Influence of multi-walled carbon nanotubes on the microbial biomass, enzyme activity, and bacterial community structure in 2,4-dichlorophenol-contaminated sediment

Effects of microplastics on microbial community structure and wheatgrass traits in Pb-contaminated riparian sediments under flood-drainage-planting conditions

The coexistence of microplastics (MPs) and heavy metals in sediments has caused a potential threat to sediment biota. However, differences in the effects of MPs and heavy metals on microbes and plants in sediments under different sediment conditions remain unclear. Hence, we investigated the influence of polyethylene (PE) and polylactic acid (PLA) MPs on microbial community structure, Pb bioavailability, and wheatgrass traits under sequential incubation of sediments (i.e., flood, drainage, and planting stages). Results showed that the sediment enzyme activities presented a dose-dependent effect of MPs. Besides, 10 % PLA MPs significantly increased the F1 fractions in three stages by 11.13 %, 30.10 %, and 17.26 %, respectively, thus resulting in higher Pb mobility and biotoxicity. MPs altered sediment bacterial composition and structures, and bacterial community differences were evident in different incubation stages. Moreover, the co-exposure of PLA MPs and Pb significantly decreased the shoot length and total biomass of wheatgrass and correspondingly activated the antioxidant enzyme activity. Further correlation analysis demonstrated that community structure induced by MPs was mainly driven by sediment enzyme activity. This study contributes to elucidating the combined effects of MPs and heavy metals on sediment ecosystems under different sediment conditions.

Effects of microplastics on sedimentary geochemical properties and microbial ecosystems combined with hydraulic disturbance

Microplastics (MPs) pollution is widely investigated owing to its potential threats to river ecosystems. However, it remains unclear whether hydraulic disturbance deepens or mitigates the effects of MPs-contaminated sediments on the river environment. Herein, we studied the impact of sediment aggregates, organic matter, and enzyme activity, with emphasis on microbial community structure and function in sediments exposed to MPs (1 %, 5 %, and 10 % w/w) in conjunction with hydraulic disturbance. The experimental results showed that the influence of MPs on the sediment under hydraulic disturbance is more significant than that of static culture, especially for various environmental factors (MWD, MBC, and sucrase activity etc.). The proportions of the >0.05 mm-fraction aggregates increased from 74-76 % to 82-88 % in the sediment throughout the entire disturbance process. It has been found that the disturbance generally promotes the interaction between MPs and sediments. FAPROTAX analysis demonstrated that the disturbance reduced the difference in effects on microbial functional genes between the control group and the MPs-added groups by up to 10 times, suggesting that the effects of disturbance on MPs-contaminated sediments are relatively complex. This work provides new insights into the effects of hydraulic disturbance on physicochemical properties and microbial communities of MPs-contaminated sediment.

An effective strategy for biodegradation of high concentration phenol in soil via biochar-immobilized Rhodococcus pyridinivorans B403

High concentration of phenol residues in soil are harmful to human health and ecological safety. However, limited information is available on the in-situ bioremediation of phenol-contaminated soil using biochar as a carrier for bacteria. In this study, bamboo -derived biochar was screened as a carrier to assemble microorganism-immobilized composite with Rhodococcus pyridinivorans B403. Then, SEM used to observe the micromorphology of composite and its bioactivity was detected in solution and soil. Finally, we investigated the effects of free B403 and biochar-immobilized B403 (BCJ) on phenol biodegradation in two types of soils and different initial phenol concentrations. Findings showed that bacterial cells were intensively distributed in/onto the carriers, showing high survival. Immobilisation increased the phenol degradation rate of strain B403 by 1.45 times (37.7 mg/(L·h)). The phenol removed by BCJ in soil was 81% higher than free B403 on the first day. Moreover, the removal of BCJ remained above 51% even at phenol concentration of 1,500 mg/kg, while it was only 15% for free B403. Compared with the other treatment groups, BCJ showed the best phenol removal effect in both tested soils. Our results indicate that the biochar-B403 composite has great potential in the remediation of high phenol-contaminated soil.

Impact of microplastics on lead-contaminated riverine sediments: Based on the enzyme activities, DOM fractions, and bacterial community structure

Microplastics (MPs) are able to interact with diverse contaminants in sediments. However, the impacts of MPs on sediment properties and bacterial community structure in heavy metal-contaminated sediments remain unclear. In this study, we investigated the adsorption of Pb(II) by sediment-MPs mixtures and the effects of different concentration MPs on sediment enzyme activities, DOM fractions, and Pb bioavailability in riverine sediments, and further explored the response of sediment microbial community to Pb in the presence of MPs. The results indicated that the addition of MPs significantly decreased the adsorption amount of Pb(II) by sediments, especially decreased by 12.6% at 10% MPs treatment. Besides, the changes in enzyme activities, DOM fractions exhibited dose-dependent effects of MPs. The higher level of MPs (5% and 10%) tends to transform Pb into more bioavailable fractions in sediments. Also, MPs amendment was observed to alter sediment bacterial community structures, and community differences were evident in the uncontaminated and lead-contaminated sediments. Therein, significant increase of Bacteroidota, Proteobacteria and decrease of Firmicutes abundance in Pb-contaminated sediment at the phylum level were observed. These findings are expected to provide comprehensive information for assessing the combined ecological risks of heavy metals and MPs in riverine sediments.

Response of microbial community to the remediation of neonicotinoid insecticide imidacloprid contaminated wetland soil by Phanerochaete chrysosporium

Imidacloprid (IMI), a typic neonicotinoid insecticide, is widely used and persist in soils with long half-time causing serious threat to ecosystem and human health. It is urgent to develop suitable and effective methods to accelerate it degradation and alleviate its negative impacts in soil. In this study, the introduction of functional microbe white-rot fungus Phanerochaete chrysosporium to remediate IMI contaminated wetland soil was carried out. The remediation performance and the response of the soil microbial community were examined. The results showed that P. chrysosporium could improve the degradation of IMI in soil no matter the soil was sterilized or not. The bioaugmentation was especially observed in non-sterilized soil under the inoculation patterns of FE and SP with the maximum IMI degradation rate of 91% and 93% in 7 days, respectively. The invertase activity in soil was also enhanced with P. chrysosporium inoculation. Microbial community analysis revealed that P. chrysosporium inoculation could increase the diversity and richness of bacterial community, and stimulate some IMI degraders genera including Ochrobactrum, Leifsonia, Achromobacter, and Bacillus. Moreover, the xenobiotic degradation and metabolism pathway was generally enhanced with P. chrysosporium inoculation based on PICRUSt analysis. These obtained results demonstrated that the introduction of white-rot fungus is of great potentially enabling the remediation of neonicotinoids contaminated soil.

Functionalization of Multi-Walled Carbon Nanotubes Changes Their Antibiofilm and Probiofilm Effects on Environmental Bacteria

Releasing multi-walled carbon nanotubes (MWCNTs) into ecosystems affects the biofilm formation and metabolic activity of bacteria in aquatic and soil environments. Pristine (pMWCNTs), oleophilic (oMWCNTs), hydrophilic (hMWCNTs), and carboxylated (cMWCNTs) carbon nanotubes were used to investigate their effects on bacterial biofilm. A pronounced probiofilm effect of modified MWCNTs was observed on the Gram-negative bacteria of Pseudomonas fluorescens C2, Acinetobacter guillouiae 11 h, and Alcaligenes faecalis 2. None of the studied nanomaterials resulted in the complete inhibition of biofilm formation. The complete eradication of biofilms exposed to MWCNTs was not observed. The functionalization of carbon nanotubes was shown to change their probiofilm and antibiofilm effects. Gram-negative bacteria were the most susceptible to destruction, and among the modified MWCNTs, oMWCNTs had the greatest effect on biofilm destruction. The number of living cells in the biofilms was assessed by the reduction of XTT, and metabolic activity was assessed by the reduction of resazurin to fluorescent resorufin. The biofilms formed in the presence of MWCNTs reduced tetrozolium to formazan more actively than the control biofilms. When mature biofilms were exposed to MWCNTs, dehydrogenase activity decreased in Rhodococcus erythropolis 4-1, A. guillouiae 11 h, and A. faecalis 2 in the presence of pMWCNTs and hMWCNTs, as well as in A. guillouiae 11 h exposed to cMWCNTs. When mature biofilms were exposed to pMWCNTs, hMWCNTs, and cMWCNTs, the metabolism of cells decreased in most strains, and oMWCNTs did not have a pronounced inhibitory effect. The antibiofilm and probiofilm effects of MWCNTs were strain-dependent.

The role of microplastics in altering arsenic fractionation and microbial community structures in arsenic-contaminated riverine sediments

The ability of microplastics (MPs) to interact with environmental pollutants is of great concern. Riverine sediments, as sinks for multi-pollutants, have been rarely studied for MPs risk evaluation. Meanwhile, MPs generated from biodegradable plastics are questioning the safety of the promising materials. In this study, we investigated the effects of typical non-degradable polyethylene (PE) and biodegradable polylactic acid (PLA) MPs on sediment enzymes, arsenic (As) fractionation, and microbial community structures in As-contaminated riverine sediments. The results indicated that the presence of MPs (1% and 3%, w/w) led As transformed into more labile and bioavailable fractions in riverine sediments, especially under higher As and MPs levels. Analysis on microbial activities and community structures confirmed the strong potential of MPs in inhibiting microbial activities and shifting bacterial community succession patterns through enrichment of certain microbiota. Moreover, biodegradable PLA MPs presented stronger alterations in arsenic fractionation and microbial community structures than PE MPs did, which might be jointly attributed to adsorption behaviors, microbial alterations, and potential PLA degradation behaviors. The study indicated that MPs contamination increased As mobility and bioavailability, and shifted microbial communities in riverine sediments. Moreover, biodegradable MPs might lead to stronger microbial alterations and increases in As bioavailability, acting as a threat to ecological safety, which needed further exploration.

Effects of biochar-based materials on the bioavailability of soil organic pollutants and their biological impacts

Motivated by the unique structure and superior properties, biochar-based materials, including pristine biochar and composites of biochar with other functional materials, are considered as new generation materials for diverse multi-functional applications, which may be intentionally or unintentionally released to soil. The influencing mechanism of biochar-based material on soil organisms is a key aspect for quantifying and predicting its benefits and trade-offs. This work focuses on the effects of biochar-based materials on soil organisms within the past ten years. 206 sources are reviewed and available knowledge on biochar-based materials' impacts on soil organisms is summarized from a diverse perspective, including the pollutant bioavailability changes in soil, and potential effects of biochar-based materials on soil organisms. Herein, effects of biochar-based materials on the bioavailability of soil organic pollutants are detailed, from the perspective of plant, microorganism, and soil fauna. Potential biological effects of pristine biochar (PBC), metal/metal compounds-biochar composites (MBC), clay minerals-biochar composites (CMBC), and carbonaceous materials-biochar composites (CBC) on soil organisms are highlighted for the first time. And possible mechanisms are presented based on the different characters of biochar-based materials as well as various environmental interactions. Finally, the bottleneck and challenges of risk assessment of biochar-based materials as well as future prospects are proposed. This work not only promotes the development of risk assessment system of biochar-based materials, but broadens the strategy for the design and optimization of environmental-friendly biochar materials.

Metal-organic frameworks as a good platform for the fabrication of multi-metal nanomaterials: design strategies, electrocatalytic applications and prospective

MOF-derived multi-metal nanomaterials are attracting numerous attentions in widespread applications such as catalysis, sensors, energy storage and conversion, and environmental remediation. Compared to the monometallic counterparts, the presence of foreign metal is expected to bring new physicochemical properties, thus exhibiting synergistic effect for enhanced performance. MOFs have been proved as a good platform for the fabrication of polymetallic nanomaterials with requisite features. Herein, various design strategies related to constructing multi-metallic nanomaterials from MOFs are summarized for the first time, involving metal nodal substitution, seed epitaxial growth, ion-exchange strategy, guest species encapsulation, solution impregnation and combination with extraneous substrate. Afterwards, the recent advances of multi-metallic nanomaterials for electrocatalytic applications, including oxygen reduction reaction (ORR), oxygen evolution reaction (OER) and hydrogen evolution reaction (HER), are systematically discussed. Finally, a personal outlook on the future trends and challenges are also presented with hope to enlighten deeper understanding and new thoughts for the development of multi-metal nanomaterials from MOFs.

A critical review of biochar-based materials for the remediation of heavy metal contaminated environment: Applications and practical evaluations

The contamination of heavy metals (HMs) in the environment has aroused a global concern. The valid remediation of HM contaminated environment is a highly significant issue. As alternative to carbon materials, biochar has been vastly documented for the remediation of HM contaminated environment. However, there are some possible imperfections to meet the actual remediation tasks as the finite properties of raw biochar, and the remediation process is complex and unexpectedly. This review focuses on the progress made on environmental HM remediation by biochar-based materials within the past six years. The property analysis and key modifications of biochar are summarized inspired by their applicability or necessity for HM decontamination, and the environmental remediation as well as the implicated mechanisms are thoroughly elaborated from multiple pivotal sides. The evaluations of practical application associated with biochar amendment are also presented. Finally, some pertinent improvements and research directions are proposed. To our knowledge, this article is the first time to make a systematic summary on the reliability and practicability of biochar-based materials for environmental HM remediation, and critically pointed out the existing issues to facilitate the judicious design of biochar-based materials and understanding the research trends. It is also aims to provide reference for subsequent research and propel the practical applications.

Recent progress of noble metals with tailored features in catalytic oxidation for organic pollutants degradation

With the increasing serious water pollutions, an increasing interest has given for the nanocomposites as environmental catalysts. To date, noble metals-based nanocomposites have been extensively studied by researchers in environmental catalysis. In detail, serving as key functional parts, noble metals are usually combined with other nanomaterials for rationally designing nanocomposites, which exhibit enhanced catalytic properties in pollutants removal. Noble metals in the nanocomposites possess tailored properties, thus playing different important roles in catalytic oxidation reactions for pollutants removal. To motivate the research and elaborate the progress of noble metals, this review (i) summarizes advanced characterization techniques and rising technology of theoretical calculation for evaluating noble metal, and (ii) classifies the roles according to their disparate mechanism in different catalytic oxidation reactions. Meanwhile, the enhanced mechanism and influence factors are discussed. (iii) The conclusions, facing challenges and perspectives are proposed for further development of noble metals-based nanocomposites as environmental catalysts.

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).

The response of microbial community structure and sediment properties to anthropogenic activities in Caohai wetland sediments

This study aimed to investigate the response of sediment microbial communities (including bacteria and archaeal groups) in Caohai Lake to anthropogenic activities. The sediment samples were collected from the regions with high anthropogenic interference and low anthropogenic interference. Their physicochemical properties and enzyme activities were analyzed, and the bacterial and archaeal communities were investigated using high-throughput sequencing technology. The results showed that the physicochemical characters changed by anthropogenic activities were the important factors that influenced enzyme activities, alpha diversity, key functional taxa, and community structure. And the impact of anthropogenic activities on microbial communities might follow a non-linear pattern. Furthermore, few significant differences of alpha indices between the high and low disturbed areas, but clear differences of microbial community composition analysis and beta-diversity analysis were observed. The hypothesis was proved that the intensity of anthropogenic impacts in Caohai had not reached the potential thresholds. The best distinguish biomarkers between the two areas and the most related key nodes among the network did not always have a high microbial abundance. The anthropogenic activities might influence the microbial community by affecting a small number of the key taxon in the ecological network. These findings provided a valuable understanding of how sediment microorganisms respond to anthropogenic activities in Caohai Lake.

Anaerobic Degradation of Propanil in Soil and Sediment Using Mixed Bacterial Culture

The widespread use of the herbicide, propanil, causes severe environmental problems. In this study, the effects of propanil on the bacterial community in a sediment slurry were determined. Moreover, the degradation of the herbicide by pure and mixed cultures was first conducted under anaerobic conditions. The results showed that propanil caused significant changes in the bacterial community under anaerobic conditions. Four bacterial strains, i.e., Geobacter sp. Pr-1, Paracoccus denitrificans Pr-2, Pseudomonas sp. Pr-3, and Rhodococcus sp. Pr-4, isolated from the an enrichment sediment slurry were the first pure cultures that degraded propanil and 3,4-dichloroaniline (3,4-DCA) under anaerobic conditions. Some individual isolates showed the slow degradation of propanil and 3,4-DCA, but the mixture of the four strains increased the degradation rates of both compounds. The mixed culture of these isolates transformed more than 90% of propanil within 10 days in liquid media with the amendment of dextrose, glucose, or acetate. The determination of degradation pathway showed that propanil was transformed to 3,4-DCA and some other products before degrading completely. This study provides valuable information on the effects of propanil on the bacterial community and the synergistic degradation of propanil under anaerobic conditions.

Effects of hydroxyl, carboxyl, and amino functionalized carbon nanotubes on the functional diversity of microbial community in riverine sediment

Nowadays, more and more attention is focused on the environmental harm brought by the wide production and use of carbon nanotubes. In this study, the metabolic function of sediment microbial community was investigated after unfunctionalized or functionalized multi-walled carbon nanotubes (MWCNTs) were incorporated. The surface functional groups on the studied functionalized MWCNTs in this work were hydroxyl, carboxyl, and amino, respectively. The metabolic functional diversity was determined by Biolog EcoPlates after one-month exposure to MWCNTs. Incorporating 0.5 wt% amino functionalized MWCNTs significantly decreased the microbial activity and diversity, and all types of MWCNTs caused great inhibition on the microbial metabolism at the dosage of 2.0 wt%. The sediment microbes preferred polymers and amino acids. Principal component and similarity analysis indicated that the microbial carbon metabolism was more affected by the MWCNT dosage compared with the functionalization, and 2.0 wt% amino functionalized MWCNTs made the greatest difference in metabolic function of sediment microbial community. These consequences may help to assess the environmental risks of MWCNTs from the aspect of ecological relevance of sediment microbial community.

Enhanced removal of pharmaceuticals and personal care products from real municipal wastewater using an electrochemical membrane bioreactor

A novel electrochemical membrane bioreactor (EMBR) was developed for enhancing PPCPs removal from real municipal wastewater. Compared to the control MBR (CMBR) without applying electric field, EMBR exhibited higher removal efficiencies for 14 PPCPs among all investigated PPCPs, including 3 fluoroquinolones, 2 macrolides, 6 sulfonamides and 3 anti-inflammatory drugs, while no significant difference was observed for the rest 8 PPCPs. The enhanced removal of 14 PPCPs was mainly attributed to electrooxidation by the direct anodic oxidation and reactive oxygen species-mediated indirect oxidation. Moreover, membrane fouling rates of EMBR (0.55 ± 0.10 kPa/d) were significantly reduced compared with CMBR (0.99 ± 0.09 kPa/d). Microbial activities and community analyses demonstrated that the applied electric field had no noticeable adverse impact on microbial viabilities, richness and diversity. These findings demonstrated that this EMBR enhanced pollutant removal and mitigated membrane fouling simultaneously, highlighting the potential of the novel technology to be used for removing PPCPs from wastewater.