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PH16 Metals in the Environment: Chemistry and Fate Issues
(PH158) Do Ligands in Natural Organic Matter from Different Sources Bind Zinc the Same?
Cheng, T1, Allen, H1, 1 University of Delaware, Newark, Delaware, USA
ABSTRACT- Zinc complexation by natural organic matter is important in understanding bioavailability and potential zinc toxicity. Models such as WHAM or BLM assume natural organic matter (NOM) from different sources are the same in zinc binding. Yet, this assumption has not been tested. We characterized organic matter from three representative surface waters and studied their zinc complexing properties using square wave anodic stripping voltammetry (SWASV). NOM from different sources have ligands with similar binding constants, but the zinc binding of NOM is not well predicted by WHAM especially at low zinc concentrations (below 10-6 M). Non-linear curve fitting of the Zn titration data showed that at least two distinctive classes of Zn binding sites are required to fit well the entire curves. A model was established to describe zinc NOM complexation. This model describes well the Zn-NOM complexation throughout the whole experimental ZnT range, and reflects the pH dependence of the complexation. Ionic strength has a significant effect on Zn-NOM complexation; increasing ionic strength resulted in weakened apparent Zn-NOM complexation. Ca competes with Zn for binding sites on NOM and high Ca concentrations reduce Zn-NOM complexation.
Key words: zinc, complexation, natural organic matter
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