TOXICOLOGY AND CARCINOGENESIS STUDIES OF 3,3',4,4',5-PENTACHLOROBIPHENYL (PCB 126) (CAS NO. 57465-28-8) IN FEMALE HARLAN SPRAGUE-DAWLEY RATS (GAVAGE STUDIES)

Background 3,3N4,4N5-Pentachlorobiphenyl (PCB 126) is one of a large family of hydrocarbons containing chlorine (PCBs) that are similar in structure to dioxins. Some dioxins or dioxin-like compounds are highly toxic and cause cancer, and usually contaminated sites contain many different varieties of these dioxin-like compounds. The National Toxicology Program conducted a series of studies to try to gauge the relative toxicity of some of the more prevalent of these compounds both alone and in mixtures. This study evaluated the effects of PCB 126 on female rats for comparison with the potency of other chemicals in that family. Methods We exposed groups of 50 female rats by depositing solutions of PCB dissolved in corn oil through a tube directly into their stomachs five days a week for two years. Daily doses of PCB 126 were 30, 100, 175, 300, 550, or 1,000 nanograms (ng) per kilogram of body weight. Tissues from more than forty sites were examined for every animal. Results Exposure to PCB 126 caused a variety of diseases in several organs. Cancers of the liver, lung, and mouth were seen in female rats exposed to PCB 126. A variety of other toxic lesions observed in exposed animals included hypertrophy, hyperplasia, and fibrosis of the liver, metaplasia of the lung, atrophy of the adrenal gland, inflammation and atrophy of the pancreas, kidney nephropathy, cardiomyopathy of the heart, hypertrophy of the adrenal gland, atrophy of the thymus and spleen, and inflammation of the mesentery. Conclusions We conclude that PCB 126 caused cancer and other toxic effects at several sites in female rats.