Organohalide-Respiring Bacteria in Polluted Urban Rivers Employ Novel Bifunctional Reductive Dehalogenases to Dechlorinate Polychlorinated Biphenyls and Tetrachloroethene.

Polluted urban river sediments could be a sink of persistent and toxic polychlorinated biphenyls (PCBs) in urban areas and provide desired growth niches for organohalide-respiring bacteria (OHRB). In this study, microcosms were set up with surface sediments of nationwide polluted urban rivers in China, of which 164 cultures could dechlorinate tetrachloroethene (PCE) to dichloroethenes (DCEs) and to vinyl chloride and/or ethene. Further in vivo tests showed extensive PCB dechlorination with different pathways in 135 PCE pregrown cultures. Taking reductive dechlorination of PCB180 (2345-245-CB) as an example, 121 and 14 cultures preferentially removed flanked para- and meta-chlorines, respectively. Strikingly, all in vitro assays with the 135 PCE pregrown cultures showed identical PCB dechlorination pathways with their living cultures, implying the involvement of bifunctional reductive dehalogenases (RDases) to dechlorinate both PCBs and PCE. Further 16S rRNA and RDase gene-based analyses, together with enantioselective dechlorination of chiral PCBs, suggested that Dehalococcoides and Dehalogenimonas in the 135 cultures largely employed distinctively different novel bifunctional RDases to catalyze PCB/PCE dechlorination. Quantitative assessment of the community assembly process with the modified stochasticity ratio (MST) indicated three different stages in enrichment of OHRB. The second stage, as the only one controlled by stochastic processes (MST > 0.5), required extra attention in monitoring community successional patterns to minimize stochastic variance for enriching the PCB/PCE-dechlorinating OHRB.

Waste activated sludge stimulates in situ microbial reductive dehalogenation of organohalide-contaminated soil.

Due to its enriched organic matter, nutrients and growth cofactors, as well as a diverse range of microorganisms, waste activated sludge (WAS) might be an ideal additive to stimulate organohalide respiration for in situ bioremediation of organohalide-contaminated sites. In this study, we investigated the biostimulation and bioaugmentation impacts of WAS-amendment on the performance and microbiome in tetrachloroethene (PCE) and polychlorinated biphenyls (PCBs) dechlorinating microcosms. Results demonstrated that WAS-amendment increased PCE- and PCBs-dechlorination rate as much as 6.06 and 10.67 folds, respectively. The presence of WAS provided a favorable growth niche for organohalide-respiring bacteria (OHRB), including redox mediation and generation of electron donors and carbon sources. Particularly for the PCE dechlorination, indigenous Geobacter and WAS-derived Dehalococcoides were identified to play key roles in PCE-to-dichloroethene (DCE) and DCE-to-ethene dechlorination, respectively. Similar biostimulation and bioaugmentation effects of WAS-amendment were observed on both PCE- and PCBs-dechlorination in three different soils, i.e., laterite, brown loam and paddy soil. Risk assessment suggested low potential ecological risk of WAS amendment in remediation of organohalide-contaminated soil. Overall, this study provided an economic and efficient strategy to stimulate the organohalide respiration-based bioremediation in field applications.

Environmental occurrence and remediation of emerging organohalides: A review.

As replacements for "old" organohalides, such as polybrominated diphenyl ethers (PBDEs) and polychlorinated biphenyls (PCBs), "new" organohalides have been developed, including decabromodiphenyl ethane (DBDPE), short-chain chlorinated paraffins (SCCPs), and perfluorobutyrate (PFBA). In the past decade, these emerging organohalides (EOHs) have been extensively produced as industrial and consumer products, resulting in their widespread environmental distribution. This review comprehensively summarizes the environmental occurrence and remediation methods for typical EOHs. Based on the data collected from 2015 to 2021, these EOHs are widespread in both abiotic (e.g., dust, air, soil, sediment, and water) and biotic (e.g., bird, fish, and human serum) matrices. A significant positive correlation was found between the estimated annual production amounts of EOHs and their environmental contamination levels, suggesting the prohibition of both production and usage of EOHs as a critical pollution-source control strategy. The strengths and weaknesses, as well as the future prospects of up-to-date remediation techniques, such as photodegradation, chemical oxidation, and biodegradation, are critically discussed. Of these remediation techniques, microbial reductive dehalogenation represents a promising in situ remediation method for removal of EOHs, such as perfluoroalkyl and polyfluoroalkyl substances (PFASs) and halogenated flame retardants (HFRs).