Lead transformation and distribution in the soils of shooting ranges in Florida, USA

Abstract

The use of lead bullets and shot at shooting ranges is under increasing scrutiny as a potentially significant source of Pb pollution. This study assessed Pb contamination in the soils of two shooting ranges (TRR and MPR) in Florida. Soil samples were collected from the two ranges and analyzed for total Pb to determine Pb contamination. Selected spent bullets and berm soil samples were mineralogically characterized to identify Pb transformation. Total Pb in the range soils was significantly elevated with the highest (up to 4.84% by weight) in the berm soils. Most soils failed the synthetic precipitation leaching procedure (SPLP) test. Also, at the MPR shooting range, a substantial amount of Pb migrated down in the subsurface soil, possibly due to the enhanced solubilization of organic Pb complexes at alkaline pH, whereas high cation exchange capacity of the profile soil may be responsible for Pb retention in the subsoil. The weathering products on the surface of the spent bullets were predominantly hydrocerussite [Pb 3(CO 3) 2(OH) 2] and cerussite (PbCO 3). Hydrocerussite was mainly found in the MPR range soils, whereas Pb was transformed into hydroxypyromorphite [Pb 5(PO 4) 3OH] in the TRR range soils because of the presence of more P. Sequential extraction and lead activity ratio modeling showed that the soil Pb solubility was controlled by Pb carbonate minerals in the MPR shooting range, and by less soluble Pb phosphate minerals in the TRR shooting range. This research suggests that it is important to develop and implement efficient management practices to minimize adverse impacts of Pb at shooting ranges. Phosphate-induced Pb immobilization may be an effective alternative for reducing Pb mobility in the shooting range soils.