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(1999)Conference Paper
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(1996)Conference PaperBioturbation is a natural process with potential to affect the dynamics of contaminants in sedimentary environments. In this investigation, two benthic organisms, the bivalve mollusc Notospisula trigonella and the eunicid polychaete Marphysa sanguinea were maintained at different densities in selenium contaminated sediments. Porewater and bulk sediment selenium concentrations were determined over a 20 day period. The benthos in this experiment appeared to raise the porewater concentrations with respect to the controls. Both animals accumulated selenium from the sediment mesocosms. Toxic effects were observed in both animals.
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(1996)Conference PaperSelenium (Se) is a contaminant of concern in environments affected by discharges from smelting and coal-burning industries. Experiments have been performed to investigate the phase associations of selenium in contaminated sediments under a range of controlled redox conditions. In this study, Se sediment associations were examined using the BCR sequential extraction technique after stabilisation at different redox states. It was shown that although most of the sediment-bound Se is associated with the operationally-defined “organic/sulfide” fraction, as the measured redox potential of the system is increased, more Se moves into the “exchangeable” and “iron/manganese oxyhydroxide” fractions. In these fractions, contaminants can be expected to be more bioavailable. As the mass of Se absorbed to sediments is typically at least an order of magnitude higher than the mass dissolved in porewaters, significant Se exposure may result from oxidative shifts in Se associations.
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(1998)Conference PaperThe ecosystem of Lake Macquarie, N.S.W., has been subject to heavy metal and metalloid inputs since 1897 from a lead-zinc smelter, and subsequently coal-fired power stations, coal mines and washeries and sewage treatment plants. Reports in 1994 of contamination of commercial fish species from the Lake with selenium levels up to twelve times those recommended for human consumption has lead to calls for bans on commercial and recreational fishing in the Lake, which could potentially devastate local fishing and tourism industries. Selenium biogeochemical cycling in estuarine environments such as Lake Macquarie is subject to factors including sediment redox potential, sediment characteristics, solubility of Se-containing mineral phases, ligand complexing ability, and microbially-mediated oxidation-reduction, mineralisation and methylation reactions. Understanding this biogeochemistry is important so as to evaluate the potential risk to ecosystems and human health posed by selenium, and to determine the likely impact of potential management strategies. The research described in this paper examines the importance and role of two of these specific factors which impact selenium biogeochemical cycling in Lake Macquarie: sediment redox potential and microbial methylation reactions. The role of sediment redox potential was examined utilising sediment from the Lake, dosed with known quantities of selenium and then studied under different conditions, comprising: addition of various macrofauna to the sediments to examine the impact of bioturbation on sediment redox status and therefore selenium availability; and exposure of sediment plugs to oxygenated and deoxygenated seawater to quantify selenium release. Bioturbation caused deepening of the oxidised conditions in the sediment, impacting upon speciation and mobility of selenium, whilst exposure of contaminated reduced sediment to oxidising porewater arising from bioturbation resulted in selenium mobilisation from the strongly binding “organic fraction” of the sediment. Separately, bacterial cultures were isolated from the Lake with the ability to tolerate high selenium levels. Organisms were cultured in flasks with nutrient broth containing selenate (Se(VI)) at 100mg/l and incubated at 28oC for several weeks. Analysis by hydride generation atomic absorption spectroscopy revealed that the mass balance on the flasks would not close, indicating loss of selenium to the culture headspace. Samples of culture headspace gases were then collected using a cryogenic trapping system and injected into a GC/MS where methylated selenium species including dimethylselenyl sulfide and dimethylselenyl disulfide were identified. These experiments indicated that both sediment redox potential and microbial methylation are important in the biogeochemical cycling of selenium in Lake Macquarie. The impact of bioturbation upon sediment redox potential is important for any consideration of capping sediments, as the depth of the cap must be sufficient to prohibit bioturbative organisms from accessing the sediment below the cap, whilst the demonstrated ability of indigenous microorganisms from the Lake to methylate selenium may represent a potential remediation options for contaminated sediments or selenium-containing waste streams.
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(1996)Conference PaperLake Macquarie, an estuarine lake on Australia's eastern seaboard, has been subject for almost a century to anthropogenic contamination by heavy metals and metalloids, including selenium, arising from industrial sources including a lead-zinc smelter, coal-fired power stations and sewage works. , Selenium tissue concentrations in fish from the Lake have recently been reported at up to twelve times those recommended for human consumption. This paper describes an integrated investigation into selenium contamination in the Lake over a four-year period. One key component of these investigations is the ability of indigenous micro-organisms to reduce selenium in estuarine sediments from higher to lower oxidation states, therefore immobilising or volatilising it, and the use of this in the treatment of industrial wastewaters or potentially the in-situ bioremediation of contaminated sediments. A second key component is a study of the mechanisms controlling sediment-stored selenium concentrations and the extent to which they can be influenced by bioturbative organisms. Integrated into these two broad areas and described here are a number of related investigations into: bioavailability of sediment-bound selenium; computer modelling of selenium biogeochemistry; representation of heavy metal data in a GIS format; and determination of the specific historical contributions of a power station to selenium loads in the Lake. Through this integrated approach we have built on synergies between the separate components of our research program to add to our understanding of the nature of selenium biogeochemistry in the Lake and to propose potential bioremediation strategies for both the Lake and contaminated industrial wastewaters or surface water.
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(1996)Conference PaperSelenium is an anthropogenic contaminant of concern in estuaries on the NSW coast. Experiments have been performed to elucidate the processes controlling selenium remobilisation from contaminated sediments. Measurements of redox potential and pH were made in sediments taken from Lake Macquarie with different populations of infaunal organisms. Depending on the feeding mechanisms and mobility of the organisms, bioturbation causes a degree of deepening of the oxidised conditions in the sediment. Thermodynamic simulations of the solubility of selenium in estuarine porewaters predict a mobilisation of the contaminant under such conditions. Preliminary experiments involving exposure of contaminated reduced sediment to oxidising porewater resulted in the mobilisation of selenium species that were strongly bound to the sediment.
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(1996)Conference PaperThe mobility and toxicity of selenium (Se) is a strong function of oxidation state, which in turn is affected by Eh and pH. Elevated levels of Se in fish from Lake Macquarie, NSW are potentially linked to reported high levels of Se in the sediment. Therefore, an understanding of the biogeochemical cycling of Se between the various environmental compartments in the Lake is important in predicting the formation and release of mobile and potentially toxic Se oxyanions to the water column. A computer-based dynamic model, developed in SPEEDUP, is described. The model simulates the biogeochemical cycling of Se in an estuarine ecosystem between the sediment and the water column. Model parameters were obtained from the literature and from data specific to Lake Macquarie. Transport of Se between and accumulation of Se within the various compartments is predicted. Selenium is expected to accumulate in volatile, organic and selenate forms in the water column, and to predominate as selenide in the sediment. The model is designed to allow future expansion into different environmental compartments, including air, biota and plants.
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(1995)Conference PaperThe voltage noise of a Bi2Sr2CaCu2O8+x single crystal below Tcis analyzed with an asymptotic power spectrum method. Low-frequency noise power Sv(T) shows a peak at T = Tp. Above Tp, the power spectrum, Sv(f), exhibits a power-law fall-off. Below Tp, Sv() dramatically deviates from the power-law behaviour, showing some wide peaks which are proposed upon a background of an exponential-law characteristic. This is qualitatively consistent with numerical simulation. It is suggested that the pinned vortex state is a deterministic motion with low-dimensional chaotic attractors while the unpinned state is an extended dissipative dynamic system with self-organized criticality.