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.

Chemical controls on the propagation rate of fracture in calcite.

Calcite (CaCO3) is one of the most abundant minerals in the Earth's crust, and it is susceptible to subcritical chemically-driven fracturing. Understanding chemical processes at individual fracture tips, and how they control the development of fractures and fracture networks in the subsurface, is critical for carbon and nuclear waste storage, resource extraction, and predicting earthquakes. Chemical processes controlling subcritical fracture in calcite are poorly understood. We demonstrate a novel approach to quantify the coupled chemical-mechanical effects on subcritical fracture. The calcite surface was indented using a Vickers-geometry indenter tip, which resulted in repeatable micron-scale fractures propagating from the indent. Individual indented samples were submerged in an array of aqueous fluids and an optical microscope was used to track the fracture growth in situ. The fracture propagation rate varied from 1.6 × 10-8 m s-1 to 2.4 × 10-10 m s-1. The rate depended on the type of aqueous ligand present, and did not correlate with the measured dissolution rate of calcite or trends in zeta-potential. We postulate that chemical complexation at the fracture tip in calcite controls the growth of subcritical fracture. Previous studies indirectly pointed to the zeta-potential being the most critical factor, while our work indicates that variation in the zeta-potential has a secondary effect.