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Complexation of 54Mn with selected organic ligands in aquatic systems

54Mn is a neutron activation product and by the controlled discharge of activated cooling water from nuclear and fuel processing plants and nuclear reactors it enters natural waters together with many other artificial radionuclides. The major factor influencing the distribution of trace metal artificial radionuclides in natural waters is the physico-chemical form in which they enter natural waters (Burton, 1975). Subsequently, their fate in natural waters depends on the physico-chemical conditions, redox state and different geochemical processes such as complexation with natural or synthetic, dissolved or suspended organic matter. The complexation of 54Mn radionuclide with ethylenediaminetetraacetic acid (EDTA), nitrilotriacetic acid (NTA), humic and fulvic acids was studied in diluted seawater system (the Ra{a Bay), and in freshwater system (the Butoniga impoundment) by high voltage paper electrophoresis (Erk et al., 1996). Comparative study has been performed in two water types because genuine seawater contains less natural organic matter than freshwater sample and has a defined macroconstituent composition. The study was conducted by measuring changes of electrophoretic mobility of 54Mn species in the ligand concentration gradient. Depending on the EDTA or NTA concentrations it was possible to detect the distribution of cationic, anionic and immobile 54Mn species, and to calculate their electrophoretic mobilities. The apparent concentration stability constants of 54Mn-EDTA and 54Mn-NTA complexes were calculated from the electrophoretic mobility changes in the transition EDTA or NTA region, where the complexation occurs (Pu~ar, 1971). The addition of humic substances (HS) and increase of pH in diluted seawater systems do not cause significant changes of cationic electrophoretic mobilities of 54Mn nor the formation of electrophoretically immobile form of 54Mn. Opposite to the interaction with low molar mass chelating agents NTA and EDTA, when defined anionic forms exist, the interaction of 54Mn with HS of freshwater sediment origin in freshwater systems is characterized: (i) with the formation of uncharged species and/or adsorption of 54Mn on undissolved or precipitated HS, (ii) with the increase of the amount of 54Mn in the cationic tailing in the HS concentration gradient, (iii) with the decrease of the amount of 54Mn cationic forms in the presence of HS, (iv) with the formation of some other cationic forms of 54Mn of lower electrophoretic mobility than Mn(H2O)62+ (Erk et al., 1996a). After the addition of HA of marine sediment origin the immobile form of 54Mn present in the freshwater system is solubilized. This effect is enhanced by increase of the HA concentration and pH (Erk et al., 1996b).

complexation; 54Mn; synthetic ligands; humic substances; high voltage paper electrophoresis

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