Measurements of Ni speciation made by competitive ligand exchange techniques indicate that a significant portion of the dissolved Ni in surface waters, wastewater effluents, and surface runoff is complexed by an extremely strong ligand. To identify this ligand, its sources, and environmental fate, simultaneous measurements of nickel ethylenediaminetetraacetate (NiEDTA 2- ) by HPLC and Ni speciation by cathodic stripping voltammetry and chelating resin column partitioning are compared. Analysis of municipal wastewater effluents indicate that NiEDTA 2- accounts for the strongly complexed Ni in wastewater effluent, even when there are few industrial sources of EDTA. Experiments conducted in natural water samples indicate that exchange kinetics have a profound impact on the results of cathodic stripping voltammetry speciation measurements, causing NiEDTA 2- complexes to appear stronger than would be predicted by equilibrium calculations. Measurements of Ni speciation in San Francisco Bay indicate a seasonal variation consistent with the discharge of stable NiEDTA 2- from wastewater effluents and weaker Ni complexes from surface runoff. The presence of nonreactive, nonbioavailable NiEDTA 2- complexes should be considered in geochemical models and in the development of site-specific water quality objectives.
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Bedsworth et al. (1999) studied this question.
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