Electrochemical investigations of interactions of trace metals : Pb(Ⅱ), Cd(ll), Cu(ll) and Mn(ll) with target trace metal Zn(ll) in binding by dissolved organic carbon in aqueous samples

This research was undertaken to achieve a better understanding of the interactions between some trace metals and dissolved organic carbon (DOC) in freshwaters and mine aqueous effluents by determining metal speciation parameters: free metal ion concentration, stability constant, association/dissociation rate coefficient and diffusion coefficient. It was found that the interaction between trace metals and DOC is related to the metal-DOC bonding properties such as the ionic potential and hardness of trace metal ions. The concentration of labile metal species which are reported to be often correlated with bioavailability and ecotoxicity to biota in the aqueous environment, were found to be affected by competition of co-present trace metals: Pb(II), Cd(II), Cu(II) and Mn(II) with the target trace metal, Zn(II), for binding by DOC in mine aqueous effluents sample. These conclusions were consistent with the dilution effects on the "free" zinc ion concentrations in mine aqueous effluents on dilution with river freshwater. Anodic Stripping Voltammetry (ASV) with a Rotating Disk Electrode (RDE) and Pseudo-polarography and van den Berg/Ruzic Titration Methods were used to determine the metal speciation parameters. These studies suggest both covalent and ionic character of the bonding between trace metals and DOC. The significance of  this work is that it has resulted in a better understanding of the interactions between trace metals and DOC and competition effects of other trace metals on a target metal, and has provided valuable information of current speciation and long term behaviour of trace metals in the aquatic environment