Comparison of the complexation of Cu and Cd by humic or fulvic acids and by ligands observed in lake waters

The complexation of Cu and Cd by ligands observed in filtered unfractionate d lakewaters is compared to the complexation by humic and fulvic acids. Com plexation parameters (conditional stability constants and ligand concentrat ions) of Suwannee River fulvic acids (FA), purified peat humic acids (HA) a nd of ligands in lakewater samples have been determined using the same meth ods (ligand-exchange and CSV (cathodic stripping voltammetry) or ASV (anodi c stripping voltammetry)), and the same titration ranges of Cu, Cd and orga nic carbon concentrations. The performance of the used techniques is first evaluated in FA and HA suspensions, and gives comparable results with the l iterature values for the same materials, according to published models (5-s ite model, NICA model) and parameters. Model calculations using the WHAM mo del for FA and HA (Tipping, 1994) are also presented. The comparison of tit rations of FA and HA with Cu and Cd with those of lakewater samples indicat es that stronger ligands than FA and HA are present at low concentrations i n the lakewaters. Specific strong ligands occur in particular in eutrophic lake waters, whereas in a lake with higher metal concentrations and low bio logical productivity the ligands more closely match the fulvic acid charact eristics.