PERFORMANCE OF THE CALIFORNIA BIOACCESSIBILITY METHOD FOR PREDICTING ARSENIC RELATIVE BIOAVAILABILITY IN CONTAMINATED SOILS

Exposure risk associated with soils contaminated with As is assessed by human health risk assessment (HHRA). Often the most important pathway for As in soil (i.e., the risk driver), associated with human exposure is soil ingestion. The use of total soil As in HHRA overestimates human exposure because soil and geomedia can sequester As. A more accurate and site-specific HHRA accounts for bioavailability of soil As. Extensive research efforts have been directed toward development and application of in vitro gastrointestinal methods to predict relative bioavailable As (RBA As). The California Bioaccessibility method (CAB) was developed to predict As bioavailability at former abandoned mine land sites in California. In vitro bioaccessible (IVBA) As by CAB and several other IVBA methods, RBA As from juvenile swine dosing trials, As speciation determined from advanced spectroscopic methods, and soil properties of 33 As contaminated soils were determined. Total As ranged from 162 to 12,483 mg/kg. Relative bioavailable As ranged from 1.30 to 60.0% . Arsenic speciation was predominantly As(V) adsorbed to hydrous ferric oxide (HFO) or iron (Fe), manganese (Mn), and aluminum (Al) oxides. Comparison of in vitro-in vivo correlation (IVIVC) CAB with other IVBA methods showed CAB was the best predictor of RBA As for mining soils contaminated with arsenic containing <1,500 mg/kg As. RBA As can be predicted by CAB using the following equation. RBA As=0.81 (IVBA) + 3.2, r² =0.91. The California Department of Toxic Substances Control (Cal DTSC) issued guidance for the use of CAB to adjust for exposure in HHRA. Cal DTSC also conducted a round robin study to validate the CAB method. Results from the robin robin and IVIVC studies will be presented.