Assessing Site-Specific Bioavailabilities for Barium, Lead and Zinc. I. S. Chaudhuri and L. J. N. Bradley, ENSR Consulting and Engineering, 35 Nagog Park, Acton, MA 01720
When conducting risk assessments on metals in soils, it is important to consider bioavailability, which is the percent of ingested material absorbed through the intestinal wall into the blood system. Most analytical methods use harsh extraction techniques in order to extract the maximum amount of compound from the soil matrix. However, these analytical methods do not provide information on the amount of metal that would be available for absorption through the human gut. To evaluate potential human exposure to three metals (barium, lead and zinc) present in soil at a tile-manufacturing facility, ENSR used an in vitro technique for measuring bioavailability (method published by Davis et al., Environ. Sci. Technol. 26(3), 1992). The analytical technique is meant to simulate conditions in the human gut. The method involves acid digesting soil samples for four hours followed by neutralization with sodium bicarbonate for two hours. Metal concentrations analyzed using this method were compared to concentrations obtained using standard EPA analytical methods (SW-846). The results showed that although the amounts of zinc measured using the two methods were similar, the amounts of lead and barium extracted using the Davis et al. method were much less than the total metal measured by SW-846. Therefore, the zinc at the site can be considered to be present in a bioavailable form, whereas significant portions of lead and barium in soil at this site are not bioavailable. The calculated site-specific lead bioavailability factor was incorporated into EPA's lead Integrated Uptake Biokinetic Model in order to provide a more realistic estimate of exposure.