This research aimed at evaluating cadmium (Cd), copper (Cu), lead (Pb) and zinc (Zn) speciation and interactions with natural dissolved organic materials in a eutrophic reservoir. Water samples were obtained in dry and rainy seasons, and PCA identified seasonal influences of metal input sources into the reservoir. The results showed higher labile Zn (Znlabile) and Pb (Pblabile) in the dry season, but complexed Zn (ZnL) dominated during the rainy season. Total dissolved Cu (CuTD) and Pb (PbTD) concentrations were higher in the dry season, with the concentration order Zn > Cu > Pb > Cd. In general, higher percentile of Cu and Zn remained complexed to the dissolved fraction, while Pb was associated with particulate materials. Chemical equilibrium modeling (MineqL+) showed that Zn2+ and Cd2+ dominated labile species, while Cu and Pb remained associated with carbonates. Cu and Zn complexes, labile Zn and Pb concentrations were directly proportional to each respective metal concentration in its dissolved form. Cd, Cu, Pb and Zn complexation capacity indicated higher ligand concentration for Cu, followed in decreasing amounts for Pb, Zn and Cd. Nevetheless, the strength of association for all metals and the respective ligands were similar. We conclude that in eutrophic environments, metals that otherwise would sink to the bottom in oligotrophic environments, in organic rich ones, these metals are likely to remain as the dissolved form in the water column. An exception to this was observed for Pb, which mostly related to particulate material and sinked to the sediments. The results revealed a high degree of deterioration of the reservoir regardless of sampling location.

Chemical behavior of Cu, Zn, Cd, and Pb in a eutrophic reservoir: Speciation and complexation capacity

247th National Meeting (2014)

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