Therefore, cultures that can more efficiently debrominate PBDEs and further be applied in in situ warrant further exploration. So far, only partial and incomplete debromination of deca- through hexa-BDEs ( Robrock et al., 2008) and a limited number of microorganisms capable of complete debromination of penta- and tetra-BDEs have been reported ( Ding et al., 2017 Zhao et al., 2021). Currently, both microcosms established from a versatile environment and isolated microorganisms have shown slower and less extensive debromination on deca- through hexa-BDEs rather than penta- and tetra-BDEs ( Lee and He, 2010). Compared with the lower BDE congeners (with 1–4 bromines), higher BDE congeners (with 5–10 bromines) are usually of lower bioavailability and are more resistant to microbial degradation ( Palm et al., 2002). As anaerobic and anoxic benthic sediments and soils are major sinks and environmental reservoirs for PBDEs, anoxic dehalogenation by microorganisms becomes an important route for eliminating PBDEs in such an environment. Products containing PBDEs are dumped into landfills from which they may leach into nearby sediments and soils and eventually partition into anaerobic or anoxic environmental compartments due to their high hydrophobicity and become a persistent emission source ( O’Driscoll et al., 2016). For example, unregulated recycling of electronics and electrical components has recently become a major source of environmental contamination in developing countries, particularly in Southeast Asia and China ( Luo et al., 2009 Li et al., 2016 Matsukami et al., 2017 Lu et al., 2021). Though restrictions and bans on manufacture and usage have significantly reduced the amounts of new BDEs introduced into the environment, these legislations have no effect on the release of BDEs from existing products or from recycled materials containing BDEs. Their toxicity and persistence have drawn great public concerns that the commercially manufactured PBDEs were listed as persistent organic pollutants by the Stockholm Convention, as well as their use were banned or gradually phasing out ( UNEP, 2009). Polybrominated diphenyl ethers (PBDEs) are a class of commonly used flame retardants and widely added in a variety of products, from construction materials, electrical and electronic equipment to household products and textiles. Therefore, the PB enrichment culture can serve as a potential candidate for in situ PBDE bioremediation since both BDE-47 and BDE-183 are dominant and representative BDE congeners and often coexist in contaminated sites. Later, a marked acceleration rate (0.021 μM Br –/day) and more extensive debromination (87.7 ± 2.1%) of 0.38 μM hepta-BDE 183 was observed in the presence of 0.44 μM tetra-BDE 47, which is achieved via the faster growth rate of responsible bacterial populations on lower BDE-47 and debromination by expressed BDE-47 reductive dehalogenases. In this study, we report a Dehalococcoides-containing enrichment culture, PB, which completely debrominates 0.44 μM tetra-brominated diphenyl ether (BDE) 47 to diphenyl ether within 25 days (0.07 μM Br –/day) and extensively debrominates 62.4 ± 4.5% of 0.34 μM hepta-BDE 183 (0.006 μM Br –/day) with a predominant generation of penta- through tri-BDEs as well as small amounts of diphenyl ether within 120 days. The lack of proper bacterial populations to detoxify these recalcitrant pollutants, in particular of higher brominated congeners, has confounded the attempts to bioremediate PBDE-contaminated sites. Polybrominated diphenyl ethers (PBDEs), commonly used as flame retardants in a wide variety of consumer products, are emerging persistent pollutants and ubiquitously distributed in the environment. School of Environmental Science and Engineering, Nanjing Tech University, Nanjing, China.Siyan Zhao *, Siyan Fan, Yide He and Yongjun Zhang *
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