Speciation of nickel in surface waters measured with the Donnan membrane technique [An article from: Analytica Chimica Acta]

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Description:
The evaluation of the ecotoxicological risk of nickel (Ni) in surface water is hampered by a lack of speciation data. Six surface waters were sampled and speciation of Ni(II) was measured by the Donnan membrane technique (DMT) combined with radiochemical determination of ^6^3Ni. The free Ni^2^+ ion fraction in the dissolved (two-fold), even when assuming that all dissolved organic matter (DOM) was present as fulvic acid (FA). The impact of several model parameters affecting the prediction of Ni speciation were evaluated, including the solubility product of Fe(OH)"3, which affects the Fe competition for complexation by DOM. The best fit (R^2=0.88) was obtained by increasing only the distribution term @DLK"2, which modifies the binding strength of multi-dentate sites, to accommodate the observed dependence of free ion fraction on Ni concentration.