THE DISTRIBUTION OF ANTHROPOGENIC LEAD IN AN URBAN SOIL: A CASE STUDY FROM ROCHESTER, NY

Due to the legacy left from past use of leaded gasoline and lead-based paint, high concentrations of anthropogenic lead in urban soils may pose health risks to residents. Over the past several decades, the focus of public health agencies has been on the remediation of lead-based paint in homes. More recently, researchers are showing that the threat from anthropogenic lead in soil, primarily through exposure to dust, is similarly disconcerting. The objective of this study is to examine the spatial distribution of Pb in 3-D, and examine its geochemical associations. The study investigates a single family residence in Rochester, NY. In this case, lead-based paint is the suspected primary source. Twenty-one core samples were collected and divided into discrete depth intervals of 0-2.5 cm, 2.5-5 cm, 5-10 cm, 10-20 cm, 20-30 cm, and 30-40 cm. Soil pH is in the range of 7.5 to 8, and organic matter content ranges from 2 to 5 wt. %. Using portable XRF, lead concentrations in the soil were determined in the field and after drying in the lab. Lead concentrations were found to range from 1679 mg kg^-1 to 68 mg kg^-1 for the air-dried samples. Horizontal spatial distributions show a decreasing trend away from the drip line of the house, increasing again at the property boundary where a former house stood. This pattern is seen at the ground surface and remains, in part, at depth. Vertical distribution of Pb suggests a downward migration. For a majority of the cores, samples with the highest concentrations were found at depth intervals 2.5-5 cm and 5-10 cm, averaging 579 and 621 mg kg^-1 Pb, respectively. Of further interest, however, are the elevated values found at greater depths with average Pb concentrations of 510 and 215 mg kg^-1 at 20-30 cm and 30-40 cm depth, respectively. This is counter to most studies which find that lead is relatively immobile, remaining near the surface. Laboratory studies are underway to validate field portable XRF values. Furthermore, a modified Tessier sequential extraction study will evaluate the distribution of Pb between the different soil physicochemical phases. This may elucidate potential causes for leaching of Pb from an organic-rich soil A horizon into the top of the soil B horizon.