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Determination of the copper complexing ligands in the Krka river estuary

The copper complexing capacities (CuCC), i.e. organic ligands capable to form stable organic complexes with copper ions, were measured in the Krka river estuary. Krka river estuary is a carstic, salt wedge estuary situated on the Eastern coast of middle Adriatic area. The measurements have been done in 1983, 1984 and in 2008 on the same sampling stations along the estuary. The measurements were performed with electrochemical method of differential pulse anodic stripping voltammetry (DPASV). It has been found that the copper complexing capacity of the fresh water layer is several times higher (from 100 up to 270 nM) than of the saline layer beneath it (from 10 up to 130nM).The concentrations of surface active substances ( SAS) were also higher in the layer above halocline (0.120 to 0.170 mg dm-3 eq. Triton-X-100), while below it the values were lower (0.085 to 0.127 mg dm-3 eq. Triton-X- 100). The average result for CuCC measured in 2008, of 103 nM is not different from the average value measured by the same technique 25 years ago ( the average value of all measurements in 1983 and 1984 is 105 nM). This indicates that there is no change in the amount of dissolved ligands capable to complex copper ions in this long period of time.The speciation modelling have shown that more than 99% of copper is present as organic complexes while free(hydrated) copper ion concentration is below the toxicity threshold of 10 -11 M, although in some situations total free (hydrated)+ inorganically complexed copper could be above this threshold level.

copper ion ; complexation ; organics ; estuary ; Krka river ; electroanalytical methods

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