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(M/EH091) Isotopic evidence of long-range transport of lead in the Gulf of St. Lawrence, Eastern Canada . Gobeil, Charles 1, Beaudin, Luc 1, Lebeuf, Michel 1, 1 ABSTRACT- The concentration of Pb is 10-25 mg/kg higher in sediments deposited recently in the 1,200 km long Laurentian Trough in the Gulf of St. Lawrence than in preindustrial sediments from the same region. The considerable difference is not due to postdepositional remobilization and redistribution but to enhanced anthropogenic Pb-fluxes to the sediment. This conclusion is supported by large differences in the stable Pb isotope ratios (206Pb/207Pb, 206Pb/204Pb and 206Pb/208Pb)between recent and preindustrial sediments. If we assume that the concentration and the isotopic signature of natural Pb in the sediment have not changed recently, we can calculate the isotopic signature of anthropogenic Pb in the sediment surface layer. The calculation reveals the presence of anthropogenic Pb from both Canadian and American sources. Canadian sources dominate over American sources at the landward end of the Trough. In the seaward end of the Trough, American sources are relatively more important, contributing up to one-third of the total anthropogenic Pb in the surface sediment. Key words: Stable Pb isotopes, Pollutant sources, Sediments, Gulf of St. Lawrence |
