Methanol monitoring. Comparison of urinary methanol concentration with formic acid excretion rate as a measure of occupational exposure.

Methods of monitoring occupational exposure to methanol were investigated in volunteer subjects who had ingested small amounts of methanol. It was confirmed that urinary methanol concentrations accurately reflected those in the blood. This relationship was maintained over a considerable range of concentrations in spite of large variations of urine flow. Concomitant ingestion of ethanolic beverages increased the urinary methanol concentration slightly. Urinary formic acid concentration was too variable to be of value but rate of urinary excretion of formic acid did reflect methanol uptake. The ratio of urinary formic acid to creatinine concentrations (F/C ratio) is a practical monitoring method. However, formic acid elimination rate is reduced by ingestion of ethanolic beverages. Urinary methanol concentration is favoured as a method of monitoring and a concentration of 10 microgram/ml measured at the end of the work shift is suggested as the level above which occupational exposure should be suspected and the appropriate action taken.