IDENTIFICATION AND DISTRIBUTION OF ANTHROPOGENIC AND NATURAL PB IN A FORMER WII AERIAL GUNNERY RANGE

Isotopic composition and concentrations of Pb are used to identify distribution and sources of anthropogenic and natural Pb in soils and native plants at a former military installation that served as a WWII era aerial gunnery range. Surficial soil and plant samples were obtained in target practice areas where copious amounts of bullets persist and areas unaffected by target practice that are devoid of bullets. A selective sequential extraction procedure was used to determine the distribution of Pb amongst different soil components: soil carbonates and ion-exchangeable minerals, organics and sulfides, oxide and hydroxide minerals, and leachate of residual silicate clays. Plants samples were obtained by sampling multiple species within 1 m square area around each soil sample location. Concentrations of Pb in samples are variable, but vary by up to three orders of magnitude in samples obtained near target practice areas versus samples obtained in areas where bullets are absent. Isotopic compositions of samples directly reflect the presence or absence of bullets in the sample area. Anthropogenic Pb in sample locations with abundant bullets display a wide range of ²⁰⁶Pb/²⁰⁷Pb values (1.140–1.234), but relatively less variation in ²⁰⁶Pb/²⁰⁸Pb values (0.473–0.488), which is hypothesized to be reflective of ore-mixing in the manufacture of bullets. Plants samples exhibit a distinction between anthropogenic and natural Pb similar to soil samples, but consistently display lighter ²⁰⁶Pb/²⁰⁷Pb values than soil samples, which is inferred to be representative of the influence of regional atmospheric deposition of contaminant Pb.