Complexation of Ni, Cu, Zn, and Cd by DOC in some metal-impacted freshwater lakes: a comparison of approaches using electrochemical determination of free-metal-ion and labile complexes and a computer speciation model, WHAM V and VI

• Published in: Analytica chimica acta 2005-01, Vol.528 (2), p.205-218
• Main Authors: Guthrie, J.W., Hassan, N.M., Salam, M.S.A., Fasfous, I.I., Murimboh, C.A., Murimboh, J., Chakrabarti, C.L., Grégoire, D.C.
• Format: Article
• Language: English
• Subjects: Analytical chemistry; Cathodic and anodic stripping voltammetry; Chemistry; Dissolved organic carbon; Electrochemical methods; Exact sciences and technology; Free-metal-ion concentration; Freshwater; Freshwaters; Kinetic and equilibrium speciation; Windermere Humic Aqueous Model V and VI
• ISSN: 0003-2670; 1873-4324
• DOI: 10.1016/j.aca.2004.10.003

Complexation of Ni(II), Cu(II), Zn(II), and Cd(II) by dissolved organic carbon (DOC) in some freshwater lakes in Rouyn-Noranda, Québec, Canada, where they were impacted by effluents from a nearby copper smelter, was measured by kinetic and equilibrium methods using cathodic and anodic stripping voltammetry. The measured free-metal-ion and labile metal-complex concentrations were compared with the predictions made by a widely-used computer speciation model, the Windermere Humic Aqueous Model (WHAM): WHAM V and its improved version WHAM VI. If it is assumed that 65% of the DOC is “active”, i.e. behaving as isolated humic substances such as fulvic acid, both versions of WHAM are able to predict the labile and free-metal-ion concentrations of Ni, Zn, and Cd reasonably well; however, both underestimate the free-copper-ion concentration by one to two orders of magnitude. WHAM VI is generally better than or equal to WHAM V for successfully predicting most of the free-metal-ion concentrations. The modelled competition by Al(III) and Fe(III) in the lake surface waters showed that in most cases Cu(II) was most affected by this competition. WHAM VI predicts a larger effect from the Al(III) and Fe(III) competition than does WHAM V.