Development of a robust method to determine arsenic and selenium by Diffusive Gradients in Thin

190 Pages·2014·3.56 MB·English

University of Wollongong
Research Online
University of Wollongong Thesis Collection University of Wollongong Thesis Collections
2013
Development of a robust method to determine
arsenic and selenium by Diffusive Gradients in
Thin Films in natural waters and marine sediments
Helen Price
University of Wollongong
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Development of a robust method to determine arsenic
and selenium by Diffusive Gradients in Thin Films in
natural waters and marine sediments

A thesis submitted in (partial) fulfilment of the requirements for the award of the
degree of

Doctor of Philosophy
(PhD, Environmental Chemistry)

from

UNIVERSITY OF WOLLONGONG

by

1,2
Helen Price
BSc (Hons 1)

Supervisors: Assoc. Prof. Dianne Jolley1, Prof. Peter Teasdale2

1School of Chemistry, University of Wollongong, NSW, 2522, Australia
2Griffith School of Environment, Gold Coast campus, Griffith University, QLD, 4222,
Australia

School of Chemistry
December, 2013

i
Certification
I, Helen L. Price declare that this thesis, submitted in partial fulfilment of the requirements for the
award of Doctor of Philosophy, in the Department of Chemistry, University of Wollongong, is
wholly my own work unless otherwise referenced or acknowledged. The document has not been
submitted for qualifications at any other academic institution.

Helen L. Price
18th December, 2013
ii
Acknowledgements

I am fortunate to have had superlative supervisors, Associate Professor Dianne Jolley and
Professor Peter Teasdale. Not only have they been a fountain of knowledge but also, especially
in the last few months, full of assistance, encouragement, precious time, raised eyebrows and
bemused expressions. Thank you for helping to swing a sledgehammer to the last few hurdles
with me. This couldn’t have been done without you.

Thank you to all in the UOW School of Chemistry (especially the technical staff), the DGT
group at Griffith University, QLD and DGT Research at Lancaster University, GB. And at the
beginning of the whole journey, during undergrad at UNE.… Marlene and Hugh thank you for
use of the spare room and all the Sunday dinners. To the friends who’ve been there for me,
Quinny, Debs, Louise, Sylvia, Melanie C., Tracy Hind and Anna, Sheila, Paul and Shirl the girl
(cuppa’s, de-stress chats, emergency nights out/in, 24/7 hospitality, cat feeding). And to the
(very) Jolley group, present and past - Cass, Elvio, Lien, Darren, Bec, Damien, Gabrielle and the
collective ‘French students’. And not least to the Jolley group washing up apprentice, otherwise
known as Felicity (Flick) Welsh.

Sadly, both Melba and Alan couldn’t be around to see this; without their help and friendship
throughout the years I doubt I’d be where I am now.

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Abstract

The principal aim of this thesis was to further develop and characterise the ferrihydrite
binding layer with the Diffusive gradients in thin films (DGT) technique for quantitative and
simultaneous uptake of oxyanions, primarily arsenic and selenium. In the course of this study
similar applications for a Metsorb™ binding layer were also investigated. This required
determining analyte specific quantitative parameters for binding layers with the DGT devices in
order to confidently apply the technique in situ in natural waters and marine sediments.
The initial study investigated several knowledge gaps with respect to the diffusive
gradients in thin films (DGT) technique for measurement of oxyanions (As(III), As(V), Se(IV),
Se(VI), PO 3−, and V(V)) using the ferrihydrite and Metsorb™ binding layers. The relative
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binding affinity for both the ferrihydrite and Metsorb™ were determined for the suite of
oxyanions (PO 3− ≈ As(V) > V(V) ≈ As(III) > Se(IV) ⋙ Se(VI)) and effective binding
4
capacities were measured in single ion solutions, and spiked synthetic freshwater and seawater,
essential knowledge that advise the practical decisions in the use of DGT devices for
environmental monitoring. Under the conditions tested the performance of both ferrihydrite and
Metsorb™ binding layers was directly comparable for As(V), As(III) Se(IV), V(V) and PO 3−
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over a deployment spanning ≤2 days for both freshwater and seawater.
The parameters of practical limitations to the use of DGT in the field deployments were
investigated. In freshwaters, longer deployment times can be considered compared to marine
waters as the high pH, the competitive ions present in seawater and the identity of co-adsorbing
ions were deemed to affect the capacity of each binding layer for the analytes of interest under
marine conditions.
The positive results from the initial study in natural waters led on to experiments to
validate the diffusive gradient in thin films (DGT) technique to measure porewater profiles of
As, Se, V and P in marine sediment. Evaluations were successfully carried out. A high-resolution
(1 and 3 mm) study (one and two dimensional profiling) was conducted in an intact sediment
core, spiked at 60 mm depth with As(V) and Se(VI). A lower resolution study was conducted in
sieved (<2 mm) sediments, aged for 8 months, then spiked at 60 mm depth with either As(III)
and Se(IV), or As(V) and Se(VI). DGT-Chelex, which has been validated elsewhere for
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measurement of metals, was used to identify the suboxic redox region (based on Fe). DGT-
ferrihydrite and -Metsorb™ both successfully bound As(III) and As(V) (as total As), Se(IV), and
natural concentrations of V(V) and PO 3- from marine sediment porewaters.
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Further laboratory based experimentation was undertaken to study the effects of
bioturbation induced heterogeneity with marine sediment. As contaminated areas become
remediated and trophic levels re-established, the burrowing and feeding activities of aquatic
organisms will result in sediment disturbance which, in turn, will affect the cycling of
contaminants within the sediment and overlying waters. This study evaluated the suitability of
utilising simultaneous deployments of DGT and Diffusive Equilibrium in Thin Film (DET)
techniques as rapid in situ measures of bioturbation effects on analyte solubility and speciation in
marine sediments. Bioturbation-induced changes to the redox sensitive elements Fe, Mn, As, Se,
P and V were specifically investigated. Sediment flux and pore-water concentrations due to
bioturbating bivalves (Tellina deltoidalis) were compared to that of non-bioturbated control
sediments.
Simultaneously deployed DGT (ferrihydrite and Chelex-100 binding layers) and DET
successfully revealed differences in DGT-labile and total dissolved species (<0.45μm) mobility
within sediments. The physical disruption to the sediments and porewaters caused by burrowing
bivalves induced changes in redox conditions, affecting the partitioning of oxyanions and metals.
These effects varied by analyte and redox (oxic, suboxic and anoxic) region. Using the DGT
technique the mobility and speciation of Fe, Mn, As, V and P were profiled in situ and found to
closely correlate to the reductive dissolution of Fe oxides. However, this was not the case for
DGT profiles for Se which showed discrete sub-surface maxima not directly linked to Fe oxide
dissolution, most likely a result of organic matter degradation. Comparison of the DGT fluxes
with DET porewater measurements demonstrated the extent of bioturbation-induced cycling of
analyte species throughout the deployment, and clearly showed the suitability of the techniques
for sediment quality assessments of disturbed sites.

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Table of Contents

Certification ii
Acknowledgements iii
Abstract iv
Table of Contents vi
List of Figures xii
List of Tables xvi
Abbreviations xviii

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Chapter 1: Introduction
1.1 Environmental monitoring of arsenic and selenium
1.2 Project focus on bio-available arsenic and selenium
1.3 Passive sampling
1.3.1 The diffusive gradients in thin films technique: overview
1.4 Research Objectives

Chapter 2: Literature Review
2.1 Introduction
2.2 Arsenic environmental contamination: sources, production and distribution
2.2.1 Arsenic: Health effects – toxicity
2.2.2 Cycling of arsenic environmental contamination
2.3 Selenium environmental contamination: sources, production and distribution
2.3.1 Selenium: Health effects – toxicity, deficiency and nutrition
2.3.2 Cycling of selenium environmental contamination
2.4 Arsenic, selenium and the iron oxides
2.4.1 Adsorption of arsenic and selenium by iron oxides and effects of competing ions
2.4.2 Sediments: biogeochemical activity and cycling
2.5 Detection and analysis at environmentally relevant concentrations
2.6 Measurement of arsenic and selenium using the DGT technique
2.7 Diffusive Gradients in Thin Films theory: in natural waters
2.7.1 Speciation using the DGT technique
2.7.2 Quantifying the Diffusive Boundary Layer
2.7.3 Diffusive Equilibrium in Thin Films (DET) Theory for use in soils and sediments
2.7.4 DGT Theory: for use in soils and sediments
2.7.5 Interpretation of soil and sediment DGT data
2.7.6 Relating bioavailability to DGT data
2.7.7 The ferrihydrite binding layer: use with the DGT technique
2.8 General conclusions
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Chapter 3: An evaluation of ferrihydrite- and MetsorbTM-DGT techniques for
measuring oxyanionic species (As, Se, V, P): effective capacity, competition
and diffusion coefficients

3.1 Introduction
3.2 Materials and methods
3.2.1 General experimental
3.2.2 DGT preparation and assembly
3.2.3 Binding gel blanks and DGT detection limits
3.2.4 Elution efficiency
3.2.5 Comparison of diffusion coefficient measurements
3.2.6 The effects of pH and ionic strength on uptake on DGT measurements
3.2.7 Quantitative uptake and effective capacity in the presence of competing ions
3.2.8 Sample analysis
3.3 Results and discussion
3.3.1 Binding gel blanks and DGT method detection limits
3.3.2 Elution efficiencies
3.3.3 Determination of oxyanion diffusion coefficients
3.3.4 The effects of pH and ionic strength on uptake
3.3.5 Quantitative uptake and effective of effective capacity in single element solutions
3.3.6 Quantitative uptake in the presence of competing ions
3.3.6.1 Arsenic (V), Arsenic (III) and orthophosphate
3.3.6.2 Vanadium (V)
3.3.6.3 Selenium (VI)
3.3.6.4 Selenium (IV)
3.3.6.5 Sumary and dsicussion
3.4 Conclusion

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