Chemical Speciation of Dissolved Copper in the Nakdong River Estuary and Its Relationship with Humic-Like Fluorescent Dissolved Organic Matter

The total dissolved copper (Cu) concentrations, chemical speciation, and intensities of humic-like fluorescent dissolved organic matter (FDOMH) components were determined in the Nakdong River Estuary. The concentrations of total dissolved Cu ranged from 4.6 to 13.3 nM and showed an inverse correlation with salinity (R2 = 0.93), indicating a conservative mixing trend in the Nakdong River Estuary. The chemical speciation of dissolved Cu was determined by competitive ligand equilibrium adsorptive cathodic stripping voltammetry, and speciation parameters were calculated using ProMCC software. The concentrations of the strong Cu-binding organic ligands (L1) ranged from 3.1 to 96 nM, whereas those of the weak ligand (L2) ranged from 10 to 3400 nM. Both L1 and L2 concentrations were relatively high at the upper sampling sites (river water sites) and decreased in proximity to the coastal sea, indicating that Cu-binding organic ligands from terrestrial sources may be dominant in the Nakdong River Estuary. Although Cu-binding organic ligands showed positive correlations with FDOMH, anomalously high concentrations of Cu-binding organic ligands were observed at river water sites, suggesting additional sources of organic ligands. Our results suggest that Cu-binding organic ligands originated from various sources in estuarine environments.