Forms and phytoavailability of lead in a soil contaminated with lead shot : a dissertation submitted in partial fulfilment of the requirements for the degree of Bachelor of Science (Honours) in Lincoln University

Abstract

Gun clubs are widespread throughout New Zealand but the environmental impact of Pb shot has not yet been characterised in this country. This dissertation presents a study of the extent of lead contamination in soil and plants resulting from the activity of a gun club with a relatively small membership operating on arable farmland in Canterbury. The study site has been used for over 60 years for clay target shooting. The spatial distribution of lead concentration in the topsoil of a gun club site was determined by carrying out a grid survey. Lead in the soil profile was also determined to a depth of 20cm. A greenhouse study was conducted to assess plant uptake of lead. Total, exchangeable, oxide-bound, organic-bound and residual lead concentrations were determined by a sequential fractionation procedure. The highest EDTA-Pb concentrations were found approximately 100 m from the shooting area (ca. 6000 - 8000 mg EDT A-extractable Pb kg⁻¹ soil) with approximately 30% of the site area above the Australian & New Zealand Environmental & Conservation Council and National Health & Medical Research Council guideline limit of 300 mg kg⁻¹. Little reduction in lead concentration was evident to a depth of 200 mm. The data confirms that shooting activities in New Zealand may cause locally intense Pb contamination. Plant roots contained considerably greater concentrations of Pb than the leaves of all plant species examined. Significant translocation of lead to the shoots occurred, causing lead concentrations in the shoots to exceed the maximum allowable limit for foodstuffs. Approximately 90% of the total Pb at the site is present in the soil in metallic form, as Pb shot. Very little Pb is present as transformation products and soil-Pb compounds, illustrating the characteristic low solubility of Pb.