Phototransformation of the herbicide sulcotrione on maize cuticular wax

Vegetation plays a key role in environmental cycling and the fate of many organic pollutants. This is especially the case for pesticides because plant leaves are their first reaction environment after application. It is commonly accepted that photochemical reactions of pollutants on plants predominantly take place in the cuticular wax coating of the leaves. Thus, we used films made of either cuticular wax extracted from maize or carnauba gray wax as a model support. Under simulated sunlight irradiation, sulcotrione (a new class of triketone herbicides) sorbed on cuticular wax films was photolyzed and mainly underwent an intramolecular cyclization. The photoproduct is a chromone derivative which was isolated and fully characterized. It is reported for the first time as a sulcotrione degradation product. The photoreactivity of formulated sulcotrione at the surface of cuticular waxes was investigated too. It photodegraded more rapidly than nonformulated sulcotrione. This study also shows that the rate of sulcotrione photolysis was much faster than the rate of penetration into the wax; photolysis should be, thus, a relevant process in real conditions.     

Effect of surface waxes on the persistence of chlorpyrifos-methyl in apples, strawberries and grapefruits

The effects of the cuticle and epicuticular waxes of grapefruit, strawberry and apple on the photodegradation and penetration of chlorpyrifos-methyl were studied. Photodegradation experiments were conducted by exposing the insecticide to the light of a xenon lamp in the presence of a film of wax extracted from the fruit surface. The half-life of chlorpyrifos-methyl irradiated in absence of waxes was 9.6 min. The half-lives of pesticide irradiated in the presence of wax extracts of apple, grapefruit and strawberry were 83, 34 and 26 min, respectively. In penetration studies, fruit with and without wax layers were treated with an aqueous suspension of pesticide. The penetration of the pesticide from the cuticle to the pulp was measured after 24 h. Samples without wax contained a higher total amount of insecticide than those with wax. No pesticide was detected in samples of apple and grapefruit pulp. Residues were detected in all fractions of strawberry. The waxes and cuticle appear to have some effect on the photodegradation and penetration of chlorpyrifos-methyl in fruit samples.     

Real-time visualization and quantification of PAH photodegradation on and within plant leaves

Vegetation plays a key role in the environmental cycling and fate of many organic chemicals. A compound's location on or within leaves will affect its persistence and significance; retention in surface compartments (i.e., the epicuticular wax and cuticle) renders the compound more susceptible to photodegradation and volatilization, while penetration into the epidermal cell walls or cytoplasm will enhance susceptibility to metabolism. Here, for the first time, methodologies which combine plant and PAH autofluorescence with two-photon excitation microscopy (TPEM) are used to visualize and quantify compound photodegradation on and within living plant leaves. Anthracene,fluoranthene, and phenanthrene were introduced to living leaves of Zea mays and monitored in real time, in control treatments, and when subject to UV-A radiation. Compound photodegradation was observed directly; different degradation rates occurred for different compounds (anthracene > fluoranthene > phenanthrene) and in different locations (at the leaf surface > within the epidermal cells). Results suggest that photodegradation on vegetation may be a more important loss mechanism for PAHs than previously thought. Compound fate in vegetation is potentially highly complex, influenced by diffusion into and location within leaf structures, the rates of supply/loss with the atmosphere, exposure to sunlight, and other environmental conditions. The techniques described here provide a real-time tool to advance insight into these issues.     

百菌清及其代谢产物(4-羟基百菌清)在油麦菜及土壤中的残留降解研究

目的建立气相色谱法(gas chromatography,GC)和液相色谱-串联质谱法(liquid chromatography-tandem mass spectrometry,LC-MS/MS)测定油麦菜及土壤中百菌清及4-羟基百菌清残留的方法,同时研究油麦菜及土壤中百菌清及4-羟基百菌清的残留降解规律。方法油麦菜和土壤中的百菌清分别采用乙腈溶液匀浆提取和振荡提取,使用固相萃取柱净化,气相色谱法带电子捕获检测器测定;油麦菜和土壤中的4-羟基百菌清分别采用乙腈溶液匀浆提取和振荡提取,氮吹至近干用甲醇复溶后过0.2μm滤膜净化,进LC-MS/MS测定分析。结果在0.01~5 mg/L范围内,百菌清及4-羟基百菌清均线性良好;在添加量均为0.01~1 mg/kg时,百菌清在油麦菜和土中的添加平均回收率分别为78.5%~79.8%、79.2%~82.4%,相对标准偏差(relative standard deviation,RSD)分别为3.01%~7.21%、5.06%~5.95%。4-羟基百菌清在油麦菜和土中的添加平均回收率分别为96.2%~116.7%、102.1%~113.9%,RSD分别为4.57%~6.22%、2.99%~4.57%。百菌清及4-羟基百菌清在油麦菜及土壤中的消解动态均符合方程C_t=C_(0e)~(-kt):百菌清在油麦菜中的半衰期为1.7 d,在土壤中半衰期为7.5 d,4-羟基百菌清在油麦菜中的半衰期为2.0 d,在土壤中半衰期为7.5 d。结论该方法简单快速,可同时测定百菌清及其代谢物,上述结果可为今后安全、合理、高效使用百菌清提供一定的参考价值。     

Volatilization of parathion and chlorothalonil from a potato crop simulated by the PEARL model

The volatilization of pesticides from crop canopies in the field should be modeled within the context of evaluating environmental exposure. A model concept based on diffusion through a laminar air-boundary layer was incorporated into the PEARL model (pesticide emission assessment at regional and local scales) and used to simulate volatilization of the pesticides parathion and chlorothalonil from a potato crop in a field experiment. Rate coefficients for the competing processes of plant penetration, wash off, and phototransformation in the canopy had to be derived from a diversity of literature data. Cumulative volatilization of the moderately volatile parathion (31% of the dosage in 7.6 days) could be simulated after calibrating two input data derived for the related compound parathion-methyl. The less volatile and more slowly transformed chlorothalonil showed 5% volatilization in 7.6 days, which could be explained by the simulation. Simulated behavior of the pesticides in the crop canopy roughly corresponded to published data.     

A robust GC-MS/MS method for the determination of chlorothalonil in fruits and vegetables

Chlorothalonil is a non-systemic fungicide that is easily degraded in contact with plants and soil or even by the effect of light and pH. A method for the determination of chlorothalonil in courgettes, strawberries, oranges, leeks and tomato by solvent extraction followed by GC-MS/MS with a triple quadrupole analyser was developed. The causes of chlorothalonil degradation during sample treatment were studied and minimised. The final method was based on extraction with acetone in the presence of 0.1?M EDTA sodium salt solution, and clean-up by SPE using OASIS HLB cartridges. Isotope-labelled hexachlorobenzene (HCB-¹³C₆) was added as an internal standard to the SPE extracts before analysis by GC-MS/MS (EI) (QqQ) analysis in order to correct for instrumental deviations. Quantification was performed by matrix-matched standard calibration using relative responses to the internal standard. Two MS/MS transitions were used for mass spectrometric determination of chlorothalonil to ensure reliable quantification and confirmation. The method was validated using blank samples (for all matrices) spiked at two levels. Recoveries between 77% and 110% and an RSD below 20% were obtained for 0.1 and 0.01?mg?kg^?1 spiking levels (n?=?5). The validated method was applied to treated and untreated samples collected from an experimental field where a chlorothalonil formulated was applied.     

Aquatic photochemistry of nitrofuran antibiotics

The aquatic photochemical degradation of a class of pharmaceuticals known as the nitrofuran antibiotics (furaltadone, furazolidone, and nitrofurantoin) was investigated. Direct photolysis is the dominant photodegradation pathway for these compounds with the formation of a photostationary state between the syn and the anti isomers occurring during the first minutes of photolysis. The direct photolysis rate constant and quantum yield were calculated for each of the three nitrofurans. Reaction rate constants with reactive oxygen species (ROS), 102 and *OH, were also measured, and half-lives were calculated using environmentally relevant ROS concentrations. Half-lives calculated for reaction with 1O2 and *OH are in the ranges of 120-1900 and 74-82 h, respectively. When compared to the direct photolysis half-lives, 0.080-0.44 h in mid-summer at 45 degrees N latitude, it is clear that indirect photochemical processes cannot compete with direct photolysis. The major photodegradation product of the nitrofurans was found to be nitrofuraldehyde, which is also photolabile. Upon photolysis, nitrofuraldehyde produces NO, which is easily oxidized to nitrous acid. The acid produced further catalyzes the photodegradation of the parent nitrofuran antibiotics, leading to autocatalytic behavior. Natural waters were found to buffer the acid formation.     

北京市蔬菜中农药残留现状及慢性膳食暴露评估

目的了解北京市蔬菜中农药残留污染现状及对北京市居民的膳食风险水平。方法采集2013年北京市主要蔬菜生产基地和大型批发市场的蔬菜样品,采用NY/T 761-2008和GB/T 20769-2008等方法检测样品中的33种农药残留,分析北京市蔬菜中农药残留现状,并结合大城市居民的蔬菜消费情况和食品安全指数法对北京市居民从蔬菜中摄入农药风险进行慢性膳食暴露评估。结果 2013年北京市抽检的蔬菜中农药残留检测合格率达99.2%(502/506),农药超标的蔬菜为白菜类和绿叶菜类,拟除虫菊酯类农药检出频次较高,其构成比占40.8%,检出超标的农药为吡虫啉、毒死蜱、哒螨灵和百菌清;对所有检出农药进行慢性膳食暴露评估结果表明,百菌清的日摄入量相对较高,然而包括百菌清在内所有检出农药的食品安全指数值均小于1。结论北京市蔬菜中农药残留量的安全风险均在可接受范围内,百菌清是潜在的风险因子,应重点防患蔬菜中百菌清的残留风险。     

基于液相色谱-四极杆飞行时间质谱法探究毒死蜱光降解行为

目的 根据农药的光解反应原理,建立一套毒死蜱的光降解模型,探究其光降解速率规律,同时对其降解产物进行物质鉴定。方法 利用液相色谱-四极杆飞行时间质谱法对毒死蜱溶液在紫外灯和氙灯照射下的降解行为进行研究,并对其降解产物进行鉴定。结果 10 mg/L毒死蜱在紫外灯照射下降解半衰期为5.35 h,在氙灯照射下降解半衰期为19.01h;毒死蜱的降解速率随温度升高不断加快,在到达40℃以后速率不再上升,同时毒死蜱光解速率随浓度的升高而降低。结论 毒死蜱的光降解符合一级动力学规律,光降解速率次序为紫外灯>氙灯,降解产物包括2-甲氧基-3,5,6-三氯吡啶、3,5,6-三氯吡啶-2-醇等。该研究可为评估毒死蜱对环境的生态毒性提供重要理论支撑。     

Photodegradation processes of the antiepileptic drug carbamazepine, relevant to estuarine waters

The photodegradation of carbamazepine was studied in artificial estuarine water, under conditions relevant to the Rh?ne delta. Chloride substantially enhances the photodegradation of carbamazepine, most likely because of the interaction between Fe(III) colloids and Cl- ions under irradiation, yielding Cl2*-. For a given compound, prerequisites for the described degradation enhancement by chloride to be significant are faster degradation via reaction with Cl2*- compared to charge-transfer processes on the surface of Fe(III) colloids and an important role of indirect phototransformation compared to direct photolysis. A major photodegradation intermediate of carbamazepine is acridine, formed by direct photolysis, while hydroxylated/ oxidized compounds are formed in the presence of *OH, and chloroderivative formation is observed in the presence of Fe(III) and chloride.     

Role of dissolved organic matter, nitrate, and bicarbonate in the photolysis of aqueous fipronil

A multivariate kinetic model of aqueous fipronil photodegradation was developed as a function of dissolved organic matter (DOM), bicarbonate, and nitrate at concentrations that bracketthose commonly observed in natural waters (ca. 0-10 mg/L). Several pathways were available for fipronil photodegradation in this system, including direct photolysis and indirect photooxidation by species produced during the illumination of natural waters (e.g., 3NOM*, 1O2*, *OH, *CO3(1-), *OOR, *OOH, e(aq)-, O2(*-)). Product studies indicated thatfipronil was quantitatively converted to fipronil desulfinyl, a product that is associated with direct photolysis alone. DOM was the only variable that affected fipronil degradation; it decreased the rate of fipronil photodegradation primarily through competitive light absorption (i.e., attenuation) and the quenching of fipronil*. The addition of sodium chloride (30 percent per thousand) resulted in a more rapid rate (approximately 20%) of fipronil loss in comparison to equivalent experiments performed without sodium chloride, implying that fipronil may be more photolabile in marine environments.     

Photochemical fate of sulfa drugs in the aquatic environment: sulfa drugs containing five-membered heterocyclic groups

The photochemical fate of five sulfa drugs with varying five-membered heterocyclic substituents (sulfamethoxazole, sulfisoxazole, sulfamethizole, sulfathiazole, and sulfamoxole) was investigated in aqueous solution. The rate of direct photolysis of these compounds is dependent upon the identity of the heterocyclic R group as well as the pH of the solution. Matrix deconvolution methods were employed to determine the absorption spectrum and photolysis rate of each protonation state (cationic, neutral, and anionic). From these data, quantum yields for direct photodegradation were calculated for each protonation state of the sulfa drugs. The quantum yields calculated range from <0.005 for the neutral state of sulfamethizole to 0.7 +/- 0.3 for the protonated state of sulfisoxazole. The protonation state that is most photoreactive varies among the sulfa drugs and cannot be attributed to the rate of photon absorption. Products arising from the direct photolysis of the sulfa drugs were also investigated. For all the compounds, sulfanilic acid was observed as a common product. The singlet oxygen quenching rates of the sulfa drugs were determined by laser flash photolysis and range from (2 +/- 1) x 10(4) M(-1) s(-1) for sulfamethoxazole to (3.0 +/- 0.7) x 10(8) M(-1) s(-1) for sulfamoxole. Reaction of the sulfa drugs with hydroxyl radical is not modulated by the R group, and the rate constants are all near the bimolecular diffusion-controlled limit of 10(10) M(-1) s(-1). The photodegradation of the sulfa drugs in natural water samples of Lake Josephine (St. Paul, MN) and Lake Superior was attributed solely to direct photolysis. This study indicates thatthese similarly structured antibiotics will be subject to a wide range of photodegradation rates with sulfathiazole degrading relatively quickly, sulfisoxazole and sulfamethizole degrading moderately, and sulfamethoxazole degrading much more slowly.     

TiO_2薄膜的制备及对罗丹明B光催化分解过程的影响

采用sol gel法在玻璃表面制备了TiO2 薄膜 .X射线衍射表明 ,该薄膜的结构为锐钛矿型 .通过考察罗丹明B的光催化分解过程 ,发现TiO2 薄膜对罗丹明B的光催化分解有很好的活性 ,可以完全分离罗丹明B .通过考察罗丹明B在TiO2 薄膜上的吸附性 ,发现当薄膜吸附罗丹明B达到一定量时 ,脱乙基反应将与降解反应同时发生     

Effect of Agitation, Sampling Location and Protective Films on Light-Induced Riboflavin Loss in Skim Milk

Photodegradation of riboflavin in skim milk as influenced by continuous agitation, location within the container and protective films was studied. High performance liquid chromatography was used to monitor the riboflavin concentration in the milk. Retention of riboflavin in light-exposed, continuously agitated milk samples was significantly lower than in unagitated samples. Sampling positions within blow-molded polyethylene milk containers also had a significant effect on light-induced riboflavin loss. After 5 days of light exposure, riboflavin retention at the top of the unagitated milk containers averaged 58% compared to 92% retention for milk located at the bottom of the containers. Metallized-oriented, polyethylene-terephthalate films used as overwraps decreased penetration of visible light into milk samples and decreased the riboflavin photodegradation.     

Solvent-specific photolytic behavior of octachlorodibenzo-p-dioxin

The photolysis of octachlorodibenzo-p-dioxin (OCDD) was investigated in various organic solvents under lambda > 300 nm irradiation. The rates of OCDD photolysis were highly solvent-specific. OCDD was photodegraded rapidly in toluene, n-hexane, CCl4, and 1-octanol, whereas it underwent negligible photodegradation in acetonitrile, acetone, and methanol. Both OCDD photolysis and fluorescence emission did not take place in very polar solvents because polar solvent molecules efficiently quenched the excited OCDD (OCDD*). The addition of acetonitrile to an OCDD solution in toluene rapidly quenched both the fluorescence emission and the photolysis rate, which can be described by Stern-Volmer analysis. The efficient photolysis in nonpolar (or less polar) solvents seems to be mediated through a charge-transfer path where the solvent and OCDD* act as an electron donor and acceptor, respectively. However, OCDD photolysis in CCl4 seems to represent the opposite case in which the solvent is an electron acceptor and OCDD* is an electron donor. Hammett sigma constants that approximately represent the electron-donating power in structurally related aromatic solvents show a good correlation with the photolysis rates. We propose that the solvent specificity in OCDD photolysis is mainly ascribed to the difference in the electron donating (or accepting) tendency among various solvents. When triethylamine that easily donates an electron to form a charge-transfer exciplex with OCDD* was added, a marked enhancement in the photolysis rate was observed.     

Plasticizing Effects of Beeswax and Carnauba Wax on Tensile and Water Vapor Permeability Properties of Whey Protein Films

ABSTRACT: The possible plasticizing effect of beeswax (viscoelastic wax) and carnauba wax (elastic wax) on tensile and water vapor permeability properties of whey protein isolate (WPI) films was studied. For the experiments, 3 groups of films with different WPI:glycerol ratios (1:1; 1.5:1; 2:1, 2.5:1, and 3:1) were prepared. The 1st group was made without the addition of wax, and the latter 2 groups were made with the addition of beeswax and carnauba wax, respectively, mixing 1 part of wax to 1 part of WPI. Lipid particle size, water vapor permeability, tensile properties, and thickness of films were analyzed and measured. The results show that the incorporation of beeswax produced a plasticizing effect in WPI:glycerol films, whereas carnauba wax produced an anti-plasticizing effect. The moisture barrier properties of WPI:glycerol films benefit from the addition of beeswax, by both increase of the hydrophobic character and decrease of the amount of hydrophilic plasticizer required in the film.     

敌草隆在棉纤维上的降解及产物分析

棉花纤维作为重要的纺织品原材料,其安全性越来越受到人们的关注。本文针对棉花种植过程中大量使用且半衰期长的敌草隆作为研究对象,通过光降解和煮练过程,利用液相色谱技术进行检测,研究敌草隆的降解及产物。结果表明,煮练条件下,在40min敌草隆能够完全从棉纤维上脱除,液相色谱能够有效的检测敌草隆在棉花纤维上的残留,重复性好,满足农药检测标准,在光解和煮练过程中敌草隆的降解产物同为3,4-二氯苯胺。     

Physical, Thermal, and Barrier Characterization of Casein-Wax-Based Edible Films

ABSTRACT: Lactic acid casein-wax-based edible films were prepared to study the effect of carnauba and candelilla waxes. Water and oxygen permeability, thermal properties, and microstructure were determined as a function of relative humidity. Scanning electron microscopy showed a partial phase separation of wax and protein. Water permeability decreased as wax content increased and as relative humidity decreased from 70 to 50%. Despite containing wax, films overall showed low decrease in water permeability. However, films with candelilla wax had lower water permeability values than those with carnauba wax. Films were able to be heat-sealed. There was no difference in oxygen permeability compared to films without wax.     

The physicochemical characteristics and hydrophobicity of high amylose starch–glycerol films in the presence of three natural waxes

The film forming behaviour and hydrophobicity of high amylose (HA) starch in the presence of three different natural waxes (beeswax, candelilla wax and carnauba wax) were studied in the presence and absence of Tween-80. The HA starch:glycerol (G) ratio was maintained at 80:20 (on dry solid basis) and the concentration of wax was varied from 5% and 10% (w/w). The melted wax samples were homogenized with HAG dispersion with or without Tween-80 and the films were prepared by solution casting. The hydrophobicity and water-barrier properties in these films were determined by using contact angle (CA), water vapour permeability (K_w) tests, and water sorption isotherm at 0.529 RH and 20 °C. The K_w values of the HAG films decreased significantly (p < 0.05) with the addition of 5% concentration of these waxes. Then the addition of Tween-80 to the HAG + wax films increased the K_w values significantly (p < 0.05). The presence of these waxes in the presence and absence of Tween-80 resulted into different sorption isotherms and the water adsorptivity and moisture diffusion coefficient values were also affected. The presence of Tween-80 increased the CA in HAG + carnauba wax films while the CA was found to decrease in the case of other two waxes. The highest hydrophobicity was observed in HAG + carnauba wax + Tween-80 films in which the CA was >80.0° both at 5% and 10% (w/w) wax concentration. These higher CA values in HAG + carnauba wax + Tween-80 films were found to be related to the higher surface roughness in these films.     

Phytophotolysis of hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) in leaves of reed canary grass

Hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) was degraded in reed canary grass leaves exposed to simulated sunlight to primary products nitrous oxide and 4-nitro-2,4-diazabutanal. This is the first time that 4-nitro-2,4-diazabutanal, a potentially toxic degradate, has been measured in plant tissues following phytotransformation of RDX. These compounds, along with nitrite and formaldehyde, were also detected in aqueous RDX systems exposed to the same simulated sunlight. Results showed that the initial products of RDX photodegradation in translucent plant tissues were similar to products formed from aqueous photolysis of RDX. Combustion analysis of leaves following 14C-RDX uptake and subsequent light exposure revealed the presence of tissue-bound material that could not be extracted with acetonitrile. No detectable formaldehyde was emitted from the leaves. The detection of similar RDX degradation products in both aqueous and plant-based systems suggests that RDX may be initially transformed by similar mechanisms in both systems. Direct photolysis of RDX via ultraviolet irradiation passing into the leaves is hypothesized to be responsible for the observed transformations. In addition, membrane-bound "trap chlorophyll" in the chloroplasts may shuttle electrons to RDX as an indirect photolysis transformation mechanism. Results from this study indicate that reed canary grass facilitates photochemical degradation of RDX, and this mechanism should be considered along with more established phytoremediation processes when assessing the fate of contaminants in plant tissues. Plant-mediated phototransformation of xenobiotic compounds is a process that may be termed "phytophotolysis".