Bioavailability and risk assessment of metals in shooting range soil – a collection of case studies

Metal pollution on shooting ranges can pose a risk to both humans and animals residing in the area, and it can affect the ecologic conditions of the soil. This report contains a collection of previously unpublished small laboratory and case studies that can provide information about the bioavailability of metals and their impact on plants and the ecologic conditions of the soil. The report consists of five case studies: uptake of metals in plants, berries and mushrooms, use of DGT in soil, leaching tests to look at the bioavailability of metals in soil, use of Bait-lamina in soil in the field and in the laboratory, and an avoidance study of earthworms.

Samples of plants, berries, mushrooms, and soil were obtained from Steinsjøen shooting range. We used diffusive gradient in thin film (DGT) in a laboratory to test soil samples that had previously been tested for uptake of metals in earthworms. DGT is a passive sampler that can provide information about the proportion of metals in the soil that is available for uptake in plants and other biota. We used Bait-lamina in both laboratory and field settings. These are used to assess variations in biological activity in soil across different areas. To determine if earthworms prefer uncontaminated soil to metal-contaminated soil, we carried out an avoidance test in a lab.

Mixed plant samples from larger areas did not contain concentrations of metals above normal or limit values for animal feed. All but one of the berry samples obtained at Steinsjøen in 2021 had lead concentrations that exceeded the EU limit value for lead in berries (0.2 mg/kg wet weight). A small intake of berries picked in lead-contaminated areas will still not be harmful. All the mushrooms that were picked had lead concentrations that exceeded the EU limit value for lead in mushrooms (0.8 mg/kg wet weight), and the concentration of lead in mushrooms was about 100 times higher than the concentration in berries. DGT results correlated with both concentration of copper and lead in soil and with uptake in earthworms. In the laboratory study, the results from the Bait-lamina test correlated well with the metal concentration in the soil, while in the field, the variation within each area was the same as between the areas. This could be due to biological activity not significantly changing between areas with high and low metal concentrations, or it could suggest that the method is less reliable in the field. The results from the earthworm avoidance study were inconclusive, suggesting no clear preference in earthworms for either contaminated or clean soil. However, the data is too limited to draw definitive conclusions.

Plant samples may be better suited than soil samples in risk assessments for grazing animals. However, in most cases, there will be little risk of metal poisoning to grazing animals on firing and training ranges. The metal concentration in berries and mushrooms growing on contaminated shooting ranges should be further investigated to find out whether to advise against picking these on the Norwegian Armed Forces’ shooting ranges. If a shooting range contains many mushrooms, this should be included in risk assessments. DGT can be regarded as a good model for uptake of metals in earthworms, but analysis of only the concentration in the soil may also be sufficient. The Bait-lamina results were inconclusive, and we therefore do not recommend Bait-lamina field testing as a suitable measure of the ecologic conditions of the soil.