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Direct aerobic biodegradation of vinyl chloride (VC) offers a remedial solution for persistent vinyl chloride plumes that are not amenable to the anaerobic process of reductive dechlorination because of either prevailing geochemical conditions or the absence of active Dehalococcoidesethenogenes. However, tools are needed to evaluate and optimize aerobic VC bioremediation. This article describes the development and testing of two techniques-a microbiological tool and a molecular tool-for this purpose. Both methods are based on detection of bacteria that can use vinyl chloride and ethene as growth substrates in the presence of oxygen. The microbiological tool is an activity assay that indicates whether bacteria capable of degrading ethene under aerobic conditions are present in a groundwater sample. This activity assay gave positive results in the area of active VC degradation of an aerobic VC bioremediation test site. A rapid semiquantitative genetic assay was also developed. This molecular tool, based on polymerase chain reaction (PCR) detection of a gene involved in the metabolism INTRODUCTIONVinyl chloride (VC), a toxin and known human carcinogen, is a common contaminant in groundwater (Agency for Toxic Substance and Disease Registry, 2006; U.S. Environmental Protection Agency, 2000). It is produced as a daughter product of the anaerobic biodegradation of more highly chlorinated ethenes, such as tetrachloroethene (PCE) and trichloroethene (TCE) (Kielhorn et al., 2000;Smith, 1984). Although these compounds can be anaerobically transformed to the nontoxic product ethene, the process is often incomplete. This leads to VC stall, a condition in which VC concentrations that are low but greater than the regulatory standard, persist in groundwater.At contaminated sites where either geochemical conditions are not appropriate for complete anaerobic biodegradation of chlorinated ethenes or Dehalococcoides ethenogenes bacteria capable of carrying out the transformation to ethene (He et al., 2003) are not present, direct aerobic treatment may be an option. This treatment methodology depends on the presence and activity of any of a wide variety of bacteria (see Exhibit 1) that have (Coleman et al., 2002;Hartmans & De Bont, 1992;Verce et al., 2000Verce et al., , 2001. These bacteria use VC as a carbon and energy source (i.e., an electron donor), in contrast to the anaerobic biodegradation process in which Dehalococcoides use chlorinated ethenes as electron acceptors and an exogenous electron donor must often be added. The bacteria that aerobically degrade VC apparently do so by way of an assimilation pathway for ethene and are referred to as ethenotrophs (Fogel et al., 2005). This is in contrast to biodegradation schemes where VC is not a growth substrate (i.e., cometabolic or anaerobic degradation). Ethenotrophs metabolize ethene and VC by the same pathway, using these compounds as carbon and energy sources for growth. Exhibit 2 shows a simplified scheme of the predicted pathways for VC and ethene metabolism (Coleman & Sp...

Contamination of groundwater with chlorinated ethenes is common and represents a threat to drinking water sources. Standard anaerobic bioremediation methods for the highly chlorinated ethenes PCE and TCE are not always effective in promoting complete degradation. In these cases, the target contaminants are degraded to the daughter products DCE and/or vinyl chloride. This creates an additional health risk, as vinyl chloride is even more toxic and carcinogenic than its precursors. New treatment modalities are needed to deal with this widespread environmental problem. We describe successful bioremediation of a large, migrating, dilute vinyl chloride plume in Massachusetts with an aerobic biostimulation treatment approach utilizing both oxygen and ethene. Initial microcosm studies showed that adding ethene under aerobic conditions stimulated the rapid degradation of VC in site groundwater. Deployment of a full‐scale treatment system resulted in plume migration cutoff and nearly complete elimination of above‐standard VC concentrations.

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