engleski

A complementary approaches for speciation of trace metals in the stratified Krka River estuary (Croatia): DGT vs. Voltammetry

The distribution and speciation of selected trace metals (TM) (Cd/Pb/Cu/Ni/Co) were studied in the water column of the highly stratified estuary by using stripping voltammetry and diffusion gradient in thin films (DGT) techniques. A very good agreement between the vertical profiles of DGT-labile and dissolved TM concentrations were obtained. DGT-labile fraction ranged from >90% for Cd, to <20% for Cu. ASV speciation of Cu showed the presence of two types of organic ligands that form strong (L1, 9.6<logK’1<11.9) and weak (L2, 7.8<logK’2<9.9) complexes. Concentration of free Cu ions at ambient conditions is regulated primarily by the complexation with strong ligands (L1). Relatively good correlation between vertical profiles of ASV-labile and DGT-labile concentrations of Cu were obtained. Modelling of Cu speciation within the salinity gradient showed that interpretation of the type of ligands which form Cu-org complexes should be carefully examined due to the fact that change in sample composition (major ions) have strong influence on estimated experimental conditional stability constant (logK’), and eventually on the prediction of free Cu concentration.

trace metals ; DGT, voltammetry ; estuary

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