SPECIFIC POLYCHLORINATED BIPHENYL CONGENER DISTRIBUTION IN BREAST-MILK OF CANADIAN WOMEN

A total of 412 breast milk samples from across Canada were analyzed fo r selected polychlorinated biphenyl congeners. The median level for th ose 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 p olychlorinated 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 congen ers were non-ortho-, 33% mono-ortho- and 66% di-orthochlorine substitu ted biphenyls. Compared to the 14 congeners measured in a 1982 study, all but one (2,3',4,4'-tetra-chlorobiphenyl) showed a decrease in resi due level, with a more than 50% decline for most of the predominant co ngeners. In addition the polychlorinated biphenyl congeners levels in this study were comparable to or lower than those reported in breast m ilk studies from other countries. Regional and/or provincial differenc es in residue levels for polychlorinated biphenyls were observed. Leve ls of the 2,2',3,4,4',5'-hexachlorobiphenyl were significantly (p=0.00 06) higher in Quebec than in any other region. Other prominent congene rs, 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) highe r in Quebec than in other regions, except for the Eastern region. An i ncrease in residue levels with mother's age was observed, although not always consistently and/or significantly. A considerable number of PC B congeners (70%) showed a significant decline in residue levels of br east milk between the first and third breastfed child.