This thesis describes the use of in situ and laboratory techniques for monitoring of trace metals
and master variables in the environment. Chapter 1 presents a general overview of trace metals, their
sources, sinks and roles in estuaries and near coastal zones, their general characteristics and the
importance of their behaviour in estuaries. Filtration and commonly used analytical methods for trace
metals detemriinations in natural waters are also discussed.
Chapter 2 highlights the importance of colloids (in the size range 0.2 to 0.4 \im) to
membrane clogging and concludes that cojloids account for a significant part of clogging of
membrane filters. The aim of this study was to extend earlier studies by examining the trends of
filtrate concentrations as a function of filtration volume in riverine and estuarine waters with
contrasting matrix composition, over two different seasons. Based on the findings presented in
this chapter some metal specific filtration protocols are suggested.
Chapter 3 provides an overview of developments in instrument automation that have led
to miniaturisation and resulting in manufacture of portable electrochemical instrumentation. Such
instrumentation has been used for continuous trace metal measurements from the banks of
estuaries and on-board ships. The most recent developments in flow-through cells with a gelcoated
Iridium (Ir) micro-electrode array have resulted in submersible in s/Yu voltammetric probes
which allow long-term trace metal measurements at sub-nanomolar concentrations in coastal
waters. Such In situ probes hold great promise for water quality monitoring.
Chapter 4 presents the optimisation and validation of a Voltammetric In situ Profiling (VIP)
system for the simultaneous determinations of Cd(ll), Cu(ll) and Pb(ll) in estuarine and coastal
waters. The trace metal faction measured by the VIP system is termed 'dynamic' and includes
and includes these free ions and small complexes with size smaller than a few nm. Systematic
studies in NaNOa and seawater were conducted and these showed that variations in ionic
strength, pH and dissolved oxygen did not affect the response of the instrument, whereas an
Arrhenius type temperature response was observed. During the work, physical and voltammetric
settings of the VIP system were considered and tested in detail in order to achieve the analytical
requirements to perform measurements in the laboratory and during in situ deployments^ The VIP
instrument has a detection limit (defined as 3cj) in seawater for Cd(II) of 23 pM, Cu(ll) 1.13 nM,
and Pb(ll) 23 pM. The accuracy of the VIP system was determined with certified reference
material (CRM), showing good agreement.
Chapter 5 discusses the results of an international laboratory inter-comparison exercise,
in order to verify precision and accuracy of measurements made by 4 laboratories that operate
VIP systems located in Plymouth, U.K; Geneva, Switzeriand and Ancona, Italy, using laboratory
reference methods as a comparison. Inter-comparison included analysis of Tamar Estuary
samples and in situ VIP system measurements in the coastal waters of the Gullmar Fjord,
Sweden.
Chapter 6 presents the results of field deployment of the automated Voltammetric In situ
Profiling (VIP) system for the simultaneous determinations of dynamic Cd(ll), Cu(ll) and Pb(ll) in
three estuaries located in the Southwest of England, UK. The VIP instrument allowed the In situ
determination of 2-4 samples h'\ In addition, the VIP system measured total filterable (0.4 pm
pore size filter) concentrations of Gd(ll) and Pb(ll) in discrete estuarine water samples. Through a
series of tidal surveys lasting 7-12 h each and totalling 7 surveys a high resolution data set
including speciation information was built up that enabled an interpretation of geochemical
processes in the studied estuaries.
Chapter 7 shows the results of In situ determination of VIP dynamic metal concentrations
in the Po plume arid Adriatic Sea. Concentrations were similar to those previously reported for
this coastal sea system. The correlation of the metals with salinity was presented and highlighted
the importance of local effluent inputs close to the river mouth for Cd(ll). The data demonstrated
that the Adriatic was not heavily contaminated with trace metals.
Chapter 8 presents the overall conclusions from the research and makes suggestions for
future work.
Date of Award | 2003 |
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Original language | English |
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Awarding Institution | |
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IN SITU MEASUREMENT OF TRACE METALS IN COASTAL WATERS
Howell, K. A. (Author). 2003
Student thesis: PhD