Predictive modelling of dispersion controlled reactive plumes at the laboratory-scale

A model-based interpretation of laboratory-scale experimental data is presented. Hydrolysis experiments carried out using thin glass tanks filled with glass beads to construct a hypothetical and inert, homogeneous porous medium were analysed using a 2D numerical model. A new empirical formula, based upon results for non-reactive (tracer) experiments is used to calculate transversal dispersivity values for a range of grain sizes and any flow velocities. Combined with effective diffusion coefficients calculated from Stokes-Einstein type equations, plume lengths arising from mixing between two solutes can be predicted accurately using numerical modelling techniques. Moreover, pH and ion concentration profiles lateral to the direction of flow of the mixing species can be determined at any given point downstream, without the need for result fitting. In our case, this approach does not lead to overpredictions of lateral mixing, as previously reported when using parameters derived from non-reactive tracer experiments to describe reactive solute transport. The theory is based on the assumption of medium homogeneity.     

Experimental and molecular dynamic simulation study of perfluorooctane sulfonate adsorption on soil and sediment components

Soil and sediment play a crucial role in the fate and transport of perfluorooctane sulfonate(PFOS) in the environment. However, the molecular mechanisms of major soil/sediment components on PFOS adsorption remain unclear. This study experimentally isolated three major components in soil/sediment: humin/kerogen, humic/fulvic acid(HA/FA), and inorganic component after removing organics, and explored their contributions to PFOS adsorption using batch adsorption experiments and molecular dynamic simulations. The results suggest that the humin/kerogen component dominated the PFOS adsorption due to its aliphatic features where hydrophobic effect and phase transfer are the primary adsorption mechanism.Compared with the humin/kerogen, the HA/FA component contributed less to the PFOS adsorption because of its hydrophilic and polar characteristics. The electrostatic repulsion between the polar groups of HA/FA and PFOS anions was attributable to the reduced PFOS adsorption. When the soil organic matter was extracted, the inorganic component also plays a non-negligible role because PFOS molecules might form surface complexes on SiO 2surface.The findings obtained in this study illustrate the contribution of organic matters in soils and sediments to PFOS adsorption and provided new perspective to understanding the adsorption process of PFOS on micro-interface in the environment.     

On the parental origin of the X's in a prenatally diagnosed 49,XXXXX syndrome

A 49,XXXXX fetus was detected in amniotic fluid cell cultures from a 39-year-old mother. On ultrasonography, growth retardation and bilateral radioulnar synostosis were found. Additional clinical manifestations were mild facial anomalies and hypoplastic ovaries depleted of oocytes. Molecular analysis showed that this aneuploidy arose by successive maternal non-disjunction.     

Methyl-triclosan binding to human serum albumin: Multi-spectroscopic study and visualized molecular simulation

Methyl-triclosan (MTCS), a transformation product and metabolite of triclosan, has been widely spread in environment through the daily use of triclosan which is a commonly used anti-bacterial and anti-fungal substance in consumer products. Once entering human body, MTCS could affect the conformation of human serum albumin (HSA) by forming MTCS–HSA complex and alter function of protein and endocrine in human body. To evaluate the potential toxicity of MTCS, the binding mechanism of HSA with MTCS was investigated by UV–vis absorption, circular dichroism and Fourier transform infrared spectroscopy. Binding constants, thermodynamic parameters, the binding forces and the specific binding site were studied in detail. Binding constant at room tempreture (T = 298 K) is 6.32 × 10³ L mol⁻¹; ΔH⁰, ΔS⁰ and ΔG⁰ were 22.48 kJ mol⁻¹, 148.16 J mol⁻¹ K⁻¹ and −21.68 kJ mol⁻¹, respectively. The results showed that the interactions between MTCS and HSA are mainly hydrophobic forces. The effects of MTCS on HSA conformation were also discussed. The binding distance (r = 1.2 nm) for MTCS–HSA system was calculated by the efficiency of fluorescence resonance energy transfer. The visualized binding details were also exhibited by molecular modeling method and the results could agree well with that from the experimental study.     

The effects of alkalinity and acidity of process water and hydrochar washing on the adsorption of atrazine on hydrothermally produced hydrochar

Hydrothermal carbonization of simulated food waste was performed at 250 °C for 20 h using deionized water (DI) and 0.01 N solutions of HCl, NaCl, and NaOH. The hydrochars produced were washed with acetone and the adsorptive capacity of the washed and unwashed hydrochars for atrazine were characterized. Using a generalized linear model, it was shown that the adsorptive capacity of the washed hydrochar was significantly higher than that of the unwashed hydrochars. The HCl processed unwashed hydrochar has a slightly higher adsorptive capacity compared to the DI processed hydrochar while both the NaOH processed washed and unwashed hydrochars were slightly lower than the corresponding DI processed hydrochars. ¹³C solid-state NMR results showed no discernible differences in surface functional groups among the washed hydrochars and among the unwashed hydrochars. A clear decrease in alkyl groups and an increase in aromatic/olefinic-C groups were observed after acetone washing. ¹H liquid-phase NMR showed carbon alkyl chains were present in the acetone wash. Interaction energies calculated using dispersion corrected density functional theory show that atrazine is more strongly adsorbed to surfaces without weakly associated alkyl groups.     

Insights into the structural and conformational requirements of polybrominated diphenyl ethers and metabolites as potential estrogens based on molecular docking

PBDEs and their metabolites are of concern due to their increasing concentrations in the environment and their toxic effects. Knowledge about the toxicological mechanisms of PBDEs and metabolites is urgently needed for further screening. The objective of the present study was to explore the structural and conformational requirements of PBDE compounds as human estrogen receptor alpha (hERα) agonists, and further screened out hERα agonists from PBDE compounds. Molecular docking and postdocking analysis were adopted to attain the aim. The obtained results revealed that PBDEs can be primarily screened for their estrogenicity using score values, hydrogen bonds interaction with amino acid residues Glu353 and/or Arg394 might be important for HO-PBDEs’ estrogenicity. For most MeO-PBDEs, hydrophobic interaction might be the key factor affecting their estrogenic activity. The current study suggested that molecular docking and postdocking analysis can serve as an efficient pre-screening technique for identifying potential estrogens.     

Application of surface molecular imprinting adsorbent in expanded bed for the adsorption of Ni(2+) and adsorption model

A new surface molecular imprinting adsorbent (SMIA) was used in an expanded bed. The expansion ratio and adsorption performance were studied at different volumetric rates, inlet concentrations, and pH values. A model based on the Adams-Bohart adsorption model of breakthrough curves was established. The predicted curves had good agreement with the experimental curves. The breakthrough time (T(1/2)) decreased with increasing inlet concentration when the outlet concentration was half the initial concentration (C/C(0)=0.5). The inlet concentration had little effect on the adsorption rate constant (k(1)) value when the initial concentration (C(0)) was above 150 mg/L. However, T(1/2) values increased with increasing initial pH of the inlet solution, and the k(1) value decreased due to the competition between H(+) and Ni(2+).     

Advances in research of airborne microbes in subway systems北大核心CSCD

Subway systems are indispensable for transportation in modern cities, with the air being easily polluted by microbes owing to the enclosed and crowded environment. The microbiological characteristics of subway aerosols have attracted the attention of researchers worldwide during recent years. This review aimed to evaluate the sampling and analyzing methods suitable for detecting airborne microbes in subway systems. Active air sampling methods and molecular biology techniques based on polymerase chain reaction (PCR) such as 16S rRNA gene sequencing, metagenomics, and quantitative PCR demonstrated great potential in microbial analysis of aerosols because they can provide accurate and comprehensive information. Temporal and spatial distributions of airborne microbes, as well as the factors influencing their distribution characteristics, were also discussed by critically reviewing worldwide literature on subway microbiome studies. The concentration and composition of airborne bacteria and fungi in subway can vary dramatically with time and space. The critical factors determining microbial community structure and composition include temperature, relative humidity, carbon dioxide concentration, number of passengers, presence of platform screen door, ventilation systems, and so on. The review suggests that future studies on standardized sampling and analyzing protocols are required to obtain contamination levels of subway airborne microbes and to establish the relationship between microbial monitoring data and public health risks. © 2018 Science Press. All rights reserved.