Browsing by Author "Lee, JH"

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    Bioaccumulation of 65Zn by the Sydney rock oyster (Saccostrea glomerata) from dissolved and particulate phases
    (SETAC Australasia, 2014-09) Lee, JH; Birch, GF; Cresswell, T; Payne, TE; Simpson, SL
    Oysters 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.
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    Dietary ingestion of fine sediments and microalgae represent the dominant route of exposure and metal accumulation for Sydney rock oyster (Saccostrea glomerata): a biokinetic model for zinc
    (Elsevier, 2015-08-01) Lee, JH; Birch, GF; Cresswell, T; Johansen, MP; Adams, MS; Simpson, SL
    Past studies disagree on the extent to which dissolved or dietary uptake contribute to metal bioaccumulation in the filter-feeding Sydney rock oyster (Saccostrea glomerata) in urbanized estuaries. Although most data support the assumption that fine sediments are a major route of metal uptake in these bivalves, some studies based in the Sydney estuary, Australia, have indicated a poor correlation. In the present study, seawater, sediment and microalgae were radiolabelled with 65Zn tracer and exposed to S. glomerata to assess the influence of dissolved and dietary sources to Zn bioaccumulation. Oysters in the dissolved-phase uptake experiment (5, 25 and 50 μg L−1 65Zn for 4 d followed by 21 days of depuration) readily accumulated 65Zn for all three concentrations with an uptake rate constant of 0.160 ± 0.006 L dry weight g−1 d−1. Oysters in the dietary assimilation experiment (1 h pulse-feed of either 65Zn-radiolabelled suspended fine-fraction (<63 μm) sediment or the microalgae Tetraselmis sp.) accumulated 65Zn, with assimilation efficiencies of 59 and 67% for fine sediment and microalgae, respectively. The efflux rates were low for the three experiments (0.1–0.5% d−1). A bioaccumulation kinetic model predicts that uptake of Zn will occur predominantly through the dietary ingestion of contaminated fine sediment particles and microalgae within the water column, with considerably greater metal bioaccumulation predicted if oysters ingested microalgae preferentially to sediments. However, the model predicts that for dissolved Zn concentrations greater than 40 μg L−1, as observed during precipitation events, the uptake of the dissolved phase may contribute ≥50% to accumulation. Overall, the results of the present study suggest that all three sources may be important exposure routes to S. glomerata under different environmental conditions, but contributions from dietary exposure will often dominate. © 2015 Elsevier
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    Superior rate capability and cycling stability in partially cation-disordered Co-free Li-rich layered materials enabled by an initial activation process.
    (American Chemical Society, 2021-06-22) Lee, JH; Yang, YJ; Jeong, MH; Dupre, N; Avdeev, M; Yoon, WS; Choi, SY; Kang, BW
    Li-rich layered materials that have Co-free and Mn-rich 3d-transition metals have the potential to increase the achievable energy density of batteries because they are inexpensive and yield high capacity by exploiting an additional oxygen redox reaction. However, these have low electrochemical activity and sustainability, with severe voltage fade, rapid capacity decay, and poor rate capability. Here, we report sustainable cycling stability and fast rate capability of Co-free Li2MnO3-based Li-rich layered materials that are governed by the electrochemical activation process during the 1st cycle and that this process can be controlled by the degree of the cation disordering in the pristine material. From the comparative study of two samples that have different degrees of cation disordering in the same composition, an increase in cation disordering in the pristine material strongly improves its tolerance to structural changes in the bulk and on the surface during the activation process at the 1st cycle, leading to less structural changes for subsequent cycles. As a result, high electrochemical activity and superior rate capability in subsequent cycles can be achieved even with the cation disordering in the pristine. Furthermore, we verified the findings by developing an additional material that had higher cation disordering in the pristine structure than the samples tested and showing that the additional sample has improved rate capability and cycle retention. This understanding that sustainable electrochemical characteristics are governed by an activation process in the 1st cycle, which can be controlled by a structural feature of the pristine material, will be useful in the design of low-cost, Li-rich layered materials that can achieve sustainable high energy density and fast rate capability for Li-ion batteries. © 2021 American Chemical Society