MOBILITY AND BIOACCESSIBILITY OF ARSENIC IN CONTAMINATED SOILS

The mobility and bioaccessibility of arsenic has been determined for the <250 micron fraction of six soil samples having different chemical compositions, mineral contents, grain size distributions, and arsenic contamination sources. Soil arsenic concentrations range from 100-900 ppm. Arsenic mobility was determined by sequential leaching of the soils by synthetic acid rain and the distribution of arsenic in the soils was assessed using a 7-step sequential chemical extraction procedure (SCEP). Arsenic bioaccessibility was estimated using a modified in vitro gastrointestinal (IVG) method in which arsenic-contaminated soil is placed in contact with simulated gastrointestinal solutions..The IVG method has been shown previously to be linearly correlative with an in vivo bioavailability model.

The data indicate that IVG bioaccessible arsenic is derived largely from the most mobile soil arsenic fractions (water soluble + exchangeable), although excellent correlations exist between IVG arsenic and the first five extraction steps, as well as the SCEP total extractable arsenic. Although the majority of arsenic is associated with the poorly reducible Fe/Al oxyhydroxides for three of the soils, this fraction does not appear to be bioaccessible. Little to no arsenic is associated with the organic & sulfide-bound fraction for any of the soils, even for those contaminated by organic arsenic sources. Further data analysis is being performed to determine relationships between soil chemistry and arsenic IVG bioaccessibility.