SS4.06 Speciation, Bioavailability, and Impacts of Atmospheric Trace Metals in Aquatic Systems
Date: Wednesday, June 12, 2002
Time: 2:45:00 PM
Location: Esquimalt
 
GallonC, Univ. Québec, Québec, Canada, gallonce@inrs-eau.uquebec.ca
Tessier, A, , Univ. Québec, Québec, Canada, 
Gobeil, C, , Institut Maurice-Lamontagne, Mont-Joli, Canada, 
Beaudin, L, , Institut Maurice-Lamontagne, Mont-Joli, Canada, 
 
ISOTOPIC DETECTION OF HISTORICAL SOURCES OF LEAD IN A CANADIAN SHIELD LAKE
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We measured Pb concentrations in a dated sediment core from a lake located in an ecological reserve 40 km North of Quebec City. The concentration of Pb increases from a constant background of 10 mg/kg in preindustrial times to as much as 170 mg/kg in the 1970s, and then decreases to a present level of 120 mg/kg. Concomitant variation of the stable Pb isotope ratios and Pb concentrations suggests that this profile reflects the history of Pb contamination and is not caused by temporal changes in natural Pb flux or a diagenetic influence. Plotting the isotopic results as 206Pb/207Pb versus 206Pb/208Pb reveals the occurrence of two isotopically-distinct sources of anthropogenic Pb over the last century: one from the combustion of leaded gasoline in Canada and the United States, the other from the combustion of North American coal. Lead derived from coal combustion appeared in the sediments prior to 1890 and reached a maximum at the end of the 1940s, at that time representing one fourth of the total anthropogenic Pb in the sediments.