Concurrent Uptake of Lead, Zinc, Cadmium and Copper and Health Risk Assessments in a Smelter Contaminated Soil.

The study area for this research was a smelter contaminated site in Harrison County, West Virginia. Soils in this site had elevated levels of lead, zinc, cadmium and copper. A multi-step chemical extraction study showed that zinc and cadmium were the most plant available elements while for Pb more than 75% was associated with the residual phase. Standard addition experiments showed readsorption rates less than 25 % for Pb and Cd, and less than 50% for Zn and Cu. Some common garden and residential plants were grown initially to study metal uptake in tissues. Radish, carrot, and chicory showed the highest uptake as well as the higher biomass yields compared to others. A health risk assessment study showed that carrot and lettuce can pose Cd and Zn risks for women and young children. Contaminated soils were mixed with top soil in five different levels using radish, carrot, and chicory as model plants to study remediation potential and health risk assessments. The 50% and 75% treatments showed promising results both in terms of biomass produced and metal uptake in tissues. Carrots had the highest translocation factor for all the elements indicating its potential for successful phytoextraction. Efficiency of phytoextraction was a function of both biomass and accumulation in harvestable tissues. Plant uptake studies also confirmed that Zn and Cd were the most bioavailable elements. A health risk assessment study showed that 25% and 50% treatments for carrots did not pose any health risks to women and young children. Total acid soluble thiol content increased linearly through the 75% treatment level and then decreased at 100% treatment in all the tissues studied. Radish roots had the highest thiol content at 1.61 mmol kg-1. Very low concentration of thiols in plants grown on control soils indicated that these compounds were triggered in plants as a result of metal stress. FTIR spectra confirmed binding to carboxylate groups in chicory and carrot. Shifts in COOR stretching vibrations with increasing metal content showed decreased pectin synthesis with metal stress, for carrots. Metal treated plant tissues also showed presence of thiol peaks. Rhizosphere was always more acidic than bulk soil indicating presence of root exudates. The highest water extractable Total Organic Carbon was observed in the rhizosphere of carrots. Carrots had the highest organic acid content followed by radish and chicory. Citric acid was the most common organic acid detected in the rhizosphere. Oxalic acid was not detected in any of the species. Other organic acids detected were citric, malic and acetic acid. No organic acids were detected in bulk soil