LEAD IN URBAN GARDEN SOIL: SOIL CHARACTERIZATION AND BIOAVAILABILITY DETERMINATION IN BOSTON, MASSACHUSETTS

Yard soil in the Boston, MA neighborhoods Dorchester and Roxbury has been shown to have elevated concentrations of lead. The increase in backyard and community gardens creates a new urban land use pattern that may alter exposure pathways and risk. Children are at a higher risk because their specific exposure pathways, such as ingestion and inhalation, are most common. Work with non-profit organization the Food Project has encouraged the use of raised bed gardens filled with compost to decrease exposure. However, deposition of fine particles with high Pb concentrations is causing recontamination of garden soils. Current research aims to pinpoint the source and transport of this airborne lead by physically and chemically characterizing the yard soil and compost and examining their behavior upon mixing through x ray fluorescence (XRF) spectroscopy analysis of size-fractionated samples. Current research also examines the bioavailability of lead in soil as a function of location through measurements of pH, loss on ignition, (LOI, as a proxy for organic matter content) and physiologically based extraction tests. Bioavailability of lead deposited in the compost matrix will depend on the interplay of two primary factors: pH, which is lower in compost and could solubilize Pb, and an increased organic ligand content which could bind and immobilize Pb. Determining risk is thus contingent on complete characterization of soil end members and mixing processes. This research will ultimately inform best practices for remediation to reduce lead exposure in urban children.