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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
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
Photochemistry and photoinduced toxicity of Acifluorfen, a diphenyl-ether herbicide
No full textPhotochemistry studies can be helpful in assessing the environmental fate of chemicals. Photochemical reactions lead to the formation of by-products that can exhibit different toxicological properties from the original compound. For this reason the photochemical behavior of the herbicide acifluorfen (5-[2-chloro-4-(trifluoromethyl)phenoxy]-2-nitrobenzoic acid) in the presence of different solvents was studied. Photochemical reactions were carried out using a high-pressure mercury arc and a solar simulator. Kinetic parameters and quantum yields were determined. The identification of photoproducts was performed by mass spectrometry and [1H] nuclear magnetic resonance (NMR). Nitrofluorfen, hydroxy-nitrofluorfen, 2-chloro-4-(trifluoromethyl)phenol, 5-trifluoromethyl-5'-nitrodibenzofuran, and other derivatives were identified. 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. Substances used as inhibitors of the excited levels T1 and S1 showed that photodegradation of acifluorfen begins from a singlet state S1 through a pi,pi* transition. The role of free radicals in the photodegradation of acifluorfen was determined and a radical mechanism was proposed. Toxicity tests against Daphnia magna Strauss showed that acifluorfen was not toxic at a concentration of 0.1 mM; however, photoproducts formed after 36 h of UV exposure of the herbicide induced a remarkable toxicity to the test organism
PHOTOLYSIS AND HYDROLYSIS OF RIMSULFURON
Get PDFThe degradation in the liquid phase of rimsulfuron and its commercial 250g/kg WG formulation (Titus) was investigated. Photolysis reactions were carried out at 25°C by a highpressure
mercury arc (Hg-UV) and a solar simulator (Suntest), while the hydrolysis rate was determined by keeping aqueous buffered samples in the dark. The effects of solvent and water pH on
reaction kinetics were studied, and the results compared to literature data. Photoreactions of the commercial product in organic solvents were faster than pure rimsulfuron. Under simulated sunlight in water, the half-life for the photolysis reaction ranged from one to nine days at pH 5 and 9, respectively. The hydrolysis rate was as high as the photolysis rate, but decreased on increasing water pH. The main metabolite identi®ed in neutral and alkaline conditions as well as in acetonitrile was N-
[(3-ethylsulfonyl)-2-pyridinyl]-4,6-dimethoxy-2-pyridinamine, while N-(4,6-dimethoxy-2-pyrimidinyl)-
N-[(3-(ethylsulfonyl)-2-pyridinyl)]urea and minor metabolites prevailed in acidic condition
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
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Photochemical degradation of acifluorfen in aqueous solution
Get PDFTo elucidate the photochemical behavior of diphenyl ether herbicides in superficial waters, the photodegradation of acifluorfen, 5-[2-chloro-4-(trifluoromethyl)phenoxy]-2-nitrobenzoic acid (CAS Registry No. 50594-66-6), was studied in water and acetonitrile. All experiments were carried out under laboratory conditions using a solar simulator (xenon arc) or jacket Pyrex reaction cell equipped with a 125 W high-pressure mercury lamp. The calculated polychromatic quantum efficiencies (Φsolvent) of acifluorfen in different solvents are as follows (units are degraded molecules photon-1): Φwater = 10-4, Φacetronitile = 10-4, Φmethanol = 10-4, and Φhexane = 10-2. The results obtained in this work are in good agreement with the literature value of monochromatic quantum yield. HPLC-MS analysis (APCI and ESI in positive and negative modes) was used to identify acifluorfen photoproducts. These results suggest that the photodegradation of acifluorfen proceeds via a number of reaction pathways: (1) decarboxylation, (2) dehalogenation, (3) substitution of chlorine group by hydroxyl or hydrogen groups, and (4) cleavage of ether linkage, giving phenols. Photorearrangement products were studied by other investigators. No such products were observed. In addition, it was found that the trifluoro functional group on acifluorfen was not affected by any transformation, and no products of a nitro group reduction were found
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