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.

    Environmental Health Criteria  196

    First draft prepared by Dr. L. Fishbein, Fairfax, Virginia, USA

    Published under the joint sponsorship of the United Nations
    Environment Programme, the International Labour Organisation, and the
    World Health Organization, and produced within the framework of the 
    Inter-Organization Programme for the Sound Management of Chemicals.

    World Health Organization
    Geneva, 1997

         The International Programme on Chemical Safety (IPCS) is a joint
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    WHO Library Cataloguing in Publication Data


    (Environmental health criteria ; 196)

    1.Alcohol, Methyl - toxicity       2.Alcohol, Methyl - adverse effects
    3.Environmental exposure           I.Series

    ISBN 92 4 157196 9                 (NLM Classification: QV 83)
    ISSN 0250-863X

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    1. SUMMARY

         1.1. Identity, physical and chemical properties, analytical
         1.2. Sources of human exposure
         1.3. Environmental levels and human exposure
         1.4. Environmental distribution and transformation
         1.5. Absorption, distribution, biotransformation and elimination
         1.6. Effects on laboratory mammals and  in vitro test systems
               1.6.1. Systemic toxicity
               1.6.2. Genotoxicity and carcinogenicity
               1.6.3. Reproductive toxicity, embryotoxicity and
         1.7. Effects on humans
         1.8. Effects on organisms in the environment


         2.1. Identity
         2.2. Physical and chemical properties
               2.2.1. Physical properties
               2.2.2. Chemical properties
         2.3. Conversion factors
         2.4. Analytical methods
               2.4.1. Environmental samples
                Methanol in air
                Methanol in fuels
                Methanol in fuel emissions
                Methanol in sewage and aqueous solutions
                Methanol in soils
               2.4.2. Foods, beverages and consumer products
               2.4.3. Biological materials
                Methanol in exhaled air
                Methanol in blood
                Methanol in urine
                Methanol in miscellaneous biological
                Methanol metabolites in biological 


         3.1. Natural occurrence
         3.2. Anthropogenic sources
               3.2.1. Production levels and processes
                Production processes
                Production figures
               3.2.2. Uses
                Use as feedstock for chemical syntheses
                Use as fuel
                Other uses
                Losses into the environment


         4.1. Transport and distribution between media
         4.2. Transformation
               4.2.1. Biodegradation
                Water and sewage sludge
                Soils and sediments
               4.2.2. Abiotic degradation
               4.3.2. Bioconcentration


         5.1. Environmental levels
               5.1.1. Air
               5.1.2. Water
               5.1.3. Food
               5.1.4. Tobacco smoke
         5.2. Occupational exposure
         5.3. General population


         6.1. Absorption
               6.1.1. Inhalation
               6.1.2. Oral
               6.1.3. Dermal
         6.2. Distribution
         6.3. Metabolic transformation
         6.4. Elimination and excretion
         6.5. Modelling of pharmacokinetic and toxicokinetic data


         7.1. Single exposure
               7.1.1. Non-primates
               7.1.2. Non-human primates

         7.2. Short-term exposure
               7.2.1. Inhalation exposure
         7.3. Long-term exposure
         7.4. Skin and eye irritation; sensitization
         7.5. Reproduction toxicity, embryotoxicity and teratogenicity
               7.5.1. Reproductive toxicity (effects on fertility)
               7.5.2. Developmental toxicity
               7.5.3. Behavioural effects
               7.5.4.  In vitro studies
         7.6. Mutagenicity and related end-points
               7.6.1.  In vitro studies
               7.6.2.  In vivo studies
         7.7. Carcinogenicity
         7.8. Special studies
               7.8.1. Effects on hepatocytes
               7.8.2. Toxic interactions
               7.8.3. Studies with exhaust emissions from methanol-
                       fuelled engines
         7.9. Mechanism of ocular toxicity


         8.1. General population and occupational exposure
               8.1.1. Acute toxicity
               8.1.2. Clinical features of acute poisonings
               8.1.3. Repeated or chronic exposure
               8.1.4. Reproductive and developmental effects
               8.1.5. Chromosomal and mutagenic effects
               8.1.6. Carcinogenic effects
               8.1.7. Sensitive sub-populations


         9.1. Aquatic organisms
               9.1.1. Microorganisms
               9.1.2. Algae
               9.1.3. Aquatic invertebrates
               9.1.4. Fish
         9.2. Terrestrial organisms
               9.2.1. Plants


         10.1. Evaluation of human health risks
               10.1.1. Exposure
               10.1.2. Human health effects
               10.1.3. Approaches to risk assessment
         10.2. Evaluation of effects on the environment


         11.1. Protection of human health
         11.2. Protection of the environment







         Every effort has been made to present information in the criteria
    monographs as accurately as possible without unduly delaying their
    publication.  In the interest of all users of the Environmental Health
    Criteria monographs, readers are requested to communicate any errors
    that may have occurred to the Director of the International Programme
    on Chemical Safety, World Health Organization, Geneva, Switzerland, in
    order that they may be included in corrigenda.

                                     * * *

         A detailed data profile and a legal file can be obtained from the
    International Register of Potentially Toxic Chemicals, Case postale
    356, 1219 Châtelaine, Geneva, Switzerland (telephone no. + 41 22 -
    9799111, fax no. + 41 22 - 7973460, E-mail irptc@unep.ch).

                                     * * *

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

                                     * * *

         Financial support for this Task Group meeting was provided by the
    United Kingdom Department of Health as part of its contributions to
    the IPCS.

    Environmental Health Criteria



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    FIGURE 1



    Dr D. Anderson, British Industry Biological Research Association
         (BIBRA) Toxicology International, Carshalton, Surrey, United

    Dr S.A. Assimon, Contaminants Standards Monitoring and Projects
         Branch, US Food and Drug Administration, Washington DC, USA

    Dr H.B.S. Conacher, Bureau of Chemical Safety, Ottawa, Ontario,

    Professor J. Eells, Department of Pharmacology and Toxicology,
         Medical College of Wisconsin Milwaukee, USA  (Chairman)

    Mr J. Fawell, National Centre for Environmental Toxicology,
         Marlow, Essex, United Kingdom

    Dr L. Fishbein, Fairfax, Virginia, USA  (Joint Rapporteur)

    Dr K. McMartin, Department of Pharmacology and Therapeutics,
         Louisiana State University Medical Center, Shreveport,
         Louisiana, USA

    Mr H. Malcolm, Institute of Terrestrial Ecology, Monks Wood,
         Huntingdon, United Kingdom  (Joint Rapporteur)

    Dr H.B. Matthews, National Institute of Environmental Health
         Sciences, Research Triangle Park, North Carolina, USA

    Professor M. Piscator, Karolinska Institute, Stockholm, Sweden

    Dr G. Rosner, Merzhausen, Germany

     Representatives of other Organizations

    Professor K.R. Butterworth, BIBRA Toxicology International,
         Carshalton, Surrey, United Kingdom (representing the
         International Union of Toxicology)

    Mr M.G. Penman, ICI Chemicals & Polymers Limited,
         Middlesbrough, Cleveland, United Kingdom (representing the
         European Centre for Ecotoxicology and Toxicology of


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

    Mr J.D. Wilbourn, Unit of Carcinogen Identification and
         Evaluation, International Agency for Research on Cancer
         (IARC), Lyon, France


         A WHO Task Group on Environmental Health Criteria for Methanol
    met at the British Industrial Biological Research Association (BIBRA)
    Toxicology International, Carshalton, Surrey, United Kingdom from 28
    to 31 October 1996.  Dr D. Anderson opened the meeting and welcomed
    the participants on behalf of the host institute. Dr E. Smith, IPCS,
    welcomed the participants on behalf of the Director, IPCS, and the
    three IPCS cooperating organizations (UNEP/ILO/WHO).  The Task Group
    reviewed and revised the draft criteria monograph and made an
    evaluation of the risks for human health and the environment from
    exposure to methanol.

         Dr L. Fishbein, Fairfax, Virginia, USA prepared the first draft
    of this monograph.  The second draft, incorporating comments received
    following the circulation of the first draft to the IPCS Contact
    Points for Environmental Health Criteria monographs, was also prepared
    by Dr Fishbein.

         Dr E.M. Smith and Dr P.G. Jenkins, both 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 monograph are gratefully acknowledged.


    ATP       adenosine triphosphate
    BCF       bioconcentration factor
    BOD       biochemical oxygen demand
    COD       chemical oxygen demand
    CNS       central nervous system
    FID       flame ionization detection
    GC        gas chromatography
    MLD       minimum lethal dose
    MS        mass spectrometry
    MTBE      methyl tertiary butyl ether
    NAD       nicotinamide adenine dinucleotide
    NCAM      neural cell adhesion molecule
    NOAEL     no-observed-adverse-effect level
    THF       tetrahydrofolate
    TLV       threshold limit value

    1.  SUMMARY

    1.1  Identity, physical and chemical properties, analytical methods

         Methanol is a clear, colourless, volatile flammable liquid with a
    mild alcoholic odour when pure. It is miscible with water and many
    organic solvents and forms many binary azeotropic mixtures.

         Analytical methods, principally gas chromatography (GC) with
    flame ionization detection (FID), are available for the determination
    of methanol in various environmental media (air, water, soil and
    sediments) and foods, as well as the determination of methanol and its
    principal metabolite, formate, in body fluids and tissues. In addition
    to GC-FID, enzymatic procedures with colorimetric end-points are
    utilized for the determination of formate in blood, urine and tissues.

         Determination of methanol in the workplace usually involves
    collection and concentration on silica gel, followed by aqueous
    extraction and GC-FID or GC-mass spectrometry analysis of the extract.

    1.2  Sources of human exposure

         Methanol occurs naturally in humans, animals and plants. It is a
    natural constituent in blood, urine, saliva and expired air. A mean
    urinary methanol level of 0.73 mg/litre (range 0.3-2.61 mg/litre) in
    unexposed individuals and a range of 0.06 to 0.32 µg/litre in expired
    air have been reported.

         The two most important sources of background body burdens for
    methanol and formate are diet and metabolic processes. Methanol is
    available in the diet principally from fresh fruits and vegetables,
    fruit juices (average 140 mg/litre, range 12 to 640 mg/litre),
    fermented beverages (up to 1.5 g/litre) and diet foods (principally
    soft drinks). The artificial sweetener aspartame is widely used and,
    on hydrolysis, 10% (by weight) of the molecule is converted to free
    methanol, which is available for absorption.

         About 20 million tonnes of methanol were produced worldwide in
    1991, principally by catalytic conversion of pressurized synthesis gas
    (hydrogen, carbon dioxide and carbon monoxide). Worldwide capacity was
    projected to rise to 30 million tonnes by 1995.

         Methanol is used in the industrial production of many important
    organic compounds, principally methyl tertiary butyl ether (MTBE),
    formaldehyde, acetic acid, glycol methyl ethers, methylamine, methyl
    halides and methyl methacrylate.

         Methanol is a constituent of a large number of commercially
    available solvents and consumer products including paints, shellacs,
    varnishes, paint thinners, cleansing solutions, antifreeze solutions,
    automotive windshield washer fluids and deicers, duplicating fluids,
    denaturant for ethanol, and in hobby and craft adhesives. Potentially

    large uses of methanol are in its direct use as a fuel, in gasoline
    blends or as a gasoline extender. It should be noted that the highest
    morbidity and mortality has been associated with deliberate or
    accidental oral ingestion of methanol-containing mixtures.

         Methanol has been identified in exhausts from both gasoline and
    diesel engines and in tobacco smoke.

    1.3  Environmental levels and human exposure

         Emissions of methanol primarily occur from the miscellaneous
    industrial and domestic solvent use, methanol production, end-product
    manufacturing and bulk storage and handling losses.

         Exposures to methanol can occur in occupational settings through
    inhalation or dermal contact. Many national occupational health
    exposure limits suggest that workers are protected from any adverse
    effects if exposures do not exceed a time-weighted average of
    260 mg/m3 (200 ppm) methanol for any 8-h day and for a 40-h working

         Current general population exposures through air are typically
    10 000 times lower than occupational limits. The general population is
    exposed to methanol in air at concentrations ranging from less than
    0.001 mg/m3 (0.8 ppb) in rural air to nearly 0.04 mg/m3 (30 ppb) in
    urban air.

         Data on the occurrence of methanol in finished drinking-water is
    limited, but methanol is frequently found in industrial effluents.

         If the projected use of methanol as an alternate fuel or in
    admixture with fuels increases significantly, it can be expected that
    there will be widespread exposure to methanol via inhalation of
    vapours from methanol-fuelled vehicles and/or siphoning or
    percutaneous absorption of methanol fuels or blends.

    1.4  Environmental distribution and transformation

         Methanol is readily degraded in the environment by photo
    oxidation and biodegradation processes. Half-lives of 7-18 days have
    been reported for the atmospheric reaction of methanol with hydroxyl

         Many genera and strains of microorganisms are capable of using
    methanol as a growth substrate. Methanol is readily degradable under
    both aerobic and anaerobic conditions in a wide variety of
    environmental media including fresh and salt water, sediments and
    soils, ground water, aquifer material and industrial wastewater; 70%
    of methanol in sewage systems is generally degraded within 5 days.

         Methanol is a normal growth substrate for many soil
    microorganisms, which are capable of completely degrading methanol to
    carbon dioxide and water.

         Methanol has a fairly low absorptive capacity on soils.
    Bioconcentration in most organisms is low.

         Methanol is of low toxicity to aquatic and terrestrial organisms,
    and effects due to environmental exposure to methanol are unlikely to
    be observed except in the case of a spill.

    1.5  Absorption, distribution, biotransformation and elimination

         Methanol is readily absorbed by inhalation, ingestion and dermal
    exposure, and it is rapidly distributed to tissues according to the
    distribution of body water. A small amount of methanol is excreted
    unchanged by the lungs and kidneys.

         Following ingestion, peak serum levels occur within 30-90 min,
    and methanol is distributed throughout the body with a volume of
    distribution of approximately 0.6 litre/kg.

         Methanol is metabolized primarily in the liver by sequential
    oxidative steps to formaldehyde, formic acid and carbon dioxide. The
    initial step involves oxidation to formaldehyde by hepatic alcohol
    dehydrogenase, which is a saturable rate-limiting process. The
    relative affinity of alcohol dehydrogenase for ethanol and methanol is
    approximately 20:1. In step 2, formaldehyde is oxidized by
    formaldehyde dehydrogenase to formic acid/or formate depending on the
    pH. In step 3, formic acid is detoxified to carbon dioxide by folate-
    dependent reactions.

         Elimination of methanol from the blood via the urine and exhaled
    air and by metabolism appears to be slow in all species, especially
    when compared to ethanol. Clearance proceeds with reported half-times
    of 24 h or more with doses greater than 1 g/kg and half-times of
    2.5-3 h for doses less than 0.1 g/kg. It is the rate of metabolic
    detoxification, or removal of formate that is vastly different between
    rodents and primates and is the basis for the dramatic differences in
    methanol toxicity observed between rodents and primates.

    1.6  Effects on laboratory mammals and  in vitro test systems

    1.6.1  Systemic toxicity

         The acute and short-term toxicity of methanol varies greatly
    between different species, toxicity being highest in species with a
    relatively poor ability to metabolize formate. In such cases of poor
    metabolism of formate, fatal methanol poisoning occurs as a result of
    metabolic acidosis and neuronal toxicity, whereas, in animals that
    readily metabolize formate, consequences of CNS depression (coma,
    respiratory failure, etc.) are usually the cause of death. Sensitive
    primate species (humans and monkeys) develop increased blood formate
    concentrations following methanol exposure, while resistant rodents,
    rabbits and dogs do not. Humans and non-human primates are uniquely
    sensitive to the toxic effects of methanol. Overall methanol has a low

    acute toxicity to non-primate animals. The LD50 values and minimal
    lethal doses after oral exposure range from 7000 to 13 000 mg/kg in
    the rat, mouse, rabbit and dog and from 2000 to 7000 mg/kg for the

         Rats exposed to levels of methanol up to 6500 mg/m3 (5000 ppm)
    for 6 h/day, 5 days/week for 4 weeks, exhibited no exposure-related
    effects except for increased discharges around the nose and eyes.
    These were considered reflective of upper respiratory irritation.

         Rats exposed to methanol vapour levels up to 13 000 mg/m3
    (10 000 ppm) for 6 h/day, 5 days/week for 6 weeks, failed to
    demonstrate pulmonary toxicity.

         In the rabbit, methanol is a moderately irritant to the eye. It
    was not skin-sensitizing in a modified maximization test.

         Toxic effects found in methanol-exposed primates include
    metabolic acidosis and ocular toxicity, effects that are not normally
    found in folate-sufficient rodents. The differences in toxicity are
    due to differences in the rate of metabolism of the methanol
    metabolite formate. For instance, the clearance of formate from the
    blood of exposed primates is at least 50% slower than for rodents.

         Monkeys receiving methanol doses higher than 3000 mg/kg by gavage
    demonstrated ataxia, weakness and lethargy within a few hours of
    exposure. These signs tended to disappear within 24 h and were
    followed by transient coma in some of the animals.

         In monkeys exposed to methanol for 6 h/day for 5 days a week, 20
    repeated exposures to 6500 mg/m3 (5000 ppm) methanol failed to elicit
    ocular effects.

    1.6.2  Genotoxicity and carcinogenicity

         Methanol has given negative results for gene mutation in bacteria
    and yeast assays, but it did induce chromosomal malsegregation in
    Aspergillus. It did not induce sister chromatic exchanges in Chinese
    hamster cells  in vitro but caused significant increases in mutation
    frequencies in L5178Y mouse lymphoma cells.

         Methanol inhalation did not induce chromosomal damage in mice.
    There is some evidence that oral or intraperitoneal administration
    increased the incidence of chromosomal damage in mice.

         There is no evidence from animal studies to suggest that methanol
    is a carcinogen, although the lack of an appropriate animal model is

    1.6.3  Reproductive toxicity, embryotoxicity and teratogenicity

         Conflicting results have been reported on the effects of
    inhalation of methanol for up to six weeks on gonadotropin and
    testosterone concentrations.

         The inhalation of methanol by pregnant rodents throughout the
    period of embryogenesis induces a wide range of concentration-
    dependent teratogenic and embryolethal effects. Treatment-related
    malformations, predominantly extra or rudimentary cervical ribs and
    urinary or cardiovascular defects, were found in fetuses of rats
    exposed 7 h/day for 7-15 days of gestation to 26 000 mg/m3
    (20 000 ppm) methanol. Slight maternal toxicity was found at this
    exposure level, and no adverse effects to the mother or offspring were
    found in animals exposed to 6500 mg/m3 (5000 ppm), which was
    interpreted as the no-observed-adverse-effect level (NOAEL) for this
    test system.

         Increased incidences of exencephaly and cleft palate were found
    in the offspring of CD-1 mice exposed 7 h/day, on days 6-15 of
    gestation, to methanol levels of 6500 mg/m3 (5000 ppm) or more. There
    was increased embryo/fetal death at 9825 mg/m3 (7500 ppm) or more and
    an increasing incidence of full-litter resorptions. Reduced fetal
    weight was observed at 13 000 and 19 500 mg/m3 (10 000 or 15 000
    ppm). The NOAEL for developmental toxicity was 1300 mg/m3 (1000 ppm)
    methanol. There was no evidence of maternal toxicity at methanol
    exposure levels below 9000 mg/m3 (7000 ppm).

         When litters of pregnant CD-1 mice were given 4 g methanol/kg by
    gavage, the incidences of adverse effects on resorption, external
    defects including cleft palate, and fetal weight were similar to those
    found in the 13 000 mg/m3 (10 000 ppm) inhalation exposure group,
    presumably due to the greater rate of respiration of the mouse. The
    mouse is more sensitive than the rat to developmental toxicity
    resulting from inhaled methanol.

         Transient neurological signs and reduced body weights were found
    in CD-1 dams exposed to 19 500 mg/m3 (15 000 ppm) for 6 h/day
    throughout organogenesis (gestational days 6-15). Fetal malformations
    found at 13 000 and 19 500 mg/m3 (10 000 and 15 000 ppm) included
    neural and ocular defects, cleft palate, hydronephrosis and limb

    1.7  Effects on humans

         Humans (and non-human primates) are uniquely sensitive to
    methanol poisoning and the toxic effects in these species is
    characterized by formic acidaemia, metabolic acidosis, ocular
    toxicity, nervous system depression, blindness, coma and death. Nearly
    all of the available information on methanol toxicity in humans
    relates to the consequences of acute rather than chronic exposures. A
    vast majority of poisonings involving methanol have occurred from
    drinking adulterated beverages and from methanol-containing products.

    Although ingestion dominates as the most frequent route of poisoning,
    inhalation of high concentrations of methanol vapour and percutaneous
    absorption of methanolic liquids are as effective as the oral route in
    producing acute toxic effects. The most noted health consequence of
    longer-term exposure to lower levels of methanol is a broad range of
    ocular effects.

         The toxic properties of methanol are based on factors that govern
    both the conversion of methanol to formic acid and the subsequent
    metabolism of formate to carbon dioxide in the folate pathway. The
    toxicity is manifest if formate generation continues at a rate that
    exceeds its rate of metabolism.

         The lethal dose of methanol for humans is not known for certain.
    The minimum lethal dose of methanol in the absence of medical
    treatment is between 0.3 and 1 g/kg. The minimum dose causing
    permanent visual defects is unknown.

         The severity of the metabolic acidosis is variable and may not
    correlate well with the amount of methanol ingested. The wide
    interindividual variability of the toxic dose is a prominent feature
    in acute methanol poisoning.

         Two important determinants of human susceptibility to methanol
    toxicity appear to be (1) concurrent ingestion of ethanol, which slows
    the entrance of methanol into the metabolic pathway, and (2) hepatic
    folate status, which governs the rate of formate detoxification.

         The symptoms and signs of methanol poisoning, which may not
    appear until after an asymptomatic period of about 12 to 24 h, include
    visual disturbances, nausea, abdominal and muscle pain, dizziness,
    weakness and disturbances of consciousness ranging from coma to clonic
    seizures. Visual disturbances generally develop between 12 and 48 h
    after methanol ingestion and range from mild photophobia and misty or
    blurred vision to markedly reduced visual acuity and complete
    blindness. In extreme cases death results. The principal clinical
    feature is severe metabolic acidosis of the anion-gap type. The
    acidosis is largely attributed to the formic acid produced when
    methanol is metabolized.

         The normal blood concentration of methanol from endogenous
    sources is less than 0.5 mg/litre (0.02 mmol/litre), but dietary
    sources may increase blood methanol levels. Generally, CNS effects
    appear above blood methanol levels of 200 mg/litre (6 mmol/litre);
    ocular symptoms appear above 500 mg/litre (16 mmol/litre), and
    fatalities have occurred in untreated patients with initial methanol
    levels in the range of 1500-2000 mg/litre (47-62 mmol/litre).

         Acute inhalation of methanol vapour concentrations below
    260 mg/m3 or ingestion of up to 20 mg methanol/kg by healthy or
    moderately folate-deficient humans should not result in formate
    accumulation above endogenous levels.

         Visual disturbances of several types (blurring, constriction of
    the visible field, changes in colour perception, and temporary or
    permanent blindness) have been reported in workers who experienced
    methanol air levels of about 1500 mg/m3 (1200 ppm) or more.

         A widely used occupational exposure limit for methanol is
    260 mg/m3 (200 ppm), which is designed to protect workers from any of
    the effects of methanol-induced formic acid metabolic acidosis and
    ocular and nervous system toxicity.

         No other adverse effects of methanol have been reported in
    humans except minor skin and eye irritation at exposures well above
    260 mg/m3 (200 ppm).

    1.8  Effects on organisms in the environment

         LC50 values in aquatic organisms range from 1300 to
    15 900 mg/litre for invertebrates (48-h and 96-h exposures), and
    13 000 to 29 000 mg/litre for fish (96-h exposure).

         Methanol is of low toxicity to aquatic organisms, and effects due
    to environmental exposure to methanol are unlikely to be observed,
    except in the case of a spill.


    2.1  Identity

         Chemical formula:             CH3OH

         Chemical structure:              H
                                      H - C - OH 

         Relative molecular mass:      32.04

         CAS chemical name:            methanol

         CAS registry number:          67-56-1

         RTECS number:                 PC 1400000

         Synonyms:                     methyl alcohol, carbinol, wood
                                       alcohol, wood spirits, wood
                                       naphtha, Columbian spirits,
                                       Manhattan spirits, colonial spirit,
                                       hydroxymethane, methylol,
                                       monohydroxymethane, pyroxylic

         Impurities in commercial methanol include acetone, acetaldehyde,
    acetic acid and water.

    2.2  Physical and chemical properties

    2.2.1  Physical properties

         Methanol is a colourless, volatile, flammable liquid with a mild
    alcoholic odour when pure. However, the crude product may have a
    repulsive pungent odour. Methanol is miscible with water, alcohols,
    esters, ketones and most other solvents and forms many azeotropic
    mixtures. It is only slightly soluble in fats and oils (Clayton &
    Clayton, 1982; Windholz, 1983; Elvers et al., 1990).

         Important physical constants and properties of methanol are
    summarized in Table 1.

    Table 1.  Some physical properties of methanola


    Appearance                     clear colourless liquid

    Odour                          slight alcoholic when pure;
                                   crude material pungent

    Boiling point                  64.7°C

    Flash point                    15.6°C (open cup)
                                   12.2°C (closed cup)

    Freezing point                 -97.68°C

    Specific gravity               0.7915 (20/4°C)
                                   0.7866 (25°C)

    Vapour pressure
         at 30°C                   160 mmHg
         at 20°C                   92 mmHg

    Henry's Law Constant (25°C)    1.35 x 10-4atm.m3/mole

    Log P (octanol/water)          -0.82; -0.77; -0.68

    Partition constant             -0.66; -0.64

    Ignition temperature           470°C

    Explosive limits in air        lower 5.5
     (% by volume)                 upper 44

    Refractive index n20           1.3284

    a    Data from: Clayton & Clayton, 1982; Elvers et al., 1990;
         Grayson, 1981; Howard, 1990; Windholz, 1983.

         In the USA, sales grade methanol must normally meet the
    following specifications: 

         methanol content (weight %) minimum      99.85

         acetone and aldehydes (ppm) maximum      30

         acid (as acetic acid) (ppm) maximum      30

         water content (ppm) maximum              1.500

         specific gravity (d2020)                 0.7928

         permanganate time, minimum               30

         odour                                    characteristic

         distillation range at 101 kPa            1°C, must include

         colour, platinum-cobalt scale, maximum   5

         appearance                               clear-colourless

         residual on evaporation, g/100 ml        0.001

         carbonizable impurities, colour          30

         platinum-cobalt scale, maximum           5

         Grade AA differs in specifying an acetone maximum (20 ppm), a
    minimum for ethanol (10 ppm), and in having a more stringent water
    content specification (1.000 ppm, maximum) (Grayson, 1981).

    2.2.2  Chemical properties

         Methanol undergoes reactions that are typical of alcohols as a
    chemical class. The reactions of particular industrial importance
    include the following: dehydrogenation and oxidative dehydrogenation
    over silver or molybdenum-iron oxide to form formaldehyde; the
    acid-catalysed reaction with isobutylene to form methyl tertiary butyl
    ether (MTBE); carbonylation to acetic acid catalysed by cobalt or
    rhodium; esterification with organic acids and acid derivatives;
    etherification; addition to unsaturated bonds and replacement of the
    hydroxyl group (Grayson, 1981; Elvers et al., 1990).

    2.3  Conversion factors

    1 ppm = 1.31 mg/m3 (25°C, 1013hPa) 1 mmol/litre = 32 mg/litre

    1 mg/m3  = 0.763 ppm (25°C, 1013hPa) 1 mg/litre =31.2 µmol/litre

    (Adapted from Clayton & Clayton, 1982) 

    2.4  Analytical methods

         Prior to the advent of sensitive gas chromatographic techniques,
    the analysis of methanol in environmental, consumer and biological
    samples was performed by procedures involving isolation of the
    volatile alcohol and titrimetry. This was followed later by more
    sensitive spectrophotometric methods based on the oxidation of
    methanol to formaldehyde with potassium permanganate then reaction
    with Schiff's reagent or rosaniline solution to produce an easily
    recognizable and stable colour (Gettler, 1920; Boos, 1948; Skaug,
    1956; Hindberg & Wieth, 1963; NIOSH, 1976).

         The earliest procedures for the determination of methanol in
    blood and urine were based on the initial distillation to isolate the
    volatile alcohol (Gettler, 1920). Feldstein & Klendshog (1954)
    determined methanol in biological fluids by initial microdiffusion
    followed by oxidation to formaldehyde and subsequent reaction with
    chromotropic acid (1,8-dihydroxy naphthalene-3,6-disulfonic acid). The
    recovery ranged from 80 to 85% for less than 0.10 mg methanol. In the
    procedure of Harger (1935), methanol was determined by oxidation with
    bichromate to carbon dioxide and water followed by titration with a
    mixture of ferrous sulfate and methyl orange. Jaselkis & Warriner
    (1966) determined methanol in aqueous solution by titrimetry employing
    xenon trioxide oxidation. Methanol was determined at a level of
    0.03 mg with a relative standard deviation of 4%.

    2.4.1  Environmental samples

         The determination of methanol by primarily GC-FID procedures has
    been frequently reported in ambient air, workplace air, fuels, fuel
    emissions, sewage and aqueous solutions, soils, coal-gasification
    condensate water and tobacco smoke.

         The measurement of methanol in ambient and workplace air, usually
    involves a preconcentration step in which the sample is passed through
    a solid absorbent containing silica gel, Tenax GC, Porapak or
    activated charcoal (NIOSH, 1976,1977,1984; CEC, 1988). It can also be
    accomplished by on-column cryogenic trapping or can be analysed
    directly. Direct reading infrared instruments with gas cuvettes can be
    used for continuous monitoring of methanol in air (Lundberg, 1985).  Methanol in air

         The use of absorption tubes to trap methanol from ambient and
    workplace air with subsequent liquid or thermal desorption prior to
    gas chromatographic analysis has been reported frequently. The US
    National Institute of Occupational Safety and Health (NIOSH,
    1977,1984) recommended the use of a glass tube (7 cm × 4 mm internal
    diameter) containing two sections of 20-40 mesh silica gel separated
    by a 2-mm portion of urethane foam (front=100 mg, back=50 mg). Water
    is used to extract the methanol, which is separated on a 2 m × 2 mm
    internal diameter glass column containing 60-80 mesh Tenax GC or the
    equivalent using flame ionization detection (FID). The working range
    is 25 to 900 mg/m3 (19 to 690 ppm) methanol for a 5-litre air sample.
    The limit of detection has been reported to be 1.05 mg/m3 in a
    3-litre air sample (NIOSH, 1976). At high concentrations of methanol
    or at high relative humidity, a large silica gel tube is required
    (700 mg silica gel front section). The injection, detector and column
    temperatures are 200°C, 250-300°C and 80°C respectively. Positive
    identification by mass spectrometry may be necessary in some cases,
    and alternative gas chromatographic columns, e.g., SP-1000, SP-2100 or
    FFAP, are also conformation aides.

         Although GC-FID provides greater sensitivity than GC-MS, the
    latter is generally considered more reliable for the measurement of
    methanol in samples containing other alcohols or low molecular weight
    oxygenates.Analysis of methanol in workplace air has been carried out
    by head-space GC-FID using a column containing 15% Carbowax 1500 on
    diatomaceous earth, 70-100 mesh operated at 100°C. The detection limit
    was below 5 ml/m3 ( Heinrich & Angerer, 1982). Methanol in workplace
    air was initially collected in silica gel tubes and the methanol
    concentrations analysed by GC-FID equipped with a 50 m silica
    capillary column containing Carbowax 20M. Additionally, methanol
    vapour concentrations in the workplace have been analysed by a Miron-B
    analyser with detection at a wavelength of 9.70 µm.

         Methanol and other low molecular weight oxygenates have been
    determined in ambient air by cryogradient sampling and two-dimensional
    gas chromatography (Jonsson & Berg, 1983). Samples were initially
    separated on a packed column (1,2,3-tris (2-cyanoethoxy)propane on
    Chromosorb W-AW), then refocused on-line in a fused-silica capillary
    cold trap, followed by on-line splitless reinjection onto a 50 m ×
    0.3 mm internal diameter fused silica capillary column. The detection
    limit for a typical oxygenate (3-methylbutanol) was 0.1 µg/m3 using a
    3-litre sample. The detection limit for methanol was slightly higher.

         Spectrophotometric methods have also been employed for the
    determination of methanol in air. Aqueous potassium permanganate
    acidified with phosphoric acid was used to absorb methanol from air
    with the simultaneous oxidation to formaldehyde. After the addition of
     p-aminoazobenzene and sulfur dioxide, the resulting pink dye was
    determined spectrophotometrically at 505 nm. The limit of detection
    was 5 µg methanol/ml air (Verma & Gupta, 1984).

         Methanol from air was absorbed by acidified potassium
    permanganate producing formaldehyde which on reaction with
    4-nitroaniline produced a yellow dye determined spectroscopically at
    395 nm (Upadhyay & Gupta, 1984).

         Infrared spectrometry and infrared lasers have also been employed
    for the determination of methanol in air (Diaz-Rueda et al., 1977;
    Sweger & Travis, 1979). Methanol together with acetone, toluene and
    ethyl acetate were recovered from 10 litres of air at a flow rate of
    11 ml/min by passage through a tube containing 150 mg of activated
    charcoal. The carbon disulfide extracts of the organic compounds were
    determined by infrared at 1300 cm-1 using caesium bromide windows.
    The minimum concentration of methanol detected quantitatively was
    0.77 mg/m3 (0.60 ppm) and the minimum concentration required for
    identification was 0.24 mg/m3 (0.18 ppm) (Diaz-Rueda et al., 1977).

         Infrared lasers have been used to detect trace organic gases
    including methanol. An air sample at 8 Tor was introduced to a
    20-litre capacity sample cell, and laser radiation was detected
    synchronously by a mercury-cadmium Te detector. The laser line
    employed was P (34), the electric field was 1.40 kV/cm and the
    measurement time was 2 min. The detection limit for methanol was
    0.105 mg/m3 (0.08 ppm) (Sweger & Travis, 1979).

         Methanol in the workplace can be measured by portable direct
    reading instruments, real-time continuous monitoring systems and
    passive dosimeters (NIOSH, 1976,1977,1984; Liesivouri & Savolainen,
    1987; Kawai et al., 1990).

         Kawai et al. (1990) described a personal diffusive badge type
    that could absorb methanol vapour in linear relation to the exposure
    duration up to 10 h and to exposure concentrations up to 1050 mg/m3
    (800 ppm) the maximum duration and concentration tested respectively.
    Additionally it was shown that the response to short-term peak
    exposure was rapid enough and that no spontaneous desorption would
    occur.  Methanol in fuels

         Agarawal (1988) determined methanol quantitatively in commercial
    gasoline via an initial extraction with ethylene glycol then by GC
    utilizing a GB-1 fused silica capillary column (OV-1 equivalent, 60 m
    × 0.32 mm internal diameter) and FID. The recovery of 4% methanol in
    gasoline by this procedure was 95.4 ± 2.34% (SD).

         In the procedure of Tackett (1987), gasoline samples were
    injected directly on a Carbowax 20M column operated at 50°C for 3.0
    min and then programmed to rise to 150°C at a rate of 10°C per min.
    The calibration curve is linear up to 10% (v/v) methanol and the
    detection limit was 0.2% employing a thermal conductivity detector.

         Low molecular weight alcohols and MTBE were determined in
    gasoline by GC-FID utilizing dual columns: 4.6 m × 3.2 mm o.d. column
    packed with 30% m/m ethylene glycol succinate on Chromosorb P (85-100
    mesh) and a 2.7 m × 3.2 mm o.d. stainless steel column packed with
    Porapak P (80-100 mesh) operated at 150°C (Luke & Ray, 1984).

         Gas chromatographic analyses of methanol, ethanol and  tert-
    butanol in gasoline have been reported by Pauls & McCoy (1981). The GC
    column was 150 cm × 3 mm in o.d. stainless steel packed with Porapak R
    (80-100 mesh) operated at 175°C and the injector and FID detector
    temperatures were maintained at 250°C.

         A direct liquid chromatographic method for the determination of
    C1-C3 alcohols and water in gasoline-alcohol blends was described by
    Zinbo (1984). The separation was performed on either one or two
    microparticulate size-exclusion columns of ultrastyragel with toluene
    as the mobile phase. The quantification of alcohols and water in the
    effluent was achieved by a differential refractometer at 30°C. The
    lower limits of detection for C1-C3 alcohols was 0.005 vol %. Methanol
    in gasoline-alcohol blends has been determined by nuclear magnetic
    resonance (Renzoni et al., 1985). The method takes advantage of a
    window in the proton nuclear magnetic resonance spectrum of gasoline
    that extends from a chemical shift of 2.8 to 6.8 ppm. Methanol was
    quantified in gasoline by integration of the methyl singlet at
    3.4 ppm. The method gave linear calibration curves in the range of
    0-25% (v/v) methanol with a detection limit of less than 0.1%.  Methanol in fuel emissions

         Methanol has been detected in motor vehicle emissions at levels
    of 0.9 mg/m3 (0.69 ppm) and in ambient air by GC-FID utilizing a
    360 cm × 0.27 cm internal diameter stainless steel column packed with
    Porapak Q (50-80 mesh) operated at 150°C (Bellar & Sigsby, 1970).

         Seizinger & Dimitriades (1972) determined methanol in simple
    hydrocarbon fuel emissions utilizing GC with time-of-flight mass
    spectrometry. The analytical procedure involved concentration of the
    exhaust oxygenates drawn through a Chromosorb bed followed by GC-FID
    initially on a 30 in by 1/4 in o.d. column packed with 10% 1,2,3-tris
    (2-cyanoethoxy) propane (TCEP) programmed from -20°C to 110°C at 
    4°C/min. The second-stage column was a 45 m × 0.05 cm internal 
    diameter by 0.03 o.d Carbowax 20M support coated on tubular (SCOT) 
    column programmed from 60°C to 210°C at 10°C/min. The column effluent 
    was split for parallel detection with FID and mass spectrometry. 
    Methanol was found at levels of 0.1-0.8 mg/m3 (0.1-0.6 ppm) in 
    the exhaust of simple hydrocarbon fuels.

         Methods for the quantification of evaporative emissions (running
    losses, hot soak, diurnal and refuelling) from methanol-fuelled motor
    vehicles (methanol/gasoline fuel mixtures of 100, 85, 50, 15 and 0%
    methanol) have been described (Snow et al., 1989; Federal Register,
    1989; Gabele & Knapp, 1993).

         Methanol emissions from methanol-fuelled cars were determined by
    GC employing a Quadrex 007 methyl silicone 50 m × 0.53 mm internal
    diameter column with 5.0 µm film thickness. The separation was
    affected isothermally at 75°C (limit of detection 0.25 µg/ml)
    (Williams et al., 1990).  Methanol in sewage and aqueous solutions

         Fox (1973) determined methanol at levels of 0.5-100 mg/litre
    (0.5-100 ppm) in sewage or other aqueous solutions by GC-FID employing
    a 0.5 m × 3.175 mm o.d. stainless steel column packed with Tenax GC
    60/80 mesh and operated at 70°C isothermal.

         C1-C4 alcohols in aqueous solution were determined
    quantitatively by GC-FID using a 1 m × 0.32 cm stainless steel column
    packed with 5% w/w Carbowax 20M on Chromosorb 101 (80-100 mesh) with a
    column temperature of 65°C for methanol and ethanol and 100°C for  n-
    propanol and  n-butanol (Sims, 1976).

         Methanol and ethanol at the mg/litre level in aqueous solution
    were determined by Komers & Sir (1976) utilizing a combination of
    stripping and GC-FID technique. The alcohols were analysed as their
    corresponding volatile nitrite on a 170 cm × 0.4 cm internal diameter
    glass column containing Chromosorb 102 (80-120 mesh) operated at
    104°C. Approximately 1 µg of the individual alcohol could be
    determined in sample volumes of about 5 ml.

         Mohr & King (1985) determined methanol in coal-gasification
    condensate water by GC. Condensate water was injected directly on a 45
    × 0.32 cm Porapak R column programmed from 80-200°C at 20°C/min.

         A standard method for the analysis of methanol in raw, waste and
    potable waters has been published by the UK Standing Committee of
    Analysts (1982). The method is based on direct injection GC-FID using
    a 2 m stainless steel column with 15% carbowax 1540 m chromosorb
    W80-100 DMCS. The limit of detection is 0.11 mg/litre.  Methanol in soils

         The biodegradation of methanol in gasolines by various soils was
    determined by Novak et al. (1985). Methanol extracted in water (25%
    v/v) was measured by direct injection GC-FID using a 2.1 m × 3 mm
    stainless steel column packed with 0.2% Carbowax 1500 0n 80/100 mesh
    Carbopak C at 120°C isothermal.

    2.4.2  Foods, beverages and consumer products

         Lund et al. (1981) determined methanol in orange and grapefruit
    juice, fresh and canned, by GC-FID using a 1.5 × 3 mm column packed
    with 50/80 mesh Porapak Q at 100°C with injector port and detector
    block at 200°C.

         Greizerstein (1981) utilized GC-FID and GC-MS for the analysis of
    alcohols, aldehydes and esters in commercial beverages (beers, wines,
    distilled spirits). Separations were carried out using a 3 m × 2 mm
    internal diameter glass column packed with 30% Carbowax 20 M at 150°C.
    A more satisfactory separation of methanol from the other congeners
    was achieved using a 180-cm Porapak P column. Methanol was found at
    levels of 6-27 mg/litre beer; 96-321 mg/litre in wines and 
    10-220 mg/litre in distilled spirits. Methanol in distilled liquors 
    and cordials has been determined by GC-FID (AOAC, 1990).

         Rastogi (1993) analysed methanol content of 26 model and hobby
    glues and found methanol in 12 of them by head-space GC-FID employing
    capillary columns of different polarity. The polar GC column was a
    Supelcowax 10, 60 m × 0.32 mm internal diameter; and the non-polar
    column was a CP-Sil-5 CB, 50 m × 0.32 mm. The detection limit for
    methanol was 20 mg/litre.

         Methanol in wine vinegars was determined by GC-MS (Blanch et al.,
    1992). Methanol with many other minor volatile components was
    fractionated using a simultaneous distillation extraction technique
    before GC analysis on a 4 m × 0.85 mm internal diameter micropacked
    column coated with a mixture of Carbowax and bis-(2-ethylhexyl)-
    sebecate (92:8), 4% on desilanized Volaspher A-2. The column
    temperature was 60°C and the injector and FID detector were at 180°C.

    2.4.3  Biological materials

         A variety of primarily gas chromatographic methods have been
    utilized for the determination of methanol in biological samples from
    normal, poisoned and occupationally exposed individuals. Methanol
    exposure has been measured in exhaled breath, blood and urine samples.  Methanol in exhaled air

         Prior to analysis, expired air samples are normally collected in
    sampling bags or glass containers or after preconcentration on Tenax
    or other solid sorbents in adsorbent tubes and thermally desorbed, or
    utilizing cryotraps (Franzblau et al., 1992a).

         Free methanol has been detected and measured by GC in the expired
    air of normal healthy humans with separations made on 1.52 m × 0.3 cm
    columns filled with Anakrom ABS, 70-80 mesh coated with 2% N,N,-N,-N-
    tetramethyl azeleamide and 8% behenyl alcohol at 86°C. The
    concentration of methanol in nine subjects ranged from
    0.06-0.32 µg/litre (Eriksen & Kulkarni, 1963). Methanol was only

    infrequently detected in samples of human expired air and saliva by
    Larsson (1965) employing GC-FID and a 1.75 mx 3.5 mm internal diameter
    glass column containing polyethylene glycol (M=1500) 20% on Chromosorb

         Methanol in expired air and in head-space analysis of plasma was
    determined as the nitrite ester utilizing GC-MS (Jones et al., 1983).
    Condensed expired air samples were analysed on Porapak Q and the assay
    of methanol nitrite ester was accomplished on a 2 m × 2 mm internal
    diameter silanized glass column containing Tenax GC (30-60 mesh) at

         Krotosynski et al. (1977) analysed expired air from normal
    healthy subjects using for sample preconcentration a 18 cm × 6 mm o.d.
    stainless steel column containing Tenax GC. Sample analysis was
    performed using GC-FID and a 91 m × 6 mm stainless steel column coated
    with Emulphoron-870. Apart from methanol, 102 organic compounds were

         Alveolar air of workers exposed to methanol was first collected
    in gas sampling tubes and then analysed by GC-FID using a Porapak Q
    (80-100 mesh) column at 150°C (Baumann & Angerer, 1979).

         The detection of methanol and other endogenous compounds in
    expired air by GC-FID with on-column concentration of sample and
    separation on a 1.5 m × 3 mm o.d. stainless steel column packed with
    Porapak Q, 80-100 mesh maintained at 35°C was described by Phillips &
    Greenberg (1987).

         The expired air of volunteer subjects exposed for periods of
    about 90 min to atmospheres artificially contaminated with low levels
    of methanol (ca. 130 mg/m3 (100 ppm)) was monitored during and
    after the exposure using an atmospheric pressure ionization mass
    spectrometer (API/MS) fitted with a direct breath analysis system
    (Benoit et al., 1985).

         A transportable Fourier Transform Infrared (FTIR) spectrometer
    was utilized for the analysis of methanol vapour in alveolar and
    ambient air in humans exposed to methanol vapour. The infrared
    spectrum region used for methanol quantification was in the 950-1100
    cm region. For the analysis of methanol in alveolar air with FTIR the
    limit of detection for methanol was 0.4 mg/m3 (0.32 ppm), and for
    methanol in ambient air the detection limit was 0.13 mg/m3 (0.1 ppm)
    (Franzblau et al., 1992a).  Methanol in blood

         A number of methods have been used to extract methanol from blood
    prior to analysis including purge-and-trap, head-space analysis and
    solvent extraction.

         Baker et al. (1969) reported the simultaneous determination of
    lower alcohols, acetone and acetaldehyde in blood by GC-FID utilizing
    a 183 cm × 5 mm internal diameter column containing Porapak Q operated
    at 100°C. The method did not require precipitation of protein prior to

         Methanol in whole blood and serum was analysed by GC-FID
    employing 1.2 m and 1.8 m × 3 mm internal diameter glass columns
    packed with 20% Hallcomid or 10% Carbowax on 60-80 mesh Diatopor TW
    operated at 70°C (Mather & Assimos, 1965).

         Blood serum was deproteinized and acetone and aliphatic alcohols
    including methanol were determined by GC-FID using a pre-column of 3%
    OV-1 on Gas Chrom Q and an analytical 30-m capillary column packed
    with SPB-1 and operated at 35°C. Methanol and other alcohols were
    separated in less than 3 min (Smith, 1984).

         Methanol in deproteinized blood samples from occupationally
    exposed workers was quantified by GC-FID employing a 1.8 m × 4 mm
    internal diameter glass column packed with 60-80 mesh Carbopak B/5%
    Carbowax 20M at 60°C. The detection limit for methanol was about
    0.4 µg/ml (Lee et al., 1992).

         Methanol in blood of occupationally exposed workers was
    determined by head-space GC-FID utilizing a column containing 15%
    Carbowax 1599 on diatomaceous earth, 70-80 mesh and operated at 70°C.
    The detection limit was 0.6 mg/litre (Heinrich & Angerer, 1982).

         The simultaneous determination of methanol, ethanol, acetone,
    isopropanol and ethylene glycol in plasma by GC-FID was accomplished
    using a 180 cm × 4 mm internal diameter glass column packed with
    Porapak Q, 50-80 mesh. The column temperature was programmed from
    199-210°C at 2°C/min, and the injection port and detector temperatures
    were 210°C and 240°C respectively. The detection limit for methanol
    was 0.1 nmol/ml. The procedure was recommended for methanol and
    ethylene glycol intoxication cases (Cheung & Lin, 1987).

         Methanol in blood from occupationally exposed workers was
    determined directly without further pretreatment by GC-FID using a 4 m
    × 3 mm glass column packed with 10% SBS 100 on Shimalite TPA, 60-80
    mesh. The detector and oven were heated at 180°C and 60°C,
    respectively (Kawai et al., 1991a).

         Head-space GC-FID on methanol in blood from workers exposed at
    sub-occupational exposure limits was reported by Kawai et al. (1992).
    A 30 m × 0.53 mm capillary column coated with 1.0 um DB-Wax was used
    with the injection port and detector heated at 200°C and the oven
    temperature kept at 40°C for 1 min after the injection and then
    elevated at a rate of 5°C/min to 110°C for 15 min. The detection limit
    for methanol in blood was 100 µg/litre.

         Leaf & Zatman (1952) utilized a colorimetric procedure for the
    determination of methanol in air as well as in the blood and urine of
    occupationally exposed workers in a methanol synthesis plant. The
    procedure involved acid permanganate oxidation of methanol to
    formaldehyde, which was then determined with a modified Schiff's
    reagent. Concentrations of methanol up to 150 mg/litre were determined
    to within 3%.

         Determination of methanol in patients with acute methanol
    poisoning was accomplished with a colorimetric procedure following
    permanganate oxidation to formaldehyde and the subsequent reaction
    with chromotropic acid (1,8-dihydroxy naphthalene 3,6-disulfonic
    acid). Quantitative recovery of 100% was found for methanol following
    the analysis of 3 ml of plasma, which required 45 min (Hindberg &
    Wieth, 1963).

         Accumulation of methanol in blood was detected in alcoholic
    subjects during a 10-15 day period of chronic alcohol intake using
    GC-FID and a 1.8 m column packed with Porapak Q, 80-100 mesh, or
    Chromosorb 101 operated at 140°C (Majchrowicz & Mendelson, 1971). The
    identity of methanol was also confirmed chemically using the
    specificity of the colour reaction between permanganate and

         Head-space GC was used to determine the concentrations of
    methanol and ethanol in blood samples from 519 individuals suspected
    of drinking and driving in Sweden. Methanol was determined in whole
    blood without prior dilution with an internal standard. Carbopack C
    (0.2% Carbowax 1500) was used as the stationary phase and the oven
    temperature was 80°C (Jones & Lowinger, 1988).

         Methanol in whole blood of poisoned patients was determined
    without pretreatment by GC-FID using a 1800 mm × 4 mm internal
    diameter glass column packed with 80-100 mesh Carbopack C/0.2% CW 1500
    operated at 80°C; the detector temperature was 120°C (Jacobsen et al.,

         Serum methanol concentrations in men after oral administration of
    the sweetening agent aspartame were determined by GC-MS utilizing a
    fused silica capillary column 26 m × 0.22 mm internal diameter of
    CPWAX 57 CB operated at 50°C isothermally (Davoli et al., 1986).

         Methanol and formate in blood and urine of rats administered
    methanol intravenously was determined by HPLC employing a REZEX-ROA-
    organic acid column (300 mm × 7.8 mm internal diameter) and a
    similarly packed pre-column (50 mm × 4.6 mm internal diameter). The
    mobile phase was 0.043 N sulfuric acid with 10% acetonitrile at a flow
    rate of 1 ml/min (Horton et al., 1992).

         Methanol in serum has also been determined by high-field (500
    MHZ) proton nuclear magnetic resonance at the 3.39 singlet peak. For
    serum containing 20-500 mg of added methanol/litre, peak area was a 

    linear function of concentration (r=0.998). This NMR technique
    permitted the determination of methanol and acetone in blood serum at
    a level of less than 1mM (Bock, 1982).

         Pollack & Kawagoe (1991) determined methanol in deproteinized
    whole blood of rats by capillary GC-FID with direct column injection
    utilizing a 15 m × 0.54 mm internal diameter fused silica capillary
    column coated with Carbowax and operated at 35°C. The limit of
    detection was 2 µg/ml.  Methanol in urine

         Sedivec et al. (1981) determined methanol in urine in five
    volunteers exposed to methanol vapour for 8 h. Head-space GC-FID was
    used with a 120 cm × 3 mm column packed with Chromosorb 102, 60-80
    mesh at 120°C. The detection limit of methanol was 0.1 mg/litre. The
    methanol content in urine of 20 subjects occupationally exposed to
    methanol was determined by head-space GC-FID utilizing a column
    containing Porapak QS, 80-100 mesh and operated at 130°C. The
    detection limit was 0.6 mg/litre (Heinrich & Angerer, 1982).

         Methanol in the urine of exposed workers was determined by
    head-space GC-FID using a 4.1 m × 3.2 mm glass column containing 10%
    SBS-100 on Shimalite TPA, 60-80 mesh. The oven and injection port
    temperatures were 60°C and 180°C respectively. The limit of detection
    for methanol in urine was 0.1 mg/litre (Kawai et al., 1991b, 1992).

         Urinary methanol as a measure of occupational exposure was
    determined by GC-FID utilizing a 2 m glass column packed with Porapak
    Q, 80-100 mesh. The detection limit for methanol was 0.32 mg/litre
    (Liesivouri & Savolainen, 1987).

         Urine concentrations of methanol in volunteers who had ingested
    small amounts of methanol was determined by head-space GC-FID using
    Tenax GC as the column packing (Ferry et al., 1980).  Methanol in miscellaneous biological tissues

         Methanol and other alcohols have been determined in tissue
    homogenates either  per se or as their nitrite esters by GC-FID
    employing a 1.8 m × 6 mm o.d. glass column packed with Chromosorb 101
    operated at 145°C. The sensitivity was 8 µg per g of tissue (Gessner,
    1970).  Methanol metabolites in biological fluids

         The principal metabolite of methanol in humans and monkeys is
    formate and it has been shown that accumulation of blood formate at
    higher levels of methanol exposure coincides with the development of
    metabolic acidosis and visual system toxicities (Clay et al., 1975;
    McMartin et al., 1975; Baumbach et al., 1977; Tephly, 1991). Formate
    is an endogenous product of single carbon metabolism and is normally
    found in the urine of healthy individuals.

         Formate has been analysed in blood and urine samples primarily by
    enzymatic methods with a colorimetric or fluorimetric end-point or by
    derivatization followed by analysis by GC-FID. Formate in plasma has
    also been determined by isotachophoresis (Sejersted et al., 1983).

         Ferry et al. (1980) measured formic acid as an ethyl ester formed
    by the treatment of urine with 30% sulfuric acid in ethanol. The
    samples were analysed by head-space GC-FID on a column packed with 10%
    silar 10C on Chrom Q.

         The analysis of formic acid in blood was performed via an initial
    transformation of formic acid by concentrated sulfuric acid into water
    and carbon monoxide, the latter being reduced to methane on a
    catalytic column and analysed directly by GC-FID (Angerer & Lehnert,
    1977; Baumann & Angerer, 1979; Heinrich & Angerer, 1982).

         Urinary formic acid was determined after the methylation of the
    acid and its conversion to N,N-dimethylformamide with GC-FID equipped
    with a 50-m silica capillary column containing Carbowax 20M liquid
    phase. The detection limit was 2.3 mg/litre (Liesivouri & Savolainen,

         Franzblau et al. (1992b) found that urinary formic acid in
    specimens collected 16 h following cessation of methanol exposure and
    analysed by head-space GC-FID may not be an appropriate approach to
    assess methanol exposure biologically.

         Enzymatic methods for the determination of formate are based
    primarily on the enzyme-catalysed conversion of formate to carbon
    dioxide in the presence of nicotinamide adenine dinucleotide (NAD),
    generating NADH as the other reaction product. NADH formation can be
    subsequently measured directly or reacted in a coupled reaction to
    generate a fluorescent or coloured complex.

         A specific assay for formic acid in body fluids based on the
    reaction of formate with bacterial formate dehydrogenase coupled to a
    diaphorase-catalysed reduction of the non-fluorescent dye resazurin to
    the fluorescent substance resorufin was reported by Makar et al.
    (1975) and Makar & Tephly (1982). This permitted the accurate
    determination of about 6 mg formate/litre blood at excitation
    wavelength of 565 nm and an emission wavelength of 590 nm (Makar et
    al., 1975; Makar & Tephly, 1982).

         A serum formate enzymic assay based on modifications of the
    formate dehydrogenase (FDH)-diaphorase procedure using NAD-diaphorase-
    iodonitrotetrazolium violet to develop a red-coloured complex, which
    is measured at 500 nm, was described by Grady & Osterloh (1986). The
    calibration curve was linear over the formate range of 0 to
    400 mg/litre.

         Formate in plasma was determined by Lee et al. (1992) employing
    an enzymatic procedure (Grady & Osterloh, 1986; Buttery & Chamberlin,
    1988) and measured spectrophotometrically at 510 nm. The detection
    limit was about 3 µg/ml.

         Lee et al. (1992) determined that formate associated with acute
    methanol toxicity in humans does not accumulate in blood when
    atmospheric methanol exposure concentrations are below the
    occupational threshold limit value of 260 mg/m3 (200 ppm) for 6 h in
    exposed healthy volunteers.

         d'Alessandro et al. (1994) found that serum and urine formate
    determinations were not sensitive biological markers of methanol
    exposure at the threshold limit value (TLV) in human volunteers.
    Formate in serum was analysed by the enzymatic-colorimetric procedure
    of Grady & Osterloh (1986). The sensitivity of the method was
    0.5 mg/litre of formate in serum.

         Buttery & Chamberlin (1988) developed an enzymatic method for the
    determination of abnormal levels of formate in plasma requiring no
    deproteinization and utilizing a stable colour reagent consisting of
    phenazine methosulfate,  p-iodonitrotetrazolium and NAD to produce a
    stable red formazan colour. The precision at 1.0 and 5.0 mmol/litre
    formate was 2.9% and 1.7%, respectively, within-day and 5.5% and 2.3%,
    respectively, between days.

         Urinary formic acid was determined using formate dehydrogenase
    (FDH) in the presence of NAD. The detection limit was 0.5 mg/litre.
    The normal formic acid excretion in urine is between 2.0 and
    30 mg/litre (Triebig & Schaller, 1980).


    3.1  Natural occurrence

         Methanol occurs naturally in humans, animals and plants (Axelrod
    & Daly, 1965; CEC, 1988). It is a natural constituent of blood, urine
    and saliva (Leaf & Zatman, 1952) and expired air (Erikssen & Kulkarni,
    1963; Larsson, 1965; Krotosynski et al., 1979; Jones et al., 1990),
    and has also been found in mother's milk (Pellizzari et al., 1982).
    Humans have a background body burden of 0.5 mg/kg  body weight (Kavet
    & Nauss, 1990).

         Levels of methanol in expired air are reported to range from 0.06
    to 0.49 µg/litre (46-377 ppb) (Eriksen & Kulkarni, 1963). Methanol has
    been detected in the expired air of normal, healthy non-smoking
    subjects at a mean level of 0.5 ng/litre (Krotosynski et al., 1979).

         It is believed that dietary sources are only partial contributors
    to the total body pool of methanol (Stegink et al., 1981). It has been
    suggested that methanol is formed by the activities of the intestinal
    microflora or by other enzymatic processes (Axelrod & Daly, 1965). The
    methanol-forming enzyme was shown to be protein carboxylmethylase, an
    enzyme that methylates the carboxyl groups of proteins (Kim, 1973;
    Morin & Liss, 1973).

         Natural emission sources of methanol include volcanic gasses,
    vegetation, microbes and insects (Owens et al., 1969; Holzer et al.,
    1977; Graedel et al., 1986). Isidorov et al. (1985) identified
    methanol emissions of evergreen cyprus in the forests of Northern
    Europe and Asia. Methanol was identified as one of the volatile
    components emitted by alfalfa (Owens et al., 1969) and it is formed
    during biological decomposition of biological wastes, sewage and
    sludges (US EPA, 1975; Howard, 1990; Nielsen et al., 1993).

    3.2  Anthropogenic sources

         The major anthropogenic sources of methanol include its
    production, storage and use, principally its use as a solvent, as a
    chemical intermediate, in the production of glycol ethers, and in the
    manufacture of charcoal, and exhaust from vehicle engines (US EPA,
    1976a,b, 1980a,b; CEC, 1988).

    3.2.1  Production levels and processes  Production processes

         The earliest important source of methanol ("wood alcohol") was
    the dry distillation of wood at about 350°C, which was employed from
    around 1830 to 1930. In countries where wood is plentiful and wood
    products form an important industry, methanol is still obtained by
    this procedure (ILO, 1983).

         In 1880, about 1.5 million litres of wood alcohol were produced
    in the USA while in 1910 the amount had increased to over 3 million
    litres (Tyson & Schoenberg, 1914). However methanol produced from wood
    contained more contaminants, primarily acetone, acetic acid and allyl
    alcohol, than the chemical-grade methanol currently available
    (Grayson, 1981; Elvers et al., 1990). Methanol was also produced as
    one of the products of the non-catalytic oxidation of hydrocarbons (a
    procedure discontinued in the USA in 1973), and as a by-product of
    Fischer-Tropsch synthesis, which is no longer industrially important
    (Grayson, 1981).

         Modern industrial scale methanol production is based exclusively
    on the catalytic conversion of pressurized synthesis gas (hydrogen,
    carbon monoxide and carbon dioxide) in the presence of metallic
    heterogenous catalysts. All carbonaceous materials such as coal, coke,
    natural gas, petroleum and fractions obtained from petroleum (asphalt,
    gasoline, gaseous compounds) can be employed as starting materials for
    synthesis gas production (Grayson, 1981; Elvers et al., 1990).

         The required synthesis pressure is dependant upon the activity of
    the particular metallic catalyst employed, with copper-containing zinc
    oxide-alumina catalysts being the most effective in industrial
    methanol plants (Elvers et al., 1990). By convention the processes are
    classified according to the pressure used: low-pressure processes,
    50-100 atmospheres; medium-pressure processes, 100-250 atmospheres;
    and high-pressure processes, 250-350 atmospheres. Low-pressure
    technology is the most widely employed globally and accounted for 55%
    of the USA methanol capacity in 1980 (Grayson, 1981).

         Almost all the methanol produced in the USA is made from natural
    gas. This is steam reformed to produce synthesis gas, which is
    converted to methanol by low-pressure processes. A small amount of
    methanol is obtained as a by-product from the oxidation of butane to
    produce acetic acid and from the destructive distillation of wood to
    produce charcoal (Grayson, 1981; Elvers et al., 1990).

         The composition of methanol obtained directly from synthesis
    without any purification or with only partial purification varies
    according to the synthesis (e.g., pressure, catalyst, feedstock). The
    principal impurities include 5-20% (by volume) water, higher alcohols
    (principally ethanol), methyl formate and higher esters, and smaller
    amounts of ethers and aldehydes (Grayson, 1981; Elvers et al., 1990).
    Methanol is purified by distillation, the complexity required
    depending on the desired methanol purity and the purity of the crude
    methanol (Grayson, 1981; Elvers et al., 1990).

         Natural gas, petroleum residues and naphtha accounted for 90% of
    worldwide methanol capacity in 1980, miscellaneous off-gas sources
    constituting the remaining 10%. Natural gas alone accounted for 70%,
    petroleum residues 15%, and naphtha 5% (Grayson, 1981). Natural gas
    feedstock accounted for 75% in the USA and 70% of global capacity in
    1980. Methanol produced from residual oil accounted for approximately

    15% of USA and worldwide capacity in 1980, while naphtha and coal
    feedstocks accounted for approximately 5% and 2%, respectively, of
    worldwide methanol capacity in 1980 (Grayson, 1981). About 90% of the
    global methanol capacity is currently based on natural gas (SRI,

         The production of methanol from coal, being independent of oil
    and natural gas supplies, is noted to be an attractive alternative
    feed stock in some quarters (Grayson, 1981; CEC, 1988). Newer
    approaches to the production of methanol that have been suggested
    include the catalytic conversion from carbon dioxide and hydrogen
    avoiding conventional steam reforming (Rotman, 1994a) and the direct
    catalytic conversion of methane to methanol (Rotman, 1994b).  Production figures

         As shown in Table 2, worldwide annual capacity for methanol
    production has increased over the past decades from approximately 15 ×
    106 tonnes in 1979 (Grayson, 1981) to 21 × 106 tonnes in 1989
    (Elvers et al., 1990) and more than 22.1 × 106 tonnes in the
    beginning of 1991 (SRI, 1992). Worldwide demand was projected to rise
    further to about 25.8 × 106 tonnes in 1994 (Anon., 1991; Nielsen et
    al., 1993) and 30.1 × 106 tonnes in 1995 (SRI, 1992). The data
    available do not allow capacity and production figures to be compared;
    however, it is assumed that approximately 80% of production capacity
    is utilized (Fiedler et al., 1990).

         The USA and Canada are the largest methanol-producing countries.
    About 85% of Canada's production is exported to the USA, Japan and
    Europe (Heath, 1991). In Western Europe, Germany, the Netherlands and
    the United Kingdom are the major methanol-producing countries,
    accounting for 7%, 3% and over 2% of the world capacity, respectively
    (SRI, 1992). The production of methanol in Germany in 1991 and 1992
    amounted to 715 000 and 770 000 tonnes respectively.

         The annual capacity in Eastern Europe was estimated to be 5.8 ×
    106 tonnes in 1987. The production in the former USSR was 3.28 × 106
    tonnes and 3.21 × 106 tonnes in 1987 and 1988, respectively (Rippen,

        Table 2.  Methanol production or production capacity (× 106 tonnes per year) from 1978 to 1995

    Year    World-wide   USA            Canada         Western        Japan         Capacity/       Reference
                                                       Europe                       production

    1978    12           3.4                           3              1             capacity        Grayson (1981)

    1979    15           4.05                          3.45           1.35          capacity        Grayson (1981)

    1980                                               2.5                          production      CEC (1988)

    1981     8                                                                      production      CEC (1988)

    1983    15.9         5.52 (33%)     1.75 (11%)     2.53           1.27 (8%)     capacity        SRI (1992)
                                                                                    production      CEC (1988)

    1988                                1.91                                        production      Anderson (1993)

    1989    21                                                                      capacity        Elvers et al. (1990)
            19                                                                      production

    1990    22.3                                                                    capacity        Anon. (1991);
                                                                                                    Nielsen et al. (1993)

    1991    22.1         4.42 (20%)     2.21 (10%)     2.65 (12%)a    0.22 (1%)     capacity        SRI (1992)

    1991                                2.22                          0.077         production      Anderson (1993)

    1992                                2.15                          0.034         production      Anderson (1993)

    1992                 3.66           2.15                                        production      Reisch (1994)

    1993                 4.78                                                       production      Reisch (1994)

    1995    30.1                                                                    capacity        SRI (1992)

    a    Only Germany, the Netherlands and the United Kingdom.
         The figures in Table 2 indicate a major shift in methanol
    production from the developed countries to the developing areas. In
    fact, the methanol industry underwent large structural changes during
    the 1980s as a result of the discovery of large natural gas fields in
    remote regions having little demand for natural gas themselves. Since
    methanol production is a very suitable alternative for marketing
    natural gases, a number of methanol production plants for export were
    built or proposed to be built in Asia (Bahrein, Oman, Qatar, Saudi
    Arabia, Indonesia, Malaysia), South America (Chile, Mexico,
    Venezuela), the Caribbean (Trinidad) and in New Zealand and Norway
    (Fiedler et al., 1990; SRI, 1992). The largest single train plant
    based on this concept came on stream in southern Chile in 1988 with an
    annual output of 750 000 tonnes (Fiedler et al., 1990).

         Future trends in methanol production and demand are being driven
    to a large extent by increasing demand for methyl tertiary butyl ether
    (MTBE), which is used in gasoline blending as an octane enhancer and
    to reduce carbon monoxide emissions (Anon., 1991; Morris, 1993;
    Nielsen et al., 1993).

    3.2.2  Uses

         During the 1890s, the market for methanol (then better known as
    wood alcohol) increased as a commercial product and as a solvent for
    use in the workplace. It was included in many consumer products such
    as witch hazel, Jamaica ginger, vanilla extract and perfumes (Wood &
    Buller, 1904). The most notorious use of wood alcohol was and
    continues to be as an adulterant in alcoholic beverages, which has led
    to large-scale episodes of poisonings since 1900 (Bennett et al.,
    1953; Kane et al., 1968).

         Historically, in terms of commercial usage, about half of all
    methanol produced has been used to produce formaldehyde. Other earlier
    large-volume chemicals based on methanol include acetic acid, dimethyl
    terephthalate, glycol methyl ethers, methyl halides, methylamines,
    methyl acrylate and various solvent uses (Grayson, 1981; CEC, 1988;
    Elvers et al., 1990; Nielsen et al., 1993).  Use as feedstock for chemical syntheses

         Approximately 70% of the methanol produced worldwide is used as
    feedstock for chemical syntheses. As shown in Table 3, formaldehyde,
    methyl tertiary butyl ether (MTBE), acetic acid, methyl methacrylate,
    and dimethyl terephthalate are, in order of importance, the main
    chemicals produced from methanol. Methyl halides produced from
    methanol include methyl chloride, methylene chloride and chloroform.

         Nearly all the formaldehyde manufactured worldwide is produced by
    oxidation of methanol with atmospheric oxygen. The annual formaldehyde
    production was projected to increase at a rate of 3%, but because
    other bulk products have higher growth rates, its relative importance
    with respect to methanol use has decreased (Elvers et al., 1990;
    Fiedler et al., 1990).

        Table 3.  Use pattern for methanol (as a percentage of production) according to region and year


                                     Global       Global         USA           USA          Japan     Western Europe    Brazil
                                      1979         1988         1973          1985          n.g.           1985          n.g.

    Use for synthesis of:

         formaldehyde                  52           40            39           30            47             50            60
         MTBE                           4           20                          8             -              5             -
         acetic acid                    6            9           3.4           12            10              5             -
         dimethyl terephthalate         4                        6.1            4             1              4            16
         methyl methacrylate            4                        3.7            4             6              3             2
         methyl halides                8a                        6.1            9             3              6             -
         methyl amines                                           3.3            4             2              4             9
         glycol methyl ethers                                    1.1                                                        

    Direct use

         solvent                                                               10             6              6             2
         fuel                                                                   6             -              5             -

    Miscellaneous                      14                       16.9           13            25             12            11

    Referenceb                        [1]          [2]           [3]          [4]           [4]            [4]           [4]

    a    together with methyl amines production
    b    Reference: [1] Kennedy & Shanks (1981); [2] Elvers et al. (1990); [3] US EPA (1980a); [4] Rippen (1990)
         n.g. = year not given
         MTBE has become an important octane-enhancing blending component
    in gasoline, particularly in the USA where the Clean Air Act
    Amendments of 1990 have prompted further steps toward reducing
    emissions from motor vehicles by changing the formulations of
    gasoline. This is achieved by using so-called oxygenated fuel, i.e.
    fuel containing at least 2% oxygen by weight in the form of
    oxygenates, but less benzene and other aromatic compounds than
    conventional fuel (Health Effects Institute, 1996). MTBE is produced
    by reacting methanol with isobutene in acid ion exchangers. In 1987,
    MTBE (production of 1.6 × 106 tonnes) ranked 32nd among the top 50
    chemicals produced in the USA (Scholz et al., 1990). In 1993, 11 ×
    106 tonnes were produced, ranking MTBE ninth of the top 50 chemicals
    (Reisch, 1994).

         Acetic acid is produced by carbonylation of methanol with carbon
    monoxide. Annual growth rates of 6% have been estimated (Fiedler et
    al., 1990).

         Methanol is present in a broad variety of commercial and consumer
    products including shellacs, paints, varnishes, mixed solvents in
    duplicating machines (95% concentration or greater), antifreeze and
    gasoline deicers (generally containing 35-95% methanol), windshield
    washer fluid (contains 35-90% methanol), cleansing solutions
    (containing around 5% methanol), model and hobby glues and adhesives,
    and Sterno ("canned heat") containing 4% methanol (Posner, 1975; US
    EPA, 1980a; CEC, 1988; ATSDR, 1993).

         Methanol is also used in the denitrification of wastewater,
    sewage treatment application (carbon source for bacteria to aid in the
    anaerobic conversion of nitrates to nitrogen and carbon dioxide), as a
    substrate for fermentation production of animal feed protein (single
    cell protein), as a hydrate inhibitor in natural gas, and in the
    methanolysis of polyethylene terephthalate (PET) from recycled plastic
    wastes (Posner, 1975; US EPA, 1980a; Kennedy & Shanks, 1981; ATSDR,
    1993).  Use as fuel

         Methanol is a potential substitute for petroleum. It can be
    directly used in fuel as a replacement for gasoline in gasoline and
    diesel blends. Methanol is in favour over conventional fuels because
    of its lower ozone-forming potential, lower emissions of some
    pollutants, particularly benzene and polycyclic aromatic hydrocarbons
    and sulfur compounds, and low evaporative emissions. On the other
    hand, the possibility of higher formaldehyde emissions, its higher
    acute toxicity and, at present, lower cost-efficiency favour
    conventional fuels (CONCAWE, 1995).

         For use in gasoline engines, pure methanol (so-called M100 fuel)
    or mixtures of 3, 15 and 85% methanol with conventional petroleum
    products (M3, M15, M85) are most common. In diesel engines methanol
    cannot be used as an exclusive fuel because of its low cetane number
    that would impose proper ignition. Therefore, methanol is injected
    into the cylinder after ignition of the conventional diesel fuel
    (Fiedler et al., 1990).  Other uses

         Methanol is used in refrigeration systems, e.g., in ethylene
    plants, and as an antifreeze in heating and cooling circuits. However,
    its use as an engine antifreeze has been replaced by glycol-based
    products. Methanol is added to natural gas at the pumping stations of
    pipelines to prevent formation of gas hydrates at low temperature and
    can be recycled after removal of water. Methanol is also used as an
    absorption agent in gas scrubbers to remove, for example, carbon
    dioxide and hydrogen sulfide. According to Table 3, large amounts of
    methanol are used as a solvent. Pure methanol is not usually used
    alone as a solvent, but is included in solvent mixtures (Fiedler et
    al., 1990).  Losses into the environment

         Given the high production volume, widespread use and physical and
    chemical properties of methanol, there is a very high potential for
    large amounts of methanol to be released to the environment,
    principally to air (US EPA, 1976a,b, 1980a,b, 1994; Nielsen et al.,
    1993). Emissions of methanol primarily occur from miscellaneous
    solvent usage, methanol production, end-product manufacturing, and
    bulk storage and handling losses. The largest source of emissions of
    methanol is the miscellaneous solvent use category.

         US EPA (1980b) estimated emission factors for the release of
    methanol and volatile organic compounds (VOC) from the low-pressure
    synthesis of methanol from natural gas in a model plant with a
    capacity of 450 000 tonnes/year. The process and capacity were typical
    of those built in the late 1970s. The overall emission factors were
    estimated to be: uncontrolled emissions, 1.56 kg methanol/tonne
    produced; controlled emissions, 0.14 kg methanol/tonne produced
    (Nielsen et al., 1993).

         It was estimated that about 1% of the methanol used in the
    production of formaldehyde would be released to the environment during
    the production process by which formaldehyde is produced by either a
    metallic silver-catalyst process or a metal oxide-catalyst process (US
    EPA, 1976a; 1980b). In the oxidation-dehydrogenation process with
    metallic silver catalyst, 0.89 kg methanol/tonne of 39% (by weight)
    formaldehyde solution was released principally from the product
    absorber vents, and 1.24 kg methanol/tonne from the fractionator
    vents. The production of formaldehyde using the catalytic oxidation,
    metal oxide catalyst process resulted in the release of 1.93 kg

    methanol/tonne of 37% formaldehyde solution with emissions from the
    absorber vent (US EPA, 1980b).

         US EPA (1994) reported that methanol was the most released
    chemical to the environment (air, water and land) based on the 1992
    Toxic Release Inventory which utilized 81 016 individual chemical
    reports from a total of 23 630 facilities (approximately 65% of
    facilities reporting). The air, water and land releases of methanol
    totalled 1.09 × 105 tonnes, consisting of 1.53 × 104 tonnes of
    fugitive or non-point air emissions, 72 956 tonnes of stack or point
    air emissions, 7444 tonnes of surface water discharges and 15 095
    tonnes released to land. Additionally, 1.283 × 104 tonnes were
    transferred via underground injection.

         Methanol had the largest off-site transfers (51 672 tonnes) to
    publicly owned treatment works (POTWs) in 1992. During the same
    period, methanol ranked third largest of the Toxic Release Inventory
    Chemicals with off-site transfers for treatment. The total transfers
    to treatment were 18 098 tonnes, consisting of 4 tonnes for
    solidification, 10 295 tonnes for incineration/thermal treatment, 1971
    tonnes of incineration/insignificant fuel value; 5311 tonnes for
    wastewater treatment and 147 tonnes to waste broker-waste treatment. A
    total of 493 980 tonnes of methanol was treated, consisting of 260 875
    tonnes treated on-site and 197 400 tonnes off-site. A total of 1510
    tonnes of methanol was released to land, primarily to on-site
    landfills (US EPA, 1994).

         The total amount of methanol release in Canada in 1993 was
    306 222 tonnes distributed as follows: air, 15 326; water, 14 248;
    underground, 819 and land, 205 (Ministry of Supply & Services Canada,

         Tail pipe emissions as well as evaporative emissions are
    monitored by a number of agencies. Emissions and air quality modelling
    results have been reported from methanol/gasoline blends in prototype
    flexible/variable fuelled vehicles (US EPA, 1991; Auto/Oil Air Quality
    Research Program, 1992, 1994). Motor vehicle emissions are affected in
    various ways by the use of methanol fuels in production flexible/
    variable fuel vehicles. Higher molecular weight hydrocarbons are
    reduced and carbon monoxide is reduced under some circumstances, while
    increases in methanol and formaldehyde can occur (US EPA, 1991).

         Methanol has been found in significant amounts in the exhaust
    from gasoline-powered vehicles as well as in diesel exhausts. Methanol
    was measured at levels of 100-226 mg/kg in the exhaust emissions from
    non-catalyst vehicles fuelled with isobutane/methanol/gasoline
    (2/15/83; M-15). Methanol emissions from a light-duty diesel vehicle
    fuelled with 95% methanol were one order of magnitude higher
    (3.4 g/kg) (Jonsson et al., 1985).

         Chang & Rudy (1990) reported methanol emission factors for
    vehicles fuelled by M-85 (85% methanol + 15% gasoline) and M-100 (100%
    methanol) in the USA. For M-85-fuelled vehicles, factors were 0.156-
    0.7 g methanol/mile driven in exhaust emissions and 0.055-0.25 g
    methanol/mile driven in evaporative emissions. For M-100 fuelled
    vehicles, they were 0.5 g methanol/mile driven in exhaust emissions
    and 0.072-0.134 g methanol/mile driven in evaporative emissions.

         Methanol was found at levels of 130-800 µg/m3 (0.1 to 0.6 ppm)
    in the exhaust from nine hydrocarbon test fuels, e.g., iso-octane,
    iso-octene, benzene, 2-methyl-2-butene, toluene,  o-xylene,
    benzene/ n-pentane, toluene/ n-pentane and iso-octane/toluene/
    iso-octene (Seizinger & Dimitriades, 1972).

         Methanol, formaldehyde and hydrocarbon emissions from methanol-
    fuelled cars were reported by Williams et al. (1990). The variable
    methanol-fuelled vehicles using fuel mixtures of 100, 85, 50, 15 and
    0% methanol and a dedicated methanol vehicle all gave similar emission
    patterns. The organic composition of the exhaust was 85-90% methanol,
    5-7% formaldehyde and 3-9% hydrocarbons.


    4.1  Transport and distribution between media

         Methanol is released into the environment from both natural and
    man-made sources, the latter being the most significant. Methanol
    is released predominantly from its production and use as a solvent
    in industrial processes (in extraction, washing, drying and
    recrystallization operations), and to a lesser degree from a variety
    of industrial processes and domestic uses (US EPA, 1980a,b; Graedel et
    al., 1986; CEC, 1988; Howard, 1990; Nielsen et al., 1993).

         Methanol volatilization half-lives of 5.3 and 2.6 days have been
    estimated for a model river (1 m deep) and an environmental pond,
    respectively (Howard, 1990).

         Methanol is expected to exist almost entirely in the vapour phase
    in the ambient atmosphere, based on its vapour pressure (Eisenreich
    et al., 1981; Graedel et al., 1986). Because of methanol's water
    solubility, rain would be expected to physically remove some methanol
    from the air (US EPA, 1980a,b; Snider & Dawson, 1985).

         Methanol has been found in the atmosphere (Graedel et al.,
    1986). It can be the product of atmospheric alkane chemistry with
    concentrations as high as 131 µg/m3 (100 ppb) being found. Methanol
    is expected to become an important additional trace gas in the
    atmosphere due to its projected increased use as an alternative fuel
    to gasoline or in a gasoline blend (CEC, 1988; Chang & Rudy, 1990).

         The miscibility of methanol in water and its low octanol/water
    partition coefficient suggest high mobility in soil. Lœkke (1984)
    studied the adsorption of methanol onto three soil types at 6°C. The
    soils tested comprised two sandy soils (organic matter contents of
    0.09 and 0.1%), and a clay soil (organic matter content of 0.22%).
    Methanol solutions with concentrations of 0.1, 1.0, 9 and 90 mg/litre
    were used in 1-h exposure studies. Adsorption coefficients for all
    soil methanol concentrations and soil types ranged from 0.13 to 0.61,
    indicating methanol has a low adsorptive capacity on these soils.
    However Nielsen et al. (1993) suggested that the soils used in the
    Lœkke (1984) study had low organic matter contents compared to typical
    agricultural surface soil which can have organic matter contents of 1
    to 2%, and up to 5% in some soils. A soil containing a typical amount
    of organic matter might therefore be expected to retain methanol and
    prevent it from reaching the subsoil.

         Additionally, the relatively high vapour pressure and low
    adsorptive capacity suggests significant evaporation from dry

    4.2  Transformation

    4.2.1  Biodegradation

         Methanol is readily biodegradable in soil and sediments, both
    under aerobic and anaerobic conditions. A large number of strains/
    genera of microorganisms have been identified as capable of using
    methanol as a growth substrate (Hanson, 1980; Braun & Stolp,
    1985; Nielsen et al., 1993). These include  Pseudomonas sp.,
     Methylobacterium organophilium; Hyphomicrobium sp.,  Desulfovibrio;
     Streptomyces sp.,  Rhodopseudomonas acidophilia; Paracoccus
     denitrificans; Microcyclus aquaticus; Thiobacillus novellus;
     Micrococcus denitrificans; Achromobacter 1L (isolated from activated
    sewage sludge) and  Mycobacterium 50 (isolated from activated sewage
    sludge). Most microorganisms possess the enzyme alcohol dehydrogenase
    which is necessary for methanol oxidation. The methanogen,
     Methanosarcine barkeri can grow on and produce methane from methanol
    (Hippe et al., 1979).

         The following genera of methanol-oxidizing yeasts have been
    reported:  Pichia; Saccharomyces; Hansenula; Rhodotorula; Kloechera;
     Candida; Torulopsis (Stensel et al., 1973; Hanson, 1980; Nielsen et
    al., 1993). Okpokwasili & Amanchukwu (1988) isolated  Candida sp.
    from Niger Delta sediment which utilized methanol as a growth
    substrate.  Water and sewage sludge

         In a closed bottle test, according to OECD guideline 301D,
    methanol was found to be readily biodegradable with 99% COD removal
    after the test period of 30 days (Hüls AG, 1978). In another closed
    bottle test using unadapted inoculum from domestic sewage the
    degradation of methanol at concentrations of 3, 7 or 10 mg/litre in
    both freshwater (settled domestic wastewater) and synthetic seawater
    incubated for a maximum of 20 days under aerobic conditions was
    studied by Price et al. (1974). Methanol was readily degraded in both
    inocula at all concentrations with average disappearance of methanol
    as follows: a) after 5 days, 76% bio-oxidation in fresh water and 69%
    in salt water; b) after 10 days, 88% bio-oxidation in fresh water and
    84% in salt water; c) after 15 days, 91% bio-oxidation in fresh water
    and 85% in salt water and d) after 20 days, 95% bio-oxidation in fresh
    water and 97% in salt water.

         Matsui et al. (1988) studied the biodegradability of methanol in
    a batch reactor using activated sludge from an industrial wastewater
    treatment plant which was acclimatized to the wastewater originating
    from a petrochemical complex in Japan. Methanol at an initial
    concentration of 100 mg/litre and an acclimation period of 1 day was
    found to be highly biodegradable with 91% COD removal and 92% TOC
    removal achieved.

         Incubation of 0.05 mg methanol/litre for 5 days in activated
    sludge from a municipal sewage plant resulted in the degradation of
    37% of the methanol (Freitag et al., 1985). Hatfield (1957) found that
    at a feed rate of 333 or 500 mg/litre, methanol was virtually
    completely oxidized (with a major portion of the BOD and COD removed)
    by acclimated microorganisms within 6 h in a settled domestic sewage

         The microbial metabolism of methanol in a model activated sludge
    system monitored by Swain & Somerville (1978) revealed that methanol
    was not broken down when added transiently (0.23% by volume) to the
    system operating with a retention time of 11 h. However adaptation of
    the sludge in such a system to 0.1% by volume occurred over a period
    of several days. After 2 days acclimation, about 50% of the methanol
    was utilized, and after 6 days acclimation more than 80% of the
    methanol had been metabolized. There were no apparent toxic effects
    caused by the addition of methanol (0.1% by volume) to the sludge
    prior to and after adaptation to methanol.

         The anaerobic treatment of wastes containing methanol and higher
    alcohols (approximately 50:50 mix) was studied by Lettinga et al.
    (1981). In batch and continuous experiments using an inoculum
    consisting of sugar beet waste and active anaerobic sludge, the
    breakdown of methanol began within a few days while the breakdown of
    higher alcohols occurred immediately depending on the initial load of
    waste applied.

         Denitrification is facilitated by heterotrophic and autotrophic
    bacteria. Heterotrophic bacteria require a carbon source for their
    growth and cell metabolism which can be supplied by methanol (Stensel
    et al., 1973; Nyberg et al., 1992; Jansen et al., 1993; Upton, 1993).
    Bacteria such as the organisms of the genera  Pseudomonas,
     Micrococcus, Achromobacter, Spirillum, and  Bacillus reduce
    nitrate, nitrogen oxide and nitrous oxide under anaerobic conditions.
    The addition of methanol to promote denitrification has been suggested
    in situations where nitrate accumulates, and methanol has been
    added as an economic exogenous organic carbon source to increase
    denitrification (Stensel et al., 1973; Nyberg et al., 1992; Jansen et
    al., 1993; Upton, 1993).

         At a wastewater treatment plant in Malmo, Sweden, complete
    denitrification was obtained after approximately one month at 10°C
    after methanol was added for denitrification. Microscopic examination
    revealed a growing population of budding and/or appendaged bacteria,
    presumably  Hyphomicrobrium spp. reaching a stable maximum at the
    time when optimal nitrate removal occurred (Nyberg et al., 1992)

         Upton (1993) described a pilot study in the United Kingdom
    indicating that denitrification in deep-bed sand filters is a feasible
    technology utilizing methanol addition. Nitrogen removals greater than
    70% were possible at winter sewage temperatures.

         Several other laboratory studies using a variety of methodologies
    have demonstrated the rapid biodegradation of methanol by sewage
    organisms. These show degradation of between 66 and 95%, and usually
    greater than 80%, within five days (Kempa, 1976; Hüls AG, 1978; Matsui
    et al., 1988).  Soils and sediments

         Methanol is biodegradable in soils and sediments, both under
    aerobic and anaerobic conditions. Methanol is a normal growth
    substrate for many soil microorganisms, which are capable of
    completely mineralizing methanol to carbon monoxide and water (CEC,
    1988; Howard, 1990; Howard et al., 1991; Nielsen et al., 1993).
    Methanol at concentrations of up to 1000 mg/litre was degraded to
    non-measurable amounts within a year or less in subsurface soil and
    ground water sites in Pennsylvania, New York and Virginia (USA)
    believed to be previously uncontaminated. Complete degradation of
    100 g methanol/litre occurred in less than 30 days in one aerobic soil
    sample from a Pennsylvania site (Novak et al., 1985).

         Scheunert et al. (1987) monitored the formation of 14CO2 from
    labelled methanol in aerobic and anaerobic suspended soil and found
    methanol to be readily degradable after 5 days incubation at 35°C.
    Rates and patterns of biodegradation of methanol in surface and
    subsurface soils from eight sites in New York, Pennsylvania and
    Virginia in static microcosms under anaerobic conditions were
    evaluated by Hickman & Novak (1989) and Hickman et al. (1989). The
    rates of methanol degradation varied considerably between sites, but
    the soils could be characterized into two general types, namely fast
    soils, in which degradation rates were high and rates were increased
    by addition of nitrate and sulfate, and slow soils, in which
    biodegradation rates were low and decreased by the addition of nitrate
    or sulfate and inhibition of sulfate increased degradation rates.
    Biodegradation rates in subsurface soils were generally within the
    range of 0.5-1.1 mg/litre per day and indicated that no acclimation
    period was required. Biodegradation rates were calculated and used to
    estimate a half-life of between 58 and 263 days for methanol in these
    soils (Hickman et al., 1989).

         Compared to other substrates studied, e.g., acetate,
    trimethylamine and methylamine, methanol (at concentrations less than
    3 µM) was degraded relatively slowly mainly to carbon dioxide,
    principally via sulfite-reducing organisms, and could not be
    considered a significant  in situ precursor in surface sediments of
    an intertidal zone in Maine, USA (King et al., 1983).

         Methanol was found to be an important substrate for methanogenic
    bacteria in anaerobic sediments (highly reduced and containing methane
    and hydrogen sulfide), collected from a salt marsh located in
    San Francisco Bay, California. The sediments were homogenized
    anaerobically with San Francisco Bay water and 310-340 µmol methanol/
    flask, resulting in 83-91% conversion to methane, carbon dioxide and
    water after 3 days (Oremland et al., 1982).

         A sulfate-reducing bacterium of the genus  Desulfovibrio, which
    is capable of degrading methanol after growth on pyruvate, malate or
    fumarate, completely converted anaerobic samples of 14C-methanol to
    carbon dioxide. However the 14C-label was not used as a carbon source
    by the bacterium and was not assimilated into cellular material (Braun
    & Stolp, 1985).

    4.2.2  Abiotic degradation  Water

         In a 5-day experiment, 14C-labelled methanol applied to
    soil-water suspensions under both aerobic and anaerobic conditions
    yielded 53.4 and 46.3% 14CO2, respectively (Scheunert et al., 1987).

         Half-lives of 5.1 years and 46.6 days for the photooxidation of
    methanol in water have been reported based on the measured rate data
    for the reaction with hydroxyl radicals in aqueous solutions (Howard
    et al., 1991). A bimolecular reaction rate constant of 8.5 × 10-13
    cm3/molecule per second for the reaction of methanol and hydroxyl
    radicals in water has been reported by Lemaire et al. (1982).

         The rate constant for the reaction of methanol with hydroxyl
    radicals in aqueous solution is approximately 1 × 109 litre/mol per
    second (Gurten et al., 1984). If the hydroxyl radical concentration of
    sunlit natural water is assumed to be 1 × 10-17 mol/litre (Mill et
    al., 1980), the half-life of methanol would be approximately 2.2 years
    (Howard, 1990).

         Sediment and clay suspensions did not photo-catalyse the
    degradation of methanol in aqueous solution during ultraviolet
    irradiation at 300 nm. However, the addition of semi-conductor powders
    such as titanium dioxide led to large increases in the yield of
    formaldehyde upon irradiation, in contrast to the small amounts of
    formaldehyde formed from the irradiation of 10% aqueous methanol
    (Oliver et al., 1979).

         Hustert et al. (1981) reported that methanol in aqueous solution
    was stable when exposed to sunlight. Alcohols are generally resistant
    to environmental aqueous hydrolysis (Lyman et al., 1982; Howard,
    1990).  Air

         Methanol reacts in the atmosphere with oxidizing species (Barnes
    et al., 1982; Lemaire et al., 1982; Whitbeck, 1983; Graedel et al.,
    1986; Montgomery, 1991; Nielsen et al., 1993; US EPA, 1994).

         The atmospheric lifetime of methanol has been estimated to be 20
    days based on the reaction of compounds with the hydroxyl radical,
    and assuming a hydroxyl free radical concentration of 5 × 105
    radicals/cm3 (Graedel et al., 1986). Methanol half-lives of 8.4 days

    (US EPA, 1979), 8.0 days (Lemaire et al., 1982) and 7.3 days (Barnes
    et al., 1982) have also been reported based on reactions at 300°K and
    equations reported in Lyman et al. (1984) and Resenblatt (1990).
    Gusten et al. (1984) reported that at 300 °K and atmospheric pressure,
    an average hydroxyl concentration of 1 × 106 molecules/cm3 and a
    reaction rate constant of 0.95 × 10-12 cm3 /mol per sec, the half-
    life of methanol was 8.4 days.

         Reaction of methanol with nitrogen dioxide in a smog chamber
    yielded methyl nitrite and nitric acid and the surface reaction of
    methanol and nitrogen dioxide was enhanced under ultraviolet light
    (Akimoto & Takagi, 1986). The reaction of methanol with nitrogen
    dioxide may be the major source of methyl nitrite found in polluted
    atmospheres (Takagi et al., 1986; Howard, 1990). Only 4.1% of the
    methanol applied to silica gel was degraded when irradiated for 17 h
    at wavelengths greater than 290 nm (Freitag et al., 1985).

    4.2.3  Bioconcentration

         Bioconcentration factors (BCFs) of methanol experimentally
    measured in aquatic organisms using a log kow value for methanol of
    -0.77 and correlation equations reported in Lyman et al. (1990) ranged
    from 0.01-0.51 (Nielsen et al., 1993). Based on the octanol/water
    partition coefficient of -0.77, the BCF value for methanol was
    estimated to be 0.2 (Howard, 1990).

         Freitag et al. (1985) reported a BCF of < 10 (wet weight basis)
    for the golden ide  (Leuciscus idus melanotus) after 3 days exposure
    to 0.05 mg methanol/litre.

         Gluth et al. (1985) proposed a BCF of about 1 for the carp
     Cyprinus carpio exposed to 14C-methanol for up to 72 h. The amount
    of radioactivity was measured in the liver, kidneys, intestine,
    muscle, blood and gills of carp exposed to methanol at 5 mg/litre. The
    initial uptake of methanol into the different tissue types was the
    same after 24 h and levels remained constant for over 72 h in the
    liver, kidneys, gills and intestines, but dropped slightly in the
    blood and muscle.

         Geyer et al. (1984) calculated a BCF of 28 400 (dry weight.
    basis) for the green alga  Chlorella fusca exposed to 0.05 mg/litre
    14C-labelled methanol for 24 h at a temperature of 20-25°C with 16 h
    illumination and with agitation. Nielsen et al. (1993) suggested that
    this high bioconcentration factor is anomalous compared to those for
    other aquatic organisms. It may be due to the fact that methanol is
    metabolized by the algae, and the 14C-label, which is measured to
    calculate the BCF value, is incorporated into the algae in metabolic
    forms other than methanol.


    5.1  Environmental levels

    5.1.1  Air

         Methanol was detected at mean ambient concentrations of 10 and
    3 µg/m3 (7.9 and 2.6 ppb) at Tucson, Arizona, USA, and two remote
    Arizona locations, respectively, during monitoring in 1982 of air
    pollutants in the USA (Snider & Dawson, 1985). It was also detected in
    rural air in Alabama (Holzer et al., 1977). Methanol was detected at
    concentrations of 0.65-1.8 µg/m3 (0.5-1.2 ppb) (average 0.77 ppb
    methanol plus ethanol) in Arctic air from Point Barrow, Alaska, in
    September 1967 (Cavanaugh et al., 1969).

         Urban air levels of methanol in the range of 10.5-131 µg/m3
    (8-100 ppb) have been reported (Graedel et al., 1986). Jonsson et al.
    (1985) reported significant amounts of methanol (0.59-94 µg/m3;
    0.45-72 ppb) at dense traffic sites in Stockholm, Sweden. Average
    ambient methanol concentrations of 5-30 µg/m3 (3.83-26.7 ppb) were
    detected at five sites in and around Stockholm.

         In 1994, methanol was listed as one of the 189 hazardous air
    pollutants (HAPs) under the Clean Air Act Amendment of 1990, Title III
    in the USA (Kelly et al., 1994). In a US EPA (1993) summary, median
    methanol levels of 6-60 µg/m3 were found in 52 samples from three
    locations (Boston, Houston, and Lima, Ohio) in the USA.

    5.1.2  Water

         Data on the occurrence of methanol in water, particularly
    finished drinking-water, is limited. Methanol was identified in water
    at 24 locations in the USA during the period 1974-1976 (US EPA,
    1976b). The frequency of occurrence was as follows: finished drinking-
    water, 12; effluents from chemical plants, 6; effluents from sewage
    treatment, 4; effluents from paper production, 1; and effluents from
    latex production, 1.

         Methanol was detected in the USA at a mean level of 22 µg/litre
    in rainwater collected during a thunderstorm in Arizona in 1982
    (Snider & Dawson, 1985).

         Methanol at levels of 17-80 mg/litre (17-80 ppm) was detected in
    wastewater effluents from a speciality chemicals manufacturing
    facility in Massachusetts, USA, but none was detected in associated
    river water or sediments (Jungclaus et al., 1978). A concentration of
    42.4 mg/litre were found in a leachate from the Love Canal in Niagara
    Falls, New York (Venkataraman et al., 1984). Methanol at a level of
    1050 mg/litre was detected in condensate waters discharged from a coal
    gasification plant at North Dakota, USA (Mohr & King, 1985).

    5.1.3  Food

         Dietary methanol can arise in large part from fresh fruits and
    vegetables where it occurs as the free alcohol, methyl esters of fatty
    acids or methoxy group on polysaccharides such as pectin (Kirchner &
    Miller, 1957; Casey et al., 1963; Self et al., 1963; Lund et al.,
    1981; Stegink et al., 1981; Monte, 1984).

         The methanol content of fresh and canned fruit juices
    (principally orange and grapefruit juices) varies considerably and may
    range from 1-43 mg/litre (Kirchner & Miller, 1957), 10-80 mg/litre
    (Lund et al., 1981; Monte, 1984) and 12-640 mg/litre with an average
    of 140 mg/litre (Francot & Geoffroy, 1956; Monte, 1984). Methanol
    evolved during the cooking of high pectin foods (Casey et al., 1963)
    has been accounted for in the volatile fraction during boiling and is
    quickly lost to the atmosphere (Self et al., 1963). However entrapment
    of the volatiles during canning is possible and probably accounts for
    the elevated methanol levels of certain fruits and vegetables during
    this process (Lund et al., 1981).

         Fermented distilled beverages can contain high levels of
    methanol, with some neutral spirits having as much as 1.5 g/litre
    (Francot & Geoffroy, 1956). Methanol was found at levels of 
    6-27 mg/litre in beer, 96-321 mg/litre in wines and 10-220 mg/litre 
    in distilled spirits (Greizerstein, 1981). The methanol content in
    representative beverage alcohol varied between 40 and 55 mg/litre
    bourbon. This value is comparable with those reported by the
    distillers. The concentration of methanol in 50% grain alcohol was
    found to be approximately 1 mg/litre (Majchrowicz & Mendelson,
    1971).The presence of methanol in distilled spirits is directly linked
    to the pectin content of the raw materials. During the process of
    making fruit spirits, pectic substances contained in different parts
    of the fruit undergo degradation by pectin methylases, which can lead
    to the formation of significant quantities of methanol (Bindler et
    al., 1988). Concentrations of methanol permitted in brandies in the
    USA, Canada and Italy range from 6-7 g/litre ethanol (Bindler et al.,

         Methanol has been identified in the volatile fraction of sherry
    wine vinegars (Blanch et al., 1992), lemon, orange and lime extracts,
    distilled liquors and cordials (AOAC, 1980, 1990).

         Methanol has been identified as a volatile component of dried
    legumes with reported levels of 1.5-7.9 mg/kg in beans, 3.6 mg/kg in
    split peas and 4.4 mg/kg in lentils (Lovegren et al., 1979). Methanol
    has also been reported (no levels stated) in roasted filberts (Kinlin
    et al., 1972) and baked potatoes (Coleman et al., 1981). It has been
    detected in low-boiling volatile fractions of cooked foods, including
    Brussels sprouts, carrots, celery, corn, onion, parsnip, peas and
    potatoes (Self et al., 1963).

         Humans can also ingest varying amounts of methanol in foods and
    or drugs isolated or recrystallized from methanol, e.g., methanol is
    used as an extraction solvent for spice oleoresins and hops (Lewis,
    1989). Additionally, certain foods and drugs, consumed or administered
    as their methyl ester, can release methanol during their metabolism
    and excretion (Stegink et al., 1981; Davoli et al., 1986). For
    example, 10% of the sweetening agent aspartame (L-aspartyl-L-
    phenylalanine methyl ester) hydrolyzes in the gastrointestinal tract
    to become free methanol. Carbonated beverages contain about 555 mg
    aspartame/litre (Medinsky & Dorman, 1994), equivalent to approximately
    56 mg methanol per litre.

         The amount of methanol present in an average serving of beverage
    sweetened by aspartame alone is considerably less than in the same
    volume of many fruit and vegetable juices. For instance, tomato juice
    will result in 6 times the amount of methanol exposure than
    consumption of an equivalent volume of aspartame sweetened beverage
    (Wucherpfennig et al., 1983).

         Exposure to several industrial compounds such as methanol,
    formaldehyde and acetone may contribute to increasing amounts of
    formate in the body (Boeniger, 1987). Formate is present in blood at
    background or endogenous levels that range from 0.07 to 0.4 mM.
    Although it is essential for survival, an excess of formate, which
    often occurs after intake of large doses of methanol, can cause severe
    toxicity and even death (Medinsky & Dorman, 1994).

         Ingestion of formate can arise from such foods as honey, fruit
    syrups and roasted coffee as well as from its use as a food
    preservative. Formate is also produced as a by-product of several
    metabolic pathways including histidine and tryptophan degradation
    (Stegink et al., 1983).

         The possible utility of formic acid as a biomarker for
    occupational exposure to methanol has been investigated (Angerer &
    Lehnert, 1977; Baumann & Angerer, 1979; Ferry et al., 1980; Heinrich &
    Angerer, 1982; Liesivouri & Savolainen, 1987; Franzblau et al., 1992b;
    Lee et al., 1992; d'Alessandro et al., 1994).

    5.1.4  Tobacco smoke

         Methanol at levels of 180 µg/cigarette has been detected in the
    vapour phase in mainstream smoke (Norman, 1977; Guerin et al., 1987).
    It has been reported to represent about 2% by weight of the mainstream
    smoke organic phase and particulate matter (Dube & Green, 1982).

    5.2  Occupational exposure

         US NIOSH (1976) estimated that 175 000 workers in the USA are
    potentially exposed to methanol. As stated in Clayton & Clayton
    (1982), the US Department of Labor reported that 72 occupations
    involve exposure to methanol. Estimates derived from the NIOSH

    1972/1974 National Occupational Hazard Survey and 1982-1983 National
    Occupational Exposure Survey indicate that approximately 1-2 million
    workers in the USA are potentially exposed to methanol (Howard, 1990).

         In a 1978-1982 survey of solvent products associated with USA
    industrial workplace exposure, methanol was identified in 9.8% of 275
    solvent samples collected. The products represented solvent classes
    such as thinners, degreasers, paints, inks and adhesives (Howard,
    1990).Workplace concentrations in the range of 29-108 mg/m3 were
    found during production of "fused collars" (Greenberg et al., 1938).
    No signs or symptoms of methanol intoxication were observed.

         In the vicinity of "spirit" duplicator machines operated with
    methanol-based duplicator fluids, methanol concentrations of between
    475 to 4000 mg/m3 were found in the breathing zone. Teacher aides and
    clerical workers exposed to these concentrations experienced typical
    symptoms of methanol intoxication (Kingsley & Hirsch, 1955; NIOSH,
    1981; Frederick et al., 1984).

         In a Japanese factory producing canned fuel containing mainly
    methanol, air levels of methanol were high (Kawai et al., 1991b). A
    mean geometric concentration of 600 mg/m3 (459 ppm) with a geometric
    standard derivation of 4.1 was found in the breathing zone of 22
    production workers (8-h sampling). This resulted in high blood and
    urine levels of methanol (see section 8.1.3 for further details).

         In a chemical plant, 30-min workplace concentrations ranged from
    about 49 to 303 mg/m3 during the course of a shift, with a geometric
    mean of 129 mg/m3. After an 8-h exposure, average methanol blood and
    urine levels of 8.9 ± 14.7 and 21.8 ± 20.0 mg/litre and a mean formic
    acid urine level of 29.9 ± 28.6 mg/litre were found (Heinrich &
    Angerer, 1982).

         Increases in blood and urine methanol and formate levels can be
    measured in humans exposed to methanol vapours in the workplace at
    concentrations below the ACGIH threshold limit value (TLV) of 260
    mg/m3 (200 ppm). The recommended limit of 260 mg/m3 for methanol was
    first proposed by Cook (1945), based on previous studies of Sayers et
    al. (1942) who observed no symptoms in dogs exposed daily (7
    days/week) for 379 days at concentrations between 590 and 655 mg/m3
    (450 and 500 ppm). Printing office and chemical workers exposed to
    approximately 130 mg/m3 (100 ppm) during the workshift exhibited a
    1.5- to 2.5-fold increase in blood and urinary formate and a 15- to
    20-fold increase in blood and urinary methanol at the end of the
    workday, whereas unexposed workers did not exhibit an increase in
    their blood and urinary methanol or formate levels (Baumann & Angerer,
    1979; Heinrich & Angerer, 1982).

    5.3  General population

         Humans are routinely exposed to methanol from both the diet and
    natural metabolic processes. Sedivec et al. (1981) reported a mean
    blood methanol level of 0.73 mg/litre in 31 unexposed subjects (range:
    0.32-2.61 mg/litre). Eriksen & Kulkarni (1963) measured a mean level
    of 0.25 µg/litre in the expired air of 9 "normal" people (range:
    0.06-0.45 µg/litre).

         Methanol is available from the ingestion of dietary fruits and
    vegetables, from the consumption of fruit juices and fermentation
    beverages, and from the use of the synthetic sweetener aspartame,
    which on hydrolysis yields 10% of its weight as free methanol, which
    is available for absorption. Estimates of intakes of methanol from
    these sources vary considerably. Consuming a 354 ml carbonated
    beverage is approximately equivalent to a methanol intake of 20 mg.
    Excluding exposure from carbonated beverages, daily aspartame intake
    can average 3-11 mg/kg (0.3-1.1 mg methanol/kg), with the 99th
    percentile ingesting up to 34 mg/kg (3.4 mg/kg methanol) (Stegink,
    1981; Medinsky & Dorman, 1994). If aspartame were used to replace all
    sucrose in the diet, its average daily ingestion would be 
    7.5-8.5 mg/kg which would be the equivalent to 0.75-0.85 mg 
    methanol/kg (Stegink et al., 1981; Davoli et al., 1986).

         The average intake of methanol from natural sources varies, but
    limited data suggest an average intake of considerably less than 10 mg
    methanol/day (US EPA, 1977; Monte, 1984).

         Estimated methanol body burdens for selected situations were
    reported by Medinsky & Dormam (1994). The "background" body burden of
    methanol was estimated to be 0.5 mg/kg. Fruit juices containing 
    12-640 mg methanol/litre would have a variable effect on body burden, 
    while personal garage exposure (200 mg/m3; 15 min) and self-service
    refuelling (50 mg/m3; 4 min) would increase the body burdens by an
    estimated 0.6 mg/kg and 0.04 mg/kg, respectively.

         Methanol, either 100% or in gasoline blends (85% methanol and 15%
    gasoline), has the potential to become a major automotive fuel
    particularly in the USA in the next century (Kavet & Nauss, 1990;
    Medinsky & Dorman, 1994). Emissions of methanol can arise from its
    release as uncombusted fuel in the exhaust or from its evaporation
    during refuelling and after the engine has stopped. Formaldehyde
    emissions can result from the incomplete combustion of methanol fuels
    (Medinsky & Dorman, 1994).

         The US EPA has modelled methanol exposure levels that might occur
    under specific conditions of use (Kavet & Nauss, 1990). For example,
    if 100% of all automobiles were powered by methanol-based fuels,
    models predict concentrations of methanol in expressways, street
    canyons, railroad tunnels or parking garages ranging from a low of
    1 mg/m3 to a high of 60 mg/m3. Methanol concentrations in a personal
    garage during engine idle or hot soak conditions are predicted to 

    range from 2.9 to 50 mg/m3, while those predicted during refuelling
    of vehicles ranged from 30 to 50 mg/m3. For comparison, the American
    Conference of Governmental Industrial Hygienists (ACGIH) Threshold
    Limit Value (TLV) for exposure to methanol over an 8-h workday is
    260 mg/m3 (200 ppm) for working populations.

         Some methanol exposure concentrations have been calculated for
    various scenarios (traffic conditions, wind patterns, meteorological
    conditions) from emission data from a few cars using methanol
    dispersion models. The highest methanol concentration projected to
    occur in a personal garage is 490 mg/m3 (375 ppm) during the cold
    start. In public garages, assuming 100% of the vehicles were fuelled
    with methanol, concentrations were projected to be as high as
    200 mg/m3 (150 ppm), while in either scenarios the concentrations
    would be expected to be lower than 65 mg/m3 (50 ppm). In the majority
    of cases, exposure to the general public would be brief but repeated
    in time (Gold & Moulif, 1988).

         Most available evidence indicates that exposure to methanol
    vapour from use as a motor fuel is not associated with adverse effects
    (Gold & Moulif, 1988). The uncertainties in this conclusion are based
    on the lack of information at reasonable projected exposure levels and
    of studies examining end-points of concern in sensitive species. Lack
    of complete data (dose-response, exposure) reveals that numerous
    uncertainties exist in the safety/risk assessments. Small effects and
    trends in behavioural and neurophysiological responses and subjective
    ratings have been reported but need to be further substantiated.


    6.1  Absorption

         The primary routes of methanol exposure are inhalation and
    ingestion, with dermal exposure currently of much less importance in
    terms of total daily intake for both the general and occupational
    populations. Regardless of the exposure route, methanol distributes
    readily and uniformly to all organs and tissues in direct relation to
    their water content (Yant & Schrenk, 1937; Haggard & Greenberg, 1939).
    Thus all exposure routes are presumed to be toxicologically equivalent
    (Tephly & McMartin, 1984). No differences exist between the
    capabilities for absorption of methanol among various animal species,
    and blood levels are entirely predictable based on the concept that
    methanol distributes uniformly to body water content.

    6.1.1  Inhalation

         Inhalation of methanol is the most common route of entry in an
    occupational setting. Experiences in occupational health and volunteer
    studies show that methanol is rapidly absorbed after inhalation
    (Angerer & Lehnert, 1977; Baumann & Angerer, 1979; Ferry et al., 1980;
    Sedivec et al., 1981; Heinrich & Angerer, 1982; Liesivouri &
    Savolainen, 1987; Kawai et al., 1992; d'Alessandro et al., 1994).

         The body burden is estimated from methanol concentration,
    ventilation rate, duration of exposure and lung retention. Around
    60-85% of inhaled methanol is absorbed in the lung of humans (Leaf &
    Zatman, 1952; Sedivec et al., 1981). Blood methanol concentration,
    frequently employed to characterize the body burden of methanol is, on
    average, equal to 83% of its aqueous concentration. Urine contains
    methanol concentrations 20-30% higher than blood (Yant & Schrenk,
    1937; Leaf & Zatman, 1952).

         Following uptake and distribution, methanol clears from the body.
    In humans, clearance proceeds after either inhalation or oral exposure
    with a half-life of 1 day or more for high doses (greater than 1 g/kg)
    and about 3 h for low doses (less than 0.1 g/kg) with first-order
    kinetics in humans, monkeys and rats (Leaf & Zatman, 1952; Teply &
    McMartin, 1984).Methanol is either excreted unchanged in the urine and
    breath or it enters a metabolic pathway whose ultimate product is
    carbon dioxide. The time course for the disappearance of methanol from
    the circulation is dependent upon the combined action of both direct
    excretion and metabolism. The elimination of methanol from the blood
    appears to be very slow in all species, especially when compared to
    ethanol (Tephly & McMartin, 1984).

         Relationships between methanol inhalation exposure,
    concentrations, duration of exposure and urinary methanol
    concentrations have been characterized in exposures of volunteers and
    in occupational settings. Ferry et al. (1980), Sedivec et al. (1981),
    and Heinrich & Angerer (1982) reported that urinary methanol 

    concentrations strictly depend on the duration and intensity of the
    methanol exposure, suggesting that measurement of urinary methanol
    concentrations would be a reliable parameter for evaluating the degree
    of methanol exposure.

         Sedivec et al. (1981) exposed four volunteers to methanol at
    concentrations of 102, 205 and 300 mg/m3 for 8 h/day. Urine was
    monitored for methanol during exposure and for 18 h afterwards. The
    concentrations in urine were proportional to the air concentrations.
    When exposure ceased, urinary methanol levels decreased exponentially
    with a half-life of about 1.5-2 h; a mean urinary level of 0.73 mg/litre
    (range 0.32-2.61 mg/litre) in 31 unexposed subjects was also
    reported. Heinrich & Angerer (1982) determined methanol in blood and
    urine and formic acid in urine from 20 subjects occupationally exposed
    to methanol. The air concentration was on average 145 mg/m3 (111 ppm)
    but varied from 49 to 303 mg/m3. An 8-h exposure resulted in methanol
    levels in blood and urine of 8.9 ± 14.7 mg/litre and 21.8 ±
    20 mg/litre, respectively. Formic acid concentrations were 29.9 ±
    28.6 mg/litre. The corresponding normal values were < 0.6, 1.1 ± 0.9
    and 12.7 ± 11.7 mg/litre.

         Volunteers exposed for 6 h to 260 mg/m3 (200 ppm) methanol, the
    current permissible US OSHA 8-h time-weighted average limit, were
    found to have a blood methanol concentration increase from a mean of
    1.8 µg/ml to 7.0 µg/ml (3.5-4 fold increase) compared to their
    pre-exposure levels. Formate did not accumulate in the blood above its
    background level (8.11 µg/ml) following the 6-h exposure (Lee et al.,

         Franzblau et al. (1993) demonstrated the absence of formic acid
    accumulation in the urine of five volunteers following 5 days of
    exposure to an atmosphere containing 260 mg/m3 (200 ppm) of methanol
    in a test chamber. These results indicated that there was no day-to-
    day accumulation of formic acid in urine in conjunction with 5
    consecutive days of near-maximal permissible airborne methanol
    exposure and that measurement of formic acid in urine specimens
    collected 16 h following cessation of exposure did not appear to
    reflect inhalation methanol exposure on the preceding day.

         Twenty-six volunteers exposed at rest to 260 mg/m3 (200 ppm) of
    methanol vapour for 4 h did not show significant differences in serum
    or urinary formate concentration. At the TLV of 260 mg/m3 (200 ppm)
    methanol exposure did not contribute substantially to endogenous
    formate formation (d'Alessandro et al., 1994).

         Inhalation of from 650 to 1450 mg/m3 (500 to 1100 ppm) methanol
    for periods of 3-4 h in humans yielded urine concentrations of about
    10-30 mg/litre at the end of the exposure period (Leaf & Zatman,
    1952). Based on their findings, it was suggested that an 8-h exposure
    to 3990 mg/m3 (3000 ppm) methanol would be necessary before a gradual
    accumulation of methanol would occur in the body.

    6.1.2  Oral

         Methanol is rapidly absorbed from the gastrointestinal tract with
    peak absorption occurring in 30-60 min depending on the presence or
    absence of food in the stomach (Becker, 1983).

         Ingestion of methanol has been the principal route of exposure in
    the many reported cases of acute poisoning (Buller & Wood, 1904; Wood
    & Buller, 1904; Bennett et al., 1953; Erlanson et al., 1965; Kane et
    al., 1968; Gonda et al., 1978; Naraqi et al., 1979; Swartz et al.,
    1981; Jacobsen et al., 1982; Becker, 1983; Litovitz et al., 1988).

         During methanol poisoning in humans, concentrations of methanol
    and formic acid in blood and urine are quite variable. Concentrations
    of both compounds are highly dependent upon dose, time following
    exposure and concomitant ingestion of ethanol (Lund, 1948a, Gonda et
    al., 1978, Jacobsen et al., 1982a). Excretion of methanol in urine is
    initially high and decreases with time following exposure. Maximum
    excretion of formic acid in urine may occur as late as the second or
    third day following ingestion (Lund, 1948a).

         Blood methanol concentrations during experimentally induced
    ethanol intoxication in alcoholics during a 10-15 day period of
    chronic alcohol intake showed that blood methanol levels increased
    progressively from 2-27 mg/litre from the first to the 11th day of
    drinking, when blood ethanol concentrations ranged between 1500 and
    4500 mg/litre. Blood methanol levels decreased at the rate of 2.9 ±
    0.4 mg/litre per h only after blood ethanol levels decreased to 700 to
    200 mg/litre. Blood methanol disappearance lagged behind the linear
    disappearance of ethanol by approximately 6-8 h and complete clearance
    of methanol required several days. Methanol probably accumulates in
    the blood as a result of the competitive inhibition of alcohol
    dehydrogenase by ethanol and the presence of endogenously formed
    methanol (Majchrowicz & Mendelson, 1971).

         Oral doses of 71-84 mg methanol/kg in humans resulted in blood
    levels of 47-76 mg/litre blood 2-3 h later. The urinary concentrations
    of methanol rapidly reached a peak capacity in 1 h and declined
    exponentially, reaching control values in 13-16 h. The urine/blood
    concentration ratio was found to be relatively constant at 0.30 (Leaf
    & Zatman, 1952). Leaf & Zatman (1952) monitored methanol disappearance
    from the circulation of three volunteers orally administered 3, 5 and
    7 ml (2.4, 4.0 and 5.6 g) (highest dose, 0.08 g/kg). Blood and urine
    methanol disappearance obeyed first-order kinetics with a half-time of
    about 3 h.

         Aspartame (see section 5.1.3) is a widely used artificial
    sweetening agent which is hydrolysed in the intestinal mucosa to 10%
    methanol by weight. Beverages totally sweetened with aspartame
    typically contain 0.5-0.6 mg aspartame/ml or approximately 195 mg/
    350 ml soft-drink; dry mixes and puddings use about 100 mg/serving and
    pre-sweetened cereal products about 60 mg/25 ml (cup). The methanol 

    body burden following ingestion of any of these products could vary
    from 6-20 mg (Stegink et al., 1981,1983). Clearance of methanol from
    human circulation after body burdens as high as 80 mg/kg follows
    first-order kinetics with a half-time of about 2.5-3 h (the rate
    constant for total clearance kt is 0.23-0.28/h (Stegink et al., 1981;
    Kavet & Nauss, 1990).

         After intake of small quantities of methanol (10-20 ml), human
    subjects showed no methanol in blood after 48 h, and the concentration
    of formic acid in the urine was normal (6.5-12.8 mg%) within 24 h
    (Lund, 1948a). Following intake of large amounts of methanol (50 ml),
    methanol was found in the blood (250-1200 mg/litre) after 48 h. Formic
    acid was found in the blood (26-78 mg/litre) as well as an increased
    excretion of formic acid in the urine (540-2050 mg/litre), and up to
    20 500 mg/litre within 24 h. Maximum excretion of formic acid was
    found to occur not later than the second or third day after intake of
    methanol (Lund, 1948a).

    6.1.3  Dermal

         It has been known for some time that pure methanol has an
    anomalously high diffusion rate through epidermis because of the
    damage it produces on the stratum corneum (the thin sheath of
    keratinized cells that comprise the outermost layer of the epidermis).
    The permeability of epidermis for pure methanol is 10.4 mg/cm2 per h
    (Scheuplein & Blank, 1971).

         Skin absorption rate studies of methanol ranging from 0.031-0.241
    mg/cm2 per min conducted in human volunteers showed that an average
    of 0.192 mg methanol/cm2 per min is absorbed through direct contact
    of the skin to methanol. Compared with absorption via the respiratory
    tract, exposure of one hand to liquid methanol for only 2 min would
    result in a body burden of as much as 170 mg methanol, similar to that
    resulting from exposure to an approximate air concentration of
    50 mg/m3 (40 ppm) methanol for 8 h (Dutkiewicz et al., 1980). It was
    also reported that in the context of a 20-min immersion of one hand in
    methanol, the cumulative urinary excretion of methanol over 8 h was
    2 mg. However, it should be noted that the assessment of Dutkiewicz et
    al. (1980) would imply that a 10-min exposure of one hand to liquid
    methanol roughly corresponds to an 8-h inhalation exposure at
    260 mg/m3 (200 ppm). Such an inhalation exposure was found to be
    accompanied with a post-shift urinary methanol concentration of about
    40 mg/litre (Sedivec et al., 1981; Kawai et al., 1991b) or 6.5
    mg/litre (Franzblau et al., 1993).

         The rate of absorption into the skin has been found to be higher
    with M-85 (85% methanol-15% gasoline) than with pure methanol. The
    gasoline was suggested to act by drying out the skin allowing the
    methanol to be more readily absorbed (Machiele, 1990). In 11 children
    treated for percutaneous methanol intoxication, methanol blood levels
    ranged from 0.57 to 11.3 g/litre (mean 4.61 g/litre) (Giminez et al.,
    1968). Methanol was identified in the urine and in peritoneal fluid
    (no quantitative estimation) in an 8-month-old boy poisoned by
    percutaneous absorption of methanol (Kahn & Blum, 1979).

         Downie et al. (1992) reported a case of percutaneous industrial
    methanol toxicity involving two workers who spent 2-3 h cleaning out a
    cargo tank with methanol while wearing positive pressure breathing
    apparatus. One of the workers, who suffered from a previous sunburn,
    wore no protective clothing during cleaning. He experienced methanol
    toxicity from percutaneous exposure and required hospitalization and
    methanol poisoning treatment.

    6.2  Distribution

         Methanol distributes readily and uniformly to organs and tissues
    in direct relation to their water content (Yant & Schrenk, 1937;
    Haggard & Greenberg, 1939). The apparent volume of distribution of
    methanol is 0.6-0.7 litres/kg, similar to that of ethanol. In methanol
    inhalation studies conducted in dogs, Yang & Schrenk (1937) reported
    that the highest concentrations of methanol were found in the blood,
    vitreous and aqueous humour, bile and urine, and the lowest in bone
    marrow and fatty tissue. In other animal studies, high concentrations
    of methanol have been reported in the kidney, liver and gastro-
    intestinal tract with smaller concentrations in brain, muscle and
    adipose tissue (Bartlett, 1950).

         Postmortem analysis of methanol concentrations in body fluids and
    tissues reported in fatal human cases of methanol poisoning has
    revealed high concentrations of methanol in cerebrospinal fluid (CSF),
    vitreous humour and bile (Bennet et al., 1953; Wu Chen, 1985).
    Methanol concentrations in these fluids were higher than blood
    concentrations. In one study the ratio of methanol in blood to
    vitreous humour was 0.82, which was similar to the ratio of ethanol in
    blood to vitreous humour of 0.89 (Coe & Sherman, 1970). In tissues the
    highest concentrations were found in brain, kidney, lung and spleen,
    with lower concentrations in skeletal muscle, pancreas, liver and
    heart (Wu Chen et al., 1985).Methanol-induced alterations in
    uteroplacental blood-flow were studied in CD-1 mice and Sprague-Dawley
    rats employing microdialysis as a tool for investigating the flux of
    toxicants across the maternal-conceptual unit. Microdialysis probes
    were inserted into the uteri of gestational day 20 rats and methanol
    was administered as either an intravenous bolus (100 or 500 mg/kg) or
    infusion (100 or 1000 mg/kg/hour).

         In separate studies, methanol (100 or 500 mg/kg) and 3H2O
    (20 µCi/kg) were administered intravenously on gestational days
    20 and 14 to rats and on gestational day 18 to mice. The methanol
    concentration-time data were consistent with saturable maternal
    elimination and apparent first-order transfer between maternal and
    conceptual compartments. At distribution equilibrium, conceptual
    methanol concentrations exceeded those in the dam by approximately
    25%. The initial rate of conceptual permeation of methanol was
    proportional to the reciprocal of maternal blood methanol
    concentration (r2 = 0.910).

         The data indicated that high circulating maternal methanol
    concentrations decrease the rate of presentation of methanol and
    3H2O to the conceptus, and, depending on the severity of the
    decrease, fetal hypoxia could also result (Ward & Pollack, 1996b).

    6.3  Metabolic transformation

         After uptake and distribution, most of the methanol is
    metabolized in the liver to carbon dioxide (96.9%), while a small
    fraction is excreted directly to the urine (0.6%) and through the
    lung. In all mammalian species studied, methanol is metabolized in the
    liver by sequential oxidative steps to form formaldehyde, formic acid
    and CO2 (Fig. 1). However, there are profound differences in the rate
    of formate oxidation in different species which determine the
    sensitivity to methanol (Rietbrock, 1969; Palese & Tephly, 1975;
    McMartin et al., 1977; Eells et al., 1981a, 1983).

         Two enzymes are important in the oxidation of methanol to
    formaldehyde, alcohol dehydrogenase and catalase. In non-human
    primates and humans, alcohol dehydrogenase mediates this reaction
    (Makar et al., 1968; Röe, 1982). In rats and other non-primate species
    this reaction is mediated by catalase. Definitive evidence of these
    differences has been provided by studies of methanol oxidation
     in vivo using alternative substrates (ethanol, 1-butanol) and
    selective inhibitors of catalase (3-amino-1,2,4-triazole) and alcohol
    dehydrogenase (4-amino-pyrazole). The hepatic microsomal mixed-
    function oxidase system (P450IIE1) has also been implicated in the
    conversion of methanol to formaldehyde, but there is no definitive
    information on its role  in vivo (Rietbrock et al., 1966; Teschke et
    al., 1975). Despite the difference in enzyme mediation, the conversion
    from methanol to formate occurs at similar rates in non-human primates
    and in rats (Tephly et al., 1964; Makar et al., 1968; Noker et al.,
    1980; Eells et al., 1981a, 1983). The metabolism of methanol can be
    significantly inhibited by co-exposure to ethanol, which acts as a
    competing substrate for alcohol dehydrogenase (Jones, 1987).

         Formaldehyde is oxidized to formate by several enzyme systems
    including a specific formaldehyde dehydrogenase. In the reaction
    catalysed by this enzyme, formaldehyde combines with reduced
    glutathione to form  S-formyl glutathione, which is hydrolysed in the
    presence of thiolase to formate and reduced glutathione (Strittmatter
    & Ball, 1955; Uotila & Koivusalo, 1974). The second step of this
    reaction is irreversible (Strittmatter & Ball, 1955). Formaldehyde
    dehydrogenase activity has been shown to be present in numerous
    species and tissues including human liver and brain (Strittmatter &
    Ball, 1955; Kinoshita & Masurat, 1958; Goodman & Tephly, 1971).

    FIGURE 2

         The elimination of formaldehyde in many species including
    primates is extremely rapid with a half-life of approximately 1 min
    (Rietbrock, 1965; McMartin et al., 1979). Malorny et al. (1965) found
    that equimolar infusions of formaldehyde, formic acid and sodium
    formate in dogs produced equivalent peak concentrations of formic
    acid, indicating that formaldehyde was rapidly metabolized to formic
    acid. In a human case of formaldehyde poisoning, toxic concentrations
    of formate (7-8 mm) were detected within 30 min of ingestion,
    confirming rapid metabolism of formaldehyde to formate in humans
    (Eells et al., 1981b). Formaldehyde has not been detected in body
    fluids or tissues following toxic methanol exposures (Makar & Tephly,
    1977, McMartin et al., 1977, McMartin et al., 1980a). Formate is
    oxidized to CO2  in vivo in mammalian species primarily by a
    tetrahydrofolate-dependent pathway (Fig. 2). Formate enters this
    pathway by combining with tetrahydrofolate (H4folate) to form
    10-formyl-H4folate in a reaction catalysed by formyl-tetrahydrofolate
    synthetase. 10-Formyl-H4folate may then be further oxidized to CO2
    and H4folate by formyl-H4folate dehydrogenase (Kutzbach & Stokstad,
    1968) (Fig. 1). Rietbrock et al. (1966) found an inverse correlation
    between plasma concentrations of folate in different animal species
    and the half-life of exogenously administered formate, suggesting that
    folates are involved in formate metabolism. Formate metabolism in rats
    and monkeys has been shown to be mediated by the folate-dependent
    pathway (Makar et al., 1968; Palese & Tephly, 1975). Inhibition of
    catalase with aminotriazole had no effect on formate oxidation,
    whereas folate-deficiency markedly reduced formate oxidation in both
    species. Tetrahydrofolate is derived from folic acid in the diet and
    is the major determinant of the rate of formate metabolism (McMartin
    et al., 1975).

         The folate-mediated oxidation of formate proceeds about twice as
    slowly in non-human primates and humans as in rats. This explains the
    susceptibility of primates to the accumulation of formate, which is
    seen to occur at doses of methanol greater than 0.5 g/kg (Tephly &
    McMartin, 1984) (Fig. 2).There is substantial clinical and
    experimental evidence that formic acid is the toxic metabolite
    responsible for the metabolic and visual toxicity characteristic of
    methanol poisoning. Specifically, formic acid is the toxic metabolite
    responsible for the metabolic acidosis observed in methanol poisoning
    in humans, in non-human primates and in folate-depleted rodents
    (McMartin et al., 1975, 1977, 1980; Eells et al., 1983; Jacobsen &
    McMartin, 1986; Eells, 1991; Murray et al., 1991; Lee et al., 1994).
    Formic acid is believed to be the toxic metabolite responsible for the
    ocular toxicity in methanol-poisoned humans (Sharpe et al., 1982), and
    is also responsible for the ocular toxicity produced in non-human
    primates and folate-depleted rodents (Martin-Amat et al., 1977, 1978;
    Eells et al., 1983; Eells, 1991; Lee et al., 1994a,b).

    FIGURE 3

         A comparative metabolism study between rodents and non-human
    primates showed that formic acid concentration in blood of rats and
    monkeys was similar at doses of 25, 125 and 600 mg methanol/kg, but
    became substantially higher in monkeys at 3000 mg/kg. Monkeys and
    rodents showed different excretion patterns for methanol. As the dose
    increased, monkeys tended to excrete an increasing percentage of
    methanol in urine, whereas in rats, the percentage of methanol
    excreted in expired air increased. Additionally, rats excreted much
    higher levels of carbon dioxide in expired air (as a percentage of
    dose) than monkeys (Katoh, 1989).

         In a study of formate metabolism in young swine (Makar et al.,
    1990), it was found that the pig, compared to other species (mouse,
    rat, monkey and humans), has extremely low levels of hepatic folates.
    Furthermore, the rate of formate elimination in the pig was much lower
    in the pig than in the rat. It was suggested that the pig might be
    sensitive to the methanol toxicity syndrome (metabolic acidosis and

         Ward & Pallack (1996a) studied the  in vitro biotransformation
    of methanol in Sprague-Dawley rat and CD-1 mouse fetal livers to
    assess the capability of the near-term rodent fetus to metabolize
    methanol. Adult near-term rodent livers metabolized methanol to
    formate (at gestational day 20) with a maximum of about 85% that in
    livers from non-pregnant rodents (p < 0.05). This was consistent with
     in vivo experiments (Ward & Pollack, 1996a).

         Fetal rat and mouse liver was capable of metabolizing methanol
     in vitro, but only at a rate of < 5% of the respective adult liver.
    The difference was in fact even greater, considering the difference in
    organ weight between the conceptus and the dam (about 10-fold).

         Fetal mouse liver homogenates converted methanol to formaldehyde
    at a significantly higher (about 40%) rate than fetal rat liver
    homogenates. These data suggest that the near-term rodent fetus does
    not possess a significant ability to biotransform methanol to
    formaldehyde and ultimately formate  in situ.

    6.4  Elimination and excretion

         The primary route of methanol elimination from the body is via
    oxidation to formaldehyde and then to formic acid, which may be
    excreted in the urine or further oxidized to carbon dioxide.

         In humans, methanol is primarily eliminated by oxidation and only
    2% of a 50 mg/kg dose of methanol is excreted unchanged by the lungs
    and kidney (Leaf & Zatman, 1952). The small excretion of unchanged
    methanol was also observed in methanol-poisoned subjects in whom the
    renal and pulmonary excretory clearances of methanol were 1 and
    6 ml/min, respectively (Jacobsen et al., 1982a, 1983b).

         The elimination of formaldehyde in many species, including
    primates, is extremely rapid with a half-life of approximately 1 min
    (McMartin et al., 1979). Toxic concentrations of formate (7-8 mM) were
    detected within 30 min of ingestion in a human case of formaldehyde
    poisoning, confirming the rapid metabolism of formaldehyde to formate
    in humans (Eells et al., 1981b).

         Following uptake and distribution methanol is either excreted
    unchanged (direct excretion) in urine or exhaled breath, or it enters
    a metabolic pathway in the liver, whose ultimate product is carbon
    dioxide. The time course of the disappearance of methanol from the
    circulation is dependent upon the combined action of both direct
    excretion and metabolism. The clearance from the circulation of humans
    following low-level exposures to methanol administered orally
    (<0.1 g/kg) (Leaf & Zatman, 1952) or by inhalation (102-300 mg/m3)
    (Sedivec et al., 1981) indicated that methanol disappearance obeyed
    first-order kinetics with a half-time of about 2.5-3 h in both studies
    as determined by blood and urinary methanol concentrations. In general
    estimated methanol dose correlated with resulting blood and urine
    methanol levels after both ingestion and inhalation, and methanol
    concentrations in urine were approximately 30% higher than in blood
    (Leaf & Zatman, 1952).

         Elimination half-lives of methanol ranging from 110-213 min were
    found in human volunteers following consumption of 1000-1500 ml red
    wine (95% w/w ethanol, 100 mg/litre methanol) the previous evening
    (Jones, 1987). After concomitant ingestion of a very low dose of
    methanol (< 2 mg/kg) and ethanol (ethanol: methanol = 10), by human
    subjects, a 10 fold increase in blood methanol was observed due to the
    combined ingestion of the alcohols (Jones, 1987). Jacobsen et al.
    (1982a) reported that during haemolysis in 2 patients being treated
    for methanol poisoning, the elimination half-lives were 219 and 
    197 min respectively.

         At higher doses of methanol, the elimination appears to become
    saturated, resulting in nonlinear elimination kinetics. In an
    untreated methanol-poisoned subject, methanol elimination was
    clearly zero order with a rate of 85 mg/litre per h, about half the
    elimination rate of ethanol (Jacobsen et al., 1988). The rates of
    elimination in two other cases appeared to be 30-50 mg/litre per h
    (Kane et al., 1968).

         The kidney apparently exerts no active control over the urinary
    concentration of methanol. The methanol content that enters the
    bladder reflects the aqueous concentration of methanol in the blood
    (Yant & Schrenk, 1937; Leaf & Zatman, 1952; Sedivec et al., 1981). The
    rate at which methanol clears into the urine is directly proportional
    to its blood level which satisfies the condition for first-order
    kinetics (Kavet & Nauss, 1990).

         In the lung, a small fraction of blood-borne methanol is exhaled.
    The amount of methanol that crosses the blood-air barrier is
    proportional to its blood concentration (first-order kinetics) and is
    governed by its blood-air partition ratio (Kavet & Nauss, 1990). In
    contrast to direct renal and pulmonary excretion, the metabolic
    conversion of methanol to carbon dioxide is not a linear function of
    concentration (Tephly et al., 1964; Makar et al., 1968).

         Elimination of methanol from the blood appears to be slow in all
    species especially when compared to ethanol (Tephly & McMartin, 1984;
    Tephly, 1991).

         One to 7 g of methanol/litre of blood (1000-7000 mg/litre) was
    found in the blood of rats following oral administration of 4 g
    methanol/kg body weight, and 70% of the methanol lost was eliminated
    in expired air (Haggard & Greenberg, 1939).

         Following administration of a 10% methanol solution (1 g/kg)
    of 14C-methanol by gavage to the rat, 89% of the administered
    radioactivity was recovered after 48 h; 65% as CO2 in expired air, 3%
    as methanol in urine; 3% as formic acid in urine and 4% fixed in
    tissues. An oxidation rate of 25 mg/kg/h was found during the first
    28 h following methanol administration (Bartlett, 1950a).

         Methanol was oxidized at a constant rate of 24 mg/kg per h during
    the first 28 h following intraperitoneal administration of a 10%
    14C-methanol solution (1 g/kg) to male albino rats. By the end of
    36 h, 77% of the methanol had been converted to 14CO2 and 24% of the
    dose was excreted unchanged. About equal quantities of methanol were
    eliminated by the pulmonary and renal plus faecal routes (Tephly et
    al., 1964).

         Comparative studies in rats and monkeys have shown that 75-80% of
    a 1 g/kg dose of 14C-methanol was recovered as 14CO2; 10-18% was
    excreted unchanged in expired air and 6-11% eliminated in the urine as
    methanol or formate within a 24-h period (Eells et al., 1981, 1983).
    Excretion of similar amounts of unchanged methanol eliminated by
    pulmonary (10-15%) and renal (3-19%) routes in rats and guinea-pigs
    have also been reported (Bartlett, 1950; Tephly et al., 1964).

         After oral administration to dogs of a single dose of methanol
    (1.97 g/kg), about 10% was excreted unchanged in the urine, over a
    period of about 100 h. The methanol concentration in the organs was
    nearly half as high as that found in the urine. About 20% of the
    administered dose was excreted as formic acid in the urine, which
    ceased after 100 h. Formic acid concentrations in tissues were about
    one-half to one-quarter that found in serum (Lund, 1948b).

         Oral administration of 2.38 g methanol/kg to male rabbits
    resulted in 10% of methanol being excreted unchanged in the urine and
    essentially no increase in formic acid in the urine. Formic acid is
    oxidized almost completely in the rabbit (Lund, 1948c).

         Damian & Raabe (1996) investigated the dose-dependent elimination
    of formate in male CD rats employing a perfused liver system to
    separate the kinetic contributions of hepatic metabolism and renal
    excretion in the total elimination of formate. Formate was eliminated
    from the perfused rat liver following Michaelis-Menten kinetics.
    The  in vitro and  in vivo dose-dependent studies of formate
    elimination, in conjunction with the proposed toxicokinetic model (a
    central, well-mixed compartment and a urine compartment, endogenous
    production of formate), indicated two main pathways of formate
    elimination in the rat: (a) hepatic metabolism via Michaelis-Menten
    kinetics which predominates at low levels, and (b) extremely rapid and
    extensive urinary excretion that predominates at high dose levels.
    Urinary excretion consists primarily of glomerular filtration with
    saturable tubular reabsorption.

    6.5  Modelling of pharmacokinetic and toxicokinetic data

         Pharmacokinetic and toxicokinetic models have been developed in
    order to gain better insight into the interspecies variation in the
    uptake, metabolic fate and excretion of methanol and its metabolites,
    both compartmentally and physiologically based (Horton et al., 1992;
    Pollack et al., 1993; Dorman et al., 1994). As has been noted, the
    elimination of formaldehyde in many species, including primates, is
    extremely rapid (McMartin et al., 1979).

         A pharmacokinetic model of inhaled methanol in humans and
    comparison to methanol disposition in mice and rats was described by
    Perkins et al. (1995). Michaelis-Menten elimination parameters (Vmax=
    115 mg/litre per h; km = 460 mg/litre) were selected for input into
    a semi-physiological pharmacokinetic model. Literature values for
    blood or urine methanol concentrations in humans and non-human
    primates after methanol inhalation were employed as input to an
    inhalation disposition model that evaluated the absorption of methanol
    expressed as the fraction of inhaled methanol concentration that was
    absorbed. Incorporation of the kinetic parameters and absorption into
    a pharmacokinetic model of human exposure to methanol, compared to a
    similar analysis in rodents, indicated that, following an 8-h exposure
    to 6550 mg/m3 (5000 ppm) of methanol vapour, blood methanol
    concentrations in the mouse would be 13-18 fold higher than in humans
    exposed to the same methanol vapour concentration. Blood methanol
    concentrations in the rat under similar conditions would be 5-fold
    higher than in humans. The prediction of higher concentrations in rats
    was due to the greater respiration rates and consequent greater
    absorption of methanol by rats.

         To address the problems associated with the appropriate design of
    chronic methanol studies, methanol pharmacokinetics were characterized
    in male Fischer-344 rats and rhesus monkeys exposed to atmospheric
    methanol concentrations ranging from 65 to 2600 mg/m3 (50-2000 ppm)
    for 6 h (Horton et al., 1992). A physiologically based pharmacokinetic
    (PBPK) model was then developed to simulate the  in vivo time course
    data. The models were used to predict the atmospheric methanol

    concentration range over which the laboratory species exhibit
    quantitative similarities with humans. Below 1500 mg/m3 (1200 ppm)
    the model predicted all three species would exhibit similar end-of-
    exposure blood methanol concentrations which would be proportional to
    atmospheric concentrations. At higher concentrations the increase of
    methanol in the blood of rats and monkeys was predicted to become
    non-linear, whereas for humans blood methanol levels were predicted to
    increase in a linear fashion (Horton et al., 1992).

         Female Sprague-Dawley rats at gestational days 7, 14 and 21 and
    CD-1 mice at gestational days 9 and 18 were exposed to methanol
    intravenously and orally (100-2500 mg/kg) or by inhalation exposure to
    1310 to 26 200 mg/m3 (1000-20 000 ppm) for 8 h and the concentrations
    of methanol were measured in blood, urine and amniotic fluid (Pollack
    & Brouwer, 1996). Methanol disposition was virtually unaffected by
    pregnancy and the fetal methanol concentrations were approximately
    similar to those in the mother. Mice accumulated methanol at a rate 2
    to 3 times faster than rats, despite the two-fold higher rate of
    elimination observed in the mouse.

         A pharmacokinetic model described the disposition of methanol in
    rats and mice with the disposition profile being partitioned into
    saturable and linear metabolic elimination pathways. The saturable
    pathway was evident at lower doses (100 and 500 mg methanol/kg) and
    displayed classical carrier-mediated Michaelis-Menten kinetics with a
    rate-limiting step. The linear pathway, which consisted of passive
    elimination via pulmonary and urinary clearance of methanol in
    approximately equal amounts, appeared at the highest dose (2500 mg/kg
    iv) and displayed the first-order kinetics of elimination that are
    characteristic of passive-diffusion mechanisms (Pollack & Brouwer,

         In further studies of the comparative toxicokinetics of methanol
    in pregnant and non-pregnant Sprague-Dawley rats and CD-1 mice (Ward &
    Pollack, 1996a), methanol disposition in the pregnant rodent was found
    to be qualitatively similar to that in non-pregnant animals. Rats
    received a single dose (100 or 2500 mg/kg) of methanol either orally
    (by gavage) or intravenously; mice received a single oral or
    intravenous dose of 2500 mg/kg.

         The maximal rate of methanol elimination (Vmax)  in vivo
    decreased at term in both species. Vmax in near-term rats and mice
    was only 65-80% of that in non-pregnant animals. The kinetic
    parameters that appeared to be most sensitive to the gestational stage
    were the rate constants associated with intercompartmental transfer
    (k12 and k21), although there was no obvious relationship between the
    estimate of these parameters and gestational stage. The data generated
    in both the  in vivo and  in vitro studies demonstrated that
    alterations in methanol disposition associated with gestational stage
    should be accounted for in the development of a toxicokinetic model
    for methanol in pregnant mammals.

         The examination of the toxicokinetics of intravenously
    administered methanol to female Sprague-Dawley rats as a single bolus
    dose of 50 or 100 mg/kg, or 2500 mg/kg administered over 2 min,
    resulted in a markedly non-linear elimination of methanol from the
    systemic circulation suggesting a significant capacity-limited rate of
    elimination. The data from the 2500 mg/kg group was described by a
    kinetic model incorporating parallel first-order and saturable
    elimination processes; a portion of this apparent linear elimination
    pathway was due to renal excretion of the unchanged alcohol (Pollack
    et al., 1993). The blood methanol concentration-time profile was
    consistent with the presence of parallel linear pathways for methanol

         The toxicokinetics of methanol in female CD-1 mice and Sprague-
    Dawley rats was examined by Ward et al. (1995). Non-linear disposition
    of methanol was reported in both female CD-1 mice administered a
    single dose of 2.5 g methanol/kg either by gavage or intravenously (as
    a 1-min infusion) and Sprague-Dawley rats receiving a single oral dose
    of 2.5 g/kg. Data obtained after intravenous administration were
    well-described by a one-compartment model with Michaelis-Menton
    elimination. Blood methanol concentration-time data after oral
    administration could be described by a one-compartment (mice) or a
    two-compartment (rats) model with Michaelis-Menton elimination
    from the central compartment and biphasic absorption from the
    gastrointestinal tract. Kinetic parameters (Vmax for elimination),
    apparent volume of the central compartment (Vc), first-order rate
    constants for intercompartmental transfer (k12 and k21), and first-
    order absorption rate constants for fast (kAF) and slow (Kas)
    absorption processes were compared between species. Mice showed a
    higher maximal elimination rate than rats (when normalized for body
    weight) (Vmax = 117 + 3 mg/kg per h versus 60.7 + 1.4 mg/kg per h for
    rats). Additionally, the contribution of the fast absorption process
    to overall methanol absorption was larger in the mouse than in the
    rat. The study demonstrated that the disposition of methanol is
    similar in rats and mice, although mice eliminated methanol nearly
    twice as rapidly as rats.

         The pharmacokinetics of 14C-methanol and 14C-formate were
    studied in normal and folate-deficient (FD) female cynomolgus monkeys
    anaesthetized and exposed by lung-only inhalation to 13, 60, 260 and
    1200 mg/m3 (10, 45, 200 and 900 ppm) 14C-methanol for 2 h to
    determine the concentration of methanol-derived formate to the total
    formate pool. The blood concentration of 14C-methanol-derived formate
    from all exposures was 10-1000 times lower than the endogenous blood
    formate concentration (0.1-0.2 mmol/litre) reported for monkeys and
    orders of magnitude lower than levels that produce acute toxicity
    (8-10 mmol/litre). This suggested that low-level exposure to methanol
    would not result in elevated blood formate concentrations in humans
    under short-term exposure conditions (Dorman et al., 1994) (Medkinsky
    & Dorman, 1985).  This was confirmed in a subsequent short-duration
    inhalation study in which anaesthetized female cynomolgus monkeys were
    exposed for 2 h to methanol vapour (tagged with radiolabelled carbon)

    at concentrations of 13, 59, 262 and 1179 mg/m3 (10, 45, 200 and
    900 ppm), and monkeys fed on a diet deficient in folic acid were
    exposed to 1179 mg/m3 (900 ppm) for the same duration (Medinsky et
    al., 1997). The blood levels of methanol increased in a dose-dependent
    manner. Blood formate levels increased by only a small extent in both
    groups of monkeys.


    7.1  Single exposure

    7.1.1  Non-primates

         The lethal oral dose of methanol for most experimental animals is
    relatively high compared to the lethal dose for humans and non-human
    primates. In all non-primate species that have been studied, methanol
    has been shown to be the least toxic of the aliphatic alcohols
    (Koivusalo, 1970). The LD50 values or minimum lethal dose for a
    single oral dose of methanol have been reported to be 9 g/kg for dogs
    (Gilger & Potts, 1955), 7 g/kg for rabbits (Hunt, 1902; Gilger &
    Potts, 1955), 7.4-13 g/kg for rats (Gilger & Potts, 1955; Rowe &
    McCollister, 1982) and 7.3-10 g/kg for mice (Gilger & Potts, 1955;
    Smith & Taylor, 1982) (Table 4). These doses are 6-10 times the lethal
    human dose of methanol (Tephly & McMartin, 1984; Jacobsen & McMartin,
    1986; HEI, 1987).

    Table 4.  Single-dose oral toxicity values for methanol in animals


    Species          LD50 (g/kg)           Reference

    Rat              6.2                   Kimura et al. (1971)

                     9.1                   Welch & Slocum (1943)

                     9.5 MLDa              Gilger & Potts (1955)

                     12.9                  Deichmann (1948)

                     13.0                  Smyth et al. (1941)

    Mouse            0.420                 Smyth et al. (1941)

                     7.3-10.0              Smith & Taylor (1982)

    Rabbit           7.0 MLD               Gilger & Potts (1955)

    Dog              8.0                   Gilger & Potts (1955)

    Monkey           2-3 MLD               Gilger & Potts (1955)

                     7.0 MLD               Cooper & Felig (1961)

    a    Minimum lethal dose

         Other reported oral LD50 values for methanol in Sprague-Dawley
    rats varied in 14-day-old, young adult and older rats ( 7.4, 13.0 and
    8.8 ml/kg respectively), suggesting that young adult rats were least
    susceptible to methanol toxicity (Kimura et al., 1971).

         Youssef et al. (1992) reported that the order of oral LD50 in
    adult female albino rats increased as follows: 95/5%-ethanol/methanol,
    pure methanol, pure ethanol, and 65/35% methanol/ethanol. Clinical
    features of intoxication in treated rats generally progressed from
    signs of inebriation to gait disturbances, dose-proportional decreases
    in response to painful stimuli, respiratory depression and coma,
    ending in death due to cardio-respiratory failure. In almost all
    instances, overnight coma was followed by death of the animal. Gross
    and histopathological examinations of the gastric mucosa revealed
    diffuse congestion with dilation of gastric blood vessels, but with
    absence of gross haemorrhage and ulceration.

         Rats exposed to 1.0, 2.0 and 3.0 g methanol/kg by gavage
    exhibited an altered response in an operant conditioning paradigm
    designed to assess motor deficits produced by neurotoxicants. Methanol
    decreased the rate of response in a dose-related fashion that
    suggested impaired coordination and/or reduced endurance (Youssef et
    al., 1993).

         Methanol administered by gavage or intraperitoneally induced
    hypothermia in Fischer and Long-Evans rats, e.g., brain temperature
    decreased 1.5°C within 35 min and colonic temperature was
    significantly lower (Mohler & Gordon, 1990). This occurred at dose
    levels of 2-3 g/kg, which is about 20% of the reported LD50 value
    of 10 g/kg in rats (Gilger & Potts, 1955).

         Among 40 strains of mice, 72 h oral LD50 values ranged from 7.3
    to 10.0 g/kg with a mean of 8.68 g/kg methanol for mice fed a standard
    laboratory chow diet (Smith & Taylor, 1982). Methanol-dosed C57BL/GCs
    (acatalasemic) mice exhibited slightly lower LD50 than Csa (normal
    catalase) mice, irrespective of their folate state (7.1-8.0 versus
    8.6-9.0 g/kg). Oral methanol 72-h LD50 values ranged from 6.4 to
    7.3 kg for mice with folic acid deficiency (FAD) diets, depending upon
    the concentration of methionine in the diet (0.2-1.8%).

         Female minipigs (Minipig YU, Charles River) treated with a single
    oral dose of methanol at 1, 2.5 and 5.0 g/kg body weight by gavage
    showed dose-dependent signs of acute methanol intoxication, including
    mild CNS depression, tremors, ataxia and recumbency, which developed
    within 0.5-2.0 h and resolved by 52 h. Methanol- and formate-dosed
    minipigs did not develop optic nerve lesions, toxicologically
    significant formate accumulation or metabolic acidosis (Dorman et al.,

         The effects of single exposures of methanol by inhalation are
    summarized in Table 5. The following signs of intoxication were noted:
    increased rate of respiration, a state of nervous depression followed
    by excitation, irritation of the mucous membranes, loss of weight,
    ataxia, partial paralysis, prostration, deep narcosis, convulsions and
    death occurring from respiratory failure (Loewy & von der Heide, 1914;
    Tyson & Schoenberg, 1914; Eisenberg, 1917; Weese, 1928; Scott et al.,
    1933; Mashbitz et al., 1936).

         Under acute inhalation conditions, folate-deficient Long-Evans
    male rats exposed to 4000 mg/m3 (3000 ppm) methanol for 20 h/day did
    not survive more than 4 days. Rhesus monkeys exposed to 4000 mg/m3
    (3000 ppm) methanol for 21 h/day survived the 20-day exposure period
    and rhesus monkeys exposed to 13 000 mg/m3 (10 000 ppm) methanol for
    21 h/day survived for more than 4 days (Lee et al., 1994).

         The LD50 for single intraperitoneal injections of methanol was
    10.5-11.0 g/kg in Swiss albino male mice. The animals initially
    entered into deep narcosis within a few minutes and death usually
    occurred within 24 h following recovery from deep narcosis (Gilger et
    al., 1952). The LD50 values (mmole/kg) for single intraperitoneal
    administration were as follows: male Wistar rats, 237; male strain H
    mice, 336; male Syrian hamster, 267 (Tichy et al., 1985). These values
    were calculated to correspond to 1489, 1493 and 1499 mmole/m2 body
    surface, respectively. Tichy et al. (1985) also determined LD50
    values for intravenous administration of methanol. The values reported
    in rats and mice were 66.5 and 147 mmole/kg, corresponding to 418 and
    653 mmole/m2 body surface, respectively.

         Studies of rats have indicated that there are changes in levels
    of dopamine, norepinephrine, serotonin and 5-hydroxyindole acetic acid
    in various brain regions after a single intraperitoneal injection of
    3 g methanol/kg (Jegnathan & Namasivayam, 1989). Studies on the
    steady-state level of rat brain showed that there was severe depletion
    of dopamine level in the striatum but a significant increase in the
    level of dopamine, serotonin and 5-hydroxyindole acetic acid in the
    hypothalamus. At the same time, norepinephrine and epinephrine levels
    were reduced in the hypothalamus as well as in the striatum. These
    effects do not seem to be induced by metabolic acidosis. The changes
    in monoamine levels are very well correlated with the blood and brain
    level of methanol as shown by maintaining a higher methanol level
    either by simultaneous administration of ethanol or by blocking
    methanol metabolism by pretreatment with 4-methyl pyrazole and
    3-amino-1,2,4-triazole. It is thus postulated that monoamine changes
    induced by methanol appear to be the direct effect of methanol
     per se on the monoaminergic neuronal membranes.

        Table 5.  Effects from single inhalation exposure to methanol


    Animal     Concentration     Duration of       Signs of        Outcome             Reference
                    ppm         exposure  (h)    Intoxication

    Mouse         72 600           54            narcosis         died          Weese (1928)
                  72 600           28            narcosis         died
                  54 000           54            narcosis         died
                  48 000           24            narcosis         survived
                  10 000           230           ataxia           survived
                 152 800           94 min        narcosis                       Mashbitz et al. (1936)
                 101 600           91 min        narcosis
                  91 700           95 min        narcosis
                  76 400           89 min        narcosis         overall
                  61 100           134 min       narcosis         mortality
                  45 800           153 min       narcosis         45%
                  30 600           190 min       narcosis

    Rat           60 000           2.5           narcosis
                                                 convulsions                    Loewy & Von Der Heide
                  22 500           8             narcosis                       (1914)
                  13 000           24            prostration
                    8800           8             lethargy
                    4800           8             none

    Dog             3000           8             none
                  32 000           8             prostration      survived
                  13 700           4             none
                    2000           24            none

    7.1.2  Non-human primates

         The lethal oral dose of methanol in monkeys (Table 4) has been
    shown by several investigators to be of the same order of magnitude as
    the lethal dose for humans. Gilger & Potts (1955) reported a minimum
    lethal dose (MLD) for methanol of 3 g/kg for the rhesus monkey
     (Macaca mulatta). Clinically the signs of toxicity were similar to
    those noted in humans. There was a slight initial CNS depression for
    1-2 h, followed by a latent period of about 12 h, a progressive
    weakness, coma and death usually in about 20-30 h. All the monkeys (4)
    given a lethal dose became severely acidotic within 24 h. Two of the
    animals showed signs typical of methanol amblyopia observed in humans
    including dilated, unresponsive pupils and changes of the retina. One
    monkey exhibited evidence of optic disc hyperaemia and retinal oedema.

         Cooper & Felig (1961) reported a MLD dose of 7 g methanol/kg
    administered orally to rhesus monkeys and observed inebriation,
    narcosis, coma and death within 24 h (usually without a latent
    period). Sixteen animals survived 6 g methanol/kg or less. Acidosis
    (an increased urinary excretion of organic acids) was reported in most

         Studies by McMartin et al. (1975) and Clay et al. (1975) were in
    agreement with earlier studies in monkeys by Gilger & Potts (1955).
    Rhesus monkeys and pigtail monkeys  (Macaca nemestrina) administered
    3 g methanol/kg orally, showed an initial slight CNS depression
    followed by a latent period of 12-16 h, during which time the animals
    showed no obvious signs of toxicity. This was followed by progressive
    deterioration characterized by anorexia, vomiting, weakness,
    hyperpnoea and tachypnoea followed by coma with shallow and infrequent
    respiration and finally death due to respiratory failure 20-30 h after
    oral administration of methanol. The gradual development of metabolic
    acidosis coincided with the accumulation of formic acid in the blood
    and the decrease of bicarbonate in the plasma (McMartin et al., 1975).

         An attenuated but prolonged syndrome was produced in monkeys by
    the administration of an initial methanol dose of 2 g/kg body weight.
    and subsequent doses (0.5-1.0 g/kg at 12-24 h intervals), producing
    profound ocular toxicity approximately 40-60 h after the initial
    dosage (Baumbach et al., 1977; Hayreh et al., 1977; Martin-Amat et
    al., 1977).

         Various species exposed to methanol by inhalation have exhibited
    haemorrhage, oedema, congestion and pneumonia in the lungs (Eisenberg,
    1917; Weese, 1928; Tyson & Schoenberg, 1914). Albuminous and fatty
    degeneration and fatty infiltration of the liver and kidneys have also
    been noted (Eisenberg, 1917; Weese, 1928). Fatty degeneration of
    cardiac muscle has been observed in rabbits exposed repeated over 2 to
    6 months to methanol via inhalation (Eisenberg, 1917). This subchronic
    exposure to methanol in rabbits was also associated with notable
    central nervous system effects such as optic nerve damage, lesion and
    atrophy of the cerebrum, cerebellum, medulla and pons, along with 

    decreases in neurocytes, Nissl's granules and in severe cases,
    parenchyma cells. Repeated inhalation of methanol resulted in
    hyperaemia of choroid, oedema of ocular tissue including the retina
    and optic disks, and degeneration of ganglion cells and nerve fibres
    in a number of species such as the dog, rabbit and monkey (Tyson &
    Schoenberg, 1914). Acute exposure to methanol via inhalation, as well
    as oral and dermal exposure, was associated with degeneration and
    necrosis of parenchymal tissue and neurons, accompanied by capillary
    congestion and oedema, and degeneration of the retina and optic nerve
    in rats, rabbits and monkeys (Scott et al, 1933).

         An approximate intraperitoneal methanol LD50 of 3-4 g/kg for
    pigtail monkeys  (Macaca nemestrina) was reported by Clay et al.
    (1975). Doses of 2 and 3 g/kg produced metabolic acidosis in the
    animals, while monkeys given 4 g/kg became severely acidotic and
    exhibited signs of toxicity that were remarkably similar to those
    reported in human poisoning (Kane et al., 1968). These animals
    displayed a sharp decrease in blood pH (7.03) at 7.5-21 h after
    methanol administration. Bicarbonate was the single blood electrolyte
    observed to change during the course of methanol acidosis. There was a
    latent period of 15-18 h prior to the onset of overt signs of
    toxicity, followed by a sequence of signs beginning with behavioural
    distress, coma within 24-30 h and death. This time-course parallels
    that reported for humans suffering from methanol poisoning (Röe,

    7.2  Short-term exposure

    7.2.1  Inhalation exposure

         Male and female Sprague-Dawley rats exposed to 650, 2600 and
    6500 mg/m3 (500, 2000 and 5000 ppm) methanol for 6 h/day, 5 days/week
    for 4 weeks, exhibited no exposure-related effects except for
    increased discharges around the nose and eyes which were considered
    reflective of upper respiratory tract irritation. No consistent
    treatment-related effects were found for organ weight or body weights
    or in histopathological or ophthalmoscopical examinations. No ocular
    effects were noted in rats from 20 repeated exposures to 6500 mg/m3
    (5000 ppm) (Andrews et al., 1987).

         Male Sprague-Dawley rats exposed to methanol vapour at
    concentrations of 260, 2600 and 13 000 mg/m3 (200, 2000 and 
    10 000 ppm) for 6 h/day, 5 days/week for 6 weeks, did not develop 
    pulmonary toxicity. No significant changes were found at the lung 
    surface and in lung tissue (White et al., 1983).

         Rats exposed to 16.8 methanol (0.022 mg methanol/litre of air)
    4 h/day for 6 months and simultaneously administered 0.7 mg
    methanol/kg daily by gavage exhibited changes in blood morphology,
    oxidation-reduction processes and liver function (Pavlenko, 1972).

         A preliminary study reported that F-344 rats fed control and
    folate-deficient diets and exposed to methanol at a concentration of
    1050 mg/m3 (800 ppm) for 20 h/day; 7 days/week for 13 weeks showed
    spontaneous degeneration of retina and optic nerve in both diet
    groups, while Long-Evans rats did not develop such ocular lesions. The
    authors suggest that F-344 rats are unsuitable for ocular toxicity
    studies (Lee et al., 1990).

         Mice exposed to 63 000 mg/m3 (48 000 ppm) methanol for
    3.5-4 h/day up to a cumulative total of 24 h were in a state of
    narcosis but survived, whereas mice became comatose when exposed to
    71 000 mg/m3 (54 000 ppm) for 54 h (Pavlenko, 1972).

         Rabbits exposed by inhalation to 61 mg/m3 (46.6 ppm) methanol
    for 6 months (duration of exposure/day not reported) exhibited
    ultrastructural changes in the photoreceptor cells of the retina and
    Müller fibres (Vendilo et al., 1971).

         Two male dogs exposed to methanol vapour in air at 13 000 mg/m3
    (10 000 ppm) for about 3 min in each of 8-h periods/day for 100
    consecutive days, exhibited no symptoms, unusual behaviour or visual
    toxicity. Methanol levels in blood measured at weekly intervals showed
    median values of 65 and 140 mg/litre blood (Sayers et al., 1944).

         In contrast to many studies of methanol toxicity that reported no
    effect of low doses, two Russian studies (Chao, 1959; Ubaidullaev,
    1966) reported evidence of neurobehavioural toxicity at low doses as
    shown by altered chronaximetry (chronaximetry is the ratio of the
    minimum time necessary for a stimulus of twice the absolute threshold
    intensity to evoke a response measured as muscle contractions in
    response to an electric current applied to an animal's hind leg).
    Normally, the flexor chronaxia is shorter than the extensor chronaxia,
    and their ratio is stated to be relatively stable.

         Chao (1959) reported that the average chronaxia ratio for rats
    exposed in the high-dose group (49.77 mg/m3) for 12 h/day, 5
    days/week for 3 months, differed significantly from that in the
    control group of animals at week 8 of exposure. The average chronaxia
    ratio returned to normal during the recovery period and the effects in
    the low-dose group (1.77 mg/m3) were insignificant. Histopathological
    changes found in the high-dose group, but not in the low-dose group,
    included poorly defined changes in the mucous membranes of the trachea
    and bronchi, hyperplasia of the submucosa of the trachea, slight
    lymphoid infiltration, swelling and hypertrophy of the muscle layer of
    arteries, slight degenerative changes to the liver and changes in the
    neurons of the cerebral cortex (Chao, 1959).Ubaidullaev (1966)
    reported that male rats exposed continuously for 90 days to a
    concentration of 5.3 mg/m3 (4 ppm) of methanol vapour, exhibited
    changes in chronaxia ratio between antagonistic muscles, in whole
    blood cholinesterase activity, in urinary excretion of coproporphyrin
    and in albumin-globulin ratio of the serum. Male rats exposed to
    0.57 mg/m3 (0.4 ppm) of methanol vapour continuously for 90 days
    showed no changes.

         It should be noted, however, that an analysis of these studies
    by Kavet & Nauss (1990) indicated that, due to flaws in the study
    designs, these studies do not provide adequate evidence of an
    association between neurobehavioural effects and low-level exposure to
    methanol. Both studies were limited by the use of small numbers of
    animals per dose group, as well as insufficient reporting of
    experimental methods, study results and statistical analysis. Kavet &
    Nauss (1990) also stated that the biological significance of changes
    in the chronaxia ratio is uncertain.

         Male and female cynomolgus monkeys  (Macaca fascicularis), three
    per sex per dose, that were exposed to 650, 2600 and 6500 mg/m3 (500,
    2000 and 5000 ppm) methanol for 6 h/day, 5 days/week for 4 weeks
    showed no upper respiratory tract irritation. Neither gross,
    microscopic nor ophthalmoscopic examinations disclosed any ocular
    effects in the monkeys exposed to 6500 mg/m3 (5000 ppm) (Andrews et
    al., 1987).

    7.3  Long-term studies

         In two 12-month chronic inhalation studies, Fischer-344 rats
    (20 female and 20 male animals per group) and B6C3F1 mice (30/30
    female/male) were exposed to 13, 130 and 1300 mg/m3 (10, 100 and 
    1000 ppm) of methanol to examine toxic effects unrelated to 
    carcinogenesis. A concentration of 130 mg/m3 (100 ppm) was found 
    to be the NOEL in both species. At the highest exposure, a slightly 
    reduced weight gain in male and female rats and a small but not 
    significant increase in the relative liver and spleen weight in female 
    rats were observed. In mice, the body weight was significantly higher 
    in the highest exposure groups in both males (after 6 months) and in 
    females (after 9 months). In addition, the incidence and degree of 
    fatty degeneration of hepatocytes was significantly enhanced in the 
    highest exposure groups of mice. However, this could have been due to 
    the higher incidence of fatty degeneration in mice of great body weight. 
    Clinical laboratory results did not show any changes attributable to
    methanol (NEDO, 1987; Katoh, 1989).

         Monkeys  (Macaca fascicularis) (eight females per group) were
    exposed to 13, 130 or 1300 mg/m3 for periods of 22 h/day for up to 29
    months. Body weight, haematological and pathological examinations did
    not reveal any dose-dependent effects except for hyperplasia of
    reactive astroglias in the nervous system. However, this effect was
    not correlated to dose or exposure time and was found to be reversible
    in a recovery test (NEDO, 1982).

    7.4  Skin and eye irritation; sensitization

         In a modified Magnusson-Kligman maximization test with 10 female
    guinea-pigs no sensitization was found after intracutaneous or
    percutaneous induction and challenge with 50% methanol solution in
    distilled water or with Freud's adjuvant. No skin irritation effects
    were observed. In a parallel test, a 25% formaldehyde solution was

    applied in order to test for possible sensitizing effects resulting
    from the metabolic transformation of methanol to formaldehyde. Again
    negative test results were seen (BASF, 1979).

         New Zealand White albino rabbits treated by application of 100 µl
    methanol into the lower conjunctival sac according to OECD test
    guidelines and Draize scoring criteria exhibited the following mean
    scores of conjunctivitis, chemosis, iritis and corneal opacity after
    1, 4, 24, 48 and 72 h (Jacobs, 1990).


    Time after application (h):      1     4     24    48    72

    Mean score of conjunctivitis:   0.89  2.00  1.67  2.28  2.22
    Mean score of chemosis:         2.00  2.00  0.67  1.00  0.50
    Mean score of irititis:         0.33  1.00  1.00  0.50  0.33
    Mean score of corneal opacity:  0.00  0.00  0.50  0.50  0.67

         This demonstrates that methanol causes significant conjunctivitis
    under the conditions of this test. Initial oedema (chemosis) seen up
    to 4 h had decreased significantly by 72 h. Other ocular lesions were
    much less significant.

    7.5  Reproductive toxicity, embryotoxicity and teratogenicity

    7.5.1  Reproductive toxicity (effects on fertility)

         When male Sprague-Dawley rats were exposed for 8 h/day, 5
    days/week to airborne methanol concentrations of 260, 2600 or 
    13 999 mg/m3 (200, 2000 or 10 000 ppm) for 1, 2, 4 or 6 weeks, 
    significantly decreased levels of circulating free testosterone were 
    found among rats exposed to 260 mg/m3 for 2 and 6 weeks and to 
    2600 mg/m3 for 6 weeks. However, the 13 000 mg/m3 group showed 
    no change. Significant changes in luteinizing hormone (LH) were found 
    after 6 weeks in animals exposed to 13 000 mg/m3, but no changes 
    in follicle-stimulating hormone (FSH) were observed at the various 
    exposure levels (Cameron et al., 1984). Sprague-Dawley rats exposed to 
    260 mg/m3 for 6 h for either 1 day or 1 week showed significant 
    depression (59%) in serum testosterone immediately after the first 
    exposure, but not after 1 week of daily 6-h exposures (Cameron et
    al., 1985).

         In a subsequent study groups of 10 male Long-Evans hooded rats,
    60 days of age and acclimatized (or not) to handling, were exposed to
    0, 260, 6500 or 13 000 mg/m3 (0, 200, 5000 or 10 000 ppm) methanol
    for 6 h and killed either immediately on removal from the chambers or
    18 h later. Similar groups of rats, acclimatized to handling or not,
    were exposed to 6500 mg/m3 during 1, 3 or 6 h and killed immediately.
    Serum testosterone levels were not significantly increased at 6 or
    24 h in acclimatized rats, but levels were increased in non-

    acclimatized rats exposed to 6500 mg/m3 and killed after 24 h. The
    serum luteinizing hormone (LH) level was increased in acclimatized
    rats exposed to 13 500 mg/m3 and killed at 6 and 24 h but the LH
    level was reduced in non-acclimatized rats exposed to 6500 or
    13 000 mg/m3 at 6 h but not 24 h. This experiment did not confirm the
    earlier report that exposure to 260 mg/m3 for 6 h reduced serum
    testosterone levels. In the second experiment serum LH and
    testosterone levels did not differ at any time point between controls
    and rats exposed to 6500 mg/m3 (Cooper et al.,1992). Methanol
    inhalation at 260 mg/m3 for 8 h/day for up to 6 weeks did not reduce
    serum testosterone levels in normal Sprague-Dawley rats (Lee et al.,
    1991). In Long-Evans rats fed either control or folate-reduced diets
    and exposed to 1040 mg/m3 for 20 h/day for 13 weeks, no adverse
    effect on testicular morphology was observed with 10-month-old rats
    fed either diet. A greater incidence of testicular degeneration was
    however noted with 18-month-old rats given the folate-reduced diet,
    suggesting that methanol potentially accelerates the age-related
    degeneration of the testes (Lee et al., 1991).

    7.5.2  Developmental toxicity

         The inhalation of methanol by pregnant rodents throughout the
    period of embryogenesis to high atmospheric concentrations (6500 to
    26 000 mg/m3; 5000 to 20 000 ppm) impaired neural tube closure and
    induced a wide range of concentration-dependent teratogenic and
    embryolethal effects (Nelson et al., 1985; Rogers et al., 1993; Bolon
    et al., 1993, 1994). In these studies, significant increase in the
    incidence of exencephaly were observed following maternal methanol
    exposures of > 6500 mg/m3 (> 5000 ppm) in mice, while similar
    effects were observed in rats following exposures of > 13 000 mg/m3
    (> 10 000 ppm), indicating that mice are more sensitive than rats to
    the embryotoxic effects of methanol.

         Pregnant Sprague-Dawley rats were given by inhalation for 7 h/day
    either 6500 or 13 000 mg/m3 (5000, or 10 000 ppm) methanol on days
    1-19 of gestation, or 26 000 mg/m3 (20 000 ppm) methanol on days 7-15
    of gestation. The blood levels of methanol in the 26 000 mg/m3 group
    ranged from 8.34 to 9.26 mg/ml after 1 day of exposure and from 4.84
    to 6.00 mg/ml after 10 days of exposure. Methanol induced a dose-
    related decrease in fetal weights and an increase in malformations.
    The highest methanol concentration (26 000 mg/m3) produced slight
    maternal toxicity (slightly unsteady gait) after the initial days
    of exposure, and a high incidence of congenital malformations
    (p < 0.001), predominantly extra or rudimentary cervical ribs and
    urinary or cardiovascular defects. Similar malformations were found in
    the groups exposed to 13 000 mg/m3 but the incidence was not
    significantly different from that of the controls. No increase in
    malformations was found in the group exposed to 6500 mg/m3 
    (5000 ppm), which was suggested to be a no-observed-effect level for 
    this test system (Nelson et al., 1985).

         Pregnant CD-1 mice were treated by inhalation to 1300, 2600,
    6500, 10 000, 13 000 or 19 500 mg/m3 (1000, 2000, 5000, 7500, 10 000
    or 15 000 ppm) of methanol for 7 h/day on days 6-15 of pregnancy.
    Significant increases were observed in the incidence of exencephaly
    and cleft palate at 6500 mg/m3 or more. Increased embryo/fetal death
    was found at exposures of 10 000 mg/m3 or more, including an
    increasing incidence of full-litter resorptions. Reduced fetal weight
    was found at 13 000 mg/m3 or more. A dose-related increase in
    cervical vertebrae was significant at 2600 mg/m3 or more. The NOAEL
    for the developmental toxicity was suggested to be 1300 mg/m3 (1000
    ppm) methanol in this test system. There was no evidence of maternal
    toxicity at methanol exposures below 10 000 mg/m3 (Rogers et al.,

         A spectrum of cephalic neural tube defects was found in near-term
    (gestation day 17) CD-1 mouse fetuses following maternal inhalation of
    methanol at high concentration (19 500 mg/m3; 15 000 ppm) for 6 h/day
    during neurulation (gestation days 7-9). Dysraphism, chiefly
    exencephaly, occurred in 15% of the fetuses, usually in association
    with reduction or absence of multiple bones in the craniofacial
    skeleton and ocular anomalies (prematurely open eyelids, cataracts,
    retinal folds).  Exposure to a high concentration of methanol 
    (19 500 mg/m3) injured the multiple stem populations in the  
    neuralating mouse embryo. Significant neural pathology may remain in 
    older conceptuses even in the absence of gross lesions (Bolon et al.,

         Transient neurological signs and reduced body weights were found
    in up to 20% of CD-1 dams exposed to 19 500 mg/m3 (15 000 ppm)
    methanol 6 h/day throughout organogenesis (gestational days 6-15).
    Near-term fetuses revealed embryotoxicity (increased resorptions,
    reduced fetal weights and/or fetal malformations) at 13 000 and 
    19 500 mg/m3 (10 000 and 15 000 ppm) methanol while 3-day exposures 
    at 6500 mg/m3 (5000 ppm) for 6 h/day yielded no observable adverse 
    effects (Bolan et al., 1993). In the studies of Bolon et al. (1993, 
    1994), terata included neural and ocular defects, cleft palate,
    hydronephrosis, deformed tails and limb (paw and digit) anomalies.
    Neural tube defects and ocular lesions occurred after methanol
    inhalation by pregnant CD-1 mice between gestational days 7 and 9,
    while limb anomalies were induced only during gestational days 9-11;
    cleft palate and hydronephrosis were observed after exposure during
    either period. The spectrum of teratogenic effects depended upon both
    the stage of embryonic development and the number of methanol

         Long-Evans rats administered single oral doses of 1.3, 2.6 or
    5.2 ml methanol/kg by gavage on day 10 of gestation, exhibited dose-
    related anomalies, e.g., undescended testes and eye defects
    (exophthalmia and anophthalmia) in the offspring. At the methanol dose
    of 5.2 ml/kg, the maternal weight loss was > 10%, which was the only
    clinical toxic manifestation/histopathological change noted for the
    dams. A significant decrease in fetal body weight (11-21%) was
    associated with oral ingestion of methanol in the dams. Methanol given

    acutely can produce anomalies in the offspring where there are no
    apparent maternal toxic responses (Youssef et al., 1991).

         Methanol was shown to impair uterine decidualization during early
    pregnancy in Holtzman rats administered 1.6, 2.4 or 3.2 g methanol/kg
    per day by gavage during days 1-8. Reductions in pregnant uterine and
    implantation site weights seen on day 9 were the result of methanol
    impedance of normal uterine decidualization as demonstrated by effects
    on decidual cell response technique. Methanol (3.2 g/kg per day)
    produced a non-specific maternal toxicity (reduction in body weight)
    by day 9, but no effect on days 11 or 20 on embryo and fetal survival
    or development were found (Cummings, 1993).

         When pregnant CD-1 mice were gavaged orally with 4 g methanol/kg,
    the incidences of fetal resorption, external defects (including cleft
    palate) and reduced fetal weight were similar to those observed in the
    13 000 mg/m3 (10 000 ppm) inhalation exposure group. Cleft palate
    (43.5% per litter) and exencephaly (29% per litter) were the
    predominant external defects seen following methanol exposure by oral
    gavage. Methanol blood level in the gavage study was 4 mg/ml, which
    was reportedly similar to the blood level at the 13 000 mg/m3
    inhalation exposure group (see above) (Rogers et al., 1993).

         No effects on reproductive performance were reported in a two-
    generation reproductive study in F-344 rats administered 13, 130 or
    1300 mg/m3 (10, 100 or 1000 ppm) methanol by inhalation for
    18-20 h/day. A statistically significant decrease in brain weight was
    found at the 1300 mg/m3 level in 3-, 6- and 8-week-old pups of the
    F1 generation. In the F2 generation reduced brain thymus and
    hypophysis weight was observed. (NEDO, 1987; Katoh, 1989).Teratology
    studies with Sprague-Dawley rats exposed to 260, 1300 or 6500 mg/m3
    (200, 1000 or 5000 ppm) methanol by inhalation for 22 h/day during
    gestational days 7-17 revealed significant weight decreases in brain,
    thyroid and thymus of the offspring resulting from maternal exposure
    to 6500 mg/m3. However, no abnormal changes were detected
    histopathologically. Evidence of maternal toxicity was found at this
    level of exposure and toxic effects to fetuses were reported,
    including death. No effects were found at 1300 kg/m3 (NEDO, 1987;
    Katoh, 1989).

         A pilot developmental toxicity study was conducted by Ryan et al.
    (1994) to assess the utility of the folic-acid-deficient rat model, a
    model that would be sensitive to methanol and potentially reflective
    of the human risk/response. Methanol was administered in drinking-
    water on days 6-15 of gestation at concentrations of 0.5, 1.0 and 2.0%
    to three groups of 7 to 9 sperm-positive Long-Evans rats. The average
    blood levels were given as 0.21, 0.26 and 0.67 mg/ml, respectively. A
    dose-dependant increase in the incidence of maternal and developmental
    effects was observed. For both end-points the NOEL was assumed to be
    less than 0.5% methanol in drinking-water, corresponding to a blood
    level of 0.21 mg/ml.

         Weiss et al. (1996) studied developmental neurotoxicity of
    pregnant Long-Evans rats and their newborn offspring exposed to 
    5900 mg/m3 (4500 ppm) of methanol by inhalation for 6 h daily, 
    beginning on gestation day 6, with both dams and pups then being
    exposed through postnatal day 21. Although findings suggested
    significant functional consequences in rats resulting from this
    exposure, these consequences were considered subtle in character.
    Exposure to 5900 mg methanol/m3 did not affect the suckling time
    and conditioned olfactory aversion test of newborn rats. Methanol-
    exposed newborn pups were less active on postnatal day 18 and more
    active on postnatal day 25 than control newborn pups (motor activity
    test). The study found only isolated positive results that were small
    and variable. The two adult assays, the fixed-ratio wheel-running
    test and the stochastic discrimination test, yielded evidence of a
    significant methanol effect.

         No evidence of brain damage emerged on the basis of neuro-
    pathology, although differences in neural cell adhesion molecules
    (NCAMs) arising from methanol exposure were observed in neonatal
    cerebella (Weiss et al., 1996). Methanol treatment caused a decrease
    in expression in both NCAM 140 and NCAM 180.

         Further elaboration of the effects of perinatal exposure on NCAM
    in Long-Evans rats exposed to 5900 mg/m3 (4500 ppm) methanol vapour
    for 6 h daily (beginning on gestation day 6 with dams and pups then
    exposed until postnatal day 21) were described by Stern et al. (1996).
    Blood methanol concentrations from samples obtained immediately
    following a 6-h exposure reached approximately 500-800 µg/ml in the
    dams during gestation, and lactation average concentrations for pups
    attained levels about twice those of the dams. Light-microscopic
    analysis showed no significant abnormalities in the brains of the
    methanol-treated animals. However, assays of NCAM in the brains of
    pups sacrificed on postnatal day 4 showed staining for both the 140
    and the 180 kDa isoforms to be less intense in the cerebellum of
    exposed animals. NCAM differences were not apparent in animals
    sacrificed after their final exposure. NCAM 140 is the primary isoform
    expressed during the stages of neuronal migration and NCAM 180 is
    expressed during synaptogenesis where it is critical to neuronal
    plasticity, learning and memory. NCAMs are developmentally regulated
    glycoproteins that serve critical roles in the formation and
    maintenance of the nervous system (Stern et al., 1996).

    7.5.3  Behavioural effects

         Neonatal behavioural toxicity was reported in studies involving
    two groups of primigravid Long-Evans rats given drinking solutions of
    2% methanol either on gestational days 15-17 or 17-19, with the
    average daily intake on these days amounting to 2.5 g methanol/kg.
    Lack of maternal toxicity was indicated by measurements of weight
    gain, gestational duration or daily fluid intake. Litter size, birth
    weight and infant mortality did not differ between the two treatment
    groups and the control. Pups from methanol-treated rats required
    longer periods than controls to begin suckling on postnatal day 1. On

    postnatal day 10, they required more time to locate nesting material
    from their home cages, suggesting that prenatal methanol exposure
    induced behavioural abnormalities early in life, unaccompanied by
    overt toxicity (Infurna & Weiss, 1986).

         Following inhalation exposure of Long-Evans rats to 19 500 mg/m3
    (15 000 ppm) methanol for 7 h/day on gestational days 7-19, maternal
    blood levels decreased significantly from 3.8 mg/litre on the first
    day of exposure to 3.1 mg/litre on the 12th day of exposure. Methanol
    transiently reduced maternal body weight by 4-7% on gestational days
    8-10 and offspring body weight by 5% on post-natal days 1-3. Motor
    activity, olfactory learning, behavioural thermoregulation, T-maze
    learning, acoustic startle response, pubertal landmarks and passive
    avoidance tests performed at the end of the exposure period failed to
    reveal significant effects. Prenatal exposure to high levels of
    inhaled methanol appeared to have little effect beyond post-natal day
    3 in this series of tests (Stanton et al., 1995).

    7.5.4  In vitro studies

         Methanol is developmentally toxic to both mouse (CD-1) and rat
    (Sprague-Dawley) embryos during organogenesis in whole embryo culture
    (WEC), a technique which removes the confounding maternal influences
    (Andrews et al., 1993). Comparable developmental stages of CD-1 mouse
    and Sprague-Dawley rat embryos were exposed to methanol (0-16 mg/ml
    for rat and 0-8 mg/ml for mouse embryos) for 24 h. Rat embryos were
    cultured for an additional 24 h without methanol in the medium, having
    a total culture time of 48 h. Concentration-dependent decreases in
    somite number, head length and developmental score occurred in both
    species, with significant effects in the rat at > 8 mg/ml and in
    the mouse at > 4 mg/ml (Andrews et al., 1993).

         In studies of 8-day mouse embryos cultured in methanol,
    concentrations greater than 2 mg methanol/ml caused a significant
    decrease in developmental score and crown-rump length; the 8 mg/ml
    group also suffered 80% embryolethality (Andrews et al., 1993). Mouse
    embryos were affected at methanol concentrations that were not
    dysmorphogenic or embryotoxic in the rat following teratogenic
     in vivo exposures (Rogers et al, 1993), suggesting that the higher
    sensitivity of the mouse was due, at least in part, to the greater
    intrinsic embryonal sensitivity of this species to methanol (Andrews
    et al., 1993).

         Depending on the concentration and duration of methanol exposure
    (0-20 mg/ml for 6 h, 12 h, or 1 or 4 days) on embryonic CD-1 mouse
    palate in serum-free organ culture, the medial epithelium either
    degenerated completely or remained intact in unfused palates (either
    condition would interfere with fusion) (Abbott et al., 1994). Cellular
    proliferation appeared to be a specific and sensitive target for
    methanol as craniofacial tissues responded to methanol with reduction
    in DNA content at an exposure that did not effect total protein.
    However both DNA and protein levels decreased with increasing exposure

    to methanol. Methanol selectively altered the morphological fate of
    the medial palatal epithelium cells and the specific effect on cell
    survival was exposure dependent (Abbott et al., 1994).

    7.6  Mutagenicity and related end-points

    7.6.1  In vitro studies

         The structure of methanol (by analogy with ethanol) does not
    suggest that it would be genotoxic.

         Methanol gave negative results when tested in  Salmonella
     typhimurium plate incorporation assays with or without metabolic
    activation using strains TA98, TA100, TA1535, TA1537 and TA1538
    (Simmon et al., 1977). It was also negative in the presence or absence
    of metabolic activation in strains TA1535, TA100, TA1538, TA98 and
    TA1537 (De Flora et al., 1984) and in a DNA repair test in  E. coli
    using strains WP 2, WP 67 and CM 871 in the presence or absence of
    metabolic activation (De Flora et al., 1984).

         Methanol (6.0% v/v) induced 3.02% chromosomal malsegregation in
     Aspergillus nidulans diploid strain P1 (Crebelli et al., 1989). The
    result was statistically significant at two concentrations and a dose-
    response relationship was evident.

         Methanol was negative for gene mutation at the ade 6 locus
    in the yeast  Schizosaccharomyces pombe with or without the
    postmitochondrial fraction from mouse liver (Abbondandolo et al.,
    1980). It was also negative in a mutagenicity test for n+1 aneuploidy
    arising from meiotic disfunction of linkage group I in the fungus
     Neurospora crassa (Griffiths, 1981).

         Methanol did not induce sister chromatid exchanges (SCEs) in
    Chinese hamster cells  in vitro during treatment for 8 days to a
    final concentration of 0.1% (v/v) (Obe & Ristow, 1977). Only in the
    presence of S-9 mix and methanol (7.9 mg/ml) was there a significant
    increase in the mutation frequency in L5178Y mouse lymphoma cells
    (McGregor et al., 1985), possibly because this assay detects
    chromosome damage as well as gene mutation.Methanol was negative in
    two  in vitro tests for cell transformation: the Syrian hamster
    embryo cell (SHE) clonal system (Pienta et al., 1977) and the Rausher
    leukaemia virus-infected rat embryo cell (RLV/RE system) (Heidelberger
    et al., 1983).

         Addition of methanol (or ethanol) to unleaded gasoline as a fuel
    extender did not appear to significantly alter the genetic toxicity of
    particulate exhaust particles when tested in  S. typhimurium strains
    TA100, TA98, TA98 NR, and TA98 DNPR with S-9 activation. In all the
    alcohol-blended fuel tests, the mass of particle-associated organics
    emitted from the exhaust was lower than that observed during the
    control tests using gasoline alone (Clark et al., 1983).

    7.6.2  In vivo studies

         No increased frequencies of micronuclei in blood cells, of
    SCEs, chromosome aberrations or micronuclei in lung cells, or of
    synaptonemal complex damage in spermatocytes were found in mice
    exposed by inhalation to 1050 or 5200 mg/m3 (800 or 4000 ppm)
    methanol for 5 days (Campbell et al., 1991).

         Urine from mice orally administered five daily doses of methanol
    (5 g/kg total) showed no mutagenic activity, and no increase in the
    incidence of abnormal sperm was reported (Chang et al., 1983). Oral
    administration of 1 g methanol/kg to mice increased the incidence of
    chromosomal aberrations, particularly aneuploidy and SCEs, as well as
    the incidence of micronuclei in polychromatic erythrocytes (Pereira et
    al., 1982).

         The oral administration of 14C-labelled methanol to rats
    resulted in covalent binding to haemoglobin, with binding exhibiting a
    linear dose relationship between 10 and 100 µmol/kg (Pereira et al.,

         B6C3F1 mice treated with five daily oral doses of 1 g
    methanol/kg exhibited abnormal (banana type) sperm morphology. The
    biological significance of these changes is unknown (Ward et al.,
    1984). It should be noted that the above results, namely altered sperm
    (Ward et al., 1984) and haemoglobin binding (Pereira et al., 1982) are
    end-points not generally used for genotoxic evaluation and their
    assessment in terms of mutagenicity is unclear.

         There is some evidence that bone marrow cytogenetic analysis
    indicated a dose-related response for structural aberrations,
    especially centric fusions in mice treated with three daily
    intraperitoneal methanol doses of between 75-300 mg/kg total dose
    (Chang et al., 1983).

          In vitro and  in vivo mutagenicity studies on methanol, i.e.,
    the Ames test, somatic mutation assay in CH-V79 cells, chromosome
    aberrations, SCEs and the micronucleus test in mice conducted by NEDO
    (1987; Katoh, 1989), were all reported to be negative.

    7.7  Carcinogenicity

         There have been no studies reported in the peer-reviewed
    literature on the potential carcinogenicity of methanol  per se in
    laboratory animals.

         The New Energy Development Organization (NEDO) in Japan reported
    carcinogenicity studies in which B6C3F1 mice and Fischer-344 rats of
    both sexes were exposed by inhalation to 13, 130 or 1300 mg/m3 (10,
    100 and 1000 ppm) methanol for 20 h/day for 18 and 24 months,
    respectively (NEDO, 1987; Katoh, 1989). No evidence of carcinogenicity
    was found in either species. High-dosed animals had a higher, but not

    statistically significant, incidence of papillary adenomas than
    controls , and histopathological examination suggested that these
    changes were between non-neoplastic and neoplastic changes.
    Additionally, seven cases of adrenal pheochromocytoma were found in
    high-dose animals compared to one case in controls. This observation
    was not statistically significant according to the Fisher exact test
    (Katoh, 1989).

         It is unlikely that methanol is carcinogenic to mouse skin. In an
    experiment using four strains of female mice (Balb/c, Sencar, CD-1 and
    Swiss) to study  N-nitrosomethylurea carcinogenesis, methanol was
    used as a solvent control. Four groups of 20 mice of each strain
    received 25 µl methanol twice weekly for 50 weeks followed by
    observation for lifespan. Only one skin tumour was observed among the
    80 control animals (Lijinsky et al., 1991).

    7.8  Special studies

    7.8.1  Effects on hepatocytes

         When Garcia & Van Zandt (1969) administered repeated doses of 3
    to 6 g/kg by gavage to rhesus monkeys  (Macaca mulata) for 3-20
    weeks, average serum levels of methanol of 4750 mg/litre were attained
    within a few hours. Animals were killed at the end of treatment and
    livers examined histologically. Hepatocytes showed nucleolar
    segregation (zoning of nucleus), hyperplasia of endoplasmic reticulum
    and swelling of mitochondria. These changes were also found in one
    monkey sacrificed 12 weeks after the end of treatment.

    7.8.2  Toxic interactions

         Inhaled methanol potentiated the hepatotoxicity produced by
    carbon tetrachloride in adult male F-344 rats. Rats were exposed to
    methanol (0 or 13 000 mg/m3) 10000 ppm for 6 h, then treated 24 h
    later with oral CCl4 (0.075 ml/kg). CCl4 alone produced a low level
    of hepatotoxicity within 3 days. Methanol plus CCl4 resulted in
    marked increases in serum aspartate aminotransferase and alanine
    aminotransferase that lasted for 7 days. Methanol also exacerbated the
    histological evidence of CCl4-induced centrilobular degeneration and
    necrosis (Simmons et al., 1995).

         Methanol exposure by inhalation induced cytochrome P4502E1
    (CYP2E1), which appeared to be the principal toxicokinetic mechanism
    underlying methanol potentiation of carbon tetrachloride
    hepatotoxicity (Allis et al., 1996).

         When dichloromethane (DCM) is metabolized carbon monoxide is
    formed, leading to increased carboxyhaemoglobin (COHb) levels in
    blood. Pankow & Jagielki (1993) found that in rats pretreated with
    methanol, methanol doses of 790-6330 mg/kg (24.7-198 mmol/kg)
    stimulated increased metabolism of DCM, as seen by further increases
    in COHb levels. When methanol was administered simultaneously with

    DCM, a decrease in COHb formation was seen at methanol doses of 4736
    to 7900 mg/kg (148-247 mmol/kg) but not at 3162 mg/kg (98.8 mmol/kg).
    Thus methanol can interact with DCM metabolism both by induction and
    by competitive inhibition, the latter only at very high doses.

         Poon et al. (1994) reported no significant interactive effects in
    young Sprague-Dawley rats exposed to vapours of methanol/toluene
    (400/110 mg/m3; 400/1100 mg/m3; 4000/110 mg/m3 and 4000/1100 mg/m3)
    for 6 h/day, 5 days/week for 4 weeks. Exposure to methanol (400 to
    4000 mg/m3) and to toluene (110 mg/m3 to 1100 mg/m3) or to a mixture
    of both produced mild biochemical effects and histological changes in
    the thyroid (moderate reduction in follicle size in the thyroids) and
    nasal passages.

         The biochemical, haematological and histological effects on
    Sprague-Dawley rats after exposure to methanol (3000 mg/m3;
    2500 ppm), gasoline (3200 ppm) and methanol/gasoline (2500/3200 ppm)
    vapour 6 h/day for 4 weeks were examined by Poon et al. (1995).
    Gasoline was largely responsible for the adverse effects, the most
    significant of which included depression in weight gain in the males,
    increased liver weight and hepatic microsomal enzyme activities in
    both sexes, and suppression of uterine eosinophilia. No apparent
    interactive effects between methanol and gasoline were observed.

    7.8.3  Studies with exhaust emissions from methanol-fuelled engines

         There are few data related to the effects of emissions from
    methanol-fuelled engines. Since most such fuels will contain a
    proportion of gasoline and other additives and the emissions will be
    complex, the interpretation of these data in relation to methanol
    toxicity is complicated.

         Maejima et al. (1992, 1993 and 1994) studied the effects of
    emissions from M-85 methanol-fuelled engines (methanol with 15%
    gasoline), without a catalyst, on Fischer-344 rats for periods up to
    12 weeks. The exhaust contained significant amounts of carbon monoxide
    (89.9 ppm), oxides of nitrogen (22.9 ppm), formaldehyde (2.3 ppm) and
    methanol (8.1 ppm). The effects observed were considered to be
    primarily related to formaldehyde. No increase in plasma methanol or
    formic acid was detected.

    7.9  Mechanism of ocular toxicity

         Formic acid, the toxic metabolite of methanol, has been
    hypothesized to produce retinal and optic nerve toxicity by disrupting
    mitochondrial energy production (Fig. 1) (Martin-Amat et al., 1977;
    Sharpe et al., 1982). It has been shown  in vitro to inhibit the
    activity of cytochrome oxidase, a vital component of the mitochondrial
    electron transport chain involved in ATP synthesis (Nicholls, 1975).
    Inhibition occurs subsequent to the binding of formic acid to the
    ferric haem iron of cytochrome oxidase, and the apparent inhibition
    constant is between 5 and 30 mM (Nicholls, 1975). Concentrations of

    formate present in the blood and tissues of methanol-intoxicated
    humans, non-human primates and rodent models of methanol-intoxication
    are within this range (Martin-Amat et al., 1977; Sejersted et al.,
    1983; Eells, 1991).

         Studies conducted in methanol-sensitive rodent models have
    revealed abnormalities in retinal and optic nerve function and
    morphology, consistent with the hypothesis that formate acts as a
    mitochondrial toxin (Fig. 2). In these animal models, formate
    oxidation is selectively inhibited by dietary (Lee et al., 1994) or
    chemical (Eells et al., 1981) depletion of folate coenzymes, thus
    allowing formate to accumulate to toxic concentrations following
    methanol administration. Methanol-intoxicated rats developed formic
    acidaemia, metabolic acidosis and visual toxicity analogous to the
    human methanol poisoning syndrome (Eells, 1991; Murray et al., 1991;
    Lee et al., 1994a,b).

         Sixty hours after the administration of the first dose of
    methanol, blood formate values ranged from 8-20 mM with blood hydrogen
    carbonate values in the range of 5-12 mEq/litre and blood pH values of
    6.83-7.08. Similar blood formate concentrations, hydrogen carbonate
    levels and pH values were reported in methanol-intoxicated monkeys
    (Martin-Amat et al., 1977) and in severe cases of human methanol
    poisoning (McMartin et al., 1980a; Sejersted et al., 1983; Jacobsen et
    al., 1988).

         Visual dysfunction was measured as reduction in the flash evoked
    cortical potential (FEP) and electroretinogram (ERG). The FEP is a
    measure of the functional integrity of the primary visual pathway from
    the retina to the visual cortex and the ERG is a global measure of
    retinal function in response to illumination (Creel et al., 1970;
    Dowling, 1987). The FEP was progressively diminished in methanol-
    intoxicated rats, indicative of a disruption of neuronal conduction
    along the primary visual pathway from the retina to the visual cortex
    (Eells, 1991). ERG analysis in methanol-intoxicated rats revealed a
    significant early deficit in  b-wave amplitude, followed by a
    temporally delayed lesser reduction in  a-wave amplitude (Murray et
    al., 1991). The  b-wave of the ERG is generated by depolarization of
    the Muller glial cells and reflects synaptic activity at the level of
    the bipolar cells (Dowling, 1987). The  b-wave of the ERG is
    extremely sensitive to conditions that interfere with retinal energy
    metabolism and is reduced or abolished following brief ischaemia or
    the administration of metabolic poisons (Bresnick, 1989; Dowling,
    1987). Both FEP and ERG alterations occurred at the same time as
    accumulation of blood formate, indicative of a causal relationship
    between formate-induced metabolic and visual disturbances. Similar ERG
    reductions have been reported in methanol-intoxicated primates
    (Ingemansson, 1983) and in human methanol intoxication (Ruedemann,
    1962; Murray et al., 1991).

         In addition to neurofunctional changes, bioenergetic and
    morphological alterations indicative of formate-induced disruption of
    retinal energy metabolism have been documented in methanol-intoxicated
    rats (Murray et al., 1991; Eells et al., 1996; Garner et al.,
    1995a,b). Morphological studies, coupled with cytochrome oxidase
    histochemistry, revealed generalized retinal oedema, photoreceptor and
    RPE vacuolation, mitochondrial swelling and a reduction in cytochrome
    oxidase activity in photoreceptor mitochondria from methanol-
    intoxicated rats (Murray et al., 1991; Eells et al., 1995, 1996). The
    most striking structural alterations observed in the retinas of
    methanol-intoxicated rats were vacuolation and mitochondrial swelling
    in inner segments of the photoreceptor cells (Murray et al., 1991).
    Photoreceptor mitochondria from methanol-intoxicated rats were swollen
    and expanded to disrupted cristae and showed no evidence of cytochrome
    oxidase reaction product. In contrast, photoreceptor mitochondria from
    control animals showed normal morphology with well-defined cristae and
    were moderately reactive for cytochrome oxidase reaction product.
    These findings are consistent with disruption of ionic homoeostasis in
    the photoreceptors, secondary to inhibition of mitochondrial function.
    Biochemical measurements also showed a significant reduction in
    retinal and brain cytochrome oxidase activity and ATP concentrations
    in methanol-intoxicated rats relative to control animals (Eells et
    al., 1995). Surprisingly, no differences from control values were
    observed in hepatic, renal or cardiac cytochrome oxidase activity or
    ATP concentrations in methanol-intoxicated rats. The reduction in
    retinal function, inhibition of retinal, optic nerve and brain
    cytochrome oxidase activity, depletion of retinal and brain ATP
    concentrations, and mitochondrial disruption produced in methanol-
    intoxicated rats are consistent with the hypothesis that formate acts
    as a mitochondrial toxin with selectivity for the retina and brain.

         Studies by Eells et al. (1996) compared the effects on retinal
    function and structure of rapidly increasing formate concentrations
    typical of acute methanol intoxication with low-level plateau formate
    concentrations more likely to be generated by subacute or chronic
    methanol exposure. Methanol-intoxicated rats that accumulated formate
    concentrations of 8-15 mM developed metabolic acidosis, retinal
    dysfunction, and retinal histopathological changes. Retinal
    dysfunction was measured as reductions in the  a- and  b-waves of
    the electroretinogram that occurred at the same time as blood formate
    accumulation. Histopathological studies revealed vacuolation in the
    retinal pigment epithelium and photoreceptor inner segments. Rats
    exposed to formate concentrations ranging from 4 to 6 mM for 48 h
    showed evidence of retinal dysfunction in the absence of metabolic
    acidosis and retinal histopathology. These data indicated that
    formate-induced retinal dysfunction in methanol-intoxicated rats can
    be produced by steadily increasing concentrations of formate and,
    importantly, can also be produced by prolonged exposure to lower
    concentrations of formate.

         Martinasevic et al. (1996) studied components of folate-dependent
    formate oxidation, e.g., folate and 10-CHO-H4-folate dehydrogenase
    (10-FDH), in human and rat retinae. Total folate levels in human and
    rat retinal tissues were much lower than the levels in liver. However,
    folate levels in human retina were only 14% of those determined in rat
    retina. Comparable amounts of this 10-FDH were present in both
    cellular compartments in each species. However, the amount of 10-FDH
    in the human retina was approximately three times the amount found in
    the rat retina. Immunohistochemical staining for 10-FDH showed that
    this enzyme was preferentially localized in Müller cells. Since Müller
    cells appear to represent the target for formate-induced ocular
    toxicity, the authors suggested that formate oxidation reactions might
    serve two roles, first a protective role and then a role in methanol-
    induced toxicity in Müller cells.

         Garner & Lee (1994) employing oscillatory potential analysis
    showed that retinal ischaemia was not involved in methanol-induced
    visual system toxicity.

         The role of retinal metabolism in methanol-induced retinal
    toxicity in folate-sufficient (FS) rats and folate-deficient (FR)
    rats, some of which were also pretreated with disulfiram (DSF), was
    examined by Garner et al. (1995). Folate-deficient rats treated with
    methanol displayed elevated blood and vitreous humour formate levels
    along with abnormal electroretinograms (ERG), whereas methanol-exposed
    folate-deficient rats pretreated with DSF did not. Formaldehyde was
    not detected in blood or vitreous humour, either with or without DSF
    treatment, suggesting that formate is the toxic metabolite in
    methanol-induced retinal toxicity. Additionally, intravenous infusion
    of formate to levels seen in methanol toxicity did not alter ERG
    levels, suggesting intraretinal metabolism of methanol to formate may
    be necessary for retinal toxicity.

         Studies measuring ATP synthesis in mitochondria isolated from
    bovine retina and bovine heart have provided additional evidence for a
    tissue-selective action of formate (Eells et al., in press). In these
    studies, mitochondrial ATP synthesis was measured in the presence of
    different metabolic substrates. Formate selectively inhibited ATP
    synthesis in mitochondria isolated from bovine retina in the presence
    of metabolic substrates supplying electrons at the level of complex I,
    complex II and complex IV in the mitochondrial respiratory chain. The
    inhibitory effect of formate on retinal mitochondrial ATP synthesis
    was concentration-dependent, significant reductions in ATP synthesis
    being produced at 10 mM formate and Ki values for inhibition ranging
    from 30 to 50 mM formate. Comparative studies conducted in
    mitochondria isolated from bovine heart showed little or no inhibition
    of ATP synthesis at formate concentrations up to 50 mM. These findings
    provide direct evidence that formate acts as retinal mitochondrial
    toxin and suggest that one component of the retinotoxic actions of
    formate may be due to tissue-specific differences in mitochondrial
    transport mechanisms or in mitochondrial metabolism.

         The apparent selective vulnerability of the retina and optic
    nerve to the toxic actions of formate in methanol poisoning has been
    the subject of considerable speculation (Röe, 1955; Sharpe et al.,
    1982; Jacobsen & McMartin, 1986). Although methanol intoxication is
    known to disrupt brain function and severe intoxication results in
    coma and death, the most common permanent consequence of methanol
    intoxication is blindness (Röe, 1955). Several factors may contribute
    to the unique vulnerability of the retina and optic nerve to the
    cytotoxic actions of formate. One component of this selectivity is
    related to the differences in the distribution of formate in the eye
    and the brain. Formate concentrations measured in the vitreous humour
    and retinas of methanol-intoxicated rats (Eells, 1991; Eells et al.,
    1996) were equivalent to or greater than corresponding blood formate
    concentrations. In contrast, the concentrations of formate in the
    brain were significantly lower than blood formate concentrations.
    These data suggest that the toxic actions of methanol on the visual
    system may be due to the selective accumulation of formate in the
    vitreous humour and the retina as compared with other regions of the
    central nervous system. Secondly, the retina has a very limited
    metabolic capacity to oxidize and thus detoxify formate (Eells et al.,
    1996). Thirdly, cytochrome oxidase activity and ATP concentrations
    have been shown to be selectively reduced in the retina, optic nerve
    and brain in methanol-intoxicated rats, suggesting that there may be
    tissue- and cell-specific differences in mitochondrial populations and
    in the actions of formate on mitochondrial function (Eells et al.,
    1995). Finally,  in vitro studies in isolated retinal and cardiac
    mitochondria have shown that formate selectively inhibits retinal
    mitochondrial ATP synthesis (Eells et al., in press). These findings
    support the hypothesis that formate acts as a selective mitochondrial
    toxin in the retina and establish a link between the effects of
    formate  in vitro and the retinal toxicity associated with formate
    accumulation in methanol intoxication.


         Acute oral and inhalation exposures, and to a lesser extent
    percutaneous absorption of high concentrations of methanol, have
    resulted in CNS depression, blindness, coma and death. The most noted
    effects resulting from longer-term exposure to lower levels of
    methanol have been a broad range of ocular effects.

    8.1  General population and occupational exposure

         The human health effects after exposure to methanol are
    qualitatively the same for the general population and for those
    exposed in the workplace, and will be considered together. Acute
    methanol intoxication in the general population is an uncommon
    occurrence, but often results in serious morbidity and mortality.
    Litovitz et al. (1988) reviewed the acute methanol exposure cases
    reported in the USA. In 1987, 1601 methanol poisonings were reported
    to the American Association of Poison Control Centers (AAPCC). Half of
    these individuals required hospitalization and the death rate was
    0.375%. It was estimated that the actual annual incidence of methanol
    poisonings in the USA in 1987 was about 6400 cases. Subsequent surveys
    of methanol exposure cases have been conducted by the AAPCC, and these
    have shown similar annual frequencies to that in 1987. These data
    result from poisoning cases that are not usually reported elsewhere,
    since case reports of methanol poisoning are rarely published in
    today's literature. Poisoning frequency surveys are not available from
    the rest of the world, but reports in the biomedical literature and in
    the press would suggest a worldwide distribution of methanol poisoning
    cases at least as great as in the USA.

    8.1.1  Acute toxicity

         Methanol (wood alcohol) has been recognized as a human toxic
    agent since the end of the 19th century. Since the early part of the
    20th century, many hundreds of cases of methanol intoxication have
    been reported as single cases and as groups in many countries. Many of
    the human cases were due to the ingestion of denatured alcohol.

         The preponderance of methanol poisonings have resulted from the
    consumption of adulterated alcoholic beverages, e.g., "moonshine", or
    "bootleg whiskey", wood alcohol and spirits mixed with whiskey. Buller
    & Wood (1904) and Wood & Buller (1904) reported 235 cases of blindness
    or death primarily connected with drinking adulterated beverages or
    wood alcohol products, but these also included 10 deaths involving
    inhalation or absorption of methanol through the skin. 

         Bennett et al. (1953) described a case that occurred in Atlanta,
    Georgia, USA, in 1951, when within a 5-day period, 323 people consumed
    bootlegged whiskey contaminated with 35-40% methanol and 41 of them
    died. Kane et al. (1968) reported the poisoning of 18 individuals, of
    whom 8 died, when a diluted paint thinner containing approximately 37%
    (by volume) methanol was used as an alcoholic beverage in Lexington,
    Kentucky, USA.

         An epidemic in the State Prison of Southern Michigan in 1979 in
    which methanol diluent used in photocopying machines was used as
    "home-made" spirits (containing approximately 3% methanol) resulted in
    46 definite cases of methanol intoxication and 3 deaths (Swartz et
    al., 1981). Methanol poisoning among 23 servicemen in an Army hospital
    in Korea who had ingested bootleg sake contaminated with methanol was
    reported by Keeney & Mellinkoff (1951). Tonning et al. (1956) reported
    acute methanol poisoning in 49 naval personnel who consumed drinks
    made from duplicating fluid containing a high concentration of

         An outbreak of acute methanol intoxication involving 28 young men
    in Papua New Guinea in 1977, each of whom consumed an equivalent of
    60-600 ml pure methanol, resulted in all becoming hospitalized within
    8-36 h due to acute metabolic acidosis, severe visual impairment and
    acute pancreatitis. Four died within 72 h after hospitalization. Of 24
    who recovered, 16 showed no residual complications, 6 had bilateral
    visual impairment and 2 had difficulty in speech as well as visual
    impairment (Dethlefs & Naraqi, 1978; Naraqi et al., 1979).

         Before 1978, many alcoholics in Sweden were reported to
    supplement their intake of alcohol with readily available cleansing
    solutions containing up to 80% methanol. Since 1978, the methanol
    content of such solutions has been limited to 5%. However, consumption
    of these solutions by alcoholics is still widely seen, exposures of
    1-2 weeks being associated with blood methanol concentrations ranging
    from 1000 to 2000 mg/litre (31-62 mmol/litre) (Heath, 1983).

         Although ingestion of methanol historically has been shown to be
    the most frequent route of poisoning, percutaneously absorption of
    methanol liquids or inhalation of its vapour is as effective as the
    oral route in producing methanol acute toxic syndrome in adult and
    pediatric poisonings (Buller & Wood, 1904; Wood & Buller, 1904;
    Giminez et al., 1968; Kahn & Blum, 1979; Dutkiewicz et al., 1980;
    Becker, 1983). Giminez et al. (1968) reported 48 children intoxicated
    with percutaneously applied alcohol. Thirty of these patients had
    severe respiratory depression, 14 were comatose, 11 had seizures, 7
    had anuria or severe oliguria and there were 12 deaths.

         About 100 cases of amblyopia (impairment of vision) and death
    from inhalation of wood alcohol were reported up to 1912, the majority
    occurring from occupational exposure to the fumes (Tyson & Schoenberg,
    1914). Toxicity has also been associated with inhalation of methanol
    vapour in excess of 400 mg/m3 (300 ppm) (Becker, 1983; Frederick et
    al., 1984).

         Hazardous inhalation exposures of methanol can occur in the
    context of intentional inhalation of volatile preparations such as
    carburettor cleaners. Frenia & Schauben (1993) reported seven cases
    involving four patients who had inhaled a carburettor cleaner
    containing toluene (43.8%), methanol (22.3%), methylene chloride
    (20.5%) and propane (12.5%). Measured blood methanol levels ranged 

    from 504 to 1286 mg/litre. Blood formic acid levels were 120, 193 and
    480 µg/ml, respectively, in three patients. Ophthalmic examinations
    revealed hyperaemic discs and decreased visual acuity in one patient.

         Acute methanol toxicity in humans evolves in a fairly defined
    pattern. A toxic exposure results in a transient mild depression of
    the CNS, similar to that of ethanol, but to a much lesser degree. The
    initial depressant period is followed by an asymptotic latent period,
    which occurs most commonly about 8-24 h after ingestion of the alcohol
    but may last from several hours to 2 or more days. During the latent
    period the patients describe no overt symptoms or signs.

         The latent period is followed by a syndrome that consists of an
    uncompensated metabolic acidosis with superimposed toxicity to the
    visual system. Physical symptoms typically may include headache,
    dizziness, nausea and vomiting, followed in more severe cases by
    abdominal and muscular pain and difficult periodic breathing (Kussmaul
    breathing), which may progress to coma and death, usually from
    respiratory distress. Death may occur if patients are not treated for
    metabolic acidosis, and blindness may result even if treatment for
    metabolic acidosis is performed (Bennett et al., 1953; Röe, 1955; Kane
    et al., 1968; Tephly & McMartin, 1984; Tephly, 1991).

         The neurotoxic effects of methanol on the visual system can
    involve transient abnormalities such as peripapillary oedema, optic
    disc hyperaemia, diminished pupillary reactions to light, and central
    scotomata. Permanent ocular abnormalities include optic disc pallor,
    attenuation of arterioles, sheathing of arterioles, diminished
    pupillary reactions to light, diminished visual acuity, central
    scotomata, and other nerve fibre bundle defects (Bennett et al., 1953;
    Dethlefs & Naraqi, 1978; Kavet & Nauss, 1990). Pallor of the optic
    disc is an end-stage sign of irreversible effects of the visual system
    and may appear 1 to 2 months after an acute methanol dosage (or
    possibly following chronic occupational exposure to methanol vapour)
    (Buller & Wood, 1904; Wood & Buller, 1904; Bennett et al., 1953).

         Within the general population, the range of the dose levels that
    is hazardous to humans and the variable susceptibility to acute
    effects are well recognized (Buller & Wood, 1904; Wood & Buller, 1904;
    Bennett et al., 1953). As little as 15 ml of 40% methanol resulted in
    the death of one individual while others survived following the
    consumption of 500 ml of the same solution in the Atlanta, Georgia,
    epidemic of 1951. There were large individual differences in the
    duration of the latency period. Symptoms of methanol poisoning
    appeared within a few hours or were delayed for up to 72 h. The
    severity of the disease was not related to the length of the latent
    period or the amount of methanol consumed (Bennett et al., 1953). (It
    should be noted that in earlier reported poisoning epidemics, large
    errors in dose estimates may have been made).

         In another example of the range of dose levels of methanol that
    are toxic, 120 ml (4 fluid ounces) of Columbian spirits, or 95 g of
    methanol (Columbian spirits is basically pure methanol), was lethal in
    40% of the poisoning cases. For a 70-kg person, this dose is
    equivalent to about 1.4 g methanol/kg body weight (Buller & Wood,
    1904). This figure is consistent with currently accepted values for
    lethality, and 0.3 to 1 g/kg is considered the range of a minimum
    lethal dose for untreated cases of methanol poisoning (Röe, 1955;
    Erlanson et al., 1965; Gonda et al., 1978).

         It has been suggested that the variability in the reaction to
    methanol may have been due to the concomitant ingestion of ethanol
    with methanol, which resulted in some patients having a longer latent
    period prior to the onset of poisoning (Röe, 1950, 1955). Another
    explanation for the variability in susceptibility to methanol
    poisoning is the different levels of folate in the diet. Folate-
    deficient individuals have a lesser capacity to metabolize formate, so
    are more susceptible to accumulation of formate to toxic levels (see
    section 8.1.7 for sensitive sub-populations).

         In some clinical cases, the blood methanol level is low in the
    last phase of the poisoning. In three such cases, blood methanol
    concentrations were 0.275, 0.277 and 0.194 g/litre, respectively
    (Erlanson et al., 1965). On the assumption that the body in diffusion
    equilibrium with the blood represents about 70% of the body weight,
    Röe (1982) calculated that 0.19-0.14 g/kg of methanol was present in
    the body. However, low blood methanol levels do not indicate a lower
    susceptibility to toxicity, i.e., blood methanol levels do not
    correlate with patient prognosis (Jacobsen & McMartin, 1986). Patients
    that are examined late after methanol ingestion are likely to have low
    blood methanol levels, yet high accumulation of formate. Such patients
    often have poor prognosis.

         Acute methanol poisoning patients with blood levels of methanol
    above 500 mg/litre are generally regarded as requiring haemodialysis
    (Becker, 1983). The dose of methanol required to achieve this blood
    concentration is very small (0.4 ml/kg body weight). This corresponds
    to the ingestion of 4 ml (less than a teaspoon of 100% methanol by a
    10-kg (1-year old) child and 28 ml (less than 1 fluid ounce) by a
    70-kg adult (Litovitz et al., 1988).

         A case was reported of a 46-year-old man who, after consuming a
    beverage containing methanol, exhibited one of the highest reported
    serum methanol levels (4930 mg/litre), well above those at which
    ethanol treatment and haemodialysis are recommended (200 mg/litre
    and 500 mg/litre, respectively). The lowest serum pH was 7.0
    with a hydrogen carbonate level of 8.8 and an anion gap of 42.8.
    Additionally, his visual acuity decreased to a complete loss of
    vision. The patient was aggressively treated with haemodialysis and
    ethanol infusion, regained his vision with a visual acuity of 20/30
    bilaterally and suffered no neurological sequelae (Pambies et al.,

         An additional number of cases are particularly informative
    regarding treatment of methanol intoxication and sequelae of
    poisoning. A case of methanol intoxication was reported involving a
    53-year-old man. Along with blindness and metabolic acidosis, this
    resulted in cerebral oedema and subarachnoid haemorrhage followed by a
    comatose state and subsequent death (del Carpio-O'Donavan & Glay,

         A 31-year-old male alcoholic who consumed ethanol containing
    methanol experienced severe signs and symptoms of poisoning. He
    underwent minimal medical treatment consisting of sodium hydrogen
    carbonate and peritoneal dialysis and exhibited necrosis and
    haemorrhage of the (bilateral) putamen and necrosis of bilateral
    subcortical white matter and post-contrast gyral enhancement at the
    otherwise normal-looking areas of the cerebral cortex by the 22nd day,
    as revealed by computed tomography (Hsieh et al., 1992).

         A 31-year-old man entered hospital with a 370 mg/litre serum
    methanol level after exhibiting the signs and symptoms of methanol
    poisoning (nausea, vomiting, diffuse abdominal pain and blurred tunnel
    vision) for 7 days. Following a complete regimen of treatment
    consisting of hydrogen carbonate, ethanol and folate combined with a
    6-h haemodialysis, which corrected the acidosis and eliminated
    methanol (methanol decreased to 100 mg/litre by the second day),
    permanent blindness still resulted (Vogt et al., 1993).

         A case study of acute methanol poisoning in a 27-year-old man
    with a previous pattern of drinking was reported by King (1992).
    Following a comprehensive treatment regimen consisting of
    administration of alkali, fluids and ethanol, intubation and
    haemodialysis, this patient exhibited significant neurological and
    physical impairment, including trauma to the vocal cords and
    hypophonic voice and urinary incontinence (of central origin), along
    with cognitive defects. However upon discharge his vision was normal
    with no atrophy of the optic nerve.

         A case of a severe methanol poisoning in a 33-year-old man with a
    history of alcoholism was reported by Burgess (1992). The individual
    required 21 h of dialysis to bring the serum methanol levels down to a
    non-toxic level. A haemodialysis treatment usually lasts approximately
    4 h but this may not be sufficient in severe poisoning. Prolonged
    haemodialysis treatment should be considered in cases of severe
    poisoning and also possibly for patients with compromised renal

         Extensive white and grey matter brain damage was seen in an
    alcoholic 37-year-old man who consumed 1900 ml of windshield washer
    fluid containing methanol. Both CT scan and MR imaging revealed
    diffuse white matter oedema and damage throughout frontal and parietal
    lobes. Bilateral changes in the basal ganglia and necrosis and
    haemorrhage of putamen were also noted (Glazer & Dross, 1993).

         Autopsies from victims of lethal methanol poisonings revealed
    gross pathology in the visceral organs, the brain, lung, liver,
    kidney and the CNS, all of which involved a variety of oedematous,
    haemorrhagic and degenerative changes (Keeney & Mellinkoff, 1951;
    Bennett et al., 1953; Tonning et al., 1956; Kaplan, 1962; Erlanson et
    al., 1965; McLean et al., 1980; Wu Chen, 1985; Suit & Estes, 1990).

         A fatal case involving a 41-year-old man who had ingested a large
    quantity of methanol disclosed a broad distribution of methanol in
    postmortem tissues and fluids. The highest content of methanol was
    found in the kidney (5.13 g/kg) followed by the liver (4.18 g/kg),
    vitreous humour (3.9 g/litre), heart (3.45 g/kg), urine
    (3.43 g/litre), pericardial fluid (3.29 g/litre), blood (2.84 g/litre)
    and stomach contents (2.21 g/litre) (Pla et al., 1991).

         Methanol toxicity can cause brain oedema, necrosis, brain atrophy
    and cerebral haemorrhage. Putaminal necrosis and haemorrhage result
    from the direct toxic effects of the methanol metabolites (e.g.,
    formate) and metabolic acidosis in the basal ganglia. The typical
    appearance of bilateral putaminal necrosis has been described as
    characteristic of methanol toxicity (Gonda et al., 1978).

         Optic neuropathy and putaminal necrosis are the two main
    complications of methanol poisoning generally occurring in combination
    after severe poisoning of either suicidal or accidental origin (Sharpe
    et al., 1982).

         A case study of a woman who drank a substantial amount of
    methylated spirits, which resulted in optic neuropathy and putaminal
    necrosis, has been reported (Pelletier et al., 1992). The woman
    exhibited tremor and rigidity, hypokinesia, altered speech and loss of
    superficial and proprioceptive sensation of the lower extremities with
    hyperpathia. Signs of moderate bilateral sensory neuropathy and
    extrapyramidal damage persisted for 2 months as did total blindness
    due to optic atrophy. Repeat CT and MRI examinations revealed the
    damage to be a core lesion of the putamen with residual bilateral
    putaminal hypodensity suggestive of an ischaemic and necrotic process
    possibly including disruption of the blood-brain barrier.

         Postmortem analysis of methanol concentrations in body fluids and
    tissues reported in fatal human cases of methanol poisoning has
    revealed higher concentrations of methanol in cerebrospinal fluid
    (CSF), vitreous humour and bile than in blood (Bennett et al., 1953;
    Wu Chen et al., 1985). In tissues, the highest concentrations were
    found in brain, kidney, lung and spleen, and there were lower
    concentrations in skeletal muscle, pancreas, liver and heart (Wu Chen
    et al., 1985).

         Postmortem signs of damage to the basal ganglia in the brain,
    specifically the putamen, have been reported in several cases
    (Erlanson et al., 1965; Aquilonius et al., 1978; Suit & Estes, 1990).
    A number of human studies have shown that survivors of severe methanol

    poisoning may suffer residual disorders as a permanent complication
    (Erlanson et al., 1965; Guggenheim et al., 1971; Aquilonius et al.,
    1978; McLean et al., 1980; Ley & Gali, 1983). Ley & Gali (1983)
    described a case of Parkinsonian syndrome after methanol intoxication.

         Co-ingestion of methanol with other solvents, e.g., methyl ethyl
    ketone (MEK) (found in multiple ink cleaning products) has resulted in
    a hyperosmolar coma without anion gap metabolic acidosis in one
    reported case of poisoning. MEK was believed to have inhibited
    methanol metabolism contributing to the low serum formate (1.3
    mmol/litre) and normal anion gap despite a blood methanol level of
    67 mmol/litre (Price et al., 1994). 

    8.1.2  Clinical features of acute poisonings

         The time course of clinical effects due to acute methanol
    poisoning is heavily dose-dependent. Blood methanol concentrations of
    > 500 mg/litre are associated with severe acute clinical signs of
    toxicity, although formate concentrations may give a better indication
    of potential toxicity (National Poisons Information Service, 1993).

         Thirty minutes to 2 h after ingestion of methanol, clinical
    effects resemble those of mild ethanol inebriation, and drowsiness,
    confusion and irritability are often noted. After a latent period,
    which can range from a few hours to 30 h (but may appear as early as
    1 h or as late as 72 h), the patient shows mild CNS depression
    followed by abdominal pain, nausea, vomiting, hypernoea, gradually
    failing vision, progressive encephalopathy, severe metabolic acidosis
    and hypokalaemia; coma and death may ensue. Patients may complain of
    blurred or "snowfield" vision with whiteness, spots or mistiness
    within the visual field. Survivors may have permanent blindness or
    various neurological sequelae. Mortality and morbidity may be more
    related to the time between ingestion and therapy rather than to the
    initial methanol levels, thus emphasizing the need for rapid treatment
    (Mahieu et al., 1989; National Poisons Information Service, 1993;
    Pambies et al., 1993a).

         Metabolic acidosis associated with high anion and osmolal gaps is
    considered an important laboratory indicator of methanol poisoning
    (Kruse, 1992). The difference between measured and calculated
    osmolality or osmolal gap permits a rough estimation of alcohol
    concentrations (Pappas et al., 1985) so that specific therapy is often
    initiated before results of quantitative methanol determinations are

         The determination of osmolal and anion gaps are readily available
    techniques in the initial handling of poisoning with unknown agents
    and of patients with a metabolic acidosis of unknown origin. A
    combined increase in both anion and osmolal gaps has been shown to be
    a sensitive marker of either ethylene glycol or methanol poisoning
    (Jacobsen & McMartin, 1986). Reported earlier reference values for

    osmolal gap and anion gap are -1 (+ 6) mosm/kg H2O and 16 (+ 2)
    mmol/litre, respectively (Jacobsen et al., 1982b). However, Aabakken
    et al. (1994) determined osmolal and anion gaps in populations that
    were consecutively admitted to a hospital emergency department and
    suggested that the present reference values for anion and osmolal gaps
    may be too narrow. They further suggested that the values for the
    osmolal gap should be 5 + 15 mosm/kg H2O (-10 to + 20 mosm/kg H2O)
    and for the anion gap should be 13 + 9 mmol/litre (4-20 mmol/litre).
    In their previous reports of methanol poisonings, all patients
    exceeded these ranges (Jacobsen et al., 1982).

         Demedts et al. (1994) hypothesized that excessive serum
    osmolality gaps that are not predictive of methanol levels as
    frequently seen in acute poisonings may be attributed to methodology
    used to measure methanol (analysing samples using head-space GC were
    compared to results found with gas-chromatography using split-mode
    injections). Although the determination of increased anion gap is
    suggestive of methanol poisoning, definitive evidence would be
    increased blood or serum formate concentrations.

         Characteristic clinical and laboratory findings in methanol
    poisoning are summarized as follows:

    *    Physical findings
         a)   Kussmaul respiration (difficult, periodic breathing)
         b)   faint odour of methanol on breath
         c)   visual disturbances
         d)   nausea, vomiting, abdominal pain
         e)   altered sensation

    *    Laboratory findings
         a)   elevated anion gap
         b)   metabolic acidosis
         c)   elevated osmol gap
         d)   positive serum methanol and/or serum formate assay

         In treating methanol poisoning a 3-step procedure is common:
    1) administration of hydrogen carbonate to combat metabolic acidosis;
    2) administration of ethanol to compete as a substrate for alcohol
    dehydrogenase, and 3) haemodialysis to remove methanol from the blood
    (Erlanson et al., 1965; Gonda et al., 1978; McCoy et al., 1979; Lins
    et al., 1980; Jacobsen et al., 1982a,b; Pappas & Silverman, 1982;
    Becker, 1983; Jacobsen & McMartin, 1986; Kruse, 1992; Pambies et al.,
    1993a,b). Current recommendations are that ethanol treatment be
    conducted for patients with blood methanol levels of 200 mg/litre or
    more, while haemodialysis be used above 500 mg/litre (Jacobsen &
    McMartin, 1986).

         The rationale for the administration of ethanol (Röe, 1950;
    Keyvan-Larijarni & Tannenbaum, 1974; McCoy et al., 1979; Becker, 1983)
    is that alcohol dehydrogenase, the enzyme responsible for converting
    methanol to formaldehyde and formic acid, is also involved in the

    metabolism of ethanol to acetaldehyde and acetate. The conversion of
    methanol to its toxic by-products is slowed in the presence of ethanol
    due to competition for the enzyme.

         4-Methyl pyrazole (4-MP) is a more specific inhibitor of alcohol
    dehydrogenase, less toxic than pyrazole and has been shown to
    dramatically inhibit production of formic acid from methanol in
    experimental animals (Blomstrand et al., 1979; McMartin et al.,
    1980b). Monkeys given usually lethal doses of methanol survived when
    treated with 4-MP following methanol administration (McMartin et al.,
    1980b). In humans the slower elimination rate and lesser degree of
    toxicity of 4-MP suggested that it might be preferable to ethanol in
    the treatment of methanol poisoning (Jacobsen et al., 1990). 4-MP is
    currently undergoing clinical trials for treatment of methanol

         Haemodialysis effectively removes methanol and formate from the
    circulation (Erlanson et al., 1965; Gonda et al., 1978; McCoy et al.,
    1979). If haemodialysis is not available, peritoneal dialysis has been
    used with some success in treating acute methanol intoxication
    (Keyvan-Larijarnc & Tannenberg, 1974). Discussion of the treatment of
    methanol poisoning can be found in the IPCS Poisons Information
    Monograph (PIM) No. 335 (IPCS, 1991).

    8.1.3  Repeated or chronic exposure

         In comparison to acute toxicity, reports of effects from repeated
    or chronic methanol exposures have been only infrequently reported.
    Information based on a limited number of case reports and even fewer
    epidemiological studies (generally containing unknown levels and/or
    durations of methanol exposure) suggests that extended exposure to
    methanol may cause effects qualitatively similar to those observed
    from relatively high levels of acute exposure, including in some cases
    CNS and visual disorders (Buller & Wood, 1904; Wood & Buller, 1904;
    Greenberg et al., 1938; Bennett et al., 1953; Kingsley & Hirsch, 1955;
    Frederick et al., 1984).

         Greenberg et al. (1938) studied 19 workers employed in the
    production of "fused collars", where solutions of acetone-methanol
    (3:1) were used to impregnate collars which were then steam-pressed.
    Methanol concentrations in the work room were 29-33 mg methanol/m3
    and 96-108 mg acetone/m3. The shortest period of employment in this
    occupation was 9 months and the longest was 2 years. No CNS symptoms
    or visual anomalies were observed.

         Frederick et al. (1984) reported on teacher aides who worked at
    or near spirit duplicators that used a 99% methanol duplicator fluid.
    The exposures ranged from 1 h/day for 1 day/week to 8 h/day for 5
    days/week and had occurred for 3 years. Since the introduction of the
    equipment, the aides began to experience headaches, dizziness and eye
    irritation, blurred vision and nausea/upset stomach while working near
    the machines. Fifteen-minute breathing zone samples near 21 operating

    machines contained between 475 and 4000 mg/m3 of methanol vapour.
    Fifteen of these samples exceeded the NIOSH recommended 15-min
    standard of 1050 mg/m3 (800 ppm). The aides were also exposed while
    collating and stapling papers impregnated with the fluid up to 3 h
    earlier and these exposures ranged from 235-1140 mg/m3 . The results
    suggested that chronic effects may occur when methanol concentrations
    exceed the threshold limit value (TLV) of 260 mg/m3 (200 ppm). The
    effects reported in the study of Frederick et al. (1984) were similar
    in nature but appeared less severe than those reported from acute
    poisoning by methanol (Buller & Wood, 1904; Wood & Buller, 1904;
    Bennett et al., 1953).

         Kingsley & Hirsch (1955) reported frequent and persistent
    headaches, but no visual effects or other permanent sequelae, in
    clerical workers located close to spirit duplicating equipment that
    used methanol-based duplicating fluid. Methanol concentrations were
    reported to be as high as 490 mg/m3 in the air surrounding the
    duplicating equipment after 60 min of operation and approximately
    130 mg/m3 about 3 m away from the device. The methanol concentration
    around the duplicating equipment always exceeded 260 mg/m3. No
    information was provided concerning the number of employees exposed or
    affected, nor on the actual duration of methanol exposure.

         NIOSH (1981) reported that 45% of "spirit" duplicating machine
    operators at the University of Washington experienced some symptoms
    (blurred vision, headache, nausea, dizziness and eye irritation),
    consistent with the toxic effects of methanol. Airborne methanol
    concentrations of 1330 mg/m3 were measured in the vicinity of the
    duplicators when windows and doors were open. No information on the
    actual length of duration of methanol exposure among the employees
    engaged in the duplicating machine operations were provided.

         A number of other studies have measured methanol and formate in
    the blood and urine of workers exposed during an 8-h day to between
    100 and 200 mg/m3 of methanol vapour (Baumann & Angerer, 1979;
    Heinrich & Angerer, 1982. Although these studies were predicated on
    issues of occupational health related to methanol exposure, no health
    effects were provided nor did the investigators imply that the workers
    studied had suffered health effects.

         Kawai et al. (1991b), utilizing methanol in urine as a biological
    indicator of occupational exposure, compared subjective complaints and
    major clinical findings among 33 methanol-exposed workers over several
    8-h workshifts. Urine levels of methanol in controls were on average
    1.9 ± 0.8 mg/litre (n = 91), and in 14 exposed workers pre-shift
    concentrations were significantly elevated compared to controls. At
    the end of the shift the urine concentrations were generally above
    100 mg/litre in 8 men with a mean exposure level of 1690 mg/m3 and
    30-100 mg/litre in 6 men with a mean exposure level of 550 mg/m3. The
    highest exposures (breathing zone, 8-h/samples) were 4000-7000 mg/m3
    and corresponding urine levels 300-500 mg/litre. The leading
    subjective complaints included: dimmed vision and nasal irritation 

    during work, and headache, dimmed vision, forgetfulness and increased
    sensitivity of the skin in the extremities when off-work. The authors
    attributed the dimmed vision to the fog created by methanol vapours
    and high humidity in air. No visual problems were noted when windows
    were kept open and fresh air was allowed to flow in. It was also noted
    that there were no complaints of photophobia (and thus perhaps no
    major corneal involvement). Fundus photography revealed that the optic
    discs were normal and thus the symptom of dimmed vision was not
    recognized as a sign of impending retinal involvement. In three
    workers with methanol exposures of 1250-2130 mg/m3, 1385-2075 mg/m3
    and 155-4685 mg/m3 (953-1626 ppm, 1058-1585 ppm and 119-3577 ppm) the
    reaction of pupils to light was slow in two subjects, and a third
    subject had slight mydriatic pupils. The duration of service of the
    workers ranged from 0.3 to 7.8 years. The exposures were high and the
    methods for measurement of visual toxicity were relatively crude, but
    the data did not indicate that occupational exposure to such
    concentrations caused permanent damage.

         The effects of methanol vapour (249 mg/m3; SD + 7 mg/m3) for
    75 min on neurobehavioural measures were studied in 12 healthy young
    men. The exposure produced significant increases (approximately 3
    fold) in blood and urine methanol levels but no changes in plasma
    formate level. Although most of the neurobehavioural end-points were
    unaffected by exposure to methanol, statistically significant effects
    and trends were found for a cluster of variables, including the
    latency of the p-200 component of event-related potentials,
    performance on the Sternberg memory task and subjective measures of
    fatigue and concentration. However, the effects were small and did not
    exceed the normal range (Cook et al., 1991).

    8.1.4  Reproductive and developmental effects

         No studies have been reported in the peer-reviewed literature on
    the reproductive and developmental effects of methanol in humans.

    8.1.5  Chromosomal and mutagenic effects

         No studies have been reported in the peer-reviewed literature on
    chromosomal or mutagenic effects of methanol in humans.

    8.1.6  Carcinogenic effects

         No studies have been reported in the literature on the
    carcinogenicity of methanol in humans.

    8.1.7  Sensitive sub-populations

         Folate-deficient individuals might be at greater risk from
    inhalation of low concentrations of methanol, compared to normal
    individuals. Human populations that are potentially at high risk of
    folate deficiency include pregnant women, the elderly, individuals
    with poor-quality diets, alcoholics and individuals on certain
    medications or with certain diseases (API, 1993).

         It has been suggested that the metabolic acidosis due to methanol
    might be exacerbated in individuals with diabetes since it is well
    known that these patients suffer from diabetic ketoacidosis (Posner,
    1975). However, there are no clinical or experimental data on any
    interaction between methanol acidosis and diabetic ketoacidosis.


    9.1  Aquatic organisms

    9.1.1  Microorganisms

         The toxicity of methanol to each of three bacterial groups, i.e.,
    aerobic heterotrophic, Nitrosomonas and methanogens (key agents in the
    natural recycling of organic material in the environment and in
    wastewater treatment systems), was described by Blum & Speece (1991).
    The following IC50 values (mg/litre) (the concentration that
    inhibited the culture by 50%) compared to the uninhibited controls
    were reported:  Nitrosomonas (after 24-h exposure), 880 mg/litre;
    methanogens (after 48-h exposure), 22 000 mg/litre; and aerobic
    heterotrophs (after 15-h exposure), 20 000 mg/litre. Methanol was
    found to be completely inhibitory to ammonia oxidation by
     Nitrosomonas bacteria at a concentration of 5 × 10-3 M (about
    160 mg/litre) (Hooper & Terry, 1973).

         A 15-min EC50 of 14 700 mg/litre for the luminescent marine
    bacterium  Photobacterium phosphoreum and a 4-h LC50 value of 1.0%
    by volume (7690 mg/litre) have been reported (Schiewe et al., 1985).
    Calleja et al. (1994) found the EC50 for the marine bacterium
     Photobacterium phosphoreum in the Microtox(R) test to be
    29 348 mg/litre. Rajini et al. (1989) reported a 10-min LC50 of 6%
    (44 860 mg/litre) for the ciliate protozoan  Paramecium caudatum.

         Toxicity threshold values for methanol in the cell multiplication
    inhibition test of 6600 mg/litre for the bacterium  Pseudomonas
     putida and > 10 000 mg/litre for the protozoa  Entosiphonsulcatum
    were reported by Bringmann & Kühn (1980).

         An experimental EC50 value (the concentration that reduced the
    maximum observed biodegradation rate by 50%) for methanol of 
    2.8 mol/litre (89.7 g/litre) was obtained in a system employing an
    enriched mixed microbial culture derived from domestic waste water in
    the USA (Vaishnav & Lopas, 1985).

    9.1.2  Algae

         Stratton (1987) determined the following EC50 values:

         Anabaena cylindrica:          2.57% (20 300 mg/litre)
         Anabaena inaequalis:          2.68% (21 179 mg/litre)
         Anaebaena sp.:                3.12% (24 650 mg/litre)
         Anaebaena variabilis:         3.13% (24 730 mg/litre)
         Nostoc sp.:                   5.48% (43 290 mg/litre)

         For the green alga  Chlorella pyrenoidosa an EC50 value of
    28 440 mg/litre was found (Stratton & Smith, 1988). Bringman & Kühn
    (1978), employing a cell multiplication test, reported a toxicity
    thresholds of 8000 mg/litre for the green alga  Scenedesmus
     quadricauda and 530 mg/litre for the cyanobacterium (blue green
    alga)  Microcystis aeruginosa.

    9.1.3  Aquatic invertebrates

         The toxicity of methanol, as reported for a broad spectrum of
    aquatic invertebrates, is summarized in Table 6. EC50 values for the
    water flea  (Daphnia magna) range from 13 240 to 24 500 mg/litre.
    Helmstetter et al. (1996) exposed the mussel,  Mytilus edulis, to
    methanol concentrations of 1, 2, 3, 5 and 10% (v/v) for 96 h. All the
    mussels in both the 5 and 10% exposure groups died within 13.5 h.
    Sublethal narcotic effects such as slow movement and sporadic filter
    feeding were reported in mussels exposed to 2 and 3%. Mussels exposed
    to 1% methanol exhibited no adverse effects during the 96-h exposure

    9.1.4  Fish

         The acute toxicity to fish is listed in Table 7. LC50 values
    reported for freshwater fish species range from 10 880 to
    29 700 mg/litre.

         The physiological changes in the carp  (Cyprinus carpio)
    affected by a sub-lethal methanol concentration of 1 ml/litre
    (790 mg/litre) included a significant increase in blood cortisol
    levels after 6 h of exposure, but not after 24 or 72 h, significant
    decreases in blood protein and cholesterol levels after 72 h of
    exposure, and reduced concentration of glycogen in the liver after
    72 h. Methanol did not produce significant changes in blood glucose
    levels after any duration of exposure (Gluth & Hanke, 1985).

         The effect of methanol on the fertilization of chum salmon
     (Oncorhynchus keta) ova was examined at methanol exposure levels of
    0.001% to 10% by volume (7.9 to 79 000 mg/litre) (Craig et al., 1977).
    Both gametes (sperm and unfertilized ova) and fertilized eggs were
    exposed to methanol for brief periods. Exposures up to and including
    1% methanol did not significantly affect fertilization, survival to
    hatching, hatching time, alevin size at hatch or physical deformities
    among alevins, although a methanol concentration of 10% was lethal in
    most cases (Craig et al., 1977).

         Cuéllar et al. (1995) determined the effect of methanol on the
    embryonic development of the medaka fish  (Oryzias latipes). The eggs
    were exposed to methanol in both Petri dishes and vials. No effects on
    embryonic development were reported at a methanol concentration of

        Table 6.  Acute toxicity of methanol to aquatic invertebrates


    Organism             Size/age   Stat/   Temp    Hardness       pH      Parameterc   Concentration   Reference
                                    flowa   (°C)    (mg/litre)b                         (mg/litre)d

    Water flea           <24 h      stat    20      (1)          7.8-8.2   48-h EC50e   >10 000   n     Kuhn et al. (1989)
    (Daphnia magna)
                         <24 h      stat    20      (1)          7.8-8.2   48-h EC0e    >10 000   n     Kuhn et al. (1989)
                         <24 h      stat    20      (2)          7.8-8.2   24-h EC50    >10 000   n     Bringmann & Kuhn
                         <24 h      stat    20      (2)          7.8-8.2   24-h EC100   >10 000   n     Bringmann & Kuhn
                         <24 h      stat    20      154.5        7.0-8.2   24-h EC50    24 500    n     Bringmann & Kuhn
                                                                           48-h LC50    13 240    n     Vaishnav &
                                                                                                        Korthals (1990)
                                                                           24-h EC50    21 402    n     Calleja et al.

    Water flea           <24 h      stat    22      23±2                   18-h-LC50    19 500    n     Bowman et al.
    (Daphnia pulex)                                                                                     (1981)

    Water flea           <24 h      stat    20±2    250          7.8±0.2   24-h EC50    23 500    n     Rossini & Ronco
    (Daphnia obtusa)     <24 h      stat    20±2    250          7.8±0.2   48-h EC50    22 200    n     (1996)

    Brown shrimp         adult      stat    15      seawater               48-h LC50    1975      n     Portmann & Wilson
    (Crangon crangon)                                                                                   (1971)
                         adult      stat+   15      seawater               96-h LC50    1340      n     Portmann & Wilson
                                    stat    24.5    seawater               24-h LC50    10 000    n     Price et al. (1974)

    Brine shrimp         24 h       stat    25      seawater               24-h LC50    1578.84   n     Barahona-Gomariz
    (Artemia salina)                                                                                    et al. (1994)
                         48 h       stat    25      seawater               24-h LC50    1101.46   n     Barahona-Gomariz
                                                                                                        et al. (1994)

    Table 6.  Continued


    Organism             Size/age   Stat/   Temp    Hardness       pH      Parameterc   Concentration   Reference
                                    flowa   (°C)    (mg/litre)b                         (mg/litre)d

    Brine shrimp         72 h       stat    25      seawater               24-h LC50    900.73    n     Barahona-Gomariz
    (Artemia salina)                                                                                    et al. (1994)
                                                    seawater               24-h LC50    43 574    n     Calleja et al.

    Glass shrimp         juvenile   stat    23±2                           18 h-LC50    21 900    n     Bowman et al.
    (Palaemonetes                                                                                       (1981)

    Streptocephalus                                                        24-h LC50    32 681    n     Calleja et al.
    proboscideus                                                                                        (1994)

    Mussel               5-7 cm     flow    15±0.5  seawater               96-h LC50    15 900    m     Helmstetter et al.
    (Mytilus edulis)                                                                                    (1996)

    Cockle               adult      stat    15      seawater               48-h LC50    7900      n     Portmann & Wilson
    (Cardium edule)                                                                                     (1971)

                         adult      stat+   15      seawater               96-h LC50    2610-           Portmann & Wilson
                                                                                        7900      n     (1971)

    Harpacticoid,        adult      stat    21±1    7s           7.9       96-h LC50    12 000    n     Bengtsson et al.
    copepod                                                                                             (1984)
    (Nitocra spinipes)

    Scud                 juvenile   stat    23±2                           18-h LC50    19 350    n     Bowman et al.
    (Hyalella azteca)                                                                                   (1981)

    Table 6.  Continued


    Organism             Size/age   Stat/   Temp    Hardness       pH      Parameterc   Concentration   Reference
                                    flowa   (°C)    (mg/litre)b                         (mg/litre)d

    Rotifer                                                                24-h LC50    35 884          Calleja et al.
    (Brachionus                                                                                         (1994)

    a    stat = static conditions (water unchanged for duration of test); stat+ = semi-static conditions (test solutions
         renewed every 24 h); flow = flow through conditions (concentration of toxicant continuously maintained);
         s = salinity, expressed as %
    b    hardness expressed as mg CaCO3 litre, unless stated otherwise; (1)- total hardness = 2.4 mmol/litre;
         (2)- total hardness = 2.5 mmol/litre
    c    All EC50 values refer to immobilization
    d    n = nominal concentration; m = measured concentration
    e    same as 24 h EC50 and EC0 values

    Table 7.  Acute toxicity of methanol to fish


    Organism          Size/age          Stat/     Temp       Hardness       pH         Parameter      Concentration  Reference
                                        flow      (°C)       (mg/litre)b                              (mg/litre)c

    Rainbow trout     (juv) 0.813 g     flow      12.7±1     46.4           7.0-8.0    24-h EC50d     13 200     m   Poirier et al.
    (Oncorhynchus                                                                                                    (1986)
                      (juv) 0.813 g     flow      12.7±1     46.4           7.0-8.0    96-h EC50e     13 000     m   Poirier et al.
                      (juv) 0.813 g     flow      12.7±1     46.4           7.0-8.0    24-h LC50      20 300     m   Poirier et al.
                      (juv) 0.813 g     flow      12.7±1     46.4           7.0-8.0    96-h LC50d     20 100     m   Poirier et al.
                      0.8 g             stat      12         44             7.4        96-h LC50      19 000     n   Mayer &
                                                                                                                     Ellersieck (1986)
                      (fingerlings)     flow      12                                   96-h LC50d     20 100     m   US EPA (1983)
                      1-6 g

    Fathead minnow    (28-32 d)         flow      23.3±1.7   46.4           7.0-8.0    24-h EC50d     29 700     m   Poirier et al.
    (Pimephales       0.126 g                                                                                        (1986)
                      (28-32 d)         flow      23.3±1.7   46.4           7.0-8.0    96-h EC50e     28 900     m   Poirier et al.
                      0.126 g                                                                                        (1986)

                      (28-32 d)         flow      23.3±1.7   46.4           7.0-8.0    24-h LC50d     29 700     m   Poirier et al.
                      0.126 g                                                                                        (1986)

                      (28-32 d)         flow      23.3±1.7   46.4           7.0-8.0    96-h LC50      29 400     m   Poirier et al.
                      0.126 g                                                                                        (1986)

                      (30 d) 0.12 g     flow      24-26      45.5           7.5        96-h LC50      28 100     m   Veith et al.

    Table 7. Continued


    Organism          Size/age          Stat/     Temp       Hardness       pH         Parameter      Concentration  Reference
                                        flow      (°C)       (mg/litre)b                              (mg/litre)c

    Bluegill sunfish  (juv) 3.07 g      flow      19.8±2.3   46.4           7.0-8.0    24-h EC50e     16 100     m   Poirier et al.
    (Leponimis                                                                                                       (1986)
                      (juv) 3.07 g      flow      19.8±2.3   46.4           7.0-8.0    24-h EC50e     16 100     m   Poirier et al.
                      (juv) 3.07 g      flow      19.8±2.3   46.4           7.0-8.0    48-h EC50e     16 000     m   Poirier et al.
                      (juv) 3.07 g      flow      19.8±2.3   46.4           7.0-8.0    96-h EC50e     12 700     m   Poirier et al.
                      (juv) 3.07 g      flow      19.8±2.3   46.4           7.0-8.0    24-h LC50d     19 100     m   Poirier et al.
                      (juv) 3.07 g      flow      19.8±2.3   46.4           7.0-8.0    96-h LC50      15 400     m   Poirier et al.
                      1.5 g             flow      25                                   24-h LC50d     19 230     m   US EPA (1983)
                      1.5 g             flow      25                                   96-h LC50      15 500     m   US EPA (1983)

    Guppy             2-3 months        stat+     21-23      25                        7-day LC50     10 860     m   Konemann (1981)g
    (Poecilia                                                                                                        Hermens &
    reticulata)                                                                                                      Leeuwangh (1982)

    Golden orfe       juv               stat      19-21      (1)            7.0-8.0    48-h LC50      >10 000f   m   Juhnke &
    (Leuciscus idus                                                                                                  Lüdemann
    melanotus)                                                                                                       (1978)
                      juv               stat      19-21      (1)            7.0-8.0    48-h LC0       7900f      m   Juhnke &
                      juv               stat      19-21      (1)            7.0-8.0    48-h LC100     >10 000f   m   Juhnke &

    Table 7. Continued


    Organism          Size/age          Stat/     Temp       Hardness       pH         Parameter      Concentration  Reference
                                        flow      (°C)       (mg/litre)b                              (mg/litre)c

    Bleak             8 cm              stat      10         7s             7.9        96-h LC50      28 000     n   Bengtsson
    (Alburnus                                                                                                        et al. (1984)

    Armed bullhead    adult             stat+     15         seawater                  96-h LC50d     7900-          Portmann &
    (Agonus                                                                                           26 070     n   Wilson (1971)

    a   stat = static conditions (water unchanged for duration of test)
        stat+ = semi-static conditions (test solutions renewed every 24 hours)
        flow = flow through conditions (concentration of toxicant continuously maintained)
        s = salinity, expressed as %
    b   hardness expressed as mg/CaCO3/litre, unless otherwise stated; (1)- total hardness = 2.7 mmol/litre;
    c   n = nominal concentration
        m = measured concentration
    d   same as 48-h LC50 or EC50 values
    e   effects on equilibrium, behaviour and coloration
    f   two laboratories following the same test protocol, same result from each laboratory
    g   consulted for experimental method only

    9.2  Terrestrial organisms

    9.2.1  Plants

         Hemming et al. (1995) determined the effect of methanol on the
    respiration of pepper  (Capsicum annuum), tomato  (Lycopersicon
     esulentum) and petunia  (Petunia hybrida). Whole plants were
    exposed to either methanol vapour or methanol solution. The general
    response to methanol was the same for the three species, with a
    respiratory rate increase of up to 50% at the lower methanol
    concentrations tested. The response was the same for exposure to
    methanol vapour or solution. Exposure of a single leaf resulted in a
    systemic response throughout the whole plant within a few hours. The
    response lasted for several weeks. Decreased metabolic rates and
    waterlogged appearance were reported in plants following a brief
    exposure of a leaf to methanol concentrations > 30%. Root tissue
    was reported to be more sensitive; a decrease in metabolic rate was
    reported following brief exposures to > 10% methanol.


    10.1  Evaluation of human health risks

    10.1.1  Exposure

         Methanol occurs naturally in humans, animals and plants. Humans
    are routinely exposed to low levels of methanol from both the diet
    (fruits, vegetables, fruit juices and foods containing the synthetic
    sweetener aspartame) and metabolic processes. Human exposure to large
    acutely toxic amounts of methanol via the oral route has principally
    been noted in a relatively small number of individuals, generally
    resulting through accidental or intentional consumption of methanol in
    illicit or contaminated alcoholic beverages.

         Methanol is produced in large amounts in many countries and is
    extensively used as an industrial solvent, a chemical intermediate
    (principally in the production of methyl tertiary butyl ether (MTBE),
    formaldehyde, acetic acid and glycol ethers), as a denaturant of
    ethanol and in a variety of consumer products.

         The most important route of occupational exposure to methanol is
    inhalation. Sources of occupational exposure include the dissipative
    emissions of methanol primarily occurring from miscellaneous solvent
    usage, methanol production, end-product manufacturing and bulk storage
    and handling.

         An increased number of people could be potentially exposed to
    environmental methanol as a result of the projected expanded use of
    methanol in methanol-blended gasolines. Exposures would principally
    arise from exhaust, evaporative emissions and normal heating of the
    engine. Simulation models based on 100% of all vehicles powered by
    methanol-based fuels predict concentrations of methanol in urban
    streets, expressways, railroad tunnels or parking garages ranging from
    a low of 1 mg/m3 (0.77 ppm) to a high of 60 mg/m3 (46 ppm).
    Predicted concentrations during refuelling of vehicles range from 30
    to 50 mg/m3 (23-38.5 ppm). For comparison and reference purposes, a
    current occupational exposure limit for methanol in many countries is
    260 mg/m3 (200 ppm) for an 8-h working day.

         There are limited data on human dermal exposure to methanol but
    the potential expanded use of methanol in automotive fuels would
    increase the potential for dermal exposure in a large number of

    10.1.2  Human health effects

         Methanol is rapidly absorbed by inhalation, ingestion and dermal
    exposure and is rapidly distributed to tissues according to the
    distribution of body water. The dose and blood concentrations of
    methanol and its metabolite formate are among the major determinants
    of the resultant toxicity in humans.

         The acute and short-term toxicity of methanol varies greatly
    between different species, toxicity being highest in species with a
    relatively poor ability to metabolize formate. Methanol has been
    studied most intensively in acute high-dose oral exposures in
    laboratory animals and as case reports of ingestion in humans. In
    general, humans and primates respond to such exposures with transient
    central nervous system (CNS) depression (intoxication), followed by an
    asymptomatic latent period culminating in metabolic acidosis and
    severe ocular toxicity (blindness).

         Non-primate animals such as rodents do not ordinarily exhibit
    metabolic acidosis or blindness on exposure to methanol although they
    exhibit the general narcotic effects noted in non-human primates and
    humans. The clearance of formate from the blood of exposed primates is
    at least 50% slower than in rodents. Formate, an endogenous biological
    substrate, is detoxified by a multi-step pathway to CO2 via a
    tetrahydrofolate (THF)-dependent pathway. Species such as rodents with
    high hepatic THF levels are less sensitive to the toxic effects of
    methanol than species with low hepatic THF levels such as humans and
    non-human primates. The faster rate of formate removal means that
    rodents do not accumulate formate above endogenous levels and hence
    are not susceptible to methanol-induced metabolic acidosis or ocular

         The primary enzymatic pathway that catalyses methanol metabolism
    in humans and non-human primates is alcohol dehydrogenase, while in
    the rat it is the catalase-peroxidase system. Available data suggest
    that methanol elimination from the systemic circulation is capacity-
    limited in both rats and in humans.

         Studies in humans and non-human primates exposed to
    concentrations of methanol ranging from 13 to 2601 mg/m3 (10 to
    2001 ppm) and the widely used occupational exposure limit of
    260 mg/mg3 (200 ppm) suggest that exposure to methanol vapour during
    the normal use of methanol fuel does not pose an unacceptable risk to
    healthy adults. General population exposures to methanol through air
    (although infrequently measured) are over 1000 times lower than
    occupational limits.

         Along with methanol, formate is present in blood at low
    endogenous concentrations, being found naturally in some foods and
    also produced as a by-product of several metabolic pathways, including
    histidine and tryptophan degradation. Background levels of formate in
    humans have been shown to range from 3 to 19 mg/litre (0.07-0.4 mM).

         Human susceptibility to the acute effects of methanol
    intoxication are extremely variable. On the basis of available human
    case reports, the minimum lethal dose in the absence of medical
    treatment is in the range of 0.3 to 1 g/kg. The major determinants of
    human susceptibility to methanol toxicity appear to be the concurrent
    ingestion of ethanol, which slows the entrance of methanol into the
    metabolic pathway, and the hepatic status of THF, which governs the
    rate of formate detoxification.

         Some human populations are at increased risk of folate
    deficiency. These include pregnant women, the elderly, individuals
    with poor-quality diets, alcoholics, and individuals on certain
    medications or with certain diseases.

         Much fewer data are available on the health effects in humans or
    laboratory animals associated with chronic or repeated exposure to
    methanol. In the absence of details of exposure (e.g., duration,
    concentrations), the effects of prolonged exposure are considered
    qualitatively very similar to those reported for acute cases, ranging
    from nausea and dizziness to blurred vision and temporary or permanent
    blindness. Chronic exposure to methanol vapour concentrations of 
    480-4000 mg/m3 (365-3080 ppm) has resulted in headache, dizziness, 
    nausea and blurred vision.

         There are no reports of carcinogenic, genotoxic, reproductive or
    developmental effects in humans due to methanol exposures.

    10.1.3  Approaches to assessment of risk

         The assessment of risk from chronic exposure requires dose-
    response information in the form of quantitative data from animal
    studies using appropriate test species and, where available, relevant
    human epidemiological and clinical data. In the case of methanol, the
    assessment of the risks of exposure is confounded by the fact that
    both methanol and its toxic metabolite, formate, are endogenous
    metabolic intermediates in all species including humans. Therefore, it
    must be assumed that there are levels of methanol exposure that do not
    represent significant risk. Determining the hazards associated with
    methanol exposure is additionally complicated by the fact that there
    are no adequate or comprehensive data from animal tests for chronic
    toxicity. Because of species differences in methanol metabolism, data
    available from normal rats appear to be inappropriate for use in
    characterizing the adverse effects of methanol in humans.
    Investigation of folate-deficient rodent models may provide valuable
    mechanistic, pharmacokinetic and toxicological effect information on
    methanol, particularly with respect to acute exposures. However, the
    nature of this animal model is such that it may have inherent
    weaknesses for the toxicological assessment of long-term exposure
    because of the adverse effects of folate deficiency itself and the
    background nutritional status of these rats in chronic studies.
    Similarities in the metabolism of methanol within primates suggest the
    use of non-human primates may be more appropriate for determining the
    nature of the hazards of methanol for humans, but adequate findings
    for chronic exposure are also lacking. Human methanol exposure data
    are extensive but primarily focus on acute exposure and clinical
    effects associated with poisoning. Although this information from
    humans does highlight the wide individual variability in the toxic
    response to methanol in humans, it contains limited comprehensive
    information on sub-chronic to chronic methanol exposure.

         Taken together, the above considerations suggest a conventional
    safety or risk assessment would not appear feasible, and would most
    likely be incomplete at present. An alternative approach might be one
    based on consideration of blood levels of the most toxic metabolite,
    formate. Since formate occurs naturally in humans, it would seem
    reasonable to assume that normal background levels should not pose any
    risk to health and consequently that levels of human exposure that do
    not result in levels of blood formate above background levels could be
    considered to pose insignificant risk. In this respect, based on
    information from limited studies in humans, it might be concluded that
    occupational exposure to current exposure limits (around 260 mg/m3)
    or single oral exposure to approximately 20 mg/kg body weight would
    fall into this category.

    10.2  Evaluation of effects on the environment

         Methanol may be released into the environment in significant
    amounts during its production, storage, transportation and use.

         Methanol is readily degraded in the environment by photo-
    oxidation. Half-lives of 7-18 days have been reported for the
    atmospheric reaction of methanol with hydroxyl radicals.

         Methanol is readily biodegradable under both aerobic and
    anaerobic conditions in a wide variety of environmental media. Many
    genera and strains of microorganisms are capable of using methanol as
    a growth substrate. Generally 80% of methanol in sewage systems is
    biodegraded within 5 days.

         Methanol is a normal growth substrate for many soil micro-
    organisms, which are capable of completely degrading methanol to
    carbon dioxide and water.

         Methanol is of low toxicity to aquatic and terrestrial organisms
    and it is not bioaccumulated. Effects due to environmental exposure to
    methanol are unlikely to be observed, unless it is released to the
    environment in large quantities, such as a spill.

         In summary, unless released in high concentrations, methanol
    would not be expected to persist or bioaccumulate in the environment.
    Low levels of release would not be expected to result in adverse
    environmental effects.


    11.1  Protection of human health

         a)   Methanol and methanol mixtures should be clearly labelled
              with a warning of the acute toxicity of methanol. Labels
              should use the description "methanol".

         b)   Storage, process and drying plants should be designed to
              protect against fire and explosion risks and exposure of
              personnel to methanol.

         c)   Workplaces where methanol is present should be provided with
              adequate ventilation to minimize inhalation exposure. Where
              necessary, personnel handling methanol should be provided
              with suitable protective clothing to prevent skin

         d)   Clinicians should be aware of the latent period and signs
              and symptoms following exposure to methanol, particularly by
              ingestion. Consideration associated with the existence of
              sensitive subgroups should be recognized, including those at
              increased risk of folate deficiency.

         e)   To avoid misuse, methanol used as fuel should be denatured
              and should contain a colour additive.

    11.2  Protection of the environment

         Although methanol is rapidly degraded in the environment and is
    of low acute toxicity to aquatic organisms, care should be taken to
    prevent spills of large quantities of methanol. Particular care should
    be taken to prevent spilled methanol reaching surface water.


         a)   Further research is needed to characterize the mechanism and
              pathogenesis of methanol-induced visual toxicity.

         b)   There is a need for definitive studies concerning the dose-
              response relationship for subtle CNS function using
              neurotoxic, neurobehavioural and ocular end-points across
              species at both single and repeated low-level exposures.

         c)   Investigation of the metabolism of methanol and formate in
              target organs, including the brain, retina, optic nerve and
              testes, under various exposure conditions is needed.

         d)   The pharmacokinetics of methanol and formate during
              pregnancy should be investigated in appropriate animal
              models to determine whether long-term exposure to methanol
              alters maternal or fetal disposition of methanol and

         e)   Additional studies are required to resolve whether methanol,
              formate or a combination of the two is responsible for
              methanol-induced developmental toxicity.

         f)   Exposure models should be developed and validated to
              estimate exposure concentrations and routes of exposure in
              specific exposure scenarios. Ambient and personal monitoring
              to determine the distribution of exposures should be

         g)   Dose-effect and time-course relationships for both acute and
              chronic effects of methanol or formate generated from
              methanol, in humans or appropriate models, have not been
              established and are essential for adequate risk assessment.

         h)   There is a need for studies into the nutritional, metabolic,
              genetic and age-related factors that may contribute to
              variation in susceptibility to methanol intoxication.

         i)   The genotoxic effects of methanol should be further
              investigated to determine whether it is clastogenic.

         j)   A rapid, practical and inexpensive assay for formate in
              blood and body tissues is needed for early diagnosis of
              methanol poisoning.

         k)   Improved therapeutic measures, including the development of
              4-methylpyrazole and new agents for reversing formate-
              induced visual neurotoxicity, are needed.


         Methanol was evaluated in 1970 as an extraction solvent by the
    Joint FAO/WHO Expert Committee on Food Additives.

         The Committee recommended that when used as an extraction
    solvent, residues should be reduced to a minimum by observing good
    manufacturing practice. It was considered that the limited uses of
    methanol as an extraction solvent for spice and hop oils meant that
    residues from these sources were insignificant in the diet (FAO/WHO,
    1971; WHO, 1971).


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    1.  Identité, propriétés physiques et chimiques et méthodes d'analyse

         Le méthanol se présente sous la forme d'un liquide incolore et
    limpide qui dégage une légère odeur alcoolique à l'état pur. Volatil
    et inflammable, il est miscible à l'eau et à de nombreux solvants
    organiques et forme un grand nombre d'azéotropes binaires.

         Il existe un certain nombre de méthodes, principalement la
    chromatographie en phase gazeuse avec détection par ionisation de
    flamme, pour la recherche et le dosage du méthanol dans divers
    échantillons prélevés dans l'environnement (air, eau, sol, et
    sédiments) ou dans les produits alimentaires. Ces méthodes sont
    également utilisées pour la recherche et le dosage du méthanol et de
    son principal métabolite, le formiate, dans les liquides et les tissus
    biologiques. Outre la chromatographie en phase gazeuse ave détection
    par ionisation de flamme, il existe des méthodes enzymatiques
    colorimétriques pour le dosage du formiate dans le sang, les urines et
    les tissus.

         Pour les analyses sur le lieu de travail, on commence
    généralement par recueillir et concentrer l'échantillon sur gel de
    silice, après quoi on procède à une extraction par l'eau, puis au
    dosage proprement dit par chromatographie en phase gazeuse avec
    détection par ionisation de flamme ou spectrométrie de masse.

    2.  Sources d'exposition humaine

         Le méthanol est présent à l'état naturel chez l'Homme, les
    animaux et les plantes. C'est un constituant du sang, de l'urine, de
    la salive et de l'air expiré. On a mesuré des concentrations moyennes
    de méthanol égales à 0,73 mg/litre dans les urines (valeurs
    extrêmes:0,3-2,61 mg/litre) chez des sujets non exposés et des valeurs
    allant de 0,06 à 0,32 µg/litre ont été observées dans l'air expiré.

         Le méthanol et le formiate naturellement présents dans
    l'organisme proviennent essentiellement de deux sources:
    l'alimentation et le métabolisme. Le méthanol d'origine alimentaire
    est principalement apporté par les fruits et les légumes frais ainsi
    que par les jus de fruits (teneur moyenne: 140 mg/litre avec des
    valeurs extrêmes de 12-640 mg/litre), les boissons fermentées
    (jusqu'à 1,5 g/litre), et autres composants du régime alimentaire
    (principalement les boissons non alcoolisées). L'aspartame est un
    édulcorant très utilisé dont l'hydrolyse donne du méthanol absorbable
    dans la proportion de 10% en poids.

         En 1991, la production mondiale de méthanol a atteint environ 20
    millions de tonnes, principalement par conversion catalytique de gaz
    de synthèse sous pression (hydrogène, dioxyde et monoxyde de carbone).
    La capacité mondiale de production devrait atteindre 30 millions de
    tonnes en 1995.

         Le méthanol est utilisé dans l'industrie pour la production
    de nombreux produits chimiques importants, principalement le
    méthyltertiobutyléther, le formaldéhyde, l'acide acétique, les éthers
    méthyliques du glycol, la méthylamine, les halogénures de méthyle et
    le méthacrylate de méthyle.

         Le méthanol entre dans la composition de nombreux solvants du
    commerce et de divers produits comme les peintures, les laques, les
    vernis, les diluants pour peintures, les détachants, les antigels,
    les liquides pour pare-brise, les dégivrants, les produits pour la
    photocopie, les solutions destinées à la dénaturation de l'éthanol
    ainsi que différent types de colles. Le méthanol pourrait également
    être utilisé directement comme combustible, ou bien encore être ajouté
    à l'essence à titre de combustible auxiliaire ou de diluant. Il est à
    noter que les cas les plus fréquents d'intoxication, mortelle ou non,
    par le méthanol, sont dus à l'ingestion volontaire ou accidentelle de
    produits qui en contiennent.

         On a trouvé du méthanol dans les gaz d'échappement des moteurs à
    essence et des moteurs diesel ainsi que dans la fumée de tabac.

    3.  Concentrations dans l'environnement et exposition humaine

         Les émissions de méthanol proviennent essentiellement des divers
    usages qui en sont faits en tant que solvant industriel ou domestique,
    des unités de production du composé lui-même ou de ses dérivés, enfin
    des pertes lors du stockage ou de la manipulation.

         Il peut y avoir exposition au méthanol sur le lieu de travail par
    inhalation ou contact cutané. A en juger d'après les limites
    d'exposition fixées par de nombreux pays, il semblerait que les
    travailleurs ne courent pas de danger tant que l'exposition exprimée
    en moyenne pondérée par rapport au temps ne dépasse pas 260 mg/m3
    (200 ppm) par journée de 8 h et semaine de 40 h.

         Actuellement la population est exposée à des concentrations qui
    sont 10 000 fois inférieures aux limites d'exposition professionnelle.
    En ce qui concerne l'exposition au méthanol contenu dans l'air, les
    concentrations vont de 0,001 mg/m3 (0,8 parties par milliard) en
    milieu rural, à près de 0,04 mg/m3 (30 parties par milliard) en
    milieu urbain.

         On ne possède guère de données sur la teneur en méthanol de l'eau
    de boisson après traitement, mais ce composé est en tout cas souvent
    présent dans les effluents industriels.

         Si les prévisions d'utilisation du méthanol comme combustible de
    substitution ou d'appoint augmentent de façon sensible, il faut
    s'attendre à ce que l'exposition à ce composé se généralise par
    suite de l'inhalation des vapeurs émises par les véhicules qui
    l'utiliseront, ou encore de son siphonage ou de son absorption
    percutanée lors de la manipulation de combustibles qui en

    4.  Distribution et transformation dans l'environnement

         Le méthanol se décompose rapidement dans l'environnement par
    photooxydation et sous l'action de processus de biodégration. Dans le
    cas de la réaction atmosphérique du méthanol avec les radicaux
    hydroxyle, on a mesuré une demi-vie de 7 à 18 jours.

         De nombreux genres et souches de microorganismes sont capables
    d'utiliser le méthanol comme substrat. Le composé est facilement
    dégradé en aérobiose ou en anaérobiose dans des milieux très divers,
    notamment les eaux douces ou salées, les sols et les sédiments,
    les eaux souterraines, les nappes phréatiques et les effluents
    industriels. En général, 70% du méthanol présent dans les eaux d'égout
    est décomposé en l'espace de 5 jours.

         Le méthanol sert normalement de substrat à de nombreux
    microorganismes terricoles, qui sont capables de le dégrader
    complètement en dioxyde carbone et en eau.

         Le méthanol est médiocrement absorbé par les sols. Sa
    bioaccumulation est faible dans la plupart des organismes.

         Le méthanol est peu toxique pour les organismes aquatiques et
    terrestres et il est peu probable que l'on observe des effets
    résultant d'une exposition environnementale à ce composé, sauf en cas
    de déversements dans la nature.

    5.  Absorption, distribution, biotransformation et élimination

         Après inhalation, ingestion ou contact cutané, le méthanol est
    facilement résorbé et se diffuse rapidement dans les tissus en
    fonction de la répartition de l'eau dans l'organisme. Une faible
    proportion est excrétée telle quelle par les poumons et les reins.

         Après ingestion, les concentrations sériques maximales sont
    atteintes en 30 à 90 minutes et le méthanol se répartit dans
    l'organisme avec un volume de distribution d'environ 0,6 litre/kg.

         Le méthanol est métabolisé principalement au niveau du foie
    selon un processus oxydatif qui le transforme successivement en
    formaldéhyde, acide formique et dioxyde de carbone. La première étape,
    celle de l'oxydation en formaldéhyde, s'effectue sous l'action de
    l'alcool-déshydrogénase hépatique; il s'agit d'une étape limitante qui
    correspond à un processus saturable. L'affinité relative de l'alcool-
    déshydrogénase pour le méthanol et pour l'éthanol est d'environ
    20:1. Lors de la seconde étape, le formaldéhyde est oxydé par la
    formaldéhyde - déshydrogénase en acide formique ou en formiate, selon
    la valeur du pH. La troisième étape consiste dans la détoxication de
    l'acide formique en dioxyde de carbone par des réactions dépendant de
    l'acide folique.

         L'élimination du méthanol présent dans le sang par la
    voie urinaire ou dans l'air expiré, soit tel quel, soit après
    métabolisation, se révèle être un processus lent chez toutes les
    espèces, en particulier par comparaison avec l'éthanol. Ainsi, la
    clairance du méthanol s'effectue avec une demi-vie de 24 h ou
    davantage pour des doses inférieures à 0,1 g/kg. C'est au niveau de la
    détoxication métabolique, c'est-à-dire de l'élimination du formiate,
    que des différences très importantes existent entre les rongeurs et
    les primates et ce sont elles qui expliquent la différence
    spectaculaire de toxicité que l'on constate entre les premiers et les

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

    6.1  Toxicité générale

         La toxicité aiguë et la toxicité à court terme du méthanol
    varient beaucoup selon les diverses espèces et alles sont maximales
    chez celles qui métabolisent relativement mal le formiate. En pareil
    cas, le méthanol provoque une intoxication mortelle par acidose
    métabolique et toxicité neuronale. En revanche, chez les animaux qui
    métabolisent bien le formiate, la mort survient habituellement par
    suite de la dépression du système nerveux central (coma, insuffisance
    respiratoire etc.). Chez les primates sensibles (comme l'Homme et les
    singes), il y a augmentation du taux sanguin de formiate après
    exposition au méthanol, alors que chez les rongeurs résistants, les
    lapins et les chiens, cette augmentation du taux de formiate ne se
    produit pas. L'Homme et les primates non humains présentent une
    sensibilité unique aux effets toxiques du méthanol. Globalement, le
    méthanol est peu toxique pour les animaux autres que les primates. La
    valeur de la DL50 et de la dose létale minimale pour une exposition
    par la voie orale, varie de 7000 à 13 000 mg/kg chez le rat, la
    souris, le lapin et le chien et de 2000 à 7000 mg/kg chez le singe.

         Chez des rats exposés à du méthanol 6 h par jour, 5 jours par
    semaine pendant 4 semaines, à des concentrations allant jusqu'à
    6500 mg/m3 (5000 ppm), on n'a observé aucun effet imputable à
    l'exposition, sauf une augmentation des écoulements au niveau du nez
    et des yeux. On estime qu'il s'agissait là de la conséquence d'une
    irritation des voies respiratoires supérieures.

         Des rats exposés à des vapeurs de méthanol à des concentrations
    pouvant atteindre 13 000 mg/m3 (10 000 ppm), 6 h par jour, 5 jours
    par semaine pendant 6 semaines, n'ont pas présenté de signes de
    toxicité pulmonaire.

         Chez le lapin, le méthanol irrite modérément la muqueuse
    oculaire. Lors d'une épreuve qui était une variante du test de
    maximalisation, il n'a pas provoqué de sensibilisation cutanée.

         Parmi les effets toxiques du méthanol observés chez les primates,
    on peut citer l'acidose métabolique et la toxicité oculaire qui ne se
    produisent en principe pas chez les rongeurs dont le taux de folate
    est suffisant. Ces différences de toxicité s'expliquent par des
    différences dans la vitesse de métabolisation du formiate, qui est un
    métabolite du méthanol. Par exemple, la clairance du formiate sanguin
    est au moins 50% plus lente chez les primates que chez les rongeurs.

         Des singes qui recevaient du méthanol par gavage à des doses
    dépassant 3000 mg/kg ont présenté une ataxie, de la faiblesse et une
    léthargie dans les quelques heures suivant l'administration du
    composé. Ces signes avaient tendance à disparaître en l'espace de 24 h
    et ils étaient suivis d'un coma passager chez certains des animaux.

         Chez des singes exposés à du méthanol à 20 reprises 6 h par jour
    et 5 jours par semaines, à la dose de 6500 mg/m3 (5000 ppm), on n'a
    pas constaté d'effets oculaires.

    6.2  Génotoxicité et cancérogénicité

         Les tests de mutation génétique effectués avec du méthanol sur
    des bactéries et des levures ont donné des résultats négatifs, mais le
    composé à provoqué une ségrégation chromosomique défectueuse chez
     Aspergillus. Il n'a pas provoqué d'échanges de chromatides soeurs
    dans des cellules de hamster chinois  in vitro, mais il a augmenté
    de façon sensible la fréquence des mutations dans des cellules
    lymphomateuses de souris L5178Y.

         L'inhalation de méthanol n'a pas provoqué de lésions chromo-
    somiques chez la souris. Par contre, on est fondé à penser, dans une
    certaine mesure, que l'administration intrapéritonéale ou buccale de
    méthanol augmente l'incidence des lésions chromosomiques chez la

         Rien n'indique, au vu de l'expérimentation animale, que le
    méthanol soit cancérogène, mais il faut admettre qu'il n'existe pas de
    modèle animal approprié pour ce genre d'étude.

    6.3  Toxicité pour la fonction reproductrice, embryotoxicité et

         Des études concernant les effets sur les taux de gonadotrophine
    et de testostérone d'une exposition au méthanol, par la voie
    respiratoire, pendant des périodes allant jusqu'à 6 semaines, ont
    donné des résultats contradictoires.

         En faisant inhaler du méthanol à des rongeurs gravides pendant
    toute la période de l'embryogénèse, on obtient toute une série
    d'effets tératogènes et embryocides qui dépendent de la concentration.
    Ainsi, on a observé des malformations attribuables au traitement et
    consistant principalement dans la présence de côtes cervicales
    surnuméraires ou rudimentaires, ou encore de malformations urinaires

    ou cardiovasculaires, chez des foetus de rats exposés 7 h par jour du
    7iéme au 15 ième jour de la gestation à une concentration de 
    26 000 mg/m3, soit l'équivalent de 20 000 ppm, de méthanol. A cette
    concentration, le méthanol était légèrement toxique pour les mères. En
    revanche, à la concentration de 6500 mg/m3 (5000 ppm), aucun effet
    indésirable n'a été noté chez les mères ou chez leur progéniture et on
    a considéré que cette valeur constituait la concentration sans effet
    nocif observable (NOAEL) pour ce système d'épreuve.

         Dans la progéniture de souris CD-1 exposées à du méthanol à des
    concentrations supérieures ou égales à 6500 mg/m3 (5000 ppm), 7 h par
    jour du 6 ième au 15 ième jour de la gestation, on a observé une
    incidence accrue d'exencéphalies et de fissures de la voûte palatine.
    Aux concentrations supérieures ou égales à 9825 mg/m3 (7500 ppm), les
    résorptions affectant la totalité de la portée étaient également plus
    fréquentes. Aux concentrations de 13 000 et 19 500 mg/m3 (10 000
    ou 15 000 ppm), on a observé une réduction du poids foetal. La
    concentration sans effet observable (NOAEL) sur le développement a été
    évaluée à 1300 mg/m3 (1000 ppm). Aux concentrations inférieures à
    9000 mg/m3 (7000 ppm), rien n'a été relevé qui puisse indiquer une
    toxicité du méthanol pour les mères.

         En donnant à la progéniture de ces souris CD-1 une dose de 4 g/kg
    de méthanol par gavage, on a constaté que l'incidence des effets
    nocifs (résorptions, fissures palatines et réduction du poids foetal)
    était analogue à celle constatée dans le groupe de rats auquels on
    avait fait inhaler le composé à la concentration de 13 000 mg/m3
    (10 000 ppm), probablement en raison de la fréquence respiratoire plus
    élevée chez la souris. La souris est plus sensible que le rat aux
    effets toxiques que le méthanol inhalé exerce sur le développement.

         Des signes neurologiques passagers et une réduction du poids
    corporel ont été enregistrés chez des souris CD-1 gravides, exposées
    6 h par jour à une concentration de 19 500 mg/m3, soit l'équivalent
    de 15 000 ppm tout au long de l'organogénèse (du sixième au quinzième
    jour). Parmi les malformations foetales observées aux doses de 19 500
    et 13 000 mg/m3, soit 15 000 et 10 000 ppm, on peut citer des
    anomalies neurales et oculaires, des fissures palatines, des
    hydronéphroses et des malformations des membres.

    7.  Effets sur l'Homme

         L'Homme (et les primates non humains) présentent une sensibilité
    unique au méthanol et les effets toxiques relevés chez ces espèces
    sont caractérisés par une acidémie formique, une acidose métabolique,
    une toxicité oculaire, une dépression du système nerveux, la cécité,
    le coma et la mort. Presque toutes les données que l'on possède sur la
    toxicité du méthanol pour l'Homme, ont trait aux conséquences des
    intoxications aiguës plutôt qu'à celles des intoxications chroniques.
    La très grande majorité des intoxications par le méthanol résultent de
    la consommation de boissons frelatées et de produits contenant du
    méthanol. C'est par ingestion que se produisent la plupart de ces

    intoxications, mais l'inhalation de vapeurs de méthanol sous forte
    concentration et l'absorption percutanée de solutions méthanoliques
    conduisent aux mêmes effets toxiques que l'ingestion. Les effets
    toxiques les plus fréquemment notés à la suite d'une exposition de
    longue durée, sont des effets oculaires très variés.

         Les effets toxiques du méthanol sont liés aux facteurs qui
    régissent la conversion du méthanol en acide formique et la
    transformation ultérieure de ce dernier en dioxyde de carbone par la
    voie des folates. Ces effets se manifestent lorsque la vitesse de
    formation du formiate est supérieure à sa vitesse de métabolisation.

         On ne sait pas avec certitude quelle est la dose mortelle pour
    l'Homme. En l'absence d'intervention médicale, la dose létale minimum
    se situe entre 0,3 et 1 g/kg. On ignore quelle est dose minimale à
    partir de laquelle se produisent des lésions oculaires permanentes.

         L'acidose métabolique est de gravité variable et alle n'est pas
    forcément en bonne corrélation avec la quantité de méthanol ingérée.
    Les intoxications méthanoliques se caractérisent par de grandes
    variations individuelles dans la dose toxique.

         Il semble que deux facteurs importants déterminent la sensibilité
    humaine aux effets toxiques du méthanol: 1) l'ingestion simultanée
    d'éthanol, qui retarde l'entrée du méthanol dans sa voie de
    dégradation métabolique; 2) le bilan des folates hépatiques, dont
    dépend la vitesse de détoxication du formiate.

         Les symptômes de l'intoxication méthanolique, qui peuvent ne se
    manifester qu'au bout de 12 à 24 h, consistent en troubles visuels,
    nausées, douleurs abdominales et musculaires, étourdissements,
    faiblesse et troubles de la conscience allant du coma au crises
    cloniques. Les troubles visuels apparaissent généralement dans les
    12 à 18 h suivant l'ingestion de méthanol et vont d'une légère
    photophobie avec une vision floue ou voilée à une réduction importante
    de l'acuité visuelle, voire à la cécité totale. Dans les cas extrêmes,
    l'intoxication peut avoir une issue fatale. Sur le plan clinique, la
    principale manifestation est une acidose métabolique grave par
    augmentation du trou anionique. L'acidose est largement attribuée à
    l'acide formique résulant de la métabolisation du méthanol.

         La concentration sanguine normale du méthanol d'origine endogène
    est inférieure à 0,5 mg/litre (0,02 mmol/litre), mais l'alimentation
    peut accroître le taux sanguin de méthanol. En général, les effets
    neurologiques centraux apparaissent lorsque la concentration sanguine
    du méthanol dépasse 200 mg/litre (6 mmol/litre); les symptômes
    oculaires se manifestent à partir de 500 mg/litre (16 mmol/litre) et
    la mort est survenue chez des patients non traités dont les taux
    sanguins initiaux de méthanol se situaient entre 1500 et
    2000 mg/litre, soit 47 à 62 mmol/litre.

         L'inhalation occasionnelle de vapeurs de méthanol à une
    concentration inférieure à 260 mg/m3 ou l'ingestion du liquide en
    quantités ne dépassant pas 20 mg/kg, ne devraient pas conduire à une
    accumulation de formiate supérieure au taux endogène, s'agissant de
    sujets en bonne santé ou présentant un déficit modéré en folate. Des
    troubles visuels de divers types (vision floue, rétrécissement du
    champ visuel, modification de la perception des couleurs et cécité
    temporaire ou permanente) ont été signalés chez des travailleurs
    exposés à des concentrations de méthanol dans l'air inférieures ou
    égales à environ 1500 mg/m3 (1200 ppm).

         On utilise largement la valeur de 260 mg/m3 (200 ppm) comme
    limite d'exposition professionnelle au méthanol. Cette valeur a été
    calculée pour protéger les travailleurs contre l'acidose formique
    induite par le méthanol et contre les effets toxiques de ce composé
    sur l'oeil et le système nerveux.

         On n'a pas signalé chez l'Homme d'autres effets nocifs qu'une
    légère irritation cutanée et oculaire aux concentrations très
    supérieures à 260 mg/m3 (200 ppm).

    8.  Effets sur les êtres vivants dans leur milieu naturel

         Pour les organismes aquatiques, la valeur de la CL50 varie de
    1300 à 15 900 mg/litre dans le cas des invertébrés (exposition de 48 h
    et de 96 h), et de 13 000 à 29 000 mg/litre dans le cas des poissons
    (exposition de 96 h).

         Le méthanol est peu toxique pour les organismes aquatiques et il
    n'est guère probable que l'on observe des effets imputables à une
    exposition environnementale, sauf en cas de déversement de méthanol
    dans la nature.


    1.  Identidad propiedades físicas y químicas y métodosanalíticos

         El metanol es un líquido transparente, incoloro, volátil e
    inflamable con un ligero olor alcohólico en estado puro. Se puede
    mezclar con el agua y con muchos disolventes orgánicos y forma
    numerosas mezclas azeotrópicas binarias.

         Hay métodos analíticos, principalmente la cromatografía de
    gases (CG) con detección por ionización de llama (DIL), para la
    determinación del metanol en diversos medios (aire, agua, suelo y
    sedimentos) y productos alimenticios, así como para la determinación
    del metanol y de su principal metabolito, el formiato, en los líquidos
    y tejidos corporales. Además de la CG-DIL, en la determinación del
    formiato en la sangre, la orina y los tejidos se utilizan
    procedimientos enzimáticos con resultados finales colorimétricos.

         Para la determinación del metanol en el lugar de trabajo se suele
    comenzar con la recolección y concentración en silicagel, seguida de
    extracción acuosa y CG-DIL o análisis de CG-espectrometría de masa del

    2.  Fuentes de exposición humana

         El metanol está presente de forma natural en el ser humano, los
    animales y las plantas. Es un elemento constitutivo natural en la
    sangre, orina, la saliva y el aire expirado. Se ha descrito una
    concentración media de metanol en orina de 0,73 mg/litro (intervalo de
    0,3-2,61 µg/litro) en individuos no expuestos y una gama de 0,06 a
    0,32 µg/litro en el aire expirado.

         Las dos fuentes más importantes de acumulación básica de
    metanol y formiato en el organismo son la alimentación y los
    procesos metabólicos. El metanol está disponible en la alimentación
    principalmente a partir de las frutas y hortalizas frescas, los zumos
    de fruta (promedio de 140 mg/litro, margen de variación de 12 a
    640 mg/litro), las bebidas fermentadas (hasta 1,5 g/litro) y los
    alimentos de dieta (sobre todo bebidas no alcohólicas). El aspartame
    es un edulcorante artificial muy utilizado, y al hidrolizarse el 10%
    (por peso) de la molécula se convierte en metanol libre, que queda
    disponible para la absorción.

         En 1991 se produjeron en todo el mundo alrededor de 20 millones
    de toneladas de metanol, fundamentalmente por conversión catalítica de
    gas de síntesis a presión (hidrógeno, anhídrido carbónico y monóxido
    de carbono). Según las proyecciones, la capacidad mundial se elevaría
    a 30 millones de toneladas en 1995.

         El metanol se utiliza en la producción industrial de numerosos
    compuestos orgánicos importantes, sobre todo metil terbutil éter
    (MTBE), formaldehído, ácido acético, éteres de metilglicol,
    metilamina, haluros de metilo y metacrilato de metilo.

         El metanol es un elemento constitutivo de un gran número de
    disolventes y productos de consumo disponibles en el comercio, como
    pinturas, gomas laca, barnices, diluyentes de pinturas, soluciones
    limpiadoras, soluciones anticongelantes, líquidos limpiaparabrisas y
    anticongelantes para automóviles, líquidos de multicopista,
    desnaturalizante para el etanol y pegamento para actividades de
    pasatiempo y artesanía. Una aplicación potencialmente en gran escala
    del metanol está en su uso directo como combustible, mezclado con
    gasolina o para aumentar su volumen. Hay que señalar que la mayor
    morbilidad y mortalidad se ha relacionado con la ingestión oral
    deliberada o accidental de mezclas con contenidos de metanol.

         Se ha detectado metanol en los gases de escape de motores tanto
    de gasolina como diésel y en el humo del tabaco.

    3.  Niveles ambientales y exposición humana

         Las emisiones de metanol se derivan principalmente de los
    diversos usos industriales y domésticos como disolvente, su
    producción, la manufactura final y las pérdidas durante el
    almacenamiento a granel y la manipulación.

         Pueden darse exposiciones al metanol en los lugares de trabajo
    mediante inhalación o contacto cutáneo. Muchos de los límites
    nacionales de exposición para la higiene del trabajo parecen indicar
    que los trabajadores están protegidos de cualquier efecto adverso si
    la exposición no supera un promedio ponderado por el tiempo de 
    260 mg/m3 (200 ppm) de metanol en cualquier jornada de trabajo 
    de 8 horas y en una semana laboral de 40 horas.

         La exposición general actual de la población por medio del aire
    es normalmente 10 000 veces inferior a los límites ocupacionales.
    La población general está expuesta al metanol en el aire a
    concentraciones que oscilan entre menos de 0,001 mg/m3 (0,8 ppm)
    en el aire del medio rural y cerca de 0,04 mg/m3 (30 ppm) en el
    aire urbano.

         Los datos sobre la presencia del metanol en el agua potable de
    uso inmediato son limitados, pero con frecuencia se encuentra metanol
    en efluentes industriales.

         En el caso de que el uso previsto del metanol como
    combustible alternativo o mezclado con otros combustibles aumente
    considerablemente, cabe prever que habrá una exposición generalizada
    al metanol por medio de la inhalación de vapores procedentes de los
    vehículos que funcionen con él y del bombeo o la absorción percutánea
    de combustibles o mezclas de metanol.

    4.  Distribución y transformación en el medio ambiente

         El metanol se degrada fácilmente en el medio ambiente mediante
    procesos de fotooxidación y biodegradación. Se han descrito semividas
    de 7-18 días para la reacción atmosférica del metanol con radicales

         Hay muchos géneros y cepas de microorganismos capaces de utilizar
    el metanol como sustrato de crecimiento. El metanol es fácilmente
    degradable en condiciones tanto aerobias como anaerobias en una amplia
    variedad de medios naturales, entre ellos agua dulce y salada,
    sedimentos y suelos, agua freática, material de acuíferos y aguas
    residuales industriales; el 70% del metanol de los alcantarillados se
    suele degradar en un plazo de 5 días.

         El metanol es un sustrato de crecimiento normal de muchos
    microorganismos del suelo, que son capaces de degradarlo completamente
    a anhídrido carbónico y agua.

         El metanol tiene una capacidad de absorción bastante baja en los
    suelos. La bioconcentración en la mayoría de los organismos es escasa.

         El metanol es poco tóxico para los organismos acuáticos y
    terrestres y no es probable que se observen efectos debidos a su
    exposición en el medio ambiente, excepto en el caso de un derrame.

    5.  Absorción, distribución, biotransformación yeliminación

         El metanol se absorbe fácilmente por inhalación, ingestión y
    exposición cutánea y se distribuye rápidamente en los tejidos
    siguiendo la distribución del agua corporal. Por los pulmones y los
    riñones se excreta una pequeña cantidad de metanol sin cambios.

         Tras la digestión se alcanzan niveles máximos en suero en un
    plazo de 30-90 minutos, y se reparte por todo el organismo con un
    volumen de distribución aproximado de 0,6 litros/kg.

         El metanol se metaboliza principalmente en el hígado siguiendo
    una fase oxidativa secuencial a formaldehído, ácido fórmico y
    anhídrido carbónico. El paso inicial consiste en la oxidación a
    formaldehído por acción de la alcohol deshidrogenasa hepática, que
    es un proceso saturable limitante de la velocidad. La afinidad
    relativa de la alcohol deshidrogenasa por el etanol y el metanol es
    aproximadamente de 20:1. En el segundo paso, el formaldehído se oxida
    por acción de la formaldehído deshidrogenasa a ácido fórmico o
    formiato, en función del pH. En el tercer paso, el ácido fórmico se
    destoxifica a anhídrido carbónico mediante reacciones dependientes del

         La eliminación del metanol de la sangre a través de la orina y el
    aire exhalado y por el metabolismo parece ser lenta en todas las
    especies, especialmente si se compara con el etanol. En el proceso se

    han descrito períodos de semieliminación de 24 horas o más con dosis
    superiores a 1 g/kg y de 2,5-3 horas para dosis inferiores a 0,1 g/kg.
    El ritmo de desintoxicación metabólica o eliminación del formiato sí
    es muy distinto entre los roedores y los primates, constituyendo la
    base de las enormes diferencias de toxicidad del metanol observadas
    entre ambos grupos.

    6.  Efectos en mamíferos de laboratorio y en sistemas deensayo
         in vitro

    6.1  Toxicidad sistémica

         La toxicidad aguda y a corto plazo del metanol varía mucho entre
    las distintas especies, siendo máxima en las especies con una
    capacidad relativamente escasa para metabolizar el formiato. En tales
    casos de metabolismo deficiente del formiato, se produce una
    intoxicación letal por metanol como consecuencia de la acidosis
    metabólica y la toxicidad neuronal, mientras que en los animales que
    metabolizan fácilmente el formiato la muerte suele deberse a las
    consecuencias de la depresión del sistema nervioso central (coma,
    insuficiencia respiratoria, etc.). En las especies de primates
    sensibles (el ser humano y los monos) aumenta la concentración del
    formiato en sangre tras la exposición al metanol, pero no en los
    roedores, los conejos y los perros resistentes. Los primates humanos y
    no humanos tienen una sensibilidad única a los efectos tóxicos del
    metanol. En conjunto, el metanol tiene una toxicidad aguda baja para
    los animales no primates. Los valores de la DL50 y las dosis letales
    mínimas tras la exposición oral oscilan entre 7000 y 13 000 mg/kg en
    ratas, ratones, conejos y perros y entre 2000 y 7000 mg/kg en el mono.

         Las ratas expuestas a concentraciones de metanol de hasta 
    6500 mg/m3 (5000 ppm) 6 horas al día y 5 días a la semana durante 
    un período de 4 semanas no mostraron ningún efecto relacionado con la
    exposición, salvo el aumento de la exudación alrededor de la nariz y
    de los ojos. Se consideró que esto era un reflejo de la irritación de
    las vías respiratorias superiores.

         Las ratas expuestas a concentraciones de vapor de metanol de
    hasta 13 000 mg/m3 (10 000 ppm) 6 horas al día y 5 días a la semana
    durante un período de 6 semanas, no mostraron ninguna toxicidad

         En el conejo el metanol es moderadamente irritante de los ojos.
    En una prueba de maximización modificada no se produjo sensibilización

         Entre los efectos tóxicos observados en primates expuestos al
    metanol cabe mencionar la acidosis metabólica y la toxicidad ocular,
    pero estos efectos no aparecen normalmente en roedores con una
    concentración suficiente de folato. Las diferencias de toxicidad se
    deben a variaciones en la tasa del metabolismo del formiato,
    metabolito del metanol. Por ejemplo, la eliminación del formiato de la

    sangre de los primates expuestos es como mínimo un 50% más lenta que
    en los roedores.

         En monos que recibieron dosis de metanol superiores a 3000 mg/kg
    con sonda se observó ataxia, debilidad y letargo a las pocas horas de
    exposición. Estos signos mostraron una tendencia a desaparecer en un
    plazo de 24 horas y los siguió un coma transitorio en algunos de los

         En monos expuestos a metanol durante 6 horas al día y 5 días a la
    semana, con 20 exposiciones repetidas a 6500 mg/m3 (5000 ppm) de
    metanol no aparecieron efectos oculares.

    6.2  Genotoxicidad y carcinogenicidad

         El metanol ha dado resultados negativos en cuanto a la mutación
    genética en ensayos con bacterias y levaduras, pero indujo anomalías
    en la segregación cromosómica en  Aspergillus. No indujo intercambios
    de cromátidas hermanas en células de hámster chino  in vitro, pero
    provocó un aumento considerable de la frecuencia de las mutaciones en
    células de linfoma de ratón L5178Y.

         La inhalación de metanol no indujo daños en los cromosomas de
    ratones. Hay algunas pruebas de que la administración oral e
    intraperitoneal ha aumentado la incidencia de daños en los cromosomas
    de ratones.

         No hay ninguna prueba en estudios con animales que indique que el
    metanol es carcinógeno, aunque se reconoce que se carece de un modelo
    animal apropiado.

    6.3  Toxicidad reproductiva, embriotoxicidad yteratogenicidad

         Se han descrito resultados contradictorios en relación con los
    efectos de la inhalación de metanol durante un período de hasta 6
    semanas sobre las concentraciones de gonadotropina y testosterona.

         La inhalación de metanol por roedores gestantes durante todo el
    período de la embriogénesis induce una amplia variedad de efectos
    teratogénicos y embrioletales dependientes de la concentración. En
    fetos de ratas expuestas 7 horas al día durante 7-15 días de gestación
    a 26 000 mg/m3  (20 000 ppm) de metanol se encontraron malformaciones
    relacionadas con el tratamiento, predominantemente costillas
    cervicales adicionales o rudimentarias y defectos del aparato urinario
    o cardiovascular. Con este nivel de exposición se observó una ligera
    toxicidad materna, pero no se detectó ningún efecto adverso para la
    madre o la descendencia en animales expuestos a 6500 mg/m3 (5000
    ppm), lo cual se interpretó como la concentración sin efectos adversos
    observados (NOAEL) para este sistema de prueba.

         Se registró una mayor incidencia de exencefalia y paladar hendido
    en la descendencia de ratones CD-1 expuestos 7 horas al día durante
    los días 6-15 de gestación a concentraciones de metanol de 6500 mg/m3
    (5000 ppm) o más. La mortalidad embriofetal aumentó a concentraciones
    de 9825 mg/m3 (7500 ppm) o más y fue mayor la incidencia de
    resorciones de toda la descendencia. A concentraciones de 13 000 y
    19 500 mg/m3 (10 000 y 15 000 ppm) se observó un peso fetal reducido.
    La NOAEL para la toxicidad del desarrollo fue de 1300 mg/m3 (1000
    ppm) de metanol. No se encontraron pruebas de toxicidad materna en la
    exposición a concentraciones de metanol inferiores a 9000 mg/m3
    (7000 ppm).

         Cuando se administraron mediante sonda 4 g/kg de metanol a la
    descendencia de ratones CD-1 gestantes, la incidencia de los efectos
    adversos en la resorción, los defectos externos como el paladar
    hendido y el peso del feto fue análoga a la observada en el grupo
    expuesto por inhalación a 13 000 mg/m3 (10 000 ppm), posiblemente
    debido al mayor ritmo de respiración del ratón. Éste es más sensible
    que la rata a la toxicidad en el desarrollo provocada por el metanol

         En hembras CD-1 expuestas a 19 500 mg/m3 (15 000 ppm) durante 6
    horas diarias a lo largo de la organogénesis (días de gestación 6-15)
    aparecieron signos neurológicos transitorios y una reducción del peso
    corporal. Entre las malformaciones fetales registradas con 13 000 y
    19 500 mg/m3 (10 000 y 15 000 ppm) cabe mencionar defectos neurales y
    oculares, paladar hendido, hidronefrosis y anomalías de las

    7.  Efectos en el ser humano

         El ser humano y los primates no humanos tienen una sensibilidad
    única a la intoxicación por metanol, caracterizándose los efectos
    tóxicos en estas especies por acidemia fórmica, acidosis metabólica,
    toxicidad ocular, depresión del sistema nervioso, ceguera, coma y la
    muerte. Casi toda la información disponible sobre la toxicidad del
    metanol en el ser humano se refiere a las consecuencias de
    exposiciones agudas más que crónicas. La inmensa mayoría de las
    intoxicaciones por metanol se han debido al consumo de bebidas
    adulteradas y de productos con metanol. Aunque la ingestión es con
    diferencia la vía más frecuente de intoxicación, la inhalación de
    concentraciones elevadas de vapor de metanol o la absorción percutánea
    de líquidos metanólicos son tan eficaces como la vía oral para la
    producción de efectos tóxicos agudos. La consecuencia más conocida
    para la salud de una exposición a plazo más largo a niveles inferiores
    de metanol es una amplia gama de efectos oculares.

         Las propiedades tóxicas del metanol se basan en factores que
    rigen tanto su conversión en ácido fórmico como el posterior
    metabolismo del formiato a anhídrido carbónico en la ruta del folato.
    La toxicidad es manifiesta si la generación de formiato continúa a un
    ritmo superior al del metabolismo.

         No se conoce con seguridad la dosis letal del metanol para el ser
    humano. La dosis letal mínima del metanol en ausencia de tratamiento
    médico está comprendida entre 0,3 y 1 g/kg. No se conoce la dosis
    mínima que provoca defectos visuales permanentes. 

         La gravedad de la acidosis metabólica es variable y puede no
    tener correlación con la cantidad de metanol ingerido. Una
    característica destacada de la intoxicación aguda por metanol es la
    enorme variabilidad interindividual de la dosis tóxica.

         Parece que dos factores determinantes importantes de la
    susceptibilidad humana a la toxicidad por metanol son: 1) ingestión
    junto con etanol, que reduce el ritmo de entrada de metanol en la ruta
    metabólica, y 2) la situación del folato hepático, que rige la tasa de
    desintoxicación del formiato.

         Los síntomas y signos de intoxicación por metanol, que pueden
    aparecer solo transcurrido un período asintomático aproximado de 12 a
    24 horas, son perturbaciones visuales, náuseas, dolor abdominal y
    muscular, mareo, debilidad y perturbaciones de la conciencia que van
    desde el coma hasta las convulsiones clónicas. Las alteraciones
    visuales aparecen en general entre las 12 y las 48 horas después de la
    ingestión del metanol y van desde la ligera fotofobia y la visión
    brumosa o borrosa hasta una reducción acentuada de la agudeza visual y
    la ceguera completa. En casos extremos se produce la muerte. La
    principal característica clínica es una acidosis metabólica grave del
    tipo de deficiencia de aniones. La acidosis se atribuye en gran medida
    al ácido fórmico producido al metabolizarse el metanol.

         La concentración normal en sangre de metanol procedente de
    fuentes endógenas es de menos de 0,5 mg/litro (0,02 mmol/litro), pero
    las fuentes alimenticias pueden elevarla. En general aparecen efectos
    en el sistema nervioso central cuando la concentración de metanol en
    sangre supera los 200 mg/litro (6 mmol/litro); se detectan síntomas
    oculares por encima de 500 mg/litros (16 mmol/litro) y se han
    registrado casos de letalidad en pacientes no tratados con
    concentraciones iniciales de metanol del orden de 1500-2000 mg/litro
    (47-62 mmol/litro).

         La inhalación aguda de concentraciones de vapor de metanol por
    debajo de 260 mg/m3 o la ingestión de cantidades de hasta 20 mg/kg de
    metanol por parte de personas sanas o con una deficiencia moderada de
    folato no debe dar lugar a la acumulación de formiato por encima de
    las concentraciones endógenas.

         Se ha informado de alteraciones visuales de varios tipos (visión
    borrosa, reducción del campo visivo, cambios en la percepción de los
    colores y ceguera temporal o permanente) en trabajadores expuestos a
    concentraciones de metanol en el aire de alrededor de 1500 mg/m3
    (1200 ppm) o más.

         Un límite muy utilizado de exposición en el trabajo para el
    metanol es el de 260 mg/m3 (200 ppm), concebido para proteger a los
    trabajadores de cualquiera de los efectos de la acidosis metabólica
    por ácido fórmico inducida por el metanol y de la toxicidad ocular y
    del sistema nervioso.

         No se ha notificado ningún otro efecto adverso del metanol en
    el ser humano, salvo una ligera irritación cutánea y ocular con
    exposiciones muy superiores a los 26 mg/m3 (200 ppm).

    8.  Efectos en los organismos del medio ambiente

         Los valores de la CL50 en organismos acuáticos oscilan entre
    1300 y 15 900 mg/litro para los invertebrados (48 y 96 horas de
    exposición) y entre 13 000 y 29 000 mg/litro para los peces (96 horas
    de exposición).

         El metanol es poco tóxico para los organismos acuáticos siendo
    poco probable la observación de efectos debidos a exposición ambiental
    al metanol, excepto en el caso de un derrame.

    See Also:
       Toxicological Abbreviations
       Methanol (HSG 105, 1997)
       Methanol (ICSC)
       Methanol (FAO Nutrition Meetings Report Series 48a)
       METHANOL (JECFA Evaluation)
       Methanol (PIM 335)