Browsing by Author "McDonald, S"

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    Bioaccumulation kinetics of cadmium and zinc in the freshwater decapod crustacean Paratya australiensis following multiple pulse exposures
    (Elsevier, 2020-06-10) McDonald, S; Cresswell, T; Hassell, KL
    Stormwater runoff has been identified as a major source of metal contaminants in urban waterways, where during storm events organisms tend to be exposed to short-term pulses, rather than a constant exposure of contaminants. Current water quality guidelines (WQGs) are generally derived using data from continuous exposure toxicity tests, where there is an assumption that chronic exposures provide a meaningful way of assessing the impacts and effects in organisms as a result of these pulsed storm events. In this current study the radioisotopes 109Cd and 65Zn were used to explore uptake, depuration and organ distribution in the decapod crustacean Paratya australiensis, over three short-term (<10 h) exposures. Exposures to radiolabelled cadmium only, zinc only or a mixture of cadmium and zinc were followed by depuration in metal- and isotope-free water for 7 days. Whole-body metal concentrations were determined by live-animal gamma-spectrometry and an anatomical distribution of the radioisotopes was visualised using autoradiography post-mortem. Both metals were significantly accumulated over the pulsed exposure period. In both treatments cadmium and zinc body burden increased at the same rate over the three pulses. Final metal body burden did not markedly differ when shrimp were exposed to metals individually compared to a binary mixture. Over the course of the depuration period, cadmium efflux was minimal, whereas zinc efflux was significant. Autoradiography indicated the presence of both metals in the gills and hepatopancreas throughout the depuration period. These results demonstrate how short-term repeated exposures result in the accumulation of contaminants by shrimp. This study highlights the importance of considering the inclusion of pulsed toxicity tests in frameworks when deriving WQGs. © 2020 Elsevier B.V
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    Effect of short-term dietary exposure on metal assimilation and metallothionein induction in the estuarine fish Pseudogobius sp.
    (Elsevier, 2021-06-10) McDonald, S; Hassell, K; Cresswell, T
    Metals introduced into the urban aquatic environment through anthropogenic activities have the potential to accumulate in organisms via multiple uptake routes. Understanding the impact different routes have on metal accumulation is important for the continued management of these ecosystems, where current water quality guidelines (WQGs) tend to be derived from aqueous metal exposure tests. In this study, the estuarine fish Pseudogobius sp. was exposed to a mixture of cadmium (Cd) and zinc (Zn) radiotracers dissolved in water or present in experimental food. Metal-spiked food was presented to fish as a single ‘pulse-chase’ feed or as three consecutive feeds, where the cumulative metal dose provided by both treatments was equal. Fish did not accumulate either metal from water, even after the length of exposure was increased from 12 h to 36 h. Fish did accumulate metals from diet and the assimilation efficiency (AE) was low following a single feed (12% for both Cd and Zn). Following multiple feeds fish displayed a significantly higher AE for zinc only, suggesting that fish are susceptible to retention of dietary Zn over an extended time period albeit at lower daily loadings. The final body burden and efflux rate did not differ between feeding regimes. Tissue accumulation of Cd and Zn indicated metal specific distribution. The gastro-intestinal (GI) tract contained >90% of total Cd body burden, whilst the carcass accounted for the majority (70–88%) of Zn body burden. There was significant induction of the biomarker metallothionein (MT) in the GI tract. These results demonstrate the differences in Cd and Zn metal uptake characteristics in this estuarine fish species, and how feeding frequency and metal loading of food may influence assimilation. This study highlights the importance of considering the inclusion of dietary exposures in WQG frameworks. ©2021 Elsevier B.V
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    Experimental design and statistical analysis in aquatic live animal radiotracing studies: a systematic review
    (Taylor & Francis, 2021-03-18) McDonald, S; Cresswell, T; Hassell, K; Keough, MJ
    Live animal gamma radioisotope tracing enables the monitoring of real-time contaminant uptake and retention in individual animals. It has been employed by ecotoxicologists to understand how animals respond to a variety of aquatic stressors. The use of the technique increases the complexity of the experimental design, resulting in the production of highly detailed and robust longitudinal data of individual animals. The greater complexity of the statistical models that underpin this data create risks from data being treated incorrectly. A systematic review of the literature was undertaken to comprehensively evaluate the experimental design and statistical approaches employed by current aquatic live animal radiotracing studies. The experimental design of current studies was categorized into one of five design “families”. Each experimental design could be described by at least one statistical model, which in turn informs a specific statistical approach. Collectively, 7% of studies provided insufficient information to determine the experimental design used, and 24% of studies undertook no formal statistical analysis of results. When the statistical approaches used in current studies were examined, in most cases the correct approach was undertaken, with only 18% of studies using a statistical approach that did not match the chosen experimental design. This review provides clear guidance on the analysis and interpretation of data collected from each experimental design and explains the advantages and disadvantages of each. Additionally, this paper identifies four key suggestions for future researchers, and provides commentary on the ethical, logistical and cost considerations associated with undertaking experiments that use live animal radiotracing. © 2021 Taylor & Francis Group.
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    Metal forms and dynamics in urban stormwater runoff: new insights from diffusive gradients in thin-films (DGT) measurements
    (Elsevier, 2022-02-01) McDonald, S; Holland, A; Simpson, SL; Gadd, JB; Bennett, WW; Walker, GW; Keough, MJ; Cresswell, T; Hassell, KL
    Stormwater runoff typically contains significant quantities of metal contaminants that enter urban waterways over short durations and represent a potential risk to water quality. The origin of metals within the catchment and processes that occur over the storm can control the partitioning of metals between a range of different forms. Understanding the fraction of metals present in a form that is potentially bioavailable to aquatic organisms is useful for environmental risk assessment. To help provide this information, the forms and dynamics of metal contaminants in an urban system were assessed across a storm. Temporal patterns in the concentration of metals in dissolved and particulate (total suspended solids; TSS) forms were assessed from water samples, and diffusive gradients in thin-films (DGTs) were deployed to measure the DGT-labile time-integrated metal concentration. Results indicate that the concentrations of dissolved and TSS-associated metals increased during the storm, with the metals Al, Cd, Co, Cu, Pb and Zn representing the greatest concern relative to water quality guideline values (GVs). The portion of labile metal as measured by DGT devices indicated that during the storm a substantial fraction (∼98%) of metals were complexed and pose a lower risk of acute toxicity to aquatic organisms. Comparison of DGT results to GVs indicate that current GVs are likely quite conservative when assessing stormwater pollution risks with regards to metal contaminants. This study provides valuable insight into the forms and dynamics of metals in an urban system receiving stormwater inputs and assists with the development of improved approaches for the assessment of short-term, intermittent discharge events. © 2021 Elsevier Ltd.
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    Metal pollution during pulse stormwater events: bioaccumulation kinetics of cadmium and zinc in a freshwater decapod crustacean
    (Australian Nuclear Science and Technology Organisation, 2019-09-03) McDonald, S; Cresswell, T; Hassell, KL
    Stormwater runoff has been identified as a major source of metal pollutants in urban waterways, where organisms that access these environments tend to be exposed to multiple pulses, rather than a constant exposure, of contaminants. Current water quality guidelines (WQGs) are generally derived using data from continuous exposure toxicity tests, where the assumption is that chronic exposures provide a meaningful way of assessing metal bioaccumulation kinetics and effects in an organism. In this study the radioisotopes 109Cd and 65Zn were used to explore the uptake, depuration and organ distribution of a non-essential and essential metal in a decapod crustacean over the course of three short-term (< 10 hours) pulse exposures followed by a 7-day depuration. The freshwater shrimp (Paratya australiensis) was exposed to radiolabelled cadmium only, zinc only and a mixture of cadmium and zinc at environmentally relevant stormwater concentrations. Whole-body metal concentrations were determined by daily live-animal gamma-spectrometry. Anatomical distribution of the radioisotopes was visualised using autoradiography at multiple time points throughout the depuration period. Metal uptake and efflux rates were similar in the individual and mixed-metal exposures, where both metals accumulated to a greater extent when presented individually. Interestingly, the rate of cadmium uptake in the whole-body of the organism over the course of the three ‘pulses’ decreased with each successive pulse. The rate of zinc uptake remained linear over the course of the three pulsed exposures. The efflux rate for cadmium regardless of exposure treatment (single or multi-metal) was close to zero. Zinc concentrations decreased in the whole-body of the organism over the course of the depuration period, with the efflux rate being greater for zinc exposed individually. Autoradiography indicated the presence of both metals in the gills and hepatopancreas of the animals regardless of depuration time. This study reveals how cadmium bioaccumulation kinetics may differ between repeated ‘pulse’ exposures where, unlike zinc, the rate of uptake decreases with each successive pulse. This demonstrates how repeated exposures, rather than a constant exposure, can influence the bioaccumulation kinetics of metals, highlighting the important consideration for incorporating pulsed toxicity tests in frameworks when deriving WQG values.
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    Phase stability of dross particles in hot-dip Zn-55wt%Al-1.6wt%Si galvanizing bath
    (MDPI, 2023-01-31) Qu, DD; Gear, M; Gu, QF; Setargew, N; Renshaw, W; McDonald, S; StJohn, D; Nogita, K
    Dross in a Zn-55wt%Al-1.6wt%Si metal coating bath is a mixture of bath metal and the quaternary intermetallic phase τ5c-Al20Fe5Si2(+Zn). Understanding the properties and formation of dross in a hot-dip Al-Zn galvanizing bath at the processing temperature (~600 °C) is critical for improving the production quality of steel sheet coating. However, dross analysis is usually conducted at room temperature with dross samples taken from the hot-dip bath and it is not known how representative these samples are of the phase(s) existing at high temperature. Using in-situ synchrotron X-ray diffraction (XRD), the crystal lattice and the coefficient of thermal expansion (CTE) of the intermetallic phase have been determined in the temperature range of 30 °C to 660 °C. Phase formation and phase stability of the intermetallic phase in the dross powder have been determined, providing fundamental knowledge for optimizing the production and quality of steel sheet coating. © 2023 The Authors.