Environmental Context. Ingestion of soil contaminated with arsenic is an important pathway for human exposure to arsenic. The risk posed by ingestion of arsenic-contaminated soil depends on how much arsenic is dissolved in the gastrointestinal tract. Aluminum oxides are common components in the soil and act as a sink for arsenic. Knowledge of the behavior of arsenic associated with aluminum oxide surfaces in a simulated gastrointestinal tract will provide an understanding of the ingestion risk of arsenic-contaminated soil to humans.

Abstract. Arsenate adsorbed to oxide surfaces may influence the risk posed by incidental ingestion of arsenic-contaminated soil. Arsenate sorbed to corundum (α-Al₂O₃), a model Al oxide, was used to simulate ingested soil that has As^V sorbed to Al oxides. An in vitro assay was used to simulate the gastrointestinal tract and ascertain the bioaccessibility of arsenate bound to corundum. The surface speciation of arsenate was determined using extended X-ray absorption fine structure and X-ray absorption near edge structure spectroscopy. The arsenate sorption maximum was found to be 470 mg kg^–1 and the surface speciation of the sorbed arsenate was inner-sphere binuclear bidenate. The As^V was found to only be bioaccessible during the gastric phase of the in vitro assay. When the sorbed As^V was <470 mg kg^–1 (i.e., the sorption maxima) the bioaccessible As was below detection levels, but when sorbed As^V was ≥470 mg kg^–1 the bioaccessible As ranged from 9 to 16%. These results demonstrate that the bioaccessibility of arsenate is related to the concentration and the arsenate binding capacity of the binding soil.