**3.1 Cadmium**

Cadmium is a relatively rare element in the earth's crust, with content of between 0.1 and 1 mg.kg−1 [15]. In soils, the mobility of cadmium is strongly dependent on the pH and organic matter content of the soil. Thus, an acid pH favours cadmium phytoavailability [16], while a high soil organic matter content significantly reduces phytoavailability [17]. Indeed, soil organic matter easily forms complexes with cadmium and thus makes it less available to plants [17, 18]. According to European Union (EU) directives, the limit value for cadmium in soils should be between 1 and 3 mg.kg−1 [19].
