Sediment contamination in Lake Erie: A 25-year retrospective analysis

Lake Erie sediment surveys were conducted in 1997 and 1998 to characterize spatial and temporal trends in contamination and for comparison with historical levels to assess the degree of improvement in environmental quality since the advent of measures to reduce impacts from sources. These surveys were also designed to assist in identification of possible sources of contamination and areas where contamination exceeded Canadian sediment quality guidelines for protection of aquatic biota. Encouragingly, lakewide contaminant concentrations were found to have significantly, decreased from levels observed in samples collected in 1971 in previous Environment Canada surveys. The lakewide average polychlorinated biphenyl (PCB) sediment concentrations decreased from 136 ng/g in 1971 to 43 ng/g in 1997. This decreasing temporal trend was also evidenced by, contaminant profiles of core samples from all three major basins. There was a lakewide spatial trend in increasing sediment contamination from the eastern basin to the western basin, and from the north-central basin to the south-central basin. Sediments in many areas of Lake Erie still exceeded Canadian Federal and Provincial sediment quality guidelines. However, exceedences of sediment guidelines describing contaminated environments in 1997/98 were largely restricted to the western basin and the southern portion of the central basin. Exceedences of Canadian Sediment Quality probable effects guidelines were most numerous for dioxins and furans (40%) followed by mercury (6%). The Canadian threshold effects guideline for PCBs (34.1 ng/g) and the Provincial lowest effect guideline (70 ng/g) were exceeded at 52% and 22% of the sites, respectively. Mercury, PCBs and polychlorinated dibenzo-p-dioxins and dibenzofurans are responsible for fish consumption advisories in Lake Erie.