Metabolism

1,1,1-TCE is mainly (90%) excreted unchanged through the lungs (Nolan et al., 1984). Small amounts of 1,1,1-TCE are slowly metabolised by oxidation to trichloroethanol, which is conjugated with glucuronic acid before excretion in the urine. This accounts for only about 2% of an absorbed dose. Trichloroethanol is further oxidised to form trichloroacetic acid and this is also found in the urine to the extent of about 1.5% of a dose (Monster et al., 1979). Simultaneous exposure to other solvents tends to increase the retention and decrease the metabolism of 1,1,1-TCE (Savolainen et al., 1981).

Toxicology of Solvents Elimination

Regardless of the route of absorption, exhalation via the lungs is the main excretory route for 1,1,1-TCE. Studies with human volunteers show that over 90% of the absorbed 1,1,1-TCE is excreted unchanged in expired air. Initial excretion is fairly rapid with 70% reduction of the concentration in expired air within two hours (Monster et al., 1977), but this is followed by slower elimination, with small amounts being detected in the breath for up to several days post-exposure. Only minor quantities (5-6%) of the absorbed solvent are excreted in the urine (as trichloroethanol glucuronide and trichloroacetic acid) (Monster et al., 1979). Less than 1% of an absorbed dose remained in the body after nine days (Nolan et al., 1984). Between 60% to 80% of an absorbed dose is exhaled within one week, however traces may found in the post exposure expired breath for as long as one month (Baselt, 2000).

At, or below, the TLV of 350 ppm, elimination (in expired air) was reported to be tri-exponential with an initial phase of 44 minutes, intermediate phase 5-7 hours and terminal phase 53 hours. The half-lives of the metabolites in urine were 13 hours for 2,2,2-trichloroethanol, and 51 hours for trichloroacetic acid. Urinary excretion of the two metabolites is very variable and provides only a rough estimate of exposure (Nolan et al., 1984).

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