| 摘要: | 奈米銀因其廣為人知的殺菌特性近來已廣被納入應用在諸如紡織服飾、醫療設備，甚至是兒童玩具等產業。然而，如此快速發展與廣泛使用奈米銀終將使得這些人造奈米顆粒進入自然環境與工程系統，並可能進而導致許多諸如營養鹽循環轉化等重要的微生物程序受到衝擊。不過儘管奈米銀的穩定性及抗菌性近期已引起相當的關注，截至目前為止大部分相關的研究都只著重在其好氧或是如同鐵還原、硫酸鹽還原以及甲烷生成等絕對厭氧狀態時的探討，對於奈米銀在系統的氧化還原電位接近好氧時的脫硝狀態卻甚少著墨。但值得注意的是，從熱力學平衡的角度來看，缺氧脫硝過程中所產生的中間產物在標準狀態下大多是具有可將無定型的零價元素銀氧化成離子態一價銀的潛力。由於微生物所主導的脫硝作用不論在自然界的元素生地化循環或是在一般廢水處理系統的營養鹽去除都具有不可或缺的重要性，因此深入了解人造奈米銀顆粒與脫硝菌之間的相互作用對於未來預測這些新興材料於特定環境中所表現出的行為與生態衝擊皆有所助益。有鑑於此，本研究將藉由縮模培養與批式反應槽試驗，深入調查人造奈米銀顆粒在脫硝條件下的氧化與殺菌特性，具體的目標包括：(1)探究脫硝中間產物與天然有機物對於奈米銀顆粒的化性轉換與殺菌作用的各別與協同效應，(2)了解奈米銀尺寸、型態與表面電性等基本顆粒特徵對其在脫硝狀態下的氧化還原性與微生物毒性的影響，以及(3)量化脫硝菌與奈米銀顆粒互動過程中所引起的生理、基因、酵素活性與菌相結構等的變化程度。本研究的結果對於降低人造奈米銀顆粒於缺氧系統中的相關風險評估與管理上的不確定性將有所幫助。 ;Engineered silver nanoparticles (AgNPs), largely known to act as antimicrobial agents, are increasingly incorporated into consumer products like clothing, medical device and even children’s toys. Such rapid development and widespread usage of AgNPs in these sectors is likely to result in the entry of AgNPs into both natural and engineered systems, which has the potential to disrupt important bacterial processes including those involved in biogeochemical cycling of essential nutrients. While the stability and antibacterial activity of AgNPs have recently drawn considerable attention, the majority of this research to date has been carried out under either aerobic or strictly anaerobic such as ferrogenic, sulfidogenic and methanogenic conditions. Little is known about the geochemistry and microbial toxicity of AgNPs in the environment where nitrate reduction is characterized as the primary terminal electron accepting process, i.e., denitrification, nor is the role of natural organic matter (NOM) involved in this process. Denitrification is an important microbially mediated process that is indispensable for nitrogen cycling in the fundamental biogeochemical processes and nitrogen removal in the conventional wastewater treatment activities. However, equilibrium models have predicted that anoxic oxidation of bulk amorphous Ag(0) to ionic Ag(I) by most dissmilatory nitrate reduction intermediates at the standard state is a thermodynamically favorable reaction. Hence, given that a better understanding of the relationship between engineered nanoparticles and response at the molecular and community levels of microbes is crucial to better predict and interpret the ultimate behavior and adverse impact of these novel materials in the environment, here we propose to conduct thorough, in-depth investigations to study transformation and bactericidal effect of engineered AgNPs under denitrifying conditions. Specifically, by performing microcosm incubation and bench-scale sequencing batch reactor experiments, we will (i) explore the roles of intermediate nitrogen species and NOM in the oxidation and toxicity of AgNPs in the denitrifying cultures/process, (ii) examining the effect of particle size, shape and charge in association with observed AgNP transformation and toxic effect, as well as (iii) characterize the resulting physiological, genetic, enzymatic and microbial community changes. Results of this study may provide insight into the assessment and management on the ecological risk associated with AgNP-exposure in the anoxic environment. |
