INTERIM 1: 1/2003 

INTERIM 2: 2/2005

INTERIM ACUTE EXPOSURE GUIDELINE LEVELS 

 (AEGLs) 

METHANOL 

(CAS Reg. No. 67-56-1) 

For 

 NAS/COT Subcommittee for AEGLs 

February 2005 
METHANOL Interim 2: 2/2005 

ii 

 PREFACE 

Under the authority of the Federal Advisory Committee Act (FACA) P. L. 92-463 of 1972, 

the National Advisory Committee for Acute Exposure Guideline Levels for Hazardous 

Substances (NAC/AEGL Committee) has been established to identify, review and interpret 

relevant toxicologic and other scientific data and develop AEGLs for high priority, acutely toxic 

chemicals. 

AEGLs represent threshold exposure limits for the general public and are applicable to 

emergency exposure periods ranging from 10 minutes to 8 hours. AEGL-2 and AEGL-3 levels, 

and AEGL-1 levels as appropriate, will be developed for each of five exposure periods (10 and 

30 minutes, 1 hour, 4 hours, and 8 hours) and will be distinguished by varying degrees of 

severity of toxic effects. It is believed that the recommended exposure levels are applicable to 

the general population including infants and children, and other individuals who may be 

sensitive or susceptible. The three AEGLs have been defined as follows: 

AEGL-1 is the airborne concentration (expressed as ppm or mg/m;) of a substance 

above which it is predicted that the general population, including susceptible individuals, could 

experience notable discomfort, irritation, or certain asymptomatic, non-sensory effects. 

However, the effects are not disabling and are transient and reversible upon cessation of 

exposure. 

AEGL-2 is the airborne concentration (expressed as ppm or mg/m;) of a substance 

above which it is predicted that the general population, including susceptible individuals, could 

experience irreversible or other serious, long-lasting adverse health effects, or an impaired 

ability to escape. 

AEGL-3 is the airborne concentration (expressed as ppm or mg/m;) of a substance 

above which it is predicted that the general population, including susceptible individuals, could 

experience life-threatening health effects or death. 

Airborne concentrations below the AEGL-1 represent exposure levels that could produce 

mild and progressively increasing odor, taste, and sensory irritation, or certain asymptomatic, 

non-sensory effects. With increasing airborne concentrations above each AEGL level, there is a 

progressive increase in the likelihood of occurrence and the severity of effects described for 

each corresponding AEGL level. Although the AEGL values represent threshold levels for the 

general public, including sensitive subpopulations, it is recognized that certain individuals, 

subject to unique or idiosyncratic responses, could experience the effects described at 

concentrations below the corresponding AEGL level. 
METHANOL Interim 2: 2/2005 

iii 

TABLE OF CONTENTS

PREFACE ..................................................................................................................................... ii 

TABLE OF CONTENTS................................................................................................................iii 

EXECUTIVE SUMMARY ............................................................................................................viii 

1. INTRODUCTION...............................................................................................................1 

2. HUMAN TOXICITY DATA ................................................................................................2 

2.1. Acute Lethality.......................................................................................................2 

2.2. Nonlethal Toxicity ..................................................................................................6 

2.2.1. Experimental Studies.................................................................................7 

2.2.2. Occupational Exposure..............................................................................9 

2.2.3. Case Studies ...........................................................................................11 

2.3. Developmental/Reproductive Toxicity .................................................................12 

2.4. Genotoxicity.........................................................................................................13 

2.5. Carcinogenicity....................................................................................................13 

2.6. Summary .............................................................................................................13 

3. ANIMAL TOXICITY DATA..............................................................................................14 

3.1. Acute Lethality.....................................................................................................14 

3.1.1. Non-human Primates...............................................................................14 

3.1.2. Cats .........................................................................................................15 

3.1.3. Rats .........................................................................................................15 

3.1.4. Mice .........................................................................................................15 

3.2. Nonlethal Toxicity ................................................................................................17 

3.2.1 Non-human Primates...............................................................................17 

3.2.2. Dogs ........................................................................................................19 

3.2.3. Cats .........................................................................................................19 

3.2.4. Rats .........................................................................................................19 

3.2.5. Mice .........................................................................................................20 

3.3. Developmental/Reproductive Toxicity .................................................................21 

3.3.1. Nonhuman Primates................................................................................22 

3.3.2. Rats .........................................................................................................23 

3.3.3. Mice .........................................................................................................24 

3.4. Genotoxicity.........................................................................................................25 
METHANOL Interim 2: 2/2005 

iv 

3.5. Carcinogenicity....................................................................................................26 

3.6. Summary .............................................................................................................26 

4. SPECIAL CONSIDERATIONS .......................................................................................27 

4.1. Metabolism and Disposition ...............................................................................27 

4.1.1. Absorption, Distribution and Elimination..................................................27 

4.1.2. Metabolism ..............................................................................................28 

4.1.3. Pharmacokinetic Models..........................................................................30 

4.2. Mechanism of Toxicity.........................................................................................35 

4.3. Pharmacokinetics and Toxic Effects in Normal and Folate-Deficient Animals ....37 

4.4. Structure-Activity Relationships...........................................................................39 

4.5. Other Relevant Information .................................................................................40 

4.5.1. Species Variability ...................................................................................40 

4.5.2. Intraspecies Variability.............................................................................40 

4.5.3. Combination Effects.................................................................................40 

4.5.4. Role of Folate in Human Birth Defects ....................................................40 

5. RATIONALE AND PROPOSED AEGL-1 ......................................................................41 

5.1. Human Data Relevant to AEGL-1 .......................................................................41 

5.2. Animal Data Relevant to AEGL-1........................................................................42 

5.3. Derivation of AEGL-1...........................................................................................42 

6. RATIONALE AND PROPOSED AEGL-2 ......................................................................43 

6.1. Human Data Relevant to AEGL-2 .......................................................................43 

6.2. Animal Data Relevant to AEGL-2........................................................................44 

6.3. Derivation of AEGL-2...........................................................................................45 

7. RATIONALE AND PROPOSED AEGL-3 ......................................................................47 

7.1. Human Data Relevant to AEGL-3 .......................................................................47 

7.2. Animal Data Relevant to AEGL-3 .......................................................................49 

7.3. Derivation of AEGL-3...........................................................................................50 

8. SUMMARY OF PROPOSED AEGLS.............................................................................52 

8.1. AEGL Values and Toxicity Endpoints..................................................................52 

8.2. Comparison with Other Standards and Criteria...................................................54 

8.3. Data Adequacy and Research Needs .................................................................57 

9. REFERENCES................................................................................................................58 
METHANOL Interim 2: 2/2005 

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APPENDIX A Time Scaling Calculations for AEGLs .................................................................69 

AEGL-1 ...........................................................................................................................70 

AEGL-2 ...........................................................................................................................71 

AEGL-3 ...........................................................................................................................72 

APPENDIX B Pharmacokinetic Calculations .............................................................................73 

Calculation of Exposure Concentrations for Humans .....................................................74 

Comparison of the Perkins et al. (1995a) and Bouchard et al. (2001) models ...............76 

APPENDIX C Level of Distinct Odor Awareness .......................................................................78 

APPENDIX D Derivation Summary for Methanol AEGLs...........................................................80 

AEGL-1 VALUES ............................................................................................................81 

AEGL-2 VALUES ............................................................................................................84 

AEGL-3 VALUES ............................................................................................................88 
METHANOL Interim 2: 2/2005 

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LIST OF TABLES

TABLE 1: CHEMICAL AND PHYSICAL DATA .............................................................................1 

TABLE 2: ACUTE ORAL METHANOL INTOXICATIONS IN HUMANS........................................5 

TABLE 3: SUMMARY OF EFFECTS ON HUMANS AFTER INHALATION OF METHANOL.....12 

TABLE 4: SUMMARY OF ACUTE LETHAL INHALATION DATA IN LABORATORY ANIMALS 16 

TABLE 5: SUMMARY OF NON-LETHAL EFFECTS IN LABORATORY ANIMALS ...................20 

TABLE 6: METABOLISM OF METHANOL AND ENZYMES INVOLVED ...................................29 

TABLE 7: KINETIC PARAMETERS OF METHANOL METABOLISM ........................................30 

TABLE 8: BLOOD METHANOL CONCENTRATIONS IN HUMANS AND ANIMALS AFTER A 

SINGLE EXPOSURE TO METHANOL ...........................................................................31 

TABLE 9: AEGL-1 VALUES FOR METHANOL ..........................................................................43 

TABLE 10: AEGL-2 VALUES FOR METHANOL ........................................................................47 

TABLE 11: AEGL-3 VALUES FOR M .........................................................................................51 

TABLE 12: SUMMARY/RELATIONSHIP OF PROPOSED AEGL VALUES...............................53 

TABLE 13. EXTANT STANDARDS AND GUIDELINES FOR METHANOL...............................55 

TABLE 14: PARAMETERS OF PHARMACOKINETIC MODEL .................................................74 

TABLE 15: CALCULATION OF CONCENTRATIONS FOR INHALATION EXPOSURE I..........75 

TABLE 16: CALCULATION OF CONCENTRATIONS FOR INHALATION EXPOSURE II.........75 

TABLE 17: CALCULATION OF METHANOL CONCENTRATIONS RESULTING IN A BLOOD 

CONCENTRATION OF 30 mg/l ......................................................................................76 

TABLE 18: CALCULATION OF METHANOL CONCENTRATIONS RESULTING IN A BLOOD 

CONCENTRATION OF 100 mg/l ....................................................................................76 

TABLE 19: CALCULATION OF METHANOL CONCENTRATIONS RESULTING IN A BLOOD 

CONCENTRATION OF 250 mg/l ....................................................................................77 
METHANOL Interim 2: 2/2005 

vii 

LIST OF FIGURES

FIGURE 1: BLOOD CONCENTRATIONS OF METHANOL IN DIFFERENT SPECIES .............34 

FIGURE 2: MEASURED BLOOD METHANOL CONCENTRATIONS IN HUMAN FATALITIES 49 

FIGURE 3: CATEGORICAL REPRESENTATION OF ALL METHANOL INHALATION DATA .54 
METHANOL Interim 2: 2/2005 

viii 

EXECUTIVE SUMMARY

Methanol (also known as wood alcohol) is a clear, colorless, volatile, flammable liquid 

with a sweet odor. It is used in paint removers, windshield washer fluid, automotive fuel, and 

antifreeze; as an industrial solvent; and as a raw material in the production of many 

commercially important organic compounds. Small amounts of methanol are produced over the 

course of normal body metabolism and are found in the exhaled air. 

Methanol is rapidly absorbed after ingestion or inhalation. Percutaneous absorption is 

also considerable. Acute methanol toxicity varies greatly between species, primarily as a result 

of differential metabolism. At very high inhaled concentrations rodents exhibit much higher blood 

methanol concentrations than do primates. Primates accumulate greater amounts of the 

important toxic metabolite formic acid (found in equilibrium in plasma with its anion, formate). 

Primates are more susceptible than rodents because of the greater accumulation of formates in 

primates. Clinical experience with those who ingested methanol (often under the mistaken 

assumption that they were consuming ethanol) demonstrates marked variations in individual 

susceptibility and delayed onset of severe, overt toxicity. The initial phase of inebriation is 

similar to that seen after ethanol but is usually mild and transient and is generally followed by an 

uneventful initial recovery. The most important clinical consequences develop between 6 and 30 

hours after the initial exposure. 

Wide individual variations in response are most likely due to individual rates of formate 

production from methanol in the liver. People with pre-existing liver disease (e.g., cirrhosis) 

often appear resistant to methanol poisoning because of their relatively inefficient conversion of 

methanol to formic acid. Accumulation of formate in primates leads to depletion of the normal 

bicarbonate buffering capacity of the body, delayed-onset metabolic acidosis and death with 

acute cerebral edema, CNS depression, and coma. The severity of the poisoning and the 

patient's prognosis are related directly to the extent of formate and lactate formation, which 

account largely for this metabolic acidosis. Among victims who survive the initial phase, vision 

can become severely impaired and permanent bilateral blindness can follow formate-induced 

retinal edema, demyelination of the temporal retina, hemorrhagic necrosis in the basal ganglia, 

and nerve head pallor. Pancreatitis has been associated with acute abdominal pain. 

Occupational methanol exposures in confined spaces or in workrooms with inadequate 

ventilation have been associated with recurrent giddiness (mild inebration), headache, nausea, 

insomnia, blurred or dim vision, and conjunctivitis. The delayed onset of symptoms, the potent 

ocular degeneration, and the metabolic acidosis seen in primates poisoned with methanol are 

not observed in rodents. In rodents, methanol can cause fetotoxic and teratogenic effects. 

Preliminary studies provided some evidence of developmental effects in monkeys.. 

The AEGL-1 was based on a study in which human volunteers inhaled 800 ppm 

methanol for 8 hours (Batterman et al., 1998). As this was a pharmacokinetic study, health 

effects were not formally evaluated. In a personal communication the coauthor Dr. Alfred 

Franzblau stated that individual symptoms were asked of some subjects, other subjects were 

only asked generally if they had symptoms, and that in some exposure sessions subjects might 

not have been queried. According to Dr. Franzblau, none of the subjects reported symptoms. 

NIOSH (1980) and Frederick et al. (1984) reported significantly higher frequencies of 
METHANOL Interim 2: 2/2005 

ix 

headaches, dizziness, blurred vision after occupational exposure at 1060 ppm (mean 

concentration). NIOSH (1981) reported eye irritation in a worker after exposure at 1025 ppm for 

25 minutes. Since the 1000-ppm level was considered already a discomfort level, the 800 ppm 

for 8 hour exposure from the Batterman et al. (1998) study was chosen as a starting point for 

AEGL-derivation. Since the local irritation effects are determined by the concentration of 

methanol in air and not to the blood methanol level, calculation of AEGL-1 values was not done 

using a pharmacokinetic model (as done for AEGL-2 and -3) based on the end-of-exposure 

blood methanol level of 30.7 mg/l reported by Batterman et al. (1998). Instead, exposure to 800 

ppm for 8 hours was used as the basis for AEGL-1 derivation. A factor of 3 was applied for 

intraspecies variability because interindividual variability with regard to slight central nervous 

system effects (e.g. headache) is likely to exist (although it cannot be quantified exactly from the 

existing experimental and epidemiological studies) and because subpopulations with a less than 

optimal folate status may be more susceptible to the health effects of methanol. The value was 

scaled to appropriate exposure periods according to the dose-response regression equation Cn

x t = k, using the default of n=3 for shorter exposure periods, due to the lack of suitable 

experimental data for deriving the concentration exponent. For the 10-minute AEGL-1, the 30-

minute value was applied because no studies were available that demonstrated the absence of 

notable discomfort (with respect to irritation) in the general population, including susceptible 

subpopulations, at 970 ppm (which would be the extrapolated value for the 10-minute period). 

A level of distinct odor awareness (LOA) for methanol of 8.9 ppm was derived on the 

basis of the odor detection threshold reported by Hellman and Small (1974). The LOA 

represents the concentration above which it is predicted that more than half of the exposed 

population will experience at least a distinct odor intensity, about 10 % of the population will 

experience a strong odor intensity. The LOA should help chemical emergency responders in 

assessing the public awareness of the exposure due to odor perception. 

The AEGL-2 values were based on developmental toxic effects. In mice, repeated 7-

hour/day exposures during gestational days 6 to 15 caused a dose-related, significant increase 

in cervical ribs at 2000 ppm or higher; other malformations, such as exencephaly and cleft 

palate occurred concentration-dependently at 5000 ppm or higher (Rogers et al., 1993). The 

same type of malformations was found after a single 7-hour exposure at 10000 ppm (no other 

concentrations tested) (Rogers et al., 1997). In another study, which has not been formally 

published up until know, Rogers and coworkers (Rogers et al. 1995, abstract; Rogers, 1999, 

personal communication) exposed mice on gestational day 7 to different concentration-time 

combinations. The most sensitive endpoint was cervical rib induction, which occurred at 

concentration-time products greater than or equal to 15000 ppm @ h, but not at concentrationtime products below 15000 ppm @ h (i.e. no effects were observed at 2000 ppm for 5 h, 2000 

ppm for 7 h or 5000 ppm for 2 h; authors expressed data only as CxT values). Thus, while 2000 

ppm for 7 hours was a LOEL in the repeated exposure study (Rogers et al., 1993), it was a 

NOEL after single exposure. Although the single exposure study had shortcomings in the 

reporting, it was very consistent with the well-documented repeated exposure study. It was 

therefore considered adequate to use an exposure at 2000 ppm for 7 hours as a starting point 

for AEGL-2 derivation. At the NOEL of 2000 ppm for 7 hours (Rogers et al. 1995, abstract; 

Rogers, 1999, personal communication), the corresponding end-of-exposure blood methanol 

concentration was measured as 487 mg/l (Rogers et al., 1993). A total uncertainty factor of 10 
METHANOL Interim 2: 2/2005 

x 

was used. An uncertainty factor of 1 was applied for interspecies variability because a sensitive 

species was used for derivation of AEGL-2 values and because toxicokinetic differences 

between species were accounted for by using a pharmacokinetic model for calculating exposure 

concentrations. An uncertainty factor of 10 was used for intraspecies variability because no 

information on developmental toxic effects of methanol on humans is available and because 

also for other chemicals the variability in susceptibility of humans for developmental toxic effects 

is not well characterized. Moreover, pregnant women are a subpopulation with a less than 

optimal folate status and, thus, may be more susceptible to the health effects of methanol. 

Using a total uncertainty factor of 10, a blood methanol concentration of 48.7 mg/l was derived 

as the basis for calculation of exposure concentrations. Application of the uncertainty factor to 

the blood methanol concentration was preferred because the calculated exposure 

concentrations in air stayed better in the concentration range for which the pharmacokinetic 

model was validated and the effect of methanol metabolism for longer exposure periods was 

more adequately taken into account. In contrast, first calculating exposure concentrations that 

would lead to a blood methanol level of 487 mg/l, and then applying a factor of 10 to the derived 

exposure concentration would result in calculation of extremely high concentrations in the fist 

step at which metabolic pathways would be saturated. After application of the uncertainty factor, 

concentrations would be below saturation level which would mean that the end-of-exposure 

methanol levels would vary for the AEGL-2 exposure concentration-time combinations. Using 

the pharmacokinetic model of Perkins et al. (1995a), inhalation exposure concentrations were 

calculated for appropriate time periods that would lead to a blood methanol concentration of 

48.7 mg/l at the end of the time period. The calculated exposure concentrations were set as 

AEGL-2 values. 

The AEGL-3 values were based on oral intoxications in humans. Several case studies 

(Naraqi et al., 1979; Erlanson et al., 1965; Bennett et al., 1955; Gonda et al., 1978; Meyer et al., 

2000) reported measured blood methanol concentrations and time periods between intoxication 

and measurement. Given the time that elapsed until blood sampling, during which part of the 

methanol was metabolized, it can be concluded that peak blood methanol concentrations have 

been above 1000 mg/l in all fatal cases. Based on the extensive clinical experience with 

methanol intoxications, the American Academy of Clinical Toxicology (AACT, 2002) published 

clinical practice guidelines on the treatment of methanol poisoning. According to these 

guidelines, peak blood methanol concentrations >500 mg/l indicate serious poisoning for which 

hemodialysis is recommended. Based on the human experience, a peak blood methanol 

concentration of 500 mg/l was chosen as the basis for AEGL-3 derivation. A total uncertainty 

factor of 3 was used. An uncertainty factor of 3 was applied for intraspecies variability because 

clinical experience with methanol intoxications is mainly based on cases involving adult men 

while much less data is available for women, children or elderly persons, and because 

subpopulations with a less than optimal folate status may be more susceptible to the health 

effects of methanol. Using a total uncertainty factor of 3, a blood methanol concentration of 167 

mg/l was derived as the basis for calculation of exposure concentrations. Application of the 

uncertainty factor to the blood methanol concentration was preferred because the calculated 

exposure concentrations in air stayed better in the concentration range for which the 

pharmacokinetic model was validated and the effect of methanol metabolism for longer 

exposure periods was more adequately taken into account. In contrast, first calculating 

exposure concentrations that would lead to a blood methanol level of 500 mg/l and then 
METHANOL Interim 2: 2/2005 

xi 

applying a factor of 3 to the derived exposure concentration would result in calculation of 

extremely high concentrations in the fist step at which metabolic pathways would be saturated. 

Using the pharmacokinetic model of Perkins et al. (1995a), inhalation exposure concentrations 

were calculated for appropriate time periods that would lead to a blood methanol concentration 

of 167 mg/l at the end of the time period. The calculated exposure concentrations were set as 

AEGL-3 values. 

The proposed AEGL values are listed in the table below. 
METHANOL Interim 2: 2/2005 

xii 

SUMMARY TABLE OF PROPOSED AEGL VALUES FOR METHANOL a

Classification 10-Minute 30-Minute 1-Hour 4-Hour 8-Hour Endpoint 

(Reference)

AEGL-1 

(Nondisabling) 

670 ppm 

(880 

mg/m;) 

670 ppm 

(880 mg/m;)

530 ppm 

(690 mg/m;)

340 ppm 

(450 mg/m;)

270 ppm 

(350 mg/m;) 

No headache or 

eye irritation 

(Batterman et al., 

1998; pers. 

commun. 

Franzblau, 1999; 

2000; Frederick et 

al., 1984; NIOSH, 

1980; 1981) 

AEGL-2 

(Disabling) 

11000 ppm 

b 

(14000 

mg/m;) 

4000 ppm 

(5200 

mg/m;) 

2100 ppm 

(2800 

mg/m;) 

730 ppm 

(960 mg/m;)

520 ppm 

(680 mg/m;) 

No developmental 

toxic effects in 

mice Rogers et al. 

(1993; 1995, 

abstract; 1997); 

Rogers (1999, 

personal 

communication) 

AEGL-3 

(Lethal) 

# 14000 ppm b 

(18000 

mg/m;) 

7200 ppm b 

(9400 

mg/m;) 

2400 ppm 

(3100 

mg/m;) 

1600 ppm 

(2100 

mg/m;) 

Lethality in 

humans after oral 

exposure (AACT, 

2002)

a

 Cutaneous absorption may occur; direct skin contact with the liquid should be avoided. 

b The 10-minute AEGL-2 value and the 30-minute and 1-hour AEGL-3 values are higher than 1/10 of the 

lower explosive limit (LEL) of methanol in air (LEL = 55,000; 1/10th LEL = 5500 ppm). Therefore, safety 

considerations against the hazard of explosion must be taken into consideration.

# The 10-minute AEGL-3 value of 40,000 ppm is higher than 50% of the lower explosive limit of methanol 

in air (LEL = 55,000 ppm; 50% of the LEL = 27,500 ppm). Therefore, extreme safety considerations 

against the hazard of explosion must be taken into account.

References

AACT, American Academy of Clinical Toxicology Ad Hoc Committee on the Treatment 

Guidelines for Methanol Poisoning: D.G. Barceloux, G.R. Bond, E.P. Krezelok, H. Cooper, and 

J.A. Vale, 2002. American Academy of Clinical Toxicology Practice Guidelines on the Treatment 

of Methanol Poisoning. Clinical Toxicology 40, 415-446 

Batterman, S.A., A. Franzblau, J.B. D>Arcy, N.E. Sargent, K.B. Gross and R.M. Schreck, 1998. 

Breath, urine, and blood measurements as biological exposure indices of short-term inhalation 

exposure to methanol. International Archives of Occupational and Environmental Health 71, 
METHANOL Interim 2: 2/2005 

xiii 

325-335. 

Becker, C.E., 1983. Methanol poisoning. Journal of Emergency Medicine 1, 51-58. 

Bennett, I., F.H. Cary, G.L. Mitchell and M.N. Cooper, 1953. Acute methyl alcohol poisoning: a 

review based on experiences in an outbreak of 323 cases. Medicine 32, 431-463. 

Erlanson, P., H. Fritz, K.-E. Hagstam, B. Liljenberg, N. Tryding and G. Voigt, 1965. Severe 

methanol intoxication. Acta Medica Scandinavica 177, 393-408. 

Franzblau, A., 1999. Dr. Alfred Franzblau, University of Michigan School of Public Health, Ann 

Arbor, Michigan, personal communication, e-mail dated 14 June 1999. 

Franzblau, A., 2000 Dr. Alfred Franzblau, University of Michigan School of Public Health, Ann 

Arbor, Michigan, personal communication, e-mail dated 3 October 2000. 

Frederick, L.J., P.A. Schulte, A. Apol, 1984. Investigation and control of occupational hazards 

associated with the use of spirit duplicators. American Industrial Hygiene Association Journal 

45, 51-55. 

Gilger, A.P. and A.M. Potts, 1955. Studies on the visual toxicity of methanol. V. The role of 

acidosis in experimental methanol poisonings. American Journal of Ophthalmology 39, 63-86. 

Gonda, A., H. Gault, D. Churchill and D. Hollomby, 1978. Hemodialysis for methanol 

intoxication. The American Journal of Medicine 64, 749-758. 

Hellman, T.M. and F.H. Small, 1974. Characterization of the odor properties of 101 

petrochemicals using sensory methods. Journal of the Air Pollution Control Association 24, 

979-982. 

Meyer, R.J., M.E.J. Beard, M.W. Ardagh and S. Henderson, 2000. Methanol poisoning. New 

Zealand Medical Journal 113, 11-13. 

Naraqi, S., R.F. Dethlefs, R.A. Slobodniuk, and J.S. Sairere, 1979. An outbreak of acute methyl 

alcohol intoxication. Australia and New Zealand Journal of Medicine 9, 65-68. 

NIOSH, National Institute for Occupational Safety and Health, 1980. Hazard evaluation and 

technical assistance report TA 80-32. Everett school district, Everett, Washington. National 

Institute of Occupational Safety and Health, Cincinnatti, OH, USA. 

NIOSH, National Institute for Occupational Safety and Health, 1981. Health hazard evaluation 

report No. HETA-81-177, 178-988, University of Washington, Seattle. National Institute of 

Occupational Safety and Health, Cincinnatti, OH, USA. 

Perkins, R.A., K.W. Ward and G.M. Pollack, 1995. A pharmacokinetic model of inhaled 

methanol in humans and comparison to methanol disposition in mice and rats. Environmental 
METHANOL Interim 2: 2/2005 

xiv 

Health Perspectives 103, 726-733. 

Rogers, J.M., M.L. Mole, N. Chernoff, B.D. Barbee, C.I. Turner, T.R. Logsdon and R.J. Kavlock, 

1993. The developmental toxicity of inhaled methanol in the CD-1 mouse, with quantitative 

dose-response modeling for estimation of benchmark doses. Teratology 47, 175-188. 

Rogers, J.M., B.D. Barbee and M.L. Mole, 1995. Exposure concentration and time (C x T) 

relationships in the developmental toxicity of methanol in mice. Toxicologist 15, 164 (abstract). 

Rogers. J.M. and M.L. Mole, 1997. Critical periods of sensitivity to the developmental toxicity of 

inhaled methanol in the CD-1 mouse. Teratology 55, 364-72. 

Rogers, J.M., 1999. US-EPA, National Health and Environmental Effects Research Laboratory, 

Research Trigangle Park, North Carolina, personal communication, letter dated 27 May 1999.
METHANOL Interim 2: 2/2005 

1 

1. INTRODUCTION 

Methanol is a clear, colorless, volatile flammable liquid with a characteristic pungent 

odor when pure. Methanol is used in the industrial production as solvent and as raw material for 

the production of many important organic compounds, principally formaldehyde, methyl tert.-

butyl ether, 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, 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 the future), in gasoline 

blends or as a gasoline extender. About 20 million tons of methanol were produced worldwide in 

1991, principally by catalytic conversion of hydrogen, carbon dioxide and carbon monoxide 

(NLM, 1998; WHO, 1997). The world-wide production capacity was about 30 million tons in 

1995 (WHO, 1997). Chemical and physical properties of methanol are listed in Table 1. 

TABLE 1: CHEMICAL AND PHYSICAL DATA

Parameter Value Reference

Molecular formula CH3OH NLM, 1998 

Molecular weight 32.04 NLM, 1998 

CAS Registry Number 67-56-1 NLM, 1998 

Physical state liquid NLM, 1998 

Color colorless NLM, 1998 

Synonyms Methyl-alcohol; carbinol; Methylalkohol; wood alcohol; 

EPA-Pesticide-Chemical-Code-053801 

NLM, 1998 

Vapor pressure 133 hPa (21.2 °C) 

125 hPa (20 °C) 

169 hPa (25 °C) 

152 hPa (25 °C) 

NLM, 1998 

Rippen, 1998 

NLM, 1998 

Rippen, 1998 

Density 0.8100 g/ml (0/4 °C), 0.7928 g/ml (20 °C) NLM, 1998 

WHO, 1977 

Melting point -97.8 °C NLM, 1998 

Boiling point 64.7 °C (1010.8 hPa) NLM, 1998 

Solubility Miscible with ethanol, ether, ketones, benzene, most organic 

solvents and water; soluble in acetone, chloroform 

NLM, 1998 

Odor Alcoholic odor; pungent odor when crude; pungent NLM, 1998 

Explosive limits in air 5.5% (lower) and 44% (upper), 6.7% (lower) and 36.5% 

(upper) 

WHO, 1977 

AIHA, 1994 

Conversion factors 1 ppm = 1.31 mg/m; (25 °C, 1010.8 hPa) NLM, 1998 
METHANOL Interim 2: 2/2005 

2 

1 mg/m; = 0.764 ppm (25 °C, 1010.8 hPa) NLM, 1998 

2. HUMAN TOXICITY DATA 

2.1. Acute Lethality

Almost all cases of acute methanol toxicity result from ingestion. Intoxication may result 

from methanol contamination of grain spirits, consumption of adulterated alcoholic beverages, 

suicidal ingestion of methanol containing products and unintended consumption of such 

products (ACCT, 2002, Buller and Wood, 1904, Becker, 1983, WHO, 1977). However, the 

majority of cases occurred at the end of the last and at the beginning of this century after 

introduction of wood alcohol as an industrial solvent, and no reliable exposure concentrations or 

durations are available for these cases. For example, Tyson and Schoenberg (1914) counted 

about 100 cases of impairment of vision and death from inhalation of methanol at the workplace. 

After early headache, dizziness, nausea, changes in color perception and blurred vision, 

delayed deaths follow, about one day after sufficiently high methanol exposure. Death and 

blindness (often bilateral) in those who survive are directly related to the extent of formateinduced metabolic acidosis.

In one methanol fatality by inhalation, a woman died after a 12-hour exposure at the 

workplace (Anonymous, 1932). The time between cessation of exposure and death was not 

stated. A postevent study of the exposure conditions revealed concentrations ranging from 4000 

to 13000 ppm. No further details were reported. 

Single Oral Exposure

From a large number of reports on methanol poisonings as a result of the consumption 

of adulterated beverages (WHO, 1977), it was concluded that the minimum oral lethal dose is 

about 1 g/kg (Buller and Wood, 1904; Röe, 1982). Buller and Wood (1904) concluded that an 

oral methanol dose of 1.4 g/kg would be lethal to 40 % of the victims. 

The American Academy on Clinical Toxicology published practice guidelines on the 

treatment of methanol poisoning (AACT, 2002). The publication reviewed mechanisms of 

toxicity, clinical features and laboratory findings. Early after intoxication methanol may produce 

a significant osmolal gap. The osmolal gap is the difference between measured osmolarity in 

blood (usually 270-290 mOsm/kg water) and the calculated osmolarity (which is equivalent to 

(1.86[Na+

]+[BUN]+[glucose])/0.93). Early in the course of methanol poisoning the osmolal gap 

usually exceeds 20 mOsm/kg water; for example a blood methanol level of 1000 mg/l will cause 

an osmolal gap of 34 mOsm/kg water. At a later stage of methanol poisoning, the formic acid 

generated will produce metabolic acidosis and an anion gap. The latter is the difference 

between the sum of the sodium and potassium concentrations and the sum of the chloride and 

bicarbonate concentrations in blood (i.e. ([Na+

]+[K+])-([HCO3

-

]+[Cl-])). The normal anion gap of 

12-16 mmol/l can be attributed to negatively charged proteins, fatty acids, sulfates and 

phosphates. A significant anion gap will not be present early in the course of methanol 

intoxication when the serum bicarbonate concentration falls while the chloride concentration 

increases. When the bicarbonate buffer capacity is depleted, blood pH will start to decline and 

this is accelerated by the accumulation of lactate as a result of formate-induced inhibition of 

mitochondrial respiration. AClinical symptoms correlate more closely to metabolic acidosis rather 

than to serum methanol concentrations. Case series suggest that visual dysfunction occurs 
METHANOL Interim 2: 2/2005 

3 

when formate concentrations exceed 200-300 mg/l. Poor prognostic indicators include serum 

formate concentrations >500 mg/l, a pH <7.0, and coma or seizures on admission to the 

emergency department.@ AA variety of factors complicate the correlation of serum methanol 

concentrations to clinical effects including differences in sample timing, individual variation, 

concentration of toxic metabolites, and the ingestion of ethanol. Clinical symptoms and mortality 

correlate more closely with metabolic acidosis rather than with serum methanol concentrations. 

Consequently, the clinical presentation and outcome of two patients with the same serum 

methanol concentrations may be substantially different.@ APeak methanol concentraions below 

200 mg/l usually are associated with asymptomatic individuals, but interpretation of the 

methanol concentration requires consideration of the time since ingestion, the co-ingestion of 

ethanol and the acid-base status. Peak methanol concentrations over 500 mg/l indicate serious 

poisoning, particularly if an anion gap metabolic acidosis is present.@ AIf a patient presents with 

ophthalmological symptoms and signs or with significant acidosis in the context of a likely 

methanol ingestion, the initial priorities are to correct the acidosis with sodium bicarbonate, 

attempt to enhance metabolism of formate to carbon dioxide by administration of folinic acid [or 

folic acid], inhibit further metabolism of methanol to formate with either fomepizole or ethanol, 

and finally to arrange hemodialysis for further correction of metabolic abnormalities, if 

necessary.@ Treatment with fomepizole or ethanol is recommended at plasma methanol 

concentration >200 mg/l, or documented recent history of ingesting toxic amounts of methanol 

and osmolal gap >10 mOsm/kg water, or history or strong clinical suspicion of methanol 

poisoning and at least two of the following criteria: arterial pH <7.3, serum bicarbonate <20 

mmol/l, osmolal gap >10 mOsm/kg water. Hemodialysis for removal of methanol and formate is 

recommended for the following conditions: significant metabolic acidosis (pH <7.25-7.30), 

abnormalities of vision, deteriorating vital signs despite intensive care support, renal failure, 

electrolyte imbalance unresponsive to conventional therapy, or serum methanol concentration 

>500 mg/l. 

Naraqi et al. (1979) described 32 men (mean age 23, range 17-39) who drank pure 

methanol. The methanol was mixed with orange juice or soft drinks. The purity of the methanol 

was confirmed later by gas chromatography. The estimated amount of methanol consumed 

ranged from 60 to 600 ml (mean 275 ml). Three patients consumed ethanol immediately prior to 

drinking methanol. The first symptoms appeared 8-36 hours (mean 18 hours) after consumption 

and comprised blurred vision, pupillary changes, fundi changes, abdominal pain, vomiting, 

nausea, headache, dizziness, lethargy, restlessness, coma, seizures, and Kussmaul 

respiration. Circulating methanol and ethanol concentrations of 15 patients were measured in 

blood drawn within the first 48 hours after hospital admission. The treatment consisted of 

sodium bicarbonate infusion; ethanol, peritoneal or hemodialysis was not used. Of 28 patients 

admitted to hospital, 4 died (one of those had an elevated blood ethanol concentration) within 

72 hours, 16 recovered without complications, 2 became totally blind, 4 developed severe visual 

impairment and 2 had severe visual disturbances as well as speech difficulties. Blood methanol 

concentrations in fatal cases (except for the case of concomitant ethanol exposure) are shown 

in Table 2. Blood methanol concentrations >500 mg/l were seen in only two non-fatal cases. 

Individual blood methanol concentrations of surviving patients were not reported. 
METHANOL Interim 2: 2/2005 

4 

Erlanson et al. (1965) described 4 patients that consumed pure methanol that had been 

sold as ethanol. Three patients died in spite of intensive care including ethanol therapy, 

bicarbonate infusion and hemodialysis. Blood methanol concentrations and symptoms are given 

in Table 2. The lowest concentration associated with fatal outcome was 275 mg/l measured 52 

hours after methanol uptake; in this patient ethanol therapy was begun after 48 hours. 

Bennett et al. (1953) reported on several cases of oral methanol poisoning. The cases in 

which no or only trace amounts of ethanol were detected in the blood are shown in Table 2. Of 

five cases, two with estimated oral doses of 0.6 and 5.6 g/kg died in spite of hospital treatment, 

while the other three cases survived ingestion of estimated doses of 1.1, 1.9 and 3.3 g/kg. 

Gonda et al. (1978) described the consequences of ingestion of windshield washer fluid 

(90-95 % methanol). All cases were treated with ethanol, sodium bicarbonate and hemodialysis 

(except for 2 cases that did not receive ethanol). Of 9 patients, 2 died and 3 of the 7 survivors 

had permanent visual impairment. Measured blood methanol concentrations are given in Table 

2. 

Meyer et al. (2000) tabulated the time between methanol ingestion and hospital 

admission along with blood methanol concentrations for 4 cases (see Table 2). 

Kahn and Blum (1979) described a fatal dermal methanol exposure in an 8-month-old 

boy. The child had been "treated" with methanol-soaked compresses during two nights (about 

12 hours each) before he was admitted to hospital. A blood methanol concentration of 400 mg/l 

was determined in the early afternoon. The child died in that evening in spite aggressive 

medical intervention. 

Although several other reports on fatal oral methanol exposures have been documented 

in the literature (e.g. Keeney and Mellinnkoff, 1949; Kane et al., 1968), these are not presented 

here because methanol exposure was combined with ethanol intake in most of these cases. 

Since ethanol at blood concentrations of about 1 g/l or higher can completely block methanol 

metabolism, reported methanol doses or blood methanol concentrations are not useful for the 

derivation of AEGL values. 

TABLE 2: ACUTE ORAL METHANOL INTOXICATIONS IN HUMANS 

Clinical 

outcome 

Sex, 

age 

Blood methanol 

conc. (mg/l) at 

time 

postexposure (h) 

Latent period, symptoms, remarks Reference 

death after 48 h male 

27 

730 (< 48 h) 8 h 

coma (admission) 

Naraqi et 

al., 1979 

death after 36 h male 

19 

1110 (< 48 h) 36 h 

coma (admission) 

Naraqi et 

al., 1979 

death after 36 h male 

20 

3260 (< 48 h) 12 h 

coma (admission) 

Naraqi et 

al., 1979 

 
METHANOL Interim 2: 2/2005 

5 

TABLE 2: ACUTE ORAL METHANOL INTOXICATIONS IN HUMANS 

Clinical 

outcome 

Sex, 

age 

Blood methanol 

conc. (mg/l) at 

time 

postexposure (h) 

Latent period, symptoms, remarks Reference 

death after 136 

h 

male 

49 

275 (52 h) 15 h failing vision, 24 h vomiting, hearing 

disturbances, 28 h restlessness, 29 h 

coma, 48 h (admission and ethanol 

therapy) 

Erlanson et 

al., 1965 

death after 79 h male 

65 

277 (53 h) 15 h nausea, vomiting, headache, 19 h 

failing eye sight, 30 h severe visual 

disturbances, cyanosis, 42 h coma, 48 h 

(admission and ethanol therapy) 

Erlanson et 

al., 1965 

death after 110 

h 

female

49 

860 (53 h) 42 h unconsciousness, 43 h respiratory 

standstill, 44 h (admission and ethanol 

therapy) 

Erlanson et 

al., 1965 

survived Female 

 39 194 (50 h) 9 h vomiting, 36 h failing eye sight, 44 h 

blindness, 45 h clouding of 

consciousness (admission and ethanol 

therapy) 

Erlanson et 

al., 1965 

death during 

treatment of 

relapse 

male 

41 

4000 (18 h) blind, headache; estimated oral dose 

about 50 ml 

Bennett et 

al., 1953 

death on 4th 

day 

male 

48 

1300 (24 h) blind, headache, abdominal pain, blind, 

stupor; estimated oral dose about 500 ml 

Bennett et 

al., 1953 

death during 

treatment of 

relapse 

male 

26 

2500 (48 h) cloudy vision, headache, nausea, 

abdominal pain, vomiting 

Bennett et 

al., 1953 

recovered male 

34 

1500 (18 h) cloudy vision, headache, abdominal 

pain, weakness, vomiting, stupor; 

estimated oral dose about 100 ml 

Bennett et 

al., 1953 

recovered female 

29 

2700 (18 h) impaired vision, retinal edema, 

headache, dizziness, nausea, vomiting; 

estimated oral dose about 150 ml 

Bennett et 

al., 1953 

recovered male 

43 

1600 (48 h) cloudy vision, retinal edema, headache, 

abdominal pain 

Bennett et 

al., 1953 

died male 

30 

5600 (12 h) comatose Gonda et 

al., 1978 

died male 

48 

3700 (24 h) confusion, progressing coma Gonda et 

al., 1978 
METHANOL Interim 2: 2/2005 

6 

TABLE 2: ACUTE ORAL METHANOL INTOXICATIONS IN HUMANS 

Clinical 

outcome 

Sex, 

age 

Blood methanol 

conc. (mg/l) at 

time 

postexposure (h) 

Latent period, symptoms, remarks Reference 

survived, eye 

damage 

male 

43 

5700 (4 h) comatose Gonda et 

al., 1978 

survived, eye 

damage 

male 

42 

250 (40 h) blurred and greenish vision Gonda et 

al., 1978 

survived, eye 

damage 

male 

45 

30 (100 h) weakness, dyspnea, vomiting, 

abdominal pain, visual impairment 

developed after 3 days 

Gonda et 

al., 1978 

survived female 

51 

530 (24 h) dizziness, headache, nausea Gonda et 

al., 1978 

survived male 

15 

740 (24 h) stupor, nausea, vomiting Gonda et 

al., 1978 

survived female 

48 

560 (24 h) slurring speech Gonda et 

al., 1978 

survived male 

36 

1020 (40 h) profound weakness, photophobia, 

blurred vision, slurred speech 

Gonda et 

al., 1978 

died male 

30 

2050 (36 h), 

970 ethanol 

coma Meyer et 

al., 2000 

survived male 

28 

1150 (36 h) nausea Meyer et 

al., 2000 

survived male 

25 

990 (36 h) visual impairment Meyer et 

al., 2000 

survived female 

41 

192 (36 h) no symptoms Meyer et 

al., 2000 

2.2. Nonlethal Toxicity

The signs and symptoms of methanol poisoning include initial headache, dizziness, 

nausea, weakness and insomnia, shooting pains, paresthesia, prickling and numbness in the 

extremities. Changes in color perception and blurred vision (Browning, 1965; NIOSH, 1976; 

Becker, 1983; Kavet and Nauss, 1990; ACCT, 2002) develop as formate concentrations 

increase over time. After a latency period (cf. Section 4.2) life-threatening metabolic acidosis 

and permanent bilateral blindness can develop. 
METHANOL Interim 2: 2/2005 

7 

2.2.1. Experimental Studies

Batterman et al. (1998), studied 4 healthy women (aged 41-63 years) exposed at 800 

ppm for 30, 60 and 120 min. Each of these exposures was repeated with the same subjects. 

Additionally, 3 other women and 12 men (age not stated) were exposed at 800 ppm methanol 

for 8 hours. All volunteers were healthy, non-smoking individuals. In the article, the authors 

made no statement on the presence or absence of any signs or symptoms of the methanol 

exposure. In a personal communication, the second author, Dr. Alfred Franzblau, stated that 

although no formal mechanism of recording symptoms was used, the subjects were generally 

asked during exposure if they experienced any discomforts. Dr. Franzblau wrote "individual 

symptoms were certainly asked of some subjects" and that "none of the subjects reported odor, 

irritation, headache or other non-specific symptoms"; likewise "none of the subjects reported 

any difficulties or alterations of visual function". Dr. Franzblau wrote that it is possible that some 

subjects were not queried in that no written notes were made. Both, investigators and subjects, 

knew the methanol concentrations during each of the sessions. Dr. Franzblau recalled that a 

meter was set up outside the window of the exposure chamber so that the subjects could see 

directly the concentration of methanol inside the chamber. The investigators also had exposure 

to methanol at the various levels, either because they spent some time in the chamber during 

the experiments, or because they conducted trail runs on themselves before conducting the 

studies on other subjects (Franzblau, 1999; 2000; personal communication). 

Chuwers et al. (1995) allowed 26 healthy subjects (15 men, 11 women) in an exposure 

chamber to inhale methanol at 200 ppm for 4 hours. The exposure concentration was 

continuously monitored by an infrared spectrophotometer and, in addition, by gas 

chromatography. The measured exposure concentration was 199"7 ppm. Immediately before 

and upon conclusion of exposure several visual (Vistech contrast sensitivity test, Lanthony 15 

Hue desaturated panel color discrimination test), neurophysiological (P-300 auditory evoked 

potentials) and neurobehavioral (2-and-7 visual scanning performance, Stroop test, Symbol 

Digit substitution test, Sternberg memory task) tests were performed. Because the time to 

complete all tests required one hour, some of the tests (2-and-7, Stroop and Symbol Digit tests) 

were started during the last half hour of exposure. Each subject was once exposed to methanol 

and once to water vapor in random order in a double-blind fashion. Methanol and formate 

concentrations in serum and urine were measured during exposure 0, 15, 30, 45, 60, 90, 120, 

150, 180, 210 and 240 minutes after beginning and 1, 2, 3 and 4 hours after the cessation of 

exposure. The effect of methanol was significantly only on two outcomes: the P300 amplitude 

when alcohol consumption and smoking accounted for between-subject variability and on the 

Symbol Digit test with age accounting for between-subject variability. A correlation with the area 

under the serum methanol curve was found for P300 amplitude, but not for the Symbol Digit 

test. Although no odor detection was reported by the subjects, 18/26 subjects (13 expected) 

guessed correctly the methanol exposure session. The possible unblinding of test subjects 

potentially could have affected the subjects’ performance. The authors concluded that a 4-hour 

exposure to 200 ppm methanol did not significantly affect neurobehavioral, neurophysiological 

and visual performance in a healthy normal population. An accompanying paper about the same 

study did not find a significant increase in urinary or serum (14.3"8.9 mg/l vs. 12.7"1.7 mg/l in 

controls) formate concentrations (D>Alessandro et al., 1994). 

In a similar experiment, Cook et al. (1991) exposed 12 healthy young men, each serving 
METHANOL Interim 2: 2/2005 

8 

as his own control, for 75 minutes to 250 mg/m; (190 ppm) methanol. The mean analytical 

concentration ("SD) measured using an infrared gas analyzer and by gas chromatography was 

249"7 mg/m;. Each subject was twice sham-exposed and twice exposed to methanol under 

double-blind control conditions. 22 neurobehavioral and neurophysiological tests were 

administered before, during, and after exposure to measure visual, behavioral, reasoning, and 

hearing functions. Methanol exposure had no effect on the subjects' performance on most of the 

tests. However, some methanol-exposed subjects reported fatigue and lack of concentration. 

Performance was also slightly impaired in the Sternberg memory task. There were also changes 

in the latency of the P200 component of the visual- and auditory-event related potential. These 

effects were small and did not exceed the range of results measured in filtered air-exposed 

subjects. 

Muttray et al. (2001) exposed 12 male, healthy, right-handed students by inhalation in an 

exposure chamber for 4 hours to 20 or 200 ppm methanol (cross-over designed study). 

Analytical concentrations were 20.3"3.8 ("SD) ppm and 203.5"2.5 ("SD) ppm, respectively. 

Electroencephalographic examinations were performed immediately after conclusion of 

exposure with closed and open eyes and during the color word stress test. Significant 

alterations in the encephalograms between exposure to 20 or 200 ppm were found only in 

measurements performed with eyes shut. No effects were found in the color word stress test. A 

German version of an Swedish Performance Evaluation System questionnaire was 

administered before, 2 h and 4 h after exposure. It contained the following 17 items: headache, 

dizziness, nausea, tiredness, pain or pressure over the chest, coughing spells, shortness of 

breath, irritation to the eyes, watering eyes, blurred sight, irritation to the nose, running nose, 

sensation of a bad smell, irritation to the throat, sensation of an unpleasant taste, irritation to the 

skin, and feeling of faintness or vertigo. Subjects were requested to check off the degree of their 

symptoms of an ordinal scale from 0 (no symptom) to 5 (severe symptom). None of the 

symptom scores increased significantly during the exposure to 20 or 200 ppm methanol. The 

authors considered the electroencephalographic alterations not as an adverse effect, but as a 

subclinical, excitatory effect of methanol. 

The American Industrial Hygiene Association critiqued odor threshold studies and 

reported a range of 4.2-5960 ppm with a geometric mean of 160 ppm for the odor detection 

threshold and a range of 53-8940 ppm with a geometric mean of 690 ppm for the odor 

recognition threshold (AIHA, 1989). Other review articles reported ranges of 10-20500 ppm 

(Ruth, 1986), 382-15280 ppm (O>Neill and Phillips, 1992) and 3-7640 ppm (Verschueren, 1983). 

In a review article, Amoore and Hautala (1983) reported a geometric mean odor detection 

threshold of 100 ppm (range 10-20500 ppm) using odor thresholds reported in the literature, but 

"omitting extreme points and duplicate quotations". Several of the reviewed studies 

(Scherberger et al., 1958, May, 1966) cannot be considered adequate for deriving a reliable 

odor threshold because of insufficient exposure conditions (sniffing at a bottle opening), 

unstated purity of the methanol used, lack of presentation of technical details and analytical 

procedures. 

Hellman and Small (1974) measured the absolute and recognition thresholds of 

methanol in air. In this study odor thresholds were determined for 101 petrochemicals using a 

trained odor panel in the Union Carbide Technical Center, South Charleston, WV. Details of the 
METHANOL Interim 2: 2/2005 

9 

procedure used were not reported. The absolute odor threshold (detection limit) for methanol 

was 4.26 ppm. At this concentration "50 % of the odor panel observed an odor". The odor 

recognition threshold was the concentration at which 50 % "of the trained odor panel defined the 

odor as being representative of the odorant being studied". The air odor recognition threshold 

was 53.3 ppm (at this concentration all subjects recognized the odor, the 50 % recognition level 

was not established). 

Leonardos et al. (1969) used a combination of a test room and an antechamber, which 

was held odor-free using an air filter system, and a trained panel of four staff members of the 

Food and Flavor Section of Arthur D. Little, Inc., determined the air odor threshold for methanol. 

At least 5 different concentrations were tested. The individual concentrations tested were not 

reported. An odor recognition threshold of 100 ppm was determined for methanol. A similar 

value was also reported in an experimental study by Ryazanov (1961). 

Flury and Wirth (1933) exposed 2 to 4 individuals for 5 minutes to methanol 

concentrations of 1, 10 or 86 mg/l (760, 7600 or 65400 ppm; nominal concentrations). Methanol 

was sprayed into the exposure chamber and dispersed by a ventilator; analytical measurements 

of the exposure concentrations were not performed. Only a weak odor perception was reported 

at 760 ppm. 7600 ppm was associated with very weak nasal irritation, while 65400 ppm induced 

a very strong (unbearable) nasal irritation, which made deep respiration impossible, and marked 

ocular irritation. From the study report it remains unclear whether the test subjects were 

examined for symptoms other than irritation. 

Leaf and Zatman (1952) studied the pharmacokinetics of methanol exposing themselves 

up to four times to methanol concentrations between 0.7 mg/l (530 ppm) for about 3.3 hours and 

1.43 mg/l (1090 ppm) for about 3 hours. The authors stated that under the conditions of the 

experiment exposures of 3-4 hours were as long as could reasonably be tolerated. They did not 

state, however, whether this limitation was due to effects caused by methanol or the 

experimental design. 

2.2.2. Occupational Exposure 

Studies with repeated inhalation exposure

NIOSH (1980) (data also published in Frederick et al., 1984) studied the exposure 

relationship and possible health effects of methanol exposure from spirit duplicators in teacher 

aides. Fifteen-minute breathing zone samples from 21 of 58 duplicators in 12 schools were 

analyzed using a Wilkes Miran 1A7

 gas analyzer. Measured methanol concentrations ranged 

from 365 to 3080 ppm (mean 1060 ppm, median 1040 ppm). Fifteen of 21 measurements 

exceeded 800 ppm. 11 measurements were between 1000 and 1500 ppm and only one was 

above this range. The authors reported that additional exposure as a result of skin absorption 

during the handling of paper wet with methanol was likely. A health questionnaire survey was 

conducted among 84 female teacher aides, of whom 66 (mean age 39.8 years, range 24-60) 

responded. Exposure times varied widely from 1 hour/day for 1 day/week to 8 hours/day for 5 

days/week during about 3 years. 302 teachers from the same schools served as a comparison 

group. Of the teachers responding, 66 female (mean age 37.5 years, range 24 to 59 years) 

were randomly selected for comparison. Part of the teachers also spent some time in the 
METHANOL Interim 2: 2/2005 

10 

duplicator rooms (the reports do not provide exact exposure information for the teachers). 

Among the aides, 4 of the 22 symptoms listed in the questionnaire were reported significantly 

(p<0.05 using Mantel-Haenszel Chi-square test) more frequently: headache (34.8% in aides vs. 

18.1% in controls), dizziness (30.3% vs. 1.5%), blurred vision (22.7% vs. 1.5%) and 

nausea/upset stomach (18.0% vs. 6.0%). Similar prevalences were found for symptoms, such 

as trouble sleeping, unusually tired, irritable, giddiness, poor memory/confusion, muscle 

weakness and dry/sore throat. No information on the exact exposure duration and the time 

between start of exposure and occurrence of symptoms was provided. The data indicated that 

the prevalence of methanol toxicity cases increased with the percentage of time spent at 

duplicators per week. The authors defined a methanol toxicity case by any of the following four 

symptom aggregations: 1) visual changes or blurred vision, 2) one acute symptom (headache, 

dizzines, numbness, giddiness, nausea or vomiting) and one chronic symptom (unusually tired, 

muscle weakness, trouble sleeping, irritability or poor memory), 3) two acute symptoms or 4) 

three chronic symptoms. 

Kawai et al. (1991) analyzed 48 personal samples of breathing-zone air from 31 different 

subjects, using tube-type diffusive samplers and gas chromatography: 5 samples indicated 

time-weighted average methanol concentrations during an 8-hour work shift between 3000 and 

5500 ppm, 10 samples were between 1000 and 2000 ppm, 4 samples were between 500 and 

1000 ppm and 19 below 500 ppm. Exposed workers were grouped into a group exposed to 

higher methanol concentrations (22 workers; geometric mean exposure concentration 459 ppm) 

and a group exposed to lower methanol concentrations (11 workers; geometric mean 31 ppm) 

(the authors did not report the concentration used as the criterion for grouping). The following 

subjective complaints were given significantly more in the high-exposure group compared to the 

low-exposure group: dimmed vision during work (11/22 vs. 0/11) and nasal irritation during work 

(7/22 vs. 0/11). 

The symptom of >dimmed vision= has been questioned by the authors who stated that "Further 

questioning disclosed that the workers in fact saw fog in the workroom air, especially on humid 

days when the factory was especially busy; the fog was probably produced by the reaction of 

methanol vapor with humidity in the air. No visual problems were noted when the windows were 

kept open and fresh air was allowed to flow in, suggesting that this symptom might not be of 

direct medical significance, although it should indicate the presence of dense methanol vapor." 

The fact that headaches did not occur more frequently supports the author>s interpretation that 

the >dimmed vision= was a physical rather than a health-related problem because in other 

occupational studies, headaches occurred at lower concentrations than effects on vision 

(Kingsley and Hirsch, 1955) or, at higher exposure concentrations, as a more frequent symptom 

than blurred vision (NIOSH, 1980; Frederick et al., 1984). In conclusion, the reported >dimmed 

vision= is considered most likely not to be a methanol-caused health effect. 

The authors did not try to correlate the symptoms with the measured breathing-air samples. No 

significant differences between the two groups were found for the following symptoms: dimmed 

vision off work, unusual feeling in the throat, unusual smell during work, headache off work, 

increased sensitivity of the skin in the extremities off work, forgetfulness off work, fainting after 

suddenly standing up off work, and chill sensation in the extremities off work. On 

ophthalmologic examination, 3/22 vs. 0/11 subjects showed clinical signs: in two subjects a slow 

light reflex of the pupils was observed and one person showed slightly mydriatic pupils. The 

geometric mean of methanol exposure of the 3 subjects was 1017 ppm. One of the two subjects 
METHANOL Interim 2: 2/2005 

11 

showing a slow light reflex had a habit of drinking an equivalent of 75 g ethanol per day. No 

information on the exposure duration and the time between start of exposure and occurrence of 

symptoms was provided. 

Kingsley and Hirsch (1955) reported that an unspecified number of employees working 

in the immediate vicinity of direct process duplicating machines complained of frequent and 

recurrent headaches. The duplicating machines used duplicating fluids containing 5-98 % 

methanol. Since the other ingredients were not identified, exposure to other volatile compounds 

cannot be ruled out. The authors stated that those individuals situated closer to the machines 

experienced more severe headaches, those who actually operated the equipment suffered the 

most, and that with the onset of cold weather, when doors and windows were closed, the 

severity and frequency of the headaches increased. Methanol concentrations measured in the 

breathing zone of the workers ranged from 15 to 375 ppm and generally were in excess of 200 

ppm. The method of analysis was not reported. No information on exposure duration was 

provided. 

2.2.3. Case Studies

Cases of methanol poisoning after inhalation have been reported in the literature (Tyson 

and Schoenberg, 1914; NIOSH, 1976; IUCLID, 1996). However, reliable information about 

exposure concentrations or durations is lacking and the incidents very often involved repeated 

or long term exposure to methanol. 

NIOSH (1981) reported the results of an environmental evaluation of a spirit duplicating 

machine workplace. Measurement was done by collecting breathing zone samples for 5 

consecutive 5-minute periods. The measured concentration range was 950-1100 ppm (mean 

1025 ppm). The operator experienced eye irritation at the end of the 25-minute period. No 

information is given regarding sex and age of the operator and whether this operator had 

experienced more or less symptoms in the past compared to other duplicating machine 

operators in the same school. 

Humperdinck (1941) reported a case of methanol poisoning during handling of damp 

nitrocellulose (35-40 % methanol) in a nitrocellulose plant. The worker had been on this job for 4 

years and had not previously reported any symptoms. He became ill following the institution of 

wartime blackout measures which impaired plant ventilation. The worker became blind in the 

right eye with marked narrowing of the visual field in the left eye. Examination of the workplace 

air revealed methanol concentrations ranging from 1600 to 10900 mg/m; (1200 to 8300 ppm). 

These symptoms were not reported in another 22 workers exposed to methanol. No statement 

was made on whether these workers experienced any other symptoms. 
METHANOL Interim 2: 2/2005 

12 

TABLE 3: SUMMARY OF EFFECTS ON HUMANS AFTER INHALATION OF METHANOL

Concentration 

 (ppm)

Exposure 

Time

Study type and effects Reference

4000-13000 

(probable 

range) 

12 h 

(workplace) 

case study; fatal case after occupational 

exposure 

Anonymous, 1932 

1200-8300 

(probable 

range) 

unknown 

(workplace) 

case study; visual disturbances, 

blindness on one eye 

Humperdinck, 1941 

65400 5 min experimental study; very strong 

(unbearable) nasal irritation, strong eye 

irritation 

Flury and Wirth, 

1933 

7600 5 min experimental study; very weak nasal 

irritation 

Flury and Wirth, 

1933 

760 5 min experimental study; weak odor 

perception, no irritation 

Flury and Wirth, 

1933 

1060 (mean) 1 h/d to 8 h/d 

(repeatedly at 

workplace) 

occupational study; more frequent 

headaches, dizziness, blurred vision, 

nausea/upset stomach 

NIOSH, 1980; 

Frederick et al., 

1984 

1025 (mean) 25 min eye irritation NIOSH, 1981 

800 8 hours experimental pharmacokinetic study with 

no statement on effects; in a personal 

communication, a coauthor stated that 

the subjects did not report any symptoms 

Batterman et al., 

1998; Franzblau, 

1999; 2000 

459 (mean) 8 hours 

(repeatedly at 

workplace) 

occupational study; dimmed vision (the 

authors suggested that visibility was 

temporarily reduced by fog in the 

workroom) and nasal irritation 

Kawai et al., 1991 

200-375 unknown 

(repeatedly at 

workplace) 

occupational study; recurrent headaches Kingsley and Hirsch, 

1955 

200 4 hours experimental study; no significant CNS 

effects 

Chuwers et al. 1995 

190 75 minutes experimental study; no significant CNS 

effects 

Cook et al., 1991
METHANOL Interim 2: 2/2005 

13 

2.3. Developmental/Reproductive Toxicity

Very little information is available regarding developmental or reproductive effects of 

methanol in humans (NTP-CEHRH, 2003; WHO, 1997). 

Lorente et al. (2000) investigated the role of maternal occupational exposure in 

occurrence of cleft lip and palate. Data from the study was obtained from a multicenter 

European case-referent study utilizing 6 congenital malformation registers between 1989 and 

1992. Occupational exposures during the first trimester were studied in 851 women; 100 cases 

had infants with oral clefts and 751 referents had infants without oral clefts. The subjects were 

interviewed to determine occupational history and the types of products used on the job. An 

industrial hygienist reviewed interview responses to determine the probability of chemical 

exposures. Confounding factors considered included maternal age, socioeconomic status, 

residence, urbanization, country of origin, and medical history. Subjects were interviewed about 

smoking, and alcohol intake but it is not clear if the analyses considered those factors. Data 

were analyzed by estimating an adjusted odds ratio for each type of exposure. Analyses 

determined that at least 10 % of the subjects were likely exposed to methanol during the first 

trimester of pregnancy. Odds ratios of 3.61 (95% C.I. 0.91-14.4) and 3.77 (95% C.I. 0.65-21.8) 

were calculated for methanol exposure and occurrence of cleft palate only and cleft lip with or 

without cleft palate, respectively. Although these ratios are elevated, they are consistent with 

the null hypothesis of no increased risk for orofacial clefts after occupational exposure to 

methanol. It should be noted that for methanol, the numbers were quite small (only 2 cases with 

cleft palate and 4 with cleft lip with or without cleft palate exposed methanol). 

2.4. Genotoxicity

No studies documenting genotoxic effects of methanol in humans were identified (WHO, 

1997). 

2.5. Carcinogenicity

No studies documenting carcinogenic effects of methanol in humans were identified 

(WHO, 1997). 

2.6. Summary

Although several case reports on lethal methanol poisoning of humans due to exposure 

by inhalation have been published in the literature, data on exposure concentration and 

exposure duration are usually lacking. Information about lethal effects on humans after oral 

uptake of methanol is available: The conclusion drawn by several authors (Buller and Wood, 

1904; Röe, 1982) that the minimum lethal oral dose is about 1 g/kg is supported by three 

studies reporting on intoxication incidents in which humans drank pure methanol (i.e. no 

concomitant ethanol consumption). Bennett et al. (1953) reported two lethal cases after uptake 

of estimated oral doses of 0.6 and 5.6 g/kg, while another three cases survived ingestion of 1.1, 

1.9 and 3.3 g/kg. In the study of Naraqi et al. (1979), the lowest blood methanol concentration 

associated with fatal outcome was 730 mg/l measured about 24 hours after uptake. Erlanson et 
METHANOL Interim 2: 2/2005 

14 

al. (1965) reported a lowest blood methanol concentration of 275 mg/l in a fatal case, measured 

about 52 h after intoxication. 

At lower exposure concentrations headache and visual disturbances are the most critical 

endpoints. In a pharmacokinetic study, 15 subjects were exposed to 800 ppm for 8 hours; the 

authors made no statement on health effects (Batterman et al., 1998), but in a personal 

communication a coauthor stated that the subjects did not report any symptoms. Chuwers et al. 

(1995) found no significant effect on neurobehavioral, neurophysiological and visual 

performance in an experimental study after a 4-hour exposure to 200 ppm. Similarly, no 

significant effects on neurobehavioral and neurophysiological test results were observed after a 

75-minute exposure to 190 ppm (Cook et al., 1991). After repeated exposure at the workplace 

to average concentrations of about 1000 ppm headache, dizziness, nausea and blurred vision 

have been reported (NIOSH, 1980; Frederick et al., 1984). Weak nasal or eye irritation has 

been reported after exposure to 7600 ppm for 5 minutes (Flury and Wirth, 1933), 1025 ppm for 

25 minutes (NIOSH, 1981) and after repeated occupational exposure to mean concentrations of 

459 ppm (Kawai et al., 1991). For the odor threshold, a very wide range of values has been 

reported in the literature, e.g. the American Industrial Hygiene Association critiqued odor 

threshold studies and reported a range of 4.2-5960 ppm with a geometric mean of 160 ppm for 

the odor detection threshold and a range of 53-8940 ppm with a geometric mean of 690 ppm for 

the odor recognition threshold (AIHA, 1989). In an experimental study, Hellman and Small 

(1974) determined an odor detection threshold of 4.26 ppm. 

3. ANIMAL TOXICITY DATA 

3.1. Acute Lethality

Data on acute lethal concentrations of methanol for single exposure periods and 

repeated exposures are available for the monkey, cat, rat and mouse. The interpretation of 

lethality data is difficult, because of the different mechanisms involved in different species: in 

rodents no accumulation of formate is observed and animals die of central nervous system 

depression after acute exposure to very high methanol concentrations; in contrast, in humans 

and non-human primates delayed death at considerable lower concentrations of methanol is 

seen due to metabolic acidosis caused by formate accumulation (see Section 4.2). In addition, 

developmental toxicity and fetal death was reported in rodents after subchronic exposure to 

methanol concentrations well below those causing death in adult animals (see Section 3.3). For 

this reasons, data from studies on monkeys and developmental toxicity studies on rodents seem 

relevant for the derivation of AEGL values. The lethality data are summarized in Table 4. 

3.1.1. Non-human Primates

McCord (1931) exposed rhesus monkeys to methanol concentrations of 40000, 20000, 

10000, 5000 or 1000 ppm. The author reported that exposure at 40000 ppm for 4 hours resulted 

in prompt death of the monkeys (probably two animals, not exactly stated) and exposure at 

40000 ppm for 1 hour (probably of one animal, not exactly stated) resulted in sickness for 2-3 

days and delayed death. The authors did not report clinical observations or number of exposed 

animals for the 20000-ppm and 10000-ppm exposures. 1000 ppm produced death in 1 of 4 
METHANOL Interim 2: 2/2005 

15 

animals after an exposure for 18 hours/day for a "total of 41 hours". Another animal "long 

survive[d] the action of 5000 ppm"; the exact exposure duration and effects were not reported. 

The author used synthetic methanol from 3 different commercial sources as well as "pure 

natural", "95% natural" and "crude natural" methanol without specifying which animal was 

exposed to which type of methanol and whether any differences in toxicity were observed. The 

monkeys were from a group of 31 rhesus monkeys taken from the wildlife and brought to the 

USA only shortly before the experiments. One of the monkeys died of pneumonia within 24 

hours of arrival and another one was killed due to "low-grade inflammation of the face". The 

group comprised male and female monkeys, but the gender of the exposed animals was not 

indicated. The exact duration and frequency of exposure as well as detailed effects were not 

reported. 

Studies with repeated inhalation exposure

NEDO (1987) exposed monkeys (Macaca fascicularis) (number of animals given in 

brackets) at 3000 (4), 5000 (3), 7000 (1) or 10000 (2) ppm methanol for 21 hours/day for 

different exposure periods; the control group comprised 6 animals. Continuous monitoring of the 

exposure concentration revealed mean concentrations of 3053"61, 5071"22 and 5018"34, 

7079"37 and 10441"402 ppm, respectively. One animal exposed at 10000 ppm showed 

lethargy and after the third exposure (i.e. the third day) was comatose and died. Another animal 

exposed to 6000-10000 ppm (duration for different exposure concentrations not clearly stated) 

died after 6 days. One animal exposed to 7000 ppm had to be killed after 6 days. Of three 

animals exposed to 5000 ppm, two died on the 5th day and the third on the 14th day. No lethality 

was observed in 4 animals exposed at 3000 ppm for 20 days. Nonlethal effects observed in this 

experiment are reported in Section 3.2.1. 

Andrews et al. (1987) exposed groups of 3 male and 3 female cynomolgus monkeys 

(Macaca fascicularis) to 0, 500, 2000 or 5000 ppm methanol for 6 hours/day, 5 days/week for 4 

weeks. The air exchange rate of the exposure chamber was 0.33 min-1. Methanol exposure 

levels were monitored with a Wilkes Miran 1A-CVF 7

 infrared analyzer and measured values 

were within "10 % of the nominal concentrations. Animals were observed for signs of toxicity 

twice each day and given a detailed physical assessment each week without observing any 

exposure-related effect. No deaths were reported after repeated exposure to methanol 

concentrations of up to 5000 ppm. See Section 3.2.1 for nonlethal effects. 

Studies with non-inhalation exposure

 Gilger and Potts (1955) gave single oral doses of 1, 2, 3, 4, 6 or 8 g/kg to rhesus 

monkeys (one animal/dose). Death was observed at 3 g/kg or higher with the time to death 

decreasing with increasing concentrations: death occurred after 32-38 h, 29-36 h, 29 h and 6-23 

h at 3, 4, 6 and 8 g/kg, respectively. After lethal doses signs of inebriation were observed; 

semicoma was seen only shortly before death. Deaths occurred from respiratory failure. At 

doses of 1 and 2 g/kg, animals did not show any symptoms. 

3.1.2. Cats

Flury and Wirth (1933) exposed groups of 2 cats to methanol concentrations of 141, 113, 

86, 59, 44 or 24 mg/l (107200, 85900, 65400, 44800, 33400 or 18200 ppm) for 6 hours. 
METHANOL Interim 2: 2/2005 

16 

Somnolence occurred at conclusion of exposure time at 33400 ppm or higher. Prostration was 

seen at 65400 ppm for 4.4 hours, 85900 ppm for 4.1 hours or 107200 ppm for 4.0 hours. 

Delayed deaths were observed for one of two animals exposed at 33400, 65400 or 107200 ppm 

and for both animals exposed at 85900 ppm methanol during the 14-day postexposure 

observation time. 

3.1.3. Rats

LC50 values for adult rats reported in industry studies include: 145000 ppm for 1 hour 

(DuPont Co., Haskell Laboratory, 1974), 97900 ppm for 4 hours (BASF, 1980a) and 66900 ppm 

for 6 hours (BASF, 1980b). NIPRI (1974) reported an LC50 of 64000 ppm for 4 hours. 

Loewy and Von der Heide (1914) exposed rats to different concentration-time 

combinations. 31600 ppm for 18-20 hours resulted in death. 22500 ppm for 8 hours and 50000 

ppm for 2.5 hours caused narcosis and 13000 ppm for 20 hours prostration. 8800 ppm for 8 

hours led to lethargy and 2000 ppm for 8 hours had no effect. 

3.1.4. Mice

Scott et al. (1979) reported that the LC50 for male mice was 41000 ppm for 6 hours. The 

observation period was 24 hours. Izmerov et al. (1982) reported an LCLo of 37594 ppm for 2 

hours in mice. Pavlenko (1972) reported coma, but no deaths, after exposure of mice to 71000 

mg/m; (54000 ppm) for 3.5-4 hours/day up to a cumulative total of 54 hours (corresponding to 

about 14 exposure days; no details reported). 

Several older studies report effects on mice: Weese (1928) observed that exposure at 

53500 ppm for 54 hours or 71800 ppm for 54 or 28 hours led to narcosis and death. Mice 

exposed at 48000 ppm for 24 hours showed narcosis and those exposed to 10000 ppm for 230 

hours showed ataxia. Lehmann and Flury (1943) reported narcosis in mice exposed at 42000 

ppm for 7 hours. Marshbitz et al. (1936) exposed white mice to methanol concentrations of 40, 

60, 80, 100,120, 133 or 200 mg/l (30560, 45480, 61120, 76400, 91680, 101610 or 152800 ppm) 

for up to 4 hours. During exposure, mice first showed a state of drowsiness, then an excited 

state, followed by an impairment of coordination and finally narcosis. Narcosis developed after 

190, 153, 134, 89, 95, 91 and 94 minutes, respectively. The overall mortality within one month 

after exposure was 45 % (mortality information for individual groups was not provided). 

TABLE 4: SUMMARY OF ACUTE LETHAL INHALATION DATA IN LABORATORY ANIMALS

Species 

Concentration 

(ppm) 

Exposure 

Time Effect Reference 

Monkey 40000 1 h sickness in 2-3 days, delayed death McCord, 1931 

Monkey 40000 4 h death McCord, 1931 

Monkey 10000 21 h/d, 3 d 

lethargy, after 3 exposures comatose 

and died NEDO, 1987 

Monkey 7000 21 h/d, 6 d animals had to be killed after 6 days NEDO, 1987 
METHANOL Interim 2: 2/2005 

17 

TABLE 4: SUMMARY OF ACUTE LETHAL INHALATION DATA IN LABORATORY ANIMALS

Species 

Concentration 

(ppm) 

Exposure 

Time Effect Reference 

Monkey 5000 21 h/d, 5 d of 3 animals, 2 died on day 5 and 

one on day 14 NEDO, 1987 

Monkey 5000 

6 h/d, 5 

d/w, 4 w no mortality Andrews et al., 1987 

Monkey 3000 

21 h/d, 20 

d no mortality NEDO, 1987 

Monkey 1000 

18 h/d, 41 

h total shortest exposure resulting in death McCord, 1931 

Cat 33400 6 h 1of 2 animals died Flury and Wirth, 1933 

Rat 145000 1 h LC50 

DuPont Co., Haskell 

Laboratory, 1974 

Rat 97900 4 h LC50 BASF, 1980a 

Rat 64000 4 h LC50 NPIRI, 1974 

Rat 66900 6 h LC50 BASF, 1980b 

Rat 50000 2,5 h no mortality, narcosis 

Loewy and Von der 

Heide, 1914 

Rat 31600 18-20 h lethal 

Loewy and Von der 

Heide, 1914 

Rat 22500 8 h narcosis Loewy and Von der 

Heide, 1914 

Rat 5000 

24 h/d, 

gd 7-17 

fetal death in late pregnancy (see 

Section 3.3.2) NEDO, 1986 

Rat 5000 

7 h/d, 

gd 1-19 no fetal death (see Section 3.3.2) Nelson et al., 1985 

Mouse 71800 54 h narcosis, death Weese, 1928 

Mouse 71800 28 h narcosis, death Weese, 1928 

Mouse 53500 54 h narcosis, death Weese, 1928 

Mouse 54000 3.5-4 h/d, 

total 24 h 

comatose, survived Pavlenko, 1972 

Mouse 48000 24 h narcosis, survived Weese, 1928 

Mouse 30560-152800 # 4 h 

narcosis after 190-94 min, overall 

mortality 45 % Marshbitz et al., 1936 

 
METHANOL Interim 2: 2/2005 

18 

TABLE 4: SUMMARY OF ACUTE LETHAL INHALATION DATA IN LABORATORY ANIMALS

Species 

Concentration 

(ppm) 

Exposure 

Time Effect Reference 

Mouse 42000 7 h narcosis Lehmann und Flury, 

1943 

Mouse 41000 6 h LC50 Scott et al., 1979 

Mouse 37594 2 h LCLLo Izmerov et al., 1982 

Mouse 10000 7 h, gd 7 fetal death (see Section 3.3.3) Rogers et al., 1995 

Mouse 7500 

7 h/d, 

gd 6-15 

fetal death; NOEL 5000 ppm (see 

Section 3.3.3) Rogers et al., 1993 

3.2. Nonlethal Toxicity

Studies reporting nonlethal effects after a single acute exposure to methanol and 

relevant for derivation of AEGL values are lacking. Several studies report nonlethal effects, 

affecting mainly liver, the nervous system and kidney, and developmental toxic effects (see 

Section 3.3). These data are summarized in Table 5. 

3.2.1 Non-human Primates

Studies with repeated inhalation exposure

NEDO (1987) exposed monkeys (Macaca fascicularis) (number of animals given in 

brackets) at 3000 (4), 5000 (3), 7000 (1) or 10000 (2) ppm methanol for 21 hours/day for up to 

20 days. As reported in Section 3.1.1, delayed mortality occurred in animals exposed to 5000 

ppm or higher. At cassation of exposure to 3000 ppm or higher, animals were restless, moving 

around the cage and had frequent blinking and yawning, which can be interpreted as signs of 

eye and respiratory tract irritation. Animals exposed to 3000 ppm became used to methanol 

exposure after approximately 4 days and recovered activity, movement and appetite. At 5000 

ppm or higher, animals showed reduced movement, crouched for a longer time, had difficulty in 

standing up, showed involuntary hand movements, vomiting and dyspnea. Exposure at 5000 

ppm or higher for 5 days or longer induced necrosis of the basal ganglia of the cerebrum, 

severe cerebral edema, severe liver necrosis and vacuolar degeneration of the kidneys. After 

exposure at 3000 ppm for 20 days, mild alterations in the cerebral tissue around ventricles 

without edema or necrosis and a slight fatty degeneration of the liver without necrosis were 

observed. 

In another experiment of this series (NEDO, 1987), monkeys (number indicated in 

brackets) were exposed at 1000 (5), 2000 (3) or 3000 (4) ppm methanol for 21 hours/day for 7 

months, and killed for pathological analysis after recovery periods of 0, 1, 6 or 10 months. 

Continuous monitoring of the exposure concentration revealed mean exposure levels of 

1013"64, 2095"73 and 3089"58 ppm, respectively. During the course of the exposure period, 
METHANOL Interim 2: 2/2005 

19 

scratching of the body, frequent yawning and runny noses were observed at all concentrations. 

Slight necrotic changes of basal ganglia nerve cells were found after exposure to 3000 ppm and 

a recovery period of one month; these alterations were not found after the animals had 

recovered for periods of 6 or 10 months. Groups exposed to 1000 or 2000 ppm showed the 

presence of responsive stellate cells in the frontal and parietal lobes, but no necrosis of basal 

ganglia. These stellate cells disappeared after a recovery period of 6 months. In contrast, the 

presence of stellate cells persisted throughout the recovery period after exposure at 3000 ppm. 

A slight increase of glial cells in the optic nerve and a slight degeneration of peripheral nerves 

was observed in the 1000-ppm group after 6 months recovery, but not in animals examined 

immediately after the end of the 7-month exposure period. Similar observations were obtained 

in animals exposed at 2000 ppm and examined after 6 or 10 months of recovery. Monkeys 

exposed at 3000 ppm showed slight optic nerve atrophy and a reduction of myelinated nerve 

fibers. In all groups a concentration-dependent round cell infiltration and slight fibrotic alterations 

of the liver was found. The liver changes were unrelated to the recovery period, but their 

strength did correlate with the exposure concentration and exposure period. 

In another experiment of this series (NEDO, 1987) monkeys were exposed for 21 

hours/day at 10, 100 or 1000 ppm methanol for 7, 19 and 29 months (groups of 2, 3 and 3 

animals, respectively). Concentrations measured in the exposure chambers were 9.9"1.3, 

101.0"8.2 and 1016"83 ppm, respectively. Runny noses were seen in animals exposed at 100 

or 1000 ppm. In the high exposure group animals scratched over the whole body and crouched 

for long periods of time. No differences in food and water intake and in body weight gain were 

seen. No signs of degeneration of the basal ganglions of the cerebrum were found in 

histopathological analysis. A diffuse increase of responsive stellate cells, centered in the 

subcortical white substance, was evident in a high proportion of cases. Histologically, these 

cells are not characteristic of degeneration, but they were nearly absent in normal monkeys in 

the control group. These responsive stellate cells were not correlated with methanol 

concentration or period of exposure. In the reparatory test, these cells were no longer observed 

after exposure was ended, so their occurrence is thought to be a reversible transient histological 

reaction to methanol inhalation. In the visual system no abnormal symptoms were observed that 

correlated with the exposure concentration. In the groups exposed to 1000 ppm, round-cell 

infiltration in the liver was seen after all periods of exposure, but only after exposure for 29 

months a fibrosis was seen in 2 of 3 monkeys. This fibrosis was strictly limited and the 

histopathological effect was considered small. No fibrotic reactions were found in the groups 

exposed to 10 or 100 ppm. 

Andrews et al. (1987) exposed groups of 3 male and 3 female cynomolgus monkeys 

(Macaca fascicularis) at 0, 500, 2000 or 5000 ppm methanol for 6 hours/day, 5 days/week for 4 

weeks. As described in Section 3.1.1, no deaths were observed. Body weights were recorded 

prior to study initiation and weekly during thereafter. No effects on body weights or organ 

weights compared to controls were observed except that female monkeys exposed at 5000 ppm 

had significantly lower absolute adrenal weights (the authors considered this difference as not 

having any apparent biological significance). Animals showed no upper respiratory tract 

irritation, gross and histological examination of 35 different tissues of control and high-dose 

monkeys revealed no effects. No details were given on which tissues were studied and, thus, it 

is unclear whether histopathology included the optic nerve and peripheral nerves, for which 
METHANOL Interim 2: 2/2005 

20 

effects were reported in the study by NEDO (1987). No ocular toxic effects were observed after 

gross, microscopic and ophthalmoscopic examinations. 

3.2.2. Dogs

Loewy and Von der Heide (1914) exposed dogs to methanol vapor. They observed no 

effects at 2000 ppm for 24 hours or 13700 ppm for 4 hours. At 36700 ppm for 8 hours or 50000 

ppm for 1 hour, dogs showed prostration and incoordination. The postexposure observation 

period and technical details were not reported. 

3.2.3. Cats

Flury and Wirth (1933) exposed groups of 2 cats to different methanol concentrations 

(see Section 3.1.2). During exposure of animals at 18200 ppm, increased salivation and 

disturbance of balance was observed. Delayed deaths were observed after exposure at 33400 

ppm) or higher (see Section 3.1.2). 

3.2.4. Rats

Studies with repeated inhalation exposure

White et al. (1983) reported no signs of pulmonary toxicity in male Sprague-Dawley rats 

exposed to 0, 260, 2600 or 13000 mg/m; (0, 200, 2000 or 10000 ppm) methanol for 6 

hours/day, 5 days/week for 6 weeks. Biochemical and cytological parameters of the lung, such 

as lung weight, DNA content, protein content, ribonuclease and protease activity were 

evaluated. No lung irritation was observed. 

Andrews et al. (1987) exposed male and female Sprague-Dawley rats at 500, 2000 or 

5000 ppm methanol for 6 hours/day, 5 days/week for 4 weeks. No effects on body or organ 

weights were found, except that female rats exposed to 2000 ppm had significantly higher 

relative spleen weights than controls. The authors considered this difference as not having any 

apparent biological significance. In all methanol-treated groups increased discharges around 

the nose and eyes, lacrimation, mucoid nasal discharges, red nasal discharge, dried red nasal 

discharge were observed. The frequency of these symptoms was increased in the treated 

groups, but only the incidence of mucoid nasal discharges appeared to be concentrationrelated. Gross and histological examination of 35 different tissues of control and high-dose rats 

revealed no effects. No ocular abnormalities were observed. The red nasal discharge was most 

likely caused by extravasation of red blood cells (chromadacryorrhea), which is caused easily in 

the rat not only by locally acting chemicals, but also by stress, dry air or upper respiratory tract 

infections. 

NEDO (1987) exposed groups of 20 male and 20 female Fischer 344 rats continuously 

for 12 months at 0, 10, 100 or 1000 ppm. During the treatment period, 1 female rat of the 10-

ppm group died on day 340, and one female rat of the 1000-ppm group had to be killed on day 

337. No alterations in general conditions and behavior were observed. The highest exposure 
METHANOL Interim 2: 2/2005 

21 

group showed a slightly reduced body weight increase. In clinical, hematological and 

biochemical examinations, no significant alterations compared to controls were observed. 

Pathological analysis revealed a slight, dose-dependent increase in liver and spleen weights. 

No neoplastic alterations were found. 

3.2.5. Mice

Studies with repeated inhalation exposure

NEDO (1987) studied groups of 30 male and 30 female B6C3F1 mice continuously 

exposed for 12 months at 0, 10, 100 or 1000 ppm. Groups of 10 animals were killed for analysis 

after 6 months. During the treatment period, one female mouse of the 100-ppm group died and 

another one had to be killed. No alterations in general conditions and behavior were observed. 

The body weights of male mice and female mice were increased after 6 and 9 months, 

respectively. This difference (4 % and 6 % relative to controls) was significant only in the groups 

exposed to 1000 ppm. A significantly reduced food uptake without any effect on body weight 

was found for the female mice of the 1000-ppm group during the first two months and after 7 

months; no correlation with body weight changes was found. In male mice exposed at 1000 

ppm an increase liver weight was observed after 6 months and increased kidney and spleen 

weights were found after 12 months, but the dose-dependency of these effects showed was 

unclear. After 12 months a fatty degeneration of hepatocytes was observed in higher frequency 

in male mice of the high exposure group, but was also reported in lower frequency in the control 

group. 

TABLE 5: SUMMARY OF NON-LETHAL EFFECTS IN LABORATORY ANIMALS 

Species 

Concentration 

(ppm) 

Exposure 

Time Effect Reference 

Monkey 5000 6 h/d, 5d/w, 

4w 

no effects on respiratory tract or eyes, no 

histopathological alterations 

Andrews et al., 

1987 

Monkey 3000 21h/d, 20 d weakness and loss of motion during 

exposure; mild fatty liver degeneration 

and cerebral tissue alterations, no NOEL 

reported 

NEDO, 1987 

Monkey 1000 21h/d, 7 m mild peripheral nerve degeneration, 

round cell infiltration and fibrotic 

alterations of in the liver 

NEDO, 1987 

Dog 50000 1 h prostration, incoordination Loewy and Von 

der Heide, 1914 

Dog 36700 8 h prostration, incoordination Loewy and Von 

der Heide, 1914 

Dog 13700 4 h none Loewy and Von 

der Heide, 1914 

 
METHANOL Interim 2: 2/2005 

22 

TABLE 5: SUMMARY OF NON-LETHAL EFFECTS IN LABORATORY ANIMALS 

Species 

Concentration 

(ppm) 

Exposure 

Time Effect Reference 

Dog 2000 24 h none Loewy and Von 

der Heide, 1914 

Cat 18200 6 h increased salivation, disturbance of 

balance 

Flury and Wirth, 

1933 

Rat 20000 7 h/d, 19 d maternal toxic effects in pregnant rats; 

unsteady gait during exposure; NOEL 

10000 ppm (see Section 3.3.2) 

Nelson et al., 

1985 

Rat 13000 20 h prostration Loewy and Von 

der Heide, 1914 

Rat 8800 8 h lethargy Loewy and Von 

der Heide, 1914 

Rat 2000 8 h none Loewy and Von 

der Heide, 1914 

Rat 10000 7 h/d, 

gd 1-19 

fetal malformations; NOEL 5000 ppm 

(see Section 3.3.2) 

Nelson et al., 

1985 

Rat 10000 6 h/d, 

5 d/w, 6 w 

no pulmonary toxicity White et al., 

1983 

Rat 500; 2000; 

5000 

6 h/d, 

5 d/wk, 4 

wk 

increased discharges around the nose 

and eyes at all concentrations 

Andrews et al., 

1987 

Mouse 15000 6 h maternal toxic effects in pregnant mice; 

ataxia, circling, tilting heads and 

depressed motor activity during 

exposure; NOEL 10000 ppm (see Section 

3.3.3) 

Bolon et al., 

1993 

Mouse 5000 7 h fetal malformations; NOEL 2000 ppm 

(see Section 3.3.3) 

Rogers et al., 

1995 

Mouse 2000 7 h/d, 

gd 6-15 

fetal malformations; NOEL 1000 ppm 

(see Section 3.3.3) 

Rogers et al., 

1993 

Mouse 1000 24 h/d, 

7 d/w, 

12 m 

reduced body weights, increased kidney / 

spleen weights, higher incidence of fatty 

liver degeneration; not seen at 100 ppm 

NEDO, 1987 

3.3. Developmental/Reproductive Toxicity

Several studies on the developmental and reproductive toxicity of methanol were carried 

out. Single and repeated inhalation exposures during the period of embryogenesis induced a 
METHANOL Interim 2: 2/2005 

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wide range of concentration-dependent teratogenic and embryolethal effects in rats and mice. 

The developmental toxicity data have been reviewed by NTP-CEHRH (2003) and US-EPA 

(2001) and these panels concluded that despite of toxicokinetic differences between rodents 

and humans, the available rodent data was relevant for humans. 

3.3.1. Nonhuman Primates 

Studies with repeated inhalation exposure

Burbacher et al. (1999a; 1999b; 2004a; 2004b) exposed groups of 11-12 female Macaca 

fascicularis in a two-cohort study at 0, 200, 600 or 1800 ppm for 2 hours/day, 7 days/week, 4 

months prior to and throughout pregnancy. During each exposure the methanol delivery to the 

exposure chamber was stopped after 2 hours, while animals remained in the chamber for 

another 30 minutes with fast declining methanol concentrations (1/6th of exposure 

concentration at 124 minutes and 0 ppm at 135 minutes). Animals were exposed individually in 

an exposure chamber; methanol concentration was measured every 10 minutes by an infrared 

analyzer and mean concentrations (" SE) during pregnancy were 0"0, 206"0, 610"1 and 

1822"1 ppm, respectively. Blood methanol concentrations, determined after the first and the 

87th exposure as well as two times during pregnancy, were 4.3-5.5 mg/l at 200 ppm (roughly 

two-fold higher than background values), 9.5-12.1 mg/l at 600 ppm and 33.2-40.4 mg/l at 1800 

ppm. The mean plasma formate concentrations did not show consistent rises following 

methanol exposure. The chronic methanol exposure did not result overt signs of toxicity, such 

as lethargy, uncoordinated movements and labored or irregular respiration. No effects were 

found on maternal weight gain during pregnancy and simple tests for visual problems and finemotor incoordination (performed after each exposure). The length of the menstrual cycle and 

the frequencies of conception and live births in the methanol-exposed and control females were 

very similar. However, all methanol-exposed groups showed a decrease in pregnancy duration 

of about 8 days (no dose-response relationship). Cesarian section was done in 2 monkeys 

exposed at 200 ppm and another 2 exposed at 600 ppm because of uterine bleedings (no 

bleedings were observed in the high exposure group or in control animals). Two cesarian 

sections were performed on monkeys exposed at 1800 ppm, one for unproductive labor and 

another because of intrauterine death of a hydrocephalic fetus. The average pregnancy 

durations of all groups were still within the range of pregnancy duration of 160-169 days 

reported in the literature for this species. There were no effects on size or body weight of the 

offspring (8-9 infants per dose group), neither did methanol-exposed infants display a higher 

incidence of signs of prematurity. Results of behavioral assessments did not indicate significant 

methanol exposure effects on early reflex responses, gross motor development, spatial and 

concept learning or memory and social behavior. Exposure was associated with a delay in early 

sensorimotor development for male, but not female infants: In the Visually Directed Reaching 

Test (ability to grasp and retrieve a small object) a delay of about 9 days for the 200-ppm group 

and of about 2 weeks in the 600-ppm and 1800-ppm groups in reaching the testing criterion 

(8/10 consecutive trials successful) was found. The HEI Institute>s Health Review Committee 

recommended to interpret these results cautiously because they are based on 3 males in the 

600-ppm and 2 males in the 1800-ppm groups and may have been influenced by the low mean 
METHANOL Interim 2: 2/2005 

24 

age reported for male control monkeys to reach the test criterion. Visual recognition memory 

was also affected according to the Fagan Test of Infant Intelligence (the test makes use of the 

infant>s proclivity to direct more visual attention to novel rather than to familiar abstract or social 

stimuli). While the control infants exhibited a significant novelty response for both the abstract 

patterns and social stimuli (monkey faces), all infants of the methanol-exposed groups failed to 

show a significant preference for novel social stimuli (results with the abstract stimuli varied 

greatly by cohort and no consistent pattern was observed); there were no mean group 

differences across the 4 groups. However, the Nonmatch-to-Sample Test, used to evaluate the 

same cognitive function, revealed no significant effects. A severe wasting syndrome (resulting in 

euthanasia) was observed in 2 of 4 females of cohort 1 and 0 of 3 females of cohort 2 after 

approximately 1 year of age; the etiology of the syndrome (e.g. a retroviral infection) could not 

be elucidated. 

3.3.2. Rats 

Studies with repeated inhalation exposure

NEDO (1987) exposed groups of 36 pregnant Sprague-Dawley rats continuously at 0, 

200, 1000 or 5000 ppm during gestational days (gd) 7-17. Maternal toxicity was observed at 

5000 ppm: one animal died and another had to be killed; body weight was significantly reduced 

compared to controls; uptake of food and water was reduced during gestational days 7-12 and 

even one week after delivery. At 5000 ppm, increased embryo lethality in the later period of 

pregnancy and a reduced birth weight was found. The F1 generation showed an increased 

incidence of deaths, which occurred during the first 4 days, and body weights of females were 

still reduced at the end of the nursing period. Morphological changes included earlier dentition, 

eye lid opening and testes descent. At 8 weeks of age, reduced relative weights of brain, 

thyroid, thymus and testes as well as an increased relative weight of the pituitary gland were 

found. No histopathological changes were recorded. No effects on the reproduction of the F1 

generation were found. In groups exposed at 1000 or 200 ppm, no developmental toxic effects 

were observed. 

Nelson et al. (1985) exposed groups of about 15 pregnant Sprague-Dawley rats for 7 

hours/day at 0, 5000 or 10000 ppm on gd 1-19 or to 20000 ppm on gd 7-15. The exposure 

atmosphere was monitored continuously using a Miran 1A infrared analyzer7

. At 20000 ppm 

dams showed unsteady gait during the first days of exposure and a significantly reduced food 

uptake, however without any effect on body weight. No signs of maternal toxicity were reported 

at 5000 or 10000 ppm. On gd 20, dams were killed and half of the fetuses were examined for 

visceral and the other half for skeletal defects. No effects of methanol were found on the 

number of yellow bodies, implantations, resorptions or fetal deaths. At 20000 ppm a significantly 

increased number of litters with malformations and a significantly reduced number of fetuses 

without malformations was found. Methanol induced a concentration-related decrease in fetal 

weights at 10000 and 20000 ppm. Skeletal and visceral malformations were significantly 

increased at 20000 ppm. Malformations predominantly comprised extra or rudimental cervical 

ribs and urinary or cardiovascular defects. Similar malformations were found at 10000 ppm, but 

the incidence was not significantly different from that in the control group. Blood methanol 

concentrations were measured in non-pregnant rats using gas chromatography (see Table 8 for 

results). Exposure at 5000 ppm did not cause any malformations. 
METHANOL Interim 2: 2/2005 

25 

Stern et al. (1996; 1997) exposed 4 cohorts of about 30 (number estimated, not explicitly 

stated by the authors) pregnant Long-Evans rats at 0 or 4500 ppm methanol for 6 hours/day 

beginning on gd 6. After birth, both dams and pups were exposed through postnatal day 21. 

Maternal blood methanol concentrations were constant during gestation (mean 0.55"0.07 (SD) 

mg/ml) and lactation (mean 0.56"0.09 (SD) mg/ml). Before weaning, pups exhibited blood 

concentrations approximately twice those attained by their dams (mean 1.26"0.23 (SD) mg/ml). 

When exposure was continued after weaning on postnatal day 21, blood concentration in pups 

slowly declined and reached the level of the dams about 48 days after birth. A panel of 

neurobehavioral tests was performed on the pups. No effects of methanol exposure on suckling 

and olfactory conditioned behavior were found. In motor activity tests, methanol-exposed 

neonates were less active on postnatal day 18, but more active on postnatal day 25 than the 

equivalent control group pups. Very subtle effects were also seen in two operant behavior tests. 

3.3.3. Mice

Rogers et al. (1995, abstract) and Rogers (1999, personal communication) exposed 

groups of pregnant CD-1 mice on gd 7 to the following concentration-time combinations (CxT) 

(exposure periods indicated in brackets): 2000 ppm (5 and 7 hours), 5000 ppm (2, 3, 5 and 7 

hours), 10000 ppm (2, 3, 5 and 7 hours) or 15000 ppm (1, 2, 3, 5 and 7 hours). The number of 

litters ranged from 5-39 for CxT combinations and was 106 in control groups. Maternal blood 

methanol levels determined at the end of the exposure time increased with the CxT to a 

maximum mean of 4966 mg/l at 15000 ppm for 7 hours. For exposures with the same CxT, 

blood methanol levels were higher with shorter duration, higher concentration exposures, i.e., 

1200 mg/l at 5000 ppm for 7 hours, 1500 mg/l at 10000 ppm for 3 hours, and 2300 mg/l at 

15000 ppm for 2 hours were measured. Dams were killed on gd 17 for assessment of 

teratogenic effects. Fetal death, cleft palate and multiple skeletal defects were significantly 

increased at CxT combinations of 70000 ppm @ h or higher (i.e., no fetal death was found at 

5000 ppm for 7 hours; authors expressed data only as CxT values). The most sensitive 

endpoint was cervical rib induction, which occurred at CxT of 15000 ppm @ h or higher (i.e., no 

effects were observed at 2000 ppm for 5 or 7 hours). Incidences for fetal effects increased with 

higher exposure concentrations for similar CxT, e.g. percentages of fetuses with C7 cervical rib 

were about 40 % at 5000 ppm for 7 h and at 10000 ppm for 3 h and about 63 % at 15000 ppm 

for 2 h (this result also corresponds with the higher blood methanol concentration for the latter 

concentration-time combination). This study has only been published as an abstract up until 

now. 

In the study of Rogers et al. (1997), groups of 12-19 pregnant CD-1 mice were exposed 

at 10000 ppm methanol or filtered air for 7 hours/day on 2 consecutive days during gestation, 

either gd 6-7, 7-8, 8-9, 9-10, 10-11, 11-12 or 12-13, or for 7 hours on a single day of gestation, 

either on gd 5, 6, 7, 8 or 9. Mice received water but not food during exposure. On analysis on gd 

17, a significant effect on maternal body weights was evident only after exposure on gd 7-8. 

Significantly more dead/resorbed fetuses per litter were found after exposures on gd 6-7 or 7-8 

or after single exposure on gd 7. After gd-7 exposure, the number of live fetuses was lower than 

on any other day. Cleft palate occurred significantly more frequently in groups exposed on gd 

6-7, 7-8 or 8-9 and in those exposed on gd 5, 6, 7, 8 or 9 (peak on gd 7). Exencephaly occurred 
METHANOL Interim 2: 2/2005 

26 

significantly more frequently after exposure on gd 6-7 or 8-9 and in those exposed on gd 5, 6, 7 

or 8 (peak on gd 7). The following significantly higher incidences of skeletal malformations were 

observed: defects of exoccipital (peak gd 6-7, gd 5), atlas (peak gd 6-7, gd 5,6), axis (peak gd 

6-7, gd 7), rib on cervical vertebra seven (peak gd 6-7, gd 7), and rib on lumbar vertebra one 

(peak gd 7-8, gd 7). Maternal blood methanol concentrations were determined at times during, 

at the end of, and subsequent to a single 7-hour exposure on gd 7 (see Table 8). 

Studies with repeated inhalation exposure

Rogers et al. (1993) exposed pregnant CD-1 mice (number of dams examined indicated 

in brackets) at 1000 (31), 2000 (61), 5000 (61), 7500 (20), 10000 (20) or 15000 (34) ppm for 7 

hours/day on gd 6-15. Controls comprised groups that were sham-exposed to filtered air, left 

untreated in their home cages or left in their home cages and food-deprived for 7 hours/day to 

match the food deprivation of methanol-exposed mice. The methanol concentration in the 

exposure chamber (15 air changes per hour) was monitored continuously with a Foxboro Miran 

1A Infrared Analyzer7

. One dam each died at 7500, 10000 and 15000 ppm. The sham-exposed 

and food-deprived controls as well as all methanol-exposed dams gained less weight than did 

unexposed dams fed ad libitum, but methanol did not exacerbate this effect. On gd 17, mice 

were killed and implantation sites, live and dead fetuses and resorptions were counted. Fetuses 

were examined externally and weighed as a litter. Half of each litter was examined for soft 

tissue anomalies, the other half for skeletal morphology. Significant increases were observed in 

the incidence of exencephaly and cleft palate at 5000 ppm or higher. At 7500 ppm or higher 

significantly increased number of dead fetuses/litter were found and full-litter resorptions were 

increased at 10000 and 15000 ppm. A concentration-related increase in cervical ribs was 

significant at 2000 ppm or higher. Using a log-logistic dose response model, the authors 

calculated maximum likelihood estimates (MLE05) corresponding to 5% added risk above 

background (BMD05 given in parenthesis). MLE05 was 4314 (3398) ppm for cleft palate, 5169 

(3760) ppm for exencephaly, 3713 (3142) ppm for cleft palate or exencephaly, 5650 (4865) ppm 

for resorptions and 824 (305) ppm for cervical rib. Blood methanol levels in dams were 

measured 15 minutes after cessation of the first exposure (see Table 8). 

Bolon et al. (1993) investigated the phase-specific developmental toxicity of methanol in 

pregnant CD-1 mice. In pilot experiments, mice (5-12 animals/group) were exposed for 6 

hours/day at 0 or 10000 ppm on gd 6-15 (i.e. organogenesis), 7-9 (i.e. period of murine 

neurulation) or 9-11 (i.e. period of potential neural tube reopening). The concentration-response 

relationship for neural tube defects was determined in a subsequent experiment by exposing 

dams (20-27 animals/group) at 0, 5000 (gd 7-9), 10000 (gd 6-15, 7-9 or 9-11) or 15000 ppm (gd 

7-9 or 9-11). The critical periods of susceptibility to neural tube defects was further narrowed by 

exposing mice (8-15 animals/group) for 1 (gd 7, 8 or 9) or 2 days (gd 7-8 or 8-9) at 15000 ppm 

for 8 hours/day. Transient maternal neuronal toxicity was observed at 15000 ppm after the first 

exposure in 20 % of dams, after the second exposure in 10% and after the third exposure in 5 

%. Signs included ataxia, circling, tilting heads and depressed motor activity were observed. 

Three dams were removed from the study on gd 7 due to the severity of clinical signs, but had 

no visible lesions. The other affected dams recovered within 12 hours. Clinical signs were not 

apparent at 5000 or 10000 ppm. Dams were killed at gd 17. In the pilot study in which a single 

exposure concentration of 10000 ppm was used, significantly reduced fetal weight was 

observed after gd-6-15 exposure, but not after exposure on gd 7-9 or 9-11. An significantly 
METHANOL Interim 2: 2/2005 

27 

increased percentage of resorptions/litter was found after exposure on gd 6-15 and 7-9, but not 

gd 9-11. Neural tube defects, cleft palate and digit malformations were found in significantly 

higher incidence after exposure on gd 6-15, cleft palate after exposure on gd 9-11. In the doseresponse experiments significantly increased percentages were found for resorptions/litter after 

15000 ppm on gd 7-9 and for the number of litters with $1 resorption after 5000 ppm or higher 

on gd 7-9. Exposure to 5000 ppm or higher on gd 7-9 significantly induced in renal pelvic 

cavitation. Exposure at 10000 ppm or higher additionally resulted in significantly increased 

percentages of ocular defects, cleft palate, hydronephrosis and deformed tails, and exposure at 

15000 ppm in neural tube defects. Neural tube defects and ocular lesions occurred after 

methanol inhalation between gd 7 and 9, while limb anomalies only occurred after exposure 

during gd 9 and 11. In the window-of-susceptibility experiment, significantly increased 

percentages of resorptions/litter and of litters with $1 resorption were observed after exposure 

at 15000 ppm only for the treatment periods gd 7, 7-8 and 7-9. A significant increase in neural 

tube defects was observed only after exposure on gd 7-8 or 7-9. The authors did not report, 

whether fetal death was observed. 

3.4. Genotoxicity

Simmon et al. (1977) found methanol to give negative results when tested in Salmonella 

typhimurium plate incorporation assays with or without metabolic activation using strains TA98, 

TA100, TA1535, TA1537 and TA1538. De Flora et al. (1984) observed no effect of methanol in 

Salmonella typhimurium plate incorporation assays with or without metabolic activation using 

strains TA1535, TA100, TA1538, TA98 and TA1537 and in a DNA repair test using Escherichia 

coli strains WP2, WP67 and CM871 in the presence or absence of metabolic activation. 

Crebelli et al. (1989) reported that methanol (6.0 % (v/v)) induced dose-dependently a 

statistically significant increased frequency of chromosomal malsegregations in Aspergillus 

nidulans diploid strain P1. Obe and Ristow (1977) did not observe sister chromatid exchanges 

in Chinese hamster ovary cells in vitro during treatment for 8 days to a final concentration of 0.1 

% (v/v). McGregor et al. (1985) reported an increase in mutation frequency in L5178Y mouse 

lymphoma cells treated with 7.9 mg/ml methanol, if S-9 mix was present (it should be noted that 

this concentration was higher than the maximum concentration proposed by the 1997 OECD 

guideline). 

Campbell et al. (1991) found no increased frequencies of micronuclei in blood cells, of 

sister chromatic exchanges, chromosome aberrations or micronuclei in lung cells in mice 

exposed by inhalation to 800 or 4000 ppm methanol 6 hours/day for 5 days. 

3.5. Carcinogenicity

In a carcinogenicity study (NEDO, 1987; Katoh, 1989), Fischer-344 rats and B6C3F1

mice were exposed at 10, 100 or 1000 ppm for 20 hours/day for 24 and 18 months, 

respectively. Compared to control groups, no increased mortality in the treated groups was 

observed. A non-significant reduction of body weight was observed in methanol-treated female 

rats between weeks 51 and 71, while in male and female mice an increased body weight was 

found between months 6 and 12 and months 9 and 12, respectively. The increase was 
METHANOL Interim 2: 2/2005 

28 

significant in female mice exposed at 1000 ppm. No evidence of carcinogenicity was found in 

either species. Male rats exposed at 1000 ppm showed a higher frequency of papillary 

adenomas than controls, which, however, was not significantly different from controls. Female 

rats exposed at 1000 ppm methanol showed a higher number of adrenal pheochromocytoma, 

which, however, was not significantly different from controls. 

3.6. Summary

With regard to lethal effects in animals, three points are important. First, very high 

methanol concentrations can lead to death by central nervous depression, e.g. 6-hour LC50

values of 41000 and 66900 ppm have been reported for mice and rats, respectively (Scott et al, 

1979; BASF, 1980b). Second, high methanol concentrations can lead to fetal death in mice, e.g. 

fetal death was observed after exposure at 7500 ppm or higher for 7 hours/day on gestational 

days (gd) 6-15 and also after a single 7-hour exposure at 10000 ppm on gd 7, while no fetal 

death occurred after single or repeated exposure to 5000 ppm (Rogers et al., 1993; 1995, 

abstract). Third, in monkeys, but not in rodents, delayed deaths can result from metabolic 

acidosis caused by accumulation of the methanol metabolite formate, e.g. delayed deaths 

occurred after repeated exposure to 10000 ppm for 21 hours/day (after 3 exposures) and 5000 

ppm for 21 hours/day (after 5 exposures), but not after repeated exposure to 5000 ppm for 6 

hours/day, 5 days/week, 4 weeks (NEDO, 1987; Andrews et al., 1987). 

Severe histopathological effects on central nervous system, liver and kidneys of 

monkeys have been reported after exposure at 5000 ppm for 21 hours/day for 20 days (NEDO, 

1987), while no histopathological effects were reported at 5000 ppm for 6 hours/day, 5 

days/week for 4 weeks (Andrews et al., 1987). While in the first study irritation was observed in 

monkeys at concentrations of 1000 ppm or higher, no irritation was found in the latter study at 

5000 ppm. 

Methanol causes developmental toxic effects. In mice, fetal malformations were found 

a) after single exposure at 5000 ppm (3, 5 or 7 hours), but not at 5000 ppm (2 hours) or 2000 

ppm (up to 7 hours), and b) after repeated exposure at 2000 ppm or higher, but not at 1000 

ppm, for 7 hours/day (Rogers et al., 1993; 1995, abstract; Rogers, 1999, personal 

communication). In rats, fetal malformations were found after exposure a) at 10000 ppm or 

higher, but not 5000 ppm, for 7 hours/day on gd 1-19 and b) at 5000 ppm, but not 1000 ppm, for 

24 hours/day on gd 7-17 (Nelson et al., 1985; NEDO, 1987). After exposure of monkeys 

(Macaca fascicularis) at 200, 600 or 1800 ppm for 2 hours/day, 7 days/week 4 months prior to 

and throughout pregnancy, some effects indicating developmental effects were observed 

(shorter pregnancy lengths, a severe wasting syndrome in some of the offspring (of unknown 

etiology), and a concentration-related delay in sensorimotor development in male offspring) 

(Burbacher et al., 1999a; 1999b; 2004a; 2004b). After exposure of rats at 4500 ppm for 6 

hours/day from gestational day 6 to postnatal day 21, very subtle effects were seen in operant 

behavior tests, but not in conditioned behavior and motor activity tests (Stern et al., 1996; 1997). 

There was no evidence of carcinogenic effects in a lifetime bioassay in rats and mice 

exposed at 1000 ppm for 20 hours/day, 7 days/week (NEDO, 1987). Methanol showed no 

mutagenicity in bacterial mutagenicity tests, sister chromatid exchange assay in Chinese 
METHANOL Interim 2: 2/2005 

29 

hamster ovary cells or the micronucleus test in mice exposed at 4000 ppm for 6 hours/day for 5 

days; it increased the mutation frequency in mouse lymphoma cells at very high concentrations 

(WHO, 1997). 

4. SPECIAL CONSIDERATIONS 

4.1. Metabolism and Disposition

4.1.1. Absorption, Distribution and Elimination

The background blood concentrations in humans ranged from 0.32 to 2.61 mg/l (mean 

0.73 mg/l) for methanol and from 3 to 19 mg/l (0.07-0.4 mmol/l) for formate. Both substances 

are taken up from the normal diet and generated in metabolic processes (Kavet and Nauss, 

1990). 

Methanol is rapidly absorbed after inhalation, the absorption percentage being around 

53-85 % (Leaf and Zatman, 1952; Sedivec et al., 1981). After ingestion, it is rapidly absorbed 

from the gastrointestinal tract with peak absorption occurring after 30-60 minutes (Becker, 1983, 

Leaf and Zatman, 1952). Liquid methanol shows a very high skin absorption rate with an 

average of 0.192 mg methanol/cm2

 per minute (Dutkiewicz et al., 1980). 

Pollack and Brouwer (1996) studied the disposition of methanol in pregnant rats on 

gestation days (gd) 7, 14 and 20 and in pregnant CD-1 mice on gd 9 and 18. In these studies, 

exposure was by the oral, intravenous and inhalation routes (1000-20000 ppm for 8 hours). 

Saline was the vehicle for oral and intravenous exposure. Three to five animals were examined 

per dose and exposure condition. Methanol concentrations were measured in blood, urine, and 

amniotic fluid by gas chromatography (GC). The disposition of methanol after oral or 

intravenous administration was similar in pregnant and nonpregnant female rats, regardless of 

the gestational stage (day 7, 14 or 20 after conception) at which the toxicokinetics of methanol 

were examined. Parallel experiments in female mice indicated that methanol elimination was 

approximately twice as rapid in mice as in rats due to a significantly higher maximal velocity for 

methanol metabolism in the smaller rodent species. As was the case in the rat, relatively small 

changes in methanol elimination were observed during the course of gestation in pregnant 

mice. In both species, the rate of methanol metabolism by fetal liver in vitro was less than 10 % 

that of the metabolic rate in adult liver. 

Methanol distributes readily and uniformly to organs and tissues in direct correlation to 

their water content; its apparent volume of distribution is 0.6-0.7 l/kg (Yant and Schrenk, 1937). 

In humans, clearance of methanol from the body proceeds with a half-life of 1 day or more for 

high doses exceeding 1 g/kg and about 3 hours for low doses, i.e., less than 0.1 g/kg (Leaf and 

Zatman, 1952). From volunteers breathing methanol concentrations between 50 and 300 mg/m;

(38-229 ppm) for 8 hours, Sedivec et al. (1981) estimated a half-life of 1.5-2 hours. From 

volunteer exposures at up to 800 ppm for 8 hours and using blood and urine sampling, 

Batterman et al. (1998) calculated a half-lifes of 1.44 and 1.55 hours, respectively. 

4.1.2. Metabolism
METHANOL Interim 2: 2/2005 

30 

During metabolic degradation, methanol is initially oxidized to formaldehyde. The 

enzymes mainly catalyzing this reaction are alcohol dehydrogenase in humans and non-human 

primates and catalase in rats and other non-primate species (see Table 6); in addition 

microsomal oxidation by cytochrome P450 2E1 may contribute to methanol transformation 

(WHO, 1997). Formaldehyde is very rapidly oxidized to formate by several enzymes including a 

specific formaldehyde dehydrogenase. Formate has to combine with tetrahydrofolate to form 

10-formyl-tetrahydrofolate in order to be further oxidized to CO2. Tetrahydrofolate is derived 

from folic acid (folate) in the diet and is the major determinant of the rate of formate metabolism 

(McMartin, 1975). The enzymes involved in the metabolism of methanol in primates respectively 

rodents are listed in Table 6. 

In humans, methanol is primarily eliminated by metabolism to formaldehyde and further 

to formate, which may be excreted in the urine or further oxidized to carbon dioxide. Of a 50-

mg/kg dose of methanol, only 2 % is excreted unchanged by the lungs and kidney (Leaf and 

Zatman, 1952). Likewise, studies on rats and monkeys have shown that about 80 % of 

administered methanol is oxidized to CO2 (WHO, 1997). 

With regard to the methanol concentrations in blood resulting from inhalation exposure, 

species differences occur: on the one hand side, the increased ventilation per unit body weight 

associated with the smaller species (about 10-fold higher in mice and 3.5-fold higher in rats 

compared to humans) leads to higher blood concentrations in rodents. On the other hand side, 

Km values are lower in rodents than in primates and thus enzymatic methanol oxidation in 

rodents is faster at low methanol exposure concentrations (enzymatic rate determined by Km), 

while it is about equal at high concentrations (enzymatic rate determined by Vmax, with similar 

Vmax values in rodents and primates; cf. Table 7). The opposing effects on blood methanol 

concentration of higher specific ventilation rate and lower Km in rodents, are responsible for the 

finding that the differences in blood methanol concentrations between rodents and humans are 

small at concentrations of up to 1000 ppm, but become increasingly larger at higher 

concentrations (see Table 8 and Figure 1) (Perkins et al., 1995a). 

The metabolic detoxification of formate in rodents occurs with a higher vmax (about 2-3-

fold higher in rats and 8-10-fold higher in mice compared to primates) and a lower Km, which 

results in a much faster elimination of formate in rodents. In contrast to rodents, formate 

accumulates in primates during exposure to high methanol concentrations, since formate is 

formed faster than it is metabolized. 

TABLE 6: METABOLISM OF METHANOL AND ENZYMES INVOLVED; 

adopted from WHO (1997) and Watkins et al. (1970) 

Metabolic step Humans and non-human primates Rodents 

Methanol CH3OH

9

Formaldehyde 

HCHO 

alcohol dehydrogenase (about 80-90% 

in monkey; Watkins et al., 1970) 

cytochrome P450 monooxygenase 

catalase (peroxidase activity) 

alcohol dehydrogenase (about 40-

45%; Watkins et al., 1970) 

Formaldehyde formaldehyde dehydrogenase formaldehyde dehydrogenase 
METHANOL Interim 2: 2/2005 

31 

HCHO

9

Formic acid HCOOH 

Formic acid HCOOH

9

Carbon dioxide CO2

10-formyl-THF-synthetase * 

10-formyl-THF-dehydrogenase 

10-formyl-THF-synthetase 

10-formyl-THF-dehydrogenase

* THF, tetrahydrofolate
METHANOL Interim 2: 2/2005 

32 

TABLE 7: KINETIC PARAMETERS OF METHANOL METABOLISM 

Metabolic 

step 

Species Vmax a Km Reference 

Methanol 

CH3OH

9

Formaldehyd

e HCHO 

monkey (Mac. mulata) 

monkey (Mac. 

fascicularis) 

monkey (Mac. 

fascicularis) 

monkey (Mac. 

nemestrina) 

monkey 

monkey (Mac. 

fascicularis) 

monkey (Mac. mulata) 

rat, non-pregnant 

rat, pregnant gd 14 

rat, pregnant gd 20 

mouse, non-pregnant 

mouse, pregnant gd 8 

mouse, pregnant gd 18 

70 mg/l h 

171 mg/h 

75 mg/l h 

27.5 mg/kg h 

44 mg/l h 

48 mg/l h 

63.2"6.3 mg/kg 

h 

60.5"6.4 mg/kg 

h 

50.6"2.5 mg/kg 

h 

134"6 mg/kg h 

131"3 mg/kg h 

96.8"6.2 mg/kg 

h 

360 mg/l b

63 "11 mg/l 

278 mg/l 

44.8"19.0 

mg/l 

33.9"15.4 

mg/l 

52.9"14.5 

mg/l 

48.7 mg/l 

48.7 mg/l 

48.7 mg/l 

Dafeldecker et al., 

1981 

Noker et al., 1980 

Burbacher et al., 

1999a; 

Burbacher et al., 

2004a 

Makar et al., 1975 

Watkins et al., 1970 

Eells et al., 1983 

Makar et al., 1968 

Ward et al., 1997 

Ward et al., 1997 

Ward et al., 1997 

Ward et al., 1997 

Ward et al., 1997 

Ward et al., 1997 

Formaldehyd

e HCHO

9

Formic acid 

HCOOH 

human 

monkey 

rat 

75 mg/kg h 

144 mg/kg h 

300 mg/kg h 

3.8 mg/l 

3.8 mg/l 

3.8 mg/l 

Horton et al., 1992 

Horton et al., 1992 

Horton et al., 1992 

Formic acid 

HCOOH 

9

Carbon 

dioxide CO2

monkey (Mac. 

fascicularis) 

monkey (Mac.) 

primates 

rat (Sprague-Dawley) 

rat 

rat 

mouse 

19.9"0.5 mg/kg 

h 

35 mg/kg h 

34 mg/kg h 

85 mg/kg h 

75 mg/kg h 

78 mg/kg h 

300 mg/kg h 

175 mg/kg 

100 mg/kg 

60 mg/kg 

Eells et al., 1983 

McMartin et al., 1977 

Greim, 1995 

Palese and Tephly, 

1975 

McMartin et al., 1977 

Johlin et al., 1987 

(Ward et al., 1995) 

Johlin et al., 1987 

(Ward et al., 1995)

a

 values of Vmax are given for substrate concentrations 

b

 values in mg/l refer to methanol concentrations in blood

4.1.3. Pharmacokinetic Models

Bouchard et al. (2001) developed a multicompartment biologically based dynamic model 

to describe the time evolution of methanol and its metabolites in rats, monkeys and humans 

following oral uptake or inhalation exposure. The dynamic of intercompartment exchanges was 
METHANOL Interim 2: 2/2005 

33 

described mathematically by a mass balance differential equation system. The model's 

conceptual and functional representation was the same for rats, monkeys, and humans, but 

relevant published data specific to the species of interest served to determine the critical 

parameters of the kinetics. For model development, the kinetic data of Horton et al. (1992) for 

rat (intravenous route), Dorman et al. (1994) for monkey and Osterloh et al. (1996) and Sedivec 

et al. (1981) for humans were used. The model was validated using inhalation data for rat and 

monkey (Horton et al., 1992) and humans (Batterman et al., 1998). Simulations provided a good 

agreement between measured data and model calculations. 

Perkins et al. (1995a) established a pharmacokinetic model allowing calculation of blood 

methanol concentrations in humans, rats and mice after inhalation exposure (see Appendix B). 

The authors calculated that an 8-hour exposure at 5000 ppm methanol would result in blood 

methanol concentrations of 2976-4188 mg/l in mice, 1018 mg/l in rats and 224 mg/l in humans, 

while exposure at 1000 ppm would result in 132-268, 93.5, and 38.5 mg/l, respectively, and 

exposure at 200 ppm in 9-12, 11, and 7.5 mg/l, respectively. 

Horton et al. (1992) developed a pharmacokinetic model of inhaled methanol based on 

data from Fischer-344 rats and rhesus monkeys. The blood methanol concentrations after a 6-

hour inhalation exposure predicted for humans, monkeys, and rats were 140, 230 and 400 mg/l 

at 5000 ppm, 50, 70 and 90 mg/l at 2000 ppm and 30, 30 and 40 mg/l, respectively, at 1200 

ppm. 

The models are in agreement with experimental data for exposure periods of up to 8 

hours, which are summarized in Table 8 and in Figure 1. For 5 individuals exposed to methanol 

concentrations between 3000 and 5500 ppm during an 8-hour-work shift (Kawai et al., 1991) 

blood methanol concentrations were calculated from the reported urine concentrations and the 

relationship between methanol concentrations in urine and blood: 

(mg/l (urine) = 0.867 x mg/l (blood) + 0.687) (Kawai et al., 1992). 

The calculated mean blood concentration of 442 mg/l at an exposure concentration of 3936 

ppm was almost a factor 2 higher than expected from the pharmacokinetic models. It remains 

unclear whether this difference was caused by the use of values of Vmax and Km estimated from 

monkey data, a concomitant ethanol consumption of the workers, higher actual ventilation rates 

than assumed in the model or genetic polymorphisms of involved enzymes present in 

Japanese. In summary, blood concentrations are similar between different species up to 

exposure concentrations of about 1000 ppm. At higher concentrations, resulting blood 

concentrations in rats and mice are about 3-fold and 10-fold, respectively, higher than in 

humans. 

Fisher et al. (2000) described a physiologically based pharmacokinetic (PBPK) model for 

the monkey, to account for fractional systemic uptake of inhaled methanol vapors in the lung. 

TABLE 8: BLOOD METHANOL CONCENTRATIONS IN HUMANS AND ANIMALS AFTER A SINGLE 

EXPOSURE TO METHANOL
METHANOL Interim 2: 2/2005 

34 

Species Exposure 

time (h) 

Exposure 

concentration 

(ppm) 

Blood methanol 

concentration at 

end of exposure 

(mg/l) 

Remarks Reference 

human 8 3936 442 occupational; n=5 Kawai et al., 1991 

human 8 800 30.7 " 6.9 (SD) experimental; 

n=15; 0.6 " 0.5 in 

controls 

Batterman et al., 

1998 

human 6 200 7.0 " 1.2 (SD) experimental; 

n=6; subjects 

resting, 1.8"1.2 

before exposure 

Lee et al., 1992 

human 6 200 8.1 " 1.5 (SD) experimental; 

n=6; exercising 

subjects 

Lee et al., 1992 

human 4 200 6.5 " 2.7 (SD) experimental; 

n=20; 1.8 " 2.6 

before exposure 

Chuwers et al., 1995 

human 1,25 190 1.9 " 0.5 experimental; 

n=24; 0.6 " 0.3 

after sham 

exposure 

Cook et al., 1991 

human 8 111 " 68 (SD) 8.9 " 14.7 (SD) occupational; 

n=16 

Heinrich and 

Angerer, 1982 

monkey 6 2000 64.4 " 10.7 (SEM) n=3 Horton et al., 1992 

monkey 2 1800 33.2-40.4 pregnant animals Burbacher et al., 

1999a; 2004a 

monkey 6 1200 37.6 " 8.5 (SEM) n=3 Horton et al., 1992 

monkey 2 600 9.5-12.1 pregnant animals Burbacher et al., 

1999a; 2004a 

monkey 6 200 3.9 " 1.0 (SEM) n=3 Horton et al., 1992 

monkey 2 200 4.3-5.5 pregnant animals Burbacher et al., 

1999a; 2004a 

rat 8 20000 3916 " 907 (SD) Perkins et al., 1995b 

rat 7 20000 8650 " 400 (SD) n=3 Nelson et al., 1985 

rat 8 15000 2667 " 372 (SD) Perkins et al., 1995b 

rat 7 15000 3826 " 162 (SE) pregnant rats; 

n=13; 2.7 " 0.8 in 

Stanton et al., 1995 
METHANOL Interim 2: 2/2005 

35 

TABLE 8: BLOOD METHANOL CONCENTRATIONS IN HUMANS AND ANIMALS AFTER A SINGLE 

EXPOSURE TO METHANOL

Species Exposure 

time (h) 

Exposure 

concentration 

(ppm) 

Blood methanol 

concentration at 

end of exposure 

(mg/l) 

Remarks Reference 

controls 

rat 8 10000 1656 " 330 (SD) Perkins et al., 1995b 

rat 7 10000 2240 " 200 (SD) n=3 Nelson et al., 1985 

rat 8 5000 1047 " 298 (SD) Perkins et al., 1995b 

rat 7 5000 1000 " 210 (SD) n=3 Nelson et al., 1985 

rat 6 4500 550 " 70 (SD) pregnant rat; n 

not state, about 

60 

Stern et al., 1996 

rat 6 2000 79.7 " 6.1 (SEM) n=4 Horton et al., 1992 

rat 6 1200 26.6 " 2.0 (SEM) n=4 Horton et al., 1992 

rat 8 1000 83 " 15 (SD) Perkins et al., 1995b 

rat 6 200 3.1 " 0.4 (SEM) n=4 Horton et al., 1992 

mouse 8 15000 11165 " 3290 

(SD) 

n=2-4; individual 

exposure; high 

activity 

Perkins et al., 1995b 

mouse 7 15000 7720 " 581 (SEM) pregnant mice; 

n=3; 1.6 " 0.4 in 

controls 

Rogers et al., 1993 

mouse 2 15000 2300 pregnant animals Rogers, 1999 

mouse 8 10000 6028 " 506 (SD) n=2-4; individual 

exposure; high 

activity 

Perkins et al., 1995b 

mouse 8 10000 3348 " 36 (SD) n=3-4; group 

exposure; 

moderate activity 

Perkins et al., 1995b 

mouse 7 10000 4653 " 552 (SEM) see above Rogers et al., 1993 

mouse 3 10000 1500 pregnant animals Rogers, 1999 

mouse 7 7500 2801 " 35 (SEM) see above Rogers et al., 1993 

mouse 8 5000 3580 " 599 (SD) n=2-4; individual 

exposure; high 

Perkins et al., 1995b 
METHANOL Interim 2: 2/2005 

36 

TABLE 8: BLOOD METHANOL CONCENTRATIONS IN HUMANS AND ANIMALS AFTER A SINGLE 

EXPOSURE TO METHANOL

Species Exposure 

time (h) 

Exposure 

concentration 

(ppm) 

Blood methanol 

concentration at 

end of exposure 

(mg/l) 

Remarks Reference 

activity 

mouse 8 5000 2313 " 338 (SD) n=3-4; group 

exposure; 

moderate activity 

Perkins et al., 1995b 

mouse 7 5000 2126 " 157 (SEM) see above Rogers et al., 1993 

mouse 7 5000 1200 pregnant animals Rogers, 1999 

mouse 8 2500 1883 " 1278 (SD) n=2-4; individual 

exposure; high 

activity 

Perkins et al., 1995b 

mouse 8 2500 718 " 57 (SD) n=3-4; group 

exposure; 

moderate activity 

Perkins et al., 1995b 

mouse 7 2000 487 " 125 (SEM) see above Rogers et al., 1993 

mouse 7 1000 63 " 4 (SEM) see above Rogers et al., 1993 
METHANOL Interim 2: 2/2005 

37 

1

10

100

1000

10000

100 1000 10000

Exposure concentration (ppm)

Blood methanol concentration (mg/l)

human monkey rat mouse

FIGURE 1: BLOOD CONCENTRATIONS OF METHANOL IN DIFFERENT SPECIES

Data for actual exposure concentrations up to 10000 ppm and exposure periods between 6 and 

8 hours were taken from Table 8.

4.2. Mechanism of Toxicity

The first effects on humans caused by methanol exposure are central nervous system 

effects, such as headache, dizziness and nausea, weakness, peripheral nervous effects, such 

as shooting pains, paresthesia, prickling and numbness in the extremities, and ocular effects, 

such as changes in color perception and, blurred vision (NIOSH, 1976; Kavet and Nauss, 1990; 

ACCT, 2002). Due to their fast appearance after exposure these effects are probably caused by 

methanol itself and not by a metabolite. More marked effects on the central nervous system, 

such as ataxia, incoordination, lethargy, prostration, narcosis and coma, are seen in rodents.

After occurrence of the immediate symptoms mentioned above, which can be rather 

weak, an asymptomatic latent period follows and may last from several hours to a few days, 

although 12 to 24 hours is most common. The latent period gives way to the onset of a 

syndrome that consists of an uncompensated metabolic acidosis with superimposed toxicity to 

the visual system (Kavet and Nauss, 1990; AACT, 2002). There is substantial clinical and 

experimental evidence that formic acid is the toxic metabolite responsible for metabolic acidosis 

(Jacobsen and McMartin, 1986) and ocular toxicity (Lee et al., 1994a; 1994b). 
METHANOL Interim 2: 2/2005 

38 

Rats rendered folate-deficient by either feeding a folate-deficient diet (Lee et al. 1994a; 

1994b) or chemical treatment (Eells, 1991), developed metabolic acidosis, ocular toxicity and 

retinal histopathological changes analogous to the human methanol-poisoning syndrome. A 

reduced folate level leads to a shortage of tetrahydrofolate, the cofactor required for metabolic 

oxidation of formate, and thus causes accumulation of formate in these animals. Martinasevic et 

al. (1996) found that total folate levels in human and rat retinal tissues were much lower than 

the respective levels in liver. Absolute folate concentrations in human retinal tissue were only 14 

% of those found in rat retina. The levels of 10-formyl tetrahydrofolate dehydrogenase were 

three times higher in human retina compared with rat retina. Taking into account the lower 

detoxification capacity of human retina, it seems probable that the ocular toxic effects of 

methanol are also caused by the metabolite formate. 

In experiments in vitro (Nicholls, 1975), formate has been shown to inhibit cytochrome c 

oxidase, a component of the mitochondrial electron transport chain, through binding to the ferric 

heme iron. Wallace et al. (1997) report that in vitro studies using isolated retinal and cardiac 

mitochondria revealed that formate selectively inhibited retinal mitochondrial ATP synthesis. 

Hayreh et al. (1977) postulated that formate interferes with ATP production in the retina and 

optic nerve, which could result in retinal dysfunction, axoplasmic flow stasis in the optic nerve, 

optic disc edema, interference with the neural conduction process, ultimately resulting in 

blindness. 

The developmental toxicity of methanol in rodents may be caused by methanol itself. 

Dorman et al. (1995) exposed pregnant CD-1 mice on day 8 of gestation at 10000 or 15000 

ppm methanol for 6 hours by inhalation. Other groups were treated by gavage with 1.5 g/kg 

methanol or 750 mg/kg sodium formate. Peak formate levels in maternal plasma and decidual 

swelling from pregnant mice given sodium formate were similar to those observed following a 

6-hour methanol inhalation at 15000 ppm. No significant effect on folate concentrations in red 

blood cells and the decidual swelling was found during and up to 16 hours after the exposure. 

Exencephaly was only observed after exposure to methanol, but not sodium formate. Sakanashi 

et al. (1996) and Fu et al. (1996) observed that a low dietary folate level, that led to a liver folate 

level of about half the normal value and that did not affect maternal hematocrit levels, led to a 4-

fold increase in methanol-induced incidences of cleft palate. Increased exencephaly was found 

in the low folate group treated with methanol, but was not increased by low dietary folate alone. 

The methanol treatment did not influence folate levels in liver and plasma, as measured on 

gestational day 18, i.e., three days (Sakanashi et al., 1996) or 10 days (Fu et al., 1996) after the 

last methanol dosing. These results do not suggest that methanol exerts its developmental toxic 

effect by decreasing folate concentrations in the body; rather it seems to exert developmental 

toxic effects in parallel to a suboptimal dietary folate concentration. 

This conclusion is supported by the results of Andrews et al. (1998) who conducted in 

vitro studies with rat embryos to compare toxicities of methanol and formate alone and in 

combination. Treatment with individual compounds produced significant decreases in 

development score, somite number, crown-rump length, and head length in Simplex 1 and 

Simplex 2. In Simplex 2, the methanol/formate mixtures also produced significant decreases in 

those parameters. However, in all cases, the reductions following exposure to either methanol 
METHANOL Interim 2: 2/2005 

39 

or formate alone were greater than reductions observed with methanol/formate mixtures. The 

observation led Andrews and colleagues to conclude that methanol and formate have an 

infra-additive (less than additive) interaction and produce effects through different mechanisms 

of toxicity. 

4.3. Pharmacokinetics and Toxic Effects in Normal and Folate-Deficient Animals

In animals rendered folate-deficient through a folate-reduced or folate-deficient diet, 

higher formate concentrations, but not higher methanol concentrations, are found in the blood. 

Lee et al. (1994b) exposed a group of 10 folate-reduced Long-Evans rats at 2000 ppm 

methanol for 20 hours/day for 3 days. Rats had been on a folate-deficient diet for at least 18 

weeks. Their liver folate levels were between 10-30 % of animals fed a normal standard diet. 

Blood methanol concentrations measured after 24, 48 and 72 hours revealed a plateau and 

were between 9 and 13 mmol/l (290 to 420 mg/l). Values of folate-sufficient and folate-reduced 

rats were not statistically different. The blood formate concentrations during the exposure period 

showed a linear increase in folate-reduced animals to about 8 mmol/l at 72 hours. Folate 

concentrations in folate-sufficient control animals were always <0.5 mmol/l and not different 

from pretreatment values. Lee et al. (1994a) exposed a group of 11 folate-reduced Long-Evans 

rats at 3000 ppm methanol for 20 hours/day for up to 14 days. One animal died after 3 days and 

another 7 animals died after 4 days. The blood formate levels in the surviving animals were 

20.8"1.2 mmol/l. After exposure of folate-reduced rats at 1200 ppm for 6 hours, blood formate 

concentrations increased to 370 % of that of unexposed controls. An additional 72 % increase 

was observed after exposure at 2000 ppm. In folate-sufficient rats, formate levels were not 

increased over the endogenous levels after a 6-hour exposure at 1200 or 2000 ppm. Horton et 

al. (1992) reported that an oral methanol dose of 2 g/kg resulted in a maximum blood formate 

concentration of 11.7 mmol/l at 48 hours post administration in folate-reduced rats. A formate 

concentration of 8.1 mmol/l was found after 24 hours. 

No increased formate blood levels were found in rhesus monkeys after exposure at 2000 

ppm methanol for 6 hours (Horton et al., 1992). In another study (Dorman et al., 1994; Medinsky 

et al. 1997) monkeys were rendered folate deficient by feeding a folate-deficient diet for 6 

weeks before methanol exposure. At that time, serum folate levels ranged from 0.5-2.4 ng/ml 

and thus were below the level of 3 ng/ml, which is considered indicative of folate deficiency in 

humans. After exposure for 2 hours at 10, 200 or 900 ppm methanol, blood methanol 

concentrations in folate-sufficient monkeys were 0.2-0.8, 10-30 and 30-200 μmol/l (0.006-0.025, 

0.32-0.96, 0.96-6.4 mg/l), respectively. In folate-deficient animals exposed at 900 ppm, 100-300 

μmol/l (0.32-9.6 mg/l) were found. Twentyfour hours after an oral dose of 2 g/kg, a peak formate 

level of 6.5 mmol/l was found in monkeys (Noker et al., 1980). 

In contrast to folate-sufficient rats, folate-deficient rats show metabolic acidosis and 

delayed deaths and are more susceptible to neurotoxic effects of methanol: In the study of Lee 

et al. (1994a), one animal died after 3 days and another 7 animals died after 4 days from 

exposure at 3000 ppm for 20 hours/day for up to 14 days, while none of 11 folate-sufficient rats 

died. The surviving animals were lethargic and their blood pH values were 6.9 " 0.04. 

Immediately cessation of exposure to 2000 ppm for 20 hours/day for 3 days, Lee et al. (1994b) 
METHANOL Interim 2: 2/2005 

40 

recorded flash-evoked potentials in anesthetized rats. In all folate-reduced and methanolexposed animals, a reduction of the b-wave amplitude in the electroretinogram by an average of 

67 % was observed, indicating an effect on the retinogeniculocortical visual pathway. After oral 

administration of 2.0 g/kg, a b-wave amplitude reduction of 61 % was obtained. The reversibility 

and persistence of the effect was not investigated. 

In rats, methanol treatment did not affect liver and plasma folate concentrations. In 

folate-deficient rats higher incidences of malformations are found than in folate-sufficient rats 

and these incidences are increased by methanol treatment. 

Sakanashi et al. (1996) assessed the influence of the maternal folate status on the 

developmental toxicity of methanol. CD-1 mice were fed a folic acid-free diet supplemented with 

400 (low), 600 (marginal) or 1200 (adequate) nmol folic acid/kg for 5 weeks prior to breeding. All 

diets contained 1 % (w/w) succinylsulfathiazole to inhibit endogenous folate production by the 

intestinal microflora. There were no effects of the dietary treatment on body weights before 

breeding. Pregnant animals of each group were exposed by gavage to 0, 2.0 or 2.5 g 

methanol/kg twice daily on gestational days (gd) 6-15. Dams receiving the lowest folate 

supplementation had significantly lower body weights at gd 12 and 18. Methanol significantly 

reduced the gestational weight gain in dams fed the 600 or 1200 nmol folate/kg diet. Mice were 

killed and fetuses analyzed on gd 18. In non-methanol exposed animals, maternal folate 

concentrations were 4.9"0.7, 14.5"0.8 and 13.0"1.7 nmol/g in the liver and 5.1"0.2, 6.3"0.6 

and 9.2"3.6 nmol/l plasma in groups receiving 400, 600 and 1200 nmol folate/kg diet, 

respectively. Methanol treatment did not significantly influence these folate concentrations. The 

reduced folate levels did not cause any effect on hematocrit. Fetal body weights were marginally 

affected by the diet alone, but significantly lowered by methanol treatment compared to the 

respective vehicle-treated groups in the low and marginal folate groups. The percent of litters 

affected by cleft palate was increased by methanol treatment and this effect was exacerbated 

by low dietary folate. In the adequate, marginal and low groups, percentages of affected litters 

were 7.4, 0.0 and 18.5 % without methanol treatment, 30.8, 6.7 and 100 % at 4.0 g/kg and 34.5, 

66.7 and 86.2 % at 5.0 g/kg, respectively. The percentage of litters affected with exencephaly 

were 0.0, 0.0 and 3.7 % without methanol treatment, 7.7, 0.0 and 0.0 % at 4.0 g/kg and 3.4, 

13.3 and 34.5 % at 5.0 g/kg. 

The same investigators performed similar experiments with a reduced exposure period 

(Fu et al., 1996): CD-1 mice were fed a folic acid-free diet supplemented with 400 (low) or 1200 

(adequate) nmol folic acid/kg for 5 weeks prior to breeding, as described by Sakanashi et al. 

(1996). Pregnant animals of each group were exposed by gavage to 0 or 2.5 g methanol/kg 

twice daily on gd 6-10. Folate concentrations in the low dietary folate group were reduced by 50 

% in maternal liver, 30 % in red blood cells and 60-70 % in fetal tissue (low dietary group: 

1.86"0.15 nmol/g in controls and 1.69"0.12 nmol/g in methanol-treated group; adequate dietary 

group: 5.04"0.22 nmol/g in controls and 5.89"0.39 nmol/g in methanol-treated group). Low 

dietary folate alone resulted in cleft palate in 14 % of the litters, while no litters were affected in 

the adequate folate group. Methanol treatment increased the incidence of cleft palate to 73 % in 

the low and 19 % in the adequate group. The incidence of exencephaly was increased by 

methanol from 14 to 23 % in the low and from 4 to 19 % in the adequate group; the increase 

was not statistically significant. 
METHANOL Interim 2: 2/2005 

41 

4.4. Structure-Activity Relationships

There are no structure-activity relationships applicable to estimating acute exposure 

limits for methanol. The nature and delayed onset of its toxicity, which involves metabolism into 

the toxic metabolite formic acid are notably different from other alcohols. 

Youssef et al. (1992) determined the 24-hour oral LD50 values of methanol and ethanol 

in female albino rats. The estimated LD50 were 12.25 ml/kg for methanol and 19.00 ml/kg for 

ethanol, which corresponds to 0.303 mol/kg for methanol and 0.325 mol/kg for ethanol. A very 

steep dose-response curve was observed for methanol-induced lethality, with 5 % lethality at a 

dose of about 2.2 mol and 95 % lethality at a dose of about 3.5 mol. 

Rogers (1995, abstract) found methanol to be a more potent developmental toxicant 

than ethanol, when pregnant mice were administered two intraperionteal injections of ethanol 

(2.45 g/kg each) or methanol (2.45 g/kg or 1.7 g/kg; the latter is the molar equivalent of the 

ethanol dose used). Unlike methanol, ethanol induced a transient ataxia lasting several hours. 

While the dose of ethanol used caused only a low incidence of microphthalmia, with no effects 

on viability or fetal weight, the higher methanol dose resulted in 100 % of live fetuses having 

holoprosencephaly spectrum malformations including absence of the forebrain, cebocephaly, 

complete premaxillary agenesis, and micro- or anophthalmia. A mean of 55 % of implants/litter 

were resorbed, and fetal weight was reduced. The lower methanol dose was still clearly more 

toxic than the equimolar ethanol dose, producing 30 % resorptions and midfacial deficiencies 

and micro- or anophthalmia in over 50 % of live fetuses. 

Nelson et al. (1985) also found methanol to be a more potent developmental toxicant as 

ethanol: groups of approximately 15 pregnant Sprague-Dawley rats were exposed for 7 

hours/day to methanol concentrations of 20000 ppm (during gestational days (gd) 7-15), 10000 

ppm (gd 1-19) or 5000 ppm (gd 1-19) (see Section 3.3.2) or to ethanol concentrations of 20000 

ppm (gd 1-19), 16000 ppm (gd 1-19) or 10000 ppm (gd 1-19). For both alcohols, unexposed 

groups served as controls. Analysis on gd 20 revealed slight maternal toxicity and a high 

incidence of congenital malformations (p< 0.001) (predominantly extra or rudimentary cervical 

ribs and urinary or cardiovascular defects) in the 20000-ppm-methanol group. Similar, but not 

significantly increased malformations were seen in the 10000-ppm group. No adverse effects 

were noted in the 5000-ppm group. Dams exposed to 20000 ppm ethanol were narcotized at 

the end of exposure, and maternal weight gain and feed intake were decreased during the first 

week of exposure. The 16000-ppm dams had significantly depressed weight gain during the first 

week of exposure, but there were no significant effects on feed consumption. There was no 

definite increase in malformations at any level of ethanol, although the incidence in the 20000-

ppm group was of borderline significance. 

In humans, fetal alcohol syndrome is the most common preventable cause of mental 

retardation. Diagnostic criteria for fetal alcohol syndrome include heavy maternal alcohol 
METHANOL Interim 2: 2/2005 

42 

consumption during gestation, pre- and postnatal growth retardation, craniofacial malformations 

including microcephaly, and metal retardation. Less complete manifestations of gestational 

alcohol exposure also occur and are referred to as fetal alcohol effects or alcohol-related 

neurodevelopmental disorder. Although the total amount of alcohol consumed and the pattern of 

drinking are both important factors, peak maternal blood alcohol level is the most important 

determinant of the likelihood and severity of effects. Overconsumption during all three trimesters 

of pregnancy can result in certain manifestations, with the particular manifestations dependent 

upon the period of gestation during which insult occurs. Despite an intensive research effort, the 

mechanisms underlying fetal alcohol syndrome remain unclear (Bruckner and Warren, 2001). 

4.5. Other Relevant Information

4.5.1. Species Variability

The species differences in methanol toxicity result from differences in metabolism of 

methanol via formaldehyde and formic acid to carbon dioxide. In contrast to rodents, formic acid 

accumulates in human and non-human primates, which leads to the symptoms of metabolic 

acidosis and, probably, is also responsible for the ocular toxicity. Rodents develop higher blood 

methanol levels after inhalation exposure compared to primates, which favors development of 

methanol-caused central nervous system and developmental toxicity. 

The mouse is considerably more susceptible for the developmental toxic effects than the 

rat: For repeated 7-hours/day exposures the LOEL for malformations was 10000 ppm in rats 

(corresponding to a blood methanol concentration of 2247 mg/l) (Nelson et al., 1985) and 2000 

ppm in mice (corresponding to 487 mg/l) (Rogers et al., 1993) and the NOEL was 5000 ppm in 

rats (corresponding to 1000 mg/l) and 1000 ppm in mice (corresponding to 63 mg/l). Thus, the 

blood methanol concentration at the LOEL was about 5fold lower and at the NOEL it was about 

16fold lower in mice compared to rats. Similar data for other species are not available. 

4.5.2. Intraspecies Variability

Several factors contribute to variability in methanol-induced toxicity between. The rate of 

methanol metabolism and formate accumulation is influenced by the folate status. Lee et al. 

(1994a) have shown that Long-Evans rats fed a folate-reduced diet and having only about 10-30 

% of the normal folate-level in the liver - unlike normal control animals - developed metabolic 

acidosis. Thus, folate-deficient individuals, which include pregnant women, the elderly, 

individuals with poor-quality diet, and alcoholics might develop higher formate concentrations 

compared to normal individuals (WHO, 1997). For the lack of data, it is very difficult to estimate 

this variability in quantitative terms. 

4.5.3. Combination Effects

Methanol shows a markedly prolonged half-life when exposure is combined with 

exposure to ethanol (WHO, 1997). This has firmly been established for oral exposure. The 

slower methanol metabolism due to the higher affinity of alcohol dehydrogenase for ethanol is 

used therapeutically in methanol poisonings in order to prevent metabolism of methanol to 

formic acid. A blood ethanol level of about 22 mmol/l (1000 mg/l) has been recommended to 
METHANOL Interim 2: 2/2005 

43 

block methanol metabolism in poisoned humans (AACT, 2002; Jacobsen and McMartin, 1986; 

Becker, 1983). In monkeys methanol oxidation was reduced by 90 % when the molar ratio of 

ethanol to methanol in the orally applied mixture was 1:1 and by 70 % when the ratio was 1:4 

(Jacobsen and McMartin, 1986). 

4.5.4. Role of Folate in Human Birth Defects

It has been estimated that about half of the neural tube defects in humans are caused by 

an insufficient intake of folic acid with the normal diet. The folate dose in normal diet is only 

about half of the value of 0.4 mg/day which is recommended for women capable of becoming 

pregnant (Butterworth and Bendich, 1996; Forman et al., 1996). A correlation with other 

congenital birth defects, such as orofacial clefts, has also been found (Tolarova and Harris, 

1995). Periconceptional folate supplementation has been shown to give effective protection 

against the development of neural tube defects (Butterworth and Bendich, 1996; Czeizel, 1996). 

Folate supplementation is only effective when given before and very early in pregnancy 

because closure of the neural tube and the palate and upper jaw occurs in week 3-4 and week 

3-8 of pregnancy, respectively. 

While a suboptimal folate status of pregnant women constitutes itself a significant risk 

factor, it is unlikely that methanol exposure lowers folate concentrations in the body and thus 

contributes indirectly to a lower folate status and an increased rate of birth defects. There are no 

experimental findings that would support the possibility that a single methanol exposure 

decreases body folate concentrations. In mice, a 6-hour exposure at 15000 ppm methanol had 

no significant effect of on folate concentrations in red blood cells and in the decidual swelling 

during and up to 16 hours after cessation of the exposure (Dorman et al., 1995). Likewise, oral 

methanol doses of up to 5 g/kg/day given on gestational days 6-15 (Sakanashi et al., 1996) or 

on gestational days 6-10 (Fu et al., 1996) did not influence liver and plasma folate 

concentrations (cf. Section 4.3) when measured 3 days and 8 days, respectively, after the last 

dosing. 

In addition, the folate status is unlikely to influence blood methanol concentrations. As 

discussed in Section 4.1.4, in folate-deficient monkeys and rats much higher formate 

concentrations accumulate in the blood, but the effect on the methanol concentration was small 

(Lee et al., 1994a; 1994b; Dorman et al., 1994; Medinsky et al., 1997). 

5. RATIONALE AND PROPOSED AEGL-1 

5.1. Human Data Relevant to AEGL-1

Batterman et al. (1998) exposed 15 healthy subjects at 800 ppm for 8 hours in a 

pharmacokinetic study. In a personal communication, the coauthor Dr. Alfred Franzblau stated 

that subjects did not report symptoms (Franzblau, 1999; 2000). Chuwers et al. (1995) exposed 

26 healthy subjects at 200 ppm for 4 hours. No symptoms were reported and in a number of 

neurobehavioral, neurophysiological and visual performance tests, no significant effects were 
METHANOL Interim 2: 2/2005 

44 

found. Likewise, Cook et al. (1991) reported neither symptoms nor effects in neurobehavioral 

and neurophysiological tests after exposure of 12 subjects at 190 ppm for 75 minutes. Muttray 

et al. (2001) reported electroencephalogram alterations, which were not considered adverse, in 

12 subjects exposed at 200 ppm for 4 hours. 

NIOSH (1980) and Frederick et al. (1984) studied the health effects of methanol 

exposure from spirit duplicators in 66 teacher aides. Measured methanol concentrations ranged 

from 365 to 3080 ppm (mean concentration 1060 ppm, median concentration 1040 ppm). 

Exposure durations ranged from 1 hour/day for 1 day/week to 8 hours/day for 5 days/week 

during about 3 years. Compared to a control group of teachers from the same schools the aides 

reported significantly higher frequencies of headaches, dizziness, blurred vision and 

nausea/upset stomach. No information on the exact exposure duration and time between start 

of exposure and occurrence of symptoms was provided. NIOSH (1981) reported that exposure 

of one worker at 1025 ppm for 25 minutes resulted in eye irritation at the end of exposure. 

Kingsley and Hirsch (1955) reported that repeated exposure at the workplace to methanol 

concentrations of about 200-375 ppm can lead to headaches. However, information about the 

exact exposure concentrations and exposure durations is lacking. In addition, simultaneous 

exposure to other volatile organic compounds cannot be ruled out. 

Flury and Wirth (1933) reported weak nasal irritation in volunteers after exposure at 

7600 ppm for 5 minutes. No irritation was observed at 760 ppm. Eye irritation was reported at 

1025 ppm for 25 minutes in a case study (NIOSH, 1981) and weak nasal irritation was reported 

after repeated exposure to mean concentrations of 459 at the workplace (Kawai et al., 1991). 

Considerable uncertainty exists in characterization of the exposure conditions in the latter study 

and the range of exposure concentrations was large (up to 5500 ppm; the authors did not state 

the lower exposure concentration limit defining the "high" exposure group). 

5.2. Animal Data Relevant to AEGL-1

NEDO (1987) exposed monkeys (Macaca fascicularis) at 1000, 2000 or 3000 ppm for 21 

hours/day for 7 months. During the first exposures, frequent yawning and runny noses were 

observed at all concentrations, which might be indicative of a weak irritative effect. At 

histopathology, the 1000-ppm group showed a dose-dependent round cell infiltration and slight 

fibrotic alterations of the liver. Andrews et al. (1987) exposed monkeys (Macaca fascicularis) at 

500, 2000 or 5000 ppm methanol for 6 hours/day, 5 days/week for 4 weeks. No irritative effects 

were observed at exposure concentrations as high as 5000 ppm. The authors did not report on 

any effects observed in the histopathological analysis. 

5.3. Derivation of AEGL-1

Several experimental human studies are available that used methanol concentrations of 

about 200 ppm. Chuwers et al. (1995) found no significant effects in a panel of 

neurophysiological and neuropsychological tests after exposure at 200 ppm for 4 hours. Using 

the same exposure conditions, Muttray et al. (2001) observed electroencephalogram alterations 

which the authors did not considered adverse; no clinical symptoms were reported by the 

subjects. Likewise, the NAC/AEGL committee considered these findings as below the threshold 
METHANOL Interim 2: 2/2005 

45 

for AEGL-1. Batterman et al. (1998) exposed volunteers at a higher level (i.e. 800 ppm for 8 

hours). As this was a pharmacokinetic study, health effects were not formally evaluated. In a 

personal communication the coauthor Dr. Franzblau stated that individual symptoms were 

asked of some subjects, other subjects were only asked generally if they had symptoms, and 

that in some exposure sessions subjects might not have been queried. According to Dr. 

Franzblau, none of the subjects reported symptoms. Since the subjects knew the exposure 

concentration by means of a meter showing the actual concentration, it might be expected that 

this would have increased the inclination of subjects to report symptoms. 

NIOSH (1980) and Frederick et al. (1984) reported significantly higher frequencies of 

headaches, dizziness, blurred vision after occupational exposure at 1060 ppm (mean 

concentration). NIOSH (1981) reported eye irritation in a worker after exposure at 1025 ppm for 

25 minutes. Since the 1000-ppm level was considered already a discomfort level, the 800 ppm 

for 8 hour exposure from the Batterman et al. (1998) study was chosen as a starting point for 

AEGL-derivation. Since the local irritation effects are determined by the concentration of 

methanol in air and not to the blood methanol level, calculation of AEGL-1 values was not done 

using a pharmacokinetic model (as done for AEGL-2 and -3) based on the end-of-exposure 

blood methanol level of 30.7 mg/l reported by Batterman et al. (1998). Instead, exposure to 800 

ppm for 8 hours was used as the basis for AEGL-1 derivation. 

Time scaling using the equation Cn

 x t = k was carried out to derive exposure durationspecific values. Due to lack of a definitive data set, a default value for n of 3 was used in the 

exponential function for extrapolation from the experimental period (8 hours) to shorter exposure 

periods. For the 10-minute AEGL-1 the 30-minute value was applied because no studies were 

available that demonstrated the absence of notable discomfort (with respect to irritation) in the 

general population, including susceptible subpopulations, at 970 ppm (extrapolated value for 

10-minute period). The calculations of exposure concentrations scaled to AEGL-1 time periods 

are shown in Appendix A. 

A total uncertainty factor of 3 was used. An uncertainty factor of 3 for intraspecies 

variability was applied because interindividual variability with regard to slight central nervous 

system effects (e.g. headache) is likely to exist (although it cannot be quantified exactly from the 

existing experimental and epidemiological studies) and because subpopulations with a less than 

optimal folate status may be more susceptible to the health effects of methanol. 

The values are listed in Table 9 below. 

TABLE 9: AEGL-1 VALUES FOR METHANOL

AEGL Level 10 minutes 30 minutes 1 hour 4 hours 8 hours 

AEGL-1 670 ppm 

(880 mg/m;) 

670 ppm 

(880 mg/m;) 

530 ppm 

(690 mg/m;) 

340 ppm 

(450 mg/m;) 

270 ppm 

(350 mg/m;)

A level of distinct odor awareness (LOA) for methanol of 8.9 ppm was derived on the 

basis of the odor detection threshold from the study of Hellman and Small (1974) (see Appendix 
METHANOL Interim 2: 2/2005 

46 

C for LOA derivation). The LOA represents the concentration above which it is predicted that 

more than half of the exposed population will experience at least a distinct odor intensity, about 

10 % of the population will experience a strong odor intensity. The LOA should help chemical 

emergency responders in assessing the public awareness of the exposure due to odor 

perception. 

6. RATIONALE AND PROPOSED AEGL-2 

6.1. Human Data Relevant to AEGL-2

Blindness can result from exposure to methanol. However, no data are available that 

would allow derivation of a threshold exposure concentration for blindness in humans. 

Appropriate data from animal models are also lacking for this endpoint. Moreover, reports about 

acute oral methanol poisoning indicate that blindness results only after live-threatening doses 

and thus no clear distinction is possible between methanol doses leading to blindness and 

those causing lethal effects (Naraqi et al., 1979; WHO, 1997; IUCLID, 1996; NIOSH, 1976). 

Humperdinck (1941) reported that one of 23 exposed workers became ill, blind in the 

right eye with marked narrowing of the visual field in the left eye after 4 years at the workplace 

without any previous symptoms. Examination of the workplace air revealed methanol 

concentrations ranging from 1200 to 8300 ppm. Effects on vision were not reported in another 

22 workers exposed to methanol, however, no statement was made on whether these workers 

experienced any other symptoms. 

NIOSH (1980) and Frederick et al. (1984) studied the health effects of methanol 

exposure from spirit duplicators in 66 teacher aides. Measured methanol concentrations ranged 

from 365 to 3080 ppm (mean concentration 1060 ppm, median concentration 1040 ppm). 

Exposure times ranged from 1 hour/day for 1 day/week to 8 hours/day for 5 days/week during 

about 3 years. Compared to a control group of teachers from the same schools the aides 

reported significantly higher frequencies of headaches, dizziness, blurred vision and 

nausea/upset stomach. No information on the exact exposure duration, time between start of 

exposure and occurrence of symptoms, and relationship between symptom severity and 

exposure time was provided. 

NIOSH (1981) reported that exposure of one worker to 1025 ppm for 25 minutes 

resulted in eye irritation.. 

Kawai et al. (1991) reported that workers exposed to higher methanol concentrations 

complained significantly more often of dimmed vision (the authors suggested that visibility was 

temporarily reduced by fog in the workroom) and nasal irritation than workers exposed to lower 

methanol concentrations. Measurement of breathing-zone air for 31 subjects revealed timeweighted average methanol concentrations during an 8-hour work shift of 3000-5500 ppm for 5 

samples, 1000-2000 ppm for 10 samples, 500-1000 ppm for 4 samples and <500 ppm for 19 

samples. The authors did not try to correlate incidence or severity of symptoms with measured 

breathing-air concentrations. 
METHANOL Interim 2: 2/2005 

47 

6.2. Animal Data Relevant to AEGL-2

Rogers et al. (1995, abstract) and Rogers (1999, personal communication) performed 

single-exposure experiments with pregnant CD-1 mice, exposing them on day 7 of gestation for 

1, 2, 3, 5 or 7 hours at 2000, 5000, 10000 or 15000 ppm (Rogers et al., 1995). Since cervical rib 

induction occurred at concentration-time products (CxT) greater than or equal to 15000 ppm @ h 

(the authors expressed results only as CxT products), a NOEL for cervical rib induction of 2000 

ppm for 7 hours can be derived from this study. This study is supported by another study of the 

same group that used repeated 7-hour exposures (Rogers et al., 1993) and found a doserelated increase in cervical ribs at exposure concentrations of 2000 or higher. In that study 

(Rogers et al., 1993), a NOEL of 1000 ppm for developmental toxic effects after repeated 

exposure was derived. 

In pregnant rats, repeated 7-hour exposures at 20000 ppm resulted in significantly 

increased numbers of litters with malformations, such as extra or rudimental cervical ribs and 

urinary or cardiovascular defects and 10000 ppm caused increased, but not statistically 

significant incidences of malformations, while 5000 ppm for 7 hours/day did not lead to an 

increase in malformations (Nelson et al., 1985). Upon continuous exposure of pregnant rats on 

days 7-17 of gestation, 5000 ppm led to maternal toxic effects, an increased embryo lethality, 

reduced birth weight and morphological changes, while 1000 ppm caused no developmental 

toxic effects (NEDO, 1987). 

In monkeys (Macaca fascicularis), exposure at 200, 600 or 1800 ppm for 2 hours/day, 7 

days/week 4 months prior to and throughout pregnancy caused effects indicating developmental 

toxicity. All methanol-exposed groups had significantly shorter pregnancy lengths. A doseresponse relationship was not observed for these effects. A severe wasting syndrome was 

observed in 2/7 female offspring of the 1800-ppm group; the etiology of the wasting syndrome 

could not be identified. A concentration-related delay in sensorimotor development was 

measured in male offspring during the first month of life (Burbacher et al., 1999a; 1999b; 2004a; 

2004b). 

NEDO (1987) reported on experiments in which monkeys (Macaca fascicularis) were 

exposed for 21 hours/day a) at 3000, 5000, 7000 or 10000 ppm methanol for 15-20 days, b) at 

2000 or 3000 ppm for 7 months and c) at 10, 100 or 1000 ppm for 7, 19 or 29 months. In 

animals exposed at 5000 ppm or higher, necrosis of the basal ganglia of the cerebrum, cerebral 

edema, kidney degeneration and necrotic lesions in the liver were described. 3000 ppm induced 

slight necrotic changes in basal ganglia after exposure for 7 months, while only mild alterations 

were found after 20 days. A prolonged exposure at 1000 ppm methanol for 7 months or longer 

resulted in round-cell infiltration and slight necrotic changes in the liver. 

6.3. Derivation of AEGL-2

Although methanol intoxication can cause blindness in humans, it is not possible to 

derive a threshold for this effect from the available data. Moreover, available reports indicate 

that blindness results only after live-threatening poisoning (Naraqi et al., 1979; WHO, 1997; 

IUCLID, 1996; NIOSH, 1976). 
METHANOL Interim 2: 2/2005 

48 

The epidemiological studies evaluating reversible effects on humans, such as slight 

neurotoxic and irritative effects at the workplace, though evaluating a relevant toxicological 

endpoint, will not be used for derivation of AEGL-2 values because data on exposure 

concentration and duration were considered insufficient. However, these reports provide 

valuable supporting evidence. 

The derivation of AEGL-2 values was based on developmental toxic effects in animals. 

The available data have been reviewed by US-EPA (2001) and NTP-CEHRH (2003) and both 

panels considered the developmental toxic effects in rodents as relevant for humans. The NTPCEHRH panel Arecognized the need to consider species differences in methanol metabolism 

and toxicity in its evaluation of the risk to reproduction posed by methanol exposure in humans. 

The Expert Panel agreed that blood methanol concentrations provide a useful dosimetric for the 

comparison of results among various studies. There are sufficient pharmacokinetic data to 

determine blood methanol concentrations in rodents associated with adverse reproductive and 

developmental effects. Mean maternal blood methanol concentrations observed in mice 

following inhalation exposure to 1000 ppm methanol for 7 hour/day on gd 6-15 (i.e., the fetal 

NOAEL for teratogenicity) was 97 mg/l. Mean maternal blood methanol concentration observed 

in mice following inhalation exposure to 2000 ppm methanol for 7 hours/day on gd 6-15 (i.e., the 

fetal LOAEL for teratogenicity) was 537 mg/l. In humans, achievement of such a blood methanol 

concentration has resulted in formate accumulation, metabolic acidosis, ocular toxicity, and 

other signs of methanol toxicity. These observations suggest that there may be overlap between 

exposures resulting in clinical signs of acute toxicity and those that might result in 

developmental toxicity in humans. The toxicity data available to the Panel that was collected in 

monkeys provide suggestive but insufficient evidence that adverse developmental effects may 

occur in primates exposed by inhalation to methanol at maternally non toxic doses. The Panel=s 

confidence in these data may have been strengthened had statistical analyses that adjust for 

multiple testing been applied to the data. The Expert Panel concludes that there is insufficient 

evidence to determine if the human fetus is more or less sensitive than the most sensitive 

rodent species (i.e., mouse) to methanol teratogenesis. Moreover, other factors (e.g., genetic 

polymorphisms in key metabolizing enzymes, maternal folate status) that alter methanol 

metabolism may predispose some humans to developmental toxicity at lower blood methanol 

concentrations (<100 mg/l). This caveat is especially important since the Expert Panel 

recognized that there are limited human exposure data for pregnant women and other 

potentially susceptible subpopulations. The Expert Panel concluded that developmental toxicity 

was the most sensitive endpoint of concern with respect to evaluating the risk to reproduction 

posed by methanol exposure in humans. In particular, the data obtained from rodent studies 

indicate that the gastrulating and early organogenesis stage embryo is particularly sensitive to 

the adverse developmental effects of methanol. The Panel concluded that methanol is the most 

likely proximate teratogen; however, the biological basis by which it induces such effects 

remains unknown. The Panel assumed the available rodent data was relevant for humans.@

(NTP-CEHRH, 2003). 

The study in monkeys by Burbacher et al. (1999a; 1999b; 2004a; 2004b), provides some 

evidence for neurobehavioral effects (delayed development of visually directed reaching and 

absence of novelty preference) in monkeys after prenatal exposure at 200, 600 and 1800 ppm 

for 2 hours/day, 7 days/week throughout pregnancy. It is difficult to decide whether these slight 
METHANOL Interim 2: 2/2005 

49 

effects would also be seen after reducing the number of exposure days to a single day. It 

seems reasonable, however, to assume that a single exposure during pregnancy would have a 

much lesser effect than a daily exposure during the whole intrauterine development. Further 

research would be necessary to establish a clear causality and dose-response relationship for 

this and the other effects (vaginal bleeding, shortened pregnancy length, wasting syndrome in 

offspring). In conclusion, the results of Burbacher et al. (1999a; 1999b; 2004a; 2004b) were not 

considered a suitable basis for derivation of AEGL-2 values. They are, however, not 

incompatible with the AEGL-2 values derived below. 

In mice, repeated 7-hour/day exposures during gestational days 6 to 15 caused a doserelated, significant increase in cervical ribs at 2000 ppm or higher; other malformations, such as 

exencephaly and cleft palate occurred concentration-dependently at 5000 ppm or higher 

(Rogers et al., 1993). The same type of malformations was found after a single 7-hour exposure 

at 10000 ppm (no other concentrations tested) (Rogers et al., 1997). In another study, which 

has not been formally published up until know, Rogers and coworkers (Rogers et al. 1995, 

abstract; Rogers, 1999, personal communication) exposed mice on gestational day 7 to different 

concentration-time combinations. The most sensitive endpoint was cervical rib induction, which 

occurred at concentration-time products greater than or equal to 15000 ppm @ h, but not at 

concentration-time products below 15000 ppm @ h (i.e. no effects were observed at 2000 ppm 

for 5 h, 2000 ppm for 7 h or 5000 ppm for 2 h; authors expressed data only as CxT values). 

Thus, while 2000 ppm for 7 hours was a LOEL in the repeated exposure study (Rogers et al., 

1993), it was a NOEL after single exposure. Although the single exposure study had 

shortcomings in the reporting, it was very consistent with the well-documented repeated 

exposure study. It was therefore considered adequate to use an exposure at 2000 ppm for 7 

hours as a starting point for AEGL-2 derivation. 

As discussed in Section 4.2, there is experimental evidence that developmental toxic 

effects are caused by methanol itself and not by a metabolite, such as formate (Dorman et al., 

1995). It is therefore reasonable use blood methanol concentrations as the dose metric. The 

corresponding end-of-exposure blood concentration in mice after exposure to 2000 ppm for 7 

hours was measured as 487 mg/l (Rogers et al., 1993). 

A total uncertainty factor of 10 was used. An uncertainty factor of 1 was applied for 

interspecies variability because a sensitive species was used for derivation of AEGL-2 values 

and because toxicokinetic differences between species were accounted for by using a 

pharmacokinetic model for calculating exposure concentrations. An uncertainty factor of 10 was 

used for intraspecies variability because no information on developmental toxic effects of 

methanol on humans is available and because also for other chemicals the variability in 

susceptibility of humans for developmental toxic effects is not well characterized. Moreover, 

pregnant women are a subpopulation with a less than optimal folate status and, thus, may be 

more susceptible to the health effects of methanol. 

Using a total uncertainty factor of 10, a blood methanol concentration of 48.7 mg/l was 

derived as the basis for calculation of exposure concentrations. Application of the uncertainty 

factor to the blood methanol concentration was preferred because the calculated exposure 

concentrations in air stayed better in the concentration range for which the pharmacokinetic 

model was validated and the effect of methanol metabolism for longer exposure periods was 
METHANOL Interim 2: 2/2005 

50 

more adequately taken into account. In contrast, first calculating exposure concentrations that 

would lead to a blood methanol level of 487 mg/l, and then applying a factor of 10 to the derived 

exposure concentration would result in calculation of extremely high concentrations in the fist 

step at which metabolic pathways would be saturated. After application of the uncertainty factor, 

concentrations would be below saturation level which would mean that the end-of-exposure 

methanol levels would vary for the AEGL-2 exposure concentration-time combinations. 

Using the pharmacokinetic model of Perkins et al. (1995a), inhalation exposure 

concentrations were calculated for appropriate time periods that would lead to a blood methanol 

concentration of 48.7 mg/l at the end of the time period (see Appendix C, Table 15). The 

calculated exposure concentrations were set as AEGL-2 values. 

The values are listed in Table 10 below. 

TABLE 10: AEGL-2 VALUES FOR METHANOL

AEGL 

Level 

10 minutes 30 minutes 1 hour 4 hours 8 hours 

AEGL-2 11000 ppm a

(14000 

mg/m;) 

4000 ppm 

(5200 mg/m;) 

2100 ppm 

(2800 mg/m;) 

730 ppm 

(960 mg/m;) 

520 ppm 

(680 mg/m;) 

a The 10-minute AEGL-2 value is higher than 1/10 of the lower explosive limit (LEL) of methanol 

in air (LEL = 55,000; 1/10th LEL = 5500 ppm). Therefore, safety considerations against the 

hazard of explosion must be taken into consideration. 

The derived AEGL-2 values are supported by the occupational exposure study of Kawai 

et al. (1991), in which 8-hour mean concentrations were 3000-5500 ppm in 5 samples and 

1000-2000 ppm in another 10 samples and resulted in dimmed vision (the authors suggested 

that visibility was temporarily reduced by fog in the workroom) and nasal irritation, but not in 

severe or irreversible toxicity. 

7. RATIONALE AND PROPOSED AEGL-3 

7.1. Human Data Relevant to AEGL-3

Although several case reports on lethal methanol poisoning of humans due to exposure 

by inhalation have been published in the literature, data on exposure concentration and 

exposure duration are usually lacking. A fatal case after occupational exposure to an estimated 

concentration of 4000-13000 ppm for 12 hours was reported (Anonymous, 1932). 

From a large number of reports on oral methanol poisonings, it was concluded that the 

minimum lethal oral dose is about 1 g/kg (Buller and Wood, 1904; Röe, 1982) (this value is also 
METHANOL Interim 2: 2/2005 

51 

supported by monkey data; see below). Using a volume of distribution of 0.65 l/kg (Yant and 

Schrenk, 1937) a theoretical maximum blood methanol concentration of 

1.0 g/kg / 0.65 l/kg = 1540 mg/l 

can be calculated. 

From the large number of case reports on methanol intoxication, the studies from Naraqi 

et al. (1979), Erlanson et al. (1965), Bennett et al. (1953), Gonda et al. (1978) and Meyer et al. 

(2000) are presented in Section 2.1, because theses studies report cases of methanol 

intoxication without concomitant ethanol uptake and report both blood methanol concentrations 

and the time between intoxication and measurement. These data are graphically presented in 

Figure 2. 

100

1000

10000

0 10 20 30 40 50 60

Time (h) from uptake to measurement

Blood methanol concentration (mg/l)

Death Permanent effects on vision No permanent effects Modelling 2000 mg/l Modelling 6000 mg/l

FIGURE 2: MEASURED BLOOD METHANOL CONCENTRATIONS IN HUMAN FATALITIES

Kahn and Blum (1979) report the case of a fatal dermal methanol exposure in an 8-

month-old boy. The child had been "treated" with methanol-soaked compresses during two 

nights (about 12 hours each) before he was admitted to hospital. A blood methanol 

concentration of 400 mg/l was determined in the early afternoon. Due to lack of information on 

methanol toxicokinetics in small children, a peak blood methanol concentration cannot be 

estimated in this case. 
METHANOL Interim 2: 2/2005 

52 

In an epidemiological study, Kawai et al. (1991) reported symptoms, such as dimmed 

vision (the authors suggested that visibility was temporarily reduced by fog in the workroom) 

and nasal irritation during work, in a group of 22 workers exposed to a time-weighted average 

methanol concentration of 459 ppm during an 8-hour work shift; a group of 5 breathing-zone 

samples revealed concentrations between 3000 and 5500 ppm. 

Data points are from studies cited in Table 2, Section 2.1. For comparison, concentration-time 

curves for blood methanol concentrations of 2000 and 6000 mg/l are shown (black lines). 

Calculations were done using the pharmacokinetic model by Perkins et al. (1995a) (see 

Appendix B). 

7.2. Animal Data Relevant to AEGL-3 

Gilger and Potts (1955) observed death of rhesus monkeys after doses of 3 g/kg or 

higher, while at doses of 1 and 2 g/kg animals did not showed any symptoms. After lethal 

doses, signs of inebriation were observed; semicoma was seen only shortly before death. 

Rogers et al. (1993) exposed pregnant CD-1 mice at 1000, 2000, 5000, 7500, 10000 or 

15000 ppm for 7 hours/day on days 6-15 of gestation. 7500 ppm or higher induced a 

significantly increased number of dead fetuses/litter, while no fetal death occurred at 5000 ppm. 

When CD-1 mice were exposed for only one time on day 7 of gestation, increased fetal death 

was observed at 10000 ppm for 7 hours or at 15000 ppm for 5 hours, but not at 5000 ppm for 7 

hours, 10000 ppm for 5 hours or 15000 ppm for 3 hours (Rogers et al., abstract, 1995; Rogers, 

personal communication, 1999). From these studies, a NOEL for fetal death of 5000 ppm for 7 

hours can be derived. 

NEDO (1987) reported on experiments in which groups of 4 monkeys (Macaca 

fascicularis) were exposed at 3000, 5000, 7000 or 10000 ppm methanol for 21 hours/day for at 

least 15 days. Animals exposed at 10000 ppm showed lethargy and after the third exposure 

were comatose and died. Animals exposed at 7000 ppm had to be killed after 6 days and of 

three animals exposed at 5000 ppm, two died on day 5 and one on day 14. No deaths occurred 

at 3000 ppm. Andrews et al. (1987) observed no deaths after exposure of 6 monkeys (Macaca 

fascicularis) at 5000 ppm for 6 hours/day, 5 days/week for 4 weeks. A NOEL of 5000 ppm for 6 

hours could be derived from the latter study. 

The reported LC50 values for adult rodents are 41000 ppm for 6 hours for mice and for 

rats 145000 ppm for 1 hour, 97400 ppm for 4 hours, 64000 ppm for 4 hours and 66500 ppm for 

6 hours (see Table 4). 

7.3. Derivation of AEGL-3

Due to the lack of data on fatalities after inhalation, AEGL-3 values were based on acute 

oral intoxication data in humans. 
METHANOL Interim 2: 2/2005 

53 

The minimum lethal oral dose of about 1 g/kg reported in review articles by Buller and 

Wood (1904) and Röe (1982) was not used as the basis for AEGL derivation because the value 

was not sufficiently supported by data in these articles. However, the reported minimum lethal 

oral dose which corresponds to a peak blood methanol level of about 1540 mg/l is supported by 

case studies on intoxication with methanol only (i.e. without concomitant ethanol consumption) 

(Naraqi et al., 1979; Erlanson et al., 1965; Bennett et al., 1955; Gonda et al., 1978; Meyer et al., 

2000). These studies reported measured blood methanol concentrations and time periods 

between intoxication and measurement. Given the time that elapsed until blood sampling, 

during which part of the methanol was metabolized, it can be concluded that peak blood 

methanol concentrations have been above 1000 mg/l in all fatal cases (see Figure 2). Based on 

the extensive clinical experience with methanol intoxications, the American Academy of Clinical 

Toxicology (AACT, 2002) published clinical practice guidelines on the treatment of methanol 

poisoning. According to these guidelines, peak blood methanol concentrations >500 mg/l 

indicate serious poisoning for which hemodialysis is recommended. Based on the human 

experience, a peak blood methanol concentration of 500 mg/l was chosen as the basis for 

AEGL-3 derivation. 

A total uncertainty factor of 3 was used. An uncertainty factor of 3 was applied for 

intraspecies variability because clinical experience with methanol intoxications is mainly based 

on cases involving adult men while much less data is available for women, children or elderly 

persons, and because subpopulations with a less than optimal folate status may be more 

susceptible to the health effects of methanol. 

Using a total uncertainty factor of 3, a blood methanol concentration of 167 mg/l was 

derived as the basis for calculation of exposure concentrations. Application of the uncertainty 

factor to the blood methanol concentration was preferred because the calculated exposure 

concentrations in air stayed better in the concentration range for which the pharmacokinetic 

model was validated and the effect of methanol metabolism for longer exposure periods was 

more adequately taken into account. In contrast, first calculating exposure concentrations that 

would lead to a blood methanol level of 500 mg/l and then applying a factor of 3 to the derived 

exposure concentration would result in calculation of extremely high concentrations in the fist 

step at which metabolic pathways would be saturated. 

Using the pharmacokinetic model of Perkins et al. (1995a), inhalation exposure 

concentrations were calculated for appropriate time periods that would lead to a blood methanol 

concentration of 167 mg/l at the end of the time period (see Appendix C, Table 16). The 

calculated exposure concentrations were set as AEGL-3 values. 

The values are listed in Table 11 below. 

TABLE 11: AEGL-3 VALUES FOR METHANOL

AEGL Level 10 minutes 30 minutes 1 hour 4 hours 8 hours 

AEGL-3 # 14000 ppm a 

(18000 mg/m;) 

7200 ppm a 

(9400 mg/m;) 

2400 ppm 

(3100 mg/m;) 

1600 ppm 

(2100 mg/m;)
METHANOL Interim 2: 2/2005 

54 

a The 30-minute and 1-hour AEGL-3 values are higher than 1/10 of the lower explosive limit (LEL) of 

methanol in air (LEL = 55,000; 1/10th LEL = 5500 ppm). Therefore, safety considerations against the 

hazard of explosion must be taken into consideration.

# The 10-minute AEGL-3 value of 40,000 ppm is higher than 50% of the lower explosive limit of methanol 

in air (LEL = 55,000 ppm; 50% of the LEL = 27,500 ppm). Therefore, extreme safety considerations 

against the hazard of explosion must be taken into account. 

The derived values are supported by the study of Kawai et al. (1991), which reported 

dimmed vision (the authors suggested that visibility was temporarily reduced by fog in the 

workroom) and nasal irritation during work, in a group of 22 workers exposed to a mean 

methanol concentration of 459 ppm for 8 hours; a group of 5 breathing-zone samples revealed 

concentrations between 3000 and 5500 ppm. 

The values are also supported by an older study that reported severe nasal and eye irritation in 

volunteers after exposure at 65400 ppm for 5 minutes (Flury and Wirth, 1933). 

With regard to fetal death observed in rodents, the derived AEGL-3 values are supported 

on basis of the following rationale: the NOEL for fetal death in mice was 5000 ppm for 7 hours 

after both single and repeated exposure (Rogers et al. 1993; 1995; Rogers, 1999). As pointed 

out in Section 7.2, methanol itself and not a metabolite is probably responsible for the 

developmental toxic effects in rodents (Dorman et al., 1995) and, therefore, it seems reasonable 

to assess the developmental toxicity on the basis of blood methanol concentrations. The 

corresponding end-of-exposure blood concentration in mice after exposure at 5000 ppm for 7 

hours was 2126 mg/l (Rogers et al., 1993). The blood methanol concentration that was used for 

derivation of AEGL-3 values was 167 mg/l, which is about 13-fold lower than the NOEL blood 

concentration for fetal death in mice, and thus should provide sufficient protection to humans 

against this effect. 

The derived values are also supported by studies on monkeys: since no toxic effects 

were observed in monkeys exposed repeatedly at 5000 ppm for 6 hours/day (Andrews et al., 

1987) it can be concluded that these exposure conditions are considerably below the lethality 

threshold. In the study of NEDO (1987) no deaths were observed after repeated exposure at 

3000 ppm for 21 hours per day. Since the biological half life of methanol and formate is in the 

order of a few hours, the short period of 3 hours between exposures in the NEDO study did not 

allow for complete elimination and, thus, after the first exposure higher blood concentrations of 

methanol and formate must have been present during subsequent exposures. This may explain 

the delayed deaths observed after repeated exposure for 21 hours/day to 10000 ppm (death 

after 3 days), 7000 ppm (death after 6 days) and 5000 ppm (death after 5 days). 

8. SUMMARY OF PROPOSED AEGLS 

8.1. AEGL Values and Toxicity Endpoints 

The AEGL values for various levels of effects and various time periods are summarized 

in Table 12. They were derived using the following key studies and methods. 
METHANOL Interim 2: 2/2005 

55 

The AEGL-1 was based on a study in which human volunteers were exposed to 800 

ppm methanol for 8 hours (Batterman et al., 1998). While the study made no statement on 

health effects, the coauthor Dr. Franzblau stated in a personal communication that the subjects 

reported no symptoms (Franzblau, 1999; 2000). A total uncertainty factor of 3 was applied. The 

other exposure duration-specific values were derived by time scaling according to the doseresponse regression equation Cn

 x t = k, using the default of n=3 for shorter exposure periods. 

For the 10-minute AEGL-1 the 30-minute value was applied. 

The AEGL-2 values were based on developmental toxic effects in mice. After a single 

exposure to different concentration-time combinations on gestational day 7, the most sensitive 

endpoint was cervical rib induction, which occurred at concentration-time products greater than 

or equal to 15000 ppm @ h, but not at concentration-time products (CxT) below 15000 ppm @ h 

(i.e. no effects were observed after exposure at 2000 ppm for 5 hours, 2000 ppm for 7 hours 

and 5000 ppm for 2 hours; authors expressed data only as CxT values) (Rogers et al. 1995, 

abstract; Rogers, 1999, personal communication). For the NOEL of 2000 ppm for 7 hours 

(Rogers et al. 1995, abstract; Rogers, 1999, personal), the corresponding end-of-exposure 

blood concentration was measured as 487 mg/l (Rogers et al., 1993). An interspecies 

uncertainty factor of 1 and an intraspecies uncertainty factor of 10 were used. The total 

uncertainty factor was applied to the blood methanol concentration resulting in a concentration 

of 48.7 mg/l. A pharmacokinetic model was used to calculate inhalation exposure 

concentrations for appropriate time periods that would lead to a blood methanol concentration of 

48.7 mg/l at the end of the time period. These exposure concentrations were set as AEGL-2 

values. 

The AEGL-3 values were based on acute lethal effects on humans after oral methanol 

uptake. Case studies (Naraqi et al., 1979; Erlanson et al., 1965; Bennett et al., 1955; Gonda et 

al., 1978; Meyer et al., 2000) reported measured blood methanol concentrations and time 

periods between intoxication and measurement. Given the time that elapsed until blood 

sampling, during which part of the methanol was metabolized, it can be concluded that peak 

blood methanol concentrations have been above 1000 mg/l in all fatal cases. Based on the 

extensive clinical experience with methanol intoxications, the American Academy of Clinical 

Toxicology (AACT, 2002) published clinical practice guidelines on the treatment of methanol 

poisoning. According to these guidelines, peak blood methanol concentrations >500 mg/l 

indicate serious poisoning for which hemodialysis is recommended. Based on the human 

experience, a peak blood methanol concentration of 500 mg/l was chosen as the basis for 

AEGL-3 derivation. An intraspecies uncertainty factor of 3 was used. The uncertainty factor was 

applied to the blood methanol concentration resulting in a concentration of 167 mg/l. A 

pharmacokinetic model was used to calculate inhalation exposure concentrations for 

appropriate time periods that would lead to a blood methanol concentration of 167 mg/l at the 

end of the time period. These exposure concentrations were set as AEGL-3 values. 

Because liquid methanol is absorbed through the skin, a skin notation was added to the 

table of values. 

TABLE 12: SUMMARY/RELATIONSHIP OF PROPOSED AEGL VALUES 

FOR METHANOL a

 
METHANOL Interim 2: 2/2005 

56 

Classification 10-Minute 30-Minute 1-Hour 4-Hour 8-Hour

AEGL-1 

(Nondisabling) 

670 ppm 

(880 mg/m;) 

670 ppm 

(880 mg/m;) 

530 ppm 

(690 mg/m;) 

340 ppm 

(450 mg/m;) 

270 ppm 

(350 mg/m;) 

AEGL-2 

(Disabling) 

11000 ppm b 

(14000 mg/m;) 

4000 ppm 

(5200 mg/m;) 

2100 ppm 

(2800 mg/m;) 

730 ppm 

(960 mg/m;) 

520 ppm 

(680 mg/m;) 

AEGL-3 

(Lethal) 

# 14000 ppm b 

(18000 mg/m;) 

7200 ppm b 

(9400 mg/m;) 

2400 ppm 

(3100 mg/m;) 

1600 ppm 

(2100 mg/m;) 

a

 Cutaneous absorption may occur; direct skin contact with the liquid should be avoided. 

b The 10-minute AEGL-2 value and the 30-minute and 1-hour AEGL-3 values are higher than 1/10 of the 

lower explosive limit (LEL) of methanol in air (LEL = 55,000; 1/10th LEL = 5500 ppm). Therefore, safety 

considerations against the hazard of explosion must be taken into consideration.

# The 10-minute AEGL-3 value of 40,000 ppm is higher than 50% of the lower explosive limit of methanol 

in air (LEL = 55,000 ppm; 50% of the LEL = 27,500 ppm). Therefore, extreme safety considerations 

against the hazard of explosion must be taken into account. 

All inhalation data are summarized in Figure 3 below. The data were classified into 

severity categories chosen to fit into definitions of the AEGL level health effects. The category 

severity definitions are "No effect"; "Discomfort"; "Disabling"; "Lethal"; "Partial lethality" (at an 

experimental concentration in which some of the animals died and some did not, this label 

refers to the animals which did not die) and "AEGL". Note that the AEGL-2 values are 

designated as triangles. 

Consistency of Data for Methanol 

with Derived AEGL Values

100

1000

10000

100000

1000000

0 60 120 180 240 300 360 420 480

Time (minutes)

Concentration (ppm)

Human - No effect Human - Discomfort Human - Disabling Animal - No effect Animal - Discomfort

Animal - Disabling Animal - Some Lethality Animal - Lethal AEGL

AEGL - 2

AEGL - 3

AEGL - 1
METHANOL Interim 2: 2/2005 

57 

FIGURE 3: CATEGORICAL REPRESENTATION OF ALL METHANOL INHALATION DATA 
METHANOL Interim 2: 2/2005 

58 

8.2. Comparison with Other Standards and Criteria

Standards and guidance levels for workplace and community exposures are listed in 

Table 13. In addition, biological exposure values exist: the ACGIH BEI (biological exposure 

index) is 15 mg methanol per liter urine at the end of shift at the end of workweek (ACGIH, 

1999). The German BAT (Biologischer Arbeitsstoff-Toleranz-Wert; biological tolerance value) is 

30 mg methanol per liter urine during the second half of shift at the end of workweek (Henschler 

und Lehnert, 1983). 
METHANOL Interim 2: 2/2005 

59 

TABLE 13. EXTANT STANDARDS AND GUIDELINES FOR METHANOL 

Exposure Duration

 Guideline 

10 minutes 30 minutes 1 hour 4 hours 8 hours 

AEGL-1 670 ppm 670 ppm 530 ppm 340 ppm 270 ppm 

AEGL-2 11000 ppm 4000 ppm 2100 ppm 730 ppm 520 ppm 

AEGL-3 # 14000 ppm 7200 ppm 2400 ppm 1600 ppm 

ERPG-1(AIHA)a 200 ppm 

ERPG-2 (AIHA) 1000 ppm 

ERPG-3 (AIHA) 5000 ppm 

EEGL (NRC)b 800 ppm 400 ppm 200 ppm 10 ppm 

[24 hours] 

PEL-TWA 

(OSHA)c

 

200 ppm 

PEL-STEL 

(OSHA)d

 

250 ppm 

[15 minutes] 

IDLH (NIOSH)e 6000 ppm 

REL-TWA 

(NIOSH)f

200 ppm 

REL-STEL 

(NIOSH)g

 

250 ppm 

[15 minutes] 

TLV-TWA 

(ACGIH)h

200 ppm 

TLV-STEL 

(ACGIH)i

250 ppm 

MAK 

(Germany)j

200 ppm 

MAK Spitzenbegrenzung 

(Germany)k

 

1000 ppm 

Einsatztoleranzwert (Germany)l

500 ppm 

MAC (The 

Netherlands)m

200 ppm 
METHANOL Interim 2: 2/2005 

60 

# The 10-minute AEGL-3 value of 40,000 ppm is higher than 50% of the lower explosive limit of 

methanol in air (LEL = 55,000 ppm; 50% of the LEL = 27,500 ppm). Therefore, extreme 

safety considerations against the hazard of explosion must be taken into account. 

a

 ERPG (Emergency Response Planning Guidelines, American Industrial Hygiene Association)

(AIHA, 1994) 

The ERPG-1 is the maximum airborne concentration below which it is believed nearly all 

individuals could be exposed for up to one hour without experiencing other than mild, transient 

adverse health effects or without perceiving a clearly defined objectionable odor. The ERPG-1 for 

methanol is based on the threshold for producing headaches and dizziness in workers exposed 

repeatedly to methanol (Frederick et al., 1984). 

The ERPG-2 is the maximum airborne concentration below which it is believed nearly all 

individuals could be exposed for up to one hour without experiencing or developing irreversible or 

other serious health effects or symptoms that could impair an individual>s ability to take protective 

action. The ERPG-2 for methanol is based on observed 1) no toxic effects in workers exposed to 

1000-2000 ppm for 0.5 hours or less (Sterner and Fassett, 1958), 2) no serious toxic effects after 

brief exposures at 3000 ppm (Frederick et al, 1984) or 8000 ppm (Humperdinck, 1941) and 3) no 

toxic effects in monkeys repeatedly exposed to 5000 ppm (Andrews et al., 1987) or rats 

repeatedly exposed to 10000 ppm (White et al., 1983). 

The ERPG-3 is the maximum airborne concentration below which it is believed nearly all 

individuals could be exposed for up to one hour without experiencing or developing lifethreatening health effects. The ERPG-3 for methanol is based on observed 1) no lethality in 

workers exposed to 3000 ppm for 15 minutes (Frederick et al., 1984) or 8000 ppm (Humperdinck, 

1941) and 2) no toxic effects in monkeys repeatedly exposed to 5000 ppm (Andrews et al., 1987). 

b

 EEGL (Emergency Exposure Guidance Levels, National Research Council) (NRC, 1985) 

is the concentration of contaminants that can cause discomfort or other evidence of irritation or 

intoxication in or around the workplace, but avoids death, other severe acute effects and long-term 

or chronic injury. The EEGL for methanol are mainly based on the LCLo of 1000 ppm in the study 

on monkeys by McCord (1931), the pharmacokinetic study by Leaf and Zatman (1952) and other 

observations summarized in the NIOSH Criteria Document (NIOSH, 1976). 

c

 OSHA PEL-TWA (Occupational Health and Safety Administration, Permissible Exposure Limits - 

Time Weighted Average) (OSHA, 1994) 

is defined analogous to the ACGIH-TLV-TWA, but is for exposures of no more than 10 hours/day, 

40 hours/week. 

d

 OSHA PEL-STEL (Permissible Exposure Limits - Short Term Exposure Limit) (OSHA, 1994)

is defined analogous to the ACGIH-TLV-STEL.

e

 IDLH (Immediately Dangerous to Life and Health, National Institute of Occupational Safety and 

Health) (NIOSH, 1996) 

represents the maximum concentration from which one could escape within 30 minutes without 

any escape-impairing symptoms, or any irreversible health effects. The IDLH for methanol is 

based on a LCLo of 37594 ppm for two hours in the mouse (Izmerov et al., 1982). 

f

 NIOSH REL-TWA (National Institute of Occupational Safety and Health, Recommended Exposure 

Limits - Time Weighted Average) (NIOSH, 1992) 

is defined analogous to the ACGIH-TLV-TWA. 
METHANOL Interim 2: 2/2005 

61 

g

 NIOSH REL-STEL (Recommended Exposure Limits - Short Term Exposure Limit) (NIOSH, 1992)

is defined analogous to the ACGIH-TLV-STEL. 

h

 ACGIH TLV-TWA (American Conference of Governmental Industrial Hygienists, Threshold Limit 

Value - Time Weighted Average) (ACGIH, 1996) 

is the time-weighted average concentration for a normal 8-hour workday and a 40-hour workweek, 

to which nearly all workers may be repeatedly exposed, day after day, without adverse effect. 

i

 ACGIH TLV-STEL (Threshold Limit Value - Short Term Exposure Limit) (ACGIH, 1996) 

is defined as a 15 minute TWA exposure which should not be exceeded at any time during the 

workday even if the 8-hour TWA is within the TLV-TWA. Exposures above the TLV-TWA up to the 

STEL should not be longer than 15 minutes and should not occur more than 4 times per day. 

There should be at least 60 minutes between successive exposures in this range. 

j

 MAK (Maximale Arbeitsplatzkonzentration [Maximum Workplace Concentration], Deutsche 

Forschungs-gemeinschaft [German Research Association], Germany) (Greim, 1995; DFG, 

1999)

is defined analogous to the ACGIH-TLV-TWA. 

k

 MAK Spitzenbegrenzung (Kategorie II,2) [Peak Limit Category II,2] (DFG, 1999) 

constitutes the maximum average concentration to which workers can be exposed for a period up 

to 30 minutes, with no more than 2 exposure periods per work shift; total exposure may not 

exceed 8-hour MAK. 

l

 Einsatztoleranzwert [Action Tolerance Levels] (Vereinigung zur Förderung des deutschen 

Brandschutzes e.V. [Federation for the Advancement of German Fire Prevention]) (Greim, 

1996) 

constitutes a concentration to which unprotected firemen and the general population can be 

exposed to for up to 4 hours without any health risks. The value is based on the estimation that 

the Biologischer-Arbeitsstoff-Toleranzwert [Biological Exposure Index] of 30 mg/l methanol in 

urine could be reached following a 4-hour exposure to 500 ppm methanol. m MAC ([Maximum Workplace Concentration], Dutch Expert Committee for Occupational 

Standards, The Netherlands) (MSZW, 1999) 

is defined analogous to the ACGIH-TLV-TWA. 

8.3. Data Adequacy and Research Needs

Definitive exposure-response data for irreversible or lethal methanol toxicity in humans 

are not available. However, qualitative information on the human experience affirms that 

methanol vapor is toxic and can cause irreversible effects (blindness) as well as lethality. Data 

from occupational exposure studies are often compromised by uncertain quantitation of 

exposure. 

For the derivation of AEGL-3 values studies on lethal effects of inhalation exposure in 

rodents were not considered appropriate due to the considerable differences in methanol 

metabolism kinetics and mechanisms of methanol toxicity between primates (humans and 

monkeys) and rodent species. Since well-described case reports of fatalities after inhalation 

were not available, the derivation was based on the extensive clinical experience with methanol 
METHANOL Interim 2: 2/2005 

62 

intoxications. The American Academy of Clinical Toxicology (AACT, 2002) published clinical 

practice guidelines on the treatment of methanol poisoning. According to these guidelines, peak 

blood methanol concentrations >500 mg/l indicate serious poisoning for which hemodialysis is 

recommended. Based on the human experience, a peak blood methanol concentration of 500 

mg/l was chosen as the basis for AEGL-3 derivation. 

Although methanol intoxication can cause blindness in humans, it is not possible to 

derive a threshold for this irreversible effect from the available data. However, available reports 

indicate that blindness results only after live-threatening poisoning. There was thus no basis for 

the derivation of AEGL-2 on health effects in humans. Therefore, the derivation of AEGL-2 

values was based on developmental toxic effects in rodents. A number of teratogenicity studies 

in mice and rats is available including a two studies reporting developmental toxic effects in 

mice after single inhalation exposures. There is experimental evidence that developmental toxic 

effects are caused by methanol itself and not by a metabolite, such as formate. It therefore was 

considered adequate to derived AEGL-2 values on the basis of blood methanol concentrations. 

The total uncertainty factor was applied to the measured end-of-exposure blood methanol 

concentration. Using a pharmacokinetic model, methanol concentrations in air were calculated 

which would result in this blood methanol concentration at the end of relevant AEGL time 

periods. With respect to developmental toxic effects, no information regarding human 

occupational, accidental or intentional exposure via the inhalation, dermal or oral route is 

available. More research is needed for an adequate evaluation of the developmental toxic 

effects of methanol reported in monkeys. 

Based on the extremely wide range of reported odor thresholds, the odor threshold data 

were not considered appropriate for derivation of AEGL-1. A number of high quality, human 

studies on asymptomatic effects of low methanol concentrations on the central nervous system 

are available. These studies usually used exposure at 200 ppm which was considered lower 

than the thresholds for irritation and discomfort. A level of 1000 ppm caused headache and eye 

irritation is workers and was considered above the discomfort level. Therefore, the 

pharmacokinetic study by Batterman et al. (1998) employing exposure at 800 ppm was used for 

the derivation of AEGL-1 values. It has to be noted though, that the study did not formally 

evaluate and report health effects. In a personal communication by one of the studies>

coauthors it was stated that none of the subjects reported symptoms. Some uncertainty to this 

data is conferred by this fact that the evaluation of health effects was not the focus of the study. 

With respect to lethal and severe toxic effects, additional inhalation studies on monkeys 

using single inhalation exposure could support the derived AEGL-2 and AEGL-3 values. 

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METHANOL Interim 2: 2/2005 

73 

 APPENDIX A 

 Time Scaling Calculations for AEGLs 
METHANOL Interim 2: 2/2005 

74 

AEGL-1

Key study: Batterman et al. (1998) and Franzblau (1999; 2000; personal 

communication); Frederick et al. (1984); NIOSH (1980); NIOSH (1981) 

Toxicity endpoint: Pharmacologic study exposing 3 female and 12 male subjects to 800 ppm 

methanol for 8 hours. One of the study>s coauthors stated in a personal 

communication that none of the subjects reported symptoms. 

Scaling: C; x t = k for extrapolation to 4, hours, 1 hour and 30 minutes 

k = 800; ppm; x 8 hours = 4.1 x 109

 ppm; h 

The AEGL-1 for 10 minutes was set at the same concentration as the 30-

minute value. 

Uncertainty factors: 3 for intraspecies variability 

Calculations: 

10-minute AEGL-1 10-min AEGL-1 = 670 ppm (880 mg/m;) 

30-minute AEGL-1 C; x 0.5 h = 4.1 x 109

 ppm; h 

C = 2017 ppm 

30-min AEGL-1 = 2017 ppm/3 = 670 ppm (880 mg/m;) 

1-hour AEGL-1 C; x 1 h = 4.1 x 109

 ppm; h 

C = 1600 ppm 

1-hour AEGL-1 = 1600 ppm/3 = 530 ppm (690 mg/m;) 

4-hour AEGL-1 C; x 4 h = 4.1 x 109

 ppm; h 

C = 1008 ppm 

4-hour AEGL-1 = 1008 ppm/3 = 340 ppm (450 mg/m;) 

8-hour AEGL-1 8-hour AEGL-1 = 800 ppm/3 = 270 ppm (350 mg/m;) 
METHANOL Interim 2: 2/2005 

75 

AEGL-2

Key study: Rogers et al. (1993; 1995, abstract; 1997); Rogers (1999, personal 

communication) 

Toxicity endpoint: Using repeated 7-hour/day exposures during gestational days 6 to 15, a 

dose-related, significant increase in cervical ribs was observed at 2000 

ppm or higher; other malformations, such as exencephaly and cleft palate 

occurred dose-dependently at concentrations of 5000 ppm or higher 

(Rogers et al., 1993). The same type of malformations occurred after a 

single 7-hour exposure to 10000 ppm (Rogers et al., 1997). In another 

study of Rogers and coworkers, which has not been formally published up 

until know, mice were exposed on gestational day 7 to different 

concentration-time combinations (Rogers et al. 1995, abstract; Rogers, 

1999, personal communication). The most sensitive endpoint was cervical 

rib induction, which occurred at concentration-time products greater than 

or equal to 15000 ppm @ h, but not at concentration-time products below 

15000 ppm @ h (i.e. no effects were observed after exposure to 2000 ppm 

x 5 h, 2000 ppm x 7 h and 5000 ppm x 2 h; authors expressed data only 

as CxT values). In these experiments, the highest no-observed-effect CxT 

product was 2000 ppm for 7 hours. The corresponding end-of-exposure 

blood concentration in mice after exposure was measured as 487 mg/l 

(Rogers et al., 1993). The uncertainty factors were applied to the blood 

methanol concentration resulting in a concentration of 48.7 mg/l, on which 

calculations of AEGL-2 exposure concentrations were based. 

Scaling: A pharmacokinetic model was used to calculate exposure concentrations 

that would lead to blood methanol concentrations at the end of periods of 

8 hours, 4 hours, 1 hour and 30 and 10 minutes. Calculations are shown 

in Appendix B, Table 15. 

Uncertainty factors: 1 for interspecies variability 

10 for intraspecies variability 

Calculations: The concentrations calculated using the pharmacokinetic (PK) model 

were set as AEGL-2 values: 

10-minute AEGL-2 10-min AEGL-2 = 11350 ppm (from PK model) = 11000 ppm (14000 

mg/m;) 

30-minute AEGL-2 30-min AEGL-2 = 3980 ppm (from PK model) = 4000 ppm (5200 mg/m;) 

1-hour AEGL-2 1-hour AEGL-2 = 2110 ppm (from PK model) = 2100 ppm (2800 mg/m;) 

4-hour AEGL-2 4-hour AEGL-2 = 730 ppm (from PK model) = 730 ppm (960 mg/m;) 

8-hour AEGL-2 8-hour AEGL-2 = 524 ppm (from PK model) = 520 ppm (680 mg/m;) 
METHANOL Interim 2: 2/2005 

76 

AEGL-3

Key study: AACT (2002) 

Toxicity endpoint: Case studies reported measured blood methanol concentrations and time 

periods between intoxication and measurement. Given the time that 

elapsed until blood sampling, during which part of the methanol was 

metabolized, it can be concluded that peak blood methanol 

concentrations have been above 1000 mg/l in all fatal cases. Based on 

the extensive clinical experience with methanol intoxications, the 

American Academy of Clinical Toxicology (AACT, 2002) published clinical 

practice guidelines on the treatment of methanol poisoning. According to 

these guidelines, peak blood methanol concentrations >500 mg/l indicate 

serious poisoning for which hemodialysis is recommended. Based on the 

human experience, a peak blood methanol concentration of 500 mg/l was 

chosen as the basis for AEGL-3 derivation. 

Scaling: A pharmacokinetic model was used to calculate exposure concentrations 

that would lead to blood methanol concentrations at the end of periods of 

8 hours, 4 hours, 1 hour and 30 and 10 minutes. Calculations are shown 

in Appendix B, Table 16. 

Uncertainty factor: 3 for intraspecies variability 

Calculations: The concentrations calculated using the pharmacokinetic (PK) model 

were set as AEGL-3 values: 

10-minute AEGL-3 10-min AEGL-3 = 39500 ppm (from PK model) = 40000 ppm (52000 

mg/m;) 

30-minute AEGL-3 30-min AEGL-3 = 13700 ppm (from PK model) = 14000 ppm (18000 

mg/m;) 

1-hour AEGL-3 1-hour AEGL-3 = 7220 ppm (from PK model) = 7200 ppm (9400 mg/m;) 

4-hour AEGL-3 4-hour AEGL-3 = 2380 ppm (from PK model) = 2400 ppm (3100 mg/m;) 

8-hour AEGL-3 8-hour AEGL-3 = 1620 ppm (from PK model) = 1600 ppm (2100 mg/m;) 
METHANOL Interim 2: 2/2005 

77 

 APPENDIX B 

 Pharmacokinetic Calculations
METHANOL Interim 2: 2/2005 

78 

Calculation of Exposure Concentrations for Humans

Study: Perkins et al. (1995a) 

Pharmacokinetic model for blood methanol concentrations after inhalation 

exposure. 

Equation: 

dC

dt

V C

V

V C

K C

h inh

d

max

m

= • • − •

+

Φ

Parameters: C blood methanol concentration [mg/l] 

Cinh methanol concentration in air [mg/l] 

t time [h] 

Φ fraction of inhaled methanol absorbed into systemic circulation 

Vh ventilation rate [l/kg h] 

Vd volume of distribution [l/kg] 

Vmax maximum rate of enzymatic methanol oxidation [mg/l h] 

Km Michaelis-Menten constant of enzymatic methanol oxidation [mg/l] 

Parameter values: Since the presentation of parameters used for calculations and the 

reasoning for the parameter values is not clear in the article of Perkins et 

al. (1995a), for calculations the parameters were not taken over 

automatically. Instead, the following parameters were used: 

TABLE 14: PARAMETERS OF PHARMACOKINETIC MODEL 

Parameter Value used for calculation 

Φ 0.7 

The mean value of the range (0.53-0.85) reported Leaf and Zatman (1952) and 

Sedivec et al. (1981) (see Section 4.1.1) was used (value used in Perkins model: 

0.75) 

Vh (l/kg h) 17.8 

(a body weight of 70 kg and a ventilation rate of 10 m;/8 h for occupational 

situations were used) (value used in Perkins model: 10.3) 

Vd (l/kg) 0.65 

The mean value of the range (0.6-0.7) reported by Yant and Schrenk (1937) was 

used (see Section 4.1.1) (value used in Perkins model: 0.7) 

Vmax (mg/l h) 115 (value used in Perkins model) 

Km (mg/l) 460 (value used in Perkins model)
METHANOL Interim 2: 2/2005 

79 

Procedure: The simulations were performed on a spreadsheet program by converting the 

differentials to finite differences with a time step of 0.1 hours. For the continuous, 

instantaneous values for the blood concentration of methanol (C), the value from 

the previous time step (Ct-1) was used. Background blood methanol in humans is 

approximately 1.0 mg/l (see Table 8 for references) from both endogenous and 

exogenous sources and this level was used for the initial time step (C0). Using 

three significant figures, the lowest exposure concentration was calculated that 

resulted at or above the desired blood methanol concentration. 

Equation: 

C

V C

V

h

V C

K C t h h inh

d

max t

m t

= • •• −

•

+

• −

−

Φ

01 01 1

1

. .

Calculations: The following exposure concentrations were calculated to result in a blood 

methanol concentration of 48.7 mg/l in humans: 

TABLE 15: CALCULATION OF CONCENTRATIONS FOR INHALATION EXPOSURE I 

Exposure time Calculated exposure concentration 

(ppm) 

Rounded value 

(ppm) 

8 h 524 520 

4 h 730 730 

1 h 2110 2100 

30 min 3980 4000 

10 min 11350 11000

Calculations: The following exposure concentrations were calculated to result in a blood 

methanol concentration of 167 mg/l in humans: 

TABLE 16: CALCULATION OF CONCENTRATIONS FOR INHALATION EXPOSURE II 

Exposure time Calculated exposure concentration 

(ppm) 

Rounded value 

(ppm) 

8 h 1620 1600 

4 h 2380 2400 

1 h 7220 7200 

30 min 13700 14000 

 
METHANOL Interim 2: 2/2005 

80 

10 min 39500 40000

Comparison of the Perkins et al. (1995a) and Bouchard et al. (2001) models

In order to demonstrate that the pharmacokinetic model of Perkins et al. (1995a) gives 

results consistent with newer models, its predictions of methanol concentrations in air, that 

would lead cause selected blood methanol concentrations were compared with those of the 

model described by Bouchard et al. (2001). Calculations using the latter model were done by 

Professor Michele Bouchard, University of Montreal, Canada (Bouchard, personal 

communication, 2003). Model parameters were chosen as described in the original publication 

by Professor Bouchard, except that the values for the volume of distribution Vd and for the 

ventilation rate Vh were adjusted to those used in the Perkins model (see Table 14). 

Exposure concentrations in air were calculated for end-of-exposure blood methanol 

concentrations of 30, 100 and 250 mg/l. As can be seen from the results tables below, both 

pharmacokinetic models gave consistent results. 

TABLE 17: CALCULATION OF METHANOL CONCENTRATIONS RESULTING IN A 

BLOOD CONCENTRATION OF 30 mg/l 

Exposure time Perkins et al. (1995a) model Bouchard et al. (2001) model 

8 h 330 450 

4 h 460 560 

1 h 1300 1400 

30 min 2500 2600 

10 min 7000 7500

TABLE 18: CALCULATION OF METHANOL CONCENTRATIONS RESULTING IN A 

BLOOD CONCENTRATION OF 100 mg/l 

Exposure time Perkins et al. (1995a) model Bouchard et al. (2001) model 

8 h 1100 1200 

4 h 1500 1700 

1 h 4400 4600 

30 min 8300 8600 

10 min 24000 25000
METHANOL Interim 2: 2/2005 

81 

TABLE 19: CALCULATION OF METHANOL CONCENTRATIONS RESULTING IN A 

BLOOD CONCENTRATION OF 250 mg/l 

Exposure time Perkins et al. (1995a) model Bouchard et al. (2001) model 

8 h 2300 2400 

4 h 3500 3600 

1 h 11000 11000 

30 min 21000 21000 

10 min 60000 61000
METHANOL Interim 2: 2/2005 

82 

 APPENDIX C 

 Level of Distinct Odor Awareness
METHANOL Interim 2: 2/2005 

83 

Derivation of the Level of Distinct Odor Awareness (LOA)

The level of distinct odor awareness (LOA) represents the concentration above which it 

is predicted that more than half of the exposed population will experience at least a distinct odor 

intensity, about 10 % of the population will experience a strong odor intensity. The LOA should 

help chemical emergency responders in assessing the public awareness of the exposure due to 

odor perception. The LOA derivation follows the guidance given by van Doorn et al. (2002). 

For derivation of the odor detection threshold (OT50), a study is available in which the 

odor threshold for the reference chemical n-butanol (odor detection threshold 0.04 ppm) has 

also been determined: 

Hellman and Small (1974): 

odor detection threshold for methanol: 4.26 ppm 

odor detection threshold for n-butanol: 0.3 ppm 

corrected odor detection threshold (OT50) for methanol: 4.26 ppm * 0.04 ppm / 0.3 ppm = 0.57 

ppm 

The concentration (C) leading to an odor intensity (I) of distinct odor detection (I=3) is 

derived using the Fechner function: 

I = kw * log (C /OT50) + 0.5 

For the Fechner coefficient, the default of kw = 2.33 will be used due to the lack of chemicalspecific data: 

3 = 2.33 * log (C /0.57) + 0.5 which can be rearranged to 

log (C /0.57) = (3-0.5) / 2.33 = 1.07 and results in 

C = (10^1.07) * 0.57 = 11.8 * 0.57 = 6.7 ppm 

The resulting concentration is multiplied by an empirical field correction factor. It takes 

into account that in every day life factors, such as sex, age, sleep, smoking, upper airway 

infections and allergy as well as distraction, increase the odor detection threshold by a factor of 

4. In addition, it takes into account that odor perception is very fast (about 5 seconds) which 

leads to the perception of concentration peaks. Based on the current knowledge, a factor of 1/3 

is applied to adjust for peak exposure. Adjustment for distraction and peak exposure lead to a 

correction factor of 4 / 3 = 1.33 

LOA = C * 1.33 = 6.7 ppm * 1.33 = 8.9 ppm 

The LOA for methanol is 8.9 ppm. 
METHANOL Interim 2: 2/2005 

84 

 APPENDIX D 

 Derivation Summary for Methanol AEGLs 
METHANOL Interim 2: 2/2005 

85 

ACUTE EXPOSURE GUIDELINES FOR METHANOL 

 (CAS NO. 67-56-1) 

AEGL-1 VALUES

10 minutes 30 minutes 1 hour 4 hours 8 hours 

670 ppm 670 ppm 530 ppm 340 ppm 270 ppm 

Reference: Batterman, S.A., A. Franzblau, J.B. D>Arcy, N.E. Sargent, K.B. Gross and R.M. 

Schreck, 1998. Breath, urine, and blood measurements as biological exposure indices of 

short-term inhalation exposure to methanol. International Archives of Occupational and 

Environmental Health 71, 325-335; Franzblau, A., University of Michigan School of Public 

Health, Ann Arbor, Michigan, personal communication, e-mail dated 14 June 1999; 

Franzblau, A., University of Michigan School of Public Health, Ann Arbor, Michigan, personal 

communication, e-mail dated 3 October 2000; Frederick, L.J., P.A. Schulte, A. Apol, 1984. 

Investigation and control of occupational hazards associated with the use of spirit 

duplicators. American Industrial Hygiene Association Journal 45, 51-55; NIOSH, National 

Institute for Occupational Safety and Health, 1980. Hazard evaluation and technical 

assistance report TA 80-32. Everett school district, Everett, Washington. National Institute of 

Occupational Safety and Health, Cincinnatti, OH, USA.; NIOSH, National Institute for 

Occupational Safety and Health, 1981. Health hazard evaluation report No. HETA-81-177, 

178-988, University of Washington, Seattle. National Institute of Occupational Safety and 

Health, Cincinnatti, OH, USA 

Test Species/Strain/Number: Humans / not applicable / in total 7 women and 12 men 

Exposure Route/Concentrations/Durations: Inhalation / 0 and 800 ppm / 0.5, 1, 2 and 8 

hours 

Effects: In this pharmacokinetic study no statement was made on the presence or absence 

of any signs or symptoms of the methanol exposure. In a personal communication, the 

second author, Dr. Franzblau, stated that although no formal mechanism of recording 

symptoms was used, the subjects were generally asked during exposure if they experienced 

any symptoms. He wrote that individual symptoms were certainly asked of some subjects 

and that "none of the subjects reported odor, irritation, headache or other non-specific 

symptoms"; likewise "none of the subjects reported any difficulties or alterations of visual 

function". Dr. Franzblau wrote that it is possible that some subjects were not queried and that 

no written notes were made. 

Endpoint/Concentration/Rationale: Several experimental human studies are available that 

used methanol concentrations of about 200 ppm. Chuwers et al. (1995) found no significant 

effects in a panel of neurophysiological and neuropsychological tests after exposure for 4 

hours to 200 ppm. After the same exposure, Muttray et al. (2001) observed 

electroencephalogram alterations which the authors did not considered adverse; no clinical 

symptoms were reported by the subjects. Likewise, the NAC/AEGL committee considered 

these findings as below the threshold for AEGL-1. Batterman et al. (1998) exposed 

volunteers at a higher level (i.e. 800 ppm for 8 hours). As this was a pharmacokinetic study, 
METHANOL Interim 2: 2/2005 

86 

health effects were not formally evaluated. In a personal communication the coauthor Dr. 

Franzblau stated that individual symptoms were asked of some subjects, other subjects were 

only asked generally if they had symptoms, and that in some exposure sessions subjects 

might not have been queried. According to Dr. Franzblau, none of the subjects reported 

symptoms. Since the subjects knew the exposure concentration by means of a meter 

showing the actual concentration, if might be expected that this would have increased the 

inclination of subjects to report symptoms. 

NIOSH (1980) and Frederick et al. (1984) reported significantly higher frequencies of 

headaches, dizziness, blurred vision after occupational exposure at 1060 ppm (mean 

concentration). NIOSH (1981) reported eye irritation in a worker after exposure at 1025 ppm 

for 25 minutes. Since the 1000-ppm level was considered already a discomfort level, the 800 

ppm for 8 hour exposure from the Batterman et al. (1998) study was chosen as a starting 

point for AEGL-derivation. Since the local irritation effects are determined by the 

concentration of methanol in air and not to the blood methanol level, calculation of AEGL-1 

values was not done using a pharmacokinetic model (as done for AEGL-2 and -3) based on 

the end-of-exposure blood methanol level of 30.7 mg/l reported by Batterman et al. (1998). 

Instead, exposure to 800 ppm for 8 hours was used as the basis for AEGL-1 derivation. 

Uncertainty Factors/Rationale: 

Total uncertainty factor: 3 

Interspecies: not applicable 

Intraspecies: 3 - because interindividual variability with regard to slight central nervous 

system effects (e.g. headache) is likely to exist (although it cannot be 

quantified exactly from the existing experimental and epidemiological studies) 

and because subpopulations with a less than optimal folate status may be 

more susceptible to the health effects of methanol. 

Modifying Factor: Not applicable 

Animal to Human Dosimetric Adjustment: Not applicable 

Time Scaling: Cn

 x t = k where the default of n = 3 was used due to the lack of substancespecific data.. For the 10-minute AEGL-1 the 30-minute value was applied because no 

studies were available that demonstrated the absence of notable discomfort (with respect to 

irritation) in the general population, including susceptible subpopulations, at 970 ppm 

(extrapolated value for 10-minute period). 

Data Adequacy: Some uncertainty to the key study used for AEGL-1 derivation is conferred 

by the fact that no formal evaluation of health effects was performed and that with regard to 

effects only a personal communication by one of the key studies> coauthors is available, who 

stated that none of the subjects has reported symptoms. Other controlled studies using 

comparable exposure concentrations are not available. Other studies describing 

asymptomatic effects on the central nervous system a lower concentration of about 200 ppm 

(Chuwers et al., 1995; Muttray et al., 2001) were not used because no dose-response 

relationships were established and in light of the study of Batterman et al. (1998) and several 

occupational exposure studies, this exposure concentration is considered lower than the 
METHANOL Interim 2: 2/2005 

87 

threshold for irritation and discomfort. 
METHANOL Interim 2: 2/2005 

88 

ACUTE EXPOSURE GUIDELINES FOR METHANOL 

 (CAS NO. 67-56-1) 

AEGL-2 VALUES

10 minutes 30 minutes 1 hour 4 hours 8 hours 

11000 ppm a 4000 ppm 2100 ppm 730 ppm 520 ppm 

a The 10-minute AEGL-2 value is higher than 1/10 of the lower explosive limit (LEL) of methanol in air 

(LEL = 55,000; 1/10th LEL = 5500 ppm). Therefore, safety considerations against the hazard of 

explosion must be taken into consideration.

Reference: Rogers, J.M., M.L. Mole, N. Chernoff, B.D. Barbee, C.I. Turner, T.R. Logsdon 

and R.J. Kavlock, 1993. The developmental toxicity of inhaled methanol in the CD-1 mouse, 

with quantitative dose-response modeling for estimation of benchmark doses. Teratology 47, 

175-188; Rogers, J.M., B.D. Barbee and M.L. Mole, 1995. Exposure concentration and time 

(C x T) relationships in the developmental toxicity of methanol in mice. Toxicologist 15, 164 

(abstract); Rogers. J.M. and M.L. Mole, 1997. Critical periods of susceptibility to the 

developmental toxicity of inhaled methanol in the CD-1 mouse. Teratology 55, 364-72; 

Rogers, J.M., 1999. US-EPA, National Health and Environmental Effects Research 

Laboratory, Research Trigangle Park, North Carolina, personal communication, letter dated 

27 May 1999. 

Test Species/Strain/Sex/Number: mouse / CD-1 / pregnant females / variable (see below) 

Exposure Route/Concentrations/Durations: 

Inhalation exposure to the following concentration-time combinations (number of pregnant 

females or litters given in brackets) were used: 

Rogers et al. (1995); Rogers (1999): 

0 ppm (time not given); 2000 ppm x 5 / 7 h; 5000 ppm x 2 / 3 / 5 / 7 h; 10000 ppm x 2 / 3 / 5 / 

7 h; 15000 ppm x 1 / 2 / 3 / 5 / 7 h (number of litters 5 to 39 for CxT combinations in 

methanol-exposed and 106 in control groups) 

Rogers et al. (1993): 

0 / 1000 / 2000 / 5000 / 7500 / 10000 / 15000 ppm x 7 h/d, bd 6-15 (number of exposed 

females 20 to 61 per group) 

Rogers et al. (1997): 

0 / 10000 ppm x 7 h/d for 1 d during period of gd 5-9 / for 2 d during period of gd 6-13 

(number of pregnant females 12 to 17 per group) 

Effects: Rogers et al. (1995); Rogers (1999): 

S no increased malformations after CxT <15000 ppm @ h, 

S significantly increased incidences of cervical ribs after CxT $15000 ppm @ h, 

S in addition significantly increased incidences of fetal death, cleft palate and other 

skeletal defects after CxT $70000 ppm @ h; 
METHANOL Interim 2: 2/2005 

89 

Effects (cont.): 

Rogers et al. (1993): 

S no increased malformations after 1000 ppm, 

S significantly increased incidences of cervical ribs after $2000 ppm, 

S in addition significantly increased incidences of exencephaly and cleft palate after 

$5000 ppm, 

S in addition significantly increased number of dead fetuses/litter after $7500 ppm, 

S in addition significantly increased number of full-litter resorptions after $10000 ppm; 

Rogers et al. (1997): several types of malformations were observed. The critical periods 

differed with maximum effects (% of fetuses per litter affected) on the following exposure 

days: 

S increased resorptions per litter after exposure on gd 7 or on gd 6-7, 

S exencephaly after exposure on gd 7 (20 %) or gd 6-7 (30 %), 

S cleft palate after exposure on gd 7 (47 %) or gd 6-7 (20 %), 

S first cervical vertebra defect after exposure on gd 5 (56 %) or gd 6 (55 %) or gd 6-7 

(72 %), 

S second cervical vertebra defect after exposure on gd 7 (29 %) or gd 6-7 (22 %), 

S cervical ribs on vertebra after exposure on gd 7 (45 %) or gd 6-7 (74 %) 

Endpoint/Concentration/Rationale: 

Although methanol intoxication can cause blindness in humans, it is not possible to derive a 

threshold for this effect from the available data. Moreover, available reports indicate that 

blindness results only after live-threatening poisoning (Naraqi et al., 1979; WHO, 1997; 

IUCLID, 1996; NIOSH, 1976). 

The epidemiological studies evaluating reversible effects on humans, such as slight 

neurotoxic and irritative effects at the workplace, though evaluating a relevant toxicological 

endpoint, will not be used for derivation of AEGL-2 values because data on exposure time 

and exposure concentration were not considered sufficient. However, these reports provide 

valuable supporting evidence. 

The derivation of AEGL-2 values was based on developmental toxic effects in animals. The 

available data have been reviewed by US-EPA (2001) and NTP-CEHRH (2003) and the 

developmental toxic effects in rodents were considered relevant for humans. 

In mice, repeated 7-hour/day exposures during gestational days 6 to 15 caused a doserelated, significant increase in cervical ribs at 2000 ppm or higher; other malformations, such 

as exencephaly and cleft palate occurred concentration-dependently at 5000 ppm or higher 

(Rogers et al., 1993). The same type of malformations was found after a single 7-hour 

exposure at 10000 ppm (no other concentrations tested) (Rogers et al., 1997). In another 

study, which has not been formally published up until know, Rogers and coworkers (Rogers 

et al. 1995, abstract; Rogers, 1999, personal communication) exposed mice on gestational 

day 7 to different concentration-time combinations. The most sensitive endpoint was cervical 

rib induction, which occurred at concentration-time products greater than or equal to 15000 

ppm @ h, but not at concentration-time products below 15000 ppm @ h (i.e. no effects were 

observed at 2000 ppm for 5 h, 2000 ppm for 7 h or 5000 ppm for 2 h; authors expressed 

data only as CxT values). Thus, while 2000 ppm for 7 hours was a LOEL in the repeated 

exposure study (Rogers et al., 1993), it was a NOEL after single exposure. Although the 
METHANOL Interim 2: 2/2005 

90 

single exposure study had shortcomings in the reporting, it was very consistent with the welldocumented repeated exposure study. It was therefore considered adequate to use an 

exposure at 2000 ppm for 7 hours as a starting point for AEGL-2 derivation. 

The corresponding end-of-exposure blood concentration was measured as 487 mg/l (Rogers 

et al., 1993). There is experimental evidence that developmental toxic effects are caused by 

methanol itself and not by a metabolite, such as formate (Dorman et al., 1995). It therefore 

was considered adequate to derived AEGL-2 values on the basis of blood methanol 

concentrations. The total uncertainty factor was applied to the blood methanol concentration 

resulting in a value of 48.7 mg/l. 

Uncertainty Factors/Rationale: 

Total uncertainty factor: 10 

Interspecies: 1 - because a sensitive species was used for derivation of AEGL-2 values and 

because toxicokinetic differences between species were accounted for by 

using a pharmacokinetic model for calculating exposure concentrations. 

Intraspecies: 10 - because no information on developmental toxic effects of methanol on 

humans is available and because also for other chemicals the variability in 

susceptibility of humans for developmental toxic effects is not well 

characterized. Moreover, pregnant women are a subpopulation with a less 

than optimal folate status and, thus, may be more susceptible to the health 

effects of methanol 

Modifying Factor: Not applicable 

Animal to Human Dosimetric Adjustment: Not applicable 

Time Scaling: Using a total uncertainty factor of 10, a blood methanol concentration of 48.7 

mg/l was derived as the basis for calculation of exposure concentrations. Application of the 

uncertainty factor to the blood methanol concentration was preferred because the calculated 

exposure concentrations in air stayed better in the concentration range for which the 

pharmacokinetic model was validated and the effect of methanol metabolism for longer 

exposure periods was more adequately taken into account. In contrast, first calculating 

exposure concentrations that would lead to a blood methanol level of 487 mg/l, and then 

applying a factor of 10 to the derived exposure concentration would result in calculation of 

extremely high concentrations in the fist step at which metabolic pathways would be 

saturated. After application of the uncertainty factor, concentrations would be below 

saturation level which would mean that the end-of-exposure methanol levels would vary for 

the AEGL-2 exposure concentration-time combinations. 

Using the pharmacokinetic model of Perkins et al. (1995a), inhalation exposure 

concentrations were calculated for appropriate time periods that would lead to a blood 

methanol concentration of 48.7 mg/l at the end of the time period. The calculated exposure 

concentrations were set as AEGL-2 values. 

Data Adequacy: The derived AEGL-2 values are supported by the occupational exposure 

study of Kawai et al. (1991), in which 8-hour mean concentrations of 3000-5500 ppm in 5 

samples and 1000-2000 ppm in another 10 samples were measured and resulted in dimmed 

vision (the authors suggested that visibility was temporarily reduced by fog in the workroom) 
METHANOL Interim 2: 2/2005 

91 

and nasal irritation, but not in severe or irreversible toxicity. 
METHANOL Interim 2: 2/2005 

92 

ACUTE EXPOSURE GUIDELINES FOR METHANOL 

 (CAS NO. 67-56-1) 

AEGL-3 VALUES

10 minutes 30 minutes 1 hour 4 hours 8 hours 

# 15000 ppm a 7200 ppm a 2500 ppm 1600 ppm 

a The 1-hour AEGL-3 values are higher than 1/10 of the lower explosive limit (LEL) of methanol in air 

(LEL = 55,000; 1/10th LEL = 5500 ppm). Therefore, safety considerations against the hazard of 

explosion must be taken into consideration.

# The 10-minute AEGL-3 value of 40,000 ppm is higher than 50% of the lower explosive limit of 

methanol in air (LEL = 55,000 ppm; 50% of the LEL = 27,500 ppm). Therefore, extreme safety 

considerations against the hazard of explosion must be taken into account.

Reference: AACT, American Academy of Clinical Toxicology Ad Hoc Committee on the 

Treatment Guidelines for Methanol Poisoning: D.G. Barceloux, G.R. Bond, E.P. Krezelok, H. 

Cooper, and J.A. Vale, 2002. American Academy of Clinical Toxicology Practice Guidelines 

on the Treatment of Methanol Poisoning. Clinical Toxicology 40, 415-446 

Test Species/Strain/Sex/Number: Humans / (not applicable) / (not applicable) 

Exposure Route/Concentrations/Durations: Oral / measured blood methanol concentrations 

are available, but no reliable information on ingested dose / exact information during which 

time period the methanol dose was consumed is not available, it was assumed that the time 

period for ingestion was short (up to a few hours) 

Effects: In fatal cases, death occurred 1.5-4 days after intoxication; when admitted to 

hospital (0.5-2 days after intoxication), subjects usually showed severe signs of intoxication 

(e.g. coma); for all cases measured blood methanol concentrations and time between 

measurement and intoxication were reported. 

Endpoint/Concentration/Rationale: The minimum lethal oral dose of about 1 g/kg reported in 

review articles by Buller and Wood (1904) and Röe (1982) was not used as the basis for 

AEGL derivation because the value was not sufficiently supported by data in these articles. 

However, the reported minimum lethal oral dose which corresponds to a peak blood 

methanol level of about 1540 mg/l is supported by information from case studies on 

intoxication with methanol only (i.e. without concomitant ethanol consumption) (Naraqi et al., 

1979; Erlanson et al., 1965; Bennett et al., 1955; Gonda et al., 1978; Meyer et al., 2000). 

These studies reported measured blood methanol concentrations and time periods between 

intoxication and measurement. Given the time that elapsed until blood sampling, during 

which part of the methanol was metabolized, it can be concluded that peak blood methanol 

concentrations have been above 1000 mg/l in all fatal cases (see Figure 2). Based on the 

extensive clinical experience with methanol intoxications, the American Academy of Clinical 

Toxicology (AACT, 2002) published clinical practice guidelines on the treatment of methanol 

poisoning. According to these guidelines, peak blood methanol concentrations >500 mg/l 

indicate serious poisoning for which hemodialysis is recommended. Based on the human 

experience, a peak blood methanol concentration of 500 mg/l was chosen as the basis for 
METHANOL Interim 2: 2/2005 

93 

AEGL-3 derivation 

Uncertainty Factors/Rationale: 

Total uncertainty factor: 3 

Interspecies: not applicable 

Intraspecies: 3 - because because clinical experience with methanol intoxications is mainly 

based on cases involving adult men while much less data is available for 

women, children or elderly persons, and because subpopulations with a less 

than optimal folate status may be more susceptible to the health effects of 

methanol 

Modifying Factor: Not applicable 

Animal to Human Dosimetric Adjustment: Not applicable 

Time Scaling: Using a total uncertainty factor of 3, a blood methanol concentration of 167 

mg/l was derived as the basis for calculation of exposure concentrations. Application of the 

uncertainty factor to the blood methanol concentration was preferred because the calculated 

exposure concentrations in air stayed better in the concentration range for which the 

pharmacokinetic model was validated and the effect of methanol metabolism for longer 

exposure periods was more adequately taken into account. In contrast, first calculating 

exposure concentrations that would lead to a blood methanol level of 500 mg/l and then 

applying a factor of 3 to the derived exposure concentration would result in calculation of 

extremely high concentrations in the fist step at which metabolic pathways would be 

saturated. 

Using the pharmacokinetic model of Perkins et al. (1995a), inhalation exposure 

concentrations were calculated for appropriate time periods that would lead to a blood 

methanol concentration of 167 mg/l at the end of the time period. The calculated exposure 

concentrations were set as AEGL-3 values. 

Data Adequacy: AEGL-3 values were based on studies reporting lethality in humans after 

oral intoxication. Available studies on lethal effects of inhalation exposure in rodents were 

not considered appropriate due to the considerable differences between primates (humans 

and monkeys) and rodent species in the kinetics of methanol metabolism and the 

mechanisms of methanol toxicity. 

The derived values are supported by the occupational exposure study of Kawai et al. (1991) 

(no effects more severe than dimmed vision (the authors suggested that visibility was 

temporarily reduced by fog in the workroom) and nasal irritation occupational exposure 

against up to 3000-5500 ppm during an 8-hour work shift) and by studies on monkeys 

(Andrews et al., 1987) (no toxic effects after repeated exposure to 5000 ppm for 6 

hours/day). 

In teratogenicity studies in mice, no fetal death was found after single or repeated exposure 

to 5000 ppm for 7 hours (measured blood methanol concentration was 2126 mg/l at the end 

of exposure) (Rogers et al., 1993; 1995; Rogers, 1999). This blood methanol concentration 

is about 11-fold higher than the blood methanol concentration of 185 mg/l, which was used 

to derive AEGL-3 values.