TCE produces many undesirable health side effects. The most alarming hazard associated with TCE exposure is cancer. In 2011, the United States Environmental Protection Agency revised its Final Health Assessment for Trichloroethylene, formally identifying TCE as a human carcinogen.
Improper disposal of TCE (and related chlorinated chemicals) is a major threat to human health and water sources due to the volume of these chemicals that have found their way into the environment, the resulting carcinogenic hazard and the significant challenges involved in cleanup.
Enter Dehalococcoides mccartyi, a group of anaerobic bacteria whose unique metabolic processes allow them to grow and thrive, using TCE as part of their respiratory machinery.
"They use these chlorinated solvents as their electron acceptor, which means they respire them," Krajmalnik-Brown says. "It's like their oxygen." (Just what Dehalococcoides was living on before the introduction of TCE remains an unresolved puzzle.)
Dehalococcoides have become an invaluable tool for the bioremediation of sites contaminated with TCE because they can convert the hazardous chemical first into cis-dichlroethene (cis-DCE), then to vinyl chloride, intermediary chlorinated byproducts, and finally into ethene, an environmentally benign, non-chlorinated end-product. As Krajmalnik-Brown notes "to date, every time we see a site where ethene is being produced, Dehalococcoides are present."
There's one problem, however. In some cases, Dehalococcoides fail to complete the transformation of TCE into ethene, stalling at the mid-stage reaction and sequentially producing two chemicals: cis-DCE and vinyl chloride. The latter is a human carcinogen and of grave concern in the environment, as it can disperse more readily than the original TCE.
The primary focus of the PLOS ONE study was to determin
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Arizona State University