AUTHOR=Xu Yan , Gregory Kelvin B. , VanBriesen Jeanne M. 

TITLE=Effects of Ferric Oxyhydroxide on Anaerobic Microbial Dechlorination of Polychlorinated Biphenyls in Hudson and Grasse River Sediment Microcosms: Dechlorination Extent, Preferences, Ortho Removal, and Its Enhancement

JOURNAL=Frontiers in Microbiology

VOLUME=9

YEAR=2018

URL=https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2018.01574

DOI=10.3389/fmicb.2018.01574

ISSN=1664-302X

ABSTRACT=<p>Microbial reductive dechlorination of polychlorinated biphenyls (PCBs) has been observed in many PCB-impacted sediments. However, this biodegradation is relatively site-specific and can be affected by PCB compositions and sediment geochemical conditions. To better understand the influence of a common competing electron acceptor, ferric oxyhydroxide (FeOOH), on dechlorination, two sediments (Hudson River and Grasse River sediments), and two PCB mixtures (PCB 5/12, 64/71, 105/114, and 149/153/170 in <italic>Mixture 1</italic> and PCB 5/12, 64/71, 82/97/99, 144/170 in <italic>Mixture 2</italic>) were used for this microcosm study. The addition of 40 mmole/kg FeOOH completely inhibited PCB dechlorination in the Hudson sediment, but only moderately inhibited PCB dechlorination in the Grasse sediment with a 3-week longer lag time. The inhibitory effect in the Grasse sediment was mainly due to the loss of unflanked <italic>para</italic> dechlorination activity. Fe(II) analysis showed that dechlorination started prior to the consumption of Fe(III), which indicates PCB reduction and Fe(III) reduction were able to take place concurrently. <italic>Dehalococcoides</italic> 16S rRNA genes increased with the commencement of dechlorination in the Grasse sediment, but not in the completely inhibited Hudson sediment. Rare <italic>ortho</italic> dechlorination pathways were identified in FeOOH-amended Grasse sediment microcosms, dominated by transformations of PCB 25(<underline>2</underline>4-3-CB) to PCB 13(3-4-CB) and PCB 28(<underline>2</underline>4-4-CB) to PCB 15(4-4-CB). The addition of carbon sources (acetate or a fatty acid mixture with acetate, propionate, and butyrate) after 27 weeks of incubation reinitiated dechlorination in FeOOH-amended Hudson sediment microcosms. Also, the addition of carbon sources greatly enhanced <italic>ortho</italic> dechlorination in FeOOH-amended Grasse microcosms, indicating the utilization of acetate and/or the fatty acid mixture for <italic>ortho</italic> dechlorination-related microorganisms. A dechlorination pathway analysis approach revealed that <italic>para</italic>-flanked <italic>meta</italic> dechlorination was primarily preferred followed by <italic>ortho-</italic>/double-flanked <italic>meta</italic> dechlorination and single-/double-flanked <italic>para</italic> dechlorination in the Grasse sediment.</p>