LEAD BIOAVAILABILITY OF URBAN SOILS ESTIMATED USING A SIMULATED GASTRIC SOLUTION: EXAMPLES FROM TERRE HAUTE, INDIANAPOLIS, AND EAST CHICAGO

Even though childhood lead poisoning rates are much lower than in prior decades, urban areas still have higher occurrences than more rural areas. While we know that the distribution of lead in soils is highly variable across an urban landscape, there are some factors that can be used to predict areas with higher risks for lead exposure, for example proximity to point sources such as lead smelters or incinerators, areas with a high percentage of older homes that may have used lead-based paints or lead water service lines, and proximity to areas with historically high traffic volumes. The purpose of this research was to evaluate lead bioavailability in urban soils using a simulated gastric solution in three different urban areas located in Indiana. The first urban area is Terre Haute, which has a high percentage of older housing stock and a history of coal processing. The other two areas, Martindale-Brightwood, a community in Indianapolis, and East Chicago are both characterized by heavy industry and proximity to a former lead smelter. Both are currently undergoing soil lead remediation. In all cases, samples were previously collected for another purpose and total lead concentrations were determined by pXRF. The samples were bulk surface soils (n=311) that had been dried and powdered. Approximately 0.25 g of each sample was reacted with 20 mL of simulated gastric solution and allowed to react for 2 hours while shaking on an orbital shaker. Following this extraction, samples were analyzed for dissolved lead using ICP-OES. For the samples analyzed, surface soil lead concentrations for bulk soil ranged between 12 - 33,000 ppm, although average concentrations for the samples analyzed were 1360 ppm for Terre Haute (n=167), 350 ppm for East Chicago (n=87), and 230 ppm for Martindale-Brightwood (n=57). Samples from all of the communities, across a range of total soil lead concentrations (<100 to >1200 ppm) had some samples with 100% bioavailability based on the comparisons between the results of the simulated gastric extraction and total lead concentrations by pXRF. Average bioavailability was 62%, 65%, and 53% respectively for Terre Haute, East Chicago, and Martindale-Brightwood. These results indicate that digestion of small quantities of soil or dust could lead to significant lead exposure.