Effects of carbonaceous materials on microbial bioavailability of 2,2',4,4'-tetrabromodiphenyl ether (BDE-47) in sediments

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.

Investigation of the effects of different substrates on the promotion of the soil microbial consortium, encompassing bacteria and fungi, in the bioremediation of decabromodiphenyl ether (BDE-209)

Decabromodiphenyl ether (BDE-209) is recognized as an emerging and hazardous pollutant in numerous ecosystems. Despite this, only a few studies have concurrently investigated the biodegradation of BDE-209 by a microbial consortium comprising both bacteria and fungi. Consequently, the interactions between bacterial and fungal populations and their mutual effects on BDE-209 degradation remain unclear. Our main objective was to concurrently assess the changes and activity of bacterial and fungal communities during the biodegradation of BDE-209 in a real soil matrix. In the present study, various organic substrates were employed to promote soil biomass for the biodegradation of BDE-209. Soil respiration and molecular analysis were utilized to monitor biological activity and biomass community structure, respectively. The findings revealed that the use of wheat straw in the soil matrix resulted in the highest soil respiration and microbial activity among the treatments. This approach obviously provided suitable habitats for the soil microflora, which led to a significant increase in the biodegradability of BDE-209 (49%). Biomass survival efforts and the metabolic pathway of lignin degradation through co-metabolism contributed to the biodegradation of BDE-209. Microbial community analysis identified Proteobacteria (Alphaproteobacteria-Betaproteobacteria), Firmicutes, Bacteroides (bacterial phyla), as well as Ascomycota and Basidiomycota (fungal phyla) as the key microorganisms in the biological community involved in the biodegradation of BDE-209. This study demonstrated that applying wheat straw can improve both the biological activity and the biodegradation of BDE-209 in the soil of polluted sites.

20 years of polybrominated diphenyl ethers on toxicity assessments

Polybrominated diphenyl ethers (PBDEs) serve as brominated flame retardants which continue to receive considerable attention because of their persistence, bioaccumulation, and potential toxicity. Although PBDEs have been restricted and phased out, large amounts of commercial products containing PBDEs are still in use and discarded annually. Consequently, PBDEs added to products can be released into our surrounding environments, particularly in aquatic systems, thus posing great risks to human health. Many studies and reviews have described the possible toxic effects of PBDEs, while few studies have comprehensively summarized and analyzed the global trends of their toxicity assessment. Therefore, this study utilizes bibliometrics to evaluate the worldwide scientific output of PBDE toxicity and analyze the hotspots and future trends of this field. Firstly, the basic information including the most contributing countries/institutions, journals, co-citations, influential authors, and keywords involved in PBDE toxicity assessment will be visualized. Subsequently, the potential toxicity of PBDE exposure to diverse systems, such as endocrine, reproductive, neural, and gastrointestinal tract systems, and related toxic mechanisms will be discussed. Finally, we conclude this review by outlining the current challenges and future perspectives in environmentally relevant PBDE exposure, potential carriers for PBDE transport, the fate of PBDEs in the environment and human bodies, advanced stem cell-derived organoid models for toxicity assessment, and promising omics technologies for obtaining toxic mechanisms. This review is expected to offer systematical insights into PBDE toxicity assessments and facilitate the development of PBDE-based research.

Insight into the enhancement effect of humic acid on microbial degradation of triclosan in anaerobic sediments

Humic acid (HA) as one class of macromolecular substances plays important roles in mediating environmental behaviors of pollutants in sediments, but its effect on microbial degradation of triclosan (TCS), a common antibacterial drug, remains unclear. In this study, the effects of HA addition with different dosages (0-5%) on TCS degradation in anaerobic sediment slurries and the underlying microbial mechanisms were investigated. The results showed that HA addition significantly accelerated the TCS removal and the maximum removal percentage (30.2%) was observed in the sediment slurry with 5% HA addition. The iron reduction rate, relative abundances of the genera Comamonas, Pseudomonas and Geobacter, and bacterial network complexity in sediment slurry were significantly enhanced due to HA addition. Based on the partial least squares path modeling analysis, the enhancement effect of HA on TCS degradation was mainly explained by Fe(II):Fe(III) ratio with the highest influence on TCS removal (total effect: 0.723), followed by dominant genera abundances (total effect: 0.391), module relative abundance (total effect: 0.272), and network topological features (total effect: 0.263). This finding enhanced our understanding of the role of HA in TCS biodegradation in contaminated sediments for bioremediation purposes.

The thermal degradation and soil recovery of thermal treatment of field-weathered decabrominated diphenyl ether-contaminated soil

A farm at Taoyuan in Taiwan was highly contaminated with decabrominated diphenyl ether (BDE-209), a widely used commercial brominated flame retardant and persistent in the environment, more than 10 years. Since crops are able to absorb and accumulate BDE-209 from soils in our previous research, posing a hazardous risk for humans, it is essential to develop a practical method of soil treatment. Thermal treatment was studied among different approaches. In our previous study (Ko et al., 2022), we found that heating to 450 °C for 30 min achieved a complete removal of BDE-209 in soil. However, the high temperature significantly decreased the original soil organic matter (SOM) from 2.47% to 0.27%, altering the soil texture, damaging microbial biomass, and thus affecting the revegetation after the thermal treatment. Sugarcane bagasse, a common agricultural residue, served as an amendment to restore soil fertility. Current results indicate that 2.5% bagasse can improve the SOM in soil by up to 2.73% and restore its bacterial composition, making the plant growth conditions similar to those of the untreated contaminated soil. In light of the high removal efficiency provided by the 450°C-thermal treatment and the high recovery efficiency of sugarcane bagasse, the strategy presented in this study serves to be a promising method for sustainable remediation.

Microbial degradation of nondesorbable organic compounds on biochars by extracellular reactive oxygen species

Knowledge of microbial degradation of biochar-adsorbed organic pollutants is essential for recovering adsorption performance of biochars and reducing secondary pollution in soil remediation. In previous study, desorption of organic compounds from biochars was perceived as a prerequisite for the microbial degradation. However, microbial degradation of the nondesorbable organic compounds on biochars has not been studied. Therefore, degradation of nondesorbable naphthalene (NAPH), phenanthrene (PHEN) and pyrene (PYR) on a wood chip-derived biochar (WBC700) by Sphingobium yanoikuyae B1 was investigated. Significant microbial degradations of nondesorbable organic compounds were observed and followed the order of NAPH < PHEN < PYR. It was newly observed in this study that the microbial degradation of nondesorbable organic compounds on WBC700 was mainly attributed to the •OH in extracellular fluid of Sphingobium yanoikuyae B1. The extracellular •OH was produced through a Fenton-like reaction involved siderophore, H₂O₂ and iron ions, which could be significantly enhanced by WBC700. Microbial degradation was higher for larger organic compound (e.g., PYR), because larger molecules were adsorbed in relatively larger micropores of WBC700 and thus could be accessible to more extracellular •OH for degradation. The obtained results could provide a new insight into the microbial degradation of biochar-adsorbed organic pollutants in soil remediation.

Responses of phenanthrene degradation to the changes in bioavailability and microbial community structure in soils amended with biochars pyrolyzed at low and high temperatures

This study investigated the impact of wheat straw biochars pyrolyzed at temperatures of 100-700 ℃ (BC100-BC700) on biodegradation of phenanthrene in soils. During a 42-day experiment, biochar amendment reduced the biodegradation ratio of phenanthrene in soils by no change-77.0%. The biodegradation ratio decreased with the increase of pyrolysis temperature from 100 to 400 ℃ and then increased with the increase of pyrolysis temperature from 400 to 700 ℃, exhibiting a U-shape. Meanwhile, desorbing fraction of phenanthrene extracted by n-butanol declined with increasing pyrolysis temperature. Biochar-derived dissolved organic carbon (DOC) obviously influenced the soil DOC contents which were negatively correlated with the total relative abundances of dominant polycyclic aromatic hydrocarbon (PAH)-degraders. These results indicated that in soils amended with biochars pyrolyzed at low temperatures (i.e. 100-400 ℃), both the reduced bioavailability of phenanthrene and the reduced PAH-degrader abundance resulted in decreasing phenanthrene degradation with pyrolysis temperature. In soils amended with biochars pyrolyzed at high temperatures (i.e. 500-700 ℃; HT-biochars), two possible reasons contribute to increasing phenanthrene degradation with pyrolysis temperature: (1) high sorbed-phenanthrene concentration due to large specific surface area and high aromaticity of the biochars, and (2) the increased dominant PAH-degrader abundance for the removal of sorbed-phenanthrene due to the impact of HT-biochars on soil properties (mainly on DOC content).

Biodegradation of PCB congeners by Paraburkholderia xenovorans LB400 in presence and absence of sediment during lab bioreactor experiments

Experiments were conducted to measure biodegradation of polychlorinated biphenyl (PCB) congeners contained in mixture Aroclor 1248 and congeners present in wastewater lagoon sediment contaminated decades earlier at Altavista, Virginia. A well-characterized strain of aerobic PCB-degrading bacteria, Paraburkholderia xenovorans LB400 was incubated in laboratory bioreactors with PCB-contaminated sediment collected at the site. The experiments evaluated strain LB400's ability to degrade PCBs in absence of sediment and in PCB-contaminated sediment slurry. In absence of sediment, LB400 transformed 76% of Aroclor 1248 within seven days, spanning all homolog groups present in the mixture. In sediment slurry, only mono- and di-chlorinated PCB congeners were transformed. These results show that LB400 is capable of rapidly biodegrading most PCB congeners when they are freely dissolved in liquid but cannot degrade PCB congeners having three or more chlorine substituents in sediment slurry. Finally, using GC/MS-MS triple quadrupole spectrometry, this work distinguishes between physical (sorption to cells) and biological removal mechanisms, illuminates the process by which microorganisms with LB400-type congener specificity can selectively transform lower-chlorinated congeners over time, and makes direct comparisons to other studies where individual congener data is reported.

Current progress in degradation and removal methods of polybrominated diphenyl ethers from water and soil: A review

The widespread of polybrominated diphenyl ethers (PBDEs) in the environment has caused rising concerns, and it is an urgent endeavor to find a proper way for PBDEs remediation. Various techniques such as adsorption, hydrothermal and thermal treatment, photolysis, photocatalytic degradation, reductive debromination, advanced oxidation processes (AOPs) and biological degradation have been developed for PBDEs decontamination. A comprehensive review of different PBDEs remediation techniques is urgently needed. This work focused on the environmental source and occurrence of PBDEs, their removal and degradation methods from water and soil, and prospects for PBDEs remediation techniques. According to the up-to-date literature obtained from Web of Science, it could be concluded that (i) photocatalysis and photocatalytic degradation is the most widely reported method for PBDEs remediation, (ii) BDE-47 and BDE-209 are the most investigated PBDE congeners, (iii) considering the recalcitrance nature of PBDEs and more toxic intermediates could be generated because of incomplete degradation, the combination of different techniques is the most potential solution for PBDEs removal, (iv) further researches about the development of novel and effective PBDEs remediation techniques are still needed. This review provides the latest knowledge on PBDEs remediation techniques, as well as future research needs according to the up-to-date literature.

Transcriptome profiling of Pseudomonas aeruginosa YH reveals mechanisms of 2, 2', 4, 4'-tetrabrominated diphenyl ether tolerance and biotransformation

Aerobic degradation of 2, 2', 4, 4'-tetrabrominated diphenyl ether (BDE-47) by Pseudomonas aeruginosa YH (P. aeruginosa YH) were investigated in this study. BDE-47 degradation was mainly through the biological action of intracellular enzymes, and the metabolites included debrominated metabolites (BDE-28 and BDE-7), hydroxylated metabolites (6-OH-BDE-47, 5-OH-BDE-47, 2'-OH-BDE-28 and 4'-OH-BDE-17), and brominated phenols (2,4-DBP and 4-BP). P. aeruginosa YH also exhibited exceptional ability to degrade intermediates, and the degradation rates of 50 μg/L BDE-28, BDE-7, and 2,4-DBP were 68.4%, 82.3% and 92.7% on the 5th day, separately. Transcriptome sequencing revealed that 991 genes were up-regulated, and 923 genes were down-regulated in P. aeruginosa YH after exposure to 0.5 mg/L BDE-47 (FDR ≤ 0.001, |log₂Ratio| ≥ 1). The differentially expressed genes were related to transport, metabolism and stress response. Harf inhibitory concentration (IC₅₀) of BDE-47 decreased from 167.5 mg/L to 68.4 mg/L when multidrug efflux pump was inactivated by 20 mg/L andrographolide, indicating that it helped the bacterial tolerance against BDE-47. Moreover, efflux pump inhibition would accelerate the adsorption of BDE-47. The adsorption rate obtained equilibrium at approximately 70% in 2 days, while 5 days in the control group. Degradation efficiency of 2 mg/L BDE-47 decreased from 26.8% to 13.9% when multidrug efflux was suppressed.

Contribution of phenanthrene in different binding sites to its biodegradation in biochar-amended soils

Biochars can strongly sorb hydrophobic organic contaminants in soils. However, contribution of contaminants in different binding sites to their biodegradation in biochar-amended soils is not clear. In this work, wheat straw biochars were prepared at pyrolysis temperatures of 400 °C (BC400) and 700 °C (BC700). During a 42-day experiment, degradation rate constant of phenanthrene in soils was in the order of treatment without biochar (1.64 × 10-2 d-1) > treatment with BC700 (0.96 × 10-2 d-1) > treatment with BC400 (0.30 × 10-2 d-1). At the beginning, amendment of BC400 and BC700 reduced the rapidly desorbing fraction of phenanthrene in soils by 44.8% and 92.5%, respectively. At the end, both phenanthrene and microbial biomass highly concentrated on the biochar separated from soils. The results of a coupled model of desorption and biodegradation revealed that only phenanthrene in rapidly desorbing sites was degraded in BC400-amended soils, whereas degradation of phenanthrene in both rapidly and slowly desorbing sites occurred in BC700-amended soils, contributing 24.4% and 75.6% of the degradation, respectively. High fraction (>95%) of biodegradable phenanthrene in slowly desorbing sites was the key reason for higher biodegradation rate of phenanthrene in soils with BC700 than in soils with BC400.

Vegetation alleviate the negative effects of graphene oxide on benzo[a]pyrene dissipation and the associated soil bacterial community

Graphene oxide (GO) will enter the soil environment in increasing amounts. The effects of GO on the dissipation of benzo[a]pyrene (B[a]P) from contaminated soil and their phytoremediation system have been explored in this study. B[a]P is a ubiquitous soil pollutant used as a representative indicator of polycyclic aromatic hydrocarbons. A pot experiment was performed to investigate the effects of GO or/and vegetation (Tagetes patula) on B[a]P dissipation and the associated bacterial communities in soil. The bacterial communities in soil were investigated by Illumina sequencing analysis. The presence of vegetation significantly enhanced the dissipation of B[a]P from soil. The addition of GO (100 mg/kg) significantly decreased the B[a]P dissipation. When vegetation and GO coexisted, the inhibition effects of GO on B[a]P dissipation were alleviated by vegetation. Compared with the control treatment, the presence of GO or vegetation had no significant effects on the richness and diversity of bacterial communities in B[a]P-contaminated soil. Compared with the presence of only vegetation, the richness and diversity all significantly decreased when vegetation and GO coexisted. And, vegetation had a greater influence on the bacterial community composition than GO. Vegetation alleviated the inhibition effects of GO on B[a]P dissipation and had a greater influence on the associated bacterial communities than GO. This work helps to understand the interactive effects of GO and vegetation on B[a]P dissipation and the associated bacterial communities in contaminated soil.

Cellular changes of microbial consortium GY1 during decabromodiphenyl ether (BDE-209) biodegradation and identification of strains responsible for BDE-209 degradation in GY1

Microbial consortium remediation has been considered to be a promising technique for BDE-209 elimination in water, soil and sediment. Herein, we studied malondialdehyde (MDA), membrane potential (MP), and reactive active species (ROS) of a microbial consortium GY1 exposed to BDE-209. The results indicated that the microbial antioxidant defense system was vulnerable by BDE-209. Both early and late apoptosis of microbial consortium induced by BDE-209 were observed. The sequencing results revealed that Stenotrophomonas, Microbacterium and Sphingobacterium in GY1 played major roles in BDE-209 degradation. Moreover, a novel facultative anaerobic BDE-209 degrading strain named Microbacterium Y2 was identified from GY1, by which approximately 56.1% of 1 mg/L BDE-209 was degraded within 7 days, and intracellular enzymes of which contributed great to the result. Overall, the current study provided new insights to deeply understand the mechanisms of BDE-209 degradation by microbial consortium.

Effects of carbon nanotubes on biodegradation of pollutants: Positive or negative?

Recently, a large quantity of carbon nanotubes (CNTs) enters the environment due to the increasing production and applications. More and more researches are focused on the fate and possible ecological risks of CNTs. Some literatures summarized the effects of CNTs on the chemical behavior and fate of pollutants. However, little reviewed the effects of CNTs on the biodegradation of pollutants. In general, the effects of CNTs on the biodegradation of pollutants and the related mechanisms were summarized in this review. CNTs have positive or negative effects on the biodegradation of contaminants by affecting the functional microorganisms, enzymes and the bioavailability of pollutants. CNTs may affect the microbial growth, activity, biomass, community composition, diversity and the activity of enzymes. The decrease of the bioavailability of pollutants due to the sorption on CNTs also causes the reduction of the biodegradation of contaminants. In addition, the roles of CNTs are controlled by multiple mechanisms, which are divided into three aspects i.e., properties of CNTs, environment condition, and microorganisms themself. The better understanding of the fate of CNTs and their impacts on the biochemical process in the environment is conducive to determine the release of CNTs into the environment.

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.

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.

TiO2 nanoparticles in sediments: Effect on the bioavailability of heavy metals in the freshwater bivalve Corbicula fluminea

Most studies investigating the influence of TiO₂ NPs on heavy metal bioavailability have focused on the aqueous phase; however, few have examined the sediments containing more nanoparticles. Here, we investigated the effects of TiO₂ NPs on heavy metal bioavailability in C. fluminea in sediments. The interactions between the TiO₂ NPs and metals in sediments, the influence of TiO₂ NPs on metals levels in aqueous phase and geochemical speciation were also explored. The results indicated the large adsorption capacity of TiO₂ NPs and the strong adsorption affinity to metals caused the metals adsorbed on nanoparticles, which decreased the metals concentrations in water phase. Changes in metal speciation caused by metals in EXC, CAR, and IMO partly transported from sediments to TiO₂ NPs during the aging of sediments. Heavy metals contents in C. fluminea tissues were in the order of gill>visceral mass>mantle>foot and increased with the increasing TiO₂ NPs contents in sediments. TiO₂ NPs enhanced the bioavailability of metals in the speciation of EXC, CAR, and IMO in sediments by the Trojan horse effects. The results can facilitate a more realistic evaluation of the environmental risks of TiO₂ NPs to benthic organisms in heavy metal-contaminated sediments.

Biochar accelerates microbial reductive debromination of 2,2',4,4'-tetrabromodiphenyl ether (BDE-47) in anaerobic mangrove sediments

A common congener of polybrominated diphenyl ethers, 2,2',4,4'-tetrabromodiphenyl ether (BDE-47), is a prevalent, persistent and toxic pollutant. It could be removed by reduction debromination by microorganisms but the rate is often slow. The study hypothesized that spent mushroom substrate derived biochar amendment could accelerate the microbial reductive debromination of BDE-47 in anaerobic mangrove sediment slurries and evaluated the mechanisms behind. At the end of 20-week experiment, percentages of residual BDE-47 in slurries amended with biochar were significantly lower but debromination products were higher than those without biochar. Such stimulatory effect on debromination was dosage-dependent, and debromination was coupled with iron (Fe) reduction. Biochar amendment significantly enhanced the Fe(II):Fe(III) ratio, Fe(III) reduction rate and the abundance of iron-reducing bacteria in genus Geobacter, thus promoting bacterial iron-reducing process. The abundances of dehalogenating bacteria in genera Dehalobacter, Dehalococcoides, Dehalogenimonas and Desulfitobacterium were also stimulated by biochar. Biochar as an electron shuttle might increase electron transfer from iron-reducing and dehalogenating bacteria to PBDEs for their reductive debromination. More, biochar shifted microbial community composition in sediment, particularly the enrichment of potential PBDE-degrading bacteria including organohalide-respiring and sulfate-reducing bacteria, which in turn facilitated the reductive debromination of BDE-47 in anaerobic mangrove sediment slurries.

Sorption, transport and biodegradation - An insight into bioavailability of persistent organic pollutants in soil

Contamination of soils with persistent organic pollutants (POPs), such as organochlorine pesticide, polybrominated diphenyl ethers, halohydrocarbon, polycyclic aromatic hydrocarbons (PAHs) is of increasing concern. Microbial degradation is potential mechanism for the removal of POPs, but it is often restricted by low bioavailability of POPs. Thus, it is important to enhance bioavailability of POPs in soil bioremediation. A series of reviews on bioavailability of POPs has been published in the past few years. However, bioavailability of POPs in relation to soil organic matter, minerals and soil microbes has been little studied. To fully understand POPs bioavailability in soil, research on interactions of POPs with soil components and microbial responses in bioavailability limitation conditions are needed. This review focuses on bioavailability mechanisms of POPs in terms of sorption, transport and microbial adaptation, which is particularly novel. In consideration of the significance of bioavailability, further studies should investigate the influence of various bioremediation strategies on POPs bioavailability.

Lead accumulation (adsorption and absorption) by the freshwater bivalve Corbicula fluminea in sediments contaminated by TiO2 nanoparticles

With the increasing production and applications of TiO₂ nanoparticles (NPs), their presence in aquatic environments, especially in sediments, will inevitably increase over time. Most studies investigating the influence of TiO₂ NPs on the bioaccumulation of co-existing contaminants have focused on the aqueous phase; however, few have examined the sediment phase, which contains more TiO₂ NPs and contaminants. We investigated the effects of TiO₂ NPs on Pb accumulation by Corbicula fluminea in sediments, and explored extracellular and intracellular Pb concentrations in the various soft tissues of the bivalve. Pb was spiked with 50 mg/kg in sediment and TiO₂ NPs/sediments ratios were within the range 0.2-3.0%. The results showed that TiO₂ NPs presented larger adsorption capacity and affinity to Pb ions than the sediments. In addition, the large adsorption capacity of TiO₂ NPs and the strong adsorption affinity to Pb ions caused part of the Pb ions released from sediments to aqueous phase were re-adsorbed by TiO₂ NPs in sediments. The concentration of TiO₂ NPs in C. fluminea tissues significantly increased with increasing TiO₂ NP content in sediments, following the order: gill > mantle > foot > visceral mass, which differed from the results found in the aqueous phase. In addition, the proportions of extracellular and intracellular Pb concentrations changed significantly in all the tissues as a result of TiO₂ NP contamination of sediments. TiO₂ NPs promote increased extracellular Pb in foot, mantle, and gill tissues, and increased intracellular Pb in the visceral mass. These results may be beneficial to more scientifically evaluate and predict the environmental risks of TiO₂ NPs to benthic organisms in sediments contaminated by heavy metals.