Environ. Sci. Technol. 2006, 40, 1364-1370
Bioaccessibility of Arsenic(V) Bound to Ferrihydrite Using a Simulated Gastrointestinal System DOUGLAS G. BEAK,† N I C H O L A S T . B A S T A , * ,† KIRK G. SCHECKEL,‡ AND SAMUEL J. TRAINA§ School of Environment and Natural Resources, The Ohio State University, 2021 Coffey Rd, Columbus, Ohio 43210, USEPA, National Risk Management Research Laboratory, 5995 Center Hill Avenue, Cincinnati, Ohio 45224, and Sierra Nevada Research Institute, University of California at Merced, P.O. Box 2039, Merced, California 95344
The risk posed from incidental ingestion to humans of arsenic-contaminated soil may depend on sorption of arsenate (As(V)) to oxide surfaces in soil. Arsenate sorbed to ferrihydrite, a model soil mineral, was used to simulate possible effects on ingestion of soil contaminated with As(V) sorbed to Fe oxide surfaces. Arsenate sorbed to ferrihydrite was placed in a simulated gastrointestinal tract (in vitro) to ascertain the bioaccessibility of As(V) and changes in As(V) surface speciation caused by the gastrointestinal system. The speciation of As was determined using extended X-ray absorption fine structure (EXAFS) analysis and X-ray absorption near-edge spectroscopy (XANES). The As(V) adsorption maximum was found to be 93 mmol kg-1. The bioaccessible As(V) ranged from 0 to 5%, and surface speciation was determined to be binuclear bidentate with no changes in speciation observed post in vitro. Arsenate concentration in the intestine was not constant and varied from 0.001 to 0.53 mM for the 177 mmol kg-1 As(V) treated sample. These results suggest that the bioaccessibility of As(V) is related to the As(V) concentration, the As(V) adsorption maximum, and that multiple measurements of dissolved As(V) in the intestinal phase may be needed to calculate the bioaccessibility of As(V) adsorbed to ferrihydrite.
Introduction Arsenic (As) is ubiquitous in nature (1-3) and can be found naturally in almost all geomedia. In the United States (U.S.) the range of naturally occurring As in the soil is
