CHEMICAL AND GEOSPATIAL DISTRIBUTION OF PB IN SOILS OF SMALLER URBAN CENTERS

Anthropogenic Pb contamination in urban soils is a widespread problem with human and environmental health implications. Most research has focused on major cities, such as New Orleans and the Twin Cities with little on smaller communities that share some, but not all of the sources of anthropogenic Pb. Our previous work has found elevated Pb concentrations in residential soils in a historic neighborhood in Appleton, WI (pop. ~70 000). Average soil Pb levels in the dripzone of houses in this neighborhood are over 1 000 ppm with some samples over 10 000 ppm. The primary goal of this project is to go beyond simply measuring soil Pb concentrations and to focus on the geospatial and chemical distribution of Pb in the soil. A fuller understanding of the distribution and residence of Pb in soil can help to determine the source of the Pb and give a better idea of the relative toxicity. To better understand the geospatial distribution of soil Pb we have conducted a high intensity sampling of a single residential block and part of Lawrence University’s campus. The residential block is owned entirely by Lawrence, with houses built between 1890 and 1905. On this 0.9 ha block, a total of 313 samples were collected between the houses and the street. An additional 253 samples were collected on a 2 ha section of Lawrence’s campus around Main Hall (the oldest structure on campus, built in 1853), the main academic greenspace, and along College Ave. (a four lane arterial that bisects campus and runs through downtown Appleton). The highest Pb concentrations are closest to the structures, with little to no elevation of Pb levels close to the streets, indicating that paint is the primary source of Pb. Additionally, we ran a series of Selective Sequential Extractions (SSE) on a subset of samples. Our SSE procedure is designed to target Pb in the exchangeable, carbonate, Fe- and Mn-oxyhydroxide, and organic fractions in the soil samples. Results of the SSE analyses indicate a high proportion of the Pb resides in the fraction bound in carbonate phases. As with the geospatial analyses, this is consistent with much of the Pb coming from paint, which historically used PbCO₃ as a whitening and stabilizing agent. Additionally this has human health implications, as Pb bound in carbonate phases is highly bioavailable as these minerals are readily broken down in our digestive system.