Heavy-metal Pollution in the Sudbury Mining and Smelting Region of Canada, II. Soil Toxicity Tests

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Abstract
Soils from the Sudbury region, Canada, which have been contaminated by the heavy metals nickel, copper, cobalt, and iron, from airborne smelter emissions, have been assayed for their toxicity to seedling growth. The extent of radicle elongation in bathing solutions of soil-water extracts has been used as a bioassay index of soil toxicity. The root growth of four species was reduced in extracts of soils which had been collected up to a distance of 49.8 km from the Coniston smelter. Inhibition was greatest in surface soils. Water extracts had metal concentrations of up to 142 ppm Ni, 59.5 ppm Cu, and 4.6 ppm Co. In addition, aluminium occurred in water extracts at 50.6 ppm at 0.8 km from the smelter, and up to 98.9 ppm somewhat farther away, even though it was not smelted in the region.All of the four metals nickel, copper, cobalt, and aluminium, were shown to be markedly inhibitory to seedling growth at concentrations below 5 ppm. In addition, all of the metals tested were concentrated markedly in the seedlings, expecially in their roots. The concentration factor was often 50- to 100-fold that of the bathing solution. Nickel appears to be the greatest single heavy-metal problem with which the vegetation has to contend. Even in the event that the major emissions of sulphur dioxide in the area be controlled, the concentrations of the toxic heavy metals nickel and copper already existing in the soils over many square kilometres present severe problems for seedling establishment and, consequently, revegetation.