Heavy-metal Pollution in the Sudbury Mining and Smelting Region of Canada, I. Soil and Vegetation Contamination by Nickel, Copper, and Other Metals

Abstract

Soil, vegetation, and rainfall, have been collected in the vicinity of a nickel–copper smelter at Sudbury, Ontario. The region is a major producer of many metals, and the large areas of forest desolation in the vicinity have been ascribed to sulphur dioxide fumigations over the past 80 years. In the present study, attention has been focused on potentially toxic heavy metals. Very elevated soil levels of nickel and copper were found, with values up to 5,104 ppm Ni and 2,892 ppm Cu within 1.1 km of the smelter. The concentrations decreased with distance to 49.8 km in one direction. Surface soils were the most contaminated, and a decline through the soil profile was found. Other metals such as iron, cobalt, and silver, showed a similar pattern of distance and depth, suggestive of an airborne source. Analyses of the foliage of three plant species also showed excessive levels of nickel and copper, as well as of aluminium. The levels declined with distance from the smelter. The relative possibilities of soil versus aerial uptake are considered. The soils within 2–3 km of the smelter were markedly more acidic than those from farther away, and this was paralleled by their increased conductivity. Dustfall–rainfall collections and analyses of the soluble heavy metals indicated that a major aerial source of metals existed, and that the problem of metallic emissions is not merely one of the past. Heavy metals are persistent in soils, and the ecological consequences to date have perhaps only been masked around Sudbury by the sulphur dioxide damage, and the particular importance attached to it in the past.