DISTRIBUTION OF LEAD AND OTHER ELEMENTS IN SOIL CORES FROM FAIRMOUNT PARK, PHILADELPHIA, PA

As part of a study of lead (Pb) in urban soils, we measured total element concentrations as a function of depth in eight soil cores obtained from a former orchard site now in Philadelphia’s Fairmount Park to determine distributions and mobilities of lead and other trace elements. Soil cores with recovery depths ranging from 8 to 17 cm were collected along a transect away from an old (>100 yr) building covered with several coats of white paint. The cores were air-dried, split, and analyzed at 1 cm increments using a bench-top mounted Niton XL3t X-Ray Fluorescence (XRF) Analyzer. Major soil minerals include quartz, muscovite, kaolinite, illite, hematite, and chlorite. Tessier-method sequential extractions of near surface samples reveal that much of the Pb is associated with the iron/manganese extractable mineral fraction. Concentrations of Fe, Mn, and Pb are strongly positively correlated in many of the cores. Maximum Pb concentrations range from 24,000 ppm (2.4%) near the building to <50 ppm in the former orchard. Soils near a highway also had slightly elevated concentrations of Pb. Given the low concentrations of As, most Pb at the site is likely derived from lead paint and aerosols rather than lead-arsenate pesticides. Pb concentrations were lower in near-surface organic-rich horizons (from ca. 0 to 2 cm) and then increased from ca. 2 to 10 cm before decreasing again at greater depths. Similar trends were also observed in Fe and Mn concentrations. Other elements that follow the same trend with depth include K, Ti, Zn, Zr, Sr, and Rb. Maximum Pb concentrations in cores were similar to those in the <75 µm fraction of bulk near-surface samples determined in a previous study.