Photochemistry of pesticides, 3: Photolysis of methyl 2-benzimidazolecarbamate (Carbendazim) in the presence of singlet oxygen

The photolysis of methyl 2-benzimidazolecarbamate (Carbendazim, $\text{1}$) in methanol and in the presence of singlet oxygen, was studied. Dimethyl oxalate $\text{4}$, 2-aminobenzimidazole $\text{7}$, benzimidazole $\text{9}$, N,N′-dicarbomethoxyguanidine $\text{13}$, monocarbomethoxyguanidine $\text{14}$, monocarbomethoxyurea $\text{15}$, and 2-guanidinobenzimidazole $\text{17}$, were isolated and identified in this reaction.A mechanism that accounts for the formation of the photoreaction products, is presented.     

Dichloroacetic acid degradation employing hydrogen peroxide and UV radiation

The degradation reaction of dichloroacetic acid employing H(2)O(2) and UVC radiation (253.7nm) has been studied in a well mixed reactor operating inside a recycling system. It has been shown that in an aqueous solution no stable reaction intermediates are formed and, at every time during the reaction, two mols of hydrochloric acid are formed for every mol of dichloroacetic acid that is decomposed and, in the same way, there is a paired agreement between the calculated TOC concentration corresponding to the unaltered dichloroacetic acid and the experimental values measured in the solution. On this basis and classical references from the scientific literature for the H(2)O(2) photolysis, a complete reaction scheme, apt for reaction kinetics mathematical modeling and ulterior scale-up is proposed.     

Photodegradation of the steroid hormones 17beta-estradiol (E2) and 17alpha-ethinylestradiol (EE2) in dilute aqueous solution

The photochemical transformation of natural estrogenic steroid 17beta-estradiol (E2) and the synthetic oral contraceptive 17alpha-ethinylestradiol (EE2) has been studied in dilute non buffered aqueous solution (pH 5.5-6.0) upon monochromatic (254 nm) and polychromatic (lambda>290 nm) irradiation. Upon irradiation at 254 nm, the quantum yields of E2 and EE2 photolysis were similar and evaluated to be 0.067+/-0.007 and 0.062+/-0.007, respectively. Upon polychromatic excitation, and by using phenol as chemical actinometer, the photolysis efficiencies have been determined to be 0.07+/-0.01 and 0.08+/-0.01 for E2 and EE2, respectively. For both estrogens, photodegradation by-products were identified with GC/MS and LC/MS. In a first step, a model compound--5,6,7,8-tetrahydro-2-naphthol (THN)--, which represents the photoactive phenolic group, was used to obtain basic photoproduct structural informations. Numerous primary and secondary products were observed, corresponding to hydroxylated phenolic- or quinone-type compounds.     

Accelerated photo-transformation of 2,2′,4,4′,5,5′-hexachlorobiphenyl (PCB 153) in water by dissolved organic matter

The ubiquitous dissolved organic matter (DOM) has an important influence on transformation of organic contaminants through the production of reactive substances, such as ^?OH, ¹O₂, and ³DOM*. The photolysis of a higher chlorinated polychlorinated biphenyl (PCB) congener (2,2′,4,4′,5,5′-hexachlorobiphenyl, PCB 153) under simulated sunlight in presence of humic acid (HA) was investigated. Degradation of PCB 153 was accelerated significantly by the addition of HA, with a rate constant of 0.0214, 0.0413, and 0.0358 h^?1 in the initial 18 h of irradiation in presence of 1, 5, and 20 mg/L HA, respectively. The main photodegradation products analyzed by gas chromatography mass spectrometry were 4-hydroxy-2,2′,4′,5,5′-pentaCB and 2,4,5-trichlorobenzoic acid. Main reactive species involved were determined by the electron spin-resonance spectroscopy, including ¹O₂ and ^?OH. Special scavengers were added to elucidate the photolysis mechanisms. By using the specific scavengers, it turned out that ^?OH accounted for 29.3 % of the degradation, and the intra-DOM reactive species (¹O₂, ^?OH, and ³DOM*) accounted for 59.6 % of the degradation. Photo-transformation sensitized by DOM, which involves both aqueous and intra-DOM reactions of PCBs with reactive species, may be one of the most important mechanisms for natural attenuation of PCBs.     

Photochemical decomposition of environmentally persistent short-chain perfluorocarboxylic acids in water mediated by iron(II)/(III) redox reactions

The photochemical decomposition of short-chain (C(3)-C(5)) perfluorocarboxylic acids (PFCAs) was investigated. Direct photolysis in water proceeded slowly with the 220- to 460-nm light emission from a xenon-mercury lamp to form F(-), CO(2), and shorter-chain PFCAs. Addition of a small amount of Fe(3+) to the aqueous solutions of the PFCAs dramatically enhanced their photochemical decomposition under an oxygen atmosphere: when the (initial PFCA)/(initial Fe(3+)) molar ratio was 13.5 (initial PFCA concentration=67.3mM), the pseudo-first-order rate constants for the PFCA decomposition were 3.6-5.3 times those with photolysis alone, and the turnover number for the catalytic PFCA decomposition [i.e., (moles of decomposed PFCA)/(moles of initial Fe(3+))] reached 6.71-8.68 after 24h of irradiation. The catalysis can be explained by photoredox reactions between PFCA, Fe(3+)/Fe(2+) and oxygen via photo-induced complexation of Fe(3+) with the PFCAs.     

Degradation of RPA 202248 [U-14C-phenyl]alpha(-(cyclopropylcarbonyl)-2-(methylsulfonyl)-beta-oxo-4-(trifluromethyl)benzenepropanenitrile), the primary degradation product of isoxaflutole, in an outdoor aquatic microcosm system

Isoxaflutole, the active ingredient in BALANCE WDG and BALANCE PRO corn herbicides and a co-formulant with the herbicide flufenacet in the product EPIC, is readily degraded in soil and water to RPA 202248 alpha(-(cyclopropylcarbonyl)-2-(methyvlsulfonyl)-beta-oxo-4-(trifluromethyl)benzenepropanenitrile). Because RPA 202248 is responsible at the molecular level for isoxaflutole's herbicidal activity it is important to understand the environmental behavior of the degradation product. Laboratory studies suggest that RPA 202248 is stable to hydrolysis and photolysis in aqueous systems and hence poses a possible environmental concern. As part of a program of work towards understanding the actual field situation, an outdoor microcosm study was carried out. Over the course of the 29-day study, residues remained predominantly in the aqueous phase. A slow but steady degradation of RPA 202248 was observed leading to the formation of RPA 203328 (2-methylsulfonyl-4-trifluoromethylbenzoic acid), which has no herbicidal activity. The half-life of RPA 202248 was calculated to be 103 days. These findings indicate that aqueous degradation should be considered as a potential route of dissipation when assessing the fate of RPA 202248 in large scale impounded water bodies, such as ponds, lakes, or reservoirs in the Mid-West Corn Belt.     

Quantitation of Hydroxyl Radicals from Photolysis of Fe(III)-Citrate Complexes in Aerobic Water (5 pp)

Background For their high photoreactivity, Fe(III)-carboxylate complexes are important sources of H2O2 for some atmospheric and surface waters. Citrate is one kind of carboxylate, which can form complexes with Fe(III). In our previous study, we have applied Fe(III)-citrate complexes to degrade and decolorize dyes in aqueous solutions both under UV light and sunlight. Results have shown that carboxylic acids can promote the photodegradation efficiency. It is indicated that the photolysis of Fe(III)-citrate complexes may cause the formation of some reactive species (e. g. H2O2 and ·OH). This work is attempted to quantify hydroxyl radicals generated in the aqueous solution containing Fe(III)-citrate complexes and to interpret the photoreactivity of Fe(III)-citrate complexes for degrading organic compounds. Methods By using benzene as the scavenger to produce phenol, the photogeneration of ·OH in the aqueous solution containing Fe (III)-citrate complexes was determined by HPLC. Results and Discussion In the aqueous solution containing 60.0/30.0 mM Fe(III)/citrate and 7.0 mM benzene at pH 3.0, 96.66 mM ·OH was produced after irradiation by a 250W metal halide light (l ≥ 313 nm) for 160 minutes. Effects of initial pH value and concentrations of Fe(III) and citrate on ·OH radical generation were all examined. The results show that the greatest photoproduction of ·OH in the aqueous solution (pH ranged from 3.0 to 7.0) was at pH 3.0. The photoproduction of ·OH increased with increasing Fe(III) or citrate concentrations. Conclusion In the aqueous solutions containing Fe(III)-citrate complexes, ·OH radicals were produced after irradiation by a 250W metal halide light. It can be concluded that Fe(III)-citrate complexes are important sources of ·OH radicals for some atmospheric and surface waters. Recommendations and Outlook It is believed that the photolysis of Fe(III)-citrate complexes in the presence of oxygen play an important role in producing ·OH both in atmospheric waters and surface water where high concentrations of ferric ions and citrate ions exist. The photoproduction of ·OH has a high oxidizing potential for the degradation of a wide variety of natural and anthropogenic organic and inorganic substances. We can use this method for toxic organic pollutants such as organic dyes and pesticides.     

Evidence of singlet oxygen and hydroxyl radical formation in aqueous goethite suspension using spin-trapping electron paramagnetic resonance (EPR)

The generation of reactive species in an aqueous goethite suspension, under room light and aeration conditions, was investigated using the electron paramagnetic resonance (EPR) technique employing spin trap agents. The trap reagents, including 5,5-dimethylpyrroline N-oxide (DMPO) and 2,2,6,6-tetramethylpiperidine (TEMP), were used for the detection of OH radicals (OH) and singlet oxygen (¹O₂), respectively. On the addition of DMPO to the goethite suspended solution, a DMPO-OH adduct was formed, which was not decreased, even in the presence of the OH scavenger, mannitol. This result implied a false positive interpretation from the DMPO-OH EPR signal. In the presence of TEMP reagent, a TEMP-O signal was detected, which was completely inhibited in the presence of the singlet oxygen scavenger, sodium azide. With both DMPO-OH and TEMP-O radicals in the presence and absence of radical scavengers, singlet oxygen was observed to be the key species formed in the room-light sensitized goethite suspension. In the goethite/H₂O₂ system; however, both OH and singlet oxygen were generated, with significant portions of DMPO-OH resulting from both OH and singlet oxygen. In fact, the DMPO-OH resulting from OH should be carefully calculated by correcting for the amount of DMPO-OH due to singlet oxygen. This study reports, for the first time, that the goethite suspensions may also act as a natural sensitizer, such as fulvic acids, to form singlet oxygen.     

Degradation of RPA 202248 [U-14C-phenyl]-α(-(cyclopropylcarbonyl)-2-(methylsulfonyl)-β-oxo-4-(trifluromethyl)benzenepropanenitrile), the Primary Degradation Product of Isoxaflutole,in an Outdoor Aquatic Microcosm System

Abstract

Isoxaflutole, the active ingredient in BALANCE® WDG and BALANCE® PRO corn herbicides and a co-formulant with the herbicide flufenacet in the product EPIC?, is readily degraded in soil and water to RPA 202248 α(-(cyclopropylcarbonyl)-2-(methylsulfonyl)-β-oxo-4-(trifluromethyl)benzenepropanenitrile). Because RPA 202248 is responsible at the molecular level for isoxaflutole's herbicidal activity it is important to understand the environmental behavior of the degradation product. Laboratory studies suggest that RPA 202248 is stable to hydrolysis and photolysis in aqueous systems and hence poses a possible environmental concern. As part of a program of work towards understanding the actual field situation, an outdoor microcosm study was carried out. Over the course of the 29-day study, residues remained predominantly in the aqueous phase. A slow but steady degradation of RPA 202248 was observed leading to the formation of RPA 203328 (2-methylsulfonyl-4-trifluoromethylbenzoic acid), which has no herbicidal activity. The half-life of RPA 202248 was calculated to be 103 days. These findings indicate that aqueous degradation should be considered as a potential route of dissipation when assessing the fate of RPA 202248 in large scale impounded water bodies, such as ponds, lakes, or reservoirs in the Mid-West Corn Belt.     

Hydroxyl (OH) radical production rates in snowpacks from photolysis of hydrogen peroxide (H2O2) and nitrate (NO3−)

Atmospheric chemistry directly above snowpacks is strongly influenced by ultraviolet (UV) radiation initiated emissions of chemicals from the snowpack. The emission of gases from the snowpack to the atmosphere is in part due to chemical reactions between hydroxyl radical, OH (produced from photolysis of hydrogen peroxide (H₂O₂) or nitrate (NO₃⁻)) and impurities in the snowpack. The work presented here is a radiative-transfer modelling study to calculate the depth-integrated production rates of hydroxyl radical from the photolysis of hydrogen peroxide and nitrate anion in snow for four different snowpacks and for solar zenith angles 30°–90°. This work also demonstrates the importance of hydrogen peroxide photolysis to produce hydroxyl radical relative to nitrate photolysis with (a) different snowpacks, (b) different ozone column depths, and (c) snowpack depths. The importance of hydrogen peroxide photolysis over nitrate photolysis for hydroxyl radical production increases with increasing depth in snowpack, column ozone depth, and solar zenith angle. With a solar zenith angle of 60° the production of hydroxyl radical from hydrogen peroxide photolysis accounts for 91–99% of all hydroxyl radical production from hydrogen peroxide and nitrate photolysis.     

Photocatalytic mechanisms of indoleamine destruction by the quinalphos metabolite 2-hydroxyquinoxaline: a study on melatonin and its precursors serotonin and N-acetylserotonin

The redox-active quinalphos main metabolite, 2-hydroxyquinoxaline, is particularly effective under excitation by light. We have studied the photocatalytic destruction of melatonin and its precursors, because the cytoprotective indoleamine has been detected in high quantities in mammalian skin. In photooxidation reactions, in which melatonin, N-acetylserotonin and serotonin are destroyed by 2-hydroxyquinoxaline, the photocatalyst is virtually not consumed. Rates of melatonin and serotonin destruction are not changed by the singlet oxygen quencher 1,4-diazabicyclo-(2,2,2)-octane, indicating that this oxygen species is not involved in the primary reactions, so that the persistence of 2-hydroxyquinoxaline has to be explained by redox cycling. This should imply formation of an organic radical, presumably the quinoxaline-2-oxyl radical, from which 2-hydroxyquinoxaline is regenerated by electron abstraction from indolic radical scavengers. Electron donation by 2-hydroxyquinoxaline is demonstrated by reduction of the 2,2′-azino-bis-(3-ethylbenzthiazolinyl-6-sulfonic acid) cation radical under ultrasound excitation. The compound 2-hydroxyquinoxaline interacts with the specific superoxide anion scavenger Tiron. Formation of oligomeric products from melatonin and serotonin is strongly inhibited by sodium dithionite. Products from photocatalytic indolamine conversion are predominantly dimers and oligomers. No kynuramines were detected in the case of serotonin oxidation, and melatonin's otherwise prevailing oxidation product N ¹-acetyl-N ²-formyl-5-methoxykynuramine, another cytoprotective metabolite, is only formed in relatively small quantities. The proportion between products from melatonin is changed by 1,4-diazabicyclo-(2,2,2)-octane: singlet oxygen, also formed under the influence of excited 2-hydroxyquinoxaline, only affects secondary reactions.     

NaNO(2)/FeCl(3) catalyzed wet oxidation of the azo dye Acid Orange 7

A combination of ferric chloride and sodium nitrite significantly improved the wet oxidation of the azo dye Acid Orange 7 (AO7) in acid aqueous media (pH 2.6) under moderate conditions (T=150 degrees C; oxygen pressure=0.5 MPa). To evaluate the catalytic system, wet oxidation of AO7 was carried out at temperatures between 90 and 150 degrees C and oxygen pressures ranging from 0.1 to 0.5 MPa. The effect of initial solution pH from 2.6 to 11.4 and the amount of catalyst on the degradation of AO7 were also investigated. AO7 initial concentration was kept 200 mg L(-1). The degradation process was monitored by UV-visible spectroscopy, HPLC, IC (ion chromatography), GC-MS and TOC analysis. At 150 degrees C and 0.5 MPa oxygen pressure, 56% TOC was removed after 4h of treatment, while no obvious TOC removal were achieved without catalyst at the same experimental condition. The main degradation products were some small organic acids: formic acid, acetic acid, pyruvic acid, oxalic acid, succinic acid (identified and quantified by IC) and phthalic acid (identified by GC-MS).     

Photolysis of 2-(2-furyl)benzimidazole (Fuberidazole)

The photooxidatior. of 2-(4-thiazolyl)-1H-benzimidazole (Thia=bendazole (1) in methanol in presence and absence of a photo=sensitizer (methylene blue), is investigated. Dimethyl oxalate, thiazole-4-(N-carbomethoxy)-carboxamide (6), methyl benzimida=zole-2-carboxylate (7), benzimidazole-2-carboxamide (8), and benzimidazole (9), were the main products of the photolysis. Some reaction mechanisms are discussed.     

Surfactant effect on persistence of oxadiazolyl 3(2H)-pyridazinones against Pseudaletia separata walker

The photodynamic decomposition of two new insect-growth inhibitors (IGRs), 2-tert-butyl-5-[5′-aryl-2′-(1′,3′,4′-oxadiazolyl)methoxy]-3(2H)-pyridazinones (OPB) and its 4-chloro substituted derivative (OPC), and effect of surfactants on persistence of their bioactivity were taken into investigation. Both chemicals were significantly induced to photolysis by ultraviolet light at 365 nm wavelength and their inhibitory activities against Pseudaletia separata larvae decreased with the increasing irradiation time. However, irradiation at 254 nm wavelength didn't cause their photodegradation. Triton X-100 and Succinic-sulfonie acidic sodium but not Tween 60 possessed strong capability to slow down the decomposition and obviously prolonged the half life of OPC in laboratory and field whilst effects of the three surfactants almost did not preserve the inhibitory activity of OPB. Data suggested that electron-withdrawing halogen (?Cl) on the π electron system in planar benzene-oxadialyl structures might reduce the efficiency of OPC on ultraviolet (UV) photoabsorption, and its hydrophobic interaction with the surfactants might be beneficial for forming stable micellar solubilization, thus sustaining the chemical's bioactivity.     

Reactivity of cycloxydim toward singlet oxygen in solution and on wax film

The reactivity of the herbicide cycloxydim (CD) toward singlet oxygen was studied in organic solution and on wax films to mimic the leaf surface. Experiments in solution were conducted in acetonitrile using phenalenone as a sensitizer. For the experiments in the solid state, phenalenone was included in paraffinic wax films and CD deposited at the film surface. By laser flash photolysis we observed that the triplet of phenalenone reacts with CD with a bimolecular rate constant of (9.6 ± 1)×10⁶ M⁻¹ s⁻¹. However, scavenging experiments using β-carotene as a singlet oxygen quencher showed that the observed CD degradation in aerated acetonitrile involves singlet oxygen essentially. The bimolecular rate constant of reaction of CD with singlet oxygen was evaluated to (1.0 ± 0.2)×10⁷ M⁻¹ s⁻¹. Phenalenone included in the wax films also significantly increased the rate of CD photodegradation, the involvement of singlet oxygen being very likely. The photoproducts formed via the singlet oxygen pathway resulted from the oxidation of the thiol group and/or the cyclohexene ring. This study should help to better understand the fate of CD after its spraying on crops.     

Enhancement of heavy metal accumulation by tissue specific co-expression of iaaM and ACC deaminase genes in plants

The aerobic riboflavin (Rf)-sensitized photodegradation of the endocrine disruptor 4,4'-isopropylidenebisphenol (bisphenol A, BPA), and of the related compounds 4,4'-isopropylidenebis(2,6-dibromophenol) and 4,4'-isopropylidenebis(2,6-dimethylphenol) has been studied in water and water-methanol mixtures through visible-light continuous photolysis, polarographic detection of oxygen uptake, stationary and time-resolved fluorescence spectroscopy, time-resolved near-IR phosphorescence detection and laser flash photolysis techniques. Bisphenols (BPs) quench excited singlet and triplet states of Rf, with rate constants close to the diffusion limit. BPs and dissolved molecular oxygen, employed in similar concentrations, competitively quench triplet excited Rf. As a consequence, superoxide radical anion and singlet molecular oxygen (O(2)((1)Delta(g))) are produced by electron- and energy-transfer processes, respectively, as demonstrated by auxiliary experiments employing selective quenchers of both oxidative species and the exclusive O(2)((1)Delta(g)) generator Rose Bengal. As a global result, the photodegradation of Rf is retarded, whereas BPs are degraded, mainly by an O(2)((1)Delta(g))-mediated mechanism, which constitutes a relatively efficient process in the case of BPA. Oxidation, dimerization and fragmentation products have been identified in the photooxidation of BPA. Results indicate that BPs in natural waters can undergo spontaneous photodegradation under environmental conditions in the presence of adequate photosensitizers.     

Biotic and abiotic transformations of methyl tertiary butyl ether (MTBE)

Background Methyl tertiary butyl ether (MTBE) is a fuel additive which is used all over the world. In recent years it has often been found in groundwater, mainly in the USA, but also in Europe. Although MTBE seems to be a minor toxic, it affects the taste and odour of water at concentrations of < 30 μg/L. Although MTBE is often a recalcitrant compound, it is known that many ethers can be degraded by abiotic means. The aim of this study was to examine biotic and abiotic transformations of MTBE with respect to the particular conditions of a contaminated site (former refinery) in Leuna, Germany. Methods Groundwater samples from wells of a contaminated site were used for aerobic and anaerobic degradation experiments. The abiotic degradation experiment (hydrolysis) was conducted employing an ion-exchange resin and MTBE solutions in distilled water. MTBE, tertiary butyl formate (TBF) and tertiary butyl alcohol (TBA) were measured by a gas chromatograph with flame ionisation detector (FID). Aldehydes and organic acids were respectively analysed by a gas chromatograph with electron capture detector (ECD) and high-performance ion chromatography (HPIC). Results and Discussion Under aerobic conditions, MTBE was degraded in laboratory experiments. Only 4 of a total of 30 anaerobic experiments exhibited degradation, and the process was very slow. In no cases were metabolites detected, but a few degradation products (TBF, TBA and formic acid) were found on the site, possibly due to the lower temperatures in groundwater. The abiotic degradation of MTBE with an ion-exchange resin as a catalyst at pH 3.5 was much faster than hydrolysis in diluted hydrochloric acid (pH 1.0). Conclusion Although the aerobic degradation of MTBE in the environment seems to be possible, the specific conditions responsible are widely unknown. Successful aerobic degradation only seems to take place if there is a lack of other utilisable compounds. However, MTBE is often accompanied by other fuel compounds on contaminated sites and anaerobic conditions prevail. MTBE is often recalcitrant under anaerobic conditions, at least in the presence of other carbon sources. The abiotic hydrolysis of MTBE seems to be of secondary importance (on site), but it might be possible to enhance it with catalysts. Recommendation and Outlook MTBE only seems to be recalcitrant under particular conditions. In some cases, the degradation of MTBE on contaminated sites could be supported by oxygen. Enhanced hydrolysis could also be an alternative. - * The basis of this peer-reviewed paper is a presentation at the 9th FECS Conference on 'Chemistry and Environment', 29 August to 1 September 2004, Bordeaux, France.     

Photolytic degradation of hexacyanoferrate (II) in aqueous media: the determination of the degradation kinetics

Upon exposure to ultraviolet (UV) radiation, non-toxic hexacyanoferrate (II) (Fe(CN)6(-4)) undergoes direct photolysis, resulting in the liberation of toxic free cyanide (HCN,CN-). This experimental study employed manipulation of several environmental parameters with the objective of characterizing their effects on the photolysis rate of hexacyanoferrate (II). The photolysis rate was not affected significantly by varying (1) the initial hexacyanoferrate (II) concentration (from 10 to 400 microg/l as total CN), (2) the solution turbidity (kaolin clay concentration from 0 to 5 mg/l), and (3) pH (from pH 4 to 12). Parameters that exhibited a significant effect (significance level, alpha < 0.05) on the photolysis rate included the intensity of incident ultraviolet radiation (from 30 to 110 micromol/m2s photons) and the concentration of dissolved organic matter (color) from added humic acid (from 0 to 10 mg/l). In addition, observations made by spiking both deionized and natural waters demonstrated that the rate of hexacyanoferrate (II) photolysis (1) significantly exceeded the rate of free cyanide formation from photolysis and (2) exhibited significant retardation that directly depended on the free cyanide concentration in solution. The hexacyanoferrate (II) photolysis data were consistent with a simple, semi-empirical kinetic model that included the reversible formation of at least one cyanoferrate intermediate. The reverse reaction, in turn, behaved in a manner that was consistent with a second order rate law with respect to free cyanide concentration.     

Genotoxic effect of ciprofloxacin during photolytic decomposition monitored by the in vitro micronucleus test (MNvit) in HepG2 cells

Purpose

Ciprofloxacin (CIP), a broad-spectrum, second-generation fluoroquinolone, has frequently been found in hospital wastewaters and effluents of sewage treatment plants. CIP is scarcely biodegradable, has toxic effects on microorganisms and is photosensitive. The aim of this study was to assess the genotoxic potential of CIP in human HepG2 liver cells during photolysis.

Methods

Photolysis of CIP was performed in aqueous solution by irradiation with an Hg lamp, and transformation products were monitored by HPLC-MS/MS and by the determination of dissolved organic carbon (DOC). The cytotoxicity and genotoxicity of CIP and of the irradiated samples were determined after 24?h of exposure using the WST-1 assay and the in vitro micronucleus (MN) test in HepG2 cells.

Results

The concentration of CIP decreased during photolysis, whereas the content of DOC remained unchanged. CIP and its transformation products were not cytotoxic towards HepG2 cells. A concentration-dependent increase of MN frequencies was observed for the parent compound CIP (lowest observed effect level, 1.2???mol?L^?1). Furthermore, CIP and the irradiated samples were found to be genotoxic with a significant increase relative to the parent compound after 32?min (P?P?Conclusions Photolytic decomposition of aqueous CIP leads to genotoxic transformation products. This proves that irradiated samples of CIP are able to exert heritable genotoxic effects on human liver cells in vitro. Therefore, photolysis as a technique for wastewater treatment needs to be evaluated in detail in further studies, not only for CIP but in general.     

Genotoxic fungicide methyl thiophanate as an oxidative stressor inducing 8-oxo-7,8-dihydro-2′ -deoxyguanosine adducts in DNA and mutagenesis

Dimethyl 4,4′ -(O-phenylene)bis(3-thioallophanate), commonly known as methyl thiophanate (MT), is a systemic fungicide and suspected carcinogen to humans. In this study, the oxidative potential of this category-III acute toxicant has been ascertained based on its capacity of inducing reactive oxygen species (ROS) and promutagenic 8-oxo-7,8-dihydro-2′ -deoxyguanosine (8-oxodG) adducts in DNA. The discernible MT dose-dependent reduction in fluorescence intensity of a cationic dye rhodamine (Rh-123) in human lymphocytes and increased fluorescence intensity of 2′,7′-Dichlorodihydro fluorescein diacetate (DCFH-DA) treated cells signifies decreased mitochondrial membrane potential (Δ Ψ m) due to intracellular ROS generation. The ³²P-post-labeling assay demonstrated the MT-induced 8-oxodG adduct formation in calf thymus DNA. Thus, it is concluded that MT, as a potent oxidative stressor, produces ROS leading to mitochondrial dysfunction, oxidative DNA damage and mutagenesis.