TOXICITY OF 2,2',4,4',5,5'-HEXACHLOROBIPHENYL IN RATS - EFFECTS FOLLOWING 90-DAY ORAL-EXPOSURE

The subchronic toxicity of 2,2',4,4',5,5'-hexachlorobiphenyl (PCB 153) was investigated in rats after 13 weeks of dietary exposure. Groups o f 10 male and 10 female rats were administered PCB 153 in their diet a t levels of 0.05, 0.50, 5.0 or 50 ppm for 13 weeks. The control groups received the diet containing 4% corn oil. Growth rate and dietary con sumption were not affected by treatment. Clinical signs of toxicity we re not observed. Enlarged, fatty liver was observed in treated animals at necropsy, but most were confined to the two highest dose groups. I ncreased hepatic microsomal ethoxyresorufin-O-deethylase, aminopyrine- N-demethylase and aniline hydroxylase activities occurred in high-dose groups of both sexes, with increased ethoxyresorufin-O-deethylase act ivity being observed starting at 0.05 ppm in females and at 0.5 ppm in males. Treatment-related reduction in hepatic and pulmonary vitamin A was seen in the highest dose group of both sexes. Changes in brain bi ogenic amines and intermediate products were observed mainly in female s; these included decreased dopamine and 5-hydroxytryptamine concentra tions in the frontal cortex region, and dihydroxyphenylacetic acid in the caudate nucleus region at 5.0 and 50 ppm. Female rats appeared to be more sensitive to the neurotoxic effects of PCB 153 than males. Dos e-dependent histological changes were observed in the thyroid and live r of rats of both sexes and significant changes occurred at 5.0 and 50 ppm. Based on these data, the no-observable-adverse-effect level (NOA EL) of PCB 153 was judged to be 0.5 ppm in the diet or 34 mu g kg(-1) body wt. day(-1).