Evaluation of <Emphasis Type="Italic">smtA</Emphasis> expression and <Emphasis Type="Italic">E. coli</Emphasis> survival against cadmium ions

Cadmium and other heavy metals lead to environmental danger, and these heavy metals are a great threat to human and other animal’s health. Investigation of the relationship between survival of E. coli and metallothionein smtA gene expression against cadmium ion is the goal of this research. Survival of recombinant bacteria containing smtA gene was analyzed against various concentrations of cadmium chloride salt using optical density (OD). At the resistive range, recombinant bacteria were subjected to different treatments. At the logarithmic phase of bacterial growth, sampling, RNA extraction and cDNA synthesis were performed and smtA gene expression was then analyzed by real-time PCR using designed primers for smtA gene and Amp resistance (as the calibrator gene). Relative gene expression was calculated using the ??C_t method. The resistive range against cadmium chloride was 0.5–0.7 mM (minimum inhibitory concentration (MIC = 0.5 mM)). Survival and gene expression analysis showed that in induced bacteria, smtA expression was increased significantly that in turn conferred resistance to cadmium chloride prominently. There was a direct relationship between increased smtA gene expression and survival of the recombinant bacteria. Therefore, our result may help to confront to cadmium metal environmental pollution using overexpression of smtA gene expression in recombinant bacteria.     

Remediation technologies for metal-contaminated soils and groundwater: an evaluation

Metals including lead, chromium, arsenic, zinc, cadmium, copper and mercury can cause significant damage to the environment and human health as a result of their mobilities and solubilities. The selection of the most appropriate soil and sediment remediation method depends on the site characteristics, concentration, types of pollutants to be removed, and the end use of the contaminated medium. The approaches include isolation, immobilization, toxicity reduction, physical separation and extraction. Many of these technologies have been used full-scale. This paper will review both the full-scale and developing technologies that are available. Contaminants can be isolated and contained to minimize further movement, to reduce the permeability of the waste to less than 1×10⁻⁷ m/s (according to U.S. guidelines) and to increase the strength or bearing capacity of the waste. Physical barriers made of steel, cement, bentonite and grout walls can be used for isolation and minimization of metal mobility. Another method is solidification /stabilization, which contains the contaminants in an area by mixing or injecting agents. Solidification encapsulates contaminants in a solid matrix while stabilization involves formation of chemical bonds to reduce contaminant mobility. Another approach is size selection processes for removal of the larger, cleaner particles from the smaller more polluted ones. To accomplish this, several processes are used. They include: hydrocyclones, fluidized bed separation and flotation. Addition of special chemicals and aeration in the latter case causes these contaminated particles to float. Electrokinetic processes involve passing a low intensity electric current between a cathode and an anode imbedded in the contaminated soil. Ions and small charged particles, in addition to water, are transported between the electrodes. This technology have been demonstrated in the U.S. full-scale, in a limited manner but in Europe, it is used for copper, zinc, lead, arsenic, cadmium, chromium and nickel. The duration of time that the electrode remains in the soil, and spacing is site-specific. Techniques for the extraction of metals by biological means have been not extensively applied up to this point. The main methods include bioleaching and phytoremediation. Bioleaching involves Thiobacillus sp. bacteria which can reduce sulphur compounds under aerobic and acidic conditions (pH 4) at temperatures between 15 and 55°C. Plants such as Thlaspi, Urtica, Chenopodium, Polygonum sachalase and Alyssim have the capability to accumulate cadmium, copper, lead, nickel and zinc and can therefore be considered as an indirect method of treating contaminated soils. This method is limited to shallow depths of contamination. Soil washing and in situ flushing involve the addition of water with or without additives including organic and inorganic acids, sodium hydroxide which can dissolve organic soil matter, water soluble solvents such as methanol, nontoxic cations, complexing agents such as ethylenediaminetetraacetic acid (EDTA), acids in combination with complexation agents or oxidizing/reducing agents. Our research has indicated that biosurfactants, biologically produced surfactants, may also be promising agents for enhancing removal of metals from contaminated soils and sediments.

In summary, the main techniques that have been used for metal removal are solidification/stabilization, electrokinetics, and in situ extraction. Site characteristics are of paramount importance in choosing the most appropriate remediation method. Phytoremediation and bioleaching can also be used but are not as well developed.     

Effects of heavy metals as stress factors on anaerobic digestion processes and biogas production from biomass

Heavy metals affect the biochemical reactions that take place during anaerobic digestion processes of organic matter. In this review, the different effects observed in anaerobic digestion processes and during the production of biomethane and biohydrogen from several substrates contaminated with and/or inheriting heavy metals from the substrates themselves were discussed. It has been found that heavy metals exert important roles in biochemical reactions. Heavy metals like copper, nickel, zinc, cadmium, chromium and lead have been overwhelmingly reported to be inhibitory and under certain conditions toxic in biochemical reactions depending on their concentrations. Heavy metals like iron may also exhibit stimulatory effects, but these effects have been scantily observed. This review also concludes that the severity of heavy metal inhibition depends upon factors like metal concentration in a soluble, ionic form in the solution, type of metal species, and amount and distribution of biomass in the digester or chain of biochemical reactions which constitute the anaerobic digestion process. A majority of studies have demonstrated that the toxic effect of heavy metals like chromium, cadmium and nickel is attributable to a disruption of enzyme function and structure by binding of the metal ions with thiol and other groups on protein molecules or by replacing naturally occurring metals in enzyme prosthetic groups. This review has not found published data on the effects of heavy metals on the hydrolysis stage of anaerobic digestion process chemistry, and hence further studies are required to depict any changes.     

Indicator Variogram Models: Do We Have Much Choice?

Many variogram (or covariance) models that are valid—or realizable—models of Gaussian random functions are not realizable indicator variogram (or covariance) models. Unfortunately there is no known necessary and sufficient condition for a function to be the indicator variogram of a random set. Necessary conditions can be easily obtained for the behavior at the origin or at large distance. The power, Gaussian, cubic or cardinal-sine models do not fulfill these conditions and are therefore not realizable. These considerations are illustrated by a Monte Carlo simulation demonstrating nonrealizability over some very simple three-point configurations in two or three dimensions. No definitive result has been obtained about the spherical model. Among the commonly used models for Gaussian variables, only the exponential appears to be a realizable indicator variogram model in all dimensions. It can be associated with a mosaic, a Boolean or a truncated Gaussian random set. In one dimension, the exponential indicator model is closely associated with continuous-time Markov chains, which can also lead to more variogram models such as the damped oscillation model. One-dimensional random sets can also be derived from renewal processes, or mosaic models associated with such processes. This provides an interesting link between the geostatistical formalism, focused mostly on two-point statistics, and the approach of quantitative sedimentologists who compute the probability distribution function of the thickness of different geological facies. The last part of the paper presents three approaches for obtaining new realizable indicator variogram models in three dimensions. One approach consists of combining existing realizable models. Other approaches are based on the formalism of Boolean random sets and truncated Gaussian functions.     

Biodiesel production using solid metal oxide catalysts

Biodiesel production is worthy of continued study and optimization of production procedures due to its environmentally beneficial attributes and its renewable nature. Heterogeneous transesterification is considered to be a green process. The process requires neither catalyst recovery nor aqueous treatment steps and very high yields of methyl esters can be obtained, close to the theoretical value. However, heterogeneously catalyzed transesterification generally requires more severe operating conditions, and the performance of heterogeneous catalysts is generally lower than that of the commonly used homogeneous catalysts. Heterogeneous catalysis for biodiesel production has been extensively investigated in the last few years. Many metal oxides have been studied for the transesterification process of oils; these include alkali earth metal oxides, transition metal oxides, mixed metal oxides and supported metal oxides. The use of solid metal oxides as catalysts in oil transesterification is well established, accordingly, researchers’ attempts are now focused on how to attain the highest catalyst activity. Catalyst activity is a function of its specific surface area, base strength and base site concentration. High specific surface area, strong base strength and high concentration of base sites are characteristics of an active transesterification catalyst. This review provides a brief overview of the different metal oxides frequently used in the process of transesterification of oils for the production of biodiesel with special reference to the various methods of catalyst preparation and catalyst characterization. Reaction conditions and catalyst leaching analysis are also highlighted. Finally, concluding remarks regarding catalyst selection and catalyst preparation steps are provided.     

Distribution of protons and Cd between bacterial surfaces and dissolved humic substances determined through chemical equilibrium modeling

Bacteria and dissolved humic substances are capable of binding significant concentrations of metals in natural environments. Recent advances in understanding bacteria-metal and humic-metal complexation have provided a framework for directly comparing the binding capacities of these components. In this study, we use chemical equilibrium modeling to construct an internally consistent set of thermodynamic equilibrium constants for proton and Cd binding onto dissolved humic substances, using a variety of published data sets. Our modeling approach allows for the direct comparison of humic substance binding constants and site densities to those previously published for proton and Cd binding onto natural consortia of bacteria. We then combine these constants into a unified model that accounts for the competition between bacterial surfaces and humic and fulvic acids in order to determine the relative importance of each component on the total Cd budget. The combined model is used to examine the relative contributions of bacteria and dissolved humic substances to Cd complexation in natural settings. Calculations are performed for three representative systems: (1) one with a maximum realistic concentration of bacteria and a minimum realistic concentration of humic substance, (2) one with a maximum realistic concentration of humic substance and a minimum concentration of bacteria, and (3) one with an intermediate concentration of both components.Our modeling results indicate that dissolved humic substances have 2 orders of magnitude more available binding sites than bacterial surfaces (per gram). Humic substances also have a greater affinity than bacterial surfaces for binding Cd over circumneutral pH ranges. The combined model results demonstrate that, depending upon their relative concentrations, both Cd-humic and Cd-bacteria complexes are capable of dominating Cd-speciation in specific natural environments. This modeling approach is useful in that it can easily be extended to include other metals and binding ligands; however, thermodynamic data must be gathered on additional components to facilitate the modeling of more realistic systems.     

河南登封晚古生代含煤地层各煤组的古生物特征

<正> 河南登封位于华北地台的南缘,区内石炭二叠系厚度大,出露全,分布广泛。根据含煤地层的岩性特征、旋迴规律、煤层结构和煤质差异,近千米的煤系地层共分为九个煤组(表1)。通过11条剖面数千块标本的研究和综合分析,发现9个煤组的生物化石各具特色,易于区别。     

Application of artificial neural networks for estimating Cd,Zn, Pb removal efficiency from wastewater using complexation-microfiltration process

Complexation-microfiltration process for removal of heavy metal ions such as lead, cadmium and zinc from water had been investigated. Two soluble derivates of cellulose was selected as complexing agents. The dependence of the removal efficiency from the operating parameters (pH value, pressure, concentration of metal ion, concentration of complexing agent and type of counter ion) was established. Two approaches of preparation of input data and two different artificial neural network architectures, general regression neural network and back-propagation neural network have been used for modeling of experimental data. The extrapolation ability of selected architectures, i.e., the prediction of rejection coefficient with inputs beyond the calibration range of original model, was also determined. The predictions were successful, and after evaluation of performances, the models that were developed gave relatively good results of mean absolute percentage error from 4 to 14% and R-squared from 0.717 to 0.852 for general regression neural network and from 0.897 to 0.955 for back-propagation neural network.     

The effect of prehatch and posthatch exposure to cadmium on salinity tolerance of larval grass shrimp,Palaemonetes pugio

Groups of embryonic grass shrimp,Palaemonetes pugio, were exposed to 0.1 and 0.3 mg/l cadmium at 30 ppt salinity and 25°C for the last 1, 4 or 8 days prior to hatching. Other groups of embryos were cultured in uncontaminated seawater. Prehatch exposure to cadmium was found to have no additive effect on the sensitivity of the larvae to cadmium exposure and salinity stress for 14 days after hatching. Only one group of larvae, exposed to 0.1 mg/l cadmium for 4 days before hatching, and transferred to 10 ppt salinity water containing 0.1 mg/l cadmium after hatching, showed a significant (X ², P<0.05) decrease in survival, compared to control survival. No significant decreases in survival were observed for any larvae transferred to 15 and 30 ppt salinity at a pre- and posthatch cadmium concentration of 0.1 mg/l. At a pre- and posthatch cadmium concentration of 0.3 mg/l, significant decreases in survival were observed for all of the larvae transferred to 10 and 15 ppt salinity after hatching. Significant decreases in survival were observed for only 2 of the groups exposed before hatching and transferred to 30 ppt salinity and 0.3 mg/l cadmium after hatching.     

Cadmium absorption and accumulation in different parts of kidney beans, radishes and pumpkins

This study is done to measure the absorption and distribution of cadmium in different parts of kidney beans, radishes and pumpkins. Three parts of a field was chosen. In one part 65 ppm of cadmium nitrate was added to water and in the other part 130 ppm, the last part was irrigated with normal water. Samples were digested by EPA 3050 method. Cadmium concentration was measured by Unicam 919 absorption unit. Beans accumulate cadmium mostly in root (70 ppm) and a little amount is mobilized through upper parts (12–16ppm), but kidneys did not accumulate a significant amount. In radishes the roots did not accumulate a significant amount of cadmium but stems had 4 ppm and leaves had 25 ppm. Cadmium concentration in soil does not affect its concentration in different parts of pumpkins and beside the stems and leaves (4 ppm) the other parts' concentrations were insignificant. In regard to the results of this study the cadmium concentrations in edible parts of the samples (kidney beans, radish roots and pumpkin fruit) were less than the U.S. EPA standards for agriculture and human beings.     

扬子地块西南缘铅锌矿床Cd、Ge与Ga富集规律初步研究

扬子地块西南缘分布着大量富含Cd、Ge与Ga的铅锌矿床，已成为我国Pb、Zn及Cd、Ge与Ga矿产资源的重要生产基地。对代表性铅锌矿床进行野外地质调查和系统采样鉴定后．应用电子探针微区分析手段，研究主要矿石矿物闪锌矿、方铅矿和黄铁矿中分散元素的富集特征。结果显示．各类矿床中闪锌矿均相对富集Cd，方铅矿富集Ge与Ga，而黄铁矿中Cd、Ge与Ga的富集系数均相对较低．未呈现出选择性富集的趋势；赋存于震旦纪一寒武纪地层且以脉状、网脉状产出的矿体中闪锌矿的Cd含量明显高于赋存于晚古生代并以层状产出的矿体中闪锌矿的Cd含量。     

Raw and calcination-modified coal waste as adsorbents to remove cadmium from simulated mining wastewater

The adsorption of cadmium from simulated mining wastewater by coal waste (CW) and calcination-modified coal waste (MCW) was investigated. Effects of pH, initial concentration, particle size of adsorbent, adsorbent dosage and temperature were studied in batch experiments. The adsorption efficiency for cadmium increased with increasing pH, and the optimum pH for cadmium adsorption onto MCW and CW was 6.0 and 6.5, respectively. Kinetic experiments showed that the adsorption equilibrium was reached within 120 min and followed pseudo-second-order model well. The adsorption isotherm data fit Langmuir and Freundlich models, and the adsorption capacity of cadmium on the two adsorbents increased with increasing temperature from 298 to 318 K. MCW had a higher adsorption capacity of cadmium than CW, because calcination treatment can make CW to have more loose structure and higher specific surface area. Thermodynamic parameters, the Gibbs free energy change (?G⁰), enthalpy change (?H⁰) and entropy change (?S⁰), were calculated and the results showed that the adsorption of cadmium on CW and MCW was spontaneous and endothermic. Fourier transform infrared studies indicated silanol and aluminol groups were responsible for cadmium binding. The desorption results indicated that the two adsorbents could be used repeatedly at least three times without significant decrease in the adsorption capacity for cadmium. The results suggested that modified CW could have high potential as low-cost adsorbent for cadmium removal.     

Removal of cadmium and humic acid from aqueous solutions using surface modified nanozeolite A

The sorption of cadmium and humic acids from aqueous solutions using surface-modified nanozeolite A has been investigated under various examination conditions. The morphology of untreated and treated nanozeolite was studied under scanning electron microscope and transmission electron microscope. Isotherms of cadmium adsorption onto surface-modified nanozeolite A were studied at different pH, solid to liquid ratio, adsorbate concentration and interaction time. Kinetic and equilibrium studies were conducted and the equilibrium data have been analyzed using Langmuir and Freundlich isotherm models. The study revealed that experimental results were in agreement with the Freundlich model. The Langmuir monolayer adsorption capacity was found to be 1666.67 g cadmium and 6.75 g humic acid per gram of modified nanozeolite A, which is higher than that of reported value for other zeolites. The sorption ability was enhanced by surface modification and reduction in size and enabled the zeolite to adsorb cadmium. The adsorption of cadmium and humic acid on nanozeolite was found to be the highest at pH 6 and 3, respectively. Results showed that solid to liquid ratio and pH are the most important factors for cadmium and humic acid removal, respectively. Effect of competitive ions was studied and results showed that there is no competition between cadmium and humic acid sorption and presence of these ions.     

Surfactant-enhanced remediation of contaminated soil: a review

Extracting aqueous solutions with or without additives are employed to solubilize contaminants in soil. Since water solubility is the controlling removing mechanism, additives are used to enhance efficiencies. These additives can reduce the time to treat a site compared to the use of water alone. Additives must be of low toxicity and biodegradable. The research in this area has focussed mainly on halogenated volatile organic compounds (VOCs) and is still quite limited for metal removal. Additives include surfactants, organic and inorganic acids, sodium hydroxide, which can dissolve organic soil matter, water-soluble solvents such as methanol, displacement of cations with nontoxic ones, complexing agents such as EDTA, acids in combination with complexing agents or oxidizing/reducing agents. Cationic, anionic and nonionic surfactants are particularly used for soil washing or flushing. They contain both hydrophobic and hydrophilic portions, making them ideal for solubilization of hydrophobic compounds. Numerous studies have indicated that surfactants enhance recoveries of non-aqueous phase liquids (NAPLs). There have also been indications that pretreatment of soil with surfactant washing to solubilize hydrophobic compounds such as PAHs enhances biodegradation of these contaminants. A few in situ field studies have been performed with surfactants. Large-scale treatment has been done mostly for organic removal. Soil pH, soil type, cation exchange capacity (CEC), particle size, permeabilities and contaminants all affect removal efficiencies. High clay and organic matter contents are particularly detrimental. Understanding the chemistry of the binding of the contaminant and the hydrogeology of the site are very important. Once the water is pumped from the soil, it must be extracted and then treated to remove the hydrocarbons and metals. Several technologies exist such as sodium hydroxide or sodium sulfide precipitation, ion exchange, activated carbon adsorption, ultrafiltration, reverse osmosis, electrodialysis and biological processes. Recycling of the surfactants is desired to decrease treatment costs.

This paper will provide an overview of the laboratory research, field demonstration and full-scale application of surfactants for the remediation of contaminated soil. The majority of pilot scale in situ flushing tests, particularly in the United States, have involved the use of surfactants and co-solvents. There are only a few full-scale projects however. Recent laboratory scale efforts by the authors concerning the use of biosurfactants, biologically produced surfactants, to enhance the removal of copper, cadmium and zinc from contaminated soils and sediments are discussed. Three types of biosurfactants were evaluated for their effectiveness. They included a lipopeptide called surfactin from Bacillus subtilis, a rhamnolipid from Pseudomonas aeruginosa and a sophorolipid from Torulopsis bombicola. The results indicated the feasibility of removing the metals with the anionic biosurfactants even though the exchangeable fractions were not significant.     

Remediation of soil co-contaminated with pyrene and cadmium by growing maize (Zea mays L.)

Sites co-contaminated with organic and metal pollutants are common and considered to be a more complex problem as the two components often causes a synergistic effect on cytotoxicity. Phytoremediation has been proposed as a cost-effective technology for treating heavy metal or organic contamination and may be suitable for remediation of co-contaminated soil. This study investigated the concurrent removal of pyrene and cadmium in co-contaminated soil by growing maize in a pot experiment. At the end of 60 day culture, pyrene in spiked soil diminished significantly, accounting for 21–31 % of the initial extractable concentration in unplanted soil and 12–27 % in planted soil. With the increment of cadmium level, the residual pyrene both in unplanted and planted soil tended to increase. Although the presence of cadmium increased the accumulation of pyrene in maize, plant accumulation only account for less than 0.30 % of the total amount of the dissipated pyrene in vegetated soils. It implied that plant-promoted microbial biodegradation was the predominant contribution to the plant-enhanced dissipation of pyrene in co-contaminated soil. Unlike pyrene, heavy metal cadmium cannot be degraded. It was observed that maize can concurrently removed about on the average 0.70 % of the total cadmium amount in soil by plant uptake, but cadmium phytoextraction would be inhibited under contamination of pyrene. Maize CT38 can normally grow in the co-contaminated soil with high level cadmium and pyrene and can effectively remedy the sites co-contaminated with these two types of contamination, which suggest the possibility of simultaneous phytoremediation of two different contaminant types.     

地理空间数据的尺度转换

尺度一般是指空间范围的大小,地理空间数据的尺度转换是尺度研究的重要问题之一。针对地理信息系统(GIS)技术支持下的地理空间数据尺度转换问题,首先回顾了尺度转换的理论基础,即等级理论、分形理论、区域化随机变量理论、地理学第一定律等理论的基本内涵;然后总结了地理学不同研究领域内主要的尺度转换方法,重点分析了重采样法、变异函数法、分形分维法及小波分析法的基本原理、模型方法与典型应用案例;最后介绍了地理空间数据尺度转换效应研究的进展。基于上述总结和分析认为:构建一套无级变换的、系统的尺度转换方法,整合不同学科领域的数据与过程模型、形成数据模型同化的技术体系,这是地理空间数据尺度转换研究的重要课题。     

第四纪沉积物光释光测年中等效剂量测定方法的对比研究

准确地测定碎屑矿物沉积后吸收的等效剂量第四纪沉积物释光测年中最关键的一环。用光释光测年技术对几年全新世坡积物,古土地和黄土等样品中的石英,长石等碎屑矿物进行了测定等效剂量的对比研究。     

遥感水文应用中的尺度问题

遥感技术在水文科学中的广泛应用，极大地拓宽了其研究的领域和范围，增加了其研究的深度。但同时也应该看到，遥感信息的空间分辨率和时间分辨率，以及水文科学自身尺度问题的复杂性，一方面对遥感水文的应用产生困难和问题，限制了水文遥感的应用；另一方面又对水文尺度问题提供了新的技术手段，为遥感水文应用增添了新的亮点。从水文机理与空间尺度、遥感信息的空间分辨率、水文参数的空间延拓，以及遥感技术与水文科学的发展等 4个方面探讨了遥感水文的空间尺度问题；从瞬时遥感信息的时间拓展和遥感信息的时间分辨率 2个方面讨论了遥感水文的时间尺度问题。     

金选矿厂含氰废水中氰化物降解及其环境风险评价

对陕西凤县四方金矿选矿过程中氰化物的迁移转化和降解进行了研究,结果表明,其尾矿库外排含氰废水氰化物浓度达到国家规定的排放标准。在此基础上对氰化物环境风险进行评价,为同类项目尾矿浆和尾矿水环境风险评价提供可信的基础数据。