Bioavailability of grain and soil-borne tritiated 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) administered to lactating Holstein cows

Holstein dairy cows weighing from 488 to 650 kg were given tritiated 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) on crushed grain or Gerald silt loam soil as a single oral dose of 0.05 ug/kg body weight. The cows were killed 14 days posttreatment. In both the grain- and soil-treated animals, tissue residues were highest in the fat, followed by liver, kidney, muscle and brain. Secretion of radioactivity into milk was highest during the first 3-4 days posttreatment with only small quantities being secreted into the milk during the following 10 days. Hepatic aryl hydrocarbon hydroxylase and ethoxyresorufin O-deethylase appeared to be slightly elevated 14 days after treatment with either grain or soil-borne TCDD. The aryl hydrocarbon (Ah) receptor was not detected using the hydroxylapatite assay procedure.