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 mu g of two structurally distinct PCB congeners (C-14-2,2',4,4'-tetraCB o r C-14-3,3',4,4'tetraCB). Total radioactivity in the acetone rinse of intac t flies, several tissues, and excrement was determined at II time points ov er a 48-h period. Ninety-seven percent of the applied 2,2',4,4'- tetraCB di sappeared from the surface following an initial rapid absorption of 79% wit hin 3 h. The absorbed 2,2',4,4'-tetraCB was immediately found within the th oracic 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 in to the tissues. Toxicities of the sublethal doses were determined by monito ring changes in activity of houseflies following dosing with 0.5 mu g of ra dioactive PCBs. Flies treated with 2,2',5-triCB and 3,3',4,4'-tetraCB remai ned very active, whereas 2,2',4,4'-tetraCB-treated flies mere less active, consistent with the previously reported toxicity of this congener. (C) 1999 Academic Press.