Analyzing the Spatial Distribution of Sediment Contamination in the Lower Great Lakes

Despite significant reductions in contaminant concentrations over the past 30 years, large areas within Lake Erie and Lake Ontario still exceed Canadian sediment quality guidelines. Hexachlorobenzene (HCB), polychlorinated biphenyls (PCBs), lead (Pb) and mercury (Hg) can persist for long periods of time in the environment and cause significant ecosystem damage. Analyses of the spatial distribution of these contaminants were carried out using a GIS-based kriging technique. Initially, sta- tistically valid results were obtained for three of four contaminants in Lake Erie (HCB, Pb, Hg) and two of four (HCB, Hg) in Lake Ontario. Acceptable concentration estimates were subsequently achieved for all contaminants following log-normal transformation kriging analyses. In general, the concentration of contaminants was lower in sediment collected in Lake Erie than in Lake Ontario. In many areas of Lake Erie, the concentrations were under both the probable effect level (PEL) and the threshold effect level (TEL), which relate to the severity of adverse biological effects that may be expected. Greater concen- trations of these contaminants were observed in Lake Ontario sediments, which can be partly explained by the bathymetry and current circulation patterns in the lake.