DISSOLUTION, TRANSPORT, AND FATE OF LEAD SHOT AND BULLETS ON SHOOTING RANGES

 

Shooting ranges concentrate heavy metals, especially lead, as spent shot and bullets on very small parcels of land. Surface lead concentrations as high as 5,000 g Pb/m² have been observed at the U.S. Forest Service¢s shotgun range located west of Blacksburg, VA in the Jefferson National Forest. Subsequent concerns have been raised about the dissolution, transport, and fate of the lead released as these shot and bullets corrode. At the Blacksburg, VA shotgun range spent lead shot rapidly oxides and forms a pale white corrosion coating of hydrocerussite (Pb₃(CO₃)₂(OH)₂).  Hydrocerussite becomes increasingly soluble in acidic pH conditions. Acidic shooting range conditions therefore have the potential to mobilize lead into the soil and possibly the groundwater. Selective sequential extractions (SSE) were performed on soil core samples taken from the shotgun range to quantify total lead concentration in five soil fractions: soil solution, exchangeable, bound to carbonates, bound to iron and manganese oxides, and bound to organic matter at four depth profiles: A horizon, A horizon - 10 cm, 10 - 30 cm, and 30 - 50 cm. SSE results indicate that carbonates, iron and manganese oxides and organic matter incorporate the majority of the lead in the A horizon. Lead transport to deeper horizons appears to be very minimal as exhibited by the pronounced lead concentrations in the A horizon and the negligible concentrations in the10 - 30 cm and 30 - 50 cm depth profiles. Application of soil amendments to the range surface has the potential to increase the lead adsorption capacity of the soil, thus effectively immobilizing the lead.

Table 1. Pb content (mg/kg) of soil fractions
	A	A - 10 cm	10 - 30 cm	30 - 50 cm
Water Soluble	BDL	BDL	BDL	BDL
Exchangeable	BDL	BDL	BDL	BDL
Carbonates	99.2	3.21	1.79	2.39
Fe & Mn Oxides	130.5	29.5	22.7	29.8
Organic Matter	237.1	39.9	2.54	2.52