Distribution of pesticides and polychlorinated biphenyls in water, sediments, and seston of the upper Great Lakes--1974.

Samples of water, seston, and sediment from the upper Great Lakes were collected during the summer of 1974 for analyses of polychlorinated biphenyls (PCS's), 15 organochlorine pesticides, and 17 organophosphorus pesticides. Samples were taken from 9 sites in Lake Huron, 2 in the North Channel, 5 in Georgian Bay, and 17 in Lake Superior. In the water samples all compounds analyzed were below quantification limits and traces of lindane were found in each sample. In seston samples, PCB's were above quantification limits at nearly every station and some traces of dieldrin and DDE were measured. Sediments contained PCB compounds at all stations. Dieldrin was occasionally observed, and DDT and/or its derivatives DDE and TDE were found in over one-third of all samples. No clear correlation was found between quantities of these compounds in sediments and either the percentage of clay or organic matter in the samples. Nor were any definite geographic trends present in terms of distributions observed, although concentrations were higher in areas of higher sedimentary deposition such as deeper basins. No organophosphorus compounds were detected in any sample. The highest level of DDT residues detected, 20 ppb, was lower than levels found in other studies in the lower Great Lakes and some tributary river sediments of Georgian Bay. In general, DDT residues were higher in Lake Huron and Georgean Bay sediments than in Lake Superior although PCB's were higher in some Lake Superior sediments.