposia and has been summarized by Baker &
    Bollmeier (1981), Goldwhite (1965), Stokinger (1982), Woo et al.
    (1985), and others. 2-NP is an acidic substance. The nitro form,
    which is mildly acidic, exists in equilibrium with its more strongly
    acidic "aci" tautomer and with the anionic form (nitronate) of the
    latter (Fig. 1). The aci tautomer is referred to as a nitronic acid
    and forms metal salts. It can be dissolved and neutralized by strong
    bases and gives a characteristic colour reaction with ferric
    chloride. Prolonged action of bases leads to decomposition. Aqueous
    acids hydrolyse 2-NP first to a hydroxamic acid and ultimately to
    carboxylic acids and hydroxylammonium salts. 2-NP reacts with
    nitrous acid to form a pseudonitrole which is colourless in
    crystalline form but blue when melted or in solution. The carbon
    atom bearing the nitro group is easily halogenated in the presence
    of a base. Photochemical chlorination, however, yields reaction
    products in which chlorine atoms are attached to the terminal
    carbons. In the presence of a base, 2-NP condenses with carbonyl
    compounds to yield a ß-nitroalcohol, which may dehydrate
    spontaneously to a nitro-olefin. Nitro-olefins thus formed, and a
    variety of other unsaturated compounds, undergo Michael addition
    reactions with 2-NP in the presence of a catalytic amount of base.
    2-NP will condense with formaldehyde and a secondary amine (the
    Mannich reaction). Mild reduction of 2-NP yields
    isopropylhydroxylamine, and strong reduction produces
    isopropylamine. Auto-oxidation catalysed by cuprous chloride yields
    2-hydroperoxy-2-nitropropane (Fieser & Fieser, 1972, 1974).

        Taste and odour are subjective biological properties derived
    from chemical and physical properties. The odour has been described
    as "sweet-solventy, rubbery, and alcohol-like" (letter from S.E.
    Ellis of Arthur D. Little, Inc. to G. Crawford of Occusafe Inc.,
    1982). There also is some uncertainty concerning odour threshold.
    Treon & Dutra (1952) stated that the odour of 2-NP was detectable at
    1070 mg/m3 (294 ppm) but not at 302 mg/m3 (83 ppm), without
    describing the methodology by which these values were determined;
    their values have nevertheless been incorporated into various
    guidelines (Crawford et al., 1984). Two recent studies redetermined
    the odour threshold for 2-NP. In one the ED50 (minimum concentration
    detected by 50% of the population) was estimated to be 18.2 mg/m3
    (5.0 ppm) with 95% confidence limits from 11.3 mg/m3 (3.1 ppm) to
    28.76 mg/m3 (7.9 ppm), and, in the other, all of a four-member
    test panel detected 2-NP at 11.3 mg/m3 (Crawford et al., 1984).
    There was no consensus as to the taste of a 6.4 g/litre (0.072
    mol/litre) solution of 2-NP in water (Marcstrom, 1967). The most
    frequent response was bitter, but other tasters found it (1) sweet,
    (2) bitter and sour, (3) bitter, cool, and anaesthetizing, (4)
    burning, (5) burning and cool, or (6) burning, sweet, bitter, and
    sour. Wilks & Gilbert (1972a) reported a taste detection threshold
    for 2-NP in water of 12.5 mg/litre.

    FIGURE 01

    2.3  Conversion factors

    1 ppm 2-NP in air = 3.64 mg/m3
    1 mg/m3 = 0.27 ppm 2-NP in air

    2.4  Analytical methods

        Analytical methods for 2-NP appear limited to the analysis of
    air, water, blood plasma, coatings, and cigarette smoke (Table 2).
    Since the colorimetric methods are less sensitive or are cumbersome,
    the method of choice is probably gas chromatography with either a
    flame ionization or an election capture detection. Charcoal is not a
    satisfactory adsorbent for 2-NP since recovery is poor (Andersson et
    al., 1983) and there may be decomposition (Glaser & Woodfin, 1981).
    In addition to Chromosorb 106, Amberlite XAD-7 appears satisfactory
    as a solid sorbent for quantitatively collecting 2-NP from the air
    (Andersson et al., 1983), although its collection efficiency is
    markedly reduced in humid air (Andersson et al., 1984). Use of a
    collection tube with two sections, however, can compensate for the
    reduced efficiency (Andersson et al., 1984). The high-performance
    liquid chromatography method developed for blood (Derks et al.,
    1988) could probably be adapted to other biological materials.

    Table 2.  Analytical techniques for determining 2-nitropropanea

    Methods                           Detection limit        Comments                                      Reference


    Trapping in ethanol;              0.1 mg/ml ethanol      absorption is linear between 0.1 and          Treon & Dutra (1952)
    concentration determined                                 2.0 mg/ml; ethanol was especially
    spectrophotometrically at                                purified and redistilled
    277.5 nm

    Trapping in concentrated          ca. 1 µg/ml sulfuric   absorption is linear between 1 and 5 µg/ml    Jones & Riddick (1952);
    sulfuric acid; resulting          acid                   sulfuric acid; no interference from primary   Jones (1963)
    nitrous acid combined                                    nitroparaffins, but all other secondary,
    with resorcinol to form a                                some tertiary and some halogenated
    red-blue colour; measured                                nitroparaffins interfere
    at 560 nm

    Trapping in solid sorbent tube    3.6 mg/m3              working range is 3.6 to 36 mg/m3; 2-NP        Glaser & Woodfin (1981)
    (Chromosorb 106, 60/80 mesh);                            stable on absorbent for at least 28 days
    desorption: ethyl acetate;
    separation-detection: GC-FID

    Methodology similar to above      3.1 mg/m3              Method is a modification of that proposed     US NIOSH (1987a)
                                                             by Glaser & Woodfin (1981); range: 3.1 to
                                                             28.3 mg/m3; no interference from methyl
                                                             butyl ketone, heptane, 1-nitropropane,
                                                             toluene, and xylene

    Table 2 (contd).

    Methods                           Detection limit        Comments                                      Reference


    Sample (40 µl) collected          ca. 0.5 mg/m3          water elutes quickly extinguishing flame      Wilks & Gilbert (1972a)
    with a syringe and injected                              in FID; flame can be reignited before 2-NP
    directly into GC;                                        emerges
    detection: FID


    Blood collected in chilled,       1 ng                   UV absorption linear from 0 to 250 ng;        Derks et al. (1988)
    screw-capped vial with heparin;                          uses 0.3 ml blood sample; samples are
    centrifuged; deproteinized with                          unstable and must be analysed promptly
    acetonitrile; Tris buffer added;
    separation: HPLC; detection:
    UV at 224 nm

    Coating (beverage can)

    Redissolve coating in solvent     not given              reference provides few details on             Wilks & Gilbert (1972b)
    suitably distinct from 2-NP;                             methodology
    acetone suitable for vinyl
    co-polymer coatings;
    separation: GC

    Table 2 (contd).

    Methods                           Detection limit        Comments                                      Reference

    Coating (beverage can)

    Can (empty) simultaneously        not given              method captures about 90% of                  Wilks & Gilbert (1972b)
    perforated and fitted with a                             residual 2-NP
    diaphragm; hypodermic needle
    inserted through diaphragm and
    fitted with stopcock; can heated
    (150 °C, 15 min); headspace
    sampled with heated syringe;
    separation: GC

    Cigarette smoke

    Steam distillation of smoke       0.8 µg/cigarette       may be adapted for air and water              Hoffmann & Rathkamp
    condensate on filters,                                   analysis                                      (1968)
    extraction re-extraction in
    NaOH, in ethyl ether,
    neutralization with H2SO4 and
    re-extraction in ethyl ether,
    concentration of extract and
    injection in GC equipped with
    FID or ECD detectors

    a   Abbreviations: ECD = electron capture detector; FID = flame ionization detector; GC = gas chromatograph;
        HPLC = high-performance liquid chromatograph; UV = ultraviolet


    3.1  Natural occurrence

        There is no evidence that 2-NP and other nitroaliphatic
    compounds are produced by biological processes, although a related
    organic compound, ß-nitropropionic acid, has been isolated from
    plants and microorganisms (Goldwhite, 1965). However, nitroaliphatic
    compounds are produced in low concentrations by combustion of
    organic matter and have been detected in tobacco smoke. Hoffmann &
    Rathkamp (1968) reported 1.1-1.2 µg 2-NP in the smoke from single
    85-mm USA blended non-filter cigarettes, and ascribed the production
    of this and other nitroaliphatics to interactions in the combustion
    zone between hydrocarbons and nitrogen dioxide generated by
    decomposition of nitrates.

    3.2  Anthropogenic sources

    3.2.1  Production levels and processes

        Although 2-NP is an important industrial chemical, current world
    production figures are not available. In 1977 production by the sole
    USA manufacturer was estimated to be 13 600 tonnes, of which 5400
    tonnes were sold in the USA and 8200 tonnes were either exported or
    used internally (Finklea, 1977). 2-NP currently is produced by two
    USA manufacturers, Angus Chemical Co., Sterlington, Louisiana, and
    W. R. Grace Co., Deer Park, Texas (SRI International, 1988, 1990;
    USITC, 1990), and by one European manufacturer, Société Chimique de
    la Grande Paroisse, France (Anon., 1976, 1982; IARC, 1982). In the
    USA, 2-NP, together with nitromethane, nitroethane and
    1-nitropropane, is manufactured by a vapour phase reaction of nitric
    acid with an excess of propane at high temperature and pressure
    (370-450 °C, 0.8-1.2 MPa (8-12 atm.)) (Baker & Bollmeier, 1981). The
    proportions of the four nitroaliphatic compounds in the reaction
    product are a function of the reaction temperature. In Europe,
    propane is reacted with nitrogen peroxide (N2O4) and an excess
    of oxygen at 150-330 °C and 0.9-1.2 MPa (9-12 atm.), yielding the
    same nitroaliphatic compounds in slightly different proportions as
    produced by the USA process (Anon., 1976). Reaction products are
    condensed, washed, and separated by fractional distillation. There
    is no evidence that 2-NP is produced through human EHC 138:
    2-Nitropropane activities except by combustion and deliberate
    manufacture, although nitromethane has been detected in vehicle
    exhaust (Seizinger & Dimitrades, 1972).

    3.2.2  Uses

        The importance of 2-NP as an industrial chemical stems mainly
    from its desirable and occasionally unique characteristics as a
    solvent (Purcell, 1967; Anon., 1976; Fishbein, 1981; Baker &
    Bollmeier, 1981; IARC, 1982; ACGIH, 1986). It is an excellent

    solvent or cosolvent for a variety of fats, waxes, gums, resins,
    dyes and other organic compounds, including vinyl, acrylic,
    polyamide and epoxy resins, chlorinated rubbers, and organic
    cellulose esters. The ability of 2-NP to form an azeotrope with
    water and the associated large heat of absorption permit it to
    displace monomolecular layers of water molecules and secure a better
    bond between pigments and the surfaces to which they are applied.
    Its major use is as a solvent for inks, paints, varnishes, adhesives
    and other coatings such as beverage container linings. It is used
    principally in blends with other solvents to impart desirable
    characteristics, such as greater solvency, better flow
    characteristics and film integrity, greater pigment dispersion,
    increased wetting ability, improved electrostatic spraying
    properties, or reduced drying time. 2-NP is also used industrially
    as a processing solvent for separating closely related substances in
    natural products or reaction mixtures. These have included, for
    example, separation of oleic acid from polyunsaturated fatty acids
    and cetyl from oleyl alcohols.

        In addition to the above, 2-NP has a number of minor uses
    (Anon., 1976; Baker & Bollmeier, 1981). These include a medium for
    chemical reactions, an intermediate for the manufacture of
    2-nitro-2-methyl-1-propanol, 2,2-dinitropropane, 2-amino-2-
    methyl-1-propanol and other propane derivatives, and a component of
    explosives, propellants, and fuels for internal combustion engines.
    The latter usage appears limited to model engines used by hobbyists
    and to racing cars. Although the addition of 2-NP to fuel improves
    diesel engine performance, it is not used commercially as a diesel
    fuel additive since superior alternatives are available (Banes,
    1989)a. In the USA, mixed isomers of nitropropane are used to
    denature ethanol (US FDA, 1987). The addition of 2-NP to hydrocarbon
    mixtures has been shown to inhibit corrosion of tin-plated steel
    aerosol cans (Flanner, 1972).

    3.3  Release into the environment

        There is some quantitative data on releases of 2-NP into the
    environment. The US Environmental Protection Agency has supported a
    thorough, though largely speculative, analysis of the problem (US
    EPA, 1980). Releases of 2-NP occur mainly into the atmosphere and
    can result from spillage, from venting of gases and fugitive
    emissions during manufacture, transfer and use, and from solvent
    evaporation from coated surfaces. The US EPA document estimated that
    of the 14 000 tonnes of 2-NP produced in the USA in 1979, 5714
    tonnes (41%) was released into the air, and 1 tonne into water. Only
    230 tonnes (1.6%) was destroyed by incineration or waste treatment.
    The major contributor to this release estimate was evaporation of
    2-NP used as a solvent in printing ink and surface coatings (4450

    a   Personal communication from the US Environmental Protection
        Agency, Ann Arbor, Minneapolis

    tonnes, 78% of releases). Manufacture of 2-NP is a largely enclosed
    process and in 1979 it accounted for only 21 tonnes (0.3%) of the
    amount released into the environment. A more recent examination of
    this problem (National Library of Medicine, 1989) reported a similar
    situation concerning environmental releases of 2-NP in the USA. Out
    of a yearly total of 299 tonnes, 205 tonnes (69%) was released into
    the air with 123 tonnes coming from point (large, easily identified)
    sources and 82 tonnes from non-point (small, not easily identified)
    sources. Only 2 tonnes (< 1%) was released directly into water, and
    1 tonne into municipal sewage treatment plants. The remainder was
    buried in closed containers (76 tonnes, 25%) or was disposed of in
    unspecified ways (15 tonnes, 5%).


    4.1  Transport in the environment

        2-NP appears to be highly mobile in the natural environment.
    Cupitt (1980) considered physical removal of 2-NP from the
    atmosphere unlikely because it was not soluble enough to be rapidly
    washed out and had a vapour pressure too great for strong adsorption
    on particles. The partition of 2-NP between air and water at
    equilibrium was estimated by the method of Swann et al. (1983) to be
    about 0.5% in air and 99.5% in water (US EPA, 1985). These values
    indicate rapid and easy exchange between air and water. The soil
    sorption coefficient (ratio of soil concentration to water
    concentration) and the bioconcentration factor were estimated by the
    methods of Kenaga (1980) to be 20 and 2.5, respectively (US EPA,
    1985). Measured values for absorption and bioaccumulation were
    somewhat greater than these estimates. Freitag et al. (1982, 1985)
    obtained concentration factors over water for activated sludge,
    unicellular algae  (Chlorella fusca), and fish (golden ide) of 70,
    20, and < 10, respectively. These values indicate that 2-NP is not
    strongly bioaccumulated and is readily desorbed from sediment
    particles and leached from soil. Thus, in summary, since 2-NP is
    slightly water soluble, slightly adsorbed by sediment, slightly
    bioaccumulated, and evaporates readily into the atmosphere, it will
    be distributed in both air and water and not accumulated in any
    individual environmental compartment.

    4.2  Biotic and abiotic transformation

        Data concerning the destruction of 2-NP by biotic and abiotic
    processes are limited. 2-NP has significant photoabsorption in the
    environmentally relevant range of > 290 nm (Sadtler, 1961) and is
    likely to undergo photolysis (Cupitt, 1980; US EPA, 1985). On the
    basis of physical and chemical properties Cupitt (1980) hypothesized
    that it would be rapidly removed from the atmosphere by photolysis
    and estimated a reduction in concentration of 1/e (0.369) in 0.2
    days. This is equivalent to a half-life of 0.14 days (3.36 h).
    However, measurements of photochemical reactivity do not support
    such a rapid destruction of 2-NP. Studies aimed at defining the
    relationship between organic solvents and photochemical smog
    production ranked 2-NP as low to moderate in terms of its
    interactions with oxidants and its ability to produce formaldehyde
    and other lachrymators (Levy, 1973). Laboratory measurements also
    suggested slow decomposition (Freitag et al., 1985). The methodology
    employed (Korte et al., 1978; Lotz et al., 1979; Freitag et al.,
    1982), i.e. irradiation of the solvent adsorbed on silica gel by
    light from a high pressure mercury lamp filtered through pyrex, was
    too different from natural conditions to permit quantitative
    extrapolation from laboratory results to rates of photolysis in the
    atmosphere. The study provided comparative photodecomposition rates
    for a large number of solvents. The rate of photodecomposition for

    2-NP was roughly half that of dichlorodiphenyltrichloroethane (DDT),
    similar to the rates for dodecane and 2,4-dichlorobenzoic acid, and
    roughly twice those for kepone and dieldrin. Paszyc (1971) reported
    that the major decomposition products for both gaseous and liquid
    2-NP under laboratory conditions were nitrogen dioxide, acetone,
    isopropyl nitrite, isopropanol, methylcyanide, water, and propane,
    regardless of whether irradiation was monochromatic 253.7 nm light
    or the full spectrum of light produced by a high pressure mercury
    lamp. Cupitt (1980) speculated that the major products of
    photodecomposition in nature would be formaldehyde and acetaldehyde.

        Biological decomposition of 2-NP appears likely, but is probably
    rather slow in nature. Enzymes capable of oxidizing or initiating
    non-enzymatic oxidation of 2-NP have been identified in horseradish
    (De Rycker & Halliwell, 1978; Porter & Bright, 1983; Indig &
    Cilento, 1987), pea seedlings (Little, 1957), and a variety of
    microorganisms including bacteria, yeasts, and fungi (Little, 1951;
    Kido et al., 1975; Soda et al., 1977; Dhawale & Hornemann, 1979;
    Patel et al., 1982). In  in vitro preparations of horseradish
    (Dhawale & Hornemann, 1979), pea seedlings (Little, 1957), a fungus
     (Streptomyces achromogenes) (Dhawale & Hornemann, 1979), and a
    yeast  (Hansenula mrakii) (Kido et al., 1975), 2-NP was converted
    to a less toxic compound, acetone, and a moderately toxic compound,
    nitrite. In addition to nitrite, some nitrate may also be formed
    (Indig & Cilento, 1987). In the yeast, nitrite was subsequently
    reduced to ammonia. The importance of these processes in nature is
    unknown. Kido et al. (1975), however, reported that only 4 out of 14
    species of microorganisms tested would grow in a medium containing
    5 g 2-NP/litre. The only study of 2-NP decomposition by a population
    of microorganisms (Freitag et al., 1985) utilized activated sludge
    grown at 25 °C. Solvent concentrations in these experiments were low
    (50 µg/litre) to prevent adaptation to the substances tested (Korte
    et al., 1978). In 5 days only 0.4% of the 2-NP was converted to
    carbon dioxide. In summary, these data suggest that in both
    terrestrial and aquatic communities 2-NP is biologically decomposed
    and that the rate may be slow, but they offer no definite
    information on the problem.


    5.1  Environmental levels and general population exposure

        General population exposure to 2-NP appears to be very low.
    There seem to be no records of its occurrence in water or in outdoor
    air away from areas of manufacture and use. The only information on
    intake exists in the form of a memorandum from Modderman (1983)a.
    The daily intake per person in the USA was estimated to be 50 to
    100 mg. The residuum from its use as a solvent for beverage can
    coatings, film laminating adhesives and printing inks for flexible
    food packaging may account for as much as 37 ng/day and from
    vegetable oils fractionated with 2-NP, 30 ng/day. 2-NP residues of
    0.077 mg/litre (77 ppb) to 0.24 mg/litre (204 ppb) have been found
    in such oils. In a further report on the evaluation of
    2-nitropropane as a food processing solvent, it was assumed that
    residues of less than 10 µg/kg would occur in oils, giving rise to
    estimated daily intakes of 10 ng/day. The use of 2-NP as a food
    processing solvent was not recommended (FAO/WHO, 1990a,b). As
    mentioned in section 3.1, smokers are exposed regularly to low
    concentrations of 2-NP. Hoffmann & Rathkamp (1968) reported 1.1 to
    1.2 µg in the smoke of a single cigarette. 2-NP was reported to
    occur in the expired air of 11.1% (5 of 54 individuals) of a sample
    of healthy adult urban dwellers (Krotoszynski et al., 1979). The
    geometric mean was 0.406 ng/litre with one-sigma limits of
    0.119 ng/litre and 1.38 ng/litre, (at 25 °C, 98 MPa (760 mmHg)). The
    sample was entirely of non-smokers who had avoided medication and
    prolonged exposure to perfume, paint, glue, aerosols, dust, tobacco
    smoke and areas polluted with industrial wastes during, and for at
    least 7 days prior to, the sampling period, and also avoided
    cosmetics, spices, seasonings, and alcoholic beverages during and
    immediately prior to sampling. The origin of the exhaled 2-NP is
    unclear. Exposure to 2-NP may be further reduced in the future since
    a number of regulations have been enacted and recommendations made
    to declare it a harmful, carcinogenic substance and a toxic waste,
    and to discourage its use (IARC, 1982; IRPTC, 1986; US FDA, 1987; US
    NIOSH, 1988).


    a   Memorandum from Modderman, J.P. to Shibko, S., Associate
        Director for Regulatory Evaluation, Department of Health & Human
        Services, USA, 8 pp. "Exposure estimates for chemicals to be
        included in the NTP annual report on carcinogens".

    5.2  Potential occupational exposure

        The number of workers in the USA who handle 2-NP or mixtures
    containing 2-NP has been variously estimated as 15 000 (US EPA,
    1977), 38 600 (Occupational Health Services, Inc., 1982), 100 000
    (Finklea, 1977), and 185 000 (Beall et al., 1980). Based on
    employment values of the US Bureau of the Census (1987) these
    estimates of exposed workers represent from 0.02% to 0.19% of the
    civilian workforce in the USA. The low estimate of 15 000, although
    quoted in a US Environmental Protection Agency report, originated
    with a manufacturer of 2-NP. The estimate generated by Occupational
    Health Services, Inc., carried out under contract with a
    manufacturer of 2-NP, was based on a detailed survey of
    distributors, manufacturers, and users, and thus may represent a
    reasonable approximation. This report considered 38 600 to be the
    best estimate of the total number of exposed workers in the USA and
    set 126 600 workers as an upper boundary. It further estimated that
    significant exposure (defined as exposure to at least 10% of the US
    OSHA exposure limit or 9.1 mg/m3 (2.5 ppm)) ranged from 4000 (best
    estimate) to 10 600 (upper boundary) workers. Sources of worker
    exposure identified in a survey conducted in the USA by the National
    Institute for Occupational Safety and Health (Finklea, 1977)
    included rotogravure and flexographic inks used in printing, and
    coatings and adhesives used in industrial construction and
    maintenance, highway marking, ship building and maintenance,
    furniture manufacture, and food packaging. A US NIOSH survey
    estimated that 9815 workers in the USA were exposed to 2-NP or to
    trade-name products containing 2-NP (US NIOSH, 1983).

        Occupational exposure limits are summarized in Table 3.

        There is little data on actual occupational exposure, although
    the limited information on conditions in the USA summarized in
    Table 4 suggests that it is highly variable. Manufacture of 2-NP, an
    enclosed process, appears to involve little employee exposure much
    of the time, but spills and operations such as filling drums can
    briefly expose a few workers to high concentrations. In general, low
    exposures may be typical in some painting operations and in the
    manufacture of tyres, but other painting and manufacturing
    operations appear, at least in the past, to have exposed workers to
    dangerously high concentrations. Workers were exposed to
    concentrations of 2-NP up to at least 2744 mg/m3 (754 pm) in a
    pigment production facility and up to at least 265 mg/m3 (73 ppm)
    in a solvent extraction plant. Evidence exists that concentrations
    of 2-NP at the solvent extraction plant prior to the investigation
    were at times substantially greater than the values measured during
    the investigation (Crawford et al., 1985). Exposure levels mentioned
    in the report by Occupational Health Services, Inc. (1982) were
    mainly in the vicinity of 3.6 mg/m3 (1 ppm), although one printing

    Table 3.  Occupational exposure limits for 2-nitropropane in aira

                     Exposure limit

    Country         mg/m3        ppm       Category of limit

    Australia          36        10              TWA
    Belgium            36        10              TWA
    Brazil             70        20              AL
    Canada             90        25              CLV
    Denmark            36        10              TWA
    Finland            18         5              TWA
                      150        40             STEL
    Germany            18         5        1-year TWA(TRK)
    Hungary            10         3              CLV
    Netherlands       3.6         1            8-h TWA
                      7.3         2               STEL
    Poland             30         8              TWA
                       70        20             STEL
    Romania            47        13              TWA
                       70        20             STEL
    Sweden             18         5              TWA
                       36        10              CLV
    Switzerland        18         5              TWA
    United Kingdom     90        25            8-h TWA
    USA                90        25        8-h TWA (OSHA)
                       36        10        8-h TWA (ACGIH)
    Yugoslavia         90        25              TWA

    a  From: IRPTC (1986)

    ACGIH =  American Conference of Governmental Industrial Hygienists
    AL    =  Acceptable or tolerable limit
    CLV   =  Ceiling value
    MAK   =  Maximum worksite concentration
    OSHA  =  Occupational Safety and Health Administration
    STEL  =  Short-term exposure limit
    TLV   =  Threshold limit value
    TWA   =  Time-weighted average (MAK in Switzerland)
    TRK   =  Technical guiding concentration

    plant (Table 4) reported a peak concentration of 237 mg/m3
    (65 ppm) which lasted 30 min, and a time-weighted average of
    36-44 mg/m3 (10-12 ppm). In addition to inhalation, it is likely
    that workers using 2-NP as a solvent will have at least occasional
    contact with the liquid. 2-NP also has been reported to be a minor
    component of both fresh and used machine cutting fluid emulsion
    (Yasuhara et al., 1986). The importance of exposure to 2-NP as a
    contaminant of 1-nitropropane is unknown. In an investigation
    involving 1-nitropropane-sensitized ammonium nitrate blasting agents
    (Cocalis, 1982), 2-NP was below the detectable limit. Occupational
    exposure may be reduced in the future since strong recommendations
    have been issued on minimizing all worker contact with 2-NP and its
    fumes and on substituting other less toxic solvents where possible
    due to the carcinogenicity of 2-NP (IRPTC, 1986; US EPA, 1986; US
    NIOSH 1988).

        Table 4.  Air concentration of 2-NP in the work place

    Activity                    mg/m3           ppm           Reference

    Manufacture of 2-NP          3.64           approx 1        Brown & Dobbin (1977)

    Manufacture of 2-NP        0.7-364;         0.2-100;        Miller & Temple (1979)
                                98% of           98% of
                                samples          samples
                              were < 36.4       were < 10

    Vulcanizing tyres           0-0.18           < 0.05         Hollett & Schloemer

    Painting (bus                0.11            < 0.03a        Love & Kern (1981)

    Painting (railway            1.46             < 0.4         Hartle (1980)

    Solvent extraction           167.4            0-100         Crawford et al. (1985)

    Laboratory (1958)            14.6             0-21          Angus Chemical Co. &
                                               (average 4)      Occusafe, Inc. (1986)

    2-NP storage &             2111-6000        580-1640        Angus Chemical Co. &
    transfer area (1962);                                       Occusafe, Inc. (1986)
    drum filling

    Pigment production         109-2745          30-754         Angus Chemical Co. &
    facility (1970)                                             Occusafe, Inc. (1986)

    Painting (battery          36.4-109           10-30         Skinner (1947)

    Manufacturing              72.8-164           20-45         Skinner (1947)
    (coating forms)

    Printing                   approx 40          1-65          Occupational Health
                                               (approx 11)      Services, Inc. (1982)

    a  below limit of detection

    6.1  Absorption

        2-NP is absorbed via the lungs, the peritoneal cavity, the
    gastrointestinal tract, and possibly, to a lesser extent, via the
    skin. Absorption via the lungs, peritoneal cavity, and
    gastrointestinal tract  have been used in experimental studies and
    have been investigated using rats and 14C-labelled 2-NP. Pulmonary
    absorption was examined by Nolan et al. (1982), Müller et al.
    (1983), and Filser & Baumann (1988). Nolan et al. (1982) considered,
    on the basis of respiratory rate and tidal volume of the rat and the
    accumulation of 2-NP during the 6-h period of exposure, that a
    minimum of 40% of the inhaled 2-NP was absorbed. This value is
    minimal since it does not include 2-NP metabolized and eliminated
    during exposure. The data of Müller et al. (1983) suggested that
    immediately following exposure to 728 mg/m3 (200 ppm) for 3 h,
    plasma contained approximately 0.4% as 2-NP and 7.2% as metabolites
    of the 2-NP inhaled. The metabolites were mainly acetone but also
    included a small amount of isopropanol. These percentages were
    estimated from the results of Müller et al. (1983) and normative
    data for the laboratory rat (Baker et al., 1979), and support rapid
    pulmonary uptake of 2-NP since 2-NP and its metabolites sequestered
    elsewhere in the body and loss of metabolized 2-NP during exposure
    were not considered. Filser & Baumann (1988) reported that uptake of
    gaseous 2-NP was rapid, the clearance rate being equal to the
    ventilation rate. The value they cite for the latter, 32
    litres.h-1.kg-1), seems large in comparison with normative data
    for the laboratory rat (Baker et al., 1979).

        The rate of 2-NP uptake by rats from intraperitoneal injection
    was examined by Müller et al. (1983). Ten minutes after an injection
    of 25 mg/kg, the blood plasma contained 3.3% of the dose as 2-NP and
    1.9% as metabolites, acetone, and isopropanol, indicating an uptake
    of greater than 5.2% since presumably some of the dose was already
    lost from the body and to other tissues in the body during this
    initial period. These percentages were estimated from the data of
    Müller et al. (1983) and normative data for the laboratory rat
    (Baker et al., 1979). A dose of 50 mg/kg yielded partially
    dissimilar results. The 10-min average value was low and also had a
    very large standard deviation. This may have reflected large
    differences among the rats in their initial uptake rates for 2-NP or
    an experimental problem such as injection into the gastrointestinal
    tract rather than the peritoneal cavity. Blood plasma contained, 10
    min after injection, only 1.4% of the dose as 2-NP and 1.3% as
    acetone and isopropanol. These data indicate that uptake from the
    peritoneal cavity is fairly rapid, and suggest that the relatively
    slower uptake of the 50-mg/kg dose may have reflected saturation of
    the uptake mechanisms, since initial concentrations in the plasma
    did not exceed those following the 25-mg/kg dose. Intraperitoneal
    injections were used by Andrae et al. (1988), Guo et

    al. (1990), Hussain et al. (1990), and Conaway et al. (1991) to
    demonstrate that 2-NP induced nucleic acid damage in the livers of
    Wistar, F-344 and Sprague-Dawley rats.

        Absorption of 2-NP via the gastrointestinal tract was
    investigated with male Wistar rats by Derks et al. (1989). They
    found that the systemic availability of orally administered 2-NP
    from a water solution was very high (90%) and absorption was rapid,
    maximum plasma values being reached within 15 min after dosage.
    Absorption of 2-NP given in olive oil was much slower and
    availability was only 34% during the initial 3 h following dosage.
    The authors suggested that absorption from oil was incomplete at 3 h
    and might ultimately be much higher, since the olive oil was
    absorbed and the 2-NP redistributed between the oil and aqueous

        Although workers are cautioned against dermal contact with 2-NP
    (Beall et al., 1980; US EPA, 1986), there appear to be no
    quantitative data on dermal absorption. The solubility of 2-NP in
    both polar and non-polar solvents, together with its small molecular
    size, suggests that it should be absorbed readily through the skin
    (Malkinson & Gehlmann, 1977). Dermal application of 2 g 2-NP/kg to
    rabbits produced no obvious symptoms (Wilbur & Parekh, 1982);
    however, as noted below, the rabbit is relatively resistant to the
    toxicity of 2-NP. 

    6.2  Distribution

        The distribution of 2-NP and its carbon-containing metabolites
    among the organs and tissues in Sprague-Dawley rats was examined by
    Nolan et al. (1982) via inhalation, and by Müller et al. (1983) via
    intraperitoneal injection. Both utilized 14C-labelled 2-NP and
    thus their data do not reveal the distribution of nitrite and other
    nitrogen-containing metabolites generated from the nitro portion of
    the 2-NP molecule. One hour after intraperitoneal injection,
    radioactivity was concentrated in fat;  there were intermediate
    amounts in the blood, liver, and kidney, and lower amounts in other
    organs and tissues (Müller et al., 1983). By 40 h, the highest
    concentrations were in bone marrow and adrenal tissue, intermediate
    amounts being found in the kidney, liver, spleen, lungs, and omental
    fat, and by 8 days only the concentration of 14C in adrenal tissue
    was noticeably greater than elsewhere in the body. However, Nolan et
    al. (1982), found, both immediately and 48 h after a 6-h period of
    2-NP inhalation, that  highest concentrations of carbon from 2-NP
    were in the liver and kidney  and relatively little in the fat.

        Differences in methodology limit intercomparison of these
    studies. Their major consistency is the presence of high
    concentrations of 2-NP and its labelled carbon in the liver and
    kidney, organs (as discussed below) actively involved in the
    metabolism of 2-NP and excretion of its metabolites.

        The relevance of these studies on tissue distribution of 2-NP
    and its carbon-containing metabolites to the toxicity of 2-NP is
    unclear, since (as discussed below) most of the dose is rapidly
    metabolized initially to acetone and nitrite. The 14C label used
    in these studies thus traced mainly the distribution of acetone and
    its metabolites in measurements made more than a few hours after

        Dequidt et al. (1972) provided limited data on the distribution
    of nitrite among body organs of the rat following inhalation and
    intraperitoneal injection of 2-NP. The data suggest a fairly uniform
    distribution among the heart, lungs, kidney, spleen, and, 
    sometimes, the liver. In the majority of experiments, however, no
    nitrite was detected in the liver. No explanation is offered for the
    latter observation, and data in the paper are so erratic as to
    suggest the possibility of analytical problems.

    6.3  Metabolic transformation

        Starting with a report by Scott (1943), there have been numerous
    studies on the metabolic transformation of 2-NP by mammals,
    mammalian cells, microorganisms, and isolated enzymes. These studies
    have shown that the major pathway for metabolic transformation of
    2-NP involves oxidation to nitrite and acetone. Evidence for the
    formation both of nitrite and acetone was reported from studies on
    liver microsomes from rats pretreated with phenobarbital or
    3-methylcholanthrene (Ullrich et al., 1978),  cultured hepatocytes
    from untreated rats (Haas-Jobelius et al., 1991), liver microsomes
    from untreated mice (Marker & Kulkarni 1986a,b; Dayal et al., 1991),
    V79 Chinese hamster cells (Haas-Jobelius et al., 1991), and a yeast
    (Kido et al., 1975). Nitrite was reported to be a major metabolite
    of 2-NP in rabbits (Scott, 1943), rats (Dequidt et al., 1972), and
    liver microsomes from rats (Sakurai et al., 1980) and mice (Marker &
    Kulkarni, 1985). Acetone was identified as a major metabolite of
    2-NP in rats and chimpanzees (Muller et al., 1983).

        Enzymatic oxidation of the nitronate form of 2-NP to nitrite and
    acetone by horseradish peroxidase (Porter & Bright, 1983), a
    dioxygenase from the yeast  Hansenula mrakii (Kido et al., 1984),
    and mouse liver microsomes (Dayal et al., 1991) was several times
    more rapid than that of 2-NP under identical conditions. In addition
    to acetone, a smaller amount of isopropanol is produced at least in
    rats and chimpanzees (Muller et al., 1983). The source of the
    isopropanol was not specified in this study, but since reduction of
    acetone in the body is negligible (De Bruin, 1976), isopropanol may
    be formed directly by oxidation of 2-NP. The formation of a
    hydroxyisopropyl radical during the oxidation of 2-NP was suggested
    by Kuo & Fridovich (1986).

        The metabolic fates of these metabolites of 2-NP are well known.
    Acetone is produced by a minor metabolic pathway in the mammalian
    body (Smith et al., 1983) and has been detected in small amounts in
    the blood, urine, and expired air of normal humans (Mabuchi, 1979;
    Conkle et al., 1975). It may be excreted directly via expired air,
    urine, and loss through the skin, or may enter into the general
    metabolism either via cleavage to a 2-carbon acetyl fragment and a
    1-carbon formyl fragment or via oxidation to pyruvic acid (De Bruin,
    1976). The proportion excreted unchanged increases with increasing
    dosage, suggesting an easily saturable metabolic pathway.
    Isopropanol is oxidized to acetone (De Bruin, 1976).

        Nitrite may exist as a minor constituent of the mammalian body.
    It is constantly replenished by ingestion and synthesis, and
    constantly removed by oxidation to nitrate. Nitrite and nitrate in
    the blood stream are rapidly and homogeneously distributed
    throughout the body (Parks et al., 1981). Nitrite rapidly oxidizes
    divalent ferrous haemoglobin to trivalent ferric methaemoglobin
    (Burrows, 1979). Little is transported to the tissues or excreted,
    at least in dogs, sheep, and ponies (Schneider & Yeary, 1975).
    Dequidt et al. (1972), however, reported substantial urinary
    excretion of nitrite by rats following inhalation or intravenous
    injection of 2-NP. Methaemoglobin is incapable of transporting
    oxygen and, during enzymatic repair of this defect, nitrite is
    reoxidized to nitrate. Parks et al. (1981) reported that 10 min
    after intratracheal instillation of labelled nitrite into mice, 70%
    of the label in plasma was in nitrate, 3% in nonionic compounds, and
    only 27% remained as nitrite. Similar results were obtained with
    rabbits. Nitrate is slowly excreted through the kidneys (Schneider &
    Yeary, 1975) and also into saliva where it is reduced back to
    nitrite by bacteria and reabsorbed into the body via the
    gastrointestinal tract (Friedman et al., 1972). Small amounts of
    nitrite in the stomach may react with secondary amines and other
    amino substrates to form N-nitroso compounds which might be absorbed
    (Sander & Schweinsberg, 1972; Fine et al., 1982).

        The enzymatic system oxidizing 2-NP to acetone and nitrite was
    identified through  in vitro experiments using microsomes isolated
    from mammalian liver. Ullrich & Schnabel (1973) determined that
    cytochrome P-450, in liver microsomes from phenobarbital-pretreated
    rats, bound 2-NP. Ullrich et al. (1978) subsequently reported that
    liver microsomes from rats pretreated with phenobarbital or
    3-methylcholanthrene rapidly catalysed the oxidation of 2-NP to
    acetone and nitrite. The latter were produced in roughly equal
    quantities. Surprisingly, however, the rate of this reaction was not
    diminished under conditions of reduced oxygen pressure. The activity
    of preparations from untreated control rats was generally very low.
    Sakurai et al. (1980) demonstrated that this enzyme system in rats
    was active in metabolizing other aliphatic nitro compounds. Marker &
    Kulkarni (1985, 1986a, 1986b), working with mice, obtained somewhat
    different results. They reported rapid denitrification of

    2-NP to nitrite and acetone by liver microsomes from untreated mice,
    and an acetone production at least twice the nitrite release. These
    authors suggested that multiple forms of cytochrome P-450 are
    involved, and claimed that nitrite is sequestered in the reaction
    mixture and that denitrification of 2-NP may involve a reductive or
    at least non-oxidative pathway as well as an oxidative pathway. They
    also noted large differences in the rates of hepatic microsomal
    enzymatic nitrite release among the five strains of mice tested.
    Jonsson et al. (1977) demonstrated that hepatic microsomes from
    uninduced rabbits could denitrify a compound related to 2-NP,

        In addition to oxidative denitrification, a reductive pathway
    has been shown to occur in cultured hepatocytes from Wistar rats and
    in V79 Chinese hamster cells. Nitroreduction was indicated by the
    fact that the cells formed acetone oxime, the tautomeric form of
    nitrosopropane (Haas-Jobelius et al., 1991).

        Evidence for the involvement of more than one pathway for the
    metabolism of 2-NP in the rat was also obtained by Denk et al.
    (1989). Their experiments on the pharmacokinetics of 2-NP in rats
    exposed by inhalation suggested that there are two different
    pathways both in male and female animals, a saturable one of low
    capacity and high affinity according to Michaelis-Menten kinetics
    and a non-saturable one following first-order kinetics. First-order
    kinetics was similar in the two sexes, but striking differences
    between sexes were observed in the kinetics of the saturable
    pathway. The authors showed that in females more 2-NP was
    metabolized by the non-saturable pathway at concentrations above 655
    mg/m3 (180 ppm), and in males at concentrations above 218 mg/m3
    (60 ppm), and linked their observations to the reported higher
    susceptibility to liver damage of males as compared to females
    (Griffin & Coulston, 1983). Denk et al. (1989) suggested that it is
    the first-order metabolic process which results in the formation of
    toxic products whereas the saturable pathway was suggested to lead
    to less toxic metabolites.

        These observations on the hepatic metabolism of 2-NP and related
    compounds by rats, mice, and rabbits indicate differences among
    species and even strains. It is probable that more than one enzyme
    system is involved. In mice as well as rats hepatic cytochrome P-450
    may be important in the metabolism of this xenobiotic. 

        Observations by Ivanetich et al. (1978) suggested an additional
    detoxifying role for hepatic microsomal cytochrome P-450. They
    demonstrated that under aerobic conditions  in vitro 2-NP could
    degrade the haem moiety of cytochrome P-450 in phenobarbital-induced
    rats and speculated that this provided an additional mechanism for
    trapping reactive metabolites before these could damage essential
    cellular constituents.

        In addition to the hepatic enzymatic systems examined in rats
    and mice, Mochizuki et al. (1988), as mentioned above, described a
    2-NP denitrifying system in adrenal microsomes of uninduced
    guinea-pigs. They identified this cytochrome-P-450-dependent
    monooxygenase as benzo[ a]pyrene hydroxylase.

    6.4  Elimination and excretion

        Elimination of 2-NP and its metabolites has been examined mainly
    in rats and, to a much lesser extent, in chimpanzees in studies
    which utilized measurements of radioactivity from 14C-labelled
    2-NP as well as measurements of 2-NP and its metabolites. Dosage by
    inhalation, intravenous injection, and intraperitoneal injection all
    yielded fairly similar results. During a 48-h period after a 6-h
    exposure of rats to 73 mg/m3 (20 ppm) and to 560.6 mg/m3
    (154 ppm) of 14C-labelled 2-NP, about 50% of the radioactivity in
    the absorbed dose was excreted via the lungs as carbon dioxide
    (Nolan et al., 1982). The proportion of the absorbed dose excreted
    via the lungs as unchanged 2-NP was 4% at the low dose level and 22%
    at the high level. Still less of the labelled carbon was eliminated
    via faeces and urine, i.e. 11% and 8%, respectively, at the low dose
    level, and 5% and 11%, respectively, at the high level.
    Disappearance of 2-NP from the blood after exposure at the high dose
    level followed a first-order relationship and yielded a half-life of
    48 min. Limited data in Müller et al. (1983) yielded a half-life for
    rats of approximately 80 min for 2-NP in plasma following a 3-h
    exposure to a concentration of 728 mg/m3 (200 ppm). Nolan et al.
    (1982), however, found that disappearance of the 14C label of the
    2-NP from the plasma was markedly slower and biphasic. During the
    first 12 h following exposure to 560.6 mg/m3 (154 ppm), the
    half-life for plasma radioactivity was 172 min and, following
    exposure to 73 mg/m3 (20 ppm), 354 min. After 12 h, loss of
    radioactivity from plasma was much slower, the half-life being
    approximtely 35-36 h for both doses. These data on loss of 2-NP and
    its 14C label indicate that 2-NP is rapidly eliminated from the
    body mainly by metabolic transformation and to a lesser degree by
    pulmonary excretion of the unchanged compound. The major
    carbon-containing metabolites of 2-NP, acetone and isopropanol,
    presumably enter into the general metabolism of the body and are
    eliminated via the intermediary metabolism as part of a much larger
    carbon pool.

        Pulmonary excretion of 2-NP, like loss of the 14C label from
    plasma, is dose dependent, biphasic, and follows first-order
    kinetics (Nolan et al., 1982). Fifty times more 2-NP was exhaled
    during the first hour following exposure to 560.6 mg/m3 (154 ppm)
    than during the first hour following exposure to 73 mg/m3
    (20 ppm). Following exposure to 73 mg/m3, 2-NP was excreted for
    the first 7 h at a rate which decreased by one half every 64 min,
    and subsequently decreased by one half every 16 h, whereas following
    exposure to 560.6 mg/m3, the half-times of excretion were 71 min

    for the first 12 h, and 16 h for the subsequent period. Changes in
    the rates of pulmonary excretion of 14C-labelled carbon dioxide
    were similar for 48 h following exposure to 73 and 560.6 mg/m3.
    Eighty seven per cent of the total was eliminated during the first
    12 h after exposure; loss was somewhat less rapid thereafter. The
    dose-dependent nature of pulmonary excretion of 2-NP suggests that
    greater concentrations of 2-NP in the blood markedly increase
    exhalation of the unchanged compound and reduce the percentage
    metabolized. Thus exposure of the tissues to 2-NP and its
    metabolites may not be a linear function of the inhaled dose.

        Derks et al. (1989) found that the plasma half-life of
    intravenous doses of 0.01-0.05 g/kg in rats was 45 min during the
    first 4 h. Loss was linear over this dose range and could be
    described by an open single-compartment model. They suggested that
    the measured loss from plasma may be due in part to spontaneous
    conversion of 2-NP to its anionic form, 2-NP nitronate.

        Elimination of 2-NP by Sprague-Dawley rats following
    intraperitoneal injection of 14C-labelled 2-NP was studied by
    Müller et al. (1983) and was generally similar to the elimination of
    2-NP following inhalation. The concentration of 2-NP in plasma
    declined exponentially with time, with half-lives of 70 and 125 min
    during at least the initial 6 h following injections of 25 and
    50 mg/kg, respectively. Metabolites of 2-NP, acetone and
    isopropanol, reached maxima 2-4 h after injection of 25 mg/kg, and
    at least 4-6 h after injection of 50 mg/kg. The concentration of
    isopropanol ranged from 1/16 to 1/34 the concentration of acetone.
    During the initial 40 h after injection of 50 mg/kg, 4.5% of the
    dose was exhaled as 2-NP, 10.4% as acetone, and 38.1% as carbon
    dioxide. Losses via urine (5.9%) and faeces (0.7%) were small in
    comparison with the 53% loss via exhalation. Müller et al. (1983),
    however, reported that only 12% of the dose was recovered from the
    carcasses, leaving a large amount (28.4%) unaccounted for and thus
    casting some doubt on their values.

        With one exception, results similar to the above were obtained
    following intravenous injection of 14C-labelled 2-NP (10 mg/kg)
    into male chimpanzees (Müller et al., 1983). The concentration of
    2-NP in plasma declined exponentially with time, the half-life being
    92 min. The concentration of acetone reached a maximum 6 h after
    injection and remained high for at least 48 h. The concentration of
    isopropanol peaked 3 h after injection when it approached that of
    acetone, but otherwise was a third to a quarter that of acetone. The
    concentration of 2-NP and its carbon-containing metabolites (i.e.
    the concentration of 14C) in plasma declined exponentially with a
    half-life of 5.5 h for the initial 10 h, and a half-life of 48 h
    thereafter. As in rats, exhalation was the major means of
    elimination of 2-NP and its carbon-containing metabolites. During
    the first 3 days after injection, only 5-6% of the 14C in the dose
    was recovered in urine and only 0.4-0.5% in faeces. Acetone,

    isopropanol, and 2-NP were mainly eliminated via renal excretion;
    urine collected during 6 to 24 h after injection contained 3.1 mg
    acetone/litre, 7.2 mg isopropanol/litre, and 1.8 mg 2-NP/litre.
    Isopropanol may thus be maintained at low concentrations in the
    plasma both by oxidation to acetone and by rapid excretion. In
    addition to acetone, isopropanol, and 2-NP, 14C was excreted as an
    unidentified polar metabolite which by 24 h after injection
    contained 90% of the radioactivity in the urine. The one striking
    difference between results with rats and with chimpanzees, i.e. the
    relatively much higher plasma concentrations of isopropanol in
    comparison to acetone, might indicate interspecific variation in the
    excretion of 2-NP and its metabolites.

        Dequidt et al. (1972) provided limited information on the
    excretion of nitrite following inhalation and intraperitoneal
    injection of 2-NP. Rats weighing approximately 250 g each were given
    a daily injection of 0.11 g/kg. Urinary excretion of nitrite was 10
    to 35 µg/animal during the first day following the initial
    injection, and reached a daily rate of 11 mg/animal by the fourth
    injection. The latter rate of excretion represents three quarters of
    the nitrogen injected daily as 2-NP, and stands in sharp contrast to
    the results of Schneider & Yeary (1975), who reported that little
    intravenously injected nitrite was excreted by dogs, sheep or
    ponies. Following exposure of rats to a 2-NP concentration of
    2766 mg/m3 (760 ppm) for 8 h on each of two successive days, daily
    elimination of nitrite was approximately 30 mg/animal. This was
    equivalent to about 20% of the 2-NP inhaled daily and possibly as
    much as 50% of the absorbed daily dose. The amount of 2-NP inhaled
    was estimated from normative data for the rat (Baker et al., 1979),
    and absorption was assumed to be 40% of the amount inhaled (Müller
    et al., 1983). No nitrite was detected in urine during exposure of
    rats to 291 mg/m3 (80 ppm) for 8 h per day on 5 successive days.

    6.5  Retention and turnover

        There is no evidence that 2-NP is retained for more than a few
    hours in the body. It is rapidly lost by exhalation and metabolic
    transformation. The known carbon-containing metabolites, acetone and
    isopropanol, are excreted rapidly and are also transformed into
    compounds which are normal to the body and enter into its general
    intermediary metabolism. There is less information on nitrite, the
    major metabolite of the nitro moiety. In rats much of the nitrite is
    excreted as such in the urine. There is no evidence for excessive
    accumulation of 2-NP or its metabolites in any organ or tissue.
    Information is also lacking on possible  N-nitroso and other toxic
    compounds synthesized from nitrite or the nitro moiety.


    7.1  Single exposure

        Data on single exposures to experimental animals, summarized in
    Table 5, indicate substantial differences in sensitivity among the
    species tested. The route of administration was mainly via
    inhalation, but other routes were also used. A quantitative
    comparison of the results from these studies is difficult due to a
    lack of information on both strain and sex of the animals used, to
    differences in the route of administration, and to large variations
    in dosage. The LC50 for mortality within 14 days following a 6-h
    exposure was estimated to be 1456 mg/m3 (400 ppm) for male rats
    and 2621 mg/m3 (720 ppm) for females (Baldwin & Williams, 1977).
    Exposure of rats (of unspecified sex) via inhalation to 14 058
    mg/m3 (3862 ppm) for 1 h or to 9584 mg/m3 (2633 ppm) for 2.25 h
    killed some of the animals within days. Exposure of rats to a much
    higher concentration of 2-NP, i.e. 53 508 mg/m3 (14 700 ppm),
    killed all animals within 4 h. An inhalation exposure of 4994
    mg/m3 (1372 ppm) or less for 2.25 h was not lethal to rats. Unlike
    rats, LC50 values were similar, i.e. 2031 and 2038 mg/m3
    (558 and 560 ppm), respectively, for male and female mice  following
    a 6-h exposure (Baldwin & Williams, 1977). Cats appeared more
    sensitive to acute exposure to 2-NP than rats. Exposure to
    8565 mg/m3 (2353 ppm) for 1 h (or lower concentrations for
    proportionately longer) was lethal to some cats. Rabbits and
    guinea-pigs, on the other hand, appeared far less sensitive to 2-NP
    than rats. Rabbits survived a 2.25-h exposure to 9584 mg/m3
    (2633 ppm) and guinea-pigs a 2.25-h exposure to 15 699 mg/m3
    (4313 ppm). The sequence in acute sensitivity of animals to inhaled
    2-NP (from most to least) was cat, rat and mouse, rabbit, and
    guinea-pig. The cat was almost an order of magnitude more sensitive
    than the guinea-pig.

        There are limited data on lethality via routes of administration
    other than inhalation. Large intraperitoneal doses were found to be
    promptly lethal to rats; 1.7 and 1.1 g/kg killed animals within 2 h
    and 4 h, respectively (Dequidt et al., 1972). The 14-day oral LD50
    for mice was 0.40 g/kg. The minimal oral lethal dose for the rabbit,
    0.50-0.75 g/kg, was much larger than the estimated minimum lethal
    dose via inhalation, 0.24 g/kg. Dermal application of 2 g/kg to
    rabbits produced no obvious local or systemic effects.

        Table 5.  Effects of single exposure to 2-nitropropane in mammalsa
              a)  Lethality

    Species                   Sex        Concentration     Estimated total   Effects/results                 Reference
                                                           doseb (g/kg)
                                       g/m3         ppm

     Oral administration

    Rabbitcd                                                                 lethal dose estimated as 0.50-  Machle et al. (1940)
                                                                             0.75 g/kg

    Mouse                     M/F                                            14-day LD50: 0.40 g/kg          Hite & Skeggs (1979)


    Ratc (Wistar)                      53.5       14 700        1.51         all animals died within         4 h Dequidt et al (1972)

    Ratcd                            5.5-14.1    1513-3865    0.10-0.17      death of some animalsc          Treon & Dutra (1952)

                                     2.6-8-57d   714-2353     0.06-0.08      no deathsd                      Treon & Dutra (1952)

    Ratcd (Wistar)                     2.77         760         0.16         death within 48 h;              Dequidtet al. (1972)

    Rate (CD)                  M       2.93         805         0.16         8/10 died within 14 days        Baldwin & Williams (1977)f

                               F       2.19         602         0.13         no deaths within 14 dayse       Baldwin & Williams (1977)f

                               M       2.10         574         0.14         8/8 died within 14 days         Baldwin & Williams (1977)f

                               M       1.68         461         0.10         7/8 died within 14 days         Baldwin & Williams (1977)f

    Table 5 (contd)

    Species                   Sex        Concentration     Estimated total   Effects/results                 Reference
                                                           doseb (g/kg)
                                       g/m3         ppm

     Inhalation (contd)

    Rate (CD)                  M       1.47         405         0.08         5/8 died within 14 days         Baldwin & Williams (1977)f

                                       1.34         367         0.08         no deaths within 14 days        Baldwin & Williams (1977)f

    Mousee (ICR)               F       2.70         740         0.47         14/14 died within 14 days       Baldwin & Williams (1977)f

                                       2.33         640         0.41         11/14 died within 14 days       Baldwin & Williams (1977)f

                                        1.8         495         0.32         2/14 died within 14 days        Baldwin & Williams (1977)f

    Mouse (ICR)                M       2.69         738         0.41         9/14 died within 14 days        Baldwin & Williams (1977)f

                                       2.08         558         0.28         7/14 died within 14 days        Baldwin & Williams (1977)f

                                       1.65         454         0.23         no deaths within 14 days        Baldwin & Williams (1977)f

    Catcd                            2.6-8.56    714-2353     0.07-0.19      death of some animals           Treon & Dutra (1952)

                                     1.19-2.87    328-787       0.02         no deaths                       Treon & Dutra (1952)

    Guinea-pigcd                     16.8-35.0   4622-9607    0.53-0.63      death of some animals           Treon & Dutra (1952)

                                     8.67-34.7   2381-9523    0.23-0.32      no deaths                       Treon & Dutra (1952)

    Rabbitc                          8.67-34.7   2381-9523    0.24-0.27      death of some animals           Treon & Dutra (1952)

                                     5.1-14.1    1401-3865    0.10-0.16      no deaths                       Treon & Dutra (1952)

    Table 5 (contd)

    Species                   Sex        Concentration     Estimated total   Effects/results                 Reference
                                                           doseb (g/kg)
                                       g/m3         ppm

     Intraperitoneal administration

    Ratcf                                                        1.7         death within 2 h                Dequidt et al. (1972)

                                                                 1.1         death within 4 h                Dequidt et al. (1972)

     Intraperitoneal administration (contd)

    Mousec                     M                                0.80         LD50                            Friedman et al. (1976)
    (Swiss ICR/HQ)

    a   Values recalculated as necessary to ppm and g/kg
    b   Estimated dose calculated by the formula: tidal volume x respiration frequency x exposure time x 2-NP conc. x alveolar
        retention/animal weight. Tidal volume and respiration frequency from Kaplan et al. (1983) for mice (0.15 ml, 163/min);
        from Baker et al. (1979) for rats (0.86 ml, 85.5/min); from Hoar (1976) for guinea-pigs (1.68 ml, 84/min); from Kozma
        et al. 81974) for rabbits (15.8 ml, 45/min); from Reece (1984) and Breazile (1971) for cats (42 ml, 31/min); alveolar
        retention in rat (0.40) from Nolan et al. (1982), used for all species; where not stated animal weights assumed to be
        average values, 20 g for mice, 250 g for rats, 500 g for guinea-pigs, 2.5 kg for rabbits, and 4.0 kg for cats
    c   Sex not specified
    d   Exposure time varied from 1 to 7 h
    e   Exposure time was 6 h
    f   Baldwin & Williams (1977) also exposed female rats for 6 h to concentrations of 2-NP lower than 2.2 g/m3 (602 ppm); these
        concentrations, i.e. 1.15, 1.35 and 1.69 g/m3 (316, 370 and 464 ppm), like 2.2 g/m3, produced no deaths within 14 days

    Table 5.  Effects of single exposure to 2-nitropropane
              b)  other effects

    Route of           Species            Sex      Estimated     Effects/results                      Reference
    administration                               total doseb

    Intraperitoneal    rat                 M         0.15        maximum hepatic injury achieved      Filser & Daumann (1988)
                       (Sprague-Dawley)                          with this dose

    Intraperitoneal    rat                 M         0.05        lipid accumulation, centrilobular    Zitting et al. (1981)
                       (Wistar)                                  necrosis, mitochondrial
                                                                 abnormalities, and changes in
                                                                 endoplasmic reticulum and
                                                                 glutathione content in liver
                                                                 within 24 h, as well as changes
                                                                 in enzyme activity in liver and

    Dermal             rabbit            M & F         2         no toxic effects observed            Wilbur & Parekh (1982)

    b  See footnote  b in Table 5a.

        The effects of acute exposure to 2-NP, in addition to lethality,
    are characterized primarily by hepatotoxicity and, at high exposure
    levels, methaemoglobin formation and depression of the central
    nervous system. Machle et al. (1940), in a description of symptoms
    resulting from exposure of laboratory animals to simple
    nitroparaffins, listed the following progression for guinea-pigs and
    rabbits after a latent period of 20 to 40 min: progressive weakness,
    unsteadiness, and incoordination ending in complete ataxia. The rate
    of respiration at first slowed and later became increasingly rapid.
    Most of these symptoms appear to reflect the narcotic effects
    normally associated with inhalation of volatile hydrocarbons, but
    the more rapid breathing may reflect an attempt by the body to
    compensate for the formation of methaemoglobin and loss of
    oxygen-carrying capacity of the red blood cells. Treon & Dutra
    (1952) noted similar progression from exposure to high
    concentrations of 2-NP vapour, i.e. lethargy and weakness, dyspnoea,
    cyanosis, prostration, and ultimately coma and death, but did not
    report more rapid breathing following a depression in rate of
    respiration. They also noted lacrimation, salivation, and gastric
    regurgitation in cats. In addition, the authors observed that, even
    with animals which died promptly (within 9.5 h) following a single
    exposure, there was a loss in body weight averaging 2.8%. Animals
    exposed to 8.56 g/m3 (2353 ppm) or higher concentrations of 2-NP
    displayed pathological  changes including hepatocellular damage,
    pulmonary oedema and haemorrhage, some disintegration of neurones in
    the brain, and widespread damage to the endothelium.

        Methaemoglobin and Heinz bodies (masses of denatured haemoglobin
    within erythrocytes) were found in the blood of animals following
    single exposures to high concentrations of 2-NP. In the case of
    cats, 60 to 80% of the haemoglobin was converted to methaemoglobin
    by exposure to 15.9 to 33.6 g/m3 (4360 to 9230 ppm) for 1 to 2 h,
    whereas much longer exposure of rabbits to these concentrations
    converted only 4 to 8% of the haemoglobin (Treon & Dutra, 1952).
    Dequidt et al. (1972) reported high levels of methaemoglobin in
    rats, i.e. 84% and 89%, following 1-h inhalation exposure to
    53.5 g/m3 (14 700 ppm) and intraperitoneal injection of 1.7 g/kg,
    respectively. Much lower methaemoglobin concentrations, 0.2 to 8.6%,
    resulted from a 1-h exposure to 2.8 g/m3 (760 ppm). One day after
    exposure to 15.4 g/m3 (4230 ppm) for 4.5 h or 8.5 g/m3
    (2335 ppm) for 2.25 h, rabbits had Heinz bodies in 45 to 80% of
    their red cells. These bodies disappeared gradually over 9 to 16
    days (Treon & Dutra, 1952). Exposure of rabbits to 13.8 g/m3
    (3790 ppm) for 1 h or 9.4 g/m3 (2580 ppm) for 2.25 h resulted in
    the formation of Heinz bodies in only 0 to 2% of the red cells.
    Formation of Heinz bodies in the cat may have reflected its high
    sensitivity to 2-NP. A 1-h exposure to 13.8 g/m3 (3790 ppm) and a
    20 min exposure to 16.4 g/m3 (4505 ppm) resulted in the appearance
    of Heinz bodies in 27% and 16% of the erythrocytes, respectively.

        Observations by Zitting et al. (1981) indicated that a single
    intraperitoneal injection of 0.05 g 2-NP/kg to rats can produce
    significant changes in the fine structure of the liver and in the
    physiology of both liver and brain. 2-NP produced a visible
    accumulation of lipid in hepatocytes, especially in periportal areas
    after 4 h, and the lipid level continued to increase for the next
    20 h. Within 4 h after injection there was also degranulation of the
    rough endoplasmic reticulum in hepatocytes and proliferation of the
    smooth endoplasmic reticulum. Within 24 h the former had almost
    disappeared and the latter was vacuolated or compacted. In addition,
    some hepatocytes had abnormal mitochondria and there was necrosis of
    hepatocytes around the central vein. The latter was reflected in a
    concurrent fourfold increase of serum alanine aminotransferase.
    Other enzymatic parameters in the liver were also markedly affected
    within 24 h. Cytochrome P-450 was markedly depressed,
    7-ethoxycoumarin  O-deethylase and 7-ethoxyresorufin  O-deethylase
    were diminished in activity, and microsomal epoxide hydratase,
    UDP-glucuronosyltransferase and glutathione peroxidase were
    increased in activity. In addition, the liver concentration of
    glutathione nearly doubled.

        The major observed neurochemical effect was a significant
    increase in acetylcholine esterase activity in the cerebrum and in
    isolated synaptosomes. There was little or no change in RNA,
    2',3'-cyclic nucleotide 3'-phosphohydrolase, or acid proteinase in
    the brain.

        Zitting et al. (1981) noted that these histopathological and
    enzymatic changes induced by 2-NP are nearly identical to the
    effects of carbon tetrachloride on the rat and are thus indicative
    of lipid peroxidation.

        Hepatotoxicity following exposure to 2-NP has also been 
    observed in mice (Dayal et al., 1989). Intraperitoneal doses of
    0.8 g/kg (9 mmol/kg) in male mice and 0.6 g/kg (6.7 mmol/kg) in
    female mice significantly increased plasma activities of enzymes
    indicative of hepatic damage (sorbitol dehydrogenase, alanine
    aminotransferase, and aspartate aminotransferase) 48, 72, and 96 h
    after injection. These enzyme activities were not elevated 24 h
    after this dosage nor after small doses of 2-NP.

    7.2  Short-term and long-term repeated exposure

        Data for repeated exposure, like that for single exposure,
    indicate that the cat is more sensitive to 2-NP than the other
    species tested (Table 6). Rats, rabbits, guinea-pigs, and monkeys
    survived 1.2 g/m3 (328 ppm) (7 h/day, 5 days/week) throughout
    approximately 6 months of exposure (Treon & Dutra, 1952). However,
    cats exposed to the same concentrations of 2-NP began dying after
    the third day of exposure and were all dead by the end of the 17th
    day (Treon & Dutra, 1952). Rats and guinea-pigs survived 5 days of

        Table 6.  Short-term and long-term toxicity of 2-nitropropane in mammalsa

    Species            Sex     Dose and/or concentrationb   Effects/results                                   Reference

     Oral studies

    Rat (Wistar)       M & F   0.25 g/kg, 5/week for 4      mortality of males (4/10); decreased growth in    Wester et al. (1989)
                               weeks                        first week; increased urine, ALAT, ASAT, and
                                                            gamma-GT (males only), anaemia, thrombocyte
                                                            and leucocyte count, liver, spleen and heart
                                                            weight, and haemosiderin content of spleen;
                                                            cellular and nuclear polymorphism, single cell
                                                            necrosis, and proliferation of oval cells
                                                            and/or bile ducts in liver

    Rat                M       0.089 g/kg (1 mmol),         some deaths by 16 week; throughout study body     Fiala et al. (1987b)
    (Sprague-Dawley)           3/week for 16 weeks,         weights significantly lower than controls; all
                               maintained but not dosed     rats exposed 16 weeks or longer developed
                               for next 61 weeks            massive hepatocellular carcinomas; metastases
                                                            to the lungs in 4 animals

    Rat                M & F   0.05 g/kg, 5/week for 4      increased anaemia, thrombocyte conc., and         Wester et al (1989)
    (Wistar)                   weeks                        heart weight

    Rat (Wistar)       M & F   0.002 and 0.01 g/kg, 5       increased water intake by males dosed with        Wester et al. (1989)
                               week for 4 weeks             0.002 g/kg

     Inhalation studies

    Ratd                       2.77 g/m3 (760 ppm), 8       animals dead within 2 h after end of second       Dequidt et al. (1972)
    (Wistar)                   h/day for 2 days;            inhalation session; 2-NP conc. in liver =
                               estimated dose over 8 h,     180 ppm; methaemoglobin = 2.4%
                               0.16 g/kg

    Table 6 (contd)

    Species            Sex     Dose and/or concentrationb   Effects/results                                   Reference

     Inhalation studies (contd)

    Rate                       2.45 g/m3 (672 ppm), 7       no deaths                                         Treon & Dutra (1952)
                               h/day for 5 days;
                               estimated dose over
                               7 h, 0.12 g/kg

                               1.20 g/m3 (328 ppm), 7       no deaths                                         Treon & Dutra (1952)
                               h/day, 5 days/week for
                               130 days over 199 days;
                               estimated dose over 7 h,
                               0.06 g/kg

    Rat                M       0.75 g/m3 (207 ppm), 7       body weight and haematological parameters         Lewis et al. (1979)
    (Sprague-Dawley)           h/day, 5 days/week for up    unaffected; some pulmonary oedema and some
                               to 24 weeks; estimated       pulmonary lesions within 3 months; liver
                               dose over 7 h, 0.04 g/kg     weight elevated; hepatocellular hypertrophy,
                                                            hyperplasia and liver necrosis in all rats
                                                            within 3 months; liver neoplasms in all rats
                                                            within 6 months; these hepatocellular
                                                            carcinomas appeared to be growing rapidly and
                                                            deforming surrounding tissues

    Rate                       0.73 g/m3 (200 ppm), 7       growth slightly reduced and SGPT elevated in      Griffin et al. (1978)
                               h/day, 5 days/week for 6     male rats; liver weight increased in both sexes;
                               months; estimated dose       morphological changes in liver more pronounced
                               over 7 h, 0.03 g/kg          in males; these included fatty metamorphosis
                                                            and hepatic nodules  consisting mainly of
                                                            hyperplastic areas with distortion of lobular
                                                            architecture, necrosis and peripheral

    Table 6 (contd)

    Species            Sex     Dose and/or concentrationb   Effects/results                                   Reference

     Inhalation studies (contd)

    Ratd                       0.73 g/m3 (200 ppm), 7       no effect on body or organ weight to end of       Griffin et al. (1986)
    (Sprague-Dawley)           h/day for 5 days             experiment (94 week) aside from a brief
                                                            decrease in weight gain immediately following
                                                            exposure; no significant effects on mortality
                                                            or pathology

    Ratc               M       0.73 g/m3 (200 ppm), 7       severe liver damage with vacolar degeneration     Coulston (1982)
                               h/day, 5 days/week for       in exposed rats after 3 months up
                               to 7 months

    Rate                       0.36 g/m3 (100 ppm), 7       male rats had lower body weight, increased        Griffin & Coulston (1983);
                               h/day, 5 days/week for up    renal calcification, elevated SGPT, and           Coulston et al. (1985)
                               to 18 months; estimated      enlarged livers with necrosis, vacuolar
                               dose over 7 h, 0.013 g/kg    degeneration and probable hepatocellular
                                                            carcinomas; female rats had increased renal
                                                            calcification and occasional hepatic masses
                                                            and nodules showing hyperplasia and vacuolar

    Rate                       0.29 g/m3 (80 ppm), 8        no deaths; no trace of 2-NP in organs at end of   Dequidt et al. (1972)
                               h/day for 5 days; estimated  experiment; methaemoglobin = 0; nitrite = 0-10
                               dose over 8 h, 0.016 g/kg    ppm in tissues, but no nitrite in urine

    Rat                M       0.1 g/m3 (27 ppm), 7         no gross or microscopic alteration of any         Lewis et al. (1979)
    (Sprague-Dawley)           h/day, 5 days/week for up    tissue, haematological parameter or serum
                               to 24 weeks; estimated       biochemistry
                               dose over 7 h, 0.005 g/kg

    Table 6 (contd)

    Species            Sex     Dose and/or concentrationb   Effects/results                                   Reference

     Inhalation studies (contd)

    Rate                       91 mg/m3 (25 ppm), 7         no changes in behaviour, appearance, rate of      Griffin et al.
                               h/day, 5 days/week for up    weight gain, final weight, serum chemistry or     (1980, 1981)
                               to 22 months; estimated      haematology; no significant increase in tumours
                               dose over 7 h, 0.003 g/kg    and lesions associated with exposure; no
                                                            evidence of methaemoglobinaemia

    Moused                     0.73 g/m3 (200 ppm), 7       depression in body weight during first 3 months   Griffin et al. (1984)
    (ICR)                      h/day, 5 days/week for       in females and throughout experiment in males;
                               48 weeks                     increased liver weight and elevation of liver
                                                            transaminases in females; toxic hyperplasia of
                                                            liver predominantly in females

    Mousee                     0.36 g/m3 (100 ppm), 7       slight depression of body weight during first 8   Coulston et al. (1986);
                               h/day, 5 days/week for       months in males; no effects on organ weight; no   Griffin et al. (1987)
                               18 months                    evidence of hepatocellular carcinoma; some
                                                            indications of liver toxicity (nodular
                                                            hyperplasia in females)

    Cate                       2.6 g/m3 (714 ppm), 4.5      deaths starting with first exposure, but          Treon & Dutra (1952)
                               h/day for 4 days;            some animals survived 4 exposures
                               estimated dose over 7 h,
                               0.10 g/kg

                               1.2 g/m3 (328 ppm), 7        deaths starting with third exposure; all          Treon & Dutra (1952)
                               h/day, 5 days/week for 17    animals dead by end of 17th exposure
                               exposures; estimated dose
                               over 7 h, 0.07 g/kg

    Table 6 (contd)

    Species            Sex     Dose and/or concentrationb   Effects/results                                   Reference

     Inhalation studies (contd)

    Cate                       1.15 g/m3 (317 ppm), 7       no deaths                                         Treon & Dutra (1952)
                               h/day for 2 days;
                               estimated dose over 7 h,
                               0.07 g/kg

                               0.3 g/m3 (83 ppm), 7         no deaths                                         Treon & Dutra (1952)
                               h/day, for 130 out of 191
                               days; estimated dose over
                               7 h, 0.02 g/kg

    Rabbite                    1.2 g/m3 (328 ppm), 7        no deaths                                         Treon & Dutra (1952)
                               h/day, ca. 5 days/wk for
                               up to 130 out of 199 days;
                               estimated dose over 7 h,
                               0.06 g/kg

    Rabbit             M       0.75 g/m3 (207 ppm), 7       no gross or microscopic alterations to            Lewis et al. (1979)
    (white, NZ)                h/day, 5 days/week for 24    tissues
                               weeks; estimated dose
                               over 7 h, 0.03 g/kg

    Rabbite                    0.3 g/m3 (83 ppm), 7 h/day   no deaths                                         Treon & Dutra (1952)
                               for 130 out of 191 days;
                               estimated dose over 7 h,
                               0.014 g/kg

    Rabbite                    0.1 mg/m3 (27 ppm), 7        no gross or microscopic alterations to            Lewis et al (1979)
                               h/day, 5 days/week for 6     tissues
                               months; estimated dose
                               over 7 h, 0.005 g/kg

    Table 6 (contd)

    Species            Sex     Dose and/or concentrationb   Effects/results                                   Reference

     Inhalation studies (contd)

    Guinea-pige                2.45 g/m3 (672 ppm), 7       no deaths                                         Treon & Dutra (1952)
                               h/day for 5 days;
                               estimated dose over
                               7 h, 0.12 g/kg

    Guinea-pige                1.2 g/m3 (328 ppm), 7        no deaths                                         Treon & Dutra (1952)
                               h/day, ca. 5 days/week
                               for 95-130 days out of
                               up to 199 days; estimated
                               dose over 7 h, 0.06 g/kg

    Monkeye                    1.2 g/m3 (328 ppm), 7        no deaths                                         Treon & Dutra (1952)
                               h/day, ca. 5 days/week
                               for 100 days exposure

                               0.3 g/m3 (83 ppm),           no deaths                                         Treon & Dutra (1952)
                               7 h/day for 130 out of
                               191 days

     Intraperitoneal studies

    Ratd                       0.11 g/kg, 1/day for         apparently no deaths prior to sacrifice           Dequidt et al. (1972)
    (Wistar)                   7 days                       3 days after the last injection;
                                                            methaemoglobin = 4.3%; nitrite = 0.29-1.15 ppm
                                                            in organs (heart, lungs, kidneys, spleen)

    Ratd                       0.11 g/kg, 1/day for 15      apparently no deaths prior to sacrifice 36 h
    (Wistar)                   days                         after the last injection; methaemoglobin = 0;
                                                            nitrite = 0-10.8 ppm in organs (heart, lungs,
                                                            kidneys, spleen)

    Table 6 (contd)

    Species            Sex     Dose and/or concentrationb   Effects/results                                   Reference

     Intraperitoneal studies

    Rat                F       0.001 g/kg, 5/week for       no significant effects on kidney function         Bernard et al. (1989)
    (Sprague-Dawley)           2 weeks

     Dermal study

    Rabbite                    1 application/day on         no skin irritation, illness, systemic effects     Machle et al. (1940)
                               clipped anterior abdomen     or deaths
                               for 5 days; dose not

    a   values from the literature recalculated as necessary to ppm or g/kg
    b   estimated dose calculated by the formula:  tidal volume x respiration frequency x 2-NP conc. x alveolar retention/animal weight.
        Tidal volume and respiration frequency from Baker et al. (1979) for rats (0.086 ml, 85.5 /min); from Hoar (1976) for guinea-pigs
        (1.68 ml, 84/min); from Kozma et al. (1974) for rabbits (15.8 ml, 45/min); from Reece (1984) and Breazile (1971) for cats
        (42 ml, 31/min); alveolar retention in rat (0.40) from Nolan et al. (1982), used for all species; where not stated in reference,
        animal weights assumed to be average values, 250 g for rats, 500 g for guinea-pigs, 2.5 kg for rabbits, and 4.0 kg for cats
    c   strain not specified
    d   sex not specified
    e   neither strain nor sex specified

    exposure (7 h/day) to 2.46 g/m3 (672 ppm), but death occurred in
    rats exposed for 2 days (8 h/day) to 2.77 g/m3 (760 ppm). Rats
    were reported to survive 15 days of daily intra-peritoneal
    injections of 0.11 g/kg (Dequidt et al., 1972). The doses used in
    these repeated exposures were found to produce no more than trace
    levels of methaemoglobin (maximum = 4.3%) and low concentrations
    (0 to 11 mg/kg) of nitrite in the tissues.

        Non-lethal chronic doses of 2-NP have been shown to produce a
    number of harmful effects in rats (Table 6). Exposure of rats to
    0.75 g/kg (207 ppm) for up to 24 weeks (7 h/day, 5 days/week)
    initially induced pulmonary lesions and oedema, hepatocellular
    hypertrophy, hyperplasia, and necrosis of the liver (Lewis et al.,
    1979). By the end of 24 weeks all the rats developed rapidly growing
    hepatocellular carcinomas. A similar exposure to a slightly lower
    concentration of 2-NP, 0.73 g/m3 (200 ppm), induced hepatic
    nodules and other destructive changes in the liver,  especially in
    male rats (Griffin & Coulston, 1983). These changes included fatty
    degeneration, nodules consisting mainly of hyperplastic areas,
    distortion of lobular architecture, necrosis and peripheral
    compression. Male rats also had an elevated serum alanine
    aminotransferase level (an indicator of liver damage) and slightly
    reduced growth. Chronic exposure of rats to 0.36 g/m3 (100 ppm)
    for up to 18 months produced similar, although slightly less severe,
    damage than that resulting from exposure to 0.73 g/m3 (200 ppm)
    (Griffin & Coulston, 1983; Coulston et al., 1985). Only male rats
    developed hepatocellular carcinoma; female rats had increased renal
    calcification and occasional hepatic masses and nodules showing
    hyperplasia and vacuolar degeneration. No toxic effects were
    reported after chronic exposure of rats to 90 mg/m3 (25 ppm) or
    100 mg/m3 (27 ppm) (Lewis et al., 1979; Griffin et al., 1980,
    1981). Daily intraperitoneal injections of 1 mg/kg (5/week for 2
    weeks) had no significant effect on kidney function (Bernard et al.,

        Chronic oral dosage of 2-NP by gavage for 16 weeks  produced
    tumours in rats (Fiala et al., 1987b). The dose was 0.089 g/kg
    (1 mmol/kg), given 3 times per week, and this yielded a weekly
    dosage of 0.27 g/kg, an amount similar to the highest sustained
    estimated inhalation dosage. The body weights of rats treated with
    2-NP were significantly lower than those of controls, and all
    treated rats surviving 16 weeks or longer developed both benign
    tumours and massive hepatocellular carcinomas. Metastases to the
    lungs were observed in four of the 22 surviving animals (Fiala et
    al., 1987b). Wester et al. (1989) treated rats with oral doses of
    0.002, 0.01, 0.05, and 0.25 g/kg, 5 times per week for 4 weeks by
    gavage. With a dose of 0.25 g/kg there was some mortality among male
    rats, and in both sexes there was decreased growth, anaemia,
    increased liver and heart weights, and severe damage to the liver.

    At a dose of 0.05 g/kg the major harmful effect appeared to be
    anaemia. Lower concentrations (0.01 and 0.002 g/kg) did not produce
    obvious harm over the period of the experiment.

        Rabbits and mice appear more resistant to the sublethal effects
    of 2-NP than rats (Table 6). Chronic inhalation exposure of five
    rabbits to 0.75 g/m3 (207 ppm) (7 h/day, 5 days/week) for 24
    weeks, a treatment which induced hepatocellular carcinomas and
    severe liver damage in rats, had no detectable effect (Lewis et al.,
    1979). Rabbits also were unaffected by repeated dermal application
    of 2-NP (Machle et al., 1940). Liver damage was found in mice,
    especially females, during chronic exposure to 0.72 g/m3 (200 ppm)
    (7 h/day, 5 days/week) for 48 weeks, but hepatocellular or other
    carcinomas were not detected (Griffin et al., 1984). Exposure of
    mice to 0.36 g/m3 (100 ppm) (7 h/day, 5 days/week) for 18 months
    produced some liver damage, especially in females, as shown by
    nodular hyperplasia (Coulston et al., 1986, Griffin et al., 1987).

    7.3  Reproduction, embryotoxicity, and teratogenicity

        There is limited information on the embryotoxicity and
    teratogenicity of 2-NP. Hardin et al. (1981) gave intraperitoneal
    injections of 0.17 g/kg (1.91 mmol/kg) of 2-NP in corn oil to
    pregnant rats on days 1-5 of gestation. The dosage was a previously
    determined maximum tolerated dose which produced no mortality, no
    marked signs of toxicity, and less than a 10% reduction in body
    weight gain during dosing or within 2 weeks following 15 daily
    intraperitoneal injections to non-pregnant rats. In pregnant rats,
    this dose was reported to give no evidence of maternal toxicity or
    teratogenicity, but produced a significant incidence of delayed
    fetal development. Harris et al. (1979) reported that 2-NP at a dose
    of 0.17 g/kg retarded fetal heart development by 1 to 2 days in pups
    from 9 out of 10 litters produced by female rats treated with 2-NP.
    In the affected litters, 30% to 86% of the pups had retarded heart

        There appear to be no studies that have examined specifically
    the effects of 2-NP on reproductive function. No effects on
    reproductive organs, however, were noted in the above two studies
    nor in any of those studies on the effects of single exposures or
    short-term or long-term administration of 2-NP (Tables 5 and 6).
    There also was no evidence of an increase in dominant lethality or
    in sperm abnormality in genetic studies relating to reproduction
    (McGregor, 1981).

    7.4  Mutagenicity and related end-points

    7.4.1  Prokaryotes and yeast

        2-NP has been found to be mutagenic in a variety of test
    systems. All investigators reported mutagenicity in several strains
    of  Salmonella typhimurium used with the Ames test, both with and
    without an exogenous activating system (S9) (Table 7). In addition,
    Kawai et al. (1987) reported mutagenicity with a strain of
    Escherichia coli, but Litton Bionetics, Inc. (1977) did not find
    mutagenicity with a strain of  Saccharomyces cerevisiae. Most
    investigators found greater mutagenicity with activation by S9 than
    without. With the strain that was generally most sensitive to 2-NP,
    i.e. TA100, most investigators providing detailed results observed
    an approximate doubling in the number of mutants at a concentration
    of 3 mg 2-NP/plate. Göggelmann et al. (1988), however, observed a
    10- to 12-fold increase in mutant numbers at 2.45 mg/plate, with or
    without activation by S9. Fiala et al. (1987a) reported that
    non-ionic 2-NP yielded only a doubling of mutant numbers at
    4.9 mg/plate with S9 activation and no increase without activation,
    whereas 2-NP nitronate at this concentration yielded a threefold
    increase in mutant numbers with activation. Without activation 2-NP
    nitronate at 2.5 mg/plate yielded a nearly 6-fold increase in mutant
    numbers; nitronate at 4.9 mg/plate was toxic to this test organism.
    Fiala et al. (1987a) concluded that the mutagenicity of 2-NP is
    produced mainly or entirely by the nitronate anion and suggested
    that the low level of mutagenicity observed with non-ionic 2-NP may
    have resulted from its conversion to the nitronate form within the
    microorganisms. A similar conclusion was drawn by Dayal et al.
    (1989) from their comparison of 2-NP, nitromethane, nitroethane, and
    their nitronates for mutagenicity in  Salmonella. Some of the
    variability in results obtained by others may stem from varying
    proportions of non-ionic 2-NP and 2-NP nitronate  in the stock 2-NP
    used in their tests. Fiala et al. (1987a) further observed that
    dimethyl sulfoxide (DMSO), a solvent used to solubilize 2-NP in
    these tests, modified the mutagenicity of 2-NP nitronate in a
    variable manner.

        Several of the studies discussed above examined the question of
    how 2-NP induces mutations in the test systems. In addition to 2-NP,
    1-and 2-aminopropane and a number of mononitroalkanes (nitromethane,
    nitroethane, 1-nitropropane, 1-and 2-nitrobutane, and 1-and
    2-nitropentane) were tested for mutagenicity with bacterial systems,
    mainly strains of  Salmonella typhimurium (Hite & Skeggs, 1979;
    Speck et al., 1982; Löfroth et al., 1986; Kawai et al., 1987;
    Göggelmann et al., 1988; Dayal et al., 1989). Only 2-NP proved to be
    significantly mutagenic. Some investigators observed weak
    mutagenicity with nitroethane, 1-nitropropane, 2-nitrobutane, and
    2-nitropentane, which, at least in the case of nitromethane and
    nitroethane, may have been produced by the 2-NP present in these
    solvents as a contaminant.

    Table 7.  Genotoxicity of 2-nitropropane

    Test system                                         Resulta    Referencesb

    Prokaryotes and yeastc

     Salmonella typhimurium

    strain TA92                                            +       1

    strain TA92 with S9                                    +       1

    strain TA98                                            +       1,2,5,7,8,9

                                                           -       6,16,19

    strain TA98 with S9                                    +       1,2,3,5,8,9,17

    strain TA98NR                                          +       2,9

    strain TA98NR with S9                                  +       2,9

    strain TA100                                           +       1,2,4,5,6,7,8,9,19

                                                           -       17

    strain TA100 with S9                                   +       1,2,3,4,5,6,8,9,17,19

    strain TA100NR                                         +       2,9

    strain TA100NR with S9                                 +       2,9

    strain TA102                                           +       4,8,19

    strain TA102 with S9                                   +       4,8,19

    Table 7 (contd)

    Test system                                         Resulta    Referencesb

    strain TA1535                                          ?       5

                                                           -       17

    strain TA1535 with S9                                  +       3

                                                           ?       5

                                                           -       17

    strain TA1537                                          -       17

    strain TA1537 with S9                                  -       3,17

    strain TA1538                                          -       17

    strain TA1538 with S9                                  -       17

     Escherichia coli

    strain WP2 uvrA/pKM101                                 +       7

    strain WP2 uvrA/pKM101                                 +       7

     Saccharomyces cerevisiae

    strain D4                                              -       17

    strain D4 with S9                                      -       17

    Table 7 (contd)

    Test system                                         Resulta    Referencesb


     In vivo


    Sex-linked recessive lethal                            -       10,11



      (micronuclei) m, f                                   -       1,16,23

    sperm (abnormality)                                    ?       11


    Liver (DNA repair synthesis) m, f                      +       12,13,23

      (micronuclei)                                        +       23

      (DNA and RNA base                                    +       18,20,21,22
       modifications) m, f

      (DNA strand breakage) m                              +       24

    Kidney (DNA strand breakage) m                         -       24

      (DNA and RNA base                                    -       22
       modifications) m, f

    Table 7 (contd)

    Test system                                         Resulta    Referencesb

    Brain (DNA strand breakage) m                          -       24

    Lung (DNA strand breakage) m                           -       24

    Bone marrow (chromosome                                -       11
    aberrations) m, f

      (micronuclei) m                                      -       23


      (dominant lethal test) m                             -       11

     In Vitro


    3T3-NIH fibroblasts                                    -       13
    (DNA repair synthesis)


    hepatocytes                                            +       12,13,26
    (DNA repair synthesis) m, f

    hepatoma cells, 2sFou                                  +       25
    (DNA repair synthesis and micronuclei)g

    hepatoma cells, C2Rev7                                 +       25
    (DNA repair synthesis and micronuclei)g

    Table 7 (contd)

    Test system                                         Resulta    Referencesb

    hepatoma cells, H4IIEC3/G-                             +       25
    (DNA repair synthesis, micronuclei and
    gene mutations)g

    208F - embryonic fibroblasts                           -       13
    (DNA repair synthesis)

    LLC WRC 256 carcinoma Walker rat                       -       13
    (DNA repair synthesis)


    CHO cells (chromosome aberrations                      -       14
    and sister chromatid exchanges)

    CHO cells (DNA repair synthesis)                       -       13

    V79 cells (DNA repair synthesis)                       -       12,13,25,26

    V79 cells (mutations)                                  +       25

    V79 cells (micrnuclei)                                 -       25,26


    Lymphocytes (chromosome aberrations                   -d       9,15
    and sister chromatid exchanges)

    Lymphocytes (chromosome aberrations                   -e       9,15
    and sister chromatid exchanges) with

    Table 7 (contd)

    Test system                                         Resulta    Referencesb

     Human (contd)

    Fibroblasts (DNA repair synthesis)                     -       11

    W138 embryonic lung fibroblasts NC1-                   -       13
    H322 adenocarcinoma lung cells A549
    adenocarcinoma lung cells HEp2 epidermal
    carcinoma larynx cells (DNA repair synthesis)

    a + = positive response;  - = negative response;  ? = inconclusive result
    b (1)  Hite & Skeggs (1979)               (2)  Speck et al. (1982)
      (3)  Haworth et al. (1983)              (4)  Simmons et al. (1986)
      (5)  Löfroth et al. (1986)              (6)  Hughes et al. (1987)
      (7)  Kawai et al. (1987)                (8)  Fiala et al. (1987a)
      (9)  Göggelmann et al. (1988)           (10) Zimmering et al. (1985)
      (11) McGregor (1981)                    (12) Ziegler-Skylakakis et al. (1987)
      (13) Andrae et al. (1988)               (14) Galloway et al. (1987)
      (15) Bauchinger et al. (1987)           (16) Kliesch & Adler (1987)
      (17) Litton Bionetics, Inc. (1977)      (18) Conaway et al. (1991a)
      (19) Conaway et al. (1991b)             (20) Fiala et al. (1989)
      (21) Hussain et al. (1990)              (22) Guo et al. (1990)
      (23) George et al. (1989)               (24) Robbiano et al. (1991)
      (25) Roscher et al. (1990)              (26) Haas-Jobelius et al. (1991)
    c Liver S9 fractions are prepared by treating rats, mice or hamsters with Aroclor
      1254 or another microsomal enzyme inducer, and, after several days, removing
      the livers, homogenizing them, and centrifuging.  The supernatant, the S9
      fraction, contains liver microsomal enzymes.
    d Bauchiner et al. (1987) (ref. 15) reported a weak but significantly positive result
      on one test, but considered results overall to be negative
    e Göggelmann et al. (1988) (ref. 9) reported a very weak positive result
    f m = male;  f = female
    g pretreated with dexamethasone

        Löfroth et al. (1986) and Fiala et al. (1987a) speculated that
    the relative mutagenicity of 2-NP and other nitroalkanes correlated
    with the concentrations of their nitronate anions. The more highly
    mutagenic compounds, such as 2-NP and 1,1-dinitroethane, had high
    concentrations of nitronate at cellular pH. A thorough comparison of
    2-NP, other secondary nitroalkanes, and their nitronates (Conaway et
    al., 1991) showed greater mutagenicity of the nitronates and
    confirmed these speculations.

        These studies do not support the hypothesis that mutagenicity of
    2-NP is produced largely or entirely by nitrite resulting from its
    metabolic breakdown, since the response of tester strains to sodium
    nitrite was quite different from their response to 2-NP (Löfroth et
    al, 1986). Unlike nitroarenes and nitroheterocyclics, 2-NP probably
    does not derive its mutagenicity exclusively from enzymatic
    reduction to a hydroxylamine. Strains of  S. typhimurium, i.e.
    TA98NR and TA100NR, lacking the "classical" nitroreductase
    demonstrated either a very slightly (Speck et al., 1982) or markedly
    (Göggelmann et al., 1988) reduced, but still significant, level of
    mutagenicity. Göggelmann et al. (1988) suggested that some of this
    mutagenicity may be due to some residual nitroreductase activity
    still present in these strains.

        The increased mutagenicity generally observed with S9 activation
    of 2-NP and the reduced mutagenicity in tester strains deficient in
    nitroreductase activity suggest an involvement of metabolism in the
    mutagenicity of 2-NP in  S. typhimurium. Fiala et al. (1987a)
    presented evidence that metabolic oxidation of the 2-NP anion can
    result in the formation of reactive species such as hydroxyl
    radicals, which are capable of damaging DNA bases. Incubation of
    2-NP nitronate under roughly physiological conditions with thymidine
    and a 1-electron oxidation system, horseradish peroxidase and
    hydrogen peroxide, yielded 2-NP free radicals (which in part
    condensed into 2,3-dimethyl-2,3-dinitrobutane) and oxidation
    products of thymidine of the type produced by hydroxyl radical
    attack. A common source of hydroxyl radicals is superoxide,  which
    is known to be produced during oxidation of 2-NP nitronate by
    horseradish peroxidase and hydrogen peroxide (Porter & Bright,
    1983). The extent to which such reactions may occur in the
     Salmonella tester strains or  in vivo is unknown. There is,
    however, evidence from the literature for microbial oxidation of
    2-NP and 2-NP nitronate (Kido et al., 1984; Fiala et al., 1987a).
    The existence of this proposed mechanism for inducing mutations
    through the production of DNA-damaging hydroxyl radicals is further
    supported by the reduction in 2-NP mutagenicity in TA102 by DMSO, a
    known scavenger of such radicals (Fiala et al., 1987a). The fact
    that DMSO had little effect on the mutagenicity of 2-NP in TA100
    indicated that formation of hydroxyl radicals cannot be the only
    mechanism inducing mutations. Fiala et al. (1987a) hypothesized that
    the 2-NP radical may act directly by forming adducts with DNA bases.

    This would provide an additional mechanism for inducing mutations
    that would not require hydroxyl radicals.

    7.4.2  Eukaryotes

        The genotoxic effects of 2-NP in eukaryotic organisms are
    summarized in Table 7. Results were negative in two sex-linked
    recessive lethal tests using  Drosophila despite exposure to high
    concentrations of 2-NP. Zimmering et al. (1985) dosed the flies by
    injection and by feeding with concentrations that induced an
    approximately 30% mortality, whereas McGregor (1981) exposed the
    flies to 2-NP vapour at a concentration of 2.55 g/m3 (700 ppm) for
    4.5 h. Sex-linked recessive lethal mutation frequency was not
    increased except in mature spermatozoa in one stock of flies. Since
    this increase was not reproducible, its significance is doubtful.

        Results were variable but mainly negative in a variety of
     in vivo mammalian test systems. In the dominant lethal test and
    the bone marrow chromosomal aberration test using rats and in the
    sperm abnormality test using mice, animals were exposed to 91 or
    728 mg/m3 (25 or 200 ppm) for 7 h/day on 5 consecutive days.
    Neither exposure level produced a positive response in any of the test
    systems used (McGregor, 1981). Negative results were obtained with
    the mouse micronucleus test even with an almost lethal oral dose of
    0.3 g/kg on 2 consecutive days (Hite & Skeggs, 1979), and with a
    single intraperitoneal dose of 0.3 g/kg (Kliesch & Adler, 1987). 

        One set of genotoxicity tests using rats, however, yielded
    strongly positive results (Andrae et al., 1988; Ziegler-Skylakakis
    et al., 1987). In both  in vivo and  in vitro tests, 2-NP induced
    DNA repair synthesis in rat liver cells. In the  in vitro
    experiments, cultures of rat hepatocytes were incubated with 2-NP,
    while in the  in vivo experiments rats were injected
    intraperitoneally with 2-NP, sacrificed 4 h later, and cultures of
    their hepatocytes were examined for DNA repair synthesis. Exposure
    of hepatocyte cultures for 18 to 20 h to concentrations of 2-NP as
    low as 2.7 mg/litre (30 µmol/litre) induced a detectable
    (approximately 2-fold above the control level) increase in repair
    synthesis. The highest concentration tested, i.e. 89 mg/litre
    (10 mmol/litre), induced a 12- to 15-fold increase above control
    levels in hepatocytes from male rats and a 25- to 30-fold increase
    in hepatocytes from female rats. The  in vivo experiments also
    demonstrated the existence of a sexual difference in susceptibility
    to 2-NP. In males, the lowest dose (20 mg/kg) induced a doubling in
    repair synthesis and the highest dose (80 mg/kg) a 3.6-fold
    increase, whereas in females these doses induced a very small
    increase and a doubling, respectively. In contrast to 2-NP, 1-NP
    given  in vivo had no effect on DNA repair synthesis and did not
    increase  in vitro repair synthesis above that expected from its
    contamination with 2-NP. Andrae et al. (1988) considered that their
    results from the  in vivo experiments were in agreement with the

    observed greater hepatocarcinogenicity of 2-NP in male rats than in
    females. Their observation that 2-NP did not induce any increase in
    repair synthesis in any of nine non-hepatic cell lines derived from
    human, mouse, hamster, and rat tissues led the authors to suggest
    that 2-NP is not a direct-acting genotoxic agent but rather requires
    metabolic activation by liver-specific metabolism.

        Several papers have confirmed and expanded these initial
    observations on the genotoxicity of 2-NP to rat liver cells. George
    et al. (1989) showed that oral dosage similarly induced unscheduled
    DNA synthesis and also resulted in the formation of micronuclei in
    rat liver. 2-NP did not, however, significantly increase the
    frequency of micronuclei in mouse bone marrow. Intraperitoneal
    injection of 0.1 g/kg produced in 6 h a significant increase in
    8-hydroxydeoxyguanosine and 8-hydroxyguanosine, products
    respectively of DNA and RNA damage caused by hydroxyl or other
    oxygen-radical-forming agents (Fiala et al., 1989; Hussain et al.,
    1990). This treatment produced significantly lower levels of
    8-hydroxydeoxyguanosine, 8-hydroxyguanosine, and other presumed
    modified nucleosides in female rats than in males, and had little
    effect on the nucleic acids of the kidney, findings that are in
    agreement with the known carcinogenicity of 2-NP (Guo et al., 1990).
    The organ specificity of the genotoxicity of 2-NP in the rat was
    confirmed by Robbiano et al. (1991) who reported that oral doses of
    45-713 mg/kg produced maximum numbers of single strand breaks in the
    liver 6 h after administration and did not induce DNA fragmentation
    in lung, kidney, bone marrow or brain. Damage to rat liver nucleic
    acids was also caused  by intraperitoneal injection of other
    secondary nitroalkanes and a ketoxime capable of being converted to
    a secondary nitroalkane, but not with a primary or a tertiary
    nitroalkane (Conaway et al., 1991). These authors suggest that the
    greater genotoxicity of the secondary nitroalkanes may stem from the
    greater stability of their nitronate forms at physiological pH

        Observations by Roscher et al. (1990) and Robbiano et al. (1991)
    suggest that cytochrome P-450-dependent monooxygenases are important
    in the activation of 2-NP in liver. Robbiano et al. (1991) found an
    increase in damage to liver DNA in rats pretreated with
    phenobarbital or ß-naphthoflavone, inducers of cytochrome
    P-450-dependent monooxygenases, and a reduction in liver DNA damage
    in rats pretreated with methoxsalen, an inhibitor of cytochrome
    P-450. Roscher et al. (1990) examined the effect of 2-NP on rat
    hepatoma cell lines that express various forms of cytochrome
    P-450-dependent monooxygenases and V79 Chinese hamster cells that
    lack these enzyme activities. 2-NP increased  DNA repair synthesis,
    micronuclei formation, and the frequency of mutants resistant to
    6-thioguanine in hepatoma cells pretreated with dexamethasone, an
    inducer of various liver-specific cytochrome P-450 forms.

    Genotoxicity was reduced or absent in hepatoma cells not treated
    with the inducer. In the V79 cells, 2-NP produced only mutations to
    6-thioguanine resistance.

        2-NP demonstrated only a very limited level of genotoxicity in
    other cell lines. Results were negative in a DNA repair synthesis
    assay with human diploid fibroblasts exposed for 3 h to 2-NP
    concentrations up to 5 g/litre (56 mmol/litre) (McGregor, 1981), as
    well as with various cell lines of extrahepatic origin (Andrae et
    al., 1988). 2-NP did not cause chromosomal aberrations or SCEs in 
    Chinese hamster ovary (CHO) cells either with or without S9
    (Galloway et al., 1987). In these experiments the maximum
    concentrations used, i.e. 1.6 and 5.0 g/litre (18 and 56 mmol/litre)
    were estimated to reduce cell growth by 50%. Weakly positive
    results, however, were obtained in cytogenetic tests using human
    lymphocytes (Bauchinger et al., 1987; Göggelmann et al., 1988).
    Exposure of cells to high concentrations of 2-NP (commercial grade,
    at least 94% 2-NP) for 1 h induced a significant increase in
    chromosomal aberrations (open breaks accompanied by gaps) at a
    concentration of 5.3 g/litre (60 mmol/litre) with S9 activation and
    at 7.1 g/litre (80 mmol/litre) without S9 activation (Bauchinger et
    al., 1987). In addition, the frequency of sister chromatid exchange
    was significantly increased at all concentrations of 2-NP (0.7 to
    7.1 g/litre; 7.5 to 80 mmol/litre), but only with S9 activation.
    Repetition of the experiment with 2-NP of greater than 99% purity
    yielded similar results (Göggelmann et al., 1988). There was no
    significant increase in chromosomal changes without S9 activation,
    but there was a small but significant increase at the highest
    treatment levels, i.e. 7.1 and 10 g/litre (80 and 111 mmol/litre),
    with S9 activation. 1-NP of 97% purity produced no significant
    mutagenic or cytogenetic effects on this test system with or without
    S9 activation. The authors concluded that 2-NP can exert a
    clastogenic effect on human lymphocytes only with metabolic
    activation, and hypothesized that it acted via a different metabolic
    pathway in the lymphocytes than it did in the bacterial
     S. typhimurium system, where it induced mutations without
    exogenous activation.

    7.5  Carcinogenicity

        That 2-NP is unquestionably a potent carcinogen in rats was
    demonstrated by Lewis et al. (1979). Inhalation exposure of male
    Sprague-Dawley rats to 0.75 g/m3 (207 ppm) for 7 h/day, 5
    days/week, over a 24-week period induced hepatocellular neoplasms in
    all surviving animals. Inhalation exposure of rats to 0.36 g/m3
    (100 ppm) similarly administered over 18 months was associated with 
    hepatocellular carcinomas in male rats and produced changes in the
    livers of female rats (nodules showing hyperplasia and vacuolar
    degeneration) which may have been precursors to carcinoma (Griffin &
    Coulston, 1983; Coulston et al., 1985). Oral dosing of male rats
    with 89 mg/kg (1 mmol/kg),  three times a week for 16 weeks, induced

    massive hepatocellular carcinomas in all rats, observed when they
    were sacrificed 40 weeks later (Fiala et al., 1987a). Metastases to
    the lungs were present in 4 out of 22 surviving animals, suggesting
    a high degree of malignancy. Long-term inhalation exposure of rats
    to low concentrations (100 mg/m3; 27 ppm) did not produce any
    evidence of increased hepatocellular carcinoma or precursor tumour
    lesions of any sort (Lewis et al., 1979; Griffin et al., 1980,
    1981). Evidence that inhalation exposure to low doses of 2-NP can
    cause DNA damage in rats was presented by Denk et al. (1990). Male
    and female Sprague-Dawley rats, 4-6 days old at the beginning of
    treatment, were exposed to 0, 91, 146, 182, 291, and 455 mg/m3 (0,
    25, 40, 50, 80 and 125 ppm) for 6 h/day, 5 days/week for 3 weeks,
    and this was followed by promotion with polychlorinated biphenyls
    (Clophen A50) for 8 weeks. This treatment produced a dose-dependent
    increase in the numbers of preneoplastic liver foci deficient in
    adenosine-5'-triphosphatase. Cunningham & Matthews (1991) showed
    that 2-NP can also induce cell proliferation in rat liver. Rats were
    exposed to daily oral doses of 20, 40 or 80 mg/kg by gavage for 10
    days, and cell proliferation during exposure was quantified by
    measuring the incorporation of bromodeoxyuridine into newly
    synthesized DNA. Exposure to 40 and 80 mg/kg resulted in
    statistically significant increases in the frequency of S-phase
    cells from 1.9% in the vehicle-treated animals to 6.3% and 11%,
    respectively. Exposure to 20 mg/kg had no effect on the labelling
    index. The non-carcinogenic isomer of 2-NP, 1-NP, did not affect DNA
    synthesis at doses of 20, 40 and 80 mg/kg.

        There is no substantial evidence that 2-NP induces cancer in
    species other than the rat (Table 6). Inhalation exposure of rabbits
    to 750 mg/m3 (207 ppm) for 1 h/day, 5 days/week for 24 weeks,
    initially produced some evidence of liver damage. At the end of 6
    months of exposure, the five rabbits examined displayed no more than
    minor changes in the liver and no evidence of carcinoma (Lewis et
    al., 1979). Exposure of mice to 728 mg/m3 (200 ppm), similarly
    administered for 48 weeks,  produced damage to the liver, especially
    in females, but no carcinoma (Griffin et al., 1984). It is possible
    that degenerative changes observed in the livers of exposed females
    may have been precursors to subsequent tumour development. A lower
    concentration of 2-NP, 360 mg/m3 (100 ppm), similarly 
    administered to ICR mice for 18 months, induced liver damage in the
    form of nodular hyperplasia in females but no increase in
    hepatocellular carcinoma (Coulston et al., 1986; Griffin et al.,
    1987). The latter study is the only inhalation study in a species
    other than the rat that was of sufficient duration to allow for
    latency in tumour development. No studies of carcinogenicity using
    oral dosing in any species except the rat have been reported. Thus,
    despite the absence of clear evidence, the possibility of
    carcinogenicity in species other than the rat cannot be discounted.

        There appear to be no laboratory studies on species other than
    rats, mice and rabbits suitable for assessing the potential
    carcinogenicity of 2-NP. As discussed in section 8.2.2, there is no
    evidence from limited epidemiological studies that 2-NP is
    carcinogenic in humans.

        Griffin & Coulston (1983) argued that 2-NP does not act as an
    initiating carcinogen in the rat, but rather induces cancer as a
    response to extensive liver damage (Angus Chemical Co., 1985). They
    offered as evidence the results of an experiment demonstrating the
    absence of long-term effects from short-term exposure to 2-NP
    (Griffin et al., 1986). Exposure of rats of both sexes to 730 g/m3
    (200 ppm), 7 h/day for 5 days, did not produce any effect on
    longevity or on the development of hepatocellular or other
    carcinomas up to the end of the experiment, which lasted for 94
    weeks. This argument is markedly weakened by the observation of
    Andrae et al. (1988) and others (Fiala et al., 1989; George et al.,
    1989; Guo et al., 1990; Conaway et al., 1991) that 2-NP is an active
    genotoxic agent in rat hepatocytes both  in vitro and  in vivo.

    7.6  Pharmacological effects

         In vivo pharmacological studies have not been performed.
    However  in vitro studies with guinea-pig tissues suggest that 2-NP
    may have several pharmacological effects. A 0.1 µM (8.9 µg/litre)
    solution inhibited oxygen consumption of polymorphonuclear
    leucocytes by 50% (Estes & Gast, 1960). These authors further
    reported that, with increasing concentrations of 2-NP, respiration
    of heart homogenate was initially depressed and subsequently

        2-NP also produces two opposite neural effects on smooth muscle
    preparations (Bergman et al., 1962). Contraction is induced partly
    by ganglionic stimulation and partly by direct liberation of a
    transmitter from nerve endings, but at the same time 2-NP inhibits
    the response to acetylcholine and other smooth muscle stimulants.
    Bergman et al. (1962) found that the action of nitroparaffins on
    smooth muscle was similar to that of nicotine in that their ability
    to induce contraction was inhibited by morphine and by high, but not
    low, concentrations of atropine.


    8.1  General population exposure

        As indicated in section 5.1, general population exposure to 2-NP
    appears to be very low, and there is no information on the effects
    of this exposure. 2-NP has been used as a component of paints and
    other consumer products. There is no evidence that exposure to 2-NP
    from the use of such products has resulted in detectable injury or
    illness in the general population.

    8.2  Occupational exposure

    8.2.1  Acute toxicity

        Significant human exposure to 2-NP is largely or entirely
    occupationally related. High concentrations are acutely toxic and
    seven industrial fatalities have been attributed to inhalation of
    2-NP fumes (Gautier et al., 1964; Hine et al., 1978; Rondia, 1979;
    Harrison et al., 1985, 1987; US NIOSH, 1987b). In all cases,
    exposure was to a solvent mixture containing 2-NP, was for a total
    of 5 to 16 h in the course of 1 to 3 days, and occurred while paints
    or coatings were being applied in confined spaces,  such as tank
    interiors, underground vaults and ship's holds, with little or no
    ventilation. The actual concentrations of 2-NP that caused deaths
    were not measured, but were thought to be high and in one case
    estimated at 2.18 g/m3 (600 ppm), as determined by GC-FID from the
    2-NP content of the victim's blood (0.013 g/litre) (Harrison et al.,
    1987). Initial symptoms requiring medical treatment appeared during
    exposure or within a few hours following exposure and included
    headache, nausea, dizziness,  drowsiness, weakness, anorexia,
    vomiting, diarrhoea, and neck, thoracic, and abdominal pain. Victims
    were hospitalized and in general initially showed improvement, in
    some cases to the point of being discharged after a day or less. But
    improvement, where present, was temporary and in all seven cases was
    followed within a few days by worsening condition and
    rehospitalization of those previously discharged. Later symptoms
    included persistent nausea, vomiting, anorexia, jaundice, reduced
    urine output, diarrhoea, bloody stools, mental confusion,
    restlessness, loss of reflexes, and increases in serum
    aminotransferases and other indicators of hepatic lesions. Death
    occurred within 4 to 26 days (average, 10 days) following exposure.
    In all cases the primary cause was acute hepatic failure.
    Contributing factors included lung oedema, gastrointestinal
    bleeding, and respiratory and kidney failure. Postmortem microscopic
    examination of the liver revealed necrosis of hepatic tissue and in
    some cases fatty degeneration. None of the victims had a past
    history of liver disease or drank excessively.

        In addition to these fatalities, there have been four additional
    serious but nonlethal cases attributed to acute exposure to 2-NP
    (Gautier et al., 1964; Hine et al., 1978; Harrison et al., 1985,
    1987; US NIOSH, 1987b). All but one were colleagues of the deceased
    described above, but may have received lesser doses. Initial
    symptoms were similar to those of the deceased, but were followed by
    full recovery rather than decline and death. Serum enzyme levels,
    however, remained mildly elevated for months following exposure. As
    in the case of the deceased, the actual concentrations of 2-NP to
    which these workers were exposed are unknown. One of the survivors
    had a 2-NP serum concentration of 8.5 mg/litre when hospitalized.
    Since his coworker hospitalized at the same time with a serum
    concentration of 13 mg/litre subsequently died, Harrison et al.
    (1987) speculated that either 2-NP has a very steep dose-response
    curve or that there are substantial differences in individual
    susceptibility. Six men (out of a group of approximately 300)
    developed toxic hepatitis after exposure to an epoxy resin coating
    containing 2-NP (Williams et al., 1974). The development of toxic
    hepatitis was ascribed to methylenedianiline in the coating, and the
    possibility that 2-NP may have been at least a partial cause was not

        Exposure to lower concentrations of 2-NP appears to produce some
    of the symptoms described above. Brief and intermittent exposure to
    concentrations above 364 mg/m3 (100 ppm) may produce headache and
    nausea (Angus Chemical Co. & Occusafe, Inc., 1986). Exposure to
    vapours (estimated to contain 73 to 164 mg/m3 (20 to 45 ppm) using
    colorimetric methods available at the time of the study) of a
    solvent mixture that polluted the workplace air produced a daily
    cycle in symptoms (Skinner, 1947). Workers started the day feeling
    well, but by noon some exhibited nausea and lack of appetite. Later
    in the working day these symptoms intensified and were accompanied
    by vomiting and diarrhoea. Vomiting continued after the workers left
    the workplace, and they were unable to eat supper but were able to
    sleep. By morning they were feeling well again. Colleagues not
    experiencing nausea and vomiting had occipital headaches, which
    appeared and gradually intensified during the working day. All of
    the workers were free of symptoms when away from the workplace for a
    day or more, and the substitution of methyl ethyl ketone for 2-NP
    brought complete relief. Skinner (1947) noted that in another plant
    exposure of workers to 36-109 mg/m3 (10-30 ppm) for less than
    4 h/day on not more than 3 days per week produced no noticeable ill

        The flaw in all but one (Hine et al., 1978) of these case
    studies is that exposure was to a solvent mixture containing 2-NP
    and not to 2-NP alone (Hine et al., 1978). Thus the observed effects
    cannot be assigned to 2-NP with total confidence. A number of
    factors, however, point to 2-NP as the main, if not sole, causative
    agent. It was the only solvent common to all the mixtures, and the
    only solvent present in the mixtures known to be hepatotoxic.

    Symptoms and damaging effects on the body from the solvent mixtures
    were fairly similar to each other despite widely different solvent
    compositions (apart from the common presence of 2-NP), and were
    fairly similar to those in the single case resulting from exposure
    to 2-NP alone. In addition, as described above, substitution of
    another solvent for 2-NP eliminated all symptoms. The weight of
    evidence thus supports the view that the symptoms and damage to the
    human body described above which followed exposure to solvent
    mixtures containing 2-NP, resulted mainly, if not entirely, from

    8.2.2  Effects of long-term exposure

        Despite the fact that 2-NP has been in use for over 40 years,
    there are very few data on long-term effects and such information is
    derived mainly from unpublished reports from manufacturers of 2-NP.

        Angus Chemical Co., a major manufacturer of 2-NP, has assembled
    information on more than 1800 occupationally exposed workers from a
    variety of plants in the USA, Mexico, Germany, Sweden, and the
    Netherlands (Table 8). Where information was available, medical
    records on living employees indicated no problems with liver
    functions and no obvious symptoms or conditions that could be
    connected with chronic exposure to 2-NP (Angus Chemical Company and
    Occusafe, Incorporated, 1986).

        A major portion of the above investigation was an earlier 
    mortality study conducted by Miller & Temple (1979) on 1481 workers
    employed in the manufacture of  2-NP during the period 1955 to 1977.
    The exposures were defined as direct, indirect or zero exposure.
    Formal industrial hygiene monitoring was not performed until 1977.
    Individual exposures were based on job titles rather than actual
    exposure data. Angus Chemical Company and Occusafe, Incorporated
    (1986) concluded that analysis of these data did not suggest any
    unusual cancer or other disease pattern in this group of workers.
    They noted, however, that because the cohort was small and the
    duration of exposure and observation was relatively short, it was
    not possible to conclude from these data that 2-NP is not
    carcinogenic to humans. In a follow-up report on the same cohort 
    (Bolender, 1983), the findings did not change the earlier

        It is necessary to emphasize that this cohort had a limited
    number of workers with long exposure (> 15 years). Since the
    individual exposure data are not available, it cannot be concluded
    from available data that 2-NP is non-carcinogenic in humans.

    Table 8.  Studies of long-term occupational exposure to 2-nitropropane

    Activitya                Exposure concentrationb  Exposure duration  No. of exposed  Reference
                                   mg/m3 (ppm)             (years)          employees
                                TWA          STEL

    Manufacture of 2-NP,        25-91        > 218         < 1-15              55        Angus Chem. Co. & Occusafe, Inc. (1986)
    1940-1955                  (7-25)       (> 60)       average 2.5

    Manufacture of 2-NP,       3.6-36       91-5970       < 5-> 21             804       Angus Chem. Co. & Occusafe, Inc. (1986);
    1946-1982,                 (1-10)      (25-1640)     average 8c                      Miller & Temple (1979); Bolender (1983)
    Sterlington, LA, USA

    Extraction of              3.6-193      109-473      < 5-ca. 25           18-19      Angus Chem. Co. & Occusafe, Inc. (1986);
    triglycerides, USA         (1-53;      (30-130)                                      Crawford et al. (1985); Tabershaw
                             average 9c)                                                 Occupational Medicine Assoc. (1980);
                                                                                         Life Extension Inst. (1983)

    Automobile assembly        unknown                    < 5-> 25             456       Angus Chem. Co. & Occusafe, Inc. (1986)
    plant, Germany

    Paint mfg., Germany        unknown                      5-10                6        Angus Chem. Co. & Occusafe, Inc. (1986)

    Paint mfg., Germany         40-91                       11-15               5        Angus Chem. Co. & Occusafe, Inc. (1986)

    Chemical mfg.,             unknown                      5-10               80        Angus Chem. Co. & Occusafe, Inc. (1986)

    Chemical mfg.,             unknown                       < 5                4        Angus Chem. Co. & Occusafe, Inc. (1986)

    Extraction plant,         3.6-18.2      73-364          5-10               15        Angus Chem. Co. & Occusafe, Inc. (1986)
    Sweden                      (1-5)      (20-100)

    Table 8 (contd)

    Activitya                Exposure concentrationb  Exposure duration  No. of exposed  Reference
                                   mg/m3 (ppm)             (years)          employees
                                TWA          STEL

    Paint mfg.,                unknown                      5-10               180       Angus Chem. Co. & Occusafe, Inc. (1986)

    Chemical Co., USA          3.6-36      65.6-364        < 5-20              41        Angus Chem. Co. & Occusafe, Inc. (1986)
                               (1-10)      (18-100)

    Printing Co., USA          1.8-87       2.5-124           ?                140       Angus Chem. Co. & Occusafe, Inc. (1986)
                              (0.5-24)     (0.7-34)

    Paint mfg., Mexico           3.6         < 91           5-10               100       Angus Chem. Co. & Occusafe, Inc. (1986)
                                 (1)        (< 25)

    Ink mfg., Mexico            11-18        73-80          5-10                8        Angus Chem. Co. & Occusafe, Inc. (1986)
                                (3-5)       (20-22)

    Coatings mfg.,             14.6-91      237-251        < 5-20              30        Angus Chem. Co. & Occusafe, Inc. (1986)
    Mexico                     (4-25)       (65-69)

    Chemical distilation,       36-55        > 91          < 5-10               2        Angus Chem. Co. & Occusafe, Inc. (1986)
    Mexico                     (10-15)      (> 25)

    Paint mfg., USA            unknown                      < 20               150       Angus Chem. Co. & Occusafe, Inc. (1986)

    Automotive mfg., USA       3.6-36         142           < 18               10        Angus Chem. Co. & Occusafe, Inc. (1986)
                               (1-10)        (39)

    a mfg. = manufacturing;  co. = company
    b TWA  = time weighted average;  STEL = short-term exposure level; values in parentheses are in ppm
    c This average is an approximation

        The limited data on the effects of 2-NP on organisms other than
    mammals is summarized below. Kido et al. (1975) reported that 2-NP
    (5 g/litre) inhibited the growth of 10 of the 14 species of
    microorganisms tested, although all 14 species contained enzymes
    capable of oxidizing 2-NP to acetone and nitrite (see section 4.2).
    Organisms inhibited by 2-NP included bacteria  (Escherichia coli,
     Pseudomonas iodinum), yeasts  (Endomyces fibuliger, Hansenula
     anomala, H. octospora, H. sauveolens, H. matritensis), and fungi
     (Aspergillus niger, Penicillium oxalicum, Fusarium oxysporum).
    Organisms capable of growing on the medium containing 2-NP similarly
    included bacteria  (Sarcina lutea, Brevibacterium protophormiae), a
    yeast  (Hansenula mrakii), and a fungus  (Rhizopus batatas).
    Fridman et al. (1976) reported that the minimum concentration of
    2-NP inhibiting the growth of  E. coli and  Staphylococcus aureus
    was 1000 mg/litre. Observations on aquatic macroorganisms appear
    more limited than those on microorganisms. The lowest concentration
    of 2-NP in sea water inducing narcosis in barnacle larvae at 18-22
    °C was approximately 0.7-0.8 g/litre (Crisp et al., 1967). At 22 °C
    the 96-h LC50 for fathead minnows  (Pimephales promelas) was >
    210 mg/litre (Curtis et al., 1980; Curtis & Ward, 1981). Aeration of
    the holding tanks during the toxicity test produced flawed results
    because 2-NP was lost continuously by volatilization and a nominal
    highest concentration of 612.5 mg/litre was reduced to 496 mg/litre
    at the start of the test and to 210 mg/litre by 96 h. There was no
    significant mortality at concentrations of 2-NP below 210 mg/litre
    although at lower concentrations it did produce severe (though
    undescribed) sublethal effects. Observations on non-mammalian
    terrestrial organisms are limited to two related species, the
    oriental fruit fly  (Dacus dorsalis) and the Mediterranean fruit
    fly  (Ceratitis capitata). Burditt et al. (1963) found that 2-NP
    was not especially effective as a fumigant against eggs and larvae
    of these species. The 2-h LC50 values for eggs and larvae of the
    oriental fruit fly were > 103 and 75 g/m3 (> 28 300 and
    20 600 ppm), respectively, and for the Mediterranean fruit fly, > 103
    and 35 g/m3 (> 28 300 and 9600 ppm), respectively. These
    observations, in summary, suggest a fairly low acute toxicity to
    non-mammalian organisms.


    10.1  Human health risks

        Although there are no known biological sources of 2-NP, very low
    level non-occupational exposure must be almost universal because
    2-NP is known to be a minor component of tobacco smoke and probably
    is present in smoke from other types of nitrate-rich organic matter.
    Residues in food products containing fatty acids separated with 2-NP
    and in beverage can linings and other coatings may represent
    additional sources of exposure to low (µg) amounts of 2-NP. The
    effects, if any, on human health of low-level exposure are unknown.

        Sources of worker exposure include rotogravure and flexographic
    inks used in printing, and coatings and adhesives used in industrial
    construction and maintenance, highway markings, ship building and
    maintenance, furniture manufacture, and food packaging. Based on a
    survey conducted in the USA in 1980, occupational exposure to 2-NP
    appeared to be limited to a fraction of 1% of the workforce, and
    significant occupational exposure (exposure to > 9.1 mg/m3 (>
    2.5 ppm)) to about 0.005% of the workforce. Thus, tens of thousands
    of workers may have received significant occupational exposure
    worldwide. The effects of this occupational exposure are unclear.

        Very few industrial fatalities have been attributed to 2-NP. All
    involved acute exposure to high concentrations of vapours from
    solvent mixtures containing 2-NP during applications of coatings in
    confined spaces; all deaths resulted primarily from hepatic failure.
    Exposure to non-lethal concentrations of 2-NP may result in
    temporary illness or discomfort, but there is no case history or
    epidemiological evidence that the chemical induces cancer or other
    long-term harmful effects in humans. On the other hand, the numbers
    of individuals studied and the periods since first exposure to 2-NP
    were inadequate to detect possible long-term harmful effects.

        Animal data has demonstrated that 2-NP is a strong
    hepatocarcinogen in rats. Chronic exposure to high but non-lethal
    concentrations (at least 0.36 g/m3, 100 ppm) induced a high
    frequency of hepatic tumours and hepatic cancer in rats but these
    observations were not reproduced in limited studies on mice and
    rabbits. The mechanism by which 2-NP induces cancer in rats has not
    been elucidated as yet. 2-NP is strongly genotoxic to rat
    hepatocytes both  in vitro and  in vivo. It appears likely that
    the hepatocarcinogenicity of the compound in rats is a consequence
    of liver-specific formation of reactive products. The DNA-damaging
    species has not yet been identified. Since it can induce liver cell
    proliferation, 2-NP may also have tumour-promoting activity.
    Similarities or differences between metabolic activation of 2-NP in
    rats and in humans are largely unknown. At present, any substance

    shown to be carcinogenic in any mammalian species is considered a
    potential human carcinogen. Accurate risk assessment from exposure
    to 2-NP requires further studies.

    10.2  Effects on the environment

        2-NP does not represent a threat to the environment. It appears
    highly mobile in the natural environment and is not accumulated in
    any individual compartment. It is likely that 2-NP will be destroyed
    by photolysis when exposed in the atmosphere to sunlight, and by
    biological processes in soil and water. There are, however,
    insufficient experimental and observational data on the behaviour of
    2-NP in the environment to validate these assumptions or to estimate
    rates of degradation in nature. Limited observations on
    microorganisms, invertebrates, and fish show a low level of acute
    toxicity to non-mammalian organisms.


        There are no indications that 2-NP is carcinogenic in humans.
    However, in view of its carcinogenicity in rats, it is recommended
    that occupational exposure and its presence in consumer products
    such as paints and varnishes be minimized and that it be replaced
    with a less toxic solvent whenever practical. Monitoring of the
    workplace should be continued to control actual worker exposure.
    Although it is not feasible to eliminate non-occupational exposure,
    such exposure should be minimized. 2-NP should not be used in food


    12.1  Environment

        Although it appears likely that 2-NP is highly mobile in the
    environment, is not accumulated in any environmental compartment,
    and is degraded in the environment to less toxic substances by
    microorganisms and ultraviolet radiation, it would be desirable to
    confirm experimentally these assumptions and to quantify the speed
    of degradation in various environmental compartments.

    12.2  Epidemiology

        Cohorts of workers in production plants as well as cohorts of
    workers using products containing 2-NP (e.g., inks, paints) should
    be investigated for incidence of cancer and other ill effects.

    12.3  Toxicokinetics

        A more detailed examination of the metabolism and distribution
    in the body of 2-NP and its metabolites is needed to facilitate an
    understanding of the marked species and sex differences in toxic
    effects. Studies on distribution and metabolism should include
    metabolites of both the carbon and the nitrogen moieties.
    Experimental data should be obtained on dermal uptake. Studies on
    the metabolism of 2-NP in human cells are needed to facilitate the
    eventual extrapolation of data obtained with laboratory animals to

    12.4  Carcinogenesis

        Continued efforts should be made to elucidate the biochemical
    and molecular mechanisms whereby 2-NP induces genotoxic effects and


        2-NP was evaluated by the Joint FAO/WHO Expert Committee on Food
    Additives in 1979 and 1981, but no ADI was allocated. The Committee
    recommended that 2-NP should not be used as a solvent in food
    processing, but it was temporarily acceptable for use as a
    fractionating solvent in the production of fats and oils (FAO/WHO,
    1984). 2-NP was re-evaluated by JECFA in 1989; it was considered to
    be a potent liver carcinogen in rats, and the temporary acceptance
    for use as a fractionating solvent in the production of fats and
    oils was not extended (FAO/WHO, 1990a, 1990b). The European Economic
    Community found 2-NP to be flammable and to be harmful by
    inhalation, ingestion, and dermal contact. It required that member
    states ensure that it receives proper packaging, labelling, and
    storage (IRPTC, 1986).

        The International Agency for Research on Cancer evaluated 2-NP
    in 1981 (IARC, 1982) and concluded that there was sufficient
    evidence for its carcinogenicity in rats but that epidemiological
    information was inadequate to evaluate its carcinogenicity to
    humans. 2-NP is classified in Group 2B, i.e. as possibly
    carcinogenic to humans (IARC, 1987).


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    1.  Propriétés et méthodes d'analyse

        Le 2-nitropropane (2-NP) est un liquide huileux, incolore, à
    l'odeur douceâtre. Il est inflammable, moyennement volatil et stable
    dans les conditions ordinaires. Il n'est que légèrement soluble dans
    l'eau mais miscible à de nombreux liquides organiques et c'est un
    excellent solvant de nombreux composés organiques. Il existe de
    bonnes méthodes d'analyse pour la recherche et le dosage du
    2-nitropropane présent dans l'environnement. On a actuellement
    recours à la chromatographie en phase gazeuse avec détection par
    ionisation de flamme ou capture d'électrons, ou bien à la
    chromatographie en phase liquide à haute performance avec détecteur
    u.v. Pour le dosage dans l'air, il faut tout d'abord  piéger le
    2-nitropropane et le concentrer par adsorption sur phase solide.

    2.  Emploi et sources d'exposition

    2.1  Production

        Les chiffres de production actuels ne sont pas connus. En 1977
    les Etats-Unis d'Amérique en ont produit environ 13 600 tonnes. Le
    2-nitropropane est actuellement produit par deux firmes américaines
    et une firme française. Il peut prendre naissance naturellement à
    l'état de traces lors de la combustion du tabac et d'autres matières
    organiques riches en nitrates mais rien n'indique qu'il puisse se
    former à l'issue d'un processus biologique quelconque.

    2.2  Emploi et passage dans l'environnement

        Le 2-nitropropane est utilisé comme solvant, principalement en
    mélange, et il a de nombreuses applications industrielles en tant
    que tel pour la confection d'encres d'imprimerie, de peintures, de
    vernis, d'adhésifs et autres revêtements, comme par exemple ceux que
    l'on utilise dans les récipients contenant des boissons. On
    l'utilise également comme solvant pour séparer des composés très
    voisins comme les acides gras, comme intermédiaire en synthèse
    chimique et comme additif dans les carburants. C'est principalement
    par l'intermédiaire de l'air qu'il passe dans l'environnement,
    surtout par évaporation à partir des surfaces enduites de produits
    qui en contiennent.

    3.  Transport et distribution dans l'environnement

        Le 2-nitropropane se révèle très mobile dans le milieu  naturel.
    Du fait que sa solubilité dans l'eau, son adsorption par les
    sédiments et sa bioaccumulation sont faibles et qu'il s'évapore
    rapidement dans l'atmosphère, il se répartit dans l'air et l'eau
    sans s'accumuler dans un compartiment particulier du milieu. Le

    2-nitropropane absorbe le rayonnement ultra-violet aux longueurs
    d'onde que l'on rencontre dans l'environnement et il est donc
    probable qu'il subisse une lente photolyse dans l'atmosphère. Il est
    également probable qu'il soit lentement transformé par voie
    biologique en composés moins toxiques, tant dans l'environnement
    aquatique que dans l'environnement terrestre.

    4.  Concentrations dans l'environnement et exposition humaine

        Il semble que l'exposition de la population générale au
    2-nitropropane soit très faible et provienne de la fumée de
    cigarettes (1,1 à 1,2 µg/cigarette), de résidus présents dans des
    enduits ou revêtements tels qu'on en utilise pour les récipients
    contenant des boissons, dans les adhésifs, les encres d'imprimerie,
    ainsi que dans les huiles végétales que l'on fractionne au moyen de
    ce solvant. On ignore quelle est l'importance de l'exposition des
    travailleurs de l'industrie dans le monde, mais aux Etats-Unis
    d'Amérique, il semble qu'elle soit limitée à 0,02-0,19 % du
    personnel. Dans ce même pays, environ 4000 travailleurs (soit à peu
    près 0,005 % de la main-d'oeuvre) subissent sans doute une
    exposition notable (de l'ordre de 9,1 mg/m3(2,5 ppm) ou
    davantage). Selon les pays, les limites d'exposition professionnelle
    dans l'air vont de 36 mg/m3 (1 ppm) (TWA) à 146 mg/m3 (40 ppm)
    (STEL). La production du 2-nitropropane s'effectue en circuit fermé
    et en général, le personnel n'est guère exposé; toutefois dans
    certaines industries (peinture, imprimerie ou extraction par
    solvant), il est arrivé que des travailleurs soient exposés à des
    concentrations dépassant largement les limites d'exposition
    professionnelle. C'est ainsi que des concentrations atteignant
    6 g/m3 (1640 ppm) dans l'air ont été enregistrées lors du
    remplissage de fûts.

    5.  Cinétique et métabolisme

        Le 2-nitropropane est principalement résorbé au niveau des
    poumons. Chez l'animal de laboratoire, on a montré qu'il était
    rapidement absorbé non seulement à ce niveau mais également au
    niveau de la cavité péritonéale et des voies digestives. On est mal
    renseigné sur son absorption percutanée. Quant aux données
    concernant sa distribution dans l'organisme du rat, elles sont
    quelque peu contradictoires. Le 2-nitropropane est rapidement
    métabolisé, essentiellement sous forme d'acétone et de nitrite. Il
    se forme peut-être aussi un peu d'alcool isopropylique. Après
    injection par voie intrapéritonéale, le 2-nitropropane et ses
    métabolites carbonés se concentrent d'abord dans les graisses, puis
    dans la moelle osseuse ainsi que dans les surrénales et les autres
    organes internes; après inhalation, ils se concentrent dans le foie
    et les reins, mais relativement peu dans les graisses. Il est
    possible que plusieurs systèmes enzymatiques interviennent dans ce
    métabolisme et les vitesses, de même que les voies de

    métabolisation, varient selon les espèces. Le 2-nitropropane et ses
    métabolites carbonés disparaissent rapidement de l'organisme par
    métabolisation, exhalation ou excrétion dans les urines et les
    matières fécales. On manque de données satisfaisantes sur la
    distribution et l'excrétion de la fraction nitrée de ces

    6.  Effets sur les mammifères de laboratoire et les systèmes
         in vitro

        La toxicité aiguë du 2-nitropropane pour les mammifères est
    modérée. Les mâles sont plus sensibles que les femelles, tout au
    moins en ce qui concerne le rat, et l'expérience montre que la
    sensibilité varie largement d'une espèce à l'autre. La CL50
    (concentration produisant une mortalité de 50 % en 14 jours) a été
    de 1,5 g/m3 (400 ppm) pour les rats mâles et de 2,6 g/m3
    (720 ppm) pour les rats femelles. Il semble que la mortalité soit
    associée principalement aux effets narcotiques, mais les mammifères
    exposés à des concentrations d'au moins 8,4 g/m3 (2300 ppm)
    pendant une heure ou davantage ont présenté des anomalies
    anatomopathologiques graves, notamment des lésions
    hépatocellulaires, un oedème du poumon et des hémorragies.

        Il est indiscutable que le 2-nitropropane est cancérogène pour
    le rat. L'exposition de rats pendant de longues durées à du
    2-nitropropane par voie respiratoire à raison de 0,36 g/m3
    (100 ppm) (pendant 18 mois à raison de sept heures par jour et cinq
    jours par semaine) a causé des lésions destructrices au niveau du
    foie, et en particulier des carcinomes hépatocellulaires chez
    certains rats mâles. A la concentration de 0,75 g/m3 (207 ppm) les
    lésions étaient encore plus graves, avec une forte incidence de
    carcinomes hépatocellulaires à survenue plus rapide.
    L'administration chronique de doses modérées par voie orale a
    également provoqué une surincidence de carcinomes hépatocellulaires.
    Toutefois, l'inhalation prolongée par des rats de 2-nitropropane aux
    doses respectives de 91 ou 98,3 mg/m3 (25 ou 27 ppm) n'a pas
    provoqué de lésions décelables. L'exposition de souris et de lapins
    à des concentrations de 2-nitropropane capables de provoquer des
    carcinomes hépatocellulaires chez le rat n'a guère eu d'effets chez
    ces animaux, mais il est vrai que les études en question étaient
    trop limitées pour qu'on puisse exclure totalement un effet
    cancérogène du 2-nitropropane chez ces deux espèces. Le
    2-nitropropane a légèrement retardé le développement foetal des rats
    mais les données relatives à l'embryotoxicité, à la tératogénicité
    et à la toxicité du 2-NP pour la fonction de reproduction restent
    très fragmentaires. Le produit s'est révélé fortement génotoxique
    pour les hépatocytes de rats tant  in vivo qu' in vitro; en
    revanche aucune génotoxicité sensible n'a été observée au niveau des
    autres organes chez le rat ou sur des lignées cellulaires d'origine
    extrahépatique, en l'absence d'activation métabolique exogène. On a
    également montré que le 2-nitropropane était mutagène chez les

    bactéries en présence ou en l'absence d'activation métabolique

    7.  Effets sur l'homme

        L'exposition humaine à de fortes concentrations de
    2-nitropropane est largement, voire totalement d'origine
    professionnelle. A concentration élevée, le 2-nitropropane présente
    une forte toxicité aiguë et il a provoqué des accidents mortels dans
    l'industrie - encore qu'on ignore la valeur exacte de cette
    concentration, sauf dans un cas où on a pu estimer l'exposition à
    2184 mg/m3, soit 600 ppm. Les premiers symptômes consistaient en
    céphalées, nausées, somnolence, vomissements, diarrhées et douleurs.
    Malgré une amélioration temporaire de l'état général, la mort est
    quelquefois survenue dans les 4 à 26 jours suivant l'exposition. La
    cause initiale de la mort était une insuffisance hépatique à
    laquelle s'ajoutaient un oedème du poumon, des hémorragies des voies
    digestives et une insuffisance respiratoire et rénale. A des doses
    évaluées à 73-164 mg/m3 (20 à 45 ppm) on a constaté que
    l'exposition professionnelle provoquait des nausées et une perte
    d'appétit pouvant persister plusieurs heures après le départ du lieu
    de travail, aucun effet indésirable n'étant observé après exposition
    à des doses de 36,4 à 109 mg/m3 (10 à 30 ppm) (moins de quatre
    heures par jour pendant une durée inférieure ou égale à trois jours
    par semaine).

        Malgré l'insuffisance des données disponibles, rien n'indique
    qu'une exposition professionelle de longue durée au 2-nitropropane
    aux concentrations généralement présentes sur les lieux de travail
    puisse provoquer des cancers du foie ou d'autres organes, ni plus
    généralement des effets indésirables à longue échéance.

    8.  Effets sur les autres organismes au laboratoire et dans
        leur milieu naturel

        Les quelques études effectuées sur des microorganismes, des
    invertébrés et des poissons montrent que le 2-nitropropane est peu
    toxique pour les organismes non mammaliens.


    1.  Propiedades y métodos analíticos

        El 2-nitropropano (2-NP) es un líquido incoloro y oleoso de olor
    ligero. Es inflamable, moderadamente volátil, y estable en
    condiciones normales. Es sólo ligeramente hidrosoluble pero miscible
    con numerosos líquidos orgánicos, y es un excelente disolvente para
    muchos tipos de compuestos orgánicos. Existen métodos analíticos
    adecuados para identificar y medir el 2-NP en concentraciones
    ambientales. Los métodos de uso corriente son la cromatografía de
    gases y un detector de ionización de llama o de captura electrónica;
    también se usa la cromatografía líquida de alto rendimiento con
    detector de ultravioleta. Para medirlo en el aire, primero es
    necesario capturarlo y concentrarlo en un sorbente sólido.

    2.  Usos y fuentes de exposición

    2.1  Producción

        No se dispone de cifras recientes de producción mundial. En
    1977, la producción en los Estados Unidos fue de aproximadamente
    13 600 toneladas. Actualmente, el 2-NP se fabrica en dos empresas
    estadounidenses y una francesa. Se origina por mecanismos naturales
    como trazas en la combustión del tabaco y de otras sustancias
    orgánicas ricas en nitratos, pero nada indica que se origine en
    procesos biológicos.

    2.2  Usos y pérdidas al medio ambiente

        El 2-NP se utiliza como disolvente, principalmente en mezclas, y
    tiene numerosas aplicaciones industriales como disolvente para
    tintas de impresión, pinturas, barnices, adhesivos y otros
    revestimientos como los de recipientes de bebidas. Se ha utilizado
    asimismo como disolvente para separar sustancias estrechamente
    relacionadas como ácidos grasos, como intermediario en síntesis
    químicas, y como aditivo en combustibles. Las pérdidas al medio
    ambiente ingresan principalmente en el aire y se deben sobre todo a
    la evaporación del disolvente a partir de superficies revestidas.

    3.  Transporte y distribución en el medio ambiente

        El 2-NP parece tener gran movilidad en el medio ambiente
    natural. Dada su baja solubilidad en el agua, escasa absorción por
    el sedimento, reducida bioacumulación y facil evaporación a la
    atmósfera, se distribuye tanto en el aire como en el agua y no se
    acumula en ningún compartimento ambiental definido. La fotoabsorción
    ultravioleta del 2-NP se encuentra en la escala de frecuencias
    normales en el medio ambiente, por lo que es probable que la

    sustancia sea objeto de fotólisis lenta en la atmósfera. La
    biotransformación lenta del 2-NP a compuestos menos tóxicos también
    parece probable en los medios acuático y terrestre.

    4.  Niveles ambientales y exposición humana

        La exposición de la población general al 2-NP parece ser muy
    baja y se debe al humo de cigarrillos (1,1 a 1,2 µg/cigarrillo), a
    los residuos en revestimientos, como los de las latas de bebidas,
    adhesivos y material impreso, y a los aceites vegetales fraccionados
    con esa sustancia. Se desconoce la exposición industrial a escala
    mundial, pero en los Estados Unidos parece limitarse al 0,02-0,19%
    de la población trabajadora. Los niveles de exposición de cierta
    importancia (exposición a 9,1 mg/m3 (2,5 ppm) o más) en los
    Estados Unidos probablemente no afectan más que a unos 4000
    trabajadores (aproximadamente 0,005% de la población trabajadora).
    Los límites de exposición ocupacional en el aire varían de un paíse
    a otro y van desde 3,6 mg/m3 (1 ppm) (promedio ponderado en
    función del tiempo) a 146 mg/m3 (40 ppm) (STEL). La fabricación
    del 2-NP es un proceso cerrado y entraña por lo general una
    exposición reducida de los trabajadores, pero algunos obreros de
    industrias como la pintura, la impresión y la extracción de
    disolventes se han visto expuestos en otras épocas a niveles muy
    superiores a los límites de exposición ocupacional. Durante ciertas
    operaciones industriales han llegado a registrarse concentraciones
    de hasta 6 g/m3 (1640 ppm) en el aire.

    5.  Cinética y metabolismo

        En el ser humano, la absorción de 2-NP se produce principalmente
    por los pulmones. En animales de experimentación, se ha demostrado
    que el 2-NP se absorbe rápidamente no sólo por vía pulmonar sino
    también a partir de la cavidad peritoneal y del tracto
    gastrointestinal. No se dispone de datos satisfactorios sobre la
    absorción por vía cutánea. La información sobre la distribución en
    la rata es ligeramente contradictoria. El 2-NP se metaboliza
    rápidamente, principalmente a acetona y nitrito. También puede
    formarse isopropil alcohol en pequeñas cantidades. Tras la inyección
    intraperitoneal, el 2-NP y sus metabolitos carbonados se concentran
    inicialmente en la grasa y después en la médula ósea, así como en
    las glándulas suprarrenales y otros órganos internos. Tras la
    inhalación, el 2-NP y sus metabolitos carbonados se concentran en el
    hígado y el riñón; la cantidad que se acumula en la grasa es
    relativamente pequeña. Varios sistemas enzimáticos diferentes pueden
    participar y existen diferencias de unas especies a otras en cuanto
    a la velocidad y las rutas metabólicas. El 2-NP y sus metabolitos
    carbonados desaparecen rápidamente del organismo por transformación
    metabólica, exhalación y excreción en orina y heces. No se dispone
    de datos satisfactorios sobre la distribución y la excreción de
    metabolitos que llevan el radical nitro.

    6  Efectos en mamíferos de laboratorio y sistemas  in vitro

        El 2-NP tiene una toxicidad aguda moderada para los mamíferos.
    Los machos son más sensibles que las hembras, por lo menos en la
    rata, y la sensibilidad difiere ampliamente entre las especies que
    se han ensayado. La CL50 (concentración que causa una mortalidad
    del 50% en un plazo de 14 días) para la rata tras una exposición de
    6 horas fue de 1,5 g/m3 (400 ppm) en los machos y 2,6 g/m3
    (720 ppm) en las hembras. La letalidad parecía asociada
    principalmente a los efectos narcóticos, si bien los mamíferos
    expuestos a concentraciones de al menos 8,4 g/m3 (2300 ppm)
    durante una hora o más mostraron alteraciones patológicas graves,
    entre ellas lesiones hepatocelulares, edema pulmonar y hemorragia.

        Existen pruebas claras de que el 2-NP es carcinogénico en la
    rata. La exposición prolongada de ratas por inhalación de
    0,36 g/m3 (100 ppm) durante 18 meses (7 h/día, 5 días/semana)
    indujo cambios destructivos en el hígado, inclusive carcinomas
    hepatocelulares en algunos machos. Una concentración de 0,75 g/m3
    (207 ppm) indujo lesiones más graves, entre ellas una elevada
    incidencia de carcinomas hepatocelulares, con más rapidez. La
    administración crónica de dosis orales moderadas indujo también un
    exceso de carcinomas hepatocelulares en ratas. En cambio, la
    inhalación prolongada de 91 o 98,3 mg/m3 (25 ó 27 ppm) no produjo
    lesiones detectables en las ratas. La exposición de ratones y
    conejos a concentraciones de 2-NP que inducían carcinomas
    hepatocelulares en la rata tuvieron escaso efecto o ninguno, pero
    esos estudios eran demasiado limitados para descartar por completo
    la carcinogenicidad de la sustancia en ambas especies. El 2-NP
    retrasó ligeramente el desarrollo fetal en la rata, pero escasean
    los datos sobre embriotoxicidad, teratogenicidad y toxicidad
    reproductiva. Se observó que el 2-NP era sumamente genotóxico en
    hepatocitos de rata tanto  in vitro como  in vivo, pero no se
    observó genotoxicidad significativa en otros órganos de la rata ni
    en líneas celulares de origen extrahepático sin activación
    metabólica exógena. Se ha demostrado que el 2-NP es mutagénico en
    bacterias tanto en presencia como en ausencia de activación
    metabólica exógena.

    7.  Efectos en el ser humano

        La exposición humana a concentraciones elevadas de 2-NP es en su
    mayor parte o totalmente de origen ocupacional. Las concentraciones
    elevadas (se desconocen los valores reales, si bien en un caso se
    calcularon en 2184 mg/m3 (600 ppm)) producen toxicidad aguda y
    accidentes mortales en la industria. Entre los síntomas iniciales
    figuran dolores de cabeza, náuseas, mareos, vómitos, diarrea y
    dolores. Las víctimas a menudo mostraban una mejoría temporal,
    aunque en algunos casos sobrevino la muerte entre 4 y 26 días
    despues de la exposición. El fallo hepático fue la principal causa

    de muerte, con edema pulmonar, hemorragias gastrointestinales fallo
    respiratorio y renal como factores contribuyentes. La exposición
    ocupacional a niveles estimados en 73 a 164 mg/m3 (20 a 45 ppm)
    indujo náuseas y pérdida de apetito, que persistieron durante varias
    horas tras abandonar el lugar de trabajo, mientras que la exposición
    ocupacional a niveles estimados en 36,4 a 109 mg/m3 (10 a 30 ppm)
    (< de 4 h/día durante < 3 días/semana) no produjo efectos
    nocivos detectables.

        Aunque los datos disponibles son insuficientes, nada indica que
    la exposición ocupacional crónica al 2-NP en concentraciones
    normales en el lugar de trabajo induzca neoplasmas hepáticos o de
    otro tipo ni otros efectos adversos a largo plazo.

    8.  Efectos en otros organismos en el laboratorio y sobre el terreno

        Los escasos estudios realizados en microorganismos,
    invertebrados y peces indican una baja toxicidad del 2-NP para
    organismos no mamíferos.

    See Also:
       Toxicological Abbreviations
       Nitropropane, 2- (WHO Food Additives Series 16)
       Nitropropane, 2- (WHO Food Additives Series 19)
       Nitropropane, 2- (WHO Food Additives Series 26)
       Nitropropane, 2- (IARC Summary & Evaluation, Volume 71, 1999)