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991.
Silver nanoparticles are widely used as antimicrobial compounds based on empirical observations. However, there is few knowledge on the mechanism ruling the antimicrobial activity and toxicity of Ag nanoparticles. Here, we investigated this mechanism. Nano-Ag was synthesised by thermal co-reduction. Mutagenicity analysis was performed using Salmonella typhimurium histidine auxotrophic strains TA 98 and TA 100 at nano-silver concentrations of 100 to 500 µg per plate. Dose-dependent analysis for reactive oxygen species generation has been performed using 2,7-dichlorofluorescein diacetate dye. Membrane integrity has been analyzed at 260 nm, before and after treatment. We also used scanning electron microscopy, membrane permeabilization test, and superoxide formation determinations. Results show that the average particle size of Ag nanoparticle is 60.4 ± 3.8 nm. The minimum inhibitory concentration of Ag nanoparticles for E.coli is 30 µg/mL; the minimum bactericidal concentration is 40 µg/mL. Ames mutagenicity tests showed negative results, which may be explained by the antimicrobial activity of nano-silver. Bacterial inner wall were indeed ruptured, and cytoplasmic content was released after 5 min of treatment in a dose-dependent manner. We thus propose that reactive oxygen generation and alteration of membrane integrity and permeability are the major mechanism of antimicrobial activity of nano-silver.  相似文献   
992.
Phytoremediation is the use of plants to decontaminate and improve waters and soils. Pleustonic macrophytes are plant models for research in waters. In a phytoremediation study, the elicitation of Pistia stratiotes with methyl jasmonate or salicylic acid suggests that oxytetracycline modification rate coefficients could be increased more than threefold. Here we present the elicitation of Pistia stratiotes apical primary root tips. We detected reactive oxygen species generation by X-band electron paramagnetic resonance spectroscopy, using the spin trap α-(4-pyridyl-1-oxide)-N-tert-butylnitrone (POBN). Elicitation using 0.8 mM methyl jasmonate during 1 h increased the relative spin-trapped radical concentration by +12 %. Further, results indicate acute plant toxicity above 0.24 mM salicylic acid.  相似文献   
993.
As the largest contributor to water impairment, agriculture-related pollution has attracted the attention of scientists as well as policy makers, and quantitative information is being sought to focus and advance the policy debate. This study applies the panel unit root, heterogeneous panel cointegration, and panel-based dynamic ordinary least squares to investigate the Environmental Kuznets Curve on environmental issues resulting from use of agricultural synthetic fertilizer, pesticide, and film for 31 provincial economies in mainland China from 1989 to 2009. The empirical results indicate a positive long-run co-integrated relationship between the environmental index and real GDP per capita. This relationship takes on the inverted U-shaped Environmental Kuznets Curve, and the value of the turning point is approximately 10,000–13,000, 85,000–89,000 and over 160,000 CNY, for synthetic fertilizer nitrogen indicator, fertilizer phosphorus indicator and pesticide indicator, respectively. At present, China is subject to tremendous environmental pressure and should assign more importance to special agriculture-related environmental issues.  相似文献   
994.
Surface sediments of rivers can exhibit spatial and temporal variations in contaminant concentrations that may significantly affect risk evaluations. As to pollution control and remediation of watershed, large-scale and further background data on PAHs in China were required urgently. Spatial distribution and compositional characteristics of 16 polycyclic aromatic hydrocarbons (PAHs) in surface sediments from Haihe River Basin were investigated. A method based on effects range (ER) was used to assess ecosystem risk of ∑PAHs (the total of 16 PAH) sensitively and accurately. The results indicated that ∑PAHs content levels ranged from 257 to 16901 μg·kg−1 dry weight. The lower rings predominated in the samples, and 2-, 3-, 4-, 5- and 6-ring PAHs accounted for 12%, 21%, 30%, 30%, and 7% respectively in total PAHs. The ratio of Fl / (Fl+ Py) uniformly distributed in the interval 0.20–0.80, indicating that it may be affected by petroleum origin, oil combustion, biomass and coal combustion jointly. ∑PAHs in Cetian (S6), Dongwushi (S19), Handan (S20), Aixinzhuang (S21) and Tianjin (S37) exceeded effects range low (ERL), in which biologic effects were in a medium level with an adverse effect on biologic organisms. Thus, it is necessary to strengthen the PAHs monitoring and research of the Haihe River Basin.  相似文献   
995.
Fly ash is a hazardous byproduct of municipal solid wastes incineration (MSWI). An alkali activated blast furnace slag-based cementitious material was used to stabilize/solidify the fly ash at experimental level. The characteristics of the stabilized/solidified fly ash, including metal leachability, mineralogical characteristics and the distributions of metals in matrices, were tested by toxic characteristic leaching procedure (TCLP), X-ray diffraction (XRD) and scanning electron microscopy-energy dispersive spectrometer (SEM-EDS) respectively. Continuous acid extraction was utilized to extract metal ions and characterize their leaching behavior. The stabilization/solidification procedure for MSWI fly ash demonstrates a strong fixing capacity for the metals by the formation of C-S-H phase, hydrated calcium aluminosilicate and ettringite. The stabilized/solidified fly ash shows a dense and homogeneous microstructure. Cr is mainly solidified in hydrated calcium aluminosilicate, C-S-H and ettringite phase through physical encapsulation, precipitation, adsorption or substitution mechanisms, and Pb is mainly solidified in C-S-H phase and absorbed in the Si-O structure.  相似文献   
996.
Metal speciation can provide sufficient information for environmental and geochemical researches. In this study, based on the speciation determination of Cu and Zn in the Yangtze Estuary sediments, roles of eight geochemical controls (i.e., total organic carbon (TOC), clay, Fe/Mn in five chemical fractions and salinity) are fully investigated and sequenced with correlation analysis (CA) and principal components analysis (PCA). Results show that TOC, clay and Fe/Mn oxides are key geochemical factors affecting the chemical speciation distributions of Cu and Zn in sediments, while the role of salinity appears to be more indirect effect. The influencing sequence generally follows the order: TOC>clay>Mn oxides>Fe oxides>salinity. Among the different fractions of Fe/Mn oxides, residual and total Fe content, and exchangeable and carbonate Mn exert the greatest influences, while exchangeable Fe and residual Mn show the poorest influences.  相似文献   
997.
In wastewater treatment plants (WWTPs), a secondary settler acts as a clarifier, sludge thickener, and sludge storage tank during peak flows and therefore plays an important role in the performance of the activated sludge process. Sludge thickening occurs in the lower portions of secondary clarifiers during their operation. In this study, by detecting the hindered zone from the complete thickening process of activated sludge, a simple model for the sludge thickening velocity, u s = aX b (a = 0.9925SSVI 3.5, b = 3.541ln(SSVI 3.5)+12.973), describing the potential and performance of activated sludge thickening in the hindered zone was developed. However, sludge thickening in the compression zone was not studied because sludge in the compression zone showed limited thickening. This empirical model was developed using batch settling data obtained from four WWTPs and validated using measured data from a fifth WWTP to better study sludge thickening. To explore different sludge settling and thickening mechanisms, the curves of sludge thickening and sludge settling were compared. Finally, it was found that several factors including temperature, stirring, initial depth, and polymer conditioning can lead to highly concentrated return sludge and biomass in a biologic reactor.  相似文献   
998.
This study described the use of clay impregnated by KI in gas phase elemental mercury (Hgo) removal in flue gas. The effects of KI loading, temperature, O2, SO2 and H2O on Hgo removal were investigated using a fixed bed reactor. The Hgo removal efficiency of KI-clay with 3% KI loading could maintain at a high level (approximately 80 %) after 3 h. The KI-clay demonstrated to be a potential adsorbent for Hgo removal when compared with activated carbon based adsorbent. O2 was found to be an important factor in improving the Hgo removal. O2 was demonstrated to assist the transfer of KI to I2 on the surface of KI-clay, which could react with Hgo directly. NO and SO2 could slightly improve Hgo removal, while H2O inhibited it greatly. The results indicated that after adsorption, most of the mercury escaped from the surface again. Some of the mercury may have been oxidized as it left the surface. The results demonstrated that the chemical reaction primarily occurred between KI and mercury on the surface of the KI-clay.  相似文献   
999.
The successful operation of any type of hydrogen-producing bioreactor depends on the performance of the microorganisms present in the system. Both substrate and partial gas pressures are crucial factors affecting dark fermentation metabolic pathways. The main objective of this study was to evaluate the impact of both factors on hydrogen production using anaerobic granular sludge as inoculum and, secondly, to study the metabolic shifts of an anaerobic community subjected to low partial gas pressures. With this goal in mind, seven different wastewater (four synthetic media, two industrial wastewater, and one domestic effluent) and the effect of applying vacuum on the systems were analyzed. The application of vacuum promoted an increase in the diversity of hydrogenproducing bacteria, such as Clostridium, and promoted the dominance of acetoclastic- over hydrogenotrophic methanogens. The application of different media promoted a wide variety of metabolic pathways. Nevertheless, reduction of the hydrogen partial pressure by application of vacuum lead to further oxidation of reaction intermediates irrespective of the medium used, which resulted in higher hydrogen and methane production, and improved the COD removal. Interestingly, vacuum greatly promoted biogenic hydrogen production from a real wastewater, which opens possibilities for future application of dark fermentation systems to enhance biohydrogen yields.  相似文献   
1000.
UV photolysis and UV based advanced oxidation processes (AOPs) are gaining more and more attention for drinking water treatment. Quantum yield (ø) and molar absorption coefficient (ε) are the two critical parameters measuring the effectiveness of photolysis of a compound. The product of the two was proposed as a fundamental measure of a constituent’s amenability to transformation by photolysis. It was shown that this product, named the photolysis coefficient, k p , can be determined using standard bench tests and captures the properties that govern a constituent’s transformation when exposed to light. The development showed the photolysis coefficient to be equally useful for microbiological, inorganic and organic constituents. Values of k p calculated by the authors based on quantum yield and molar absorption coefficient data from the literature were summarized. Photolysis coefficients among microorganisms ranged from 8500 to more than 600000 and are far higher than for inorganic and organic compounds, which varied over a range of approximately 10 to 1000 and are much less sensitive to UV photolysis than the microorganisms.  相似文献   
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