4.2. Total concentration of pollutants in soils
These differences between sectors may be due to the joint influence of soil properties and applied treatments. The T1 and T2 treatments contributed with large amounts of carbonates to soils that received a higher concentration of pollutants, but had poor properties to cope with contamination (moderately acidic pH, low or no calcium carbonate content and sandy textures), so the dynamic of the pollutants in these soils was influenced by a high mobility in the soil matrix which, together with the high evapotranspiration of the area, caused the precipitation of the pollutants in the first centimeters of the soils, which is where liming was effective (Simón et al., 2005a). However, the soils on which T3 and T4 treatments were applied, in addition to receiving a lower load of contaminants, had better properties (basic pH, carbonates and fine textures), which allowed the contaminants to penetrate to a lesser extent in the soils and, in the cases where they entered in depth, the precipitation in the soil matrix prevented its capillary rise and its concentration on the soil surface, favoring the dilution effect of the contamination (Martín et al., 2008).
These data show that twenty years after the accident, and after the remediation measures were completed, there are still potentially contaminated soils in the GGC according to current legislation. However, the clean and application of amendments to these soils were effective in most of the GGC, promoting the immobilization of potentially harmful elements, the restoration of essential soil functions and the growth of vegetation, although the full recovery in some of the soils located closest to the mine is still needed (Pastor-Jáuregui et al., 2020).