LEAD SPECIATION IN URBAN SOILS AT THE HOUSE-SCALE

The historical use of lead (Pb) continues to pose a health risk via inhalation and/or ingestion of urban soils and dust. However, there is little information on Pb speciation at the local scale which is a better predictor of potential bioavailability compared to total Pb concentrations. This study investigates the speciation of Pb at the house yard-scale and the importance of deposition source(s) (e.g. paint versus historical gasoline use). Soil samples were collected from three houses in the greater-Akron, Ohio (USA) area which were known to have used Pb-based paint in the past, in horizontal transects from the front of the house to the tree lawn (~30 m distance, in 1 m increments); soil cores collected near the front of each house (50 cm depth, at 10 cm increments); and 2-3 samples collected from the back of each house. A modified sequential extraction method was used to determine operationally defined exchangeable, reducible, oxidizable, and residual metal content before analyzing each fraction with the ICP-OES. Solid-phase characterization of the samples was performed with XRD, XRF and SEM-EDS to determine bulk mineralogy and composition, and grain-scale particle morphology and texture. Pearson statistical analyses examined correlations between metal speciation and bulk properties. Total extractable Pb concentrations were highest closest to the homes (21,720.2, 1,865.1, and 11,115.0 mg/kg, respectively) and decreased quickly towards the edge of the property near the road (100.5, 84.24 and 466.22 mg/kg, respectively). Most of the extractable Pb in the soil is present in the reducible fraction (avg. 51+/-13%) followed by the residual fraction (avg. 31+/-14%). The proportion of Pb in the reducible fraction decreases with an increase in the residual fraction with distance from the homes. In contrast to Pb, the other metals did not exhibit the same change in speciation. Statistical analysis (Pearson values) indicates that Pb is correlated with Zn (0.96), Cd (0.92), and Cu (0.65), and negatively correlated with Co (-0.37), Fe (-0.36), Ni (-0.32), and Ti (-0.15). Ongoing XRD and XRF analyses will be incorporated into statistical analyses. Preliminary results indicate that potential remediation of soil can be focused on areas closest to residential buildings, but assessments of Pb speciation must be considered.