The environmental effects of microplastics and microplastic derived dissolved organic matter in aquatic environments: A review.

Currently, microplastics (MPs) have ubiquitously distributed in different aquatic environments. Due to the unique physicochemical properties, MPs exhibit a variety of environmental effects with the coexisted contaminants. MPs can not only alter the migration of contaminants via vector effect, but also affect the transformation process and fate of contaminants via environmental persistent free radicals (EPFRs). The aging processes may enhance the interaction between MPs and co-existed contaminants. Thus, it is of great significance to review the aging mechanism of MPs and the influence of coexisted substances, the formation mechanism of EPFRs, environmental effects of MPs and relevant mechanism. Moreover, microplastic-derived dissolved organic matter (MP-DOM) may also influence the elemental biogeochemical cycles and the relevant environmental processes. However, the environmental implications of MP-DOM are rarely outlined. Finally, the knowledge gaps on environmental effects of MPs were proposed.

Transfer of antibiotic resistance genes from soil to wheat: Role of host bacteria, impact on seed-derived bacteria, and affecting factors.

The transfer of antibiotic resistance genes (ARGs) from soils to plants is poorly understood, especially the role of host bacteria in soils and its impact on seed-derived bacteria. Wheat (Triticum aestivum L.) was thus used to fill the gap by conducting pot experiments, with target ARGs and bacterial community analyzed. Results showed that the relative abundances of target ARGs gradually decreased during transfer of ARGs from the rhizosphere soil to root and shoot. Host bacteria in the rhizosphere soil were the primary source of ARGs in wheat. The 38, 21, and 19 potential host bacterial genera of target ARGs and intI1 in the rhizosphere soil, root, and shoot were identified, respectively, and they mainly belonged to phylum Proteobacteria. The abundance of ARGs carried by pathogenic Corynebacterium was reduced in sequence. During transfer of ARGs from the rhizosphere soil to root and shoot, some seed-derived bacteria and pathogenic Acinetobacter obtained ARGs through horizontal gene transfer and became potential host bacteria. Furthermore, total organic carbon, available nitrogen of the rhizosphere soil, water use efficiency, vapor pressure deficit, and superoxide dismutase of plants were identified as the key factors affecting potential host bacteria transfer in soils to wheat. This work provides important insights into transfer of ARGs and deepens our understanding of potential health risks of ARGs from soils to plants.

Effects of freeze-thaw dynamics and microplastics on the distribution of antibiotic resistance genes in soil aggregates.

This is the first study investigating the effects of freeze-thaw (FT) and microplastics (MPs) on the distribution of antibiotic resistance genes (ARGs) in soil aggregates (i.e., soil basic constituent and functional unit) via microcosm experiments. The results showed that FT significantly increased the total relative abundance of target ARGs in different aggregates due to the increase in intI1 and ARG host bacteria. However, polyethylene MPs (PE-MPs) hindered the increase in ARG abundance caused by FT. The host bacteria carrying ARGs and intI1 varied with aggregate size, and the highest number of hosts was observed in micro-aggregates (<0.25 mm). FT and MPs altered host bacteria abundance by affecting aggregate physicochemical properties and bacterial community and enhanced multiple antibiotic resistance via vertical gene transfer. Although the dominant factors affecting ARGs varied with aggregate size, intI1 was a co-dominant factor in various-sized aggregates. Furthermore, other than ARGs, FT, PE-MPs, and their integration promoted the proliferation of human pathogenic bacteria in aggregates. These findings suggested that FT and its integration with MPs significantly affected ARG distribution in soil aggregates. They amplified antibiotic resistance environmental risks, contributing to a profound understanding of soil antibiotic resistance in the boreal region.

Comprehensive study on the hydrochar for adsorption of Cd(II): preparation, characterization, and mechanisms.

Hydrothermal carbonization process via converting invasive plants into functional materials may provide a novel strategy to comprehensively control and utilized the exotic invasive plants. In this study, Eupatorium adenophorum was utilized to fabricate the hydrochar via hydrothermal carbonization process, which was further applied to remove Cd(II). The results showed that the hydrochar was a mesoporous material with abundant O-containing functional groups (OFPs) on the surface. The adsorption isotherms were fitted by both the Langmuir and Freundlich models, and the maximum adsorption amount achieved 24.53 mg/g. The adsorption dynamics were governed by surface adsorption and film diffusion. pH and ionic strength can exert a strong influence on the adsorption efficiency. The mechanisms on the adsorption of Cd(II) on the hydrochar concluded the pore-filling effects, electrostatic interactions, ion exchange, precipitation, coordination with π electrons, and surface complexation with the OFPs, such as hydroxyl, carboxylic, phenol, acetyl, and ester groups. Thus, hydrothermal carbonization process may provide a promising technique to fabricate the hydrocar for the treatment of Cd(II), which may facilitate comprehensive control of invasive plants and boost to the carbon neutrality.

Interactions between Cr(VI) and the hydrochar: The electron transfer routes, adsorption mechanisms, and the accelerating effects of wood vinegar.

Conversion of the low-valued invasive plant biomass into high-grade carbonaceous materials may provide a novel strategy to tackle the global issues of climate changes and exotic plant invasion. In this study, the hydrochar was fabricated from the biomass of Eupatorium adenophorum spreng. via hydrothermal carbonization (HTC) process to remove Cr(VI). The adsorption thermodynamics and kinetics were investigated via batch experiments, and the electron transfer routes and adsorption mechanisms were further revealed based on systematic characterization. The adsorption isotherms were well fitted by the Langmuir model with a maximum adsorption amount of 7.76 mg/g. The adsorption was spontaneous, and the surface adsorption and intraparticle diffusion may be the speed-limiting steps. Both -OH group and furan structures may donate the electrons to reduce Cr(VI), and the adsorption was governed by the surface complexation with the oxygen-containing functional groups including hydroxyl and carboxyl. Furthermore, the wood vinegar, as the by-product, can significantly accelerate the reduction rate of Cr(VI). Thus, this study provided a new strategy to fabricate carbonaceous materials which may facilitate to boost the carbon neutrality and control of invasive plants.

Simultaneous enhancement of power generation and chlorophenol degradation in nonmodified microbial fuel cells using an electroactive biofilm carbon felt anode.

Microbial fuel cells (MFCs) are an emerging technique presenting remarkable potential. In the current MFC, an electroactive biofilm anode was inoculated with activated sludge from a local municipal sewage treatment plant. The output voltage peaked at 0.60 V and 0.56 V in MFCs cultured with 2-chlorophenol (MFC-2-CP) and 2,4-dichlorophenol (MFC-2,4-DCP), respectively. The degradation and mineralization efficiency in MFC-2-CP were 100.0% and 82.0%, respectively. Based on the bacterial 16S rRNA gene sequence analysis, abundant Acinetobacter and Azospirillum existed during both the bioelectricity and biodegradation stages in MFC-2-CP, but different patterns were exhibited in MFC-2,4-DCP. The electrogenic bacteria relied on the electron transfer pathway of nicotinamide adenine dinucleotide dehydrogenase, succinate dehydrogenase and terminal oxidase, while the electrons were transferred to the extracellular electrode by cytochrome C, riboflavin, degradation products of CPs and flagella. 2-CP and 2,4-DCP were biodegraded into less toxic cyclohexanol via dichlorination, hydroxylation, and hydrogenation; hereafter, the ring was opened to generate long-chain hydrocarbons, and finally mineralized into CO2 and H2O. This work provided a new strategy for MFCs in power generation and contaminant treatment.

Uptake of Pb(II) onto microplastic-associated biofilms in freshwater: Adsorption and combined toxicity in comparison to natural solid substrates.

In the present study, microplastic-associated biofilms were cultivated in an urban lake and a reservoir using virgin expanded polystyrene (PS). The uptake of Pb(II) onto both natural (suspended particles and surficial sediment) and anthropogenic (virgin microplastics and microplastic-associated biofilms) solid substrates was investigated and compared as a function of contact time, pH, and ionic strength in batch adsorption experiments. The adsorption isotherms revealed that biofilms enhanced the adsorption capacity of Pb(II) onto microplastics; however, natural substrates still exhibited a higher capacity. Ionic strength and pH significantly influenced the adsorption of Pb(II) onto all of the solid substrates. Under neutral conditions, competitive adsorption of Pb(II) was observed between anthropogenic solid substrates and natural substrates, which may further alter the distribution of Pb(II) among these solid substrates. The combined toxicity tests of Pb(II) and each solid substrate were carried out using Daphnia magna, the results indicated biofilm enhanced the combined toxicity of Pb(II) and microplastics. Therefore, biofilms not only intensified the vector role of microplastics in the migration of heavy metals in freshwater, but also enhanced their combined toxicity, which may have further potential ecological risks to freshwater ecosystems.

Graphite-bridged indirect Z-scheme system TiO2-C-BiVO4 film with enhanced photoelectrocatalytic activity towards serial bisphenols.

Due to the increase in the occurrence of bisphenols (BPs) in the environments, it is urgent to develop efficient and ecofriendly methods for their removal. A novel, indirect Z-scheme TiO2-C-BiVO4 film was prepared by a sol-gel method combined with hydrothermal carbonization. The doped graphite carbon was generated in situ from glucose, which acted as an electron-transfer bridge for the Z-scheme system to enhance the heterojunction tightness between TiO2 and BiVO4. This resulted in an increasing separation efficiency of photogenerated electrons and holes and a stronger redox ability of the TiO2-C-BiVO4 film for the degradation and detoxification of BPs. The degradation efficiency of BPs was over 95% in 240 min, except for that of 4,4'-sulphonyldiphenol (BPS) due to the presence of the OSO group, and all of the BPs were nearly completely mineralized when the reaction time reached 360 min. Consequently, the inhibition ratio towards Vibrio fischeri decreased significantly along with the loss and mineralization of aromatic intermediates during photoelectrocatalytic degradation. 2,2-bis(4-Hydroxyphenyl) butane (BPB), 4,4'-(1-phenylethylidene)-bisphenol (BPAP), and (4,4'-hexafluoroisopropylidene) diphenol (BPAF), with relatively high toxicity levels and lipophilicity and as toxic product precursors, require attention in terms of environmental safety. Overall, this work provides a promising and environmentally friendly way to remove BPs from water.

Microplastics as an emerging anthropogenic vector of trace metals in freshwater: Significance of biofilms and comparison with natural substrates.

Microplastics (MPs) are ubiquitous in freshwater environments, and represent an emerging anthropogenic vector for contaminants, such as trace metals. In this study, virgin expanded polystyrene (PS) particles were placed in a eutrophic urban lake and a reservoir serving as the resource of domestic water for 4 weeks, to develop biofilms on the surface. For comparison, natural adsorbents in the form of suspended particles and surficial sediment were also sampled from these waterbodies. The trace metal adsorption properties of anthropogenic (virgin and biofilm covered microplastics) and natural substrates were investigated and compared via batch adsorption experiments. The adsorption isotherms fitted the Langmuir model, revealed that biofilms could enhance the trace metal adsorption capacity of MPs. However, natural substrates still had a greater adsorption capacity. Biofilms also alter the adsorption kinetics of trace metals onto MPs. The process of adsorption onto virgin MPs was dominated by intraparticle diffusion, whereas film diffusion governed adsorption onto biofilm covered microplastics and natural substrates. The trace metal adsorption of all the substrates was significantly dependent on pH and ionic strength. The adsorption mechanisms were further analyzed by SEM-EDS and FT-IR. The enhancement of adsorption was mainly attributed to complexation with functional groups contained in the biofilms, including carboxyl, amino, and phenyl-OH. Collectively, biofilm development intensifies the role of MPs in the migration and fate of trace metals in freshwater, since it does not give MPs an edge over natural substrates in adsorption.

Effects of conversion from boreal natural wetlands to rice paddy fields on the dynamics of total dissolved iron during extreme precipitation events.

Natural wetlands play a critical role in increasing the total dissolved Fe (TDFe) concentration in boreal fluvial systems. In the Sanjiang Plain, which is the largest concentrated distribution area of natural wetlands in China, over 80% of the natural wetlands have been converted to rice paddy fields (RPFs) during the last six decades; the altered hydrological processes are hypothesized to influence the dynamics of TDFe, particularly during extreme precipitation events (EPEs). In the current study, the TDFe dynamics in typical natural freshwater wetlands in the Sanjiang Plain were elucidated. The TDFe species including Fe(II), Fe(III) and colloidal Fe, were monitored in a Deyeucia angustifolia wetland (DAW), Carex lasiocarpa wetland (CLW), and RPF during the rainy season from 2012 to 2014. Compared to normal precipitation days, the average TDFe concentration increased significantlys in all wetlands during the EPEs, among which the fluctuation of TDFe during the EPEs was more largely in the RPF than in the natural wetlands. The dynamics of the TDFe speciation in the different wetlands also showed different patterns; moreover, TDFe and its species showed a significantly positive relationship with dissolved organic matter. With an increasing frequency of EPEs anticipated by climate change models, our results suggest higher levels of TDFe will be transported to the Amur River and Okhotsk Sea, which may potentially affect TDFe cycling, water quality and ecosystem dynamics.

Synthesis of graphene/black phosphorus hybrid with highly stable P-C bond towards the enhancement of photocatalytic activity.

Black phosphorus (BP), a superior two-dimensional (2D) semiconductor, has attracted much attention due to its unique properties. The graphene (GR)-BP hybrid was synthesized through one pot chemical vapor transport (CVT) approach. The characterization results indicated that P atom was successfully incorporated into GR by the formation of P-C bond. Remarkably, the newly-synthesized GR-BP represented high photocatalytic activity towards 2-chlorophenol (2-CP) degradation, due to the high efficiency of charge separation and transformation caused by the direct band gap of BP and carrier mobility of GR. The removal efficiency for 2-CP reached up to 87.08% within visible light irradiation for 180 min (λ > 420 nm). The degradation rate of GR-BP hybrid for 2-CP was approximately 7.29-fold than that of BP within 30 min. In addition, the little increasing of the peak for P-O bond in GR-BP hybrid was observed after being exposed in air for 15 days, meant that the stability of BP was significantly enhanced. It was caused by the decreasing of the oxidation sites in BP due to the formation of P-C bond in hybrid. In brief, our synthetic method for GR-BP not only provides a novel route for the improvement of the stability of BP, but also constitutes an insight into the promising practical application of BP in the photocatalysis field.

Heavy metals in Yinma River sediment in a major Phaeozems zone, Northeast China: Distribution, chemical fraction, contamination assessment and source apportionment.

Yinma River is a typical river in the major Phaeozems zone of Northeast China. It has been suffering an increasing environmental pressure from heavy metal contamination due to the rapid development of population, social-economy and urbanization as well as long term over cultivation. This study investigated the spatial distribution, chemical fraction of heavy metals (Cu, Pb, Zn, Cr, Cd, Ni, As, and Hg) in sediments of Yinma River based on BCR procedure, assessed the contamination level, and identified their sources via multivariate statistical analysis. The chemical fraction results indicated that Cd, Pb, Ni, and Zn exhibited higher mobility susceptibility and bioavailability with a significant and late anthropogenic origin. Hg and Cd might exert a potential hazardous influence on aquatic biota according to the geo-accumulation index (Igeo). The pollution load index (PLI) assessment suggested that all of the sediment samples have been contaminated. Multivariate statistical analysis revealed that Zn, Cu, Hg, Cd, and Pb reflected the anthropogenic sources with a close correlation with TOC and socio-economic development; Ni, As and Cr tended to represent the geochemical background. Furthermore, Changchun City and Shitoukoumen Reservoir as the major drinking water source may be hotspots of the heavy metal contamination in the watershed.

Preparation of the CNTs/AG/ITO electrode with high electro-catalytic activity for 2-chlorophenol degradation and the potential risks from intermediates.

A novel carbon nanotubes (CNTs)/agarose (AG)/ITO electrode with high electro-catalytic activity was prepared using a simple sol-gel method. Characterization results showed that the prepared CNTs/AG membrane, coated on the ITO conductive glass, was consisted of C and O. The electro-catalytic degradation for 2-chlorophenol (2-CP) and the influence factors were investigated. The results meant that electro-catalytic degradation for 2-CP was highly dependent on pH, bias voltage, and catalyst dosage. At pH 2, 4 V bias voltage, and 5 wt% CNTs dosage, the electro-catalytic efficiency of CNTs/AG/ITO electrode for 2-CP (20 mg/L) achieved 98% within 180 min. Afterwards, the electro-catalytic properties of recycling electrode, roles of the generated reactive oxygen species, and the reaction pathways were also investigated and proposed. In addition, the toxicities of the generated intermediates from the electro-catalytic degradation were calculated by easy methods. The results indicated that the toxicities of some intermediates were higher than the parent pollutant, especially the formation of 2-CP dimer which was seldom reported in the advanced oxidation process. The findings of using AG as the carrier and conductive adhesive for catalytic material and the assessment methods for the possible increasing risks from the intermediates were reported firstly in this paper.

A label-free electrochemical system for comprehensive monitoring of o-chlorophenol.

o-Chlorophenol (OCP) is a priority pollutant that poses serious health threats to the public. The following study designs a simple electrochemical system to monitor the concentration and toxicity of OCP. This system was primarily characterized by the integration of both physicochemical and biological monitoring procedures that had a synergistic effect between the functionalized carbon nanotubes and rhodamine B. This resulted in excellent electrocatalytic activities toward OCP and cellular purine bases. The peak current of OCP was linear with concentrations ranging from 0.05-125.0 µM and the detection limit was 0.028 µM under optimal testing conditions. There was an enhanced voltammetric signal detected that was caused by the guanine/xanthine of human hepatoma (HepG2) cells. The cytotoxicity of OCP to HepG2 cells was assessed using the proposed system. The obtained IC50 value was 512.86 µM. This study provided a fast, label-free, and low-cost platform for the comprehensive assessment of OCP. This is highly beneficial for simplifying the environmental monitoring process.

Design of plasmonic Ag-TiO2/H3PW12O40 composite film with enhanced sunlight photocatalytic activity towards o-chlorophenol degradation.

A series of plasmonic Ag-TiO2/H3PW12O40 composite films were fabricated and immobilized by validated preparation technique. The chemical composition and phase, optical, SPR effect and pore-structure properties together with the morphology of as-prepared composite film are well-characterized. The multi-synergies of as-prepared composite films were gained by combined action of electron-capture action via H3PW12O40, visible-response induced by Ag, and Schottky-junction formed between TiO2-Ag. Under simulated sunlight, the maximal K app of o-chlorophenol (o-CP) reached 0.0075 min-1 which was 3.95-fold larger than that of TiO2 film, while it was restrained obviously under acid condition. In the photocatalytic degradation process, ·OH and ·O2- attacked preferentially ortho and para position of o-CP molecule, and accordingly the specific degradation pathways were speculated. The novel composite film exhibited an excellent applicability due to self-regeneration of H3PW12O40, well-protection of metal Ag° and favorable immobilization.

Quantitative determination and toxicity evaluation of 2,4-dichlorophenol using poly(eosin Y)/hydroxylated multi-walled carbon nanotubes modified electrode.

This study aimed at developing simple, sensitive and rapid electrochemical approach to quantitatively determine and assess the toxicity of 2,4-dichlorophenol (2,4-DCP), a priority pollutant and has potential risk to public health through a novel poly(eosin Y, EY)/hydroxylated multi-walled carbon nanotubes composite modified electrode (PEY/MWNTs-OH/GCE). The distinct feature of this easy-fabricated electrode was the synergistic coupling effect between EY and MWNTs-OH that enabled a high electrocatalytic activity to 2,4-DCP. Under optimum conditions, the oxidation peak current enhanced linearly with concentration increasing from 0.005 to 0.1 µM and 0.2 to 40.0 µM, and revealed the detection limit of 1.5 nM. Moreover, the PEY/MWNTs-OH/GCE exhibited excellent electrocatalytic activity toward intracellular electroactive species. Two sensitive electrochemical signals ascribed to guanine/xanthine and adenine/hypoxanthine in human hepatoma (HepG2) cells were detected simultaneously. The sensor was successfully applied to evaluate the toxicity of 2,4-DCP to HepG2 cells. The IC50 values based on the two electrochemical signals are 201.07 and 252.83 µM, respectively. This study established a sensitive platform for the comprehensive evaluation of 2,4-DCP and posed a great potential to simplify environmental toxicity monitoring.

Comparative Study of Carbon Materials Synthesized "Greenly" for 2-CP Removal.

Carbon nanotubes (CNTs), graphene (GA) and carbon nanospheres (CNSs) were prepared respectively using grass (Festucaarundinace) as the sole carbon resource by solvothermal method and characterized as adsorbent and photocatalyst for 2-chlorophenol (2-CP) removal in water. With H2O2/HNO3/H2SO4, the CNTs were firstly produced from grass (Festucaarundinace) at 300 °C by hydrolysis and oxidization, the CNTs were secondly opened to form the GA by oxidization at 400 °C, and the GA was lastly rolled-up to form the CNSs by oxidization at 500 °C. All adsorption equilibration of the CNTs, GA, and CNSs for 2-CP were achieved within 120 min, and 60.35%, 20.12%, and 76.22% of 2-CP (5 mg L(-1), pH = 6.3) were adsorbed, respectively. Furthermore, the high removal rates of 2-CP were about 88.23%, 92.90%, and 79.64% by the CNTs, GA, and CNSs, after 120 min adsorption and 160 min irradiation. On the basis of these results, the CNSs were suitable for removal 2-CP as adsorbent, and the GA was suitable as photocatalyst. The photooxidation of 2-CP was mainly initiated by O2(·-) or ·OH which was generated from the combine with simulated sunlight and the CNTs or GA, respectively. However, the CNTs was not suitable for removal 2-CP owing to the increasing toxicity.

Flux characteristics of total dissolved iron and its species during extreme rainfall event in the midstream of the Heilongjiang River.

The occurrence of extreme rainfall events and associated flooding has been enhanced due to climate changes, and is thought to influence the flux of total dissolved iron (TDI) in rivers considerably. Since TDI is a controlling factor in primary productivity in marine ecosystems, alteration of riverine TDI input to the ocean may lead to climate change via its effect on biological productivity. During an extreme rainfall event that arose in northeastern China in 2013, water samples were collected in the midstream of the Heilongjiang River to analyze the concentration and species of TDI as well as other basic parameters. The speciation of TDI was surveyed by filtration and ultrafiltration methods. Compared with data monitored from 2007 to 2012, the concentration of TDI increased significantly during this event, with an average concentration of 1.11 mg/L, and the estimated TDI flux reached 1.2×10(5) tons, equaling the average annual TDI flux level. Species analysis revealed that low-molecular-weight complexed iron was the dominant species, and the impulse of TDI flux could probably be attributed to the hydrological connection to riparian wetlands and iron-rich terrestrial runoff. Moreover, dissolved organic matter played a key role in the flux, species and bioavailability of TDI. In addition, there is a possibility that the rising TDI flux could further influence the transport and cycling of nutrients and related ecological processes in the river, estuary coupled with the coastal ecosystems, which merits closer attention in the future.

Speciation of Cu and Zn during composting of pig manure amended with rock phosphate.

Pig manure usually contains a large amount of metals, especially Cu and Zn, which may limit its land application. Rock phosphate has been shown to be effective for immobilizing toxic metals in toxic metals contaminated soils. The aim of this study work was to investigate the effect of rock phosphate on the speciation of Cu and Zn during co-composting of pig manure with rice straw. The results showed that composting process and rock phosphate addition significantly affected the changes of metal species. During co-composting, the exchangeable and reducible fractions of Cu were transformed to organic and residue fractions, thus the bioavailable Cu fractions were decreased. The rock phosphate addition enhanced the metal transformation depending on the level of rock phosphate amendment. Zinc was found in the exchangeable and reducible fractions in the compost. The bioavailable Zn fraction changed a little during the composting process. The composting process converted the exchangeable Zn fraction into reducible fraction. Addition of an appropriate amount (5.0%) of rock phosphate could advance the conversion. Rock phosphate could reduce metal availability through adsorption and complexation of the metal ions on inorganic components. The increase in pH and organic matter degradation could be responsible for the reduction in exchangeable and bioavailable Cu fractions and exchangeable Zn fraction in rock phosphate amended compost.