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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
Kinetics of photochemical degradation of imazapyr in aqueous solutions
Get PDFKinetic parameters of imazapyr photodegradation in aqueous solutions are presented at two pH values and different concentrations. To study the effect of UV and sunlight irradiation, reactions were carried out by using a pyrex reactor equipped with UV high pressure mercury arc and a solar simulator (Heraeus Suntest CPS+). The depletion of imazapyr concentration always followed first order kinetic. The half-lives were 19.0 and 24.7 minutes at pH 7.0 and 4.0, respectively. The influence of organic matter on the photolytic process was studied irradiating a solution of imazapyr with suspended humic acids (1:1 w:w)
Influence of humic fractions on retention of isoproturon residues in two Moroccan soils
No full textThe influence of different fractions of soil organic matter on the retention of the herbicide isoproturon (IPU) has been evaluated.
Water and methanol extractable residues of 14C labeled isoproturon have been determined in two Moroccan soils by β-counting–liquid chromatography. The quantification of bound residues in soil and in different fractions of soil humic substances has been performed using pyrolysis/scintillation-detected gas-chromatography. Microbial mineralization of the herbicide and soil organic matter has been also monitored. Retention of isoproturon residues after 30-days incubation ranged from 22% to 32% (non-extractable fraction). The radioactivity extracted in an aqueous environment was from 20% to 33% of the amount used for the treatment; meanwhile, methanol was able to extract another 48%. Both soils showed quantities of bound residues into the humin fraction higher than humic and fulvic acids. The total amount of residues retained into the organic matter of the soils was about 65 % of non-extractable fraction, and this percentage did not change with incubation time; on the contrary, the sorption rate of the retention reaction is mostly influenced by the clay fraction and organic content of the soil. Only a little part of the herbicide was mineralized during the experimental time
Influence of soil organic matter on isoproturon sorption
Get PDFSoil organic matter is the result of the biological and chemical degradation of dead plant residues or animal remains. The exact structure of the organic matter is not known, but it is know the influence of this soil component on the sorption phenomena of xenobiotics and on the formation of bound residues.
IUPAC (the International Union of Pure and Applied Chemistry) has found it relevant to define the term bound residues as "chemical species (active ingredient, metabolites and fragments) originating from pesticides that are un-extracted by methods that do not significantly change the chemical nature of these residues, but which remain in the soil”.
Bound residues appear in various forms: the entire molecule of the xenobiotic or parts of it may have entered a new molecular structure as a part of the organic matter, it may be sequestrated in inaccessible sites in the soil aggregates or it may be strongly sorbed.
The aim of this research was to evaluate the influence of different fractions of soil organic matter on the sorption of isoproturon (IPU), a phenyl urea herbicide used against annual grasses and broad-leaved weeds in cereal production across Europe and Mediterranean Countries.
Two Moroccan soils (1.4 and 1.5% O.C.; 58 and 69% clay; 34 and 30% silt; 8 and 1% sand) were treated with a solution of 14C labelled Isoproturon (80 mCi mmol-1) and extracted after 0, 7, 15 and 30 days at first with water, to evaluate the residue quickly available, and afterwards with methanol. On the same soil samples organic matter was extracted and the different organic fractions were separated as humic acids, fulvic acids and humine. Mineralization of the herbicide was also monitored. Isoproturon was determined in the different soil extracts using a liquid chromatograph equipped with a liquid scintillator. The localisation of bound residues in the different fractions of the organic matter was performed using pyrolysis/GC equipment furnished of a gas-scintillation detector.
Retention of Isoproturon after 30 days of incubation ranged from 22 to 32 % (non extractable fraction). The herbicide extracted in aqueous environment was from 20 to 33% of the amount used for the treatment; meanwhile, methanol was able to extract another 48%. Both soils showed quantities of bound residues into the humine fraction higher than humic and fulvic acids. The amount of Isoproturon retained into the organic fraction of the soil did not change with time; on the contrary, the sorption rate of the retention reaction is mostly influenced by the clay fraction of the soil. Only a little part of the herbicide was mineralized during the experimental time
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
Kinetics of photochemical degradation of imazapyr in aqueous solutions
No full textKinetic parameters of imazapyr photodegradation in aqueous solutions are presented at two pH values and different concentrations. To study the effect of UV and sunlight irradiation, reactions were carried out by using a pyrex reactor equipped with UV high pressure mercury arc and a solar simulator (Heraeus Suntest CPS+). The depletion of imazapyr concentration always followed first order kinetic. The half-lives were 19.0 and 24.7 minutes at pH 7.0 and 4.0, respectively. The influence of organic matter on the photolytic process was studied irradiating a solution of imazapyr with suspended humic acids (1:1 w:w)
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
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