Pb Isotopic Compositions of Soils and the Impact of Heavy Metal Smelters in Urbanized Industrial Settings, East Los Angeles, California, U.S.A.

Lead isotopes of soil profiles were measured to survey possible sources of lead. Thirty-seven soil profiles (n > 150 samples) were obtained near two lead battery recycling smelters: Exide (recently shutdown) and Quemetco/Ecobat (currently in operation) affecting thousands of residential sites. Preliminary soil Pb isotopic compositions plot as a band in Pb isotope space from radiogenic values typical of rock-derived lead to lower values that likely indicate anthropogenic lead. Three overlapping soil groups were established based on Pb isotope analysis by TIMS (Thermal Ionization Mass Spectrometry). Group 1 consists mainly of soils near the Exide smelter and nearby residential sites. Group 1 has low isotopic values with moderate variations in ²⁰⁶Pb/²⁰⁷Pb ~1.167–1.176, ²⁰⁸Pb/²⁰⁷Pb ~ 2.432–2.438, ²⁰⁶Pb/²⁰⁴Pb ~18.24–18.344. Group 2 has more radiogenic values than Group 1: ²⁰⁶Pb/²⁰⁷Pb ~1.178–1.190, ²⁰⁸Pb/²⁰⁷Pb ~2.439–2.443, ²⁰⁶Pb/²⁰⁴Pb ~18.34–18.56 and consists mostly of residential soils surrounding the Exide smelter. Group 3 is more radiogenic than Groups 1 and 2: ²⁰⁶Pb/²⁰⁷Pb >~1.190, ²⁰⁸Pb/²⁰⁷Pb >~2.443, ²⁰⁶Pb/²⁰⁴Pb >~18.56. Soils near the Quemetco facility have similar variations and overlap the three groups.  About 80% of the Pb isotopes in leached soils near Exide have Pb compositions that match those of the smelters. Group 2 has up to about 67% Pb resembling the Exide smelter output and Group 3 yields up to about 18% matching Pb. Sites near Quemetco contained up to about 86% Pb isotopically similar to the Exide signature. Sites containing lead that isotopically matches soils near the Exide smelter are interpreted as contaminated by human activities. Smelter isotopic signatures are found as deep as 30 cm in the soil profiles.  Our results demonstrate the need for establishing baselines and background concentrations of lead (and other metals such as As, Cd, Zn, Sb, and Cu) and Pb isotopic compositions of soils, waters, and air before smelters and other industrial facilities are in operation (which are commonly located in disadvantaged communities, for example in East Los Angeles), and especially during property transitions. Elemental and isotopic data can be used to assess legal liability and assist local, State, and national agencies for effective cleanup and proper remediation.