From Denver, at a meeting of the Geological Society of America
The lead used in bullets and shotgun pellets can be a threat to the environment near rifle ranges, but many of its hazards are manageable, a new study suggests.
During the 20th century, U.S. hunters and target shooters fired ammunition that contained a total of about 4.5 million metric tons of lead. Most of that lead is concentrated at shooting ranges, says J. Donald Rimstidt of Virginia Polytechnic Institute and State University in Blacksburg. Although many jurisdictions today restrict the use of lead shot, Rimstidt estimates that shooters still pump about 60,000 metric tons of lead into the environment each year.
A soil survey at a rifle range operated by the U.S. Forest Service near Blacksburg—a facility that’s been open only 10 years—suggests that the soil there contains about 12 metric tons of lead from bullets. The shotgun range next door harbors about 11 metric tons of lead.
The outside of a lead bullet corrodes into a white, crusty mineral called hydrocerrusite, which dissolves in water seeping through the ground after a rain. Analyses of soil at the Blacksburg ranges show that the top few centimeters of soil contain an average of 340 parts per million of lead, a concentration about 30 times that found in soil nearby. The analyses also suggest that the dissolved lead hasn’t migrated to soil depths below 10 cm, because concentrations there aren’t significantly higher than those in soil away from the ranges.
Any lead dissolved in rainwater sticks to carbonate compounds and other minerals in the soil, says Rimstidt. This phenomenon minimizes the concentrations of dissolved lead in streams near the ranges. Therefore, the largest threat to nearby ecosystems is erosion of a shooting range’s soil. Basins could be constructed to capture that lead-tainted earth before it washes downstream, says Rimstidt.
Only about one-sixth of the lead found on the Blacksburg shotgun range turned up in the 60-meter-long area in front of the earthen backstop there. The rest ended up in the backstop or in the forest beyond, at distances of up to 300 m from where shooters stand, says Rimstidt. There are so many lead bullets embedded in the trees behind the rifle range that that wood, when disposed of, may need to be treated as hazardous waste.
