Degradation Of Trifluralin Research Articles

Evaluation of dissipation kinetic models to describe trifluralin degradation in soil and assessing the uncertainty of the half-life estimate

In Australia, trifluralin is one of the commonly used herbicides to manage annual grasses and some broadleaf weeds. However, it may have some ecosystem impacts such as high toxicity to terrestrial and aquatic life, so it is vital to monitor the degradation of trifluralin for a considerable period for environmental safety. For risk assessment purposes, it is necessary to estimate the half-life of trifluralin, which is often evaluated using derived mathematical dissipation models. In the literature, bi-exponential (BEXP) and gamma models were suggested for modelling the dissipation of trifluralin in soil. Both models provide the half-life estimate without discussing the uncertainty of the estimate, which is a shortcoming in the literature. In this paper, we used simulation to illustrate the importance of estimate's uncertainty (standard error) and demonstrated a method to compute the standard error for the half-life estimate mathematically for kinetic dissipation models. Later, we evaluated the performance of the two suggested models using statistical indices. The computation of the half-life and the standard error of the half-life estimate were discussed. This allows us to describe the inference of the half-life parameter and determine whether the half-life estimates are significantly different against the co-variate (moisture) levels. We demonstrated the method to calculate the standard error of the half-life of trifluralin, which allows us to determine the statistical difference between the estimates. In this study, we found that the half-life of trifluralin in soil tends to increase with increasing moisture levels, and the half-life of trifluralin in soil with 100% moisture level is significantly greater than 40% and 70% moisture levels. Our findings suggest that soil moisture levels should be carefully considered before trifluralin application to minimize the non-target environmental damage.

Degradation of organic pollutants combining plasma discharges generated within soil with TiO2 and ZnO catalysts: Comparative analysis, optimization and mechanisms

An advantageous plasma-catalytic setup was developed and applied towards the degradation of trifluralin in soil. For the first time, TiO2 and ZnO catalysts were compared when employed in conjunction with micro-discharges generated directly into the interconnected soil channels. In the presence of catalysts, a significant increase in degradation efficiency was observed; after 5 min, trifluralin degradation increased from 66.5% (plasma alone) to 94.2% and 93% with the addition of TiO2 and ZnO, respectively. In terms of degradation kinetics, TiO2 was a slightly superior catalyst compared to ZnO whereas both catalysts performed better under oxygen than in air atmosphere. Compared to plasma alone, the plasma-catalytic treatment considerably increased (∼3fold) the process energy efficiency. Moreover, the inhibitory effect of soil moisture was less pronounced during TiO2 plasma-catalysis where a reduction of ∼19% in pollutant degradation was observed at 5 wt% soil moisture compared to a ∼54% reduction during plasma alone. The addition of TiO2 and ZnO resulted in a significant increase in NO2 concentration and a noticeable reduction in O3 generation associated with an increase of certain plasma species concentration and the generation of additional and more active ROS, respectively. Liquid chromatography (UPLC/MS) data at the early stages of the trifluralin degradation revealed similar intermediates and degradation processes between plasma-alone and plasma-catalysis. The present effort supports the potential of future implementation of a plasma-catalytic soil remediation method being a rapid, highly efficient, low energy demanding and green method.

Acute Toxicity, Oxidative Stress, Toxicity Mechanism, and Degradation Dynamics of Trifluralin in Eisenia foetide (Annelida: Lumbricidae)

Abstract Trifluralin is a preemergent herbicide that is applied to soil to control annual grasses and broadleaf weeds. It is widely used in cotton, Gossypium hirsutum L., production in China; however, the ecological safety of its continued use is a controversial issue. We studied the interaction of trifluralin and earthworms, Eisenia foetide Savigny (Annelida: Lumbricidae), to provide additional information for assessing the risk of trifluralin to ecological safety in soils. Contact toxicity assays established median lethal concentrations (LC50) of 726.298 µg/L at 24 h, 418.783 µg/L at 48 h, and 82.007 µg/L at 72 h of exposure to trifluralin. Within 24 to 48 h of exposure to trifluralin, antioxidant activity (e.g., superoxide dismutase, catalase, peroxidase) increased in vivo, but by 72 h of exposure the activity was inhibited and, at high concentrations of trifluralin, death occurred. Based on the activity of glutathione S-transferase (GST) and multifunction oxidase (MFO), it appears that GSTs may be involved in the detoxification of trifluralin in vivo, and that MFOs may be the key detoxification enzymes involved. Earthworm degradation of trifluralin shortened the half-life of trifluralin in soil by as much as 1.78 d. These results provide useful information on the toxicity mechanism of trifluralin in earthworms, the role of earthworms in trifluralin degradation, as well as the ecological safety of trifluralin.

Bioremediation of a trifluralin contaminated soil using bioaugmentation with novel isolated bacterial strains and cyclodextrin

Trifluralin (TFL) is a highly persistent with a strong adsorption capacity on soil particles herbicide. This study was to isolate microbial consortia and bacterial strains from a soil with a historical application of pesticides to evaluate their potential to degrade TFL in soil. Different bioremediation techniques were considered for increasing the effectiveness of TFL degradation in soil. These techniques consisted of: i) biostimulation, using a nutrients solution (NS); ii) bioaugmentation, using a natural microbial consortium (NMC), seven individual bacterial strains isolated from NMC, and an artificial bacterial consortium formed by the seven TFL-degrading bacterial strains (ABC); iii) bioavailability enhancement, using a biodegradable compound, a randomly methylated cyclodextrin, RAMEB.Biostimulation using NS leads up to 34 % of soil TFL biodegraded after 100 d. When the contaminated soil was inoculated with NMC or ABC consortia, TFL loss increased up to 62 % and 74 %, respectively, with DT50 values (required time for the pollutant concentration to decline to half of its initial value) of 5.9 and 11 d. In the case of soil inoculation with the isolated individual bacterial strains, the extent of TFL biodegradation ranged widely from 2.3 % to 55 %. The most efficient bacterial strain was Arthrobacter aurescens CTFL7 which had not been previously described in the literature as a TFL-degrading bacterium. Bioaugmentation with CTFL7 bacterium was also tested in the presence of RAMEB, provoking a drastic increase in herbicide biodegradation up to 88 %, achieving a DT50 of only 19 d. Cyclodextrins had never been tested before for enhancement of TFL biodegradation.An ecotoxicity assay was performed to confirm that the proposed bioremediation techniques were also capable to reduce toxicity. A Microtox® test showed that after application A. aurescens CTF7 and A. aurescens CTF7 + RAMEB, the TFL-contaminated soil, which initially presented acute toxicity, became non-toxic at the end of the biodegradation experiments.

Simultaneous monitoring of the photocatalytic degradation process of trifluralin and pendimethalin herbicides by SBA-15/TiO2 nanocomposite

Today, The occurrence of herbicides in environments attitudes a potential hazard to aquatic life and displays development forbidding of human embryonic cells, therefore their elimination from the environment is a vigorous job. In this paper, the SBA-15/TiO2 nanocomposite were synthesized utilizing amorphous nanosilica, which was extracted from stem cane ash (SCA) with 92.56% purity. FESEM and TEM images of pure SBA-15 and SBA-15/TiO2 nanocomposite demonstrates which their mean particle size was under 50 nm. The average particles size of TiO2 anatase calculated to be 27.6 nm using the Scherrer’s equation. The BET surface area, total pore volume and average pore diameter of the SBA-15/TiO2 was obtained to be 279.2 m2 g−1, 0.39 cm3 g−1 and 5.64 nm, respectively. For the first time, this nanocomposite was used as photocatalysts for degradation of trifluralin (Tri) and pendimethalin (Pen) herbicides in the aqueous solution. Partial least squares-1 (PLS-1) regression was used for simultaneous measurement of them in aqueous solutions before and after photocatalytic degradation with SBA-15/TiO2 nanocomposite. The values of some parameters such as R2(0.9951, 0.9872), recovery (101.5, 102.0%) and root mean square error of prediction (0.231, 0.239) for both Tri and Pen were attained by the PLS-1 regression, respectively. The influence of some operational parameters such as initial herbicide concentrations, photocatalyst dosage, irradiation time and pH were also investigated on the photocatalytic performance using the response surface methodology. Conferring to the ANOVA test, the most important factor on the decomposition of herbicides was photocatalyst dosage. The results displayed that the maximum elimination efficiencies under the optimum conditions (pH = 10, photocatalyst dosage 0.2 g L−1, irradiation time 30 min and initial herbicide concentration 60 mg L−1) from the river water for Tri and Pen were attained to be 90% and 82.5%, respectively.

Photocatalytic Degradation of Trifluralin in Aqueous Solutions by UV/S2O82− and UV/ZnO Processes: A Comparison of Removal Efficiency and Cost Estimation

Trifluralin is one of the most widely used herbicides, being accounted as the cause of cancer in human. In the present research, the UV/S2O82− and ZnO/UV processes’ efficiency in the removal of trifluralin was investigated. A lab scale equipped with a UV lamp was applied. The parameters were studied, including initial trifluralin concentration (0.4–1.2 mg/L), contact time (20–60 min), S2O82− concentration (20–60 μM), and ZnO concentration (50–150 mg/L). The remained trifluralin concentration was measured by HPLC. This study proved the trifluralin removal of 92.90 ± 1.6% and 87.91 ± 19.22% for UV/S2O82− and UV/ZnO processes in the best operation conditions (contact time of 60 min, the persulfate concentration of 40 μM, and the ZnO concentration of 100 mg/L). The optimal trifluraline concentrations were 1.2 mg/L and 0.6 mg/L for UV/S2O82− and UV/ZnO processes, respectively. In both processes, the removal efficiency of trifluralin increased significantly with increasing contact time. The findings exhibited that both processes UV/S2O82− and UV/ZnO followed the zero-order kinetic. The electrical energy consumed of UV/S2O82 and UV/ZnO was about 43.95 and 20.41 Kwh/kg, respectively. The results show that UV/S2O82− and ZnO/UV processes were appropriate as the effective treatment method for trifluralin removal. Therefore, it is proposed to study the performance of these processes as an environmentally friendly practice in full scale with real wastewater.

Novel combination of high voltage nanopulses and in-soil generated plasma micro-discharges applied for the highly efficient degradation of trifluralin

Cold plasma is considered a highly competitive advanced oxidation process for the removal of organic pollutants from soil. Herein, we describe for the first time the combination of in-soil generated plasma micro-discharges with the advantageous high voltage nanosecond pulses (NSP) towards the high-efficient degradation of trifluralin in soil. We performed a detailed parametric analysis (pulse frequency, pulse voltage, soil thickness, soil type, energy efficiency) to determine the optimum operational conditions. High trifluralin degradation was achieved even at the higher soil thickness, indicating that the production of plasma discharges directly inside the soil pores enhanced the mass transfer of plasma reactive oxygen and nitrogen species (RONS) in soil. The energy efficiency achieved was outstanding, being up to 2–3 orders of magnitude higher than those reported for other plasma systems. We identified the intermediate degradants and proposed the most dominant degradation pathways whereas a thorough exhaust gases analysis, optical emission spectroscopy (OES) and active species inhibition by using trapping agents revealed the main RONS involved. This effort constitutes a significant advancement in the "green" credentials and application of plasma-induced degradation of pollutants as it describes for the first time the removal of the highly harmful and toxic pesticide trifluralin from soil and provides a novel perspective towards the future development of cold plasma-based soil remediation technologies.

Biodegradation and Abiotic Degradation of Trifluralin: A Commonly Used Herbicide with a Poorly Understood Environmental Fate.

Trifluralin is a widely used dinitroaniline herbicide, which can persist in the environment and has substantial ecotoxicity, especially to aquatic organisms. Trifluralin is very insoluble in water (0.22 mg/L at 20 °C) and highly volatile (vapor pressure of 6.7 mPa at 20 °C); these physicochemical properties determine a large part of its environmental fate, which includes rapid loss from soils if surface-applied, strong binding to soil organic matter, and negligible leaching into water. The trifluralin structure contains a tertiary amino group, two nitro-groups and a trifluoromethyl- group. Despite the strongly xenobiotic character of some of these substituents, biodegradation of trifluralin does occur, and pure cultures of bacteria and fungi capable of partially degrading the molecule either by dealkylation or nitro-group reduction have been identified. There are many unanswered questions about the environmental fate and metabolism of this herbicide; the genes and enzymes responsible for biodegradation are largely unknown, the relative roles of abiotic processes vs growth-linked biodegradation vs cometabolism are unresolved, and the impact of different environmental factors on the rates and extents of biodegradation are not clear. Here, we summarize the relevant literature on the persistence and environmental fate of trifluralin with a focus on biodegradation pathways and mechanisms, and we identify the current major knowledge gaps for future research.

A comprehensive kinetic model for the process of electrochemical peroxidation and its application for the degradation of trifluralin

The aim of this manuscript was to investigate indirectly the kinetics of formation of hydroxyl/hydroperoxyl radicals responsible for the degradation of persistent pollutants by electrochemical peroxidation. Experiments involving iron electrodes with and without H2O2 were initially carried out in a batch reactor at 0.2–0.6 A and 25 °C in the absence of any pollutants. Concentrations of Fe2+, H2O2, Fe3+, and H+ were determined experimentally as a function of time, and from them a detailed kinetic model comprising 25 electrolysis, dissociation, flotation and Fenton reactions was established. The tuned parameters were only the Faradaic yields for the reactions on the anode, the rate constant for the forward reaction of water dissociation, and flotation of Fe3+. A set of three kinetic experiments of electroperoxidation of trifluralin performed at 0.2 to 0.6 A and 25 °C was correctly described by the already presented subset of reactions, plus two others involving trifluralin and hydroxyl/hydroperoxyl radicals.

Kinetic and thermodynamic study of Trifluralin photo-degradation by ultra violet light

The photo degradation of Trifluralin by ultra violet light region has been studied in liquid phase. In this research, different concentration with different temperature has been investigated. The results have shown that increasing temperature lead to increases rate constant, but when we change concentration the rate constant dose not changed regularly. That may be due to the fact that it is not pure secondary order photo-degradation reaction. All thermodynamic parameters have been measured using second order kinetic plot and Arrhenius plot.

Effect of ozonization in degradation of trifluralin residues in aqueous and food matrices

This study investigates the oxidation of trifluralin residues during ozonation in aqueous and food matrices (tomato). Domestic ozonation equipment with average production of 23.9 mg O3 L−1 h−1 was used in the tests. Modern chromatographic systems (SPME-GC-IT/MS/MS and QuEChERS-GC-IT/MS/MS) were applied for extraction and detection of trifluralin residue in fortified samples of ultrapure water, tap water, superficial water and tomato fruit. The samples were submitted to the ozonation process during 0, 5, 10 and 20 min. Treatment at 5 min was able to degrade 71.5% of herbicide trifluralin in surface water. The removal (%) in ultrapure water reached 83.4% after 20 min of ozonation. The degradation of trifluralin in fortified tomato samples (0.025–0.1 mg kg−1) were conducted with ozonation at 20 min, and it ranged from 84.4 to 92.7%. After treatment, levels of trifluralin in tomato remained within the established MRLs to EU, USEPA and ANVISA (Brazil). The data provided evidence that ozone is effective for removing trace trifluralin from water and foods.

Preparation, characterization and trifluralin degradation of laccase-modified cellulose nanofibers

Laccase, an oxidoreductase enzyme, can biodegrade persistent pesticides and other xenobiotics to less toxic monomers. The present work involves immobilization of laccase onto activated nanocellulose fibers (CNFs) extracted from bagasse. The laccase grafted CNFs were characterized by different techniques. %Immobilization and the activity, stability and reusability of the immobilized laccase was studied using 2,2-azino-bis-(3-ethylbenzthiazoline-6-sulfonic acid) as substrate. The %immobilization was calculated to be 85% with a maximum activity of 0.38 U/mg. 60.5% activity was retained even after 15 repeated uses of the immobilized enzyme. Moreover the immobilized enzyme was found to be stable with 75% relative activity after a period of 45 days. The laccase grafted CNFs were evaluated in degradation of trifluralin, a toxic pesticide resistant to natural transformation or degradation processes, in the presence of humic monomers, guiacol and catechol. Results show 100% degradation of trifluralin in 24 h in the presence of guiacol as mediator.

Photo-assisted electrochemical abatement of trifluralin using a cathode containing a C60-carbon nanotubes composite

This work reports the potential application of modified gas-diffusion electrode (GDE) with C60-CNT composite, as a stable and efficient cathode material for degradation of trifluralin (TRL) pesticide by photo-assisted electrochemical (PE) process. C60-CNT composite was prepared and characterized. Subsequently, a novel C60-CNT composite modified GDE cathode was developed and the electrochemical and physical characteristics of the modified GDEs were studied. C60-CNT composite/GDE showed great efficiencies for electro-generating H2O2, owing to huge surface area and high conductivity. Afterwards, a comparative study of TRL oxidation via photolysis, anodic oxidation (AO) and PE processes using C60-CNT composite/GDE revealed the degradation percentages of 42.2, 48.5 and 93.4%, respectively, after 180 min of treatment. The TRL degradation followed a pseudo-first-order kinetics, being faster in the order: photolysis < AO < PE. The effects of various operational conditions were assessed on the degradation of TRL. From the results, PE process using C60-CNT composite/GDE exhibited great performance for the degradation of TRL (20 mg L−1) under its original pH, Na2SO4 electrolyte concentration of 0.05 mol L−1, applied current intensity of 300 mA, and flow rate of 12.5 L h−1. TOC results displayed that 92.8% of TRL was mineralized after 8 h of PE process. In addition, a plausible pathway for mineralization of TRL was proposed according to the identified by-products detected by means of gas chromatography–mass spectroscopy (GC–MS), High-performance liquid chromatography (HPLC) and ion chromatography analyses.

Simulating the Transport and Fate of Trifluralin in Soil

Understanding herbicide dynamics in agricultural soils is crucial to evaluate herbicide application efficiency and its environmental consequences. A model for herbicide trifluralin (α,α,α-reifluoro-2,6-dinitro-N,N-dipropyl-ρtoluidine) dynamics namely runoff, erosion, leaching, volatilization, and degradation losses in agricultural soils was developed using the software package Structural Thinking and Experiential Learning Laboratory with Animation (STELLATM). The model was calibrated using field data with a good agreement between model predictions and field measurements before its applications. A simulation scenario was then performed to predict trifluralin dynamics in a 1.26 ha soybean field. Simulation results showed that in general, the rate of water runoff decreased with the rate of rainfall; however, the rates of trifluralin and sediment losses in runoff depended not only on the rate of rainfall but also on the content of trifluraline in the liquid and solid phases. The rates of trifluralin leaching and volatilization decreased sharply within the first couple of days following the surface spray of trifluralin due to its strong adsorption and soil incorporation. Simulation results further revealed that the rate of trifluralin degradation in the soil decreased exponentially with time. About 6% of the total applied trifluralin remained in the soil at the end of the simulation period (120 days). This study suggests that the model, developed with STELLATM, is a useful tool for estimating herbicide dynamics in agricultural soils.

Response surface methodology for ozonation of trifluralin using advanced oxidation processes in an airlift photoreactor

Degradation of trifluralin, as a wide used pesticide, was investigated by advance oxidation process comprising O3/UV/H2O2 in a concentric tube airlift photoreactor. Main and interactive effects of three independent factors including pH (5–9), superficial gas velocity (0.05–0.15 cm/s) and time (20–60 min) on the removal efficiency were assessed using central composite face-centered design and response surface method (RSM). The RSM allows to solve multivariable equations and to estimate simultaneously the relative importance of several contributing parameters even in the presence of complex interaction. Airlift photoreactor imposed a synergistic effect combining good mixing intensity merit with high ozone transfer rate. Mixing in the airlift photoreactor enhanced the UV light usage efficiency and its availability. Complete degradation of trifluralin was achieved under optimum conditions of pH 9 and superficial gas velocity 0.15 cm/s after 60 min of reaction time. Under these conditions, degradation of trifluralin was performed in a bubble column photoreactor of similar volume and a lower efficiency was observed.

Photocatalytic Degradation of Trifluralin, Clodinafop-Propargyl, and 1,2-Dichloro-4-Nitrobenzene As Determined by Gas Chromatography Coupled with Mass Spectrometry

Phototransformation is considered one of the most key factors affecting the fate of pesticides. Therefore, our study focused on photocatalytic degradation of three selected pesticide derivatives: trifluralin (1), clodinafop-propargyl (2), and 1,2-dichloro-4-nitrobenzene (3). The degradation was carried out in acetonitrile/water medium in the presence of titanium dioxide (TiO2) under continuous purging of atmospheric air. The course of degradation was followed by thin-layer chromatography and gas chromatography-mass spectrometry techniques. Electron ionization mass spectrometry was used to identify the degradation species. GC-MS analysis indicates the formation of several intermediate products which have been characterized on the basis of molecular ion, mass fragmentation pattern, and comparison with NIST library. The photocatalytic degradation of pesticides of different chemical structures manifested distinctly different degradation mechanism. The major routes for the degradation of pesticides were found to be (a) dealkylation, dehalogenation, and decarboxylation, (b) hydroxylation, (c) oxidation of side chain, if present, (d) isomerization and cyclization, (e) cleavage of alkoxy bond, and (f) reduction of triple bond to double bond and nitro group to amino.

Photo-catalytic degradation of trifluralin by SnO2-doped Cu2O crystals

The SnO2-doped Cu2O has been produced in aqueous solution using hydrazine as the reducing agent. Techniques such as X-ray diffraction (XRD), scanning electron microscopy (SEM) and UV–vis spectroscopy were used to comprehend the relation between structure and properties of the SnO2-doped Cu2O. The effects of SnO2 insertion on the Cu2O photo-catalytic activity for the degradation of trifluralin were reported here. The results show that SnO2-doping can greatly enhance catalytic activity of Cu2O nano-crystals.

Kinetic study of heterogeneous ozonolysis of alachlor, trifluralin and terbuthylazine adsorbed on silica particles under atmospheric conditions

To better understand the atmospheric behaviour of pesticides, heterogeneous ozonolysis of three herbicides (alachlor, terbuthylazine and trifluralin) adsorbed on silica particles were performed in a flow reactor. The experimental setup used in this study and previously validated ( Pflieger et al., 2009) has been specially developed to investigate extremely slow reactivity. The pesticides were adsorbed on particles using a gas/solid adsorption equilibrium, in order to simulate atmospheric conditions. After exposure to ozone concentrations ranging from 5 to 41 ppm during 90 min to 6 h, the kinetics were calculated by comparing the initial and the remaining amounts of pesticides adsorbed on silica particles. This work offers the first results of heterogeneous ozonolysis of alachlor and trifluralin adsorbed on mineral particles. Although alachlor and terbuthylazine were expected to react with ozone, no degradation was observed which leads to a lifetime higher than 8 months towards ozonolysis (for 40 ppb of O 3). A significant degradation of trifluralin adsorbed on silica particles by heterogeneous ozonolysis was observed. The experimental data could be fit by both the Langmuir–Rideal and the Langmuir–Hinshelwood models resulting in atmospheric lifetimes (towards heterogeneous ozonolysis) of 40 and 32 days respectively (for 40 ppb of O 3). These results are discussed and compared to other studies.

Trifluralin: Photolysis under sunlight conditions and reaction with HO [rad] radicals

The gas phase atmospheric degradation of trifluralin (a widely used herbicide) has been investigated at the EUPHORE facility. Its photolysis has been studied under sunlight conditions and its reaction rate constant with HO radicals was measured using the relative rate method. Using 1,3,5-trimethylbenzene as reference compound, the rate constant of HO reaction with trifluralin was obtained to be k HO = ( 1.7 ± 0.4 ) × 10 - 11 cm 3 molecule s −1 at (300 ± 5) K and atmospheric pressure. The mean photolysis rate measured under solar radiation was J trifluralin = (1.2 ± 0.5) × 10 −3 s −1 ( J NO 2 = 8 × 10 - 3 s - 1 ) . The photolysis of trifluralin was found to generate organic aerosols with a yield of (20 ± 10)%. The data obtained enabled us to discuss the atmospheric fate of trifluralin in the gas phase.

Time evolution and competing pathways in photodegradation of trifluralin and three of its major degradation products

The herbicide trifluralin (I)(N,N-di-n-propyl-2,6-dinitro-4-trifluoromethylaniline) decomposes, by the action of UV-Vis light (lambda > 300 nm), to several products, the most important (because they give subsequent photochemical reactions) being N-n-propyl-2,6-dinitro-4-trifluoromethylaniline (VI), 2-ethyl-7-nitro-5-trifluoromethyl-1H-benzimidazole 3-oxide (VII) and 2,6-dinitro-4-trifluoromethylaniline (XII). The time evolution of degradation of trifluralin (I) and the aforementioned three main photoproducts was studied in water and acetonitrile as solvents. The pseudo-first order rate constants allow one to calculate the branching ratios for some of the reactions involved. The preference for either N-dealkylation or cyclization depends on the solvent employed. Dissolved oxygen accelerates the photodegradation, especially the dealkylation.