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Environmental Health - Toxic Substances

Research Projects

Application of Molecular Methods in Microbial Ecology to Understand the Natural Attenuation of Chlorinated Solvents

USGS scientists measuring field water-quality parameters
USGS scientists measured a variety of chemical constituents in the field, using portable test kits, in order to evaluate real-time conditions and choose appropriate sampling times.

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Degradation of chlorinated solvents and other contaminants in the subsurface requires that the proper kinds of bacteria are present. Traditional methods used to evaluate the kinds of bacteria in environmental samples were based on growing these bacteria in the laboratory. This is time-consuming and many bacteria cannot be readily grown. New methods in microbiology, based on analyses of DNA, allow microbiologists to study and interpret the kinds of bacteria present in the environment without growing them. These "molecular methods" can provide new information to those involved in understanding, modeling, and remediating contaminated sites.

The USGS has applied these new DNA-based methods in order to understand how the variation with location and time in bacterial community structure affects the natural biodegradation of fuels and chlorinated solvents. Bacterial DNA extracted from subsurface samples provides information on the identities of the bacteria present and their ability to degrade contaminants. At the former Wurtsmith Air Force Base, Michigan, analyses based on DNA sequences have shown that the kinds of bacteria vary with depth in contaminated ground water. The variation in the kinds of bacteria can help to explain the variation in contaminants with depth and also over time. The variation in bacteria can explain why certain degradation processes occur while others do not.

well figure
At about 20 feet depth, Dojka and other found
  • a methane-producing bacterium, Methanosaeta concilli,
  • other bacteria involved in the formation of methane from benzene derivatives
  • two kinds of bacteria that degrade chlorinated solvents

At about 30 feet depth, DNA sequences indicated
  • different kinds of solvent-degrading bacteria
  • no methane-producing bacteria

A different approach uses DNA banding patterns or "fingerprints" to compare samples from different locations, without identifying the bacteria present. This can be useful in site characterization.

How can this information be used?

  • To understand variation in chemistry in water taken from different wells.
  • To choose the proper place to take samples for further laboratory testing or to design engineered remediation approaches.
  • To choose the proper reactions to incorporate in models that predict contaminant degradation time.
  • To evaluate why natural attenuation processes are not the same at all geographic locations across the United States.

More Information

Chlorinated Solvent Remediation Related Activates from Other Projects

Back to Chlorinated Solvents Contamination Research Projects

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