微生物胞外呼吸电子转移驱动稻田溴代物厌氧还原及矿化机制

The paddy soils are widely distributed in southern provinces, but it is facing the potential pollution danger by brominated organic compounds due to the recycling activities of e-waste. The degradation of brominated flame retardants, such as PBEDs and TBBPA, have been attracted wide concern, and now it is a research focus in the field of soil environmental chemistry. In this research, typical brominated organic compound in paddy soils would be selected as model, and its two important degradation processes, i.e., reductive debromination and subsequent oxidation driven by microorganism under anaerobic conditions, would be coupled to be emphatically studied. In simulated anoxic environment of paddy soils, the key effect of microbial extracellular respiration to the degradation of brominated compounds, such as typical humus respiration and iron respiration, would be discussed through anaerobic sequencing batch culture experiments. Under different substrates in simple and complex systems, i.e., different soil types, different organic matter content and external sources, etc., the degradation processes of brominated compounds in paddy soils would be different and they would be also researched. Furthermore, the degradation kinetics of the brominated compound would be revealed by coupling the research of these internal or external effect factors to the results of the changes of the microbial communities and the oxidation-reduction potential. In the processes of anaerobic sequencing batch culture experiments, the intermediates of the selected brominated compound would be analyzed, and the results could provided some important information of the degradation pathway of the model in the paddy soils. We hope, through the research of this project, the results could provided valuable strategies of in situ remediation and the feasible measures of enhanced degradation for polluted paddy soils in southern China.

水稻土在我国南方分布广泛，但面临溴代物污染的潜在风险日益增加，多溴联苯醚、四溴双酚A等稻田土壤溴代物降解转化受到强烈关注，是目前土壤环境化学领域研究热点之一。项目以南方水稻土壤典型溴代物为目标模型物，通过微生物，将厌氧条件下溴代物降解转化的两个重要过程，即溴代物还原脱溴及脱溴产物矿化脱毒耦联进行研究，探讨微生物胞外呼吸电子转移驱动水稻土溴代物还原脱溴及矿化机制。通过模拟稻田缺氧环境，进行序批式厌氧培养实验，研究微生物在典型胞外呼吸铁呼吸、腐殖质呼吸过程中，强化溴代物还原脱溴、直至矿化脱毒的核心作用。探讨简单和复杂体系不同底物条件下，即不同土壤类型、土壤有机质含量、不同外加源措施等，对水稻土溴代物降解转化的影响机制，结合不同体系微生物群落特性及氧化还原电位变化研究，揭示水稻土体系中溴代物降解转化动力学，以及溴代物厌氧脱毒转化途径，以期为溴代物污染水稻土原位修复及可行性强化措施提供科学依据。

项目从南方稻田土壤受到溴代物污染潜在风险日益增加的实际情况出发，围绕“微生物胞外呼吸电子转移驱动稻田溴代物厌氧还原及矿化机制”这一科学问题，以南方水稻土为研究对象，以四溴双酚A（TBBPA）为研究目标模型物，研究南方典型电子垃圾拆解区土壤TBBPA和双酚A（BPA）分布特征及来源，构建厌氧-好氧培养体系，研究稻田土壤中TBBPA还原脱溴及矿化动力学过程，以及微生物群落结构变化，探讨不同外源措施对TBBPA降解转化的影响，揭示水稻土体系中TBBPA还原脱溴及矿化脱毒的微生物降解机制。研究结果表明：广东龙塘电子垃圾拆解区农田土壤普遍受到TBBPA和BPA污染，且BPA含量高于TBBPA，而土壤剖面中TBBPA及BPA主要分布于表层土壤（0~40 cm），对地下水污染潜在风险较小。厌氧培养过程中，灭菌土壤没有明显的铁还原作用，TBBPA未发生还原脱溴；而活性土壤中Fe(III)发生还原，生成溶解态Fe(II)， TBBPA还原脱溴，生成低溴中间产物与BPA，表明微生物活性是土壤中铁还原过程与TBBPA降解转化的主要驱动力。土壤中TBBPA逐个脱去溴原子，三溴双酚A、二溴双酚A、一溴双酚A、双酚A依次生成。乳酸组溶解态Fe(II)的增加量大于原土组，TBBPA还原脱溴的速率常数（k = 0.0766）高于原土组的（k = 0.0377），表明乳酸可作为微生物的碳源和电子供体，促进微生物生长代谢和铁还原过程，强化微生物胞外呼吸电子传递，从而加快TBBPA还原脱溴。经过厌氧培养，乳酸组与原土组的脱卤微生物均变为优势门类。好氧培养过程中，脱溴产物BPA迅速降解，TBBPA和低溴中间产物从结合态残留物解吸。乳酸一方面促进了微生物生长代谢从而加快BPA的降解，另一方面提高了溶解有机质含量从而增强结合态残留物中溴代物的解吸。AQDS轻微促进TBBPA的还原转化（k = 0.0381），而磁铁矿、零价铁+AQDS和磁铁矿+AQDS则起抑制作用（k值分别为0.0266、0.0218和0.0121）。AQDS、磁铁矿、零价铁+AQDS和磁铁矿+AQDS对TBBPA及低溴中间产物的还原脱溴均是先抑制后促进，表明微生物需要一个适应的过程。研究成果表明微生物胞外呼吸是驱动稻田TBBPA还原脱溴及矿主要驱动力。本项目共发表SCI论文3篇，培养硕士研究生2人。