Development of Magnetic Porous Polymer Composite for Magnetic Solid Phase Extraction of Three Fluoroquinolones in Milk.

In this study, a magnetic porous polymer composite with both hydrophilic and hydrophobic groups was synthesized for magnetic solid phase extraction (MSPE) of milk substrates. Optimization was conducted on various parameters, including adsorption dose, solution pH, adsorption time, and some elution conditions. Coupled with a high-performance liquid chromatography fluorescence detector, a novel MSPE method for determination of norfloxacin (NFX), ciprofloxacin (CIP), and enrofloxacin (ENR) in milk was developed based on magnetic metal organic framework polystyrene polymer (Fe3O4@MOF@PLS) as adsorbent. The Fe3O4@MOF@PLS exhibited significantly improved adsorption performance compared to MOF and PLS. Under optimized experimental conditions, the method exhibited good linearity for the three fluoroquinolones (FQs) in the range of 0.5-1000 µg/kg, with limit of detections (LODs) ranging from 0.21 to 1.33 µg/kg, and limit of quantitations (LOQs) from 0.71 to 4.42 µg/kg. The relative standard deviation (RSD) for the three FQs were 3.4-8.8%. The recoveries of three FQs in milk samples ranged from 84.2% to 106.2%. This method was successfully applied to the detection of three FQs in 20 types of milk, demonstrating its simplicity, speed, and effectiveness in analyte enrichment and separation. The method presented advantages in adsorbent dosage, adsorption time, LODs, and LOQs, making it valuable for the analysis and detection of FQs in milk.

Development of a NiFe2O4 covalent organic framework based magnetic solid-phase extraction approach for specific capture of quinolones in animal innards prior to UHPLC-Q-Orbitrap HRMS detection.

This study aimed to present a selective and effective method for analyzing quinolones (QNs) in food matrix. Herein, a NiFe2O4-based magnetic sodium disulfonate covalent organic framework (NiFe2O4/COF) was prepared using a simple solvent-free grinding method, and was adopted as a selective adsorbent for magnetic solid phase extraction of QNs. Coupled with UHPLC-Q-Orbitrap HRMS, an efficient method for simultaneous detection of 18 kinds of QNs was established. The method exhibited good linearity (0.01-100 ng g-1), high sensitivity (LODs ranging from 0.0011 to 0.0652 ng g-1) and precision (RSDs below 9.5%). Successful extraction of QNs from liver and kidney samples was achieved with satisfactory recoveries ranging from 82.2% to 108.4%. The abundant sulfonate functional groups on NiFe2O4/COF facilitated strong affinity to QNs through electrostatic and hydrogen bonding interactions. The proposed method provides a new idea for the extraction of contaminants with target selectivity.

Fabrication of a magnetic metal-organic framework/covalent organic framework composite for simultaneous magnetic solid-phase extraction of seventeen trace quinolones residues in meats.

Effective capture of quinolones (QNs) in animal-derived food is a vital procedure for food safety monitoring. However, the lack of adsorption specificity and difficult to recycle in complex substrate conditions have been major problems for most of the adsorbents. In this work, a magnetic Fe3O4/MOF/COF composite (named Fe3O4@NH2-MIL-125@TpPa-SO3H) was successfully synthesized with good magnetic responsiveness and conspicuous affinity towards QNs. The Fe3O4/MOF/COF composite was used as a magnetic solid-phase extraction (MSPE) adsorbent for pretreatment and determination of QNs in meat samples. Under optimal MSPE conditions in combination with high performance liquid chromatography-quadrupole orbitrap high resolution mass spectrometer (HPLC-Q-Orbitrap HRMS), the proposed method had good linearity (R2 ≥ 0.9978) from 0.01 to 100ng g-1, low limits of detection (0.0016 to 0.0940ng g-1), good precision with relative standard deviations lower than 5.8%. This method was effectively applied to the detection of 17 QNs in the spiked pork, chicken and beef samples with satisfactory recoveries from 83.9 to 106.2%. The separation selectivity mainly due to the π-π interaction, hydrogen bonding, and electrostatic attraction between QNs and the sulfonic acid and amino functional groups of the composite. After verification, the stability and reusability of the composite meet the requirements of complex matrix sample pretreatment. The developed MSPE method based on the magnetic Fe3O4/MOF/COF composite provided an ideal sample pretreatment alternative for determining trace QNs in complex matrixes with selectivity, simplicity, rapidity, and efficiency.

Distribution, sources, and ecological risk assessment of polycyclic aromatic hydrocarbons in sediments from Baiyang Lake, China.

The issue of polycyclic aromatic hydrocarbons (PAHs) has been an environmental focus worldwide. In this study, the contents, sources, and ecological risks of sixteen PAHs in the sediment of Baiyang Lake were estimated, and a list of priority pollutants was established. The total PAH contents ranged from 114 to 1010 ng·g-1. The composition of PAHs indicated that 4- to 6-ring PAHs predominated in the sediment samples. The diagnostic ratio analysis showed that combustion sources were predominant for PAHs in Baiyang Lake. Specifically, the positive matrix factorization model indicated that diesel engine emissions, gasoline engine emissions, wood combustion sources, and coal combustion sources contributed 22, 32, 24, and 22% of ∑PAHs, respectively. Based on the sediment quality guidelines, mean effects range median quotient, ecological risk quotient, and toxicity equivalent quotient methods, the comprehensive assessment results of PAHs in Baiyang Lake sediments indicated that the ecological risks were at medium and low levels. The priority pollutant list showed that benzo[b]fluoranthene and benzo[a]pyrene were the highest-priority pollutants and thus should be given more attention.

Distribution, Source Apportionment and Risk Assessment of Phthalate Esters in the Overlying Water of Baiyang Lake, China.

As a kind of endocrine disruptor compounds, the presence of phthalate esters (PAEs) has become a global concern. In this study, the pollution levels and spatial distribution of sixteen PAEs were investigated. Their potential sources and eco-environmental health risk were discussed in Baiyang Lake and its upstream rivers during different periods. PAEs were detected in all of samples, ranging from 1215 to 3014 ng·L-1 in October 2020 and 1384 to 3399 ng·L-1 in May 2021. Dibutyl phthalate (DBP) and di-isobutyl phthalate (DIBP) were the predominant monomers, with a detection rate of 100% and the highest concentrations in the overlying water. Restricted by multiple factors, the spatial distribution difference between Baiyang Lake and its upstream rivers in October was more significant than in May. The source apportionment revealed that agricultural cultivation and disorderly use and disposal of plastic products were the primary factors for the contamination. The human health risk assessment indicated that eight PAE congeners did not pose significant carcinogenic and non-carcinogenic harms to males, females and children. However, the ecological risks of DBP, DIBP and di (2-ethylhexyl) phthalate to algae, crustaceans and fish species were moderate or high-risk levels. This study provides an appropriate dataset for the assessment of the pollution of PEs to the water ecosystem affected by anthropogenic activities.

Facile synthesis of triazine-based microporous organic network for high-efficient adsorption of flumequine and nadifloxacin: A comprehensive study on adsorption mechanisms and practical application potentials.

Flumequine (FLU) and nadifloxacin (NAD), as emerging contaminants, have received extensive attention recently. In this study, a triazine-based microporous organic network (TMON) was synthetized and developed as an excellent adsorbent for FLU and NAD. The adsorption behavior and influence factors were investigated in both single and binary systems. Insight into the adsorption mechanisms were conducted through experiments, models, and computational studies, from macro and micro perspectives including functional groups, adsorption sites, adsorption energy and frontier molecular orbital. The results showed that the maximum adsorption capacities of TMON for FLU and NAD are 325.27 and 302.28 mg/g under 30 °C higher than records reported before. TMON exhibits the better adaptability and anti-interference ability for influence factors, leading to the preferable application effect in kinds of real water samples. TMON also shows the application potentials for the adsorption of other quinolone antibiotics and CO2 capture. Hydrogen-bonding interaction played the most critical role compared to π-π stacking effect, π-π electron-donor-acceptor interaction, CH-π interaction, and hydrophobic interaction during the adsorption. TMON could be regarded as a promising environmental adsorbent for its large surface area, stable physical and chemical properties, excellent recyclability, and wide range of applications.

Screening and quantification of 146 veterinary drug residues in beef and chicken using QuEChERS combined with high performance liquid chromatography-quadrupole orbitrap mass spectrometry.

This work aimed to develop an integrated high-throughput screening and quantification for multi-class veterinary drug residues by HPLC-Q-Orbitrap mass spectrometry. A qualitative screening mass database of 171 veterinary drugs was created using full scanning mode, which improved the screening accuracy and scope. Beef and chicken samples were chosen to validate the quantification method at three spiked concentration levels. The quantification method of 146 veterinary drug residues was developed. After enzymatic hydrolysis, beef and chicken samples were treated using optimized QuEChERS. The calibration curves showed good linearities with correlation coefficients of 0.9921-0.9994. The recovery rates were within 52.1-138.2 % with relative standard deviations 0.4-17.7 %. The limits of detection and limits of quantification were in the range of 0.15-3.03 µg/kg and 0.5-10 µg/kg, respectively. The proposed method was demonstrated to be reliable for the simultaneous analysis of multi-class veterinary drugs. It is of significance to expand the screening scope and quantitative analysis efficiency.

Parabens, Triclosan and Bisphenol A in Surface Waters and Sediments of Baiyang Lake, China: Occurrence, Distribution, and Potential Risk Assessment.

The extensive use of the parabens triclosan (TCS) and bisphenol A (BPA) has potential adverse effects on human health and aquatic organisms. However, their monitoring information in freshwater lakes is still limited. This study simultaneously summarized the concentrations, spatial distribution characteristics, and correlations of four types of parabens, TCS, and BPA in the surface water and sediment of Baiyang Lake. Finally, the potential risks of target pollutants were evaluated from two aspects: human health risks and ecological risks. The average contaminations of target compounds in surface water and sediment-BPA, TCS, and ∑4 parabens-was 33.1, 26.1, 0.7 ng/L and 24.5, 32.5, 2.5 ng/g, respectively. The total concentration of target compounds at the inlet of the upstream Fu River and Baigouyin River is significantly higher than that near Hunan and the outlet. In addition, Spearman's correlation analysis showed a significant positive correlation between compounds. The health hazards of target compounds in surface water were all within safe limits. However, the risk quotient results indicate that in some locations in surface water, TCS poses a high risk to algae and a moderate risk to invertebrates and fish, and appropriate attention should be paid to these areas.

Residual levels and dietary exposure risk assessment of banned pesticides in fruits and vegetables from Chinese market based on long-term nontargeted screening by HPLC-Q-TOF/MS.

The negative impact of banned pesticides is of special importance for their high toxicity. In this study, nationwide screening of banned pesticides in 37462 fruit and vegetable samples was carried out from 2012 to 2018 using a self-developed HPLC-Q-TOF/MS technique. The dietary exposure risks associated with the banned pesticides were assessed. The results showed that 66.62 % of the samples were detected at least one pesticide. Among the pesticide-positive samples, a total of 18 banned pesticides were detected in 1798 samples for 1896 times. The risk assessment revealed that 11.71 % of the positive detections exceeded the safety limits and posed an unacceptable risk, while 37.29 % of the positive detections posed acceptable risks. According to the screening and assessment results, two national maps were presented to show the total detection ratios of the banned pesticides and the unacceptable risks of dietary exposure. It should be noted that omethoate had higher residual concentration, unacceptable risk frequency and unacceptable risk proportion. This is the first nationwide comprehensive report on screening and risk assessment banned pesticides.

Prioritization of micropollutants in municipal wastewater and the joint inhibitory effects of priority organic pollutants on Vibrio qinghaiensis sp.-Q67.

Treatment of wastewater in municipal wastewater treatment plants has become a major barrier to organic pollutants entering the aquatic environment. In this study, qualitative screening of organic micropollutants was conducted in a typical municipal wastewater treatment plant (MWWTP) using gas chromatography-mass spectrometry (GC-MS). The identified compounds were prioritized according to their comprehensive scores ranked by detection frequency, semi-quantitative concentration, bioaccumulation, ecotoxicity, and biodegradability. The results showed dibutyl phthalate, antioxidant 2246, methyl stearate, 2,4,6-tri­tert-butylphenol, and dioctyl phthalate had the top five scores and were ranked as priority organic pollutants in the municipal wastewater. The individual and joint toxicity determinations of the five compounds were carried out by a bioluminescence inhibition assay using Vibrio qinghaiensis sp.-Q67 (V. qinghaiensis). The individual toxicity assay results of these pollutants on V. qinghaiensis demonstrated that the order of the acute toxicity of the five priority organic pollutants was as follows: dioctyl phthalate> dibutyl phthalate> methyl stearate> antioxidant 2246> 2,4,6-tri­tert-butylphenol. The joint toxicity showed partial addition or antagonism among these pollutants. The prediction results of the mixed toxicity were compared between the concentration addition model and the independent action model, indicating that a single traditional prediction model could not accurately predict the mixed toxicity of different types of organic pollutants, and that a comprehensive application of model prediction could improve the accuracy of mixed toxicity prediction. This method could provide a theoretical basis for systematic screening and toxicity prediction of pollutants in wastewater.

Risk assessment of carbofuran residues in fruits and vegetables at the Chinese market: A 7-year survey.

The United Nations designated 2021 as the International Year of Fruits and Vegetables (IYFV), with the goal of educating populations regarding the role of such produce in nutrition, food safety, and overall health. Carbofuran is a highly toxic insecticide and nematocide, and its use to treat fruit trees, vegetables, tea, and medicinal herbs is thus prohibited. However, carbofuran residues are still detectable via LC-Q-TOF/MS in fruit and vegetable samples collected from 138 sites in 31 regions. In the present study, carbofuran levels were sampled at 1388 sampling sites in 31 regions (provinces, autonomous regions, and municipalities) not including Hong Kong, Macao, or Taiwan. In total, over 36,000 samples (including 12,547 samples of 41 kinds of fruits and 23,785 samples of 83 kinds of vegetables) were randomly collected from supermarkets and farmer's markets. These data were used to conduct a risk assessment pertaining to dietary carbofuran exposure through the consumption of fruits and vegetables. In total, carbofuran residues were detectable in 2.0% of fruits and 2.3% of vegetables. Risk assessments indicated that the intake of fruits and vegetables harboring carbofuran residues did not pose a chronic health risk. However, peaches, grapes, sweet peppers, celery, Chinese chives, leaf lettuce, spinach, small rape, mustard greens, cucumbers, watermelons, Chinese wolfberry leaves, wax gourds, snap beans, bitter melons, green Chinese vegetables, lettuce, shallot, cowpeas, eggplants, tomatoes, tangerines, summer squash, oranges, lemons, Chinese cabbage, peppers, and strawberries were associated with an unacceptable acute risk to both children and adults. Moreover, crown daisies, nectarines, citrus fruits, pitayas, melons, kale, cabbages, milk Chinese cabbage, carrots, and melons were associated with an unacceptable acute risk to children. Substantial acute risk to children and adults was observed for fruits and vegetables from surveyed regions other than Inner Mongolia, Yunnan, Liaoning, Fujian, Xinjiang, and Hubei. Together, these data provide a foundation for future research aimed at the management of carbofuran residues in fruits and vegetables in an effort to better protect consumer health.

Occurrence and Removal of Triazine Herbicides during Wastewater Treatment Processes and Their Environmental Impact on Aquatic Life.

Wastewater treatment plants (WWTPs) represent a major point source for pesticide residue entry to aquatic environment and may threaten ecosystems and biodiversity in urban area. Triazine herbicides should be paid attention to for their ubiquitous occurrence in the environment and long-term residue. The present study aimed to quantify eleven compounds of triazine herbicides during wastewater treatment processes. The solid phase extraction and gas-chromatography mass spectrometry (GC-MS) determination method were developed to identify the target herbicides with approving sensitivity. The pollution levels, removal rates of eleven triazine herbicides along five different treatment stages in WWTP were investigated. The results showed that three herbicides including atrazine, simetryn and prometryn were detected. Their concentrations in influent were among 28.79 to 104.60 ng/L. Their total removal rates from influent to effluent were 14.92%, 10.79% and 4.41%, respectively indicating that they were difficult to be effectively remove during wastewater treatment. Regarding the negative impact of triazine herbicides discharged from WWTPs on downstream water quality and aquatic life, the environmental risks were assessed by calculating the Environmental Relevance of Pesticides from Wastewater Treatment Plants Index (ERPWI) and water cycle spreading index (WCSI). The risk assessment results denoted the possible high risks for atrazine and simetryn to alage, and simetryn concurrently posed a high risk for the daphnia, while prometryn was at medium risk to alage. Atrazine and simetryn in effluent posed high risk for algae, meanwhile, simetryn had high risk for Daphnia. These results suggested a possible threat to the aquatic environment, rendering in this way the ERPWI method as a useful assessment tool. Further extensive study is needed for atrazine and simetryn in order to better understand their migration mechanism in aquatic environment.

Determination of Vancomycin and Norvancomycin Residues in Milk by Automated Online Solid-Phase Extraction Combined With Liquid Chromatography-High Resolution Mass Spectrometry.

BACKGROUND: Vancomycin and norvancomycin, as potent antibacterial retention drugs, were used illegally on animals bred for food, which directly affected the quality and safety of animal-derived food, and even harmed human health. OBJECTIVE: A fast analysis method, which was adopted to detect residues of vancomycin and norvancomycin in milk, was implemented on a chromatographic system containing online solid-phase extraction (SPE) device that combined with high-resolution mass spectrometer (HRMS). METHOD: First, the analytes were added to the blank milk sample were extracted with water [containing 0.1% trifluoroacetic acid (TFA)]-acetonitrile (ACN) (8:2, v/v), and then were purified and enriched on a C18-XL column, whereafter eluted from the purification column onto the analytical column (Shiseido Capcell Pak ADME column) for chromatographic separation prior to hybrid quadrupole-Orbitrap (Q-Orbitrap) detection. RESULTS: The results showed that the limit of detection (LOD) for each analyte and the limit of quantitation (LOQ) were 0.15 and 0.5 µg/kg, respectively. The correlation coefficient(s) of vancomycin and norvancomycin ranged from 0 to 200 ng/mL were greater than 0.9983. CONCLUSIONS: These validations reflected that it was suitable for the established method to rapidly analyze vancomycin and norvancomycin residues in milk. HIGHLIGHTS: The method for detecting vancomycin and norvancomycin residues in milk by online SPE combined with LC-HRMS. Online SPE technology realized automation, and the application of HRMS greatly improved the reliability of qualitative and quantitative analyses. The developed method is fast, simple, and reliable; each methodological index can meet requirements of trace analyses of vancomycin and norvancomycin in milk.

New insight into the co-adsorption of oxytetracycline and Pb(II) using magnetic metal-organic frameworks composites in aqueous environment: co-adsorption mechanisms and application potentials.

The present study aimed to investigate the co-adsorption and application of water stabilized Fe3O4@ZIF-8 composite with magnetic cubic crystal structure. This new material was successfully prepared by facile modification strategy and rational design, which was used for simultaneous adsorption of oxytetracycline (OTC) and Pb(II) in aqueous solution. The co-adsorption behavior and mechanism of the composite for OTC and Pb(II) were systematically investigated by characterization techniques and batch experiments, and its application potential was effectively evaluated. The results showed that the synthesized Fe3O4@ZIF-8 composite innovatively retained the cubic crystal structure of ZIF-8 and was successfully loaded on the surface of Fe3O4 particles with small particle size to form a core-shell structure. The Fe3O4@ZIF-8 composite possessed a large specific surface area (1722 m2/g), magnetic separation performance (13.4 emu/g), and rich functional groups. The co-adsorption of OTC and Pb(II) on Fe3O4@ZIF-8 had fast reaction kinetics (equilibrium within 90 min) and large adsorption capacity (310.29 mg/g and 276.06 mg/g respectively). The adsorption process for both contaminants followed pseudo-second order kinetics and Langmuir isotherm models and had synergistic and competitive effects at the same time. π-π stacking and electrostatic interaction were the main mechanisms of adsorption. Fe3O4@ZIF-8 had good adsorption performance after cyclic adsorption for 4 times and it performed well in the treatment of real waste water. This study provided a new sight for the control of combined pollution of OTC and Pb(II) and proved Fe3O4@ZIF-8 composites have great application potentials for complex wastewater treatment.

Recent advances in porous organic frameworks for sample pretreatment of pesticide and veterinary drug residues: a review.

Rapid and accurate detection of pesticide and veterinary drug residues is a continuing challenge because of the complex matrix effects. Thus, appropriate sample pretreatment is a crucial step for the effective extraction of the analytes and removal of the interferences. Recently, the development of nanomaterial adsorbents has greatly promoted the innovation of food sample pretreatment approaches. Porous organic frameworks (POFs), including polymers of intrinsic microporosity, covalent organic frameworks, hyper crosslinked polymers, conjugated microporous polymers, and porous aromatic frameworks, have been widely utilized due to their tailorable skeletons and pores as well as fascinating features. This review summarizes the recent advances for POFs to be utilized in adsorption and sample preparation of pesticide and veterinary drug residues. In addition, future prospects and challenges are discussed, hoping to offer a reference for further study on POFs in sample pretreatment.

Simultaneous determination and risk assessment of highly toxic pesticides in the market-sold vegetables and fruits in China: A 4-year investigational study.

This study investigated the levels of highly toxic pesticides (HTPs) in 6554 vegetable and fruit samples from 31 regions of China, along with the associated risk of dietary exposure for the population between 2014 and 2017. 18 HTPs were detected in 325 (4.96%) samples, and the levels of HTPs in 103 (1.57%) samples were found to be higher than the maximum residue limits (MRLs) of China. The rate of detection of HTPs in six types of vegetables and fruits, in a decreasing order, was found to be as follows: eggplant (8.84%) >grape (5.58%) >tomato (5.43%) >cucumber (5.43%) >pear (3.12%) >apple (2.30%). The level of contamination of HTPs was found to be higher in vegetables compared with fruits. The vegetable and fruit samples with the highest percentages of HTPs exceeding MRLs were found in eggplants from Guangxi (20%) and grapes from Inner Mongolia (12.5%), respectively. Both, the average target hazard quotient (THQ) of a single highly toxic pesticide (HTP) and the average hazard index (HI) of the mixture of HTPs for adults and children from vegetables and fruits from the 31 regions were found to be less than one. Omethoate, carbofuran, ethoprophos, triazophos, and phorate were identified as the major contributors to the average HI for vegetables, and carbofuran, ethoprophos, omethoate, phorate, and phosphamidon were identified as the primary contributors to the average HI for fruits. The results of this study revealed that HTPs in vegetables and fruits did not cause any significant chronic risk of dietary exposure. The detection of HTPs exceeding MRLs in some of the samples implied that appropriate management guidelines for HTPs should be implemented to protect the health of the consumers.

Occurrence and removal of organic pollutants by a combined analysis using GC-MS with spectral analysis and acute toxicity.

The presence of xenobiotic compounds especially organic micro-pollutants in municipal wastewater treatment plant (MWWTP) is a major concern worldwide. The occurrence and removal of trace organic pollutants in a MWWTP by a combined analysis using GC-MS with spectral analysis and acute toxicity were studied in this work. Non-target screening and toxicity analysis of organic compounds were conducted to understand the types of toxic and refractory pollutants in municipal wastewater and evaluated the toxicity removal efficiency of MWWTP. The results showed that most of the effects were significantly reduced or completely eliminated during the wastewater treatment process, while some compounds, such as antioxidants, drugs, and organic plasticizers, had detection rates of up to 100% at each site, indicating that these harmful substances remained throughout wastewater treatment process. Based on Pearson correlation analysis, paired correlation analysis showed a positive correlation between UV254, humification index, conventional parameters, and organic acute toxicity, while acute toxicity was negatively correlated with biological index and fluorescence index. The results indicated that the composition of MWWTP had a similar influence law in different locations, and the combination of spectral analysis provided a new insight to qualitatively and quantitatively showed the distribution of organic pollutants in the wastewater treatment system.

Evaluation of the fouling potential of sludge in a membrane bioreactor integrated with microbial fuel cell.

This study focused on the fouling characteristics evaluation of the sludge in a membrane bioreactor integrated with microbial fuel cell (MFC-MBR) to reveal the mechanisms of membrane fouling mitigation. The filtration of soluble microbial products (SMPs) in MFC-MBR showed lower flux decline rate than those in the control system (C-MBR). Based on the extended Derjaguin-Landau-Verwey-Overbeek analysis, decreases in free energies of adhesion between the SMPs and clean membrane or SMP-fouled membrane were observed in MFC-MBR. When approaching the clean membrane or SMP-fouled membrane, the SMPs in MFC-MBR had to overcome a higher energy barrier compared to those in C-MBR, indicating the inhibition of adsorption of SMPs on the membrane surface in MFC-MBR. Additionally, sludge flocs in MFC-MBR exhibited lower hydrophobicity and were less negative surface charged in comparison to those in the C-MBR. In MFC-MBR, the sludge flocs approaching the clean membrane, SMP-fouled membrane and cake layer all experienced higher energy barriers and lower secondary energy minimums compared to those in C-MBR, exhibiting the lower potential of cake layer formation. These results confirmed that decreases of the fouling potentials of SMPs and sludge flocs were essential for the membrane fouling mitigation in the MFC-MBR.

The change of accumulation of heavy metal drive interspecific facilitation under copper and cold stress.

Plant diversity has important functions in ecosystem productivity overyielding and community stability. Little is known about the mechanism causing productivity overyielding and stability under harsh conditions. This study investigated the photosynthetic response and subcellular distribution of uni- and co-cultured duckweeds (Lemna aequinoctialis and Spirodela polyrhiza) under excess copper (1.0 mg/L) and low temperature (5 °C) conditions. The results showed that the growth of uni-cultured L. aequinoctialis was not different from that of uni-cultured S. polyrhiza across copper treatments at control temperature (25 °C). The growth rate of L. aequinoctialis increased by 55.5 % under excess copper concentration when it coexisted with S. polyrhiza, compared with uni-culture. Subcellular distributions of copper were predominantly distributed in cell walls. S. polyrhiza accumulated more copper in cell walls than L. aequinoctialis under uni-cultured condintion at excess copper concentration. Co-cultured S. polyrhiza increased copper accumulation in cell walls of co-cultured L. aequinoctialis to decrease toxicity at excess copper concentration, compared with L. aequinoctialis. Low temperature increased copper toxicity, with duckweeds having lower growth rate and photosynthetic activities (Fv/Fm). The L. aequinoctialis growth rate in co-culture was higher than in uni-culture under excess copper concentration and low temperature conditions, indicating that S. polyrhiza decreased the copper toxicity for L. aequinoctialis. The photosynthetic activity (Fv/Fm) of co-cultured L. aequinoctialis was higher than that of uni-cultured L. aequinoctialis exposed to excess copper concentration at low temperature. The community that formed by co-culturing S. polyrhiza and L. aequinoctialis produced more biomass by avoiding the toxicity of excess copper through heavy metal compartmentalization and photosynthetic activities.

The effectiveness of nanobiochar for reducing phytotoxicity and improving soil remediation in cadmium-contaminated soil.

There is growing concern that Cd in soils can be transferred to plants, resulting in phytotoxicity and threats to human health via the food chain. Biochar has been reported to be a soil amendment capable of reducing the bioavailability of metals in soil by electrostatic interactions, ionic exchange and the specific binding of metal ions by surface ligands. To determine the effects of Cd contamination and nanobiochar on the growth characteristics of plants, the dynamics of Cd in soil were explored in Petri dish and pot experiments (0%, 0.2%, 0.5% and 1% nanobiochar), respectively. The diversity, distribution and composition of the bacterial community in treated soil were monitored by high-throughput sequencing. The results showed that the germination potential and height and weight of plants were significantly decreased in Cd-treated soil samples (P < 0.05). The Cd content of Brassica chinensis L. in the treated soil groups was lower than that in the untreated soil groups (P < 0.05) after nanobiochar application. The application of biochar significantly improved the microbial biomass, microorganism abundance and diversity of Actinobacteria and Bacteroidetes in Cd-contaminated soil and reduced the diversity of Proteobacteria, which was relatively more persistent than in the contaminated sites without biochar application. The results of this study provide theoretical and technical support for understanding the environmental behavior of nanopassivators, thus enhancing the role of biochar in the remediation of soil pollution.