Analysis and toxicity of pCufree in seawater
Creators: name: Eriksen, Ruth Signe
Publisher: name: University Of Tasmania
Year: 2023

description: This thesis describes the development of an analytical technique to measure the free copper ion concentration (pCurree) in seawater. Ion-Selective Electrode (ISE) potentiometry is the only analytical technique that can directly measure pCufree without manipulating the sample matrix, or making assumptions about the thermodynamic behaviour of the metal species. Flow analysis techniques were investigated with the aim of overcoming problems inherent in batch analysis, including sluggish response at low analyte concentrations, cross contamination from one sample to another, contamination by membrane dissolution and/or silver chloride precipitation, and an offset in response due to adsorption of natural organic matter present in seawater. Surface studies of a rotating disk ISE by Electrochemical Impedance Spectroscopy (EIS) confirmed that the effect of organic matter was small (- 0.1 pCu units) and was unlikely to significantly effect the analysis of marine samples. Flow analysis studies showed that the chloride interference was less significant in a flow system than in batch mode, and that the chloride signal could be separated from the copper signal by kinetic discrimination. On the basis of preliminary flow injection studies and the EIS results, Continuous Flow Analysis (CFA) was tested and a method for the routine analysis of openocean and contaminated samples was developed. CFA reduced the effect of membrane dissolution and silver chloride precipitation, and eliminated sample cross contamination, by virtue of the sample stream flowing past the electrode. Low sample throughput, a result of sluggish response at low concentrations of copper, was increased by using an extrapolation technique. This technique is based on the fitting of an empirical mathematical expression to the electrode time-response curve, enabling the prediction of the final steady-state potential. Predicted potentials fell within 0.5 mV of the true steady state potential, and sample analysis time was reduced by a factor of 3 - 6. The CFA method was used to study the effect of copper on the unicellular benthic marine diatom Nitzschia closterium (Ehrenberg) W. Smith. N. closterium is extremely sensitive to low concentrations of copper, and a strong relationship between pCurree and growth inhibition was established at two salinities. Growth inhibition bioassays of samples from a severely contaminated estuary showed no toxic effects, despite elevated levels of total and \labile\" copper. Speciation measurements in salinity 20 waters showed that labile copper grossly overestimated the toxicity of the samples while pCufree measurements indicated that there was insufficient free copper to cause a toxic effect. Mild toxicity was observed in some samples at salinity 30 however this could not be explained by ISE measurements as pCufree levels were below the toxic threshold. In contrast to earlier studies of the copper complexing capacity of the estuary ISE results showed that more than 99.9% of the total copper was bound to ligands probably originating from the surrounding button grass and hardwood forests in the catchment areas of the two major freshwater sources."