engleski

Assessing trace metals contamination and organic matter in the brackish lakes as the major source of potable water

On small and medium karstic coastal islands in the Adriatic Sea, brackish lakes are often the only source of fresh water. Therefore, it is important to adequately evaluate the biogeochemical processes occurring in these complex water systems, as well as to determine the origin of contaminants present. In this study, the distribution and origin of trace metals (Tl, Hg, Cd, Pb, Cu, Zn, Ni, Co) and organic matter in the water column, sediment and surrounding soil of the brackish lakes on Mljet Island, South Adriatic Sea, Croatia, were evaluated. Thallium and mercury concentrations in the lake water were up to two orders of magnitude higher compared to ranges found in the adjacent coastal seawater. Elevated thallium concentrations were of anthropogenic origin resulting from previous use of rodenticide, while elevated mercury content was naturally enhanced. Levels for the other metals were characteristic of uncontaminated water systems. Speciation modelling showed that dissolved trace metals Cu, Pb and Zn were mostly associated to organic matter, while Tl, Co and Ni were present predominantly as free ions and inorganic complexes. The presence of organic matter (OM) clearly influenced the speciation and distribution of some trace metals. OM was characterized by the determination of the complexing capacity for Cu ions (CuCC), surface active substances (SAS) and catalytically active compounds (CAC). Reduced sulphur species (RSS) (glutathione and other thiols) representing significant Cu binding ligands were determined and discussed as well.

Brackish water ; Karstic coastal island ; Trace metals ; Organic matter ; Speciation

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