For countries where metal resources represent an important economic sector, one of the main challenges of environmental research is to distinguish between natural and anthropogenic accumulations of potentially toxic metals in mining districts. The present work aims to evaluate a new environmental monitoring tool combining dendrochronology with natural (Ca, Ca/Mn, δ13C) and anthropogenic (Cd, Pb, 206Pb/207Pb, 208Pb/206Pb) geochemical tracers in tree rings in such a region. We compare spruce trees sampled at a control site near Hudson Bay, with those sampled near the Horne smelter active since 1928 in Rouyn-Noranda.
The first effect of smelter emissions is detected by the tree-ring carbon isotope records. The δ13C values obtained on trees near the smelter show major changes immediately after 1928. This is due to the presence of atmospheric SO2 which generates a rapid response of the foliar system. The Ca/Mn ratios in tree-ring pairs of 1936–1937 and younger suggest a SO2-related soil acidification. The concentrations in Cd and Pb show a major increase starting in 1944 which coincides with a decrease of the 206Pb/207Pb ratios. The smelter activities likely generated this increase and the apparent delay of 14 years may have been generated mainly by the residence time of metals in airborne particulates, the buffering effect of the soils and, to a lesser extent, perhaps by mobility of heavy metals in tree stems. The 206Pb/207Pb and 208Pb/206Pb ratios indicate that the growth rings contain at least three types of Pb: natural, derived from the mineral soil horizons; industrial, from coal burning urban pollution; and mining, typical of the volcanogenic massive sulphides treated at the Horne smelter. This new combination of natural and anthropogenic tracers allows recognition of the succession of atmospheric and pedogeochemical changes related to industrial activities in the Rouyn-Noranda mining area.