Iron amendments to reduce bioaccessible arsenic

Former sugarcane lands on the Island of Hawaii have elevated levels of soil arsenic (As) from historical use of arsenical pesticides. The bioaccessible fraction of total As (As_TOT), a measure of the potential for human As uptake by incidental ingestion of soil, is used in the assessment of human health risk and the determination of the need for remedial action. Ferric chloride plus lime and ferrous sulfate plus lime were applied to As-contaminated soils in a field plot setting to determine the potential for reducing in vitro bioaccessible As (As_IVBA) by increasing As sequestration by the formation of additional iron (Fe) oxyhydroxides. The two Fe sources performed similarly in reducing As_IVBA over a 2-year observation period, with 30-41% reduction in As_IVBA for 0.25wt% Fe dosing (dry soil basis) and 59-63% reduction for 0.5wt% Fe dosing. Addition of phosphate (PO₄) to treated and untreated soils caused a significant increase in As_IVBA. Iron-treated and control soils showed more than twice the As_IVBA after the addition of 1500mgPkg^-1. The cost of in situ treatment of As-contaminated soil with ferrous sulfate plus lime to lower As_IVBA was estimated to be an order of magnitude less than excavation and landfill disposal on the Island of Hawaii, making the technology a viable alternative when remedial action objectives were based on As_IVBA levels.