Overview

Evaluates the risks to human health and the environment posed by exposure to methanol. Although methanol occurs naturally in humans, animals, and plants, anthropogenic sources are far more significant. Methanol is produced in large amounts in many countries and is extensively used as an industrial solvent, a chemical intermediate, mainly in the production of methyl tertiary butyl ether, formaldehyde, acetic acid, and glycol ethers, as a denaturant of ethanol, and in a variety of consumer products. Products containing methanol include paints, shellacs, varnishes, mixed solvents in duplicating machines, antifreeze and gasoline deicers, windshield washer fluids, cleansing solutions, and model and hobby glues and adhesives. The general population is routinely exposed to low levels from metabolic processes and from such dietary sources as fruits, vegetables, fruit juices, and foods and soft-drinks containing the synthetic sweetener aspartame. The most notorious use of methanol is as an adulterant in alcoholic beverages, which has led to large-scale episodes of poisoning and numerous fatalities. A review of data on environmental levels and human exposure notes that most emissions to the environment arise from the production and use of methanol as a solvent in industrial processes and, to a lesser extent, from a variety of other industrial processes and consumer applications. Concerning the behavior of methanol in the environment, the report cites abundant evidence that the compound is readily and rapidly degraded in a wide variety of environmental media, and has low bioconcentration and low toxicity. Evidence supports the conclusion that methanol is unlikely to have adverse effects on the environment except in the case of accidental spills. The report also draws attention to the potential large increase in environmental levels associated with the use of methanol as a replacement for gasoline and its predicted role as a major automotive fuel in the next century. A section on kinetics and metabolism in laboratory animals and humans concludes that inhalation and ingestion are the primary routes of methanol exposure, with dermal exposure currently of much less importance in terms of total daily intake for both the general population and exposed workers. Studies indicate that methanol is readily absorbed by all three routes and widely and rapidly distributed to tissues according to the distribution of body water. A review of findings from animal studies and in vitro test systems notes the great variation in acute and short-term toxicity observed in different species, with toxicity highest in species, such as humans and non-human primates, characterized by a poor ability to metabolize formate. Studies show that exposure to methanol induces a wide range of concentration-dependent teratogenic and embryolethal effects. Although no evidence from animal studies indicates that methanol is a carcinogen, the report notes the absence of an appropriate animal model for carcinogenicity assessment. The evaluation of effects on human health draws on numerous reports of acute exposure following deliberate or accidental ingestion of adulterated alcoholic beverages. The clinical features of acute methanol poisoning are identified as transient central nervous system depression, followed by an asymptomatic latent period culminating in metabolic acidosis, severe ocular toxicity, blindness, coma, and death. Although data on the health effects of chronic exposure are limited, the report cites evidence of visual disturbances observed in workers exposed to high concentrations of methanol vapors. The report found no evidence of carcinogenic, genotoxic, reproductive, or developmental effects in humans attributed to methanol exposure.

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