Transfer of Organochlorine Residues from Blubber through the Circulatory System to Milk in the Lactating Grey Seal Halichoerus grypus

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Abstract
Residues of the DDT group of insecticides and the polychlorinated biphenyls (PCBs) were measured in maternal blubber, milk, and blood or serum and in pup blubber and blood or serum of grey seals (Halichoerus grypus) from Sable Island, N.S. sampled in 1984 and 1985. DDT-group and PCB concentrations in blubber samples were lower in 1984 than in a sample of this population taken in the mid-1970's, but not lower than those in a sample taken in 1982. Concentrations in 1985 samples were slightly higher than those in the 1984 samples, for unknown reasons. On a lipid weight basis, residue concentrations in blood or serum were consistently about 50% of those in blubber lipid. The more highly chlorinated and therefore more lipid-soluble PCB components were transferred less efficiently from blubber to the circulatory system. Net transfer of residues from maternal blubber to maternal milk was about 70% efficient; this implies considerable degradation of circulatory lipid and resynthesis, probably to milk carbohydrates and other compounds. There was some selection against movement of especially the lower chlorinated PCB congeners from circulatory lipids into milk lipids, compared with transfer of the DDT group. Thus, a nonselective barrier exists to quantitative transfer of residues from blubber lipid to circulatory lipid, and a partially selective barrier exists against PCBs in the transfer of residues from circulatory to milk lipids; at least the latter barrier seems to involve lipid solubility.