Browsing by Author "McOrist, GD"
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- ItemArsenic microdistribution and speciation in toenail clippings of children living in a historic gold mining area(Elsevier, 2010-05-15) Pearce, DC; Dowling, K; Gerson, AR; Sim, MR; Sutton, SR; Newville, M; Russell, RA; McOrist, GDArsenic is naturally associated with gold mineralisation and elevated in some soils and mine waste around historical gold mining activity in Victoria, Australia. To explore uptake, arsenic concentrations in children's toenail clippings and household soils were measured, and the microdistribution and speciation of arsenic in situ in toenail clipping thin sections investigated using synchrotron-based X-ray microprobe techniques. The ability to differentiate exogenous arsenic was explored by investigating surface contamination on cleaned clippings using depth profiling, and direct diffusion of arsenic into incubated clippings. Total arsenic concentrations ranged from 0.15 to 2.1 µg/g (n = 29) in clipping samples and from 3.3 to 130 µg/g (n = 22) in household soils, with significant correlation between transformed arsenic concentrations (Pearson's r = 0.42, P = 0.023) when household soil was treated as independent. In clipping thin sections (n = 2), X-ray fluorescence (XRF) mapping showed discrete layering of arsenic consistent with nail structure, and irregular arsenic incorporation along the nail growth axis. Arsenic concentrations were heterogeneous at 10 × 10 µm microprobe spot locations investigated (< 0.1 to 13.3 µg/g). X-ray absorption near-edge structure (XANES) spectra suggested the presence of two distinct arsenic species: a lower oxidation state species, possibly with mixed sulphur and methyl coordination (denoted As≈ III(–S, –CH3)); and a higher oxidation state species (denoted As≈ V(–O)). Depth profiling suggested that surface contamination was unlikely (n = 4), and XRF and XANES analyses of thin sections of clippings incubated in dry or wet mine waste, or untreated, suggested direct diffusion of arsenic occurred under moist conditions. These findings suggest that arsenic in soil contributes to some systemic absorption associated with periodic exposures among children resident in areas of historic gold mining activity in Victoria, Australia. Future studies are required to ascertain if adverse health effects are associated with current levels of arsenic uptake. © 2009, Elsevier Ltd.
- ItemDensity correction — a better method for difficult samples(South Pacific Radioactivity Association, 2008-11-25) McOrist, GD; Bowles, CJWhen most powdered samples are analysed using gamma-ray spectrometry, the ability to accurately determine the concentration of low energy nuclides such as Pb-210 (46.5 keV), Th-234 (63.3 keV), and Th-230 (67.7 keV) requires some degree of density correction. A general method has been previously discussed using a Ra-226 point source to determine attenuation through the sample. However relatively dense samples and those containing certain elements require a more complex correction process to obtain correct concentration data. In these cases it is not possible to accurately measure the Pb-210 peak in the point source through these samples. The point source method was extended using major element data and incorporated into an Excel spreadsheet. Results obtained from a number of different samples and matrices were compared with nuclide data obtained using a density correction algorithm incorporated in existing proprietary software. These will be discussed.
- ItemThe effect of sulfate-reducing bacteria on adsorption of 137Cs by soils from arid and tropical regions(Elsevier, 2004-03-05) Russell, RA; Holden, PJ; Payne, TE; McOrist, GDSoils from different climatic regions of Australia were studied to determine their adsorption of 137Cs, and the effect of microbial sulfate reduction on this adsorption. The soils consisted of a surface and regolith samples from the site of a proposed low and intermediate level radioactive waste repository in arid South Australia, and two red earth loam soils from an experimental plot in the tropical Northern Territory. The process of bacterial sulfate reduction substantially decreased the adsorption of 137Cs to the arid and tropical soils, although extended incubation resulted in greater adsorption to the regolith sample. This could have implications for the mobility of radionuclides entering these soil ecosystems. Crown Copyright 2004 Published by Elsevier Ltd.
- ItemFinal report on a field study of soil-to-plant transfer of radioactive caesium, strontium and zinc in tropical Northern Australia to the IAEA/FAO/IUR CRP on classification of soils systems on the basis of transfer factors of radionuclides from soil to reference plants(Australian Nuclear Science and Technology Organisation, 2003-09) Twining, JR; Shotton, P; Tagami, K; Payne, TE; Itakura, T; Russell, RA; Wilde, KL; McOrist, GD; Wong, HKYSoil-to-plant radionuclide transfer factors for cesium (134Cs), strontium (85Sr) and zinc (65Zn) into sorghum and mung plants grown in tropical Australia have been determined over a four-year study period. The crops were grown on two types of red earth soils. Transfer factors for Cs and Sr are not substantially different from the expected values based on previous studies, reported in the general literature and compiled in the IUR database, mainly performed within temperate climates. In contrast, the values for zinc (Zn) are more than an order of magnitude greater than anticipated. Most of the radioactivity added to the soils has been retained in the top 5 cm of both soils. There has been a general decline in soil-to-plant transfer of Cs and Zn as time has increased.
- ItemLaboratory studies of the diffusive transport of 137Cs and 60Co through potential waste repository soils(Elsevier, 2010-09) Itakura, T; Airey, DW; Leo, CJ; Payne, TE; McOrist, GDTests using reconstituted samples have been performed to assess the diffusive transport of 137Cs and 60Co through natural regolith materials from a region in South Australia being considered for a radioactive waste repository. A double diffusion cell apparatus made of polycarbonate resin was developed to estimate the effective diffusion (De) and sorption coefficients (Kd) that allowed large withdrawals from the source and collector cells and has enabled tests with low concentrations of radioactivity. An alternative to porous stainless steel filter plates has also been used to reduce uncertainty in test interpretation. Analysis of the transient data used a staged method of the Laplace transform to take into consideration the volume of the samples withdrawn from the apparatus during testing. At test completion samples were cut into slices and analysed for radionuclide concentration. Data obtained from the sliced samples confirmed that both numerical and experimental data produced acceptable mass balance. The De values obtained in this study were of the order of 10−6 cm2 s−1 for both species, higher than previously published data. The Kd values from the diffusion and batch sorption tests were in reasonable agreement for 137Cs, but an order of magnitude different for 60Co. The sorption of the latter radionuclide was strongly pH dependent, and this dependency during diffusion tests would benefit from further investigation. © 2010, Elsevier Ltd.
- ItemRadionuclide applications in laboratory studies of environmental surface reactions(Elsevier B. V., 2004) Payne, TE; Hatje, V; Itakura, TD; McOrist, GD; Russell, RAThe advantages of using radionuclides for laboratory studies of environmental processes include the wide range of element concentrations that can be studied, the capability to simultaneously study several isotopes in a single experiment, the direct applicability to the behaviour of radioactive waste or fallout, and the ability to study the mechanisms, reversibility and kinetics of environmental reactions under controlled conditions. These attributes are demonstrated using specific examples drawn from case studies in Australia, including radionuclide fallout onto tropical soils, the association of trace metals with harbour sediments and the behaviour of uranium in natural and contaminated systems. © 2004 Elsevier B.V.