Contemporary and retrospective investigations of human milk in the trend studies of organochlorine contaminants in Sweden.

Milk from the Mothers' Milk Centre in Stockholm has been analysed for organochlorine contaminants in different time periods between 1967 and 1989. The contemporary investigations showed a decrease of the levels of certain pesticides and polychlorinated biphenyls (PCBs). The changes were related to the prohibitions and restrictions applied on the usage of the compounds. Milk samples, remaining from the contemporary studies, were archived from 1972 and onward. These samples were later reanalyzed and the investigations were extended to also include polychlorinated dibenzo-p-dioxins (PCDDs), dibenzofurans (PCDFs) and specific congeners of PCBs, including non-ortho and mono-ortho coplanar PCBs. These retrospective investigations, of the same milk, showed a time related decrease in the concentrations also for these compounds. Calculating the levels by toxic equivalency factors relative to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) it was found that PCBs contributed the major part of the toxic equivalents in milk.