Procedures from samples to sulfur isotopic data: A review.

RATIONALE: Sulfur isotopes have been widely used to solve some key scientific questions, especially in the last two decades with advanced instruments and analytical schemes. Different sulfur speciation and multiple isotopes analyzed in laboratories worldwide and in situ microanalysis have also been reported in many articles. However, methods of sampling to measurements are multifarious, and occasionally some inaccuracies are present in published papers. Vague methods may mislead newcomers to the field, puzzle readers, or lead to incorrect data-based correlations. METHODS: We have reviewed multiple methods on sulfur isotopic analyses from the perspectives of sampling, laboratory work, and instrumental analysis in order to help reduce operational inhomogeneity and ensure the fidelity of sulfur isotopic data. We do not deem our proposed solutions as the ultimate standard methods but as a lead-in to the overall introduction and summary of the current methods used. RESULTS: It has been shown that external contamination and transformation of different sulfur species should be avoided during the sampling, pretreatment, storage, and chemical treatment processes. Conversion rates and sulfur isotopic fractionations during sulfur extraction, purification, and conversion processes must be verified by researchers using standard or known samples. The unification of absence of isotopic fractionation is needed during all steps, and long-term monitoring of standard samples is recommended. CONCLUSION: This review compiles more details on different methods in sampling, laboratory operation, and measurement of sulfur isotopes, which is beneficial for researchers' better practice in laboratories. Microanalyses and molecular studies are the frontier techniques that compare the bulk sample with the elemental analysis/continuous flow-gas source stable isotope ratio mass spectrometry method, but the latter is widely used. The development of sulfur isotopic measurements will lead to the innovation in scientific issues with sulfur proxies.

Multiple Sulfur Isotopic Evidence for Sulfate Formation in Haze Pollution.

The mechanism of sulfate formation during winter haze events in North China remains largely elusive. In this study, the multiple sulfur isotopic composition of sulfate in different grain-size aerosol fractions collected seasonally from sampling sites in rural, suburban, urban, industrial, and coastal areas of North China are used to constrain the mechanism of SO2 oxidation at different levels of air pollution. The Δ33S values of sulfate in aerosols show an obvious seasonal variation, except for those samples collected in the rural area. The positive Δ33S signatures (0‰ < Δ33S < 0.439‰) observed on clean days are mainly influenced by tropospheric SO2 oxidation and stratospheric SO2 photolysis. The negative Δ33S signatures (-0.236‰ < Δ33S < ∼0‰) observed during winter haze events (PM2.5 > 200 µg/m3) are mainly attributed to SO2 oxidation by H2O2 and transition metal ion catalysis (TMI) in the troposphere. These results reveal that both the H2O2 and TMI pathways play critical roles in sulfate formation during haze events in North China. Additionally, these new data provide evidence that the tropospheric oxidation of SO2 can produce significant negative Δ33S values in sulfate aerosols.

A modified high-yield method for primary culture of rat retinal microglial cells.

Microglial cells are the main immune cells of the retina. The primary culture of the retinal microglia is critically important in investigating the cells' properties and behaviors in neurodegenerative and inflammatory retinal disease. Here, we described a modified protocol of a microglial cell culture from the neonatal rat retina. In our culture protocol, the retina was isolated from the neonatal rat eye from postnatal day 1 to day 3 and trypsinized into a single-cell suspension. The cells were seeded into a T75 flask, which was pre-coated with poly-D-lysine (PDL) and cultured with dulbecco's modified eagle medium-F12 (DMEM/F12) that contained 10% fetal bovine serum (FBS) with different concentrations. Small bright rounded cells were observed on the top of mixed glial cells on the seventh day, and attained the maximum cell number on the 14th day. Then, the isolation was performed by a shaking method and isolated cells were identified with microglia markers ionized calcium-binding adaptor molecule 1 (IBA1), transmembrane protein 119 (TMEM119), cluster of differentiation 11b (CD11b), as well as astrocyte marker glial fibrillary acidic protein (GFAP) by immunofluorescence staining. Additionally, the initial plating ratio of the mixed glial cell, culture period of isolation, procedures of the isolation, as well as the purification procedure, were optimized for our primary microglial cell culture. The morphological changes and phagocytic function were performed after lipopolysaccharide (LPS) stimulation. Moreover, the release of pro-inflammatory cytokines at different time points of LPS activation were measured. In the present study, we found that the concentration of one retina/T75 flask could harvest the largest number of microglial cells. Besides, we continuously cultured the mixed glial cells as long as one month and isolated the mixed glial cells as much as three times. In our study, we used an isolation-shaking rate of 200 rpm for 2h, which guaranteed the steady rate and resulted in high purification of the primary retinal-microglial cells, with no need of an additional purification procedure. In conclusion, we provided a high-producing protocol for the primary culture of purified rat retinal-microglial cells.

Multiple Sulfur Isotope Constraints on Sources and Formation Processes of Sulfate in Beijing PM2.5 Aerosol.

Recently air pollution is seriously threatening the health of millions of people in China. The multiple sulfur isotopic composition of sulfate in PM2.5 samples collected in Beijing is used to better constrain potential sources and formation processes of sulfate aerosol. The Δ33S values of sulfate in PM2.5 show a pronounced seasonality with positive values in spring, summer and autumn and negative values in winter. Positive Δ33S anomalies are interpreted to result from SO2 photolysis with self-shielding, and may reflect air mass transport between the troposphere and the stratosphere. The negative Δ33S signature (-0.300‰ < Δ33S < 0‰) in winter is possibly related to incomplete combustion of coal in residential stoves during the heating season, implying that sulfur dioxide released from residential stoves in more rural areas is an important contributor to atmospheric sulfate. However, negative Δ33S anomalies (-0.664‰ < Δ33S ← 0.300‰) in winter and positive Δ33S anomalies (0.300‰ < Δ33S < 0.480‰) in spring, summer, and autumn suggest sulfur isotopic equilibrium on an annual time frame, which may provide an implication for the absence of mass-independent fractionation of sulfur isotopes (S-MIF) in younger sediments. Results obtained here reveal that reducing the usage of coal and improving the heating system in rural areas will be important for efficiently decreasing the emissions of sulfur in China and beyond.

TNF-α mediates choroidal neovascularization by upregulating VEGF expression in RPE through ROS-dependent ß-catenin activation.

PURPOSE: Inflammation, oxidative stress, and angiogenesis have been proposed to interact in age-related macular degeneration. It has been postulated that external stimuli that cause oxidative stress can increase production of vascular endothelial growth factor (VEGF) in retinal pigment epithelial (RPE) cells. In this study, we tested the hypothesis that the inflammatory cytokine, tumor necrosis factor alpha (TNF-α), contributed to choroidal neovascularization (CNV) by upregulating VEGF in RPE through intracellular reactive oxygen species (ROS)-dependent signaling and sought to understand the mechanisms involved. METHODS: In a murine laser-induced CNV model, 7 days after laser treatment and intravitreal neutralizing mouse TNF-α antibody or isotype immunoglobulin G (IgG) control, the following measurements were made: 1) TNF-α protein and VEGF protein in RPE/choroids with western blot, 2) CNV volume in RPE/choroidal flatmounts, and 3) semiquantification of oxidized phospholipids stained with E06 antibody within CNV with immunohistochemistry (IHC). In cultured human RPE cells treated with TNF-α or PBS control, 1) ROS generation was measured using the 2',7'-dichlorodihydrofluorescein diacetate (DCFDA) fluorescence assay, and 2) NOX4 protein and VEGF protein or mRNA were measured with western blot or quantitative real-time PCR in cells pretreated with apocynin or nicotinamide adenine dinucleotide phosphate-oxidase (NADPH) inhibitor, VAS 2870, or transfected with p22phox siRNA, and each was compared to its appropriate control. Western blots of phosphorylated p65 (p-p65), total p65 and ß-actin, and quantitative real-time PCR of VEGF mRNA were measured in human RPE cells treated with TNF-α and pretreatment with the nuclear factor kappa B inhibitor, Bay 11-7082 or control. Western blots of ß-catenin, VEGF, and p22phox and coimmunoprecipitation of ß-catenin and T-cell transcriptional factor were performed in human RPE cells treated with TNF-α following pretreatment with ß-catenin transcriptional inhibitors, XAV939 or JW67, or transfection with p22phox siRNA and compared to appropriate controls. RESULTS: Compared to the non-lasered control, TNF-α and VEGF protein were increased in the RPE/choroids in a murine laser-induced CNV model (p<0.05). An intravitreal neutralizing antibody to mouse TNF-α reduced CNV volume, and VEGF protein in the RPE/choroids (p<0.01) and oxidized phospholipids within CNV compared to IgG control (p<0.05). In cultured RPE cells and compared to controls, TNF-α induced ROS generation and increased activation of NOX4, an isoform of NADPH oxidase; both were prevented by pretreatment with the apocynin or VAS2870 or knockdown of p22phox, a subunit of NADPH oxidase. TNF-α treatment increased VEGF expression (p<0.001) and the formation of a transcriptional complex of ß-catenin and T-cell transcriptional factor; both were prevented by pretreatment with apocynin or knockdown of p22phox. Inhibition of ß-catenin by XAV939, but not the nuclear factor kappa B inhibitor, Bay 11-7082, prevented TNF-α-induced VEGF upregulation. CONCLUSIONS: Our results support the thinking that TNF-α contributes to CNV by upregulating VEGF production in RPE cells through ROS-dependent activation of ß-catenin signaling. These results provide mechanisms of crosstalk between inflammatory mediator, TNF-α, and ROS in RPE cells.

Interaction between sulfur and lead in toxicity, iron plaque formation and lead accumulation in rice plant.

Human activities have resulted in lead and sulfur accumulation in paddy soils in parts of southern China. A combined soil-sand pot experiment was conducted to investigate the influence of S supply on iron plaque formation and Pb accumulation in rice (Oryza sativa L.) under two Pb levels (0 and 600 mg kg(-1)), combined with four S concentrations (0, 30, 60, and 120 mg kg(-1)). Results showed that S supply significantly decreased Pb accumulation in straw and grains of rice. This result may be attributed to the enhancement of Fe plaque formation, decrease of Pb availability in soil, and increase of reduced glutathione (GSH) in rice leaves. Moderate S supply (30 mg kg(-1)) significantly increased Fe plaque formation on the root surface and in the rhizosphere, whereas excessive S supply (60 and 120 mg kg(-1)) significantly decreased the amounts of iron plaque on the root surface. Sulfur supply significantly enhanced the GSH contents in leaves of rice plants under Pb treatment. With excessive S application, the rice root acted as a more effective barrier to Pb accumulation compared with iron plaque. Excessive S supply may result in a higher monosulfide toxicity and decreased iron plaque formation on the root surface during flooded conditions. However, excessive S supply could effectively decrease Pb availability in soils and reduce Pb accumulation in rice plants.

Effects of Cu(II)-DOM complexation on DOM degradation: Insights from spectroscopic evidence.

The fate of dissolved organic matter (DOM) is primarily governed by its sources, degradation, and transformation processes within the environment. However, the influence of metal-DOM complexation on DOM degradation remains ambiguous. In this study, controlled laboratory experiments were conducted using Cu(II) and natural water from the Duliujian River and the Beidagang Wetland to examine the effects of metal-DOM binding on the degradation pathway of DOM. Our results showed that Cu(II)-DOM complexation affected the distribution of DOM molecular weight with elevated Mw after complexed with Cu(II). Nevertheless, the concentration of DOM decreased over the incubation period due to degradation. In the absence of Cu(II) binding, both wetland and river DOM followed similar degradation pathways, transforming from high to low molecular weight with changes predominantly in the 1-10 kDa size-fraction during DOM degradation. In contrast, in the presence of Cu(II) and thus Cu(II)-DOM binding, the degradation of DOM was enhanced, resulting in higher kinetic rate constants for both wetland and river DOM. The results of differential spectra further confirmed the degradation of DOM with a decrease in bulk spectroscopic properties and an increase in the degree of DOM-Cu(II) complexation. These findings imply a mutually reinforcing relationship between metal-DOM complexation and the degradation of DOM in aquatic environments, providing new insights into the biogeochemical behavior and environmental fate of DOM.

Tremella polysaccharide-based conductive hydrogel with anti-freezing and self-healing ability for motion monitoring and intelligent interaction.

The application of conductive hydrogels in flexible wearable devices has garnered significant attention. In this study, a self-healing, anti-freezing, and fire-resistant hydrogel strain sensor is successfully synthesized by incorporating sustainable natural biological materials, viz. Tremella polysaccharide and silk fiber, into a polyvinyl alcohol matrix with borax cross-linking. The resulting hydrogel exhibits excellent transparency, thermoplasticity, and remarkable mechanical properties, including a notable elongation (1107.3 %) and high self-healing rate (91.11 %) within 5 min, attributed to the dynamic cross-linking effect of hydrogen bonds and borax. A strain sensor based on the prepared hydrogel sensor can be used to accurately monitor diverse human movements, while maintaining exceptional sensing stability and durability under repeated strain cycles. Additionally, a hydrogel touch component is designed that can successfully interact with intelligent electronic devices, encompassing functions like clicking, writing, and drawing. These inherent advantages make the prepared hydrogel a promising candidate for applications in human health monitoring and intelligent electronic device interaction.

Multi-functional bio-film based on sisal cellulose nanofibres and carboxymethyl chitosan with flame retardancy, water resistance, and self-cleaning for fire alarm sensors.

Flexible and environmentally friendly bio-based films have attracted significant attention as next-generation fire-responsive sensors. However, the low structural stability, durability, and flame retardancy of pure bio-based films limit their application in outdoor and extreme environments. Here, we report the design of a sustainable bio-based composite film assembled from carboxymethyl-modified sisal fibre microcrystals (C-MSF), carboxymethyl chitosan (CMC), graphene nanosheets (GNs), phytic acid (PA), and trivalent iron ions (Fe3+). Cross-linking between Fe3+ and the C-MSF/CMC matrix and the formation of PA-Fe3+ complexes on the surface of the film imparted excellent mechanical properties, chemical stability, self-cleaning ability, and flame retardancy to the bio-film. Furthermore, the bio-film produced a reversible and sensitive response to temperature at 55.3-214.1 °C, and a fire alarm system made from the bio-film had a fire-response time of 4.6 s. In addition, the char layer of the bio-film retained a stable cyclic response to temperature, enabling it to serve as a fire resurgence sensor with a response time of 2.3 s and recovery time of 11.2 s. This work provides a simple pathway for the fabrication of self-cleaning, flame retardant, and water-resistant bio-films that can be assembled into fire alarm systems for the real-time monitoring of fire accidents and resurgence.

Multifunctional bio-films based on silk nanofibres/peach gum polysaccharide for highly sensitive temperature, flame, and water detection.

Given their environment friendliness, light weight, and availability, bio-films have attracted wide interest for various applications in sensor materials. However, obtaining sensors with good environmental stability, excellent flame retardancy, and high wet strength remains a challenge. Herein, we prepared sensitive water, temperature and flame-responsive multi-function bio-films (named as PSCG bio-films) by combining peach gum polysaccharide, silk nanofibres, citric acid, and graphene. The PSCG bio-films demonstrated good flexibility, rapid and consistent water absorption, and stable wet strength at different temperatures. The bio-films showed excellent water sensitivity and rapid fire responsiveness within a short time frame (2 s); moreover, the response and recovery times of the bio-films in the temperature range of 50-150 °C were 0.1 and 0.3 s, respectively. In addition, the bio-films can be applied to micro-sized fire early warning devices and personalized breath monitoring. Our work presents a facile and green approach (without toxic solvent) to fabricate multi-function sensors with applications in various industries.

Differences in the spectral characteristics of dissolved organic matter binding to Cu(II) in wetland soils with moisture gradients.

The environmental behavior of heavy metals in soil is significantly regulated by their binding with dissolved organic matter (DOM), which is affected by soil moisture contents. However, the mechanism of this interaction in soils with varying moisture is still not well understood. Using a combination of ultrafiltration, Cu(II) titration, and multispectral (ultraviolet-visible absorption, 3D fluorescence, Fourier transform infrared) analysis techniques, we studied the differences in the spectral characteristics and Cu(II) binding properties of soil dissolved organic matter (DOM) and its different molecular weight (MW) fractions with moisture gradients. We found that the abundance and spectral characters of soil DOM changed with increasing soil moisture, i.e., the increase in abundance while the decrease in aromaticity and humification index. The components of DOM, shown by Fluorescence region-integration (FRI) analysis, also changed, with an increase in the proportion of protein-like substances and a decrease of humic-like and fulvic-like substances. The overall Cu(II) binding potential of soil DOM diminished with increasing soil moisture, as indicated by the fluorescence parallel factor (PARAFAC) analysis. This is aligns with the changes in DOM composition, as the humic-like and fulvic-like fractions exhibited higher Cu(II) binding potential compared to the protein-like fractions. The low MW fraction of the MW-fractionated samples showed a stronger binding potential for Cu(II) compared to the high MW fraction. Finally, the active binding site of Cu(II) in DOM, as revealed by UV-difference spectroscopy and 2D-FTIR-COS analysis, decreased with increasing soil moisture, with the order of preferentially functional groups shifting from OH, NH, and CO to CN and CO. This study emphasizes the impact of moisture variations on the characteristics of DOM and its interaction with Cu(II), providing insight into the environmental fate of heavy metal contaminants in soil in areas with alternating land and water conditions.

Slight transition in Chinese atmospheric Pb isotopic fingerprinting due to increasing foreign Pb.

Atmospheric lead (Pb) pollution negatively affects human health and ecosystem, and extensive research is required to identify its sources and develop robust mitigation methods. In this study, the concentration and isotopic composition of Pb in fine particulate matter (PM2.5) at five sites in the China's Beijing-Tianjin-Hebei (BTH) region were analyzed. The results showed that the Pb concentration in the BTH region declined along the northwest direction in winter owing to the East Asian monsoon. Pb isotopic signatures confirmed that anthropogenic activities significantly contributed to Pb pollution, compared with natural sources. With the increasing import of foreign Pb (with a relatively lower 208Pb/206Pb ratio) to China, we hypothesized that the unique isotopic signature of Pb in Chinese aerosols may decline over time. Therefore, the application of the isotopic approach for quantifying Pb transported from China should be carefully appraised in future research to provide a realistic estimate of the contribution of local sources and the transboundary effect consistent with air mass trajectories analysis. This study provides a theoretical reference for supporting the utilization of Δ208Pb values for better clarify the transboundary impact of Pb pollution and to reduce international disputes.

Role of molecular weight-dependent spectral properties in regulating Cu(II) binding by dissolved organic matter from different sources.

The complexation of metals with dissolved organic matter (DOM) under different compositions and molecular weights (MWs) will result in different environmental fate and toxicity, but the specific role and impact of DOM MWs remain less well understood. This study explored the metal binding characteristics by DOM with different MWs from different sources, including sea, river, and wetland waters. The results of fluorescence characterization showed that the >1 kDa high-molecular-weight (HMW)-DOM were mainly from terrestrial sources while the low-molecular-weight (LMW)-DOM fractions were mostly from microbial sources. Based on UV-Vis spectroscopic characterization, the LMW-DOM contained more unsaturated bonds than its HMW counterpart, and the substituents are generally dominated by polar functional groups. Summer DOM had more unsaturated bonds and a higher metal binding capacity than winter DOM. Furthermore, DOM with different MWs had significantly different Cu binding properties. In addition, Cu binding with microbially derived LMW-DOM mainly caused the change in the peak at 280 nm, while binding with terrigenous HMW-DOM resulted in the change of the 210 nm peak. Compared with the HMW-DOM, most of the LMW-DOM had stronger Cu-binding ability. Correlation analysis indicates that metal binding ability of DOM mainly depends on its concentration, number of unsaturated bonds and benzene rings, and types of substituents during interactions. This work provides an improved understanding of the metal-DOM binding mechanism, the role of composition- and MW-dependent DOM from different sources, and thus the transformation and environmental/ecological role of metals in aquatic systems.

Triple Silicon, Phosphorous, and Nitrogen-Grafted Lignin-Based Flame Retardant and Its Vulcanization Promotion for Styrene Butadiene Rubber.

In this study, we present an innovative environmental silicon-, phosphorus-, and nitrogen-triple lignin-based flame retardant (Lig-K-DOPO). Lig-K-DOPO was successfully prepared by condensation of lignin with flame retardant intermediate DOPO-KH550 synthesized via Atherton-Todd reaction between 9, 10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) and γ-aminopropyl triethoxysilane (KH550A). The presence of silicon, phosphate, and nitrogen groups was characterized by FTIR, XPS, and 31P NMR spectroscopy. Lig-K-DOPO exhibited advanced thermal stability compared with pristine lignin supported by TGA analysis. The curing characteristic measurement showed that addition of Lig-K-DOPO promoted the curing rate and crosslink density to styrene butadiene rubber (SBR). Moreover, the cone calorimetry results indicated Lig-K-DOPO conferred impressive flame retardancy and smoke suppression. The addition of 20 phr Lig-K-DOPO reduced SBR blends 19.1% peak heat release rate (PHRR), 13.2% total heat release (THR), 53.2% smoke production rate (SPR), and 45.7% peak smoke production rate (PSPR). This strategy provides insights into multifunctional additives and greatly extends the comprehensive utilization of industrial lignin.

The isotopic patterns and source apportionment of nitrate and ammonium in atmospheric aerosol.

Nitrate (NO3-) and ammonium (NH4+) are the major components in inorganic aerosol. However, their sources and formation processes remain unclear. This study conducted a year-round field measurement of TSP, PM2.5 and PM1.0 in five different sites in the Beijing-Tianjin-Hebei (BTH) region to determine the concentrations of water-soluble inorganic ions (WSIIs) and the isotopic compositions of inorganic nitrogen (δ15N-NH4+, δ15N-NO3-, and δ18O-NO3-). The results showed the highest concentration of WSIIs in winter and lowest in summer. δ15N-NO3-, δ18O-NO3-, and δ15N-NH4+ were in the range of -6.1-18.2, 52.2-103.8, and -28.7-36.2‰, respectively. The seasonal variations of δ15N-NO3- and δ15N-NH4+ were an indication of relative contributions of the main sources and effects of meteorological conditions. The source apportionment identified fossil fuel combustion (38.2-50.6%), agricultural emissions (18-24.7%), biomass burning (16.3-22.7%), and road dust/soil (8.7-23.4%) were the main sources of inorganic aerosols. The local sources and regional migration contributed to the level of inorganic aerosol pollution. In winter, the aerosol in the BTH region was affected by the air mass from the northwest. While in spring and summer, the air mass was mainly from the South China. The low temperature and high relative humidity favored to the formation of inorganic nitrogen aerosol, and solar radiation affected the formation processes of inorganic aerosols by changing the oxidation pathway of NO3- and accelerating the volatilization and dissociation of ammonium nitrate (NH4NO3). This study discovered the main source contributions of inorganic nitrogen aerosol using N and O isotopes composition, and the obtained information has a great importance in understanding the effects of meteorological conditions on formation and the contribution of regional transport.

Sulfate concentrations affect sulfate reduction pathways and methane consumption in coastal wetlands.

Coastal wetlands are an important source of methane emissions, and understanding the mechanisms that control methane emissions from coastal wetlands is of great significance to global warming. Anaerobic oxidation of methane driven by sulfate is an important process to prevent methane emissions from coastal wetlands. The effects of environmental changes on this process and the function of the sulfate-methane transition zone (SMTZ) are poorly understood. In this study, spatiotemporal variations in pore-water geochemistry (concentrations of SO42-, CH4 and DIC as well as δ13C-DIC and δ13C-CH4) in the Beidagang wetland, Tianjin, China, were investigated to unravel factors controlling the role of anaerobic oxidation of methane in coastal wetlands. Results show that the geochemical profile of pore-water is characterized by significant spatial and temporal variability, which may be related to changes in sulfate concentration, temperature and dissolved oxygen. The carbon isotope fractionation factors (εC) during methane oxidation range from 8.9‰ to 12.5‰, indicating that the sulfate-driven anaerobic oxidation of methane (S-AOM) dominates the methane oxidation in the Beidagang coastal wetland in both winter and summer, in both high and low salinity wetlands, and in both open water and littoral areas. However, sulfate concentration has a strong influence on the sulfate reduction pathways and methane consumption. The consumption of methane and sulfate by S-AOM is more significant in coastal wetlands with high sulfate concentrations, with S-AOM consuming nearly all of the upward-diffusing methane (96%) and downward-diffusing sulfate (96%). In addition, the dissolved inorganic carbon (DIC) produced in the pore-water mainly comes from methanogenesis, accounting for more than 80% of the total DIC pool, but in the areas with high sulfate concentrations in water column, the contribution of S-AOM to the DIC pool is greater, although only a small fraction of the total DIC pool (9%). The depth and width of the SMTZ show a clear spatial and temporal pattern, with active methanogenesis activity and upward high methane flux shoaling the SMTZ and increasing the risk of high methane emissions from coastal wetlands with low sulfate concentrations. Our findings highlight the importance of sulfate-driven anaerobic oxidation of methane in coastal wetlands and the effect of sulfate concentration on it. It contributes to our understanding of the mechanism of methane production and emissions from the coastal wetland system, particularly in light of the increased demand for coastal wetland restoration under global warming.

Differences in the spectroscopic characteristics of wetland dissolved organic matter binding with Fe3+, Cu2+, Cd2+, Cr3+ and Zn2.

Understanding of the binding characteristics of wetland dissolved organic matter (DOM) and different metals is important for the quantitative assessment of the environmental behavior of metals in wetlands. In this study, different types of spectroscopy including ultraviolet-visible absorption, Fourier transform infrared, and fluorescence spectroscopy was used to investigate the binding characteristics of Fe3+, Cu2+, Cr3+, Cd2+, and Zn2+ with DOM from wetland water. Differential absorption spectra identified binding sites for these five metals in this wetland DOM at 210 nm, 280 nm, 335 nm, and > 400 nm regions. The low binding capacity of DOM in this wetland with Cd and Zn indicated that the toxicity and environmental effects of these metals in this wetland warrant further study. The calculated △EEM combined with fluorescence regional integration (FRI) analysis clearly revealed that Fe and Cu preferred to bind with humic-like DOM while Cd and Zn preferred to bind with protein-like DOM in this wetland. △EEM successfully demonstrated the characteristics of DOM complexing with different metals and could be a compelling tool in evaluating metal-DOM interactions. In addition, 2D-FTIR-COS identified the binding sites and the dynamic processes of binding at the functional group level. Metals preferentially bind with the CO, CO functional group, and then binds to the OH functional group. This study revealed that different DOM components will facilitate the migration of different metals in the environment and provided new slights into an improved understanding of migration and transformation of metals in aquatic environments.

Atmospheric lead pollution in a typical megacity: Evidence from lead isotopes.

Atmospheric lead (Pb) pollution has adverse health effects on humans, while the sources and atmospheric process of Pb are key scientific problems. In this study, the concentrations and isotopic composition of Pb in fine particulate matter (PM2.5), coal and street dust samples collected from a typical megacity Beijing were analyzed to identify the sources of atmospheric Pb. Results showed that the Pb concentrations in PM2.5 were high in winter (168.1 ± 32.0 ng/m3) and low in summer (27.7 ± 9.1 ng/m3), whereas Pb isotopic values presented opposite variation trends. The abnormally elevated Pb concentrations in winter were probably related to coal combustion, while declined Pb concentration in summer may be attributed to favorable meteorological parameters such as high temperature, high wind speed, and frequent rain events. Pb isotopic ratios indicated that anthropogenic sources (coal combustion and vehicle exhaust) and natural sources were the main contributors to Pb in PM2.5. Combined with the binary model, the anthropogenic sources predominantly contributed to Pb in the Beijing atmosphere by approximately 85% annually, while the natural sources accounted for the rest of 15%. More specifically, the contribution of natural sources was about 9.4% in spring, 29.7% in summer, 16.0% in autumn and 6.1% in winter, suggesting that natural sources might contribute more lead into the atmosphere during clear days. Furthermore, the contribution of the vehicle exhaust to atmospheric Pb was nonnegligible in megacity, highlighting that the ownership of motor vehicles in megacity should be regulated and more efforts should be paid to strengthen vehicle emission standard. This study may enrich the reservoir of Pb isotopic composition in nature and provides a new method to investigate the Pb migration and transformation in the environment, and also serve as a theoretical reference for pollution control measures.

Exosomes derived from retinoblastoma cells enhance tumour deterioration by infiltrating the microenvironment.

The survival of young children (under 5 years of age) with malignant retinoblastoma remains poor, and clarification of the mechanism underlying tumour development is urgently needed. The present study aimed to reveal the role of exosomes (EXOs) from retinoblastoma cells in tumour development. The in vitro data indicated that EXOs derived from WERI­Rb1 cells significantly inhibited the antitumour activity of macrophages and induced bone marrow mesenchymal stem cells to promote tumour growth via an increase in monocyte chemotactic protein 1 (also known as C­C motif chemokine ligand 2) levels. In vivo data from a xenotransplantation model also showed that EXOs infiltrated the spleen, which induced a decrease in leukocytes and natural killer (NK) cells. Accordingly, the proportion of tumour­associated macrophages was increased and the proportion of NK cells was decreased in tumours injected with EXOs compared with those injected with the control. EXOs were absorbed by Kupffer cells, and more metastases were observed in the liver. Thus, these results suggested that EXOs derived from retinoblastoma promoted tumour progression by infiltrating the microenvironment. Moreover, microRNAs (miRs), including miR­92a, miR­20a, miR­129a and miR­17, and C­X­C chemokine receptor type 4 and thrombospondin­1 were detectable in EXOs, which might account for EXO­mediated tumour deterioration.

Temporal and spatial variations in stable isotopic compositions of precipitation during the typhoon Lekima (2019), China.

A clear understanding of factors governing stable isotopic variations in precipitation of tropical cyclones is critical for constraining atmospheric hydrological model simulations. The temporal and spatial variations in stable isotopic compositions of precipitation during the typhoon Lekima (2019) were investigated, based on rainwater samples collected at four sampling sites along its track between August 10 and August 12, 2019. Results showed that the δ18O and δD values of rainwater samples varied from -15.5‰ to -2.9‰ and from -112.4‰ to -17.3‰, respectively. The large ranges of δ18O and δD values in rainwater from the typhoon Lekima were most likely caused by the changes in rainfall intensity and its complex interaction with local water vapor. In addition, it was observed that the δ18O and δD values gradually decreased from the outer rainbands to the inner rainbands, and their values were more depleted of heavy isotopes than those of local rain. We speculated that both the high stratiform precipitation fractions and the deep convection system may be responsible for the isotopic depletion of rainwater related with the typhoon Lekima. It reveals that the rain type fractions and the intensity of convection should be considered in the elucidation of δ18O signals in extreme precipitation events. This study also has important implications for understanding atmospheric moisture cycles in tropical cyclones.