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391.
392.
393.
Occurrence and possible sources of polychlorinated biphenyls in surface sediments from the Wuhan reach of the Yangtze River, China 总被引:8,自引:0,他引:8
Twenty-seven surface sediment samples were collected from the mainstream and eight tributaries of the Wuhan reach of the Yangtze River, China, in 2005, in order to assess the distribution, possible sources, and potential risk of polychlorinated biphenyls (PCBs) in the environment. The total concentrations of PCBs (the sum of 39 congeners) ranged from 1.2 to 45.1 ng g−1 dry weight, with a mean value of 9.2 ng g−1. Sediment samples with the highest PCB concentrations came from the tributary sites, which are closer to PCB sources. Conversely, PCB concentrations in the sediment from the mainstream sites of Yangtze River were relatively low. The observed PCB levels were higher than those found in the sediments of other rivers in China, but lower than those in river sediments from other urban areas and harbors around the world. Low-chlorinated PCBs, dominated by tetra-PCBs and penta-PCBs, were identified as being prevalent in the surface sediments. Correlation analyses between the PCBs and the geochemistry and heavy metal content of the sediments suggest that the washing of these compounds from the land into the river by floods and heavy rains, or industrial wastewater and domestic sewage, may be the major sources of the PCBs. According to established sediment quality guidelines, the risk of adverse biological effects from the levels of PCBs recorded at most of the studied sites should be insignificant, although the higher concentrations at other sites could cause acute biological damage. 相似文献
394.
室内空气污染的防治对策 总被引:1,自引:0,他引:1
本文根据室内空气污染物的特性,从污染源控制、法律法规、建筑管理以及其他控制措施等方面,有针对性地提出了各种室内空气污染的防治对策,从而达到改善室内环境空气质量的目的。 相似文献
395.
对脉冲变频电磁场作用下,扫描频率和磁感应强度的变化对水华鱼腥藻细胞活性和生长的影响进行了研究。结果显示,扫描频率从25~27 Hz增大到1~60 kHz时,磁场对藻细胞活性的抑制作用减小,但增大到60 kHz以上,磁场对藻细胞产生强烈抑制作用,累积水力停留时间4 min的藻样在48 h培养时间内已失去活性停止生长。扫描频率为50~100 Hz和1~60 kHz时,累积水力停留时间2 min的藻样,细胞受到磁场刺激生长加快;只有累积水力停留时间>6 min,才表现出对藻活性的抑制作用。磁感应强度增大至120 G,磁场对细胞活性产生明显抑制作用,增大磁感应强度有利于对细胞活性和生长的抑制。 相似文献
396.
397.
Selecting Sites for Converting Farmlands to Wetlands in the Sanjiang Plain, Northeast China, Based on Remote Sensing and GIS 总被引:4,自引:0,他引:4
Wetlands in the Sanjiang Plain are rich in biodiversity and natural resources in the northeast of China. However, this wetland
area has decreased in size and deteriorated in quality owing to expanded agricultural activities since the 1950s. Converting
farmlands to wetlands is necessary to improve these conditions. Using Remote Sensing (RS) and Geographic Information Systems
(GIS) technologies, we derived farmland productivity data and hydrology data for the Sanjiang Plain. The farmland productivity
data were derived from land use and net primary productivity (NPP) data of the MODIS products. We obtained three productivity
farmland classes (low, medium, and high) through the NPP anomaly percentage method. We were only concerned with the low-productivity
farmland. Hydrology data were modeled with a wetness index, which was derived from Digital Elevation Model (DEM) data. Based
on these two data layers, we identified and prioritized sites for the conversion of farmlands to wetlands. The areas with
low farmland productivity and medium or high wetness values have potential to support the conversion of farmlands to wetlands.
Potential sites were prioritized in terms of patch size and proximity to natural wetlands and water bodies. We obtained three
priority classes, among which the high-priority class would be used as the areas for the recent conversion of farmlands to
wetlands. The area of this class was 75,888 ha and accounted for 1.3% of the total farmland area. 相似文献
398.
399.
Electro-bioremediation is an innovative method to remedy organic-polluted soil. However, the principle of electrokinetic technology enhancing the function of microbes, especially the relationship of electric intensity and biodegradation efficiency, is poorly investigated. Petroleum was employed as a target organic pollutant at a level of 50 g/kg (mass of petroleum/mass of dry soil). A direct current power supply was used for tests with a constant direct current electric voltage (1.0 V/cm). The petroleum concentrations were measured at 3275–3285 nm after extraction using hexane, the group composition of crude oil was analyzed by column chromatography. The water content of soil was kept 25% (m/m). The results indicated the degradation process was divided into two periods: from day 1 to day 40, from day 41 to day 100. The treatment of soil with an appropriate electric field led the bacteria to have a persistent effect in the whole period of 100 days. The highest biodegradation efficiency of 45.5% was obtained after treatment with electric current and bacteria. The electric-bioremediation had a positive effect on alkane degradation. The degradation rate of alkane was 1.6 times higher in the soil exposed to electric current than that treated with bacteria for 100 days. A proper direct current could stimulate the microbial activities and accelerate the biodegradation of petroleum. There was a positive correlation between the electric intensities and the petroleum bioremediation efficiencies with a coefficient of 0.9599. 相似文献
400.
低有机碳含量表层土中Fe2O3对γ-666光解的催化作用 总被引:8,自引:0,他引:8
考察5种低有机碳含量天然土中Fe2O3光催化降解γ-666的光解动力学,γ-666的光解符合准一级动力学方程.从所得的γ-666光解动力学常数可知,随Fe2O3质量分数从0.40%增加到5.40%,γ-666的一级光解动力学常数也增大,且两者的线性相关系数为0.952,其在5种天然土中的半衰期随Fe2O3含量的增加依次为133.3h,82.5h,44.1h,28.5h,20.4h.由此可见,低有机碳含量天然土中Fe2O3对γ-666的光解具有明显的催化作用. 相似文献