Louis M. McDonald
Division of Plant and Soil Sciences, West Virginia University, USA

Metal contaminated soils occur everywhere in the world and are a risk to human and ecosystem health. Spelter, WV, USA is adjacent to a zinc smelting factory and wastes from the smelting process have contaminated residential soils with Zn, Pb, Cd and Cu. Our objective was to determine if mixing contaminated residential soil with uncontaminated soil would reduce heavy metal concentrations in the common home garden plantsin a greenhouse experiment. Additionally, we sought to determine how these plants were responding the stress of these growing conditions. Contaminated top soil from Spelter was mixed with an uncontaminated soil of similar pH at five different weight-percent concentrations (0, 25, 50, 75 and 100% contaminated soil). At maturity the edible and above ground portions (roots, stems and leaves) were harvested, weighed and acid-digested. Dry weight tissue concentrations of Zn, Pb, Cd and Cu were determined and compared to published health standards. Rhizosphere pH and concentrations of citrate, malate and oxalate, and tissue thiol concentrations were used to determine plant stress response. Increasing the percent contaminated soil significantly decreased plant yield. Maximum tissue metal concentrations were different for each metal-plant combination, however, concentrations in edible portions were reduced to below health advisory levels by mixing with between 25 and 50% uncontaminated soil. Rhizosphere pH decreased approximately 0.10 units. Rhizosphere citrate concentrations increased by a factor of 2 with chicory and by a factor of 100 with radish. Tissue thiol concentrations also increased significantly in all plants. Additional field experiments and comparisons with other treatment technologies are needed.