BIOAVAILABILITY OF LEAD IN URBAN SOILS

Children living in urban areas continue to have a higher risk of Pb poisoning than those living in rural areas. Sources for this Pb often come from legacy pollution such as industrial emissions, leaded fuels, and deteriorating Pb-based paint. Significant efforts have focused on the need for the abatement of leaded paints, but urban soils are often an overlooked source for Pb exposure despite a significant amount of research demonstrating elevated soil Pb concentrations are common in many urban areas characterized by high traffic volumes, older housing stock, and a history of industry. The bioavailability of Pb in these urban soils, however, is not well known. Two different geochemical approaches were used here to evaluate Pb bioavailability of urban soils from areas with known high soil Pb loads. Most of the samples from this study come from surface soils collected in Terre Haute, Indiana that have already been characterized for total Pb concentrations. New samples were collected in May 2015 from a residential area located in a historic neighborhood in Terre Haute. Samples were identified with soil Pb >200 ppm (n = 210) and subjected to an extraction using a simulated gastric solution. These samples were shaken for two hours to approximate the residence time of food in the stomach. Samples with Pb > 1200 ppm (n= 50) were subjected to a Tessier style sequential extraction that isolates Pb that is adsorbed, exchangeable, and associated with Mn-oxides, Fe-oxides, and carbonates. Residual Pb concentratrations were determined by difference (sum of all steps subtracted from total Pb). All Pb concentrations were determined by ICP-OES. Preliminary results suggest that as much as 20% of the total soil Pb is bioavailable based on the simulated gastric solution extraction. Based on previous interpretations of sequential extractions, it might be expected that any residual Pb would not be bioavailable; however, comparisons between the simulated gastric solution extraction and the sequential extraction suggest that significant amounts of residual Pb may still be bioavailable. Ongoing work includes completing sequential extractions for soils with soil Pb < 1200 ppm.