TRACING URBAN SOIL LEAD FROM THE SOURCE TO THE HUMAN SYSTEM

Urban environments suffer a disproportionate burden of heavy metal contamination. In this study, over 130 backyard gardens in Boston communities were screened for lead contamination using FP-XRF and it was found that more than 85% contain soil lead concentrations above the EPA reportable limit. To fingerprint the sources of lead in this environment, lead isotope analyses were conducted and 70% of the gardens analyzed can be described by a mixing line trend between lead-based paint and leaded gasoline. Since bulk lead concentration is not an accurate measure of the risk lead posses to humans, a sequential extraction procedure was conducted on bulk and size fractionated soil samples to estimate the bioavailable fraction.

These urban gardens are used for growing produce that is an important part of residents' diet and this study investigated two pathways of exposure: inhalation or ingestion of dust and consumption of produce grown in contaminated soil. Garden soil was size fractionated to PM 10 and lead concentrations were measured by ICP-MS. Several plant species that are popular with resident gardeners were grown in the contaminated soil and plant tissue lead concentrations were measured by pED-XRF. To connect lead sources with bioavailability, lead isotope analyses were conducted on the plant samples. Given the elevated levels of lead observed in fine size fractions of urban garden soils it is speculated that inhalation/ingestion of fine particulate matter is a significant contributor to lead body burden and that consumption of produce represents a quantifiable, non-trivial pathway of exposure. This integrated approach of assessing lead inventories in urban garden soil and evaluating the bioavailable fractions by the analysis of both soil geochemical characteristics and plant uptake pathways suggests that site-specific remediation efforts are needed to limit exposure to lead and reduce lead poisoning in urban children.