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201.
Heeb NV Schweizer WB Mattrel P Haag R Gerecke AC Kohler M Schmid P Zennegg M Wolfensberger M 《Chemosphere》2007,68(5):940-950
Hexabromocyclododecanes (HBCDs) are high production volume chemicals used as flame retardants for plastics and textiles. They are currently produced in quantities exceeding 20,000 t/y. Despite this fact, the correct stereochemistry of most HBCDs is still not known. Six stereocenters are formed during bromination of cyclododecatrienes, resulting in mixtures of different stereoisomers. Considering all elements of symmetry, 16 different stereoisomers including six pairs of enantiomers as well as 4 meso forms are possible theoretically. Recently, we isolated 8 of the 16 possible stereoisomers from a technical HBCD mixture and assigned their relative configurations. Herein, we report on the isolation of 6 enantiomerically pure alpha-, beta-, and gamma-HBCDs, obtained from preparative chiral-phase liquid chromatography, and we present their absolute configurations, which were determined from X-ray diffraction analysis. The absolute configuration of (-) alpha-HBCD was found to be (1R,2R,5S,6R,9R,10S), while the one of (+) beta-HBCD is assigned to (1S,2S,5S,6R,9S,10R), whereas the one of (-) gamma-HBCD corresponds to (1S,2S,5S,6R,9R,10S). The given structural information allows the unambiguous identification of the six most important HBCD stereoisomers, which typically account for more than 95% of technical HBCDs. In addition, we compared the solid-state conformations of racemic and enantiomerically pure alpha-, beta-, and gamma-HBCDs. In all cases, vicinal dibromides adopted a synclinal (sc) conformation with torsion angles of 69+/-6 degrees. A unique structural motive was common to all examined HBCD solid-state conformations. This conserved structure was described as an extended triple turn consisting of an arrangement of three pairs of synclinal and two antiperiplanar torsion angles. 相似文献
202.
Smits JE Bortolotti GR Baos R Jovani R Tella JL Hoffmann WE 《Environmental pollution (Barking, Essex : 1987)》2007,145(2):538-544
In 1998, the Aznalcóllar mine tailings dyke in southwestern Spain broke, flooding the Agrio-Guadiamar river system with acid tailings up to the borders of one of the largest breeding colonies of white storks in the western Palearctic, Dehesa de Abajo. Over the following years, a high proportion of nestlings developed leg defects not seen before the spill, prompting this study. Nestlings with deformed legs had significantly lower plasma phosphorous (P) and higher Ca:P ratios than non-deformed cohorts in the first two years, but in the third year, when more, younger birds were studied, plasma P ranged from much higher to much lower in the affected colony compared with reference birds. Coefficients of variation for phosphorous were 19% and 60%, in reference and contaminated colonies, respectively. Storks from the contaminated colony were unable to control P levels and Ca:P ratios within the narrow limits necessary for normal bone development. 相似文献
203.
Stress Resistance and Environmental Dependency of Inbreeding Depression in Drosophila melanogaster 总被引:2,自引:1,他引:1
Abstract: Both inbreeding and environmental stress can have adverse effects on fitness that affect the conservation of endangered species. Two important issues are whether stress and inbreeding effects are independent as opposed to synergistic, and whether inbreeding effects are general across stresses as opposed to stress-specific. We found that inbreeding reduced resistance to acetone and desiccation in adult Drosophila melanogaster , whereas resistance to knockdown heat stress was not affected. Inbred flies, however, experienced a greater proportional decrease in productivity than outbreds following heat stress. Correlations using line means indicated that all resistance traits were uncorrelated in the inbred as well as in the outbred flies. Recessive, deleterious alleles therefore did not appear to have any general deleterious effects on stress resistance. Inbreeding within a specific environment and selection for resistant genotypes may therefore purge a population of deleterious genes specific to only one environmental stress. 相似文献
204.
Heeb NV Schweizer WB Mattrel P Haag R Kohler M Schmid P Zennegg M Wolfensberger M 《Chemosphere》2008,71(8):1547-1556
Hexabromocyclododecanes (HBCDs) are high production volume chemicals currently produced in quantities exceeding 20000ty(-1). They are used as flame retardants for plastics and textiles. HBCDs are thermally labile compounds, rapidly decomposing at temperatures above 250 degrees C to form bromine radicals, which scavenge other radicals formed during pyrolysis. But certain HBCD stereoisomers must reach the environment without decomposition, because their levels in soils, sediments, and biota are increasing worldwide. The fate of individual HBCD stereoisomers during production, product use, disposal, and transformation in the environment remains unclear. Herein we report on the thermally induced, highly selective isomerization of (+) and (-)beta-HBCD. Regio- and stereoselective migration of only two of the six bromine atoms resulted in the racemization of both beta-HBCDs. First order rate constants (k(rac)) increased from 0.005, 0.011, 0.021, to 0.055min(-1) at 130, 140, 150, and 160 degrees C, corresponding to half life times tau(1/2) of 143, 63, 29, and 14min, respectively. From the deduced kinetic model, we conclude that any thermal treatment of enantiomerically enriched beta-HBCDs in the range of 100-160 degrees C will result in a loss of most optical activity within few hours. The simultaneous inversion of two asymmetric centers occurred with perfect stereocontrol. Selectively, vicinal dibromides with the RR- and the SS-configurations migrated at these temperatures. An intramolecular reaction mechanism with a four-center transition state is postulated, based on the obtained stereoisomer pattern and the observed reaction kinetics. Crystal structure analysis revealed that all vicinal dibromides in beta-HBCDs prefer synclinal (gauche) conformations. However, an antiperiplanar (staggered) conformation is assumed to facilitate the concerted 1.2-shifts of both bromine atoms, resulting in an inversion of both neighboring carbon atoms. First experiments with other HBCD stereoisomers suggest that the presented isomerization mechanism is of relevance for those stereoisomers as well. 相似文献
205.
Jeffrey Alan Hoffmann 《Environmental Communication: A Journal of Nature and Culture》2018,12(6):807-824
The following study looks at how traditional, organic, cooperative farmers starting a new farming cooperative in the US Southwest communicate about their farming as a set of (sustainable) cultural practices. The study draws on environmental communication theory, the theory of the coordinated management of meaning, and Vandana Shiva’s three-tiered economic model to construct a communication-based framework through which to view farmers’ stories about sustainability. This framework is productive, showing how some Nuevo Mexicano farmers (and others) orient toward farming, sustenance, and human-nature relationships through community, family, heritage, and education. Moreover, in addition to a conceptualization of sustainability as specific practices for nurturing and enduring in environments, communities, and organizations/institutions, sustainability can be understood as embedded ecocultural and historical experience with cross-cultural parallels in land-based communities. This study advances the ethical duty of environmental communication to better understand the ways in which environmental discourse and ecocultural and material realities are imbricated, as well as the call for such discursive study to be grounded in phenomenological experience of the natural world. 相似文献
206.
Szabolcs Péter Tallósy László Janovák Judit Ménesi Elisabeth Nagy Ádám Juhász László Balázs István Deme Norbert Buzás Imre Dékány 《Environmental science and pollution research international》2014,21(19):11155-11167
Nanosilver-modified TiO2 and ZnO photocatalysts were studied against methicillin-resistant Staphylococcus aureus on the surface and against naturally occurring airborne microorganisms. The photocatalysts/polymer nanohybrid films were prepared by spray coating technique on the surface of glass plates and on the inner surface of the reactive light source. The photoreactive surfaces were activated with visible light emitting LED light at λ?=?405 nm. The optical properties of the prepared photocatalyst/polymer nanohybrid films were characterized by diffuse reflectance measurements. The photocatalytic properties were verified with the degradation of ethanol by gas chromatography measurements. The destruction of the bacterial cell wall component was examined with transmission electron microscope. The antibacterial effect of the photocatalyst/polymer nanohybrid films was tested with different methods and with the associated standard ISO 27447:2009. With the photoreactive coatings, an extensive disinfectant film was developed and successfully prepared. The cell wall component of S. aureus was degraded after 1 h of illumination. The antibacterial effect of the nanohybrid films has been proven by measuring the decrease of the number of methicillin-resistant S. aureus on the surface and in the air as the function of illumination time. The photocatalyst/polymer nanohybrid films could inactivate 99.9 % of the investigated bacteria on different thin films after 2 h of illumination with visible light source. The reactive light source with the inner-coated photocatalyst could kill 96 % of naturally occurring airborne microorganisms after 48 h of visible light illumination in indoor air sample. The TEM results and the microbiological measurements were completed with toxicity tests carried out with Vibrio fischeri bioluminescence bacterium. 相似文献
207.
208.
Paul J. Weldon Yasmin J. Cardoza Robert K. Vander Meer W. Clint Hoffmann John W. Daly Thomas F. Spande 《Die Naturwissenschaften》2013,100(2):185-192
Nearly 500 alkaloids, representing over 20 structural classes, have been identified from the skin of neotropical poison frogs (Dendrobatidae). These cutaneous compounds, which are derived from arthropod prey of the frogs, generally are believed to deter predators. We tested the red imported fire ant (Solenopsis invicta) for toxicosis following contact with 20 alkaloids (12 structural classes) identified from dendrobatids or other anurans. Individual ants forced to contact the dried residues of 13 compounds exhibited convulsions and/or reduced ambulation. We estimated the cutaneous concentrations of several compounds based on their reported recoveries from skin extracts of free-ranging frogs and our measurements of the skin surface areas of museum specimens. Pumiliotoxin 251D exhibited contact toxicity below its estimated cutaneous concentration in the Ecuadorian frog, Epipedobates anthonyi, an observation consistent with the hypothesized role of this compound in anuran chemical defense. Our results and those of a previous study of mosquitoes indicate that some anuran skin compounds function defensively as contact toxins against arthropods, permeating their exoskeleton. 相似文献
209.
Elie Gaget Alison Johnston Diego Pavón-Jordán Aleksi S. Lehikoinen Brett K. Sandercock Alaaeldin Soultan Luka Božič Preben Clausen Koen Devos Cristi Domsa Vitor Encarnação Sándor Faragó Niamh Fitzgerald Teresa Frost Clemence Gaudard Lívia Gosztonyi Fredrik Haas Menno Hornman Tom Langendoen Christina Ieronymidou Leho Luigujõe Włodzimierz Meissner Tibor Mikuska Blas Molina Zuzana Musilová Jean-Yves Paquet Nicky Petkov Danae Portolou Jozef Ridzoň Laimonas Sniauksta Antra Stīpniece Norbert Teufelbauer Johannes Wahl Marco Zenatello Jon E. Brommer 《Conservation biology》2022,36(4):e13877
Protected area networks help species respond to climate warming. However, the contribution of a site's environmental and conservation-relevant characteristics to these responses is not well understood. We investigated how composition of nonbreeding waterbird communities (97 species) in the European Union Natura 2000 (N2K) network (3018 sites) changed in response to increases in temperature over 25 years in 26 European countries. We measured community reshuffling based on abundance time series collected under the International Waterbird Census relative to N2K sites’ conservation targets, funding, designation period, and management plan status. Waterbird community composition in sites explicitly designated to protect them and with management plans changed more quickly in response to climate warming than in other N2K sites. Temporal community changes were not affected by the designation period despite greater exposure to temperature increase inside late-designated N2K sites. Sites funded under the LIFE program had lower climate-driven community changes than sites that did not received LIFE funding. Our findings imply that efficient conservation policy that helps waterbird communities respond to climate warming is associated with sites specifically managed for waterbirds. 相似文献
210.