PB AND SR ISOTOPIC DISCRIMINATION OF SOURCES OF LEAD IN WELL WATER AND SOILS: DOCUMENTING THE LEGACY OF ANTHROPOGENIC CONTAMINATION IN FORMER ORCHARDS, PENNSYLVANIA, USA

Isotopic discrimination can be an effective tool in establishing a direct link between sources of Pb contamination and the presence of anomalously high concentrations of Pb in waters, soils, and organisms. Residential wells supplying water containing up to 1600 ppb Pb to houses built on the former Mohr orchards commercial site, near Allentown, PA, were evaluated to discern anthropogenic from geogenic sources. Pb (n=144) and Sr (n=40) isotopic data and REE (n= 29) data were determined for waters from residential wells, test wells (drilled for this study), and surface waters from pond and creeks. Local soils, sediments, bedrock, Zn-Pb mineralization and coal were also analyzed (n=94), together with locally used Pb-As pesticide (n=5). Waters from residential and test wells show overlapping values of ²⁰⁶Pb/²⁰⁷Pb, ²⁰⁸Pb/²⁰⁷Pb and ⁸⁷Sr/⁸⁶Sr. Larger negative Ce anomalies (Ce/Ce*) distinguish residential wells from test wells. Results show that residential and test well waters, sediments from residential water filters in water tanks, and surface waters display broad linear trends in Pb isotope plots. Pb isotope data for soils, bedrock, and pesticides have contrasting ranges and overlapping trends. Contributions of Pb from soils to residential well waters are limited and implicated primarily in wells having shallow water-bearing zones and carrying high sediment contents. Pb isotope data for residential wells, test wells, and surface waters show substantial overlap with Pb data reflecting anthropogenic actions (e.g., burning fossil fuels, industrial and urban processing activities). Limited contributions of Pb from bedrock, soils, and pesticides are evident. High Pb concentrations in the residential waters are likely related to sediment build up in residential water tanks. Redox reactions are implicated, which were triggered by influx of groundwater via wells into the residential water systems. Precipitation of Fe oxyhydroxides, oxidative scavenging of Ce(IV), and desorption on clay minerals can explain the changes in Ce(IV) and the release of Pb into the residential water systems. The Pb isotope features in the residences and the region are best interpreted as reflecting a legacy of anthropogenic Pb rather than geogenic Pb.