In this doctoral dissertation, some analytical parameters and steps were examined including the testing of different extraction procedures for Se compounds in marine and aquatic biological samples, which is one of the most critical steps in Se analysis. Water, buffer and enzymatic extraction were tested under conditions where temperatures and incubation times varied. The enzyme protease XIV proved to be the best extraction medium for Se, since the amount of extractable Se varied from 60 % to 80 %. Several marine fish species, including the most commonly consumed sea bass and freshwater fish species such as trout, were examined for Se content, its distribution and speciation. It was shown that marine fish species have a higher concentrations of Se compared to freshwater fish, but the percentage of identified organic Se species was more or less in the same range; 80 % to 100 % in muscle tissue, while in liver tissue only about 20 % of soluble Se could be identified. Also, wild fish have higher levels of Se compared to those from fish farms. The mussels Mytilus galloprovincialis is one of the most commonly used biomonitoring organisms. Se species were identified in raw and cooked samples in order to evaluate the possible loss of selenium during the cooking process. Comparing the percentage of Se species identified (SeCys2, SeMet and one unidentified compound) in raw and cooked samples showed that the amount of identified Se in cooked mussels is higher (around 40 %) compared to the amount in the raw tissues (around 20 %) regarding the amount of the extracted Se. Selenium has a very well-known antagonistic role towards mercury (Hg), which has been proven in all forms of animal life, especially in liver tissue and several fish species. Se and Hg distribution in fish muscle from the Slovenian market, muscle and liver samples from Argentina and bull ray liver tissue samples from Adriatic coast were studied. It was shown that in most of the samples analysed Hg was all present as MeHg; moreover after enzymatic extraction in the insoluble bull ray liver fraction the molar ratio between Se and Hg was 1, where Hg and Se levels were high, while in samples with lower Hg levels this ratio was not proven. Some other elements (Fe, Cu, Zn, Cr, Mn, Ni, As, Cd and Pb) were monitored in a study that included several fish, molluscs and the mussels Mytilus galloprovincialis, which gave a better overview of the element levels in mussels on the North Adriatic coast during the last decade. The elemental composition of mussel samples showed that none of the elements monitored exceeds the provisional tolerable weekly intake. Further comparison of elemental concentrations over the last ten years showed the same range in Mytilus galloprovincialis mussels from the North Adriatic Coast.
D.09 Tutoring for postgraduate students
COBISS.SI-ID: 274201600/
B.03 Paper at an international scientific conference
COBISS.SI-ID: 2923656