Degradation of azoxystrobin, methoxyfenozide, and propyzamide by ultrasound treatment.

Ultrasound as a green and efficient process gains special attention in wastewater treatment. The ultrasound-assisted degradation of azoxystrobin, methoxyfenozide, and propyzamide as widely used pesticides for vine treatment was investigated. A wide range of ultrasonic power (40 to 140 W) and a single frequency (20 kHz) were applied. Degradation experiments were carried out according to the parameters set by a central composite design (CCD) under response surface methodology (RSM) via JMP software. The treatment efficiency was quantified using degradation rates and hydrogen peroxide (H2O2) measurements. Results indicated that the pesticide's degradation was negligible at 40 W but by increasing the power setting from 80 to 140 W, the degradation rate constants of azoxystrobin, methoxyfenozide, and propyzamide increased from 3.6 × 10-2 min-1 to 0.2 min-1, from 6.1 × 10-2 min-1 to 0.3 min-1, and from 3.1 × 10-2 min-1 to 0.1 min-1, respectively. The hydrogen peroxide (H2O2) measurements confirmed this trend. Besides, electric energy per order of pollutant removal (EE/O) was also evaluated for the same treatment duration and results revealed that treatment conditions of 20 kHz and 140 W were the less energy-guzzling. Finally, profiles obtained with RSM illustrated linear degradation kinetics for azoxystrobin and propyzamide. Indeed, treatment efficiency increased when increasing both studied parameters. However, both linear and quadratic degradation kinetics occurred for methoxyfenozide degradation indicating a parameter threshold beyond which the trend is reversed. Overall, this study confirms the effectiveness of ultrasound for the degradation of pesticides in aqueous medium.

Aqueous chlorination of sulfamethazine and sulfamethoxypyridazine: Kinetics and transformation products identification.

Sulfonamides (SNs) are synthetic antimicrobial agents. These substances are continually introduced into the environment, and they may spread and maintain bacterial resistance in the different compartments. The chlorination of 2 SNs, namely, sulfamethazine (SMT) and sulfamethoxypyridazine (SMP), was investigated to study their reactivity with chlorine at typical concentrations for water treatment conditions. Experiments conducted in purified water show an acceleration of SMT and SMP degradation of a factor 1.5 by comparison to drinking water matrix. This difference is due to pH variation and competitive reactions between SNs and mineral and organic compounds, with chlorine in drinking water. In the presence of an excess of chlorine (6.7 µmol·L-1 ) in ultrapure water at pH 7.2, second-order degradation rate constants were equal to 4.5 × 102 M-1 ·s-1 and 5.2 × 102 M-1 ·s-1 for SMT and SMP, respectively. The structures of transformation products were investigated by liquid chromatography tandem mass spectrometry analyses with equimolar concentrations between chlorine and SNs. SO2 elimination, cyclization, and electrophilic substitutions were the main pathways of by-products formation. Moreover, the toxicity of the proposed structures was predicted by using toxicity estimation software tool program. The results indicated that most by-products may present developmental toxicity.

Photodegradation of novel oral anticoagulants under sunlight irradiation in aqueous matrices.

Kinetics of photodegradation of novel oral anticoagulants dabigatran, rivaroxaban, and apixaban were studied under simulated solar light irradiation in purified, mineral, and river waters. Dabigatran and rivaroxaban underwent direct photolysis with polychromatic quantum yields of 2.2 × 10-4 and 4.4 × 10-2, respectively. The direct photodegradation of apixaban was not observed after 19 h of irradiation. Kinetics of degradation of rivaroxaban was not impacted by the nature of the aqueous matrix while photosensitization from nitrate ions was observed for dabigatran and apixaban dissolved in a mineral water. The photosensitized reactions were limited in the tested river water (Isle River, Périgueux, France) certainly due to the hydroxyl radical scavenging effect of the dissolved organic matter. The study of photoproduct structures allowed to identify two compounds for dabigatran. One of them is the 4-aminobenzamidine while the second one is a cyclization product. In the case of rivaroxaban, as studied by very high field NMR, only one photoproduct was observed i.e. a photoisomer. Finally, seven photoproducts were clearly identified from the degradation of apixaban under simulated solar light.

Study of the degradation process of ofloxacin with free chlorine by using ESI-LCMSMS: Kinetic study, by-products formation pathways and fragmentation mechanisms.

This study was conducted to gain a better understanding of the fate of fluoroquinolone antibacterial ofloxacin (OFX) which is the free available chlorine (FAC) in order to determine its effect during water chlorination process. The Direct reactions of FAC with OFX were quite rapid. A half-life of 7.7 s was measured under pseudo-first order conditions in the presence of an excess of total chlorine ([FAC]0 = 13 µM and [OFX]0 = 0.55 µM at pH 7.2 and 20 °C in buffered reagent water. Free chlorine reactions rates were of first-order type in both substrate and oxidant with specific second-order rate constants of 6.8 × 103 M-1 s-1. No induced back reactions or other interference by using thiosulfate to stop the chlorination reaction was shown. The seven products of the reaction were determined by using the LC/MS/MS analysis. Structures were investigated due to the explication of transitions obtained at different CID energies by LC-ESI-MS/MS. Pathways of the formations of these by-products were presented in this study and pathways of the fragmentations of pseudo molecular ions of the structures proposed were presented in supplementary files.

Oxidation of danofloxacin by free chlorine-kinetic study, structural identification of by-products by LC-MS/MS and potential toxicity of by-products using in silico test.

In this study, we aimed to investigate the kinetics and the mechanism of reaction of the fluoroquinolone antibacterial danofloxacin (DANO) by free available chlorine (FAC) during water chlorination process. Kinetic study was thus performed at pH 7.2, 20 °C in the presence of an excess of total chlorine. Under these experimental conditions, a second-order reaction rate constant (first-order relative to DANO concentration and first-order relative to FAC concentration) was evaluated to k~1446 M-1 s-1. Five degradation products were identified at different reaction times. Their structures were investigated by using fragmentations obtained at different CID collision energies in MS/MS experiments. Moreover, the toxicity of the proposed structures was predicted by using T.E.S.T. PROGRAM: The results indicated that all by-products may have a developmental toxicity. The oral rat LD50 concentration was predicted to be lower than that of DANO. Furthermore, two degradation compounds presented a concentration level for fathead minnow LC50 (96 h) lower than that of DANO and presented toxicity for the marine animals.

Photolysis of natural ß-triketonic herbicides in water.

The fate of four natural ß-triketones (leptospermone, isoleptospermone, grandiflorone and flavesone, pKa = 4.0-4.5) in aqueous solution, in the dark and upon simulated solar light irradiation was investigated. In anionic form, ß-triketones undergo slow dark oxidation and photolysis with polychromatic quantum yields varying from 1.2 × 10(-4) to 3.7 × 10(-4). Leptospermone and grandiflorone are the most photolabile compounds. In molecular form, ß-triketones are rather volatile. Polychromatic quantum yields between 1.2 × 10(-3) and 1.8 × 10(-3) could be measured for leptospermone and grandiflorone. They are 3-5 times higher than for the anionic forms. Photooxidation on the carbon atom bearing the acidic hydrogen atom is the main oxidation reaction, common to all the ß-triketones whatever their ionization state. However, leptospermone shows a special photoreactivity. In molecular form, it mainly undergoes photoisomerization. Based on this work, the half-lives of ß-triketones in surface waters should be comprised between 7 and 23 days.

Partitioning of the pesticide trifluralin between dissolved organic matter and water using automated SPME-GC/MS.

Solid-phase microextraction (SPME) was used to determine the equilibrium association constant for a pesticide, trifluralin (TFR), with dissolved organic matter (DOM). After optimization of the SPME method for the analysis of TFR, partition coefficients (K DOM) with three different sources of DOM were determined in buffered solutions at pH 7. Commercial humic acids and DOM fractions isolated from two surface waters were used. The values of log K DOM varied from 4.3 to 5.8, depending on the nature of the organic material. A good correlation was established between log K DOM and DOM properties (as measured with the H/O atomic ratio and UV absorbance), in agreement with literature data. This is consistent with the effect of polarity and aromaticity for governing DOM-pollutant associations, regardless of the origin of DOM. This association phenomenon is relevant to better understand the behavior of pesticides in the environment since it controls part of pesticide leaching and fate in aquatic systems.

Polar organic chemical integrative samplers for pesticides monitoring: impacts of field exposure conditions.

This study focuses on how Polar Organic Chemical Integrative Samplers (POCIS) work in real environmental conditions. A selection of 23 polar pesticides and 8 metabolites were investigated by exposure of triplicates of integrative samplers in two rivers in France for successive 14-day periods. The pesticides and metabolites were trapped not only in Oasis HLB sorbent but also in the polyethersulfone (PES) membrane of the POCIS. The distribution of pesticides depended on the molecular structure. The use of the Performance Reference Compound (PRC) is also discussed here. The impact of some environmental parameters and exposure setup on the transfer of pesticides in POCIS sorbent was studied: river flow rate, biofouling on membranes, sampler holding design and position in the stream. Results show a significant impact of river flow velocity on PRC desorption, especially for values higher than 4 cm·s(-1). Some fouling was observed on the PES membrane which could potentially have an impact on molecule accumulation in the POCIS. Finally, the positioning of the sampler in the river did not have significant effects on pesticide accumulation, when perpendicular exposures were used (sampler positioning in front of the water flow). The POCIS with PRC correction seems to be a suitable tool for estimating time-weighted average (TWA) concentrations, for all the molecules except for one of the nine pesticides analyzed in these two French rivers.

Quantitative on-line preconcentration-liquid chromatography coupled with tandem mass spectrometry method for the determination of pharmaceutical compounds in water.

One of the current environmental issues concerns the presence and fate of pharmaceuticals in water bodies as these compounds may represent a potential environmental problem. The characterization of pharmaceutical contamination requires powerful analytical method able to quantify these pollutants at very low concentration (few ng L(-1)). In this work, a multi-residue analytical methodology (on-line solid phase extraction-liquid chromatography-triple quadrupole mass spectrometry using positive and negative electrospray ionization) has been developed and validated for 40 multi-class pharmaceuticals and metabolites for tap and surface waters. This on-line SPE method was very convenient and efficient compared to classical off-line SPE method because of its shorter total run time including sample preparation and smaller sample volume (1 mL vs up to 1 L). The optimized method included several therapeutic classes as lipid regulators, antibiotics, beta-blockers, non-steroidal anti-inflammatories, antineoplastic, etc., with various physicochemical properties. Quantification has been achieved with the internal standards. The limits of detection are between 0.7 and 15 ng L(-1) for drinking waters and 2-15 ng L(-1) for surface waters. The inter-day precision values are below 20% for each studied level. The improvement and strength of the analytical method has been verified along a monitoring of these 40 pharmaceuticals in Isle River, a French stream located in the South West of France. During this survey, 16 pharmaceutical compounds have been detected.

Degradation of naproxen by UV, VUV photolysis and their combination.

Naproxen is a widely used nonsteroidal anti-inflammatory drug. Recently, this medicine was detected both in natural waters (up to 1.5 µg L(-1)) and in sewage treatment plant effluents (up to 5.2 µg L(-1)). Moreover, naproxen is only partly eliminated by classical processes used in sewage treatment plants. Therefore, its degradation is of utmost interest. Advanced oxidation processes proved to be the most suitable methods for the elimination of persistent organic contaminants. In this work ultraviolet (UV, 254 nm), vacuum ultraviolet photolysis (VUV, 172 nm) and their combination (UV/VUV, 254/185 nm) were investigated. The efficiency of the methods increased in the following order: UV < VUV < UV/VUV photolysis. However, VUV irradiation was found to mineralize the contaminant molecule most effectively. The chemical structures of three out of four aromatic by-products and of some aliphatic carboxylic acids were presumed. The effects of dissolved O2 and the initial concentration of naproxen on the degradation were also investigated.

Photodegradation of estrone enhanced by dissolved organic matter under simulated sunlight.

In the present work the degradation of estrone (E1) a natural estrogenic hormone has been studied under simulated solar irradiation. The photodegradation of E1 has been investigated in the absence and in the presence of 7.7-8.9 mg L(-1) of dissolved organic carbon (DOC), under solar light simulation with irradiance approximating that of the sun. DOC extracts from different origins have been used. Half-lives ranging between 3.9 h and 7.9 h were observed. Results indicated that E1 was photodegraded even in the absence of DOC. The presence of DOC was found to enhance the degradation of E1. Experiments performed with the addition of reactive species scavengers (azide ions and 2-propanol) have shown that these two species play a significant role in the photodegradation. Some experiments have been performed with a DOC previously submitted to solar irradiation. Changes in optical and physico-chemical properties of DOC strongly affect its photoinductive properties, and hence its efficiency on E1 degradation. A part of the study consisted in the investigation of photoproducts structures. Five photoproducts were shown by chromatographic analysis: one arising from direct photolysis and the four others from DOC photoinduced degradation.

Liquid chromatography coupled with tandem mass spectrometry method for thirty-three pesticides in natural water and comparison of performance between classical solid phase extraction and passive sampling approaches.

The aim of this study is to propose an analytical method for determining different classes of pesticides in water using LC-ESI-MS/MS. Two techniques of field-sampling and analyte extraction were used: solid phase extraction (SPE) of water samples from active sampling and field exposure of Polar Organic Chemical Integrative Samplers (POCIS). We have worked with thirty-three molecules representing eight pesticide classes: carbamates, chloroacetanilides, dicarboximides, morpholines, organophosphorous, phenylureas, strobilurines and triazines. First, liquid chromatography separation protocols and the optimization of the ESI-MS/MS parameters were developed. Then, the SPE step was optimized to obtain acceptable levels of recovery for the various classes of molecules. The matrix effect that may significantly lower the ionization efficiency with ESI interfaces was evaluated and minimized. The performances (limits of quantification, accuracy and precision) of the SPE and POCIS techniques were evaluated, and a comparison between the active and passive sampling techniques was carried out with a field application.

Evaluation of the use of performance reference compounds in an Oasis-HLB adsorbent based passive sampler for improving water concentration estimates of polar herbicides in freshwater.

Passive samplers such as the Polar Organic Chemical Integrative Sampler (POCIS) are useful tools for monitoring trace levels of polar organic chemicals in aquatic environments. The use of performance reference compounds (PRC) spiked into the POCIS adsorbent for in situ calibration may improve the semiquantitative nature of water concentration estimates based on this type of sampler. In this work, deuterium labeled atrazine-desisopropyl (DIA-d5) was chosen as PRC because of its relatively high fugacity from Oasis HLB (the POCIS adsorbent used) and our earlier evidence of its isotropic exchange. In situ calibration of POCIS spiked with DIA-d5 was performed, and the resulting time-weighted average concentration estimates were compared with similar values from an automatic sampler equipped with Oasis HLB cartridges. Before PRC correction, water concentration estimates based on POCIS data sampling rates from a laboratory calibration exposure were systematically lower than the reference concentrations obtained with the automatic sampler. Use of the DIA-d5 PRC data to correct POCIS sampling rates narrowed differences between corresponding values derived from the two methods. Application of PRCs for in situ calibration seems promising for improving POCIS-derived concentration estimates of polar pesticides. However, careful attention must be paid to the minimization of matrix effects when the quantification is performed by HPLC-ESI-MS/MS.

Photodegradation of the steroid hormones 17beta-estradiol (E2) and 17alpha-ethinylestradiol (EE2) in dilute aqueous solution.

The photochemical transformation of natural estrogenic steroid 17beta-estradiol (E2) and the synthetic oral contraceptive 17alpha-ethinylestradiol (EE2) has been studied in dilute non buffered aqueous solution (pH 5.5-6.0) upon monochromatic (254 nm) and polychromatic (lambda>290 nm) irradiation. Upon irradiation at 254 nm, the quantum yields of E2 and EE2 photolysis were similar and evaluated to be 0.067+/-0.007 and 0.062+/-0.007, respectively. Upon polychromatic excitation, and by using phenol as chemical actinometer, the photolysis efficiencies have been determined to be 0.07+/-0.01 and 0.08+/-0.01 for E2 and EE2, respectively. For both estrogens, photodegradation by-products were identified with GC/MS and LC/MS. In a first step, a model compound--5,6,7,8-tetrahydro-2-naphthol (THN)--, which represents the photoactive phenolic group, was used to obtain basic photoproduct structural informations. Numerous primary and secondary products were observed, corresponding to hydroxylated phenolic- or quinone-type compounds.

Oxidation of bisphenol A by ozone in aqueous solution.

Based on the literature data, an efficient removal of bisphenol A (BPA) during ozonation can be expected under water treatment conditions. However, up to now, the degradation products have not been identified. This has been the main point of this study. Aqueous solutions of BPA have been analyzed by LC-UV, LC-MS or MS/MS at different ozone doses. Under our experimental conditions, up to five major transformation products were evidenced. According to UV, MS and MS/MS spectra characteristics, chemical structures are consistent with catechol, orthoquinone, muconic acid derivatives of BPA, benzoquinone and 2-(4-hydroxyphenyl)-propan-2-ol. Moreover, three additional minor transformation products have been observed for which chemical structures have been tentatively proposed. In the case of major transformation products, the reaction pathway may involve an initial ozone reaction by electrophilic substitution or 1,3-dipolar cycloaddition. In the presence of ozone, these primary transformation products were shown to be unstable. Further transformation products, with smaller molecular weight and more polar character such as aliphatic acids or aldehydes, are then expected during ozonation. The identification of minor transformation products was more complex to assess. However, oligomeric structures have been evidenced, certainly arising from secondary reaction between various oxidation products of BPA. The formation of these latter products would not be favored under water treatment conditions.

A comparison of fenuron degradation by hydroxyl and carbonate radicals in aqueous solution.

A comparative study of the transformation of the herbicide fenuron (1,1-dimethyl-3-phenylurea) by hydroxyl radicals and carbonate radicals in aqueous solution (pH 7.2-phosphate buffer) has been undertaken. Hydroxyl radical was generated by the well-known photolysis of hydrogen peroxide at 254 nm and carbonate radical was formed by photolysis of Co(NH(3))(5)CO(3)(+) at 254 nm. Competitive kinetic experiments were performed with atrazine used as the main competitor for both processes. Accordingly, the second-order rate constant of reaction between fenuron and carbonate radical was found to be (7-12+/-3)x10(6)M(-1)s(-1) [(7+/-1)x10(9)M(-1)s(-1) for hydroxyl radical]. The formation of degradation products was studied by LC-MS in the two cases and a comparison has been performed. The reaction with carbonate radical leads to the formation of a quinone-imine derivative which appears as the major primary product together with ortho and para hydroxylated compounds. These two compounds represent the major products in the reaction with hydroxyl radicals. The reaction of both radicals also leads to the transformation of the dimethylurea moiety.

Kinetic and mechanistic investigations of progesterone reaction with ozone.

The removal of progesterone by ozone in aqueous solution was studied in this work. The absolute rate constant was evaluated and first by-products were identified. The reaction was studied in the 2.0-8.0 pH range and was found to be a second-order reaction, first-order relative to each compound concentration. The rate constant, determined by kinetic experiments in presence of an OH radical scavenger (tert-butanol), was independent of pH. The value was evaluated to be equal to 480+/-30 M(-1)s(-1) by two kinetic methods. Mass spectrometry analyses were performed to investigate primary degradation products generated by the reaction of ozone with progesterone. Two by-products were evidenced. According to these results, a degradation pathway of progesterone reacting with ozone was proposed.

Phototransformation of selected organophosphorus pesticides in dilute aqueous solutions.

The photochemical transformation of four selected organophosphorus pesticides (OPs) has been studied in water. Because of their extensive use, disulfoton, isofenfos, isazofos and profenofos were chosen for this study. A solid phase extraction method has been developed to allow low-concentration experiments. Photolysis experiments have been performed both in purified water and in Capot river water (natural water from Martinique) using either monochromatic light at 253.7 nm (purified water) or polychromatic light greater than 285 nm (purified and Capot river waters). Kinetic investigations coupled with analytical studies (identification of degradation products) were performed for the four pesticides. Upon monochromatic irradiation, quantum yields of OP photolysis have been evaluated and in polychromatic irradiation experiments, apparent first-order kinetic constants have been determined. The reactivity is similar in purified and natural water, but differences are observed for each pesticide according to the role that natural organic matter (NOM) plays: filter effect of the light or photosensitizer. For each organophosphorus pesticide, experiments have been performed to identify the photodegradation products. Some photoproduct structures will be proposed according to mass spectral informations.

Transformation of 4-tert-octylphenol by UV irradiation and by an H2O2/UV process in aqueous solution.

The transformation of the organic pollutant 4-(1,1,3,3-tetramethylbutyl)phenol (4-tert-octylphenol; OP) upon irradiation at 253.7 nm and by hydroxyl radicals generated by the photolysis (lambda(exc) = 253.7 nm) of hydrogen peroxide in aqueous solution has been studied. The quantum yield of direct OP photolysis in pure aqueous solution was evaluated to be 0.058 +/- 0.004 in aerated conditions ([O2] = 272 microM). The rate of photoreaction depends on oxygen concentration; it increases with increasing [O2]. 4-tert-Octylcatechol has been identified as one of the degradation products, together with a dimeric structure. The probable mechanism of OP photolysis involves photoejection of an electron from the singlet state, leading to the formation of the 4-tert-octylphenoxyl radical. In the presence of hydrogen peroxide, the degradation of octylphenol by hydroxyl radicals has been observed. The second-order rate constant was found to be (6.4 +/- 0.5) x 10(9) M(-1) s(-1) by direct measurement at various high concentrations of hydrogen peroxide and competitive kinetic measurements using atrazine as the competitor. The degradation products are 4-tert-octylcatechol, again, and 2-hydroxy-5-tert-octylbenzoquinone. The later product may arise from the oxidation of 4-tert-octylcatechol by hydrogen peroxide or from a subsequent reaction of hydroxyl radicals with 4-tert-octylcatechol. Kinetic modelling when using either purified water or natural water successfully simulated the elimination of 4-tert-octylphenol by UV and H2O2/UV processes.