Photocatalytic degradation of the herbicide clomazone in natural water using TiO2: Kinetics, mechanism, and toxicity of degradation products (original) (raw)
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Photochemistry and Photobiology, 2009
The photodegradation of the herbicide clomazone in the presence of S 2 O 8 2or of humic substances of different origin was investigated. A value of (9.4 ± 0.4) · 10 8 M M -1 s -1 was measured for the bimolecular rate constant for the reaction of sulfate radicals with clomazone in flash-photolysis experiments. Steady state photolysis of peroxydisulfate, leading to the formation of the sulfate radicals, in the presence of clomazone was shown to be an efficient photodegradation method of the herbicide. This is a relevant result regarding the in situ chemical oxidation procedures involving peroxydisulfate as the oxidant. The main reaction products are 2-chlorobenzylalcohol and 2-chlorobenzaldehyde. The degradation kinetics of clomazone was also studied under steady state conditions induced by photolysis of Aldrich humic acid or a vermicompost extract (VCE). The results indicate that singlet oxygen is the main species responsible for clomazone degradation. The quantum yield of O 2 (a 1 D g ) generation (k = 400 nm) for the VCE in D 2 O, F D = (1.3 ± 0.1) · 10 )3 , was determined by measuring the O 2 (a 1 D g ) phosphorescence at 1270 nm. The value of the overall quenching constant of O 2 (a 1 D g ) by clomazone was found to be (5.7 -0.3) · 10 7 M M -1 s -1 in D 2 O. The bimolecular rate constant for the reaction of clomazone with singlet oxygen was k r = (5.4 -0.1) · 10 7 M M -1 s -1 , which means that the quenching process is mainly reactive.
Journal of The Brazilian Chemical Society, 2008
This study evaluated the degradation of the herbicide clomazone in distilled water and from irrigated rice fields, through UV irradiation and under natural conditions. After a solid phase extraction (SPE) as preconcentration step, the remained concentration of clomazone was determined by high performance liquid chromatography with diode array detection (HPLC-DAD) and the identification of the degradation products was achieved by gas chromatography-mass spectrometry (GC-MS). Under UV irradiation, the clomazone was degraded faster in distilled water than in surface water. In irrigated rice water, under sunlight irradiation, clomazone presented a half-life time average of 3.2 days in three consecutive harvests, and after application the concentration in water remained higher than 0.1 μg L-1 for 20 days. Several by-products, like 2-chlorobenzaldehyde and 2-chlorobenzene methanol, were identified by GC-MS, which evidenced that the concentration of intermediates at the begining increase and then they also undergo degradation.
Materials, 2024
This study aimed to compare the effectiveness of adsorption and photocatalysis techniques at removing the herbicide clomazone (CLO) and the antidepressant known as amitriptyline (AMI) from water. This study employed kinetic models to analyze the removal processes and assess the potential toxicity of the treated water. The structure and morphology of the prepared multi-walled carbon nanotubes were characterized as adsorbents by transmission electron microscopy, X-ray diffraction, Fourier transform infrared techniques, and Raman spectroscopy. The adsorption kinetics of CLO and AMI were studied on the pristine and functionalized multi-walled carbon nanotubes. Kinetic studies were performed by modeling the obtained experimental data using three kinetic models: pseudo-first-order, pseudo-second-order, and Elovich kinetic models. On the other hand, the efficiency of CLO and AMI photodegradation was examined as a function of the type of irradiation (UV and simulated solar irradiation) and type of TiO2 photocatalyst (Aeroxide and Kronos). Under the experimental conditions employed, the reaction followed pseudo-first-order kinetics. Additionally, in order to assess the toxicity of water containing CLO, AMI, and their intermediates, toxicity assessments were conducted using human fetal lung fibroblast cells. The results obtained indicate the effectiveness of both methods and provide valuable insights into their removal mechanisms, contributing to the advancement of sustainable water treatment strategies.
Photolytic versus microbial degradation of clomazone in a flooded California rice field soil
Pest Management Science, 2012
Clomazone is a popular herbicide used on California rice fields and exhibits rapid anaerobic microbial degradation (t(1/2) = 7.9 days). To test the potential of direct and indirect photolytic degradation as a cofactor in the overall degradation rate, sacrificial time-series microcosms were amended with water, non-sterilized soil + water and sterilized soil + water. Clomazone was added to each microcosm, which was then exposed to natural and artificial sunlight over 35 days. Water and acetonitrile extracts were analyzed for clomazone and metabolites via LC/MS/MS. The calculated pseudo-first-order degradation rate constants (k) were k(water) = 0-0.005 ± 0.003 day(-1) , k(sterile) = 0-0.005 ± 0.003 day(-1) and k(non-sterile) = 0.010 ± 0.002-0.044 ± 0.007 day(-1) , depending on light type. The formation of ring-open clomazone, a microbial metabolite, correlated with clomazone degradation. Trace amounts of 5-hydroxyclomazone (m/z = 256 → 125), aromatic hydroxyclomazone (m/z = 256 → 141) and an unknown product (m/z = 268 → 125) were observed. The photolytic degradation rate depends on both light type and the quality of the chromophores that induce indirect photolysis. Microbial degradation was found to be sensitive to temperature fluctuations. Overall, microbes are shown to be more detrimental to the environmental fate of clomazone than photolysis.
Mechanism of clomazone photocatalytic degradation: hydroxyl radical, electron and hole scavengers
Reaction Kinetics, Mechanisms and Catalysis, 2014
The role of • OH radicals (adsorbed and free) and valence band holes as primary oxidants in the photodegradation of clomazone in UV-illuminated TiO 2 suspension was investigated. Significant inhibition of the photodegradation of clomazone in the presence of NaI (hole and surface • OH scavenger) suggesting that the surface degradation mechanism played a crucial role rather than the bulk degradation pathway. Also, less impact of tert-butanol on the photodegradation indicated that free • OH radicals were not majorly involved in the photodegradation process of clomazone. On the other hand, when the surface is covered by fluoride, it was concluded that the kinetic pathways for reaction with subsurface holes and with free •
Oxidation of Mixed Active Pharmaceutical Ingredients in Biologically Treated Wastewater by ClO2
2011
Biologically treated wastewater containing a mixture of 53 active pharmaceutical ingredients (APIs) was treated with 0-20 mg/l chlorine dioxide (ClO 2) solution. Wastewater effluents were taken from two wastewater treatment plants in Sweden, one with (low COD) and one without (high COD) extended nitrogen removal. The removal of the APIs varied from no significant removal at the highest dose of ClO 2 (20 mg/l) to 90% removal at a dose of 0.5 mg/l of the oxidant. From the low COD effluent, only 4 APIs were removed by more than 90% at the lowest oxidant dose of 0.5 mg/l whereas most of the APIs were removed at 5 mg/l ClO 2 dose. Removal of the same APIs from the high COD effluent was observed when the ClO 2 dose was increased to 1.25 mg/l and an increase in API removal only after treatment with 8 mg/l ClO 2. This illustrates that treatment of wastewater effluents with chlorine dioxide has potential to remove pharmaceuticals traces from wastewater treatment plant effluents.
2012
The aim of this paper is to find out the optimal degradation condition for two potential environmental pollutants, chloridazon and metribuzin (herbicide derivatives), employing advanced oxidation process using TiO 2 photocatalyst in aqueous suspensions. The degradation/mineralization of the herbicide was monitored by measuring the change in pollutant concentration and depletion in TOC content as a function of time. A detailed degradation kinetics was studied under different conditions such as types of TiO 2 (anatase/anatase-rutile mixture), catalyst concentration, herbicide concentration, initial reaction pH, and in the presence of electron acceptors (hydrogen peroxide, ammonium persulphate, potassium persulphate) in addition to atmospheric oxygen. The photocatalyst, Degussa P25, was found to be more efficient catalyst for the degradation of both herbicides as compared with two other commercially available TiO 2 powders like Hombikat UV100 and PC500. Chloridazon (CHL) was found to degrade more efficiently under acidic condition, whereas metribuzin (MET) degraded faster under alkaline medium. All three electron acceptors tested in this study were found to enhance the degradation rate of both herbicides.
Effects of advanced oxidation processes (AOPs) on the toxicity of a mixture of pharmaceuticals
The possibility of applying main AOP techniques, namely ozonation, H 2 O 2 /UV photolysis and TiO 2 photocatalysis to provide a significant reduction of toxicity of pharmaceutical mixtures has been evaluated. For the preparation of the mixture six pharmaceuticals were chosen among those found at highest concentrations in Sewage Treatment Plant effluents, namely carbamazepine, clofibric acid, diclofenac, sulfamethoxazole, ofloxacin and propranolol.
Water Research, 2020
Advanced oxidation using UV and hydrogen peroxide (UV/H 2 O 2) has been widely applied to degrade contaminants of emerging concern (CECs) in wastewater for water reuse. This study investigated the degradation kinetics of mixed CECs by UV/H 2 O 2 under variable H 2 O 2 doses, including bisphenol A, estrone, diclofenac, ibuprofen, and triclosan. Reverse osmosis (RO) treated water samples from Orange County Water District's Groundwater Replenishment System (GWRS) potable reuse project were collected on different dates and utilized as reaction matrices with spiked additions of chemicals (CECs and H 2 O 2) to assess the application of UV/H 2 O 2. Possible degradation pathways of selected CECs were proposed based on high resolution mass spectrometry identification of transformation products (TPs). Toxicity assessments included cytotoxicity, aryl hydrocarbon receptor-binding activity, and estrogen receptor-binding activity, in order to evaluate potential environmental impacts resulting from CEC degradation by UV/H 2 O 2. Cytotoxicity and estrogenic activity were significantly reduced during the degradation of mixed CECs in Milli-Q water by UV/H 2 O 2 with high UV fluence (3200 mJ cm À2). However, in GWRS RO-treated water samples collected in April 2017, the cytotoxicity and estrogen activity of spiked CEC-mixture after UV/H 2 O 2 treatment were not significantly eliminated; this might be due to the high concentration of target CEC and their TPs, which was possibly affected by the varied quality of the secondary treatment influent at this facility such as sewer-shed and wastewater discharges. This study aimed to provide insight on the impacts of post-UV/H 2 O 2 CECs and TPs on human and ecological health at cellular level.