Ligands are present in the environment due to a plethora of natural and anthropogenic events. They affect metal adsorption onto natural oxides, the dissolution of natural oxides and of metal scales, metal ion removal and uptake by biological systems, metal-solubilization in soils, and the like. Thus, an understanding of the environmental reactions and fate of ligands and metal complexes is of keen importance.

As discussed in Chapters 2 and 6, natural light induces many processes of environmental significance either directly (when light is absorbed by the species of interest) or indirectly (when light excites or produces an intermediate species called mediator that then reacts with the species of interest). For example, the photolysis of metal complexes is important because it obviously affects their concentration and fate (see Section 6.3). A typical example is the photolysis of iron—carboxylato complexes (i.e., complexes with oxalate, aminopolycarboxylates, citrate and humic and fulvic acids) that can occur with high quantum yields. For this reason, in the present experiment an FeEDTA complex is formed and pho-tolyzed, and its metal ion product made evident by a color-producing reaction. EDTA was selected because it is a strong complexing agent for many metal ions and a persistent pollutant due to its high stability (it is even resistant to decomposition by ionizing radiation and heat) and low biodegradability.

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