4051 research outputs found
Sort by
Investigating the kinetics of Cd transport between internal organs of the freshwater decapod Macrobrachium australiense
No full textThe bioaccumulation of metals by aquatic organisms can be studied in great detail using radiotracers, allowing insights into rates of uptake and fate of the metals accumulated in tissues. While there have been numerous studies on the whole-body bioaccumulation of metals by organisms, little is known about the kinetics of organ-specific bioaccumulation. This study used the radioisotope 109Cd to explore the internal uptake kinetics of this non-essential metal following accumulation from solution by the freshwater decapod crustacean Macrobrachium australiense. The first stage of the study involved exposing 24 organisms for up to 2 weeks to 0.55 µg Cd/L in synthetic river water with three individuals being removed at pre-defined time points. Following exposure, animals were rinsed in a 0.1 mM EDTA solution to remove any loosely-bound metal, rapidly frozen and the anatomical distribution of the radionuclide visualised from fresh frozen sections (20 um) using autoradiography. The second phase of the study consisted of exposing organisms to the same radiotracer solution for a short period (6 h) and long period (7 d), followed by depuration in metal- and isotope-free water for up to 3 weeks. Organisms were removed from depuration at pre-defined time points, rapidly frozen, the anatomical distribution of the radionuclide determined as above. Preliminary results suggest that the gills appeared to saturate after 7 d exposure, with negligible increase over another 7 d of exposure. However, the ratio of Cd between the hepatopancreas and gills increased over time, suggesting the organism was actively processing accumulated metal. Rates of accumulation into different internal compartments in response to changes in uptake and depuration durations will be discussed. The findings of the study provide new information on the processing of a non-essential metal by M. australiense and could potentially be used to estimate the exposure history of field-caught organisms
Nuclear techniques for monitoring sediment dynamics in the coastal zone
No full textPaper presented at the Proceedings IAEG-XII Congress, Torino.
The knowledge of sediment transport in the coastal region is of vital importance to the management of this critical interface between land and sea, where most of the world population lives. For the assessment of sediment behaviour, hydraulic and sediment measurements, bathymetric survey, mathematical and physical models, are applied. Sediment tracers provide a unique capability for understanding sediment transport assisting in sediment management which cannot be obtained any other way, whether conventional monitoring or physical and numerical models because tracers integrate all the hydrodynamic actions in time and space. Computational fluid dynamics (CFD) is now an essential tool for the management of the natural systems and is increasingly used to study the fate and behaviour of particulates and contaminants. Tracer techniques are often employed to validate hydrodynamic models to enhance confidence in the predictive value of the models. In-situ detection afforded by the use of a radioactive tracer allows accurate quantitative determination of the rate of sediment transport, compared with other tracer methods. Also, it is cost effective and safe: its radiological impact to the environment is minimal. Several case studies, performed in different regions of the world, are presented. 2014, Springer International Switzerland
A radon-only technique for characterising baseline constituent concentrations at Cape Grim
No full textNine years (2004-2013) of hourly Radon-222, carbon dioxide and ozone concentration observations at Cape Grim are used to assess the residual terrestrial influence on air masses with radon concentrations below the 100 mBq m-3 threshold traditionally used for ‘baseline’ delineation (Figure 1a). Subsequently, a two step radon-only approach for estimating ‘baseline’ constituent concentrations on monthly timescales is proposed. Based on a stringent 40mBq m-3 radon threshold followed by a simple 10th/90th percentile constitute outlier removal, the technique is completely independent of meteorological or aerosol observations. An initial evaluation of the techniqueusing hourly carbon dioxide and ozone records yielded monthly ‘baseline’ concentration estimates more consistent with expectations of minimally perturbed Southern Ocean air masses than existing baseline selection techniques (Figure 1c). This work builds upon prior studies that have identified radon as a valuable baseline criteria [e.g Gras and Whittlestone, 1992; Molly and Galbally, 2014]. CSIRO Oceans and Atmosphere Flagship Aspendale, Victoria, Australia
A first 10Be cosmogenic glacial chronology from the High Atlas, Morocco, during the last glacial cycle
Get PDFGlacial geomorphological mapping, 10Be cosmogenic exposure ages of 21 erratics from cirque-valley systems and
paleo-glacier climate modelling in the High Atlas Mountains, Morocco (31.1°N, 7.9°W), provides new and novel
insights as to the history and evolution of the largest desert region on Earth. The Atlas Mountains display evidence
of extensive and multiple Late Pleistocene glaciations whose extent is significantly larger than that recognised by
previous workers. The largest glaciers formed in the Toubkal massif where we find 3 distinct phases of glacial
advances within the last glacial cycle. The oldest moraines occurring at the lowest elevations have yielded eight
10Be ages ranging from 30 to 88 ka. Six of eight samples from moraines at intermediate elevations gave ages of
19 to 25 ka (2 outliers) which correlates well with the global Last Glacial Maximum (ca. 26-21 ka) and the last
termination during marine isotope stage 2. Five erratics from the youngest and most elevated moraines yielded
a suite of normally distributed exposure ages from 11 to 13 ka which supports a correlation with the northern
hemisphere Younger Dryas (12.9-11.7 ka). The glacial record of the High Atlas effectively reflects moisture supply
to the north-western Sahara Desert and can provide an indication of shifts between arid and pluvial conditions. The
plaeo equilibrium line altitudes (ELA) of these three glacier phases was more than 1000 m lower than the predicted
ELA based on today’s temperatures. Glacier-climate modelling indicates that for each of these glacier phases
climate was not only significantly cooler than today, but also much wetter. The new evidence on the extent, timing
and palaeoclimatic significance of glaciations in this region has major implications for understanding moisture
transfer between the North Atlantic Ocean and the Sahara Desert during Pleistocene cold stages. © Author(s) 2014, CC Attribution 3.0 License
Analysis of the residual stress in ARMOX 500T armour steel and numerical study of the resultant ballistic performance
No full textArmour steels and their response to ballistic and blast threats have been dutifully studied in light of increased conflict and advances in protection levels. The strength of these quenched and tempered martensitic steels is a result of micro alloying, Ni Cr, and Mn, a combination of hot and
cold rolling of the steel and proprietary heat treatments. The resultant hardness and toughness are
pronounced and are reflected in the ballistic performance of the steel, although the role of the residual stress (RS) has not been unambiguously confirmed. To elucidate the effects of the RS on
ballistic properties a two-step study was performed. Firstly, stress measurements were carried out on ARMOX 500T on the RS diffractometer KOWARI at ANSTO on a 8.3 mm thick plate. Stress components in rolling and transverse directions were calculated. Using the experimentally measured stress profiles as an input, numerical analysis was carried out on the ballistic response of the plate to the 7.62 mm APM2 round. Since numerical modelling inherently require the
evaluation of material properties at elevated strain rates, to gauge the impact driven stress-strain
response, the material’s responses were derived using experiments utilising quasi-static testing and instrumented high strain rate experiments using the Split Hopkinson Pressure Bar (SHPB) at
Swinburne University, Australia. These experimentally determined high strain rate data were incorporated into the Johnson-Cook (J-C) computational models for the flow stress along with literature sourced parameters for the failure model of the plate. Analysis of the two starting
conditions, with and without residual stress, allows the authors to draw some conclusion about the role of the residual stress on the ballistic performance of ARMOX 500T armour steel. © 2017 by authors
Bioaccumulation of 65Zn by the Sydney rock oyster (Saccostrea glomerata) from dissolved and particulate phases
No full textOysters and other similar bivalves are popular ‘biomonitors’ or ‘sentinels’ of the environment and are commonly used to assess the health of marine ecosystems. It has been generally accepted that uptake and bioaccumulation in bivalves is influenced predominantly by dietary ingestion of contaminated particles as well as from dissolved sources. An organism of relevance to Australian ecosystems is the Sydney rock oyster (SRO; Saccostrea glomerata), an intertidal, suspension filter-feeder commonly found on the coasts and estuaries of Victoria, New South Wales, and Queensland, Australia. Farmed SRO organisms were used for a 2 month mesocosm study where specimens were exposed to a gradient of resuspended sediment loads and sediment-bound trace metal concentrations. The results indicated poor correlations between SRO tissue metal concentrations and either sediment metal concentration or resuspended volume, with the greatest bioaccumulation being observed in the control tank containing no sediment. These results suggested that SRO metal bioaccumulation was driven primarily from a dissolved source. To investigate this further, a radiotracer study using the gamma-emitting radioisotope 65Zn was conducted, in which SRO organisms were exposed to the dissolved 65Zn radioisotope at three concentrations (5, 25 and 50 µg/L) for 4 days, followed by 20 days of depuration. Dietary assimilation of Zn was examined through pulse-chase experiments where SRO specimens were fed either 65Zn labelled fine-fraction sediments in suspension, or algae. The outcome of this experiment was to outline the relative importance of dissolved, sedimentary, and algal metal sources, and conclusively determine the primary uptake pathway for metal bioaccumulation. The resulting data were used to establish uptake and efflux rate constants from dissolved sources, and assimilation efficiencies from the dietary sources, which were then incorporated into a biodynamic accumulation model. The results of this study are discussed in the context of the use of bivalves as indicators of sediment quality
Where is the water going: An irrigation experiment using a natural isotopic tracer in karst SE, Australia.
Get PDFThe karst unsaturated zone is a fractured rock environment associated with very heterogeneous water movement; spatial variability in the subsurface water storage; and fast preferential flow through fractures and fissures. These factors dominate the way in which water moves within the unsaturated zone in these environments, giving rise to flow path complexities less common in homogenous media. Currently there is limited research regarding karst infiltration/storage processes and potential evaporation in the unsaturated zone. Such processes may have the potential to alter the stable isotopic composition of groundwater. Caves provide a unique environment within which to examine exfiltration variability and flow dynamics in situ. In semi-arid environments evaporative processes in the unsaturated zone have been shown to directly alter the isotopic δ18O composition of cave drip waters, fractionating them towards heavier ratios, by a magnitude of 1-3 per mil relative to mean annual rainfall (Bar Matthews et al., 1996; Cuthbert et al., 2014). Here we present a novel isotopic drip water study from an artificial infiltration experiment at Wellington Caves, SE Australia. A series of four artificial infiltration events were initiated directly over Cathedral Cave, Wellington over as many days. The first event was spiked with a deuterium tracer and the subsurface response was monitored during several sampling campaigns over the following year. The infiltration study revealed: (1) isotopic break-through curves suggest a front of older water from the unsaturated zone storage arrived ahead of the infiltration water, (2) water residence times in the unsaturated zone were found to be longer than 6 months and, (3) large spatial heterogeneities existed in the proportion of exfiltrated deuterium tracer at different drip sites in the cave suggesting unique pathways and sources of water in the unsaturated zone. Implications from this study include the interpretation of paleo-climate speleothem records from semi-arid to arid environments
Impact of meteorology on fine aerosols at Lucas Heights, Australia.
No full textIon Beam Analysis (IBA) techniques were used to assign nine years of PM2.5 observations to seven source types, at Lucas Heights, a topographically complex urban fringe site of Sydney. The highest contributions to total PM2.5 were from motor vehicles (Autos, 26.3%), secondary sulfur (2ndryS, 23.7%), a mixture of industry and aged sea air (IndSaged, 20.6%), and smoke (Smoke, 13.7%). The Autos contribution was highest in winter, whereas 2ndryS was highest in summer, indicating that mitigation measures targeting SO2 release in summer and vehicle exhaust in winter would be most effective in reducing the PM2.5 concentrations at this site. Since concentrations of particulate matter can be significantly affected by local meteorology, generalised additive model (GAM) techniques were employed to investigate relationships between PM2.5 source types and meteorological conditions. The GAM predictors used included: time (seasonal to inter-annual variations), mixing layer depth, temperature, relative humidity, wind speed, wind direction, and atmospheric pressure. Meteorological influences on PM2.5 variability were found to be 58% for soil dust, 46% for Autos, 41% for total PM2.5, and 35% for 2ndryS. Effects were much smaller for other source types. Temperature was found to be an important variable for the determination of total PM2.5, 2ndryS, IndSaged, Soil and Smoke, indicating that future changes in temperature are likely to have an associated change in aerosol concentrations. However, the impact on different source types varied. Temperature had the highest impact on 2ndryS (sometimes more than a factor of 4 increase for temperatures above 25 °C compared to temperatures under 10 °C) and IndSaged, being predominantly secondary aerosols formed in the atmosphere from precursors, whereas wind speed and wind direction were more important for the determination of vehicle exhaust and fresh sea salt concentrations. The marginal effect of relative humidity on 2ndryS increased up to relative humidity of 70–80% and then plateaued, confirming previous findings that (NH4)2SO4 is present in the solid phase below relative humidity of about 80%. © 2016, Elsevier Ltd
Hydrogeochemistry and isotopes in groundwater from the Condamine Catchment Alluvial Aquifer System (SE QLD)- implications for residence times and recharge
No full textNot available
Plasma polymerization of sulfur-rich and water-stable coatings on silica particles
No full textThe plasma polymerization of thiophene has been applied to develop sulfur-rich coatings on silica particles. A range of plasma input energies (0.06–2.4 kJ ⋅ cm− 3) and deposition times (2–30 min) were applied in the plasma polymerization process. The surface chemistry of plasma polymerized thiophene (PPT)-coated particles was evaluated via X-ray photoelectron spectroscopy (XPS), while the distribution of sulfur-containing groups was studied by time of flight secondary ion mass spectroscopy (ToF-SIMS). Washburn capillary rise measurements quantified the hydrophobicity of uncoated and PPT-coated particles. The stability of PPT-coated particles in water was evaluated for immersion durations of 5 min to 24 h. Surface chemistry analyses showed a rapid and homogenous formation of sulfur-rich PPT layers on particles at a low plasma input energy of 0.06 kJ ⋅ cm− 3. ToF-SIMS results suggested the formation of high density thiol functionalities on surfaces. PPT coatings demonstrated high stability in water, which was attributed to their highly hydrophobic character. The deposition rate of PPT on particles and planar surfaces has also been compared in this investigation. It has been shown that the plasma polymerization of a monomer on a 2-D surface produces significantly thicker coatings in comparison to a 3-D surface. The plasma polymerization of thiophene via a rotating reactor was found to be an effective method for the fabrication of sulfur-rich coatings on particulate surfaces. © 2017 Elsevier B.V