Polychlorinated Biphenyls in Dated Sediment Cores from Green Bay and Lake Michigan

Abstract

Ten sediment cores from Lake Michigan and Green Bay are analyzed for PCB, 2l0Pb, and l37Cs. Analyses include identification of historical patterns of PCB inputs to the lake and bay and estimation of historical annual average PCB fluxes to the sediment that are corrected for sediment redistribution (focus correction). A correction for focusing has not been utilized in previous investigations of PCB flux to Lake Michigan and Green Bay sediments. From these analyses, we conclude that PCB inputs have declined following the 1977 ban on new uses of PCB, and that the atmosphere is the largest source of PCB to parts of Lake Michigan. We estimate that the average annual atmospheric PCB flux to the Lake Michigan region is about 1.0 ng/cm 2/yr, + /- 0.34, which is the approximate flux to three of our five Lake Michigan cores. This amount is consistent with another recent flux estimate. Green Bay sediments have higher PCB concentrations and greater relative amounts of lower molecular weight PCB (Aroclor 1242) than lake sediments which are dominated by Aroclor 1254. Aroclor 1260 is also found in Green Bay but not observed in the lake. PCB concentrations in Green Bay sediment are highest near the mouth of the Fox River, and decline in areas of the bay where the Fox River plume is more dispersed. Atmospheric inputs account for no more than 11% of PCB flux to any Green Bay core we analyzed.