Aquatic sediments constitute a large sink for released and improperly disposed PCB mixtures. Left untreated these recalcitrant compounds bioacccumlate and biomagnify within the food chain and present a threat to human and environmental health. Biodegradation of PCBs offers a pathway for the transformation of these persistent organic pollutants to less toxic compounds. To enhance understanding of the microbial community structure and the enzymes which catalyze the PCB biodegradation process and simultaneously help the community deal with this extensive contamination, sediment samples were collected from a highly contaminated wastewater lagoon in Altavista, Virginia. Total PCB congener analysis from 27 sample locations revealed profiles very similar to that of Aroclor 1248 with a range of concentrations from 6.3 mg/kg to 12,700 mg/kg. Among the 27 samples, several perceived hotspots of dechlorination became evident. Illumina sequencing of extracted DNA revealed variation in microbial community structure, but was consistently dominated by Proteobacteria and Firmicutes. Chloroflexi, the phylum containing known anaerobic PCB dechlorinators, ranged from 1.43-10.70% in the samples. A PCR survey conducted to isolate and identify reductive dehalogenase genes resulted in 11 sequences most closely related to those found in Dehalococcoides mccartyi strain CG5 and PCB-dechlorinating D. mccartyi strain CBDB1. These results represent the first time reductive dehalogenase genes were isolated from unenriched sediments. An enrichment culture study to better understand the PCB dechlorinating microbial community present at these hotspots shows increased abundances of Geobacter and Dehalococcoides. PCBs are highly hydrophobic and sorb strongly to aquatic sediments, which limits PCB bioavailability. Solid-phase microextraction fibers coated with poly-dimethylsiloxane were utilized as passive samplers to determine the congener profile of bioavailable PCBs. The pore water congener profile is dominated by PCB 4 and PCB 19, both of which represent terminal endpoints of reductive dechlorination. Understanding microbially catalyzed reductive dechlorination of bioavailable PCBs at the Altavista contaminated site will lead to the design of more effective bioremediation technologies. Such technologies will be valuable alternatives to excavation and dredging which are expensive, ecologically disruptive, and commonly used strategies to remediate aquatic PCB contaminated sediments.

PCB dechlorination hotspots and reductive dehalogenase genes in sediments from a contaminated wastewater lagoon

255th National Meeting (2018)

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