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.