Polychlorinated biphenyls in dated sediments of Milwaukee Harbour, Wisconsin, USA

A sediment core from Milwaukee Harbour was dated by the Pb-210 and Cs-137 methods and analysed for polychlorinated biphenyls (PCBs). The mass sedimentation rate of 1·10 g cm⁻² year⁻¹ was significantly higher than for Lake Michigan. The Cs-137 inventory of 162·9 dpm cm⁻² was 11·7 times higher than that calculated from atmospheric deposition data. There was a significant degree of PCB pollution in the sediments, as evidenced by the fact that the PCB flux was 596 times higher than the average atmospheric input to Lake Michigan. The vertical distribution of PCBs in the relatively undisturbed core followed the available national sales records (1957–1974) remarkably well. In addition, there was a sharp drop in layers from the late 1970s which would be expected in view of the recent curtailment of PCB usage and production. Relatively high levels of Aroclor 1254 point to local electrical component manufacturers. Several users of hydraulic fluids and lubricants containing PCBs have probably also contributed to the increased levels in the harbour sediments.