Toxicity reference values for the toxic effects of polychlorinated biphenyls to aquatic mammals

Threshold tissue residue concentrations of polychlorinated biphenyls (PCBs) and 2,3,7,8-tetrachlorodibenzo-pdioxin equivalents (TEQs) were derived from the published results of semi-field (i.e., field collected food items were used as a medium of exposure to PCBs in laboratory reared animals) or field toxicity studies conducted with seals, European otters and mink. Based on biomagnification factors (BMFs) and concentrations of PCBs or TEQs measured in fish fed in the diet of experimental aquatic mammals, dietary threshold concentrations were estimated. Hepatic vitamin A, thyroid hormone concentration, suppression of natural killer (NK) cell activity and proliferative response of lymphocytes to mitogens were the toxicity endpoints measured in aquatic mammals. Threshold concentrations for PCBs or TEQs in livers of aquatic mammals to elicit the physiological effects ranged from 6.6 to 11 mu g PCBs/g (geometric mean: 8.7 mu g/g) and 160 to 1400 pg TEQs/g (geometric mean: 520 pg/g), lipid weight, respectively. The BMFs for PCBs and TEQs varied depending on the marine mammal species, and therefore the dietary threshold concentrations could be referred only by a range of values (rather than a mean value), which were 10 to 150 ng PCBs/g and 1.4 to 1.9 pg TEQs/g, wet weight, for PCBs and TEQs, respectively.