Solubility of Cu, Zn, Pb and as in variously treated soils of historical mining sites subjected to waterlogged conditions

Abstract Purpose The Sudetes, a mountain range in the south-western Poland have a complex geological structure. They were the targets of mining for centuries, beginning from medieval times. Ore mining and processing produced large amounts of wastes disposed as mine dumps, tailings and spread material with high concentrations of potentially toxic elements. Solubility of toxic elements in soils that developed from that material depends on various sets of factors, including the kind of rocks, input of external substances, pH and redox. In this study, we assessed the contamination degree of soils in those areas and examined the influence of varying environmental conditions on the solubility of Cu, Zn, Pb and As under prolonged waterlogging in the presence of various amendments. Materials and methods Four kinds of soil material were collected from different mining sites in the Sudetes. They were treated with FeOx-rich wastes (DFW) and beech forest litter (FL), acidified or left unamended, and kept in waterlogged conditions in a 140-day incubation experiment. Soil pore water was collected with MacroRhizon suction samplers after 2, 7, 14, 28, and 140 days. The concentrations of Cu, Zn, Pb and As in pore water were measured using ICP-MS. Results The concentrations of Cu, Zn, Pb and As in soils were in the ranges: 261–918 130–2460, 87.8-57300, and 69.2-44500 mg kg −1 . The study confirmed high concentrations of all metal(loid)s in pore water, depending on the kind of treatment. Prolonged waterlogging considerably reduced Cu, Zn and Pb concentrations in pore water, while As concentrations increased with time, irrespectively of the kind of treatment. The factor that had the greatest effect on the mobilization of metals: Cu, Zn and Pb, was pH, while it was the addition of organic matter in the form of beech litter that had the strongest mobilizing effect on As. Conclusions The results showed that changes in environmental conditions can strongly affect the release of metal(loid)s into groundwater. Factors that cause the mobilization of various elements may act in opposite ways. Therefore, applicability of any treatments designed for remediation of soils affected by mining activity should be thoroughly examined in relation to the properties of those particular soils and their behavior under various treatment. All possible changes in environmental conditions should be considered, including the possibility of long-term waterlogging, induced soil acidification and the influx of organic matter.