Sediment cores were taken from two isolated Canadian lakes, a southern lake in the boreal forest region of northwestern Ontario and a northern one in the tundra on the west coast of Hudson Bay, for the purpose of comparing current and historical loadings of several contaminants. There are no sources of anthropogenic contaminants within either basin, yet both lakes showed increases in polycyclic aromatic hydrocarbon and mercury in more recent sediments as compared with older, deeper sediments. We have interpreted these as indications of increased loadings as a result of atmospheric fallout. When compared on the basis of the sum of sixteen PAHs, both lakes showed peak inputs in the middle years of this century, followed by more recent declines; although current values still exceed those from deep slices. With respect to mercury, the concentrations found in the southern lake were somewhat higher than those in the northern lake, and loadings were clearly greater in the south. Both lakes showed enrichment of mercury in top layers of the cores relative to bottom layers, and this enrichment was proportionately greater in the north. Both mercury profiles showed a slow rate of increase for a long period before 1850, suggesting influences from areas industrialized before North America. The northern lake also showed increases in PAH loadings prior to 1850, but the southern lake did not.

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