A release of toxic elements from military shooting range soils as affected by pH and treatment with compost

Abstract

A screening part of this study examined soil enrichment in 7 potentially toxic elements: Cd, Cr, Cu, Ni, Pb, Sb and Zn, in two complexes of military shooting ranges situated in SW Poland. For those elements that pose a real threat to the environment, their release into pore water was examined more thoroughly. The highest values of geoaccumulation index Igeo, with the median values above 1.5, were found for Sb, Pb and Cu, therefore further release-oriented experiments focused on these three elements. Their maximum concentrations in soils were: 89.6, 48,400 and 1230 mg kg−1, respectively. A 140-day incubation experiment was carried out with 5 strongly enriched soils treated with acid, lime and commercial green-waste compost, to illustrate the effects of pH and exogenous organic matter on the release of Sb, Pb and Cu into soil pore water. The treatment with lime and/or compost is usually believed to immobilize metals, while various authors reported contradictory effects of soil amendment with organic matter on the solubility of Sb. The present work indicated that liming can induce a release of Sb and Cu into soil pore water, and the treatment with compost can result in increased Cu and Pb solubility in alkaline conditions. The effect of immobilization observed in acid- and lime-treated soils after a prolonged incubation, was in the case of Pb and Cu explained by simple buffering rather than by aging. Long incubation with compost ensured immobilization of Pb, but not necessarily of Sb and Cu. The overall effects of soil treatment with moderately mature compost on the release of Sb, Pb and Cu into pore water of shooting range soils are ambiguous, and for this reason, each case of planned application of compost to polluted soils should be preceded by a thorough experimental examination.