Elshahed_et_al 2001_ESTv35 p682

Elshahed_et_al 2001_ESTv35 p682 - Environ. Sci. Technol....

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Signature Metabolites Attesting to the In Situ Attenuation of Alkylbenzenes in Anaerobic Environments MOSTAFA S. ELSHAHED, LISA M. GIEG,* MICHAEL J. MCINERNEY, AND JOSEPH M. SUFLITA Department of Botany and Microbiology, The University of Oklahoma, Norman, Oklahoma 73019 Accurate assessment of the fate of hydrocarbons spilt in aquifers is essential for gauging associated health and ecological risks. Regulatory pressure to actively remediate such contaminated ecosystems can be substantially diminished if solid evidence for in situ microbial destruction of pollutants is obtained. In laboratory incubations, sediment- associated microorganisms from a gas condensate- contaminated aquifer anaerobically biodegraded toluene, ethylbenzene, xylene, and toluic acid isomers with stoichiometric amounts of sulfate consumed or methane produced. The activation of the alkylated aromatic contaminants involved conversion to their corresponding benzylsuccinic acid derivatives, a reaction known to occur for toluene and m -xylene decay, but one previously unrecognized for ethylbenzene, o- and p- xylene, and -toluate metabolism. Benzylsuccinates were further biodegraded to toluates, phthalates, and benzoate. In laboratory incubations, these metabolites were transiently produced. Several of the metabolites were also detected in groundwater samples from an aquifer where alkylbenzene concentrations decreased over time, suggesting that anaerobic microbial metabolism of these contaminants also occurs in situ. Our studies confirm the utility of the aforementioned compounds as signature metabolites attesting to the natural attenuation of aromatic hydrocarbons in anaerobic environments. Introduction Hydrocarbon mixtures are accidentally released in the environment during energy production, usage, and storage. Benzene, toluene, ethylbenzene, and the xylene isomers (BTEX) pose great environmental and regulatory concern due to their relatively high water solubility and toxicity ( 1 - 3 ). Mounting evidence shows that BTEX hydrocarbons can be degraded anaerobically under a variety of terminal electron-accepting conditions ( 4 ). The susceptibility of these substrates to microbial decay has led to greater acceptance of natural attenuation for the management of hydrocarbon pollutants instead of active intervention with technologies to increase the rate of biodegradation. However, there is growing concern that the regulatory acceptance of natural attenuation occurs too readily in the absence of credible scientific evidence ( 5 ). Reliable indicators, such as the detection of unique metabolites formed in situ, would help provide a solid scientific foundation for regulatory decisions to use natural attenuation. However, the metabolic pathways for BTEX destruction by anaerobic microorganisms are still incompletely known, and thus the task of identifying signature metabolites is substantially more difficult. Labora- tory studies to elucidate the biodegradation pathways and to identify prospective metabolites involved are required to substantiate the detection of the latter at contaminated sites.
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This note was uploaded on 08/06/2008 for the course ESM 214 taught by Professor Holden during the Spring '05 term at UCSB.

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Elshahed_et_al 2001_ESTv35 p682 - Environ. Sci. Technol....

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