Emergency and Continuous Exposure Guidance Levels for Selected Submarine Contaminants Volume 1 (2007) / Chapter Skim
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7 Methanol
7 Methanol
Pages 167-194
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From page 167... ...
, 24-h, and 90-day exposure guidance levels for methanol. The subcommittee's recommendations for methanol exposure levels are provided at the conclusion of this chapter along with a discussion of the adequacy of the data for defining those levels and the research needed to fill the remaining data gaps.
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97.8°C Melting point Flash point 12°C (closed cup) Explosive limits 6.0% to 36.5% Specific gravity 0.7915 at 20°C/4°C Vapor pressure 127 mmHg at 25°C Solubility Miscible with water, ethanol, ether, benzene, and most organic solvents 1 ppm = 1.31 mg/m3 ; 1 mg/m3 = 0.76 ppm Conversion factors a Data on vapor pressure are from HSDB (2004)
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From page 169... ...
depression, weakness, headache, vomiting, severe metabolic acidosis, optic disc edema, and bilateral necrosis of the putamen also occur in people during methanol intoxication. Other adverse effects of methanol exposure in humans include minor skin and eye irritation.
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. Other complications of severe acute methanol intoxication include coma, seizures, blindness, oliguric renal failure, cardiac failure, cerebral edema, cerebral or subarachnoid hemorrhage, and pulmonary edema (Davis et al.
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Many of those studies exposed healthy men of an age range comparable to that of submariners. Limitations inherent in each of those studies include small sample size, limited numbers of exposure concentrations, relatively short exposure durations, and an inability to completely mask the odor of methanol from subjects and the experimenters.
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(1992) exposed six healthy male volunteers (29-55 years of age)
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TABLE 7-2 Blood Methanol and Formate Concentrations Observed in Humans Following Experimental Methanol Exposures Methanol Plasma/Serum Methanol Plasma/serum formate Concentration Exposure Concentration (mg/L) a Concentration (mmol/L)
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. Because the study authors failed to report whether any symptoms were observed, this study could not be used to establish exposure guidance levels for methanol.
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One of the first studies was conducted by Tyson and Schoenberg (1914) who described about 100 cases of methanol intoxication resulting from occupational inhalation exposures.
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Like humans, monkeys exposed to methanol develop increased blood formate concentrations, metabolic acidosis, and blindness (Roe 1982; Tephly and McMartin 1984)
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for repeated methanol exposure in monkeys. Chronic Toxicity NEDO exposed female cynomolgus monkeys (eight per group)
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For example, stellate cells were no longer observed in monkeys 6 months after the end of a 20-day near-continuous exposure to methanol at 3,000 ppm. The NEDO report (1986)
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. The NTP panel concluded that "the blood levels of methanol associated with reproductive toxicity in rodents are 700 mg/L and greater.
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(2001) reported that methanol exposure was associated with increased incidence of oral mucosa micronuclei in fuel-pump operators in São Paulo, Brazil, after the introduction of a fuel composed of 33% methanol, 60% ethanol, and 7% gasoline.
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Formate is the metabolic product of methanol thought to be responsible for the acute toxic effects of methanol exposure (McMartin et al. 1980; Tephly and McMartin 1984)
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182 EEGLs and CEGLs for Selected Submarine Contaminants nonlinearity observed in the blood methanol concentrations suggested that methanol elimination proceeds by a saturable pathway and that monkeys demonstrate dose-dependent kinetics at exposure concentrations between 200 and 2,000 ppm. Although blood formate concentrations varied considerably among the individual monkeys, the authors were unable to detect any changes in total blood formate concentrations following 6-h methanol exposures at 200, 1,200, or 2,000 ppm.
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INHALATION EXPOSURE LEVELS FROM THE NRC AND OTHER ORGANIZATIONS A number of organizations have established or proposed inhalation exposure limits or guidelines for methanol. Selected values are summarized in Table 7-4.
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No value was proposed in 1985. Abbreviations: ACGIH, American Conference of Governmental Industrial Hygienists; AEGL, acute exposure guideline level; CEGL, continuous exposure guidance level; EEGL, emergency exposure guidance level; h, hour; NAC, National Advisory Committee; NASA, National Aeronautics and Space Administration; NIOSH, National Institute for Occupational Safety and Health; NRC, National Research Council; OSHA, Occupational Safety and Health Administration; PEL, permissible exposure limit; ppm, parts per million; REL, recommended exposure limit; SMAC, spacecraft maximum allowable concentration; STEL, short-term exposure limit; TLV, Threshold Limit Value; TWA, time-weighted average.
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From page 185... ...
(1999a,b; 2004a,b) in cynomolgus monkeys failed to produce any evidence of visual toxicity or narcosis in monkeys exposed to methanol at 1,800 ppm for 2.5 h per day, 7 days per week through an initial 4-month exposure period, during breeding, and throughout pregnancy.
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From page 186... ...
U.S. Navy Values NRC Recommended Exposure Level Current Proposed Values EEGL 1h 200 200 600 24 h 10 10 50 CEGL 90 days 10 7 10 Abbreviations: CEGL, continuous exposure guidance levels; EEGL, emergency exposure guidance level; h, hour; NRC, National Research Council; ppm, parts per million.
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. However, even susceptible people would not be expected to develop blood methanol concentrations high enough to result in neurotoxicity following exposure at the recommended 24-h EEGL of 50 ppm.
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of about 48 mg/kg/h. The hourly rate at which an individual would metabolize methanol is greater than the anticipated rate of intake from inhalation exposures at 10 ppm.
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REFERENCES ACGIH (American Conference of Governmental Industrial Hygienists)
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2004. Acute Exposure Guideline Levels (AEGLs)
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191 Methanol [Online]
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1992. Lack of blood formate accumulation in humans following exposure to methanol vapor at the current permissible exposure limit of 200 ppm.
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Pp. 69-81 in Emergency and Continuous Exposure Guidance Levels for Selected Airborne Contaminants, Vol.
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194 EEGLs and CEGLs for Selected Submarine Contaminants Tephly, T.R., and K.E. McMartin.
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