Soil contamination by heavy metals is common in high mining activity regions, which poses a risk to the ecosystem and human health. These heavy metals are persistent in the soil, so it is a question of recovering contaminated soils through the application of effective techniques in their immobilization such as the use of organic amendments. In this context, the use of biotransformed dry olive residue can be considered as a useful tool in the chemical stabilization of these compounds in the soil, allowing the partial or total restoration of its functionality. The general purpose of our research was to study the effect of dry olive residue biotransformed by the saprobic fungi: Bjerkandera adusta, Coprinellus radians, Coloriolopsis rigida and Penicillium chrysogenum on a soil contaminated by heavy metals. For this, we determined the main soil physicochemical properties (pH, electrical conductivity, carbon, nitrogen, assimilable phosphorus) and enzymatic activities (β-glucosidase and dehydrogenase). In addition, the biomass of the wheat plants (Triticum aestivum) and contents of heavy metals (Cu, Zn, Cd, Pb) in soil and plant were determined. The obtained results showed that most of the treatments with biotransformed dry olive residue promoted the stabilization of heavy metals in the soil, reducing their accumulation in wheat plants. The current results highlighted that dry olive residue biotransformed by C. radians reduced the concentration of Zn and Pb by 25 and 35% in the plant compared to the control, respectively, inducing an improved growth of wheat plants in the presence of these pollutants, increasing their biomass by more than 0.1 g compared to those grown on the soil without amendments. It should be noted that, in the case of dry olive residue biotransformed by B. adusta, phytoextraction was stimulated, increasing concentrations in the shoot by 44% Cu, 35% Zn, 57% Pb and 100% Cd with respect to soil control.
