Biomedical Engineering Reference
In-Depth Information
Methanol is readily absorbed through the skin. A worker who had
methanol spilled over his legs and did not change his shoes or clothes
went blind the next day. After 7 months only transient improvement was
noted (MAK, 1991). In another case of dermal exposure, metabolic
acidosis was reported in a man, who cleaned a tank with methanol. He
wore a positive pressure breathing apparatus, but no protective clothing.
He did not change his methanol-saturated clothing for another hour
after finishing the job. It was concluded that dermal exposure from
clothing was responsible for his acidosis (Downie et al., 1992).
The odor threshold has been reported to be 1500-2000 ppm (Scher-
berger et al., 1958) while May (1966) reports a higher odor threshold
(5900 ppm). In any case, the odor threshold of methanol is much higher
than the workplace exposure standard of 200 ppm; and the odor will not
warn the individual of exposure until it is much higher than the
workplace exposure standard.
The workplace standard, established more than 50 years ago, of
200 ppm appears to be adequate to protect the worker from the effects
of airborne methanol for 8 hours work day (MAK, 1958; ACGIH, 1959).
3.3 METABOLISM IN HUMANS
3.3.1 Normal
In humans, methanol is readily absorbed into the body by all routes of
exposure. Because, it is water-soluble methanol is found in tissues in
direct relation to the tissue water content. Methanol is metabolized to
formaldehyde by ADH in humans. Formaldehyde is then broken down
to formic acid and then to formate and hydrogen ion by NAD formal-
dehyde dehydrogenase. Formate forms a complex with terahydrofolate
(from dietary folic acid), which is the broken down by formic acid
dehydrogenase to carbon dioxide and water. At low levels of methanol,
such as what is found in the diet, the breakdown of methanol in humans
is rapid and complete (Kavet and Nauss, 1990). See Chapter 7 for more
details.
Low levels of methanol are normally found in the saliva, blood, and
expired breath in normal individuals, not occupational exposed (Eriksen
