TOXICITY OF PCB-77 (3,3',4,4'-TETRACHLOROBIPHENYL) AND PCB-118 (2,3',4,4',5-PENTACHLOROBIPHENYL) IN THE RAT FOLLOWING SUBCHRONIC DIETARY EXPOSURE

The toxicity of 3,3',4,4'-tetrachlorobiphenyl (PCB 77) and 2,3',4,4',5 -pentachlorobiphenyl (PCB 118) was investigated in rats following subc hronic dietary exposure. Groups of 10 male and 10 female weanling Spra gue-Dawley rats were administered PCB 77 in the diet at 0, 10, 100, 10 00, or 10,000 ppb for 13 weeks. PCB 118 was administered to males in t he diet at 0, 10, 100, 1000, and 10,000 ppb, while the female groups r eceived 0, 2, 20, 200, or 2000 ppb of the congener for 13 weeks. Growt h rate and food consumption were not affected by treatment. No clinica l signs of toxicity were observed. Increased spleen weight occurred in male rats fed 1000 or 10,000 ppb PCB 77. Male rats receiving 10,000 p pb PCB 118 had increased liver weight and hepatic ethoxyresorufin O-de ethylase (EROD) activity. Increased hepatic EROD activity but not live r weight was observed in female rats given the 2000-ppb PCB 118 diet. Increased EROD activity was also noted in male rats given 10,000 ppb a nd in female groups receiving 1000 or 10,000 ppb PCB 77. Male rats exp osed to 10,000 ppb PCB 77 had decreased vitamin A in the liver and lun g and elevated levels in the kidney. Liver vitamin A of both 1000- and 10,000-ppb PCB 77 female groups was decreased. PCB 118 had no effects on tissue vitamin A at the levels studied. No hematological changes o r serum biochemical changes were seen in any of PCB 118- and PCB 77-tr eated groups, nor were liver uroporphyrin levels altered. A reduction in dopamine and homovanillinic acid in the substantia nigra region of the brain was observed in female rats fed 2000 ppb PCB 118, while 10,0 00 ppb PCB 77 was associated with an elevation in 3,4-dihydroxyphenyla cetic acid in the nucleus accumbens region of male rat brains. Mild to moderate changes were observed in the liver and thyroid of rats given PCB 77 or PCB 118. PCB 118 accumulated in a dose-dependent manner in fat and to a much lesser extent in liver. In contrast, very tow levels of PCB 77 residue were found in the tissues examined. Based on the ab ove data it was concluded that the NOAEL of PCB 77 is 100 ppb in diet or 8.7 mu g/kg and that of PCB 118 is 200 ppb in diet or 17 mu g/kg bo dy wt/day.