LEAD (PB) IN ATLANTA SOILS AND ROAD DUST I: BACKGROUND, METHODS, AND ANALYTICAL RESULTS

Urban soil and road dust are well-known reservoirs of Pb from the historical use of leaded gasoline and lead-based paint. A variety of methods have been used in the past to analyze spatial distribution and composition of heavy metals in urban environments, but rarely in tandem. The purpose of this study is to determine the quantity and form of Pb in Neighborhood Planning Unit V (NPU-V) in Atlanta, GA, using a mixed methodology drawing from geochemical, microanalytical, and statistical techniques. Complementary soil and road dust samples were both taken from 150 sites and the Pb, Zn, and Cu contents for all 300 samples were determined using energy-dispersive X-ray fluorescence (XRF); the bulk road dust samples were sieved and the <250μm size fraction was re-tested. Samples with the highest lead content were then analyzed using powder X-ray diffraction (XRD) and scanning electron microscopy (SEM). The median soil, bulk dust, and <250μm dust Pb concentrations were 70 mg/kg, 53mg/kg, and 74 mg/kg respectively, with the highest value, 968 mg/kg, found in a road dust sample. Whereas bulk dust and <250µm dust are strongly correlated, bulk soil and bulk dust are not, suggesting different sources and modes of transport for the two sample types. Although all median Pb concentrations are below 100mg/kg, Pb throughout the neighborhoods of NPU-V is elevated above background level and at some sites, far exceeds toxic levels. Road dust <250µm has the highest Pb concentrations, and these finer particles can become airborne more readily. The lack of detection from microanalysis may show that Pb is not found in distinct particulate form but is widely dispersed atomically. XRD did not further inform this supposition, however, additional sample preparation to isolate lead-bearing minerals or particles could supplement the microanalytical work. The findings in this study give us insight into the state of lead in NPU-V by cataloging its quantity and potential sources. A complete geochemical analysis is particularly important for understanding potential health outcomes of residents living in these neighborhoods. This study shows the importance that statistical, microanalytical, and geochemical methods have in informing one another and providing a comprehensive understanding of urban Pb deposition.