Kinetic and thermodynamic studies on partitioning of polychlorinated biphenyls (PCBs) between aqueous solution and modeled individual soil particle grain sizes

The significance of soil mineral properties and secondary environmental conditions such as pH, temperature, ionic strength and time in the partitioning of eight selected polychlorinated biphenyl(PCB) congeners between aqueous solution and soil particles with different grain sizes was studied. The mineral properties of a model soil sample were determined, and Brunauer–Emmett–Teller(BET) adsorption–desorption isotherms were employed to observe the surface characteristics of the individual modeled soil particles.Batch adsorption experiments were conducted to determine the sorption of PCBs onto soil particles of different sizes. The results revealed that the sorption of PCB congeners onto the soil was dependent on the amount of soil organic matter, surface area, and pore size distribution of the various individual soil particles. Low pH favored the sorption of PCBs,with maximum sorption occurring between pH 6.5 and 7.5 with an equilibration period of 8 hr.Changes in the ionic strength were found to be less significant. Low temperature favored the sorption of PCBs onto the soil compared to high temperatures. Thermodynamic studies showed that the partition coefficient(K_d) decreased with increasing temperature, and negative and low values of ΔH° indicated an exothermic physisorption process. The data generated is critical and will help in further understanding remediation and cleanup strategies for polluted water.     

长江流域粮食资源及生产发展方向

论述长江流域发展粮食生产的重要性，分析粮食资源分布，生产状况，生产结构和地域差异，指出粮食合理布局的方向，提出以粮食集中产区为重点，建设长江流域粮食生产专业化地并以建设商品粮基地为建带突破口。     

Resource Potentials and Limitations of A Nicaraguan Agricultural Region

Food production has to be increased in a sustainable way to meet the future global demand. A key position is attributed to developing countries. A deepened understanding of their agricultural regions with specific resource endowments and constraints is therefore crucial. In this study we propose a methodology based on material flux analysis (MFA) to assess the resource potentials and limitations of a Nicaraguan agricultural region. We focus on current regional and farm resource management and explore them under two scenarios. Indicators are nitrogen and the degrees of self-sufficiency (DSS) for energy, and the staples maize and beans. As data is scarce, most information is based on interviews with farmers of four categories and key persons, and on literature. The results show that nitrogen management does not differ considerably among categories. Nitrogen is mined mostly from staple plots. Self-sufficiency for beans is given in an average year. Yet, landless and small farmers neither produce enough maize for autoconsumption, nor are they self-sufficient for firewood. Energy supply is also the core problem of the region, since the DSS is 70%. Soil nitrogen stocks last at most for three more generations. Analyses with the scenario technique show that: (a) Unlimited population growth has serious consequences in the near future e.g. severe shortage of energy and food. (b) Alternative farming systems are possible, but they require reducing the population by a factor 2, and thus the creation of jobs in a Hinterland. Readers should send their comments on this paper to: BhaskarNath@aol.com within 3 months of publication of this issue.     

Preliminary Studies on Converting Agricultural Waste into Biodegradable Plastics—Part IV: Polysaccharide Containing Natural Materials

Corn distillers’ dry grain, corncob powder, hardwood powder, and sugar beet pulp were separately anionized by oxidation with sodium hypochlorite in aqueous solution. Solid reaction products instantly precipitated upon admixing each of the above-oxidized materials with soy protein isolate. Infrared spectra and differential scanning calorimetry supported the hypothesis that soy protein isolate complexed with all of the above-oxidized polysaccharides. Reaction products with either oxidized corn distillers’ dry grain or oxidized sugar beet pulp provided hard, brittle pellets with tensile strengths as high as 9.5 MPa, suggesting that these materials could be viable as biodegradable plastics.     

大气臭氧浓度升高对丛枝菌根(AM)及其功能的影响

通过模拟大气O₃浓度(0.02μL·L^-1、0.1μL·L^-1和0.2μL·L^-1)升高,观察其对丛枝菌根(AM)及功能的影响.结果表明,大气O₃浓度升高对菌根侵染率影响较小,但对孢子和外生菌丝影响显著,高浓度O₃时的孢子数比自然O₃浓度时增加1倍,低、高浓度O₃分别使AM外生菌丝量比自然浓度时下降48.7%和85.6%.随着O相似文献   

丁布的分离、纯化和结构鉴定及其对麦长管蚜

从玉米苗中分离、纯化得到丁布，利用纸层析，紫外分光光度扫描和核磁共振^1H NMR等技术对其作结构鉴定。结果与文献报道基本一致，且纯度在96.7%以上，以纯化的丁布为标样，用HPLC方法分析了不同抗性级别的小麦品种中丁布的含量。结果表明：品种之间丁布的含量差异显著，丁布的浓度与小麦的抗蚜级别呈显著负相关，与麦长管蚜的内禀增长率rm亦呈显著负相关，借助麦长管蚜全纯人工饲料研究表明，丁布对麦长管蚜有明显的拒食性作用。图3表2参13。     

油料作物对土壤老化残留DDT的吸收积累

油料作物对亲脂性DDT的吸收富集能力是否会更强是一个值得研究的问题。采用DDT老化残留土壤,温室盆栽油料作物花生(Arachishypogaea),大豆(Glycinemax)和芝麻(Sesamumindicum)。果实成熟后将植株分成根、茎、果壳和果仁四部分,GC-ECD测定各部位中的DDT浓度。研究了油料作物对土壤老化残留DDT的吸收积累情况,结果表明,∑DDT在三种作物不同部位中的浓度顺序都是:根>茎>果壳>果仁。含油量高的花生果仁和芝麻果仁中∑DDT浓度都明显高于大豆果仁的∑DDT浓度,这种差异有可能是由果仁含油量的差异造成的。单株植物吸收积累∑DDT的总量顺序为:花生>芝麻>大豆。花生、大豆和芝麻三种作物的根和茎的生物富集系数都比较高,特别是花生的,说明这三种油料作物根部从土壤中吸收积累老化残留DDT的能力以及从根部向茎部运输DDT的能力都是相当强的。     

我国部分商品粮基地粮食重金属污染的差异分析与综合评价

本文根据1988年全国农业环境质量状况调查资料,选取我国部分商品粮基地县粮食重金属污染数据,通过多元统计分析,揭示了各商品粮基地粮食重金属污染的差异与分类。最后采用模糊综合评判方法,对各商品粮基地粮食重金属污染程度进行了综合评价,得到了相对污染程度的排序。     

Variation of grain Cd and Zn concentrations of 110 hybrid rice cultivars grown in a low-Cd paddy soil

Enhanced Cd uptake and Zn depletion in rice grains and high potential for food Cd exposure by the high-yielding hybrid cultivars of China had been addressed. A field experiment was conducted in 2006 to determine the di erence in grain Cd and Zn between cultivars. Total 110 cultivars including super rice and common hybrid rice cultivars were grown on a single paddy soil (Entic Haplaquept) with a neutral reaction and low total Cd content. Grain Cd and Zn concentrations were determined with graphite atomic adsorption spectrophotometer (GFAAS) and flame atomic adsorption spectrophotometer (AAS) respectively.Wide variation of Cd content in grain was found in a range of 0.004–0.057 mg/kg, while the Zn content in a range of 10.25–30.06 mg/kg among the cultivars. Higher Cd but lower Zn concentration in grains of super rice cultivars was observed compared to the common hybrid ones. A highly significant positive linear correlation of grain Cd/Zn with grain Cd was found for super rice and common hybrid cultivars, meanwhile much higher slope for these hybrid cultivars than the reported non-hybrid cultivars was also observed. Using the limit value of the Chinese chemical guidelines for foods (MOHC and SSC, 2005), calculated potential risk of food Cd exposure with “Zn hungry” through diet intake was prominent with all the studied 110 hybrid rice cultivars, possessing high potential health problems for rice production in South China using the super rice cultivars. Breeding of genotypes of rice cultivars with low grain Cd and low Cd/Zn ratio is needed for rice production in acidic red soils where Cd bioavailability is prevalently high.     

基于多级有限元方法的导弹武器定寿延寿研究

提出了多级有限元的概念,将导弹结构定寿延寿工作划分为3个有限元分析步骤进行,在有限元分析的过程中考虑了导弹结构原始状态、老化缺陷状态及修理/换件的影响,对导弹结构强度及剩余寿命进行了科学准确的评判.利用该理论对含有老化和裂纹等损伤因素的药柱结构质量状态和对出现的裂纹损伤进行修复的效果进行了评价.结果表明,该方法科学合理...