Browsing by Author "Gerson, AR"

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    Arsenic 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, GD
    Arsenic 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.
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    Crystal growth through progressive densification identified by synchrotron small-angle x-ray scattering
    (American Chemical Society, 2008-05) Li, J; Cookson, DJ; Gerson, AR
    For the first time, evolution of the interfacial structure of aluminum hydroxide nuclei forming within concentrated caustic solutions has been examined in situ in real time. In both dilute and concentrated caustic aluminate solutions (NaOH = 1.0 and 3.0 M, respectively, [NaOH]/[Al] = 1.22), the measured synchrotron small-angle X-ray scattering data indicate distinctly different surface structures throughout the maturation process. In the dilute solution, the data are consistent with a thin layer of less dense, recently accreted material on the surface of large fully dense particles-consistent with the familiar model process of species attachment to well-faceted surfaces. In contrast to this, the data for the concentrated solution are consistent with large diffuse particles growing with a mass fractal dimension of approximately 2.5 which density to form rough surface fractal particles on maturation. This unusual densification crystallization mechanism may occur in analogous concentrated systems where the fractal structures may be entropically stablized. © 2008, American Chemical Society