Long-term toxicity assessment of soils in a recovered area affected by a mining spill

- 15 years after the Aznalcóllar mine spill residual pollution remains in some areas.
- Toxic levels were exceeded for total As and Pb and for soluble As, Zn and Cu.
- Metals responsible for soil toxicity are different depending on the tested organism.
- pH and organic carbon content reduce metal availability and therefore soil toxicity.
- Regulatory guidelines in the area should be revised to reduce the risk of toxicity.

Residual pollution in the Guadiamar Green Corridor still remains after Aználcollar mine spill in 1998. The polluted areas are identified by the absence of vegetation, soil acidic pH and high concentrations of As, Pb, Zn and Cu. Soil toxicity was assessed by lettuce root elongation and induced soil respiration bioassays. In bare soils, total As and Pb concentrations and water-extractable levels for As, Zn and Cu exceeded the toxicity guidelines. Pollutants responsible for toxicity were different depending on the tested organism, with arsenic being most toxic for lettuce and the metal mixture to soil respiration. Soil properties, such as pH or organic carbon content, are key factors to control metal availability and toxicity in the area. According to our results, there is a risk of pollution to living organisms and the soil quality criteria established in the area should be revised to reduce the risk of toxicity.