Ultraviolet absorption redshift induced direct photodegradation of halogenated parabens under simulated sunlight.

As disinfection by-products of parabens, halogenated parabens are frequently detected in aquatic environments and exhibit higher persistence and toxicity than parabens themselves. An interesting phenomenon was found that UV absorption redshift (∼45 nm) occurs after halogenation of parabens at circumneutral pH, leading to overlap with the spectrum of terrestrial sunlight. This work presents the first evidence on the direct photodegradation of seven chlorinated and brominated parabens under simulated sunlight. These halogenated parabens underwent rapid direct photodegradation, distinguished from the negligible degradation of the parent compounds. The photodegradation rate depended on their forms and substituents. The deprotonation of halogenated parabens facilitated the direct photodegradation. Brominated parabens exhibited higher degradation efficiency than chlorinated parabens, and mono-halogenated parabens had higher degradation than di-halogenated parabens. The pseudo-first-order rate constants (kobs) for brominated parabens (0.075-0.120 min-1) were approximately 7-fold higher than those of chlorinated parabens (0.011-0.017 min-1). A quantitative structure-activity relationship (QSAR) model suggested that the photodegradation was linearly correlated with the C-X bond energies, electronic and steric effects of halogen substituents. The photodegradation products were identified using QTOF-MS analyses and a degradation pathway was proposed. The yeast two-hybrid estrogenicity assay revealed that the estrogenic activities of the photoproducts were negligible. These findings are important for the removal of halogenated parabens and predictions of their fate and potential impacts in surface waters.

Kinetics of ethyl paraben degradation by simulated solar radiation in the presence of N-doped TiO2 catalysts.

Ethyl paraben (EP), an emerging micro-pollutant representative of the parabens family, has been subject to photocatalytic degradation under simulated solar radiation at a photon flux of 1.3·10(-4) E/(m(2) s). Six nitrogen-doped titania catalysts synthesized by annealing a sol-gel derived TiO2 powder under ammonia flow and their un-doped counterparts, calcined in air at different temperatures in the range 450-800 °C, were compared under solar and visible light and the most active one (N-doped TiO2 calcined at 600 °C) was used for further tests. Experiments were performed at EP concentrations between 150 and 900 µg/L, catalyst loadings between 100 and 1000 mg/L, pH between 3 and 9, different matrices (ultrapure water, water spiked with humic acids or bicarbonates, drinking water and secondary treated wastewater) and hydrogen peroxide between 10 and 100 mg/L. For EP concentrations up to 300 µg/L, the degradation rate can be approached by first order kinetics but then shifts to lower order as the concentration increases. The rate increases linearly with catalyst loading up to 750 mg/L and hydrogen peroxide up to 100 mg/L. Near-neutral (pH = 6.5-7.5) and alkaline conditions (pH = 9) do not affect degradation, which is reduced at acidic pH. The presence of humic acids at 10-20 mg/L impedes degradation due to the competition with EP for the oxidizing species and this is more pronounced in actual wastewater matrices. UPLC-ESI-HRMS and HPLC-DAD were employed to follow EP concentration changes, as well as identify and quantify transformation by-products during the early stages of the reaction. Five such products were successfully detected and, based on their concentration-time profiles, a reaction network for the degradation of EP is proposed. Hydroxyl radical reactions appear to prevail during the initial steps as evidenced by the rapid formation of hydroxylated and dealkylated intermediates.

Identification of halogenated photoproducts generated after ultraviolet-irradiation of parabens and benzoates in water containing chlorine by solid-phase microextraction and gas chromatography-mass spectrometry.

This work presents a new solid-phase microextraction (SPME)-based approach to investigate the formation of halogenated by-products generated by the UV-induced photodegradation of parabens and their congener benzoates in water containing chlorine. Degradation of parent species, and further identification of their transformation by-products were monitored by gas chromatography coupled to mass spectrometry (GC/MS). In order to improve detectability, SPME was applied as a preconcentration step after UV-irradiation of target preservatives. Experiments performed with dechlorinated water, ultrapure water, and tap water showed that under UV-light, the presence of even low levels of free chlorine, increases the photodegradation rate of target preservatives, enhancing the formation of halogenated photoproducts. Monobrominated, dibrominated and bromochlorinated hydroxybenzoates were identified, and the transformation of benzoates into halogenated parabens was also confirmed. Bromination is expected to occur when free chlorine is present, due to the presence of traces of bromide in water samples. Five halogenated phenols (mainly brominated) were detected as breakdown photoproducts from both families of target preservatives. On the basis of the appearance of the aforementioned by-products, a tentative transformation pathway, consistent with the photoformation-photodecay kinetics of the by-products, is proposed herein for the first time.

The aqueous photosensitized degradation of butylparaben.

The photosensitized oxidation of butyl p-hydroxybenzoate (butylparaben, BP), the endocrine disrupting compound, in aqueous solution using rose bengal (RB) and aluminium phthalocyanine chloride tetrasulfonic acid (PC) as sensitizers was examined. A xenon lamp simulating solar radiation was used as a light source. The influence of pH of the reaction mixture, oxygen content, irradiation intensity and initial sensitizers and BP concentration on the reaction rate was studied. Based on the kinetic model, the rate constants of singlet oxygen quenching and reaction with BP as well as the rate constant of excited sensitizer quenching by BP were determined.

Combined activation of methyl paraben by light irradiation and esterase metabolism toward oxidative DNA damage.

Methyl paraben (MP) is often used as a preservative in foods, drugs, and cosmetics because of its high reliability in safety based on the rapid excretion and nonaccumulation following administration. Light irradiation sometimes produces unexpected activity from chemicals such as MP; furthermore, there is ample opportunity for MP to be exposed to sunlight. Here, we investigated whether MP shows DNA damage after sunlight irradiation. Two major photoproducts, p-hydroxybenzoic acid (PHBA) and 3-hydroxy methyl paraben (MP-3OH), were detected after sunlight irradiation to an aqueous MP solution. Both photoproducts were inactive in the in vitro DNA damage assay that measures oxidized guanine formed in calf thymus DNA in the presence of divalent copper ion, a known mediator of oxidative DNA damage. Simulated MP metabolism using dermal tissues after light irradiation produced these two photoproducts, which reacted with a microsomal fraction (S9) of the skin. A metabolite from MP-3OH, not PHBA, caused distinct DNA damage in the in vitro assay. This active metabolite was identified as protocatechuic acid, a hydrolyzed MP-3OH product. In addition, NADH, a cellular reductant, enhanced DNA damage by approximately five times. These results suggest that reactive oxygen species generated by the redox cycle via metal ion and catechol autoxidation are participating in oxidative DNA damage. This study reveals that MP might cause skin damage involving carcinogenesis through the combined activation of sunlight irradiation and skin esterases.

Single crystal EPR studies of an organic NLO material: methyl-p-hydroxy benzoate.

Single crystals of an organic nonlinear optical (NLO) material methyl-p-hydroxy benzoate (MHB) were grown by solvent evaporation technique. EPR spectra were recorded for Er3+: MHB and gamma-irradiated MHB at room temperature at X-band frequencies. The angular variation studies of the spectra were observed and the principal values of g were determined. The grown crystals were characterized by single crystal X-ray diffraction studies.

Kinetics of p-hydroxybenzoic acid photodecomposition and ozonation in a batch reactor.

The decomposition of p-hydroxybenzoic acid, an important pollutant present in the wastewaters of the olive oil industry, has been carried out by a direct photolysis provided by a polychromatic UV radiation source, and by ozone. In both processes, the conversions obtained as a function of the operating variables (temperature, pH and ozone partial pressure in the ozonation process) are reported. In order to evaluate the radiation flow rate absorbed by the solutions in the photochemical process, the Line Source Spherical Emission Model is used. The application of this model to the experimental results provides the determination of the reaction quantum yields which values ranged between 8.62 and 81.43 l/einstein. In the ozonation process, the film theory allows to establish that the absorption process takes place in the fast and pseudo-first-order regime and the reaction is overall second-order, first-order with respect to both reactants, ozone and p-hydroxybenzoic acid. The rate constants are evaluated and vary between 0.18x10(5) and 29.9x10(5) l/mol s depending on the temperature and pH.