Dissolution, Transport, and Fate of Lead on Shooting Ranges

Abstract

Shooting ranges concentrate significant quantities of heavy metals, especially lead as spent shot and bullets, on very small parcels of land. Samples taken from a shooting range near Blacksburg, VA, USA provide information about the reservoirs and pathways of lead at shooting ranges in an upland setting and humid environment. Metallic lead corrodes rapidly and develops a coating of corrosion products. The type and amount of corrosion products found on lead shot and bullets are best understood through examination of Eh-pH relationships. X-ray diffraction analysis identified hydrocerussite (Pb₃(CO₃)₂(OH)₂) as the corrosion phase present on lead shot recovered from the range. Hydrocerussite dissolution can produce soluble lead concentrations ranging from 2 ppb to 2 ppm for the soil pH values at this site. This soluble lead is captured by the soil. Sequential chemical extractions revealed that vertical lead migration beyond the A-horizon was minimal. The bound-to-Fe & Mn oxides and bound-to-carbonates soil fractions were identified as significant reservoirs for sequestration of lead in the soil. The highest concentration of extractable lead contained in the soil was directly correlated with the highest concentration of lead shot and bullets measured on the shotgun range surface. The geochemical framework for understanding the corrosion process, identifying the corrosion product(s) that control lead solubility, and identifying the geochemical barriers to lead migration that were employed at the Blacksburg, VA shotgun range, provides a basis for selecting best management practices for this and other shooting ranges.