The extent and variation of Cu, Hg, Ni, and Pb loading in soil profiles (humus, B-horizon, C-horizon) were examined in the vicinity of four Canadian industrial sources of airborne metal particulates located in different ecozones and geological terrains: the Cu smelter at Rouyn-Noranda, Québec; the Cu-Zn smelter at Flin Flon, Manitoba; the Pb–Zn smelter at Trail, British Columbia; and the inactive Pinchi Lake Hg Mine, British Columbia. Three major controlling factors on the metal concentrations in soils have been assessed: (1) distance from the anthropogenic point source, (2) organic matter content, and (3) geology of the substrate. Distance from source largely controls smelter-related metal concentrations in humus, with concentrations decreasing with increasing distance according to specific parameters for each element and at each location. In the B-horizon, variations in organic matter content and substrate geology are important controls on metal concentrations, except in areas close to the source where sub-surface contamination was recognized for certain metals. The metal content of the C-horizon is predominantly determined by the nature and composition of the substrate. Variations in humus/C-horizon and B-horizon/C-horizon metal ratios are useful to help distinguish anthropogenic from natural sources of metal enrichments in soils.

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