Temporal changes in some chlorinated hydrocarbon residue levels of Canadian breast milk and infant exposure

Between 1967 and 1986, five national surveys were carried out to determine organochlorine residues in Canadian breast milk. In these surveys the number of samples, their geographic sampling distribution and fat content changed over the years. In addition, the number of samples obtained from younger mothers decreased, while those from older mothers (31-40 years) increased. Total DDTs showed the most consistent decline of all declining residues, while PCBs only decreased after 1982. Levels of oxychlordane and trans-nonachlor remained constant. Ratios of p,p'-DDE/p,p'-DDT gradually increased from 3.1 to 10.0 over the same period of time. With few exceptions, regional trends in residue levels followed those observed for the whole country. Although the number of reported chemicals increased since 1967, this was not necessarily reflected in the total accumulated residues in breast milk. By 1986, the daily intakes of all compounds at 8 weeks of nursing were well below the established acceptable daily intakes.