The soil–plant transfer of metals is a very complex process governed by several factors, both natural and anthropogenic, such as sorptive capacity of soil, redox conditions, organic matter and pH. These control the processes of mobility and availability of metals in soils, which in general have a geochemical, climatic or biological origin [16–19]. In addition, the mobility of metals plays an important role in the rhizosphere compartment, which corresponds to the whole inter- face between roots and soil where interactions between the soil microorganisms, roots and soil constituents takes place [20]. The release of protons, exudates and metabolites into the rhizosphere by the roots and the microorganisms can modify the pH, depending on the available source of nitrogen nutrients or iron deficiency [21], thus modifying the fixation and mobility of heavy metals in soils