Complexation of iron by salicylic acid and its effect on atrazine photodegradation in aqueous solution
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Photodegradation
Photodegradation
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The worldwide increase in the number and use of agrochemicals impacts nearby soil and freshwater ecosystems. Beyond the excess in applications and dosages, the inadequate management of remnants and the rinsing water of containers and application equipment worsen this problem, creating point sources of pollution. Advanced oxidation processes (AOPs) such as photocatalytic and photo-oxidation processes have been successfully applied in degrading organic pollutants. We developed a simple prototype to be used at farms for quickly degrading pesticides in water solutions by exploiting a UV–H2O2-mediated AOP. As representative compounds, we selected the insecticide imidacloprid, the herbicide terbuthylazine, and the fungicide azoxystrobin, all in their commercial formulation. The device efficiency was investigated through the disappearance of the parent molecule and the degree of mineralization. The toxicity of the pesticide solutions, before and during the treatment, was assessed by Vibrio fischeri and Pseudokirchneriella subcapitata inhibition assays. The results obtained have demonstrated a cost-effective, viable alternative for detoxifying the pesticide solutions before their disposal into the environment, even though the compounds, or their photoproducts, showed different sensitivities to physicochemical degradation. The bioassays revealed changes in the inhibitory effects on the organisms in agreement with the analytical data.
Terbuthylazine
Pesticide degradation
Biocide
Photodegradation
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The photodegradation of three triazines, atrazine, simazine, and prometryn, in aqueous solutions and natural waters using UV radiation (lambda > 290 nm) has been studied. Experimental results showed that the dark reactions were negligible. The rate of photodecomposition in aqueous solutions depends on the nature of the triazines and follows first-order kinetics. In the case of the use of hydrogen peroxide and UV radiation, a synergistic effect was observed. The number of photodegradation products detected, using FIA/MS and FIA/MS/MS techniques, suggests the existence of various degradation routes resulting in complex and interconnected pathways.
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Simazine
Triazine
Natural Organic Matter
Degradation
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Photodegradation of chlorbromuron, atrazine, and alachlor in aqueous systems under solar irradiation
Homogeneous and heterogeneous aqueous systems of the herbicides of chlorbromuron, atrazine, and alachlor were irradiated with a nonexpensive solar irradiation using a photoreactor with recirculation. Photodegradation of these herbicides occurred in both aqueous systems; however the presence of TiO2 clearly accelerated the degradation of the three herbicides in comparison with direct photolysis. Degradation was followed by measuring the chemical oxygen demand (COD) as a function of reaction time for each aqueous system. Over 90% of COD abatement in the heterogeneous aqueous system was obtained in a short time period showing that mineralization of chlorbromuron, atrazine, and alachlor was achieved.
Alachlor
Photodegradation
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Photodegradation
Scavenger
Degradation
Reaction intermediate
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Terbuthylazine
Alachlor
Metribuzin
Simazine
Photodegradation
Pendimethalin
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ABSTRACT The photochemical degradation of herbicides belonging to different chemical groups has been investigated in different types of natural waters (ground, river, lake, marine) and distilled water as well as in soils with different texture and composition. Studied herbicides and chemical groups included atrazine, propazine, and prometryne ( s ‐triazines); propachlor and propanil (acetanilides); and molinate (thiocarbamate). The degradation kinetics were monitored under natural conditions of sunlight and temperature. Photodegradation experiments were performed in May through July 1998 at low concentrations in water samples (2–10 mg/L) and soil samples (5–20 mg/kg), which are close to usual field dosage. The photodegradation rates of all studied herbicides in different natural waters followed a pseudo–first order kinetics. The half‐lives of the selected herbicides varied from 26 to 73 calendar days in waters and from 12 to 40 d in soil surfaces, showing that the degradation process depends on the constitution of the irradiated media. The presence of humic substances in the lake, river, and marine water samples reduces degradation rates in comparison with the distilled and ground water. On the contrary, the degradation in soil is accelerated as the percentage of organic matter increases. Generally, the photodegradation process in soil is faster than in water. The major photodegradation products identified by using gas chromatography–mass spectrometry (GC–MS) techniques were the hydroxy and dealkylated derivatives for s ‐triazines, the dechlorinated and hydroxy derivative for the anilides, and the keto‐derivative for the thiocarbamate, indicating a similar mode of degradation for each chemical category.
Photodegradation
Terbuthylazine
Metribuzin
Thiocarbamates
Degradation
Distilled water
Ultrapure water
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The photodegradation of atrazine induced by UV-irradiation in aqueous solution was investigated initially. The affecting factors on the photodetradation were studied and described in details such as atrazine initial concentration, temperature, pH value, exposure intensity, oxidant and co-existing substances. It was found that the atrazine initial concentration had no obvious effect on the photodegradation. With the pH value increasing, photodegradation rates decreased. However, we also observed a positive correlation between the degradation rate of atrazine and temperature, exposure intensity and oxidant while the coexisting organic compounds may decelerate photodegradation of the atrazine in water. In this paper, the degradation products had also been confirmed by using LC-MS.
Photodegradation
Degradation
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Photodegradation of metolachlor [2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-1-methylethyl)acetamide] at 253.7 nm was carried out in water containing soil minerals (kaolinite, montmorillonite, and goethite) and fulvic acid under two different pH conditions. The rate of photolysis was dependent on the nature of the soil constituents and the initial pH of the medium. Based on the regression analysis, it was shown that the photodegradation followed the first-order kinetics with respect to the metolachlor concentration, and the half-life of the herbicide under UV irradiation was longer in the absence of soil constituents. Hydroxylation, dehalogenation, oxoquinoline formation, and demethylation were the main processes observed during the photolysis of metolachlor. More degradation products were formed in the presence of kaolinite, montmorillonite, and goethite than with fulvic acid and water alone. The major degradation product formed under UV irradiation in all the treatments was identified as 4-(2-ethyl-6-methylphenyl)-5-methyl-3-morpholine. Keywords: Photodegradation; metolachlor; soil minerals; fulvic acid; degradation products
Photodegradation
Metolachlor
Ultrapure water
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