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The Use of Molecular and Genomic Techniques Applied to Microbial Diversity, Community Structure, and Activities at DNAPL and Metal Contaminated Sites
Citation:
AZADPOUR-KEELEY, A., M. J. BARCELONA, K. Duncan, AND J. SUFLITA. The Use of Molecular and Genomic Techniques Applied to Microbial Diversity, Community Structure, and Activities at DNAPL and Metal Contaminated Sites. U.S. Environmental Protection Agency, Washington, DC, EPA/600/R-09/103, 2009.
Impact/Purpose:
observation of subsurface microbial communities
Description:
A wide variety of in situ subsurface remediation strategies have been developed to mitigate contamination by chlorinated solvent dense non-aqueous phase liquids (DNAPLS) and metals. Geochemical methods include: zerovalent iron emplacement, various electrolytic applications, electrosmotic mobilization, as well as the addition of various oxidants, or reductants, chelating agents, and surfactants. Physical methods (primarily for the chlorinated solvents) include in situ heating by various methods, steam injection/vacuum extraction, and gas sparging. Bioremediation methods applied to these classes of contaminants can be broadly categorized as active (enhanced) or passive (monitored natural attenuation; MNA) approaches. In the former, additions of carbon substrates including organic esters, acids, mulch, emulsified oils, or fats are intended to stimulate the growth of microorganisms capable of degrading chlorinated solvents or causing immobilization of metals, via reduction or removal as insoluble precipitates. Also, active approaches may be supplemented by the addition of cultured microorganisms capable of carrying out degradation or immobilization under selected conditions. This approach is called bioaugmentation. Regardless of the basis for the remedial action, it is critical to recognize that subsurface microbial communities will respond to both the presence of the contaminants or the engineered manipulation of subsurface conditions. Responses of the microbiota may include stress or changes in diversity, community structure, biomass, and activity among others. Their response may have profound effects on remedial progress; effective time-frames to reach regulatory decision points, and consequences for the environment. Therefore, it is quite important for subsurface scientists, engineers, regulatory officials, policy makers and the general public to recognize the roles that microorganisms play during in situ remedial efforts and the value of subsurface ecology to soil and water resources quality. It is also important that we employ and improve on modern methods to measure microbial responses to contamination and remediation strategies so that subsurface ecology may be better understood. The molecular and genomic techniques to identify and track the response of microbial ecosystems to human influences hold great promise in our efforts to protect the environment. One should keep in mind that the inherent variability in subsurface hydrogeology, flow phenomena and geochemical parameters are of the order of ± 20% (combined sampling and analytical error). Measured contaminant distributions can easily vary as much as ± 140% over the time frame of initial site characterization or tracer release (Keeley and Barcelona, 2006). Therefore, we should carefully consider how the measures of microbial responses to the presence of contaminants might be expected to vary considerably over time and space. The purpose of this document is to provide an overview of the molecular and genetic techniques applicable in ground-water investigations and to present examples of the use of these techniques to draw site-specific inferences.
URLs/Downloads:
THE USE OF MOLECULAR AND GENOMIC TECHNIQUES APPLIED TO MICROBIAL DIVERSITYAbstract
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