Marko Branica

Determination of the apparent copper complexing capacity of seawater by anodic stripping voltammetry

Abstract A new experimental technique using differential pulse anodic stripping voltammetry with a thin-film mercury electrode and efficient mixing of the electrolyte for the apparent copper complexing capacity of seawater is proposed. The effects of some factors such as type of electrode and cell, pH of the solution, potential of deposition, time of equilibration, and influence of a non-ionic surface active agent on the measurements are examined. Experimental results for the apparent copper complexing capacity of seawater are calculated presuming 1:1 inert complex formation. By using EDTA as a model ligand, it is shown that the proposed procedure with efficient mixing of the solution excludes any appreciable kinetic influence upon the electroanalytical results.

Trace metal adsorption on inorganic solid phases under estuarine conditions

The adsorption of trace metals (Pb, Zn, Cu, Cd and Hg) on calcite, kaolinite and bentonite has been studied in Krka river water of various salinities (S = 3, 20 and 38‰). Model experiments were performed at pH 8 in natural water and in UV-irradiated water samples to determine the importance of natural soluble organic matter. Cold vapour atomic absorption spectrometry was used for the Hg determination, and a differential pulse anodic stripping voltammetry (DPASV) method for determination of other trace metals, using either a hanging mercury drop electrode or a mercury-coated glassy carbon working electrode. The following results have been obtained on calcite: 1. (1) a powerful absorption of Pb and Zn was observed for both natural and UV-irradiated waters at S=20‰; 2. (2) a strong adsorption of Hg was observed in natural water, and significantly lower adsorption in UV-irradiated water at all three salinities, particularly at low salinity; 3. (3) Cd adsorption was of medium intensity in both waters at S=20‰; 4. (4) Cu was practically not adsorbable in both waters at S=20‰ if the total Cu ion concentration was lower than the copper complexing capacity value; 5. (5) Cu adsorption was of a medium intensity at S=38‰. It has not influenced by the EDTA model ligand. Trace metals Pb, Zn and Cu are adsorbable on kaolinite and bentonite at S=38‰, whereas Cd is practically not adsorbed. The Krka River is a calcareous river, which supplies the sea with calcite and aluminosilicates. In the light of our model experiments, we suggest that the self-purification of the Krka River is remarkable in respect to Pb, Zn and Hg; this occurs to a lesser extent for Cu, and is negligible in the case of Cd.

A comparison of anthropogenic mercury pollution in Kaštela Bay (Croatia) with pristine estuaries in Öre (Sweden) and Krka (Croatia)

Anthropogenic mercury pollution was studied in Kastela Bay (Croatia), 10 years after chloralkaline plant (PVC) stopped production. The concentration of total mercury determined in sediments which are composed mainly of calcite and quartz, are in the range 14,280-30,400 ng/g. The values are higher than reported in the literature for Elbe and Seine estuaries and also above 25,000 ng/g used for criterion in remediation project in Minamata Bay. The concentration of methylmercury 6.05-36.74 ng/g are typical for slightly to highly contaminated estuarine sediments. The low ratio of methylmercury to total mercury found in sediments of Kastela Bay is in the range 0.04-0.18%. It can be explained that in this region predominate conditions which do not promote in-situ methylation. Sediments were found to be highly anoxic. Concentrations of total mercury in unfiltered surface waters are in the range 69-145 ng/l and in unfiltered bottom waters in the range 230-1,418 ngl(-1). High concentrations found in bottom waters suggest that either resuspension or partial dissolution of sediments takes place. An experiment performed on filtered and unfiltered waters showed that about 85% of total mercury in surface water and almost 100% in bottom water was retained on 45 microm filters. To demonstrate contrasts, two pristine estuaries from norths and south Europe were studied. Silicious sediments of Ore estuary (Sweden) and calcareous sediments of Krka estuary (Croatia) have total mercury concentrations close to accepted background level. The ratio of methylmercury to total mercury is < or = 1% in all samples with one exception. The highest observed ratio (2.70%) was in the surface sediment from E2 station in Krka estuary measured in March 2000. This location is suitable for studying methylmercury formation in pristine environment.

Distribution of Cd, Pb, Cu and Zn in carbonate sediments from the Krka river estuary obtained by sequential extraction

Abstract Distribution of Cd, Pb, Cu and Zn in oxic carbonate sediments from the Krka estuary was studied by a sequential extraction technique, designed to distinguish: exchangeable cations (F1), carbonates (F2), hydrous oxides of Fe and Mn (F3), organic matter (F4) and residual fractions (F5). The procedure was performed on the sediments of selected grain size fractions: 150–300, 61–150 and 5–61 μm. Trace metal concentrations were generally low (Cd 0.156–0.399, Pb 17.3–118.6, Cu 19.1–52.1 and Zn 66.2–168.1 μg/g dry wt, even in the smallest size fraction). Distribution of trace metals differed for varying size fractions. Generally, there was no relation between metal concentrations in fractions F2, F3 and F4, and the concentrations of sediment components (CaCO3, organic matter, Fe and Mn). The highest metal concentrations were obtained in F2 (Pb in 61–5 μm and Cd and Zn in 300-150 μm size fractions) and in F3 (Cu, Zn and Cd in 61-5 μm). The concentrations in other fractions were lower. Despite the fact that carbonates are not known as trace metal collectors, such a distribution did not seem to be merely the result of the metal desorption from other sediment components.

Adsorption of Cd(II) and Pb(II) on bentonite under estuarine and seawater conditions

Abstract The adsorption of cadmium and lead ions to natural iron bentonite has been studied in seawater of various dilutions. Both ions are well adsorbed under freshwater conditions. However, negligible adsorption of cadmium, as distinguished from lead ions was observed under seawater conditions. The influence of particular seawater constituents on the decrease in cadmium adsorption has been studied. Among the inorganic ions of seawater, magnesium and chloride show the greatest inhibiting effect. The inhibition of cadmium adsorption decreases in the order Mg2+ > Ca2+ > Sr2+. This is at variance with the ion-exchange theory and is probably due to the significant difference in concentration ratios of these elements found in seawater (Mg, 0.053; Ca, 0.010; Sr, 0.00015 mol dm−3). Organic ligands of marine origin, as well as selected sugars, amino sugars and amino acids, decrease cadmium adsorption, while artificial surface active substances (Triton X-100, dodecyl benzene sulphonic acid-sodium salt, dodecyl piridinium chloride), added in concentrations lower than the critical micellar concentration, show no effect. The experiments performed in this work suggest the mechanism of a self-purification ability of river water containing suspended bentonite. However, upon entering the sea, cadmium will be remobilized from the particles of the organically coated bentonite.

Distribution of zinc, lead, cadmium and copper between different size fractions of sediments I. The Limski Kanal (North Adriatic Sea)

Abstract The distribution of zinc, cadmium, lead and copper in different grain-size fractions of sediment from the upper part of the Limski Kanal (North Adriatic Sea) has been studied. The results are discussed in relation to the textural, mineralogical and chemical characteristics of the sediments. Sediment particles μ m normally contained a high proportion of all studied metals. The coarser particles (> 63–300 μ m), depending on the sampling site, incorporate metals in amounts similar to, or even higher than, the finest grains. Metal distributions are significantly correlated with the organic material in the sediments from the Limski Kanal. A significant difference was obtained for metal concentrations between sediments collected in June and December 1979.

Iodine speciation in the water column of the Rogoznica Lake (Eastern Adriatic Coast)

Abstract Specific concentration profiles of iodate, iodide and organo-iodine in the water column of the Rogoznica Lake, where both oxic and anoxic conditions occur, were observed. Iodate and iodide concentrations were determined directly in water samples by differential pulse voltammetry (DPV) and cathodic stripping square wave voltammetry (CSSWV), respectively. Concentrations of ‘labile’ and ‘stabile’ organo-iodine were determined by DPV in the samples pretreated with chlorine water and UV-irradiation (combined with hydrogen peroxide and followed by chlorine water addition), respectively. In this stratified water column (salinity and dissolved oxygen gradients) with pronounced biological productivity, high concentrations of iodide (up to 0.87 μM) and significant percentages of ‘labile’ and ‘stabile’ organo-iodine, up to 37% and 30% respectively, were found. The formation of ‘labile’ organo-iodine is primarily governed by chemical reactions with dissolved sulphur forms and organic compounds, as well as remineralization processes of ‘stabile’ organo-iodine.

Trace metals in sediments from the adriatic sea

Abstract Concentrations of Zn, Cd, Pb, Cu and Hg were determined in sediments (grain-size fraction μ m) from different parts of the Adriatic Sea. The results were compared with data obtained in sediments of similar granular composition by other authors concerned with pollution problems in the Adriatic Sea. Data obtained and summarized in the present work were derived from unpolluted marine and estuarine sediments, with the exception of sediments from locations under direct anthropogenic influence. Lead concentrations in the sediments along the Adriatic coast are significantly higher than those found in 1976. This might be attributed to an increase in recreational ship traffic during the summer along the coast, using leaded gasoline.

Mercury distribution in the krka river Estuary (Eastern Adriatic Coast)

Abstract The investigation of the distributions of total and organic mercury was carried out in the water, sediments and mussels of the Krka River Estuary and the Kornati Archipelago (eastern Adriatic coast) during 1985–1987. The mercury content of the silt/clay sediment fraction ( 80% ) of the stratified Krka River Estuary. Mercury accumulation was observed at the interface of these two layers (at the halocline). The concentrations of mercury in mussels (Mytilus galloprovincialis, Link.) (10–50 μg kg−1 wet wt.) were significantly affected by internal biological factors, and their distribution differed from the pattern observed for sediments and water. Despite the fact that organic mercury has been detected in sediments (≈0.5% of total) and the edible part of the mussels (13–65%), it has not for a certainty been established in water. A tendency to consider the Mediterranean as an area of higher ‘natural mercury levels’ has been challenged by the fact that the concentrations obtained are in the same range as those obtained for other unpolluted marine areas throughout the world.

Marine sampling by scuba diving. 3. Sampling procedures for measurement of mercury concentrations in estuarine waters and seawater

Abstract A method for sampling estuarine waters and seawater by scuba diving is described. Samples taken from the Krka River Estuary on the eastern Adriatic coast were analysed for mercury content using cold vapour atomic absorption spectrometry (CVAAS). Mercury levels as low as 1 ng dm −3 were determined and these are among the lowest values reported to date. A simple contamination free procedure for the preconditioning of sample containers in the sea was applied. Sampling of water by divers is particularly useful when the intermediate layer in an estuary has to be identified and sampled, as well as for obtaining detailed vertical concentration profiles for mercury and other trace elements.