地球化学特征对太湖底泥中多氯联苯微生物厌氧脱氯的影响研究

Polychlorinated biphenyls (PCBs) are typical persistent organic pollutants. Their fate in the environment is of great concern. Despite microbial-catalyzed reductive dechlorination is believed to take place in natural sediments, little is known about the influence of geochemical properties on PCB dechlorination activities. To overcome this obstacle, sediments collected from Taihu Lake, China, and a carefully selected PCB mixture will be used for this PCB dechlorination study. Sediment microcosms will be prepared with 50 ml serum bottles. Each sediment microcosm contains PCB-spiked dry sediment substrate, reduced anaerobic mineral medium (RAMM) medium and wet sediment inoculum. SO42- or FeOOH will be amended to selected microcosms to mimic different geochemical conditions. After around 6 months of incubation, supplemental carbon and energy source, acetate, will be added to some sediment microcosms. Periodic samplings will be performed within one year of incubation. Gas chromatography coupled with micro-electron capture detector (GC-μECD) based PCB congener-specific analysis will be applied to track the shifts PCB dechlorination rate, extent and pathways in conjunction with geochemical condition change. A molecular biology tool-quantitative polymerase chain reaction (qPCR), will be utilized to estimate 16S rRNA genes from the bacterial domains, putative dechlorinating organisms in the phylum Chloroflexi, the Dehalococcoides genus, and two PCB degrading organism strains o-17 and DF-1. Similarly, three reductive dehalogenase genes, ardA, tecA and rdh12 will be quantified. The relationships between the shifts of PCB congeners and microorganisms will be examined to find out the most suitable indicator microorganisms/genes for dechlorination potential prediction. This study will lead to a better understanding of geochemical effects on microbial-catalyzed anaerobic dechlorination of PCBs in Taihu Lake sediment, as well as dominant geochemical factors in dechlorination control. Furthermore, this study is expected to better support monitored natural attenuation as a viable strategy for PCB long term remediation.

多氯联苯是一种典型的持久性有机污染物，其在环境中的转化归趋倍受关注。底泥中多氯联苯可以通过微生物脱氯降解，但该脱氯方式所受的地球化学影响调控机制尚不明晰。本项目将选取太湖底泥为研究对象，考察微环境中外加电子受体SO42- （硫酸根）和FeOOH（以及碳源乙酸等地球化学特征对多氯联苯脱氯降解的影响，通过检测底泥中的多氯联苯单体变化深入探讨不同地球化学特征下多氯联苯脱氯速率、效率和路径的变化规律。通过研究脱氯过程中总细菌、 PCB脱氯细菌及关键脱卤酶基因的变化规律，结合多氯联苯脱氯特征，筛选出脱氯指示微生物/基因，揭示太湖底泥多氯联苯脱氯降解的地球化学影响调控机制，为监测自然衰减法修复多氯联苯污染底泥提供科学依据。

微生物厌氧脱氯降解是多氯联苯（PCBs）在底泥中的主要降解方式，该降解在中国淡水底泥中的研究尚不多见。项目以太湖底泥构建反应微环境，研究9种常见多氯联苯单体在不同地球化学条件下的降解规律。已发表SCI论文3篇，EI论文2篇，CSCD论文2篇，出版专著1部，培养研究生4名。取得主要研究成果：（1）建立并优化了底泥中209种多氯联苯的提取、纯化和痕量检测分析方法，气相色谱可分出171个多氯联苯特征峰，且绝大部分单体回收率>85%；（2）首次证实了太湖底泥中的天然微生物具备厌氧脱氯降解多氯联苯的能力，并以间位和对位脱氯为主。在添加多氯联苯的微环境中，9种母体PCBs总浓度从初始的49.56 ± 0.38 mg/kg降至24周时的24.30 ± 0.97 mg/kg和66周时的8.21 ± 2.56 mg/kg，降低53.0%和83.4%。竞争电子受体羟基氧化铁（FeOOH）的添加部分抑制了多氯联苯脱氯，第24周时母体PCBs总浓度为41.84± 7.64 mg/kg，此后脱氯加快，到第66周时母体PCBs总浓度为11.41 ± 3.45 mg/kg。竞争电子受体SO42-的添加也抑制了多氯联苯脱氯，且抑制能力较FeOOH更强，第24周和第66周时母体PCBs总浓度分别为47.67 ± 0.66 mg/kg 和28.30 ± 1.40 mg/kg；在硫酸盐还原条件下对位脱氯相对较强。对于贫碳的太湖底泥在反应初始补充碳源并不能有效提高脱氯效果，但在不改变脱氯路径的前提下对部分多氯联苯单体尤其是类二噁英多氯联苯的降解起促进作用。太湖底泥中类二噁英多氯联苯PCB 105和PCB 114的降解要快于多氯联苯污染严重的美国哈德逊河和格拉斯河底泥，表现出更强的解毒作用，有利于原位修复。（3）采用实时荧光定量PCR（qPCR）技术研究总细菌（Bacteria）、绿弯菌门中的脱氯菌Chloroflexi、Dehalococcoides、o-17/DF-1的16S rRNA 基因以及2种还原脱卤酶基因ardA和rdh12在各种地球化学条件下的变化情况发现， Dehalococcoides、Chloroflexi、ardA和rdh12均可作为太湖底泥脱氯指示基因，其中还原脱卤酶基因ardA和rdh12最为灵敏，可考虑用于多氯联苯脱氯启动和潜能的预测。