Mechanism of OH-initiated atmospheric photooxidation of dichlorvos: a quantum mechanical study

Dichlorvos (2,2-dichlorovinyl phosphate, DDVP) is a widely used organophosphorus insecticide. DDVP may be released into the atmosphere, where it may be transported for long distances and undergo chemical transformations. The mechanisms of the atmospheric reactions of DDVP have not been fully understood because of the short lifetime of its oxidized radical intermediates and the extreme difficulty in the detection of these species experimentally. In this paper, we carried out molecular orbital theory calculations for the OH-initiated atmospheric photooxidation of DDVP. The profile of the potential energy surface was constructed, and the possible channels involved in the reaction are discussed. Several energetically favorable reaction pathways are revealed for the first time. The calculated results were compared with the available experimental observations. Four product pathways are energetically feasible for DDVP degradation initiated by OH radicals in the atmosphere and are consistent with the experimentally observed products CCl2O and CO, but the additional products CCl2CHO, (CH3O)2P(O)OH, HO2, and a closed-shell organophosphorus compound denoted P10 are also predicted.     

The OH-initiated oxidation of hexylene glycol and diacetone alcohol

The OH-initiated oxidation of two VOCs directly emitted to the atmosphere through their use as industrial solvents, hexylene glycol (HG, (CH3)2C(OH)CH2CH(OH)CH3) and diacetone alcohol (DA, (CH3)2C(OH)CH2C(O)CH3), has been studied in two photoreactors: a 140 L Teflon bag irradiated by lamps at CNRS-Orleans and the 200 m3 European photoreactor, EUPHORE, irradiated by sunlight. The rate constants for the reactions of HG and DA with OH radicals have been determined at (298 +/- 3) K using a relative rate method: k(HG) = (1.5 +/- 0.4) x 10(-11) and k(DA) = (3.6 +/- 0.6) x 10(-12) cm(3) molecule(-1) s(-1) and have been found in good agreement with estimations from structure-reactivity relationships. The study at Orleans and EUPHORE of the OH-initiated oxidation of hexylene glycol showed the formation of diacetone alcohol, acetone, and PAN as the principal products. The branching ratio of the H-atom abstraction from the > CH- group of HG has been estimated to be (47 +/- 4)% corresponding to the measured formation yield of DA. The formation yields of acetone and PAN lead to the determination of a lower limit of (33 +/- 7)% for the branching ratio of the H-atom abstraction of the -CH2- group of HG. For diacetone alcohol, studies at EUPHORE have shown negligible photolysis under atmospheric conditions (J < 5 x 10(-6) s(-1)) and the formation of acetone, PAN, HCHO, and CO in the OH-initiated oxidation experiments. The molar yield of acetone, close to 100%, corresponds to the branching ratio of the H-atom abstraction from the -CH2- group of DA. The present study has allowed the identification of the nature and the fate of the oxy radicals as intermediates in the oxidation mechanism of both HG and DA. The atmospheric implication of these results, especially the ozone formation potential of HG and DA, is discussed.     

Monitoring OH-initiated oxidation kinetics of isoprene and its products using online mass spectrometry

A novel technique has been developed to simultaneously monitor the kinetics of the OH radical-initiated oxidation of isoprene and formation and oxidation of its products (methyl vinyl ketone, methacrolein, 3-methylfuran, and formaldehyde) using online mass spectrometry. The kinetics of isoprene and its products were investigated at 323 K and at 1 atm total pressure. The responses of 30 representative ions for isoprene and its products were monitored during the reaction, and their concentration profiles were calculated by linear algebraic equations, which resolve the measured mass spectra of representative ions into the responses of individual target organics, and by calibrations, which converted the responses to individual target concentrations. Using this method, yields of methyl vinyl ketone, methacrolein, and 3-methylfuran at 323 K were measured to be 14.4+/-0.1%, 19.0+/-0.2%, and 2.9+/-0.2%, respectively, in excellent agreement with previously reported yields under NOx-free conditions. The reaction kinetics of isoprene and its oxidation products measured by the experimental procedure developed in this study were compared with those estimated by a kinetic model of isoprene oxidation. The observed methacrolein concentrations as a function of time were reproduced reasonably well by this model, while the observed methyl vinyl ketone concentration could be reproduced by including secondary reactions of some of the hydroperoxide products of isoprene oxidation. The observed 3-methylfuran concentrations could be reproduced using secondary cyclization reactions of some of the 1,4-hydroxycarbonyl products of isoprene oxidation. These results suggest that under low NOx conditions reactions of some of the hydroperoxides and hydroxycarbonyls produced from the OH-initiated oxidation of isoprene may be a significant source of methyl vinyl ketone and 3-methylfuran in the atmosphere.     

Atmospheric degradation of perfluoro-2-methyl-3-pentanone: photolysis, hydrolysis and hydration

Perfluorinated carboxylic acids are widely distributed in the environment, including remote regions, but their sources are not well understood. Perfluoropropionic acid (PFPrA, CF(3)CF(2)C(O)OH) has been observed in rainwater but the observed amounts can not be explained by currently known degradation pathways. Smog chamber studies were performed to assess the potential of photolysis of perfluoro-2-methyl-3-pentanone (PFMP, CF(3)CF(2)C(O)CF(CF(3))(2)), a commonly used fire-fighting fluid, to contribute to the observed PFPrA loadings. The photolysis of PFMP gives CF(3)CF(2)C·(O) and ·CF(CF(3))(2) radicals. A small (0.6%) but discernible yield of PFPrA was observed in smog chamber experiments by liquid chromatography-mass spectrometry offline chamber samples. The Tropospheric Ultraviolet-Visible (TUV) model was used to estimate an atmospheric lifetime of PFMP with respect to photolysis of 4-14 days depending on latitude and time of year. PFMP can undergo hydrolysis to produce PFPrA and CF(3)CFHCF(3) (HFC-227ea) in a manner analogous to the Haloform reaction. The rate of hydrolysis was measured using (19)F NMR at two different pHs and was too slow to be of importance in the atmosphere. Hydration of PFMP to give a geminal diol was investigated computationally using density functional theory. It was determined that hydration is not an important environmental fate of PFMP. The atmospheric fate of PFMP seems to be direct photolysis which, under low NO(x) conditions, gives PFPrA in a small yield. PFMP degradation contributes to, but does not appear to be the major source of, PFPrA observed in rainwater.     

FTIR kinetic, product, and modeling study of the OH-initiated oxidation of 1-butanol in air

A kinetic and product study was performed on the reaction of OH radicals with 1-butanol in a 480 L indoor photoreactor and also in the EUPHORE outdoor smog chamber in Valencia, Spain. Long path in situ FTIR spectroscopy and gas chromatography with photoionization detection were used to analyze reactants and products. Using a kinetic relative rate technique, a rate coefficient of k(OH + 1-butanol) = (8.28 +/- 0.85) x 10(-12) cm3 s(-1) was measured in 740 Torr synthetic air at 298 +/- 2 K. The reaction products observed and their fractional molar yields were (in percent) butanal (51.8 +/- 7.1), propanal (23.4 +/- 3.5), ethanal (12.7 +/- 2.2), and formaldehyde (43.4 +/- 2.4). In addition, the results support the probable formation of 4-hydroxy-2-butanone. Propanal, ethanal, and formaldehyde could also be formed in secondary reactions of some of the primary aldehydic products. However, under the conditions employed in the experiments, the contribution from secondary reactions is very minor. On the basis of the product studies, a detailed atmospheric degradation mechanism was constructed and tested against experimental data by chemical box model calculations. Measured and simulated concentration-time profiles for selected reactants were in excellent agreement.     

Atmospheric chemistry of perfluoroalkanesulfonamides: kinetic and product studies of the OH radical and Cl atom initiated oxidation of N-ethyl perfluorobutanesulfonamide

Perfluorooctanesulfonamides [C8F17SO2N(R1)(R2)] are present in the atmosphere and may, via atmospheric transport and oxidation, contribute to perfluorocarboxylates (PFCA) and perfluorooctanesulfonate (PFOS) pollution in remote locations. Smog chamber experiments with the perfluorobutanesulfonyl analogue N-ethyl perfluorobutanesulfonamide [NEtFBSA; C4F9SO2N(H)CH2CH3] were performed to assess this possibility. By use of relative rate methods, rate constants for reactions of NEtFBSA with chlorine atoms (296 K) and OH radicals (301 K) were determined to be kCL) = (8.37 +/- 1.44) x 10(-12) and kOH = (3.74 +/- 0.77) x 10(-13) cm3 molecule(-1) s(-1), indicating OH reactions will be dominant in the troposphere. Simple modeling exercises suggestthat reaction with OH radicals will dominate removal of perfluoroalkanesulfonamides from the gas phase (wet and dry deposition will not be important) and that the atmospheric lifetime of NEtFBSA in the gas phase will be 20-50 days, thus allowing substantial long-range atmospheric transport. Liquid chromatography/tandem mass spectrometry (LC/MS/MS) analysis showed that the primary products of chlorine atom initiated oxidation were the ketone C4F9SO2N(H)COCH3; aldehyde 1, C4F9SO2N(H)CH2CHO; and a product identified as C4F9SO2N(C2H5O)- by high-resolution MS but whose structure remains tentative. Another reaction product, aldehyde 2, C4F9SO2N(H)CHO, was also observed and was presumed to be a secondary oxidation product of aldehyde 1. Perfluorobutanesulfonate was not detected above the level of the blank in any sample; however, three perfluoroalkanecarboxylates (C3F7CO2-, C2F5CO2-, and CF3CO2-) were detected in all samples. Taken together, results suggest a plausible route by which perfluorooctanesulfonamides may serve as atmospheric sources of PFCAs, including perfluorooctanoic acid.     

Indirect polarographic determination of trichlorfon and dichlorvos

Summary A method of indirect polarographic determination of trichlorfou and dichlorvos was elaborated. Glyoxal, the product of alkaline hydrolysis of both these organophosphorus insecticides, condenses with o-phenylendiamine to forming quinoxaline, which is polarographically reduced, giving a well-developed two-electron wave. The relation of the concentration of the insecticides and corresponding diffusion current is recti linear in the broad concentration range of 0–8 mg. The standard deviation of this method is ± 1.2% for 400 jig and ± 5.2% for 3.0 g of trichlorfon respectively.

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Indirekte polarographische Bestimmung von Trichlorfon und Dichlorvos

Zusammenfassung Es wurde eine Methode zur indirekten polarographischen Bestimmung von Trichlorfon und Dichlorvos ausgearbeitet. Das Produkt der alkalischen Hydrolyse der beiden Organophosphor-Insecticiden, Glyoxal, wird mito-Phenylendiamin bei der Entstehung von Chinoxalin kondensiert. Chinoxalin wird bei gegebenen Arbeitsbedingungen auf der Quecksilber-Tropfelektrode bei Entstehung einer gut entwickelten Zwei-Elektronenwelle reduziert. Die Linearität der Abhängigkeit der Intensität des polarographischen Diffusions-Stromes von der Konzentration der Insecticide ist gültig bei den experimentellen Bedingungen im breiten Konzentrationsbereich von 0–8 mg. Die Standardabweichung der polarographischen Methode betragt für 400 g ± 1,2 und für 3 g ± 5,2%.

     

Radical dependence of the yields of methacrolein and methyl vinyl ketone from the OH-initiated oxidation of isoprene under NO(x)-free conditions

Formation yields of methacrolein (MAC), methyl vinyl ketone (MVK), and 3-methyl furan (3MF) from the hydroxyl radical (OH) initiated oxidation of isoprene were investigated under NO(x)-free conditions (NO(x) = NO + NO(2)) at 50 °C and 1 atm in a quartz reaction chamber coupled to a mass spectrometer. Yields of the primary products were measured at various OH and hydroperoxy (HO(2)) radical concentrations and were found to decrease as the HO(2)-to-isoprene-based peroxy radical (ISORO(2)) concentration ratio increases. This is likely the result of a competition between ISORO(2) self- and cross-reactions that lead to the formation of the primary products, with reactions between these peroxy radicals and HO(2) which can lead to the formation of peroxides. Under conditions with HO(2)/ISORO(2) ratios close to 0.1, yields of MVK (15.5% ± 1.4%) and MAC (13.0% ± 1.2%) were higher than the yields of MVK (8.9% ± 0.9%) and MAC (10.9% ± 1.1%) measured under conditions with HO(2)/ISORO(2) ratios close to 1. This radical dependence of the yields was reproduced reasonably well by an explicit model of isoprene oxidation, suggesting that the model is able to reproduce the observed products yields under a realistic range of atmospheric HO(2)/ISORO(2) ratios.     

Laboratory studies on the fate of perfluoroalkyl carboxylates and sulfonates during snowmelt

Perfluoroalkyl acids (PFAAs) are anthropogenic chemicals that occur in snow from both remote and source regions. Experiments were conducted to determine how PFAAs are released from a melting snowpack. Different PFAAs eluted from the snowpack at different times, those with short chains eluting early, those with long chains eluting late. The concentrations in the meltwater of PFAAs with medium chain lengths of 6 to 9 perfluorinated carbon atoms first increased and then decreased during the melt period. Such a peak elution had not been previously observed for any other chemicals. The specific snow surface area (SSA) influenced this elution type, with peak concentrations occurring earlier in a snowpack with lower SSA. Model simulations suggested that the snow surface decrease during the melt alone was insufficient to explain the observations. It was ruled out that the calcium concentration affected PFAA sorption to the snow surface in a similar way as sorption to sediments. Adsorption coefficients of PFAAs to the snow surface were estimated by fitting the measured and modeled elution profiles.     

Toxicity of dichlorvos vapour to insects in aerated and non-aerated wheat and comparison of the vapour action of dichlorvos and malathion

Bioassay tests demonstrated the potent vapour toxicity of dichlorvos to Sitophilus oryzae and Rhyzopertha dominica. On freshly treated wheat at 20°C the lethal effect of dichlorvos was predominantly due to a mobile form of dichlorvos. This contrasts with the action of malathion. Dichlorvos vapour at toxic concentrations was moved through grain for up to 4 m using air flows comparable to those used in aeration of bulk stored wheat. There was a marked increase in efficiency of dichlorvos under forced air-flow conditions. Effect of air flow on movement of dichlorvos through wheat is discussed quantitatively.     

Free radical initiation in proteins and amino acids by ionizing and ultraviolet radiations and lipid oxidation — part II: Ultraviolet radiation and photolysis

Parallels and similarities in chemical and functional damage to proteins by ionizing and UV radiations and oxidizing lipids have been recognized for some time. However, only recently have oxidizing lipids been shown directly by electron spin resonance to be radiomimetic also in their capacity for protein free radical production. Free radicals play a key role in the transformation of energy to molecular and cellular damage. It is thus of critical importance to elucidate the general mechanisms of free radical formation and reactions in proteins in order to understand protein involvement in various pathological conditions and in food deterioration. Accordingly, this review is a detailed comparison of γ radiation, UV radiation, and lipid oxidation for what is presently known concerning (1) the specific modes of energy deposition and free radical formation, (2) the free radicals formed in proteins and amino acids, and (3) the typical damage correlating with these radicals.     

Degradation of endocrine disrupting chemicals bisphenol A, ethinyl estradiol, and estradiol during UV photolysis and advanced oxidation processes

The degradation of three endocrine disrupting chemicals (EDCs), bisphenol A, ethinyl estradiol, and estradiol, was investigated via ultraviolet (UV) radiation photolysis and the UV/hydrogen peroxide advanced oxidation process (AOP). These EDCs have been detected at low levels in wastewaters and surface waters in both the United States and European countries, can cause adverse effects on humans and wildlife via interactions with the endocrine system, and thus must be treated before entering the public drinking water supply. Because many EDCs can only be partially removed with conventional water treatment systems, there is a need to evaluate alternative treatment processes. For each EDC tested, direct UV photolysis quantum yields were derived for use with both monochromatic low-pressure (LP) UV lamps and polychromatic medium-pressure (MP) UV lamps and second-order hydroxyl radical rate constants were developed. These parameters were utilized to successfully model UV treatment of the EDCs in laboratory and natural waters. The polychromatic MP UV radiation source was more effective for direct photolysis degradation as compared to conventional LP UV lamps emitting monochromatic UV 254 nm radiation. However, in all cases the EDCs were more effectively degraded utilizing UV/H2O2 advanced oxidation as compared to direct UV photolysis treatment.     

UV photolysis of trichloroethylene: product study and kinetic modeling

Direct UV photolysis of trichloroethylene (TCE) in dilute aqueous solution generated chloride ions as a major end product and several reaction intermediates, such as formic acid, di- and monochloroacetic acids, glyoxylic acid, and, to a lesser extent, mono- and dichloroacetylene, formaldehyde, dichloroacetaldehyde, and oxalic acid. Under prolonged irradiation, these byproducts underwent photolysis, and a high degree of mineralization (approximately 95%) was achieved. TCE decays through the following major pathways: (1) TCE + h nu --> ClCH=C*Cl + Cl*; (2) TCE (H2O) + h nu --> ClCH(OH)-CHCl2; (3) TCE + h nu --> HC[triple bond]CCl + Cl2; (4) TCE + h nu --> ClC[triple bond]CCl + HCl; (5) TCE + Cl* --> Cl2HC-C*Cl2. A kinetic model was developed to simulate the destruction of TCE and the formation and fate of byproducts in aqueous solution under irradiation with polychromatic light. By fitting the experimental data, the quantum yields for the four photolysis steps were predicted as phi(1) = 0.13, phi(2) = 0.1, phi(3) = 0.032, and phi(4) = 0.092, respectively. The reaction mechanism proposed for the photodegradation of TCE accounts for all intermediates that were detected. The agreement between the computed and experimental patterns of TCE and reaction products is satisfactory given the complexity of the reaction mechanism and the lack of photolytic kinetic parameters that are provided in the literature.     

Research Watch: Munitions sorption and fate

Remediation.     

Simultaneous determination of dichlorvos and trichlorfon in agricultural products by GC-FPD

We studied a gas chromatographic method for the determination of dichlorvos (DDVP) and trichlorfon (DEP) in agricultural products. DDVP and DEP were extracted from agricultural products with acetone and re-extracted with ethyl acetate instead of dichloromethane. DDVP and DEP were eluted in one fraction on a silica gel column using n-hexane-acetone (1:1). DEP is a thermally labile compound, so it was derived to a more thermally stable compound by acylation with N-methylbis(trifluoroacetamide) and pyridine in acetone at 60 degrees C for 2 hours. DDVP and the DEP-TFA derivative were determined simultaneously by GC-FPD. The recoveries of DDVP and DEP from agricultural products spiked at levels of 0.1 microgram/g were 72.6-117.7% and 86.2-106.6%, respectively. The detection limits were 0.03 microgram/g in powdered tea and < or = 0.01 microgram/g in other samples. An interlaboratory study by 6 laboratories was conducted to validate this proposed method for 6 crops. Repeatability ranged from 3.1 to 7.8% for DDVP and from 3.4 to 8.3% for DEP, and reproducibility, from 6.9 to 15.5% for DDVP, and from 7.9 to 21.8% for DEP. Precision values were well within statistically predicted levels.     

Monitoring oxidation of chlorinated ethenes by permanganate in groundwater using stable isotopes: laboratory and field studies

Permanganate injection is increasingly applied for in situ destruction of chlorinated ethenes in groundwater. This laboratory and field study demonstrates the roles that carbon isotope analysis can play in the assessment of oxidation of trichloroethene (TCE) by permanganate. In laboratory experiments a strong carbon isotope fractionation was observed during oxidation of TCE with similar isotopic enrichment factors (-25.1 to -26.8 per thousand) for initial KMnO4 concentrations between 67 and 1,250 mg/L. At the field site, a single permanganate injection episode was conducted in a sandy aquifer contaminated with TCE as dense nonaqueous liquid (DNAPL). After injection, enriched delta13C values of up to +204% and elevated Cl- concentrations were observed at distances of up to 4 m from the injection point. Farther away, the Cl- increased without any change in delta13C of TCE suggesting that Cl- was not produced locally but migrated to the sampling point Except for the closest sampling location to the injection point, the delta13C rebounded to the initial 613C again, likely due to dissolution of DNAPL Isotope mass balance calculations made it possible to identify zones where TCE oxidation continued to occur during the rebound phase. The study indicates that delta13C values can be used to assess the dynamics between TCE oxidation and dissolution and to locate zones of oxidation of chlorinated ethenes that cannot be identified from the Cl- distribution alone.     

Electrochemical and XAFS studies of effects of carbonate on the oxidation of arsenite

Measurements of electrochemical (EC) arsenite oxidation demonstrated thatthe arsenite oxidation current increased in the presence of carbonate while the potential of the onset of EC arsenite oxidation exhibited a strong shift toward less positive values. Examination of pH and total carbonate concentration effects on the EC arsenite oxidation parameters showed that they were affected solely by the concentration of carbonate ion CO3(2-), which appeared to form relatively weak mono- and dicarbonate complexes with arsenite. The EC activity of these complexes was determined to be almost an order of magnitude higher than that of free arsenite. However, X-ray absorption fine-structure (XAFS) measurements did not show any changes in the properties of the As(III) inner complexation shell associated with the presence of the bound carbonate ions. It was accordingly concluded that the strength of bonds between the bound carbonate and As(III) is close to that for As(III)-OH- interactions. The acceleration of the oxidation of carbonate-As(III) complexes was hypothesized to be associated with an additional pathway of the formation of As(IV) intermediates, in which the carbonate group present in the As(III) inner shell provides an electron to form a bound carbonate radical and also a good leaving group for facile cleavage from the transient As(IV) species.     

气相色谱-质谱联用法测定玉米汁中敌敌畏和 马拉硫磷的含量

目的建立高灵敏度、精确度的敌敌畏和马拉硫磷的检测方法。方法利用DB-17MS(30 m×0.25 mm,0.25μm)色谱柱及气质联用色谱建立敌敌畏和马拉硫磷的检测条件,确定检出物的保留时间,绘制基于含量-峰面积线性关系的标准曲线。测定长春市市售玉米汁中的敌敌畏、马拉硫磷的含量,并根据标准曲线对结果进行分析计算。结果敌敌畏、马拉硫磷的标准曲线分别为:Y=0.0096X2+44.561X-100.48,Y=0.0023X2+36.339X+341.95,相关系数均为0.9999。长春市售玉米汁中未检出敌敌畏、马拉硫磷。结论本方法准确、可靠,可为玉米汁中有毒有害物质的检验提供参考。