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Abstract

By combining a large variety of analytical techniques this study aimed at elaborating methods to follow up the degradation of sulfonamides in an advanced oxidation process (AOP): irradiation with ionizing radiation in dilute aqueous solution. In this process, besides other radicals, hydroxyl radicals are produced. As pulse radiolysis experiments show the basic initial reaction is hydroxyl radical addition to the benzene ring, forming cyclohexadienyl radical intermediates. In aerated solutions these radicals transform to peroxy radicals. Among the first formed products aromatic molecules hydroxylated in the benzene rings or in some cases in the heterocyclic rings were observed by LC-MS/MS. Chemical oxygen demand (COD) measurements indicate that at the early reaction period of degradation one hydroxyl radical induces incorporation of 1.5 O atoms into the products. Comparison of the COD and TOC (total organic carbon content) results shows gradual oxidation. Simultaneously with hydroxylation ring opening also takes place. The kinetics of inorganic SO4(2-) and NH4(+) formation, analyzed by ion chromatography, is similar to the kinetics of ring degradation (UV spectroscopy), however, there is a delayed formation of NO3(-). The latter ions may be produced in oxidative degradation of smaller N containing fragments. The S atoms of the sulfonamides remain in the solution (ICP-MS measurements) after degradation, whereas some part of the N atoms leaves the solution probably in the form of N2 (total nitrogen content (TN) measurements). Degradation is accompanied by a high pH drop due to formation of SO4(2-), NO3(-) and smaller organic acids. The degradation goes through many simultaneous and consecutive reactions, and with the applied methods the different stages of degradation can be characterized.

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... In these papers, the rate constants of these reactions and the most probable sites of radical attacks have been published together with the first formed radical intermediates (transient products). In another group of papers the authors investigated the stable products (usually qualitatively) (e.g., Sági et al., 2015;Tegze et al., 2018) and among the products small fragmented organic molecules, mainly small molecular mass acids, were also observed (e.g., Liu et al., 2014;Panizza et al., 2014;Giannakis et al., 2015;Chu et al., 2019). At the end of degradation, small inorganic molecules remain in the solution (H 2 O, CO 2, etc.). ...
... The theoretical values for formaldehyde and acetic acid are 0, for formic acid the value is +2 and for oxalic acid it is +3 (Al Momani et al., 2004). In agreement with the formation of organic acids, the pH in irradiated solutions strongly decreased during the treatment in all systems investigated (e.g., Sági et al., 2015). In gamma radiolytic degradation of sulfamethazine, Liu et al. (2014) observed the formation of several acids (e.g., formic acid, acetic acid). ...
... These data show that at early parts of the process, the number of O 2 molecules in the products is on average 0.75, higher than in the starting molecules. In agreement with the high value, in addition to simple phenols, some products with higher oxidized state should also form even at low doses (Sági et al., 2015). These results are consistent with LC-MS/MS results, which evidenced incorporation of not only 1 but also 2 or more OH groups into the structure of initial molecules (formation of hydroxylated, dihydroxylated, etc., products) in the 0.2 -0.8 kGy absorbed dose range (Sági et al., 2015). ...
... Gradient type elution and positive ionization mode was applied with electrospray ionization (ESI), using Agilent 1200 LC and Agilent 6410 MS devices. Further details are described in our previous study (Sági et al., 2015). Advanced oxidation was carried out at room temperature by a 60 Co panoramic type γ-irradiation facility (dose rate = 7.6 kGy h -1 ). ...
... The major reactant under the experimental conditions used is the hydroxyl radical ( • OH) . The solutions irradiated with 1 kGy absorbed dose contain hydroxylated products overwhelmingly, but initial molecules are also present in low amounts (Guo et al., 2012;Sági et al., 2015). Prolonged irradiation with 2.5 kGy leads to decomposition of all these molecules and entails appearance of low molecular mass acids (Liu and Wang, 2013;Sági et al., 2015). ...
... The solutions irradiated with 1 kGy absorbed dose contain hydroxylated products overwhelmingly, but initial molecules are also present in low amounts (Guo et al., 2012;Sági et al., 2015). Prolonged irradiation with 2.5 kGy leads to decomposition of all these molecules and entails appearance of low molecular mass acids (Liu and Wang, 2013;Sági et al., 2015). As these two product groups (hydroxylated products and low molecular mass acids) separate distinctively, 1 kGy and 2.5 kGy doses were used for the sample treatment. ...
Article
AOP are in the focus of interest as a result of their high efficiency in persistent organic pollutant removal. In the vast majority of experiments targeting quantification of changes in biodegradability or toxicity, conclusions are drawn by a simple comparison of solutions obtained at different stages of the oxidation. These results do not express properly the toxic potential or biodegradability of distinctive product groups, due to performing investigations without taking into account the decrease of organic content caused by mineralization. Moreover, the presence of H2O2 is very often also neglected, although it usually exerts strong interfering effects in the analytical methods applied routinely. The aim of present study was to draw attention towards these effects. In this work, the H2O2 content was removed by catalytic decomposition with MnO2, while exposure to equal pollutant concentrations was achieved by setting the solutions to equal COD or TOC values. Results obtained in such way (biological approach) have been compared to data obtained by neglecting both factors (technological approach). Biodegradation and ecotoxicity experiments were performed on the example of 0.1 mmol dm−3 sulfamethoxazole solutions oxidized during gamma irradiation. Significant differences were evidenced between the two approaches. Technological approach indicted only moderate transformation to bioavailable substances (BOD5 COD−1 = 0.33), while the biological approach referred to ready biodegradability (0.82). Ecotoxicity assessment performed with Vibrio fischeri bacteria demonstrated differences not only in the extent but also in the tendency of inhibition changes. In order to make reliable ecotoxicity assays, the H2O2 concentrations should be reduced to at least 0.05 mmol dm−3 in V. fischeri and P. subcapitata experiments, while, practically complete removal is needed in case of D. magna. In BOD measurements performed by manometric techniques, reducing the H2O2 concentration to at least 0.05 mmol dm−3 is also recommended.
... Folic acid synthesis and sulfonamides site of folic acid metabolism inhibition are presented schematically in Figure 6. Table 2. Commercial sulfonamide drugs available in RS and USA market 6(1) (2017) [58][59][60][61][62][63][64][65][66][67][68][69][70][71] Sulfonamides application in therapy Nowadays, sulfonamides are most frequently used in the treatment of urinary tract infections caused by susceptible strains of bacteria. Acute, uncomplicated urinary tract infections caused by E. coli and other bacteria can be adequately treated with sulfamethoxazole (SMX) and trimethoprim (TMP) combination [18]. ...
... Antimicrobial sulfonamides and their metabolites are classified as persistent organic pollutants, due to their resistance to biodegradation [60]. Conventional purification techniques, such as filtration, coagulation, flocculation and sedimentation are not sufficiently effective in the case of sulfonamides and their metabolites. ...
... Ionizing radiation In addition to all above mentioned AOPs, ionizing radiation at the dose of 0.6 kGy can be also applied for sulfonamides degradation [60]. Sulfonamide degradation begins with the hydroxyl radical addition to a benzene ring resulting in the cyclohexadienyl radical. ...
Article
Full-text available
Sulfonamides are the first successfully synthesized antimicrobial drugs. The mechanism of sulfonamides antimicrobial action involves competitive inhibition of folic acid synthesis which prevents the growth and reproduction of microorganisms. Due to this mechanism of action, sulfonamides belong to the group of bacteriostatic agents. Although they have been applied in therapy for more than 70 years, sulfonamides are still the drugs of choice for the treatment of several conditions and diseases. A wider sulfonamides application in the therapy is limited by bacterial resistance and sulfonamides side effects. Antimicrobial sulfonamides and their metabolites are classified as persistent organic pollutants. For sulfonamides degradation and removal from the environment, various techniques can be applied such as different oxidation techniques, including chlorination and advanced oxidation processes, adsorption processes, membrane processes and combined processes.
... Changes in the solution composition due to addition of MnO 2 or CAT have been followed up by a Jasco 550 UV-Vis spectrophotometer and by an Agilent Technologies 6410 Triple Quadrupole LC-MS/MS system as described previously Kovács et al., 2014Kovács et al., , 2015Kovács et al., , 2016Sági et al., 2015). The H 2 O 2 content was determined by using the Cu(II)/phenanthroline test (Merck test) before and after H 2 O 2 removal. ...
... According to the chromatographic analyses, about 50% of the starting SMX molecules decomposed at this dose. At the same time, the concentration of the first products (mainly molecules hydroxylated in the aromatic ring) showed a maximum at this stage (Sági et al., 2015). These products highly disturb the H 2 O 2 determination by the technique applied. ...
... The intensity of this absorbance steadily decreased with the increasing amount of oxidizing radicals and a new absorption band appeared between 270 and 320 nm as a shoulder on the 258 nm band (Fig. 4A). This new band was assigned to molecules hydroxylated in the aromatic ring (Sági et al., 2015). The intensity of the shoulder was the highest at 0.17 mmol dm −3 • OH dose. ...
Article
Being a toxic substance, hydrogen peroxide (H2O2) formed during application of advanced oxidation processes disturbs the biological assessment of the treated solutions. Therefore, its removal is necessary when the concentration exceeds the critical level relevant to the biological tests. In this study, H2O2 removal was tested using catalase enzyme or MnO2 as catalysts and the concentration changes were measured by the Cu(II)/phenanthroline method. MnO2 and Cu(II) ions were found to react not only with H2O2 but also with the partly oxidized intermediates formed in the hydroxyl radical induced degradation of aromatic antibiotic and pesticide compounds. Catalase proved to be a milder oxidant, it did not show significant effects on the composition of organic molecules. The Cu(II)/phenanthroline method gives the correct H2O2 concentration only in the absence of easily oxidizable compounds, e.g. certain phenol type molecules.
... The influence of solution pH, additives, and radical scavengers on the degradation of sulfadiazine [29] and sulfamethoxazole [30] were broadly investigated. Recently, Sági et al., also conducted pulse radiolysis of SAs and observed gradual oxidation of target compounds with various intermediates, especially including the hydroxylated and inorganic ion products [31]. However, the fate of SAs and their degradation intermediates treated by ionizing radiation with high selectivity and accurate structural information is not sufficient. ...
... In case of nitrite and nitrate, they were not identified in any sample. A similar result was also reported in the study conducted by Sági et al., showing a delayed and low formation of nitrate after ionizing radiation treatment of sulfonamide antibiotics [31]. The formation of nitrate may require higher energy to decompose. ...
... The formation of nitrate may require higher energy to decompose. Nitrate can be produced after destruction of aromatic ring structure, so it was not observed in measurable quantity at lower absorbed doses [31]. Overall, some products caused by bond cleavage and hydroxylation were commonly observed, when compared with other oxidation processes for degrading SMX. ...
... [14][15][16] The effect of ionizing radiation on the removal efficiency, degradation mechanisms and ecotoxicity of SMX or TMP solutions have been previously described. [17][18][19][20] However, there have been no reports, to the best of our knowledge, on the efficacy of this technology in terms of residual antimicrobial activity either singly or when present in mixtures of these two antimicrobials. ...
... The analytical procedures were similar to what we had described earlier. [18] The data was analyzed and presented as a C/C 0 ratio (final concentration/initial concentration). The G-values (radiation chemical yields) were calculated as described by Buxton. ...
Article
The response of the antimicrobial compounds sulfamethoxazole (SMX) and trimethoprim (TMP) – individually and in mixtures – to ionizing radiation was investigated using laboratory prepared mixtures and a commercial pharmaceutical formulation. The residual antibacterial activity of the solutions was monitored using Staphylococcus aureus and Escherichia coli test strains. Based on antibacterial activity, SMX was more susceptible to ionizing radiation as compared to TMP. The antibacterial activity of SMX and TMP was completely eliminated at 0.2 kGy and 0.8 kGy, respectively. However, when SMX and TMP were in a mixture, the dose required to eliminate the antibacterial activity was 10 kGy, implying a synergistic antibacterial activity when these are present in mixtures. Only when the antibiotic concentration was below the Minimum Inhibitory Concentration of TMP (i.e., 2 µmol dm–3) did the antibacterial activity of the SMX and TMP mixture disappear. These results imply that the synergistic antimicrobial activity of antimicrobial compounds in pharmaceutical waste streams is a strong possibility. Therefore, antimicrobial activity assays should be included when evaluating the use of ionizing radiation technology for the remediation of pharmaceutical or municipal waste streams.
... The slow increases of COD and TOC removal percentages with the dose should be connected to the high molecular masses of these compounds (CIP 331.3 and NOR 319.3 Da mol −1 ). About two times higher removal efficiencies were found in the case of smaller molecules like fenuron, monuron, diuron or sulfometoxazole (Kovács et al., 2014(Kovács et al., , 2015(Kovács et al., , 2016Sági et al., 2015). Slow COD and TOC removals were also observed in fluoroquinolone solutions in Fenton, electro-Fenton, direct photolytic, photocatalytic and ozonation experiments (Yahya et al., 2014;de Souza Santos et al., 2015;Vasconcelos et al., 2009). ...
... The nitrogen content remained constant over the dose-range investigated, indicating that nitrogen containing volatile compounds did not form in course of irradiation. This finding is similar to those reported for other antibiotics (Liu and Wang, 2013;Sági et al., 2015). ...
Article
This work aimed at investigating the ionizing radiation induced degradation of two fluoroquinolone antibiotics: norfloxacin and ciprofloxacin. At 0.1 mmol dm−3 concentration a low dose, 2 kGy was sufficient to degrade the initial molecules. However, despite of the high removal efficiency the degrees of both the mineralization and the oxidation were low,∼10% and ∼25%, respectively. (The difference between the results obtained in norfloxacin and ciprofloxacin solutions was not statistically significant.) Broth microdilution tests carried out on Staphylococcus aureus evidenced removal of antibacterial activity in samples irradiated with 2 kGy. Acute toxicity determined on Vibrio fischeri bacteria showed increased toxicity at low doses indicating that the early degradation products were more toxic than the initial molecules. The results of biodegradation experiments performed in activated sludge have shown that the degradation products have become available to the metabolic processes of the microorganisms.
... Sulfonamide antibiotics, which prevent the multiplication of bacteria, are usually applied in combination with trimethoprim [20]. The COD meas /ThOD values for sulfonamides are in the 0.82-1.05 ...
Article
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The long time (2 h) required for measurement, expensive chemicals (Ag2SO4), and toxic reagents (K2Cr2O7, HgSO4) limit the application of the standard method for measuring the oxygen equivalent of organic content in wastewater (chemical oxygen demand, COD). In recent years, the COD has increasingly been replaced by the total organic carbon (TOC) parameter. Since the limit values of the pollution levels are usually given in terms of the COD, efforts are being made to find the correlation between these parameters. Several papers have published correlation analyses of COD and TOC for industrial and municipal wastewater, but the relationship has not been discussed for individual chemicals. Here, this relationship was investigated using 70 contaminants (laboratory chemicals, pharmaceuticals, and pesticides). The calculated COD values, in most cases, agreed, within ~10%, with the experimental ones; for tetracyclines and some chloroaromatic molecules, the measured values were 20–50% lower than the calculated values. The COD/TOC ratios were between 2 and 3: for macrolides, they were ~3; for fluoroquinolones and tetracyclines, they were ~2. The molecular structure dependence of the ratio necessitates the establishing of the correlation on an individual basis. In advanced oxidation processes (AOPs), the ratio changes during degradation, limiting the application of TOC instead of COD.
... Moreover, various studies showed that the aging significantly promoted the sorption of various chemicals (antibiotics, heavy metals etc.) on the aged microplastics (Zhou et al. 2020;Liu et al. 2019b,c). In addition, the occurrences of reactive species are also contributing to photo transformation processes such as oxidation kinetics and inducing the degradation of substances (Ge et al. 2019;Sági et al. 2015). ...
Article
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The presence of microplastics in the indoor environment presents growing environmental and human health risks because of their physicochemical and toxic characteristics. Therefore, we aimed to isolate, identify, and characterize plastic debris in settled house floor dusts. This study is a rare study which assess the risks of plastic debris in settled house dust through multiple approaches including the estimated daily intake, pollution loading index, and polymer hazard index. The results indicated that polyethylene and polypropylene were the predominate polymer type of plastic debris in settled house dust with various shapes and colors. The risk assessment results also indicated the serious impact of microplastics in terms of extremely dangerous contamination as well as the fact that they present a polymer hazard. Results indicated that humans have a higher risk of exposure to microplastics via ingestion rather than inhalation. In addition, infants had a higher risk of potential intake compared to other age groups.
... Yadav et al. studied that the concentration of SDZ degradation though photocatalytic reactions and AOPs, and the results showed that the photo-sulfate oxidation (UV-C/PS) system is efficient and economical in removing SDZ and others organic pollutants with similar physical and chemicals properties [17]. Furthermore, radical-based advance oxidation processes particularly •OH and SO 4 •− generated by UV irradiation to activate H 2 O 2 and peroxymonosulfate (PMS) or peroxydisulfate (PDS), are strongly oxidizing for the sulfonamides, with rate constants of (2.62 − 11) × 10 9 M − 1 s − 1 (k SDZ+•OH ) [18][19][20][21][22][23] and 8.6 × 10 9 M − 1 s − 1 (k SDZ+SO4•− ) [24] reported between SDZ and •OH and SO 4 •− , respectively. The other reactive species, like CO 3 •− , also play great attentions due to the presence in the aqueous environment and wastewater, with the importance of carbonate radicals identified [23,25,26]. ...
... During Fenton and photo-Fenton reactions, HO• radicals can react non-selectively with organic compounds [24,26,27,[30][31][32][33] (Equations (4)-(6)): ...
Article
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Sulfonamides used in veterinary medicine can be degraded via the Fenton processes. In the premise, the process should also remove the antimicrobial activity of wastewater containing antibiotics. The kinetics of sulfathiazole degradation and identification of the degradation products were investigated in the experiments. In addition, their toxicity against Vibrio fischeri, the MARA® assay, and unselected microorganisms from a wastewater treatment plant and the river was evaluated. It was found that in the Fenton process, the sulfathiazole degradation was described by the following kinetic equation: r0 = k CSTZ−1 or 0 CFe(II)3 CH2O20 or 1 CTOC−2, where r0 is the initial reaction rate, k is the reaction rate constant, C is the concentration of sulfathiazole, Fe(II) ions, hydrogen peroxide and total organic carbon, respectively. The reaction efficiency and the useful pH range (up to pH 5) could be increased by UVa irradiation of the reaction mixture. Eighteen organic degradation products of sulfathiazole were detected and identified, and a possible degradation mechanism was proposed. An increase in the H2O2 dose, to obtain a high degree of mineralization of sulfonamide, resulted in an increase in the ecotoxicity of the post-reaction mixture.
... Currently, experiments on extending the useful irradiation spectrum in the heterogenous photocatalysis are carried out [28,29]. They even initiate the decomposition of non-biodegradable organic compounds [30][31][32][33][34][35][36][37][38]. In addition to the effective degradation of antibiotics, the photocatalytic process also affects the inactivation of ARGs, the disinfection of the processed material, and sometimes the complete mineralization of pollutants [34,39]. ...
Article
Full-text available
The aims of the study were to determine the kinetics of the photocatalytic degradation of six sulfonamides in the presence of TiO2-P25 in acidic, neutral, and alkaline solutions and to identify the structures of the stable products. It was stated that the pH of the solution significantly affected the photocatalytic degradation rate of sulfonamides in acidic and alkaline environments, and the effect likely depended on the susceptibility of sulfonamides to attack by hydroxyl radicals. In the post-reaction mixture, we identified the compounds resulting from the substitution of the aromatic rings with a hydroxyl group; the amide hydrolysis products; the hydroxylamine-, azo, and nitro derivatives; and the compounds formed via the elimination of the sulfone group. Moreover, previously unknown azo compounds were detected. Some degradation products of sulfonamides may exhibit marked bacteriostatic activity and high phytotoxicity. The azo and nitro compounds formed in an acidic environment may be potentially more toxic to aquatic ecosystems than the initial compounds.
... As previous researches reported, the role of 1 O 2 was mainly oxidized at the amino-N site which belonged to the organic compounds with six-membered heterocyclic groups (Ge et al., 2019). Similar degradation pathways on sulfapyridine and sulfamethazine were observed as previously reported (Sagi et al., 2015;Xu et al., 2014). Therefore, the compound with the chemical formula C 10 H 8 N 4 O was determined as the intermediate caused by 1 O 2 . ...
Article
Occurring naturally siderite (FeCO3) was used as the heterogeneous catalyst to activate peroxodisulfate (PDS) for the degradation of sulfadiazine under different initial pH values. The findings of this system exhibited various ROS (e.g. ¹O2, SO·4⁻ and ·OH) present during a wide range of pH values. Among them, ¹O2 could significantly facilitate the initial degradation rate, and the increased pH enhanced the role of ¹O2. The factors including initial pH values, siderite dosage, PDS concentration, initial contaminants concentration, and water matrix were discussed. The role of each ROS was investigated through quenching test and electron paramagnetic resonance (EPR). Furthermore, the comprehensive degradation process was proposed based on the LC-MS results. And the cycle test demonstrates the reusability of siderite at a pH of 3. Accordingly, this study is of great significance for understanding the degradation of such sulfonamide pollutants in the siderite/PDS system.
... Carbonate-radicals and hydroxyl radicals are capable of oxidizing sulfonamide-based compounds, which suggest that the sulfonamide-based polyfluorinated compounds in AFFFimpacted waters also are likely susceptible to transformation via carbonate and hydroxyl radicals. 15,16 However, the relative impacts of these radicals on transformation of the polyfluorinated compounds present in AFFF have not been evaluated. ...
Article
Bench-scale experiments were performed to evaluate the electrochemical oxidation, via direct anodic oxidation and indirect oxidation from salt-derived species, of diluted aqueous film forming foam (AFFF) in brine solutions to mimic anion exchange resin regenerant solutions that are loaded with poly- and perfluoroalkyl substances (PFASs). Results showed that initial transformations of the polyfluorinated compounds, which accounted for approximately 45% of the organic fluorine in the initial mixtures, occurred primarily via an indirect oxidation pathway that targeted the non-fluorinated head groups. Depending on the brine solution, this indirect oxidation likely occurred via hydroxyl radical production or salt-derived oxidants (e.g., SO4•- derived from anodic oxidation of sulfate). However, perfluoroalkyl acid (PFAA) transformation and the overall rate of defluorination were controlled via a combination of direct and indirect electron transfer. Chloride levels (>0.2% by weight) and the presence of 100 mM of the radical scavenger tert-butyl alcohol substantially reduced pseudo first order defluorination rate constants by up to 80%. Evaluation of fluorine mass balances (via fluoride generation and PFAS levels) suggested that up to approximately 41% (based on a fluorine mass balance) electrochemically transformed intermediate products were not identified under some conditions. Thus, evaluating electrochemical treatment effectiveness solely on the disappearance of PFAAs and other suspect analytes described in current analytical libraries could substantially underestimate the PFAS mass remaining in AFFF-impacted waters.
... S7) which is due to sulfate acid employed for adjusting pH value at 4.5. Meanwhile, they are subsequently detected at 3.21, 3.63, 8.88, 9.61 min with increasing in intensities when the reaction is ongoing, implying that SMX has been decomposed in BF-PMCs/ H 2 O 2 system associated with both desulfonation and denitrification by bond cleavage [59,60]. Therefore, according to HO Å detected above in BF-PMCs/H 2 O 2 system, possible pathways of SMX are proposed in Fig. 9. ...
Article
Sulfonamides as the major antibiotic have become emerging contaminants worldwide in aquatic environments. Herein, a heterogeneous Fenton-like oxidation driven by a novel BF-PMCs bismuth ferrites reported firstly for efficient degradation of sulfamethoxazole (SMX) in which the possible degradation pathways are thoroughly analyzed through identifying some of key intermediates (i.e., C8H11N3O4S, C4H4NO2, etc.) using liquid chromatography-mass spectrum (LC-MS), monitoring organic acids (i.e., acetic acid, pyruvic acid) and inorganic anions (i.e., sulfate, nitrate) using ion chromatography (IC), and detecting radical species (i.e., HO•) using both chemical quenchers and fluorescence technique, simultaneously. The optimal operations in BF-PMCs/H2O2 system for SMX degradation are recommended at the conditions of initial pH ∼4.5, 1.5 mg L⁻¹ [SMX], 70 mM [H2O2], and BF-PMCs loading of 0.2 g L⁻¹. The degradation rates (kinetic value of kapp) for SMX, azoxystrobin, bisphenol A, and 2,4-dichlorophenol are 9.5 × 10⁻³, 13.6 × 10⁻³, 7.3 × 10⁻³, and 5.9 × 10⁻³ min⁻¹, respectively. Meanwhile, the degradation rates in BF-PMCs/H2O2 system for SMX degradation are slightly slower in the presence of inorganic anions (e.g., Cl–, NO3–) and NOM (e.g., humic acid). Based on an overall consideration, the BF-PMCs/H2O2 system has great potential for degradation of emerging organic pollutants (EOPs) in natural water systems.
... Klebsiellapneumoniaee, Pseudomonas and Enterococcusspecies in medical institutions causes treatment failure, which can lead to further complications, especially in children, old people and immune compromised patients. The use of sulfonamides and other antimicrobial medications in the various treatments leads to a continuous introduction into the environment, spreading over and maintaining drug bacterial (23). ...
Article
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Carbon nanotubes (CNTs) were synthesized via liquefied petroleum gas (LPG) as precursor using flame fragments deposition (FFD) technique. In vitro, biological activates of carbon nanotubes (CNTs) synthesized by FFD technique were investigated. The physiochemical characterizations of synthesized CNTs are similar to other synthesized CNTs and to the standard sample. Pharmaceutical application of synthesized CNTs was studied via conjugation and adsorption with different types of medicines as promote groups. The conjugation of CNTs was performed by adsorption the drugs such as sulfamethoxazole (SMX) and trimethoprim (TMP) on CNTs depending on physical properties of both bonded parts. The synthesized CNTs almost have the same performance in antibiotic activity compared with standard sample of CNTs (commercial CNTs).The products were effective antibiotic in the treatment as resistant bacteria, may higher concentration of CNTs would have antibacterial activity on multi-drug resistant bacteria such as Acinetobacter and also on resistant E.coli. The bioactivity synthesized and standard samples of CNTs were almost the same against different types of bacteria.
... These byproducts were also identified by other authors (Sailo et al., 2017). The hydroxylation is expected to be a common reaction responsible for SNs degradation (S� agi et al., 2015;Dong et al., 2018). Moreover, the initial reaction corresponds with the addition of the hydroxyl radical to the benzene ring . ...
Article
This study was aimed at the degradation of sulfonamides (SNs) via oxidation with Fe(VI). The reaction kinetics, identification of degradation byproducts and their toxicity were investigated. The pH solution and Fe(VI) loading had significant effects on the degradation of the sulfonamides. The maximum degradation rate occurred at pH 3.0 with a 6:1 ratio Fe(VI): sulfonamide, obtaining 100% degradation of 15 mg L À 1 SN within 5 min. Although Fe (VI) also showed an appreciable reactivity towards SNs (k app ¼ 9.85-19.63 � 10 2 M À 1 s À 1) at pH 7. The influence of solution pH on the values of k app can be explained considering the specific reaction between Fe(VI) and SNs. Degradation rates are also influenced by the presence of inorganic ions in different water matrixes. For this reason, ions present in groundwater enhanced the SNs degradation through a synergistic effect among carbon-ates, sulfates and Fe(VI). Degradation byproducts identified, through UPLC analysis, allowed us to proposed three degradation pathways depending on pH. At acid pH there is a cleavage of C-S and S-N bonds. At neutral pH nitroso and nitro-derivates are formed. At basic pH hydroxylation is the main reaction. The cytotoxicity assay of HEK-293 and J774 cell lines exposed to Fe(VI) indicated that transformation byproducts had a lower toxicity than SNs as baseline products. Accordingly, this research suggests that Fe(VI) can act as a chemical oxidant to remove SNs antibiotics and it can be used to treat antibiotic pollution in wastewater.
... Since SDMD was mainly degraded through direct photolysis, indirect photolysis induced by ·OH only played a minor role in SDMD removal. In view of the nonselectivity of ·OH to react with organic pollutants and high reactivity to sulfonamides [43], ·OH formed in natural sunlit waters might play important roles in the photodegradation of SDMD and other sulfonamides. ...
Article
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Background The extensive uses of sulfadimidine (SDMD) resulted in its presence in water bodies, and subsequent posed risks to eco-environment and human health. In this study, photodegradation of SDMD in water was studied under UV–Visible irradiation. The intermediates, degradation pathways of SDMD photodegradation and ecological risk of SDMD were investigated as well. Results SDMD was rapidly degraded under alkaline conditions. Nitrate ion enhanced SDMD degradation under UV–Vis irradiation, while dissolved organic matter and Fe(III) inhibited its decay, and bicarbonate ion did not exert any effect. The reactive species involved in the SDMD photodegradation was singlet oxygen. Four major transformation products were identified by high-performance liquid chromatography–mass spectrometry (HPLC–MS), and the photolytic pathway was also proposed. Photoinduced hydrolysis, desulfonation and photooxidation were the major photodegradation mechanisms for SDMD. Toxicity analysis with Vibrio fischeri showed an obvious decrease in toxicity of the reaction solution, from the initial inhibition rate of 38.5% to 0% after 150-min irradiation. Conclusion Initial pH and common water constituents influence the photo-degradation of SDMD under UV–Vis irradiation. Photodegradation of SDMD could reduce its ecological risk in the aqueous solution.
... The corresponding MS and MS 2 mass spectra in positive ionisation mode are displayed in Fig. S6. Referring to the Nitrogen rule and the analytical approaches in previous studies (Baena-Nogueras et al., 2017;S agi et al., 2015), chemical structures were proposed and tentative phototransformation pathways for the four SAs are presented in Fig. 4. ...
Article
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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.
... Next, given the oxidation of OH% radical during the process, hydroxylation is expected to be a common reaction responsible for SMZ degradation, generating by-products P3-1, P3-2, P5-1 or P5-2. Sági et al. (2015) reported that the basic initial reaction is the addition of the hydroxyl radical to the benzene ring or, in some cases, heterocyclic rings, forming radical intermediates of cyclohexadiene accompanied by a fall in pH due to the formation of SO 4 2− and smaller organic acids. A break in the eSO 2 e and eNHe bond allows identification of by-product P2, of low molecular weight, as previously reported in the mineralization pathway . ...
Article
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 kλ 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.
... The best-fitting formulas of them were C 10 H 11 N 3 O 4 S and C 4 H 6 N 2 O, respectively. These two compounds were reported in many research papers as intermediate products of SMX by various types of advanced oxidation processes (AOPs), too (Trovó et al., 2009;Xu et al., 2012;Sági et al., 2015). The attack of one hydroxyl radical to the SMX molecule led to the generation of intermediate C8, a hydroxylated benzene ring, while the cleavage of the S\ \N bond resulted in the formation of intermediate C9, a methylated amino isoxazol. ...
Article
Fe(II) activated sodium percarbonate (SPC) process (SPC/Fe(II)) could efficiently remove sulfamethoxazole (SMX) in the aqueous phase, and has the potential in groundwater remediation. However, the degradation mechanisms, especially the degradation products and pathways till now have remained unclear. In the present study, intermediate products were identified using high resolution liquid chromatography coupled with ion trap and time-of-flight mass spectrometry (LCMS-IT-TOF). Nine intermediate products were identified, six of which have not yet been reported during the oxidation of SMX. The oxidation mechanisms involved hydroxyl substitution, the cleavage of sulfonamide bond, isoxazole ring opening and a rearrangement following the loss of the SO2-group. Based on the identified intermediate products, the degradation pathways of SMX by SPC/Fe(II) process were illustrated. Fenton's reaction after the dissolution of SPC was proposed as the main reaction mechanisms, which was checked and confirmed by radical species detection tests and radical species scavenging studies. The results showed that although both O2[rad]⁻ and HO[rad] were present in SPC/Fe(II) system, HO[rad] was dominant in the system while O2[rad]⁻ was seldom involved in the degradation of SMX. These findings provided useful information and supported the application of this advanced oxidation process for antibiotics elimination in the groundwater.
... Sulfadiazine is a kind of synthetic antimicrobial agent, which is the derivative of sulfanilamide. There are several investigations in the literature dealing with identifications of products formed in %OH reactions with sulfonamides in AOPs [28][29][30][31][32]. These study suggest that the basic initial reaction is hydroxyl radical addition to the benzene ring, forming hydroxylate aromatic molecules. ...
Article
Antibiotics degradation remains a longstanding challenge in wastewater treatment. Towards this objective, we have developed a novel technique combining cavitating jets impingement with multiple synergetic methods, i.e., UV/Fenton, analogous Fenton, and photocatalytic oxidation in the present work. Three kinds of antibiotics namely amoxicillin, doxycycline and sulfadiazine sodium, are selected as model pollutants. Individual application of cavitating jets impingement is firstly conducted to evaluate the effects of jets impinging forms and nozzle inlet pressure. The effects of impingement on promoting antibiotics degradation and weakening the coalescing effects of cavitation bubbles are confirmed. Perpendicular double cavitating jets impingement is proved to be the most effective impinging form and brought a COD (chemical oxidation demand) reduction of 30.04% with the impinging effect index 1.22 at jet inlet pressure 10 MPa. Increasing the jet inlet pressure can improve the COD reduction and the effectiveness of impingement. Subsequently, UV/Fenton process is introduced to intensify the degradation process. The effects of important parameters are investigated by means of orthogonal experiments and the maximum COD reduction is up to 71.16% under the optimum conditions. Then, analogous Fenton process and photocatalytic oxidation are adopted for further enhancing the COD reduction. Different approaches used in the present work are assessed in view of multiple aspects. With COD reduction of 79.92%, the combination of cavitating jets impingement, UV/Fenton, analogous Fenton and photocatalytic oxidation is proved to be optimum method for antibiotic wastewater treatment.
... Liquid chromatography tandem mass spectrometry (LC-MS/MS), total organic carbon (TOC) and chemical oxygen demand (COD) measurements LC-MS/MS experiments were carried out by gradient type elution and positive ionization mode with electrospray ionization (ESI), using Agilent 1200 LC and Agilent 6410 MS devices. Further details are described in our previous study (Sági et al., 2015). TOC, a good indicator of mineralization, was measured with a Shimadzu TOC-L CSH/CSN analyzer, based on catalytic combustion and non-dispersive infrared detection. ...
Article
Numerous studies have been published on the radiolysis of sulfonamide antibiotic solutions but little effort has been made to monitor the biological properties of degradation products. A complex approach should also clarify the changes in antibacterial activity and biodegradability, besides the usual screening of toxicity. To fill this gap, the ionizing radiation induced degradation of four sulfonamide antibiotics was investigated in dilute aqueous solutions, with emphasis on the biological assessment of decomposition products. Complete removal of sulfonamides was achieved by a low absorbed dose (1.5 kGy). 2–2.5 kGy dose was needed to transform the persistent initial molecules to substances biodegradable in both river water and activated sludge. The ratio of the biological and chemical oxygen demand increased from < 0.21 to at least 0.59, but values as high as 0.80 were also measured. It was demonstrated that antibacterial activity is due to the initial molecules, as it disappeared when the sulfamethoxazole concentration decreased below the minimal inhibitory concentration (30 μM). This means that the products have no antibacterial activity. Toxicity testing performed on test organisms from three different trophic levels and activated sludge evidenced that the toxicity depends both on the test organism and on the sulfonamide used. The degradation of initial molecules is not always enough to eliminate the environmental risk due to the toxic products formed e.g. inhibitory effects to Vibrio fischeri increased by 34% at 2.5 kGy. For this reason, complex biological assessment of treated solutions has to play an important role in development and optimization of advanced treatment techniques.
... Promising results have been achieved using UV-irradiation in the presence and absence of H 2 O 2 and titanium dioxide as heterogeneous catalyst (S agi et al. 2015;Oppenl€ ander 2003;Parsons 2004;Andreozzi et al. 1999;Babi c et al. 2015;Zhang et al. 2016). Photoinduced degradation was found less effective without catalyst when the wastewater contained UV-light absorbing compounds. ...
Article
This study focuses on the degradation of the sulfonamide antibiotics, sulfadiazine, sulfamethazine, sulfamethoxazole and sulfathiazole, using ultraviolet irradiation in various conditions. Different pH's were investigated in combination with the addition of hydrogen peroxide and further oxygen removal. High-performance liquid chromatography electrospray ionization ion-trap mass spectrometry was used to identify and elucidate degradation products and to establish concentration-time curves. Previously unknown degradation products could be characterized. Reaction rate constants of all compounds and transformation products were determined. The parent sulfonamides decayed according to first-order kinetics, while the concentrations of the transformation products varied with time according to a subsequent reaction of an intermediate product. Quantum efficiencies were analyzed for mechanistic purposes. As example, sulfamethoxazole was added to effluents from a wastewater treatment plant and irradiated. Phototoxicity and environmental hazard were assessed through quantitative structure activity relationship computations. In addition, the minimal inhibition concentrations were determined for Pseudomonas fluorescens and Bacillus subtilis. Conclusions for UV-C irradiation as a fourth purification wastewater treatment stage were derived.
... Hydroxylation could take place at the aromatic ring or amine-N, but less likely at the pyridine ring due to its lower electron density (Majewsky et al., 2015;Jesús García-Galán et al., 2016). Product ion scan mass spectrum (MS/MS) revealed several characteristic fragments of m/z 266, such as m/z 186, 172, and 95, implying that hydroxylation did occur at the aromatic ring ( Fig. S4) (Sági et al., 2015). This structural assignment of m/z 266 was consistent with that reported by Majewsky et al. (2015) in activated sludge batch experiment. ...
Article
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.
... The rate constants of reactions with aromatics (Table 1). The k ÁOH s show some regular Benzene 7.8 9 10 9 Selected [13] Phenol 8.4 9 10 9 Selected [13] p-Cresol 9.2 9 10 9 Selected [13] Aniline 8.6 9 10 9 Selected [13] Chlorobenzene 5.6 9 10 9 [12] Nitrobenzene 3.5 9 10 9 Average [13] Benzoic acid 1.9 9 10 9 [12] Benzoate ion 5.9 9 10 9 Recommended [17] 17b-estradiol 5.3 9 10 9 [25] p-Nonylphenol 1.1 9 10 10 [26] Bisphenol 6.9 9 10 9 [27] Dimethyl-phthalate 3.4 9 10 9 [28] 2,4-Dichlorophenol 6.0 9 10 9 Average [29] 2,4-Dichlorophenoxyacetic acid 5.5 9 10 9 Recommended [29] Atrazine 2.4 9 10 9 Recommended [29] Simazine 2.6 9 10 9 Average [29] Prometon 2.8 9 10 9 Average [29] Fenuron 8.3 9 10 9 Recommended [29] Monuron 7.3 9 10 9 [29] Diuron 6.0 9 10 9 Average [29] Chloramphenicol 2.5 9 10 9 [30] Sulfacetamide 5.3 9 10 9 [31] Sulfamethoxazole 8.5 9 10 9 [32] Sulfamethazine 8.3 9 10 9 [32] trend with the Hammett substituent constants, but the logarithms of the rate constants do not give straight lines as a function of the substituent constants, because the k ÁOH s are controlled by both the chemical reactivity and the diffusion. The logarithms of rate constants corrected for diffusion (Eq. ...
Article
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In water treatment by ionizing radiation, and also in other advanced oxidation processes, the main goal is to destroy, or at least to deactivate harmful water contaminants: pharmaceutical compounds, pesticides, surfactants, health-care products, etc. The chemical transformations are mainly initiated by hydroxyl radicals, and the reactions of the formed carbon centered radicals with dissolved oxygen basically determine the rate of oxidation. The concentration of the target compounds is generally very low as compared to the concentration of such natural ‘impurities’ as chloride and carbonate/bicarbonate ions or the dissolved humic substances (generally referred to as dissolved organic carbon), which consume the majority of the hydroxyl radicals. The different constituents compete for reacting with radicals initiating the degradation. This manuscript discusses the radiation chemistry of this complex system. It includes the reactions of the primary water radiolysis intermediates (hydroxyl radical, hydrated electron/hydrogen atom), the reactions of radicals that form in radical transfer reactions (dichloride-, carbonate- and sulfate radical anions) and also the contribution to the degradation of organic compounds of such additives as hydrogen peroxide, ozone or persulfate.
... The rate constants with $OH (k $OH/ SAs ) were in a narrow range (6.21 Â 10 9 À9.26 Â 10 9 M À1 s À1 ) due to the low selectivity of $OH. For the sulfonamides whose rate constants have been previously determined (shown in Table 2), the rate constants measured in this study are comparable to the reported values (Baeza and Knappe, 2011;Sagi et al., 2015;Wols et al., 2015a). Compared with $OH, larger reactivity differences in the rate constants with CO 3 $ À (k CO 3$ À /SAs ) were shown due to higher selectivity of CO 3 $ À . ...
Article
Sulfonamide antibiotics have been frequently detected in the aquatic environment and are of emerging concern due to their adverse bio-effect and potential of inducing antibiotic resistance. This study investigated the degradation kinetics of sulfonamide antibiotics in synthetic wastewater and hydrolyzed human urine by low pressure (LP) UV, UV/H2O2 and UV/peroxydisulfate (PDS). Direct photolysis rates of sulfonamide antibiotics varied and depended on the structures. Sulfonamides with a five-membered heterocyclic group underwent faster direct photolysis. For indirect photolysis processes, second-order rate constants of sulfonamide antibiotics with hydroxyl radical, sulfate radical and carbonate radical were determined, which were (6.21-9.26) × 10(9), (0.77-16.1) × 10(10) and (1.25-8.71) × 10(8) M(-1) s(-1), respectively. A dynamic model was applied and successfully predicted the degradation kinetics of sulfonamides in different water matrices. In synthetic wastewater, carbonate radical contributed to approximately 10% of the overall removal, whereas in synthetic hydrolyzed urine, carbonate radical was the dominant reactive species to degrade sulfonamides. Sulfonamide antibiotics were eliminated more efficiently in synthetic hydrolyzed urine than in synthetic wastewater and UV/PDS was more efficient than UV/H2O2 to degrade most sulfonamides. Energy evaluation showed that UV/PDS costs less energy than LPUV and UV/H2O2 under the experimental conditions applied in this study, particularly for sulfonamides whose indirect photolysis overweighed direct photolysis. By varying UV dose and oxidant dose, the UV/H2O2 process can be optimized to achieve higher efficiency than the UV/PDS process in synthetic wastewater.
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Ionizing radiation has attracted significant interests in water purifying. However, it suffers from poor mineralization performance during the decontamination of organic micropollutants such as antibiotics. Herein, the radiolytic degradation of sulfathiazole (STZ) by gamma radiation was investigated. STZ could be completely degraded at 2.0 kGy absorbed dose but TOC removal efficiency was only 22.62 %. Quenching experiments demonstrated that •OH was the main reactive species. Toxicity assessment and phytotoxicity experiments indicated that gamma radiation can comprehensively decrease the toxicity of STZ. Significant enhancements of degradation and mineralization were observed in gamma/persulfate (Gamma/PS) and gamma/periodate (Gamma/PI) processes. The rate constant (k) increased by 1.08 times and TOC removal efficiency increased by 2.01 times with PS addition (1 mM). The k value enhanced by 4.05 times and TOC removal ratio enhanced by 2.66 times with the presence of PI (1 mM). Mechanistic investigation indicated that 1O2 played a major role in STZ degradation in the Gamma/PS and Gamma/PI systems. PI was almost completely transferred into the nontoxic iodate (IO3-), and no toxic reactive iodine species were produced in the Gamma/PI process. Moreover, Gamma/PS and Gamma/PI systems showed a broad-spectrum ability to remove a series of antibiotics. The removal performances and the costs of these systems were competitive compared with other advanced oxidation processes for antibiotics elimination. This study supplied an efficient and sustainable choice for the degradation of antibiotics, and clarified the intrinsic reaction mechanisms in the ionizing radiation-activated PS and PI systems.
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Sulfonamides (SAs) are an important group of antibiotics. Due to their widespread use, they have been found as micropollutants in different ecosystems. The presence of SAs in the environment is a serious threat to human health. Degradation reactions of SAs with OH radicals are important for their removal from the environment. This study aims to predict the reaction mechanisms of selected six SAs with •OH radical by the DFT method. For this purpose conceptual DFT has been applied to SA + OH degradation reactions to find possible reaction paths. The electronic properties, global and local descriptors of SAs have been calculated. Global and local descriptors are good parameters to predict the reaction mechanisms. Local descriptors were used to find the most suitable sites for the attack of the hydroxyl radical and to predict all possible products. The proposed products and mechanism of the reactions are in agreement with experimental data.
Chapter
Municipal wastewater treatment plants and pharmaceutical manufacturing facilities are the major sources of pharmaceutical pollution. Pharmaceutical products when disposed off into the environment causes a variety of ecosystem and human health effects. The management of pharmaceuticals containing wastewater is extremely important. Traditionally, common pharmaceuticals‐laden wastewaters treatment includes biological treatment processes, membrane technology, advanced or a combination of these. Ionizing technology for the removal of pharmaceuticals in wastewater is technically feasible. Several studies have elucidated the degradation pathways of several antibiotics in aqueous solutions. Hydroxylation, desulfonation, ring cleavage, and ultimately fragmentation and mineralization are the key mechanisms involved for example in sulfonamide degradation. Toxicity and antibacterial inhibition studies of the treated wastewaters are important to rule out any undesirable toxicity or residual antibacterial activity of the breakdown products. Scavengers that could impair the efficiency of ionizing technology are also a strong possibility in wastewater. A major advantage of using ionizing technology for pharmaceutical wastewater management is that no additional chemical additives are needed.
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A method is proposed that encompasses visible light/anodic oxidation‐derived persulfates as well as the formation of a novel polyferric flocculation agent, which can synergistically treat oilfield wastewater. In this method, under irradiation of visible light, the anodic oxidation online generated sulfate is partly converted into sulfate radicals for oxidation of organic pollutants. It partly oxidizes divalent iron ions added at the end of electrolysis into polyferric species that can flocculate and degrade organic pollutants in the wastewater. The advantages of this process are environmental safety and overall low cost. Under optimal conditions (pH = 7.0, electrolysis time of 50 min, applied current intensity of 1.2 A, [Na2SO4] = 0.8 mol/L), the system exposed to simulated sunlight achieved 73.3% TOC removal, showing high efficiency in degrading organic pollutants. The experiment proved that the Na2SO4 in the electrolyte can be partially recovered.
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Green bismuth-based photocatalysts have attracted extensive attention in the field of PPCPs photodegradation. The improved carrier separation efficiency still remains a key factor to enhance photocatalytic performance. Herein, N-doped biomass carbon quantum dots (N-CQDs) decorated p-n heterojunction photocatalyst BiO2-x/BiOCl was prepared using a facile ion-etching strategy, and it displayed a markedly enhanced catalytic activity in the photodegradation of sulfonamide antibiotics. Calculated by the differential charge density, the doped N-CQDs could gather photogenerated electrons, which indicated that the introduction of N-CQDs into BiO2-x/BiOCl would effectively inhibit the recombination of photogenerated charge carriers. In addition, photocatalytic performance and density functional theory (DFT) calculation results revealed that the photogenerated electrons tended to transfer from p-BiOCl to n-BiO2-x through N-CQDs, which could generate ·O2⁻ and photogenerated h⁺ to oxidize the target pollutants. Benefiting from the synergistic effect of accelerated separation of e⁻-h⁺ in p-n heterojunction and the electron-rich performance of N-CQDs, the superb TOC removal efficiencies (89.40% within 120 min visible-light irradiation) and toxicity reduction performance of photodegradation intermediates were achieved. As a consequence, this work will provide a design of high-quality photocatalysts and a green-promising strategy for bismuth-based photocatalysts in the water treatment of PPCPs.
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The mechanism of sulfisoxazole (SFF) selective removal by photocatalysis in the presence of titanium (IV) oxide (TiO2) and iron (III) chloride (FeCl3) was explained and the kinetics and degradation pathways of SFF and other antibiotics were compared. The effects of selected inorganic ions, oxygen conditions, pH, sorption processes and formation of coordination compounds on the photocatalytic process in the presence of TiO2 were also determined. The Fe3+ compounds added to the irradiated sulfonamide (SN) solution underwent surface sorption on TiO2 particles and act as acceptors of excited electrons. Most likely, the SFF degradation is also intensified by organic radicals or cation organic radicals. These radicals can be initially generated by reaction with electron holes, hydroxyl radicals and as a result of electron transfer mediated by iron ions and then participate in propagation processes. The high sensitivity of SFF to decomposition caused by organic radicals is associated with the steric effect and the high bond polarity of the amide substituent.
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The novel heterojunction photocatalysts also known as carbon quantum dots-decorated BiOCOOH/ultrathin g-C3N4 nanosheets (CQDs/BiOCOOH/uCN) were designed, where carbon quantum dots (CQDs) acted as mediators to shuttle electrons between BiOCOOH and ultrathin g-C3N4 nanosheets (uCN). The physicochemical properties of as-obtained composites were systematically characterized by scanning electron microscopy, transmission electron microscopy, X-ray diffractometry, Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy. The 4-CQDs/BiOCOOH/uCN consisting of 50 wt% ultrathin g-C3N4 nanosheets (uCN) and 4 mL CQDs solution manifested the optimal photoactivity. After 90 min of LED lamp irradiation, the STZ degradation efficiency by 4-CQDs/BiOCOOH/uCN reached 99.28% ± 1.04, and the corresponding degree of mineralization was 49.58% ± 1.36. The enhanced photocatalytic performance of 4-CQDs/BiOCOOH/uCN was owing to the fast photogenerated charges transfer and separation revealed by photoluminescence (PL), transient photocurrent responses and electrochemical impedance spectra (EIS) measurements. By means of the radicals quenching experiments and electron spin resonance spectroscopy (ESR) analysis, it was demonstrated that •O2– and •OH were the dominant reactive species of STZ degradation. Besides, the effects of catalyst dosage (0.2 – 1.2 g/L), pH value (3.0 – 11.0), natural organic matter and different anions (Cl⁻, SO4²⁻, NO3⁻) on the photocatalytic activity of 4-CQDs/BiOCOOH/uCN composite were systematically explored. 17 main intermediates were found based on high-resolution mass spectrometry (HRMS) detection. Eventually, the 4-CQDs/BiOCOOH/uCN composite showed favorable reusability in recycling experiments, and displayed satisfactory degradation abilities for STZ in deionized water (99.28% ± 1.04), tap water (97.15% ± 1.16), river water (96.44% ± 0.76), and wastewater treatment plant effluent (96.19% ± 1.20).
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Rate coefficients (k•OH) of hydroxyl radical + antibiotic molecule reactions (c.a. 200 k•OH values for 70 molecules) were collected from published studies. Data measured in different laboratories, occasionally by different methods, were compared. Excluding the rate coefficients with values above the diffusion controlled limit and adjusting rate coefficients determined by competition kinetics, the data were averaged and the most probable values were selected. Rate coefficients for compounds with aromatic rings (e.g., amoxicillin) or conjugated double bonds (e.g., tylosin) are in the (6 – 8) × 10⁹ mol⁻¹ dm³ s⁻¹ range. The basic reaction is radical addition. The value may be smaller when strong electron withdrawing substituent, like –NO2 is attached to the ring, and N-atoms in the aromatic ring also reduce the rate coefficient. The rate coefficients for molecules without aromatic rings are smaller with values in the (3 – 6) × 10⁹ mol⁻¹ dm³ s⁻¹ range, where hydrogen abstraction reactions dominate. Carefully executed pulse radiolysis and steady-state experiments (with correct reference values) give similar rate coefficients.
Thesis
Dans ce travail, nous avons étudié la dégradation de la sulfaclozine, un antibiotique, dans des solutions aqueuses par photocatalyse (TiO2 en suspensions) ainsi que par oxydation par les ions persulfate. L'utilisation d'inhibiteurs spécifiques (KI et alcools) nous a permis de comprendre l'intervention de chacune des espèces réactives (électrons, trous, radicaux •OH) dans la dégradation de la sulfaclozine. En outre, l'identifications des produits de dégradation par LC-MS/MS et le suivi de leur cinétique d'apparition et de disparition avec et sans alcool nous a permis de proposer un mécanisme de dégradation photocatalytique faisant intervenir les trous, les radicaux •OH, les électrons, et les radicaux O2•–. Nous avons également évalués plusieurs méthodes d'activation du persulfate (UV, irradiation solaire, UV/TiO2 et Fe(II)) afin de générer des radicaux SO4•– pour dégrader la sulfaclozine. Nous avons montré qu'à pH 7, le système présentant la plus grande efficacité quelque soit la concentration de persulfate, était le système UV/TiO2/K2S2O8. L'utilisation des inhibiteurs spécifiques des radicaux •OH et SO4•– a permis de constater que le pH a un effet important sur le rôle de chacun de ces radicaux dans la dégradation de la sulfaclozine. Les constantes de vitesse de la réaction de la sulfaclozine avec les radicaux •OH et SO4•– ont été déterminées et des valeurs proches ont été trouvées (?109 M-1s-1). Nous avons également étudié l'effet des principaux ions constituants de l'eau sur la dégradation de la sulfaclozine dans les trois systèmes suivants: UV/TiO2, UV/TiO2/K2S2O8 et UV/K2S2O8. Cette étude a montré que les bicarbonates et les phosphates accélèrent la dégradation photocatalytique alors qu'aucun effet n'a été observé dans le système UV/K2S2O8. En ce qui concerne les ions chlorures et nitrates nous avons montré qu'ils augmentaient l'adsorption de la sulfaclozine à la surface de TiO2 mais n'accéléraient pas significativement la réaction de dégradation
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The potential of horseradish peroxidase (HRP) to catalyze the removal of sulfonamides from water and the effects of different H2O2and HRP concentrations were investigated. Six sulfonamides, each with a five- or six-membered heterocyclic group, including sulfamethoxazole (SMX), sulfathiazole (STZ), sulfapyridine (SPD), sulfadiazine (SDZ), sulfamerazine (SMR) and sulfamethoxypyridazine (SMP) were selected as target compounds. All sulfonamides exhibit a pseudo-first-order dependence of the concentration versus the reaction time. The decay rate (k, h-1) of the six sulfonamides spiked individually exhibit a trend following the order of STZ > SMP, SPD > SMR > SDZ » SMX. When spiked together, the coexistent sulfonamides might act as mediators for the enhancement of SMX removal and as competitors for the decreased removal of most sulfonamides. Moreover, six transformation products of SDZ are identified by the Thermo Scientific LTQ Orbitrap Elite technique. SDZ transformation involves two steps: one is the Smiles re-arrangement of the structure, and the other is oxidation and sulfur dioxide extrusion. This study is the first to report the removal dynamics of sulfonamides in HRP-catalyzed reactions and the identified products of SDZ.
Article
The widespread occurrence of pharmaceuticals and their metabolites in natural waters has raised great concerns about their potential risks on human health and ecological systems. This study systematically investigates the degradation of sulfasalazine (SSZ) and its two human metabolites, sulfapyridine (SPD) and 5-aminosalicylic acid (5-ASA), by UV and UV/peroxydisulfate (UV/PDS) processes. Experimental results show that SPD and 5-ASA were readily degraded upon UV 254 nm direct photolysis, with quantum yields measured to be (8.6 ± 0.8) × 10−3 and (2.4 ± 0.1) × 10−2 mol Einstein−1, respectively. Although SSZ was resistant to direct UV photolysis, it could be effectively removed by both UV/H2O2 and UV/PDS processes, with fluence-based pseudo-first-order rate constants determined to be 0.0030 and 0.0038 cm2 mJ−1, respectively. Second-order rate constant between SO4•− and SSZ was measured as (1.33 ± 0.01) × 109 M−1s−1 by competition kinetic method. A kinetic model was established for predicting the degradation rate of SSZ in the UV/PDS process. Increasing the dosage of PDS significantly enhanced the degradation of SSZ in the UV/PDS process, which can be well predicted by the developed kinetic model. Natural water constituents, such as natural organic matter (NOM) and bicarbonate (HCO3−), influenced the degradation of SSZ differently. The azo functional group of SSZ molecule was predicted as the reactive site susceptible to electrophilic attack by SO4•− by frontier electron densities (FEDs) calculations. Four intermediate products arising from azo bond cleavage and SO2 extrusion were identified by solid phase extraction-liquid chromatography-triple quadrupole mass spectrometry (SPE-LC-MS/MS). Based on the products identified, detailed transformation pathways for SSZ degradation in the UV/PDS system were proposed. Results reveal that UV/PDS could be an efficient approach for remediation of water contaminated by SSZ and its metabolites.
Chapter
In water treatment by ionizing radiation, and also in other advanced oxidation processes, the main goal is to destroy, or at least to deactivate harmful water contaminants: pharmaceutical compounds, pesticides, surfactants, health-care products, etc. The chemical transformations are mainly initiated by hydroxyl radicals, and the reactions of the formed carbon centered radicals with dissolved oxygen basically determine the rate of oxidation. The concentration of the target compounds is generally very low as compared to the concentration of such natural ‘impurities’ as chloride and carbonate/bicarbonate ions or the dissolved humic substances (generally referred to as dissolved organic carbon), which consume the majority of the hydroxyl radicals. The different constituents compete for reacting with radicals initiating the degradation. This manuscript discusses the radiation chemistry of this complex system. It includes the reactions of the primary water radiolysis intermediates (hydroxyl radical, hydrated electron/hydrogen atom), the reactions of radicals that form in radical transfer reactions (dichloride-, carbonate- and sulfate radical anions) and also the contribution to the degradation of organic compounds of such additives as hydrogen peroxide, ozone or persulfate.
Research
PhD Thesis Summary. Thesis title: Free Radical Chemistry of Penicillin Derivatives.
Article
Full-text available
Sulfonamide residues have been detected in all kinds of environmental water matrix. However, little attention has been so far paid to their metabolites and degradation products, and very few articles have included them in their analytical scope. The main goal of this article is to review those research studies in which both parent drugs and their respective metabolites have been considered together. We review the analytical methodologies used and assess biotic and abiotic degradation mechanisms of these antibiotics, and briefly evaluate their potential toxicity in the environment.
Article
Understanding of the molecular basis of DNA damage and its repair has increased dramatically in recent years, and substantial knowledge now exists concerning the products arising from free-radical attack on DNA. Free-radical DNA damage may lead to mutations, cancer, and cell death. Free radicals have various sources, notably ionizing radiation and oxidative stress. In radiotherapy for cancer and with some anticancer drugs, use is made of cell death by excessive DNA damage. The mechanisms leading to products of free-radical attack which have been studied in models and with small double-stranded DNA fragments are discussed in detail, and the basics of the underlying free-radical chemistry are dealt with in separate chapters.
Article
Nowadays huge amounts of pharmaceuticals, among them ibuprofen (IBU), are consumed worldwide. After administration approximately 40% of the medicine and its metabolites are excreted. Moreover, in spite of the broad campaigns about the proper disposal of the unused or expired drugs, uncontrolled quantities land every day in the wastewater. Due to their low biodegradability the wastewater treatment plants (WWTPs) are not able to remove them completely from the effluent; therefore they are present in the environment in their initial form and as their metabolites (1-hydroxy-ibuprofen (1-OH-IBU), 2-hydroxy-ibuprofen (2-OH-IBU), 3-hydroxy-ibuprofen (3-OH-IBU), carboxy-ibuprofen (CA-IBU) and carboxy-hydratropic acid (CA-HA). Several studies investigate the occurrence of these compounds and IBU itself in WWTP influents and effluents, drinking and natural waters. The detected values are mainly in the 10-12 - 10-9 mol dm-3 range. Advanced Oxidation Processes (AOPs) are effective methods to oxidize and mineralize IBU by using non-selective and highly reactive (mainly hydroxyl, •OH) radicals, which can be generated by vacuum-ultraviolet (VUV) irradiation, high-energy ionizing radiation, photocatalysis, Fenton reaction, through the degradation of hydrogen peroxide or ozone. The efficiency of these processes depends on the rate constant of •OH with the contaminant molecule (in the case of IBU k = (7.4±1.2) × 109 mol-1 dm3 s-1). Combined AOP techniques like photo-Fenton, UV/VUV, UV/H2O2 and O3/H2O2 are also efficient in the degradation of IBU; in general the combined methods show higher elimination rates. This book chapter summarises the results obtained with various AOP techniques tested to eliminate IBU. The degradation kinetics, formation of degradation products, as well as their ecotoxicity is also discussed.
Article
A new water falling film dielectric barrier discharge was applied to the degradation of sulfadiazine in the aqueous solution. The various parameters that affect the degradation of sulfadiazine and the proposed evolutionary process were investigated. The results indicated that the inner concentrations of 10 mg/L sulfadiazine can be all removed within 30 min. The optimum pH value was 9.10 and both strong acidic and alkaline solution conditions were not suitable for the degradation. The degradation of sulfadiazine can be enhanced by the addition of hydrogen radical scavengers, but be inhibited by adding hydroxyl radical scavengers. The water falling film dielectric barrier discharge was rather ineffective in mineralization, because of the intermediates were recalcitrant to be degraded. The existence of Fe2+ and CCl4 in the liquid phase can promote the degradation and mineralization of sulfadiazine. It was found that the degradation of SDZ was enhanced by CCl4 was mainly because of the increase of OH due to the reaction of CCl4 with H that reduce the chances of their recombination with OH. Based on the 8 intermediate products identified by LC–MS, the proposed evolution of the degradation process was investigated.
Article
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Article
Under radiolytic conditions at a concentration of 0.1 mmol dm−3 the reactions of sulfamethoxazole, a worldwide used anti-infective sulfonamide antibiotic, were mainly induced by hydroxyl radicals. With a dose of 5 kGy complete degradation of aromatic system was observed. The sulfur of the molecule was entirely transformed to SO42–, while NO3– and NH4+ were formed from the nitrogen content. The chemical oxygen demand and total organic carbon values indicated complete mineralization during irradiation. In pursuance of toxicity tests, the observed increase in mortality of Vibrio fischeri bacteria was mainly due to H2O2 formed during the radiolytic procedure. The results showed that the degradation was effective; therefore, the irradiation technology can be recommended for treatment of wastewater containing sulfamethoxazole.
Article
The one-electron oxidation of sulphacetamide by specific oxidizing radicals such as N.3, Br2.-, Cl.-, Tl2+ and SO4.- in the pH range 2-9.2 has been studied employing pulse radiolysis technique. The semi-oxidized species formed exhibits a pKa at pH 5.4 indicating the presence of two conjugate acid-base forms whose spectral and kinetic features have been evaluated. Reaction of OH radicals with sulphacetamide resulted in the formation of a transient which in neutral and alkaline solutions decayed by first-order kinetics (k = 1.7 × 104 s-1) to yield the semi-oxidized species. The latter, formed both by decay of OH-adduct, as well as directly, has been observed to react rapidly with the biological antioxidant ascorbic acid (kASC + SA = 1.9 × 105 dm3 mol-1 at pH 9.2) forming the ascorbate radical. The effect of oxygen on the decay behaviour of the OH-adduct and semi-oxidized species has also been investigated.
Article
The radiation-induced degradation of sulfamethazine (SMT) was carried out by gamma irradiation. SMT with initial concentration of 20 mg/L was irradiated in the presence of 0, 0.1, 0.2, 0.4 and 0.6 mM extra Fe2+. The results showed that ferrous ion (Fe2+) could enhance the degradation of SMT by gamma irradiation in aqueous solution. SMT could be almost completely removed at 1 kGy without extra Fe2+, however, TOC removal efficiency was less than 10%. Several intermediate products, such as 4,6-dimethylpyrimidin-2-amine, 4-aminobenzenesulfonic acid, 4-nitrophenol 4-nitrobenzenesulfonic acid, 2-amino-6-methylpyrimidine-4-carboxylic acid, and 4-amino-N-carbamimidoyl-benzenesulfonamide and formic acid, acetic acid, and sulfate were identified. Possible pathway of SMT degradation in aqueous solution was tentatively proposed.
Article
Kinetic data for the radicals H⋅ and ⋅OH in aqueous solution,and the corresponding radical anions, ⋅O− and eaq−, have been critically pulse radiolysis, flash photolysis and other methods. Rate constants for over 3500 reaction are tabulated, including reaction with molecules, ions and other radicals derived from inorganic and organic solutes.
Article
Solutions of the antimicrobial sulfanilamide have been degraded in acidic medium by anodic oxidation (AO) using an undivided or divided cell with a boron-doped diamond (BDD) anode and a stainless steel cathode at constant current density. Almost total mineralization was attained in solutions with 0.50 M Na2SO4 at regulated pH 3.0 contained in the anodic compartment of the divided cell due to the efficient destruction of organics with hydroxyl radicals generated at the BDD anode from water oxidation. This cell had higher oxidation ability than the undivided one using 0.05 M Na2SO4, which yielded slower degradation and lower efficiency. In each cell, a similar degradation rate was found at a pH interval 2.0–6.0, indicating the existence of the same electroactive species for sulfanilamide. The mineralization current efficiency was always enhanced at lower current density and higher initial substrate concentration. The sulfanilamide decay was followed by reversed-phase HPLC, always showing a pseudo-first-order kinetics that was faster in the divided cell. 1,2-Benzenediol and 1,3-benzenediol were detected as aromatic intermediates in the undivided cell by gas chromatography–mass spectrometry, while p-benzoquinone formed in both cells was identified by reversed-phase HPLC. Generated carboxylic acids like maleic, fumaric, acetic, formic, oxalic and oxamic were quantified by ion-exclusion HPLC. The initial N content of sulfanilamide was mainly released as NH4+ ion and in much smaller proportion as NO3- ion. A reaction sequence for sulfanilamide mineralization in acidic medium by AO with a BDD anode considering all detected intermediates is finally proposed.
Article
Gamma irradiation-induced removal of sulfadiazine (SD) under different conditions was investigated. The results show that SD can be effectively degraded using gamma irradiation. The removal efficiencies of low-concentration SD can be remarkably improved in an acid solution, and SD degradation was in accordant with the pseudo-first-order kinetic model. The additives, such as H2O2 and Fenton reagent, were favorable for removing SD during gamma irradiation. However, SD removal was restrained with the addition of Na2CO3. Adding CH3OH in solution, we found that SD removal was restrained at low-irradiation dose while markedly promoted at high-irradiation dose. Based on the results of quantum chemical calculations and LC–MS analysis, SD degradation using gamma irradiation in aqueous solution is mainly ascribed to OH oxidation and the direct decomposition of SD molecules.
Article
The rate coefficients of hydroxyl radical addition to the rings of simple aromatic molecules (kOH) were evaluated based on the literature data. By analyzing the methods of kOH determination and the data obtained the most probable values were selected for the kOH's of individual compounds and thereby the most reliable dataset was created for monosubstituted aromatics and p-substituted phenols. For these compounds the rate coefficients fall in a narrow range between 2×109 mol−1 dm3 s−1 and 1×1010 mol−1 dm3 s−1. Although the values show some regular trend with the electron donating/withdrawing nature of the substituent, the log kOH−σp Hammett substituent constant plots do not give straight lines because these high kOH's are controlled by both, the chemical reactivity and the diffusion. However, the logarithms of the rate coefficients of the chemical reactivity controlled reactions (kchem), are calculated by the equation 1/kOH=1/kchem+1/kdiff, and accepting for the diffusion controlled rate coefficient kdiff=1.1×1010 mol−1 dm3 s−1, show good linear correlation with σp.
Article
The reactions of several five-membered oxygen and nitrogen heterocyclics with OH{sup {sm bullet}} and SOâ{sup {sm bullet}-} radicals have been investigated in aqueous solution using in-situ radiolysis and photolysis ESR, and optical and conductometric pulse radiolysis techniques for detection. The absolute rate constants determined for the reaction of SOâ{sup {sm bullet}} with the five-membered heteroaromatics (k = 3 à 10⁸ à 10⁹ M⁻¹ s⁻¹) reflect the electrophilicity of the SOâ{sup {sm bullet}-} radical.
Article
We describe our method based on pulse radiolysis with optical detection developed for the examination of the kinetics and mechanism of the first steps of high-energy radiation initiated polymerization. The absorption spectra of the intermediates were obtained in cyclohexane solution of hexanediol diacrylate (HDDA) of different concentrations. In dilute solution (10 mmol·dm–3) and short time (10 μs) after the pulse, the spectrum of the monomer radicals was observed. On increasing the monomer concentration, the maximum of the spectrum was shifted to longer wavelength indicating the start of the oligomerization reaction. The increase in the time of observation resulted in a similar shift in dilute solution. From the kinetic curves the rate coefficients of termination for the monomer radicals (2·kt,m) and average rate coefficients of termination for the oligomer radicals of different chain length (2·kt) were determined. The average rate coefficient of termination was found to decrease in time (that is with increasing chain-length).
Article
The reactions of several five-membered oxygen and nitrogen heterocyclics with OH. and SO4.- radicals have been investigated in aqueous solution using in-situ radiolysis and photolysis ESR, and optical and conductometric pulse radiolysis techniques for detection. OH. reacts with (the saturated) oxazolidone, imidazolidinone, hydantoin, and oxazoline derivatives by hydrogen abstraction, preferentially from the carbon adjacent to the nitrogen atom. With (the unsaturated) oxazoles and isoxazoles, OH. reacts by addition to the carbon at the 5-position of the ring to produce allylic radicals. In basic and acidic solutions of oxazole a ring opening process follows the OH. addition. SO4.- reacts with oxazoles and isoxazoles by addition to C5 yielding SO4- adducts, whereas with imidazole, pyrazole, and pyrrole derivatives, SO4.- gives rise to neutral, conjugated radicals with the unpaired electron delocalized over the entire ring, which are derived from the parent compounds by one-electron oxidation followed by deprotonation. In the case of N-methylimidazole, the radical cation is obtained. The absolute rate constants determined for the reaction of SO4.- with the five-membered heteroaromatics (k = 3 × 108 to 8 × 109 M-1 s-1) reflect the electrophilicity of the SO4.- radical.
Article
In connection with the radiolysis of aqueous nitric acid it has been reported that the reaction of OH radical with sulphanilamide (SA) is faster than that with isopropyl alcohol. In the present communication a method is described based on the competing reactions of Fe(CN) 6 and SA for OH radical to determine the rate constant for the reaction of SA with OH radical.
Article
G(-sulphonamide) values obtained for the radiation degradation in nitrogen-saturated solutions range from 2.7–3.2. In nitrous oxide saturated solution G(-sulphonamide) values are 3.4–4.8. Accordingly, both e-aq and HO radicals contribute to the radiation degradation, with HO attack predominating. Attack by e-aq on all three sulphonamides formed sulphanilic acid in different yields. Sulphamerazine degradation resulted in 2-amino-4-methyl pyrimidine formation by scission of the sulphonamide group S-N bond. Similar compounds arose from degradation of sulphadiazine and sulphamethazine. In addition, a phenolic compound was formed during irradiation of the three sulphonamides.
Article
The acid dissociation constant is an important physicochemical parameter of a substance, and knowledge of it is of fundamental importance in a wide range of applications and research areas. We present a critical review of published methods and approaches for the determination of acid dissociation constants, with a special emphasis on the pKa values of active pharmaceutical ingredients.
Article
The gamma irradiation-induced degradation of sulfamethazine (SMT) in aqueous solution in the presence of hydrogen peroxide (H(2)O(2)) was investigated. The initial SMT concentration was 20mg/L and it was irradiated in the presence of extra H(2)O(2) with initial concentration of 0, 10 and 30mg/L. The results showed that gamma irradiation was effective for removing SMT in aqueous solution and its degradation conformed to the pseudo first-order kinetics under the applied conditions. When initial H(2)O(2) concentration was in the range of 0-30mg/L, higher concentration of H(2)O(2) was more effective for the decomposition and mineralization of SMT. However, the removal of total organic carbon (TOC) was not as effective as that of SMT. Total nitrogen (TN) was not removed even at absorbed dose of 5kGy, which was highest dose applied in this study. Major decomposition products of SMT, including degradation intermediates, organic acids and some inorganic ions were detected by high performance liquid chromatography (HPLC) and ion chromatography (IC). Sulfate (SO(4)(2-)), formic acid (HCOOH), acetic acid (CH(3)COOH), 4-aminophenol, 4-nitrophenol were identified in the irradiated solutions. Possible pathways for SMT decomposition by gamma irradiation in aqueous solution were proposed.
Article
Hydroxyl radical induced degradation of maleic acid, fumaric acid and 20 aromatic molecules was investigated in air saturated aqueous solutions. Hydroxyl radicals were generated by an advanced oxidation process (AOP), water radiolysis. Oxidation was followed by chemical oxygen demand (COD) and total organic carbon content (TOC) measurements. Up to ∼30-50% decrease of COD the dose dependence was linear. By the ratio of the decrease of COD and the amount of reactive radiolysis intermediates introduced into the solution the oxidation efficiencies were calculated. Efficiencies around 0.5-1 (O(2) molecule built in products/()OH) found for most of the compounds show that the one-electron-oxidant ()OH induces 2-4 electron oxidations. The high oxidation rates were explained by ()OH addition to unsaturated bonds and subsequent reactions of dissolved O(2) with organic radicals. In amino substituted molecules or in Acid Red 1 azo dye, O(2) cannot compete efficiently with unimolecular transformation of organic radicals and the efficiency is lower (0.2-0.5).
Article
The reactions of peroxyl radicals occupy a central role in oxidative degradation. Under the tenn Advanced Oxidation Processes in drinking-water and wastewater processing, procedures are summarized that are based on the formation and high reactivity of the OH radical. These react with organic matter (DOC). With O2, the resulting carbon-centered radicals O2 give rise to the corresponding peroxyl radicals. This reaction is irreversible in most cases. An exception is hydroxycyclohexadienyl radicals which are formed from aromatic compounds, where reversibility is observed even at room temperature. Peroxyl radicals with strongly electron-donating substituents eliminate O2-, those with an OH-group in a-position HO2,. Otherwise organic peroxyl radicals decay bimolecularly. The tetroxides fonned in the first step are very short-lived intermediates and decay by various pathways, leading to molecular products (alcohols, ketones, esters and acids, depending on the precursor), or to oxyl radicals, which either fragment by scission of a neighbouring C-C bond or, when they carry an a-hydrogen, undergo a (water-assisted) 1,2-H-shift.
Article
Sulfanilic acid and anilinedisulfonic acids (ADS) react with OH radicals (k = 8.2 x 10(9) and 5.9 x 10(9) M-1 s-1) to form the corresponding OH adducts. In acid solutions the adducts react with protons to yield cation radicals (k = 5.3 x 10(8) and 8.7 x 10(8) M-1 s-1). N3 oxidizes sulfanilic acid directly to the cation radical by an electron-transfer reaction at a diffusion-controlled rate constant, k = 6.5 x 10(9) M-1 s-1, while the rate of oxidation of ADS by N3 is only 7.6 x 10(7) M-1 s-1. SO4- on the other hand oxidizes ADS to the cation radical at a rate of 1.8 x 10(9) M-1 s-1. Both cation radicals deprotonate to the anilino-type radicals in acid-base equilibria. The pK(a) of deprotonation of the sulfanilic cation radical is 5.8 +/- 0.05 and that of the ADS cation radical is 4.3 +/- 0.05.
Article
Two carbon materials (multi-walled carbon nanotubes, MWCNTs, and activated carbon) were investigated as ozonation catalysts for the mineralization of the antibiotic sulphamethoxazole (SMX). MWCNTs presented a higher catalytic performance than activated carbons, which was justified by their differences in surface chemistry and by the higher internal mass transfer resistances expected for activated carbons. 3-Amino-5-methylisoxazole and p-benzoquinone were detected as primary products of single and catalytic ozonation of SMX, whereas oxamic, oxalic, pyruvic and maleic acids were identified as refractory final oxidation products. The original sulphur of the SMX was almost completely converted to sulphate and part of the nitrogen was converted to NH(4)(+) and NO(3)(-). The presence of the radical scavenger tert-butanol during catalytic and single ozonation evidenced the participation of HO radicals in the oxidation mechanisms of SMX, especially in the mineralization of several intermediates. Microtox tests revealed that simultaneous use of ozone and MWCNTs originated lower acute toxicity. The time course of all detected compounds was studied and the transformation pathway for the complete mineralization of SMX by single and catalytic ozonation in the presence of the selected materials was elucidated.
Article
Recently, the occurrence of antibiotics in sewage treatment plant effluent, as well as drinking water, has raised concern about their potential impacts on the environment and public health. Antibiotics are found in surface and ground waters, which indicate their ineffective removal by conventional wastewater treatment processes. Therefore, advanced oxidation processes (AOPs) have received considerable attention for the removal of antibiotics. This study was conducted to evaluate the degradation and mineralization of antibiotics (sulfamethoxazole and chlortetracycline) using an electron beam, ozone and UV, and the change of toxicity. Also, the electrical energy consumption based on the EE/O parameter (the electrical energy required per order of pollutants removal in 1 m(3) wastewater) was used to quantify the energy cost associated with the different AOPs (electron beam, ozone and UV) for the degradation of antibiotics. The results showed that an electron beam effective for the removals of both sulfamethoxazole and chlortetracycline in aqueous solutions. However, degradation of the target compounds by ozone and UV showed different trends. The oxidation efficiency of each organic compound was very dependent upon the AOP used. Algal toxicity was significantly reduced after each treatment. However, based on the electrical energy, the electron beam was more efficient than ozone and UV. Electron beam treatment could be an effective and safe method for the removal of antibiotic compounds.
Article
This study was conducted to investigate the decomposition of three γ-irradiated antibiotics (e.g., tetracycline, sulfamethazine, and lincomycin) and to compare the toxic effects on Daphnia magna, Vibrio fischeri, and Pseudokirchneriella subcapitata. The median cell growth inhibition concentrations (IC50) of tetracycline, lincomycin, and sulfamethazine for P. subcapitata dramatically increased (e.g., toxicity decreased) after radiolysis. The results demonstrated that γ-radiation treatment was efficient to decompose antibiotics and thereby their toxicity on P. subcaptitata remarkably decreased due to reduced parent compounds.
Article
The photocatalytic degradation of sulfanilamide, sulfacetamide, sulfathiazole, sulfamethoxazole and sulfadiazine in aqueous solutions was examined during their irradiation with UV-A (366 nm) with TiO2, Fe salts and TiO2/FeCl3 catalysts. The study was carried out by HPLC-UV, HPLC/MS-EI and total organic carbon (TOC) methods.It was found that sulfonamides underwent photocatalytic degradation in the presence of TiO2, TiO2/FeCl3 and Fe3+ salts, and the optimum catalyst for this process can be FeCl3. Based on the identified intermediate products, a degradation pathway was proposed. Moreover, the rate of photocatalytic process carried out with FeCl3 as well as the relationship between the pH of irradiated solutions, initial concentrations of sulfanilamide and FeCl3 were stated.
Article
Over the past few years, antibiotics have been considered emerging pollutants due to their continuous input and persistence in the aquatic ecosystem even at low concentrations. They have been detected worldwide in environmental matrices, indicating their ineffective removal from water and wastewater using conventional treatment methods. To prevent this contamination, several processes to degrade/remove antibiotics have been studied. This review addresses the current state of knowledge concerning the input sources, occurrence and mainly the degradation and removal processes applied to a specific class of micropollutants, the antibiotics. In this paper, different remediation techniques were evaluated and compared, such as conventional techniques (biological processes, filtration, coagulation, flocculation and sedimentation), advanced oxidation processes (AOPs), adsorption, membrane processes and combined methods. In this study, it was found that ozonation, Fenton/photo-Fenton and semiconductor photocatalysis were the most tested methodologies. Combined processes seem to be the best solution for the treatment of effluents containing antibiotics, especially those using renewable energy and by-products materials.
Article
Two agricultural antibiotics used heavily in agriculture, sulfamethazine and sulfadiazine, were degraded in an aqueous system by anodic Fenton treatment (AFT), an advanced oxidation technique that has been shown to be effective in degrading various pesticides but has not been applied to antibiotics. The effects of the H(2)O(2)/Fe(2+) ratio, Fe(2+) delivery rate, and initial contaminant concentration on the degradation of sulfamethazine by AFT were determined. The optimal H(2)O(2)/Fe(2+) ratio was determined to be 10:1, and the optimal Fe(2+) delivery rate was found to be between 38.9 and 54.4 microM min(-1). Under these conditions, sulfamethazine was completely degraded within 10 min at a range of concentrations (18-250 microM) commonly found in manure lagoons, contaminated rivers, and groundwater. Using the same optimal conditions, the effect of pH on the degradation of sulfadiazine by AFT was analyzed, and 100 microM sulfadiazine was degraded within 6-8 min of treatment at a range of pH values (3.1-7.1) that could potentially be found in aquatic environments. Degradation products and pathways were proposed for both compounds, and it was inferred that AFT degradation products of sulfadiazine and sulfamethazine are unlikely to retain the bacteriostatic properties of their parent compounds. An aquatic toxicity test employing Lemna gibba confirmed that AFT removes the bacteriostatic properties of sulfamethazine and sulfadiazine during degradation.
Article
In this work, the photocatalytic degradation of the antibiotic sulfamethoxazole (SMX) by solar photo-Fenton at pilot plant scale was evaluated in distilled water (DW) and in seawater (SW). Degradation and mineralization of SMX were strongly hindered in SW compared to DW. The influence of H(2)O(2) and iron concentration on the efficiency of the photocatalytic process was evaluated. An increase in iron concentration from 2.6 to 10.4 mg L(-1) showed only a slight improvement in SMX degradation and mineralization. However, an increase in H(2)O(2) concentration up to 120 mg L(-1) during photo-Fenton in DW decreased SMX solution toxicity from 85% to 20%, according to results of Daphnia magna bioassays. The same behaviour was not observed after photo-Fenton treatment in SW. Despite 45% mineralization in SW, toxicity increased from 16% to 86% as shown by Vibrio fischeri bioassays, which suggests that the intermediates generated in SW are different from those in DW. A SMX degradation pathway during the photo-Fenton treatment in DW is proposed.
Article
Rate constants for reactions of hydroxyl radicals with nucleic acid bases and the related compounds were determined by the p-nitrosodimethylaniline method. For addition reaction of hydroxyl radical to the compounds, reactivity indices, namely free valence, localization energy, frontier-electron-density and superdelocalizability, were calculated by Hückel MO method. Among the examined reactivity indices, superdelocalizability was found to have a linear correlation with logarithms of relative rate constants of pyrimidine bases, while the correlation was not observed for purine bases.
Article
The effects of γ-irradiation on sodium sulphacetamide in aqueous solutions and in the solid state have been studied. Pulse radiolysis and steady-state experiments demonstrate that hydrated electrons (eaq)({\rm e}_{{\rm aq}}^{-}) and hydroxyl radicals (OH) are mainly responsible for the degradation between 1041.2 M10^{-4}-1.2\ M solute concentrations. The reaction with eaq{\rm e}_{{\rm aq}}^{-} yields sulphanilic acid and an additional unidentified product. Hydroxyl radicals give two products which have tentatively been identified as monomeric and dimeric phenolic derivatives of sulphacetamide. Suitable eaq{\rm e}_{{\rm aq}}^{-} and OH scavengers selectively remove these products. G(-sulphacetamide) is a maximum of 4.8 in aqueous solution and
Article
The effects of γ-irradiation on five sulphonamides have been studied in aqueous solution and in the solid state. On irradiation in solution sulphathiazole yields sulphanilic acid (G = 0.6), sulphasuccidine yields sulphathiazole (G = 0.7), and thalamyd gives sulphacetamide (G = 1.4) and phthalic acid (G ∼ 1.0). Each of these transformations are initiated by reaction with the hydrated electron. The hydroxyl radical initiates degradation also and forms an adduct by addition to the aromatic ring, which eventually yields phenol products. The rates of reaction of the sulphonamides and certain related compounds with the hydrated electron and the hydroxyl radical and transient products of radiolysis have been determined using pulse radiolysis and steady state competition methods. G (- sulphonamide) values in aqueous solution vary from 3.5-5.1, and in the solid state from 0.15-0.6. The implications of the results in the radiation steralization of sulphonamide formulations are discussed.
Article
A method has been developed for the trace analysis of two classes of antimicrobials consisting of six sulfonamides (SAs) and five tetracyclines (TCs), which commonly are used for veterinary purposes and agricultural feed additives and are suspected to leach into ground and surface water. The method used solid-phase extraction and liquid chromatography/mass spectrometry (LC/MS) with positive ion electrospray. The unique combination of a metal chelation agent (Na2EDTA) with a macroporous copolymer resulted in quantitative recoveries by solid-phase extraction (mean recovery, 98 +/- 12%) at submicrogramper-liter concentrations. An ammonium formate/formic acid buffer with a methanol/water gradient was used to separate the antimicrobials and to optimize the signal intensity. Mass spectral fragmentation and ionization characteristics were determined for each class of compounds for unequivocal identification. For all SAs, a characteristic m/z 156 ion representing the sulfanilyl fragment was identified. TCs exhibited neutral losses of 17 amu resulting from the loss of ammonia and 35 amu from the subsequent loss of water. Unusual matrix effects were seen only for TCs in this first survey of groundwater and surface water samples from sites around the United States, requiring that TCs be quantitated using the method of standard additions.
Article
The photochemical fate of five sulfa drugs with varying five-membered heterocyclic substituents (sulfamethoxazole, sulfisoxazole, sulfamethizole, sulfathiazole, and sulfamoxole) was investigated in aqueous solution. The rate of direct photolysis of these compounds is dependent upon the identity of the heterocyclic R group as well as the pH of the solution. Matrix deconvolution methods were employed to determine the absorption spectrum and photolysis rate of each protonation state (cationic, neutral, and anionic). From these data, quantum yields for direct photodegradation were calculated for each protonation state of the sulfa drugs. The quantum yields calculated range from <0.005 for the neutral state of sulfamethizole to 0.7 +/- 0.3 for the protonated state of sulfisoxazole. The protonation state that is most photoreactive varies among the sulfa drugs and cannot be attributed to the rate of photon absorption. Products arising from the direct photolysis of the sulfa drugs were also investigated. For all the compounds, sulfanilic acid was observed as a common product. The singlet oxygen quenching rates of the sulfa drugs were determined by laser flash photolysis and range from (2 +/- 1) x 10(4) M(-1) s(-1) for sulfamethoxazole to (3.0 +/- 0.7) x 10(8) M(-1) s(-1) for sulfamoxole. Reaction of the sulfa drugs with hydroxyl radical is not modulated by the R group, and the rate constants are all near the bimolecular diffusion-controlled limit of 10(10) M(-1) s(-1). The photodegradation of the sulfa drugs in natural water samples of Lake Josephine (St. Paul, MN) and Lake Superior was attributed solely to direct photolysis. This study indicates thatthese similarly structured antibiotics will be subject to a wide range of photodegradation rates with sulfathiazole degrading relatively quickly, sulfisoxazole and sulfamethizole degrading moderately, and sulfamethoxazole degrading much more slowly.
Article
The aquatic photochemical behavior of a class of sulfa drugs containing six-membered heterocyclic substituents (sulfamethazine, sulfamerazine, sulfadiazine, sulfachloropyridazine, and sulfadimethoxine) was investigated. Photodegradation of the sulfa drugs in a natural water sample was significantly enhanced relative to the degradation in deionized water, with the exception of sulfadimethoxine. This indicated an indirect photochemical process that was identified through the use of quenchers to be attributable to interaction with triplet excited-state dissolved organic matter (3DOM). The direct photolysis rate constant and quantum yield for both the neutral and anionic species of each sulfa drug were calculated using matrix deconvolution methods. The quantum yield values range from 0.01 x 10(-3) for the neutral form of sulfadimethoxine to 5 x 10(-3) for the anionic form of sulfamethazine and are significantly lower than those observed in a previous study for sulfa drugs containing five-membered heterocyclic substituents, although the rate constants are of similar magnitude. The primary product formed in both direct and indirect photodegradation for all five compounds was identified as a sulfur dioxide extrusion product. The predicted environmental half-lives solely attributable to direct photolysis range from 8.6 h in midsummer at 30 degrees latitude in pH 7 surface water for sulfachloropyridazine to 420 h in midwinter at 45 degrees in pH 7 surface water for sulfadimethoxine. These half-lives, except for sulfadimethoxine, will be decreased by interaction with 3DOM.