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Potential Formation (potential + formation)
Selected AbstractsAbrupt community change on a rocky shore , biological mechanisms contributing to the potential formation of an alternative stateECOLOGY LETTERS, Issue 6 2004Robert T. Paine Abstract The 1997/1998 El Niño initiated a major shift in the intertidal assemblage on the Washington State outer coast. A 25 year time series (1978,2003) shows stands of dominant canopy algae replaced by mussel beds. A prior experiment had indicated that mussels can become too large to be eaten by starfish; newly initiated starfish removals predict mussel attainment of a size refuge. Such escapes inhibit recovery towards prior community composition and enhance development of alternative community states which may persist long after the originating forcing has lessened or disappeared. [source] Aquatic photochemistry of chlorinated triclosan derivatives: Potential source of polychlorodibenzo- P -dioxins,ENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 12 2009Jeffrey M. Buth Abstract Triclosan (TCS; 5-chloro-2-(2,4-dichlorophenoxy)phenol), a common antimicrobial agent, may react with residual chlorine in tap water during transport to wastewater treatment plants or during chlorine disinfection of wastewater, generating chlorinated TCS derivatives (CTDs): 4,5-dichloro-2-(2,4-dichlorophenoxy)phenol (4-Cl-TCS), 5,6-dichloro-2-(2,4-dichlorophenoxy)phenol (6-C1-TCS), and 4,5,6-trichloro-2-(2,4-dichlorophenoxy)phenol (4,6-Cl-TCS). The photochemistry of CTDs was investigated due to the potential formation of polychlorodibenzo- p -dioxin (PCDD) photoproducts. Photolysis rates were highly dependent upon CTD speciation, because the phenolate species degraded 44 to 586 times faster than the phenol forms. Photolysis quantum yield values for TCS, 4-Cl-TCS, 6-Cl-TCS, and 4,6-Cl-TCS of 0.39, 0.07, 0.29, and 0.05, respectively, were determined for the phenolate species. Photolyses performed in Mississippi River and Lake Josephine (USA) waters gave similar quantum yields as buffered, pure water at the same pH, indicating that indirect photolysis processes involving photosensitization of dissolved organic matter are not competitive with direct photolysis. The photochemical conversion of the three CTDs to PCDDs under solar irradiation was confirmed in natural and buffered, pure water at yields of 0.5 to 2.5%. The CTD-derived PCDDs possess higher toxicities than 2,8-dichlorodibenzo- p -dioxin, a previously identified photoproduct of TCS, due to their higher chlorine substitution in the lateral positions. The load of TCS- and CTD-derived PCDDs to United States surface waters is estimated to be between 46 and 92 g toxicity equivalent units per year. Other identified photoproducts of each CTD were 2,4-dichlorophenol and reductive dechlorination products. [source] Modeling the environmental fate of perfluorooctanoate and its precursors from global fluorotelomer acrylate polymer useENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 11 2008Rosalie van Zelm Abstract The environment contains various direct and indirect sources of perfluorooctanoic acid (PFOA). The present study uses a dynamic multispecies environmental fate model to analyze the potential formation of perfluorooctanoate (PFO), the anion of PFOA, in the environment from fluorotelomer acrylate polymer (FTacrylate) emitted to landfills and wastewater, residual fluorotelomer alcohol (8:2 FTOH) in FTacrylate, and residual PFOA in FTacrylate. A multispecies version of the SimpleBox model, which is capable of determining the fate of a chemical and its degradation products, was developed for this purpose. An uncertainty analysis on the chemical-specific input parameters was performed to examine for uncertainty in modeled concentrations. In 2005, residual 8:2 FTOH made up 80% of the total contribution of FTacrylate use to PFO concentrations in global oceans, and residual PFOA in FTacrylate contributed 15% to PFO concentrations from FTacrylate use in global oceans. After hundreds of years, however, the main source of PFO from total historical FTacrylate production is predicted to be FTacrylate degrading in soil following land application of sludge from sewage treatment plants, followed by FTacrylate still present in landfills. Uncertainty in modeled PFO concentrations was up to a factor of 3.3. Current FTacrylate use contributes less than 1% of the PFO in seawater, but because direct PFOA emission sources are reduced and PFOA continues to be formed from FTacrylate in soil and in landfills, this fraction grows over time. [source] Synthesis and Characterisation of Novel Complexes Containing Group 15 Elements and Their Potential Use as Molecular Precursors for the Formation of Transition Metal PnictidesEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 1 2005Manfred Scheer Abstract The reaction of [{W(CO)5}2PCl] with K[Co(CO)4] yields the novel compounds [{W(CO)4Co2(CO)6}{µ3 -PW(CO)5}2] (3) and [{(CO)4WCo3(CO)6}{µ3 -PW(CO)5}3] (4) along with known derivatives [Co2(CO)6{,,,2 -PW(CO)5}2] (1) and [Co3(CO)9{,3 -PW(CO)5}] (2). The complex [{W2(CO)8(,-CO)}{,,,2:,1:,1 -PW(CO)5}2)] (5) was synthesised by treating Na2[W2(CO)10] with PBr3. Reaction of K[Mn(CO)5] with SbCl3 affords [Sb{Mn(CO)5}3] (6) in high yields. The spectroscopic and structural characterisation of the novel products is discussed, as well as the thermolytic behaviour of 2, 3 and 6 for the potential formation of novel phases of transition metal pnictides. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005) [source] | ||||||||||