Distribution and mobility of lead in soils at an outdoor shooting range

Abstract

The distribution of total Pb in surface and subsurface soil horizons at an outdoor shooting range in southeastern Michigan was determined by single extraction elemental analysis (AAS and ICP‐AES). Significant Pb enrichment of the site's soils coincides closely with Pb vapor and particulate matter produced from shot shell primers and the downfall of Pb/Sb pellets associated with the recreational shooting of skeet and trap. Surface concentrations in these locations are 10 to 100 times greater than the background concentration found on adjacent properties. The distribution of Pb in the subsurface soil horizons corresponds to the distribution of Pb at the surface, which suggests the Pb is mobilizing and migrating downward through the vadose zone. This mobilization appears to be occurring despite the clay‐rich nature of the soils, and may be due to the transformation of metallic Pb into soluble Pb compounds of carbonate and sulfate: Both compounds appear to be present in crust material found coating many of the pellets found at the site. The downward migration of soluble Pb is a potential threat to groundwater that is present at the site at a depth of less than 1 m. The protection of surface water quality is also a concern because Pb pellets from the shooting range have been found in the bed sediments of a nearby stream.