Biogeochemistry of Isotopically-distinct Sources of Lead in a Former WWII Aerial Gunnery Range

Isotopic composition and concentrations of Pb are used to identify sources of anthropogenic and natural Pb and to assess Pb bioavailability in soils and native plants at a former military installation that served as a WWII era aerial gunnery range. Surficial soil and plant samples are obtained both 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 is used to determine the distribution of Pb amongst different soil components: soil carbonates and ion-exchangeable minerals, organics, oxide and hydroxide minerals, and leachate of residual silicate clays. Plants samples are obtained by sampling multiple species within 1 m square area for each soil sample location. 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 ^(206)Pb/^(207)Pb values (1.140?1.234), but relatively less variation in ^(206)Pb/^(208)Pb values (0.473?0.488), which is hypothesized to be reflective of ore-mixing in the manufacture of bullets. Plant samples exhibit a distinction between anthropogenic and natural Pb similar to soil samples, but consistently display lighter ^(206)Pb/^(207)Pb values than soil samples, which is inferred to be representative of the influence of regional atmospheric deposition of contaminant Pb.