Environmental Health - Toxic Substances
Microbial Degradation of Chloroethenes in Ground Water Systems
The chloroethenes, tetrachloroethene (PCE) and trichloroethene (TCE), are among the most common contaminants detected in ground water systems. As recently as 1980, the consensus was that chloroethene compounds were not significantly biodegradable in ground-water. Consequently, efforts to remediate chloroethene contaminated ground water were limited to largely unsuccessful pump and treat attempts. Subsequent investigation revealed that, under reducing conditions, aquifer microorganisms can reductively dechlorinate PCE and TCE to the less chlorinated daughter products, dichloroethene (DCE) and vinyl chloride (VC). Although recent laboratory studies conducted with halorespiring microorganisms suggest that complete reduction to ethene is possible, in the majority of ground-water systems reductive dechlorination apparently stops at DCE or VC. However, a number of recent USGS investigations conducted with aquifer and stream bed sediments have demonstrated that microbial oxidation of these reduced daughter products can be significant under anaerobic redox conditions. The combination of reductive dechlorination of PCE and TCE under anaerobic conditions followed by anaerobic microbial oxidation of DCE and VC provides a possible microbial pathway for complete degradation of chloroethene contaminants in ground-water systems. Thus making monitored natural attenuation a potential alternative to pump and treat remediation for many sites contaminated with chloroethenes.
Since 1995, a team of USGS researchers have been studying the potential for anaerobic microbial oxidation of chlorinated ethenes.
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