Under aerobic conditions (Figure ), the distribution diagrams for Ni II , Mg II , Mn II , Co II and Zn II , do not change with respect to those shown in Figure . In fact, Ni II and Zn II are stable in their divalent form under the investigated redox conditions and a similar behaviour is detected for Mn II and Co II as confirmed by the literature . In contrast, the complexation of PDMA with Cu II , Fe III and Fe II , changes with Eh and pH, in line with the findings shown in Figure . Moreover, Cu II complexation starts at a very acidic pH (pH< 3), Fe III is complexed around pH 5.5, whilst only 2 and 1% of Fe II and Mg II are complexed at alkaline pH (Figure and 5b).