Simultaneously reducing methane emissions and arsenic mobility by birnessite in flooded paddy soil: Overlooked key role of organic polymerisation.

Flooding of paddy fields enhances methane (CH4) emissions and arsenic (As) mobilisation, which are crucial issues for agricultural greenhouse gas emissions and food safety. Birnessite (δ-MnO2) is a common natural oxidant and scavenger for heavy metals. In this study, birnessite was applied to As-contaminated paddy soil. The capacity for simultaneously alleviating CH4 emissions and As mobility was explored. Soil microcosm incubation results indicated that birnessite addition simultaneously reduced CH4 emissions by 47 %-54 % and As release by 38 %-85 %. The addition of birnessite decreased the dissolved organic carbon (DOC) contents and altered its chemical properties. Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS) results showed that birnessite reduced the labile fractions of proteins, carbohydrates, lignins, tannins, and unsaturated hydrocarbons, however, increased the abundance of condensed aromatic structures, suggesting the polymerisation of dissolved organic matter (DOM) by birnessite. The degradation of labile fractions and the polymerisation of DOM resulted in an inventory of recalcitrant DOM, which is difficult for microbes to metabolise, thus inhibiting methanogenesis. In contrast, birnessite addition increased CH4 oxidation, as the particulate methane monooxygenase (pmoA) gene abundance increased by 30 %. The enhanced polymerisation of DOM by birnessite also increased As complexation with organics, leading to the transfer of As to the organic bound phase. In addition, the decrease in ferrous ion [Fe(II)] concentrations with birnessite indicated that the reductive dissolution of Fe oxides was suppressed, which limited the release of arsenite [As(III)] under reducing conditions. Furthermore, birnessite decreased As methylation and shaped the soil microbial community structure by enriching the metal-reducing bacterium Bacillus. Overall, our results provide a promising method to suppress greenhouse gas emissions and the risk of As contamination in paddy soils, although further studies are needed to verify its efficacy and effectiveness under field conditions.

Nanoscale exopolymer reassembly-trap mechanism determines contrasting PFOS exposure patterns in aquatic animals with different feeding habitats: A nano-visualization study.

The behavior and fate of PFOS (perfluorooctanesulfonate) in the aquatic environment have received great attention due to its high toxicity and persistence. The nanoscale supramolecular mechanisms of interaction between PFOS and ubiquitous EPS (exopolymers) remain unclear though EPS have been widely-known to influence the bioavailability of PFOS. Typically, the exposure patterns of PFOS in aquatic animals changed with the EPS-PFOS interaction are not fully understood. This study hypothesized that PFOS exposure and accumulation pathways depended on the PFOS-EPS interactive assembly behavior and animal species. Two model animals, zebrafish and chironomid larvae, with different feeding habitats were chosen for the exposure and accumulation tests at the environmental concentrations of PFOS in the absence and presence of EPS. It was found that PFOS triggered the self-assembly of EPS to form large aggregates which significantly trapped PFOS. PFOS accumulation was significantly promoted in zebrafish but drastically reduced in chironomid larvae because of the nanoscale interactive assembly between EPS and PFOS. The decreased dermal uptake but increased oral uptake of PFOS by zebrafish with large mouthpart size could be ascribed to the increased ingestion of PFOS-enriched EPS aggregates as food. For the chironomid larvae with small mouthpart size, the PFOS-EPS assemblies reduced the dermal, oral and intestinal uptake of PFOS. The nano-visualization evidences confirmed that the PFOS-enriched EPS-PFOS assemblies blocked PFOS penetration through skin of both animals. These findings provide novel knowledge about the ecological risk of PFOS in aquatic environments.

Encapsulation and release of tetrabromobisphenol A in microplastics: Trade-off in their individual toxicity to Xenopus tropicalis tadpoles.

The toxicity of microplastics (MPs) to aquatic animals is closely related to the presence and release kinetics of contained additives, as most plastic products contain various additives. However, the relationship between the occurrence and release of additives from MPs, and their individual or combined toxicity remains unclear. In this study, the nanoscale distribution and release of tetrabromobisphenol A (TBBPA, a common flame retardant with endocrine-disrupting effect) in polystyrene (PS) MPs, and the long-term (60 days) toxicity of TBBPA and MPs containing TBBPA (at doses of 0 %, 1 %, 10 %, w/w) to Xenopus tropicalis tadpoles were investigated. Exposure to 10 µg/L TBBPA alone was the most toxics, while the encapsulation of TBBPA in MPs significantly delayed its lethal toxicity to tadpoles by inhibiting the rapid and extensive release of TBBPA. PS MPs alone and MPs containing 10 % TBBPA exhibited delayed survival toxicity compared to TBBPA alone, whereas PS MPs containing 1 % TBBPA did not show this effect but inhibited growth. These findings suggest that chronic toxicity assessments should be based on long-term (months or even years) exposure experiments due to the encapsulation-controlled slow release of toxic additives.

MGDA-assisted plant washing agent for improving the removal of Cd and Cu from farmland soils.

Utilizing plant extracts for soil washing is a promising and cost-efficient strategy to permanently remove toxic metals from farmland soils. However, the efficiency of current plant extracts in heavy metals removal is constrained by the need of excessively high liquid-solid ratios (>10:1), which limits their practical application in the farmland soils. To address this challenge, we developed a novel binary washing agent consisting of Fructus mume residue extract (RPM) and methylglycinediacetate acid (MGDA). Through optimization experiments, we determined an optimal composition of 50 g L-1 RPM and 0.34 g L-1 MGDA (RPMG3), which exhibited a remarkable synergistic effect on the removal of Cd and Cu from two polluted farmland soils. Compared to the single use of RPM or MGDA, RPMG3 increased metal removal efficiency by 44.6%-303.8% in the alkaline dryland soil and 55.8%-141.9% in the slightly acidic paddy soil, at an optimum liquid-solid ratio of 2:1. The contents of soil Cd and Cu can be reduced to below the risk screening values via acid activation, metal ion exchange, and complexation of functional groups. Moreover, the potential ecological risks associated with Cd in the soils were significantly mitigated due to the decrease in exchangeable and reducible Cd fractions following RPMG3 washing. Additionally, RPM and RPMG3 washing led to enhancements in soil organic carbon and nutrient concentrations, as well as increased activities of soil enzymes including catalase, urease, and ß-glucosidase. Notably, RPMG3 washing exhibited the most pronounced promotion effect on wheat seed germination and growth. Taken together, the binary complex of RPMG3 demonstrates potential as an environmentally friendly green washing agent capable of in reducing heavy metals from farmland soil with great efficiency, even at low liquid-solid ratios.

Non-radical oxidation driven by iron-based materials without energy assistance in wastewater treatment.

Chemical oxidation is extensively utilized to mitigate the impact of organic pollutants in wastewater. The non-radical oxidation driven by iron-based materials is noted for its environmental friendliness and resistance to wastewater matrix, and it is a promising approach for practical wastewater treatment. However, the complexity of heterogeneous systems and the diversity of evolutionary pathways make the mechanisms of non-radical oxidation driven by iron-based materials elusive. This work provides a systematic review of various non-radical oxidation systems driven by iron-based materials, including singlet oxygen (1O2), reactive iron species (RFeS), and interfacial electron transfer. The unique mechanisms by which iron-based materials activate different oxidants (ozone, hydrogen peroxide, persulfate, periodate, and peracetic acid) to produce non-radical oxidation are described. The roles of active sites and the unique structures of iron-based materials in facilitating non-radical oxidation are discussed. Commonly employed identification methods in wastewater treatment are compared, such as quenching, chemical probes, spectroscopy, mass spectrometry, and electrochemical testing. According to the process of iron-based materials driving non-radical oxidation to remove organic pollutants, the driving factors at different stages are summarized. Finally, challenges and countermeasures are proposed in terms of mechanism exploration, detection methods and practical applications of non-radical oxidation driven by iron-based materials. This work provides valuable insights for understanding and developing non-radical oxidation systems.

Vanadium as a Ti-like mediator boosting electronic transmission in Fe-based MOFs for photocatalytic sterilization.

Efficient metal-organic frameworks (MOFs) photocatalytic bactericidal catalysts are urgently needed in water purification. Herein, a Fe-MOF (MIL-88B-NH2(V1Fe5) with promoted electron transport was achieved by vanadium (V) ions doping and V/Fe ratio optimization, showing excellent photocatalytic bactericidal activity againstE. coliunder visible light irradiation (99.92%). The efficient antibacterial mechanism, V as a Ti-like mediator boosting electronic transmission in MIL-88B-NH2(V1Fe5), was revealed by its band structure, transient photocurrent, electrochemical impedance spectroscopy, and scavenger quenching experiments. The enhancement of photocatalytic bactericidal performance of Fe-MOFs by V-ion-doping was confirmed by two other Fe-MOFs, MIL-53-NH2(V1Fe5) and MIL-101-NH2(V1Fe5), with the same metal ions and ligands, both of which have higher performance than the corresponding undoped MOFs. Among them, MIL-88B-NH2(V1Fe5) exhibits the highest photocatalytic bactericidal activity due to its suitable metal clusters ([M(µ3-O)] cluster) and topological structure (three-dimensional rhomboid network structure). This work demonstrated the amplification effect of V ion doping on electron transport in Fe-MOFs photocatalysts.

Engineering valence-mismatched Ti4+ into Fe-based metal-organic-frameworks for enhanced photocatalytic CO2 reduction.

A series of low-dose high-valence Ti4+ doped MIL-53-NH2(Fe) photocatalysts were synthesized for visible-light-driven CO2 reduction. The highest CO2-to-CO conversion rate of Ti4+ doped MIL-53-NH2(Fe) was 7.24 mmol g-1 h-1 and the highest CO selectivity was 94% in acetonitrile solvent using [Ru(bpy)3]2+ and triethanolamine.

How micro-/nano-plastics influence the horizontal transfer of antibiotic resistance genes - A review.

Plastic debris such as microplastics (MPs) and nanoplastics (NPTs), along with antibiotic resistance genes (ARGs), are pervasive in the environment and are recognized as significant global health and ecological concerns. Micro-/nano-plastics (MNPs) have been demonstrated to favor the spread of ARGs by enhancing the frequency of horizontal gene transfer (HGT) through various pathways. This paper comprehensively and systematically reviews the current study with focus on the influence of plastics on the HGT of ARGs. The critical role of MNPs in the HGT of ARGs has been well illustrated in sewage sludge, livestock farms, constructed wetlands and landfill leachate. A summary of the performed HGT assay and the underlying mechanism of plastic-mediated transfer of ARGs is presented in the paper. MNPs could facilitate or inhibit HGT of ARGs, and their effects depend on the type, size, and concentration. This review provides a comprehensive insight into the effects of MNPs on the HGT of ARGs, and offers suggestions for further study. Further research should attempt to develop a standard HGT assay and focus on investigating the impact of different plastics, including the oligomers they released, under real environmental conditions on the HGT of ARGs.

Active anaerobic methane oxidation in the groundwater table fluctuation zone of rice paddies.

Rice paddies are globally important sources of methane emissions and also active regions for methane consumption. However, the impact of fluctuating groundwater levels on methane cycling has received limited attention. In this study, we delved into the activity and microbial mechanisms underlying anaerobic oxidation of methane (AOM) in paddy fields. A comprehensive approach was employed, including 13C stable isotope assays, inhibition experiments, real-time quantitative reverse transcription PCR, metagenomic sequencing, and binning technology. Geochemical profiles revealed the abundant coexistence of both methane and electron acceptors in the groundwater table fluctuation (GTF) zone, at a depth of 40-60 cm. Notably, the GTF zone exhibited the highest rate of AOM, potentially linked to the reduction of iron oxides and nitrate. Within this zone, Candidatus Methanoperedens (belonging to the ANME-2d group) dominated the Archaea population, accounting for a remarkable 85.4 %. Furthermore, our results from inhibition experiments, RT-qPCR, and metagenome-assembled genome (MAG) analysis highlighted the active role of Ca. Methanoperedens GTF50 in the GTF zone. This microorganism could independently mediate AOM process through the intriguing "reverse methanogenesis" pathway. Considering the similarity in geochemical conditions across different paddy fields, it is likely that Ca. Methanoperedens-mediated AOM is prevalent in the GTF zones.

Traceability of Microplastic Fragments from Waste Plastic Express Packages Using Near-Infrared Spectroscopy Combined with Chemometrics.

The pollution from waste plastic express packages (WPEPs), especially microplastic (MP) fragments, caused by the blowout development of the express delivery industry has attracted widespread attention. On account of the variety of additives, strong complexity, and high diversity of plastic express packages (PEPs), the multi-class classification of WPEPs is a typical large-class-number classification (LCNC). The traceability and identification of microplastic fragments from WPEPs is very challenging. An effective chemometric method for large-class-number classification would be very beneficial for the comprehensive treatment of WPEP pollution through the recycling and reuse of waste plastic express packages, including microplastic fragments and plastic debris. Rather than using the traditional one-against-one (OAO) and one-against-all (OAA) dichotomies, an exhaustive and parallel half-against-half (EPHAH) decomposition, which overcomes the defects of the OAO's classifier learning limitations and the OAA's data proportion imbalance, is proposed for feature selection. EPHAH analysis, combined with partial least squares discriminant analysis (PLS-DA) for large-class-number classification, was performed on 750 microplastic fragments of polyethylene WPEPs from 10 major courier companies using near-infrared (NIR) spectroscopy. After the removal of abnormal samples through robust principal component analysis (RPCA), the root mean square error of cross-validation (RMSECV) value for the model was reduced to 0.01, which was 21.5% lower than that including the abnormal samples. The best models of PLS-DA were obtained using SNV combined with SG-17 smoothing and 2D (SNV+SG-17+2D); the latent variables (LVs), the error rates of Monte Carlo cross-validation (ERMCCVs), and the final classification accuracies were 6.35, 0.155, and 88.67% for OAO-PLSDA; 5.37, 0.103, and 87.33% for OAA-PLSDA; and 3.12, 0.054, and 96.00% for EPHAH-PLSDA. The results showed that the EPHAH strategy can completely learn the complex LCNC decision boundaries for 10 classes, effectively break the tie problem, and greatly improve the voting resolution, thereby demonstrating significant superiority to both the OAO and OAA strategies in terms of classification accuracy. Meanwhile, PLS-DA further maximized the covariance and data interpretation abilities between the potential variables and categories of microplastic debris, thereby establishing an ideal performance identification model with a recognition rate of 96.00%.

Phthalocyanine blue leaching and exposure effects on Microcystis aeruginosa (cyanobacteria) of photoaged microplastics.

Light-stabilizing additives may contribute to the overall pollution load of microplastics (MPs) and potentially enter the food chain, severely threatening aquatic life and human health. This study investigated the variation between polystyrene (PS) MPs and phthalocyanine blue (CuPC)-containing MPs before and after photoaging, as well as their effects on Microcystis aeruginosa. The presence of PS-MPs increased cell mortality, antioxidant enzyme activity, and the variation in extracellular components, while the presence of CuPC exacerbated these variations. CuPC-containing MPs caused different increasing trends in superoxide dismutase and malondialdehyde activities due to electron transfer across the membrane. Transcriptomic analysis revealed that the MPs and CuPC affected various cellular processes, with the greatest impact being on cell membranes. Compared with MPs, CuPC negatively affected ribosome and polysaccharide formation. These findings provide insights into the molecular mechanisms underlying the cellular response to MPs and their associated light-stabilizer pollution and imply the necessity for mitigating the pollution of both MPs and light-stabilizers.

Microbial antagonistic mechanisms of Hg(II) and Se(IV) in efficient wastewater treatment using granular sludge.

The antagonistic effects of mercury (Hg) and selenium (Se) have been extensively studied in higher animals and plants. In this study, the microbial antagonistic effects of Hg and Se were utilized for wastewater treatment. We developed and optimized a new granular sludge approach to efficiently remove Hg(II) and Se(IV) from wastewater. Under anaerobic-oxic-anaerobic (AOA) conditions, the removal rates of Hg(II) and Se(IV) reached up to 99.91±0.07 % and 97.7 ± 0.8 %, respectively. The wastewater Hg(II) was mostly (97.43±0.01 %) converted to an inert mineral called tiemannite (HgSe) in the sludge, and no methylmercury (MeHg) was detected. The HgSe in sludge is less toxic, with almost no risk of secondary release, and it can be recovered with high purity. An inhibition experiment of mercury reduction and the high expression of the mer operon indicated that most Hg(II) (∼71 %) was first reduced to Hg0, and then Hg0 reacted with Se0 to synthesize HgSe. Metagenomic results showed that the final sludge (day 182) was dominated by two unclassified bacteria in the orders Rhodospirillales (27.7 %) and Xanthomonadales (6.3 %). Their metagenome-assembled genomes (MAGs) were recovered, suggesting that both of them can reduce Hg(II) and Se(IV). Metatranscriptomic analyses indicate that they can independently and cooperatively synthesize HgSe. In summary, granular sludge under AOA conditions is an efficient method for removing and recovering Hg from wastewater. The microbial transformation of Hg2+to Hg0 to HgSe may occur widely in both engineering and natural ecosystems.

Macronutrient and PFOS bioavailability manipulated by aeration-driven rhizospheric organic nanocapsular assembly.

Ubiquitous presence of the extremely persistent pollutants, per- and polyfluoroalkyl substances, is drawing ever-increasing concerns for their high eco-environmental risks which, however, are insufficiently considered based on the assembly characteristics of those amphiphilic molecules in environment. This study investigated the re-organization and self-assembly of perfluorooctane sulfonate (PFOS) and macronutrient molecules from rhizospheric organic (RhO) matter induced with a common operation of aeration. Atomic force microscopy (AFM) with infrared spectroscopy (IR)-mapping clearly showed that, after aeration and stabilization, RhO nanocapsules (∼ 1000 nm or smaller) with a core of PFOS-protein complexes coated by "lipid-carbohydrate" layers were observed whereas the capsule structure with a lipid core surrounded by "protein-carbohydrate-protein" multilayers was obtained in the absence of PFOS. It is aeration that exerted the disassociation of pristine RhO components, after which the environmental concentration PFOS restructured the self-assembly structure in a conspicuous "disorder-to-order" transition. AFM IR-mapping analysis of faeces combined with quantification of component uptake denoted the decreased ingestion and utilization of both PFOS and proteins compared with lipids and carbohydrates when Daphnia magna were fed with RhO nanocapsules. RhO nanocapsules acted as double-edged swords via simultaneously impeding the bioaccessibility of hazardous PFOS molecules and macronutrient proteins; and the latter might be more significant, which caused a malnutrition status within merely 48 h. Elucidating the assembly structure of natural organic matter and environmental concentration PFOS, the finding of this work could be a crucial supplementation to the high-dose-dependent eco-effect investigations on PFOS.

Influence mechanism of anions on iron doping into swine bone char: Promoting non-radical oxidation of acetaminophen in a Fenton-like system.

The application of iron-doped biochar in peroxymonosulfate (PMS) activation systems has gained increasing attention due to their effectiveness and environmental friendliness in addressing environmental issues. However, the behavioral mechanism of iron doping and the detailed 1O2 generation mechanism in PMS activation systems remain ambiguous. Here, we investigated the effects of three anions (Cl-, NO3-and SO42-) on the process of iron doping into bone char, leading to the synthesis of three iron-doped bone char (Fe-ClBC, Fe-NBC and Fe -SBC). These iron-doped bone char were used to catalyze PMS to degrade acetaminophen (APAP) and exhibited the following activity order: Fe-ClBC > Fe-NBC > Fe-SBC. Characterization results indicated that iron doping primarily occurred through the substitution of calcium in hydroxyapatite within BC. In the course of the impregnation, the binding of SO42- and Ca2+ hindered the exchange of iron ions, resulting in lower catalytic activity of Fe-SBC. The primary reactive oxygen species in the Fe-ClBC/PMS and Fe-NBC/PMS systems were both 1O2. 1O2 is produced through O2•- conversion and PMS self-dissociation, which involves the generation of metastable iron intermediates and electron transfer within iron species. The presence of oxygen vacancies and more carbon defects in the Fe-ClBC catalyst facilitates 1O2 generation, thereby enhancing APAP degradation within the Fe-ClBC/PMS system. This study is dedicated to in-depth exploration of the mechanisms underlying iron doping and defect materials in promoting 1O2 generation.

Probing the molecular interaction between photoaged polystyrene microplastics and fulvic acid.

As emerging contaminants, microplastics (MPs) are becoming a matter of global concern, and they have complex interactions with dissolved organic matter (DOM) widely present in aqueous environments. Here, we investigate the molecular interactions between aged polystyrene microplastics (PS-MPs) and fulvic acid (FA) under neutral conditions using a series of analytical techniques. The structural changes of FA and the binding interactions of PS-MPs with FA at a molecular level were explored by fluorescence and FT-IR combined with two-dimensional correlation spectroscopy (2D-COS). Results showed that photoaging of PS-MPs changed the sequence of structural variations with FA. Atomic force microscopy-infrared spectroscopy (AFM-IR) strongly demonstrated that the surface roughness of both pristine and aged PS-MPs greatly increased after FA addition. Meanwhile, AFM-IR and Raman spectroscopy revealed a stronger interaction between aged PS-MPs and FA. The content of oxygen-containing functional groups in PS-MPs increased after aging and after binding with FA, and surface distribution of these functional groups also changed. XPS analyses indicated that the oxygen content in PS-MPs increased after the interaction with FA and the increase in oxygen content was even greater in aged PS-MPs. Overall, these research findings are useful to understand the environmental impacts of DOM-MPs interactions and to address the uncertainty of MPs aging effect on their environmental behavior in aquatic ecosystems.

A systematic review of antibiotic resistance driven by metal-based nanoparticles: Mechanisms and a call for risk mitigation.

Elevations in antibiotic resistance genes (ARGs) are due not only to the antibiotic burden, but also to numerous environmental pressures (e.g., pesticides, metal ions, or psychotropic pharmaceuticals), which have led to an international public health emergency. Metal-based nanoparticles (MNPs) poison bacteria while propelling nanoresistance at ambient or sub-lethal concentrations, acting as a wide spectrum germicidal agent. Awareness of MNPs driven antibiotic resistance has created a surge of investigation into the molecule mechanisms of evolving and spreading environmental antibiotic resistome. Co-occurrence of MNPs resistance and antibiotic resistance emerge in environmental pathogens and benign microbes may entail a crucial outcome for human health. In this review we expound on the systematic mechanism of ARGs proliferation under the stress of MNPs, including reactive oxygen species (ROS) induced mutation, horizontal gene transfer (HGT) relevant genes regulation, nano-property, quorum sensing, and biofilm formation and highlighting on the momentous contribution of nanoparticle released ion. As antibiotic resistance pattern alteration is closely knit with the mediate activation of nanoparticle in water, soil, manure, or sludge habitats, we have proposed a virulence and evolution based antibiotic resistance risk assessment strategy for MNP contaminated areas and discussed practicable approaches that call for risk management in critical environmental compartments.

Polysaccharide preferred minority-dominant community assembly and exoenzyme enrichment in transparent exopolymer particles: Implication for global carbon cycle in water.

The ubiquitous transparent exopolymer particles (TEPs) are an important organic carbon pool and an ideal microhabitat for bacteria in aquatic environments. They play a crucial role in the global carbon cycle. Organic matter transformation and carbon turnover in TEPs strongly depend on the assembly of their associated bacterial communities and enzyme activity. However, the mechanisms of bacterial community assembly and their potential effects on the organic carbon cycle in TEPs are still unclear. In this study, we comparatively explored the community assembly of TEP-associated bacteria and bacterioplankton from surface freshwater using metagenomics. It was found that the bacterial community assembly in TEPs followed a minority-dominant rule and was governed by homogeneous selection. Pseudomonadota and Actinomycetota, which are responsible for polysaccharide degradation, serve as taxon-specific biomarkers among the abundant and diverse bacteria in TEPs. The network of TEP-associated bacteria displayed stronger robustness than that of bacterioplankton. Bin 76 (majorly Acinetobacter) was the overwhelmingly dominant taxa in TEPs, whereas there was no clearly dominant taxa in TEP-free water. Exoenzyme analysis showed that 64 out of 71 identified polysaccharide hydrolases were markedly linked with the dominant bin 76 in TEPs, while no such linkage was observed for bacterioplankton. Generally, Acinetobacter, which is capable of utilizing polysaccharides, is preferred to be assembled in TEPs together with high polysaccharide hydrolase activity. This may significantly accelerate the turnover of organic carbon in the giant global TEP pool. These findings are important for a deep understanding of the carbon cycle in water.

Photochemical demethylation of methylmercury (MeHg) in aquatic systems: A review of MeHg species, mechanisms, and influencing factors.

Photodemethylation is the major pathway of methylmercury (MeHg) demethylation in surface water before uptake by the food chain, whose mechanisms and influence factors are still not completely understood. Here, we review the current knowledge on photodemethylation of MeHg and divide MeHg photolysis into three pathways: (1) direct photodemethylation, (2) free radical attack, and (3) intramolecular electron or energy transfer. In aquatic environments, dissolved organic matter is involved into all above pathways, and due to its complex compositions, properties and concentrations, DOM poses multiple functions during the PD of MeHg. DOM-MeHg complex (mainly by sulfur-containing molecules) might weaken the C-Hg bond and enhance PD through both direct and indirect pathways. In special, synergistic effects of both strong binding sites and chromophoric moieties in DOM might lead to intramolecular electron or energy transfer. Moreover, DOM might play a role of radical scavenger; while triplet state DOM, which is generated by chromophoric DOM under light, might become a source of free radicals. Apart from DOMs, transition metals, halides, NO3-, NO2-, and carbonates also act as radical initialaters or scavengers, and significantly pose effects on radical demethylation, which is generally mediated by hydroxyl radicals and singlet oxygen. Environmental factors such as pH, light wavelength, light intensity, dissolved oxygen, salinity, and suspended particles also affect the PD of MeHg. This study assessed previously published works on three major mechanisms, with the goal of providing general estimates for photodemethylation under various environment factors according to know effects, and highlighting the current uncertainties for future research directions.

Iron-doped swine bone char as hydrogen peroxide activator for efficient removal of acetaminophen in water.

Bone char is a functional material obtained by calcining animal bones and is widely used for environmental remediation. In this work, iron was inserted into porcine bone-derived bone char via ion exchange to synthesize iron-doped bone char (Fe-BC) for efficient catalysis of hydrogen peroxide. This is the first time that Fe-BC has been used as a catalyst for the activation of H2O2. The effectiveness of the Fe-BC catalyst was influenced by the annealing temperature and the amount of iron doping. The results showed that the activation of H2O2 by the Fe-BC catalyst with the best catalytic performance could achieve 97.6% of APAP degradation within 30 min. Insights from electron paramagnetic resonance (EPR), free radical scavenging experiments and linear sweep voltammetry (LSV) proposed a reaction mechanism based on free radicals dominated degradation pathways (OH and O2-). Iron served as the primary active site in Fe-BC, with defect sites and oxygen-containing groups in the catalyst also contributing to the removal of pollutants. The Fe-BC/H2O2 system demonstrated resilience to interference from common anions (Cl-, NO3-, SO42- and HCO3-) in water, but was less effective against humic acid (HA). Based on the detection of intermediates produced during APAP degradation, possible degradation pathways of APAP were proposed and the toxicity of intermediates was evaluated. This work provides fresh insights into the use of heterogeneous Fenton catalysts for the removal of organic pollutants from water.

Deterioration of single-use biodegradable plastics in high-humidity air and freshwaters over one year: Significant disparities in surface physicochemical characteristics and degradation rates.

More single-use plastics are accumulating in the environment, and likewise biodegradable plastics (BPs), which are being vigorously promoted, cannot escape the fate. Currently, studies on the actual degradation of BPs in open-air and freshwaters are underrepresented despite they are potentially headmost leakage and contamination sites for disposable BPs. Herein, we compared the degradation behavior of six BP materials and non-degradable polypropylene (PP) plastics over a 1-year in situ suspension in the high-humidity air, a eutrophic river, and an oligotrophic lake. Moreover, a 3-months laboratory incubation was performed to detect the release of dissolved organic carbon (DOC) from BPs. In both air and freshwaters, poly(p-dioxanone) (PPDO) degraded significantly while PP and polylactic acid (PLA) showed no signs of degradation. The average degradation rates of three poly(butylene adipate-co-terephthalate) (PBAT)-based films varied: 100% in river, 55% in lake, and 10% in air. In addition to PLA, surface chemical groups, hydrophilicity, and thermal stability of BPs changed, and microplastics were found on their surfaces. Correspondingly, BPs with faster degradation rates released relatively higher amounts of DOC. Environmental microbial and chemical characteristics may contribute to differences in BP degradation besides polymer specificity. Altogether, our results indicate the need for appropriate monitoring of BPs.