1,1,1‐trichloroethane (methyl chloroform) in urine as biological index of exposure

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Abstract
Fifteen human volunteers were exposed to 1,1,1‐trichloroethane (methyl chloroform) vapor at 72–495 mg/m3 for a period of 2 to 4 hours at rest (ten cases) and during light physical exercise (five cases). Subsequently 60 workers occupationally exposed to 1,1,1‐trichloroethane in a refrigerator manufacturing plant were studied (median value: 178 mg/m3; geometrical standard deviation: 2.19 mg/m3). As expected, the relative uptake (R) of 1,1,1‐trichloroethane decreased in the course of exposure at rest (R = 0.44 after 20 minutes of exposure; R = 0.26 after 240 minutes of exposure). Both in the experimentally exposed subjects and in the occupationally exposed workers, the urinary concentration of 1,1,1‐trichloroethane showed a linear relationship to the corresponding environmental time‐weighted average concentration. The correlation coefficients (r) were 0.95 in occupationally exposed subjects and more than 0.90 in experimentally exposed groups. A linear equation also existed between urinary concentration and amount of 1,1,1‐trichloroethane absorbed (r = 0.88). The findings indicate that the urinary concentration of 1,1,1‐trichloroethane can be used as an appropriate biological exposure indicator. In occupationally exposed subjects performing moderate work, the urinary 1,1,1‐trichloroethane concentration corresponding to the time‐weighted average of the threshold limit value was found to be 860 μg/L and its 95% lower confidence limit (biological threshold) 805 μg/L.