Isotopic evidence of trace metal sources and transport in eastern Canada as recorded from wet deposition

Abstract

Abundances of heavy metals and Pb and Sr isotope ratios have been determined in precipitation collected between December 1997 and June 1999 at St. Anicet and L'Assomption, near Montréal, Canada. Median enrichment factors for the heavy metals, relative to upper crustal abundances, are all ≫10 indicative of an anthropogenic origin. The 206Pb/207Pb values exhibit a large variation at both stations, with values of 1.170-1.190 and 1.130-1.150 recorded during the winter and summer seasons, respectively. The Pb isotope systematics defined by most of the samples from both stations may be explained by mixing of anthropogenic emissions from U.S. and Canadian sources. Comparison of Pb isotope ratios and heavy metal abundances between the same, individual precipitation events from both stations, however, do not systematically yield similar values and may be attributable to significant, local anthropogenic sources. The 87Sr/86Sr values for precipitations also exhibit a seasonal variation at both stations with the least radiogenic values being recorded, in general, during the winter months (<0.7085). These are possibly related to increased atmospheric emissions during the winter season from coal-fired power plants located in North America. For the remaining months the 87Sr/86Sr values are either variable (0.7085-0.7100) at St. Anicet or constant (0.7085-0.7088) at L'Assomption. The latter possibly reflect Sr anthropogenic emissions from urban activity associated with Montreal. Copyright 2000 by the American Geophysical Union.