Short-term study of the combined effects of mirex, photomirex, and kepone with halogenated biphenyls in rats.

The combined effects of polychlorinated biphenyls (PCBs) or a polybrominated biphenyl (PBB) with mirex, kepone, or photomirex were investigated in rats. Groups of 10 animals were fed diets containing the organohalogens alone or in various combinations for 28 d. Body weight gain and food consumption were not affected by any treatment. Liver weight was increased in the group fed Aroclor 1260/photomirex and in all groups receiving PBB. Hepatic microsomal enzyme activities were elevated in the groups treated with halogenated biphenyls alone; this effect was not potentiated in the presence of mirex-related compounds. Serum biochemical parameters were, for the most part, normal. Hematology tests revealed no abnormalities. Histological changes occurred in the liver, thyroid, and kidney of rats treated with the organohalogens alone or in combination. Liver alterations consisted of central lobular cytoplasmic enlargement, exaggerated periportal perinuclear halos, and increased nuclear hyperchromicity and anisokaryosis. Fatty degeneration was observed in all treated groups. Thyroid changes were characterized by a generalized reduction in follicular size and colloid density with collapse of the follicles. Kidneys suffered mild eosinophilic cytoplasmic inclusions in the proximal convoluted tubule and focal lymphoid aggregates. Histological changes due to PCBs and PBB were aggravated by mirex and related compounds. The degree of damage appeared to be additive rather than potentiative. Mirex and photomirex levels in livers of rats concomitantly exposed to halogenated biphenyls were four to six times higher than those in rats fed mirex-related compounds alone. However, the toxic response in this organ was not potentiated as a result of the increased accumulation. It was concluded that mirex-related compounds at the dose levels studied did not potentiate the effects produced by halogenated biphenyls and vice versa.