Products from Photolysis Reactions of Tetracycline Mediated by Clay and Humic Substance Induce Contrasting Expressions of Target Resistance Genes.

Phototransformation is a key process affecting the fate of many antibiotics in the environment, but little is known about whether their photoproducts exert selective pressure on bacteria by inducing antibiotic resistance genes (ARGs). Here, we examined the expression of tetracycline resistance gene tet(M) of a fluorescent Escherichia coli whole-cell bioreporter influenced by the phototransformation of tetracycline. The presence of suspended smectite clay (montmorillonite or hectorite, 1.75 g/L) or dissolved humic substance (Pahokee Peat humic acid or Pahokee peat fulvic acid, 10 mg C/L) in aqueous solutions markedly facilitated the transformation of tetracycline (initially at 400 µg/L) with half-life shortened by 1.4-2.6 times. Despite the similar phototransformation ratios (80-90%) of the total loaded tetracycline after 60 min irradiation, the decreased ratios of cell fluorescence intensity (which was proportional to the expression amount of ARG tet(M)) were much higher with the two clays (94 and 93%) than with the two humic substances (44 and 69%) when compared to the respective dark controls. As illustrated by mass spectroscopic and chemical analyses, tetracycline was proposed to be mainly transformed to amide (ineffective in inducing ARGs) with the presence of clays by reaction with self-photosensitized singlet oxygen (1O2), while the humic substances might catalyze the production of another two demethylated and/or deaminated compounds (still effective in inducing ARGs) in addition to the amide compound via reaction with triplet excited state dissolved organic matter (3DOM*). As clay minerals and humic substances are important soil constituents and ubiquitously present in surface environments, the observed clay and humic-dependent photooxidation pathways of tetracycline and the differing selective pressures of the associated products highlight the need for monitoring the transformation compounds of antibiotics and provide critical insight into the development of antibiotic treatment protocols.

Comparing molecular signatures of dissolved organic matter (DOM) in four large freshwater lakes differing in hydrological connectivity to the Changjiang River.

Freshwater lakes serve as active conduits for processing terrestrial dissolved organic matter (DOM), playing a crucial role in global carbon cycle. Little attention has been paid to how hydrological connectivity to a large river would affect the molecular signatures of DOM in lakes. Here, we systematically characterized and compared the molecular signatures of DOM in surface waters of four large freshwater lakes in the middle and lower Changjiang River basin that are directly connected to the river (Lake Dongting and Lake Poyang, referred to as Lakeconnected) or indirectly connected to the river (Lake Chao and Lake Tai, referred to as Lakenonconnected). The DOM in Lakeconnected was found to have similar total organic carbon (TOC)-normalized contents and characteristics of lignin phenols to the DOM in surface waters from the upstream Changjiang river, indicating allochthonous/terrestrial sources from riverine inputs. As indicated by the UV-vis and fluorescence analyses, the DOM in Lakeconnected overall had higher aromaticity and larger average molecular weight as well as stronger allochthonous feature compared to the DOM in Lakenonconnected. Consistently, the FT-ICR MS analysis revealed that the DOM in Lakeconnected had higher molecular diversity, higher unsaturation degree, and larger proportions of highly aromatic compounds. In contrast, the DOM in Lakenonconnected had larger proportions of lipids and peptide-like structures, but lower proportions of aromatic compounds, which could be ascribed to the enhanced autochthonous production and photodegradation due to pollution and eutrophication as well as longer water residence time. The results highlight the strong impacts of the hydrological connectivity to a large river on the molecular signatures of lake DOM. CAPSULE: The hydrological connectivity of the lakes to the Changjiang River has strong impacts on the molecular signatures of lake DOM.

Revealing Molecular Structures of Nitrogen-Containing Compounds in Dissolved Black Carbon Using Ultrahigh-Resolution Mass Spectrometry Combined with Thermodynamic Calculations.

Landscape wildfires generate a substantial amount of dissolved black carbon (DBC) annually, yet the molecular nitrogen (N) structures in DBC are poorly understood. Here, we systematically compared the chemodiversity of N-containing molecules among three different DBC samples from rice straw biochar pyrolyzed at 300, 400, and 500 °C, one leached dissolved organic carbon (LDOC) sample from composted rice straw, and one fire-affected soil dissolved organic matter (SDOMFire) sample using Fourier-transform ion cyclotron resonance mass spectrometry (FT-ICR MS). N-Containing molecules contributed 20.0%, 36.1%, and 43.7% of total compounds in Combined DBC (pooling together the three DBC), LDOC, and SDOMFire, respectively, and molecules with fewer N atoms had higher proportions (i.e., N1 > N2 > N3). The N-containing molecules in Combined DBC were dominated by polycyclic aromatic (62.2%) and aromatic (14.4%) components, while those in LDOC were dominated by lignin-like (50.4%) and aromatic (30.1%) components. The composition and structures of N-containing molecules in SDOMFire were more similar to those in DBC than in LDOC. As the temperature rose, the proportion of the nitrogenous polycyclic aromatic component in DBC significantly increased with concurrent enhanced oxidation and unsaturation of N. As indicated by density functional theory (DFT)-based thermodynamic calculations, the proportion of aliphatic amide N decreased from 23.2% to 7.9%, whereas that of nitroaromatic N increased from 10.0% to 39.5% as the temperature increased from 300 to 500 °C; alternatively, the proportion of aromatic N in the 5/6 membered ring remained relatively stable (∼31%) and that of aromatic amide N peaked at 400 °C (32.7%). Our work first provides a comprehensive and thorough description of molecular N structures of DBC, which helps to better understand and predict their fate and biogeochemical behavior.

Efficient Catalytic Oxidation of Ethylene at 0 °C on an in Situ Carbon Modified Pt Catalyst Supported on SBA-15.

The design of efficient catalysts for catalytic ethylene (C2H4) oxidation is of crucial importance for extending the shelf life of fruits and vegetables. Herein, a carbon modified SBA-15 supported Pt catalyst (Pt/CSBA-15) was prepared in situ by a facile solid phase grinding-infiltration-inert atmosphere calcination method. Characterization results reveal that in the Pt/CSBA-15 catalysts thin carbon layers are successfully formed in the hexagonal pores of SBA-15. Additionally, Pt particles are well dispersed in the channels of SBA-15, and Pt/CSBA-15 has a smaller Pt particle size than the catalyst without carbon modification (i.e., Pt/SBA-15). O2 is more feasibly adsorbed and activated on small-sized Pt particles, and in situ formed carbon species enhance the hydrophobicity of catalysts. As a result, both 3Pt/CSBA-15 and 5Pt/CSBA-15 are able to maintain 100% conversion of 50 ppm of C2H4 for more than 7 h at 0 °C. 3Pt/CSBA-15 even achieves 81.5% C2H4 conversion and 71.6% CO2 yield after 20 h, exhibiting much more prominent catalytic performances than 3Pt/SBA-15. DFT calculations and in situ FTIR measurements confirm that small-sized Pt particles possess strong O2 affinity to promote O2 adsorption, and in situ formed hydrophobic carbon layers efficiently suppress competitive H2O adsorption. Such a unique one-step catalyst preparation method for regulating the size of metal particles and the hydrophobicity of catalysts can be perfectly utilized to develop simple and efficient hydrophobic catalysts applied in low-temperature oxidation of C2H4.

Mechanism of intestinal microbiota disturbance promoting the occurrence and development of esophageal squamous cell carcinoma--based on microbiomics and metabolomics.

Esophageal squamous cell carcinoma (ESCC) is a high-risk malignant tumor that has been reported in China. Some studies indicate that gut microbiota disorders can affect the occurrence and development of ESCC, but the underlying mechanism remains unclear. In this study, we aimed to explore the possible underlying mechanisms using microbiomics and metabolomics. Fifty ESCC patients and fifty healthy controls were selected as the study subjects according to sex and age, and fecal samples were collected. 16S rDNA sequencing and LC‒MS were used for microbiomics and nontargeted metabolomics analyses. We found significant differences in the composition of the gut microbiota and metabolites between the ESCC patients and control individuals (P < 0.05). ESCC patients exhibited increased abundances of Fusobacteriaceae and Lactobacillus, increased levels of GibberellinA34 and decreased levels of 12-hydroxydodecanoic acid; these metabolites could be diagnostic and predictive markers of ESCC. An increase in the abundance of Enterobacteriaceae and Lactobacillus significantly reduced the content of L-aspartate and pantothenic acid, which may be involved in the occurrence and development of ESCC by downregulating the expression of proteins in the pantothenate and coenzyme A biosynthesis pathways. An imbalance in the intestinal flora may decrease the number of eosinophils in peripheral blood, resulting in the activation of an inflammatory response and immune dysfunction, leading to ESCC deterioration. We hypothesize that this imbalance in the gut microbiota can cause an imbalance in intestinal metabolites, which can activate carcinogenic metabolic pathways, affect inflammation and immune function, and play a role in the occurrence and development of ESCC.

Benzenepoly(carboxylic acid)s as Exclusive Intrinsic Markers to Assess Riverine Export of Dissolved Black Carbon.

Landscape fires annually generate large quantities of black carbon. The water-soluble fraction of black carbon (i.e., dissolved black carbon/DBC) is an important constituent of the dissolved organic carbon (DOC) pool, playing a crucial role in the global budget of refractory carbon and climate change. A key challenge in constraining the flux and fate of riverine DBC is to develop targeted and accurate quantification methods. Herein, we report that benzenepentacarboxylic acid (B5CA) intrinsically present in DBC can be used as an exclusive and holistic marker (representing both condensed aromatics and less-/nonaromatic fractions) for DBC quantification. B5CA was universally detected in water extractions of biochar and fire-affected soils with relatively large abundance but not produced by nonthermogenic processes. It has good mobility in the environment as it is not readily precipitated by cations or adsorbed by common geosorbents. B5CA also represents the recalcitrant components of DBC with excellent stability against photodegradation and biodegradation. Applying B5CA as the DBC marker in surface waters of the Changjiang River (i.e., the third largest river in the world), we calculate the DBC concentration in the downstream Changjiang River to be 4.8 ± 5.5% of the DOC flux. Our work provides a simple and reliable approach for the accurate quantification and source tracking of DBC in the soil and aquatic carbon pools.

Ni12P5 Confined in Mesoporous SiO2 with Near-Unity CO Selectivity and Enhanced Catalytic Activity for CO2 Hydrogenation.

CO2 hydrogenation via the reverse water gas shift (RWGS) reaction is a promising strategy for CO2 utilization while constructing Ni-based catalysts with high catalytic activity and perfect CO selectivity remains a great challenging. Here, we demonstrate that the product selectivity for CO2 hydrogenation can be significantly tuned from CH4 to CO by phosphating of SiO2-supported Ni catalysts due to the geometric effect. Interestingly, nickel phosphide catalysts with different crystalline phases (Ni12P5 and Ni2P) differ sharply in CO2 conversion, and Ni12P5 is remarkably more active. Furthermore, we developed a facile strategy to confine small Ni12P5 nanoparticles in mesoporous SiO2 channels (Ni12P5@SBA-15). Enhanced activity is exhibited on Ni12P5@SBA-15, ascribed to the highly effective confinement effect. The in situ diffuse reflectance infrared Fourier transform spectroscopy and density functional theory calculations unveil that catalytic CO2 hydrogenation follows a direct CO2 dissociation route with adsorbed CO as the key intermediate. Notably, strong multibonded CO (threefold and bridge-bonded CO) is feasibly formed on the Ni catalyst accounting for CH4 as the dominant product whereas only weak linearly bonded CO exists on nickel phosphide catalysts resulting in almost 100% CO selectivity. The present results indicate that Ni12P5@SBA-15 combining the geometric effect and the confinement effect can achieve near-unity CO selectivity and enhanced activity for CO2 hydrogenation.

New Mechanism via Dichlorocarbene Intermediate for Activated Carbon-Mediated Reductive Dechlorination of Carbon Tetrachloride by Sulfide in Aqueous Solutions.

Although activated carbon (AC) is widely used as an adsorbent and barrier for contaminated sediment remediation, little attention has been paid to its mediation effects on reductive dechlorination of chlorinated solvents by commonly presenting sulfide. Here, we reported that highly porous, graphitized AC (250 mg L-1) suspended in deoxygenated aqueous solutions could increase the pseudo-first-order rate constant of sulfide-induced dechlorination of carbon tetrachloride (CCl4) by more than 1 order of magnitude. Carbon disulfide (CS2) was the only main product, with no production of chloroform or dichloromethane. The minimum promotion of CCl4 reduction observed with electro-conductive but nonporous graphite and a microporous but electro-insulative resin (XAD-4) indicates that graphitic carbons and micropores both play key roles in AC-mediated dechlorination of CCl4 by sulfide. The detection of dichlorocarbene (:CCl2) by free radical trapping experiments combined with the high suitability of the Langmuir-Hinshelwood model led us to propose a new mediation mechanism: CCl4 molecules adsorbed within the deep regions of AC micropores formed by graphitic carbons accept two electrons transferred from sulfide to form :CCl2, which is impeded from hydrolysis and hydrogenolysis by the hydrophobic micropore and further reacts with sulfide to generate CS2. Consistently, the production of :CCl2 was very low when AC was replaced with graphite or XAD-4. The proposed mechanism was further validated by the enhanced mediation effects of another two carbonaceous materials (template-synthesized mesoporous carbon and covalent triazine-based framework) that are electro-conductive and have well-developed micropore structures. These findings highlight the importance of pore properties of carbonaceous materials as mediators or catalysts for reductive dechlorination reactions and shed light on the development of coupled adsorption-reaction systems for remediation.

Bacterial community assembly and antibiotic resistance genes in soils exposed to antibiotics at environmentally relevant concentrations.

Understanding how bacterial community assembly and antibiotic resistance genes (ARGs) respond to antibiotic exposure is essential to deciphering the ecological risk of anthropogenic antibiotic pollution in soils. In this study, three loam soils with different land management (unmanured golf course, dairy-manured pasture, and swine-manured cornfield) were spiked with a mixture of 11 antibiotics at the initial concentration of 100 and 1000 µg kg-1 for each antibiotic and incubated over 132 days, mimicking a scenario of pulse disturbance and recovery in soils, with unspiked soil samples as the control treatment. The Infer Community Assembly Mechanisms by Phylogenetic-bin-based null model (iCAMP) analysis demonstrated that drift and dispersal limitation contributed to 57%-65% and 16%-25%, and homogeneous selection 12%-16% of soil bacterial community assembly. Interestingly, antibiotic exposure to 1000 µg kg-1 level significantly increased the contribution of drift to community assembly, largely due to the positive response from Acidobacteria-6 in the golf course and pasture soils and from Chthoniobacteraceae in the cornfield soil to the antibiotic exposure. However, ARG abundance and diversity in the three soils exhibited antibiotics-independent temporal fluctuations, but were associated with the changes in soil bacterial communities over time. This study provides the first insight into the relative contributions of different bacterial community assembly processes in soils upon antibiotic exposure at environmentally relevant concentrations.

A nanozyme-like colorimetric sensing strategy based on persulfate activation on Co-based metal-organic frameworks.

A nanozyme-like colorimetric sensing strategy based on persulfate activation on Co-based metal-organic frameworks is developed for biomolecule detection in solution and on paper strips. By switching from H2O2 activation on nanozymes to catalytic persulfate activation, this general strategy provides higher sensitivity, faster speed, and wider application ranges for detection.

Mechanism for selective binding of aromatic compounds on oxygen-rich graphene nanosheets based on molecule size/polarity matching.

Selective binding of organic compounds is the cornerstone of many important industrial and pharmaceutical applications. Here, we achieved highly selective binding of aromatic compounds in aqueous solution and gas phase by oxygen-enriched graphene oxide (GO) nanosheets via a previously unknown mechanism based on size matching and polarity matching. Oxygen-containing functional groups (predominately epoxies and hydroxyls) on the nongraphitized aliphatic carbons of the basal plane of GO formed highly polar regions that encompass graphitic regions slightly larger than the benzene ring. This facilitated size match-based interactions between small apolar compounds and the isolated aromatic region of GO, resulting in high binding selectivity relative to larger apolar compounds. The interactions between the functional group(s) of polar aromatics and the epoxy/hydroxyl groups around the isolated aromatic region of GO enhanced binding selectivity relative to similar-sized apolar aromatics. These findings provide opportunities for precision separations and molecular recognition enabled by size/polarity match-based selectivity.

Impact of the initial hydrophilic ratio on black carbon aerosols in the Arctic.

Black carbon (BC) contributes to patterns of Arctic warming, yet the initial hydrophilic ratio (IHR) of BC emitted from various sources and its impact on Arctic BC remain uncertain. With the use of a tagged tracer method of BC implemented in the global chemistry transport model GEOS-Chem, IHRs were partitioned into 7 BC combustion source categories according to the PKU-BC-v2 emission inventory. The results show that as the IHR increased, the concentration of BC decreased globally. The impact on Arctic BC was mainly reflected in the vertical profile and the burden rather than at the surface. Specifically, the greatest impact of IHR on Arctic BC appeared in summer, with the largest perturbation appearing at an altitude of approximately 600 hPa, reaching 8%. This change in BC vertical profile was mainly caused by the IHR change of wildfire combustion in Russia (44%) and Canada (51%), and the emissions from these two regions were also the two most important contributors to the BC concentration and burden in the middle and lower Arctic atmosphere in summer. In the other three seasons, anthropogenic combustion sources (oil, coal, and biomass) in East Asia, Russia, and Europe accounted for 19-40%, 14-28%, and 7-23%, respectively, of the monthly BC burden. Emissions from Russia were the most important contributor (27-43%) to the monthly BC surface concentration. Due to the large adjustment in IHR from 20% to 70%, biomass burning in Europe was shown to be the dominant contributor causing both burden (39%) and surface concentration (88%) changes in all seasons except summer.

Source and formation process impact the chemodiversity of rainwater dissolved organic matter along the Yangtze River Basin in summer.

Rainwater dissolved organic matter (DOM) plays an important role in the biogeochemical cycle and evolution of organic matter in the land-atmosphere interface. To better understand their sources and molecular composition in the atmosphere, rainwater samples were collected at six different locations along the Yangtze River Basin. Based on the application of a combined approach including excitation-emission matrix (EEM) fluorescence and Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS), various sources (terrestrial, anthropogenic, and autochthonous sources) of rainwater DOM were revealed. Results show that the derivatives of biogenic volatile organic compounds were widely distributed and contributed to rainwater DOM along the Yangtze River Basin. In the up-river city Batang, rainwater DOM was affected by the long-range atmospheric transport due to the Indian summer monsoon. Lijiang, a city on the southeastern edge of Tibetan plateau, was related to strong local biomass burning. The industrial cities of Panzhihua and Luzhou showed large differences in organic composition due to distinct industrial types. Fuling, a district in Chongqing Municipality, was significantly contributed by aged organics from biomass burning. While rainwater DOM in Shanghai, a coastal megacity, contained a high fraction of sea spray organics. Further, more than 70% of rainwater DOM molecules are associated with 36 typical transformation mechanisms during rainwater-scavenging processes, e.g., oxidation reactions, dealkylation and decarboxylation. Our study demonstrates that local natural and anthropogenic emissions and climatic conditions strongly shaped the chemodiversity and possible precursor-product pairs of rainwater DOM along the Yangtze River Basin, which helps to better understand the biogeochemical cycles of organic matter in a large-scale watershed under the influence of human activities.

Comparing Photoactivities of Dissolved Organic Matter Released from Rice Straw-Pyrolyzed Biochar and Composted Rice Straw.

Here, we systematically compared the photoactivity and photobleaching behavior between dissolved black carbon (DBC) from rice straw biochar and leached dissolved organic carbon (LDOC) from rice straw compost using complementary techniques. The Fourier transform-ion cyclotron resonance mass spectrometry (FT-ICR MS) analysis showed that DBC was dominated by polycyclic aromatic (55.1%) and tannin-like molecules (24.1%), while LDOC was dominated by lignin-like (58.9%) and tannin-like molecules (19.7%). Under simulated sunlight conditions, DBC had much higher apparent quantum yields for 3DOM* and 1O2 but much lower apparent quantum yields for •OH than LDOC. After a 168 h irradiation, the total number of LDOC formulas identified by FT-ICR MS decreased by 40.1% with concurrent increases in O/C and H/C ratios and also decreases in double bond equivalence minus oxygen (DBE - O) and average molecular weight identified by gel permeation chromatography. However, despite the large decreases in UVA254 and DOC, the total number of DBC formulas decreased only by 12.0% with nearly unchanged O/C ratio, DBE - O values, molecular weight distribution, and benzenepolycarboxylic aromatic condensation (BACon) index regardless of the decreased percentage of condensed aromatic carbon (ConAC %). Compared with LDOC, the photolysis of DBC was much less oxidative and destructive mainly via breakup of a small portion of the highly condensed aromatic rings, probably accompanied by photodecarboxylation.

Molecular signature of soil organic matter under different land uses in the Lake Chaohu Basin.

The concentration and molecular composition of soil organic matter (SOM) are important factors in mitigation against climate change as well as providing other ecosystem services. Our quantitative understanding of how land use influences SOM molecular composition and associated turnover dynamics is limited, which underscores the need for high-throughput analytical approaches and molecular marker signatures to clarify this etiology. Combining a high-throughput untargeted mass spectrometry screening and molecular markers, we show that forest, farmland and urban land uses result in distinct molecular signatures of SOM in the Lake Chaohu Basin. Molecular markers indicate that forest SOM has abundant carbon contents from vegetation and condensed organic carbon, leading to high soil organic carbon (SOC) concentration. Farmland SOM has moderate carbon contents from vegetation, and limited content of condensed organic carbon, with SOC significantly lower than that of forest soils. Urban SOM has high abundance of condensed organic carbon markers due to anthropogenic activities but relatively low in markers from vegetation. Consistently, urban soils have the highest black carbon/SOC ratio among these land uses. Overall, our results suggested that the molecular signature of SOM varies significantly with land use in the Lake Chaohu Basin, influencing carbon dynamics. Our strategy of molecular fingerprinting and marker discovery is expected to enlighten further research on SOM molecular signatures and cycling dynamics.

Prediction of hydrophobic organic compound partition to algal organic matter through the growth cycle of Microcystis aeruginosa.

Algal organic matter (AOM) is an important source for the dissolved organic matter (DOM) pool in aquatic systems, particularly in eutrophic waters. In this study, we reported the dynamic pattern of AOM hydrophobicity during the growth cycle of Microcystis aeruginosa using the partition coefficients of AOM in the aqueous two-phase system (KATPS) as a simple quantitative measure. AOM hydrophobicity had significant and non-monotonic changes during the growth cycle. It increased in the lag and early exponential phases, then decreased in the late exponential and stationary phases, and rebounded in the decline phase. AOM hydrophobicity determined using the resin fractionation, SUVA254, and nuclear magnetic resonance methods shared similar non-monotonic pattern. Nevertheless, the correlations among these indicators were poor. The partition behavior of polycyclic aromatic hydrocarbons and chlorobenzenes to AOM was assessed based the KATPS dataset and the two-phase system (TPS) model. The TPS model showed good prediction power for the partition behavior of AOM with an RMSE of 0.23, suggesting that it was applicable to AOM from Microcystis aeruginosa. Our results indicate that algae activity will influence the overall hydrophobicity of the DOM pool depending on the growth phase, resulting in changes in the bioavailability of hydrophobic organic compounds in aquatic systems.

Sulfide induces physical damages and chemical transformation of microplastics via radical oxidation and sulfide addition.

Transformation of microplastics in aquatic environments and engineered systems (e.g., wastewater treatment plants) significantly affects their transport, fate and effects. Here, we present the counterintuitive finding that sulfide, a prevalent nucleophile and reductant, can result in oxidation of microplastics, in addition to sulfide addition. Treating four model microplastics (thermoplastic polyurethane, polystyrene, polyethylene terephthalate and polyethylene) with 0.1 mM sulfide in a Tris-buffer solution (pH 7.2, 25 °C) resulted in physical damages (embrittlement and cracking) and chemical transformation (increased O/C ratio and formation of C-S bonds) of the materials. Pre-aging of the microplastics with O3 or UV treatment had varied effects on their reactivities toward sulfide, depending on the specific structural and surface chemistry properties of the polymers. Electron paramagnetic resonance and radical trapping/quenching experiments showed that sulfide underwent spontaneous oxidation to form •OH radicals, which acted as the primary oxidant to attack the carbon atoms in the polymer chains, leading to surface oxidation and chain scission. Notably, sulfide addition, verified with X-ray photoelectron spectroscopy and 13C-nuclear magnetic resonance spectroscopy analyses, likely contributed to the physicochemical transformation of microplastics together with radical oxidation in a synergistic manner. The findings unravel an important transformation route (and a potential source) of microplastics in the environment.

Spatially Resolved Emission Factors to Reduce Uncertainties in Air Pollutant Emission Estimates from the Residential Sector.

The residential sector is a major source of air pollutant emission inventory uncertainties. A nationwide field emission measurement campaign was conducted in rural China to evaluate the variabilities of realistic emission factors (EFs) from indoor solid fuel combustion. For a total of 1313 burning events, the overall average EFs (±standard deviation) of PM2.5 were 8.93 ± 6.95 and 7.33 ± 9.01 g/kg for biomass and coals, respectively, and 89.3 ± 51.2 and 114 ± 87 g/kg for CO. Higher EFs were found from burning of uncompressed straws, while lower EFs were found from processed biomass pellets, coal briquettes, and relatively clean anthracite coals. Modified combustion efficiency was found to be the most significant factor associated with variations in CO EFs, whereas for PM2.5, fuel and stove differences determined its variations. Weak correlations between PM2.5 and CO indicated high uncertainties in using CO as a surrogate for PM2.5. EFs accurately fit log-normal distributions, and obvious spatial heterogeneity was observed attributed to different fuel-stove combinations across the country. Emission estimation variabilities, which are determined by the interquartile ranges divided by the median values, were notably reduced when spatially resolved EFs were adopted in the inventory.

Variations of root-associated bacterial cooccurrence relationships in paddy soils under chlorantraniliprole (CAP) stress.

Root-associated microbiomes are beneficial for plant development and health. However, the assembly of root-associated bacterial communities and their feedback under chlorantraniliprole (CAP) stress are unclear. This study investigated the response of root-associated bacterial microbiota to CAP dosage during the two developmental phases of rice. The results showed that CAP application had little effect on the bacterial diversity of bulk and rhizosphere soils, whereas that of the endosphere samples demonstrated a large variability. Moreover, the CAP stress exhibited less influence than the plant compartment and developmental stage contributing to microbiome variation. The core bacterial co-occurrence relationships also changed with the CAP application, especially, in the endosphere of the roots. These results further elucidate the impacts of CAP application on root-associated bacterial communities in intensive agricultural ecosystems and provide new insights for CAP ecological risk assessments.

Combined analyses of hygroscopic properties of organic and inorganic components of three representative black carbon samples recovered from pyrolysis.

Hygroscopicity of black carbon (BC) aerosols is a key factor determining their climate forcing effect and atmospheric lifetime. However, the compositional dependence of BC hygroscopicity is not well understood. Here, a variety of different compositional components were separated from three representative BC samples recovered from pyrolysis (grass and wheat straw derived BC, household soot), including water extracted fraction of BC (WEBC, 9-21 wt%), residue fraction of BC after water extraction (R-WEBC, 79-91 wt%), water extracted minerals (WEM, 9-18 wt%), alkali extracted organic carbon (OCAE, 1-9 wt%), and elemental carbon (EC, 37-48 wt%). The bulk BC and separated BC components were analyzed in detail by elemental analysis and combined spectroscopic analyses. Their equilibrium hygroscopicity was measured by gravimetric method over a range of relative humidity (RH) levels (10-94%). Compared with the two organic components (OCAE and EC), the inorganic component (WEM) exhibited much stronger water uptake at all RH levels. At 94% RH level, WEM accounted for 16-139% of the overall water uptake by BC, whereas OCAE and EC accounted for only 1-3% and 6-26%, respectively. The XRD analysis of WEBC and WEM from household soot at varying RH levels indicated that the enhanced water uptake by these two components as well as that by bulk BC at high RH levels was due to the deliquescent salts (e.g., KCl, NH4Cl, KNO3, and NaCl). The strong hysteresis loops observed for bulk BC and WEBC could be attributed to the organic-facilitated drastic structural and morphological rearrangement of mineral particles as evidenced by the optical microscope analysis. The diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) analysis reaffirmed the dominant role played by the inorganic component in the hygroscopic behaviors of BC.