Ferguson J F, Pietari J M
Department of Civil and Environmental Engineering, University of Washington, Seattle, WA 98195, USA.
Environ Pollut. 2000 Feb;107(2):209-15. doi: 10.1016/s0269-7491(99)00139-6.
Chlorinated aliphatic compounds, notably the chlorinated solvents, are common contaminants in soil and groundwater at hazardous waste sites. While these compounds are often recalcitrant, under favorable conditions they can be transformed and degraded through microbially mediated processes. There is great interest in understanding the transformations that are observed at contaminated sites and in manipulating these systems to achieve remediation. An important class of transformations occurs in anaerobic environments. Many of the transformations are reductive, and many yield useful energy to specific anaerobic bacteria. They include reductive dechlorination, dehydrochlorination and dichloroelemination. Of these, reductive dechlorination is often a growth-supporting reaction, while the others may be abiological or catalyzed by biological molecules. The reactions may result in chlorinated products, but there are often reaction sequences leading to completely dechlorinated products. The behavior of carbon tetrachloride (CT), 1,1,2,2-tetrachloroethane (TeCA) and the chloroethenes, perchloroethylene (PCE) and trichloroethylene (TCE), illustrate the range of anaerobic transformations that are possible, as well as the limited transformation that often is seen in the environment. CT undergoes reductive and substitutive reactions that are catalyzed by biological molecules but do not support bacterial growth. The anaerobic degradation of TeCA, which is a major contaminant at a site near Tacoma, WA, USA, provides examples of each type of transformation, and the products formed are consistent with the chlorinated compounds that are found in groundwater extraction wells. A laboratory study, using anaerobic sludge that had been fed chlorinated compounds, a cell-free extract from the sludge, and killed controls, showed that TeCA was transformed to four products and that these were further transformed, suggesting that it might be possible to degrade TeCA to innocuous products. Reductive dechlorination of PCE and TCE has been studied in many laboratories. Studies with mixed anaerobic consortia and with several dehalogenating bacteria, including strain 195 (. Isolation of a bacterium that reductively dechlorinates tetrachloroethane to ethane. Science 276, 1568-1571) that transforms PCE to ethene, have demonstrated that reductive dechlorination supports growth of the novel bacteria that carry out the reactions. Hydrogen has been shown to be an electron donor for the bacterial dehalogenation reactions, and kinetic and thermodynamic considerations indicate that dehalogenators can compete in some, but not all, anaerobic environments, pointing to applications of in situ bioremediation and to its limitations. Selected field studies of anaerobic transformations help delineate the applications of this type of bioremediation.
氯代脂肪族化合物，尤其是氯代溶剂，是危险废物场地土壤和地下水中常见的污染物。虽然这些化合物通常具有顽固性，但在有利条件下，它们可以通过微生物介导的过程进行转化和降解。人们对了解污染场地中发生的转化以及操纵这些系统以实现修复非常感兴趣。一类重要的转化发生在厌氧环境中。许多转化是还原反应，并且许多反应能为特定的厌氧细菌产生有用的能量。它们包括还原脱氯、脱氯化氢和二氯消除反应。其中，还原脱氯通常是一种支持生长的反应，而其他反应可能是无生物活性的或由生物分子催化的。这些反应可能会产生氯代产物，但通常也存在导致完全脱氯产物的反应序列。四氯化碳（CT）、1,1,2,2 - 四氯乙烷（TeCA）以及氯乙烯类化合物全氯乙烯（PCE）和三氯乙烯（TCE）的行为，说明了可能发生的厌氧转化范围以及在环境中常见的有限转化情况。CT会发生由生物分子催化但不支持细菌生长的还原和取代反应。TeCA是美国华盛顿州塔科马附近一个场地的主要污染物，其厌氧降解提供了每种转化类型的示例，并且形成的产物与从地下水抽取井中发现的氯代化合物一致。一项实验室研究使用了投喂过氯代化合物的厌氧污泥、该污泥的无细胞提取物以及灭活对照，结果表明TeCA被转化为四种产物，并且这些产物进一步发生了转化，这表明有可能将TeCA降解为无害产物。许多实验室都对PCE和TCE的还原脱氯进行了研究。对混合厌氧菌群以及几种脱卤细菌（包括将PCE转化为乙烯的菌株195（一种将四氯乙烷还原脱氯为乙烷的细菌的分离。《科学》276, 1568 - 1571））的研究表明，还原脱氯支持进行这些反应的新型细菌的生长。氢气已被证明是细菌脱卤反应的电子供体，动力学和热力学考虑表明，脱卤菌在一些但不是所有的厌氧环境中都能竞争，这指出了原位生物修复的应用及其局限性。一些关于厌氧转化的现场研究有助于阐明这类生物修复的应用。
