Organic complexation of copper in estuarine waters: An assessment of the multi-detection window approach

Speciation of dissolved Cu in seawater is mainly dominated by organic complexation. However, the analysis is complicated by the presence of many different classes of naturally-occurring organic ligands. In this study, we successfully determined the total dissolved Cu concentrations, Cu-complexing ligand concentrations and their conditional stability constants in Japanese estuarine waters using competitive ligand exchange adsorptive stripping voltammetry (CLE-AdCSV) coupled with a multi detection window approach. The Cu speciation parameters were calculated using ProMCC software. The use of the 5 μM SA detection window was sufficient and effective in detecting two ligand classes in the waters of Otsuchi Bay. The concentrations of the strong ligands (L1) were between 1.95 and 4.21 nM, while the concentrations of the weak ligand (L2) were in the range of 6.3-33 nM. The conditional stability constants of the strong ligand were around 1015, while those of the weak ligands averaged around 1013. In all of the samples, the L1 concentrations exceeded the total dissolved Cu concentrations, and the two parameters were strongly correlated. Free Cu2+ concentrations were between 10−13 and 10−15 M, a range that is not toxic for most phytoplankton.