Excretion of hydroxylated polychlorinated biphenyl metabolites in cows' milk

Four lactating Holstein cows were each given a single oral dose of either 0.5 g 2,5,2',5'-tetrachlorobiphenyl, 0.5 g 2,5,2',4',5'-pentachlorobiphenyl, 1.5 g Aroclor 1242, or 1.5 g Aroclor 1254 in gelatin capsules. Milk samples were collected twice daily at the am and pm milkings and were analyzed for polychlorinated biphenyl (PCB) metabolites and PCBs. Excretion of metabolites in the milk paralleled excretion of the parent PCBs, with maximum amounts eliminated 1 day after dosing. Less than 0.06% of the initial doses of the 2 single components appeared as metabolites in milk over a period of 10 days. Most of the metabolites occurred as conjugates. Only the 4-hydroxy metabolites were found in the milk of cows given single components. Milk samples from cows given Aroclor 1242 or Aroclor 1254 contained 10 and 4 monohydroxy metabolites, respectively. Using the same methodology, no monohydroxy metabolites were detected in whole milk samples from herds accidentally contaminated with a polybrominated biphenyl mixture.