IN-SITU STABILIZATION OF ARSENIC IN SOILS AMENDED WITH WATER TREATMENT RESIDUALS

Anthropogenic processes such as the indiscriminate use of pesticides have resulted in higher than background levels of arsenic in soils. There is an increasing risk of human exposure to this class A carcinogen as cities expand and housing developments take place on former agricultural lands. Remediation of arsenic-contaminated soils by traditional excavation methods is cost-prohibitive and destructive with respect to ecological balance. Effective in-situ stabilization techniques are gradually becoming the methods of choice in reducing the risk of human exposure to arsenic-contaminated soils. The reported study explores arsenic geochemistry in two types of soils amended with three types of water treatment residuals (WTRs) to evaluate their potential in developing as an ideal in-situ stabilization strategy. WTRs are end products of flocculation processes at municipal water treatment facilities, normally composed of Fe, Al, or Ca. All forms of WTRs possess an amorphous structure and generally have high positive charge. It is anticipated that environmental species of arsenic, which are oxyanions will be strongly adsorbed by WTR-amended soils, resulting in a lowering of its bioavailable concentration. A laboratory incubation study is in progress to determine the role of WTR-amendment in reducing arsenic bioavalability in pesticide-contaminated soils. The soils were initially characterized for soil properties that control arsenic fate, and hence, mobility. This was followed by the analysis of the WTRs to ensure that leachable heavy metal concentrations do not exceed federal biosolids application standards. Two sandy Spodosols from Florida were contaminated with 450 mg/kg of arsenic in the form of sodium arsenate. Following four months of soil-pesticide equilibration, WTRs were applied to the arsenic-contaminated soils at four rates (0, 2.5, 5.0 &10% by weight). The soils will be periodically (0-time, 6 mo, 1y) subjected to a sequential extraction procedure to determine the geochemical forms of arsenic, which will then be correlated with in-vitro bioavailable arsenic concentrations. If successful, this remedial option could be further developed into a cost-effective technique to reduce health risk from exposure to arsenic in pesticide-contaminated soils.