Abe Yumiko, Aravena Ramon, Zopfi Jakob, Parker Beth, Hunkeler Daniel
Centre for Hydrogeology, University of Neuchâtel, Neuchâtel, Switzerland.
J Contam Hydrol. 2009 Jun 26;107(1-2):10-21. doi: 10.1016/j.jconhyd.2009.03.002. Epub 2009 Mar 19.
The occurrence of chlorinated ethene transformation in a streambed was investigated using concentration and carbon isotope data from water samples taken at different locations and depths within a 15 x 25 m study area across which a tetrachloroethene (PCE) plume discharges. Furthermore, it was evaluated how the degree of transformation is related to groundwater discharge rates, redox conditions, solid organic matter content (SOM) and microbial factors. Groundwater discharge rates were quantified based on streambed temperatures, and redox conditions using concentrations of dissolved redox-sensitive species. The degree of chlorinated ethene transformation was highly variable in space from no transformation to transformation beyond ethene. Complete reductive dechlorination to ethane and ethene occurred at locations with at least sulfate-reducing conditions and with a residence time in the samples streambed zone (80 cm depth) of at least 10 days. Among these locations, Dehalococcoides was detected using a PCR method where SOM contents were >2% w/w and where transformation proceeded beyond ethene. However, it was not detected at locations with low SOM, which may cause an insufficient H(2) supply to sustain a detectably dense Dehalococcoides population. Additionally, it is possible that other organisms are responsible for the biodegradation. A microcosm study with streambed sediments demonstrated the potential of VC oxidation throughout the site even at locations without a pre-exposure to VC, consistent with the detection of the epoxyalkane:coenzyme M transferase (EaCoMT) gene involved in the degradation of chlorinated ethenes via epoxidation. In contrast, no aerobic transformation of cDCE in microcosms over a period of 1.5 years was observed. In summary, the study demonstrated that carbon isotope analysis is a sensitive tool to identify the degree of chlorinated ethene transformation even in hydrologically and geochemically complex streambed systems. In addition, it was observed that the degree of transformation is related to redox conditions, which in turn depend on groundwater discharge rates.
利用在一个15×25米的研究区域内不同位置和深度采集的水样中的浓度和碳同位素数据，对河床中氯乙烯转化情况进行了调查，该研究区域有一个四氯乙烯（PCE）羽流排放。此外，还评估了转化程度与地下水排放速率、氧化还原条件、固体有机物含量（SOM）和微生物因素之间的关系。基于河床温度对地下水排放速率进行了量化，并利用溶解的对氧化还原敏感的物种的浓度确定了氧化还原条件。氯乙烯的转化程度在空间上变化很大，从无转化到乙烯以上的转化。在至少有硫酸盐还原条件且样品在河床区域（80厘米深度）的停留时间至少为10天的位置，发生了完全还原脱氯生成乙烷和乙烯的情况。在这些位置中，使用PCR方法检测到了脱卤球菌，这些位置的SOM含量>2%（重量/重量）且转化过程超过乙烯。然而，在SOM含量低的位置未检测到脱卤球菌，这可能导致氢气供应不足，无法维持可检测到的密集脱卤球菌种群。此外，也有可能是其他生物体负责生物降解。一项对河床沉积物的微观研究表明，即使在未预先接触氯乙烯的位置，整个场地都有氯乙烯氧化的潜力，这与检测到通过环氧化作用参与氯乙烯降解的环氧烷：辅酶M转移酶（EaCoMT）基因一致。相比之下，在长达1.5年的时间里，微观世界中未观察到顺式二氯乙烯的好氧转化。总之，该研究表明，碳同位素分析是一种灵敏的工具，即使在水文和地球化学复杂的河床系统中也能识别氯乙烯的转化程度。此外，还观察到转化程度与氧化还原条件有关，而氧化还原条件又取决于地下水排放速率。
