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Browsing by Author "Kinsela, AS"

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Aqueous phase speciation and chemistry of cobalt in terrestrial environments
(Elsevier, 2010-05) Collins, RN; Kinsela, AS
The solution speciation of a metal has a critical influence on its biological activity in the environment and is now an important focus of research. In this review, pertinent aspects related to the aqueous speciation and chemistry of cobalt (Co) in terrestrial environments are critically assessed. Although there is a lack of comprehensive data on aqueous Co concentrations in soil porewaters, groundwaters and surface waters, existing reports indicate that natural Co concentrations vary within a picomolar to micromolar range. Cobalt chemistry is dominated by the Co(II) oxidation state in the aqueous phase of terrestrial environments primarily due to the extremely low solubility of Co(III). There is no universal agreement on the importance of Co(II) complexation in the solution phase of terrestrial environments and, furthermore, on the nature of the major binding organic ligands. The kinetics of Co(II) complexation to, and dissociation from, natural organic complexing ligands are such that the speciation of Co is likely to significantly diverge from estimates based on thermodynamic equilibrium calculations. As a result, an accurate understanding of Co bioavailability, toxicity and transport in terrestrial aquatic environments will only be achieved when thermodynamics can be reconciled with reaction kinetics. © 2010, Elsevier Ltd.
Contaminant release, mixing and microbial fluctuations initiated by infiltrating water within a replica field-scale legacy radioactive waste trench
(Elsevier B. V., 2022-12-10) Kinsela, AS; Payne, TE; Bligh, MW; Vázquez-Campos, X; Wilkins, MR; Comarmond, MJ; Rowling, B; Waite, TD
Numerous legacy near-surface radioactive waste sites dating from the mid 20th century have yet to be remediated and present a global contamination concern. Typically, there is insufficient understanding of contaminant release and redistribution, with invasive investigations often impractical due to the risk of disturbing the often significantly radiotoxic contaminants. Consequently, a replica waste trench (~5.4 m3), constructed adjacent to a legacy radioactive waste site (Little Forest Legacy Site, LFLS), was used to assist our understanding of the release and mixing processes of neodymium (Nd) — a chemical analogue for plutonium(III) and americium(III), two significant radionuclides in many contaminated environments. In order to clarify the behaviour of contaminants released from buried objects such as waste containers, a steel drum, representative of the hundreds of buried drums within the LFLS, was placed within the trench. Dissolved neodymium nitrate was introduced as a point-source contaminant to the base of the trench, outside the steel drum. Hydrologic conditions were manipulated to simulate natural rainfall intensities with dissolved lithium bromide added as a tracer. Neodymium was primarily retained both at its point of release at the bottom of the trench (>97 %) as well as at a steel container corrosion point, simulated through the emplacement of steel wool. However, over the 8-month field experiment, advective mixing initiated by surface water intrusions rapidly redistributed a small proportion of Nd to shallower waters (~1.5–1.7 %), as well as throughout the buried steel drum. Suspended particulate forms of Nd (>0.2 μm) were measured at all depths in the suboxic trench and were persistent across the entire study. Analyses of the microbial communities showed that their relative abundances and metabolic functions were strongly influenced by the prevailing geochemical conditions as a result of fluctuating water depths associated with rainfall events. The site representing steel corrosion exhibited divergent biogeochemical results with anomalous changes (sharp decrease) observed in both dissolved contaminant concentration as well as microbial diversity and functionality. This research demonstrates that experimental trenches provide a safe and unique method for simulating the behaviour of subsurface radioactive contaminants with results demonstrating the initial retention, partial shallow water redistribution, and stability of particulate form(s) of this radioactive analogue. These results have relevance for appropriate management and remediation strategies for the adjacent legacy site as well as for similar sites across the globe. © 2022 Elsevier B.V.
Influence of calcium and silica on hydraulic properties of sodium montmorillonite assemblages under alkaline conditions
(Elsevier, 2010-03-01) Kinsela, AS; Tjitradjaja, A; Collins, RN; Waite, TD; Payne, TE; Macdonald, BCT; White, I
A sodium-washed montmorillonite was exposed to calcium and silica under alkaline conditions in order to gain insight into possible interactions of engineered clay barriers and cementitious leachates found in many waste storage facilities. The changes in physico-chemical properties of the material were investigated using a combination of dead-end filtration, electrophoresis and scanning electron microscopy. The results show minimal differentiation between unaltered Na-montmorillonite samples at the two pH values tested (9 and 12), with the structure of the resulting assemblages arising from repulsive tactoid interactions. The addition of calcium (50 mM) greatly decreases the size of the structural network, and in doing so, increases the hydraulic conductivity ~65-fold, with the effect being greatest at pH 12. Whilst the addition of silica alone (10 mM) produced little change in the hydraulic properties of montmorillonite, its combined effect with calcium produced alterations to the structural assemblages that could not be accounted for by the presence of calcium alone. The likely binding of calcium with multiple silanol groups appears to enhance the retention of water within the Na-montmorillonite assemblage, whilst still allowing the fluent passage of water. The results confirm that polyvalent cations such as Ca2+ may have a dramatic effect on the structural and hydraulic properties of montmorillonite assemblages while the effects of solutions containing both silicate and calcium are complex and influenced by silica–cation interactions. © 2010, Elsevier Ltd.
Influence of dissolved silicate on rates of Fe(II) oxidation
(American Chemical Society, 2016-10-05) Kinsela, AS; Jones, AM; Bligh, MW; Pham, AN; Collins, RN; Harrison, JJ; Wilsher, KL; Payne, TE; Waite, TD
Increasing concentrations of dissolved silicate progressively retard Fe(II) oxidation kinetics in the circum-neutral pH range 6.0–7.0. As Si:Fe molar ratios increase from 0 to 2, the primary Fe(III) oxidation product transitions from lepidocrocite to a ferrihydrite/silica-ferrihydrite composite. Empirical results, supported by chemical kinetic modeling, indicated that the decreased heterogeneous oxidation rate was not due to differences in absolute Fe(II) sorption between the two solids types or competition for adsorption sites in the presence of silicate. Rather, competitive desorption experiments suggest Fe(II) was associated with more weakly bound, outer-sphere complexes on silica-ferrihydrite compared to lepidocrocite. A reduction in extent of inner-sphere Fe(II) complexation on silica-ferrihydrite confers a decreased ability for Fe(II) to undergo surface-induced hydrolysis via electronic configuration alterations, thereby inhibiting the heterogeneous Fe(II) oxidation mechanism. Water samples from a legacy radioactive waste site (Little Forest, Australia) were shown to exhibit a similar pattern of Fe(II) oxidation retardation derived from elevated silicate concentrations. These findings have important implications for contaminant migration at this site as well as a variety of other groundwater/high silicate containing natural and engineered sites that might undergo iron redox fluctuations. © 2016 American Chemical Society
Installation of a pilot experimental trench at the Little Forest legacy site
(Australian Nuclear Science and Technology Organisation, 2018-07-30) Payne, TE; Kinsela, AS; Rowling, B; Hankin, SI; Cendón, DI; Comarmond, MJ; Bligh, MW; Hughes, CE; Anderson, D; Wilsher, KL
During 2017, a pilot experimental trench was constructed at the Little Forest Legacy Site (LFLS). The objective of installing this trench was to facilitate experimental field-work aimed at further characterising the site, in particular the hydrology of the excavated trenches and of the near-surface layers in which the trenches are located. The test trench is of similar depth to the waste disposal trenches at the legacy site (3 metres) and extends 6 m in length. However, unlike the disposal trenches, the experimental trench contains no waste materials of any kind. Instead, the trench contains a number of sampling points and other instrumentation, and is back filled with river gravel to provide a uniform composition and maintain structural stability. It is intended that the pilot trench will be followed by other trenches with specific experimental objectives. The purposes of this report are to discuss the background, rationale for, and implementation of the facility; to provide a detailed description of the pilot trench; and to compile information and photographs documenting the excavation process. Although some preliminary hydrological data and comparisons with the legacy trenches are presented, the scientific data will be fully discussed and interpreted in future scientific reports.
Installation of an experimental trench at the Little Forest Legacy Site
(South Pacific Environmental Radioactivity Association, 2018-11-06) Payne, TE; Kinsela, AS; Bligh, M; Anderson, D; Rowling, B; Hughes, CE; Hankin, SI; Cendón, DI; Wilsher, KL; Comarmond, MJ
During 2017, a pilot experimental trench was constructed at the Little Forest Legacy Site (LFLS), a 1960s era disposal site for low-level radioactive waste. The objective of installing this trench was to facilitate experimental field-work aimed at further characterising the site, in particular the hydrology of the excavated trenches and of the near-surface layers in which the trenches are located. The test trench is of similar depth to the waste disposal trenches at the legacy site (8 metres) and extends 6 m in length. However, unlike the disposal trenches, the experimental trench does not contain waste materials. instead, the trench contains a number of sampling points and other instrumentation, and is back filled with river gravel to provide a uniform composition and maintain structural stability. in this paper, the excavation of the trench is described, together with observations made during the excavation. in addition, some preliminary hydrological data and comparisons with the legacy trenches are presented.
Measurement of tributyl phosphate (TBP) in groundwater at a legacy radioactive waste site and its possible role in contaminant mobilisation
(Elsevier B. V., 2017-11) Rowling, B; Kinsela, AS; Comarmond, MJ; Hughes, CE; Harrison, JJ; Johansen, MP; Payne, TE
At many legacy radioactive waste sites, organic compounds have been co-disposed, which may be a factor in mobilisation of radionuclides at these sites. Tri-butyl phosphate (TBP) is a component of waste streams from the nuclear fuel cycle, where it has been used in separating actinides during processing of nuclear fuels. Analyses of ground waters from the Little Forest Legacy Site (LFLS) in eastern Australia were undertaken using solid-phase extraction (SPE) followed by gas chromatographic mass spectrometry (GCMS). The results indicate the presence of TBP several decades after waste disposal, with TBP only being detected in the immediate vicinity of the main disposal area. TBP is generally considered to degrade in the environment relatively rapidly. Therefore, it is likely that its presence is due to relatively recent releases of TBP, possibly stemming from leakage due to container degradation. The ongoing presence and solubility of TBP has the potential to provide a mechanism for nuclide mobilisation, with implications for long term management of LFLS and similar legacy waste sites. © 2021 Elsevier B.V.
Radionuclide distributions and migration pathways at a legacy trench disposal site
(Elsevier B. V., 2020-01) Payne, TE; Harrison, JJ; Cendón, DI; Comarmond, MJ; Hankin, SI; Hughes, CE; Johansen, MP; Kinsela, AS; Mokhber-Shahin, L; Silitonga, A; Thiruvoth, S; Wilsher, KL
This paper examines the distributions of several anthropogenic radionuclides (239+240Pu, 241Am, 137Cs, 90Sr, 60Co and 3H) at a legacy trench disposal site in eastern Australia. We compare the results to previously published data for Pu and tritium at the site. Plutonium has previously been shown to reach the surface by a bath-tubbing mechanism, following filling of the former trenches with water during intense rainfall events. This has led to some movement of Pu away from the trenched area, and we also provide evidence of elevated Pu concentrations in shallow subsurface layers above the trenched area. The distribution of 241Am is similar to Pu, and this is attributed to the similar chemistry of these actinides and the likely in-situ generation of 241Am from its parent 241Pu. Concentrations of 137Cs are mostly low in surface soils immediately above the trenches. However, similar to the actinides, there is evidence of elevated 137Cs and 90Sr concentrations in shallow subsurface layers above the trenched area. While the subsurface radionuclide peaks suggest a mechanism of subsurface transport, their interpretation is complicated by the presence of soil layers added following disposals and during the subsequent years. The distribution of 90Sr and 137Cs at the ground surface shows some elevated levels immediately above the trenches which were filled during the final 24 months of disposal operations. This is in agreement with disposal records, which indicate that greater amounts of fission products were disposed in this period. The surface distribution of 239+240Pu is also consistent with the disposal documents. Although there is extensive evidence of a mobile tritium plume in groundwater, migration of the other radionuclides by this pathway is limited. The data highlight the importance of taking into account multiple pathways for the mobilisation of key radioactive contaminants at legacy waste trench sites. Crown Copyright © 2019 Published by Elsevier Ltd.
Response of microbial community function to fluctuating geochemical conditions within a legacy radioactive waste trench environment
(American Society for Microbiology, 2017-08-17) Vázquez-Campos, X; Kinsela, AS; Bligh, MW; Harrison, JJ; Payne, TE; Waite, TD
During the 1960s, small quantities of radioactive materials were codisposed with chemical waste at the Little Forest Legacy Site (Sydney, Australia) in 3-meter-deep, unlined trenches. Chemical and microbial analyses, including functional and taxonomic information derived from shotgun metagenomics, were collected across a 6-week period immediately after a prolonged rainfall event to assess the impact of changing water levels upon the microbial ecology and contaminant mobility. Collectively, results demonstrated that oxygen-laden rainwater rapidly altered the redox balance in the trench water, strongly impacting microbial functioning as well as the radiochemistry. Two contaminants of concern, plutonium and americium, were shown to transition from solid-iron-associated species immediately after the initial rainwater pulse to progressively more soluble moieties as reducing conditions were enhanced. Functional metagenomics revealed the potentially important role that the taxonomically diverse microbial community played in this transition. In particular, aerobes dominated in the first day, followed by an increase of facultative anaerobes/denitrifiers at day 4. Toward the mid-end of the sampling period, the functional and taxonomic profiles depicted an anaerobic community distinguished by a higher representation of dissimilatory sulfate reduction and methanogenesis pathways. Our results have important implications to similar near-surface environmental systems in which redox cycling occurs. © 2017 Vázquez-Campos et al.
Speciation and transport of arsenic in an acid sulfate soil-dominated catchment, eastern Australia
(Elsevier, 2011-02) Kinsela, AS; Collins, RN; Waite, TD
Factors controlling the transport of geogenically-derived arsenic from a coastal acid sulfate soil into downstream sediments are identified in this study with both solid-phase associations and aqueous speciation clearly critical to the mobility and toxicity of arsenic. The data from both sequential extractions and X-ray adsorption spectroscopy indicate that arsenic in the unoxidised Holocene acid sulfate soils is essentially non-labile in the absence of prolonged oxidation, existing primarily as arsenopyrite or as an arsenopyrite-like species, likely arsenian pyrite. Anthropogenically-accelerated pedogenic processes, which have oxidised this material over time, have greatly enhanced the potential bioavailability of arsenic, with solid-phase arsenic almost solely present as As(V) associated with secondary Fe(III) minerals present. Analyses of downstream sediments reveal that a portion of the arsenic is retained as a mixed As(III)/As(V) solid-phase, though not at levels considered to be environmentally deleterious. Determination of arsenic speciation in pore waters using high performance liquid chromatography/Inductively Coupled Plasma-Mass Spectrometry shows a dominance of As(III) in upstream pore waters whilst an unidentified As species reaches comparative levels within the downstream, estuarine locations. Pore water As(V) was detected at trace concentrations only. The results demonstrate the importance of landscape processes to arsenic transport and availability within acid sulfate soil environments. © 2010, Elsevier Ltd.

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