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年度	102	專案性質	實驗性質
專案類別	研究專案	研究主題	調查
申請機構	國立中央大學	申請系所	環境工程研究所
專案主持人	林居慶	職等/職稱	助理教授
專案中文名稱	調查焚化爐周圍水稻田地土壤及作物受現地地質化學與微生物影響之總汞與甲基汞含量變化
中文關鍵字
專案英文名稱	Geochemical and microbial controls on the levels of total- and methyl-mercury in the soil and rice plants in a paddy field in the vicinity of a local municipal solid waste incinerator
英文關鍵字	mercury, rice paddy, geochemistry, microbial controls, municipal solid waste incinerator
執行金額
執行期間	2012/12/10 至 2013/12/9
計畫中文摘要	由於其獨特的化性，已被認定為全球性的污染物。目前已知釋放至環境中 的汞，主要是人為活動所產生，由以焚化廠及燃煤發電廠的貢獻量為最大。氧化 態的無機汞因其大氣停留時間相對短暫，被排放後將因沉降作用回到地表，並有 機會被環境中的厭氧菌轉化成為毒性更強的甲基汞，之後再經由食物鏈的放大效 應而對環境生態與人類健康造成威脅。以往的觀念中，甲基汞所帶來的毒害問題 幾乎都是經由對魚蝦貝類的攝食而造成；然而，近期的文獻顯示，高濃度的甲基 汞已從生長在離汞排放源相近之田地中的稻米被檢測出來，暗示著除了水相生態 系統外，陸地生態系統中的食物也可能成為甲基汞的攝食途徑。由於稻米是台灣 也是許多亞洲地區人民的主食，雖然藏於米粒內的汞濃度或許不高，但若以長期 攝取的總量觀點來看，其對健康所帶來的影響值得關注。基於此，對於水稻田為 何易成為甲基汞生成的環境，環境生物地化的作用與循環機制如何涉入其過程， 以及排放源對於甲基汞在近區稻米的累積效應需進一步的調查研究。 本研究選用四處北投焚化廠周圍的水稻田進行採樣分析。所採集的樣品包含 覆蓋於田地的表水、表土 (0-2 公分) 以及根系周圍的土壤。分析的項目除了總汞 與甲基汞外，也涵蓋可能會影響無機汞在現地生物可得性分佈的地質化學參數， 如土壤的有機質與鐵含量，以及孔隙水中的硫化物與鐵的含量。總汞和甲基汞的 分析結果指出，北投焚化爐周圍水稻田的土壤及孔隙水，以及栽種在此區的稻米， 其內的總汞與甲基汞含量皆與一般環境或農地的背景值相近，皆無超過法規所定 的環境與食米標準，除顯示此區未受汞污染外，也間接代表焚化爐內運轉的空污 防治措施可有效管控汞的排放，因其所排出之煙道氣體並未造成此區農地顯著的 汞累積。根據現地地質化學與微生物族群的分析可知：(1)孔隙水中的甲基汞與無 機汞濃度呈現顯著正相關，(2)硫與鐵的循環所造成的孔隙水化學造成此根系環境 中無機汞的生物有效性偏高，(3)硫酸鹽還原菌極有可能是此區域最主要的汞甲基 化微生物族群，而這些因素加總起來某種程度上暗示，若此區的總汞濃度增加， 其根系土壤環境仍有可能具有促進甲基汞生成與累積的潛力。藉由不同形式的配 位基的添加而改變甲基汞的孔隙水化學組成，測試結果顯示甲基汞的錯和化學將 會造成稻作不同程度的甲基汞攝取與累積量，然此部分的機制原理仍需進一步的 探究。
計畫英文摘要	Current inventories of mercury (Hg) emissions show that coal combustion and solid waste incineration account for more than half of the total emissions. Aside from intake of fish that has long been considered as the primary route for human and wildlife exposure to methylmercury (MeHg), recent studies have reported high levels of MeHg in the seed of rice grown in the vicinity of anthropogenic Hg emission sources, suggesting that ingestion of rice may be another important human exposure to MeHg. As a result, it is important to conduct thorough investigation of this exposure pathway by examining why rice paddies are conductive for Hg methylation, and also how additional inputs of Hg resulted from the combustion of municipal solid waste (MSW) may lead to the potential uptake and accumulation of Hg and MeHg in rice plants. Four paddy sites were chosen within the agricultural land in the vicinity of the Beitou MSW incinerator. During the sampling trips, topsoil, surface water and roo-soil cores were collected using ultra-clean sampling techniques in order to measure Hg levels in the parts-per-trillion range. Great care was also taken in laboratory processing to minimize external contamination. In addition to Hg and MeHg analysis, ancillary geochemical and microbiological parameters including pore water/sediment sulfide and iron concentrations were measured to probe potential factors that may control the bioavailability of inorganic Hg and the dominant Hg-methylating microbial species. Results show that concentrations of total Hg and MeHg in roo-soil, porewater as well as rice grains collected from 4 rice paddy sites were in the range of background levels reported from other researchers and below the regulations for soil and edible rice, suggesting that this agricultural area near the Beitou incinerator is not polluted by Hg and the air control device employed in the incinerator has been efficient for control Hg emission. Geochemical and microbial analyses indicated that sulfate-reducing bacteria might be the principal anaerobic microbes for in situ MeHg formation in this root-soil area. In addition, geochemical conditions showed potential to enhance Hg methylation if elevated Hg inputs occurred. Data from MeHg chemical speciation experiments showed that complexation between MeHg and ligands might influence uptake of MeHg in rice.