Elimination

Approximately 80-100% of absorbed tetrachloroethylene is excreted unchanged by the lungs (Monster et al., 1979). Elimination is slow. In a volunteer study more than two weeks was required to eliminate tetrachloroethylene after 8 hours of exposure to 100 ppm (Fernandez et al., 1976). The respiratory and urinary half-lives of tetrachloroethylene are 65 hours and 144 hours, respectively (Ikeda, 1977). The urinary concentration of tetrachloroethylene correlates with the exposure concentration (Imbriani et al., 1988). Tetrachloroethylene can be detected in breath days after cessation of exposure (Stewart et al., 1961a; 1961b; Stewart et al., 1970).

Elimination of tetrachloroethylene from the blood after ingestion of 545-727 mg/kg (total 8-10 ml) in a 6 year old child was biphasic, with half-lives of 30 minutes and 36 hours during hyperventilation therapy. This treatment reduced the rapid elimination phase from 160 to 30 minutes but the slow phase was unchanged (Koppel et al., 1985).

Only about 1% of absorbed tetrachloroethylene is excreted as trichloroacetic acid in the urine. The half-life of this metabolite in urine and blood is 65-90 hours (Monster et al., 1979; Monster et al., 1983). In the work by Ikeda (1977) the half-life of the total trichloro compound metabolites was 123 hours in six male (30-100 ppm, 8 hours/day, 5 days/week) and 190 hours in six female workers (10-20 ppm, 8 hours/day, 5 days/week). Although this extreme difference was questioned, it probably reflects the larger proportion of body fat in females. The urinary concentration of total trichloro compounds does not reflect the exposure concentration (Ikeda et al., 1972). A plateaux metabolite concentration is reached at tetrachloroethylene concentrations well below 100 ppm (Ikeda et al., 1972; Ikeda, 1977).

Tetrachloroethylene is excreted in breast milk. A mother who was exposed to tetrachloroethylene during lunchtime visits to her husband at work, had a blood tetrachloroethylene concentration of 3 mg/l about 2 hours later. The concentration of tetrachloroethylene in breast milk about 1 hour after a visit was 10 mg/l; 24 hours later it was 3 mg/l. No metabolites were detected in the mother's urine (Bagnell and Ellenberger, 1977). Preferential uptake of lipophilic compounds such as tetrachloroethylene into breast milk occurs because it is high in fat.

There is accumulation of tetrachloroethylene in fatty tissues with prolonged exposure because of slow elimination. In subjects exposed to 100 ppm for 7 hours on 5 consecutive days, those with a greater body mass had higher alveolar concentrations of tetrachloroethylene in the post exposure period. The difference was more pronounced at 300 hours than 100 hours after exposure (Stewart et al., 1970). In a study of workers exposed to tetrachloroethylene the decrease in blood and breath concentrations over a weekend of non-exposure was more pronounced in slim subjects than in those who were obese (Monster et al., 1983). The cumulative behaviour of tetrachloroethylene has been confirmed with mathematical modelling (Guberan and Fernandez, 1974).

In experimental animals, elimination of tetrachloroethylene is primarily thorough the lungs (Daniel, 1963). In some cases a greater proportion of absorbed tetrachloroethylene is metabolised compared to humans (Yllner, 1961; Pegg et al., 1979; Schumann et al., 1980). This is probably a dose dependent effect.

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