Determination of trace metals and copper complexation in freshwater systems of the Bonavista Peninsula, Newfoundland by stripping voltammetry

Jin, Li (1997) Determination of trace metals and copper complexation in freshwater systems of the Bonavista Peninsula, Newfoundland by stripping voltammetry. Masters thesis, Memorial University of Newfoundland.

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Abstract

The speciation of trace metals in natural waters is important in determining their bioavailability and toxicity. For instance, inorganically bound (often referred to as labile) copper in natural waters is toxic to most phytoplankton species but complexation by natural organic ligands considerably reduces or eliminates this toxicity. In order to be able to understand the effects of trace metals, it is important to determine the amount of labile metals and degree of metal complexation (types and strengths of such complexation). -- Labile zinc, cadmium and lead in freshwater samples from the Bonavista Peninsula area of Newfoundland were analyzed by differential pulse anodic stripping voltammetry (DPASV) and labile copper was determined by adsorptive-cathodic stripping voltammetry with 8-hydroxyquinoline (oxine) (ACSV or oxine-CSV). The oxine-CS V method used to determine labile copper in seawater has been modified for use in freshwater. Trace metal results reflected industrial and residential impacts on the watersheds even though concentrations of labile metals were within the typical range of the metals in freshwater. -- Copper complexation was investigated by complexing capacity titrations using the oxine-CS V method to determine concentrations of natural copper complexing ligands and their conditional stability constants. The effect of the adsorption potential on the determination of copper complexation was also studied at three potentials of -0.15 V, -0.7V and -1.1 V. It was found that the detected complexing ligand concentrations decreased 6.1 -69.4 % when the potential used was more negative than -0.15V. The decrease was more severe at more negative potential and lower detection windows. Detailed measurements of copper complexation in freshwater were carried out at three detection windows by varying the oxine concentrations from 7.3 to 36.7 µM and confirmed the presence of several complexing ligands. The detected complexing ligand concentrations were found to decrease with increasing detection window, whereas the conditional stability constants were found to increase.

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