Kinetics and metabolism of inhaled methyl chloroform (1,1,1-trichloroethane) in male volunteers.

The kinetics of inhaled methyl chloroform (MC) and its principal metabolites, trichloroethanol (TCE) and trichloroacetic acid (TCA), were defined in six healthy male volunteers following single 6-hr exposures of 350 and 35 ppm. Blood and expired air MC concentrations were proportional to the exposure concentration and indicated that about 25% of the MC inhaled during the 6-hr exposure was absorbed. Elimination of MC was triexponential with half-lives estimated as 44 min, 5.7 hr, and 53 hr for the initial, intermediate, and terminal phases. Over 91% of the absorbed MC was excreted unchanged via the lungs, 5-6% was metabolized and excreted as TCE and TCA, and less than 1% remained in the body after 9 days. Urinary TCE and TCA excretion was extremely variable and indicated that urinary TCE and TCA measurements provide at best only a rough estimate of the exposure. These data suggest that the kinetics of MC in man are essentially first order at or below the current TLV of 350 ppm. Based on a comparison of the blood MC levels and amounts of MC metabolized, the rat is a better model than the mouse to predict the toxicity of MC in man.