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Abstract
The potential effectiveness and time scales for monitored natural attenuation of polychlorinated biphenyl (PCB)-contaminated sediments are difficult to predict. Little is known about the depth- and time-dependent dechlorination of PCBs and the microbial communities that give rise to dechlorination processes. The present work describes evaluation of a single sediment core from the Grasse River (Massena, New York) using a combination of molecular techniques to provide detailed insight of dechlorination potential. Primers specific for 16S rRNA genes from the bacterial domains, putative dechlorinating organisms in the phylum Chloroflexi, the Dehalococcoides genus, and two PCB degrading organism strains, o-17 and DF-1, were used to construct phylogenetic microbial community profiles using denaturing gradient gel electrophoresis (DGGE). Further, quantitative polymerase chain reaction (Q-PCR) was used to estimate population numbers of putative PCB-related organisms in the sediments along the depth of the core. PCB congener analysis was used in conjunction with Molar Dechlorination Product Ratio (MDPR, the sum of five PCB end products over total PCBs), chlorine content, chlorine per biphenyl (CPB), and PCB composition changes with depth in the core to evaluate the extent of dechlorination. All core samples contained populations of Chloroflexi, Dehalococcoides, and o-17/DF-1 related organisms, representing the first report of putative dechlorinating organisms with depth in PCB-contaminated sediment. A clear pattern of dechlorination was observed, with deeper (older) sediments showing more extensive dechlorination and middle sediments showing less dechlorination. The evaluation of putative dechlorinating bacterial populations in conjunction with congener shifts resulting from dechlorination enables a critical association that may lead to better prediction of successful natural attenuation of PCB-contaminated sediment.
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