Trace Element Concentrations in Saltmarsh Soils Strongly Affected by Wastes from Metal Sulphide Mining Areas

Abstract

Soil and water samples were analysed for trace metals and As in two watercourses and 14 sampling plots in a salt marsh polluted by mine wastes in SE Spain. Groundwater levels, soil pH and Eh were measured ‘in situ’ for a 12-month period in each sampling plot, and total calcium carbonate was also determined. Low concentrations of soluble metals (maximum Mn 1.089 mg L⁻¹ and maximum Zn 0.553 mg L⁻¹) were found in the watercourses. However, total metal contents were extremely high in the soils of a zone of the salt marsh (maximum 1,933 mg kg⁻¹ of Mn, 62,280 mg kg⁻¹ of Zn, 16,845 mg kg⁻¹ of Pb, 77 mg kg⁻¹ of Cd, 418 mg kg⁻¹ of Cu and 725 mg kg⁻¹ of As), and soluble metals in the pore water reached 38.7 mg L⁻¹ for Zn, 3.15 mg L⁻¹ for Pb, 48.0 mg L⁻¹ for Mn, 0.61 mg L⁻¹ for Cd and 0.29 mg L⁻¹ for As. Variable concentrations with depth indicate a possible re-mobilisation of the metals, which could be related to spatial and temporal variations of water table level, pH and Eh and to the presence of calcium carbonate. A tendency for the Eh to decrease in the warmest months and to increase in the coldest ones was found, especially, in plots that received water with a high content of dissolved organic carbon. Hence, the existence of nutrient effluent-enriched water may modify the physical–chemical conditions of the soil–water system and influence metal mobility.