Distribution and kinetics of PBB residues in cattle.

Cows fed a constant amount of polybrominated biphenyl (PBB) reached a steady-state concentration in milk fat within 30 days. This concentration was approximately four times the concentration in the total diet. When feeding of PBB was stopped, the concentration in milk was adequately described as a sum of two first-order elimination rates. Biological half-life in environmentally contaminated cows, studied for 6 months about a year after contamination, was 60 days. The stage of lactation affected the rate of elimination, and in some concentrations increased shortly after calving. Residues were distributed in body tissues proportionally to concentration of fat in the tissues. Liver and brain were exceptions. Concentration in liver fat was generally higher than other tissues and possibly related to the treatment of some cows with phenobarbital. Residues in brain fat were significantly lower than all other tissues. The ratio of the concentrations in milk fat to concentration of residues in the blood of calves and fat of fetal tissues to the concentration in the corresponding tissue in the dams was 0.36:1. It was estimated that people consuming milk from the highly contaminated Michigan cows could have received PBB doses as great as 10 g from this source alone.