English  |  正體中文  |  简体中文  |  Items with full text/Total items : 73032/73032 (100%)
Visitors : 23294833      Online Users : 386
RC Version 7.0 © Powered By DSPACE, MIT. Enhanced by NTU Library IR team.
Scope Tips:
  • please add "double quotation mark" for query phrases to get precise results
  • please goto advance search for comprehansive author search
  • Adv. Search
    HomeLoginUploadHelpAboutAdminister Goto mobile version

    Please use this identifier to cite or link to this item: http://ir.lib.ncu.edu.tw/handle/987654321/66959

    Title: 鄰近汞排放源之水稻田受現地地質化學與微生物影響之甲基汞生成與累積作用-以北投垃圾焚化爐為例;Probing the biogeochemical processes of methylmercury formation and accumulation in the paddy system in the vicinity of a municipal solid waste incinerator
    Authors: 張惟竣;Chang,Wei-Chun
    Contributors: 環境工程研究所
    Keywords: 甲基汞生成;水稻田;現地環境生物地質化學;焚化爐
    Date: 2015-01-28
    Issue Date: 2015-03-16 16:07:44 (UTC+8)
    Publisher: 國立中央大學
    Abstract: 自工業革命開始,環境中汞的排放源已知主要與人為活動有關,特別是焚化廠及燃煤發電廠的運作。汞經排出後,部分(當中絕大多數為氧化態的無機二價汞)會因沉降作用降至附近地表,並有機會被現地異營性的厭氧微生物轉化成毒性更強的甲基汞。早期的研究認為,甲基汞的曝露與中毒都是透過魚類海鮮的攝取而造成,但近期文獻發現,高濃度的甲基汞可從生長在離汞排放源相近的稻米中檢測出來,暗示著陸域生態系中的食物也可能成為甲基汞的攝食途徑之一。由於稻米是台灣也是許多亞洲地區人民的主食,因此對於水稻田為何易成為甲基汞的生成環境,生地化循環如何涉入其過程,以及排放源造成甲基汞在稻米的累積效應為何是值得深入探討的課題。
    ;Since the industrial revolution, the release of mercury (Hg) from emission sources to the environment has been predominantly resulted from human activities, with burning of fossil fuels and waste being the leading contributors. Once released, a partial amount of Hg (mostly in its divalent inorganic forms) would return to the Earth’s surface by wet or dry deposition and then be converted in situ by certain heterogeneous anaerobic bacteria to methylmercury (MeHg), the most toxic form of Hg and known for its great bioaccumulation tendency . While consumption of predatory fish and seafood has been considered the primary route for human exposed to MeHg, recent studies have reported high levels of MeHg in rice grown in the vicinity of anthropogenic Hg releasing sources, suggesting that ingestion of crops from the terrestrial food chain may be another critical route of human exposure to MeHg. Given that (i) rice is a staple food in Taiwan and throughout Asia and (ii) the potential for maternal MeHg exposure (even at low-level) through ingestion of rice that may subsequently impact health of the offspring, it is important to conduct thorough investigation of this exposure route by examining why rice paddies are conductive for Hg methylation, which biogeochemical reactions may have been involved in this process, and also how additional inputs resulted from anthropogenic perturbations may eventually lead to the potential accumulation of Hg and MeHg in rice plants.
    In this study, four paddy sites within the agricultural area of the Beitou municipal solid waste (MSW) incinerator were chosen to sample surface water, topsoil and root soil. Total Hg, MeHg, as well as ancillary geochemical/microbiological parameters in soil, porewater, and rice grains were analyzed. In addition, microcosm and hydroponic experiments were carried out to probe (i) the primary Hg methylators in the root soil of the study sites and (ii) the influence of coordination chemistry on the uptake of MeHg by roots of rice plants. Results showed that the levels of total Hg and MeHg in paddy soil and rice grains did not exceed the current standards set for farmland soil and edible rice, suggesting that our study sites are not contaminated with Hg and the air control devices employed in the Beitou MSW incinerator may have been efficient for the control of Hg emission. However, it is observed that both the bioavailability of inorganic Hg and the activity of Hg-methylating microbes increased during the early and mid rice growing season, presumably due to the anoxia created under flooded conditions. This suggested that the paddy ecosystem has a great potential for enhanced Hg-methylation if elevated inputs of Hg occurred, and hence there is a need for constant monitoring of the Hg level in this area. Results of microcosm experiments revealed that sulfate-reducing bacteria may be the principal Hg-methylators in the rhizospheric zones of the study sites. Molecular identification of the hgcA gene in the root soil samples further confirmed the existence of Hg-methylating microbes. Lastly, using different forms of ligands to alter MeHg speciation in the growing medium, preliminary results from the hydroponic culturing of rice implied that both passive diffusion and active transport mechanisms may all take place in the root uptake of MeHg in rice.
    Appears in Collections:[環境工程研究所 ] 博碩士論文

    Files in This Item:

    File Description SizeFormat

    All items in NCUIR are protected by copyright, with all rights reserved.

    社群 sharing

    ::: Copyright National Central University. | 國立中央大學圖書館版權所有 | 收藏本站 | 設為首頁 | 最佳瀏覽畫面: 1024*768 | 建站日期:8-24-2009 :::
    DSpace Software Copyright © 2002-2004  MIT &  Hewlett-Packard  /   Enhanced by   NTU Library IR team Copyright ©   - Feedback  - 隱私權政策聲明