THE GEOLOGIC, GEOMORPHIC, AND GEOGRAPHIC INFLUENCE ON LEAD AND OTHER HEAVY METAL CONCENTRATIONS IN THE SOILS OF FAIRMOUNT PARK, PHILADELPHIA

Abstract

The city of Philadelphia is an amalgamation of extremely diverse land uses, both currently and historically, including: transportation, industrial, commercial, parks and residential areas. This urban tapestry of historical and current land use creates the potential for human exposure to heavy metals in contaminated soils. In order to evaluate this potential public health hazard, soil samples from open spaces in Philadelphia's Fairmount Park (the largest inner-city park system in the U.S.) were analyzed using a handheld x-ray fluorescence (XRF) analyzer and inductively coupled plasma-mass spectrometry (ICP-MS), focusing on Lead (Pb). Three distinct types of land use were identified for detailed analysis: undisturbed parkland, recently disturbed parkland and urbanized park/recreational land. At each location bulk and core samples were taken at specific geomorphic positions along a toposequence or, if little to no topographic change was present, samples were collected at specific intervals from structures or roads. These sites were compared to the geologic background Pb concentration (33 ppm). Less than 1% of samples analyzed were at or below the background Pb concentration for the region, suggesting anthropogenic input of Pb into the system. In total, 24 sites were sampled with three sites chosen for additional core and sequential extraction analysis. Selected samples were sequentially digested to determine Pb fractionation via ICP-MS. In most samples the Pb distribution was: Fe/Mn oxides > residuals > organic > carbonate > exchangeable fraction. Thus, most Pb was in less biologically available fractions. From the total Pb concentration data comparisons were made to a previously published model explaining Pb distributions in the urban environment, incorporating buildings to act as a baffle for aerosolized Pb particles, thus leading to increased Pb concentrations at the base of structures. By modifying this model and using a hill slope as the baffle, these data indicate that geomorphology can concentrate Pb at the bottom of hill slopes in a similar manner. Using the data collected in this study, we can develop an improved sampling model to characterize the potential public health risk associated with these three types of land use in Fairmount Park. This same approach can be used on public lands throughout the Philadelphia region in order to better assess the potential public health hazard posed by Pb and other toxic metals.