Trace Metal Detection in Šibenik Bay, Croatia: Cadmium, Lead and Copper with Anodic Stripping Voltammetry and Manganese via Sonoelectrochemistry. A Case Study

D. Omanoviæ^a, Ž. Kwokal^a, A. Goodwin^b, A. Lawrence^b, C.E. Banks^b, R.G. Compton^b,* and Š. Komorsky-Lovriæ^a,*

^aCentre for Marine and Environmental Research, "Rudjer Boškoviæ" Institute, P.O.Box 180, 10002 Zagreb, Croatia

^bPhysical and Theoretical Chemistry Laboratory, Oxford University, South Parks Road, Oxford OX1 3QZ, United Kingdom

(Received 16 October 2005, Accepted 1 February 2006)

      The vertical profiles of the concentration of reactive Mn and total concentrations of Cd, Pb, and Cu ions in the water column of the Šibenik Bay (Krka river estuary) were determined. The measured ranges of concentrations are: 60-1300 ng l^-1 for Mn, 5-13 ng l^-1 for Cd, 70-230 ng l^-1 for Pb, and 375-840 ng l^-1 for Cu. These values are comparable with the concentrations found in the unpolluted estuaries. The Krka river estuary is highly stratified, with the measured salinity gradient of 20% within a half meter of the freshwater-seawater interface (FSI). The main changes in the vertical profiles of the measured parameters occur in the FSI: the temperature increases for 1 °C and the pH decreases for 0.1 unit, whereas the metal concentrations show different behaviour. Generally, Mn, Pb, and Cd ions show the increase of concentrations in the FSI, while copper concentration profile indicates anthropogenic pollution in the brackish layer caused by agriculture activities and by the paint with copper basis used as an antifoulant biocide for the ships. UV-digested samples show an increase in manganese concentrations for at least 3.5 times comparing to non UV-digested. This suggests that in natural water manganese exists mainly in the form of inert complexes and as associated to particulate matter (about 70-80%). UV irradiation has no influence on the concentration of cadmium, while for lead an increase of 50% in the seawater layer is observed. The twofold increase of the copper concentration in the upper freshwater layer and at least the fourfold one in the seawater layer were measured in the UV-digested samples. These results show that copper is strongly bound to inert complexes, and that UV-digestion is necessary step in determination of the total metal concentrations in natural water samples. No significant increase of the metal concentrations in the deeper seawater layer was observed, indicating the absence of the processes of remobilization or dissolution of metals from the sediment. Presented results confirm that the new method for the determination of manganese by CSV on boron-doped diamond electrode with ultrasound enhanced accumulation can be successfully applied to natural waters.
 

Keywords: Sono-electrochemistry, Anodic stripping voltammetry, Manganese, Lead, Copper and Cadmium, Seawater, Estuary