Datta, Rupali¹, Dibyendu Sarkar¹
(1) University of Texas at San Antonio, San Antonio, TX

ABSTRACT: Effect of Soil-Aging on Geochemical Fate of Arsenic in Pesticide-Contaminated Soils

Excessive use of arsenical pesticides has resulted in elevated levels of arsenic, a group A carcinogen, in agricultural soils. Encroachment of suburban development on agricultural lands has greatly increased the potential for human contact with arsenic. An accurate health risk assessment due to exposure to arsenic-rich soils requires an estimate of bioavailable arsenic. Current protocols assume that all arsenic present in soil is bioavailable, due to the expenses and logistic difficulties in conducting "in-vivo" animal studies. Arsenic bioavailability is a function of its geochemical forms, which in turn is dependent on soil properties and equilibration time. An incubation study was conducted to identify the relationship between geochemical speciation and “in-vitro” bioavailability of arsenic as a function of soil aging. We used two soils, Immokalee, a sand with minimum arsenic retention capacity and Millhopper, a sandy loam with relatively high concentration of Fe/Al-oxides, and hence higher arsenic retention potential. The soils were amended with sodium arsenate at three rates. A sequential extraction scheme was used to identify the various geochemical forms of arsenic, which were correlated with the “in-vitro” bioavailable fractions. Comparative arsenic speciation and bioavailability studies at 0 time (immediately after spiking the soils with pesticides), four-month and one-year incubation period were done. Our results indicate significant effect of soil properties and equilibration time on arsenic bioavailability. This study will provide realistic starting points in site- and composition-specific health risk assessment associated with exposure to low doses of arsenic in soils.

AAPG Search and Discovery Article #90026©2004 AAPG Annual Meeting, Dallas, Texas, April 18-21, 2004.