Browsing by Author "Melvin, SD"

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    Bioaccumulation and biodistribution of selenium in metamorphosing tadpoles
    (American Chemical Society, 2017-04-19) Lanctôt, CM; Cresswell, T; Callaghan, PD; Melvin, SD
    Selenium is an important macronutrient with a very narrow margin between essentiality and toxicity. Amphibians are hypothesized to be particularly sensitive due to the potential for metamorphosis-driven mobilization, which could transfer or concentrate contaminant burdens within specific organs. We explored the potential role of tissue degeneration and remodeling during anuran metamorphosis as a mechanism for altering tissue-specific Se burdens. Limnodynastes peronii tadpoles were exposed to dissolved 75Se (as selenite) for 7 days and depurated until completion of metamorphosis. Bioaccumulation and retention kinetics were assessed in whole tadpoles and excised tissues using gamma spectroscopy, and temporal changes in biodistribution were assessed using autoradiography. Tadpoles retained Se throughout metamorphosis, and partitioned the element predominantly within digestive and excretory tissues, including livers > mesonephros > guts > gallbladder. Importantly, our results demonstrate that Se biodistribution varies significantly throughout development. This is indicative of tissue transference, and particularly in tissues developing de novo after depuration. To the best of our knowledge, this is the first study demonstrating Se transference during metamorphic tissue remodelling. Further research is warranted to explore the fate and metabolism of Se (and other metal and metalloids) during anuran development and the implications of transference for influencing toxicity. © 2017 American Chemical Society
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    Selenium speciation influences bioaccumulation in Limnodynastes peronii tadpoles
    (Elsevier, 2017-06) Lanctôt, CM; Melvin, SD; Cresswell, T
    Despite being essential for animal health and fitness, Se has a relatively narrow range between deficiency and toxicity, and excess Se can cause a variety of adverse effects in aquatic organisms. Amphibians are particularly vulnerable to contaminants during larval aquatic life stage, because they can accumulate toxic ions through various routes including skin, gills, lungs and digestive tract. Few attempts have been made to understand the tissue-specific accumulation of trace elements, including the impacts of chemical speciation in developing amphibian larvae. We used radiolabelled 75Se to explore the biokinetics and tissue distributions of the two dominant forms occurring in surface waters, selenite (SeIV) and selenate (SeVI). Tadpoles of the native Australian frog Limnodynastes peronii were exposed to Se in both forms, and live-animal gamma spectroscopy was used to track accumulation and retention over time. Tissue biodistributions were also quantified at the end of the uptake and depuration phases. Results showed the bioconcentration of SeIV to be 3 times greater compared to SeVI, but rates of elimination were similar for both forms. This suggests a change of Se speciation within the organism prior to excretion. Depuration kinetics were best described by a one-phase exponential decay model, and tadpoles retained approximately 19% of the accumulated Se after 12 days of depuration in clean water. Selenium bioaccumulation was greatest in digestive and excretory organs, as well as the eye, which may directly relate to previously reported Se-induced impairments. Results demonstrate how the use of radiotracing techniques can significantly improve our understanding of trace element toxicokinetics and tissue distributions in developing amphibians. From an environmental monitoring perspective, the findings highlight the importance of considering chemical speciation as this could influence the accuracy of risk assessment. Crown Copyright © 2017 Published by Elsevier B.V.
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    Uptake and tissue distributions of cadmium, selenium and zinc in striped marsh frog tadpoles exposed during early post-embryonic development
    (Elsevier, 2017-10) Lanctôt, CM; Cresswell, T; Melvin, SD
    Metals and metalloids released through anthropogenic activities can accumulate in aquatic organisms, resulting in adverse effects in sensitive species. We investigated the influence of feeding regime and exposure complexity (i.e., mixture) on bioaccumulation kinetics and body distribution of common metal(loid) pollutants in Limnodynastes peronii during early post-embryonic development. Tadpoles were exposed to radiolabelled 109Cd, 75Se and 65Zn alone and in a mixture for 4 days, followed by 3 days depuration in clean water. One group was fed directly in exposure aquaria, whereas a second group was transferred to clean water for feeding, to investigate the potential influence of sorption to food on uptake. Bioconcentration factor and retention was observed to be greatest for Se. Results demonstrate that tadpoles accumulated and retained half the amount of Cd when exposed in mixture, suggesting that Se and/or Zn may have antagonistic effects against Cd uptake. Additionally, tadpoles fed directly in exposure water accumulated 2–3–times more Cd and Zn compared to tadpoles fed in clean water, indicating that the presence of food particles is an important factor that may influence uptake. Interestingly, this had a negligible impact on Se uptake. The study reveals how exposure conditions can influence the bioaccumulation of metal(loid)s, highlighting experimental factors as important considerations for both controlled toxicity experiments and for understanding exposure risks for amphibian populations. © 2017 Elsevier Inc.