The activities of 2,2',5,5'-tetrachlorobiphenyl, its 3,4-oxide metabolite, and 2,2',4,4'-tetrachlorobiphenyl in tumor induction and promotion assays.

Sensitive assays for the induction of lung adenomas in A/J mice or skin papillomas in SENCAR mice failed to show activity for either 2,2',5,5'-tetrachlorobiphenyl or 2,2',5,5'-tetrachlorobiphenyl 3,4-oxide. Injections of the 3,4-oxide into preweanling A/J mice caused considerable mortality, whereas the parent hydrocarbon did not. Both 2,2',5,5'- and 2,2',4,4'-tetrachlorobiphenyl showed promoting activity for hepatic gamma-glutamyl transpeptidase-positive foci initiated in rat liver by treatment with diethylnitrosamine. The promoting activity of 2,2',4,4'-tetrachlorobiphenyl was approximately 10-fold greater than that of the 2,2',5,5'-isomer.