Organochlorine Insecticides and PCB in Surficial Sediments of Lake Michigan (1975)

Abstract

Analyses of 286 surficial sediments (0-3 cm), collected in August 1975, were found to contain residues of DDT and its metabolites (∑DDT), heptachlor epoxide (HE), HEOD (dieldrin), chlordane, and polychlorinated biphenyls (PCB), but no detectable residues of endrin, endosulfan, or methoxychlor. Sixty-two samples were checked for mirex but no residues were detected to a limit of 0.2 ng/g. ∑DDT residues were measurable in 93.4% of bottom sediments, HEOD in 48.3%, HE in 53.9%, chlordane in 21.6%, and PCB in 79.6% above detection limits for each compound. The mean residuesfor the whole lake were calculated to be 11.9 ng/g ∑DDT, 0.25 ng/g HEOD, 0.67 ng/g HE, 0.37 ng/g chlordane, and 9.7 ng/g PCB. Depositional zones were two to four times higher in the concentrations of these organochlorine compounds than the non-depositional zones. Basins varied in the levels of contamination for the different compounds. ∑DDT was highest in the Milwaukee basin (40.8 ng/g), HEOD was highest in the Waukegan basin (0.77 ng/g), chlordane was highest in the Grand Haven basin (1.47 ng/g), and HE and PCB were highest in the Fox basin (2.70 and 73.5 ng/g). The distribution of ∑DDT conformed well with the depositional basins of the lake as related to the redistribution of sediment following restrictions on DDT use. For HEOD, HE, and PCB the sediment distributions indicated active usage in 1975 and the probable location of loading sources.