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151.
The pyrolysis of chlorinated phenates at a temperature of about 280 degrees C results in the formation of definite chlorinated dibenzodioxin (PCDD) congeners [1-3]. It is shown that in gas phase reactions chlorophenols react in the presence of oxygen above 340 degrees C not only to PCDD but also to chlorinated dibenzofurans (PCDF). The mechanism of this reaction of chlorophenols to PCDD and PCDF was elucidated. In a first step phenoxyradicals are formed which are capable of forming PCDDs and PCDFs. This is confirmed by the oxygen dependency of the reaction. In an argon atmosphere no dimerization of chlorophenols could be observed at 420 degrees C. By the identification of intermediates and by analyzing the PCDF isomers formed from individual chlorophenols the reaction pathway is elucidated. As intermediates in the formation of PCDFs polychlorinated dihydroxybiphenyls (DOHB) were identified. These are most likely formed by the dimerization of two phenoxy radicals at the hydrogen substituted carbons in ortho-positions under simultaneous movement of the hydrogen atoms to the phenolic oxygen PCDDs are formed in the gas phase via ortho-phenoxyphenols (POP) analogous to the pyrolysis of phenates, but due to the radical mechanism in the first condensation step to POPs not only a chlorine atom is capable for substitution but also the hydrogen atoms. The formation of the DOHBs and their condensation to PCDFs and hydroxylated PCDFs as well as the ratio of PCDD to PCDF formed show a strong dependency on the reaction temperature, the substitution pattern of the chlorophenols and the oxygen concentration. 相似文献
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Ultrastructural evidence is presented of a chromatophoresystem in the zooxanthellae containing hermatypic, deep-water coral Leptoseris fragilis (Milne Edwards and Haime). It consists of multilobed cells which mainly occupy the intercellular space of the oral gastrodermis. The cellular processes are filled with electron-dense granules up to 1-m-long and 0.5-m-wide. Within the cytoplasm an elaborate system of microtubules is established. The ramifications of the pigment cells, containing the pigment granules, form a dense and nearly continuous layer close to the overlying zooxanthellae. It is speculated that host pigments may transform the violet portion of the incident light into longer wavelengths, thus increasing the photosynthetic efficiency of the zooxanthellae. 相似文献
155.
Everett SE Tims SG Hancock GJ Bartley R Fifield LK 《Journal of environmental radioactivity》2008,99(2):383-393
Following atmospheric nuclear weapons testing in the 1950s and 1960s significant quantities of (137)Cs and (239+240)Pu were deposited worldwide. In recent decades, (137)Cs has been commonly used as a tracer of soil erosion and sedimentation, particularly in the Northern Hemisphere where atomic deposition was three times as great as in the Southern Hemisphere. The relatively short 30-year half-life of this isotope means that its sensitivity as a tracer is rapidly decreasing. In contrast, with half-lives of 24,110 and 6561 years, the sensitivity of the two plutonium isotopes remains essentially the same as when it was deposited. Here we use the technique of Accelerator Mass Spectrometry to demonstrate the potential of anthropogenic Pu as an alternative to (137)Cs as a tracer of soil transport in Australia. We measure an average (137)Cs/(239+240)Pu activity ratio of 27.3+/-1.5 and an average (240)Pu/(239)Pu atom ratio of 0.149+/-0.003, both slightly lower than the global average. 相似文献
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Jess W. Everett Ramesh Dorairaj Sumit Maratha Patrick Riley 《Resources, Conservation and Recycling》1998,22(3-4)
Curbside collection of recyclable material can be expensive because the inherent costs of curbside collection are high, but also because amounts collected per residence are small compared to the total waste stream, and extra activity may be required, such as sorting. In this paper a simulation model is used to investigate the effect of collection method and route characteristics on route time. The simulation models presented calculate set-out amount based on route characteristics, set-out rate (SOR), and participation rate (PR). Route times are estimated for various conditions: constant SOR, constant PR, and constant set-out amount. Furthermore, a method for using route time to estimate vehicle and labor needs is presented, and used to estimate economic costs for one and two-person crew collection methods for the three simulation conditions mentioned above. The two-person crew is found to cost less than the one-person crew, for most simulated conditions. 相似文献
160.
S.-K Chong Brian P. Klubek John T. Weber 《Journal of the American Water Resources Association》1998,34(3):687-693
ABSTRACT: The Great Flood of 1993 inundated more than 355,000 ha of illinois cropland, creating great concern for the possible contamination of farmland by herbicides. The objective of this study was to assess the herbicide contamination of floodwaters and farmland due to the great flood of 1993. Floodwater samples were collected between August 5 and December 20, 1993, at the Horseshoe Lake State Game Reserve in Alexander County, Illinois, USA. Water and suspended sediment were tested separately for the more commonly used herbicides in Illinois and the midwestern USA: alachior, atrazine, and cyanazine. These herbicides were detected in the floodwater samples, but concentrations were all below the health advisory concentration of 3 μg/L established for drinking water by the United States Environmental Protection Agency. No herbicides were detected in the suspended sediment. After the recession of the flood, soil samples from flooded and non-flooded corn fields were collected for comparison. Soil samples taken from two out of three sampling locations had a 0.4 to 0.8 μg/kg increase in atrazine at the flooded verses the non-flooded sites. Concentrations were 500 to 1,000 times lower than the recommended 1 mg/kg rate at which this herbicides typically applied to soil. 相似文献