Lead and antimony from bullet weathering in newly constructed target berms: Chemical speciation, mobilization, and remediation strategies.

Understanding lead (Pb) and antimony (Sb) speciation associated with the weathering of bullets at shooting ranges is essential for identifying species migration potential to local watersheds and for assessing the overall toxicity of shooting range soils. In the present study, we fired 2000 5.56 mm bullets into newly constructed and instrumented target berms composed of well-characterized test soils (sand, sandy loam, loamy sand, silt loam) and collected berm pore water runoff and soil samples over five summers (2011 to 2015). We tracked the chemical transformations of Pb and Sb released during bullet weathering as a function of time and soil properties. During 2014 summer, an amendment of ferrous chloride (FeCl2) with a calcium carbonate (CaCO3) buffer was added to a subset of the berms of each soil type to test this remediation strategy. Bulk speciation analysis coupled with micro-scale spectroscopic methods show that both Sb(III) and Sb(V) species are present in soil solution depending on the soil matrix type, but Sb(III) was not observed after 9 months of weathering. In general, Sb was found to be more mobile than Pb, attributable to the relatively low solubility of the dominant Pb phases present in the crust forming around bullet fragments and within soil. The oxidation of Pb(0) resulted in a mixture of lead oxide, lead carbonate, and lead sorbed onto iron(III) oxides. We found a higher degree of metal(loid) mobilization (higher dissolved metal concentrations) in the berms made from the sandy soils. In contrast, silt loam soil was found to be more effective at immobilizing metal(loid)s. Furthermore, we observed that an iron-oxide type amendment may be effective at further reducing Pb and Sb runoff. Results from this study provide insight into the fate and transport of metal(loid)s within small arms target ranges and address a potential method for metal(loid) immobilization.

Pb(II) distributions at biofilm-metal oxide interfaces.

The distribution of aqueous Pb(II) sorbed at the interface between Burkholderia cepacia biofilms and hematite (alpha-Fe(2)O(3)) or corundum (alpha-Al(2)O(3)) surfaces has been probed by using an application of the long-period x-ray standing wave technique. Attached bacteria and adsorbed organic matter may interfere with sorption processes on metal oxide surfaces by changing the characteristics of the electrical double layer at the solid-solution interface, blocking surface sites, or providing a variety of new sites for metal binding. In this work, Pb L(alpha) fluorescence yield profiles for samples equilibrated with 10(-7) to 10(-3.8) M Pb(II) were measured and modeled to determine quantitatively the partitioning of Pb(II) at the biofilm-metal oxide interface. Our data show that the reactive sites on the metal oxide surfaces were not passivated by the formation of a monolayer biofilm. Instead, high-energy surface sites on the metal oxides form the dominant sink for Pb(II) at submicromolar concentrations, following the trend alpha-Fe(2)O(3) (0001) > alpha-Al(2)O(3) (1102) > alpha-Al(2)O(3) (0001), despite the greater site density within the overlying biofilms. At [Pb] > 10(-6) M, significant Pb uptake by the biofilms was observed.