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1.
Chemosphere ; 256: 127081, 2020 May 15.
Artigo em Inglês | MEDLINE | ID: mdl-32447112

RESUMO

Discharging coloring products in water bodies has degraded water quality irreversibly over the past several decades. Order mesoporous carbon (OMC) was modified by embedding neodymium(III) chloride on the surface of OMC to enhance the adsorptive removal towards these contaminants. This paper represents an artificial neural network (ANN) based approach for modeling the adsorption process of sunset yellow onto neodymium modified OMC (OMC-Nd) in batch adsorption experiments. Neodymium modified OMC was characterized using N2 adsorption-desorption isotherm, TEM micrographs, FT-IR and XPS spectra analysis techniques. 2.5 wt% Nd loaded OMC was selected as the final adsorbent for further experiments because OMC-2.5Nd showed highest removal efficiency of 93%. The ANN model was trained and validated with the adsorption experiments data where initial concentration, reaction time, and adsorbent dosage were selected as the variables for the batch study, whereas the removal efficiency was considered as the output. The ANN model was first developed using a three-layer back propagation network with the optimum structure of 3-6-1. The model employed tangent sigmoid transfer function as input in the hidden layer whereas a linear transfer function was used in the output layer. The comparison between modeled data and experimental data provided high degree of correlation (R2 = 0.9832) which indicated the applicability of ANN model for describing the adsorption process with reasonable accuracy.

2.
Mol Ecol Resour ; 2020 May 23.
Artigo em Inglês | MEDLINE | ID: mdl-32445592

RESUMO

Antheraea pernyi is a semi-domesticated lepidopteran insect species valuable to the silk industry, human health, and ecological tourism. Owing to its economic influence and developmental properties, it serves as an ideal model for investigating divergence of the Bombycoidea super family. However, studies on the karyotype evolution and functional genomics of A. pernyi are limited by scarce genomic resource. Here, we applied PacBio sequencing and chromosome structure capture technique to assemble the first high-quality A. pernyi genome from a single male individual. The genome is 720.67 Mb long with 49 chromosomes and a 13.77-Mb scaffold N50. Approximately 441.75 Mb, accounting for 60.74% of the genome, was identified as repeats. The genome comprises 21,431 protein-coding genes, 85.22% of which were functionally annotated. Comparative genomics analysis suggested that A. pernyi diverged from its common ancestor with A. yamamai ~30.3 million years ago, and that chromosome fission contributed to the increased chromosome number. The genome assembled in this work will not only facilitate future research on A. pernyi and related species but also help to progress comparative genomics analyses in Lepidoptera.

3.
J Environ Manage ; 265: 110472, 2020 Jul 01.
Artigo em Inglês | MEDLINE | ID: mdl-32421550

RESUMO

Dry microalgae Spirulina platensis shows a high capacity for heavy metal uptake, but there is a concern about dissolved organic carbon (DOC) residue, which is the precursor of disinfection by-products (DBPs). Vsp, a kind of Spirulina platensis powder prepared by vacuum freeze-drying, and Osp, a kind of Spirulina platensis powder prepared by the conventional oven drying-pulverization method, were subjected to assessments of their adsorption potential for Pb2+ and DOC residue. The adsorption mechanism of Pb2+ by the two adsorbents was studied by SEM, FT-IR, EDX and N2-BET. The effects of pH, adsorbent dosage, initial Pb2+ concentration and contact time on the biosorption process were investigated. The results showed that Pb2+ biosorption by Vsp and Osp were fit well by a pseudo-second-order kinetic model and the Langmuir model. The maximum amount of Pb2+ biosorption by Vsp was 253 mg/g, which was 33 mg/g greater than that of Osp. In comparison with Osp, Vsp reached adsorption saturation 8 h earlier and had a remarkable effect on the control of DOC residue in water. When both adsorption capacity and environmental risks were considered, it was determined that the dosage of 0.5 g/L Vsp for 2 h of contact time was the best method, with 85.89 mg/g of Pb2+ removal and 3.45 mg/L of DOC residue. In summary, Vsp is a highly efficient and environmentally friendly biosorbent that can be used for heavy metal removal from water.


Assuntos
Microalgas , Poluentes Químicos da Água , Adsorção , Concentração de Íons de Hidrogênio , Cinética , Chumbo , Medição de Risco , Espectroscopia de Infravermelho com Transformada de Fourier
4.
Artigo em Inglês | MEDLINE | ID: mdl-32365834

RESUMO

Microbial immobilization is considered as a novel and environmentally friendly technology that uses microbes to reduce heavy metals accumulation in plants. To explore microbial resources which are useful in these applications, three water spinach rhizosphere soils polluted by different levels of heavy metals (heavy pollution (CQ), medium pollution (JZ), and relative clean (NF)) were collected. The community composition of heavy metal-immobilizing bacteria in rhizosphere soils and its effects on reducing the Cd2+ and Pb2+ concentrations in water spinach were evaluated. Four hundred strains were isolated from the CQ (belonging to 3 phyla and 14 genera), JZ (belonging to 4 phyla and 25 genera) and NF (belonged to 6 phyla and 34 genera) samples, respectively. In the CQ sample, 137 strains showed a strong ability to immobilize Cd2+ and Pb2+, giving Cd2+ and Pb2+ removal rates of greater than 80% in solution; Brevundimonas, Serratia, and Pseudoarthrobacter were the main genera. In total, 62 strains showed a strong ability to immobilize Cd2+ and Pb2+ in the JZ sample and Bacillus and Serratia were the main genera. A total of 22 strains showed a strong ability to immobilize Cd2+ and Pb2+ in the NF sample, and Bacillus was the main genus. Compared to the control, Enterobacter bugandensis CQ-7, Bacillus thuringensis CQ-33, and Klebsiella michiganensis CQ-169 significantly increased the dry weight (17.16-148%) of water spinach and reduced the contents of Cd2+ (59.78-72.41%) and Pb2+ (43.36-74.21%) in water spinach. Moreover, the soluble protein and Vc contents in the shoots of water spinach were also significantly increased (72.1-193%) in the presence of strains CQ-7, CQ-33 and CQ-169 compared to the control. In addition, the contents of Cd and Pb in the shoots of water spinach meet the standard for limit of Cd2+ and Pb2+ in vegetables in the presence of strains CQ-7, CQ-33 and CQ-169. Thus, the results provide strains as resources and a theoretical basis for the remediation of Cd- and Pb-contaminated farmlands for the safe production of vegetables.

5.
Enzyme Microb Technol ; 136: 109513, 2020 May.
Artigo em Inglês | MEDLINE | ID: mdl-32331718

RESUMO

L-Phenylglycine (L-PHG) is a member of unnatural amino acids, and becoming more and more important as intermediate for pharmaceuticals, food additives and agrochemicals. However, the existing synthetic methods for L-PHG mainly rely on toxic cyanide chemistry and multistep processes. To provide green, safe and high enantioselective alternatives, we envisaged cascade biocatalysis for the one-pot synthesis of L-PHG from racemic mandelic acid. A engineered E. coli strain was established to co-express mandelate racemase, D-mandelate dehydrogenase and L-leucine dehydrogenase and catalyze a 3-step reaction in one pot, enantioselectively transforming racemic mandelic acid to give L-PHG (e.e. >99 %). After the conditions for biosynthesis of L-PHG optimized by response surface methodology, the yield and space-time yield of L-PHG can reach 87.89 % and 79.70 g·L-1·d-1, which was obviously improved. The high-yielding and enantioselective synthetic methods use cheap and green reagents, and E. coli whole-cell catalysts, thus providing green and useful alternative methods for manufacturing L-PHG.

6.
Chemosphere ; 253: 126705, 2020 Aug.
Artigo em Inglês | MEDLINE | ID: mdl-32302904

RESUMO

Polystyrene microplastics (PSMPs) with different sizes, surface charges and aging statuses simulated field PSMPs and were applied to understand their cytotoxicity to Escherichia coli. The PSMPs hardly affected the viability, membrane integrity, ROS generation and ATPase activity of E. coli, and the cytotoxicity of field PSMPs is marginal and assumed to be overestimated. Low concentrations (1.0 mg L-1) of PSMPs dynamically affect the cytotoxicity of Ag+ to E. coli through various toxic mechanisms. PSMPs likely mitigated the cytotoxicity of Ag+ during the initial 24 h of co-exposure by protecting the cell membrane, inhibiting ROS generation and/or recovering ATPase activity (p < 0.05 or p < 0.01). During prolonged co-exposure for 48 h, nonfunctionalized polystyrene (PS-NF) still mitigated the cytotoxicity of Ag+ by protecting the integrity of the cell membrane, and aged PS-NF slightly affected cytotoxicity. PS-NH2 and PS-COOH intensified the cytotoxicity of Ag+ because PS markedly promoted ROS generation and inhibited ATPase activity. Thus, field PSMPs were assumed to exhibit marginal cytotoxicity to E. coli and can combine with surrounding Ag+ to modify the E. coli population levels and even the structure of aquatic ecosystems. Accordingly, the environmental and health risks of field PSMPs require further intensive investigation, and the combined toxicity effects of field PSMPs with Ag+ should be considered carefully due to their dynamic toxic effects and mechanisms.

7.
FEMS Microbiol Ecol ; 96(5)2020 May 01.
Artigo em Inglês | MEDLINE | ID: mdl-32275304

RESUMO

The relative importance of local environments and dispersal limitation in shaping denitrifier community structure remains elusive. Here, we collected soils from 36 riverine, lacustrine and palustrine wetland sites on the remote Tibetan Plateau and characterized the soil denitrifier communities using high-throughput amplicon sequencing of the nirS and nirK genes. Results showed that the richness of nirS-type denitrifiers in riverine wetlands was significantly higher than that in lacustrine wetlands but not significantly different from that in palustrine wetlands. There was no clear distinction in nir community composition among the three kinds of wetlands. Irrespective of wetland type, the soil denitrification rate was positively related to the abundance, but not the α-diversity, of denitrifying communities. Soil moisture, carbon availability and soil temperature were the main determinants of diversity [operational taxonomic unit (OTU) number] and abundance of thenirS-type denitrifier community, while water total organic carbon, soil NO3- and soil moisture were important in controlling nirK-type denitrifier diversity and abundance. The nirS community composition was influenced by water electrical conductivity, soil temperature and water depth, while the nirK community composition was affected by soil electrical conductivity. Spatial distance explained more variation in the nirS community composition than in the nirK community composition. Our findings highlight the importance of both environmental filtering and spatial distance in explaining diversity and biogeography of soil nir communities in remote and relatively undisturbed wetlands.

8.
Arch Microbiol ; 2020 Apr 23.
Artigo em Inglês | MEDLINE | ID: mdl-32328753

RESUMO

A Gram-stain-negative, aerobic, and motile strain, TJ48T, was isolated from pakchoi-cultivated soil contaminated with Cd and Pb in Xinxiang (China). Cells of the strain were rod-shaped and colonies on LB agar were faint yellow. Strain TJ48T was positive for catalase and oxidase and the optimal condition for growth was 28 °C, with 1% (w/v) NaCl and at pH 7.0. Phylogenetic analysis based on the 16S rRNA gene sequences showed that strain TJ48T was closely related to the genus Rhodobacter and the closest relatives were Rhodobacter ovatus JA234T (97.4%, 16S rRNA gene sequence similarity) and Rhodobacter azotoformans KA25T (96.5%). The DNA G + C content of strain TJ48T was 64.7 mol%. Genome-to-genome distance calculations (GGDC) and ANIb values from genomic comparison between the genomes of strain TJ48T and the related reference species were less than 70% and 95%, respectively. The major cellular fatty acids were summed feature 8 (C18:1ω7c and/or C18:1ω6c) and C17:0. The only isoprenoid quinone detected was Ubiquinone-10 (Q-10). The polar lipid profile contains diphosphatidylglycerol, phosphatidylglycerol, phosphatidylethanolamine, one unidentified aminophospholipid, one unidentified phospholipids, and three unidentified lipids. Strain TJ48T significantly increased the dry weight of roots (26.2-66.3%) and shoots (16.7-37.8%) of pakchoi and reduced the Cd (50.2-60.1%) and Pb (55.6-60.9%) contents in pakchoi shoots and roots. On the basis of the physiological, genotypic and genomic characteristics, the strain TJ48T represent a novel species of the genus Rhodobacter, and the name Rhodobacter xinxiangensis sp. nov. is proposed (type strain TJ48T = CCTCC AB2019120T = KCTC 72510T).

9.
Artigo em Inglês | MEDLINE | ID: mdl-32291646

RESUMO

Functionalized ordered mesoporous carbon (MOMC-NP) was synthesized by chemical modification using HNO3 and H3PO4 to enhance Pb(II) adsorption. The phosphate functional group represented by P-O-C bonding onto the surface of OMC was verified by FT-IR and XPS. Batch adsorption experiments revealed the improvement of adsorption capacity by 39 times over the virgin OMC. Moreover, the Pb(II) adsorption results provided excellent fits to Langmuir model and pseudo-second-order kinetic model. The adsorption mechanism of Pb(II) onto MOMC-NP revealed the formation of metal complexes with carboxyl, hydroxyl, and phosphate groups through ion exchange reactions and hydrogen bondings. The calculated activation energy was 22.09 kJ/mol, suggesting that Pb(II) adsorption was a chemisorption. At pH>pHpzc, the main Pb(II) existing species of Pb(II) and Pb(OH)+ combine with the carboxyl, hydroxyl, and phosphate functional groups via electrostatic interactions and hydrogen bonding. All these findings demonstrated that MOMC-NP could be a useful and potential adsorbent for adsorptive removal of Pb(II). Graphical abstract.

10.
Ecotoxicol Environ Saf ; 195: 110375, 2020 Jun 01.
Artigo em Inglês | MEDLINE | ID: mdl-32200142

RESUMO

Microbial immobilization is a novel and environmentally friendly technology that uses microbes to reduce metal availability in soil and accumulation of heavy metals in plants. We used urea agar plates to isolate urease-producing bacteria from the rhizosphere soil of pakchoi in Cd- and Pb-contaminated farmland and investigated their effects on Cd and Pb accumulation in pakchoi and the underlying mechanisms. The results showed that two urease-producing bacteria, Bacillus megaterium N3 and Serratia liquefaciens H12, were identified by screening. They had higher ability to produce urease (57.5 ms cm-1 min-1 OD600-1 and 76.4 ms cm-1 min-1 OD600-1, respectively). The two strains allowed for the immobilization of Cd and Pb by extracellular adsorption, bioprecipitation, and increasing the pH (from 6.94 to 7.05-7.09), NH4+ content (69.1%-127%), and NH4+/NO3- ratio (from 1.37 to 1.67-2.11), thereby reducing the DTPA-extractable Cd (35.3%-58.8%) and Pb (37.8%-62.2%) contents in the pakchoi rhizosphere soils and the Cd (76.5%-79.7%) and Pb (76.3%-83.5%) contents in the leaves (edible tissue) of pakchoi. The strains were highly resistant to heavy metal toxicity; produced IAA, siderophores and abscisic acid; and increased the NH4+/NO3- ratio, which might be related to the two strains protectiing pakchoi against the toxic effect of Cd and Pb and increasing pakchoi biomass. Thus, the results were supposed to strain resources and a theoretical basis for the remediation of Cd- and Pb-contaminated farmlands for the safe production of vegetables.

11.
Poult Sci ; 99(2): 791-796, 2020 Feb.
Artigo em Inglês | MEDLINE | ID: mdl-32029161

RESUMO

In this study, loop-mediated isothermal amplification (LAMP) was used to establish a rapid, specific, and visual detection method for duck hepatitis B virus (DHBV). The design and synthesis of 4 specific LAMP primers were based on the conserved gene region of the DHBV genome, and the optimum temperature and time of the LAMP reaction were 63°C and 50 min, respectively. The LAMP assay was confirmed to be specific for DHBV detection and had the same sensitivity as the quantitative PCR assay. A visual detection method for rapid determination of results was developed using a color indicator containing phenol red and cresol red. A color change was produced based on a pH change in the reaction system, indicating a positive reaction. For the detection of samples from ducks and geese, the LAMP method has the advantages of simplicity, high sensitivity and specificity, good visibility, and low cost. Moreover, it is more practical and convenient than PCR-related assays for the clinical detection of DHBV.

12.
J Hazard Mater ; 384: 121258, 2020 02 15.
Artigo em Inglês | MEDLINE | ID: mdl-32028547

RESUMO

An innovative advanced oxidation process was successfully developed to photocatalytic-degradation of estrone through the synergistic effect of biochar and Bi/Bi2O3 in bismuth-containing photocatalytic biochar (BiPB). The highest reaction rate constant (kobs) of estrone degradation by BiPB was 0.045 min-1 under the conditions of initial concentration of estrone =10.4 µmol L-1, [BiPB] =1 g L-1, pH = 7.0. The kobs was almost tenfold and more than 20 times than that of biochar without bismuth impregnation and pristine Bi/Bi2O3, respectively. The best photocatalytic performance of BiPB composites for the degradation of estrone was primarily attributed to generation of OH radicals. Impregnation of bismuth helped control the concentration of persistent free radicals (PFRs) and develop a hierarchical porous structure of biochar. The presence of biochar facilitated pre-concentration estrone on BiPB and improved the separation and transfer efficiency of charge carriers. The synergistic effect between biochar and Bi/Bi2O3 contributed to the generation of OH radicals for estrone degradation under neutral pH conditions. The transformation pathway of estrone was also proposed based on the measured transformation products in the presence of BiPB. The high efficiency of BiPB composites indicated that this easily-obtained material was promising for estrone-wastewater treatment applications as a low-cost composite photocatalyst.

13.
Environ Sci Technol ; 54(6): 3267-3277, 2020 03 17.
Artigo em Inglês | MEDLINE | ID: mdl-32101417

RESUMO

Wetlands have numerous critical ecological functions, some of which are regulated by several nitrogen (N) and carbon (C) biogeochemical processes, such as denitrification, organic matter decomposition, and methane emission. Until now, the underlying pathways of the effects of environmental and biological factors on wetland N and C cycling rates are still not fully understood. Here, we investigated soil potential/net nitrification, potential/unamended denitrification, methane production/oxidation rates in 36 riverine, lacustrine, and palustrine wetland sites on the Tibet Plateau. The results showed that all the measured N and C cycling rates did not differ significantly among the wetland types. Stepwise multiple regression analyses revealed that soil physicochemical properties (e.g., moisture, C and N concentration) explained a large amount of the variance in most of the N and C cycling rates. Microbial abundance and diversity were also important in controlling potential and unamended denitrification rates, respectively. Path analysis further revealed that soil moisture and N and C availability could impact wetland C and N processes both directly and indirectly. For instance, the indirect effect of soil moisture on methane production rates was mainly through the regulating the soil C content and methanogenic community structure. Our findings highlight that many N and C cycling processes in high-altitude and remote Tibetan wetlands are jointly regulated by soil environments and functional microorganisms. Soil properties affecting the N and C cycling rates in wetlands through altering their microbial diversity and abundance represent an important but previously underestimated indirect pathway.


Assuntos
Solo , Áreas Alagadas , Carbono , Nitrogênio , Microbiologia do Solo , Tibet
14.
J Environ Sci (China) ; 89: 180-193, 2020 Mar.
Artigo em Inglês | MEDLINE | ID: mdl-31892390

RESUMO

Released Ag ions or/and Ag particles are believed to contribute to the cytotoxicity of Ag nanomaterials, and thus, the cytotoxicity and mechanism of Ag nanomaterials should be dynamic in water due to unfixed Ag particle:Ag+ ratios. Our recent research found that the cytotoxicity of PVP-Ag nanoparticles is attributable to Ag particles alone in 3 hr bioassays, and shifts to both Ag particles and released Ag+ in 48 hr bioassays. Herein, as a continued study, the cytotoxicity and accumulation of 50 and 100 nm Ag colloids in Escherichia coli were determined dynamically. The cytotoxicity and mechanisms of nano-Ag colloids are dynamic throughout exposure and are derived from both Ag ions and particles. Ag accumulation by E. coli is derived mainly from extracellular Ag particles during the initial 12 hr of exposure, and thereafter mainly from intracellular Ag ions. Fe3+ accelerates the oxidative dissolution of nano-Ag colloids, which results in decreasing amounts of Ag particles and particle-related toxicity. Na+ stabilizes nano-Ag colloids, thereby decreasing the bioavailability of Ag particles and particle-related toxicity. Humic acid (HA) binds Ag+ to form Ag+-HA, decreasing ion-related toxicity and binding to the E. coli surface, decreasing particle-related toxicity. HA in complex conditions showed a stronger relative contribution to toxicity and accumulation than Na+ or Fe3+. The results highlighted the cytotoxicity and mechanism of nano-Ag colloids are dynamic and affected by environmental factors, and therefore exposure duration and water chemistry should be seriously considered in environmental and health risk assessments.


Assuntos
Escherichia coli/efeitos dos fármacos , Nanopartículas Metálicas/toxicidade , Prata/toxicidade , Coloides , Escherichia coli/metabolismo , Ferro/química , Concentração Osmolar , Prata/metabolismo
15.
BMC Vet Res ; 16(1): 1, 2020 Jan 03.
Artigo em Inglês | MEDLINE | ID: mdl-31900161

RESUMO

BACKGROUND: Enterobacter hormaechei is commonly considered a causative pathogen for nosocomial infections and it does not usually cause diseases in animals. However, researchers have recently dissociated the pathogenic Enterobacter hormaechei from foxes and piglets. Here, the Enterobacter hormaechei was first found to be associated with respiratory disease in unweaned calves in China. CASE PRESENTATION: A 2-month-old calf was severely sick and diagnosed with respiratory infection by a rural veterinarian, and it died 5 days after treatment with penicillin G. The lung sample was then run through histopathological analysis and pathogen isolation. The sequence analysis and biochemical tests results showed the isolated bacterium strain to be Enterobacter hormaechei, and drug sensitivity tests showed resistance to all ß-lactam antimicrobials and sensitivity to quinolones. Thickened alveoli septum, inflammatory cell infiltration, and erythrocyte diapedesis around the pulmonary alveoli septum were visible in lung histopathological sections. One week later, at the same farm, another calf showed similar clinical signs, and the Enterobacter hormaechei strain was isolated from its nasal discharge; after a week of treatment with enrofloxacin, as suggested by the results of drug sensitivity tests, this calf fully recovered. CONCLUSIONS: To the best of our knowledge, this is the first case report of calves with respiratory disease that was associated with E. hormaechei, and multi-drug resistance was observed in isolates.

16.
Environ Sci Pollut Res Int ; 27(8): 8707-8718, 2020 Mar.
Artigo em Inglês | MEDLINE | ID: mdl-31912394

RESUMO

Excess Cd and Pb in agricultural soils enter the food chain and adversely affect all organisms. Therefore, it is important to find an eco-friendly way to reduce heavy metal accumulation in vegetables. We used urea agar plates to isolate urease-producing bacteria from the rhizosphere soil of lettuce in Cd- and Pb-contaminated farmland and investigated their ability to produce urease and immobilize heavy metals. The effects of these strains on the biomass, quality, and Cd and Pb accumulation of lettuce were also studied. The results showed that two urease-producing bacteria, Enterobacter bugandensis TJ6 and Bacillus megaterium HD8, were screened from the rhizosphere soil of lettuce. They had a high ability to produce urease (44.5 mS cm-1 min-1 OD600-1 and 54.2 mS cm-1 min-1 OD600-1, respectively) and IAA (303 mg L-1 and 387 mg L-1, respectively). Compared with the control, inoculation with strains TJ6 and HD8 reduced the Cd (75.3-85.8%) and Pb (74.8-87.2%) concentrations and increased the pH (from 6.92 to 8.13-8.53) in solution. A hydroponic experiment showed that the two strains increased the biomass (31.3-55.2%), improved the quality (28.6-52.6% for the soluble protein content and 34.8-88.4% for the vitamin C (Vc) content), and reduced the Cd (25.6-68.9%) and Pb (48.7-78.8%) contents of lettuce shoots (edible tissue). In addition, strain HD8 had a greater ability than strain TJ6 to reduce lettuce Cd and Pb uptake and water-soluble Cd and Pb levels in solution. These data show that the urease-producing bacteria protect lettuce against Cd and Pb toxicity by extracellular adsorption, Cd and Pb immobilization, and increased pH. The effects of heavy metal immobilization by the two strains can guarantee vegetable safety in situ for the bioremediation of heavy metal-polluted farmland.


Assuntos
Bactérias/metabolismo , Cádmio/metabolismo , Chumbo/metabolismo , Alface/metabolismo , Metais Pesados , Poluentes do Solo , Urease/metabolismo , Bactérias/isolamento & purificação , Alface/microbiologia , Solo , Microbiologia do Solo
17.
Aquat Toxicol ; 220: 105407, 2020 Mar.
Artigo em Inglês | MEDLINE | ID: mdl-31945654

RESUMO

ZnO nanoparticles (NPs) form binary mixtures of ZnO particles and released Zn2+ in the environment, and the quantitative contributions of these components to toxicity are still uncertain. Herein, quantitative contribution of ZnO particle and Zn2+ to cytotoxicity of ZnO NPs to Escherichia coli were determined during 48 h bioassay. The cytotoxicity and mechanisms of ZnO NPs were dynamic and affected by ionic strength, Fe3+, humic acid, and temperature due to the unfixed ZnO particle:Zn2+ ratio. ZnO NPs and ZnO bulk particles (BPs) had comparable cytotoxicity but distinct cytotoxic mechanisms. ZnO NPs cytotoxicity arises mainly from ZnO particles for 3 h and from Zn2+ afterwards (8-48 h). The cytotoxicity of ZnO BPs depends predominantly on ZnO particles for 12 h and on Zn2+ from 24 to 48 h. The cytotoxicity of ZnO NPs and BPs is partially attributable to Zn accumulation, and dependent on ZnO particle:Zn2+ ratio. The linear regressions of acute toxicity for ZnO NPs vs. BPs and Zn2+ yielded excellent r2 (0.9994 and 0.9998) from literature data and good r2 (≥ 0.714) under certain environmental factors, which can be applied to assess environmental risk of ZnO NPs. Furthermore, dynamic cytotoxicity and mechanisms should be seriously considered during the environmental risk assessment of ZnO NPs.


Assuntos
Escherichia coli/efeitos dos fármacos , Nanopartículas/toxicidade , Poluentes Químicos da Água/toxicidade , Óxido de Zinco/toxicidade , Escherichia coli/metabolismo , Viabilidade Microbiana/efeitos dos fármacos , Nanopartículas/metabolismo , Poluentes Químicos da Água/metabolismo , Óxido de Zinco/metabolismo
18.
Sci Total Environ ; 708: 135102, 2020 Mar 15.
Artigo em Inglês | MEDLINE | ID: mdl-31812399

RESUMO

Soil redistribution by terrace construction, as one of the most evident anthropogenic imprints on hill-slopes, may influence soil organic carbon (SOC) dynamics through re-shaping topography and altering water and oxygen availability. However, the fundamental role and mechanisms by which terrace construction affects in situ soil CO2 emissions and its temperature sensitivity (Q10) remain poorly understood. In this study, topsoil removal-addition approach was used to simulate topsoil redistribution during terrace construction. Compared with the nearby undisturbed soil, the average annual soil CO2 emission over two years was reduced by 24% in the topsoil removed field but enhanced by 33% in the topsoil added field. The decreased soil CO2 emission at the topsoil removed field was largely associated with the depletion of SOC stocks and microbial biomass carbon, while the increments of SOC available for decomposition at the topsoil added field contributed to its increased soil CO2 emissions. However, the average Q10 value in the topsoil removed field was 23% greater at seasonal scale and 28% greater at diurnal scale than that in the undisturbed soil. The increased Q10 in the topsoil removed field is mainly due to higher aromaticity of water-extractable organic carbon (WEOC) and the domination of Actinobacteria in keystone taxa. Overall, our results show that changes in both aromaticity of WEOC and soil microbial community composition induced by soil redistribution during terrace construction may alter the response of soil CO2 emission to elevated temperature. Our study indicates that the impact of man-made soil redistribution should not be neglected when studying regional carbon cycling.

19.
J Contam Hydrol ; 228: 103562, 2020 Jan.
Artigo em Inglês | MEDLINE | ID: mdl-31672254

RESUMO

Phosphate modified ordered mesoporous carbon (MOMC-NP) has been synthesized and proven to be an effective adsorbent for Pb(II) removal from aqueous solutions. However, the key application components of the mass transfer operations and diffusion coefficient have not been determined. In this study, a modified Finite Bath Diffusion Control Model was mathematically developed containing a constant related to the radius of the adsorbent particle and the fractional attainment of adsorption. The adsorption experiments were conducted under various initial Pb(II) concentrations ranging from 60 mg L-1 to 100 mg L-1. The results suggested that the modified Finite Bath Diffusion Control Model was more applicable to the experimental data than the original Finite Bath Diffusion Control Model. The average value of the diffusion coefficient (λD¯) obtained from the modified finite bath diffusion control model was 1.63 × 10-2 cm2 s-1 indicating the effective diffusivity in the adsorption of Pb(II) on MOMC-NP. Overall, the modified Finite Bath Diffusion Control Model exhibited the precise description and simulation of the mass transfer kinetics for Pb(II) adsorption onto MOMC-NP. Therefore, the modified Finite Bath Diffusion Control Model could be effectively used to investigate the mass transfer kinetics of the adsorption process.

20.
Huan Jing Ke Xue ; 40(11): 5133-5141, 2019 Nov 08.
Artigo em Chinês | MEDLINE | ID: mdl-31854583

RESUMO

To investigate the diversity of culturable bacteria and heavy metal-immobilizing bacteria in vegetable rhizosphere soil with high concentrations of heavy metals and explore these microbial resources, two samples of Italian lettuce rhizosphere soil with high heavy metal concentration (HY) and low heavy metal concentration (DK) were collected from Xinxiang, Henan Province. The diversity of culturable bacteria and heavy metal-immobilizing bacteria in the rhizosphere soil of lettuce was compared by culturable separation technology and a solution adsorption experiment. The enhancement of Cd and Pb immobilization and lettuce growth by the strains was also investigated in a hydroponic experiment. The results showed that 400 strains belonging to 3 phyla and 14 genera were isolated from the HY sample, with ß-Proteobacteria being the dominant phylum. Meanwhile, 400 strains belonging to 4 phyla and 30 genera were isolated from the DK sample, with Firmicutes being the dominant phylum. A total of 146 strains had a strong ability to immobilize heavy metal and the Cd and Pb removal rates were greater than 80% in the HY sample; Brevundimonas, Serratia, Arthrobacter, and Pseudarthrobacter were the main genera. However, 44 strains had a strong ability to immobilize heavy metal and the Cd and Pb removal rates were greater than 80% in the DK sample, with Bacillus being the main genus. Compared with the control, inoculation with Serratia liquefaciens HY-22, Bacillus thuringiensis HY-53, and Acinetobacter lwoffii HY-157 significantly increased the dry weight of roots (7.5%-77.6%) and shoots (15.4%-67.2%) of the Italian lettuce and cauliflower lettuce and reduced the contents of Cd (38.7%-66.6%) and Pb (34.7%-62.5%) in roots and shoots of Italian lettuce. In addition, the contents of Cd and Pb in the fresh shoots of Italian lettuce and cauliflower lettuce in the presence of Bacillus thuringiensis HY-53 were lower than the Cd and Pb limits set by national food safety standards. Thus, the results provided strain resources and a theoretical basis for the remediation of Cd-and Pb-contaminated farmlands for the safe production of crops.


Assuntos
Metais Pesados , Poluentes do Solo , Bactérias , Alface , Rizosfera , Solo
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