Bioavailability of Arsenic, Beryllium, and Vanadium from Soil. C. Petito Boyce, M. V. Ruby, and R. A. Schoof, PTI Environmental Services, 15375 SE 30th Place, Suite 250, Bellevue, WA 98007; and PTI Environmental Services, 4940 Pearl East Circle, Suite 300, Boulder, CO 80301
In humans, the orally administered dose of a compound is seldom completely absorbed, and differences in the extent of absorption following ingestion can exist depending on the form of the compound and its presence in different exposure media. In particular, the extent of absorption of compounds found in soil collected from contaminated sites is typically less than the absorption of these compounds from the dosing media (e.g., food or water) typically used in toxicological studies. If these differences in absorption are not accounted for, use of toxicity factors based on administered doses of compounds in food or water can overestimate the risks associated with exposures to compounds in soil. In this study, the relative bioavailability of ingested arsenic, beryllium, and vanadium was examined using soil samples collected at an alloy production and chemical manufacturing facility located in Ohio. These efforts included speciation analyses using electron microprobe techniques to assess the mineral species present in the soil samples. In addition, an in vitro analysis that replicates human gastrointestinal tract chemistry and function was used to determine the fraction of the compound that would be soluble and available for absorption in the gastrointestinal tract (i.e., the fraction that is bioaccessible). Results from these analyses were also evaluated in light of previous efforts to assess the relative bioavailability of arsenic and lead, including bioavailability studies in laboratory animals. To account for differences in the bioavailability of these compounds from site soil relative to the bioavailability associated with the dosing media used in the critical toxicity studies, these evaluations indicated that exposure estimates calculated for site soil should be reduced by a factor of 5 for arsenic, of 2.5-5 for beryllium, and of 2.5-7 for vanadium. These results and their implications for risk analyses at the site will be reviewed.