Toluene Degradation Research Articles

The response of microbial compositions and functions to chronic single and multiple antibiotic exposure by batch experiment

Understanding the response of the microbial community to external disturbances such as micropollutants is vital for ecological risk evaluation. In this study, the effect of chronic antibiotic exposure on community compositions and functions was investigated by two batch experiments. The first experiment investigated the effect of chronic sulfamethoxazole (SMX) exposure, while the second investigated the combined effect of dissolved organic matter (DOM) sources and multi-antibiotic exposure. The results showed that the community responses to chronic antibiotic exposure depended on the dynamic balance among community resistance, adaptation, recovery, and selection, leading to nonlinear composition diversity variations. The disturbance strength of chronic SMX exposure increased with concentration (0.5–50 μg/L). However, complex sources and structures of coexisting organic matter might delay the disturbance by elevating metabolic activity and generating functional redundancy. Especially, when nutrient was a limiting factor, the disturbance strength by DOM source was greater than that by chronic antibiotic exposure. The resistance of abundant taxa to external distributions resulted in a low explanation of community diversity, while rare taxa played key roles in response to community variation and thereby affected community assembly. Long-term SMX exposure reduced the number of key species and favored the deterministic assembly process by 21%. However, elevated community adaptability might weaken the influence of antibiotic selection. Chronic SMX exposure elevated the relative abundance of sulfonamide resistance genes (sul1, sul2) by a factor of 1.2–4.3, while that of nitrogen-fixing genes (nifH, nifK) and the metabolic pathways related to the toluene, ethylbenzene, and dioxin degradation decreased. However, the combined influence of DOM sources and multi-antibiotic exposure barely caused the difference in the genes linking to element metabolism and drug resistance of microbial communities between blank and exposed groups. This study suggested that more concern should be given to the chronic environmental effect of organic micropollutants.

Stable Loading of TiO2 Catalysts on the Surface of Metal Substrate for Enhanced Photocatalytic Toluene Oxidation.

To promote the practical application of TiO2 in photocatalytic toluene oxidation, the honeycomb aluminum plates were selected as the metal substrate for the loading of TiO2 powder. Surface-etching treatment was performed and titanium tetrachloride was selected as the binder to strengthen the loading stability. The loading stability and photocatalytic activity of the monolithic catalyst were further investigated, and the optimal surface treatment scheme (acid etching with 15.0 wt.% HNO3 solution for 15 min impregnation) was proposed. Therein, the optimal monolithic catalyst could achieve the loading efficiency of 42.4% and toluene degradation efficiencies of 76.2%. The mechanism for the stable loading of TiO2 was revealed by experiment and DFT calculation. The high surface roughness of metal substrate and the strong chemisorption between TiO2 and TiCl4 accounted for the high loading efficiency and photocatalytic activity. This work provides the pioneering exploration for the practical application of TiO2 catalysts loaded on the surface of metal substrate for VOCs removal, which is of significance for the large-scaled application of photocatalytic technology.

TiN nanoparticles/OMS-2 nanorods/carbonized wood composites for simultaneous solar water evaporation and abatement of volatile organic compound from undrinkable water

Severe air pollution, water pollution, and climate change have led to an increasing shortage of clean water. Solar interface water evaporation is becoming important to obtain distilled water from undrinkable water such as seawater and contaminated water. However, the as-obtained distilled water usually contains excessive volatile organic compounds (VOCs), which are serious harmful to human health. In this article, a novel bi-functional material is prepared by depositing manganese oxide octahedral molecular sieve (OMS-2) nanorods on carbonized wood (CW), which can simultaneously realize solar water evaporation and VOCs abatement. OMS-2 nanorods synthesized at lower hydrothermal temperature possess higher oxygen vacancy defects, which can improve not only the solar absorption and solar water evaporation rate but also solar driven photothermo-catalytic activity for the oxidation of VOCs. Doping TiN nanoparticles into CW/OMS-2 can further enhance the solar water evaporation performances and VOCs removal efficiencies because of its excellent solar absorption ability, which can further increase the temperature of OMS-2 catalyst and accelerate the solar water evaporation and the toluene degradation. The as-designed bifunctional composites possess an outstanding water evaporation rate over 1.436 kg m−2 h−1 and a toluene removal efficiency of 92.96% under 2.5 sun irradiation, indicating exciting prospects for efficiently producing clean water from undrinkable water with VOCs.

Boosting toluene mineralization and ozone decomposition in plasma catalytic system by regulating the oxygen vacancy over Ag-based catalyst

Incomplete mineralization and high outlet ozone concentration are two urgent issues that need to be overcome in plasma catalytic systems for the purification of volatile organic compounds (VOCs). Herein, we attempted to address these issues by coupling Ag/ZSM-5 catalyst reduced by hydrogen at different temperatures with a dielectric barrier discharge (DBD) reactor during toluene degradation. The catalyst characterization (including XRD, UV–vis, XPS, XAFS, Raman, EPR) combined with density functional theory (DFT) calculations indicated that hydrogen reduction lowered the energy between metal ions and oxygen, generating more oxygen vacancies and facilitating the transition from Ag ions to Ag0. The abundant vacancies influenced the electron properties in the adjacent atoms, making them catalytically active and thereby promoting the adsorption and activation of CO and O3. Thus, the mineralization rate and O3 decomposition performance were significantly enhanced for the hydrogen-reduced Ag/ZSM-5 catalysts. Moreover, the L-H, E-R and MVK mechanisms were first experimentally verified in plasma catalytic system by changing the background atmosphere during toluene adsorption and discharge degradation stages. This study provides insights into the rational design of highly effective catalysts in a plasma catalytic system for the removal of VOCs.

The resin-supported iron-copper bimetallic composite as highly active heterogeneous Fenton-like catalysts for degradation of gaseous toluene.

In this study, a resin-supported iron-copper bimetallic heterogeneous Fenton catalyst with excellent removal performance, superior economy and outstanding recoverability was synthesized by an impregnation method and used to remove gaseous toluene. Experiments disclosed that 3-FeCu@LXQ-10 possessed extremely high catalytic capacity. At a temperature of 30 °C, an initial toluene concentration of 200 mg/m3 and H2O2 atomization amount of 3 mmol/h, the toluene removal efficiency of 3-FeCu@LXQ-10 was 97.50%. Experimental tests had revealed that the bimetallic supported catalysts exhibited higher catalytic activity than single metal-supported catalysts, owing to an interaction effect between iron and copper metal ions. Furthermore, electron paramagnetic resonance (EPR) and radical quenching tests were carried out, and the results indicated •OH radicals performed a key role in the Fenton-like process. In addition, the iron-copper bimetallic catalysts exhibited good reusability and stability characteristics during six degradation cycles. This study shows promising potential in using FeCu@LXQ-10 as a heterogeneous catalyst for removing toluene.

Regulating electronic metal-support interaction by synthetic methods to enhance the toluene degradation over Pt/Co3O4 catalysts

The synthesis method of precious metal catalysts would affect the electronic metal-support interaction (EMSI) of catalysts, which further affected the catalytic activity. In this paper, Co3O4 was obtained as support by the pyrolysis of ZIF-67 as a template sacrificial agent, and Pt species were loaded by three different reduction methods. Among them, the catalyst produced by the NaBH4 reduction method possessed the best activity with T90 of 168 °C. Through a series of characterization and experiments, it was found that the EMSI of the catalyst was optimized by this synthesis method, which led to electron transfer among Pt species and Co3O4. The catalysts also exhibited excellent water resistance, stability, and recycling performance. The possible degradation mechanism of toluene was also revealed by in situ DRIFTS and GC–MS. This paper provided ideas for the construction of catalysts and a theoretical reference for the relevant verification of EMSI.

Genome analysis of a coral-associated bacterial consortium highlights complementary hydrocarbon degradation ability and other beneficial mechanisms for the host

Here we report the oil degradation genetic potential of six oil-degrading bacteria (ODB), previously used as a bioremediation consortium, isolated from the hydrocoral Millepora alcicornis and seawater. The strains were identified as Halomonas sp. (LC_1), Cobetia sp. (LC_6), Pseudoalteromonas shioyasakiensis (LC_2), Halopseudomonas aestusnigri (LC_3), Shewanella algae (LC_4), and Brucella intermedia (LC_5). The taxonomic identification differed from that of the original paper when we used whole genome gene markers instead of just 16S rRNA gene. Genes responsible for the degradation of aromatic hydrocarbons and n-alkanes were found in all genomes, although different (and complementary) steps of the metabolic pathways were unique to each strain. Genes for naphthalene and toluene degradation were found in various strains. We annotated quinate degradation genes in LC_6, while LC_3 and LC_5 presented genes for biosurfactant and rhamnolipid biosynthesis. We also annotated genes related to beneficial mechanisms for corals, such as genes involved in nitrogen and DMSP metabolism, cobalamin biosynthesis and antimicrobial compounds production. Our findings reinforce the importance of using bacterial consortia for bioremediation approaches instead of single strains, due to their complementary genomic arsenals. We also propose a genome-based framework to select complementary ODB that can provide additional benefits to coral health.

Thermally oxidized PAN as photocatalyst support layer for VOCs removal

Photocatalytic filter plays a key role in VOCs removal and ensuring the long-term durability of photocatalytic filter is essential for increasing their lifespan in real-world industrial application. However, how to unlock the stability of organic supporting materials as photocatalytic filter has not been taken into account. In this work, photocatalyst TiO2 nanoparticles were successfully immobilized on a polyacrylonitrile (PAN) nonwoven using a solvent swelling method, followed by a thermal oxidation treatment. The photocatalytic efficiency of prepared PAN nonwovens in VOCs removal was investigated and the effect of surface treatments and thermal oxidation process on fibers photostability and thermal characteristics were explored. The obtained thermal-oxidized TiO2@PAN nonwoven showed photocatalytic efficiencies of 75% and 92% for the degradation of toluene and formaldehyde gases, respectively, under simulated sunlight. Compared with the TiO2@PAN nonwoven, the photo-induced degradation rate of oxidized-TiO2@PAN nonwoven decreased by 43%, and TGA-DTG results demonstrated a superior thermal stability of the oxidized PAN sample. The findings of this research can facilitate the application of novel PAN-based nonwoven filters in photocatalytic removal of VOCs by providing higher efficiency, improved thermal stability and photostability.

Study on the regulation of BiOCl and its mechanism of photocatalytic degradation of toluene

The use of green photocatalytic technology to remove low-concentration organic waste gas has piqued the interest of many people in recent years, and it is expected to be used to solve the problem of disorganized emission of low-concentration waste gas on the factory floor due to its wide range of applications and high catalytic efficiency. To this end, this paper firstly explores and simulates the unorganized emission scenario of toluene from low-concentration organic waste gas in the factory floor; secondly, it investigates the effect of BiOCl photocatalysts obtained by crystal surface modulation and morphology modulation on the performance of photocatalytic degradation of toluene, and in this process, the mechanism of photocatalytic degradation of toluene is explored by combining material characterization analysis and theoretical analysis. Finally, it was concluded as follows: the BiOCl −010 sample prepared by crystal surface modulation was the optimal catalyst with 94.8% degradation rate of toluene in 120 min. The cyclic experiments and characterization analysis means proved that the catalytic activity of the reacted sample was slightly enhanced while maintaining stability, attributed to the generation of oxygen vacancies. Oxygen vacancies, as defects, can become the center for capturing photogenerated electrons and improve the separation efficiency of photogenerated electrons and holes, thus enhancing the photocatalytic activity. Combined with the radical capture experiments and GC/MS analysis, the main pathway of toluene degradation in the course of photocatalytic reaction was deduced, i.e., toluene → benzene → ring-opening products → short chain-like compounds → carbon dioxide + water.

Decorating {0 0 1} TiO2 nanosheets on hydrophobic NaY zeolite: An efficient deactivation-resistant photocatalyst for gaseous toluene removal

Photocatalysis is regarded as a promising in situ air purification technology for the removal of volatile organic compounds. However, the deactivation of photocatalysts remains a serious issue that needs to be addressed. Herein, we report a novel dual-functional photocatalyst (TiO2@HYZ) with spatially separated catalytic sites and adsorption sites, which has been obtained by combining hydrophilic {001} TiO2 nanosheets with hydrophobic NaY zeolite. TiO2@HYZ showed excellent photocatalytic activity for the degradation of gaseous toluene under UV irradiation in humid air. The optimized TiO2@HYZ-2 (containing 45.7 wt% TiO2) achieved 96.6% toluene removal and 87.4% mineralization within 120 min. The specific reaction rate constant of TiO2@HYZ-2, pristine TiO2 and P25 normalized by the unit amount of TiO2 during the photocatalytic degradation process were calculated to be 0.481, 0.230 and 0.250 min−1 g−1, respectively. Moreover, TiO2@HYZ-2 showed superior durability, maintaining stable performance over repeated toluene degradation processes, even at high toluene concentration, whereas pristine TiO2 incurred severe deactivation with increasing number of photocatalysis cycles. The significantly enhanced activity and anti-deactivation property was attributed to a synergistic effect between HYZ and TiO2 in the catalyst structure, which strengthened the adsorption of toluene on HYZ and facilitated effective separation of photoexcited charge carriers on TiO2, thus avoiding the deposition of degradation intermediates on the active sites and simultaneously improving mineralization. This work provided a new perspective for the design of efficient and deactivation-resistant photocatalysts for air pollution remediation.

Design and Synthesis of NTU-9/C3N4 Photocatalysts: Effects of NTU-9 Content and Composite Preparation Method.

Hybrid materials based on graphitic carbon nitride (g-C3N4) and NTU-9 metal-organic frameworks (MOF) were designed and prepared via solvothermal synthesis and calcination in air. The as-prepared photocatalysts were subsequently characterized using Brunauer-Emmett-Teller (BET) analysis, UV-Vis diffuse reflectance spectroscopy (DRS), photoluminescence (PL) emission spectroscopy, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and scanning electron microscopy (SEM). The obtained NTU-9/C3N4 composites showed a greatly improved photocatalytic performance for the degradation of toluene in the gas phase under LED visible-light irradiation (λmax = 415 nm). The physicochemical properties and photocatalytic activities of the obtained NTU-9/C3N4 materials were tuned by varying the NTU-9 content (5-15 wt%) and preparation method of the composite materials. For composites prepared by calcination, the photocatalytic activity increased with decreasing NTU-9 content as a result of the formation of TiO2 from the MOFs. The best photocatalytic performance (65% of toluene was photodegraded after 60 min) was achieved by the NTU-9/C3N4 sample prepared via the solvothermal method and containing 15 wt% MOF, which can be attributed to the appropriate amount and stable combination of composite components, efficient charge separation, and enhanced visible-light absorption ability. The photocatalytic mechanisms of the prepared hybrid materials depending on the preparation method are also discussed.

Toluene-driven anaerobic biodegradation of chloroform in a continuous-flow bioelectrochemical reactor

Subsurface co-contamination by multiple pollutants can be challenging for the design of bioremediation strategies since it may require promoting different and often antagonistic degradation pathways. Here, we investigated the simultaneous degradation of toluene and chloroform (CF) in a continuous-flow anaerobic bioelectrochemical reactor. As a result, 47 μmol L−1 d−1 of toluene and 60 μmol L−1 d−1 of CF were concurrently removed, when the anode was polarized at +0.4 V vs. Standard Hydrogen Electrode (SHE). Analysis of the microbial community structure and key functional genes allowed to identify the involved degradation pathways. Interestingly, when acetate was supplied along with toluene, to simulate the impact of a readily biodegradable substrate on process performance, toluene degradation was adversely affected, likely due to competitive inhibition effects. Overall, this study proved the efficacy of the developed bioelectrochemical system in simultaneously treating multiple groundwater contaminants, paving the way for the application in real-world scenarios.

Health and Carcinogenic Risk Assessment of Exposure to by-Products of Photocatalytic Degradation of Toluene in a Spouted Bed Reactor with Porous and Non-Porous Draft Tube.

This study was performed to assessment the health and carcinogenic risk of exposure to by-products of photocatalytic degradation of toluene in a spouted bed reactor Equipped with porous and non-porous draft tube. For this purpose, titanium dioxide nanoparticles were used as photocatalysts and UV lamps as radiation sources. Degradation efficiency and CO2 selectivity were compared. By-products were also detected in three spouted bed reactors with and without a porous and non-porous draft tube. The results revealed that the degradation efficiency of toluene in the spouted bed reactor without a draft tube was 30.75%. The insertion of porous and non-porous draft tubes in the spouted bed reactor increased the degradation efficiency up to 54.88% and 47.63%, respectively. Meantime, CO2 selectivity decreased from 100% to 50.8% within 180 min irradiation time in the spouted bed reactor without draft tube, while in the spouted bed reactors with porous and non-porous draft tube maintained at 89.85% and 84.35%, respectively. Toluene and four by-products with carcinogenic and non-carcinogenic risk of 0.002176 and 182.2, respectively, were detected in the spouted bed reactors without draft tube. However, no by-products with carcinogenic risk were found in the spouted bed reactor with porous and non-porous draft tube. photocatalytic degradation of toluene in a spouted bed reactor without a draft tube produces by-products with health and carcinogenic risks. The insertion of a porous and non-porous draft tube in spouted bed reactors provided mineralization more complete than spouted bed reactor without a draft tube by reducing the dead zone and providing appropriate contact between the toluene, photocatalyst, and UV. Therefore, prevent the formation of dangerous and carcinogenic by-products.

Promoting the performance of Nb2O5 by doping transition metal oxide for catalytic degradation of monochlorobenzene and toluene

A string of niobium–based transition metal composite oxides (named as Nb2O5-MOx, M = Cr, V, Ti, Cu, Co, Fe, Mn and Ni, respectively) were synthesized, and their catalytic performances for the elimination of monochlorobenzene/toluene as typical VOCs were studied. Research result of structure–property relationship showed that nanocrystalline/amorphous state and mesoporous structure were formed, and transition metal elements were highly dispersed into Nb2O5, which were conducive to adjusting the physico-chemical properties of Nb2O5-MOx and enhancing the synergistic catalysis effect. The mesoporous and surface acidity of material promoted the adsorption, sensitization and breakage of chemical bonds in the organic reactants, and then reaction intermediates were oxidized and transformed into CO2 and H2O by the redox sites of material. Oxidation properties and electron density of catalysts were the most important factors affecting the catalytic combustion reaction. The order of apparent catalytic activity for monochlorobenzene elimination was: Nb2O5–Cr2O3 > Nb2O5–CuO > Nb2O5–Co3O4 > Nb2O5–Fe2O3 > Nb2O5–V2O5 > Nb2O5–Mn3O4 > Nb2O5 > Nb2O5–NiO, and the order for toluene degradation was: Nb2O5–CuO > Nb2O5–Mn3O4 > Nb2O5–V2O5 > Nb2O5–Fe2O3 > Nb2O5–Cr2O3 > Nb2O5–Co3O4 > Nb2O5 > Nb2O5–NiO. Considering the toxicity of Cr and V, the by-products produced by Cu and the high price of Co, Nb2O5–Fe2O3 was selected as the most suitable catalyst. Its catalytic activity could reach 69% conversion for monochlorobenzene (320 °C), 80% for toluene (320 °C) and 81% for 1,2-dichloroethane elimination (270 °C), and also maintain 120 h without significant deactivation, indicating that the applicability of Nb2O5–Fe2O3 was worthy of more attention and further study.

Study on catalytic degradation of toluene by copper manganese composite oxide

AbstractHerein, Cu–Mn catalysts were used to study the catalytic oxidation system of toluene, revealing the optimal preparation conditions for catalytic oxidation of toluene and the effects of other factors on catalytic performance (oxygen concentration, toluene concentration, temperature, humidity, space velocity). The as‐synthesized Cu2Mn1Ox exhibited the best catalytic activity and stability. The BET, XRD, and O2‐TPD results indicated that the synthesized Cu2Mn1 catalyst can effectively form the Cu1.4Mn1.6O4 phase at the optimal calcination temperature (500–600°C) and accelerate the toluene degradation at 220°C. Although water vapor can promote the progress of catalytic reactions, excessive water vapor tends to form competitive adsorption at active sites, inhibiting the progress of catalytic reactions. In addition, oxygen concentration plays a key role in catalytic reactions. Based on the results, it was found that at lower oxygen concentrations or higher toluene concentrations, the catalyst was easy to react with toluene to generate Cu and MnO, resulting in catalyst deactivation.

Nitrogen amendment enhances the biological methanogenic potential of bituminous coal

Improving the bioavailability of coals is an effective way to increase the production of secondary biogenic coalbed methane (CBM); however, information on the influence of different elements on the biological methane yield is lacking. In this study, the effect of high nitrogen amendment on biological methane yield was analyzed by indoor anaerobic culture experiments with two samples from different coal seams in a mining area. The results showed that the methanogenic rate increased by 1.89–3.43 times after 40 days under the high nitrogen amendment. The high nitrogen amendment changed the microbial community structure and increased 40.78% of the metabolites in the coal samples, 62 of which were related to methane metabolism, degradation of aromatic compounds, fatty acid degradation, polycyclic aromatic hydrocarbon degradation, and degradation of other benzene series. Metagenomic analysis showed that high nitrogen amendment also caused significant changes in functional gene composition and increased the abundance of functional genes related to methane metabolism, β-oxidation and the degradation of toluene and phenol. In addition, the high nitrogen amendment increased the relative abundance of methanogenic Methanosarcina and Methanoculleus and some bacterial taxa belonging to orders Clostridiales and Thermoanaerobacterales. Among them, a total of 17 metagenome assembled genomes (MAGs) were reconstructed, most of which can produce hydrogen and have the ability to degrade aromatic compounds into acetate. In summary, this study indicated the importance of nitrogen as a single element in biological methanogenesis that helps to stimulate biological methane yield for the exploration and development of CBM.

Excellent degradation of toluene by non-thermal plasma coupled with M-BTC MOF（M=Mn, Cu, Ce）

In view of the unsatisfactory synergy between plasma technology and catalyst, a series of M-BTC MOFs (M=Mn, Cu, Ce) were introduced to couple with non-thermal plasma using for toluene degradation. M-BTC MOFs containing multi-carboxylic groups were successfully synthesized and presented the excellent crystallinity, morphology and thermal stability. DBD-catalysis systems presented the more excellent toluene degradation performance than single DBD alone system. Due to the porous structure and the multivalent form of manganese, the highest toluene degradation efficiency of 96.27%, the energy efficiency of 22.32 g/kW·h, the CO2 selectivity of 53.5% and the mineralization degree of 70.17% were acquired for DBD coupled with Mn-BTC under SED of 766.35 J/L. Besides, DBD/Mn-BTC had the lowest ozone and NOx production. Moreover, the toluene degradation mechanism was analyzed by plasma emission spectra analysis, XPS spectra and GC-MS diagram analysis. It indicated plasma discharge can produce abundant free radicals and reactive species to decompose toluene firstly, and the residual toluene and intermediates in the gas can be then adsorbed on Mn-BTC and further oxidized by metal active species. Furthermore, more reactive oxygen species will be generated by activating ozone through Mn-BTC, which was beneficial for toluene degradation.

Process optimization of BTEX degradation from petrochemical effluent using integrated advanced oxidation

In this study, an integral treatment consisted of UV/Fenton/ TiO2 system in the batch systems was developed to perform degradation of synthetic Benzene, Toluene, Ethyl Benzene, and Xylene (BTEX). Initially, the efficiency of photo Fenton catalytic degradation was compared with conventional treatment methods. Later, optimum levels of selected variables such as the initial concentration of BTEX, pH, temperature, reaction time, and initial dosage of TiO2 were analyzed using one factor at a time method. Further, screening of variables and optimization were performed using Planckett-Burman design and central composite design, respectively. Photo Fenton catalytic process showed about 1.15 fold increase in efficiency when compared with photo Fenton process. Among the selected seven variables, four variables namely, initial pH, BTEX concentration, H2O2 dosage and TiO2 dosage were identified as significant factors. Under the optimal conditions, chemical oxygen demand reduction reached about 84.54 ± 2.57% using UV/Fenton/ TiO2 system. Finally, first-order kinetic model resulted in prediction of 19.43 kJ/mol of activation energy. Thus, process optimization and kinetic study using the developed photo Fenton catalytic system could be beneficial for real time waste containing BTEX pollutants.

Characterization of chemical components of fresh and aged aerosol from vehicle exhaust emissions in Hong Kong

The chemical properties of fresh and aged aerosol emitted during controlled vehicular exhaust emissions were characterized in the analysis. Pyrene (10417.1 ± 534.9 ng kg−1) is the most abundant of all analyzed compounds in total fresh emission and succinic acid (57359.8 ± 4000.3 ng kg−1) is for the total aged emission. The fresh emission factors (EFfresh) of all compounds in the n-alkanes group demonstrate higher average emissions for the two vehicles with EURO 3 standard compared to the other vehicles. The EFfresh for benzo [a]pyrene is in descending order: G1 (183.1 ± 144.7 ng kg−1) > G3 (103.4 ± 60.1 ng kg−1) > G4 (91.2 ± 80.1 ng kg−1) > G2 (88.6 ± 93.9 ng kg−1). Aged/fresh (A/F) emission ratios (>20) confirmed that these diacid compounds are generated by the photooxidation of primary pollutants that emitted from gasoline combustions. High A/F ratios (>200) in phthalic acid, isophthalic acid and terephthalic acid under idling mode imply relatively more intense photochemical reactions for their productions compared with other chemical groups. Strong positive correlations (r > 0.6) were observed between the degradation of toluene and formations of pinonic acid, succinic acid, adipic acid, terephthalic acid, glutaric acid and citramalic acid after the aging process, suggesting possible photooxidation of toluene that can lead to secondary organic aerosol (SOA) formation in the urban atmosphere. The findings demonstrate that vehicle emission standards for pollution in relation to the change of particulate matter chemical compositions and SOA formations. The results warrant a need for regulated reformulation for such vehicles.

Metagenomics-metabolomics analysis of microbial function and metabolism in petroleum-contaminated soil

Contamination of soil by petroleum is becoming increasingly serious in the world today. However, the research on gene functional characteristics, metabolites and distribution of microbial genomes in oil-contaminated soil is limited. Considering that, metagenomic and metabonomic were used to detect microbes and metabolites in oil-contaminated soil, and the changes of functional pathways were analyzed. We found that oil pollution significantly changed the composition of soil microorganisms and metabolites, and promoted the relative abundance of Pseudoxanthomonas, Pseudomonas, Mycobacterium, Immundisolibacter, etc. The degradation of toluene, xylene, polycyclic aromatic hydrocarbon and fluorobenzoate increased in Xenobiotics biodegradation and metabolism. Key monooxygenases and dioxygenase systems were regulated to promote ring opening and degradation of aromatic hydrocarbons. Metabolite contents of polycyclic aromatic hydrocarbons (PAHs) such as 9-fluoronone and gentisic acid increased significantly. The soil microbiome degraded petroleum pollutants into small molecular substances and promoted the bioremediation of petroleum-contaminated soil. Besides, we discovered the complete degradation pathway of petroleum-contaminated soil microorganisms to generate gentisic acid from the hydroxylation of naphthalene in PAHs by salicylic acid. This study offers important insights into bioremediation of oil-contaminated soil from the aspect of molecular regulation mechanism and provides a theoretical basis for the screening of new oil degrading bacteria.