Trace metal detection in Sibenik Bay, Croatia: Cadmium, lead and copper with anodic stripping voltammetry and manganese via sonoelectrochemistry. A case study

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 1-1 for Mn, 5-13 ng 1-1 for Cd, 70-230 ng 1-1 for Pb, and 375-840 ng 1-1 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

Influence of sulphur cycle on mercury methylation in estuarine sediment (Seine estuary, France)

In order to investigate interaction between mercury speciation and reduced sulfur, speciation of mercury and sulfur were determined in sediment cores sampled in saline and freshwater wetlands of the Seine estuary, France. Solid phase was analyzed for total (HgT) and monome- thyl mercury (MMHg), total sulfur, acid volatile sulfides (AVS), chro- mium reducible sulfur (CRS) and organic carbon. In porewater, in addition to total and methyl mercury, ion, manganèse and sulfates were aiso determined. Levels of the HgT (0. 5 – 2.0 mgkg$^{-1}$ d.w.) in sediment of the Seine estuary were relatively high and typical for sedirnents in industrial area. The sediment contained 0.5 – 1. 5 $\mu$gkg$^{-1}$ d.w. of MMHg, which made an average 0. 1% of the HgT in sediment. Concentration of MMHg was found to be dependant more on the chemical conditions in sediment than on the level of HgT. Depth profiles of MMHg in the solid phase and HgT in porewater at two sites studied could be related to the production of AVS in sediment as well as to the redox conditions of porewater (defined by Eh and dissolved iron and manganese)