Toxicity and Tissue Distribution of 2,2′,4,4′- and 3,3′,4,4′-Tetrachlorobiphenyls in Houseflies

Insects selectively retain different polychlorinated biphenyls (PCBs) which are then contributed to the food chain. To quantitate specific differences, adult female houseflies (Musca domestica L.) were topically dosed with 0.5 μg of two structurally distinct PCB congeners (14C-2,2′,4,4′-tetraCB or14C-3,3′,4,4′-tetraCB). Total radioactivity in the acetone rinse of intact flies, several tissues, and excrement was determined at 11 time points over a 48-h period. Ninety-seven percent of the applied 2,2′,4,4′-tetraCB disappeared from the surface following an initial rapid absorption of 79% within 3 h. The absorbed 2,2′,4,4′-tetraCB was immediately found within the thoracic cuticle, then spreading laterally to the abdominal cuticle and head, through the wax layers, or penetrating to the alimentary canal and ovaries. Penetration of 3,3′,4,4′-tetraCB was markedly slower; even though 87% of the applied dose was absorbed within 48 h, only 19% of the dose penetrated into the fly body within the first 3 h. This PCB very slowly distributed into the tissues. Toxicities of the sublethal doses were determined by monitoring changes in activity of houseflies following dosing with 0.5 μg of radioactive PCBs. Flies treated with 2,2′,5-triCB and 3,3′,4,4′-tetraCB remained very active, whereas 2,2′,4,4′-tetraCB-treated flies were less active, consistent with the previously reported toxicity of this congener.