Assessment of the environmental risks associated with two mine tailing soils from the La Unión-Cartagena (Spain) mining district

• Potential risks associated to two abandoned mine tailings have been evaluated.
• The soils showed elevated total and soluble trace element (TE) concentrations.
• TEs were mostly present as highly mobile and available species in pore water.
• Soils and pore waters proved to be highly toxic for plants and aquatic organisms.
• These soils pose a significant risk to the environment and need remediation.

Abandoned former mine spoil accumulation ponds are important sources of contamination for the surrounding areas, including villages and agricultural land. Characterisation of the contamination in these sites is therefore needed to assess the environmental risk associated with the possible dissemination of the pollutants. With this aim, physico-chemical parameters, trace element (TE) concentrations, solubility and speciation and the ecotoxicity of soils from two different sites, one acidic and the other neutral, within the mining district of La Unión-Cartagena (SE Spain) were determined. All the soils had very high total, soluble and extractable TE concentrations, and free ions, metal-sulphates and organo-metal complexes were the predominant metallic forms found in pore water. In the case of As, H2AsO4− dominated in the samples from the acidic site. The soils showed elevated toxicity for different plant species (bean, sunflower and lettuce growth, as well as lettuce and cress germination, were strongly inhibited) and aquatic organisms (mortality was very high for both Thamnocephalus platyurus and Vibrio fischeri), due to both their high salinity and TE content. These soils are therefore in need of remediation, to reduce the environmental risk that they pose.