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Environmental toxicity of three fungicides and their photoderivatives on freshwater crustaceans
No full textThe fungicides Carboxin, Oxycarboxin and Furalaxyl occur mainly on the soil, even if surface-waters are subjected to contamination due to phenomena of run off with continuous exposure of non-target aquatic organisms. Carboxin and Furalaxyl undergo photooxidation that may induce the conversion of pesticides into noxious derivatives. These photoproducts may constitute a further potential risk for aquatic biota. Here we report the effects of the three pesticides and their photoproducts, obtained by sunlight exposure in water, on freshwater crustaceans.
The photoderivatives were isolated by chromatographic techniques and/or identified by spectroscopic means. All the compounds were tested to evaluate acute and chronic toxicity on freshwater crustaceans. Thamnocephalus platyurus, Daphnia magna and Ceriodaphnia dubia were used in acute bioassays, while chronic tests were performed only on Ceriodaphnia dubia. The acute results about the parent compounds showed that Furalaxyl was particularly active on T. platyurus (LC50=0.46 mg/L), while Carboxin and Oxycarboxin were less toxic, showing the highest effect on C. dubia (LC50=10.32 mg/L and 8.63 respectively). A different behavior was found for the photoderivatives, in fact the 2(5H)-furanone (the main photoproduct obtained from Furalaxyl) was one-fold more toxic than the parent compound while the main photoproduct obtained from Carboxin, the sulfoxide, was found to be less toxic than the parent compound. Chronic data demonstrated that Carboxin and Furalaxyl had a toxic potential in the same order found for acute toxicity towards T. platyurus while an EC50=0.02 was found for Oxycarboxin. The Furalaxyl photoderivative showed a toxicity two order of magnitude higher than the parent compound (EC50=0.0065 mg/L). From these data it appears that the risk characterization of pesticides have to consider their potential photochemical changes that may or not lead to a toxicological activation process and interfere with fate and effects on non-target organisms
Photochemical fate and eco-genotoxicity assessment of the drug etodolac
No full textThe photochemical behavior of etodolac was investigated under various irradiation conditions. Kinetic data were obtained after irradiation of 10-4M aqueous solutions by UVB, UVA and direct exposure to sunlight. The Xenon lamp irradiation was used in order to determine the photodegradation quantum yield under sun-simulated condition (φsun). The value was determined to be=0.10±0.01. In order to obtain photoproducts and for mechanistic purposes, experiments were carried out on more concentrated solutions by exposure to sunlight and to UVA and UVB lamps. The drug underwent photooxidative processes following an initial oxygen addition to the double bond of the five membered ring and was mainly converted into a spiro compound and a macrolactam. Ecotoxicity tests were performed on etodolac, its photostable spiro derivative and its sunlight irradiation mixture on two different aquatic trophic levels, plants (algae) and invertebrates (rotifers and crustaceans). Mutagenesis and genotoxicity were detected on bacterial strains. The results showed that only etodolac had long term effects on rotifers although at concentrations far from environmental detection values. A mutagenic and genotoxic potential was found for its derivative
Sensitized photooxygenation of the fungicide furalaxyl
No full textBackground. The photolysis of pesticides is of high current interest since light is one of the most important abiotic factors which are responsible for the environmental fate of these substances and may induce their conversion into noxious products. The action of light can also be mediated by oxygen and synthetic or naturally occurring substances which act as sensitizers. Our objective in this study was to investigate the photochemical behaviour of the systemic fungicide furalaxyl in the presence of oxygen and various sensitizers, and to compare the toxicity of the main photoproduct(s) to that of the parent compound. Previous reports on the direct photolysis of the pesticide demonstrated a very slow degradation and the only identified photoproducts were N-2,6-xylyl-D,L-alaninate and 2,6-dimethylaniline. Methods. Solutions of furalaxyl in CH3CN were photooxygenated using a 500W high-pressure mercury lamp (through a Pyrex glass filter, λ>300 nm) or a 650W halogen lamp or sunlight and the proper sensitizer. When sunlight was used, aqueous solutions were employed. The photodegradation was checked by NMR and/or GC-MS. The photoproducts were spectroscopically evidenced and, when possible, isolated chromatographically. Acute toxicity tests were performed on the rotifer Brachionus calyciflorus, the crustacean cladoceran Daphnia magna and the anostracan Thamnocephalus platyurus, while chronic toxicity tests (sublethal endpoints) comprised a producer, the alga Pseudokirchneriella subcapitata and the crustacean Ceriodaphnia dubia, as a consumer. Results and Discussion. In the presence of both oxygen and sensitizer, furalaxyl underwent rapid photochemical transformations mainly to N-disubstituted formamide, maleic anhydride and a 2(5H)-furanone derivative. The formation of these products was rationalized in terms of a furan endoperoxide intermediate derived from the reaction of furalaxyl with active dioxygenated species (singlet oxygen, superoxide anion or ground state oxygen). The 2(5H)-furanone exhibited a higher toxicity than the parent compound. Conclusion. This work reports the first data on the photosensitized oxygenation of furalaxyl with evidence of the high tendency of the pesticide to undergo photodegradation under these conditions leading, among other things, to a 2(5H)-furanone, which is more toxic than the starting furalaxyl towards aquatic organisms. Recommendations and Outlook. Investigation highlights that the photolytic fate of a pesticide, although quite stable to direct photoreaction due to its low absorption of solar radiation at ground level, can be significantly influenced in the environment by the presence of substances with energy or electron-transfer properties as natural dyes, e.g. chlorophyll, or synthetic pollutants, e.g. polycyclic aromatic hydrocarbons (PAH)
Transformation and ecotoxicity of carbamic pesticides in water
No full textBackground. N-methylcarbamate insecticides are widely used chemicals for crop protection. This study examines the hydrolytic and photolytic cleavage of benfuracarb, carbosulfan and carbofuran under natural conditions. Their toxicity and that of the corresponding main degradation products toward aquatic organisms were evaluated. Methods. Suspensions of benfuracarb, carbosulfan and carbofuran in water were exposed to sunlight, with one set of dark controls, for 6 days, and analyzed by 1H-NMR and HPLC. Acute toxicity tests were performed on Brachionus calyciflorus, Daphnia magna, and Thamnocefalus platyurus. Chronic tests were performed on Pseudokirchneriella subcapitata, and Ceriodaphnia dubia. Results and Discussion. Under sunlight irradiation, benfuracarb and carbosulfan gave off carbofuran and carbofuran-phenol, while only carbofuran was detected in the dark experiments. The latter was degraded to phenol by exposure to sunlight. Effects of pH, humic acid and KNO3 were evaluated by kinetics on dilute solutions in the dark and by UV irradiation, which evidenced the lability of the pesticide at pH 9. All three pesticides and phenol exhibited acute and higher chronic toxicity towards the aquatic organisms tested. Conclusion. Investigation on the hydrolysis and photolysis of benfuracarb and carbosulfan under natural conditions provides evidence concerning the selective decay to carbofuran and/or phenol. Carbofuran is found to be more persistent and toxic. Recommendations and Outlook. The decay of benfuracarb and carbosulfan to carbofuran and the relative stability of this latter pesticide account for many papers that report the detection of carbofuran in water, fruits and vegetables. © 2006 ecomed publishers (Verlagsgruppe Hüthig Jehle Rehm GmbH)
Chlorpropham and phenisopham: phototransformation and ecotoxicity of carbamates in the aquatic environment
No full textIn this study, a comparison of two carbamic pesticides, chlorpropham and phenisopham, was carried out in terms of both photodegradability and ecotoxicity. The photochemical behaviour of the two pesticides was investigated under environmental-like conditions (aqueous media, UVB or solar irradiation). The photochemical kinetic parameters were calculated by irradiating 5 × 10-5 M solutions (H2O-CH3CN, 9:1 v/v) using UVB lamps. For chlorpropham and phenisopham similar half-life times (39.0 and 55.0 min) were determined. Irradiation by sunlight leads to longer degradation half-life times (about 3 months), while it is possible to observe the formation of the same photoproducts. The well-known dechlorination reaction to a hydroxyphenylcarbamate was observed for chlorpropham. Phenisopham undergoes photo-Fries reaction to give rearranged products (hydroxybenzamides) and fragmentation products (hydroxyphenylcarbamate and N-ethylaniline). Acute and chronic toxicity tests of pesticides and their photoproducts were performed on organisms from two levels of the freshwater aquatic chain, the anostraca crustacean Thamnocephalus platyurus, the rotifer Brachionus calyciflorus and the alga Pseudokirchneriella subcapitata. The acute results showed that chlorpropham had median lethal concentrations for the crustacean T. platyurus and the rotifer B. calyciflorus of 10.16 and 35.19 mg L-1, respectively, and phenisopham did not show any acute toxicity as the derivatives up to 10 mg L-1. The only exception was N-ethylaniline which exhibited an acute LC50 value of 0.46 mg L-1. Phenisopham was the most toxic in the long term exposure while its five derivatives showed lower chronic potential for rotifers and algae. The same trend was observed for chlorpropham except for rotifers. This journal is © the Partner Organisations 2014
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe 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
Un mondo frattale, parte prima
No full textQuesto articolo è il sunto della conferenza tenuta durante la PLS Virtual Summer School 2020. Scopo della conferenza, e quindi dell'articolo, è stato quello di avvicinare gli studenti alla geometria frattale, facendo scoprire loro la nozione matematica di autosimilarità e l'esistenza di oggetti aventi dimensione non intera. L'ultima sezione dell'articolo contiene gli esercizi (e le relative soluzioni) proposti agli studenti alla fine della conferenza
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