Effect of the epicuticular waxes of fruits and vegetables on the photodegradation of rotenone

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.     

Metabolism of fenitrothion and conjugation of 3-methyl-4-nitrophenol in tomato plant (Lycopersicon esculentum)

The metabolism of (14)C-labeled fenitrothion (Sumithion, [O,O-dimethyl-O-(3-methyl-4-nitrophenyl)phosphorothioate]) in tomato plant (Lycopersicon esculentum Mill., cv. Ponderosa) grown in the greenhouse equipped with quartz glass was conducted to investigate the effect of sunlight on the behavior of fenitrothion and to elucidate the detailed structure of conjugated metabolites. Tomato plants (BBCH 85) were topically treated with (14)C-labeled fenitrothion twice with a 2 week interval between applications. At 15 days after the second application, more than half of the recovered (14)C was detected as unaltered fenitrothion, glucose, and cellobiose esters of 3-methyl-4-nitrophenol (NMC) in extracts from tomato fruit. The photoinduced formation of the S-methyl isomer of fenitrothion via thiono-thiolo rearrangement was detected only in the surface rinse but at trace amounts. In the whole tomato fruit, fenitrothion, the S isomer, NMC-beta-glucoside, and NMC cellobioside were detected at 34.16, 1.28, 7.47, and 15.07% of the recovered (14)C, respectively. Trace amounts of the oxon analogue of fenitrothion were detected only on tomato leaves. The chemical structure of the cellobiose conjugate of NMC, 1-O-beta-d-glucopyranosyl-(1-->4)-beta-d-glucopyranosyl-3-methyl-4-nitrophenol, was determined by spectroscopic analyses (liquid chromatography-mass spectrometry, NMR), using the metabolite obtained from leaves and stems of tomato plant hydroponically grown with (14)C-labeled NMC.     

Gas chromatographic method for determination of fenitrothion in fenitrothion technical and in formulated products: collaborative study

A gas chromatographic (GC) method for determination of fenitrothion in fenitrothion technical and formulated products has been subjected to a collaborative study with 7 participating laboratories. Formulations are extracted with chloroform containing dibutyl sebacate as an internal standard and are analyzed by gas chromatography using an OV-210 column. Collaborators were furnished matched pairs of technical product and water-dispersible powder and emulsifiable concentrate formulations. Relative standard deviations for reproducibility (RSDR) for the paired samples were 0.54, 1.00, and 1.56%, respectively, for technical fenitrothion, water-dispersible powders, and emulsifiable concentrates. The method has been approved interim official first action as an alternative to the present official first action AOAC method 6.A19-6.A24, which uses a polyphenyl ether, 6 ring (PPE-6R) column packing and fluoranthene as internal standard.     

Photodegradation of imidacloprid

The photolytic decomposition of the insecticide imidacloprid (1) in HPLC grade water and of imidacloprid as the formulated product Confidor insecticide in tap water was studied using HPLC methodology. The structures of several degradates have been determined in aquatic medium, and the DT(50) values of imidacloprid and Confidor have been measured. In addition, the influence of TiO(2) on the photodegradation of Confidor was studied. The photoproduct 1-(6-chloro-3-pyridinyl)methyl-2-imidazolidinone (5) has been identified as the main degradate in each of the three series of experiments by several analytical techniques. The photolytic half-lives for imidacloprid under the conditions of this study were 43 min in HPLC grade water, 126 min formulated as Confidor in tap water, and 144 min formulated as Confidor in tap water in the presence of TiO(2).     

Photodegradation of penoxsulam

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.     

碘甲磺隆钠盐在水溶液中的光解研究

为了解碘甲磺隆钠盐在水溶液中的光降解特性,评价其环境安全性,以太阳光和高压汞灯为光源,进行光解试验,研究了碘甲磺隆钠盐在不同水溶液中的光解行为及水体pH值对其光解的影响。结果表明,碘甲磺隆钠盐在所有试验水体中的降解均符合一级动力学方程,不同水体中碘甲磺隆钠盐的半衰期分别为14.29～21.26h（太阳光）与2.29～3.76min（高压汞灯）,两种光源下碘甲磺隆钠盐在各自然水体中的降解速率依次为井水〉河水〉池塘水〉稻田水。不同pH值水体中的光解实验表明,碘甲磺隆钠盐在酸性介质中的光解比在碱性介质中快,顺序为pH5〉pH7〉pH9〉pH11。     

Photodegradation of cassava and corn starches

The baking expansion properties of sour cassava starch (Polvilho azedo) are attributable to photochemical starch degradation induced by heterolactic fermentation after sun-drying. This study investigated the effects of UV irradiation on the different structural levels of cassava starch as compared to those of corn starch and dextrins. Photosensitive compounds excited at 360 and 290 nm in cassava starch were photodegraded when starch was exposed to sunlight or 360 nm irradiation. UV irradiation depolymerized cassava and corn starches, inducing modifications due, at least in part, to a mechanism involving free radicals. Lactic acid was also photodegraded. Photodegradation induced by UV absorption could have been due to fluorescent chromophores found in starches and nonfluorescent chromophores present in glucosidic units.     

Organic matter and parathion degradation in flooded soil

The effect of rice straw on parathion degradation in a flooded alluvial soil was investigated. In soils inoculated with an enrichment culture which exhibited an exceptionally high ability to hydrolyze parathion, rice straw amendments inhibited parathion hydrolysis to p-nitrophenol and diethyl thiophosphoric acid. On the other hand, in uninoculated soils, rice straw enhanced the degradation of parathion via nitro reduction. During the enhanced breakdown of parathion in uninoculated soils amended with rice straw, aminoparathion and an unidentified metabolite evidently possessing a PS bond were detected. Thus, the influence of organic matter on the persistence of parathion in flooded soil is governed by the metabolic pathway involved in the degradation.     

Salinity and the persistence of parathion in flooded soils

The persistence of parathion in five coastal saline soils of varying electrical conductivity and in one nonsaline soil sample was studied under flooded conditions. Parathion was decomposed faster in nonsaline soil than in saline soils and its stability increased with increasing electrical conductivity. The addition of salts to the nonsaline soil at 4, 8 and 16 dS^?1 increased the persistence of parathion. Nitro-group reduction, and not hydrolysis, was the major route of parathion degradation in saline and nonsaline soils. The accumulation of aminoparathion was less pronounced in saline soils than in nonsaline soil concomitant with slow degradation of parathion in saline soils. The inhibition of nitro-group reduction in saline soils was related to low microbial activities as reflected in decreased dehydrogenase activity and slow iron reduction.     

Evidence for surfactant solubilization of plant epicuticular wax

The solubilization of isolated, reconstituted tomato (Lycopersicon esculentum Mill.) fruit and broccoli (Brassica oleracaea var. botrytis L.) leaf epicuticular waxes (ECW) by nonionic octylphenoxypolyethoxy ethanol surfactant (Triton X-100) was demonstrated in a model system by TLC and fluorescence analysis using pyrene as a fluorescent probe. ECW was solubilized at or above the surfactant critical micelle concentration; solubilization increased with an increase in micelle concentration. As shown by the fluorescence quenching of pyrene, surfactant solubilization of the ECW increased rapidly for the first 12 h, then approached a plateau, increased linearly with an increase in temperature (22--32 degrees C), and decreased linearly with the log of the polyoxyethylene chain length (range 5--40 oxyethylenes). These data are discussed in relation to surfactant effects on phytotoxicity and performance of foliar spray application of agrochemicals.     

Determination of benzene in polypropylene food-packaging materials and food-contact paraffin waxes

An analytical procedure was developed for determination of benzene in polypropylene food packaging and was adapted for determination of benzene in commercial paraffin waxes intended for food-contact use. The polymer was dissolved in hexadecane at 150 degrees C. The wax was melted in an 80 degrees C oven. A simple helium-sparging apparatus was used to remove the volatile chemical from the polymer or wax. The contaminant was collected in methanol, distilled water was added, and the resulting solution was analyzed by headspace gas chromatography. The instrument was equipped with a 30 m fused silica open tubular capillary column and a photoionization detector. Average recoveries of benzene from polymer and paraffin wax at low parts-per-billion concentrations were 63 and 70%, respectively. Limits of detection and quantitation for analysis of polypropylene were 8 and 17 ppb, respectively; the limit of quantitation for analysis of paraffin wax was 2 ppb. In several commercial polypropylene products examined, benzene levels ranged from none detected to 426 ppb. In 3 commercial waxes examined, concentrations of 16-73 ppb benzene were determined. The presence of benzene was confirmed by gas chromatography/mass spectrometry.     

Biologically-induced hydrolysis of parathion in soil: Kinetics and modelling

The hydrolysis of the organophosphorus insecticide, parathion (O,O-diethyl O-p-nitrophenyl phosphorothioate) in a silty loam sierozem soil (Gilat, Israel) occurred primarily through microbial action. Parathion (labelled with ¹⁴C in the alkyl chain) was applied at levels of 10–160 μg dry soil^?1 to soil remoistened to 20% and incubated at 25°C for 8 days. Bacterial numbers increased to a maximum 4–5 days after application of parathion and the increase was proportional to the concentration of parathion added. The rate of hydrolysis of parathion per μg applied was independent of the concentration of parathion. A model developed to predict the relationship between parathion concentration, microbial numbers and hydrolysis kinetics was in general agreement with the data experimentally obtained. The course of decomposition of successive additions of parathion, determined experimentally and predicted by the model, was characterized by rapid hydrolysis of parathion and successive increases in bacterial numbers. A portion of the ¹⁴C applied in these experiments was strongly absorbed by the soil and was not used by the soil microorganisms during the incubation period tested.     

Photodegradation of triazine herbicides in aqueous solutions and natural waters

The photodegradation of three triazines, atrazine, simazine, and prometryn, in aqueous solutions and natural waters using UV radiation (lambda > 290 nm) has been studied. Experimental results showed that the dark reactions were negligible. The rate of photodecomposition in aqueous solutions depends on the nature of the triazines and follows first-order kinetics. In the case of the use of hydrogen peroxide and UV radiation, a synergistic effect was observed. The number of photodegradation products detected, using FIA/MS and FIA/MS/MS techniques, suggests the existence of various degradation routes resulting in complex and interconnected pathways.     

Photodegradation of Sulfamethoxazole Applying UV- and VUV-Based Processes

The efficiency of UV- and VUV-based processes (UV, VUV, UV/H₂O₂, and VUV/H₂O₂) for removal of sulfamethoxazole (SMX) in Milli-Q water and sewage treatment plant (STP) effluent was investigated at 20??C. The investigated factors included initial pH, variety of inorganic anions (NO ₃ ^? and HCO ₃ ^? ), and humic acid (HA). The results showed that the degradation of SMX in Milli-Q water at both two pH (5.5 and 7.0) followed the order of VUV/H₂O₂ > VUV > UV/H₂O₂ > UV. All the experimental data well fitted the pseudo-first order kinetic model and the rate constant (k) and half-life time (t _1/2) were determined accordingly. Indirect oxidation of SMX by generated ^?OH was the main degradation mechanism in UV/H₂O₂ and VUV/H₂O₂, while direct photolysis predominated in UV processes. The quenching tests showed that some other reactive species along with ^?OH radicals were responsible to the SMX degradation under VUV process. The addition of 20?mg?L^?1 HA significantly inhibited SMX degradation, whereas, the inhibitive effects of NO ₃ ^? and HCO ₃ ^? (0.1?mol?L^?1) were observed as well in all processes except in UV irradiation for NO ₃ ^? . The removal rate decreased 1.7?C3.6 times when applying these processes to STP effluent due to the complex constituents, suggesting that from the application point of view the constituents of these complexes in real STP effluent should be considered carefully prior to the use of UV-based processes for SMX degradation.     

Photodegradation of rotenone in soils under environmental conditions

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.     

拟除虫菊酯类农药光降解的研究进展

拟除虫菊酯类农药的广泛使用,引起的环境问题及农业生产与日常生活中的安全问题日益突出。本文综述了拟除虫菊酯类农药的光降解行为,包括自然光照降解、紫外光照降解、光催化降解、光照下的微生物降解及辐照降解;探讨了影响光降解的因素,如光照强度、p H、氧气、溶剂、金属离子、腐殖质,及与其他农药的交互作用等。最后,总结了拟除虫菊酯类农药的光降解机理。