The role of reactive oxygen species in sulfamethazine degradation using UV-based technologies and products identification

Full-Spectrum Utilization of ZIF-67/Ag NPs/NaYF4:Yb,Er Photocatalysts for Efficient Degradation of Sulfadiazine: Upconversion Mechanism and DFT Calculation

In this work, novel ternary composite ZIF-67/Ag NPs/NaYF4:Yb,Er is synthesized by solvothermal method. The photocatalytic activity of the composite is evaluated by sulfadiazine (SDZ) degradation under simulated sunlight. High elimination efficiency of the composite is 95.4% in 180 min with good reusability and stability. The active species (h+, ·O2 - and ·OH) are identified. The attack sites and degradation process of SDZ are deeply investigated based on theoretical calculation and liquid chromatography-mass spectrometry analysis. The upconversion mechanism study shows that favorable photocatalytic effectiveness is attributed to the full utilization of sunlight through the energy transfer upconversion process and fluorescence resonance energy transfer. Additionally, the composite is endowed with outstanding light-absorbing qualities and effective photogenerated electron-hole pair separation thanks to the localized surface plasmon resonance effect of Ag nanoparticles. This work can motivate further design of novel photocatalysts with upconversion luminescence performance, which are applied to the removal of sulphonamide antibiotics in the environment.

Cobalt-bismuth bimetallic composite anchored on carbon derived from cigarette butts as peroxymonosulfate activator for rapid removal of chloramphenicol

Chloramphenicol (CAP) is a typical kind of antibiotics, which has posed a severe threat to nature and human beings due to its wide application. In this study, cobalt-bismuth bimetallic composite anchored on carbon derived from cigarette butts (Co-Bi@CCB) was prepared to activate peroxymonosulfate (PMS) for the removal of CAP. Our results demonstrated Co-Bi@CCB not only possessed excellent catalytic performance, but also significantly limited metal ions dissolution. Over 98% of CAP (10 mg/L) was degraded in the presence of Co-Bi@CCB (0.05 g/L) and PMS (1 mM) within 20 min at pH = 7. Quenching tests and electron paramagnetic resonance (EPR) spectrometry confirmed that SO₄^•-, ^•OH, and ¹O₂ led to the rapid decomposition of CAP. Combined with X-ray photoelectron spectroscopy (XPS) of Co-Bi@CCB before and after reaction, the mechanism of PMS activation was deduced. Finally, the possible pathways of CAP degradation was further speculated according to the intermediates determination by high-performance liquid chromatography equipped with high resolution mass spectrometer (HPLC-HRMS). Thus, the present study provides a new strategy to utilize discarded cigarette butts (recycled materials) as a carrier to fabricate novel and efficient catalysts to activate PMS for the removal of organic contaminants.

Degradation of saccharin by UV/H2O2 and UV/PS processes: A comparative study

Artificial sweeteners have raised emerging concern due to their potential threats to human health, which were frequently detected in aquatic environment with median concentrations. Although current researches have widely reported that ultraviolet light-activated persulfate process (UV/PS) was superior to UV/H₂O₂ process for the degradation of refractory organic contaminants, UV/H₂O₂ process presented a more satisfactory saccharin (SAC) removal efficiency than UV/PS process, completely degraded 20 mg/L SAC within 45 min. Hence, quenching and probe experiments were employed to investigate the difference between hydroxyl radical (OH)- and sulfate radical (SO₄^-)-mediated oxidation mechanisms, which revealed the higher reactivity of OH (1.37-1.56 × 10⁹ M^-1 s^-1) toward SAC than SO₄^- (3.84-4.13 × 10⁸ M^-1 s^-1). A combination of density functional theory calculation and transformation products identification disclosed that OH preferred to attack the benzene ring of SAC via hydrogen atom transfer pathway, whereas SO₄^- oxidation was conducive to the cleavage of -C-NH₂ bond. Increasing oxidant concentration significantly accelerated SAC degradation in both processes, while UV/H₂O₂ process consumed lower electrical energy with respect to UV/PS process. Additionally, UV/H₂O₂ system presented excellent adaptability and stability under various water matrices parameters (e.g. pH, anions and humic acid). While both UV/H₂O₂ and UV/PS processes promoted the generation of disinfection by-products (DBPs) during subsequent chlorination, and prolonging pretreatment time posed positive effect on reducing the formation of DBPs. Overall, the results clearly demonstrate the high efficiency, economy and practicality of UV/H₂O₂ process in the remediation of SAC-contaminated water.

Removal of sulfamethoxazole, sulfadiazine, and sulfamethazine by UV radiation and HO• and SO4•- radicals using a response surface model and DFT calculations

In this work, the degradation of sulfamethazine (SMT), sulfadiazine (SMD), and sulfamethoxazole (SMX) by using UV light, UV/H₂O₂, and UV/S₂O₈^-2 was analyzed. Direct photolysis was studied by varying the lamp power and the solution pH. DFT calculations were carried out to corroborate the efficiency of the degradation as a function of the solution pH. The variation of the apparent rate constant, k_ap, was determined in the indirect photolysis by employing an experimental Box-Behnken-type response surface design. The results evidenced that SMX can be efficiently degraded by applying UV radiation independent of the operating conditions. Nevertheless, the quantum yields for SMT and SMD were close to zero, indicating a low energy efficiency for their photochemical transformation. The effect of the solution pH showed that the photodegradation of sulfonamides depends both on the amount of radiation absorbed as the electronic density. Calculations based on density functional theory and supported by the quantum theory of atoms in molecules allowed to describe fragmentation patterns in the systems under study, proving the lability of S₁₄-C₂, N₁₇-C₁₈, and N₂₂-O₂₂ bonds, for SMT, SMD, and SMX, respectively. From response surface methodology, four statistically reliable equations were obtained to determine the k_ap value as a function of the system operating conditions. Finally, SO₄^•- radicals proved to have a higher reactivity to degrade SMT and SMD compared with HO^• radicals regardless of the operating conditions of the system.

Photodegradation of sulfadiazine in different aquatic environments - Evaluation of influencing factors

The presence of antibiotics, such as sulfadiazine (SDZ), in the aquatic environment contributes to the generation of antimicrobial resistance, which is a matter of great concern. Photolysis is known to be a major degradation pathway for SDZ in surface waters. Therefore, influencing factors affecting SDZ photodegradation in different aquatic environments were here evaluated in order to have a better knowledge about its persistence in the environment. Photodegradation of SDZ was found to be more efficient at higher pH (t_1/2 = 6.76 h, at pH = 7.3; t_1/2 = 12.2 h, at pH = 6.3), in the presence of humic substances (HS) (t_1/2 between 1.76 and 2.42 h), as well as in the presence of NaCl (t_1/2 = 1.00 h) or synthetic sea salts (t_1/2 = 0.78 h). Using ˙OH and ¹O₂ scavengers, it was possible to infer that direct photolysis was the main pathway for SDZ photodegradation in ultrapure water. Furthermore, results under N₂ purging confirmed that ¹O₂ was not relevant in the phototransformation of SDZ. Then, the referred observations were used for the interpretation of results obtained in environmental matrices, namely the final effluent of a sewage treatment plant (STPF), fresh and brackish water (t_1/2 between 2.3 and 3.48 h), in which SDZ photodegradation was found to be much faster than in ultrapure water (t_1/2 = 6.76 h).

Phototransformation of zinc oxide nanoparticles and coexisting pollutant: Role of reactive oxygen species

In this study, the photochemistry of ZnO NPs and their effect on phototransformation of coexisting pollutants (sulfamethazine, SMZ) were systematically investigated under UV illumination. SMZ (40 μM) degradation was accelerated by ZnO NPs, as the observed reaction rate constant (k_obs) increased from 0.0809 h^-1 to 0.7982 h^-1 at the concentration of 5-50 mg/L ZnO NPs. Free radical quenching and quantification experiments indicated the reactive oxygen species, especially the hydroxyl radicals (OH) and singlet oxygen (¹O₂), made great contributions to SMZ degradation. Moreover, SMZ was prone to be degraded at high pH with k_obs reaching upto 0.5734 h^-1 at pH 12.0. The presence of Cl^- (1000 mM) reduced the SMZ decomposition greatly by 2.4-fold while the effects of SO₄^2- (30 mM) were very limited. Natural organic matter including humic acid and tannic acid both inhibited the degradation of SMZ with k_obs decreasing by 35.4-fold and 132-fold, respectively. During the photoreaction process, ZnO NPs fragmented into relative small size pieces obviously along with the release of Zn²⁺. Finally, the possible cotransformation pathways of ZnO NPs and SMZ were proposed based on SMZ degradation intermediates and the above results. These findings of the present study suggested that the photoreactions of ZnO NPs greatly influenced the transformation of contaminants and ZnO NPs themselves in aquatic environment, which may have significant implications for the fate assessment of NPs and environmental pollutants.

Comparative Study of the Oxidative Degradation of Different 4-Aminobenzene Sulfonamides in Aqueous Solution by Sulfite Activation in the Presence of Fe(0), Fe(II), Fe(III) Or Fe(VI)

This study is focused on advanced oxidation technologies (AOTs) using the combined effect of Fe(0–VI)/sulfite systems, that produce mainly SO4•− radicals, to remove different 4-aminobenzene sulfonamides (SAs), namely sulfamethazine, sulfadiazine, sulfamethizole, from aqueous solutions. Results obtained showed that neither sulfite nor iron alone is able to degrade SAs; however, the combined effect depends on the oxidation state of iron species whose effectiveness to activate sulfite to promote the degradation of SAs increased following this order: Fe(III) < Fe(II) < Fe(0) < Fe(VI). Using Fe(VI)/sulfite, the complete removal of SAs was obtained in 5 min largely surpassing the effectiveness of the other three systems. The sulfonamides’ removal percentage was markedly influenced by sulfite concentration and dissolved oxygen, which improved the generation of oxidant radicals. Response surface methodology was applied, and a quadratic polynomial model was obtained, which allowed us to determine the percentage of SAs degradation as a function of both the iron species and sulfite concentrations. The study of the influence of the water matrix on these AOTs revealed an inhibition of SAs’ removal percentage when using ground water. This is probably due to the presence of different anions, such as HCO3−, Cl−, and SO42− in relatively high concentrations. According to the byproducts identified, the proposed degradation pathways include hydroxylation, SO2 extrusion, and different bond-cleavage processes. Cytotoxicity of degradation byproducts, using MTS assay with HEK 293 and J774 cell lines for the first time, did not show an inhibition in cell proliferation, sustaining the safety of the process.

Mechanism of methylphosphonic acid photo-degradation based on phosphate oxygen isotopes and density functional theory

Methylphosphonic acid (MPn) is an intermediate in the synthesis of the phosphorus-containing nerve agents, such as sarin and VX, and a biosynthesis product of marine microbes with ramifications to global climate change and eutrophication. Here, we applied the multi-labeled water isotope probing (MLWIP) approach to investigate the C-P bond cleavage mechanism of MPn under UV irradiation and density functional theory (DFT) to simulate the photo-oxidation reaction process involving reactive oxygen species (ROS). The results contrasted with those of the addition of the ROS-quenching compounds, 2-propanol and NaN3. The degradation kinetics results indicated that the extent of MPn degradation was more under alkaline conditions and that the degradation process was more rapid at the initial stage of the reaction. The phosphate oxygen isotope data confirmed that one exogenous oxygen atom was incorporated into the product orthophosphate (PO4) following the C-P bond cleavage, and the oxygen isotopic composition of this free PO4 was found to vary with pH. The combined results of the ROS-quenching experiments and DFT indicate that the C-P bond was cleaved by OH-/˙OH and not by other reactive oxygen species. Based on these results, we have established a mechanistic model for the photolysis of MPn, which provides new insights into the fate of MPn and other phosphonate/organophosphate compounds in the environment.

The importance of reactive oxygen species on the aqueous phototransformation of sulfonamide antibiotics: kinetics, pathways, and comparisons with direct photolysis

Sulfonamide antibiotics (SAs) are increasingly detected as aquatic contaminants and exist as different dissociated species depending on the pH of the water. Their removal in sunlit surface waters is governed by photochemical transformation. Here we report a detailed examination of the hydroxyl radical (•OH) and singlet oxygen (¹O₂) mediated photooxidation of nine SAs: sulfamethoxazole, sulfisoxazole, sulfamethizole, sulfathiazole, sulfamethazine, sulfamerazine, sulfadiazine, sulfachloropyridazine and sulfadimethoxine. Both •OH and ¹O₂ oxidation kinetics varied depending on the dominant protonated states of the SA in question (H₂SAs⁺, HSAs⁰ and SAs^-) as a function of pH. Based on competition kinetic experiments and matrix deconvolution calculations, HSAs⁰ or SAs^- (pH ∼5-8) were observed to be more highly reactive towards •OH, while SAs^- (pH ∼8) react the fastest with ¹O₂ for most of the SAs tested. Using the empirically derived rates of reaction for the speciated forms at different pHs, the environmental half-lives were determined using typical ¹O₂ and •OH concentrations observed in the environment. This approach suggests that photochemical ¹O₂ oxidation contributes more than •OH oxidation and direct photolysis to the overall phototransformation of SAs in sunlit waters. Based on the identification of key photointermediates using tandem mass spectrometry, ¹O₂ oxidation generally occurred at the amino moiety on the molecule, whereas •OH reaction experienced multi-site hydroxylation. Both these reactions preserve the basic parent structure of the compounds and raise concerns that the routes of phototransformation give rise to intermediates with similar antimicrobial potency as the parent SAs. We therefore recommend that these phototransformation pathways are included in risk assessments concerning the presence and fate of SAs in waste and surface waters.

Mechanisms and toxicity evaluation of the degradation of sulfamethoxazole by MPUV/PMS process

In this work, a sulfate radical (SO4-)-based advanced oxidation process was applied to the degradation of sulfamethoxazole (SMX). In these experiments, a medium pressure UV (MPUV) lamp was employed to active peroxymonosulfate (PMS). It was found that 98% of SMX was removed by MPUV/PMS at a UV dose of 200 mJ cm-2 (3.95 μM SMX, 0.2 mM PMS, pH0 = 3.7). Direct MPUV photolysis played a remarkable role in SMX removal by MPUV/PMS process. As for the indirect photolysis, SO4- was the major reactive species under acidic and neutral conditions in MPUV/PMS system, while the hydroxyl radical (OH) became the predominant radical under alkaline conditions. The transformation products (TPs) of SMX that formed in the MPUV-only and MPUV/PMS experiments were identified, and the possible degradation pathways were proposed. Photoisomerization of the isoxazole ring was the major pathway of SMX during MPUV-only process. Hydroxylation/oxidation of the aniline and isoxazole ring was the predominant degradation mechanism of SMX by MPUV/PMS. Toxicity evaluation showed that MPUV/PMS was effective at reducing the antibacterial activity of SMX solutions, while MPUV-only was not. However, some TPs with equivalent or even higher antibacterial activity than SMX were formed during the initial degradation period in MPUV/PMS system. Ecotoxicity of SMX and its TPs was also hypothetically predicted via the ECOSAR program, and the results indicated that some TPs could be more toxic than SMX.

Sulfonamides degradation assisted by UV, UV/H2O2 and UV/K2S2O8: Efficiency, mechanism and byproducts cytotoxicity

The objective of this study was to analyze the effectiveness of UVC, UVC/H₂O₂ and UVC/K₂S₂O₈ on the degradation of SAs. Rate constant values increased in the order SMZ < SDZ < SML and showed the higher photodegradation of sulfonamides with a penta-heterocycle. Quantum yields were 1.72 × 10^-5 mol E^-1, 3.02 × 10^-5 mol E^-1, and 6.32 × 10^-5 mol E^-1 for SMZ, SDZ and SML, respectively, at 60 min of treatment. R₂₅₄ values show that the dose habitually utilized for water disinfection is inadequate to remove this type of antibiotic. The initial sulfonamide concentration has a major impact on the degradation rate. The degradation rates were higher at pH 12 for SMZ and SML. SMZ and SML photodegradation k_λ values are higher in tap versus distilled water. The presence of radical promoters generates a greater increase in the degradation rate, UVC/K₂S₂O₈ cost less energy, a mechanism was proposed, and the degradation by-products are less toxic than the original product.

Photocatalytic degradation of sulfamethazine in aqueous solution using ZnO with different morphologies

In this study, photocatalytic experiments of 20 mg l-1 sulfamethazine (SMN) in aqueous solution containing ZnO with different morphologies, tetra-needle-like ZnO (T-ZnO), flower-like ZnO (F-ZnO) and nanoparticles ZnO (P-ZnO), were performed. The results indicated that photocatalytic degradation of SMN was effective and followed the pseudo-first-order reaction, but the degree of SMN mineralization showed obvious differences using ZnO with different shapes. After 12 h irradiation, 86%, 71% and 50% of the initial total organic carbon was eliminated in SMN suspension containing T-ZnO, F-ZnO and P-ZnO, respectively. The release ratio of sulfur was close to 100% in the presence of T-ZnO, but reached to 86% and 67% in the presence of F-ZnO and P-ZnO, respectively. The release ratio of nitrogen was about 76%, 63% and 40% using T-ZnO, F-ZnO and P-ZnO as photocatalyst, respectively. The morphology of ZnO played an important role in determining its catalytic activity. Seven intermediates were observed and identified in the UV/T-ZnO reaction system by LC-MS/MS analysis, and a possible degradation pathway was proposed.

Photolysis of sulfamethazine using UV irradiation in an aqueous medium

Although many studies have been focused on the photochemistry of antibiotics, the roles of reactive species in photolysis and the effects of dissolved substances on antibiotic photochemical behavior have been poorly examined. The photolytic behaviors of sulfamethazine (SMN) in pure water were investigated via adding different scavengers to quench the active species. Results showed that decomposition of the triplet-excited state of SMN (³SMN*) by direct photolysis was the main path of SMN photolysis in water. Moreover, self-sensitized SMN cannot be ignored during SMN photodegradation. The main photoproducts of SMN were identified by LC-MS/MS, which indicated that SMN could not be mineralized although the photolysis under UV was effective. The effects of Cl⁻, NO₃⁻, and fulvic acid (FA) (common substances in natural water) on SMN photolytic behaviors were also studied. The triplet-induced halogenation of SMN increases the ionic strength and reduces the ground state SMN; these are the primary causes of promotion of SMN photolysis by Cl⁻. More ˙OH produced in the presence of NO₃⁻ could promote SMN photolysis. Competitive absorption of photons of FA with SMN and ROS scavenged by FA were the main reasons for the inhibition of SMN photolysis. The research findings are helpful for further studies on the environmental risks of ACs in natural waters and promoting the development of AC pollution treatment technology.

The role of reactive species in SMN photolysis and the effects of dissolved substances on SMN photochemical behavior.

Sulfamethazine removal by means of a combined process coupling an oxidation pretreatment and activated sludge culture - preliminary results

A coupled electrochemical process and biological treatment was used to remove a biorecalcitrant antibiotic: sulfamethazine (SMT). The pretreatment was performed in a home-made flow cell involving graphite felt as a working electrode at potentials of 1 and 1.6 V/saturated calomel electrode (SCE); it was followed by a biological process involving activated sludge purchased from a local wastewater treatment plant. Activated sludge cultures of pretreated and non-pretreated SMT solution were carried out for 3 weeks, and different parameters were monitored, especially total organic carbon (TOC) and SMT concentrations. high-performance liquid chromatography results revealed that the target molecule was not assimilated by activated sludge. However, and confirming the improvement previously observed for the biological oxygen demand/chemical oxygen demand (BOD₅/COD) ratio, from 0.08 before electrolysis to 0.58 after electrolysis, a pretreatment step in oxidation at 1.6 V/SCE led to a fast decrease of TOC during the subsequent biological treatment, since the mineralization yields increased from 10% for a non-pretreated SMT solution to 76.6% after electrolysis in oxidation (1.6 V/SCE), confirming the efficiency of coupling the electro-oxidation process with a biological treatment for the mineralization of SMT. Moreover, when the electrolysis was performed at 1 V/SCE, no biodegradation was observed, underlining the importance of the electrochemical pretreatment.

Sulfate radical-based oxidation of antibiotics sulfamethazine, sulfapyridine, sulfadiazine, sulfadimethoxine, and sulfachloropyridazine: Formation of SO2 extrusion products and effects of natural organic matter

The widespread occurrence of sulfonamide antibiotics in the environment has raised great concerns about their potential to proliferate antibacterial resistance. Sulfate radical (SO₄^•-) based advanced oxidation processes (SR-AOPs) are promising in-situ chemical oxidation (ISCO) technologies for remediation of soil and groundwater contaminated by antibiotics. The present study reported that thermally activated persulfate oxidation of sulfonamides (SAs) bearing six-membered heterocyclic rings, e.g., sulfamethazine (SMZ), sulfapyridine (SPD), sulfadiazine (SDZ), sulfadimethoxine (SDM), and sulfachloropyridazine (SCP), all produced SO₂ extrusion products (SEPs), a phenomenon that is of potential importance, but not systematically studied. As an electrophilic oxidant, SO₄^•- tends to attack the aniline moiety, the reactive site of SAs, via electro-transfer mechanism. The resulting anilinyl radical cations are subjected to further intermolecular Smiles-type rearrangement to produce SEPs. Formation of SEPs is expected to occur in other SR-AOPs as well. The temperature-dependent evolution pattern of SEP of SMZ, 4-(2-imino-4,6-dimethylpyrimidin-1(2H)-yl)aniline, can be well fitted by kinetic modeling concerning sequential formation and transformation of intermediate product. The presence of natural organic matter (NOM) influenced the evolution patterns of 4-(2-imino-4,6-dimethylpyrimidin-1(2H)-yl)aniline significantly. Toxicological effects of SEPs on ecosystem and human health remain largely unknown, thus, further monitoring studies are highly desirable.

Diclofenac degradation in water by FeCeOx catalyzed H2O2: Influencing factors, mechanism and pathways

The degradation of diclofenac in a like Fenton system, FeCeO_x-H₂O₂, was studied in details. The influencing factors, reaction kinetics, reaction mechanism and degradation pathways of diclofenac were investigated. The optimum conditions were at a solution pH of 5.0, H₂O₂ concentration of 3.0mmol/L, diclofenac initial concentration of 0.07mmol/L, FeCeO_x dosage of 0.5g/L, and 84% degradation of diclofenac was achieved within 40min. The kinetics of FeCeO_x catalyzed H₂O₂ process involved adsorption-dominating and degradation-dominating stages and fitted pseudo-second order model and pseudo-first order model, respectively. Singlet oxygen ¹O₂ was the primary intermediate oxidative species in the degradation process; superoxide radical anion O₂^- also participated in the reaction. The surface cerium and iron sites and the oxygen vacancies in the FeCeO_x catalyst were proposed to play an important role in H₂O₂ decomposition and active species generation. The detected intermediates were identified as hydroxylated derivatives (m/z of 310, 326 and 298), quinone imine compounds (m/z of 308, 278 and 264) and hydroxyl phenylamine (m/z of 178). The majority intermediates were hydroxylated derivatives and the minority was hydroxyl phenylamine. The degradation pathways were proposed to involve hydroxylation, decarboxylation, dehydrogenation and CN bond cleavage.

Sonocatalytic degradation of diclofenac with FeCeOx particles in water

This paper studies the sonocatalytic degradation of diclofenac in water using FeCeO_x-catalyzed ultrasound. The effects of pre-adsorption and gas addition were investigated. Nitrogen adsorption/desorption, SEM, XRD, Raman and XPS analyses of FeCeO_x before and after sonication were characterized. The proposed mechanism was based on the microstructure changes of FeCeO_x and reactive-species-scavenging performances. The results show that FeCeO_x has excellent performance in catalyzing an ultrasonic system in water, and 80% of diclofenac was removed in 30min ([Diclofenac]=20mg/L, FeCeO_x amount=0.5g/L, pH=6, ultrasonic density=3.0W/cm³, ultrasonic frequency=20kHz, temperature=298K). The Fe, Ce, and O elements remained highly dispersed in the structure of FeCeO_x, and the solid solution structure of FeCeO_x remained stable after the reaction. Ce (III) was gradually oxidized to Ce (IV) and Fe (III) was gradually reduced to Fe (II) after the reaction, which indicates that Fe and Ce ions with different valences coexisted in dynamic equilibrium. The amount of oxygen vacancies in FeCeO_x significantly decreased after the reaction, which indicates that oxygen vacancy participated in the ultrasonic process. Singlet oxygen ¹O₂ was the primary reactive species in the degradation process, and the hydroxyl radicals OH and superoxide radical anion O₂^- also participated in the reaction. FeCeO_x had excellent chemical stability with negligible leaching ions in the ultrasonic process.

Tolfenamic acid degradation by direct photolysis and the UV-ABC/H2O2 process: factorial design, kinetics, identification of intermediates, and toxicity evaluation

This study employed direct UV-ABC photolysis and the UV-ABC/H₂O₂ process to investigate the degradation of tolfenamic acid (TA), a common anti-inflammatory drug used in both human and veterinary medicine. A 2³ factorial design with added center point was used to evaluate the effect of three independent variables-namely, H₂O₂ concentration ([H₂O₂]), TA concentration ([TA]), and experiment time (time)-on TA degradation and H₂O₂ photolysis during UV-ABC/H₂O₂ treatment using a high-pressure mercury vapor lamp (photon flux of 2.6307 × 10⁴ J s^-1) as the UV irradiation source. The responses yielded similar values, revealing a linear behavior, with correlation coefficients R = 0.9968 and R_adj = 0.9921 for TA degradation and R = 0.9828 and R_adj = 0.9570 for H₂O₂ photolysis. The most efficient combination of variables was [H₂O₂] = 255 mg L^-1 and [TA] = 25 mg L^-1, resulting in 100% TA degradation and 98.87% H₂O₂ photolysis by 90 min of treatment. Additionally, the second-order kinetic constant of the reaction between TA and HO^● was determined using a competitive kinetic model, employing 2,4-dichlorophenoxyacetic acid (2,4D) as the reference compound. The kinetic constant was 1.9 × 10¹⁰ M^-1 s^-1 in alkaline medium. TA degradation by direct photolysis generated quinone imines as by-products, responsible for the formation of a dark red "internal filter" that increased the value of acute toxicity to Artemia salina. The UV-ABC/H₂O₂ process did not promote formation of quinone imines by 90 min of treatment and therefore did not increase acute toxicity values. Several by-products generated during TA degradation were identified and possible degradation pathways for the UV-ABC and UV-ABC/H₂O₂ processes were proposed.

Analytical tools employed to determine pharmaceutical compounds in wastewaters after application of advanced oxidation processes

Today, the presence of contaminants in the environment is a topic of interest for society in general and for the scientific community in particular. A very large amount of different chemical substances reaches the environment after passing through wastewater treatment plants without being eliminated. This is due to the inefficiency of conventional removal processes and the lack of government regulations. The list of compounds entering treatment plants is gradually becoming longer and more varied because most of these compounds come from pharmaceuticals, hormones or personal care products, which are increasingly used by modern society. As a result of this increase in compound variety, to address these emerging pollutants, the development of new and more efficient removal technologies is needed. Different advanced oxidation processes (AOPs), especially photochemical AOPs, have been proposed as supplements to traditional treatments for the elimination of pollutants, showing significant advantages over the use of conventional methods alone. This work aims to review the analytical methodologies employed for the analysis of pharmaceutical compounds from wastewater in studies in which advanced oxidation processes are applied. Due to the low concentrations of these substances in wastewater, mass spectrometry detectors are usually chosen to meet the low detection limits and identification power required. Specifically, time-of-flight detectors are required to analyse the by-products.

Degradation and acute toxicity removal of the antidepressant Fluoxetine (Prozac(®)) in aqueous systems by electron beam irradiation

Electron beam irradiation (EBI) has been considered an advanced technology for the treatment of water and wastewater, whereas very few previous investigations reported its use for removing pharmaceutical pollutants. In this study, the degradation of fluoxetine (FLX), an antidepressant marketed as Prozac(®), was investigated by using EBI at FLX initial concentration of 19.4 ± 0.2 mg L(-1). More than 90 % FLX degradation was achieved at 0.5 kGy, with FLX below the detection limit (0.012 mg L(-1)) at doses higher than 2.5 kGy. The elucidation of organic byproducts performed using direct injection mass spectrometry, along with the results of ion chromatography, indicated hydroxylation of FLX molecules with release of fluoride and nitrate anions. Nevertheless, about 80 % of the total organic carbon concentration remained even for 7.5 kGy or higher doses. The decreases in acute toxicity achieved 86.8 and 9.6 % for Daphnia similis and Vibrio fischeri after EBI exposure at 5 kGy, respectively. These results suggest that EBI could be an alternative to eliminate FLX and to decrease residual toxicity from wastewater generated in pharmaceutical formulation facilities, although further investigation is needed for correlating the FLX degradation mechanism with the toxicity results.