Photochemical acetochlor degradation induced by hydroxyl radical in Fe-amended wetland waters: Impact of pH and dissolved organic matter.

Iron (Fe) plays a critical role in the formation of hydroxyl radical (OH) which may participate in the indirect photodegradation of aquatic contaminants. While Fe photochemistry has been extensively studied, the efficacy of iron amendments for contaminant attenuation in sunlit natural waters has not been well researched. We studied the efficacy of this approach by monitoring OH induced acetochlor (AC) degradation and determining OH production rates with terephthalate (TPA) as a probe. Surface wetland waters as well as model fulvic acid (FA) solutions were amended with Fe(III) salt at different concentrations at pH values of 2.7, 5, and 7.6. We observed no significant enhancement in the AC degradation rate at circumneutral pH. At pH 5, AC degradation increased by more than 50% with an Fe addition up to an [Fe]T ≈ 6 µM and plateaued at high [Fe]T. At the highly acidic pH of acid mine drainage (AMD) waters, AC degradation was enhanced by two-orders-of magnitude with increasing [Fe]T and no plateau was observed under the conditions tested ([Fe]T ≤ 500 µM). While the Fe induced relative difference in OH production rates determined using TPA was useful in elucidating the reaction mechanism for different dissolved organic matter types at different pH values, the absolute value of OH production rates over-predicted the transformation of AC suggesting the existence of unknown side reactions and/or alternative reactive intermediates.

Zn- vs Bi-based oxides for o-toluidine photocatalytic treatment under solar light.

The photodegradation of the highly toxic o-toluidine pollutant was deeply investigated both under UV and solar irradiations by using three different semiconductors: pure ZnO, Bi-impregnated ZnO, and Bi2O3 nanopowders (synthesized by precipitating method). All the samples were deeply characterized on structural, morphological, surface, and optical points of view. The disappearance and the relative mineralization of o-toluidine molecules were followed by linear sweep voltammetry (LSV) and total organic carbon (TOC) determinations, respectively. Hence, correlations between their physico-chemical properties and the photocatalytic performances, passing from UV to solar light, were drawn and a hypothesis on the photodegradation mechanism has been proposed, on the basis of the HPLC/MS results. Bare Bi2O3 samples, due to the exploitation of both their visible light absorption and the negligible intermediates formation, resulted to be higher performing under solar irradiation than either pure or Bi-doped ZnO nanopowders. Graphical abstract.

A derivative photoelectrochemical sensing platform for herbicide acetochlor based on TiO2-poly (3-hexylthiophene)-ionic liquid nanocomposite film modified electrodes.

Nonelectroactive acetochlor can be indirectly determined through the photocatalytical degradation of acetochlor. A derivative visible light photoelectrochemical sensor for indirect detection of the herbicide acetochlor using TiO2-poly(3-hexylthiophene)-ionic liquid nanocomposite is constructed. Poly(3-hexylthiophene) (P3HT) was synthesized via chemical oxidative polymerization with anhydrous FeCl3 as oxidant, 3-hexylthiophene as monomer, chloroform as solvent, and the functional TiO2 nanoparticles were facilely prepared by blending TiO2 nanoparticles and P3HT at room temperature ionic liquid, 1-Butyl-3-methylimidazolium hexafluorophosphate solution. Operational parameters, including the photolysis time, ratios of TiO2 to P3HT, bias voltage and pH of buffer solution have been optimized. Under optimal conditions, the proposed photoelectrochemical method could detect acetochlor ranging from 0.5 to 20 µmol L(-1) with a detection limit of 0.2 nmol L(-1) at a signal-to-noise ratio of 3. The assay results of acetochlor in water samples with the proposed method were in acceptable agreement with those of the gas chromatograph-mass spectrometer (GC-MS) method. The promising sensor opens a new opportunity for fast, portable, and sensitive analysis of acetochlor in environmental samples.

Contaminant-mediated photobleaching of wetland chromophoric dissolved organic matter.

Photolytic transformation of organic contaminants in wetlands can be mediated by chromophoric dissolved organic matter (CDOM), which in turn can lose its reactivity from photobleaching. We collected water from a small agricultural wetland (Ohio), Kawai Nui Marsh (Hawaii), the Everglades (Florida), and Okefenokee Swamp (Georgia) to assess the effect of photobleaching on the photofate of two herbicides, acetochlor and isoproturon. Analyte-spiked water samples were irradiated using a solar simulator and monitored for changes in CDOM light absorbance and dissolved oxygen. Photobleaching did not significantly impact the indirect photolysis rates of either herbicide over 24 hours of irradiation. Surprisingly, the opposite effect was observed with isoproturon, which accelerated DOM photobleaching. This phenomenon was more pronounced in higher-CDOM waters, and we believe that the redox pathway between triplet-state CDOM and isoproturon may be responsible for our observations. By contrast, acetochlor indirect photolysis was dependent on reaction with the hydroxyl radical and did not accelerate photobleaching of wetland water as much as isoproturon. Finally, herbicide indirect photolysis rate constants did not correlate strongly to any one chemical or optical property of the sampled waters.

Using mass spectrometry to highlight structures of degradation compounds obtained by photolysis of chloroacetamides: case of acetochlor.

The photooxidation of acetochlor (a pesticide belonging to the acetamides group) using a polychromatic UV irradiation in ultrapure water was studied. This study reports the efficiency of mass spectrometry for the characterization of photodegradation products of acetochlor. Decompositions of protonated ions MH+are proposed in electrospray (ESI) mode for LC­MS, while electron ionization (EI) and chemical ionization modes (CI) are used for GC­MS. The knowledge of fragmentation and the use of a combination of experiments (MS/MS, high resolution) allow the characterization of photoproducts. Structural elucidation is assisted by the use of photolysed deuterated compounds. Fifteen major degradation products have been characterized, five by LC-QTOF, six photoproducts by GC-ITMS, and four are observed by both techniques. In vitro bioassays based on the quantification of receptor-mediated activity demonstrated that acetochlor photolysis engenders a moderate but significant estrogenic activity. Moreover, a quantitative structure­activity relationship (QSAR) approach was used to assess the potential toxicity effect of acetochlor and its by-products. The predictions were analyzed showing a variety of toxicity profiles of acetochlor photoproducts depending on the toxicological investigated endpoint.

Photocatalytic decomposition of crotamiton over aqueous TiO(2) suspensions: determination of intermediates and the reaction pathway.

The photocatalytic degradation of crotamiton in aqueous solution using TiO(2) was investigated. To investigate the effect of initial pH, the photodegradation behaviors of three types of pharmaceuticals were compared (crotamiton, clofibric acid, sulfamethoxazole). The degradation rates of crotamiton in the pH range 3-9 were nearly equal, but those of clofibric acid and sulfamethoxazole were affected by pH. At pH>6.5, TiO(2) particles, clofibric acid and sulfamethoxazole had negative charge, therefore, the repulsive force between TiO(2) particles and anionic pharmaceuticals occurred and a low reaction rate at high pH was observed. The effect of UV intensity and TiO(2) concentration on photodegradation efficiency was also investigated. Linear and logarithmical relationships between UV intensity, TiO(2) concentration and the reaction rate constant were confirmed. Furthermore, the structures of photodegradation intermediates formed concomitantly with the disappearance of crotamiton were estimated. Seven intermediates were characterized by LC/MS/MS analyses, and it was assumed that the photocatalytic degradation of crotamiton was initiated by the attack of electrophilic hydroxyl radicals on aromatic rings and alkyl chains.

Protective effects of antioxidants on micronuclei induced by irradiated 9-fluorenone/N,N-dimethyl-p-toluidine in CHO cells.

9-Fluorenone (9F), the aromatic photosensitizer, is widely used as an initiator in visible-light (VL) cured resin systems. There is growing concern that 9F may produce genetic damage by inducing mutation. In this study, 9F in the presence or absence of reducing agent N,N-dimethyl-p-toluidine (DMT) with or without VL irradiation was analyzed for the induction of chromosomal aberrations indicated by micronuclei (MN) induced in CHO cells. Our data demonstrated that a dose-related increase in the frequency of MN and prolonged cell cycles in 9F with or without DMT in the presence or absence of VL irradiation (p < 0.05). The rank orders with respect to genotoxicity and cytotoxicity were found to be as follows: 9F/DMT +VL > 9F/DMT = 9F + VL > 9F. To determine whether oxidative stress could modulate MN induced by 9F/DMT with or without VL irradiation in CHO cells, cells were pretreated with N-acetyl-L-cysteine (NAC), ascorbic acid, and alpha-tocopherol. The pretreatment with antioxidants could diminish not only the prolonged cell cycle but also the decreased frequency of MN which is induced by 9F with or without DMT in the presence or absence of VL irradiation in CHO cells (p < 0.05). Our findings provide the evidences for the induction of MN by 9F in the presence or absence of DMT with or without VL irradiation in CHO cells, indicating clastogenic activity of 9F/DMT in vitro. These antioxidants act as the antagonists against the genotoxicity and cytotoxicity of 9F/DMT. Thus, leaching photoinitiator and reducing agent might be contributing the sources of oxidative stress.

Microbial toxicity of pesticide derivatives produced with UV-photodegradation.

Our study aimed at acquiring information about the biological effect of pesticides and their degradates produced by UV-treatment on microbiological activity. Five photosensitive pesticides (carbendazim, acetochlor, simazine, chlorpyrifos, EPTC) and six representative soil microbes (Bacillus subtilis, Pseudomonas fluorescens, Mycobacterium phlei, Fusarium oxysporum, Penicillium expansum, Trichoderma harzianum) were applied throughout our model experiments. The antimicrobial effects of the pesticides and their degradates were assessed with filter paper disk method. The antimicrobial effect of the degradation products exhibited marked differences in terms of pesticide types, irradiation time, and the test organisms. Acetochlor and its photolytic degradation products were found to be more toxic to bacteria than fungi. All the three bacteria proved to be sensitive to the basic compound and its degradation products as well. The end product of carbendazim was weakly antibacterial against P. fluorescens and B. subtilis but strongly antifungal against T. harzianum. Chlorpyrifos and its end product inhibited neither test organisms, but the degradates hindered the growth of four of them. The basic compound of EPTC and the degradates of simazine exhibited significant toxicity to the test bacteria. It might be claimed that the pesticide photodegradation may result in significant changes in soil microbiota, as well as formation of biologically harmful degradates.

Effects of combinations of ROS scavengers on oxidative DNA damage caused by visible-light-activated camphorquinone/N,N-dimethyl-p-toluidine.

The objective of this investigation was to analyze whether various combinations of the ROS scavengers glutathione (GSH), N-acetyl-cysteine (NAC), and vitamins C and E decrease DNA damage due to visible-light-irradiated (VL-irradiated) camphorquinone/N,N-dimethyl-p-toluidine (CQ/DMT) compared with individual vitamin C or E. PhiX-174 RF plasmid DNA was used to determine single and double strand breaks as parameters of DNA damage. Individual ROS scavengers and combinations of the antioxidants were added to plasmid DNA treated with VL-irradiated CQ/DMT/Cu (II). After incubation, DNA was loaded into a 1% agarose gel. Following electrophoresis, gels stained with 0.5 microg/mL ethidium bromide were photographed under ultraviolet illumination and analyzed with NIH ImageJ software. Results were evaluated between groups for statistical significance using Student's paired t-test (p < 0.05). Glutathione significantly reduced oxidative DNA damage at all test concentrations when combined with vitamin C or vitamin E. The concentration of damaged DNA observed in the presence of combinations of GSH with vitamin C or vitamin E was significantly lower compared with all other combinations of antioxidants investigated in our study (p < 0.05). In contrast to GSH, NAC was not able to compensate the pro-oxidative effects of vitamin C and vitamin E. Only at a concentration of 2 mM, NAC combined with vitamin C efficiently prevented CQ/DMT/Cu (II)-associated DNA damage. Our data indicate that solely the combinations of GSH with vitamin C or vitamin E significantly reduce the severity of oxidative DNA damage caused by CQ/DMT, whereas NAC may even increase the pro-oxidant activity of vitamin C and vitamin E.

Effect of humic acids on photodegradation of chloroacetanilide herbicides under UV irradiation.

The effects of two humic acids (HAs) of different origins on the photodegradation of the chloroacetanilide herbicides acetochlor, propisochlor and butachlor were investigated in this study. One of the tested HAs was a standard sample that was purchased from a commercial source, and the other was isolated from the black soil of Northeast China. The photolysis of all three herbicides followed pseudo-first-order kinetics under ultraviolet (UV) irradiation conditions, regardless of whether HAs were present or not. Both HAs improved the photolysis rates of acetochlor in a dose-reversed way, whereas they inhibited butachlor degradation under all experimental concentrations. The two HAs differed in their effects on propisochlor photolysis, changing from enhancement to inhibition, depending on the origin and concentration of HAs. Element and Fourier Transform Infrared spectroscopy analyses showed that the isolated HAs had more polysaccharides and less aliphatic groups than the commercial HAs, and it was indicated that some characteristic radicals (C=O, O-H and phenolic hydroxyls) in HAs were involved in the photolysis of the herbicides. Gas chromatography/mass spectrometry (GC/MS) analyses indicated that the presence of HAs had no effects on the photolysis pathway and photoproduct species of the three herbicides.

The effect of antioxidants on oxidative DNA damage induced by visible-light-irradiated camphorquinone/N,N-dimethyl-p-toluidine.

Previous investigations have found that visible-light (VL)-irradiated camphorquinone (CQ), in the presence of a tertiary amine (e.g., N,N-dimethyl-p-toluidine, DMT), generates reactive oxygen species and causes oxidative DNA damage in vitro. In this study, oxidative DNA damage produced by VL-irradiated CQ/DMT, in the presence and absence of antioxidants (glutathione, N-acetyl-L-cysteine (NAC), mannitol, vitamin C, and vitamin E), was measured by the conversion of PhiX-174 RF I supercoiled (SC) double-stranded plasmid DNA into open and linear forms. VL-irradiated CQ/DMT, lacking antioxidant, damaged 99.4 +/- 1% of the PhiX-174 RF I SC double-stranded plasmid DNA. Our results revealed that glutathione (10.0, 5.0, 2.5, 1.0, and 0.5 mm) and NAC (10.0, 5.0, and 2.5 mm) significantly (p < 0.02) reduced oxidative DNA damage produced by VL-irradiated CQ/DMT. Vitamin E, vitamin C, and mannitol were ineffective at reducing oxidative DNA damage produced by VL-irradiated CQ/DMT. Furthermore, vitamin E (10.0 and 5.0 mm) and vitamin C (10.0, 5.0, 2.5, 1.0, 0.5 mm) treatment significantly (p < 0.02) enhanced VL-irradiated CQ/DMT-induced oxidative DNA damage and caused significant (p < 0.001) DNA damage following VL-irradiation in the absence of CQ/DMT. As a result, future studies should evaluate whether glutathione and NAC effectively reduce or prevent oxidative damage induced by VL-irradiated CQ/DMT in vivo.

Kinetics and mechanisms of radiation-induced degradation of acetochlor.

The radiation-induced degradation of acetochlor was investigated in this work. In a mixed solvent composed of acetonitrile and water at a ratio of 20/80 in volume, the acetochlor degradation rate was proportional to the radiation dose rate and acetochlor concentration. The acetochlor degradation efficiency was higher under alkali conditions and lower under acidic conditions. The contribution to the acetochlor degradation by the radicals was in the order of: e(aq)->.OH>H.. The quantum efficiency ratios of .OH, e(aq)- and H. for the degradation of acetochlor were calculated as 1:3:1.

Photolysis of fluchloralin in aqueous methanol.

The photodegradation of fluchloralin by UV irradiation or sunlight in aqueous methanolic solution has been examined. In the presence of titanium dioxide five photoproducts were obtained, but only four in its absence. One photoproduct, 2, 2'-azoxy-bis(alpha,alpha,alpha-trifluoro-6-nitro-p-toluidine) is reported for the first time as a metabolite of fluchloralin. In natural sunlight the rate of degradation was higher than in UV light and titanium dioxide had almost no effect on the rate of degradation.

Development of new photopolymerizable dental sealants.

This paper describes the results obtained in the optimization of the composition of dental sealants in relation to the nature and proportions of monomer mixtures and photoinitiating system employed. The quantification and variation of certain parameters which determine the quality of a dental sealant (such as viscosity and penetrating power, residual double bonds, solubility and absorption, volume shrinkage and certain specific mechanical properties) have resulted in the development of new formulations. The composition which has achieved the best results of all the above properties was that corresponding to the monomer mixture bis-GMA/tri(ethylene glycol) dimethacrylate (TEGDMA) 40/60 wt%, and the photoinitiating system camphorquinone (CQ) with co-initiators N,N,3,5-tetramethyaniline (TMA) or N,N-dimethyl-p-toluidine (DMPT) in the ratio 1:1. The final properties and characteristics of the obtained formulations are superior to those of commercial dental sealants currently in use.

Photochemical degradation of acetochlor.

Photochemical degradation of acetochlor--2-chloro-N-(ethoxymethyl)-N-(2-ethyl-6-methyl-phenyl)- acetamid--was studied at ambient temperature. The herbicide was irradiated by UV-light in methanol and water-methanol solvent mixture. It was found that the photodecomposition of acetochlor obeys first order kinetics under the condition of photolysis. The half-life of the reactant was found as 1.2 h in water-methanol solvent mixture, while just half of that could be observed in pure methanol. The first step of the photolysis is the dehalogenation which is indicated by fast increasing of chloride concentration in the solution, and simultaneously an equivalent amount of protons is forming, too. The aromatic ring seems to be intact but the substituents connected to the nitrogen can be changed in many different ways. Among the photo-products 10 metabolites were identified by GC-MS method, they showed higher photochemical stability than the parent herbicide.