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Title: Mineralization of PAH's in a Coal-Tar Impacted Aquifer Sediments and Associated Microbial Community Structure Investigated with FISH

Author
item ROGERS, SHANE - US EPA
item ONG, SAY KEE - IA STATE UNIVERSITY
item Moorman, Thomas

Submitted to: Chemosphere
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/24/2007
Publication Date: 7/6/2007
Citation: Rogers, S.W., Ong, S., Moorman, T.B. 2007. Mineralization of PAH's in a Coal-Tar Impacted Aquifer Sediments and Associated Microbial Community Structure Investigated with FISH. Chemosphere. 69:1563-1573.

Interpretive Summary: Microbial communities in aquifers are sometimes effective in degrading pesticides and industrial chemical contaminants. Recent development of DNA-based techniques, such as fluourescent in situ hybridization (FISH) has allowed us to gain new information on these microbial communities. We applied these techniques to understand how microorganisms were degrading polyaromatic hydrocarbons derived from coal tar manufacturing. Microbial populations in contaminated aquifer sediments were greater than nearby unpolluted sediments and the microbial metabolism of phenanthrene and napthalene (PAH) was enhanced. Actinobacteria, beta and gamma Proteobacteria, and Cytophaga/Flavobacters were the dominant groups in the microbial community. PAH-degrading bacteria of these groups are commonly isolated from PAH contaminated soils and sediments globally. Extensive mineralization of naphthalene and phenanthrene were observed in aerobic microcosms and resulted in enrichment of beta and gamma Proteobacteria, potentially explaining their elevated presence in situ. Similar enrichment was not apparent for Actinobacteria, the most prevalent microbial taxa observed in situ. PAH degradation was also observed to a lesser extent in anaerobic sediments when iron sulfate was available. The study provides data showing that the intrinsic microbial community is actively degrading the coal-tat derived contaminants. The study also shows that activity coincides with increases in specific groups of microorganisms. The research is useful to scientists and engineers who must devise active or passive remediation strategies for these and other pollutants.

Technical Abstract: The microbial community structure and mineralization of polycyclic aromatic hydrocarbons (PAHs) in a coal-tar contaminated aquifer were investigated spatially using fluorescence in situ hybridization and with laboratory-scale incubations. Microbial populations in the contaminated sediments were three orders of magnitude greater than nearby non-affected sediments, suggesting growth on coal-tar constituents in situ. Mineralization of naphthalene in nitrate- and sulfate-amended microcosms was observed using aquifer sediments from locations where groundwater chemistry indicated nitrate-and sulfate-reduction, respectively. Sulfate-reducing bacteria comprised 37% of the intrinsic microbial community in these sediments. Mineralization of naphthalene and phenanthrene in iron-amended microcosms was observed, but not in sediments spatially co-located to groundwater measurements of elevated ferrous iron. Actinobacteria, beta and gamma Proteobacteria, and Cytophaga/Flavobacters dominated the intrinsic aerobic (>1 mg per liter dissolved oxygen) microbial community. PAH-degrading bacteria of these taxa are commonly isolated from contaminated soils and sediments globally. Extensive mineralization of naphthalene and phenanthrene were observed in aerobic microcosms and resulted in enrichment of beta and gamma Proteobacteria, potentially explaining their elevated presence in situ. Similar enrichment was not apparent for Actinobacteria, the most prevalent microbial taxa observed in situ. The results of this study highlight the utility of these methods for linking results from laboratory microcosms to intrinsic conditions to better demonstrate natural attenuation at complex PAH contaminated sites.