Absorption

Methanol is absorbed by all routes. Inhalation and dermal absorption are the main routes of exposure in the occupational setting. In a study of 33 methanol exposed workers, the amount of methanol absorbed by inhalation correlated with the vapour concentration and the duration of exposure. The rate of absorption of inhaled methanol in this group was calculated as 173.5 ng/ppm/hour, or 0.1735 mg methanol after 15 minutes exposure at 4,000 ppm (Kawai et al., 1991). Approximately 58% of the inhaled dose of methanol is retained by the lungs (Sedivec et al., 1981).

The rate of dermal absorption in volunteers was found to be 0.192 mg/cm2/min. Exposure of one hand to liquid methanol for only 2 minutes could lead to the absorption of as much methanol (170 mg) as would be taken up by the lungs from an 8 hour exposure to the maximum allowable concentration (MAC) of 50 mg/m3 (38 ppm) (Dutkiewicz et al., 1980).

On ingestion, peak methanol concentrations are seen at 30-60 minutes. Initial symptoms occur at 30 minutes to 2 hours post ingestion or inhalation. The onset of clinical effects may be delayed for several hours following dermal exposure (Downie et al., 1992).

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