碩士 / 國立臺灣大學 / 農業化學研究所 / 105 / Thallium (Tl) is a trace element with high toxicity to mammals and classified as a priority pollutant by the U.S. EPA. Tl exists in the environment as monovalent Tl(I) and trivalent Tl(III) states. Tl(I) is thought to be more thermodynamically stable than Tl(III); but, recent studies indicate that Tl(III) may persistently exist in surface water. However, environmental transformation between Tl(I) and Tl(III) and their toxicities to higher tropic levels of aquatic organisms such as fish remain unclear. In this study, we aim to understand the stability and redox dynamics of Tl(III) in EPA dilution water. The toxic effect of three different Tl species [Tl(I), Tl(III) and DTPA-Tl(III)] and associated modes of toxic action are investigated using medaka (Oryzias latipes). Tl(III) is unstable in EPA dilution water, but it can be stabilized in EPA dilution water of < pH 5 or with addtion of DTPA in EPA dilution water. Our results showed that Tl(I) and Tl(III) caused greatest and less acute mortality in medaka larvae and DTPA-Tl(III) had the least mortality with 7 day exposure at 30-400 μg/L. The MDA content was significantly induced in the DTPA-Tl(III) group. The CAT activity was suppressed in either Tl(I) or Tl(III) groups, whereas both Tl(III) and DTPA-Tl(III) suppressed the SOD activity. The osmoregulation biomarker Na-K ATPase was only suppressed by DTPA-Tl(III). After 14 day exposure to 3 Tl species (15-30 μg/L), the trend of Tl content in fish was similar to acute mortality. Next generation sequencing (NGS) differential gene expression (DGE) profiles showed that Tl(I) (50 μg/L) significantly induced alteration in cholesterol synthesis, steroid hormone metabolism and phase I metabolism related genes. These Tl-induced transcriptional alteration was confirmed by qPCR analysis and related enzymatic assays. Phase I metabolism related gene (cyp3a38 and cyp3a40) expression were significantly induced by Tl(I) and Tl(III). However, pxr was significantlty suppressed by Tl(I) and Tl(III). The CYP1A activity was also induced in three kinds of Tl treatment. Cholesterol synthesis related gene (hmgr) expression was significantly induced by three Tl species, but cholesterol content in fish body was not altered by all treatments. Tl(I) and Tl(III) suppressed steroid hormone cortisol synthesis related gene (cyp21) expression, but induced degradation gene (hsd11b), whereas cortisol content in fish body was not altered. In the summary, Tl(I) has higher acute toxicity and bioaccumulation potential to medaka than Tl(III). Both Tl(I) and Tl(III) induce oxidative stress and phase I metabolism, but they may have different toxicity mechanisms which need for further investigation.
| Identifer | oai:union.ndltd.org:TW/105NTU05406022 |
| Date | January 2017 |
| Creators | Ching-Hsin Yang, 楊景昕 |
| Contributors | 陳佩貞 |
| Source Sets | National Digital Library of Theses and Dissertations in Taiwan |
| Language | zh-TW |
| Detected Language | English |
| Type | 學位論文 ; thesis |
| Format | 141 |
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