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Multi-techniques study of the trace metal dynamic in the stratified Krka River estuary (Croatia): combination of DGT and voltammetry

Trace metal dynamic in the stratified Krka River estuary (Šibenik bay), oligotrophic with ultratrace levels of heavy metals [1], has been studied by combination of different analytical tools. According to depth variations of physic-chemical parameters (T/S/pH/%O2), samples were collected by scuba diving in April-2007 and March-2008, at 4 depths. Additionally, in March-2008, samples were collected in the Krka river and the Adriatic sea to obtain the 2 end-members of the estuarine water mixing. These samples were characterized by: DOC and dissolved metal (by DPASV) measurements ; titration by Cu additions in logarithmic scale with analysis of the ASV-labile Cu fraction and further modelling to define the binding parameters (kinetic and equilibrium) of the dissolved organic matter [1]. DOC and Cu concentrations showed non-conservative variations. The increasing Cu concentration at the freshwater/seawater interface seemed to be controlled by the organic ligands (probably produced by biologic activity), leading to calculated free-Cu concentrations lower than the toxicity limit of 10-11M [2]. In summer, important metal contamination of the estuary surface has been recorded, due to increasing boat traffic [3]. Under such conditions, predicted free-Cu concentrations using the previously defined binding parameters showed that the toxicity level is over-passed for the whole water column, except at the bottom. Two field campaigns were performed in July-2008 and 2009. Diffusive- and restrictive-DGT were deployed during 3 to 4 days at 6 depths, at 2 distinctive sites: a “clean” site, and a “polluted” one (in a nautical marina). DGT-labile metal levels were determined by HR-ICP-MS. Samples were collected 1 to 2 times a day at each DGT-depth, leading to discrete and composite samples analysed for DOC, total/dissolved metal concentrations, and Cu/organic matter interactions. Results showed that the main Cu source is antifouling paint release, comparable trends between DGT- and total-metal concentrations, and good correlation between measured DGT-labile and calculated ASV-labile Cu levels were observed.

metal speciation; DGT; estuary; stripping voltammetry

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