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Arsenic speciation in estuarine and oceanic waters by hydride generation-atomic fluorescence spectroscopy

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Featherstone, Alison Mary (1999) Arsenic speciation in estuarine and oceanic waters by hydride generation-atomic fluorescence spectroscopy. PhD thesis, University of Tasmania.

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Abstract

A method has been developed for the routine determination of four arsenic species
(arsenite, arsenate, monomethylarsenic and dimethylarsenic) in natural water, and has
been applied to a study of arsenic cycling in open ocean (Atlantic and Southern Ocean)
and estuarine (Huon Estuary, Tasmania) waters.
The method uses hydride generation and cold trapping of the hydrides, coupled with
atomic fluorescence detection (AFS) at 193.7 nm. With the optimised system, detection •
limits for As(11), As(V), MMA and DMA are 2.3, 0.9, 2.4 and 3.7 ng L-1 , respectively,
in a 5-mL sample. The precision for nine sample replicates was better than 3.5% for all
the arsenic species. Accuracy of the method was determined by analysis of a seawater
certified reference material (NASS-4) and by recovery studies on natural samples.
The manual method was semi-automated and modified for shipboard use by automating
several of the procedures in the analytical sequence, including addition of NaBH4 to
samples, cooling and heating the U-trap used for preconcentration and separation of the
arsines, and logging the AFS output. The semi-automated method has a number of
advantages over the earlier manual HG-AFS method, namely, shorter sample
throughput time, increased precision and, most significantly, ease of use under
shipboard conditions.
The absence of pure standards for MMA and DMA was identified and methods were
developed to purify and characterise suitable standards.
Samples were collected from tropical and subtropical regions in the western basin of the
Atlantic Ocean during an Intergovernmental Oceanographic Commission (IOC)
baseline contaminant survey. The biogeochemical cycling of arsenic in this environment
is discussed briefly. In addition, an interlaboratory comparison has been carried out to
compare the results determined by HG-AFS analysis of stored samples, with those
obtained during the IOC voyage by hydride generation-gas chromatography-photo
ionisation detection (HG-GC-PID). In the interlaboratory comparison particular
emphasis was placed on the results for the methyl arsenic species, for which no certified
reference materials are currently available in seawater. Surface and vertical seawater profiles were obtained in the Subantarctic Zone of the
Southern Ocean along a transect between 42° and 55° S along 141° 30' E, south of
Australia. The transect line passes through four different oceanic environments: the
Subtropical Convergence Zone (STCZ), Subantarctic Zone (SAZ), the Subantarctic Front (SAF) and the Polar Frontal Zone (PFZ). These represent some of the first
measurements of arsenic in the Southern Ocean. Cycling of arsenic is interpreted using
the chemical and biology data obtained from the cruise, and the shipboard performance
of the semi-automated method is also discussed.
A detailed study of arsenic cycling in the Huon estuary, in south east Tasmania, was
undertaken. Arsenic species data were obtained during eight 3-monthly spatial surveys,
and weekly sampling from a single site in the estuary over a six-month period. The data
has been correlated with other chemical measurements, including nutrients, salinity and
dissolved oxygen, and also with biological information about the phytoplankton species
present.
Arsenic concentrations in the Huon estuary are very low, even when compared with
other pristine systems. The seasonal cycle of arsenic is similar to that found in other
temperate estuaries of the Northern Hemisphere. Arsenic cycling is almost entirely
biologically influenced and the uptake of arsenic, particularly by the phytoplankton
Pseudo-nitzschia, is discussed in detail.
Chapter 6 provides a final summary of the work presented in this thesis, and also
recommendations for further development of the analytical method and research
opportunities revealed in the estuarine study of arsenic.

Item Type: Thesis (PhD)
Keywords: Arsenic, Arsenic cycle (Biogeochemistry), Hydrides, Fluorescence spectroscopy
Copyright Holders: The Author
Copyright Information:

Copyright 1999 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 (Ph.D.)--University of Tasmania, 1999. Includes bibliographical references

Date Deposited: 09 Dec 2014 00:04
Last Modified: 16 Aug 2016 00:30
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