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Analysis and toxicity of pCufree in seawater

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Eriksen, Ruth Signe (2000) Analysis and toxicity of pCufree in seawater. PhD thesis, University of Tasmania.

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Abstract

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.

Item Type: Thesis (PhD)
Keywords: Copper, Marine pollution
Copyright Holders: The Author
Copyright Information:

Copyright 2000 the Author - The University is continuing to endeavour to trace the copyright owner(s) and in the meantime this item has been reproduced here in good faith. We would be pleased to hear from the copyright owner(s).

Additional Information:

Thesis (PhD)--University of Tasmania, 2000. Includes bibliographical references

Date Deposited: 09 Dec 2014 00:05
Last Modified: 15 Aug 2016 04:06
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