HR: 09:00h
AN: B21C-05    [Abstracts]
TI: Stable Pb isotope ratios as indicators of historical atmospheric Pb sources around a Canadian smelter.
AU: * Gallon, C
EM: gallon@etox.ucsc.edu
AF: University of California Santa Cruz, Environmental Toxicology, 1156 High Street, Santa Cruz, CA 95064 United States
AU: Tessier, A
EM: atessier@ete.inrs.ca
AF: INRS-ETE, Universite du Quebec, 490 rue de la Couronne, Quebec, QC G1K 9A9 Canada
AU: Gobeil, C
EM: cgobeil@ete.inrs.ca
AF: INRS-ETE, Universite du Quebec, 490 rue de la Couronne, Quebec, QC G1K 9A9 Canada
AU: Carignan, R
EM: Richard.Carignan@umontreal.ca
AF: Universite de Montreal, Departement de Sciences Biologiques, C. P. 6128, Montreal, QC H3C 3J7 Canada
AB: Dated sediment cores from four Canadian Shield headwater lakes were analyzed for Pb concentrations and isotopic compositions by ICP-MS. These remote lakes, whose lonely sources of anthropogenic lead were from atmospheric depositions, are situated along an east-west transect 10 km, 25 km, 150 km, and 300 km from a copper smelter that historically emitted relatively large amounts of lead into the atmosphere. Analyses of total dissolved (<0.2 micrometer) lead concentrations of sediment porewaters from the lakes, collected by in situ dialysis, revealed post-depositional mobility of Pb, but diagenetic modeling indicated that mobility did not substantially alter particulate Pb profiles in the cores. Consequently, total Pb concentrations and stable Pb isotope ratios (206Pb/208Pb, 206Pb/207Pb, and 206Pb/204Pb) were used in mass balance equations to determine the chronology of Pb contributions to the lakes from various sources over the last century. These analyses showed that the isotopic composition of Pb originating from the smelter (e.g., 206Pb/207Pb = 0.99) was distinct from those of Pb in aerosols collected at other remote sites in Eastern Canada (e.g., 206Pb/207Pb = 1.15 - 1.20), and that smelter Pb was measurably present in the three lakes within 150 km from the smelter, but not in the lake 300 km from the smelter. The smelter Pb flux was determined to have peaked around 1980 and to account for 89%, 88% and 5-34% of the total inventory of anthropogenic Pb deposited to the sediments of lakes located 10 km, 25 km, and 150 km from the smelter, respectively. Moreover, the total amount of Pb emitted by the smelter since the beginning of its operations was calculated to be ~ 88,000 metric tons, equivalent to about 29% of the total amount released by leaded gasoline combustion in Canada, and a large fraction of that lead (20-40%) was estimated to have been deposited within 150 km of the smelter. Finally, sharp decreases in the Pb fluxes to lake sediments in the last 25 years indicate that measures taken to reduce metal emissions from the smelter were effective.
DE: 0345 Pollution: urban and regional (0305, 0478, 4251)
DE: 0454 Isotopic composition and chemistry (1041, 4870)
DE: 0461 Metals
SC: Biogeosciences [B]
MN: Fall Meeting 2005