Organic substances in the rainfall of Lake Superior: 1983

In 1983, sampling for organic substances in rainfall was undertaken at two, open-lake locations at opposite ends of Lake Superior — Isle Royale and Caribou Island. Triplicate samples, averaging 22 litres, were collected in each time period (approximately 6 weeks) and analysed for α-BHC, lindane, heptachlor epoxide, dieldrin, endrin, DDT residues, methoxychlor, polychlorinated biphenyls and hexachlorobenzene. α- and δ-chlordane, mirex and toxaphene were also investigated but were not found in any of the samples. Concentrations of these compounds ranged from 0.01 to 65 ng/L. The east side of the lake received considerably lower concentrations in rainfall (on average, roughly 65% less) and the levels of most of the observed substances were higher at both locations in the spring and early summer. Estimates of direct loadings to the lake were made using volume-weighted concentrations. The highest was for α-BHC at 860 kg/year and the lowest for hexachlorobenzene at 3.7 kg/year; the loading estimate for polychlorinated biphenyls was 300 kg/year.