IMPACTS OF COMPETITIVE SORPTION PROCESSES ON PB BIOACCESSIBILITY IN URBAN SOILS

The wide use of lead (Pb) in house paint and the subsequent weathering of paint on exterior surfaces has led Pb to be a contaminant of high concern in soils, especially in areas such as the northeastern US, where older housing stock is concentrated. Geospatial studies suggest that blood lead levels (BLLs) are linked to the bioavailable fraction in a given soil, rather than total lead concentrations, indicating a need for bioavailability-based remediation. Through multiscale analysis of column experiments, this project aims to model competitive sorption processes affecting metal bioaccessibility, using Pb as an element of concern, with the goal of constructing a quantitative prediction tool for soil competitive sorption to be applied toward bioaccessibility-based, sustainable soil remediation. Representative soil samples containing as much as 11,500 mg kg-1 Pb were sourced from a Burlington, VT site contaminated with legacy Pb from exterior paint. Pb mobility as a function of rainwater pH was initially tested in flow-through column experiments. Next, synthesized rainwater was amended with PO₄, decreasing the extent to which Pb was mobilized in column effluent, and columns were amended with goethite (FeO[OH]) to initiate sorbent competition. Column effluent and leached soil were then examined for changes in Pb speciation and bioaccessibility using a range of molecular, micro- and macro-scale tools, including IC, ICP-OES, XAS, XRD, SEM, XRF, elemental analysis, and EPA in vitro glycine extraction method. Using the reactive transport modeling program CRUNCHFLOW, these experimental results are then assembled into a model coupling observations of Pb bioaccessibility as a function of the presence of competitive sorbents and predicted sorption behavior. Ultimately, the goal of this research is to generate sustainable Pb remediation techniques that decrease Pb bioaccessibility and are effective in a range of soil types.