Biodegradation of diphenyl ether and transformation of selected brominated congeners by Sphingomonas sp. PH-07

Unveiling triclosan biodegradation: Novel metabolic pathways, genomic insights, and global environmental adaptability of Pseudomonas sp. strain W03

The polychlorinated aromatic antimicrobial agent triclosan (TCS) is widely used to indiscriminately and rapidly kill microorganisms. The global use of TCS has led to widespread environmental contamination, posing significant threats to ecosystem and human health. Here we reported a newly isolated Pseudomonas sp. W03 for degrading TCS metabolically at concentrations up to 10 mg/L. This strain exhibited optimal degradation activity at 30°C and pH 7.0, and retained substantial activity at pH 4.0, although it was sensitive to alkaline conditions. Genomic analysis of strain W03 revealed a circular chromosome comprising 6075,907 bp with a GC content of 65.08 %. A novel TCS degradation pathway, involving dechlorination, oxidation, ether bond fission, and reoxidation processes, was identified. Also, the study mapped the global distribution of analogous Pseudomonas using 16S rRNA gene sequences, revealing their widespread presence in diverse aquatic environments, with a significant abundance in wastewater systems. These findings indicated that these bacteria play a critical ecological role in both natural and engineered environments, particularly in the degradation of organic pollutants. This study enhances our understanding of microbial degradation of emerging contaminants and presents a promising candidate for bioremediation strategies aimed at mitigating TCS-related water pollution.

Maternal probiotic supplementation protects against PBDE-induced developmental, behavior and metabolic reprogramming in a sexually dimorphic manner: Role of gut microbiome

Polybrominated diphenyl ethers (PBDEs) are endocrine-disrupting persistent organic pollutants (POPs) used as flame retardants in a wide range of commercial applications. We have previously reported neurobehavioral and metabolic reprogramming produced by developmental PBDEs. PBDEs perturb the microbiome, an influencer of life-long health, while probiotic supplementation with Limosilactobacillus reuteri (LR) can avert neurobehavioral and endocrine disruption. We, therefore, tested the hypothesis that perinatal maternal LR supplementation would protect gut microbiome richness and diversity, developmental milestones, adult neurobehavior and metabolic homeostasis in PBDE-exposed offspring. C57BL/6N dams were orally exposed to a commercial penta-mixture of PBDEs, DE-71, at 0.1 mg/kg/day, or corn oil vehicle (VEH/CON) during gestation and lactation. Mice offspring received DE-71 or VEH/CON with or without co-administration of LR (ATCC-PTA-6475) indirectly via their mother from gestational day (GD) 0 until postnatal day (P)21 (Cohort 1), or continued to receive LR directly from P22 through adulthood (Cohort 2). Results of fecal 16S rRNA sequencing indicated age- and sex-dependent effects of DE-71 on gut microbial communities. Maternal LR treatment protected against DE-71-induced reduction in α-diversity in P22 females and against β-diversity alterations in P30 males. In females, DE-71 changed the relative abundance of specific bacterial taxa, such as Tenericutes and Cyanobacteria (elevated) and Deferribacterota (reduced). In males, several Firmicutes taxa were elevated, while Proteobacteria, Chlamydiae, and several Bacteroidota taxa were reduced. The number of disrupted taxa normalized by maternal LR supplementation was as follows: 100% in P22 females and 33% in males at P22 and 25% at P30. Maternal LR treatment protected against DE-71-induced delay of postnatal body weight gain in males and ameliorated the abnormal timing of incisor eruption in both sexes. Further, DE-71 produced exaggerated digging in both sexes as well as locomotor hyperactivity in females, effects that were mitigated by maternal LR only in females. Other benefits of LR therapy included normalization of glucose tolerance, insulin-to-glucose ratio and plasma leptin in adult DE-71 females (Cohort 2). This study provides evidence that probiotic supplementation can mitigate POP-induced reprogramming of neurodevelopment, adult neurobehavior, and glucose metabolism in association with modified gut microbial community structure in a sex-dependent manner.

The role of iron materials in the abiotic transformation and biotransformation of polybrominated diphenyl ethers (PBDEs): A review

Polybrominated diphenyl ethers (PBDEs), widely used as flame retardants, easily enter the environment, thus posing environmental and health risks. Iron materials play a key role during the migration and transformation of PBDEs. This article reviews the processes and mechanisms of adsorption, degradation, and biological uptake and transformation of PBDEs affected by iron materials in the environment. Iron materials can effectively adsorb PBDEs through hydrophobic interactions, π-π interactions, hydrogen/halogen bonds, electrostatic interactions, coordination interactions, and pore filling interactions. In addition, they are beneficial for the photodegradation, reduction debromination, and advanced oxidation degradation and debromination of PBDEs. The iron material-microorganism coupling technology affects the uptake and transformation of PBDEs. In addition, iron materials can reduce the uptake of PBDEs in plants, affecting their bioavailability. The species, concentration, and size of iron materials affect plant physiology. Overall, iron materials play a bidirectional role in the biological uptake and transformation of PBDEs. It is necessary to strengthen the positive role of iron materials in reducing the environmental and health risks caused by PBDEs. This article provides innovative ideas for the rational use of iron materials in controlling the migration and transformation of PBDEs in the environment.

Modeling and optimization of triclosan biodegradation by the newly isolated Bacillus sp. DL4: kinetics and pathway speculation

Triclosan is a widely used antibacterial agent and disinfectant, and its overuse endangered ecological safety and human health. Therefore, reducing residual TCS concentrations in the environment is an urgent issue. Bacillus sp. DL4, an aerobic bacterium with TCS biodegradability, was isolated from pharmaceutical wastewater samples. Response surface methodology (RSM) and artificial neural network (ANN) were carried out to optimize and verify the different condition variables, and the optimal growth conditions of strain DL4 were obtained (35 °C, initial pH 7.31, and 5% v/v). After 48 h of cultivation under the optimal conditions, the removal efficiency of strain DL4 on TCS was 95.89 ± 0.68%, which was consistent with the predicted values from RSM and ANN models. In addition, higher R2 value and lower MSE and ADD values indicated that the ANN model had a stronger predictive capability than the RSM model. Whole genome sequencing results showed that many functional genes were annotated in metabolic pathways related to TCS degradation (e.g., amino acid metabolism, xenobiotics biodegradation and metabolism, carbohydrate metabolism). Main intermediate metabolites were identified during the biodegradation process by liquid chromatography-mass spectrometry (LC-MS), and a possible pathway was hypothesized based on the metabolites. Overall, this study provides a theoretical foundation for the characterization and mechanism of TCS biodegradation in the environment by Bacillus sp. DL4.

Quantifying the removal of polybrominated diphenyl ethers (PBDEs) in physical, chemical, and biological sludge treatment systems

Polybrominated diphenyl ethers (PBDE) are priority contaminants historically used as flame retardants. PBDEs are known to occur in wastewater biosolids posing potential concerns with the beneficial land application of the biosolids. This study evaluated the removal of 21 congeners in nine full-scale sludge treatment systems including pelletization (P), alkaline stabilization (AS), and aerobic (AE) and anaerobic (AN) digestion. It is the first study to conduct a mass balance analysis of a broad spectrum of PBDEs during physical, chemical, and biological sludge treatment. The PBDE congener pattern in raw sludge and biosolids samples was consistent with commercial formulations. The fully brominated congener BDE-209 dominated biosolids from all sites with an average concentration of 620 ng/g dry weight (dw), followed by BDE-99 (173 ng/g dw) and BDE-47 (162 ng/g dw). Mass balance analysis on the P and AS processes showed no change in PBDE mass flows with treatment. However, aerobic and anaerobic digestion processes reported significant levels of removal and formation of individual congeners, though the results were not consistent between facilities. One aerobic digestion process (AE2) reported an overall average removal of 48%, whereas the other (AE1) reported very high levels of accumulation of tri- and tetraBDE congeners. Similarly, there were significant variations in PBDE behavior across the five anaerobic digestion plants studied. The plant with the longest solids retention time (SRT) (AN1) reported a moderate removal (50%) of overall PBDE loading and lower congeners, whereas other plants (AN2-AN5) showed significant low (-19%) to high (-166%) levels of formation of lower congeners. The results suggest that reduced SRTs result in formation of lower congeners while extended SRTs can lead to moderate removal of some PBDEs. Conventional sludge treatment result in low to moderate PBDE removal and advanced thermal conversion technologies may be needed to improve the contaminant removal during sludge treatment.

Assessment of metal pollution and effects of physicochemical factors on soil microbial communities around a landfill

The physicochemical properties, chemical fractions of six metals (Cu, Zn, Pb, Cd, Cr, and Mn), and microbial communities of soil around a typical sanitary landfill were analyzed. The results indicate that soils around the landfill were from neutral to weak alkalinity. The contents of organic matter (OM), total nitrogen (TN), total phosphorous (TP), and activities of catalase, cellulase, and urease were significantly higher in landfill soils than those in background soils. Negative correlations were found between pH and metals. Cr was the dominant metal. Cu, Pb, Cr, and Mn were accumulated in the nearby farmland soils. Cd had the highest percentage of exchangeable fraction (33.7%-51.8%) in landfill and farmland soils, suggesting a high bioavailability to the soil environment affected by the landfill. Pb, Cr, and Mn existed mostly in oxidable fraction, and Cu and Zn were dominant in residual fraction. There was a low risk of soil metals around the landfill based on the RI values, while according to RAC classification, Cd had high to very high environmental risk. The MisSeq sequencing results showed that Actinobacteria, Proteobacteria, Chloroflexi, and Acidobacteria were the dominant phyla of bacteria, and the most abundant phylum of fungi was Ascomycota. The NMDS analysis revealed that the landfill could influence soil fungal communities more intensely than bacterial communities. TN, cellulase, and bioavailable metals (Pb-Bio and Cr-Bio) were identified to have main influences on microbial communities. Pb-Bio was the most dominant driving factor for bacterial community structures. For fungi, Pb-Bio was significantly negatively related to Olpidiomycota and Cr-Bio had a significantly negative correlation with Ascomycota. It manifests that bioavailable metals play important roles in assessing environmental risks and microbial community structures of soil around landfill.

Concentrations and legislative aspects of PBDEs in plastic of waste electrical and electronic equipment in Brazil

Brominated flame retardants (BFRs) have been widely used as additives in polymeric products such as electronic and electrical equipment (EEE) to help meet fire safety regulations. However, some BFRs like polybrominated diphenyl ethers (PBDEs), are now listed under the Stockholm Convention on persistent organic pollutants (POPs) and banned in many countries, due to their adverse health impacts, environmental persistence, and capacity for bioaccumulation and long-range atmospheric transport. Despite this, in Brazil, only a few studies exist of the presence of these contaminants in the environment, and even fewer in waste EEE (WEEE). Against this backdrop, this study measured the presence of PBDEs in samples (n = 159) of WEEE in the metropolitan region of Sorocaba, Sao Paulo, Brazil. PBDEs were detected in 149 samples, with concentrations in 18 samples exceeding the European Union's Low POP Content Limit (LPCL) of 1000 mg/kg. Decabromodiphenyl ether (BDE-209) was the congener present at the highest concentration in most samples, with those of other PBDEs such as BDE-47 much lower. In general, samples containing >1000 mg/kg are those categorised as display items and miscellaneous EEE (n = 15.27 %), comprising: parts from cathode ray tube TVs (n = 11), audio systems (n = 2), and LCD TVs (n = 2). In addition, in 5 % (n = 3) of IT and telecommunications equipment samples (computer parts) PBDE concentrations exceeded 1000 mg/kg. Our results show the need for greater control and monitoring of the presence of these pollutants in WEEE before recycling and final disposal, to prevent PBDEs entering the recycling stream.

Biological treatment of triclosan using a novel strain of Enterobacter cloacae and introducing naphthalene dioxygenase as an effective enzyme

In recent years, triclosan (TCS) has been widely used as an antibacterial agent in personal care products due to the spread of the Coronavirus. TSC is an emerging contaminant, and due to its stability and toxicity, it cannot be completely degraded through traditional wastewater treatment methods. In this study, a novel strain of Enterobacter cloacae was isolated and identified that can grow in high TCS concentrations. Also, we introduced naphthalene dioxygenase as an effective enzyme in TCS biodegradation, and its role during the removal process was investigated along with the laccase enzyme. The change of cell surface hydrophobicity during TCS removal revealed that a glycolipid biosurfactant called rhamnolipid was involved in TCS removal, leading to enhanced biodegradation of TCS. The independent variables, such as initial TCS concentration, pH, removal duration, and temperature, were optimized using the response surface method (RSM). As a result, the maximum TCS removal (97%) was detected at a pH value of 7 and a temperature of 32 °C after 9 days and 12 h of treatment. Gas chromatography-mass spectrometry (GC/MS) analysis showed five intermediate products and a newly proposed pathway for TCS degradation. Finally, the phytotoxicity experiment conducted on Cucumis sativus and Lens culinaris seeds demonstrated an increase in germination power and growth of stems and roots in comparison to untreated water. These results indicate that the final treated water was less toxic.

Uncovering the metabolic pathway of novel Burkholderia sp. for efficient triclosan degradation and implication: Insight from exogenous bioaugmentation and toxicity pressure

Triclosan (TCS), a synthetic and broad-spectrum antimicrobial agent, is frequently detected in various environmental matrices. A novel TCS degrading bacterial strain, Burkholderia sp. L303, was isolated from local activated sludge. The strain could metabolically degrade TCS up to 8 mg/L, and optimal conditions for TCS degradation were at temperature of 35 °C, pH 7, and an increased inoculum size. During TCS degradation, several intermediates were identified, with the initial degradation occurring mainly through hydroxylation of aromatic ring, followed by dechlorination. Further intermediates such as 2-chlorohydroquinone, 4-chlorocatechol, and 4-chlorophenol were produced via ether bond fission and C-C bond cleavage, which could be further transformed into unchlorinated compounds, ultimately resulting in the complete stoichiometric free chloride release. Bioaugmentation of strain L303 in non-sterile river water demonstrated better degradation than in sterile water. Further exploration of the microbial communities provided insights into the composition and succession of the microbial communities under the TCS stress as well as during the TCS biodegradation process in real water samples, the key microorganisms involved in TCS biodegradation or showing resistance to the TCS toxicity, and the changes in microbial diversity related to exogenous bioaugmentation, TCS input, and TCS elimination. These findings shed light on the metabolic degradation pathway of TCS and highlight the significance of microbial communities in the bioremediation of TCS-contaminated environments.

Isolation and characterization of Rhodococcus sp. GG1 for metabolic degradation of chloroxylenol

The coronavirus disease 2019 (COVID-19) pandemic has significantly increased the demand of disinfectant use. Chloroxylenol (para-chloro-meta-xylenol, PCMX) as the major antimicrobial ingredient of disinfectant has been widely detected in water environments, with identified toxicity and potential risk. The assessment of PCMX in domestic wastewater of Macau Special Administrative Region (SAR) showed a positive correlation between PCMX concentration and population density. An indigenous PCMX degrader, identified as Rhodococcus sp. GG1, was isolated and found capable of completely degrading PCMX (50 mg L-1) within 36 h. The growth kinetics followed Haldane's inhibition model, with maximum specific growth rate, half-saturation constant, and inhibition constant of 0.38 h-1, 7.64 mg L-1, and 68.08 mg L-1, respectively. The degradation performance was enhanced by optimizing culture conditions, while the presence of additional carbon source stimulated strain GG1 to alleviate inhibition from high concentrations of PCMX. In addition, strain GG1 showed good environmental adaptability, degrading PCMX efficiently in different environmental aqueous matrices. A potential degradation pathway was identified, with 2,6-dimethylhydroquinone as a major intermediate metabolite. Cytochrome P450 (CYP450) was found to play a key role in dechlorinating PCMX via hydroxylation and also catalyzed the hydroxylated dechlorination of other halo-phenolic contaminants through co-metabolism. This study characterizes an aerobic bacterial pure culture capable of degrading PCMX metabolically, which could be promising in effective bioremediation of PCMX-contaminated sites and in treatment of PCMX-containing waste streams.

Comparative evaluation and prioritization of key influences on biodegradation of 2,2',4,4'-tetrabrominated diphenyl ether by bacterial isolate B. xenovorans LB400

Polybrominated diphenyl ethers (PBDEs) are a class of persistent organic pollutants being widely distributed and harmful to human health and wildlife, and the development of sustainable rehabilitation strategies including microbial degradation is of great concern. Although the increasing number of bacteria, especially the broad-spectrum and potent aerobes have been isolated for the efficient removal of PBDEs, the external influences and the corresponding influential mechanism on biodegradation are not fully understood yet. Given the wide-spectrum biodegradability of aerobic bacterial isolate, B. xenovorans LB400 for PBDEs, the dual impacts of many pivotal factors including pH, temperature, presence of dissolved organic matter (DOM) and cadmium ion etc. were comprehensively revealed on biodegradation of 2,2',4,4'-tetrabromodiphenyl ether (BDE-47). Due to the structural resemblance and stimulation of specific enzyme activity in bacteria, the biphenyl as substrates showed the greater capacity than non-aromatic compounds in improving biodegradation. The individual adaptation to neutrality and cultivation at about 30 °C was beneficial for biodegradation since the bacterial cellular viability and enzyme activity was mostly preserved. Although it was possibly good for the induction of hormesis and favorable to enhance the permeability or bioavailability of pollutant, the exceeding increase of Cd²⁺ or DOM may not give the profitable increase of biodegradation yet for the detrimental effect. For biodegradation, the mechanistic relationship that took account of the integrative correlation with the influential factors was artfully developed using partial least square (PLS) regression technique. Relative to the most significant influence of culture time and initial concentration of BDE-47, the larger relevance of other factors primarily marked as pH and DOM was consecutively shown after the quantitative prioritization. This may not only help understand the influential mechanism but provide a prioritizing regulation strategy for biodegradation of BDE-47. The PLS-derived relationship was validated with the certain predictability in biodegradation, and could be used as an alternative to accelerate a priori evaluation of suitability or improve the feasibility of such bacteria in remediation of PBDEs in the environment.

Contrasting responses of bacterial community to 4,4'-dibromodiphenyl ether (BDE-15) contamination in soil microcosms at different temperatures

Polybrominated diphenyl ethers (PBDEs) are biodegradable organic pollutants and pose potential risks to microorganisms exposed to the contamination, which are also affected by a variety of factors, such as temperature, in real environmental settings. A better understanding of the microbial community responses to PBDEs at different temperatures has practical significance for assessing ecological risks or possible degraders of these widely used flame retardants. In this study, soil microcosms spiked with or without 100 mg kg^-1 4,4'-dibromodiphenyl ether (BDE-15) were established and incubated at four different temperatures (4 °C, 20 °C, 37 °C, and varying ambient temperature) for up to 180 days. Concentration and carbon isotope analyses were used to verify the transformation of BDE-15. Bacterial communities were monitored during the incubation to evaluate the community succession under the PBDE stress. The results showed the majority of added BDE-15 remained after the incubation period, with limited degradation occurred at all four temperatures. Temperature significantly shaped the richness, diversity, composition and co-occurrence network of soil bacterial community, while the impacts of PBDE on soil bacteria were temperature dependent. When incubated at 4 °C, BDE-15 substantially reduced the network complexity and changed the ratio of negative to positive interactions between taxa (nodes), highlighting the PBDE-associated risks at low temperature. At higher temperatures, BDE-15 had negligible influence on the community characteristics and network. Random forest model identified distinct taxa that might be related to PBDE degradation at different incubation temperatures. These findings demonstrate contrasting bacterial community effects of PBDE at different temperatures, thus attention should be paid to the ecological impacts of soil pollution under real environmental conditions.

Discovery of diphenyl ether-degrading Streptomyces strains by direct screening based on ether bond-cleaving activity

Diphenyl ethers (DEs), which are widely used in the agricultural and chemical industries, have become hazardous contaminants in the environment. Although several DE-degrading bacteria have been reported, discovering new types of such microorganisms could enhance understanding of the degradation mechanism in the environment. In this study, we used a direct screening method based on detection of ether bond-cleaving activity to screen for microorganisms that degrade 4,4'-dihydroxydiphenyl ether (DHDE) as a model DE. Microorganisms isolated from soil samples were incubated with DHDE, and strains producing hydroquinone via ether bond cleavage were selected using hydroquinone-sensitive Rhodanine reagent. This screening procedure resulted in the isolation of 3 bacteria and 2 fungi that transform DHDE. Interestingly, all of the isolated bacteria belonged to one genus, Streptomyces. To our knowledge, these are the first microorganisms of the genus Streptomyces shown to degrade a DE. Streptomyces sp. TUS-ST3 exhibited high and stable DHDE-degrading activity. HPLC, LC-MS, and GC-MS analyses revealed that strain TUS-ST3 converts DHDE to its hydroxylated analogue and generates hydroquinone as an ether bond-cleavage product. Strain TUS-ST3 also transformed DEs other than DHDE. In addition, glucose-grown TUS-ST3 cells began to transform DHDE after incubation with this compound for 12 h, and produced 75 μM hydroquinone in 72 h. These activities of streptomycetes may play an important role in DE degradation in the environment. We also report the whole genome sequence of strain TUS-ST3.

The interaction mechanisms of co-existing polybrominated diphenyl ethers and engineered nanoparticles in environmental waters: A critical review

This review focuses on the occurrence and interactions of engineered nanoparticles (ENPs) and brominated flame retardants (BFRs) such as polybrominated diphenyl ethers (PBDEs) in water systems and the generation of highly complex compounds in the environment. The release of ENPs and BFRs (e.g. PBDEs) to aquatic environments during their usage and disposal are summarised together with their key interaction mechanisms. The major interaction mechanisms including electrostatic, van der Waals, hydrophobic, molecular bridging and steric, hydrogen and π-bonding, cation bridging and ligand exchange were identified. The presence of ENPs could influence the fate and behaviour of PBDEs through the interactions as well as induced reactions under certain conditions which increases the formation of complex compounds. The interaction leads to alteration of behaviour for PBDEs and their toxic effects to ecological receptors. The intermingled compound (ENPs-BFRs) would show different behaviour from the parental ENPs or BFRs, which are currently lack of investigation. This review provided insights on the interactions of ENPs and BFRs in artificial, environmental water systems and wastewater treatment plants (WWTPs), which are important for a comprehensive risk assessment.

Congener-specificity, dioxygenation dependency and association with enzyme binding for biodegradation of polybrominated diphenyl ethers by typical aerobic bacteria: Experimental and theoretical studies

Polybrominated diphenyl ethers (PBDEs) are a group of organic pollutants that have attracted much concerns of scientific community over the ubiquitous distribution, chemical persistence and toxicological risks in the environment. Though a great number of aerobic bacteria have been isolated for the rapid removal of PBDEs, the knowledge about biodegradation characteristics and mechanism is less provided yet. Herein, the congener-specificity of aerobic biodegradation of PBDEs by typical bacteria, i.e. B. xenovorans LB400 was identified with the different biodegradation kinetics, of which the changes were largely hinged on the bromination pattern. The more bromination isomerically at ortho-sites other than meta-sites or the single bromination at one of aromatic rings might always exert the positive effect. The biodegradation of PBDEs should be thermodynamically constrained to some extent because the calculated Gibbs free energy changes of initial dioxygenation by quantum chemical method increased with the increase of bromination. Within the transition state theory, the high correlativity between the apparent biodegradation rates and Gibbs free energy changes implied the predominance and rate-limiting character of initial dioxygenation, while the regioselectivity of dioxygenation at the ortho/meta-sites was also manifested for the more negative charge population. The molecular binding with the active domain of dioxygenase BphA1 in aerobe was firstly investigated using docking approach. As significantly illustrated with the positive relationship, the higher binding affinity with BphA1 should probably signify the more rapid biodegradation. Besides the edge-on π-π stacking of PBDEs with F227 or Y277 and π-cation formulation with histidines (H233, H239) in BphA1, the reticular hydrophobic contacts appeared as the major force to underpin the high binding affinity and rapid biodegradation of PBDEs. Overall, the experimental and theoretical results would not only help understand the aerobic biodegradation mechanism, but facilitate enhancing applicability or strategy development of engineering bacteria for bioremediation of PBDEs in the environment.

Diversity-triggered bottom-up trophic interactions impair key soil functions under lindane pollution stress

A growing amount of evidence suggests that microbial diversity loss may have negative effects on soil ecosystem function. However, less attention has been paid to the determinants of the relationship between community diversity and soil functioning under pollution stress. Here we manipulated microbial diversity to observe how biotic and abiotic factors influenced soil multi-functions (e.g. lindane degradation, soil respiration and nutrient cycling). Results showed that protist community was more sensitive to dilution, pollution stress, and sodium acetate addition than bacterial and fungal community. Acetate addition accelerated the lindane removal. Any declines in microbial diversity reduced the specialized soil processes (NO₃-N production, and N₂O flux), but increased soil respiration rate. Dilution led to a significant increase in consumers-bacterial and fungi-bacterial interaction as evidenced by co-occurrence network, which possibly played roles in maintaining microbiome stability and resilience. Interestingly, pollution stress and resource availability weaken the relationship between microbial diversity and soil functions through the bottom-up trophic interaction and environmental preference of soil microbiome. Overall, this work provides experimental evidence that loss in microbial diversity, accompanied with changes in trophic interactions mediated biotic and abiotic factors, could have important consequences for specialized soil functioning in farmland ecosystems.

Functional bacterial consortium responses to biochar and implications for BDE-47 transformation: Performance, metabolism, community assembly and microbial interaction

The influence of biochar on the biodegradation of persistent organic pollutants (POPs) has been extensively studied. However, the underlying mechanisms behind the response of functional microbial consortia to biochar remain poorly understood. Herein, we systematically explored the effect of biochar on 2,2',4,4'-tetrabrominated ether (BDE-47) biodegradation, and investigated the interaction and assembly mechanism of the functional bacterial consortium QY2. The results revealed that the biodegradation efficiency of QY2 for BDE-47 increased from 53.85% to 94.11% after the addition of biochar. Fluorescence excitation-emission matrix and electrochemical analysis showed that biochar-attached biofilms were rich in redox-active extracellular polymeric substances (EPS, 3.03-fold higher than free cell), whose strong interaction with biochar facilitated the electron transfer of the biofilm, thus enhancing the debromination degradation of BDE-47. Meanwhile, the assembly model and molecular ecological networks analysis indicated that bacterial community assembly in biofilms was more driven by deterministic processes (environmental selection >75.00%) upon biochar stimulation and exhibited closer interspecific cooperative interactions, leading to higher biodiversity and broader habitat niche breadth for QY2 in response to BDE-47 disturbance. Potential degraders (Methylobacterium, Sphingomonas, Microbacterium) and electrochemical bacteria (Ochrobactrum) were selectively enriched, whose role as keystone bacteria may be participated in biofilm formation and redox-active EPS secretion (r > 0.5, P < 0.05). These findings deepen the understanding of the mechanisms by which biochar promotes microbial degradation of PBDEs and provided a theoretical basis for better regulation of functional bacterial communities during environmental remediation.

Transcriptome Profiling of Stenotrophomonas sp. Strain WZN-1 Reveals Mechanisms of 2,2',4,4'-Tetrabromodiphenyl Ether (BDE-47) Biotransformation

The brominated flame retardant 2,2',4,4'-tetrabromodiphenyl ether (BDE-47) is extensively used, stable, and difficult to degrade in the environment. The existence of BDE-47 could pose a certain risk to the environment and human health. However, the biotransformation mechanisms of BDE-47 by microorganisms remain unclear. In this study, aerobic degradation of BDE-47 by Stenotrophomonas sp. strain WZN-1 and transcriptome analysis were carried out. BDE-47 degradation by Stenotrophomonas sp. strain WZN-1 was mainly through the biological action of intracellular enzymes via the route of debromination and hydroxylation. The results of the transcriptome sequencing indicated the differentially expressed genes were related to transport, metabolism, and stress response. The key processes involved the microbial transmembrane transportation of BDE-47, energy anabolism, synthesis, and metabolism of functional enzymes, stress response, and other biological processes of gene regulation. In particular, bacterial chemotaxis played a potential role in biodegradation of BDE-47 by Stenotrophomonas sp. strain WZN-1. This study provides the first insights into the biotransformation of Stenotrophomonas sp. strain WZN-1 to BED-47 stress and shows potential for application in remediation of polluted environments.

Aerobic and anaerobic biodegradation of BDE-47 by bacteria isolated from an e-waste-contaminated site and the effect of various additives

Degradation experiments are conducted to specifically compare the degradation of 2,2',4,4'-tetrabromodiphenyl ether (BDE-47) by aerobic and anaerobic strains isolated from real e-waste sites contaminated by BDE-47. The effect of carbon sources, inducers and surfactants on the degradation was examined to strengthen such a comparison. An aerobic strain, B. cereus S1, and an anaerobic strain, A. faecalis S4, were obtained. The results indicated that BDE-47 could be used as the sole carbon source by B. cereus S1 and A. faecalis S4 under aerobic and anaerobic conditions, respectively. The degradation of BDE-47 by B. cereus S1 and A. faecalis S4 was illustrated a first-order kinetics process obtaining a removal efficiency of 61.6% and 51.6% with a first-order rate constant of 0.0728 d^-1 and 0.0514 d^-1, and corresponding half-life of 8.7 d and 13.5 d, respectively. The addition of carbon sources (yeast extract, glucose, acetic acid and ethanol) and inducers (2,4-dichlorophenol, bisphenol A and toluene) promoted BDE-47 degradation by both B. cereus S1 and A. faecalis S4 under aerobic and anaerobic conditions, while hydroquinone as the inducer inhibited the degradation. All of the surfactants tested (CTAB, Tween 80, Triton X-100, rhamnolipid and SDS) showed inhibitory effect. BDE-47 degradation by B. cereus S1 under aerobic condition was more efficient than A. faecalis S4 under anaerobic condition whether with or without the additives. The results of the study indicated that in the field sites contaminated by BDE-47, the aerobic condition can be more favorable for BDE-47 removal and the degradation can be further enhanced by applying suitable carbon sources and inducers.

Release, transformation, and risk factors of polybrominated diphenyl ethers from landfills to the surrounding environments: A review

Polybrominated diphenyl ethers (PBDEs) serve as brominated flame retardants when added to various products. When these products reach their end of life, a large amount of domestic waste containing PBDEs enters the landfills. Given their weak chemical bonds, they are easily affected by physical, chemical, and biological processes. These processes result in their release and the subsequent contamination of the surrounding soil, groundwater, and atmosphere, causing harm to humans and ecosystems. However, despite the progress made in the research of PBDEs over the years, understanding of the environmental behavior and fate of pollutants is still limited. With the development of cities, the release of PBDEs in old landfills will gradually increase the risk to the surrounding environment. Here we review the biological and nonbiological transformation of PBDEs and their derivatives in landfills and surrounding areas, as well as their distribution in soil, groundwater, and atmosphere. Specifically, this review aims to provide insights into the following aspects: 1) the biological (plant, animal, and microbial) and nonbiological (metal catalysis and photodegradation) conversion of PBDEs and their derivatives in landfills and surrounding areas; 2) the distribution of landfill-sourced PBDEs in the soil, groundwater, atmosphere and cross-media migration; and 3) suggestions and future research directions for the management and control of PBDEs in landfills.

Current insights into the microbial degradation for pyrethroids: strain safety, biochemical pathway, and genetic engineering

As a biologically inspired insecticide, pyrethroids (PYRs) exert evident toxic side effects on non-target organisms. PYRs and their general toxic intermediate 3-phenoxybenzoic acid (3-PBA) have shown high detection rates/levels in human beings recently, for which diet was identified as the major exposure route. Microbial mineralization has emerged as a versatile strategy in addressing such escalating concern. Herein, PYRs and 3-PBA biodegradation with regards to strain safety, application and surfactant were summarized. Numerous PYRs-degrading microbes have been reported yet with a minority focused on 3-PBA. Most isolates were from contaminated sites while several microbial food cultures (MFCs) have been investigated. MFCs such as Bacillus spp. and Aspergillus spp. that dominate in PYRs-degrading microbial pools are applicable candidates for agricultural by-products detoxification during the postharvest process. Subsequently, we discussed committed degradation steps, wherein hydrolase responsible for PYRs ester linkage cleavage and oxygenase for 3-PBA diphenyl ether bond rupture play vital roles. Finally, comprehensive information of the key enzyme genes is outlined along with methodologies concerning gene cloning. Cytochrome P450 monooxygenases (CYP) is competent for diphenyl ether scission. Newly-developed omics has become a feasible gene and enzyme mining technology. To achieve PYRs mineralization in feed and food commodities, the screening of MFCs rich in related enzymes and the construction of MFCs-derived genetically modified microbes (GMMs) exhibit great potential considering the safety issues.

Mechanistic insight into hydroxylation of 2,2',4,4'-tetrabromodiphenyl ether during biodegradation by typical aerobic bacteria: Experimental and computational studies

Polybrominated diphenyl ethers (PBDEs) are a group of persistent pollutants in the environment. Though aerobic biodegradation of PBDEs have been extensively studied, the involved hydroxylation mechanism decisive for whole biotransformation is not clear yet. During the effective biodegradation of 2,2',4,4'-tetrabromodiphenyl ether (BDE-47) by B. xenovorans LB400, the depletion of endogenous ∙OH by scavenger could bring about the significant decrease of biodegradation efficiency whereas ·O₂^- was nearly not influential. Given the importance of ∙OH in hydroxylation, the reaction mechanisms along major pathways of electrophilic addition and hydrogen abstraction were theoretically examined by density functional theory (DFT). For the less demand of activation energy, the relative preference of electrophilic addition was shown at aromatic C3-site. When the secondary reaction was considered after addition at C4-site, the barrierless association of ∙OH at C3-site and deprotonation by H₂O was validated as the energetically-favorable pathway that may cause dihydroxylation of BDE-47 into 3,4-dihydroxyl-BDE-17. The electrophilic addition followed by seconary barrierless trans-association of ∙OH and then dehydration seemed favorable for monohydroxylation as regards energetic barrier merely up to 194.01 kJ mol^-1, while the hydrogen abstraction by ∙OH from C5-site was more privileged actually. The theoretical insights would help well understand the hydroxylation mechanism of PBDEs by aerobes.

Effects of methanol on the performance of a novel BDE-47 degrading bacterial consortium QY2 in the co-metabolism process

2,2',4,4'-tetrabrominated diphenyl ether (BDE-47), frequently detected in the environment, is arduous to be removed by conventional biological treatments due to its persistence and toxicity. Herein effects of methanol as a co-metabolic substrate on the biodegradation of BDE-47 was systematically studied by a functional bacterial consortium QY2, constructed through long-term and successive acclimation from indigenous microorganisms. The results revealed that BDE-47 (0.25 mg/L) was completely removed within 7 days in the 2.5 mM methanol treatment group, and its degradation efficiency was 3.26 times higher than that without methanol treatment. The addition of methanol dramatically accelerated the debromination, hydroxylation and phenyl ether bond breakage of BDE-47 by QY2. However, excessive methanol (>5 mM) combined with BDE-47 had strong stress on microbial cells, including significant (p < 0.05) increase of reactive oxygen species level, superoxide dismutase activity, catalase activity and malondialdehyde content, even causing 20.65% cell apoptosis and 11.27% death. It was worth noting that the changes of QY2 community structure remained relatively stable after adding methanol, presumably attributed to the important role of the genus Methylobacterium in maintaining the functional and structural stability of QY2. This study deepened our understanding of how methanol as co-metabolite substances stimulated the biodegradation of BDE-47 by microbial consortium.

Aerobic degradation of decabrominated diphenyl ether through a novel bacterium isolated from municipal waste dumping site: Identification, degradation and metabolic pathway

In the present study, a novel bacterium capable of degrading BDE-209 aerobically was isolated from a municipal waste dumping site and identified as Bacillus tequilensis strain BDE-S1 through 16S rRNA gene sequencing. A correlation between BDE-209 and bromide concentration, COD, TOC, and cell biomass was established. 65% of 50 mg/L initial concentration of BDE-209 was degraded within eight days of incubation by BDE-S1 strain. Two hexa, two penta, one tetra-BDE congener, and benzamide were detected as metabolites. The bromide release, COD, TOC and cell biomass were found to be significantly correlated parameters with BDE-209 degradation. Based on the metabolite analysis, ortho and meta debromination, cleavage of diphenyl ether bond and ring-opening were suggested as possible degradation pathways. This is the first study demonstrating the use of indigenously isolated Bacillus tequilensis strain BDE-S1 for aerobic degradation of BDE-209, which could provide new comprehension for bioremediation of PBDEs from contaminated environments.

Biodegradation of aromatic pollutants meets synthetic biology

Ubiquitously distributed microorganisms are natural decomposers of environmental pollutants. However, because of continuous generation of novel recalcitrant pollutants due to human activities, it is difficult, if not impossible, for microbes to acquire novel degradation mechanisms through natural evolution. Synthetic biology provides tools to engineer, transform or even re-synthesize an organism purposefully, accelerating transition from unable to able, inefficient to efficient degradation of given pollutants, and therefore, providing new solutions for environmental bioremediation. In this review, we described the pipeline to build chassis cells for the treatment of aromatic pollutants, and presented a proposal to design microbes with emphasis on the strategies applied to modify the target organism at different level. Finally, we discussed challenges and opportunities for future research in this field.

Molecular Modifications and Control of Processes to Facilitate the Synergistic Degradation of Polybrominated Diphenyl Ethers in Soil by Plants and Microorganisms Based on Queuing Scoring Method

In this paper, a combination of modification of the source and regulation of the process was used to control the degradation of PBDEs by plants and microorganisms. First, the key proteins that can degrade PBDEs in plants and microorganisms were searched in the PDB (Protein Data Bank), and a molecular docking method was used to characterize the binding ability of PBDEs to two key proteins. Next, the synergistic binding ability of PBDEs to the two key proteins was evaluated based on the queuing integral method. Based on this, three groups of three-dimensional quantitative structure-activity relationship (3D-QSAR) models of plant-microbial synergistic degradation were constructed. A total of 30 PBDE derivatives were designed using BDE-3 as the template molecule. Among them, the effect on the synergistic degradation of six PBDE derivatives, including BDE-3-4, was significantly improved (increased by more than 20%) and the environment-friendly and functional evaluation parameters were improved. Subsequently, studies on the synergistic degradation of PBDEs and their derivatives by plants and microorganisms, based on the molecular docking method, found that the addition of lipophilic groups by modification is beneficial to enhance the efficiency of synergistic degradation of PBDEs by plants and microorganisms. Further, while docking PBDEs, the number of amino acids was increased and the binding bond length was decreased compared to the template molecules, i.e., PBDE derivatives could be naturally degraded more efficiently. Finally, molecular dynamics simulation by the Taguchi orthogonal experiment and a full factorial experimental design were used to simulate the effects of various regulatory schemes on the synergistic degradation of PBDEs by plants and microorganisms. It was found that optimal regulation occurred when the appropriate amount of carbon dioxide was supplied to the plant and microbial systems. This paper aims to provide theoretical support for enhancing the synergistic degradation of PBDEs by plants and microorganisms in e-waste dismantling sites and their surrounding polluted areas, as well as, realize the research and development of green alternatives to PBDE flame retardants.

Microbial debromination of hexabromocyclododecanes

Hexabromocyclododecanes (HBCDs), a new sort of brominated flame retardants (BFRs), are globally prevalent and recalcitrant toxic environmental pollutants. HBCDs have been found in many environmental media and even in the human body, leading to serious health concerns. HBCDs are biodegradable in the environment. By now, dozens of bacteria have been discovered with the ability to transform HBCDs. Microbial debromination of HBCDs is via HBr-elimination, HBr-dihaloelimination, and hydrolytic debromination. Biotic transformation of HBCDs yields many hydroxylated and lower brominated compounds which lack assessment of ecological toxicity. Bioremediation of HBCD pollution has only been applied in the laboratory. Here, we review the current knowledge about microbial debromination of HBCDs, aiming to promote the bioremediation applied in HBCD contaminated sites. KEY POINTS: • Microbial debromination of HBCDs is via hydrolytic debromination, HBr-elimination, and HBr-dihaloelimination. • Newly occurred halogenated contaminants such as HBCDs hitch the degradation pathway tamed by previously discharged anthropogenic organohalides. • Strategy that combines bioaugmentation with phytoremediation for bioremediation of HBCD pollution is promising.

Insights into the Occurrence, Fate, and Impacts of Halogenated Flame Retardants in Municipal Wastewater Treatment Plants

Halogenated flame retardants (HFRs) have been extensively used in various consumer products and many are classified as persistent organic pollutants due to their resistance to degradation, bioaccumulation potential and toxicity. HFRs have been widely detected in the municipal wastewater and wastewater treatment solids in wastewater treatment plants (WWTPs), the discharge and agricultural application of which represent a primary source of environmental HFRs contamination. This review seeks to provide a current overview on the occurrence, fate, and impacts of HFRs in WWTPs around the globe. We first summarize studies recording the occurrence of representative HFRs in wastewater and wastewater treatment solids, revealing temporal and geographical trends in HFRs distribution. Then, the efficiency and mechanism of HFRs removal by biosorption, which is known to be the primary process for HFRs removal from wastewater, during biological wastewater treatment processes, are discussed. Transformation of HFRs via abiotic and biotic processes in laboratory tests and full-scale WWTPs is reviewed with particular emphasis on the transformation pathways and functional microorganisms responsible for HFRs biotransformation. Finally, the potential impacts of HFRs on reactor performance (i.e., nitrogen removal and methanogenesis) and microbiome in bioreactors are discussed. This review aims to advance our understanding of the fate and impacts of HFRs in WWTPs and shed light on important questions warranting further investigation.

Microbial capability for the degradation of chemical additives present in petroleum-based plastic products: A review on current status and perspectives

Plastic additives are present as pollutants in the environment because they are released from plastics and have been reported to be toxic to mammals. Due to this toxicity, it is crucial to develop ecofriendly tools to decontaminate the environment. Microorganisms are a promising alternative for efficient and effective plastic additive removal. This review describes the current knowledge and significant advances in the microbial degradation of plastic additives (i.e. plasticizers, flame retardants, stabilizers and antioxidants) and biotechnological research strategies that are being used to accelerate the biodegradation process of these additives. It is expected that further research supported by advances in genomics, proteomics, gene expression, enzyme immobilization, protein design, and nanotechnology can substantially increase our knowledge to enhance the enzymatic degradation efficiency, which will accelerate plastic additive degradation and establish successful and cost-effective bioremediation processes. Investigations should also address the identification of the enzymes involved in the degradation process and their catalytic mechanisms to achieve full metabolization of organopollutants (i.e. plastic additives) while avoiding harmful plastic additive biodegradation products. Microorganisms and their enzymes undoubtedly represent a potential resource for developing promising environmental biotechnologies, as they have the best systems for pollutant degradation, and their actions are essential for decontaminating the environment.

A Review on the Fate of Legacy and Alternative Antimicrobials and Their Metabolites during Wastewater and Sludge Treatment

Antimicrobial compounds are used in a broad range of personal care, consumer and healthcare products and are frequently encountered in modern life. The use of these compounds is being reexamined as their safety, effectiveness and necessity are increasingly being questioned by regulators and consumers alike. Wastewater often contains significant amounts of these chemicals, much of which ends up being released into the environment as existing wastewater and sludge treatment processes are simply not designed to treat many of these contaminants. Furthermore, many biotic and abiotic processes during wastewater treatment can generate significant quantities of potentially toxic and persistent antimicrobial metabolites and byproducts, many of which may be even more concerning than their parent antimicrobials. This review article explores the occurrence and fate of two of the most common legacy antimicrobials, triclosan and triclocarban, their metabolites/byproducts during wastewater and sludge treatment and their potential impacts on the environment. This article also explores the fate and transformation of emerging alternative antimicrobials and addresses some of the growing concerns regarding these compounds. This is becoming increasingly important as consumers and regulators alike shift away from legacy antimicrobials to alternative chemicals which may have similar environmental and human health concerns.

The key active degrader, metabolic pathway and microbial ecology of triclosan biodegradation in an anoxic/oxic system

A lab-scale anoxic/oxic (A/O) system was used to reveal the key active triclosan-degrading bacteria (TCS-DB) in this study. The results showed that TCS was mainly removed by metabolism of heterotrophic bacteria (accounting for about 62%), and the potential metabolic pathway was the break of ether bond in TCS formed 2,4-dichlorophenol, and further dechlorination formed phenol or other metabolic end products. DNA-based stable isotope probing (DNA-SIP) assay further revealed that Methylobacillus accounting for 20.75% in ¹³C sample was the key active TCS-DB. Furthermore, methylotrophy and methanol oxidation were found to be the potential metabolic routes of TCS degradation by functional annotation of prokaryotic taxa analysis. Interestingly, TCS accelerated the propagation of antibiotic resistance genes (fabI) and intI1 which positively correlated with several functional microorganisms (p < 0.05). This study contributes to comprehend the potential mechanism, metabolic pathway and microbial ecology of TCS biodegradation in A/O system.

Metabolites of the anaerobic degradation of diethyl ether by denitrifying betaproteobacterium strain HxN1

The constitutions of five metabolites formed during co-metabolic, anaerobic degradation of diethyl ether by the denitrifying betaproteobacterium Aromatoleum sp. strain HxN1 were elucidated by comparison of mass spectrometric and gas chromatographic data with those of synthetic reference standards. Furthermore, the absolute configurations of two stereogenic centers in the metabolites were established. Based on these results a degradation pathway for diethyl ether by Aromatoleum sp. HxN1 analogous to that of n-hexane is proposed. Synthesis of both enantiomers of methyl (E)-4-ethoxy-2-pentenoate was accomplished by etherification of ethyl (R)- or (S)-lactate, followed by hydrolysis of the ester group and reduction to furnish 2-ethoxy-1-propanol. The primary alcohol was converted by a Swern oxidation followed by a Horner-Wadsworth-Emmons reaction to methyl (E)-4-ethoxy-2-pentenoate that was finally hydrogenated to methyl 4-ethoxypentanoate. Methyl (S)-4-ethoxy-3-oxopentanoate was prepared by conversion of (S)-2-ethoxypropanoyl chloride with Meldrum's acid. Reduction of the resulting β-oxoester with NaBH4 or baker's yeast gave both diastereoisomers of methyl 4-ethoxy-3-hydroxypentanoate. The stereocenter at C-3 of the main diastereoisomer produced with baker's yeast was determined by Mosher ester analysis to be (R)-configurated. Dimethyl 2-(1-ethoxyethyl)succinate was prepared by Michael addition of nitroethane to diethyl maleate, followed by conjugate addition of sodium ethanolate, hydrolysis and esterification with diazomethane.

Understanding the role of bacterial cellular adsorption, accumulation and bioavailability regulation by biosurfactant in affecting biodegradation efficacy of polybrominated diphenyl ethers

Microbiological degradation is often considered as an important strategy to reduce the risks of polybrominated diphenyl ethers (PBDEs), which are environmentally widespread and harmful to human health and wildlife. With the well-identified aerobic bacteria, i.e. B. xenovorans LB400, the biodegradation of 2,2',4,4'-tetrabrominated diphenyl ether (BDE-47) occurred efficiently in conformity to the first-order kinetics and showed the strong dependence on initial concentration of pollutant and bioavailability regulation by biosurfactant. The mild increase of initial concentration of BDE-47 would enhance biodegradation whereas the excessive increase failed due to the oxidative stress or cytotoxicity to bacteria. Rather than the bacterial extracellular adsorption that was bioactively-mediated in thermodynamics, the intracellular accumulations at different time gradients showed the negative correlation with biodegradation efficiency of BDE-47. The spontaneous biodegradation of pollutant should be sourced from the gradual reduction of intracellular accumulation. Though the improved bioavailability of BDE-47 by sucrose fatty acid ester (SFAE) hardly altered the extracellular adsorption, the bacterial intracellular accumulation was indicated to increase continuously with used amount of biosurfactant and then decrease for the cellular morphological damage, and interestingly it appeared to be temporary reservoir for prompt delivery to biodegradation in light of the opposite variation tendency with time.

Fate of 4-bromodiphenyl ether (BDE3) in soil and the effects of co-existed copper

The quantitative fate of polybrominated diphenyl ethers (PBDEs) in soil is unknown. Furthermore, the effects of co-contamination by toxic copper on the behavior of PBDEs have not been investigated. Using a ¹⁴C-tracer, we studied mineralization, metabolism, and formation of non-extractable residues (NERs) of one PBDE congener, i.e., the 4-bromodiphenyl ether (BDE3) in oxic soil for 50 days, without and with amendment of Cu (400 mg kg^-1 soil dw). BDE3 rapidly dissipated with a half-life of 5.5 days and large amounts of CO₂ (38.8 ± 0.3% of initial applied amount at the end of incubation) and NERs (42.5 ± 0.4%) were rapidly produced. One hydroxylated metabolite (4'-HO-BDE3) was formed (8.1 ± 0.6%) at the beginning of the incubation, but then decreased to 2.2 ± 0.4%. Only BDE3 occurred in physico-chemically entrapped NERs, amounting to 9.2 ± 0.7%, while only 4'-HO-BDE3 in ester-linked NERs (10.9 ± 0.7%). The addition of Cu strongly reduced the kinetics constants of the transformations (including dissipation, mineralization, and NER-formation), the predicted maximal amounts of mineralization, as well as covalent binding of 4'-HO-BDE3 to soil. The results provide first quantitative insights into the fate of low-brominated congeners of PBDEs in soil and indicate that co-contamination by Cu may increase the environmental risks of biodegradable PBDEs in soil by increasing their persistence.

Concentrations and distributions of polybrominated diphenyl ethers (PBDEs) in surface soils and tree bark in Inner Mongolia, northern China, and the risks posed to humans

Three functional zones, namely the industrial (IND), the agricultural (AGR), and the grassland (GRA) areas from Inner Mongolia (a remote province in northern China), were selected to evaluate the levels and distributions of PBDEs and the risks posed to local humans. PBDEs concentrations in surface soils and tree bark were detected and the air levels were estimated based on bark measurements. The total concentrations (∑₈PBDEs) of BDE-28, -47, -100, -99, -154, -153, -183, and -209 in soils were 1.71-64.9 ng/g dry weight (d.w.), 0.720-4.08 ng/g d.w., and 0.604-3.76 ng/g d.w. in the IND, AGR and GRA areas respectively. The average total concentrations in bark and air were 0.792 ng/g d.w. and 0.125 ng/m³ in the AGR areas respectively, which were lower than those (1.69 ng/g d.w. in the bark and 0.476 ng/m³ in the air) in the IND areas. BDE-209 was the dominant congener, consistent with DeBDE being the dominant commercial products used in China. However, except for BDE-209, BDE-28 and BDE-47 in the AGR and GRA areas averagely contributed about half of the total PBDEs concentrations in soils. BDE-28 concentrations in the bark samples of the AGR areas were significantly higher (p < 0.05) than in the IND areas, and the average total hazard quotients (∑₈PBDEs) were higher for humans in the AGR areas (0.12) than in the IND areas (0.08). Degradation of higher-brominated congeners (e.g., BDE-209) and migration of lower-brominated congeners (mainly BDE-28 and BDE-47) may increase the risks to humans in pristine areas.

Characterization of a Sequential UV Photolysis-Biodegradation Process for Treatment of Decabrominated Diphenyl Ethers in Sorbent/Water Systems

Decabrominated diphenyl ether (BDE-209) is a primary component of the brominated flame retardants used in a variety of industrial and domestic applications. BDE-209 bioaccumulates in aquatic organisms and has been identified as an emerging contaminant that threatens human and ecosystem health. Sequential photolysis-microbial biodegradation processes were utilized here to treat BDE-209 in clay- or soil-water slurries. The removal efficiency of BDE-209 in the clay-water slurries was high; i.e., 96.5%, while that in the soil-water slurries was minimal. In the clay-water slurries the first order rate constants for the UV photolysis and biodegradation of BDE-209 were 0.017 1/day and 0.026 1/day, respectively. UV wavelength and intensity strongly influenced the BDE-209 photolysis and the subsequent biodegradation of photolytic products. Facultative chemotrophic bacteria, including Acidovorax spp., Pseudomonas spp., Novosphingobium spp. and Sphingomonas spp., were the dominant members of the bacterial community (about 71%) at the beginning of the biodegradation; many of these organisms have previously been shown to biodegrade BDE-209 and other polybrominated diphenyl ether (PBDE) congeners. The Achromobacter sp. that were isolated (NH-2; NH-4; NH-6) were especially effective during the BDE-209 degradation. These results indicated the effectiveness of the sequential UV photolysis and biodegradation for treating certain BDE-209-contaminated solids; e.g., clays; in bioreactors containing such solids as aqueous slurries. Achieving a similar treatment effectiveness for more heterogeneous solids containing natural organic matter, e.g., surface solids, appears to be significantly more difficult. Further investigations are needed in order to understand the great difference between the clay-water or soil-water slurries.

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.

Enhanced solubilization and reductive degradation of 2,2',4,4'- tretrabromodiphenyl ether by PAC-Pd/Fe nanoparticles in the presence of surfactant

2,2',4,4'-Tretrabromodiphenyl ether (BDE47) is known as a typical polybrominated diphenyl ethers (PBDEs) due to its high environmental abundance, ecological toxicity, and bioaccumulation. In this study, the influences of three typical surfactants (CTAB, SDS, and TX-100) on BDE47 solubilization and degradation by the polyanionic cellulose-stabilized Pd/Fe (PAC-Pd/Fe) nanoparticles were investigated. The results showed that BDE47 solubilities increased linearly when surfactant concentrations were above their critical micelle concentrations (CMCs), and the solubilization capacities of surfactants for BDE47 followed the order of TX-100 > CTAB > SDS. The appropriate dosages of surfactants were favorable for BDE47 degradation due to enhancing solubilization and accelerating mass transfer, while excessive surfactants inhibited BDE47 degradation due to excessive and thicker micelles formed, but still higher than no surfactant. The influences of various factors (PAC-Pd/Fe nanoparticle dosage, solution pH, and temperature) on BDE47 degradation in TX-100 solution were also tested. The results showed that BDE47 degradation followed the pseudo first-order kinetics model. The degradation rates of BDE47 increased as PAC-Pd/Fe nanoparticle dosage and temperature increased. Weak acidic condition (pH 5.5) was favorable for BDE47 degradation with 96.8% BDE47 was removed within 7.5 min, while alkaline condition (9.0) was not conducive to the degradation of BDE47. The degradation of BDE47 by PAC-Pd/Fe nanoparticles was a catalytic reductive debromination process via active H-species attack, wherein the sequential debromination was the dominant reaction. This study suggests that in the presence of moderate surfactant, PAC-Pd/Fe nanoparticles may be potentially employed to eliminate BDE47 in contaminated water.

The occurrence of polybrominated diphenyl ether (PBDE) contamination in soil, water/sediment, and air

As a kind of brominated flame retardants (BFRs), polybrominated diphenyl ethers (PBDEs) are extensively used in different types of electronic equipment, furniture, plastics, and textiles. PBDEs are ubiquitous environmental contaminants that may impact human health and ecosystems. Here we highlight recent findings on the occurrence, contamination status, and transport of PBDEs in soil, water/sediment, and air. Four aspects are discussed in detail: (1) sources of PBDEs to the environment; (2) occurrence and transport of PBDEs in soil; (3) PBDEs in aquatic ecosystems (water/sediment) and their water-sediment partitioning; and (4) the occurrence of PBDEs in the atmosphere and their gas-particle partitioning. Future prospects for the investigation on PBDEs occurrence are also discussed based on current scientific and practical needs.

Biochar combined with compost to reduce the mobility, bioavailability and plant uptake of 2,2',4,4'-tetrabrominated diphenyl ether in soil

Biochar application to soil is recognised for its capacity to immobilise pollutants (through sorption) while composted inputs can accelerate the biodegradation of organic pollutants. However, little is known about the influence of combined incorporation on plant uptake of organic pollutants. Therefore, we investigated the effects of maize straw-derived biochar (MSB), compost derived from maize straw and pig manure (SMC), and their combination (MSB-SMC) as soil amendments on bioavailability of 2,2',4,4'-tetrabrominated diphenyl ether (BDE-47) and carrot (Daucus carota L.) uptake in a horticultural soil. We found that biochar alone performed well in reducing BDE-47 bioavailability, but was less effective at degrading the pollutant. Conversely, addition of compost stimulated BDE-47 biodegradation. MSB-SMC enhanced BDE-47 biodegradation in soil, reduced contamination of carrot roots, and caused significant reductions in soil extractable BDE-47. The combination of contrasting approaches to remediation thus resulted in the most favorable outcome for a contaminated soil: immobilisation of contaminant from vegetable crops (via biochar) with simultaneous bioremediation of the growing medium. These findings point towards an effective strategy for reducing plant uptake of PDBEs through the combined use of biochar and compost as soil amendment - reducing mobility and facilitating degradation of the accessible contaminant fractions.

Variation of Microbial Communities in Aquatic Sediments under Long-Term Exposure to Decabromodiphenyl Ether and UVA Irradiation

Abiotic components create different types of environmental stress on bacterial communities in aquatic ecosystems. In this study, the long-term exposure to various abiotic factors, namely a high-dose of the toxic chemical decabromodiphenyl ether (BDE-209), continuous UVA irradiation, and different types of sediment, were evaluated in order to assess their influence on the bacterial community. The dominant bacterial community in a single stress situation, i.e., exposure to BDE-209 include members of Comamonadaceae, members of Xanthomonadaceae, a Pseudomonas sp. and a Hydrogenophaga sp. Such bacteria are capable of biodegrading polybrominated diphenyl ethers (PBDEs). When multiple environmental stresses were present, Acidobacteria bacterium and a Terrimonas sp. were predominant, which equipped the population with multiple physiological characteristics that made it capable of both PBDE biodegradation and resistance to UVA irradiation. Methloversatilis sp. and Flavisolibacter sp. were identified as representative genera in this population that were radioresistant. In addition to the above, sediment heterogeneity is also able to alter bacterial community diversity. In total, seventeen species of bacteria were identified in the microcosms containing more clay particles and higher levels of soil organic matter (SOM). This means that these communities are more diverse than in microcosms that contained more sand particles and a lower SOM, which were found to have only twelve identifiable bacterial species. This is the first report to evaluate how changes in bacterial communities in aquatic sediment are affected by the presence of multiple variable environmental factors at the same time.

Occurrence and distribution of polybrominated diphenyl ethers in soils from an e-waste recycling area in northern China

Polybrominated diphenyl ethers (PBDEs) are widespread persistent organic pollutants (POPs) because of their extensive use in diverse electronic products, which have posed great threats to human health and ecosystem. In this study, a total of 54 soil samples were collected from an e-waste recycling area in Tianjin, northern China for analyzing the occurrence and distribution of 14 PBDE congeners. The concentrations of BDE 209, ∑₁₃PBDEs and ∑₁₄PBDEs in the soils from Ziya e-waste recycling area were 2.9-2666 ng/g dw (dry weight) (average 90 ng/g dw), 3.0-41 ng/g dw (average 13 ng/g dw) and 5.9-2699 ng/g dw (average 103 ng/g dw), respectively. The ∑₁₄PBDEs concentration showed a dramatic decrease from the central area to the surrounding area. Generally, PBDEs in the northern part showed higher levels than the southern part of the e-waste recycling area due to the wind direction in Tianjin. Deep soil was less polluted by PBDEs, which largely comes from the deposition, migration and infiltration of PBDEs in the surface soils. Overall, PBDEs level in the studied area was much lower than some typical e-waste recycling areas in south China, such as Guiyu and Qingyuan, but significantly higher than the non-e-waste recycling areas. BDE 209, BDE 138 and BDE 28 were the three dominant PBDE congeners in the soil. Principal component analysis (PCA) indicated that the commercial penta-BDEs and deca-BDE could be considered as the main sources of PBDEs pollution in this region. Redundancy analysis (RDA) suggested that the local PBDEs sources rather than soil properties influenced the PBDEs distribution in Ziya e-waste recycling area. This study systematically revealed the occurrence and distribution of PBDEs in soils from the biggest established circular economy park in northern China.

Simultaneous degradation of β-cypermethrin and 3-phenoxybenzoic acid by Eurotium cristatum ET1, a novel "golden flower fungus" strain isolated from Fu Brick Tea

Beta-cypermethrin (β-CY) and its major metabolite 3-phenoxybenzoic acid (3-PBA) spread extensively in the environment because of utilization in agricultural and home formulations, exerting negative impact on environment as well as human health. Several golden flower fungi were isolated from fu brick tea, by which the biodegradation of β-CY and 3-PBA was evaluated, turning out strain Eurotium cristatum ET1 had the highest capacity. Furthermore, β-CY and 3-PBA degradation rates were positively correlated with biomass of E. cristatum ET1, and the processes of degradation fitted well with a first-order kinetic equation. The half-lives of β-CY and 3-PBA ranged from 3.382 to 11.517 days and 1.749 to 3.194 days, respectively, under different substrate concentrations, incubation temperatures, and pH values. The degraded products were analyzed using gas chromatography-mass spectrometry and liquid chromatography-mass spectrometry, and results showed that E. cristatum ET1 degrades β-CY by transforming it into 3-PBA, which is then gradually metabolized into phenol and catechol. Moreover, E. cristatum ET1 showed efficiency in degrading these metabolites. Our results suggest that this strain is a potential microorganism for bioremediation of pesticide-contaminated environments and fermented foods.

Toxicity responses of bacterial community as a biological indicator after repeated exposure to lead (Pb) in the presence of decabromodiphenyl ether (BDE209)

Continuous exposure of chemicals could cause various environmental impacts. Decabromodiphenyl ether (BDE209) and lead (Pb) can co-exist and are discharged simultaneously at e-waste recycling sites (EWRSs). Extensive concerns have been attracted by their toxic effects on soil microorganisms. Thus, by using high-throughput sequencing, this study explored bacterial community responses in a soil system after repeated Pb exposure in the presence of BDE209 in the laboratory during 90-day indoor incubation period. Gene sequencing of 16S rDNA performed on an Illumina MiSeq platform proved that one-off Pb exposure caused higher microbial abundance and community diversity. Additionally, both repetitive Pb treatment and exogenous BDE209 input could change bacterial community composition. Twenty-three different bacterial phyla were detected in the soil samples, while more than 90% of the sequences in each treatment belonged to a narrow variety. The sequence analyses elucidated that Proteobacteria, Acidobacteria, and Bacteroidetes were the top three dominant phyla. Our observations could provide a few insights into the ecological risks of Pb and BDE209 co-existed contamination in soils at EWRSs.

Bacterial Biodegradation of 4-Monohalogenated Diphenyl Ethers in One-Substrate and Co-Metabolic Systems

The use of diphenyl ether (DE) and its 4-monohalogenated derivatives (4-HDE) as flame retardants, solvents, and substrates in biocide production significantly increases the risk of ecosystem contamination. Their removal is important from the point of view of environmental protection. The aim of this study was to evaluate the degradation processes of DE and 4-HDE by enzymes of the environmental bacterial strains under one-substrate and co-metabolic conditions. The study is focused on the biodegradation of DE and 4-HDE, the enzymatic activity of microbial strains, and the cell surface properties after contact with compounds. The results show that the highest biodegradation (96%) was observed for 4-chlorodiphenyl ether in co-metabolic culture with P. fluorescens B01. Moreover, the activity of 1,2-dioxygenase during degradation of 4-monohalogenated diphenyl ethers was higher than that of 2,3-dioxygenase for each strain tested. The presence of a co-substrate provoked changes in dioxygenase activity, resulting in the increased activity of 1,2-dioxygenase. Moreover, the addition of phenol as a co-substrate allowed for increased biodegradation of the diphenyl ethers and noticeable modification of the cell surface hydrophobicity during the process. All observations within the study performed have led to a deeper understanding of the contaminants’ biodegradation processes catalyzed by environmental bacteria.

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.

Efficient degradation of triclosan by an endophytic fungus Penicillium oxalicum B4

Triclosan (TCS), a widely used antimicrobial and preservative agent, is an emerging contaminant in aqueous and soil environment. Microbial degradation of TCS has not been reported frequently because of its inhibition of microbe growth. To explore the new microbial resources for TCS biodegradation, fungal endophytes were isolated and screened for the degradation potential. The endophytic strain B4 isolated from Artemisia annua L. showed higher degradation efficiency and was identified as Penicillium oxalicum based on its morphology and ITS sequences of ribosomal DNA. In both medium and synthetic wastewater, TCS (5 mg/L) was almost completely degraded within 2 h by the strain B4. The high capacity of TCS uptake (127.60 ± 8.57 mg/g dry weight, DW) of fungal mycelium was observed during the first 10 min after TCS addition. B4 rapidly reduced initial content (5.00 mg/L) of TCS to 0.41 mg/L in medium in 10 min. Then, the accumulation of TCS in mycelium was degraded from 0.45 to 0.05 mg/g DW after 1-h treatment. The degradation metabolites including 2-chlorohydroquinone, 2, 4-dichloropheno, and hydroquinone were found to be restrained in mycelia. The end products of the biodegradation in medium showed no toxicity to Escherichia coli. The new characteristics of high adsorption, fast degradation, and low residual toxicity highlight the potential of endophytic P. oxalicum B4 in TCS bioremediation.

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.

Effects of coexisting BDE-47 on the migration and biodegradation of BDE-99 in river-based aquifer media recharged with reclaimed water

Two prominent polybrominated diphenyl ether (PBDE) congeners have been included in the persistent organic pollutant list, 2,2',4,4',5-tetrabromodiphenyl ether (BDE-99) and 2,2,4,4'-tetrabromodiphenyl ether (BDE-47), which have been detected in treated municipal wastewater, river water, and sediments in China. A lab-scale column experiment was established to investigate the effects of the competitive sorption of BDE-47 on BDE-99 biodegradation and migration in two types of river-based aquifer soils during groundwater recharge with reclaimed water. Two types of recharge columns were used, filled with either silty clay (SC) or black carbon-amended silty clay (BCA). The decay rate constants of BDE-99 in the BCA and SC systems were 0.186 and 0.13 m^-1 in the single-solute system and 0.128 and 0.071 m^-1 in the binary-solute system, respectively, showing that the decay of BDE-99 was inhibited by the coexistence of BDE-47. This was particularly evident in the SC system because the higher hydrophobicity of BDE-99 determined the higher affinity and competition for sorption sites onto black carbon. The biodegradation of BDE-99 was suppressed by the coexistence of BDE-47, especially in the SC system. Lesser-brominated congeners (BDE-47 and BDE-28) and higher-brominated congeners (BDE-100, BDE-153, BDE-154, and BDE-183) were generated in the four recharge systems, albeit at different ratios. Bacterial biodiversity was influenced by the presence of BDE-47 in the SC system, while it had no significant effect on the BCA system, because the high sorption capacity of black carbon on the hydrophobic PBDEs effectively reduced their toxicity. The ranking order of the most abundant classes changed markedly due to the coexistence of BDE-47 in both the SC and BCA systems. The ranking order of the most abundant genera changed from Azospira, Methylotenera, Desulfovibrio, Methylibium, and Bradyrhizobium to Halomonas, Hyphomicrobium, Pseudomonas, Methylophaga, and Shewanella, which could be involved in PBDE degradation.