Extent, Characterization, and Sources of Soil Lead Contamination in Small-Urban Residential Neighborhoods

Abstract

We present high spatial-resolution mapping of soil lead (Pb) concentrations in a small-urban residential setting. X-ray fluorescence was used to measure soil Pb at170 properties in the City Park neighborhood of Appleton, Wisconsin. Greater than two-thirds of soil samples collected from drip lines contained more than 400 μg g of Pb, and one third exceeded 1200 μg g. Soils adjacent to homes built before 1960 contained significantly higher Pb levels than those near younger homes. Three front yard locations (drip line, mid-yard, and terrace) were sampled at 71 properties. A general decline in soil Pb with increasing distance from the house was observed. Detailed sampling of individual homes within a single residential block revealed Pb-contaminated soil radiating outward from homes in all directions, creating a "bulls-eye" pattern. Approximately 40% of yard space exceeded concentrations of 400 μg g. These patterns of contamination are consistent with Pb paint as the main contributor of Pb to soil. This has important implications because spatial distribution of Pb contamination is fundamentally different if paint, rather than automobile exhaust, is the primary source. Selective sequential extraction analyses suggest that roughly half of the soil Pb resides in chemically reactive and bioavailable phases. The extent and persistence of soil Pb, the resurgence of home gardening, and the serious health consequences of Pb ingestion argue for attention to this problem, not just in dense urban centers but also in smaller urban settings across the country.