Toxicokinetics of 2,2′,5-Trichlorobiphenyl in House Flies Following Topical Administration

Abstract Adult female house flies ( Musca domestica L.) were dosed topically with 10-, 15-, and 20-μg doses of [2,2′ ,5- 14 C]trichlorobiphenyl in acetone, chosen to bracket the narrow range wherein a dramatic increase in toxicity was observed in previous studies. Total radioactivity in acetone rinses of flies, extracts of flies, extracts of excrement, and unextractable fly tissues and/or excrement were determined at eight time points over a 50-hr period to develop a toxicokinetic model. About 90% of a topical PCB dose was absorbed from the surface of the integument in 12 hr, apparently by simultaneous rapid and slow absorption processes. A small fraction of the absorbed dose was irreversibly bound to fly tissues and the majority of the remaining dose was excreted by 50 hr. Although polar metabolites were measured in all extracts, individual rate constants of elimination for parent PCB and metabolites could not be determined. Biotransformation enzymes apparently became saturated between the 10- and 15-μg doses which may account for the previously observed increase in toxicity within this narrow dose range. Extensive metabolism of the lower dose (more closely related to environmental exposure) suggests that the large biomass of insects may contribute to conversion of environmental PCBs to more polar metabolites.