LEAD ISOTOPIC DETERMINATION OF HISTORICAL SOURCES OF LEAD TO LAKE ERIE, NORTH-AMERICA

Measurements of lead concentrations and stable lead isotopic compositions (Pb-204, Pb-206, Pb-207, Pb-208) in sediment cores from Lake Erie document both temporal and spatial variations in lead sources to the lake. These analyses track the history of lead contamination in the lake, as well as the transport of particulate matter which governs the redistribution of particle-reactive contaminants within the lake. The isotopic compositions of the sediments reveal two sources of natural lead (fluvial and shoreline bluff erosion) and three primary sources of anthropogenic lead (coal combustion, gasoline additives, and municipal waste water discharges) to the lake. Lead concentrations and isotopic compositions of Pb-210-dated sediment cores record historical variations in the inputs from these sources. The heterogeneous isotopic composition of the three basins of Lake Erie indicates that lead from municipal effluent is most prominent in the urbanized western region of the lake and that atmospheric deposition is most prominent in the more rural eastern areas. Calculations based on a Pb-207/Pb-206 vs. Pb-208/Pb-206 linear mixing model show that as much as 70% of sediment in the Central Basin and 25% in the East Basin originates from the West Basin of Lake Erie. These calculations attest to the interbasinal redistribution of particle-reactive contaminants within the lake.