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261.
262.
The natural degradation of monophenylheptamethylcyclotetrasiloxane and 2,6-cis-diphenylhexamethylcyclotetrasiloxane in soil was evaluated under laboratory conditions. Both monophenyl and 2,6-cis underwent rapid degradation in dry soil generating the same products in varying proportions. During the first 24 hr, approximately 99% of the two materials underwent significant chemical transformations forming silanols of various structures, dimethyl cyclic siloxanes of the structure (Me2SiO)x, and rearrangement products (geometrical isomers) of diphenylhexamethylcyclotetrasiloxane. Among the silanols, the following were identified as trimethylsilyl derivatives: HOSiMe2OH, HOSiMePhOH, HOSiMe2OSiMe2OH, HOSiMePhOSiMe2OH, HOSiMePhOSiMePhOH, HOSiMe2OSiMe2OSiMe2OH, HOSiMePhOSiMe2OSiMe2OH, HOSiMe2OSiMePhOSiMe2OH, HOSiMePhSiMe2OSiMePhOH, HOSiMePhOSiMePhOSiMe2OH, HOSiMePhOSiMe2OSiMe2OSiMe2OH, HOSiMe2OSiMePhOSiMe2OSiMe2OH, HOSiMePhOSiMe2OSiMePhOSiMe2OH, HOSiMePhOSiMePhOSiMe2OSiMe2OH, HOSiMePhOSiMe2OSiMe2OSiMePhOH, HOSiMe2OSiMePh-OSiMePhOSiMe2OH. Derivatization was carried out using bis(trimethylsilyl)trifluoroacetamide. Gas chromatography-mass spectrometry and liquid chromatography-mass spectrometry (atmospheric pressure chemical ionization) analyses were used to derive structures. Structures were confirmed by gas chromatography-mass spectrometry comparisons of synthetic standards. Degradation was slower in wet soil. Nevertheless, in 14 days, the chemical transformation was essentially found to be complete as soil was allowed to dry. Detection of phenol as one of the degradation products revealed the occurrence of carbon–silicon bond cleavage promoted by soil. 相似文献
263.
研究以ClO^-/Cl^-作媒介,间接电化学降解亚甲基蓝模拟废水的可行性。结果表明,亚甲基蓝的电化学降解与电极材料、电流密度以及添加剂种类等因素有关。以石墨为阳极,不锈钢为阴极,在无隔膜的烧杯中放置50ml浓度为1000mg/L的亚甲基蓝模拟废水,在室温25℃,pH6.0-8.0,槽电压10V,电流密度30.0mA/cm^2,Cl^-加入量2g/L的条件下,电解60min后,亚甲基蓝溶液的平均消色率达到98.0%,CODcr降解率为97.0%,BOD5降解率为99.0%;用浸涂过MnO2薄膜的石墨棒作阳极可显著加快其消解速率,而用浸涂过CeO2薄膜的石墨棒作阳极对其消解速率无明显的影响。并初步讨论了其降解机理。 相似文献
264.
实验研究了有机废气中的1.1-二氧乙烯(CH2=CCl2)在101.3kPa和288~308K下气相臭氧化降解过程及其反应动力学。结果表明,总的反应级数是2级,相对于臭氧和二氯乙烯浓度均为1级。反应速率常数可用方程Arrhenius(k2=8.32exp[-389.7/T])表示。 相似文献
265.
Owen P. Graham 《Environmental management》1992,16(2):205-223
A survey of land degradation was undertaken in New South Wales, Australia during 1987–1988. The aims of the survey were to
assess the location, extent, and severity of ten forms of degradation and to present the data in map and statistical form.
Sample points were located on a regular grid. The method was designed so that data could be acquired from aerial photographs,
expert local knowledge, and limited field checking. Individual statewide maps were prepared for each form of degradation.
Map data were shown in pixel form. Sheet and rill erosion and soil structure decline were confined mostly to lands used for
cropping. Gully erosion was commonly found across the state, while mass movement was confined to steeper lands. There were
three severe areas of dryland salinity; irrigation salinity was mapped in parts of the southern irrigation lands. Induced
soil acidity was severe in some cropping and pasture lands. Absence of tree regrowth was a noticeable feature of lands used
for cropping. The survey enabled community awareness of the problems of land degradation to be increased, in addition to assisting
regional land managers in resource allocation. The survey also provided the basis for the future location of sites that could
be used to monitor the trends in the status of land degradation. 相似文献
266.
Anthony L. Andrady Jan E. Pegram Shuji Nakatsuka 《Journal of Polymers and the Environment》1993,1(1):31-43
Studies on three types of enhanced photodegradable polyethylenes showed tensile elongation at break to be a suitable parameter for assessing disintegration due to outdoor weathering. Disintegration rates varied greatly with exposure location, with Arizona the harshest environment and Washington and New Jersey the mildest. The rate of breakdown of the enhanced degradable polyethylenes relative to unmodified plastic was termed an enhancement factor. For the materials studied, average enhancement factors generally ranged from five to fifteen. The location-dependent variability in rate parameters can be mostly explained in terms of different average radiation levels and temperatures at these locations. A duplicate exposure protocol was developed to determine if the test data were complicated by short-term fluctuations in sunlight or temperature during exposure. 相似文献
267.
Thomas Jahns Roswitha Schepp Christof Siersdorfer Heinrich Kaltwasser 《Journal of Polymers and the Environment》1999,7(2):75-82
The biodegradation of urea and condensation products thereof (ureaforms or methyleneureas), their nitrification, and their influence on the respiratory rate of soil was studied over periods of up to 100 days. The total methyleneurea content of the soil was determined after its acidic extraction, using a convenient colorimetric assay, and an HPLC protocol was established to analyze for specific components of methyleneureas. Urea, unfractionated methyleneureas, and hot-water soluble methyleneureas were rapidly metabolized to ammonium, which accumulated to high concentrations and was consequently oxidized to nitrate; an accumulation of nitrite was observed during urea but not during methyleneurea degradation. Hot water-insoluble methyleneureas were degraded much more slowly, and ammonium formed from these compounds was oxidized to nitrate without being released in significant amounts. These results suggest that the use of methyleneureas of optimized composition with regard to their water solubility may help to resolve problems such as the toxicity of ammonia to plant growth as well as nitrogen loss by leaching of nitrate, denitrification and volatilization. 相似文献
268.
贵州喀斯特地区旅游资源的变异与可持续利用 总被引:6,自引:0,他引:6
殷红梅 《中国人口.资源与环境》1999,9(2):68-72
喀斯特景观与民族文化是不可再生的旅游资源,其开发在促进喀斯特地区经济、文化发展的同时,也加剧了环境的损耗和地方特色的消失,旅游资源变异现象普遍发生。文中分析了资源变异的几种情况,并指出控制资源变异,实现可持续利用的途径 相似文献
269.
270.