Doctor of Philosophy
School of Chemistry
Price, Helen, Development of a robust method to determine arsenic and selenium by Diffusive Gradients in Thin Films in natural waters and marine sediments, Doctor of Philosophy thesis, School of Chemistry, University of Wollongong, 2013. http://ro.uow.edu.au/theses/4137
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), PO4 3−, and V(V)) using the ferrihydrite and Metsorb™ binding layers. The relative binding affinity for both the ferrihydrite and Metsorb™ were determined for the suite of oxyanions (PO4 3− ≈ As(V) > V(V) ≈ As(III) > Se(IV) ⋙ Se(VI)) and effective binding 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 PO4 3− 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 (
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 (