Quick Dips

Shooting the Soil

Metallic lead in the environment is inert, right? Wrong! Corinne Rooney has been investigating what happens to lead shot deposited on the soil at shooting clubs, while completing a BSc (Hons) degree at Lincoln University.

Affected by the air, soil and moisture, the lead shot oxidises to form a crust consisting mainly of lead carbonate salts. The lead salts subsequently dissolve into the soil and bind to soil particles. This contrasts with lead shot in aquatic environments, where water prevents the oxidation process from occurring.

While just 10% of the total lead present at the study site had dissolved, soil lead concentrations were substantially elevated, hundreds of times greater than background concentrations, and with concentrations of lead in soil and plants that are well above guideline limits for environmental and human health. The maximum level of contamination was similar to, or greater than, that from lead sources such as mining and smelting, vehicle emissions and lead-based paint.

"This confirms that soil contamination by lead shot at clay target shooting clubs is a potential problem in New Zealand," says Rooney, who was involved in a recent Canterbury Regional Council survey of lead concentrations at Canterbury clay target shooting clubs.

One of the objectives of her present work is quantification of the rate of lead shot dissolution. The potential for lead to be leached from contaminated sites is also important, she says, as the capacity of the soil to hold lead will be exhausted at some stage.

While the site studied for her honours work was taken out of agricultural production once the contamination was found, correct management of such areas has not been established. Rooney has designed her work so that this issue can be addressed.