Congener-specific exposure of grey seals (Halichoerus grypus) pups to chlorinated biphenyls during lactation

We determined total and daily exposure of young grey seals (Halichoerus grypus) to 25 chlorinated biphenyl (CB) congeners in their mothers' milk at the Isle of May, Scotland, in 1990, 1991, and 1992. Total exposure for 36 pups born to 13 different females varied between 8.8 and 58.9 mg, IUPAC congeners CB-153 and CB-138 were the dominant components in milk, accounting for 42.1% of total CB exposure. The quantity of milk consumed by pups each day and the lipid content of that milk increased during lactation. As a result, daily exposure to CBs increased sharply in the first half of the 18-day lactation period. There were significant among-female differences in milk CB concentrations and in the relative contribution of individual congeners to total CB exposure. When the effects of among-female variation were removed, there were significant changes in concentrations of less chlorinated CBs during lactation and among years. A grey seal pup's exposure to CBs can be accurately estimated from its mother's identity, its mass at weaning, and the CB concentration in a single milk sample taken towards the end of lactation.