On the lability of dissolved Cu, Pb and Zn in freshwater: Optimization and application to the Deûle (France)

A procedure to determine lead and zinc by anodic stripping voltammetry and copper by cathodic stripping voltammetry in natural river samples was developed and validated. Cu determination involves the adsorption of Cu complexes with 8-hydroxyquinoline (oxine) onto a hanging mercury drop electrode. All samples were studied at natural pH and following optimal conditions were found: an accumulation step at −1.3 V (all potential values in the paper are given versus the Ag/AgCl, [KCl] = 3 M reference electrode) during 30 s for determination of Zn contents and at −0.7 V during 60 s for determination of Pb contents. Concerning Cu analysis, the optimal oxine concentration was found to be 10−5 M with a deposition potential of −1.1 V during 30 s followed by an adsorption step at −0.25 V during 15 s. This procedure was afterwards validated by using certified reference freshwater and performing an intercalibration exercise. Finally the method was successfully applied in the Deûle River, highly contaminated by dissolved Zn and to a lesser extent by Pb and Cu, due to past and present activities of metallurgical plants. Under these optimal conditions, metal concentrations measured by our voltammetric procedures in the Deûle River were found in the range 12.4–23.2 nM for Zn, 1.7–3.2 nM for Pb and 4.9–7.6 nM for Cu.