At low Eh (-300 mV) representing anoxic conditions (Figure ), iron is mainly present as Fe II (see Figure ), therefore, no Fe III complex forms. Due to its very low logK value, Mg II is not complexed by PDMA at any pH value. In acidic pH, PDMA forms complexes with Ni II , Zn II , and Co II (from pH 4.5 to 5.5); at mildly acidic pH (6.5), the PDMA started the complexation of divalent iron; and at pH between 7.5 and 8, PDMA complexed Mn II and Cu II . This result confirms that for less stable metal-PDMA complexes the pH range of formation shifted to more basic values.