Lorah Michelle M, Voytek Mary A
U.S. Geological Survey, Water Resources Division, MD-DE-DC District, Baltimore, MD 21237, USA.
J Contam Hydrol. 2004 May;70(1-2):117-45. doi: 10.1016/j.jconhyd.2003.08.010.
The biodegradation pathways of 1,1,2,2-tetrachloroethane (TeCA) and 1,1,2-trichloroethane (112TCA) and the associated microbial communities in anaerobic wetland sediments were evaluated using concurrent geochemical and genetic analyses over time in laboratory microcosm experiments. Experimental results were compared to in situ porewater data in the wetland to better understand the factors controlling daughter product distributions in a chlorinated solvent plume discharging to a freshwater tidal wetland at Aberdeen Proving Ground, Maryland. Microcosms constructed with wetland sediment from two sites showed little difference in the initial degradation steps of TeCA, which included simultaneous hydrogenolysis to 112TCA and dichloroelimination to 1,2-dichloroethene (12DCE). The microcosms from the two sites showed a substantial difference, however, in the relative dominance of subsequent dichloroelimination of 112TCA. A greater dominance of 112TCA dichloroelimination in microcosms constructed with sediment that was initially iron-reducing and subsequently simultaneously iron-reducing and methanogenic caused approximately twice as much vinyl chloride (VC) production as microcosms constructed with sediment that was methanogenic only throughout the incubation. The microcosms with higher VC production also showed substantially more rapid VC degradation. Field measurements of redox-sensitive constituents, TeCA, and its anaerobic degradation products along flowpaths in the wetland porewater also showed greater production and degradation of VC with concurrent methanogenesis and iron reduction. Molecular fingerprinting indicated that bacterial species [represented by a peak at a fragment size of 198 base pairs (bp) by MnlI digest] are associated with VC production from 112TCA dichloroelimination, whereas methanogens (190 and 307 bp) from the Methanococcales or Methanobacteriales family are associated with VC production from 12DCE hydrogenolysis. Acetate-utilizing methanogens (acetotrophs) appear to be involved in the biodegradation of VC. The relative abundance of Methanosarcinaceae, the only methanogen group with acetotrophic members, doubled in microcosms in which degradation of VC was observed. In addition, molecular analyses using primers specific for known dehalorespiring bacteria in the Dehalococcoides and Desulfuromonas groups showed the presence of these bacteria in microcosm slurry from the site that showed the highest VC production and degradation. Determination of biogeochemical controls and microbial consortia involved in TeCA degradation is leading to a better understanding of the heterogeneity in biodegradation rates and daughter product distribution in the wetland, improving capabilities for developing remediation and monitoring plans.
在实验室微观实验中，通过同步的地球化学和基因分析，对厌氧湿地沉积物中1,1,2,2-四氯乙烷（TeCA）和1,1,2-三氯乙烷（112TCA）的生物降解途径及相关微生物群落进行了长期评估。将实验结果与湿地中的原位孔隙水数据进行比较，以更好地了解控制向马里兰州阿伯丁试验场的淡水潮汐湿地排放的氯化溶剂羽流中次生产物分布的因素。用来自两个地点的湿地沉积物构建的微观模型显示，TeCA的初始降解步骤差异不大，初始降解步骤包括同时氢解为112TCA和脱氯生成1,2-二氯乙烯（12DCE）。然而，来自两个地点的微观模型在112TCA后续脱氯的相对优势方面存在显著差异。在用最初进行铁还原、随后同时进行铁还原和产甲烷的沉积物构建的微观模型中，112TCA脱氯的优势更大，导致氯乙烯（VC）的产量约为在整个培养过程中仅进行产甲烷的沉积物构建的微观模型的两倍。VC产量较高的微观模型中，VC的降解也明显更快。对湿地孔隙水中沿流动路径的氧化还原敏感成分、TeCA及其厌氧降解产物的现场测量也表明，在产甲烷和铁还原的同时，VC的生成和降解更多。分子指纹分析表明，细菌物种[由MnlI消化后片段大小为198个碱基对（bp）的峰表示]与112TCA脱氯产生VC有关，而来自甲烷球菌目或甲烷杆菌目家族的产甲烷菌（190和307 bp）与12DCE氢解产生VC有关。利用乙酸的产甲烷菌（乙酸营养型产甲烷菌）似乎参与了VC的生物降解。在观察到VC降解的微观模型中，唯一具有乙酸营养型成员的产甲烷菌群——甲烷八叠球菌科的相对丰度增加了一倍。此外，使用针对脱卤球菌属和脱硫单胞菌属中已知脱卤呼吸细菌的特异性引物进行的分子分析表明，在显示出最高VC产量和降解的地点的微观模型浆液中存在这些细菌。确定参与TeCA降解的生物地球化学控制和微生物群落，有助于更好地理解湿地中生物降解速率和次生产物分布的异质性，提高制定修复和监测计划的能力。
