Distribution and clearance of polybrominated biphenyls in cows and calves.

The distribution and clearance of polybrominated biphenyls were determined in two cows and a calf fed polybrominated biphenyls by boluses, by placental transport to a calf from a contaminated dam, and to another calf via milk from the contaminated dam. Feces were an important route of excretion of polybrominated biphenyls during exposure and the period when the contaminated feed was cleared from the digestive tract. Approximately 50% of single intraruminal doses of these hydrocarbons were cleared by 168 h. Free polybrominated biphenyls in urine could not be quantitated. However, 24% of carbon-14 from tetrachlorobiphenyl was recovered, suggesting that significant quantities of halogenated biphenyl may be excreted in urine. Milk was also an important excretion route with one cow excreting 23% of the polybrominated biphenyl dose in 168 days. Concentrations of polybrominated biphenyls in the fat of most tissues were similar, with higher concentrations in liver and lower in the nervous system. Gross or histopathologic lesions of tissues collected at necropsy could not be related specifically to polybrominated biphenyl toxicity.