Effect of organic amendment and plant roots on the solubility and mobilization of lead in soils at a shooting range

Lead (Pb) dissolving gradually from spent pellets constitutes a serious environmental risk in and near shooting ranges, and remediation measures are necessary to prevent its movement to deeper soil layers and ground water. In this study, the effectiveness of organic amendment and plant roots in stabilizing Pb was assessed in a microcosm experiment. Planted (Scots pine, Pinus sylvestris L.) and unplanted microcosms consisting of coarse-textured mineral soil covered with Pb-contaminated humic topsoil were coated with uncontaminated peat layers of 1 to 3 cm and incubated for 77 d. In a percolation test, the microcosms were washed with ultra pure water to simulate heavy rain so as to rinse water-soluble lead (Pbw) from the topsoil layer. Although Pbw remained below detection limits in the mineral soils in all test units, acid-soluble lead (Pba) increased. Peat amendment diminished Pba in the mineral soil layer, this effect being more pronounced in planted soils, indicating that Pb was taken up by the plants. The percolation test showed that the effect of Scots pine seedlings on Pb movement was minor when peat was added. A long-term dissolution test revealed that considerably more Pb was released from old pellets into soil extracts than from new ones, whereas only traces of Pb, if any, were dissolved in sterilized pure water.