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1.
This study was carried out to characterize the photodegradation of penoxsulam and to evaluate the significance of photolysis for its fate and dissipation. Degradation studies of (14)C-labeled isotopes of penoxsulam in a "merry-go-round" reactor suggest that aqueous photodegradation proceeds via three possible pathways: cleavage of the sulfonamide bridge, stepwise degradation of the triazolopyrimidine system and its substituents, and photooxidation of the sulfonyl group. Seven major photoproducts were found, and six were identified. Two of the identified photodegradation products seem to be either rapidly biodegraded when formed or not formed in significant amounts in environmental conditions.  相似文献   

2.
To elucidate the photochemical behavior of diphenyl ether herbicides in superficial waters, the photodegradation of acifluorfen, 5-[2-chloro-4-(trifluoromethyl)phenoxy]-2-nitrobenzo?c 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 (Phi(solvent)) of acifluorfen in different solvents are as follows (units are degraded molecules photon(-1)): Phi(water) = 10(-4), Phi(acetonitrile) = 10(-4), Phi(methanol) = 10(-4), and Phi(hexane) = 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.  相似文献   

3.
The photodegradation of imazethapyr, 5-ethyl-2-(4-isopropyl-4-methyl-5-oxo-4,5-dihydroimidazol-1H-3-yl)nicotinic acid, has been investigated in phosphate buffers and in buffered solutions containing natural organic matter (NOM). Imazethapyr degrades most quickly under 253.7 nm light and at pH values >4. The presence of NOM in solution caused the reaction rate constants for the photodegradation to decrease, with higher concentrations of NOM having a larger effect. Calculations suggest light screening is the major effect of the NOM. Seven photoproducts have been identified, and a photodegradation mechanism is proposed.  相似文献   

4.
Photodegradation of rotenone in soils under environmental conditions   总被引：1，自引：0，他引：1  
An environmental fate study was performed to analyze the effects of soil components on the photochemical behavior of rotenone. Photodegradation experiments were carried out on three types of soil collected in southern Italy, Valenzano (VAL), Turi (TUR), and Conversano (CON), from April to June 2006. Soil thin-layer plates (1 mm thick) were spiked with 1.5 mg/kg of rotenone and exposed under natural conditions of sunlight and temperature. The plates were removed from the sunlight at predetermined intervals of continuous irradiation. Other soil samples, control and sterilized, were kept in the dark to evaluate possible effects of chemical and microbiological degradation during the irradiation experiment. The time for 50% loss of the initially applied rotenone varied from 5 to 7 h, following the order TUR < CON < VAL. In environmental studies, changes in temperature and/or moisture affected the degradation rate and caused deviations from first-order kinetics. The photolysis reaction fit the two compartment or the multiple compartment model pathways better. A fast initial decrease during the first 5 h of rotenone irradiation was followed by a much slower decline, which clearly indicates the rather complex chemical process of rotenone photodegradation on soil surfaces. Also, the degradation was shown to be directly related to the soil concentration of clay and organic matter. Rotenolone (12abeta-hydroxyrotenone) was detected by HPLC/DAD/MS analysis as the only photodegradation byproduct of rotenone in soil thin layers. Results provide additional insights on the rates and the mechanisms of rotenone degradation, aiming to describe more clearly the degradation performance of chemical residues in the environment.  相似文献   

5.
Pyrazosulfuron ethyl (PE) and halosulfuron methyl (HM) are two new highly active sulfonylurea herbicides that have been widely used for weed control in a variety of vegetables and other crops. These two herbicides have similar molecular structures, differing only in the substitutions on the pyrazole ring. Chemical hydrolysis is a primary process affecting the environmental fate of sulfonylurea pesticides. The hydrolytic transformation kinetics of PE and HM were investigated as a function of pH and temperature. For both herbicides, the hydrolysis rate was pH-dependent and increased with increasing temperature. The hydrolysis of both sulfonylureas was much faster in acidic or basic media than under neutral conditions. Identification of hydrolytic products by liquid chromatography-mass spectrometry (LC-MS) suggested that both PE and HM were subject to cleavage and contraction of the sulfonylurea bridge. The hydrolysis rate of HM was significantly higher than that of PE in alkaline solutions, despite their structural similarity. A chlorine substitution on HM's pyrazole ring makes HM more susceptible to bridge contraction than PE under basic conditions. The hydrolysis of HM and PE was relatively unaffected by the presence of cyclic oligosaccharides (cyclodextrins), indicating that natural OH-containing organic compounds occurring in aquatic environments may have little impact on the transformation of these sulfonylurea herbicides.  相似文献   

6.
To elucidate the photochemical behavior of pesticide metolachlor, degradation was carried out in aqueous media of different compositions such as sea, river, lake, and distilled water under natural and simulated solar irradiation. In addition, the effect of important constituents of natural water such as dissolved organic matter (DOM, isolated from Pamvotis Lake) and nitrate ions was also examined. It was found that photodegradation proceeds via a pseudo-first-order reaction in all cases. The presence of DOM inhibits the photolysis reaction with half-lives ranging from 87 to 693 h whereas the degradation rate was accelerated up to 11 times in the presence of NO(3)(-). In addition, the toxicity of the degradation products formed (generally through hydroxylation, dealkylation, and cyclization reactions) was also performed using the marine luminescent bacterium Vibrio fisheri. Our results indicated a toxicity increase of the irradiated solution showing that photoproducts of higher acute toxic effects were formed.  相似文献   

7.
The photodegradation of the sulfonylurea herbicide azimsulfuron, N-[[(4,6-dimethoxypyrimidin-2-yl)amino]carbonyl]-1-methyl-4-(2-methyl-2H-tetrazole-5-yl)-1H-pyrazole-5-sulfonamide (AZS), was studied in water at different wavelengths and in the presence of photocatalysts. AZS was rapidly degraded by UV light, affording three photoproducts. The main product, accounting for about 70% of photodegraded herbicide, was identified as 6-amino-5-[(4,6-dimethoxypyrimidin-2-yl)methylamino]-1,5,6,8-tetrahydro-7-oxa-8lambda(6)-tia-1,2,5,6-tetraza-azulen-4-one (ADTA) by single-crystal X-ray diffraction. With simulated sunlight irradiation, the reaction was slower and 2-amino-4,6-dimethoxypyrimidine (DPA) and 1-methyl-4-(2-methyl-2H-tetrazole-5-yl)-1H-pyrazole-5-sulfonamide (MPS), arising from a photohydrolytic cleavage of the sulfonylurea bridge, were the only byproducts observed. The reactions followed first-order kinetics. The addition of dissolved organic matter (DOM) did not modify significantly the AZS photodegradation rate. The presence of Fe2O3 accelerated more than twice the reaction rate affording two major products, DPA and MPS, together with minor amounts of N-[[(5-hydroxy-4,6-dimethoxypyrimidin-2-yl)amino]carbonyl]-1-methyl-4-(2-methyl-2H-tetrazole-5-yl)-1H-pyrazole-5-sulfonamide (AZS-OH). The greatest degradation rate was detected in the presence of TiO2. Only the photohydroxylation product AZS-OH was observed, which was transformed rapidly into oxalic acid.  相似文献   

8.
The photodegradation of the carboxamide acaricide hexythiazox in three different solvent systems (aqueous methanolic, aqueous isopropanolic, and aqueous acetonitrilic solutions) in the presence of H(2)O(2), KNO(3), and TiO(2) under ultraviolet (UV) light (λ(max) ≥ 250 nm) and sunlight (λ(max) ≥290 nm) has been assessed in this work. The kinetics of photodecomposition of hexythiazox and the identification of photoproducts were carried out using liquid chromatography-mass spectrometry. The rate of photodecomposition of hexythiazox in different solvents followed first-order kinetics in both UV radiation and natural sunlight, and the degradation rates were faster under UV light than under sunlight. Hexythiazox was found to be more efficiently photodegraded in the presence of TiO(2) than in the presence of H(2)O(2) and KNO(3). Two major photoproducts were separated in pure form using column chromatography and identified according to IR, (1)H NMR, and mass spectral information as cyclohexylamine and 5-(4-chlorophenyl)-4-methylthiazolidin-2-one. Another nine photoproducts were identified according to LC-MS/MS spectral information. The plausible photodegradation pathways of hexythiazox were proposed according to the structures of the photoproducts.  相似文献   

9.
Photodegradation of four pharmaceuticals (i.e. carbamazepine, ibuprofen, ketoprofen and 17α-ethinylestradiol) in aqueous media was studied using a solar light simulator (Xe lamp irradiation) and sunlight experiments. These experiments were carried out in river and seawater and compared to distilled water. The latter was used to evaluate the direct photodegradation pathways. Irradiation time was up to 400 min and 24 days for the solar light simulator and sunlight assays, respectively. Pharmaceutical photodegradation followed a first-order kinetics and their half-lives calculated in every aqueous matrix. Moreover, the sensitizing effect of DOC was evaluated by comparison with the kinetics obtained in distilled waters. Ketoprofen was rapidly transformed via direct photolysis in all the waters under both sunlight (t 1/2?=?2.4 min) and simulated solar light simulator test (t 1/2?=?0.54 min). Under xenon lamp radiation, ibuprofen and 17α-ethinylestradiol were photodegraded at moderate rate with half-lives from 1 to 5 h. Finally, carbamazepine had the lowest photodegradation rate (t 1/2?=?8–39 h) attributable to indirect photodegradation. Indeed, its elimination was strongly dependent on the DOC concentration present in solution. Finally, several ketoprofen photoproducts were identified and plotted against solar light simulator irradiation time. Accordingly, the photodegradation pathway of ketoprofen was postulated.  相似文献   

10.
The effect of epicuticular waxes extracted from fruits (apple, nectarine, pear, and plum) and vegetables (tomato and eggplant) on the photodegradation of rotenone was studied. The waxes affected the decay rate and the degradation pathway of this botanical insecticide. Tomato, nectarine, and plum waxes decreased the photodegradation rate compared to controls, whereas apple and pear waxes increased it. Rotenone irradiated under sunlight without waxes gave seven photoproducts; in contrast, in the presence of waxes it changed its behavior, leading to different pathways according to the wax employed. The main photoproduct formed was 12abeta-rotenolone.  相似文献   

11.
The abiotic degradation of iodosulfuron-methyl-ester was investigated under both alkaline and acidic pH conditions in the dark, and results showed it to be a rather stable molecule in neutral or slightly alkaline environments. Photochemical reactions were studied using a high-pressure mercury arc lamp, and results showed that direct phototransformation is possible under normal environmental conditions (lambda > 290 nm). High-performance liquid chromatography (HPLC-UV and HPLC-MS) analyses were used to identify the degradates and to study the kinetics of photodecomposition and hydrolysis. Five main products of iodosulfuron-methyl-ester degradation were tentatively identified, and one of them (4-methoxy-6-methyl-1,3,5-triazin-2-amine) was confirmed using an authentic standard. Among the phototransformation mechanisms, photosubstitution of the iodide atom by a hydroxyl group, photodissociation of the N-S bond, and photoassisted hydrolysis were observed. The quantum efficiencies (multiwavelength quantum yield) of the photodegradation under different conditions were determined, and values of 0.054 +/- 0.02 (pH 9.6), 0.08 +/- 0.02 (pH 7), and 0.044 +/- 0.008 (pH 5.3) were obtained.  相似文献   

12.
Thin layer chromatographic and liquid chromatographic procedures were used to show that sulfonamides containing a heterocyclic amine moiety and free N1 acidic hydrogen will photodegrade under fluorescent light in model systems containing riboflavin. The photodegradation product was characteristic of the drug. In-depth studies on sulfamethazine showed that the drug also photodegraded in the presence of lumichrome and flavin mononucleotide; the rate of photodegradation depended on the photosensitizer and its concentration. Crude polar liver extracts sensitized the photodegradation of sulfamethazine, but to a degree less than expected on the basis of reported riboflavin content of livers. It is recommended that procedures for quantitating sulfa drugs and their metabolites be performed in subdued lighting and/or that amber or low actinic vessels be used to prevent losses due to photochemical reactions.  相似文献   

13.
The photodegradation of [(14)C]niclosamide was studied in sterile, pH 5, 7, and 9 buffered aqueous solutions under artificial sunlight at 25.0 +/- 1.0 degrees C. Photolysis in pH 5 buffer is 4.3 times faster than in pH 9 buffer and 1.5 times faster than in pH 7 buffer. In the dark controls, niclosamide degraded only in the pH 5 buffer. After 360 h of continuous irradiation in pH 9 buffer, the chromatographic pattern of the degradates was the same regardless of which ring contained the radiolabel. An HPLC method was developed that confirmed these degradates to be carbon dioxide and two- and four-carbon aliphatic acids formed by cleavage of both aromatic rings. Carbon dioxide was the major degradate, comprising approximately 40% of the initial radioactivity in the 360 h samples from both labels. The other degradates formed were oxalic acid, maleic acid, glyoxylic acid, and glyoxal. In addition, in the chloronitroaniline-labeled irradiated test solution, 2-chloro-4-nitroaniline was observed and identified after 48 h of irradiation but was not detected thereafter. No other aromatic compounds were isolated or observed in either labeled test system.  相似文献   

14.
The photodegradation pathway of the commonly used herbicide fenoxaprop-p-ethyl (FE) was elucidated, and the effects of the photodegradation on its toxicity evolution were investigated. Under solar irradiation, FE could undergo photodegradation, and acetone enhanced the photolysis rates significantly. The same photoproducts formed under the irradiation of lambda > 200 nm and lambda > 290 nm through rearrangement, loss of ethanol after rearrangement, de-esterification, dechlorination, photohydrolysis, and the breakdown of the ether linkages. One of the main transformation products, 4-[(6-chloro-2-benzoxazolyl)oxy] phenol (CBOP), was resistant to photodegradation under the irradiation of lambda > 290 nm, and its photolysis rate was seven times slower than the parent under the irradiation of lambda > 200 nm. Among the metabolites, CBOP (48 h EC50 of 1.49-1.64 mg/L) and hydroquinone (48 h EC50 of 0.25-0.28 mg/L) were more toxic to Daphnia magna than the parent FE (48 h EC50 of 4.2-6.9 mg/L). Thus, more toxic and photoresistant products were generated from photolysis of the herbicide. Ecotoxicological effects of phototransformed products from pesticides should be emphasized for the ecological risk assessment of these anthropogenic pollutants.  相似文献   

15.
In arid ecosystems, abiotic processes facilitate the physical and chemical degradation of plant litter to the extent that decomposition models that use climatic and litter composition variables as surrogates for microbial activity are not predictive. The purpose of this study was to estimate the potential contribution of photodegradation to the decomposition of plant litters that varies in architecture and chemical composition. Litter of Pinus edulis, Juniperus monosperma and Populus deltoides were exposed to ambient and attenuated sunlight, with and without supplemental water additions, at a riparian forest site along the Middle Rio Grande (New Mexico, USA). Mass loss, elemental composition, and microbial extracellular enzyme activities (EEA) were measured over 639 days. The composition of the fungal communities associated with the decomposing litters was compared by analyses of fungal ITS nrDNA sequences. Litter exposed to ambient sunlight had greater mass loss rates than shaded litter, independent of the water treatment: Populus increased by 100%, Pinus by 86% and Juniperus by 46%. The increases were proportional to exposed litter surface area per g dry mass. EEA potentials, particularly oxidative activities, were low in comparison to those measured in mesic ecosystems. For Populus litter, the principal driver of photoacceleration appeared to be photodegradation of cellulose; for Pinus, it was photodegradation of polyphenols; for Juniperus accelerated mass loss was associated with photodegradation of both polysaccharides and polyphenols. Fungal community composition varied by litter type, but the dominant colonizers were yeasts and dark-septate hyphal taxa; a finding consistent with the low enzymatic oxidation potential. This study shows that photochemical oxidation can supplement enzymatic oxidation and increase decomposition rates. As a result, organic matter decomposition in arid ecosystems is not restricted to periods of high moisture availability as is plant production. This decoupling may partly account for the low soil organic matter content of these ecosystems.  相似文献   

16.
Using an atmospheric photochemical model, the photochemical ozonecreation potential (POCP) values of non-methane hydrocarbon(NMHC) species are studied under different NMHC/NOx ratios. The behavior of POCP values of NMHC changing with time is also discussed under the condition of higher NMHC/NOx ratios, referring to the situation of China. The following results can beobtained. Alkenes, high-reactivity alkanes and aromatics, andformaldehyde are the primary contributors of photochemicalozone; The POCP values of NMHC species vary withNMHC/NOx ratios systematically. The POCP values of highreactivity species decrease with NMHC/NOx ratio increasing,but the POCP values of low reactivity species changelittle. The POCP value for a given NMHC species varieswith time of photochemical reactions. The POCP values oflow reactivity species increase with time, but the POCPvalues of high reactivity species change little. NOx, alkenes,aromatics, and aldehydes have higher reactivity and shorterlifetimes, therefore their transportation distances arelimited and they mainly produce local pollution. Alkanes havelower chemical reactivity and longer lifetimes so that theycan transport farther distance from their sources.  相似文献   

17.
Phototransformation of propiconazole in aqueous media.   总被引：2，自引：0，他引：2  
The photolysis of propiconazole in pure water, in water containing humic substances, and in natural water was investigated. The reaction rates were determined, and the main photoproducts were identified with the help of HPLC-mass spectrometry and by NMR. The quantum yield for direct photolysis was 0.11 +/- 0.01 at the maximum of absorption (269 nm). Photocyclization after HCl elimination and photohydrolysis of the cyclized intermediate were the main reaction pathways at 254 nm. By contrast, oxidation prevailed over dechlorination in simulated or natural solar light. Humic substances (10 mg x L(-)(1)) and naturally occurring chromophores contained in natural water enhanced the rate of propiconazole photodegradation in solar light. Half-life in June in Clermont-Ferrand (latitude 46 degrees N) was found to be 85 +/- 10 h in pure water and 60 +/- 10 h in natural water; showing that photodegradation of propiconazole in natural waters involves both direct photolysis and photoinduced reactions.  相似文献   

18.
Kinetics and mechanism of imazosulfuron hydrolysis   总被引：5，自引：0，他引：5  
Knowledge of the kinetics and pathways of hydrolytic degradation is crucial to the prediction of the fate and transport mechanism of chemicals. This work first describes the kinetics of the chemical hydrolysis of imazosulfuron, a new sulfonylurea herbicide, and evaluates the results to propose a degradation pathway. The hydrolysis of imazosulfuron has been studied in aqueous buffers both within the pH range 1.9-12.3 at ambient temperature (thermostated at 25 +/- 2 degrees C) and at pH 3.6 within the temperature range of 15-55 degrees C. The hydrolysis rate of imazosulfuron was characterized by a first-order kinetics, pH- and temperature-dependent, and accelerated by acidic conditions and higher temperatures. The calculated half-lives at pH 4.5 and 5.9 were 36.5 and 578 days, respectively. At pH 6.6, 7.4, 9.2, and 12.3 no significant change in imazosulfuron concentration was observed after 150 days. Half-lives were much lower at pH <4 (= imazosulfuron pK(a)), at which they ranged from 3.3 to 6.3 days. Moreover, a change in temperature from 15 to 25 degrees C in acidic conditions (pH 3.6) decreased the half-life of imazosulfuron by a factor of approximately 4.0; in any case, a 3-5-fold increase in the rate of hydrolysis was found for each 10 degrees C increase in temperature. In acidic conditions the only hydrolysis products were the two molecules resulting from the cleavage of the sulfonylurea bridge.  相似文献   

19.
The photochemical behavior of the neonicotinoid insecticide imidacloprid was studied with regard to different chemical environments. Different model solvents simulated the structure moieties mainly occurring in waxes and cutin of the plant cuticle. Cyclohexane and cyclohexene substituted saturated and unsaturated hydrocarbon chains, whereas ethanol and 2-propanol were models for primary and secondary alcohol groups of cuticular components. After 5 h of irradiation, imidacloprid was completely degraded in all solvents. With 88-96 mol% 1-[(6-chloropyridin-3-yl)methyl]imidazolidin-2-imine was formed as the main product, whereas 1-[(6-chloropyridin-3-yl)methyl]imidazolidin-2-one was identified as minor product in the range 4-6 mol%. By contrast, besides the photoproducts formed in organic solvents, irradiation of the solid imidacloprid on a glass surface delivered a complex variety of unidentified photoproducts. The nucleophilic addition reaction of the main photoproduct, 1-[(6-chloropyridin-3-yl)methyl]imidazolidin-2-imine, with both cyclohexene oxide and methyl 9,10-epoxystearate as model compounds indicates that epoxidized cutin acids are possible reaction partners for the formation of plant cuticle bound residues of imidacloprid, which could explain the reported findings of nonextractable residues of imidacloprid in plants.  相似文献   

20.
Direct degradation of imazapic, an herbicide of the imidazoline family, has been investigated in aqueous solution at different concentrations, pH values, and temperatures. The efficiency of the photodegradation process has been evaluated through degradation rate constants that could be fitted best with pseudo-first-order kinetics ( Ct = C0 e(- kt )). Ultrahigh resolution mass spectrometry (FTICR/MS) was used in electrospray ionization mode as a tool to study the photolysis process on a molecular level, whereas UV-vis and high-performance liquid chromatography/mass spectrometry analysis were used to follow, by time, the evolution of the intermediates. Taking advantage of the high resolving power of FTICR/MS to perform precise formula assignments taking account of the natural abundance of isotopes, we herein propose and demonstrate an approach using 2D-derived van Krevelen visualization (O/C, H/C, m/z) to confirm the formation of imazapic intermediates. Such an approach allows a qualitative analysis of intermediates and elucidates the plausible reaction pathways of the photolysis process. More than eight photoproducts were separated and identified as a phototransformation of the imidazole ring. A mechanistical pathway was proposed.  相似文献   

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