Minimizing Human Exposure to Contaminants in Urban Soils.

Potential for contaminant transfer from urban soils will be discussed using examples from urban garden sites located in different regions in the US. These sites had elevated levels of lead (Pb) and/or arsenic (As). Measures focussing on reducing both direct (soil-human) and indirect (soil-plant-human) exposure of Pb and/or As to the gardeners and their children were tested. Lead and As bioaccessibility and speciation in garden soils were investigated using an in vitro bioaccessibility test and X-ray absorption fine structure (XAFS) spectroscopy.  The change of soil Pb and As speciation upon in situ soil amendments over time were also evaluated.  In general, concentrations of Pb and As in vegetables harvested at test sites were low, indicating the pathway from contaminated soil to plant to human was insignificant.  Our research confirm that the potential exposure pathway of concern is direct exposure of humans to contaminated soils. The bioaccessibility of soil Pb and As were low in tested urban soils, most likely due to inherently high sorption capacity of these soils due to high concentrations of active Fe species, or soil organic carbon.