- Wet peroxide degradation of atrazine
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The high temperature (150-200 °C), high pressure (3.0-6.0 MPa) degradation of atrazine in aqueous solution has been studied. Under these extreme conditions atrazine steadily hydrolyses in the absence of oxidising agents. Additionally, oxygen partial pressure has been shown not to affect atrazine degradation rates. In no case mineralisation of the parent compound was observed. The addition of the free radical generator hydrogen peroxide to the reaction media significantly enhanced the depletion rate of atrazine. Moreover, partial mineralisation of the organics was observed when hydrogen peroxide was used. Again, oxygen presence did not influence the efficiency of the promoted reaction. Consecutive injections of hydrogen peroxide throughout the reaction period brought the total carbon content conversion to a maximum of 65-70% after 40 min of treatment (suggesting the total conversion of atrazine to cyanuric acid). Toxicity of the effluent measured in a luminometer decreased from 93% up to 23% of inhibition percentage. The process has been simulated by means of a semi-empirical model.
- Rodriguez, Eva M.,Alvarez, Pedro M.,Rivas, F. Javier,Beltran, Fernando J.
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- Photosensitized degradation of terbuthylazine in water
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We investigated the photodegradation of terbuthylazine, an s-triazine herbicide, in the presence of hydrogen peroxide (H2O2), titanium dioxide (TiO2), acetone or humic substances. In the presence of H2O2 and UV light, the degradation of terbuthylazine quickly leads to the formation of ammeline. The degradation pathway consists of dealkylation reactions giving 2-chloro-4,6-diamino-1,3,5-triazine, and then ammeline through hydroxylation. Irradiation of terbuthylazine with simulated solar light in the presence of titanium dioxide gives also dealkylation products in the first stage of degradation. Acetone at 1% (v/v) produces a 7-fold enhancement of the degradation rate. In the presence of humic substances, different results were obtained, depending on the origin of the substances tested. The humic acids isolated from a soil accelerate the degradation speed, whereas the fulvic acids from a small stream reduce it.
- Sanlaville,Guittonneau,Mansour,Feicht,Meallier,Kettrup
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- Study of the mechanisms of the photodegradation of atrazine in the presence of two photocatalysts: TiO2 and Na4W10O32
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The mechanisms of the photodegradation of atrazine under direct photolysis and in the presence of two different photocatalysts, TiO2 and Na4W10O32, are investigated by the means of GC/MS, total radioactivity counting, HPLC and TLC analysis on 14C ring-labelled atrazine solutions. Integration of photo- and biodegradation processes is studied.
- Texier, Isabelle,Ouazzani, Jamal,Delaire, Jacques,Giannotti, Charles
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- Metalloporphyrins as biomimetic models for cytochrome P-450 in the oxidation of atrazine
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The aim of this work was to evaluate whether metalloporphyrin models could mimic the action of cytochrome P-450 in the oxidation of atrazine, a herbicide. The commercially available second-generation metalloporphyrins 5,10,15,20-tetrakis(2,6-dichlorophenyl)porphyrin metal(III) chloride [M(T-DCPP)Cl] and 5,10,15,20-tetrakis(pentafluorophenyl)porphyrin metal(III) chloride [M(TFPP)Cl] (metal = Fe or Mn) and the oxidants iodosylbenzene and metachloroperbenzoic acid were employed in this study. Results showed that the metalloporphyrins used here can oxidize atrazine. Yields as high as 32% were obtained for the Mn(TFPP)Cl/PhIO system, which shows that these catalysts can mimic both the in vivo and the in vitro action of cytochrome P-450, with formation of the metabolites DEA and DIA. The formation of five other unknown products was also detected, but only one of them could be identified, since the other four were present in very low concentrations. The compound COA, identified by mass spectrometry, was the main product in most of the oxidation reactions.
- Gotardo, Maria C. A. F.,De Moraes, Luiz A. B.,Assis, Marilda D.
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- Integrated photocatalytic-biological treatment of triazine-containing pollutants
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The degradation of triazine-containing pollutants including simazine, Irgarol 1051 and Reactive Brilliant Red K-2G (K-2G) by photocatalytic treatment was investigated. The effects of titanium dioxide (TiO2) concentration, initial pH of reaction mixture, irradiation time and ultraviolet (UV) intensity on photocatalytic treatment efficiency were examined. Complete decolorization of K-2G was observed at 60 min photodegradation while only 15 min were required to completely degrade simazine and Irgarol 1051 under respective optimized conditions. High-performance liquid chromatography (HPLC), gas chromatography/mass spectrometry (GC/MS) and ion chromatography (IC) were employed to identify the photocatalytic degradation intermediates and products. Dealkylated intermediates of simazine, deisopropylatrazine and deethyldeisopropylatrazine, and Irgarol 1051 were detected by GC/MS in the initial phase of degradation. Complete mineralization could not be achieved for all triazine-containing pollutants even after prolonged (>72 h) UV irradiation due to the presence of a photocatalysis-resistant end product, cyanuric acid (CA). The toxicities of different compounds before and after photocatalytic treatment were also monitored by three bioassays. To further treat the photocatalysis-resistant end product, a CA-degrading bacterium was isolated from polluted marine sediment and further identified as Klebsiella pneumoniae by comparing the substrate utilization pattern (Biolog microplate), fatty acid composition and 16S rRNA gene sequencing. K. pneumoniae efficiently utilized CA from 1 to 2000 mg/L as a good nitrogen source and complete mineralization of CA was observed within 24 h of incubation. This study demonstrates that the biodegradability of triazine-containing pollutants was significantly improved by the photocatalytic pre-treatment, and this proposed photocatalytic-biological integrated system can effectively treat various classes of triazine-containing pollutants.
- Chan, Cho Yin,Chan, Ho Shing,Wong, Po Keung
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- Efficient removal of atrazine in water with a Fe3O4/MWCNTs nanocomposite as a heterogeneous Fenton-like catalyst
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Fe3O4 and multi-walled carbon nanotube hybrid materials (Fe3O4/MWCNTs) were synthesized by a coprecipitation combined hydrothermal method. The nanocomposites were applied for adsorption and degradation of atrazine (ATZ) in the presence of H2O2. The obtained catalysts were characterized by TEM, XRD, BET, XPS and Raman spectroscopy. The effects of solution pH, catalysts dosage, H2O2 concentration and iron leaching on the degradation of ATZ were investigated. Fe3O4/MWCNTs showed a higher utilization efficiency of H2O2, higher ability of adsorption for ATZ and higher degradation efficiency of ATZ than Fe3O4 nanoparticles in the batch degradation experiment. The degradation efficiency increased with the solution pH decreasing from 8.0 to 3.0. The catalytic results showed that Fe3O4/MWCNTs presented good performance for the degradation of ATZ, achieving 81.4% decomposition of ATZ after 120 min at reaction conditions of H2O2 concentration 3.0 mmol L-1, catalysts dosage 0.1 g L-1, ATZ concentration 10.0 mg L-1, pH 5.0 and T 30 °C. Three degradation products (desethylatrazine, desisopropylatrazine, and 2-hydroxyatrazine) were detected during a heterogeneous Fenton reaction in solution. The stability, and reusability of Fe3O4/MWCNTs for ATZ degradation were also investigated.
- Yu, Lian,Yang, Xiaofang,Ye, Yushi,Wang, Dongsheng
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- Factors affecting formation of deethyl and deisopropyl products from atrazine degradation in UV/H2O2 and UV/PDS
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In this study, the formation of deethyl products (DEPs) (i.e., atrazine amide (Atra-imine) and deethylatrazine (DEA)) and deisopropyl product (i.e., deisopropylatrazine (DIA)) from parent atrazine (ATZ) degraded in UV/H2O2 and UV/PDS processes under various conditions was monitored. It was found that SO4- displayed a more distinctive preference to the ethyl function group of ATZ than HO, leading to the higher ratio of DEPs/DIA in UV/PDS system than that in UV/H2O2 system in pure water. The effects of water matrices (i.e., natural organic matter (NOM), carbonate/bicarbonate (HCO3-/CO32-), and chloride ions (Cl-)) on ATZ degradation as well as formation of DEPs and DIA were evaluated in detail. The degradation of ATZ by UV/PDS was significantly inhibited in the presence of NOM, HCO3-/CO32- or Cl-, because these components could competitively react with SO4- and/or HO to generate lower reactive secondary radicals (i.e., organic radicals, carbonate radicals (CO3-) or reactive chlorine radicals (RCs)). The yields of these DEPs and DIA products from ATZ degradation were not impacted by NOM or HCO3-/CO32-, possibly due to the low reactivity of organic radicals and CO3- toward the side groups of ATZ. Howbeit, the increase of DIA yield companied with the decrease of DEPs yield was interestingly observed in the presence of Cl-, which was attributed to the promotion of Cl- at moderate concentration (mM range) for the conversion of SO4- into HO. Comparatively, in the UV/H2O2 process, NOM and HCO3-/CO32- exhibited a similar inhibitory effect on ATZ degradation, while the influence of Cl- was negligible. Differing from UV/PDS system, all these factors did not change DEPs and DIA yields in UV/H2O2 process. Moreover, it was confirmed that RCs had a greater selectivity but a lower reactivity on attacking the ethyl function group than that of SO4-. These findings were also confirmed by monitoring the degradation of ATZ as well as the formation of DEPs and DIA in three natural waters.
- Luo, Congwei,Jiang, Jin,Guan, Chaoting,Ma, Jun,Pang, Suyan,Song, Yang,Yang, Yi,Zhang, Jianqiao,Wu, Daoji,Guan, Yinghong
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- Manganese dioxide as a catalyst for oxygen-independent atrazine dealkylation
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The herbicide atrazine is widely distributed in the environment, and its reactivity with soil minerals is an important issue. We have studied atrazine degradation on the surface of synthetic hydrous (10% H2O) δ-MnO2 (birnessite) using UV resonance Raman spectroscopy and gas chromatography. The products are mainly mono-and didealkyl atrazine. Atrazine disappearance is rapid (τ(1/2) ~ 5 h at 30 °C), independent of whether O2 is present or not. MnO2 reduction is a minor reaction, and the alkyl chains are converted mainly to the alkenes, in a nonredox process. A novel dealkylation mechanism is proposed involving proton transfer to Mn(IV)-stabilized oxo and imido bonds. When O2 is present, olefin oxidation and ring mineralization are also observed as secondary reactions in addition to those discussed above. Thus δ-MnO2, a common soil constituent, is found to promote efficient N- dealkylation of the herbicide atrazine at 30 °C, via a nonoxidative mechanism. The herbicide atrazine is widely distributed in the environment, and its reactivity with soil minerals is an important issue. We have studied atrazine degradation on the surface of synthetic hydrous (10% H2O) δ-MnO2 (birnessite) using UV resonance Raman spectroscopy and gas chromatography. The products are mainly mono- and didealkyl atrazine. Atrazine disappearance is rapid (τ1/2 approximately 5 h at 30 °C), independent of whether O2 is present or not. MnO2 reduction is a minor reaction, and the alkyl chains are converted mainly to the alkenes, in a nonredox process. A novel dealkylation mechanism is proposed involving proton transfer to Mn(IV)-stabilized oxo and imido bonds. When O2 is present, olefin oxidation and ring mineralization are also observed as secondary reactions in addition to those discussed above. Thus δ-MnO2, a common soil constituent, is found to promote efficient N-dealkylation of the herbicide atrazine at 30 °C, via a nonoxidative mechanism.
- Wang, Daojing,Shin, Jin Y.,Cheney, Marcos A.,Sposito, Garrison,Spiro, Thomas G.
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- The process of atrazine degradation, its mechanism, and the formation of metabolites using UV and UV/MW photolysis
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The photolytic degradationmechanism of atrazine using a UV reactor andUV/MW (electrodeless discharge lamp (Hg-EDL)) was investigated. After 120?s of UV photolysis partial degradation of atrazine had been observed and a subsequent formation of degradation products of atrazine-2-hydroxy, therefore, defining the path of atrazine degradation through UV photolysis. This system after 1200?s of exposure to UV radiation had not reached full degradation of atrazine, and its metabolite (atrazine-2-hydroxy), was the main by-product obtained for the process. When performing photolysis through the UV/Microwave combined methodcomplete atrazine degradation was obtained within a 5?s interval, besides the formation of five (5) degradation products, which are HAT, DEAT, DIAT, DEHAT and DIHAT. Therefore, defining the path of the photolytic degradation process through the UV/Microwave combined method. The total degradation of its metabolite (HAT) was observed for the period of 120?s of exposure to UV/MW radiation, and after that time there had been no signcorresponding to the respective compounds. The tests with the isolated microwave radiation were not efficient in the degradation of the atrazine and, therefore, the respective isolated energy is not applicable.The control of atrazine degradation and consequent formation of metabolites were accompanied by a high-performance liquid chromatography with a UV/Vis detector.
- Moreira, Ailton. J.,Borges, Aline C.,Gouvea, Luis F.C.,MacLeod, Tatiana C.O.,Freschi, Gian P.G.
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- Cytochrome P450-catalyzed dealkylation of atrazine by Rhodococcus sp. strain NI86/21 involves hydrogen atom transfer rather than single electron transfer
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Cytochrome P450 enzymes are responsible for a multitude of natural transformation reactions. For oxidative N-dealkylation, single electron (SET) and hydrogen atom abstraction (HAT) have been debated as underlying mechanisms. Combined evidence from (i) product distribution and (ii) isotope effects indicate that HAT, rather than SET, initiates N-dealkylation of atrazine to desethyl- and desisopropylatrazine by the microorganism Rhodococcus sp. strain NI86/21. (i) Product analysis revealed a non-selective oxidation at both the αC and βC-atom of the alkyl chain, which is expected for a radical reaction, but not SET. (ii) Normal 13C and 15N as well as pronounced 2H isotope effects (εcarbon: -4.0‰ ± 0.2‰; εnitrogen: -1.4‰ ± 0.3‰, KIEH: 3.6 ± 0.8) agree qualitatively with calculated values for HAT, whereas inverse 13C and 15N isotope effects are predicted for SET. Analogous results are observed with the Fe(iv)O model system [5,10,15,20-tetrakis(pentafluorophenyl)porphyrin-iron(iii)- chloride + NaIO4], but not with permanganate. These results emphasize the relevance of the HAT mechanism for N-dealkylation by P450.
- Meyer, Armin H.,Dybala-Defratyka, Agnieszka,Alaimo, Peter J.,Geronimo, Inacrist,Sanchez, Ariana D.,Cramer, Christopher J.,Elsner, Martin
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p. 12175 - 12186
(2014/08/05)
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- Biomimetic simazine oxidation catalyzed by metalloporphyrins
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The metalloporphyrin-mediated simazine oxidation was investigated, in order to evaluate whether metalloporphyrins were good biomimetic models for the oxidation of this herbicide. The commercially available second-generation metalloporphyrins: 5,10,15,20-tetrakis(2,6-dichlorophenyl)porphyrin metal(III) chloride, [M(TDCPP)]Cl; 5,10,15,20-tetrakis(pentafluorophenyl)porphyrin metal(III) chloride, [M(TFPP)]Cl; and 5,10,15,20-tetrakis(N-methyl-4-pyridyl) porphyrin metal(III) chloride, [M(TMPyP)]Cl5 (metal = Fe or Mn), and the oxidants iodosylbenzene (PhIO), hydrogen peroxide, and 3-chloroperoxy benzoic acid (m-CPBA) were employed in this study. Results demonstrated that these metalloporphyrins can mimic both the in vivo and in vitro action of cytochrome P450 for simazine oxidation, with formation of the dechlorinated metabolites OEET and OEAT mainly, as well as production of two other unknown compounds, identified by HPLC/mass spectrometry as ODET and ODDT. Among the systems, [Fe(TDCPP)]Cl/m-CPBA was the most efficient for simazine oxidation, giving up to 49% total conversion. Although hydrogen peroxide did not afford the best results (about 14% simazine conversion), it can be considered the most efficient oxidant from the point of view of toxicity, because it leads to less toxic products, namely OAAT and OEAT. The effect of some reaction conditions was investigated, and product evolution as a function of time was also monitored. Based on these results, simplified reaction mechanisms have been proposed.
- Santos, Joicy Santamalvina Dos,Palaretti, Vinícius,Faria, André Luiz De,Crevelin, Eduardo José,Moraes, Luiz Alberto Beraldo De,Assis, Marilda Das Dores
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p. 163 - 170
(2012/05/04)
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- Identification of Fenton's reagent-generated atrazine degradation products by high-performance liquid chromatography and megaflow electrospray ionization tandem mass spectrometry
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High-performance liquid chromatography megaflow electrospray tandem mass spectrometry (HPLC/ES-MS/MS) with an on-line radioisotope detector was used to identify [2,4,6-14C]atrazine degradation products generated by treatment with Fenton's reagent (Fe2+ and H2O2). Fenton's reagent produced dealkylated and/or partially oxidized [2,4,6-14C]atrazine products in preference to dechlorinated products. Seven major products were identified by collision-induced dissociation spectra: 4-acetamido-2-chloro-6-(isopropylamino)-s-triazine, 4-amino-2-chloro-6-(isopropylamino)-s-triazine, 4-acetamido-2-chloro-6-(ethylamino)-s-triazine, 6-amino-2-chloro-4(ethylamino)-s-triazine, 4-acetamido-6-amino-2-chloro-s-triazine, 2-chloro-4,6-diamino-s-triazine and the first report of 4-acetamido-2-hydroxy-6-(isopropylamino)-s-triazine. HPLC/ES-MS/MS provided a rapid method for identifying a wide range of atrazine transformation products in aqueous samples and obviated the need for fraction collection, extraction, and chemical derivatization of the more polar atrazine products. Furthermore, because analyte retention times in HPLC/UV and HPLC/ES-MS/MS were similar, compound identities determined using the latter could be directly assigned to peaks in UV chromatograms.
- Arnold,Talaat,Hickey,Harris
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p. 452 - 460
(2007/10/02)
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