172-3 Changes In the Physical Speciation of Lead (Pb) and Other Toxic Metals in Urban Soils During Soil Weathering Linked to Increases in Potential Bioaccessibility

Session: Urban Geochemistry

Presenting Author:

Authors:

Abstract:

The breakdown of lead (Pb)-based paints and other metal sources in soils leads to changes in chemical and physical speciation, which may result in bioaccessible phases of the metals being retained, particularly in the fine fraction. However, there is limited data about the relationship between labile Pb in different particle fractions and the influence of physical properties and morphology on the potential bioaccessibility of Pb and other metals. In this study, we (i) investigated the relationship between particle size and the potential bioavailability of Pb and other elements determined by simulated gastric acid (GA) extraction, and (ii) characterized the (sub)-grain-scale speciation of Pb and other metals. Soil samples from horizontal transects at three homes in Akron, OH (USA) were collected from the front of the home towards the street. Each home had Pb-based paint on its exterior before recent renovations. Soils were fractionated into sand (63 µm – 2 mm), silt (28 ± 19 µm avg. diameter), and clay–fine silt (16 ± 9 µm avg. diameter) using sieving, sedimentation, and laser scattering. ICP-OES measured GA-extractable metals, and soil phases were identified by XRD and SEM-EDS analyses. Total GA-extractable concentrations of Pb and Zn were sub-weight percent concentrations near the houses. The contribution of each particle-size fraction to Pb was invariant across the transects. Average concentration of GA-extractable Pb for sand, silt, and clay–fine silt was, respectively: 29%, 31%, 40%; 26%, 26%, 48%; and 25%, 29%, 46% at Sites 1, 2, and 3. However, the contribution of the silt and clay-fine silt fractions increased from Site 1 to Site 3, likely due to weathering and erosion of Pb paint particles, corresponding with the time since renovation before sampling (2, 11, and 25 years for Sites 1, 2, and 3, respectively). Lead-bearing particles included primary phases (paint chips) and weathering products (Pb-bearing Fe and Mn oxides, clays, and phosphate), in both silt and clay–fine silt fractions. The abundance of paint chips decreased from Sites 1 through 3, while the abundance of secondary phases increased. These results suggest that breakdown and re-sequestration of metal phases increases the exposure risk through ingestion and/or inhalation of fine particles following renovations of older urban housing.

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-10212

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