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Enhancement of Trichloroethene (TCE) Biodegradation in a Simulated Groundwater System

USGS scientist at a laboratory fume hood preparing experiments
Shaun M. Baesman, a USGS scientist, at a laboratory fume hood preparing experiments to test if adding acetylene-fermenting bacteria to microcosms can enhance the biodegradation of trichloroethylene (TCE) in groundwater. Photo Credit: Ronald S. Oremland, USGS.

This laboratory-based study provides information for understanding enhancement of trichloroethene (TCE) biodegradation in a simulated groundwater system.

Groundwater contamination by TCE and other persistent contaminants can present an exposure risk for humans through ingestion of contaminated drinking water, inhalation of TCE vapors that can enter home basements that lie over contaminated areas, and inhalation of TCE vapors released from contaminated water during showering and other household activities.

TCE is a volatile solvent used for degreasing during the manufacture of products. TCE can enter soil, groundwater, and surface water from leaking storage tanks or from improper disposal of wastes. Once TCE reaches groundwater aquifers, it can contaminate private and public drinking water wells.

Native bacteria in aquifers can biodegrade TCE and remove it from the groundwater; however, biodegradation often stalls at intermediate products, such as vinyl chloride, that are equally if not more toxic than the parent compounds. In groundwater aquifers with geologic materials containing iron minerals, abiotic degradation of TCE can occur along with natural biodegradation. Abiotic degradation produces acetylene, which can have the detrimental effect of inhibiting the process of biological TCE degradation.

In this study, scientists sought to develop a better understanding of ways to enhance biodegradation of TCE in groundwater. The scientists conducted laboratory experiments to determine if the inhibitory effect of acetylene on biodegradation of TCE could be minimized by adding bacteria that ferment acetylene and to determine if the fermentation produces products that can support the bacteria that biodegrade TCE without a buildup of harmful products such as vinyl chloride.

These laboratory-based results indicate that when TCE and acetylene are present, addition of acetylene-fermenting bacteria can enhance bioremediation of TCE and reduce its harmful breakdown products. The scientists determined that TCE biodegradation was slowed when acetylene was present in high concentrations, and that this inhibition was removed when an acetylene-fermenting bacteria was added. They also determined addition of acetylene and acetylene-fermenting bacteria transformed TCE to innocuous products. These results provide information to understand potential strategies for enhancement of TCE biodegradation to innocuous products at contaminated sites containing both TCE and acetylene.

This study is part of a long-term goal of the Environmental Health Mission Area to provide the science needed to understand how to economically and effectively minimize the actual, as opposed to the perceived, risk to the health of humans and other organisms exposed to contaminants in groundwater resources used for drinking water.

The U.S. Geological Survey (USGS) Toxic Substances Hydrology Program funded this study.

Reference

Mao, X., Oremland, R.S., Liu, T., Gushgari, S., Landers, A.A., Baesman, S.M., and Alvarez-Cohen, L., 2017, Acetylene fuels TCE reductive dechlorination by defined Dehalococcoides/Pelobacter consortia: Environmental Science and Technology, v. 51, no. 4, p. 2366-2372, doi:10.1021/acs.est.6b05770.

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