The ACGIH biological exposure index for methanol is an end of shift urinary methanol concentration of 15 mg/l. Methanol may be present in the urine of individuals who have not been exposed and this may affect interpretation. Such background concentrations are incorporated in the BEI value (ACGIH, 2000).

Methanol is produced from the distillation of wood and it is sometimes referred to as wood alcohol or wood naphtha. It is a colourless liquid with an alcoholic odour when pure. Crude methanol may have an unpleasant pungent odour. Methanol is used extensively as a solvent, chemical intermediate, in the production of glycol ethers, and in the manufacture of charcoal. It is also widely available in windshield washing and de-icing products, as well as in antifreeze and model engine fuels. The majority of toxic exposures to methanol have occurred following intentional ingestion. Inhalation and dermal absorption are the main routes of exposure in the occupational setting.

The degree of toxicity following exposure to methanol is related to many factors including the amount of methanol ingested, the extent of folate deficiency, the activity of alcohol dehydrogenase (ADH) and concurrent ingestion of ethanol. Severe intoxication can lead to metabolic acidosis, coma, convulsions and respiratory arrest. It also causes visual and neurological effects that may be permanent (McLean et al., 1980; Anderson et al., 1987).

The toxic dose of methanol reported in the literature varies widely. Bennett et al. (1953) reported an outbreak of 323 cases of methanol poisoning due to adulterated 'moonshine'. The lowest fatal dose was 15 ml of 40% methanol, however, in this outbreak survival was reported following ingestion of approximately 500 ml of methanol. In an outbreak in Papua New Guinea similar disparity between the ingested dose and the severity of the outcome was observed. Blindness and death followed consumption of 100 ml of methanol, while ingestion of 500 ml produced no apparent disability (Scrimgeour, 1980).

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