Effects of electron donors on anaerobic microbial debromination of polybrominated diphenyl ethers (PBDEs)

A critical review on BDE-209: Source, distribution, influencing factors, toxicity, and degradation

As the most widely used polybrominated diphenyl ether, BDE-209 is commonly used in polymer-based commercial and household products. Due to its unique physicochemical properties, BDE-209 is ubiquitous in a variety of environmental compartments and can be exposed to organisms in various ways and cause toxic effects. The present review outlines the current state of knowledge on the occurrence of BDE-209 in the environment, influencing factors, toxicity, and degradation. BDE-209 has been detected in various environmental matrices including air, soil, water, and sediment. Additionally, environmental factors such as organic matter, total suspended particulate, hydrodynamic, wind, and temperature affecting BDE-209 are specifically discussed. Toxicity studies suggest BDE-209 may cause systemic toxic effects on living organisms, reproductive toxicity, embryo-fetal toxicity, genetic toxicity, endocrine toxicity, neurotoxicity, immunotoxicity, and developmental toxicity, or even be carcinogenic. BDE-209 has toxic effects on organisms mainly through epigenetic regulation and induction of oxidative stress. Evidence regarding the degradation of BDE-209, including biodegradation, photodegradation, Fenton degradation, zero-valent iron degradation, chemical oxidative degradation, and microwave radiation degradation is summarized. This review may contribute to assessing the environmental risks of BDE-209 to help develop rational management plans.

Regulatory mechanisms of submerged macrophyte on bacterial community recovery in decabromodiphenyl ether contaminated sediment: Microbiological and metabolomic perspectives

Polybrominated diphenyl ether contamination in sediments poses serious threats to human health and ecological safety. Despite the broad application of submerged macrophytes for remediating pollutants, their regulatory influence on bacterial communities in contaminated sediments remains unclear. Herein, we analyzed the effects of decabromodiphenyl ether (BDE-209) and Hydrilla verticillata on sediment bacterial community and function using 16S rRNA gene sequencing and sediment metabolomics. Results showed that BDE-209 significantly inhibited sediment bacterial diversity and metabolic functions. It also enhanced bacterial interactions and altered both the bacterial community and metabolite composition. Uridine and inosine were critical metabolites that positively co-occurred with bacterial taxa inhibited by BDE-209. Notably, planting H. verticillata effectively alleviated the adverse impacts of BDE-209 by reducing its residuals, increasing the total organic carbon, and modifying metabolic profiles. Such mitigation was evidenced by enhancing bacterial diversity, restoring metabolic functions, and attenuating bacterial interactions. However, mitigation effectiveness depended on treatment time. Additionally, propionic acid, palmitic acid, and palmitoleic acid may facilitate the restoration of phylum Proteobacteria and class Planctomycetacia in H. verticillata planted sediment. Together, these findings improve understanding of BDE-209's impacts on aquatic ecosystems and provide valuable insights for ecological restoration using submerged macrophytes.

Manure- and straw-derived biochars reduce the ecological risk of PBDE and promote nitrogen cycling by shaping microbiomes in PBDE-contaminated soil

Pyrolysis of agricultural waste into biochar for soil remediation is a useful solid waste management strategy. However, it is still unclear how different agricultural feedstocks affect the properties of biochars and their effectiveness in remediation of PBDE-contaminated soil. In this study, we systematically investigated dynamic alterations of soil properties, microbial communities, and PBDE dissipation and bioavailability induced by the application of biochars from manure (MBC) and straw (SBC) to PBDE-contaminated soil. The results showed that soil properties, microbial community structure, and diversity changed differently with the incorporation of the two biochars. MBC had a larger surface area (17.4 m²/g) and a higher nutrient content (45.1% ash content), making it more suitable for use as a soil additive to improve soil quality and nutrient conditions, as well as to stimulate microbial growth. SBC showed higher adsorption capacity for 2,2',4,4'-Tetrabromodiphenyl Ether (BDE-47) (26.73 ± 0.65 mg/g), thus lowering the bioavailability and ecological risk of BDE-47 in soil. BDE-47 was stepwise debrominated into lower brominated PBDE by PBDE-degrading bacteria. MBC accelerated the debromination of BDE-47 (10.1%) by promoting PBDE-degrading microorganisms, while this was inhibited by SBC (3.5%) due to strong adsorption of BDE-47. In addition, we found that both types of biochar favored Nitrospirae bacteria and promoted N cycling. Overall, biochars from manure and straw can positively shape soil microbial communities differently by altering soil properties, soil fertility and nutrient availability, and the fate and the effects of contaminants, which ultimately led to a difference in the potential of biochars for their use in soil remediation.

Microplastics habituated with biofilm change decabrominated diphenyl ether degradation products and thyroid endocrine toxicity

Microplastics (MPs) are rapidly colonized by microbial biofilms in a natural aquatic environment, and the nature of the microbial community and type of MP can result in different degradation products of organic pollutants. Here, we quantified the degradation products of a ubiquitously detected pollutant, decabrominated diphenyl ether (BDE-209), under both light-only and biota conditions and in the absence or presence of three kinds of MPs, styrofoam polystyrene, hard polyamide, and polypropylene film. The results showed that the BDE-209 concentration increased by 0.7-2.8 fold in the presence of MPs, probably due to the "sustained release" desorption effect. Under light-only conditions, the penta- and hexa-BDE concentrations in the presence of styrofoam or hard MPs were significantly reduced, which can be deemed a beneficial effect. However, when biota were present, the debromination products increased with the addition of MPs, particularly in the presence of styrofoam MPs. These products caused a 1.7-fold upregulation in triiodothyronine content and a 5.9-fold upregulation of thyroid stimulating hormone β expression in zebrafish larvae. The increase in debromination products could be attributed to the distinct high abundance of the bacteria Chloroflexi, Proteobacteria, and Basidiomycotina on styrofoam MPs that can participate in pollutant degradation. Collectively, our results indicate that MPs can alter the degradation pathways of BDE-209 and increase the toxicity to the endocrine system and the thyroid in aquatic organisms.

Comparison of decabromodiphenyl ether degradation in long-term operated anaerobic bioreactors under thermophilic and mesophilic conditions and the pathways involved

Anaerobic digestion of decabromodiphenyl ether was carried out and compared in two continuously stirred anaerobic bioreactors for 210 days under thermophilic and mesophilic conditions. Results show that the degradation of decabromodiphenyl ether followed the first-order reaction kinetics, which exhibited a higher removal rate in the thermophilic reactor when compared to the mesophilic one, reaching its maximum of 1.1 μg·day^-1. The anaerobic digestion of decabromodiphenyl ether was found to involve the replacement of bromines from polybrominated diphenyl ether by hydrogen atoms, gradually forming nona-, octa- and hepta-brominated diphenyl ether, respectively. Under the thermophilic condition, the reactors were dominated by Bacillus sp. and Methanosarcina sp. with high bioactivity and high concentrations of debromination microorganisms.

Biotechnology-based microbial degradation of plastic additives

Plastic additives are agents responsible to the flame resistance, durability, microbial resistance, and flexibility of plastic products. High demand for production and use of plastic additives is associated with environmental accumulation and various health hazards. One of the suitable methods of depleting plastic additive in the environment is bioremediation as it offers cost-efficiency, convenience, and sustainability. Microbial activity is one of the effective ways of detoxifying various compounds as microorganisms can adapt in an environment with high prevalence of pollutants. The present review discusses the use and abundance of these plastic additives, their health-related risks, the microorganisms capable of degrading them, the proposed mechanism of biodegradation, and current innovations capable of improving the efficiency of bioremediation.

Polybrominated diphenyl ethers (PBDEs) in the Danjiangkou Reservoir, China: identification of priority PBDE congeners

Although the production of polybrominated diphenyl ethers (PBDEs) has been phased out over the past decade worldwide, they are still potentially hazardous to the environment due to their persistence and toxicity. This study investigated the levels of 55 PBDEs in water and sediments from the Danjiangkou Reservoir, China. The levels of PBDEs were in the range of not detected (ND)-286.67 ng/L in water and ND-236.04 ng/g in sediments. BDE209 was the predominant PBDE congener and constituted 15-50% and 44-68% of the total PBDEs in water and sediments, respectively. Commercial pentaBDE products (70-5DE, DE-71) were the dominant source of tetraBDE, pentaBDE, and hexaBDE, while commercial octaBDE (79-8DE) and decaBDE (102E and 82-0DE) products were the main sources of nonaBDE and decaBDE in water. PBDEs in sediments mainly stemmed from commercial decaBDE products and combustion sources. BDE-209 posed high ecological risks to aquatic organisms and dominated the total ecological risks of PBDEs. No cancer risks and non-cancer risks were observed for PBDEs. A ranking method based on four criteria, i.e., detection frequency, concentration, ecological risk, and health risks, was proposed, and 17 PBDEs were identified as high priority PBDEs for future monitoring and management in the Danjiangkou Reservoir.

Inevitable human exposure to emissions of polybrominated diphenyl ethers: A perspective on potential health risks

Polybrominated diphenyl ethers (PBDEs) serve as flame retardants in many household materials such as electrical and electronic devices, furniture, textiles, plastics, and baby products. Though the use of PBDEs like penta-, octa- and deca-BDE greatly reduces the fire damage, indoor pollution by these toxic emissions is ever-growing. In fact, a boom in the global market projections of PBDEs threatens human health security. Therefore, efforts are made to minimize PBDEs pollution in USA and Europe by encouraging voluntary phasing out of the production or imposing compelled regulations through Stockholm Convention, but >500 kilotons of PBDEs still exist globally. Both 'environmental persistence' and 'bioaccumulation tendencies' are the hallmarks of PBDE toxicities; however, both these issues concerning household emissions of PBDEs have been least addressed theoretically or practically. Critical physiological functions, lipophilicity and toxicity, trophic transfer and tissue specificities are of utmost importance in the benefit/risk assessments of PBDEs. Since indoor debromination of deca-BDE often yields many products, a better understanding on their sorption propensity, environmental fate and human toxicities is critical in taking rigorous measures on the ever-growing global deca-BDE market. The data available in the literature on human toxicities of PBDEs have been validated following meta-analysis. In this direction, the intent of the present review was to provide a critical evaluation of the key aspects like compositional patterns/isomer ratios of PBDEs implicated in bioaccumulation, indoor PBDE emissions versus human exposure, secured technologies to deal with the toxic emissions, and human toxicity of PBDEs in relation to the number of bromine atoms. Finally, an emphasis has been made on the knowledge gaps and future research directions related to endurable flame retardants which could fit well into the benefit/risk strategy.

Contribution of autochthonous diazotrophs to polycyclic aromatic hydrocarbon dissipation in contaminated soils

Understanding the role played by autochthonous functional microbes involved in the biotransformation of pollutants would help optimize bioremediation performance at contaminated sites. However, our knowledge of the remediation potential of indigenous diazotrophs in contaminated soils remains inadequate. Using a microcosm experiment, soil nitrogen fixation activity was manipulated by molybdenum (Mo) and tungsten (W), and their effect on the removal of polycyclic aromatic hydrocarbons (PAHs) was determined in agricultural and industrial soils. Results showed that after 42 days of incubation, PAH dissipation efficiency was significantly enhanced by 1.06-fold in 600 μg kg^-1 Mo-treated agricultural soil, compared with that in the control. For the industrial soil, 1200 μg kg^-1 Mo treatment significantly promoted PAH removal by 90.76% in 21 days, whereas no significant change was observed between treatments and control at the end of the incubation period. W also exerted a similar effect on PAH dissipation. The activity and gene abundance of nitrogenase were also increased under Mo/W treatments in the two soils. Spearman's correlation analysis further indicated that removal of PAHs was positively correlated with nitrogenase activity in soil, which could be due to the elevated abundances of PAH-degrading genes (PAH-RHDα) in these treatments. Our results suggest the importance of autochthonous diazotrophs in PAH-contaminated soils, which indicates a feasible and environmentally friendly biostimulation strategy of manipulating nitrogen fixation capacity.

Degradation of BDE-47 in mangrove sediments with amendment of extra carbon sources

Polybrominated diphenyl ethers (PBDEs) are widely detected in coastal wetlands but their remediation is still difficult. In this study, different carbon sources, namely formate, acetate, pyruvate, lactate, succinate, methanol and ethanol, were added to mangrove sediments contaminated with BDE-47, a common PBDE congener, to enhance its degradation. After 2-month incubation, all carbon addition significantly enhanced degradation percentages. The residual BDE-47 percentage significantly correlated with the abundance of total bacteria and Dehalococcoides spp. The addition of methanol, acetate and succinate also achieved significantly higher degradation rates and shorter half-lives than sediments without carbon amendment at the end of 5-month incubation, although degradation percentages were comparable between sediments with and without extra carbon. The degradation pathway based on the profiles of degradation products was also similar among treatments. The results indicated the stimulatory effect of extra carbon sources on BDE-47 degradation in contaminated sediments was carbon- and time-specific.

New insights into the anaerobic microbial degradation of decabrominated diphenyl ether (BDE-209) in coastal marine sediments

Severe contamination of decabrominated diphenyl ether (BDE-209, an emerging persistent organic pollutant) in coastal marine sediments has posed a serious threat to the marine ecosystems. Anaerobic microbial degradation can affect the toxicity and environmental fate of BDE-209 in anoxic marine sediments. However, little is known about the anaerobic microbial degradation of BDE-209 in anoxic marine/coastal sediments. In this study, the anaerobic degradation of BDE-209 in microcosms containing coastal marine sediments from a contaminated bay located in Southern China was investigated. It was observed that over 70% of the BDE-209 (5 μmol) added to the anaerobic sediment microcosms disappeared after 90-day of incubation. Thirty-five debrominated products (tetra- to nonaBDEs) were identified by GC-MS. Remarkably, a majority of these products (i.e. 20 products, including BDE-52, -92, -101, -102, -103, -133, -144, -146, -150, -161, -171, -172, -175, -177, -178, -180, -182, -188, -193, -199) have not been previously reported in the literature on the anaerobic microbial degradation of BDE-209 in sediments. There was no preferential debromination among ortho-, meta-, and para-bromines on BDE-209 and higher-brominated diphenyl ethers were the predominant debromination products. High-throughput sequencing revealed that the relative abundances of 9 microbial genera in the sediment microcosms increased as the anaerobic degradation of BDE-209 progressed, indicating their involvements in the degradation process. Taken together, our findings provided new insights into the anaerobic microbial degradation of BDE-209 in anoxic marine sediments.

Enhanced degradation of triphenyl phosphate (TPHP) in bioelectrochemical systems: Kinetics, pathway and degradation mechanisms

Triphenyl phosphate (TPHP) is one of the major organophosphate esters (OPEs) with increasing consumption. Considering its largely distribution and high toxicity in aquatic environment, it is important to explore an efficient treatment for TPHP. This study aimed to investigate the accelerated degradation of TPHP in a three-electrode single chamber bioelectrochemical system (BES). Significant increase of degradation efficiency of TPHP in the BES was observed compared with open circuit and abiotic controls. The one-order degradation rates of TPHP (1.5 mg L^-1) were increased with elevating sodium acetate concentrations and showed the highest value (0.054 ± 0.010 h^-1) in 1.0 g L^-1 of sodium acetate. This result indicated bacterial metabolism of TPHP was enhanced by the application of micro-electrical field and addition acetate as co-substrates. TPHP could be degraded into diphenyl phosphate (DPHP), hydroxyl triphenyl phosphate (OH-TPHP) and three byproducts. DPHP was the most accumulated degradation product in BES, which accounted more than 35.5% of the initial TPHP. The composition of bacterial community in BES electrode was affected by the acclimation by TPHP, with the most dominant bacteria of Azospirillum, Petrimonas, Pseudomonas and Geobacter at the genera level. Moreover, it was found that the acute toxic effect of TPHP to Vibrio fischeri was largely removed after the treatment, which revealed that BES is a promising technology to remove TPHP threaten in aquatic environment.

Degradation of decabromodiphenyl ether (BDE-209) in microcosms mimicking sediment environment subjected to comparative bioremediation strategies

The aim of this study was to examine bioremediation strategies for BDE-209 contaminated sediments. Sediment microcosms were established to observe anaerobic debromination of BDE-209 under conditions representing three bioremediation strategies: biostimulation, bioaugmentation and natural attenuation. To simulate biostimulation, a defined mineral medium containing both a carbon source (sodium formate) and electron donor (ethanol) was added into sediments. Bioaugmentation was established by enrichment of the sediments using a culture of Dehalobium chlorocoercia strain DF-1, previously shown to dechlorinate polychlorinated biphenyls, to sediments. No amendments were made to the third set in order to represent natural attenuation. The biostimulation, bioaugmentation and natural attenuation strategies resulted in 55.3%, 40.2% and 30.9% reductions in BDE-209, respectively, after 180 days. Nona- through tri-BDEs were observed as products, with 17 PBDE congeners detected in 25 different proposed debromination pathways. At the end of the 180 day incubation period, the products for bioaugmentation, biostimulation and natural attenuation were tri-BDEs, tetra-BDEs and penta-BDEs, respectively. The proposed pathways revealed that meta- and ortho-Br removal were favored in sediments, and that debromination regiospecificity varied with each bioremediation strategy applied. Lastly, pseudo-first-order rate constants for BDE-209 reduction were calculated as 0.0049 d^-1, 0.0028 d^-1, 0.0025 d^-1 for biostimulation, bioaugmentation and natural attenuation, respectively.

Reductive Debromination of Polybrominated Diphenyl Ethers - Microbes, Processes and Dehalogenases

Extensive utilization of polybrominated diphenyl ethers (PBDEs) as flame retardants since the 1960s in a variety of commercial products has resulted in ubiquitous environmental distribution of commercial PBDE mixtures. Dangers posed to biological populations became apparent after the discovery of elevated levels of PBDEs in biota, most notably in human breast milk and tissues. Environmental persistence of PBDEs results in significant transboundary displacement, threatening fragile ecosystems globally. Despite efforts to curtail usage of PBDEs, public concern remains about the effects of legacy PBDEs contamination and continued discharge of PBDEs in regions lacking restrictions on usage and manufacture. Among available technologies for remediation of PBDEs such as ex-situ soil washing, electrokinetic degradation, and biodegradation, this review focuses on bioremediation by microbes under anaerobic conditions. Bioremediation is generally preferred as it is less disruptive to contaminated ecosystems, is cost-effective, and can be implemented at sites that may be inaccessible to more traditional ex-situ methods. The aims of this review are to (1) summarize current knowledge of anaerobic microbes that debrominate PBDEs and their associated synergistic partnerships with non-dehalogenating microbes; (2) explore current understandings of the metabolic reductive debromination of PBDE congeners; (3) discuss recent discoveries on dehalogenase genes involved in debromination of PBDEs.

Diversity and Dynamics of Microbial Community Structure in Different Mangrove, Marine and Freshwater Sediments During Anaerobic Debromination of PBDEs

Little is known about the diversity and succession of indigenous microbial community during debromination of polybrominated diphenyl ethers (PBDEs). This study examined the diversity and dynamics of microbial community structure in eight saline (mangrove and marine) and freshwater sediment microcosms exhibiting different debrominating capabilities for hexa-BDE 153, a common congener in sediments, using terminal restriction fragment length polymorphism (T-RFLP) and clone library analyses. The results showed that microbial community structure greatly differed between the saline and freshwater microcosms, likely leading to distinct variations in their debrominating capabilities and pathways. Higher relative abundances of Chloroflexi and Deltaproteobacteria succeed by Alphaproteobacteria and Betaproteobacteria were detected in the two mangrove microcosms with the fastest debrominating capabilities mainly via para pathway, respectively; the dominance of Alphaproteobacteria resulted in less accumulation of tetra-BDEs and more complete debromination of lower brominated congeners (from di- to tetra-BDEs). Meanwhile, the shifts in both microbial community structure and PBDE profiles were relatively small in the less efficient freshwater microcosms, with relatively more ortho and meta brominated products of BDE-153 resulted. Coincidently, one of the freshwater microcosms showed sudden increases of Chloroflexi and Deltaproteobacteria by the end of incubation, which synchronized with the increase in the removal rate of BDE-153. The significant relationship between microbial community structure and PBDEs was confirmed by redundancy analysis (18.7% of total variance explained, P = 0.002). However, the relative abundance of the well-known dechlorinator Dehalococcoides showed no clear correlation with the debrominating capability across different microcosms. These findings shed light in the significance of microbial community network in different saline environments on enhancement of PBDE intrinsic debromination.

Biodegradation of decabromodiphenyl ether (BDE 209) by a newly isolated bacterium from an e-waste recycling area

Polybrominated diphenyl ethers (PBDEs) have become widespread environmental pollutants all over the world. A newly isolated bacterium from an e-waste recycling area, Stenotrophomonas sp. strain WZN-1, can degrade decabromodiphenyl ether (BDE 209) effectively under aerobic conditions. Orthogonal test results showed that the optimum conditions for BDE 209 biodegradation were pH 5, 25 °C, 0.5% salinity, 150 mL minimal salt medium volume. Under the optimized condition, strain WZN-1 could degrade 55.15% of 65 μg/L BDE 209 under aerobic condition within 30 day incubation. Moreover, BDE 209 degradation kinetics was fitted to a first-order kinetics model. The biodegradation mechanism of BDE 209 by strain WZN-1 were supposed to be three possible metabolic pathways: debromination, hydroxylation, and ring opening processes. Four BDE 209 degradation genes, including one hydrolase, one dioxygenase and two dehalogenases, were identified based on the complete genome sequencing of strain WZN-1. The real-time qPCR demonstrated that the expression level of four identified genes were significantly induced by BDE 209, and they played an important role in the degradation process. This study is the first to demonstrate that the newly isolated Stenotrophomonas strain has an efficient BDE 209 degradation ability and would provide new insights for the microbial degradation of PBDEs.

Uptake, translocation and metabolism of decabromodiphenyl ether (BDE-209) in seven aquatic plants

Terrestrial plant uptake of PBDEs from contaminated soils has been widely reported recently. In this study the fate of deca-BDE within a plant/PBDEs/aquatic environment system was investigated through simulated pot experiments. Accumulations of the total PBDEs and deca-BDE were observed in tissues of seven test aquatic plant species, namely Phragmites australis, Cyperus papyrus, Alternanthera philoxeroides, Colocasia esculenta, Scirpus validus, Acorus calamus and Oryza sativa. In all seven plants, O. sativa leads the uptake and accumulation both in the total PBDEs (444.8 ng g(-1)) and deca-BDE (368.0 ng g(-1)) in roots. Among the six common phytoremediation aquatic plants, A. calamus leads the uptake (236.2 ng g(-1)), and P. australis leads the translocation (Cshoot/Croot = 0.35), while A. philoxeroides (43.4%) and P. australis (80.0%) lead in the metabolism efficiencies in the root and shoot, respectively. The detection of seventeen lesser brominated PBDE congeners provided the debromination evidence, and the specific PBDEs profiles in test plant species indicated there is no common metabolic pattern. Furthermore, a relative high proportion of lesser brominated PBDE congeners in shoots suggested the possible metabolic difference between roots and shoots. Finally, a noticeable percentage of penta- and octa-BDE derived from deca-BDE also hint the ecological risk in deca-BDE use. This comparative research on the aquatic plants provide a broad vision on the understanding of plant/PBDEs/aquatic environment interaction system, and may be applied to remediate PBDEs in contaminated waters and sediments.

Biosorption and degradation of decabromodiphenyl ether by Brevibacillus brevis and the influence of decabromodiphenyl ether on cellular metabolic responses

There is global concern about the effects of decabromodiphenyl ether (BDE209) on environmental and public health. The molecular properties, biosorption, degradation, accumulation, and cellular metabolic effects of BDE209 were investigated in this study to identify the mechanisms involved in the aerobic biodegradation of BDE209. BDE209 is initially absorbed by wall teichoic acid and N-acetylglucosamine side chains in peptidoglycan, and then, BDE209 is transported and debrominated through three pathways, giving tri-, hepta-, octa-, and nona-bromodiphenyl ethers. The C-C bond energies decrease as the number of bromine atoms on the diphenyl decreases. Polybrominated diphenyl ethers (PBDEs) inhibit protein expression or accelerate protein degradation and increase membrane permeability and the release of Cl(-), Na(+), NH4 (+), arabinose, proteins, acetic acid, and oxalic acid. However, PBDEs increase the amounts of K(+), Mg(2+), PO4 (3-), SO4 (2-), and NO3 (-) assimilated. The biosorption, degradation, accumulation, and removal efficiencies when Brevibacillus brevis (1 g L(-1)) was exposed to BDE209 (0.5 mg L(-1)) for 7 days were 7.4, 69.5, 16.3, and 94.6 %, respectively.

Microbial degradation of decabromodiphenyl ether (DBDE) in soil slurry microcosms

Decabromodiphenyl ether (DBDE), which has been identified as an endocrine disrupting compound, is used as brominated flame retardant, and this can result in serious bioaccumulation within ecological systems. The objective of this study was to explore DBDE bioremediation (25 mg/kg) using laboratory scale soil slurry microcosms. It was found that effective biodegradation of DBDE occurred in all microcosms. Various biometabolites were identified, namely polybrominated diphenyl ethers congeners and hydroxylated brominated diphenyl ether. Reductive debrominated products such as tri-BDE to hepta-BDE congeners were also detected, and their total concentrations ranged from 77.83 to 91.07 ng/g. The mechanism of DBDE biodegradation in soil slurry microcosms is proposed to consist of a series of biological reactions involving hydroxylation and debromination. Catechol 2,3-oxygenase genes, which are able to bring about meta-cleavage at specific unbrominated locations in carbon backbones, were identified as present during the DBDE biodegradation. No obvious effect on the ecological functional potential based on community-level physiological profiling was observed during DBDE biodegradation, and one major facultative Pseudomonas sp. (99 % similarity) was identified in the various soil slurry microcosms. These findings provide an important basis that should help environmental engineers to design future DBDE bioremediation systems that use a practical microcosm system. A bacterial-mixed culture can be selected as part of the bioaugmentation process for in situ DBDE bioremediation. A soil/water microcosm system can be successfully applied to carry out ex situ DBDE bioremediation.

Aerobic debromination of BDE-209 by Rhodococcus sp. coupled with zerovalent iron/activated carbon

In this study, an aerobic strain identified as Rhodococcus sp. was isolated from the sediment of a typical electronic waste disassemble site, Taizhou, China. This strain could use BDE-209 as the sole carbon and energy source and degrade 65.1% of BDE-209 (initial concentration being 50 mg/L) within 144 h. To explore the BDE-209 degradation properties of this strain with the co-existed electronic donor, zerovalent iron/activated carbon (ZVI/AC) was introduced to build a microbial-chemical coupling system, which was found to promote the degradation of BDE-209 slightly (74.7% in 144 h). Moreover, the debromination products in both of the batch experiments were determined with GC/MS, which showed that lower brominated PBDE congeners were produced almost in order of the number of bromine ions, ranged from nona- to di-BDEs. In addition, the possible debromination pathways of BDE-209 for each system were proposed respectively, which confirmed the microbial activity of BDE-209 debromination. Since some of the lower-brominated BDE congeners are much toxic than BDE-209, these microbial activities might bring potential hazards to the environment with BDE-209 contamination. It is the first time to investigate the transformation of BDE-209 with microbial-chemical coupling system, which is universal in the nature, thus suggesting that the ecological safety of environment exposed to PBDEs should be focused in the future.

Dynamics of brominated flame retardants removal in contaminated wastewater sewage sludge under anaerobic conditions

Disposal of solid waste to landfills from waste water sewage treatment plants (WWTPs) serves as a potential source of contamination by polybrominated diphenyl ethers (PBDEs) and hexabromocyclododecane (HBCD). Native microbial communities have been found to degrade a variety of xenobiotics, such as PBDEs and HBCDs. This study investigates the potential of autochthonous microflora to remove 11 PBDE congeners and HBCDs in waste water sludge under anaerobic conditions. Laboratory microcosms were constructed with sewage sludge from the WWTPs of Hradec Kralove and Brno. BDE 209 was detected as the prevailing congener in concentrations 685 and 1403 ng/g dw and the total amounts of 10 lower PBDEs (BDE 28, 47, 49, 66, 85, 99, 100, 153, 154, 183) were 605 and 205 ng/g dw in sludge from Hradec Kralove and Brno, respectively. The levels of HBCD were detected in both sludge lower than 24 ng/g dw. The experiment was carried out for 15 months. After three months of incubation, HBCD was completely degraded to below detection limits. In sewage from both WWTPs, the higher brominated DEs were removed faster than the lower brominated congeners. One exception was tri-BDE, which was degraded completely within 15 months of cultivation. A significant increase in congener tetra-BDE 49 concentrations was observed over the course of the experiment in all tested sewage. The relative distribution of individual congeners among all PBDEs changed after 15 months of the incubation in favour of lower brominated congeners. This indicates that debromination is the major mechanism of anaerobic biodegradation. Despite of the increase of BDE 49, the overall removal of all 11 PBDEs achieved the levels of 47.4 and 68.7% in samples from WWTPs Hradec Kralove and Brno, respectively.

Solubilization of 4,4'-dibromodiphenyl ether under combined TX-100 and cosolvents

This paper is focused on the selection of cosolvents in the remediation of contaminated soils. The aim of this study was to investigate the combined effects of Triton X-100 (TX-100) and different cosolvents on the solubilization behavior of 4,4'-dibromodiphenyl ether (BDE-15) and the washing of BDE-15 from a contaminated soil. (1)H NMR spectroscopies were used to elucidate the interactions among TX-100, cosolvents, and BDE-15 in aqueous micellar solution. Results showed that the solubility of BDE-15 was enhanced by the observed synergism among TX-100, BDE-15, and cosolvents, and the TX-100/dimethyl sulfoxide (DMSO) system exhibited the best performance in the solubilization of BDE-15. Similar synergism was further evidenced in the washing of BDE-15 from a contaminated soil. With 10 % (v/v) DMSO and 6.4 mM TX-100 solution added, considerable synergistic effect was achieved in TX-100/DMSO system, leading to the highest removal efficiency (92.9 %) of BDE-15 from the soil, relative to that of 67.3 % with TX-100 alone at the same concentration.

Aerobic biodegradation of selected polybrominated diphenyl ethers (PBDEs) in wastewater sewage sludge

Due to widespread accumulation of polybrominated diphenyl ethers (PBDEs) in our surroundings, it is important to clarify their fate in the environment and the options of their elimination. The aim of this study was to monitor the biodegradation of the most frequent congeners (BDE 28, 47, 49, 66, 85, 99, 100, 153, 154, 183 and 209) under aerobic condition by indigenous microflora in 2 industrially contaminated sewage sludge samples. BDE 209 was detected as the predominating congener in concentrations 685 ng/g and 1403 ng/g dry weight in sewage sludge from WWTPs (waste water treatment plants) Hradec Kralove and Brno, respectively. The total amount of 10 lower PBDEs was 605 and 205 ng/g dry weight, respectively. The aerobic degradation was significantly enhanced by the addition of yeast extract and 4-bromobiphenyl. The total concentrations of all 11 PBDE congeners were lowered and their elimination was detected reaching 62–78% of their initial amounts after 11 months of cultivation. The degradation of most abundant congener BDE 209 followed the first-order kinetics with constant detected between 2.77 × 10(−3) d(−1) and 3.79 × 10−(3)d(−1) and the half-lives of BDE 209 degradation ranged between 6.0 and 8.2 months. This work clearly demonstrates that both lower brominated PBDEs as well as the major representative BDE 209 could be successfully removed from municipally contaminated sludge under aerobic conditions.

Aerobic transformation of BDE-47 by a Pseudomonas putida sp. strain TZ-1 isolated from PBDEs-contaminated sediment

A bacterial isolate, TZ-1, was isolated from contaminated sediment near electronic waste dismantling workshops, Taizhou, China that degraded 2,2',4,4'-tetrabrominated diphenyl ether (BDE-47). The isolate was identified as Pseudomonas putida sp. with respect to its morphology, biochemical characteristics and 16SrDNA sequence analysis. TZ-1 can use BDE-47 as the sole carbon and energy source for growth in mineral salt medium. The isolate degraded BDE-47 up to 49.96 % of the initially applied concentration of 50 μg L(-1) after 7 days of incubation at 150 rpm, 30°C. Static conditions with pH 6.5 and temperature 30°C were considered to be optimum for BDE-47 biodegradation. Addition of co-substrates promoted cell growth, but decreased the degradation rate for BDE-47.

Interactive effects of hypoxia and polybrominated diphenyl ethers (PBDEs) on microbial community assembly in surface marine sediments

Hypoxia alters the oxidation-reduction balance and the biogeochemical processes in sediments, but little is known about its impacts on the microbial community that is responsible for such processes. In this study, we investigated the effects of hypoxia and the ubiquitously dispersed flame-retardant BDE47 on the bacterial communities in marine surface sediments during a 28-days microcosm experiment. Both hypoxia and BDE47 alone significantly altered the bacterial community and reduced the species and genetic diversity. UniFrac analysis revealed that BDE47 selected certain bacterial species and resulted in major community shifts, whereas hypoxia changed the relative abundances of taxa, suggesting slower but nonetheless significant community shifts. These two stressors targeted mostly different taxa, but they both favored Bacteroidetes and suppressed Gammaproteobacteria. Importantly, the impacts of BDE47 on bacterial communities were different under hypoxic and normoxic conditions, highlighting the need to consider risk assessments for BDE47 in a broader context of interaction with hypoxia.

Biodegradation of decabromodiphenyl ether (BDE-209) by a metal resistant strain, Bacillus cereus JP12

A metal resistant bacterial strain, Bacillus cereus JP12, could use decabromodiphenyl ether (BDE-209) as the sole carbon and energy source for growth in mineral salt medium. Under the conditions of pH 6.0, 30°C, 150 rpm and an inoculum of OD600=0.6, more than 88% of the initial BDE-209 (1mg/L) was degraded after 12 days. The addition of appropriate surfactants and additional carbon sources could enhance the biodegradation efficiency of BDE-209. The presence of Cu(2+) (≤ 8 mg/L) and Zn(2+) (≤ 15 mg/L) provided a slight stimulating effect on BDE-209 removal. However, BDE-209 biodegradation efficiency was decreased when adding higher levels of metals due to reduced substrate availability caused by excess metal adsorption into the cell surface. Biosorption of heavy metals by JP12 led to release of light metals such as K(+) and Na(+). A BDE-209 biodegradation pathway was proposed on the basis of metabolite identification.

Microbial electricity generation enhances decabromodiphenyl ether (BDE-209) degradation

Due to environmental persistence and biotoxicity of polybrominated diphenyl ethers (PBDEs), it is urgent to develop potential technologies to remediate PBDEs. Introducing electrodes for microbial electricity generation to stimulate the anaerobic degradation of organic pollutants is highly promising for bioremediation. However, it is still not clear whether the degradation of PBDEs could be promoted by this strategy. In this study, we hypothesized that the degradation of PBDEs (e.g., BDE-209) would be enhanced under microbial electricity generation condition. The functional compositions and structures of microbial communities in closed-circuit microbial fuel cell (c-MFC) and open-circuit microbial fuel cell (o-MFC) systems for BDE-209 degradation were detected by a comprehensive functional gene array, GeoChip 4.0, and linked with PBDE degradations. The results indicated that distinctly different microbial community structures were formed between c-MFCs and o-MFCs, and that lower concentrations of BDE-209 and the resulting lower brominated PBDE products were detected in c-MFCs after 70-day performance. The diversity and abundance of a variety of functional genes in c-MFCs were significantly higher than those in o-MFCs. Most genes involved in chlorinated solvent reductive dechlorination, hydroxylation, methoxylation and aromatic hydrocarbon degradation were highly enriched in c-MFCs and significantly positively correlated with the removal of PBDEs. Various other microbial functional genes for carbon, nitrogen, phosphorus and sulfur cycling, as well as energy transformation process, were also significantly increased in c-MFCs. Together, these results suggest that PBDE degradation could be enhanced by introducing the electrodes for microbial electricity generation and by specifically stimulating microbial functional genes.

Pollutant dehalogenation capability may depend on the trophic evolutionary history of the organism: PBDEs in freshwater food webs

Organohalogen compounds are some of the most notorious persistent pollutants disturbing the Earth biosphere. Although human-made, these chemicals are not completely alien to living systems. A large number of natural organohalogens, part of the secondary metabolism, are involved in chemical trophic interactions. Surprisingly, the relationship between organisms’ trophic position and synthetic organohalogen biotransformation capability has not been investigated. We studied the case for polybromodiphenyl ethers (PBDE), a group of flame-retardants of widespread use in the recent years, in aquatic food webs from remote mountain lakes. These relatively simple ecosystems only receive pollution by atmospheric transport. A large predominance of the PBDE congener currently in use in Europe, BDE-209, largely dominated the PBDE composition of the basal resources of the food web. In contrast, primary consumers (herbivores and detritivores) showed a low proportion of BDE-209, and dominance of several less brominated congeners (e.g. BDE-100, BDE47). Secondary consumers (predators) showed large biomagnification of BDE-209 compare to other congeners. Finally, top predator fish characterized by low total PBDE concentrations. Examination of the bromine stable isotopic composition indicates that primary consumers showed higher PBDE biotransformation capability than secondary consumers. We suggest that the evolutionary response of primary consumers to feeding deterrents would have pre-adapted them for PBDE biotransformation. The observed few exceptions, some insect taxa, can be interpreted in the light of the trophic history of the evolutionary lineage of the organisms. Bromine isotopic composition in fish indicates that low PBDE values are due to not only biotransformation but also to some other process likely related to transport. Our finding illustrates that organohalogen compounds may strongly disturb ecosystems even at low concentrations, since the species lacking or having scarce biotransformation capability may be selectively more exposed to these halogenated hydrophobic semi-volatile organic pollutants due to their high bioaccumulation potential.

Bar-coded pyrosequencing reveals the responses of PBDE-degrading microbial communities to electron donor amendments

Polybrominated diphenyl ethers (PBDEs) can be reductively degraded by microorganisms under anaerobic conditions. However, little is known about the effect of electron donors on microbial communities involved in PBDEs degradation. Here we employed 454 Titanium pyrosequencing to examine the phylogenetic diversity, composition, structure and dynamics of microbial communities from microcosms under the conditions of different electron donor amendments. The community structures in each of the five alternate electron donor enrichments were significantly shifted in comparison with those of the control microcosm. Commonly existing OTUs between the treatment and control consortia increased from 5 to 17 and more than 50% of OTUs increased around 13.7 to 186 times at least in one of the microcosms after 90-days enrichment. Although the microbial communities at different taxonomic levels were significantly changed by different environmental variable groups in redundancy analysis, significant correlations were observed between the microbial communities and PBDE congener profiles. The lesser-brominated PBDE congeners, tri-BDE congener (BDE-32) and hexa-BDE, were identified as the key factors shaping the microbial community structures at OTU level. Some rare populations, including the known dechlorinating bacterium, Dehalobacter, showed significant positive-correlation with the amounts of PBDE congeners in the consortia. The same results were also observed on some unclassified bacteria. These results suggest that PBDEs-degrading microbial communities can be successfully enriched, and their structures and compositions can be manipulated through adjusting the environmental parameters.