Oxidative degradation of emerging micropollutant acesulfame in aqueous matrices by UVA-induced H2O2/Fe2+ and S2O82-/Fe2+ processes.

In the present study, UVA/H2O2/Fe2+ and UVA/S2O82-/Fe2+ processes were applied to degrade the artificial sweetener, acesulfame (ACE) in ultrapure water (UW), groundwater (GW), and secondary effluent (WW). The degradation time and mineralization of 75 µM of ACE determined the efficacy of the procedures. The results indicated that the UVA-induced H2O2/Fe2+ and S2O82-/Fe2+ systems are a promising alternative for the removal of ACE from different aqueous matrices as both studied processes completely degraded the target compound at an ACE/oxidant/Fe2+ molar ratio of 1/10/1 and pH 3. In the case of UVA-induced systems application without pH adjustment, the ACE decomposition was achieved only in ultrapure water. The maximum mineralization of ACE in ultrapure water by the UVA/H2O2/Fe2+ system (molar ratio of 1/10/1) at pH 3 resulted in residual TOC of 18.3%. The oxidative effectiveness of the UVA/S2O82-/Fe2+ system was proved to be mainly formed by the hydroxyl radicals. The obtained results indicate that UVA light can be successfully used for the oxidation of the studied artificial sweetener in various aqueous matrices with carefully adjusted process conditions.

The oxidative stress in the liver of Carassius auratus exposed to acesulfame and its UV irradiance products.

Acesulfame (ACE) is listed as an emerging contaminant due to its environmental persistence and wide occurrence in the environment. ACE can be degraded partially in the regular UV disinfection process but the eco-toxicity of its irradiation products remains unclear. This study focused on the possible oxidative status change in the liver of Carassius auratus exposed to ACE and its irradiation products. The UV degradation of ACE follows pseudo-first-order kinetics, and eight irradiation products were identified. Fish were exposed 7days to 0.1 and 10mg/L ACE (ACE group) and ACE after UV irradiance (ACE-UV group). The oxidative stress in fish liver exposed to ACE group had no distinct change. However, in the ACE-UV group, the quantity of OH was induced by 17.96-55% and the MDA content increased by 16.28-68.28% compared to control. Time-effect exposure in the ACE-UV group showed that in the first 3days the quantity of OH reached its peak, causing severe inhibition of SOD and continuous inducement of GPx. GSH helped scavenge OH and decreased below control after 3days. An increased toxicity of ACE after UV irradiance was observed and its transfer after into aquatic environment needs to be recognized as an environmental risk.

Degradation of artificial sweeteners via direct and indirect photochemical reactions.

We studied the direct and indirect photochemical reactivity of artificial sweeteners acesulfame, saccharin, cyclamic acid and sucralose in environm entally relevant dilute aqueous solutions. Aqueous solutions of sweeteners were irradiated with simulated solar radiation (>290 nm; 96 and 168 h) or ultraviolet radiation (UVR; up to 24 h) for assessing photochemical reactions in surface waters or in water treatment, respectively. The sweeteners were dissolved in deionised water for examination of direct photochemical reactions. Direct photochemical reactions degraded all sweeteners under UVR but only acesulfame under simulated solar radiation. Acesulfame was degraded over three orders of magnitude faster than the other sweeteners. For examining indirect photochemical reactions, the sweeteners were dissolved in surface waters with indigenous dissolved organic matter or irradiated with aqueous solutions of nitrate (1 mg N/L) and ferric iron (2.8 mg Fe/L) introduced as sensitizers. Iron enhanced the photodegradation rates but nitrate and dissolved organic matter did not. UVR transformed acesulfame into at least three products: iso-acesulfame, hydroxylated acesulfame and hydroxypropanyl sulfate. Photolytic half-life was one year for acesulfame and more than several years for the other sweeteners in surface waters under solar radiation. Our study shows that the photochemical reactivity of commonly used artificial sweeteners is variable: acesulfame may be sensitive to photodegradation in surface waters, while saccharin, cyclamic acid and sucralose degrade very slowly even under the energetic UVR commonly used in water treatment.

Effect of dissolved ozone or ferric ions on photodegradation of thiacloprid in presence of different TiO2 catalysts.

Combining TiO(2) photocatalysis with inorganic oxidants (such as O(3) and H(2)O(2)) or transition metal ions (Fe(3+), Cu(2+) and Ag(+)) often leads to a synergic effect. Electron transfer between TiO(2) and the oxidant is usually involved. Accordingly, the degree of synergy could be influenced by TiO(2) surface area. With this in mind, the disappearance of thiacloprid, a neonicotinoid insecticide, was studied applying various photochemical AOPs and different TiO(2) photocatalysts. In photocatalytic ozonation experiments, synergic effect of three different TiO(2) photocatalysts was quantified. Higher surface area resulted in a more pronounced synergic effect but an increasing amount of TiO(2) did not influence the degree of the synergy. This supports the theory that the synergy is a consequence of adsorption of ozone on the TiO(2) surface. No synergy was observed in photocatalytic degradation of thiacloprid in the presence of dissolved iron(III) species performed under varied experimental conditions (concentration, age of iron(III) solution, different TiO(2) films, usage of TiO(2) slurries). This goes against the literature for different organic compounds (i.e., monuron). It indicates different roles of iron(III) in the photodegradation of different organic molecules. Moreover, TiO(2) surface area did not affect photodegradation efficiency in iron(III)-based experiments which could confirm absence of electron transfer between TiO(2) photocatalyst and iron(III).

Photocatalytic degradation of basic blue 9 by CoS nanoparticles supported on AlMCM-41 material as a catalyst.

In this investigation photocatalytic degradation of basic blue 9 or methylene blue (MB) as color pollutants was studied. Cobalt sulfide was supported on AlMCM-41 material using ion-exchange method. The results show that CoS/AlMCM-41 is an active photocatalyst. The catalyst is characterized by X-ray diffraction (XRD) UV-vis diffused reflectance spectra (UV-vis DRS) and scanning electron microscopy (SEM) techniques. The maximum effect of photodegradation was observed at 7 wt% CoS/AlMCM-41. Pseudo-first order reaction with k=0.032 was observed for the photocatalytic degradation reaction. The effect of some parameters such as pH, amount of photocatalyst and initial concentration of dye were also examined. The effect of dosage of photocatalyst was studied in the range 0.04-1.2g/L. It was seen that 0.8 g/L of photocatalyst is an optimum value for the dosage of photocatalyst. In the best conditions, the degradation efficiency was obtained 0.32 ppm for MB dye.

Effect of light on the degradation of two neonicotinoids viz acetamiprid and thiacloprid in soil.

Persistence of two neonicotinoids viz thiacloprid and acetamiprid in soil as affected by UV and sunlight exposure was studied. Treated soil was placed in petri-plates, brought to field capacity moisture and then exposed to UV and sunlight. Dissipation for both the pesticides followed monophasic first order kinetics under sunlight, however under UV-light biphasic dissipation was recorded. Residues of acetamiprid and thiacloprid in soil dissipated with half-lives of 11.1 and 12.8 days under UV light and 25.1 and 19.1 days under sunlight, respectively. Residues of both the neonicotinoids dissipated quickly under UV light as compared to sunlight. Exposure of thin film of acetamiprid and thiacloprid to UV and sunlight revealed that acetamiprid is more photo labile than thiacloprid. More than 95% acetamiprid dissipated within 24 h as compared to approximately 70% dissipation observed for thiacloprid.

Ultrafast absorption and photothermal studies of decarboxytrichochrome C in solution.

The trichrochromes are natural constituents of pheomelanins. Herein, time-resolved spectroscopic techniques are used to quantify the energetics and dynamics of the primary photoprocesses of trichochromes following excitation into the lowest excited singlet state of the molecule. The absorption spectrum of decarboxytrichochrome C (dTC) reveals multiple electronic states are accessible upon visible and UV excitation. Emission is not observed upon excitation into the lowest energy absorption band. Photothermal measurements reveal 91% of the photon energy is promptly released as heat. Femtosecond time-resolved absorption studies reveal a ground-state recovery time of approximately 2.4 ps. Complete recovery of the ground state is not observed; 15% of the initially excited molecules do not recover on the approximately 150 ps timescale. The combination of ultrafast absorption and photoacoustic data suggest photoexcitation produces a long-lived intermediate and the energy of this species is at least 133 kJ mol(-1) above the ground state of the dTC molecule.

Piroxicam-induced photosensitivity. In vivo and in vitro studies of its photosensitizing potential.

A 36-year-old woman developed a photolocalized erythematous papulovesicular eruption while taking piroxicam. Histologic study revealed a superficial and deep spongiotic dermatitis. Phototesting with ultraviolet B (UVB) and ultraviolet A (UVA) was abnormal at the time the patient was seen and after oral challenge with the drug for 5 days. A modified lymphocyte transformation test was positive. The photosensitizing potential of the drug was evaluated in vivo and in vitro. In vivo studies consisted of phototesting twelve medical students before and after intake of piroxicam during 5 consecutive days. No lowering of the minimal erythema dose (MED) values or abnormal reactions to UV and visible light were observed in these students. In vitro studies by the Candida plate method and by photohemolysis showed negative results. Our studies suggest a systemic photoallergy mechanism requiring wavelengths in the UVA range for the reaction. This drug should be avoided in patients receiving photochemotherapy.

[Radiation-induced binding of 2-amino-5,6-dihydro-1,3-4H-thiazine to DNA]. / O radiatsionno indutsirovannom sviazyvanii 2-amino-5,6-digidro-1,3-4H-tiazina s DNK.

A study was made of the nature of radiation--induced bonds between DNA and 2-amino-5,6-dehydro-4H-thiazine (2-ADT) having a radioprotective action. Using the gelfiltration method and 35S-2-ADT, it was shown that the amount of the radioprotector bound to DNA increased with radiation dose and did not depend on the postirradiation treatment with 3 M LiCl or 3 M urea. No marked binding was noted after mixing the separately exposed DNA and the protector. It is concluded that a covalent linkage of DNA and 2-ADT occurs, upon irradiation, via short-living states of DNA and (or) the protector.