RESUMEN
MAIN CONCLUSION: Glufosinate is primarily toxic to plants due to a massive light-dependent generation of reactive oxygen species rather than ammonia accumulation or carbon assimilation inhibition. Glutamine synthetase (GS) plays a key role in plant nitrogen metabolism and photorespiration. Glufosinate (C5H12NO4P) targets GS and causes catastrophic consequences leading to rapid plant cell death, and the causes for phytoxicity have been attributed to ammonia accumulation and carbon assimilation restriction. This study aimed to examine the biochemical and physiological consequences of GS inhibition to identify the actual cause for rapid phytotoxicity. Monocotyledonous and dicotyledonous species with different forms of carbon assimilation (C3 versus C4) were selected as model plants. Glufosinate sensitivity was proportional to the uptake of herbicide between species. Herbicide uptake also correlated with the level of GS inhibition and ammonia accumulation in planta even with all species having the same levels of enzyme sensitivity in vitro. Depletion of both glutamine and glutamate occurred in glufosinate-treated leaves; however, amino acid starvation would be expected to cause a slow plant response. Ammonia accumulation in response to GS inhibition, often reported as the driver of glufosinate phytotoxicity, occurred in all species, but did not correlate with either reductions in carbon assimilation or cell death. This is supported by the fact that plants can accumulate high levels of ammonia but show low inhibition of carbon assimilation and absence of phytotoxicity. Glufosinate-treated plants showed a massive light-dependent generation of reactive oxygen species, followed by malondialdehyde accumulation. Consequently, we propose that glufosinate is toxic to plants not because of ammonia accumulation nor carbon assimilation inhibition, but the production of reactive oxygen species driving the catastrophic lipid peroxidation of the cell membranes and rapid cell death.
Asunto(s)
Amaranthus/efectos de los fármacos , Aminobutiratos/toxicidad , Bassia scoparia/efectos de los fármacos , Herbicidas/toxicidad , Poaceae/efectos de los fármacos , Especies Reactivas de Oxígeno/metabolismo , Amaranthus/metabolismo , Amaranthus/efectos de la radiación , Aminobutiratos/efectos de la radiación , Amoníaco/metabolismo , Bassia scoparia/metabolismo , Bassia scoparia/efectos de la radiación , Carbono/metabolismo , Muerte Celular/efectos de los fármacos , Membrana Celular/efectos de los fármacos , Glutamato-Amoníaco Ligasa/antagonistas & inhibidores , Herbicidas/efectos de la radiación , Luz , Peroxidación de Lípido/efectos de los fármacos , Hojas de la Planta/efectos de los fármacos , Hojas de la Planta/metabolismo , Hojas de la Planta/efectos de la radiación , Proteínas de Plantas/antagonistas & inhibidores , Poaceae/metabolismo , Poaceae/efectos de la radiación , Especies Reactivas de Oxígeno/efectos de la radiaciónRESUMEN
Nanosized BaFe1-xCuxO3 powders were prepared using the Pechini method. To limit grain growth and agglomeration, the temperature of calcination was limited to 800⯰C. For all samples, the cubic form of BaFeO2.75 was predominant with minor additional phases. Cu doping was found to have a remarkable effect on the structural cubic unit cell parameter as the Cu concentration increased. As shown by XRD,the samples were in the nanometer size range (17-63â¯nm). However, as the Cu concentration increases, the agglomeration increases with the highest surface area for the BaFe0.95Cu0.05O3 composition, which also displays the highest photocatalytic atrazine degradation. For this sample, more than 90% degradation of atrazine was obtained at the optimum conditions (120â¯min irradiation under visible light at pH 11 using 0.75â¯mg of the catalyst). The Atrazine degradation was found to follow the pseudo-order kinetics. GC/MS was used to detect the intermediates and the reaction pathways. All the prepared samples and produced waters at the end of the experiment were found to be nontoxic.
Asunto(s)
Atrazina/efectos de la radiación , Herbicidas/efectos de la radiación , Luz , Óxidos/química , Atrazina/química , Catálisis , Herbicidas/química , Cinética , Óxidos/efectos de la radiación , Fotólisis , TemperaturaRESUMEN
Semiconductor-mediated hydrogen peroxide-assisted photocatalytic degradation of a selected herbicide, Bentazone (1) has been investigated in aqueous suspensions of TiO2 under a variety of conditions. The degradation was studied by monitoring the depletion in total organic carbon content as a function of irradiation time. The degradation kinetics was investigated under different conditions such as type of TiO2 (Anatase/Anatase-Rutile mixture), reaction pH, catalyst dosage and hydrogen peroxide (H202) concentration. The degradation rates were found to be strongly influenced by all the above parameters. Titanium dioxide Degussa P25 was found to be more efficient as compared with other two commercially available TiO2 powders like Hombikat UV100 and PC500 from Millennium Inorganic Chemicals. Gas Chromatography-Mass Spectrometry (GC-MS) analysis of the irradiated mixture of Bentazone (1) indicates the formation of several intermediate products which have been characterized on the basis of molecular ion/mass fragmentation pattern and also on comparison with the National Institute of Standards and Technology (NIST) library. Plausible mechanism for the formation of different products during photocatalytic treatment of Bentazone in the presence of TiO2 has been proposed. The use of H202 substantially increased the efficiency of TiO2 photocatalytic degradation.
Asunto(s)
Benzotiadiazinas/química , Herbicidas/química , Minerales/química , Titanio/química , Contaminantes Químicos del Agua/química , Purificación del Agua/métodos , Agua/química , Benzotiadiazinas/aislamiento & purificación , Benzotiadiazinas/efectos de la radiación , Herbicidas/aislamiento & purificación , Herbicidas/efectos de la radiación , Luz , Fotoquímica/instrumentación , Fotoquímica/métodos , Semiconductores , Suspensiones , Titanio/efectos de la radiación , Contaminantes Químicos del Agua/aislamiento & purificación , Contaminantes Químicos del Agua/efectos de la radiación , Purificación del Agua/instrumentaciónRESUMEN
We used a ultrasound/Fe(2+)/H2O2 process in continuous dosing mode to degrade the alachlor. Experimental results indicated that lower pH levels enhanced the degradation and mineralization of alachlor. The maximum alachlor degradation (initial alachlor concentration of 50 mg/L) was as high as 100% at pH 3 with ultrasound of 100 Watts, 20 mg/L of Fe(2+), 2 mg/min of H2O2 and 20°C within 60 min reaction combined with 46.8% total organic carbon removal. Higher reaction temperatures inhibited the degradation of alachlor. Adequate dosages of Fe(2+) and H2O2 in ultrasound/Fe(2+)/H2O2 process not only enhance the degradation efficiency of alachlor but also save the operational cost than the sole ultrasound or Fenton process. A continuous dosing mode ultrasound/Fe(2+)/H2O2 process was proven as an effective method to degrade the alachlor.
Asunto(s)
Acetamidas/química , Herbicidas/química , Peróxido de Hidrógeno/química , Hierro/química , Contaminantes Químicos del Agua/química , Acetamidas/efectos de la radiación , Estudios de Factibilidad , Herbicidas/efectos de la radiación , Sonido , Temperatura , Aguas Residuales/química , Contaminantes Químicos del Agua/efectos de la radiaciónRESUMEN
Photochemical degradation of atrazine under different conditions was studied and compared, namely degradation via photocatalysis on TiO2, UV C photolysis, and homogeneous photocatalysis in the presence of added ferric ions. The reaction rate constants in heterogeneous photocatalytic reactions on TiO2 and of photolytic degradation by means of UV C light are similar, 0.018 min(-1) and 0.020 min(-1), respectively. The reaction rate constants in homogeneous photocatalytic reactions with Fe(III) added depend strongly on the Fe(III) concentration, 0.0017 min(-1) for 1.6 × 10(-6) mol l(-1) Fe(III) to 0.105 min(-1) for 3.3 × 10(-4) mol l(-1) Fe(III). In all types of reactions, dechlorination was observed; in homogeneous photocatalytic reactions and in UV C (250-300 nm) photolysis, dechlorination proceeds with a 1 : 1 stoichiometry to atrazine degradation, in photocatalytic reactions on TiO2, dechlorination measured as chloride ion release reaches only 1/5 of the substrate degradation. In photocatalytic reactions on TiO2, mineralisation of 40% carbon was observed.
Asunto(s)
Atrazina/química , Herbicidas/química , Rayos Ultravioleta , Atrazina/efectos de la radiación , Catálisis , Cloruros/química , Compuestos Férricos/química , Herbicidas/efectos de la radiación , Fotólisis , Titanio/químicaRESUMEN
Surface chemistry determines the interactions of sorbate and solvent molecules with the pore wall surfaces of microporous minerals, and affects the transmission and absorption of microwave radiation for a given solvent-sorbate-sorbent system. The sorption and microwave-induced degradation of atrazine in the micropores of nine Y zeolites with different densities (0.16-2.62 site/nm(2)) and types (Mg(2+), Ca(2+), H(+), Na(+), and NH(4)(+)) of surface cations were studied. The influence of the content of cosorbed water in the mineral micropores on atrazine degradation rate was also examined. The results indicate the presence of surface cations at around 0.23 site/nm(2) on the pore wall surface was optimal for atrazine degradation, probably due to formation of insufficient number of "hot spots" with too few cations but excessive competition for microwave energy with too many hydrated cations. Atrazine degraded faster in the presence of cations with lower hydration free energies, which could be attributed to less microwave energy consumption to desorb the bounded water molecules. Reducing the content of coadsorbed water in the micropores also increased atrazine degration rate because of less competition for microwave energy from water. Such mechanistic understanding can guide the design and selection of microporous minerals in the practical application of microwave-induced degradation.
Asunto(s)
Atrazina/química , Herbicidas/química , Microondas , Zeolitas/química , Adsorción , Atrazina/efectos de la radiación , Herbicidas/efectos de la radiación , Porosidad , Propiedades de SuperficieRESUMEN
Photolysis of oxyfluorfen, an herbicide of the nitrodiphenyl ether class, was studied in aqueous methanol under UV and sunlight. UV irradiation was carried out in a borosilicate glass photoreactor (containing 250 ppm oxyfluorfen in 50% aqueous methanol) equipped with a quartz filter and 125 watt mercury lamp (maximum output 254 nm) at 25 ± 1°C. Sunlight irradiation was conducted at 28 ± 1°C in borosilicate Erlenmeyer flasks containing 250 ppm oxyfluorfen in 50% aqueous methanol. The samples from both the irradiated conditions were withdrawn at a definite time interval and extracted to measure oxyfluorfen content by gas chromatography-flame ionization detector for rate study. The half-life values were 20 hours and 2.7 days under UV and sunlight exposure, respectively. Photolysis of oxyfluorfen yielded 13 photoproducts of which three were characterized by infrared spectrophotometer and (1)H NMR and (13)C NMR spectroscopy. The rest of the photoproducts were identified by gas chromatography-mass spectrometry (GC-MS) and thin layer chromatography (TLC). An ionization potential 70 eV was used for electron impact-mass spectrometry (EI-MS) and methane was used as reagent gas for chemical ionization-mass spectrometry (CI-MS). Two of the photoproducts were also synthesized for comparison. The main phototransformation pathways of oxyfluorfen involved nitro reduction, dechlorination, and hydrolysis as well as nucleophiles displacement reaction.
Asunto(s)
Éteres Difenilos Halogenados/efectos de la radiación , Herbicidas/efectos de la radiación , Fotólisis , Luz Solar , Rayos Ultravioleta , Cromatografía en Capa Delgada , Cromatografía de Gases y Espectrometría de Masas , Semivida , Éteres Difenilos Halogenados/química , Herbicidas/química , Espectroscopía de Resonancia Magnética , Metanol/química , Espectrofotometría InfrarrojaRESUMEN
The degradation of atrazine in aqueous solution by UV or UV/H2O2 processes, and the toxic effects of the degradation products were explored. The mineralization of atrazine was not observed in the UV irradiation process, resulting in the production of hydroxyatrazine (OIET) as the final product. In the UV/H2O2 process, the final product was ammeline (OAAT), which was obtained by two different pathways of reaction: dechlorination followed by hydroxylation, and the de-alkylation of atrazine. The by-products of the reaction of dechlorination followed by hydroxylation were OIET and hydroxydeethyl atrazine (OIAT), and those of de-alkylation were deisopropyl atrazine (CEAT), deethyl atrazine (CIAT), and deethyldeisopropyl atrazine (CAAT). OIAT and OAAT appeared to be quite stable in the degradation of atrazine by the UV/H2O2 process. In a toxicity test using Daphnia magna, the acute toxic unit (TUa) was less than 1 of TUa (100/EC50, %) in the UV/H2O2 process after 30 min of reaction time, while 1.2 to 1.3 of TUa was observed in the UV process. The TUa values of atrazine and the degradation products have the following decreasing order: OIET> Atrazine> CEAT≈CIAT> CAAT. OIAT and OAAT did not show any toxic effects.
Asunto(s)
Atrazina/química , Atrazina/efectos de la radiación , Herbicidas/química , Herbicidas/efectos de la radiación , Peróxido de Hidrógeno/química , Rayos Ultravioleta , Animales , Cromatografía Liquida , Daphnia/efectos de los fármacos , Espectrometría de Masas , Pruebas de ToxicidadRESUMEN
The breakdown of pesticides has been promoted by many methods for clean up of contaminated soil and wastewaters. The main goal is to decrease the toxicity of the parent compound to achieve non-toxic compounds or even, when complete mineralization occurs, carbon dioxide and water. Therefore, electrochemical degradation (potentiostatic and galvanostatic) of both the pesticide atrazine and cyanuric acid (CA) at boron-doped diamond (BDD) and Ti/Ru0.3Ti0.7O2 dimensionally stable anode (DSA) electrodes, in different supporting electrolytes (NaCl and Na2SO4), is presented with the aim of establishing the influence of the operational parameters on the process efficiency. The results demonstrate that both the electrode material and the supporting electrolyte have a strong influence on the rate of atrazine removal. In the chloride medium, the rate of atrazine removal is always greater than in sulfate under all conditions employed. Furthermore, in the sulfate medium, atrazine degradation was significant only at the BDD electrode. The total organic carbon (TOC) load decreased by 79% and 56% at the BDD and DSA electrodes, respectively, in the chloride medium. This trend was maintained in the sulfate medium but the TOC removal was lower (i.e. 33% and 13% at BDD and DSA electrodes, respectively). CA, a stable atrazine degradation intermediate, was also studied and it is efficiently removed using the BDD electrode in both media, mainly when high current densities are employed. The use of the BDD electrode in the chloride medium not only degrades atrazine but also mineralized cyanuric acid leading to the higher TOC removal.
Asunto(s)
Atrazina/química , Boro/química , Diamante/química , Electroquímica/instrumentación , Triazinas/química , Contaminantes Químicos del Agua/química , Purificación del Agua/instrumentación , Atrazina/aislamiento & purificación , Atrazina/efectos de la radiación , Electrodos , Diseño de Equipo , Análisis de Falla de Equipo , Herbicidas/química , Herbicidas/aislamiento & purificación , Herbicidas/efectos de la radiación , Óxidos/química , Triazinas/aislamiento & purificación , Triazinas/efectos de la radiación , Contaminantes Químicos del Agua/aislamiento & purificación , Contaminantes Químicos del Agua/efectos de la radiaciónRESUMEN
The herbicide atrazine is a common pollutant in reservoirs and other sources of drinking water worldwide. The adsorption of atrazine from water onto zeolites CBV-720 and 4A, mesoporous silica MCM-41, quartz sand, and diatomite, and its microwave-induced degradation when sorbed on these minerals, were studied. Dealuminated HY zeolite CBV-720 exhibited the highest atrazine sorption capacity among the mineral sorbents because of its high micropore volume, suitable pore sizes, and surface hydrophobicity. Atrazine sorbed on the minerals degraded under microwave irradiation due to interfacial selective heating by the microwave, while atrazine in aqueous solution and associated with PTFE powder was not affected. Atrazine degraded rapidly in the micropores of CBV-720 under microwave irradiation and its degradation intermediates also decomposed with further irradiation, suggesting atrazine could be fully mineralized. Two new degradation intermediates of atrazine, 3,5-diamino-1,2,4-triazole and guanidine, were first identified in this study. The evolution of degradation intermediates and changes in infrared spectra of CBV-720 after microwave irradiation consistently indicate the creation of microscale hot spots in the micropores and the degradation of atrazine following a pyrolysis mechanism. These results indicate that microporous mineral sorption coupled with microwave-induced degradation could serve as an efficient treatment technology for removing atrazine from drinking water.
Asunto(s)
Atrazina/efectos de la radiación , Herbicidas/efectos de la radiación , Microondas , Contaminantes Químicos del Agua/efectos de la radiación , Zeolitas/química , Adsorción , Atrazina/química , Herbicidas/química , Espectrofotometría Infrarroja , Contaminantes Químicos del Agua/químicaRESUMEN
Photocatalytic degradation of paraquat using mesoporous-assembled Cu-TiO2/SBA15 under UV and visible light was investigated. The catalyst was synthesized by impregnation of Cu-TiO2 colloids onto SBA-15. The colloids of Cu-TiO2 were prepared via sol-gel method while the mesoporous support was prepared using hydrothermal technique. The catalyst was characterized using X-ray diffraction, nitrogen adsorption-desorption, transmission electron microscopy, UV diffuse reflectance spectroscopy, Zeta potential and X-ray adsorption spectroscopy. Results from characterizations showed that Cu doped TiO2 had a small crystalline size and was well-dispersed on SBA-15. The inclusion of SBA-15 significantly enhanced the photocatalytic activity of the catalyst. Among the three types of undoped catalyst in this study (P25, TiO2, TiO2/SBA-15), TiO2/SBA-15 yielded the highest degradation of paraquat for all pH under UV illumination. Meanwhile 2 wt.% Cu-TiO2/SBA-15 yielded the highest activity under visible light.
Asunto(s)
Cobre/química , Herbicidas/química , Paraquat/química , Dióxido de Silicio/química , Titanio/química , Contaminantes Químicos del Agua/química , Catálisis , Cobre/efectos de la radiación , Herbicidas/efectos de la radiación , Concentración de Iones de Hidrógeno , Luz , Nanopartículas/química , Nanopartículas/efectos de la radiación , Paraquat/efectos de la radiación , Fotólisis , Dióxido de Silicio/efectos de la radiación , Titanio/efectos de la radiación , Rayos Ultravioleta , Contaminantes Químicos del Agua/efectos de la radiación , Purificación del Agua/métodosRESUMEN
The work describes a study of the oxidation power of N-doped and undoped anatase TiO(2), as well as TiO(2) Degussa P25 suspensions for photocatalytic degradation of the herbicides RS-2-(4-chloro-o-tolyloxy)propionic acid (mecoprop) and 3,6-dichloro-pyridine-2-carboxylic acid (clopyralid) using visible and UV light. Undoped nanostructured TiO(2) powder in the form of anatase was prepared by a sol-gel route. The synthesized TiO(2), as well as TiO(2) Degussa P25 powder, were modified with urea to introduce nitrogen into the structure. N-doped TiO(2) appeared to be somewhat more efficient than the starting TiO(2) (anatase) powder when visible light was used for mecoprop degradation. N-doped TiO(2) Degussa P25 was also slightly more efficient than TiO(2) Degussa P25. However, under the same experimental conditions, no degradation of clopyralid was observed in the presence of any of the mentioned catalysts. When the kinetics of mecoprop degradation was studied using UV light, more efficient were the undoped powders, while in the case of clopyralid, N-doped TiO(2) Degussa P25 powder was most efficient, which is probably a consequence of the difference in the molecular structure of the two herbicides.
Asunto(s)
Ácido 2-Metil-4-clorofenoxiacético/análogos & derivados , Herbicidas/química , Fotólisis , Ácidos Picolínicos/química , Titanio/química , Ácido 2-Metil-4-clorofenoxiacético/química , Ácido 2-Metil-4-clorofenoxiacético/efectos de la radiación , Catálisis , Restauración y Remediación Ambiental/métodos , Herbicidas/efectos de la radiación , Nanoestructuras/química , Ácidos Picolínicos/efectos de la radiación , SuspensionesRESUMEN
Degradation of atrazine herbicide in humic substances (HS) aqueous solutions and distilled water solutions was investigated on a laboratory scale upon gamma-irradiation from a (60)Co source. In addition, the effect of ionizing radiation on the atrazine residues removal efficiency was investigated in relation to degradation of by-products. gamma-Irradiation experiments were carried out for three targeted concentrations (i.e. 0.464, 2.318 and 4.636 microM) with doses over the range 0.1-60 kGy. The initial concentration of herbicide, scavengers and irradiation doses play a significant role in the degradation efficiency as shown by decay constants of atrazine residues. gamma-Radiolysis showed that atrazine exhibited high degradation percentages at low absorbed doses in HS aqueous solutions compared to distilled water solutions. Absorbed doses from 0.6 to 21 kGy and from 6 to 72 kGy at a dose rate of 14.52 kGyh(-1) achieved 90% degradation for atrazine with initial concentrations over the range 0.464-4.636 microM in humic and distilled water solutions, respectively. The radiolytic degradation by-products and their mass balances were qualitatively determined with good confidence using gas chromatography/quadruple mass spectrometry (GC/MS) with electron impact ionization (EI(+)) mode.
Asunto(s)
Atrazina/efectos de la radiación , Herbicidas/efectos de la radiación , Sustancias Húmicas/efectos de la radiación , Residuos de Plaguicidas/efectos de la radiación , Contaminantes Químicos del Agua/efectos de la radiación , Purificación del Agua/métodos , Atrazina/química , Descontaminación , Relación Dosis-Respuesta en la Radiación , Monitoreo del Ambiente , Restauración y Remediación Ambiental , Rayos gamma , Cromatografía de Gases y Espectrometría de Masas , Herbicidas/química , Residuos de Plaguicidas/química , Contaminantes Químicos del Agua/químicaRESUMEN
The photolysis of a rice herbicide Bispyribac sodium (Sodium 2, 6-bis [(4, 6-dimethoxypyrimidin-2-yl) oxy] benzoate) has been studied in different aqueous medium (distilled water, pond water and Irrigation water) under the influence of UV (lambda max > or = 250 nm) and sunlight in presence or absence of sensitizers (TiO(2) and KNO(3)). The study was conducted under laboratory simulated condition which made it possible to evaluate the contribution of different factors viz. source of irradiation, solvent and sensitizers towards the photolysis of bispyribac sodium. The photodegradation proceeds via first order reaction Kinetics in all the cases. Five photo metabolites (M(1)-M(5)) were isolated in pure form by column chromatographic method from the irradiation system under UV influenced and TiO(2) as sensitizer. From the different spectral data (IR, NMR, UV-VIS, Mass) the structure of these five metabolites were assigned as M(1) (Phenol), M(2) [2, 6-Dihydroxy benzoic acid], M(3) [2, 6-bis [(4, 6 dimethoxypyrimidin-2yl) oxy] benzoic acid], M(4) [2-(3-Hydroxy-phenoxy)-pyrimidine-4, 6-diol] and M(5) as [2,4-Dihydroxy-3, 5-dimethoxy-6-(4-methoxy pyrimidine-2-yloxy)-benzoic acid]. Moreover, another six photometabolites (M(6)-M(11)) were identified from the different irradiation system on the basis of Micromass analysis. On the basis of MS/MS data analysis, the structure of these six photometabolites were assigned as M(6) [2-(4, 6-Dimethoxy-pyrimidin-2-yloxy)-6-hydroxy-benzoic acid], M(7) [2-Hydroxy-6-(4-hydroxy-6-methoxy-pyrimidin-2-yloxy)-benzoic acid], M(8) [4, 6-Dimethoxy-pyrimidin-2-ol], M(9) [6-Methoxy-pyrimidine-2, 4-diol], M(10) [2-Hydroxy-6-(pyrimidin-2-yloxy)-benzoic acid] and M(11) [2, 4, 6-Trimethoxy-pyrimidine]. The plausible Photodegradation pathways of bispyribac sodium in the present investigation were portrayed which proceeds via hydrolysis, hydrolytic cleavage, O-dealkylation, decarboxylation, dehydroxylation, O-alkylation and hydroxylation.
Asunto(s)
Benzoatos/efectos de la radiación , Herbicidas/efectos de la radiación , Fotólisis/efectos de la radiación , Fármacos Fotosensibilizantes/farmacología , Pirimidinas/efectos de la radiación , Sodio/efectos de la radiación , Luz Solar , Rayos Ultravioleta , Agua/química , Alquilación , Benzoatos/química , Herbicidas/química , Hidrólisis , Hidroxilación , Cinética , Nitratos/química , Fotólisis/efectos de los fármacos , Compuestos de Potasio/química , Pirimidinas/química , Sodio/química , Soluciones/química , Análisis Espectral , Titanio/químicaRESUMEN
The paper studies, with the help of HPLC-DAD-MS/MS technique, the hydrolytic and photoinduced degradation processes that take place in aqueous solutions of tribenuron methyl, both when preserved in the dark and when undergoing solar box irradiation under conditions that simulate sun light. The results indicate that the degradation products formed by hydrolysis alone and by photoirradiation are the same, but kinetics of the hydrolysis reaction is much slower. The degradation products are identified as 2-methoxy-4-methylamino-6-methyl-1,3,5-triazine (P1), methyl 2-aminosulfonylbenzoate (P2), and saccharin (P3) and quantified. Ecotoxicological biotests performed on 0.1 microg L(-1) photoirradiated solutions of the herbicide give a border line toxicity situation comparable to that of the precursor and indicate that the herbicide is characterized by low persistence in the environment, as required. Its degradation, however, does not lead to mineralization but to the formation of products of comparable toxicity. To evaluate the matrix effects, the photodegradation of the herbicide is also studied in the presence of rice paddy waters: the process is slower than in ultrapure water but leads to the same products. Experiments performed for comparison by irradiating ultrapure water solutions with UV lamp (254 nm) show that the degradation process is not only faster with respect to sunlight, but gives a different pathway, without in anyway leading to mineralization.
Asunto(s)
Arilsulfonatos/química , Herbicidas/química , Agricultura , Arilsulfonatos/efectos de la radiación , Cromatografía Líquida de Alta Presión , Oscuridad , Herbicidas/efectos de la radiación , Hidrólisis , Cinética , Luz , Espectrometría de Masas , Oryza , Oxígeno/química , Residuos de Plaguicidas/análisis , Fotoquímica , Soluciones , Luz Solar , Rayos Ultravioleta , Contaminantes Químicos del Agua/análisisRESUMEN
The present investigation covers immobilization of TiO2 using a simple solid state dispersion technique over mesoporous Al-MCM-41 support for the treatment of isoproturon herbicide. Catalysts are characterized by XRD, X-ray photo electron spectroscopy (XPS), surface area, UV-Vis diffused reflectance spectra (DRS), SEM and TEM. A detailed photocatalytic degradation study of isoproturon under solar light in aqueous suspensions is reported. The 10 wt% TiO2/Al-MCM-41 composite system found to be optimum with high degradation activity. The reaction follows pseudo-first order kinetics. The parameters like TiO2 loading over Al-MCM-41, amount of catalyst, concentration of substrate, pH effect, durability of the catalyst, activity comparison of TiO2 and Al-MCM-41 supported system are studied. The mineralization of isoproturon is monitored by TOC. Based on the degradation products detected through LC-MS, a plausible degradation mechanism is proposed. The data indicates that TiO2/Al-MCM-41 composite system is an effective photocatalyst for treatment of isoproturon in contaminated water.
Asunto(s)
Herbicidas/química , Compuestos de Fenilurea/química , Dióxido de Silicio/química , Luz Solar , Titanio/química , Contaminantes Químicos del Agua/química , Catálisis/efectos de la radiación , Cromatografía Liquida , Herbicidas/efectos de la radiación , Concentración de Iones de Hidrógeno , Espectrometría de Masas , Minerales/química , Compuestos de Fenilurea/efectos de la radiación , Fotoquímica , Porosidad , Titanio/efectos de la radiación , Contaminantes Químicos del Agua/efectos de la radiación , Difracción de Rayos XRESUMEN
A novel and simple flow injection chemiluminescence method is reported for the determination of simetryn, a common herbicide. The method is based on the direct oxidation of luminol by the photoproducts of the simetryn in alkaline medium in the absence of catalyst/oxidant. The linear concentration range was 0.01 - 2 microg mL(-1) simetryn with a correlation coefficient (r(2)) of 0.9997 and relative standard deviations (RSD; n = 4) in the range of 0.9 - 2.3%. The limit of detection (S/N = 3) was 7.5 ng mL(-1) with a sample throughput of 100 h(-1). The proposed method has been applied to determine simetryn in natural waters using Sep-Pak C(18) cartridges for solid phase extraction (SPE) procedure. The recoveries were in the range of 97 +/- 1 to 104 +/- 2%. The mechanism of chemiluminescence reaction has also been discussed briefly.
Asunto(s)
Análisis de Inyección de Flujo/métodos , Herbicidas/análisis , Mediciones Luminiscentes/métodos , Luminol/química , Extracción en Fase Sólida/métodos , Triazinas/análisis , Calibración , Análisis de Inyección de Flujo/instrumentación , Herbicidas/efectos de la radiación , Mediciones Luminiscentes/instrumentación , Oxidación-Reducción , Fotólisis , Reproducibilidad de los Resultados , Sensibilidad y Especificidad , Hidróxido de Sodio/química , Factores de Tiempo , Triazinas/efectos de la radiaciónRESUMEN
The photocatalytic degradation and mineralization of isoproturon herbicide was investigated in aqueous solution containing TiO2 over H-mordenite (H-MOR) photocatalysts under solar light. The catalysts are characterized by X-ray diffraction (XRD), UV-Vis diffused reflectance spectra (UV-Vis DRS), Fourier transform-infra red spectra (FT-IR) and scanning electron microscopy (SEM) techniques. The effect of TiO2, H-MOR support and different wt% of TiO2 over the support on the photocatalytic degradation and influence of parameters such as TiO2 loading, catalyst amount, pH and initial concentration of isoproturon on degradation are evaluated. 15wt% TiO2/H-MOR composite is found to be optimum. The degradation reaction follows pseudo-first order kinetics and is discussed in terms of Langmuir-Hinshelwood (L-H) kinetic model. The extent of isoproturon mineralization studied with chemical oxygen demand (COD) and total organic carbon (TOC) measurements and approximately 80% mineralization occurred in 5h. A plausible mechanism is proposed based on the intermediates identified by liquid chromatography-mass spectroscopy (LC-MS).
Asunto(s)
Silicatos de Aluminio/química , Herbicidas/química , Compuestos de Fenilurea/química , Energía Solar , Titanio/química , Catálisis , Cromatografía Líquida de Alta Presión , Conservación de los Recursos Naturales , Herbicidas/efectos de la radiación , Espectrometría de Masas , Microscopía Electrónica de Rastreo , Oxígeno/análisis , Compuestos de Fenilurea/efectos de la radiación , Fotoquímica , Espectrofotometría Ultravioleta , Espectroscopía Infrarroja por Transformada de Fourier , Difracción de Rayos XRESUMEN
Biodegradability of aqueous solutions of the herbicide alachlor and the fungicide pyrimethanil, partly treated by photo-Fenton, and the effect of photoreaction intermediates on growth and DOC removal kinetics of the bacteria Pseudomonas putida CECT 324 are demonstrated. Toxicity of 30-120 mg L(-1) alachlor and pyrimethanil has been assayed in P. putida. The biodegradability of photocatalytic intermediates found at different photo-treatment times was evaluated for each pesticide. At a selected time during batch-mode phototreatment, larger-scale biodegradation kinetics were analysed in a 12 L bubble column bioreactor. Both alachlor and pyrimethanil are non-toxic for P. putida CECT 324 at the test concentrations, but they are not biodegradable. A approximately 100 min photo-Fenton pre-treatment was enough to enhance biodegradability, the biological oxidation response being dependent on the pesticide tested. The different alachlor and pyrimethanil respiration and carbon uptake rates in pre-treated solutions are related to change in the growth kinetics of P. putida. Reproducible results have shown that P. putida could be a suitable microorganism for determining photo-Fenton pre-treatment time.
Asunto(s)
Acetamidas , Fungicidas Industriales , Herbicidas , Hierro/química , Pseudomonas putida/metabolismo , Pirimidinas , Rayos Ultravioleta , Contaminantes Químicos del Agua , Acetamidas/química , Acetamidas/metabolismo , Acetamidas/efectos de la radiación , Acetamidas/toxicidad , Biodegradación Ambiental , Fungicidas Industriales/química , Fungicidas Industriales/metabolismo , Fungicidas Industriales/efectos de la radiación , Fungicidas Industriales/toxicidad , Herbicidas/química , Herbicidas/metabolismo , Herbicidas/efectos de la radiación , Herbicidas/toxicidad , Oxidación-Reducción , Pseudomonas putida/efectos de los fármacos , Pseudomonas putida/crecimiento & desarrollo , Pirimidinas/química , Pirimidinas/metabolismo , Pirimidinas/efectos de la radiación , Pirimidinas/toxicidad , Eliminación de Residuos Líquidos/métodos , Contaminantes Químicos del Agua/química , Contaminantes Químicos del Agua/metabolismo , Contaminantes Químicos del Agua/efectos de la radiación , Contaminantes Químicos del Agua/toxicidad , Purificación del Agua/métodosRESUMEN
Photocatalytic degradation of the herbicide, pendimethalin (PM) was investigated with BaTiO3/TiO2 UV light system in the presence of peroxide and persulphate species in aqueous medium. The nanoparticles of BaTiO3 and TiO2 were obtained by gel to crystallite conversion method. These photo catalysts are characterized by energy dispersive x-ray analysis (EDX), scanning electron microscope (SEM), x-ray diffraction (XRD), and Brunauer-Emmett-Teller (BET) adsorption isotherm and reflectance spectral studies. The quantum yields for TiO2 and BaTiO3 for the degradation reactions are 3.166 Einstein m(-2) s(-1) and 2.729 Einstein m(-2) s(-1) and catalytic efficiencies are 6.0444 x 10(-7) mg(-2)h(-1)L2 and 5.403 x 10(-7) mg(-2)h(-1)L2, respectively as calculated from experimental results. BaTiO3 exhibited comparable photocatalytic efficiency in the degradation of pendimethalin as the most widely used TiO2 photocatalyst. The persulphate played an important role in enhancing the rate of degradation of pendimethalin when compared to hydrogen peroxide. The degradation process of pendimethalin followed the first-order kinetics and it is in agreement with Langmuir-Hinshelwood model of surface mechanism. The reason for high stability of pendimethalin for UV-degradation even in the presence of catalyst and oxidizing agents were explored. The higher rate of degradation was observed in alkaline medium at pH 11. The degradation process was monitored by spectroscopic techniques such as ultra violet-visible (UV-Vis), infrared (IR) and gas chromatography mass spectroscopy (GC-MS). The major intermediate products identified were: N-propyl-2-nitro-6-amino-3, 4-xylidine, (2, 3-dimethyl-5-nitro-6-hydroxy amine) phenol and N-Propyl-3, 4-dimethyl-2, 6-dinitroaniline by GC-MS analysis and the probable reaction mechanism has been proposed based on these products.