Impact of a base metal smelter on the geochemistry of soils of the Flin Flon region, Manitoba and Saskatchewan

The regional dispersal patterns of six trace metals (As, Cd, Cu, Hg, Pb, Zn) emitted from the base metal smelter at Flin Flon were examined in surface soils and at depth, using an extensive regional geochemical database for humus and the underlying till. Humus is enriched in those elements emitted from the smelter, and regional dispersal patterns reflect the historical record of smelter contamination. The concentrations of the smelter metals decrease with increasing distance from the stack, until background values are reached, indicating atmospheric fallout from the smelter plume. Smelter contamination is generally restricted to the surface organic-rich horizons, and concentrations of smelter metals in till reflect the absence of significant contamination at depth in the upper C horizon of soils. The maximum radius of contamination varies among the major smelter metals, ranging from 70 km for Cd to 104 km for As. No direct relationship exists among emission, deposition, and sink concentrations, reflecting the complexity of factors influencing total metal concentrations in soils. Factors considered in this study include the natural geochemical signature of the underlying substrate, natural soil-forming processes such as biogeochemical enrichment in the surface organic layer and post-depositional mobilization of metals, and the variation in total metal concentrations among the different fractions and types of samples analysed. With increasing distance from the smelter, these factors become significant and the relative proportion of anthropogenic contamination in the surface terrestrial environment is more difficult to estimate.