On-board determination and ecological risk of Cu species in Yellow River Estuary

Copper (Cu) speciation was highly dynamic and could be biased by sample handling, storage and transport. In this study, an on-board electrochemical speciation analysis was used to quantify natural labile Cu (NL Cu) and total dissolved Cu (TD Cu) in surface and bottom waters of the Yellow River Estuary in winter immediately after collection. Along the main flow path toward the Bohai Sea (C1-C4), NL Cu was higher in surface water (0.87 μg/L) than in bottom water (0.73 μg/L) in the river-sea mixing zone because of the salinity as a key driver. The NL/TD Cu ratio decreased from nearshore to offshore. An integrated assessment combining contamination factor (C_f, TD Cu-based) with NL Cu-based ecological risk (SSD-derived PNEC and risk quotient, RQ) indicated that although C_f suggested relatively good water quality (C_f < 1), medium to high ecological risks could occur when NL Cu constituted a high proportion of TD Cu. This on-board approach coupled with the integrated framework might be applicable to Cu speciation research and ecological risk assessment in other estuaries.