engleski

Organic matter-metal ions interaction-some highlights

In 1970 some investigations and measurements have suggested that the free metal ion, rather than total metal ion concentration, was a biologically important form that better correlated with the toxicity to sensitive aquatic organisms, such as bacteria and algae (Stumm and Morgan, 1981). In 70’s a development of a very sensitive electroanalytical technique ASV (anodic stripping voltammetry) enabled the study of free metal ion concentrations of environmentally important metals such as copper, lead, cadmium and zinc in natural waters (Merian et al., 2004). ASV is a specific speciation technique which responds only to those metal species that are reducible at the mercury electrode at the chosen deposition potential. This operationally defined “labile” fraction contained the free metal ion and its weak complexes (Rayeshwar and Ibanez, 2002). The pioneers of this method applied to natural water studies were for e.g. the groups of M. Branica in Rudjer Bošković Institute in Croatia, T.M. Florence in the Chemical Technology Division of the Australian Energy Division, Australia and H.W. Nürnberg in the KFA Institute in Jülich, Germany. A major objective of metal speciation measurements is that they provide quantitative information on metal bioavailability. Bioavailability as a concept is commonly assumed as the ability of metals to cross a biological membrane and presumably be taken up. Most of current information on metal complexation by dissolved organic matter comes from methods that rely on the titration of water samples by addition of known increments of metal ion and measurement of the concentration of labile metal ion species after a period of equilibration by ASV. This procedure is called complexing capacity determination is similary to the concept of pH representing the “metal ion buffering capacity”. Dissolved organic carbon (DOC) which makes a pool of organic ligands in seawater originates from different sources. The concentration of DOC in seawater varies between 0.3 to 3 mg C/L (Stumm and Morgan, 1981). A part of DOC exibits the property of surface activity, i.e. the accumulation at different phase boundaries (seawater/atmosphere, seawater/particles, seawater/biological membranes) due to its hydrophilic/hydrophobic moieties and change the physico –chemical properties of these interfaces. The surfactants present in sea-surface microlayer are mostly of biological origin (primary production) and are seasonally dependant (Ćosović, B., 1985). Literature: Buffle, J. Complexation Reactions in Aquatic Systems, Ellis Horwood, Chichester 1988 . Ćosović, B., Aqueous surface chemistry.Adsorption characteristic of organic solutes. Electrochem. Evaluation.In W.Stumm (ed.)Chemical processes in Lakes, Wiley, pp 55-88. Merian, E., Anke, M., Ihnat M., Stoeppler M: Elements and Their Compounds in the Environment, 2nd edition, Wiley-VCH Verlag, 2004. Rajeshwar, K., Ibanez J.R., Environmental Electrochemistry, Fundamentals and Applications in Pollution Abatement, Academic Press, San Diego, 2002. Stumm, W., Morgan, J.J., Aquatic Chemistry 2nd ed., Wiley, New York , 1981.

voltammetry; metal ions; organic matter

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