5. Conclusions
Our results indicate that the combination of organic and inorganic amendments used represents an efficient method to recover soils contaminated by heavy metals and arsenic. The different doses used mainly increased the pH, CaCO3 and organic carbon content of the soils, reduced the EC and decreased the solubility and bioavailability of the contaminants. The effect of the different treatments became very evident 6 years after the accident, and the positive evolution over time has produced a homogenization of soil recovery in all sectors. Nevertheless, treatments T1 and T2 were applied in doses that were not sufficient to improve the properties of these soils at the same rate as in the other treatments, mainly due to the higher degree of the initial contamination received and the worse properties of the soils where these treatments were applied. Moreover, in certain sectors where T1 and T2 treatments were applied, total concentrations of Pb and As have been detected exceeding the intervention levels of the current regulations, indicating the presence of potentially contaminated soils. Additional treatments with higher doses of organic amendment, iron-rich material and calcium carbonate amendments are recommended to complete the full recovery of these residual areas.