Long-term assessment of remediation treatments applied to an area affected by a mining spill in Spain

This study evaluated the effectiveness of remediation treatments in the long-term (20 years) for one of the largest mine spills in the world, the Aznalcollar accident. Soil recovery was carried out through the application of various rates of organic (compost and manure) and inorganic amendments (materials rich in iron oxides and calcium carbonate). Different amendment combinations were grouped in four treatments (T1 to T4) and applied in different sectors depending on the soil properties and the degree of initial contamination. To assess the degree of soil recovery, physicochemical properties, total, water-soluble, and bioavailable concentrations of the main contaminants (Pb, As, Zn, and Cu) were determined over time. Applied treatments increased pH, calcium carbonate, and organic carbon content of soils, reduced electrical conductivity, and decreased mobility of contaminants, indicating that remediation treatments were efficient recovering soils contaminated by potentially harmful elements (PHEs). However, 20 years after the accident, total concentrations of Pb and As still exceed the intervention levels of the current regulations in certain areas. These areas are located in the sectors closest to the mine and where treatments T1 and T2 were applied. In these cases, the added doses of organic amendments, iron oxide-rich soils, and carbonate amendments were not sufficiently effective, so the application of new treatments is recommended to complete the total recovery of the Guadiamar Green Corridor.