Impact of soil particle size on lead distribution, geochemical speciation, and bioaccessibility in lead paint-contaminated residential soils.

Deteriorating lead (Pb)-based paint is a major source of Pb contamination in urban areas. Lead contamination in homes poses significant health risks, especially to children. Children ingest Pb-contaminated soil through their hand-to-mouth activity. The Bioaccessibility Research Group of Europe (BARGE) recommends using the < 250 μm soil fraction for oral bioaccessibility assessment, while the USEPA suggests the < 150 μm fraction for Human Health Risk Assessment (HHRA). However, these practices may underestimate risk, as smaller soil particles are more likely to adhere to children's hands and be ingested; moreover, real-world exposure often involves a mix of particle sizes. Research on Pb speciation and bioaccessibility across soil sizes in residential soils is crucial for accurate risk assessment. This study examined the total Pb, geochemical fractionation, and bioaccessibility of Pb in different size fractions in Pb paint-contaminated residential soils in Detroit, Michigan, to identify the optimal particle size for health risk assessments. Lead-contaminated soil was collected from 10 homes known to have Pb-based paint contamination and separated into 3 size fractions, i.e., < 250 μm, < 150 μm, and < 63 μm. Total Pb concentrations in the soils ranged from approximately 36-650 mg/kg across the size fractions, with the highest concentrations observed in the < 63 μm fraction. Each fraction was analyzed for total and bioaccessible Pb concentrations, and geochemical speciation of Pb was performed. Results showed that overall, the highest Pb fraction was organic matter-bound (47.5%). However, Pb was mainly in the exchangeable form in the < 63 μm fraction (33.1%) and contained higher total and bioaccessible Pb (22%) compared to the < 250 μm (13%) and < 150 μm (17%) size fractions. The study suggests that including < 63 μm fractions in risk assessment may improve health risk prediction; however, comprehensive assessments should consider contributions from multiple particle size fractions to better reflect real-world exposure.