CURRENT AND HISTORICAL INPUTS OF MERCURY TO HIGH-LATITUDE LAKES IN CANADA AND TO HUDSON-BAY

Sediment cores collected from several lakes in northern Canada have be en analyzed for mercury and several other chemical contaminants. Sites ranged from the Experimental Lakes Area of northwestern Ontario, nort h to Cornwallis Island, and west to the: southern Yukon. Cores were sl iced at sites of collection and individual slices were freeze dried an d analyzed for Pb-210 and Cs-137 to estimate average time intervals of deposition. The earliest date estimated by Pb-210 was about 1850, and mercury concentrations in some lakes were clearly increasing before t hen, assuming no vertical movements of mercury within the sediments. E xtrapolation of dates downward to deeper slices, assuming a constant s edimentation rate, indicated that in some lakes mercury inputs increas ed slowly even in the 1500's, more rapidly after 1750, and more rapidl y yet over the current century. These increases are interpreted as inc reased fluxes of mercury to the lakes as a result of long-range transp ort of atmospheric mercury, since there are no local industrial source s of mercury. Slices taken near the bottom of a core are taken to esti mate the geological component while elevations in excess of that in su rface slices are taken to represent contamination from fallout. This p artitioning suggests that sediments in tile eastern Northwest Territor ies are dominated by pollution while those from the western Northwest Territories are influenced more by their geological settings. Two core s from Hudson Bay suggest that mercury is increasing there too, but ha s not yet exceeded geological sources. Mercury shows little or no tend ency to decline in the most recent slices; indicating that inputs of m ercury remain at or near their historical maxima. Given relatively hig h and continuing inputs of mercury to northern lakes it seems likely t hat some portion of that mercury may find its way into the food chain, hence the long-term prospect is for increasing levels of mercury in n orthern fish.