Ingestion of soil contaminated with 2,3,7,8-tetrachlorodibenzo- p-dioxin (TCDD) alters hepatic enzyme activities in rats

Abstract

Female rats were treated with 2,3,7,8-tetrachlorodibenzo- p-dioxin (TCDD) in either corn oil or contaminated soil from the Minker site in Missouri. Eight doses ranging from 0.015 to 5 μg TCDD/kg were used in the corn oil group; the range was 0.015 to 5.5 μg TCDD/kg in the TCDD-contaminated soil group. Rats in a third group were given equal amounts of soil uncontaminated with TCDD. No acute toxicity or effects on body weight gain were observed at these doses. In general, equivalent doses of TCDD in corn oil or TCDD in soil produced similar increases in hepatic aryl hydrocarbon hydroxylase activity (AHH) and UDP glucuronyltransferase activity although effects were slightly greater in the TCDD-corn oil groups. In the corn oil groups, the induction of AHH ranged from about 30-fold at the highest dose to twofold at the lowest dose studied. TCDD also caused an increase in cytochrome P-450 concentration and a shift in spectral peak from 450 to 448 nm. There was no effect of TCDD on ethylmorphine N-demethylase, consistent with previous reports. Liver concentrations of TCDD (mean ± SD) in the 5-μg/kg groups were 40.8 ± 6.3 ppb in the TCDD-corn oil group and 20.3 ± 12.9 ppb in the TCDD-contaminated soil group. Our results suggest that the bioavailability of TCDD in soil in rats is approximately 50%. Therefore, ingestional exposure to TCDD-contaminated soil may constitute a significant health hazard in view of its extremely high toxicity and relatively high bioavailability.