Structure-stability relationships of metal complexes and metal speciation in environmental aqueous solutions

The methods employed to determine critical stability constants from the published literature are described and the best approach for estimating stability constants to establish a sufficiently broad and extensive database that substantially defines all of the metal complex systems encountered in the environment is recommended. With these estimated formation constants, it is possible, with modern computer techniques, to calculate the speciation and concentrations of the metal complexes in multicomponent systems containing thousands of ligands and 10 to 100 times that number of metal complex species. The structure-stability relationships developed by other investigators are compared with the methods employed herein. Examples of measured, selected and estimated constants are presented for several metal complexes. The distributions of metal complex species in seawater in the absence and presence of an added complexing pollutant are calculated to illustrate the use of the stability constant database and the adjustment of the constants to the conditions required (i.e., ionic strength) for the system under consideration.