Photodegradation of butylparaben in aqueous solutions by 254nm irradiation

Efficiency of ozonation and O3/H2O2 as enhanced wastewater treatment processes for micropollutant abatement and disinfection with minimized byproduct formation

Ozonation, a viable option for improving wastewater effluent quality, requires process optimization to ensure the organic micropollutants (OMPs) elimination and disinfection under minimized byproduct formation. This study assessed and compared the efficiencies of ozonation (O₃) and ozone with hydrogen peroxide (O₃/H₂O₂) for 70 OMPs elimination, inactivation of three bacteria and three viruses, and formation of bromate and biodegradable organics during the bench-scale O₃ and O₃/H₂O₂ treatment of municipal wastewater effluent. 39 OMPs were fully eliminated, and 22 OMPs were considerably eliminated (54 ± 14%) at an ozone dosage of 0.5 gO₃/gDOC for their high reactivity to ozone or ^•OH. The chemical kinetics approach accurately predicted the OMP elimination levels based on the rate constants and exposures of ozone and ^•OH, where the quantum chemical calculation and group contribution method successfully predicted the ozone and ^•OH rate constants, respectively. Microbial inactivation levels increased with increasing ozone dosage up to ∼3.1 (bacteria) and ∼2.6 (virus) log₁₀ reductions at 0.7 gO₃/gDOC. O₃/H₂O₂ minimized bromate formation but significantly decreased bacteria/virus inactivation, whereas its impact on OMP elimination was insignificant. Ozonation produced biodegradable organics that were removed by a post-biodegradation treatment, achieving up to 24% DOM mineralization. These results can be useful for optimizing O₃ and O₃/H₂O₂ processes for enhanced wastewater treatment.

A novel approach to interpret quasi-collimated beam results to support design and scale-up of vacuum UV based AOPs

UV-C at 254 nm and vacuum UV (VUV) at 185 nm are the two major emission lines of a low-pressure mercury lamp. Upon absorption of VUV photons, water molecules and selected inorganic anions generate hydroxyl (HO^.) and other redox radicals, both capable of degrading organic micropollutants (OMPs), thereby offering the opportunity to reduce H₂O₂ and energy consumption in UV-based advanced oxidation process (AOP). To be successfully scaled-up, the dual-wavelength VUV+UV/H₂O₂ AOP requires laboratory-scale experiments to establish design criteria. The figures of merit typically used for reporting and interpreting quasi-collimated beam results for UV-based AOPs (time, dose, absorbed energy and E_EO) are insufficient and inaccurate when employed for dual-wavelength AOP such as the VUV+UV/H₂O₂ AOP, and do not support system scale-up. In this study, we introduce a novel figure of merit, useful absorbed energy (uAE), defined as fraction of absorbed energy that results in the generation of oxidative radicals. Here, results of quasi-collimated beam VUV+UV/H₂O₂ AOP experiments on four different water matrices are used to introduce 2D plots that employ both uAE_UV and uAE_VUV as a novel method to represent laboratory-scale experiments of VUV+UV/H₂O₂ AOP and demonstrate how the 2D plots sufficiently support scale-up of the AOP.

An evaluation on the intra-day dynamics, seasonal variations and removal of selected pharmaceuticals and personal care products from urban wastewater treatment plants

Pharmaceuticals and personal care products (PPCPs) in wastewater have become an emerging issue due to their negative effects on human health and aquatic ecosystems. Two full-scale municipal and industrial wastewater treatment plants (WWTPs) along the Songhua River were chosen to evaluate the intra-day dynamics, seasonal variations and removal of 12 selected PPCPs. Our results suggested that the selected PPCPs were frequently detected in the influent and effluent. Caffeine was the predominant compound in the influent; while the selected PPCPs was dominated by TCS in the effluent, suggesting the different fates of selected PPCPs in the WWTPs. The intra-day dynamics of PPCPs in the influent were evaluated, suggesting that the 12 PPCPs can be grouped into three categories because of their different use patterns. The analysis of seasonal changes of PPCPs concentrations in the WWTPs suggested that the concentrations of some PPCPs were influenced by the chemical usage, degradation and temperature. The removal efficiency for the PPCPs were very high with the values ranged from 70.0% to 99.7% for WWTP#1, and from 62.5% to 99.4% for WWTP#2. Significant seasonal variations of PPCPs removal efficiency were observed. Base on the mass loading of PPCPs in the two WWTPs, our results suggested that WWTP#1 in the urban core received much more PPCPs in comparison to WWTP#2 in the suburban regions, suggesting that influences of the service population.

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 (k_obs) 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.

Photolysis of parabens using medium-pressure mercury lamps: Toxicity effects in MCF7, Balb/c 3T3 cells and Ceriodaphnia dubia

Degradation studies of the propylparaben (PrP), butylparaben (BuP) and of the propylparaben-butylparaben mixture (PrP-BuP) in deionized water and surface river water was investigated as a function of pH and initial concentration of the reactants using a medium-pressure mercury lamp. The photolysis of parabens (concentration ranging from 5 to 30 mg L^-1) followed apparent pseudo-first-order kinetics, with rate constants (k) in deionized water and surface river water changed from 1.80 × 10^-1 to 3.68 × 10^-2 min^-1 and 1.43 × 10^-1 to 1.45 × 10^-2 min^-1, respectively. Degradation reaction was faster at pH 5 in comparison with pH 7 or 11. The photolysis of parabens was greater than 91%, with low mineralization (26.15%) observed in acidic medium after 95 min. Analysis by chromatography coupled to mass spectrometry (LC-MS/MS) showed that only one product was generated during the degradation reaction and has UV bands similar to 3,4-dihydroxybenzoic acid. Estrogenic activity tests showed that non-degraded parabens stimulated the growth of breast adenocarcinoma (MCF-7) cells and this effect was evaluated after the photolysis. Cytotoxicity assays using fibroblasts cells (Balb/C 3T3 clone A31) indicated that the parental compounds and degradation products were not cytotoxic. On the contrary, non-degraded parabens were toxic to Ceriodaphnia dubia, but the product of photolysis was not. Overall, the photolytic method presented was able to degrade these parabens providing safe and non-estrogenic reaction product.

Heat-activated persulfate oxidation of methyl- and ethyl-parabens: Effect, kinetics, and mechanism

We evaluated the degradation of methylparaben (MeP) and ethylparaben (EtP), two representative parabens, using the heat-activated persulfate system in a laboratory. Both sulfate and hydroxyl radicals contributed to the removal of the two parabens. The degradations of both MeP and EtP were improved by increasing the heating temperature or persulfate dose in accordance with a pseudo-first-order reaction model. The oxidation efficiency of parabens was found to be pH-dependent; decreasing in the order pH 5.0 > 7.0 > 9.0. The presence of chloride, bicarbonate, or humic acid was found to inhibit the degradation of the two parabens to some extent because of competition for the reactive radicals, with humic acid having the most serious effect. Dealkylation of the methyl unit, decarboxylation of the carboxylic group, and subsequent hydrolysis are proposed to be involved in the degradation pathway of MeP. The results suggest that the heat-activated persulfate system might be efficiently applied in the treatment of paraben-containing water samples. This was also supported by the results of applying this system to treat a real water sample containing both MeP and EtP.

Contribution of the Hair Follicular Pathway to Total Skin Permeation of Topically Applied and Exposed Chemicals

Generally, the blood and skin concentration profiles and steady-state skin concentration of topically applied or exposed chemicals can be calculated from the in vitro skin permeation profile. However, these calculation methods are particularly applicable to chemicals for which the main pathway is via the stratum corneum. If the contribution of hair follicles to the total skin permeation of chemicals can be obtained in detail, their blood and skin concentrations can be more precisely predicted. In the present study, the contribution of the hair follicle pathway to the skin permeation of topically applied or exposed chemicals was calculated from the difference between their permeability coefficients through skin with and without hair follicle plugging, using an in vitro skin permeation experiment. The obtained results reveal that the contribution of the hair follicle pathway can be predicted by using the chemicals’ lipophilicity. For hydrophilic chemicals (logarithm of n-octanol/water partition coefficient (log K_o/w) < 0), a greater reduction of permeation due to hair follicle plugging was observed than for lipophilic chemicals (log K_o/w ≥ 0). In addition, the ratio of this reduction was decreased with an increase in log K_o/w. This consideration of the hair follicle pathway would be helpful to investigate the efficacy and safety of chemicals after topical application or exposure to them because skin permeation and disposition should vary among skins in different body sites due to differences in the density of hair follicles.

Influence of dissolved organic matter in natural and simulated water on the photochemical decomposition of butylparaben

BACKGROUND

In the last few decades the quality of natural water has often deteriorated as a variety of novel pollutants have contaminated rivers and lakes. Trace amounts of some man-made chemicals can be hazardous to plants, animals as well as human health as carcinogens, mutagens or endocrine disruptors. Light radiation may help in its decomposition, aided by naturally occurring colored organic compounds (humic substances) in the water. The aim of these studies was to check the influence of presence of organic and inorganic matter on the removal of endocrine disrupting compound - butylparaben (BP) from water.

METHODS

Photochemical decomposition of BP in aqueous solution using: photolysis by ultraviolet-C (UVC) and visible (VIS) irradiation, advanced oxidation in H2O2/UV system and photosensitized oxidation was examined. The degradation processes were carried out in different type of water matrix: natural water from Sulejow Reservoir, simulated natural water with humic acids and buffered solution.

RESULTS

The presence of dissolved organic matter in water did not influence much on UVC photolysis and increases only about 8% of BP depletion rate in H2O2/UV system. While during visible light photolysis and photosensitized oxidation the addition of natural water matrix causes the acceleration of reaction rate by 16% and 36%, respectively. Moreover BP degradation proceeds via singlet oxygen generated from humic substances.

CONCLUSIONS

Butylparaben undergoes both direct and indirect photodegradation in aqueous solution under UVC and visible radiation. The efficiency of the H2O2/UV process, photolysis as well as photosensitized oxidation processes is strongly dependent on composition of the water.

One-pot synthesis of micro/nano structured β-Bi2O3 with tunable morphology for highly efficient photocatalytic degradation of methylparaben under visible-light irradiation

Micro/nanostructures β-Bi₂O₃ with tunable morphologies were synthesized via an one-pot solvothermal–calcining route for efficient visible-light photocatalytic removal of methylparaben from water.

Photosonochemical degradation of butyl-paraben: optimization, toxicity and kinetic studies

The objective of the present work is to evaluate the potential of a photosonolysis process for the degradation of butyl-paraben (BPB). After 120 min of treatment time, high removal of BPB was achieved by the photosonolysis (US/UV) process (88.0±0.65%) compared to the photochemical (UV) and the conventional ultrasonication (US) processes. Several factors such as calorimetric power, treatment time, pH and initial concentration of BPB were investigated. Using a 2(4) factorial matrix, the treatment time and the calorimetric power are the main parameters influencing the degradation rate of BPB. Subsequently, a central composite design methodology has been investigated to determine the optimal experimental parameters for BPB degradation. The US/UV process applied under optimal operating conditions (at a calorimetric power of 40 W during 120 min and under pH7) is able to oxidize around 99.2±1.4% of BPB and to record 43.3% of mineralization. During the US/UV process, BPB was mainly transformed into 1 hydroxy BPB, dihydroxy BPB, hydroquinone and 4-hydroxybenzoic acid. Microtox biotests (Vibrio fisheri) showed that the treated effluent was not toxic. The pseudo-first order kinetic model (k=0.0367 min(-1)) described very well the oxidation of BPB.

Computational consideration on advanced oxidation degradation of phenolic preservative, methylparaben, in water: mechanisms, kinetics, and toxicity assessments

Hydroxyl radicals ((•)OH) are strong oxidants that can degrade organic pollutants in advanced oxidation processes (AOPs). The mechanisms, kinetics, and toxicity assessment of the (•)OH-initiated oxidative degradation of the phenolic preservative, methylparaben (MPB), were systematically investigated using a computational approach, as the supplementary information for experimental data. Results showed that MPB can be initially attacked by (•)OH via OH-addition and H-abstraction routes. Among these routes, the (•)OH addition to the C atom at the ortho-position of phenolic hydroxyl group was the most significant route. However, the methyl-H-abstraction route also cannot be neglected. Further, the formed transient intermediates, OH-adduct ((•)MPB-OH1) and dehydrogenated radical ((•)MPB(-H)α), could be easily transformed to several stable degradation products in the presence of O2 and (•)OH. To better understand the potential toxicity of MPB and its products to aquatic organisms, both acute and chronic toxicities were assessed computationally at three trophic levels. Both MPB and its products, particularly the OH-addition products, are harmful to aquatic organisms. Therefore, the application of AOPs to remove MPB should be carefully performed for safe water treatment.

Parabens. From environmental studies to human health

Parabens are a group of substances commonly employed as preservatives, mainly in personal care products, pharmaceuticals and food. Scientific reports concerning their endocrine disrupting potential and the possible link with breast cancer raised wide discussion about parabens' impact and safety. This paper provides holistic overview of paraben usage, occurrence in the environment, methods of their degradation and removal from aqueous solution, as well as hazards related to their endocrine disrupting potential and possible involvement in carcinogenesis.

Photodegradation of parabens by Fe(III)-citrate complexes at circumneutral pH: matrix effect and reaction mechanism

The photodegradation of four parabens including methyl-, ethyl-, propyl-, and butyl-paraben in the presence of Fe(III)-citrate complexes under simulated sunlight was investigated. The degradation of parabens increased with decreasing pH within the range of 5.0-8.0 at the Fe(III)-to-citrate ratio of 10:150 (μM). The addition of low-molecular-weight carboxylic acids showed different effects on the photodegradation of methylparaben. The low-photoreactive carboxylic acids inhibited the photodegradation of methylparaben in the order of formic acid>succinic acid>acetic acid>malonic acid. In contrast, oxalic acid enhanced the photodegradation and exhibited appreciable synergistic effect with Fe(III)-citrate at concentration higher than 500 μM. Up to 99.0% of substrate was degraded after 30 min at pH6.0 in the Fe(III)-citrate-oxalate system. The various fractions of fulvic acid inhibited the photodegradation of methylparaben. The inhibition increased with increasing nominal molecular weight of fractionated fulvic acid. Moreover, the photodegradation of methylparaben was inhibited in natural waters in the order of Liangzi Lake<Donghu Lake<Changjiang River≈Seawater. The photoproducts of methylparaben were identified by GC-MS analyses and the degradation pathway was proposed.

Degradation of bisphenol A using UV and UV/H2O2 processes

Bisphenol A (BPA; 4-[2-(4-hydroxyphenyl)propan-2-yl]phenol) is a substance typically used in the plastic industry. It is used in the production of epoxy resins, polycarbonate, or fire retardants or as a stabilizer and an antioxidant in numerous types of plastics. Bisphenol A is introduced into the environment via municipal and industrial wastewater. Because of its hydrophobic properties, BPA has the potential for sorption on activated sludge during the biological wastewater treatment processes. This study investigated the degradation of BPA by means of UV-radiation and in the UV/H2O2 process with the presence and absence of hydrocarbonate ions (HCO3(-)) as hydroxyl radicals (OH*) scavengers. The calculated value of quantum yield was equal to 0.18, and the value of BPA rate constant with hydroxyl radicals was equal to 3.3 x 10(9) M(-1) s(-1).