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Effect of soil organic matter destruction on sorption and photolysis rate of rimsulfuron
Get PDFIn order to elucidate the behaviour of sulphonylurea herbicides in soil and the influence of soil organic matter (OM), the sorption and photolysis reactions of rimsulphuron have been studied in a soil suspension and on the sorbed phase. An Italian soil sampled from Sellata Mountain was utilized for sorption and light irradiation experiments. Natural soil samples and samples oxidized with H2O2 (to destroy OM) were treated with the herbicide and exposed to light irradiation or kept in the dark, as control sorption samples. The irradiation was carried out using a solar simulator (Suntest). Kinetic parameters of reactions were calculated. Herbicide sorption was ascertained to be the more important reaction in the soil, but the retention of rimsulphuron was significantly diminished after H2O2 treatment of soil and the consequent reduction of the natural organic matter content. Photoreaction kinetics of the herbicide were influenced by the sorbent capability of soil samples used in the experiments and the natural organic content
Influence de la matière organique du sol sur la photodégradation du rimsulfuron
No full textLes sulfonylurées constituent une classe d'herbicides d'efficacité élevée pour de faibles doses d'application.
Lors du traitement herbicide une partie du produit se dépose sur les feuilles des plantes traitées, en formant une mince pellicule de matériau exposé à la lumière solaire, l’autre partie se retrouve sur le sol. Dans ces conditions l’irradiation solaire peut intervenir de façon notable et la photodégradation s’avère être un facteur important de disparition des pesticides.
Des travaux antérieurs ont mis en évidence l’influence de la matière organique naturelle (M.O.N.) du sol sur les cinétiques de photodégradation des pesticides à l’état déposé. Ainsi, afin de poursuivre dans ce domaine et de prévoir le comportement du rimsulfuron dans l'environnement, des études de photodégradation en suspension de sol et en phase déposée ont été effectuées. Le sol de Sellata, une localité du sud de l'Italie, a été choisi pour les essais car il est très riche en M.O.N. Des expériences ont été faîtes sur le sol tel quel (solt.q.) et sur le sol privé de sa matière organique naturelle par traitement avec H2O2 à chaud (soloxydé). Les études de photodégradation ont été effectuées en laboratoire en utilisant un simulateur solaire.
En phase déposée, un effet protecteur du support sur la molécule a été constaté. Les études comparatives de cinétiques d’adsorption et de photodégradation montrent que le ralentissement de la photodégradation est d’autant plus important que la capacité d’adsorption est grande.
Par contre en suspension, la vitesse de photodégradation de l'herbicide est plus élevée dans les échantillons qui contiennent de la matière organique naturelle. On constate au départ une adsorption plus forte en présence de M.O.N mais celle-ci n’empêche pas ni la dégradation chimique et la dégradation photochimiqu
Abiotic degradation of the herbicide rimsulfuron on minerals and soil
Get PDFThe photochemical behaviour of the sulfonylurea herbicide rimsulfuron, N-[[(4,6-dimethoxy-2-
pyrimidinyl)amino]carbonyl]-3-(ethylsulfonyl)-2-pyridinesulfon amide, on silica and clay minerals,
used as soil surrogates, was investigated and compared to a natural soil sample. The antagonistic
behaviour of adsorption process and chemical degradation with respect to photodegradation was
assessed and the formation of photoproducts was also determined. Results showed that all chemical
and photochemical processes responsible for the disappearance of the herbicide follow a second
order kinetic. The photochemical degradation of rimsulfuron was strongly affected by retention
phenomena: with increasing of the adsorption capability of supports the photoreactivity of
the herbicide decreased. The extraction rate of the herbicide covered the following values: soil 59.5%,
illite 48.5%, aerosil 22.2%, montmorillonite 21.0%, showing that silica and clay minerals can retain
and protect rimsulfuron from photodegradation much more than soil. Though, adsorption of the
herbicide was always accomplished to a chemical reactivity of solid substrates. N-[(3-ethylsulfonyl)-
2-pyridinyl]-4,6-dimethoxy-2-pyridineamine and N-(4,6-dimethoxy-2-pyrimidinyl)-N-[(3-(ethylsulfonyl)-
2-pyridinyl)]urea were found both as photochemical and chemical metabolites
PHOTOCHEMICAL BEHAVIOUR OF OXYFLUORFEN: A DIPHENYL-ETHER HERBICIDE
Get PDFThe photochemical behaviour in different solvents of the herbicide oxyfluorfen [2-chloro-1-(3-ethoxy-4-nitrophenoxy)-4-(trifluoromethyl) benzene (CAS RN 42874–03–3)] was studied. Photochemical reactions were carried out by using a high pressure mercury arc and a solar simulator. Kinetic parameters and quantum yields were determined. Identification of the photoproducts was performed by GC-MS and the main compounds were confirmed by [1H] NMR. The photochemical reactions were also carried out in the presence of either a singlet or a triplet quencher, and in the presence of either a radical initiator or a radical inhibitor. Results indicate that the first excited singlet state can undergo both homolytic and heterolytic cleavage of the ethyl-oxygen bond in the side chain of oxyfluorfen. Moreover, the presence of reduction products in the reaction mixture is supposed to occur via a monoelectron transfer process with the formation of a transient exciplex during the reaction
Photodegradation de l’acifluorfene et de l’oxyfluorfene en phase aqueuse, influence des substances humiques
No full textL'acifluorfene et l'acifluofene sont deux herbicides qui appartiennent à la famille des diphényléthers. Nous avons étudié leur comportament photochimique dans differents solvants afin de mettre en évidence leurs mécanismes de dedégradation. L'étude en phase aqueuse a èté faite en absence et en presence d'acides humiques. Ces deux herbicides adsorbent dans le proche ultraviolet avec des coefficients d'absorption molaire compris enter 4000 et 5000 mol-1 cm-1. Il sont donc susceptibles de se transformer par photoreactions directe et indirecte. Leur stabilité à la lumiere est relativament faible puisque leur efficacité quantique de photodegardation est comprise entre 10-4 et 10-2 molecule degradée par photon absorbé en solution aqueuse ou alcoliqu
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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