Specimc polychlorinated biphenyl congener distribution in breast milk of Canadian women

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Abstract
A total of 412 breast milk samples from across Canada were analyzed for selected polychlorinated biphenyl congeners. The median level for those congeners present in more than 80% of the samples ranged from 0.11–0.87 ng/g whole milk. Of these the most predominant (>5% of total polychlorinated biphenyls) congeners were: the 2,4,4’,5‐tetra‐, 2,2’,4,4’,5‐ and 2,3’,4,4'5‐penta‐, 2,2’,3,4,4’,5'‐ and 2,2’,4,4’,5,5'‐ hexa‐ and 2,2’,3,4,4’,5,5'‐ heptachlorobiphenyls. Two percent of the congeners were non‐ortho‐, 33% mono‐ortho‐ and 66% di‐orthochlorine substituted biphenyls. Compared to the 14 congeners measured in a 1982 study, all but one (2,3’,4,4'‐tetra‐chlorobiphenyl) showed a decrease in residue level, with a more than‐ 50% decline for most of the predominant congeners. In addition the polychlorinated biphenyl congeners levels in this study were comparable to or lower than those reported in breast milk studies from other countries. Regional and/or provincial differences in residue levels for polychlorinated biphenyls were observed. Levels of the 2,2’,3,4,4’,5'‐hexachlorobiphenyl were significantly (p=0.0006) higher in Quebec than in any other region. Other prominent congeners, such as the 2,2’,4,4’,5‐penta‐, 2,2’,4,4’,5,5'‐hexa‐ and 2,2’,3,4,4’,5,5'‐heptachlorobiphenyls, were also significantly (p<0.0023) higher in Quebec than in other regions, except for the Eastern region. An increase in residuc levels with mother's age was observed, although not always consistently and/or significantly. A considerable number of PCB congeners (70%) showed a significant decline in residue levels of breast milk between the first and third breastfed child.