水稻土中有机质介导的多氯联苯脱氯机制研究

Polychlorinated biphenyls (PCBs) are typical widespread persistant organic pollutants all over the world. The vast area of paddy soil is an important sink for these compounds. High-chlorinated PCBs in environment is extremely difficult to be degraded, needing to be reductively dechlorinated to lower chlorinated PCBs before it could be carried out for aerobic mineralization. It has been proved that PCBs could be reductively dechlorinated effectively in paddy soil, though the mechanisms are still unknown. In ordinary environment, PCBs could not be chemically dechlorinated for absence of strong reducing substance. Meanwhile PCBs were also hard to be microbial-dechlorinated as the absence of sustained electron donor or the low efficiency of electron transport. The rich organic matter and the anaerobic environment may be the key which improves the PCBs dechlorination in paddy soil. With the help of microelectrode, synchrotron radiation, electric reaction cell and non-culture-based molecular ecological analysis such as metagenomics, PCR-DGGE, FISH, real-time PCR, the mechanisms of PCBs dechlorination in paddy soil will be studied on sensitization photodegradation by dissolved organic matter, sustained electron donor offering by organic matter mineralization, electron transport enhanced by humus shuttle. This work will provide theoretical supporting for the accelerated natural attenuation of PCBs in paddy soil or other natural wetland all over the world, as well as for the remediation of PCBs contaminated site applying artificial wetland.

持久性有机污染物多氯联苯（PCBs）在全球范围内广泛迁移，面积广大的水稻土是其重要的受纳体。高氯代PCBs在环境中极难降解，须脱氯为低氯代PCBs后方可进行矿化。已有研究表明水稻土还原条件下PCBs可较快脱氯，但具体机理不明。一般环境中，PCBs化学脱氯缺少强还原性物质，微生物脱氯则缺少持续电子供体且电子传递效率低，水稻土厌氧环境及丰富有机质条件可克服以上瓶颈。本研究借助微电极、电反应池、同步辐射及基于非培养的宏基因组、PCR-DGGE、FISH、real-time PCR等分子生物学技术，探索水稻土中溶解性有机质对PCBs的敏化光解，研究有机质矿化提供电子供体、腐殖质穿梭提高电子传递效率的PCBs微生物高效脱氯机理，以此揭示水稻土中有机质介导的PCBs脱氯机制。希望能为阐明水稻田等湿地厌氧环境下氯代有机物自然衰减机理提供新的思路，也为氯代有机物污染场地的人工湿地修复提供理论依据。

有机卤化物是典型且备受关注的环境污染物。环境中卤代有机物长期持留，关键在于很多有机卤化物如高氯代多氯联苯（PCBs）必须先脱氯才能彻底好氧降解，而自然脱氯极其缓慢。有机质的存在可加速有机氯脱氯，但其机理尚不明确。本研究以存在厌氧环境且有机质丰富的天然人工湿地稻田土壤为研究对象，以最难脱氯的卤代物之一PCBs为目标污染物，在我国东南沿海电子电器废弃物拆解PCBs典型污染水稻产区开展研究。研究以PCBs脱氯的本质——电子传递为主线，从有机质光敏化产生非生物脱氯强电子供体，有机质微生物矿化提供氢、小分子有机酸等微生物脱氯电子供体，腐殖质穿梭加速电子传递等三个方面，系统研究了水稻土中有机质介导的PCBs脱氯机理。主要得到了以下结果：.（1）野外调查与室内微宇宙模拟均表明，淹水稻田有利于PCBs厌氧生物脱氯的进行，根际深层土壤微域最利于PCBs的消减。.（2）有机质可以显著介导促进PCBs敏化光解。有机质介导的敏化光解可能是自然界重要但长期被人们忽略的有机物非生物降解机制。羟基自由基（•OH）和天然有机质内部疏水微区中的单线态氧（1O2）起着主要的作用。.（3）有机质可以显著介导促进PCBs的微生物脱氯，有机质矿化为PCBs专性脱氯呼吸菌Dehalococcoides mccartyi等提供了有效的电子供体，腐殖质电子穿梭加速了电子在电子供体、共代谢兼性脱氯菌及PCBs间的传递。.研究结果将有助于系统阐明稻田及其他人工湿地、潮间带、江河湖海底泥等厌氧环境下卤代有机物自然衰减的机理，也可为卤代有机物污染环境的修复提供理论基础。