Urban Sprawl and "Green" Remediation of Residential Soils: A Case Study With Arsenic.

Arsenical pesticides have been used extensively in agriculture until recently that has left a legacy of arsenic-rich soils in the farmlands. Widespread urban sprawl - particularly in the last three decades - converted a larger number of former farmlands to residential properties in many metropolitan areas in the United States. This change in landuse from agricultural to residential has tremendously increased the potential of human exposure to soil arsenic, primarily via soil ingestion by hand-to-mouth activity in children. One of the more logical and cost-effective remediation methods for arsenic in residential scenarios is in-situ immobilization, which results in lowering arsenic bioavailability, hence, in reducing human health risk from chronic exposure to arsenic-rich soils. Drinking water treatment residuals (WTRs) promote soil immobilization of arsenic in a way that is both inexpensive and less ecologically disruptive. WTRs are by-products of the drinking water purification process that typically contain - depending on the treatment process - large amount of Al/Fe oxides that are largely amorphous and have high affinity for oxyanions due to both high specific surface and favorable pH dependent surface charge. We conducted short- and long-term, laboratory and greenhouse studies to investigate arsenic retention-release by Fe- and Al-based WTRs and WTR-amended soils. Arsenic bioaccessibility and in-vivo bioavailability were evaluated using in-vitro physiologically based extraction tests, and nude mice model, respectively. Aqueous and surface speciation of arsenic were studied, and risk analysis was performed. Although not yet tested in a landscape scale under natural conditions, incubation and greenhouse studies indicate that WTR amendment has the potential to develop into a cost-effective "green" remediation technology for arsenic enriched soils.