Major Photodegradation Products Research Articles

Aqueous photodegradation of fenthion by ultraviolet B irradiation: contribution of singlet oxygen in photodegradation and photochemical hydrolysis

The objective of this study was to evaluate the photodegradation of the organophosphorus pesticide fenthion in the environment from a human health effect viewpoint. The major photodegradation products of fenthion in an aqueous solution under UVB irradiation (280–320 nm radiation) were identified as fenthion sulfoxide, 3-methyl-4-methylthiophenol (MMTP), dimethyl phosphorothioate and 3-methyl-4-methylsulfinylphenol (MMSP). MMTP, dimethyl phosphorothioate and MMSP were discovered as novel photodegradation products of fenthion. Kinetic analysis of these products showed the formation of MMTP and dimethyl phosphorothioate by the photochemical hydrolysis of fenthion, which was accelerated under alkaline conditions. The former was further oxidized to MMSP. Fenthion sulfoxide was directly produced by the oxidative reaction of fenthion. Contribution of dissolved oxygen in this photooxidation was observed by replacing the air with nitrogen gas in the reaction system, which prevented oxidative formation of fenthion sulfoxide from fenthion and MMSP from MMTP. These oxidative compounds were also formed from fenthion in the presence of singlet oxygen ( 1O 2) generated by the visible light irradiation of rose bengal solution, while 1O 2 scavengers, l-histidine and sodium azide (NaN 3) inhibited this reaction. The aqueous photolysis mechanisms of fenthion were proposed from a kinetic photolysis experiment study as follows: there were two kinds of UVB photodegradation pathways of fenthion, one being photochemical hydrolysis of the phosphorus- O-phenyl ester to form MMTP and dimethyl phosphorothioate, and the other oxygenation triggered by 1O 2 and producing fenthion sulfoxide and MMSP. Therefore, the steady photodegradation products of fenthion in the water environment may be fenthion sulfoxide and MMSP.

Photophysics and photochemistry of azole fungicides: triadimefon and triadimenol

Photophysics and photochemistry of pesticides triadimefon {1-(4-chlorophenoxy)-3,3-dimethyl-1-(1H-1,2,4-triazol-1-yl) butanone} and triadimenol {1-(4-chlorophenoxy)-3,3-dimethyl-1-(1H-1,2,4-triazol-1-yl) butan-2-ol} were studied in the solution. The excited singlet states were identified by comparison with the absorption spectra of adequate model compounds, in several solvents. The first excited singlet state of triadimefon is an n, π ∗ state localized on the carbonyl group, while higher excited states are localized on the chlorophenoxy group and have a π, π ∗ character. The lowest singlet state of triadimenol is a π, π ∗ state, since a methoxyl group replaces the carbonyl group of triadimefon. Triadimefon shows a weak fluorescence from the n, π ∗ state, upon excitation at both 310 and 250 nm. This suggests a fast intramolecular energy transfer process from the localized π, π ∗ state of the chlorophenoxy group to the n, π ∗ state of the carbonyl group. The photodegradation quantum yield of triadimefon in cyclohexane at 313 nm is 0.022. Triadimenol is photostable under the same conditions. Two major photodegradation products of triadimefon and triadimenol were identified: 4-chlorophenol and 1,2,4-triazole. 4-Chlorophenoxyl radicals were detected by flash photolysis, suggesting a homolytic cleavage of the C–O bond of the asymmetric carbon.

Photodegradation of selected herbicides in various natural waters and soils under environmental conditions.

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.

The role of carbonate radical in limiting the persistence of sulfur-containing chemicals in sunlit natural waters

Carbonate radical (  CO 3 − ) is a selective oxidant that may be important in limiting the persistence of a number of sulfur-containing compounds in sunlit natural waters. Thioanisole, dibenzothiophene (DBT), and fenthion were selected to investigate the degradation pathway initiated by  CO 3 − ; electron-rich sulfur compounds are particularly reactive towards the  CO 3 − . Using HPLC, GC, GC–MS and LC–MS for structural confirmation, the major photodegradation products of thioanisole and DBT were the corresponding sulfoxides. The sulfoxide products were further oxidized through reaction with  CO 3 − to the corresponding sulfone derivatives. Fenthion showed a similar pathway with appearance of fenthion sulfoxide as the major product. The proposed mechanism involves abstraction of an electron on sulfur to form a radical cation, which is then oxidized by dissolved oxygen. Each of the sulfur probes were further investigated in a sunlight simulator under varying matrix conditions. The highest rate constants occurred in the  CO 3 − matrix, and the lowest occurred in a matrix of dissolved organic carbon (DOC) and bicarbonate. In synthetic and natural field water, thioanisole photodegraded faster than under direct photolysis, with half-lives of 75.1 and 85.8 min, respectively. Fenthion photodegraded more rapidly than thioanisole. DBT photodegraded rapidly in a  CO 3 − matrix with a half-life of 24.8 min, while the half-life of direct photolysis was 350 min. Photodegradation products of each compound were also investigated. Ultimately,  CO 3 − was found to contribute toward the photodegradation of sulfur-containing compounds in natural waters.

Photodegradation studies on Atenolol by liquid chromatography

The photostability of the β-blocker drug Atenolol was evaluated at pH 9, 7.4 and 4.0. The drug was exposed to UVA–UVB radiations and the photoproducts were detected by reversed phase LC methods. The photodegradation was found to increase with the pH value decreasing. The major photodegradation product at pH 7.4 was identified as 2-(4-hydroxyphenyl)acetamide. The LC method developed for routine analyses (column: C-18 Alltima; mobile phase: TEA acetate (pH 4; 0.01 M)–acetonitrile 96:4) was found to be suitable for the stability — indicating determination of Atenolol in pharmaceutical dosage forms.

Environmental fate of pesticides used in Australian viticulture IV. Aqueous stability of dithianon

Dithianon formulations are unstable in slightly basic aqueous solutions (pH 9, 20°C, t ½ = 5.6 h) but relatively stable in neutral or acidic solution (pH 4,20°C, t ½ = 6443 h). To ensure the efficacy of this fungicide it is important to prepare the spray mix fresh with neutral or slightly acidic water. Dithianon is unstable towards natural sunlight in the solid and aqueous phase, with half‐lives of approximately 68 and 42 days, respectively. Thermal hydrolysis does not seem to be the preferred degradation pathway when aqueous solutions are heated by the South Australian summer sun. The major aqueous phase photodegradation product has been identified as 2,3‐dihydro‐1,4‐dithiaanthraquinone. These results strongly suggest that should dithianon be accidentally released into basic Australian waters then it is likely to be rapidly chemically hydrolysed and pose little long term environmental threat. However, dithianon is only slowly chemically and photo‐lytically hydrolysed in neutral and acidic waters, and in this case accidentally release may pose a significant short term environmental threat.

Photodegradation Products of Methylprednisolone Suleptanate in Aqueous Solution—Evidence of a Bicyclo[3.1.0]hex-3-en-2-one Intermediate

□ Two major photodegradation products of methylprednisolone suleptanate (sodium 11/β,17α-dihydroxy-6α-methyl-21-[[8- [methyl(2-sulfoethyl)amino]-1,8-dioxooctyl]oxy]-pregna-1,4-diene-3,20- dione) in aqueous solution irradiated with white fluorescent light at 2000 lux for 28days at 25°C were isolated by preparative highperformance liquid chromatography and characterized. structures of the photodegradation products were determined as sodium 11β,17α- dihydroxy-5α,6α-dimethyl-21-[[8-[methyl(2-sulfoethyl)amino]-1,8-dioxooctyl]- oxy]-19-norpregna-1(10),3-diene-2,20-dione and sodium 1β,11β-epoxy- 17α-hydroxy-6α-methyl-21-[[8-[methyl(2-sulfoethyl)amino]-1,8- dioxooctyl]oxy]-19α-pregn-4-ene-2,20-dione. Formation of these compounds, especially the 1, 11-epoxy analogue, strongly supports the existence of the bicyclo[3.1.0]hex-3-en-2-one intermediate in the photorearrangement of steroidal cross-conjugated dienones. The intermediate can account for all the major ketonic and phenolic products; these products are generated from the intermediate after subsequent transformations and/or further skeletal rearrangements. The 1, 11-epoxy analogues were obtained from the prednisolone steroids in high yields by irradiation with a high-pressure mercury lamp.

Photodegradation Products of a New Antibacterial Fluoroquinolone Derivative, Orbifloxacin, in Aqueous Solution.

A new antibacterial fluoroquinolone derivative, orbifloxacin (ORFX), is decomposed photochemically in aqueous solution. When ORFX solution was irradiated with a chemical lamp or sunlight, three major photodegradation products were isolated by preparative HPLC. These degradation products were identified by electron-impact mass spectrometry, liquid-secondary-ion mass spectrometry and 1-H-NMR spectroscopy. Moreover, the photodegradation pathway was investigated by a similar study using several fluoroquinolone derivatives which were presumed to be the intermediates of the photoreaction of the ORFX. Consequently, it was found that two main photochemical reactions, the decomposition of the dimethylpiperazinyl moiety and the elimination of the cyclopropyl group, take place in ORFX. The detected structures of photodegradation products and the photodegradation studies of the postulated intermediates suggested that the photodecomposition of the dimethylpiperazinyl ring at the 7-position and the elimination of the cyclopropyl group at the 1-position occurred concurrently with the release of fluorine at the 8-position.

Degradation Studies of the Non-lethal Bird Repellent, Methyl Anthranilate

Methyl anthranilate (MA), a food grade flavor and fragrance additive, has been reported to be an effective non-lethal bird repellent in a variety of situations. Despite the experimental success of MA, field studies have yielded widely differing levels of efficacy. Diminished efficacy in some field trials prob- ably results from the failure of specific formulations to retain or protect the active ingredient under natural conditions. Therefore, a clearer understanding of the physical and chemical factors affecting the stability of MA is needed. We undertook a series of laboratory studies on hydrolysis, photolysis and microbial degradation of MA, the results of which could be useful in the development of appropriate formulation strategies and residue analyses. We found the n- octanol : water partition coefficient, (P) to be 84. MA is not subject to hydrolysis at 25°C in phosphate buffer media at pH 5.0, 7.0 and 9.0. MA slowly photo- degrades under simulated UV 'sunlight'. Forty-four percent of MA is lost after 432 h illuminance at 1.25 mW cm-', which is equivalent to approximately 1200 h natural sunlight (40N, noontime, June). Kinetic data indicate that the initial step of photolysis, subsequent to excitation, is a second-order reaction with respect to MA. A major photodegradation product appeared in an amount of about 10% of the mass balance and was determined to be an oxidized trimer of MA. MA is primarily affected by aerobic microbial degradation. For a 12 : 12 h light : dark, under laboratory illumination, 12% of water-solubilized material can be lost in the first seven days. Losses were 30% and 42% at 16 and 27 days, respectively. Under conditions of optimal bacterial growth (warmth and darkness) loss of MA was 22% at nine days and 100% by 20 days. The suscepti- bility of MA to microbial degradation is promising for the prospects of developing formulated, environmentally safe, bird repellents.

Degradation Studies of the Non‐lethal Bird Repellent, Methyl Anthranilate

Methyl anthranilate (MA), a food grade flavor and fragrance additive, has been reported to be an effective non-lethal bird repellent in a variety of situations. Despite the experimental success of MA, field studies have yielded widely differing levels of efficacy. Diminished efficacy in some field trials probably results from the failure of specific formulations to retain or protect the active ingredient under natural conditions. Therefore, a clearer understanding of the physical and chemical factors affecting the stability of MA is needed. We undertook a series of laboratory studies on hydrolysis, photolysis and microbial degradation of MA, the results of which could be useful in the development of appropriate formulation strategies and residue analyses. We found the n-octanol:water partition coefficient, (P) to be 84. MA is not subject to hydrolysis at 25°C in phosphate buffer media at pH 5·0, 7·0 and 9·0. MA slowly photodegrades under simulated UV ‘sunlight’. Forty-four percent of MA is lost after 432 h illuminance at 1·25 mW cm−2, which is equivalent to approximately 1200 h natural sunlight (40°N, noontime, June). Kinetic data indicate that the initial step of photolysis, subsequent to excitation, is a second-order reaction with respect to MA. A major photodegradation product appeared in an amount of about 10% of the mass balance and was determined to be an oxidized trimer of MA. MA is primarily affected by aerobic microbial degradation. For a 12:12 h light:dark, under laboratory illumination, 12% of water-solubilized material can be lost in the first seven days. Losses were 30% and 42% at 16 and 27 days, respectively. Under conditions of optimal bacterial growth (warmth and darkness) loss of MA was 22% at nine days and 100% by 20 days. The susceptibility of MA to microbial degradation is promising for the prospects of developing formulated, environmentally safe, bird repellents.

Photodegradation of Benthiocarb

Abstract The photodegradation of 14C-benthiocarb in water, on a glass surface, on soil and silica gel TLC plates was studied. the study was designed to obtain some information of its dissipation and photodegradation under various laboratory conditions. Benthiocarb degrades readily when exposed to either sunlight or UV light (254 nm). However, it is degraded much faster by UV light than by sunlight. Also, benthiocarb decomposes faster in water or on a glass surface or silica gel surface than on a soil surface. the half-life of benthiocarb exposed to UV light was: 1 hr on glass surface; 1.5 hrs in water; 2 hrs on silica gel TLC plate; 20 hrs on soil TLC plate. Benthiocarb in water, and exposed to sunlight, had a half-life of approximately 3 days. the following major photodegradation products were identified: 4-chlorobenzyl alcohol; 4-chlorobenzaldehyde; 4-chlorobenzoic acid.

Comparative photodegradation rates of alachlor and bentazone in natural water and determination of breakdown products

AbstractThe photochemical degradation of the herbicides alachlor (2‐chloro‐2′,6′‐diethyl‐N‐methoxymethylacetanilide) and bentazone (3‐isopropyl‐(1H)‐2,1,3‐benzothiadiazin‐4(3H)‐one‐2,2‐dioxide) in distilled water and in river water, under xenon arc lamp irradiation, was investigated. Analytical determinations were carried out by using a xenon arc photoreactor and online solid‐phase extraction coupled to liquid‐chromatography diode‐array and liquid‐chromatography mass‐spectrometry detection systems. Photolysis experiments were performed at low concentration (20 μg/L), and the advantages of this methodology over conventional techniques are discussed. The photodegradation of alachlor and bentazone is a process depending on the water type, humic substances, and pH. When using a solution of 4 mg/L of humic matter, the estimated alachlor and bentazone half‐lives were 84 and 150 min, respectively, using a total irradiance of 550 W/m2 in the range of 300 to 800 nm. The degradation of alachlor and bentazone followed pseudo second‐ and first‐order kinetics, respectively. The major photodegradation products of both herbicides were identified either by on‐line solid‐phase extraction (SPE)‐liquid chromatography‐thermospray mass spectrometry (LC/TSP‐MS) or on‐line‐SPE‐LC/TSP‐tandem mass spectrometry (LC/TSP‐MS/MS). In addition to that, a total of six transformation products of alachlor were synthesized in our laboratory and their MS spectra were compared with those of the breakdown products obtained. After photodegradation, a total of 14 photoproducts resulted from alachlor dechlorination with subsequent hydroxylation and cyclization processes. The two major photoproducts were identified as hydroxy‐alachlor and 8‐ethyl‐1‐methoxymethyl‐4‐methyl‐2‐oxo‐1,2,3,4‐tetrahydroquinone. No significant breakdown products of bentazone could be identified.

Isolation and Structure Elucidation of the Major Photodegradation Products of Pirmenol Hydrochloride

Column chromatography, thin-layer chromatography, high-performance liquid chromatography, nuclear magnetic resonance spec-trometry, and high-resolution mass spectrometry were employed to separate and identify the photodegradation products of pirmenol hydro-chloride [(±)-cis-α-[3-(2,6-dimethyl-1-piperidinyl)propyl]-α-phenyl-2-py-ridinemethanol monohydrochloride monohydrate], a new antiarrhythmic drug. A methanol solution of pirmenol was irradiated using a low-pressure mercury lamp. The solution afforded four major degradation products, three of which were identified as 3-(cis-2,6-dimethylpiperidinyl)propyl 2-(2-pyridyl)phenyl ketone, 2-(2-pyridyl)benzoic acid, and methyl 2-(2-pyridyl)-benzoate. The degradation followed apparent-first-order reaction kinetics. In addition, the possible photodegradation pathways are discussed with reference to reaction mechanisms.

Photodegradation of the organophosphorus pesticides chlorpyrifos, fenamiphos and vamidothion in water

The photodegradation of the pesticides chlorpyrifos, fenamiphos and vamidothion in water containing 2–4% methanol was examined. Acetone (5%) was added as photosensitizer in the photolysis of vamidothion. A suntest apparatus equipped with a xenon arc lamp which exhibits a radiation very close to natural sunlight was employed. Analyses were performed by direct injection of the water samples containing the photoproducts into a liquid chromatograph with diode array and thermospray mass spectrometric detection. The major photodegradation products were identified by matching their diode‐array spectra with the corresponding spectra of the authentic standards, their retention times and the spectra obtained using positive and/or negative thermospray mass spectrometry. 3,5,6‐trichloro‐2‐pyridinol, fenamiphos sulfoxide and vamidothion sulfoxide were the major photodegradation products from chlorpyrifos, fenamiphos and vamidothion, respectively.

Structure-photodegradation of 2-thiomethyl-N-methylphenylcarbamate

2-Thiomethyl-N-methylphenylcarbamate was prepared, and Huckel Molecular Orbital(HMO) calculations were carried out for both the ground state and its excited state phenoxy radical.Pi-bond orders and charge densities obtained from the HMO calculations were successfully used to predict the major photodegradation product of the photolysis of this compound in ethanol. Photodegradation product was characterized to be 3-thiomethyl-4-hydroxy-N-methylbenzamide. Also, the rate of photodegradation of the carbamate was determined to be first order, with an average half-life ( t 1 2 ) of 32.3 hours.

Structure-photodegradation of 4-thiomethyl-N-methylphenylcarbamate

4-Thiomethyl-N-methylphenylcarbamate was prepared, and Huckel Molecular Orbita(HMO) calculations were carried out for both the ground state and its excited state phenoxy radical. Pi-bond orders and charge densities obtained from the HMO calculations were successfully used to predict the major photodegradation products of the photolysis of this compound in ethanol. Photodegradation products were characterized to be 4-thiomethylphenol and 3-N-methylamide-4-hydroxythioanisole. Also, the rate of photodegradation of the carbamate was determined to be first order, with an average half-life ( t 1 2 ) of 8.3 hours.

Photodegradation of the carbamate pesticides aldicarb, carbaryl and carbofuran in water

The photodegradation of the pesticides aldicarb, carbofuran and carbaryl. in distilled, pond and artificial sea-water samples with or without humic acids was examined. In addition, two different light sources, a xenon arc lamp and a high-pressure mercury lamp, were used to compare the photolysis behaviour. The effect of temperature on hydrolysis was also studied. The major photodegradation products were identified by matching their diode-array spectra with the corresponding spectra of the authentic standards, using peak purity software of the diode array and their retention times. Aldicarb sulphoxide was the major photodegradation product from aldicarb whereas 1-naphthol was the main hydrolysis product from carbaryl. Acetone (5%) was added as a photosensitizer in this instance. For carbofuran, one main unidentified hydrolysis product was detected. Analyses were made by direct injection of water samples into a liquid chromatograph with diode-array detection.

On the photolysis of selected pesticides in the aquatic environment

The photodegradation (UV λ > 290nm) of the herbicides atrazine and diuron was examined in distilled water and artificial seawater containing humic acids. Major photodegradation products were hydroxyatrazine and monuron, respectively. The results showed a faster degradation in seawater as compared to distilled water for atrazine whereas for diuron a quenching effect was observed thus retarding photodegradation. The photodegradation of fenitrothion was also investigated. For this pesticide, the hydrolysis predominates in seawater whereas the photolysis is very slow in distilled water, so that acetone was needed as photosensitizer. The advantages of direct analysis of water samples by liquid chromatography with diode array and mass spectrometric detection is illustrated.

Aqueous photolysis of napropamide

Photolysis of napropamide [N,N-diethyl-2-(1-naphthalenyloxy)propanamide] has been examined at 25 °C in aqueous solution buffered at pH 7 by using radiation from a xenon arc lamp. The pseudo-first-order photolysis half-life and rate constant were 5.7 min and 1.2 × 10 −1 min −1 , respectively. Three major photodegradation products were produced in yields up to 20 %, 27 %, and 9 %. The three photodegradation products were isolated by HPLC and their structures identified by NMR and mas spectrometry

Utilisation of liquid chromatography in aquatic photodegradation studies of pesticides: A comparison between distilled water and seawater

The advantages of liquid chromatography with diode array and mass spectrometric detection are described for the direct characterization of the photodegradation products of Fenitrothion, Atrazine and Diuron in distilled water and artifical seawater samples. The photodegradation (UV λ>290 nm) of the herbicides Atrazine and Diuron was examined in distilled water and in artificial seawater containing humic acids. Major photodegradation products were hydroxyatrazine and Monuron, respectively. The results showed a faster degradation in seawater as compared to distilled water for Atrazine whereas for Diuron a quenching effect was observed thus retarding photodegradation. The photodegradation of Fenitrothion was also investigated. For this pesticide, hydrolysis predominates in seawater and photolysis is very slow in distilled water, so that acetone was needed as photosensitizer.