Metal mixture effects in soils contaminated with Cu, Ni and Zn

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The toxicity of individual trace metals in soils has been studied for many years. However, trace metals are rarely found alone in soils and so the toxicity of metal mixtures needs to be understood in order to determine safe levels of metals in the environment. Research will be carried out collaboratively with three international metal associations, funded in part by the Canadian metal mining and refining industry, (International Copper Association, International Zinc Association and the Nickel Producers Environmental Research Association), a private firm that specializes in environmental modeling (HydroQual) and a university research group led by William Hendershot (McGill University). Metal environmental research associations are becoming increasingly concerned that the toxicity of Cu, Ni and Zn in soils will be over-estimated leading to greater restrictions on the use of these metals. In this context, the possible augmentation in toxicity when more than one metal is found in elevated concentrations in soils could lead to much more stringent limits being put on the release of metals into the environment. Tighter regulations on the use of these metals would lead to decreased exports by Canadian mining and metal producing companies, which would have a negative impact on the Canadian economy. The experiments will determine how metals interact in soil and on the surfaces of plant roots. The experiments will be conducted in such a way that the data can be used to calibrate a terrestrial biotic ligand model that will predict toxicity of metal mixtures based on 1) the interactions between metals in the soil solution and adsorbed on soil particles and 2) the amounts of metals that are sorbed by the plant root from the soil solution. The model that is being developed by HydroQual, one of our collaborators, will provide the metal industry a tool to evaluate the effects of metal mixtures under different metal release scenarios.