Degradation of sulfonamide antibiotic via UV/MgO2 system: kinetic, application, and mechanism

In response to antibiotic residues in the water, a novel advanced oxidation technology based on MgO2 was used to remediate sulfamethazine (SMTZ) pollution in aquatic environments. Upon appropriate regulation, the remarkable removal efficiency of SMTZ was observed in a UV/MgO2 system, and the pseudo-first-order reaction constant reached 0.4074 min-1. In addition, the better performance of the UV/MgO2 system in a weak acid environment was discovered. During the removal of SMTZ, the pathways of SMTZ degradation were deduced, including nitration, ring opening, and group loss. In the mineralization exploration, the further removal of residual products of SMTZ by the UV/MgO2 system was visually demonstrated. The qualitative and quantitative researches as well as the roles of reactive species were valuated, which revealed the important role of ·O2-. Common co-existing substances in actual wastewater such as NO3- HA, Cl-, Fe2+, Co2+, and Mn2+ can slightly inhibit the degradation of SMTZ in the UV/MgO2 system. Finally, the capacity of efficient degradation of SMTZ in actual wastewater by the UV/MgO2 system was proved. The results indicated that the innovative UV/MgO2 system was of great practical application prospect in antibiotic residue wastewater remediation.

Boron promoted Fe3+/peracetic acid process for sulfamethazine degradation: Efficiency, role of boron, and identification of the reactive species

In this work, boron (B) was used to promote Fe3+/peracetic acid (Fe3+/PAA) for the degradation of sulfamethazine (SMT). An SMT degradation efficiency of 9.1% was observed in the Fe3+/PAA system over 60 min, which was significantly increased to 99.3% in the B/Fe3+/PAA system over 10 min. The B/Fe3+/PAA process also exhibited superior resistance to natural substances, excellent adaptability to different harmful substances, and good removal of antibiotics in natural fresh water samples. The mechanism of action of boron for Fe3+ reduction was determined using scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared (FT-IR) spectroscopy, density functional theory (DFT) calculations, and electrochemical tests. The dominant role of •OH was confirmed using quenching experiments, electron spin resonance (EPR) spectroscopy, and quantitative tests. Organic radicals (R-O•) and Fe(IV) also significantly contribute to the removal of SMT. DFT calculations on the reaction between Fe2+ and the PAA were conducted to further determine the contribution from •OH, R-O•, and Fe(IV) from the perspective of thermodynamics and the reaction pathways. Different boron dosages, Fe3+ dosages, and initial pH values were also investigated in the B/Fe3+/PAA system to study their effect of SMT removal and the production of the reactive species. Fe(IV) production determined the kR-O•+Fe(IV) value suggesting that Fe(IV) may play a more important role than R-O•. A comparison of the results with other processes has also proved that the procedure described in this study (B/Fe3+/PAA) is an effective method for the degradation of antibiotics.

[Effect of Manure Application on the Adsorption of Antibiotics to Soil]

Sulfonamide antibiotics and florfenicol(FFC) are commonly used antibiotics in Zhejiang Province. They have weak adsorption on soil and are easy to migrate, with high environmental risks. In recent years, most of the studies on the potential risk of fecal-derived antibiotics to farmland soil were conducted by adding manure under laboratory conditions; therefore, it is impossible to assess the risk of antibiotic pollution under natural fertilization. Therefore, batch balance experiments were conducted to explore the effects of different soil types and manure types on the adsorption of antibiotics in the soil, in which five types of dryland farmland soils[Lin'an(LA), Jiashan(JS), Longyou(LY), Kaihua(KH), and Jinhua(JH)]in Zhejiang Province that have been used with different fertilizers(chicken manure, pig manure, and chemical fertilizer) for a long time were chosen, and four types of commonly used antibiotics[sulfadiazine(SD), sulfamethazine(SMT), sulfamethoxazole(SMZ), and FFC]were selected. The results showed that the adsorption of the four antibiotics in the experimental soil was weak, and the adsorption capacity decreased in the order of:SMT(1.44-13.23 mg1-(1/n)·L1/n·kg-1)>SMZ(0.73-6.05 mg1-(1/n)·L1/n·kg-1)>SD(0.16-5.57 mg1-(1/n)·L1/n·kg-1)>FFC(0.27-3.81 mg1-(1/n)·L1/n·kg-1). The Freundlich model was superior to the linear model in fitting the isotherm adsorption of SD, SMT, and FFC, in which SD and FFC belonged to "S" type adsorption, and SMT belonged to "L" type adsorption. For SMZ, the fitting effect of the linear model was better than that of the Freundlich model. The contents of total organic carbon(TOC) and dissolved organic carbon(DOC) could better predict the adsorption capacity of the four antibiotics(r=0.548-0.808), and the values of cation exchange capacity(CEC) and electrical conductivity(EC) could better predict the adsorption capacity of SMT and FFC(r=0.758-0.841). Compared with the application of chemical fertilizer, manure application increased the values of TOC, DOC, CEC, and EC in acidic and neutral soils, which was conducive to the adsorption of antibiotics on the soil. Meanwhile, manure application also increased pH in acidic and neutral soils, which was not conducive to the adsorption of antibiotics on the soil. In addition, manure application reduced the values of TOC, DOC, CEC, EC, and pH in alkaline soils. The lower pH was conducive to antibiotic adsorption on the soil, whereas the lower content of the other four was not conducive to antibiotic adsorption on the soil. For the acidic soil with low fertility, the application of manure increased soil fertility and thus increased the adsorption of antibiotics on the soil, such as the LA soil with chicken manure, the LY(1) soil with pig manure, and the JH soil with chicken manure and pig manure. However, for the acidic and neutral soils with high fertility, the application of manure had significantly increased soil pH and thus reduced the adsorption of antibiotics on the soil, such as the JS soil with chicken manure and pig manure and the LY(2) soil with chicken manure. For calcareous soil with high fertility and pH(such as KH soil), the adsorption profiles of the four types of antibiotics on the soil showed diversity after the application of manure:the adsorption capacity of SD increased significantly after the application of chicken manure and pig manure, whereas the adsorption capacity of SMT and SMZ decreased significantly, and the adsorption capacity of FFC declined significantly after the application of chicken manure. Therefore, manure application according to soil fertility could effectively control the environmental risk of fecal antibiotics.

Enhanced removal of sulfonamide antibiotics from water by phosphogypsum modified biochar composite

Antibiotic pollution has become a global eco-environmental issue. To reduce sulfonamide antibiotics in water and improve resource utilization of solid wastes, phosphogypsum modified biochar composite (PMBC) was prepared via facile one-step from distillers grains, wood chips, and phosphogypsum. The physicochemical properties of PMBC were characterized by scanning electron microscope (SEM), Fourier transform infrared spectroscopy (FTIR), Zeta potential, X-ray diffraction (XRD), etc. The influencing factors, adsorption behaviors, and mechanisms of sulfadiazine (SD) and sulfamethazine (SMT) onto PMBC were studied by batch and fixed bed column adsorption experiments. The results showed that the removal rates of SD and SMT increased with the increase of phosphogypsum proportion, while decreased with the increase of solution pH. The maximum adsorption capacities of modified distillers grain and wood chips biochars for SD were 2.98 and 4.18 mg/g, and for SMT were 4.40 and 8.91 mg/g, respectively, which was 9.0-22.3 times that of pristine biochar. Fixed bed column results demonstrated that PMBC had good adsorption capacities for SD and SMT. When the solution flow rate was 2.0 mL/min and the dosage of PMBC was 5.0 g, the removal rates of SD and SMT by modified wood chips biochar were both higher than 50% in 4 hr. The main mechanisms of SD and SMT removal by PMBC are hydrogen bonding, π-π donor-acceptor, electrostatic interaction, and hydrophobic interaction. This study provides an effective method for the removal of antibiotics in water and the resource utilization of phosphogypsum.

Oxidation of sulfamethazine by peracetic acid activated with biochar: Reactive oxygen species contribution and toxicity change

Peracetic acid (PAA) as an emerging oxidative has been concerned increasingly due to its high oxidation capacity and low byproducts formation potential. This study was to investigate the oxidation of sulfamethazine (SMZ) by PAA activated with activated biochar (ABC) after thermal modification. The results demonstrated that PAA could be effectively activated by ABC to degrade SMZ in a wide pH range (3-9), which followed the pseudo-second-order kinetics (R² > 0.99). Both non-radicals (singlet oxygen) and free radicals (alkoxy radicals, hydroxyl radicals) existed in the ABC/PAA system, and the degradation of SMZ was dominated by singlet oxygen. Humic acid (HA), SO₄^2- and HCO₃^- slightly inhibited the degradation of SMZ in the ABC/PAA process, while Cl^- and Br^- promoted the degradation of SMZ. The cleavage of S-N, S-C bond, and SO₂ extraction reaction rearrangement was the main oxidation process of SMZ. Meanwhile, the results of the ECOSAR program showed that the acute toxicity of most by-products was significantly reduced compared to SMZ, which revealed the potential applicability of the ABC/PAA process in the treatment of antibiotics pollution and their detoxification.

Amorphous Co@TiO2 heterojunctions: A high-performance and stable catalyst for the efficient degradation of sulfamethazine via peroxymonosulfate activation

Persulfate-based advanced oxidation processes (AOPs) cannot easily achieve the efficient degradation of persistent organic pollutants (POPs) with high stability. In this study, a simple in situ precipitation method was used to prepare an amorphous Co@TiO₂ heterojunction catalyst. The deposition of Co oxide on TiO₂, which is relatively nontoxic, efficiently activated peroxymonosulfate (PMS) to degrade sulfamethazine (SMT) and reduce the leaching of Co ions (0.915%). A catalytic system prepared using 0.3 g L^-1 Co@TiO₂ and 0.5 g L^-1 PMS could degrade SMT within 30 min with a degradation rate of 95.8%. Co@TiO₂ could activate PMS over a wide pH range (5.00-9.00) to efficiently degrade other antibiotics and dyes. Radical-capture experiments and electron paramagnetic resonance analysis suggested that SMT degradation occurs through a combination of the free radical and non-radical pathways, in which singlet ¹O₂ played a major role. Owing to the novelty of the proposed composite materials, the degradation path of SMT, which was determined through liquid chromatography-mass spectrometry, differed from that reported previously. This study provides not only an advanced and renewable catalyst for SMT degradation but also a feasible strategy for designing materials for AOPs.

Long-term sulfamethazine leaching simulation in two different soils using the MACRO model

Physically based models have been part of many risk assessment studies concerning pesticide or nutrient transport within (sub)catchments or at plot scale, but they are only poorly validated for simulating the transport of veterinary medicinal products. Veterinary medicinal products not only pose a risk to the quality of our waters but also tend to accumulate in soils, where they are associated with the appearance of resistant bacteria and long-term leaching. In this study, the physically based leaching model MACRO 5.2 was applied for simulating sulfamethazine (SMZ) transport over a period of more than 10 yr. The model was set up using reversible kinetic adsorption and equilibrium adsorption forming non-extractable residues. Two different calibration periods were used to estimate uncertainties in predicted SMZ leaching associated with calibration based on short-term data. Using the whole period for model calibration, SMZ leaching could be simulated adequately, but parameter ranges were wide due to correlation between the parameters. When using only the first period for calibration, the quality of the prediction strongly depended on the information content of the data set. The calculation of temporal sensitivity indices revealed that the effect of complex sorption parameters on the model output increased with time. Thus, parameters that appeared insensitive in a short-term calibration were required for reliable long-term simulations. In conclusion, a temporal sensitivity analysis beyond the calibration period might identify parameters that were not constrained enough by the calibration procedure. This could help to confirm leaching predictions even for periods without sampling data.

High yield M-BTC type MOFs as precursors to prepare N-doped carbon as peroxymonosulfate activator for removing sulfamethazine: The formation mechanism of surface-bound SO4•- on Co-Nx site

M-BTCs (M = Fe, Co and Mn)/melamine were used to prepare N-doped carbon materials, and their performances as activator of peroxymonosulfate (PMS) for sulfamethazine (SMZ) removal were compared. M-BTC type metal-organic frameworks (MOFs) were synthesized under room temperature, with their yield about 7.5 times of ZIF-67 which is the most used MOFs to prepare N-doped carbon materials as the catalyst of persulfate-based advanced oxidation processes. Co-BTC/melamine derived N-doped carbon materials (Co-BTC/5MNC) performed the best, even better than that of ZIF-67 derived N-doped carbon materials. Initial pH (3-9), 0-10 mM inorganic anions (Cl^-, NO₃^-, HCO₃^- and H₂PO₄^2-) and humic acid (5 and 10 mg/L) had no obvious inhibition on SMZ removal with Co-BTC/5MNC as catalyst. The results of both X-ray photoelectron spectroscopy and density functional theory (DFT) calculations indicated that N-coordinated cobalt single atom site (Co-N_x) was the possible active site of Co-BTC/5MNC. Importantly, surface-bound SO₄^•- was identified as the dominant reactive oxygen species for SMZ removal. The SO₄^•- generated through the charge transfer between PMS and catalyst, and was tightly adsorbed on Co-N_x site.

Temperature and pH-responsive in situ hydrogels of gelatin derivatives to prevent the reoccurrence of brain tumor

Glioblastoma multiforme (GBM) is a grade IV malignant brain tumor with a median survival time of approximately 12-16 months. Because of its highly aggressive and heterogeneous nature it is very difficult to remove by surgical resection. Herein we have reported dual stimuli-responsive and biodegradable in situ hydrogels of oligosulfamethazine-grafted gelatin and loaded with anticancer drug paclitaxel (PTX) for preventing the progress of Glioblastoma. The oligosulfamethazine (OSM) introduced to the gelatin backbone for the formation of definite and stable in situ hydrogel. The hydrogels transformed from a sol to a gel state upon changes in stimuli. pH and temperature and retained a distinct shape after subcutaneous administration in BALB/c mice. The viscosity of the sol state hydrogels was tuned by varying the feed molar ratio between gelatin and OSM. The porosity of the hydrogels was confirmed to be lower in higher degree OSM by SEM. Sustained release of PTX from hydrogels in physiological environments (pH 7.4) was further retarded up to 63% in 9th days in tumor environments (pH 6.5). While the empty hydrogels were non-toxic in cultured cells, the hydrogels loaded with PTX showed antitumor efficacy in orthotopic-GBM xenograft mice. Collectively, the gelatin-OSM formed porous hydrogels and released the cargo in a sustained manner in tumor environments efficiently suppressing the progress of GBM. Thus, gelatin-OSM hydrogels are a potential candidate for the direct delivery of therapeutics to the local areas in brain diseases.

A novel photocatalytic reactor for the extended reuse of W-TiO2 in the degradation of sulfamethazine

In this study, a photocatalytic reactor with a novel engineering design has been used for the extended degradation of sulfamethazine (SMZ). The reactor employed four consecutive stainless-steel plates immobilized by tungsten-dope TiO₂ (W-TiO₂) using polysiloxane. The characterization of W-TiO₂ by X-ray diffraction (XRD), Raman spectroscopy, and energy-dispersive X-ray (EDX) denoted successful doping of tungsten in the lattice of anatase crystals of TiO₂ suggesting a high photocatalytic activity under UV and visible light. A Box-Behnken experimental design was employed for the optimization of the operating parameters such as solution pH, flow rate, and the initial SMZ concentration. The residual SMZ concentration was below the detection limit after 30 min of the photocatalytic reaction under the optimum operating conditions. A highly remarkable degradation of SMZ was observed in five consecutive cycles, which reveals an extended stable photocatalytic activity offered by the reactor design. The transformation products were identified by tandem mass spectrometry, and they were employed to propose the degradation pathway. These results highlight the importance of using the photocatalysts in retained forms and open additional avenues for the practical application of photocatalysis in wastewater treatment.

Cu2+ activated persulfate for sulfamethazine degradation

Sulfonamide antibiotics (SAs) are widely used in veterinary medicine but are poorly metabolized in biological systems; thus, they can cause a selective pressure to promote the proliferation of antibiotic resistant pathogens and threaten human health. Persulfate (PS)-based advanced oxidation processes (AOPs) have been applied for SA degradation, but using transition metal ions as PS activators is relatively limited. In this study, sulfamethazine (SMZ) was used as a model SA to evaluate the performance of a Cu²⁺ -activated PS system. Cu²⁺-PS exhibited better SMZ removal than other metal ions, and 25 mg/L SMZ can be degraded in the presence of 0.2 mM Cu²⁺ and 2.5 g L^-1 PS within 120 min. Various anions inhibited SMZ degradation to different degrees except HCO₃^-. Among the cations, Fe³⁺ significantly inhibited SMZ removal, while Ni²⁺ increased the removal rate. High concentrations of humic acid and protein also increased the degradation rate of SMZ. Radical and singlet oxygen quenching experiments, together with the results of electron spin-resonance spectroscopy (ESR), showed that the main active species generated from Cu²⁺-PS are SO₄·^- and ·OH. The degradation pathway of SMZ was identified through HPLC-HRMS. Direct SO₄·^- and ·OH oxidation products of SMZ were not found, suggesting that the complex formed between Cu²⁺ and SMZ may affect the fate of SMZ. On the other hand, the efficiency and selectivity of Cu²⁺-PS against different SAs were confirmed. Overall, this study provides a facile and effective method for SMZ and other SA removal.

Biochar-mediated Fenton-like reaction for the degradation of sulfamethazine: Role of environmentally persistent free radicals

Swine manure biochar (SBC) pyrolyzed at 300 °C, 600 °C and 900 °C were utilized to degrade sulfamethazine (SMT) in heterogeneous Fenton-like systems which achieved excellent degradation efficiency (over 85% in 30 min). Experiments results demonstrated that SBC possessed the poor SMT adsorption capacity but high catalytic performance. Electron Paramagnetic Resonance (EPR) and X-ray photoelectron spectroscopy (XPS) analysis revealed that there were oxygen-centered environmentally persistent free radicals (EPFRs) and carbon-centered EPFRs with an adjacent oxygen atom in SBC. The oxygen-centered EPFRs played a major role in the catalytic process which tended to convert to carbon-centered EPFRs after the reaction. Besides, the electron transfer pathways were the most likely catalytic mechanism of SBC and the contribution of OH was dominant through Electron capture experiments and Linear sweep voltammetry (LSV) measurements. The acidic or alkaline condition can promote the catalytic ability of SBC. The presence of dissolved salts (NaCl) inhibited the catalytic process but the inhibition was slightly weakened at high concentration of NaCl, which showed the high tolerance of Cl^- in Fenton/Fenton-like systems. Moreover, real wastewater application suggested that SBC600/H₂O₂ system possessed excellent catalytic efficiency and good adaptability. This research provides a novel swine manure reuse process with high practicability and presents a more explicit perspective about the reaction mechanisms of EPFRs in biochar.

Effects of pine bark amendment on the transport of sulfonamide antibiotics in soils

In the present work, laboratory column experiments were carried out to study the effect of pine bark amendment (at doses of 0, 12, 48 and 96 Mg ha^-1) on the transport of three sulfonamide antibiotics (sulfadiazine -SDZ-, sulfamethazine -SMT-, and sulfachloropyridazine -SCP-) through two crop soils. All three sulfonamides showed high mobility in the unamend soils, with absence of retention in most cases. However, some differences were detected regarding the degree of interactions between sulfonamides and soils, being higher for soil 1, which was attributed to its higher organic carbon content. For both soils, interactions with the antibiotics studied followed the sequence SDZ < SMT < SCP, indicating an increase as a function of the hydrophobicity of sulfonamides. Pine bark amendment significantly increased the retention of the three sulfonamides in both soils. Specifically, in the case of soil 1, the incorporation of the highest dose of pine bark (96 Mg ha^-1) caused that retention increased from 0% to 70.3% for SDZ, from 2.7% to 71.3% for SMT, and from 0% to 85.4% for SCP. This effect of pine bark is mainly attributed to its high organic carbon content (48.6%), including substances with potential to interact and retain antibiotics, as well as to its acidic pH (4.5). Therefore, pine bark amendment would be an effective alternative to reduce the transport of sulfonamides in soils and, thus, decrease risks of passing to other environmental compartments, as well as harmful effects on the environment and public health.

Adsorption of Sulfamethazine Drug onto the Modified Derivatives of Carbon Nanotubes at Different pH

The sulfamethazine drug interaction with carbon nanotubes was investigated with the aim of improving the adsorption capacity of the adsorptive materials. Experiments were performed to clarify how the molecular environment affects the adsorption process. Single-walled carbon nanotubes have a higher removal efficiency of sulfamethazine than pristine or functionalized multi-walled carbon nanotubes. Although the presence of cyclodextrin molecules improves the solubility of sulfamethazine, it reduces the adsorption capacity of the carbon nanotube towards the sulfamethazine drug and, therefore, inhibits the removal of these antibiotic pollutants from waters by carbon nanotubes.

Enhancement of ionizing radiation-induced catalytic degradation of antibiotics using Fe/C nanomaterials derived from Fe-based MOFs

In present work, we studied a novel Fe/C nanomaterial fabricated using Fe-based metal organic frameworks (MOFs) as precursors through thermal pyrolysis to catalyze gamma irradiation-induced degradation of antibiotics, cephalosporin C (CEP-C) and sulfamethazine (SMT) in aqueous solution. The MOFs-derived Fe/C nanomaterials (DMOFs) had the regular octahedrons structure of MOFs and contained element C, Fe and O, while Fe° with a fraction of Fe₃O₄ and Fe₂O₃ were identified. Results showed that DMOFs addition could accelerate the generation of OH during gamma irradiation, while the intermediates of bonds cleavages of antibiotic molecules and OH addition were identified. DMOFs were more effective to improve the decomposition of antibiotic having the higher adsorption capacity like SMT. The degradation rate of CEP-C and SMT increased by 1.3 times and 1.8 times, and TOC reduction at 1.0 kGy reached 42 % and 51 %, respectively by gamma/DMOFs treatment, while only 20.2 % (CEP-C) and 4.5 % (SMT) of TOC reduction were obtained by γ-irradiation alone. The crystal structure, functional groups and magnetism of DMOFs changed slightly after gamma irradiation, which made it possible to be reused. DMOFs were promising to enhance the degradation of antibiotics during gamma irradiation.

Effect of molecular structure on the adsorption affinity of sulfonamides onto CNTs: Batch experiments and DFT calculations

In order to investigate the adsorption behaviors of sulfonamides onto hydroxylated multi - walled carbon nanotubes (CNTs) with a porous structure and large specific surface area, six typical sulfonamides including sulfanilamide (SAM), sulfamerazine (SMR), sulfadimethoxine (SMX), sulfadiazine (SDZ), sulfamethazine (SMT) and sulfametoxydiazine (SMD) were selected to be adsorbed respectively on CNTs, and in the same time the structural parameters of the six sulfonamides molecules were calculated according to the density functional theory (DFT). Based upon above mentioned experiments and the structural parameters, the quantitative correlation between the structural parameters of sulfonamides molecules and their adsorption affinity (e.g. adsorption capacity and adsorption rate constant) onto CNTs was established, respectively. The adsorption data of sulfonamides fitted well with the pseudo - second - order kinetic model and the Langmuir isotherm model. The order of both pseudo - second - order kinetic constant and maximum adsorption capacity of the six sulfonamides were SAM < SMR < SMX < SDZ < SMT < SMD. The frontier molecular orbital energy (E_HOMO) and dipole moment (μ) could be used as indicators for the adsorption affinity of sulfonamides onto CNTs. Accordingly, the possible adsorption mechanism was proposed.

Effect of sulfamethazine on surface characteristics of biochar colloids and its implications for transport in porous media

Antibiotics are contaminants of emerging concern due to their potential effect on antibiotic resistance and human health. Antibiotics tend to sorb strongly to organic materials, and biochar, a high efficient agent for adsorbing and immobilizing pollutants, can thus be used for remediation of antibiotic-contaminated soil and water. The effect of ionizable antibiotics on surface characteristics and transport of biochar colloids (BC) in the environment is poorly studied. Column experiments of BC were conducted in 1 mM NaCl solution under three pH (5, 7, and 10) conditions in the presence of sulfamethazine (SMT). Additionally, the adsorption of SMT by BC and the zeta potential of BC were also studied. The experimental results showed that SMT sorption to BC was enhanced at pH 5 and 7, but reduced at pH 10. SMT sorption reduced the surface charge of BC at pH 5 and 7 due to charge shielding, but increased surface charge at pH 10 due to adsorption of the negatively charged SMT species. The mobility of BC was inhibited by SMT under acidic or neutral conditions, while enhanced by SMT under alkaline conditions, which can be well explained by the change of electrostatic repulsion between BC and sand grains. These findings imply that pH conditions played a crucial role in deciding whether the transport of BC would be promoted by SMT or not. Biochar for antibiotics remediation will be more effective under acidic and neutral soil conditions, and the mobility of BC will be less than in alkaline soils.

Thermodynamic Characterization of the Interaction between the Antimicrobial Drug Sulfamethazine and Two Selected Cyclodextrins

Sulfamethazine is a representative member of the sulfonamide antibiotic drugs; it is still used in human and veterinary therapy. The protonation state of this drug affects its aqueous solubility, which can be controlled by its inclusion complexes with native or chemically-modified cyclodextrins. In this work, the temperature-dependent (298–313 K) interaction of sulfamethazine with native and randomly methylated β-cyclodextrins have been investigated at acidic and neutral pH. Surprisingly, the interaction between the neutral and anionic forms of the guest molecule and cyclodextrins with electron rich cavity are thermodynamically more favorable compared to the cationic guest. This property probably due to the enhanced formation of zwitterionic form of sulfamethazine in the hydrophobic cavities of cyclodextrins. Spectroscopic measurements and molecular modeling studies indicated the possible driving forces (hydrophobic interaction, hydrogen bonding, and electrostatic interaction) of the complex formation, and highlighted the importance of the reorganization of the solvent molecules during the entering of the guest molecule into the host’s cavity.

Sorption of antibiotics onto aged microplastics in freshwater and seawater

Microplastics in environments undergo aging processes and may sorb antibiotics from surrounding water. Understanding the interaction between aged microplastics and antibiotics is important to assess the impact of microplastics on environments. In this paper, the sorption of three typical antibiotics, i.e., sulfamethoxazole (SMX), sulfamethazine (SMT), and cephalosporin C (CEP-C) onto the naturally aged microplastics (polystyrene (PS) and polyethylene (PE)) derived from aged plastics samples from the coast of East China Sea and Yellow Sea, China in freshwater and simulated seawater systems were studied. The results indicated that the mixed order (MO) model provided good prediction for the kinetics data. The linear isotherm represented adequately the sorption equilibrium data in freshwater. The K_d values ranged from 0.0236 L·g^-1 to 0.0383 L·g^-1. In simulated seawater, only CEP-C could be sorbed onto the microplastics. The main sorption mechanisms are hydrophobic, van der Waals, and electrostatic interactions.

Nitrogen-doped flower-like porous carbon nanostructures for fast removal of sulfamethazine from water

The increasing concern for the toxicity of sulfamethazine (SMT) in water requires the establishment of effective water treatment processes to remove it. In this study, a novel adsorbent of nitrogen-doped flower-like porous carbon nanostructures (N-doped FPC) was proposed for the adsorption removal of SMT. The N-doped FPC possessed high surface area, good water dispersibility, and alkaline surface, endowing it with great adsorption efficiency towards SMT. The adsorption equilibrium data can be well fitted by both the Langmuir and Temkin models, and the maximum monolayer adsorption capacity of N-doped FPC was 610 mg g^-1 for SMT at 298 K. The N-doped FPC exhibited fast adsorption rate for SMT and adsorption equilibrium reached within only 5 min. The pseudo-first-order model described adsorption kinetics data well and the external mass transport was the rate-limiting step. The thermodynamic parameters (ΔG, ΔH, and ΔS) showed that the adsorption of SMT onto N-doped FPC was a feasible, spontaneous, and endothermic physisorption process. After five consecutive sorption/desorption cycles, the N-doped FPC retained more than 85% adsorption capacity. This study confirmed the promising potential of N-doped FPC as high-performance adsorbents for water purification.

Adsorption/desorption and transport of sulfadiazine, sulfachloropyridazine, and sulfamethazine, in acid agricultural soils

Batch-type experiments were used to study adsorption-desorption of three sulfonamides: sulfadiazine (SDZ) sulfachloropyridazine (SCP), and sulfamethazine (SMT), in five crop soils, whereas laboratory soil column experiments were employed to obtain data on transport processes. Adsorption results were satisfactorily adjusted to Linear and Feundlich equations, with R² values above 0.95. Adsorption followed the sequence SDZ < SMT < SCP, showing higher values for soils with higher levels of organic carbon (OC) content. Conversely, desorption was higher in soils with less OC, and lower in soils with higher OC contents. The temporal moment analysis method gave values for the transport parameters τ and R which were significantly correlated with soil parameters related to organic matter, specifically OC and N concentrations. The higher retention of the three sulfonamides in soils with high organic matter content is a relevant fact, with value when programming management practices in agricultural soils, and specifically in relation to the spreading of animal manures, slurries, or waste containing these emerging pollutants.

Multiresidue Determination of 27 Sulfonamides in Poultry Feathers and Its Application to a Sulfamethazine Pharmacokinetics Study on Laying Hen Feathers and Sulfonamide Residue Monitoring on Poultry Feathers

A method for the simultaneous determination of 27 sulfonamides in poultry feathers using ultra performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) was established in this study. The samples were extracted using 0.1 mol/L HCl solutions in a 60 °C water bath for 2 h, purified using hydrophilic-lipophilic balance solid-phase extraction, nitrogen-dried, and then reconstituted for UPLC-MS/MS analysis, which was performed with a CSH-C18 column. Linearity, limit of detection, limit of quantification, recovery, and precision were calculated in accordance with Commission Decision 2002/657/EC. For linearity, all standard curves showed a standard coefficient greater than 0.99, and the recoveries and coefficient of variation were 89-115% and <20%, respectively. The limit of detection and limit of quantification were 0.2-5 and 0.5-20 ng/g, respectively. The method was successfully applied to sulfamethazine (SMZ) residue accumulation monitoring in laying hen feathers and sulfonamide residue monitoring on poultry feathers. SMZ residue accumulation in the laying hen feathers was studied after administration with 100 mg/kg of SMZ for 21 consecutive days. SMZ residues were still detected in feathers 14 days after drug administration and persisted for up to 85 days. Results from 42 poultry feather samples showed that the feather is a suitable medium to monitor the illegal use of sulfonamides in poultry production.

Graphene modified anatase/titanate nanosheets with enhanced photocatalytic activity for efficient degradation of sulfamethazine under simulated solar light

Graphene modified anatase/titanate nanosheets (G/A/TNS) synthesized through hydrothermal treatment were used for solar-light-driven photocatalytic degradation of a typical pharmaceutically active compound, sulfamethazine (SMT). The optimal material was synthesized with 0.5 wt% of graphene loading (G/A/TNS-0.5), which could efficiently degrade 96.1% of SMT at 4 h. G/A/TNS-0.5 showed enhanced photocatalytic activity compared with the neat anatase and unmodified anatase/titanate nanosheets (A/TNS). UV-vis diffuse reflection spectra indicated that G/A/TNS-0.5 had a lower energy band gap (E_g) of 2.8 eV than A/TNS (3.1 eV). The grafted graphene acted as an electron transfer mediator after photoexcitation, resulting in inhibition on rapid recombination of electron-hole pairs. More importantly, architecture of graphene and titanate nanosheets both with two-dimensional structures greatly facilitated the photoexcited electron transfer. •OH and ¹O₂ were the primary reactive oxygen species (ROS) to SMT degradation. Fukui index (f^-) derived from density functional theory (DFT) calculation predicted the active sites on SMT molecule, and then SMT degradation pathway was proposed by means of intermediates identification and theoretical calculation. Furthermore, G/A/TNS-0.5 could be well reused and 90.5% of SMT was also degraded after five runs. The developed new photocatalysts show great potential for degradation of emerging organic contaminants through photocatalysis under solar light.

Photochemical reaction kinetics and mechanistic investigations of nitrous acid with sulfamethazine in tropospheric water

Nitrous acid (HONO) is an important atmospheric pollutant that can strongly absorb ultraviolet irradiation in the region of 300-400 nm, as previously reported. Since the solar irradiance that reaches the surface of the earth has wavelengths greater than 290 nm, the photodissociation of HONO is considered the major method of hydroxyl radical formation in the troposphere. Thus, the photoinduced chemical reactivity of HONO is important. The present work investigated the reaction mechanism and kinetic parameters of HONO and sulfamethazine by using a laser flash photolysis technique and liquid chromatography-mass spectrometry. The results indicated that the sulfamethazine degradation rate was influenced by the HONO concentration and the initial concentration of sulfamethazine. Hydroxyl radicals derived from the photolysis of HONO attacked the aromatic ring of sulfamethazine to form sulfamethazine-OH adducts with a second-order rate constant of (3.8 ± 0.3) × 10⁹ L mol^-1 s^-1. This intermediate would then react with HO· and oxygen molecules. The reaction rate constants of sulfamethazine-OH adducts with oxygen are (1.3 ± 0.1) × 10⁷ L mol^-1 s^-1. The generation of sulfanilic acid and pyrimidine implies that the breaking down of S-N bonds of sulfamethazine and its HO adducts probably occur at the same time.

Sorption of sulfamethazine onto different types of microplastics: A combined experimental and molecular dynamics simulation study

Microplastics are becoming a global concern due to their potential to accumulate pollutants in aquatic environments. In this paper, sulfamethazine (SMT) sorption onto six types of microplastics, including polyamide (PA), polyethylene (PE), polyethylene terephthalate (PET), polypropylene (PP), polystyrene (PS), and polyvinyl chloride (PVC) was investigated by experimental and molecular dynamics simulation methods. The experimental results indicated that SMX sorption reached equilibrium within 16 h. The kinetics of SMT sorption by PA, PVC, PE, and PP could be fitted by pseudo first-order model, while SMT sorption by PA and PET could be described by pseudo second-order model. The partition coefficient K_d values were 38.7, 23.5, 21.0, 22.6, 18.6 and 15.1 L·kg^-1 for PA, PE, PS, PET, PVC and PP, respectively. SMT sorption onto microplastics decreased when pH and salinity increased. The molecular dynamics simulation results indicated that the main mechanisms involved in sorption are electrostatic and Van der Waals interaction.

Determination and toxicity evaluation of the generated byproducts from sulfamethazine degradation during catalytic oxidation process

Sulfamethazine (SMZ), a kind of sulfonamide antibiotics, can exist for a long periods of time and has been widely detected in the environment, which could pose a potential health threat to human beings. In this study, sludge-derived carbon (SC) catalyst was modified and applied to degrade SMZ during catalytic oxidation process. Degradation products and possible transformation pathways were investigated based on data of GC-MS. The toxicity evolution of SMZ degradation after catalytic oxidation process was tested with zebrafish and microbial degradation respirometer. As a consequence, SC modified with nitric acid (SCHNO₃) exhibited highly catalytic efficiency reached 92.2% SMZ conversion and 75.2% total organic carbon (TOC) removal rate after 480 min. Ten kinds of possible products were identified by GC-MS during degradation process of SMZ, indicating two possible pathways. No pronounced malformation was observed in the toxicity experiments with zebrafish until 120 h post fertilization (hpf). However, further analysis showed that zebrafish incubated with SMZ solution had higher mortality, lower hatching rate, slower spontaneous movement and shorter body length, compared with the group used normal nutrient solution, while the water after treatment had lower toxicity effects on zebrafish. The toxicity experiments with microbial degradation respirometer showed that SMZ solution had lower value of oxygen uptake, which indicated that SMZ solution had higher values of toxicity and inhibition of pharmaceutical compounds. This study provides a catalyst with low cost and high catalytic efficiency for degradation process of SMZ and gives a deeper insight into the ecotoxicity of treated water.

Biochar-mediated sorption of antibiotics in pig manure

Using manure contaminated with antibiotics as fertilizer is a primary source of soil pollution with antibiotics and concomitantly with antibiotic resistance genes (ARG). Bioavailable antibiotics trigger further ARG amplification during manure storage. Consequently it is aimed to facilitate the immobilization of antibiotics in manure. To this end, five biochars derived from pine cone (BCP), rice husk, sewage sludge, digestate and Miscanthus were tested as additional sorbents in liquid pig manure for sulfamethazine, ciprofloxacin, oxytetracycline and florfenicol. Non-linear sorption was best-fit using the Freundlich isotherm (R² > 0.82) and the pseudo-second-order model best described sorption kinetics (R² > 0.94). Antibiotics' sorption onto manure increased in the order sulfamethazine < florfenicol < ciprofloxacin < oxytetracycline. Admixtures of BCP to manure changed the order to sulfamethazine < oxytetracycline < florfenicol = ciprofloxacin. Generally, with the addition of biochar, sorption coefficients of florfenicol increased most (by factors>2.7) followed by sulfamethazine and ciprofloxacin. Yet, oxytetracycline was mostly mobilized probably due to competitive adsorption. Effects depended on the proportion of biochar added and the type of biochar, whereby plant-derived biochar exhibited better immobilization of antibiotics. Depending on the type and portion of biochar, admixtures to manure can be used to lower the mobility and hence bioavailability of fenicols, fluoroquinolones and sulfonamides.

Effects of individual and combined zinc oxide nanoparticle, norfloxacin, and sulfamethazine contamination on sludge anaerobic digestion

This work investigated the individual and combined effects of zinc oxide, norfloxacin, and sulfamethazine on sludge anaerobic digestion-associated methane production, protein and carbohydrate metabolism, and microbial diversity. Norfloxacin and sulfamethazine (500 mg/kg) did not inhibit methane production, but inhibited its production rate. Zinc oxide nanoparticles with antibiotics inhibited hydrolysis, fermentation, and methanogenesis over varying digestion periods. Complex pollution had a greater impact on methane production than zinc oxide alone, with acute, synergistic toxicity to methanogenesis over short periods. Complex pollution also had varying effects on bacterial and archaeal communities during digestion. These results aid understanding of the toxicity of emerging contaminants in sludge digestion, with the potential to improve pollution removal and reduce associated risks.

Transformation of sulfamethazine during the chlorination disinfection process: Transformation, kinetics, and toxicology assessment

Various disinfection byproducts (DBPs) form during the process of chlorination disinfection, posing potential threats to drinking water safety and human health. Sulfamethazine (SMT), the most commonly used and frequently detected veterinary antibiotic, was investigated in detail with regard to its transformation and kinetics in reactions with free available chlorine (FAC). Using liquid chromatography coupled to quadrupole time-of-flight tandem mass spectrometry, several DBPs were identified based on different confidence levels, and a variety of reaction types, including desulfonation, S-N cleavage, hydroxylation, and chlorine substitution, were proposed. The kinetic experiments indicated that the reaction rate was FAC- and pH-dependent, and SMT exhibits low reactivity toward FAC in alkaline conditions. The DBPs exhibited a much higher acute toxicity than SMT, as estimated by quantitative structure activity relationship models. More importantly, we observed that the FAC-treated SMT reaction solution might increase the genotoxic potential due to the generation of DBPs. This investigation provides substantial new details related to the transformation of SMT in the chlorination disinfection process.

Sulphamethazine derivatives as immunomodulating agents: New therapeutic strategies for inflammatory diseases

Sulfamethazine (SMZ) (1) is an antibacterial sulfa drug which suppresses the synthesis of dihydrofolic acid. It is used for the treatment of infections in livestock; such as gastrointestinal, and respiratory tract infections. During the current study, synthesis, characterization, and evaluation of immunomodulatory activities of derivatives of sulfamethazine (SMZ) (3-39) was carried out. These derivatives were synthesized by the reaction of sulfamethazine with a range of acid chlorides. All the compounds were characterized by using modern spectroscopic techniques, such as 1H-, and 13C-NMR, EI-MS, and HRFAB-MS. Compounds 3-10, 14, and 15 were identified as new compounds. Immunomodulatory effect of compounds 3-39 on different parameters of innate immune response was evaluated, including the production of Reactive Oxygen Species (ROS) from human whole blood and isolated polymorphonuclear neutrophils (PMNs), nitric oxide (NO), and pro-inflammatory cytokine TNF-α. All the new compounds, except 14 and 15, showed a significant anti-inflammatory activity. Compounds 3-39 were also evaluated for their anti-bacterial activity and cytotoxicity (3T3 mouse fibroblast cell lines). All the compounds were found to be non-cytotoxic against normal cell lines.

Degradation of sulfadiazine, sulfachloropyridazine and sulfamethazine in aqueous media

Antibiotics discharged to the environment constitute a main concern for which different treatment alternatives are being studied, some of them based on antibiotics removal or inactivation using by-products with adsorbent capacity, or which can act as catalyst for photo-degradation. But a preliminary step is to determine the general characteristics and magnitude of the degradation process effectively acting on antibiotics. A specific case is that of sulfonamides (SAs), one of the antibiotic groups most widely used in veterinary medicine, and which are considered the most mobile antibiotics, causing that they are frequently detected in both surface- and ground-waters, facilitating their entry in the food chain and causing public health hazards. In this work we investigated abiotic and biotic degradation of three sulfonamides (sulfadiazine -SDZ-, sulfachloropyridazine -SCP-, and sulfamethazine -SMT-) in aqueous media. The results indicated that, in filtered milliQ water and under simulated sunlight, the degradation sequence was: SCP > SDZ ≈ SMT. Furthermore, the rate of degradation clearly increased with the raise of pH: at pH 4.0, half-lives were 1.2, 70.5 and 84.4 h for SCP, SDZ and SMT, respectively, while at pH 7.2 they were 2.3, 9.4 and 13.2 h for SCP, SMT and SDZ. The addition of a culture medium hardly caused any change in degradation rates as compared to experiments performed in milliQ water at the same pH value (7.2), suggesting that in this case sulfonamides degradation rate was not affected by the presence of some chemical elements and compounds, such as sodium, chloride and phosphate. However, the addition of bacterial suspensions extracted from a soil and from poultry manure increased the rate of degradation of these antibiotics. This increase in degradation cannot be attributed to biodegradation, since there was no degradation in the dark during the time of the experiment (72 h). This indicates that photo-degradation constitutes the main removal mechanism for SAs in aqueous media, a mechanism that in this case was favored by humic acids supplied with the extracts from soil and manure. The overall results could contribute to the understanding of the environmental fate of the three sulfonamides studied, aiding to program actions that could favor their inactivation, which is especially relevant since its dissemination can involve serious environmental and public health risks.

Rapidly probing the interaction between sulfamethazine antibiotics and fulvic acids

Antibiotics residuals in the environments receive wide concerns due to the high risk of generating antibiotic resistance. Natural organic matters (NOM) existed in the environments are considered to have the capacity of binding with organic contaminants, consequently influencing their speciation and transformation in the natural environments. To assess the migration of antibiotics in the environments, it is crucial to understand the binding mechanisms between NOM and antibiotics, which is still unclear due to the limit of available research methods. In this study, the interaction between fulvic acids (FA), one of the main components of NOM, and sulfamethazine (SMZ) was characterized by nuclear magnetic resonance (NMR) combined with surface plasmon resonance (SPR) and isothermal titration calorimetry (ITC) technology. The parameters related to kinetics and thermodynamics of the interaction were determined, and the possible mechanisms driving the interaction were also proposed. In addition, density functional theory (DFT) was used to predict the binding mode between FA and SMZ to reveal the interaction mechanism. Results indicate that FA can effectively bound with SMZ to form a stable complex with a binding constant at the level of 10³ L/mol. The kinetic parameters including association and dissociation constants were 29.4 L/mol/s and 6.64 × 10^-3 1/s, respectively. Hydrophobic interaction might play significant roles in the binding interaction with ancillary contribution of π-π conjunction arising from the aromatic rings stacking of FA and SMZ.

Fenton oxidation of municipal secondary effluent: comparison of Fe/Ce-RGO (reduced graphene oxide) and Fe2+ as catalysts

The advanced treatment of municipal secondary effluent by heterogeneous and homogeneous Fenton processes using Fe/Ce-RGO (reduced graphene oxide) and Fe²⁺ as catalysts was studied and compared. Sulfamethazine (SMT) was spiked in the effluent to examine the effectiveness of the emerging contaminant removal. The Fe/Ce-RGO catalyst was characterized using a scanning electron microscope (SEM) and cycle voltammetry curves. The removal of dissolved organic carbon (DOC), soluble chemical oxygen demand (SCOD), SMT, and ultraviolet-visible spectroscopy in 254 nm (UV₂₅₄) of municipal secondary effluents was examined. The DOC removal efficiency of secondary effluent (without addition of SMT) was 36.30% and 11.74% using Fe/Ce-RGO and Fe²⁺ as catalysts, respectively. The removal efficiency of DOC, SCOD, and SMT in heterogeneous Fenton process was higher than that in homogeneous Fenton process. The changes of three-dimensional excitation-emission matrix (3DEEM) fluorescence, soluble microbial products (SMPs), humic acids, and UV₂₅₄ were determined, and the results indicated that UV_254, aromatic proteins, and humic acids decreased rapidly in both processes; however, polysaccharides and protein-like substances were difficult to degrade. Although some toxic substances produced after Fenton-like treatment, the biodegradability of the treated effluent was enhanced.

Copper complex with sulfamethazine and 2,2'-bipyridine supported on mesoporous silica microspheres improves its antitumor action toward human osteosarcoma cells: cyto- and genotoxic effects

Ideal drugs to cure cancer leave normal cells unharmed while selectively turning tumor cells unviable. Several copper complexes have been able to selectively slow down tumor proliferation. We hypothesized that Cu(smz)₂(bipy)·H₂O (1)-a copper-complex that has two ligands capable of interacting with DNA-would outperform Cu(smz)₂(OH₂)·2H₂O (2), and also that supporting 1 on mesoporous silica spheres would decrease even further tumor cell viability in vitro. After exposing osteosarcoma cells (MG-63) and normal phenotype cells of bone origin (MC3T3-E1) to either complex, we studied their toxic effect and mechanisms of action. We determined cell viability (MTT assay) and quantified formation of reactive oxygen species (oxidation of DHR-123 to rhodamine). Moreover, we assessed genotoxicity from (i) formation of micronucleus (MN assay) and (ii) damage of DNA (Comet assay). After the exposure of 1 supported on silica spheres, we tested cell viability. Our results confirm our hypotheses: inhibition of tumor cells follows: supported 1 > dissolved 1 > 2. Future work that enhances the load of the complex exclusively in mesopores may improve the ability of 1 to further inhibit tumor cell viability.

Removal mechanism of sulfamethazine and its intermediates from water by a rotating advanced oxidation contactor equipped with TiO2-high-silica zeolite composite sheets

The removal of antibiotic sulfamethazine (SMT) and its intermediates from water was investigated using a rotating advanced oxidation contactor (RAOC) equipped with TiO₂-high-silica zeolite composite sheets. SMT was readily removed from water through adsorption onto high-silica zeolite and photocatalytic decomposition by TiO₂ inside the composite sheet. Some degradation intermediates were retained and photocatalytically decomposed inside the composite sheet. Relatively hydrophobic intermediates such as hydroxylated SMT were captured inside the sheets, whereas hydrophilic intermediates were distributed in water. This was attributed to the hydrophobic interactions in the adsorption mechanism of high-silica zeolite. The time courses of the NH₄⁺, NO₃^-, and SO₄^2- ion concentration during the RAOC treatment of SMT were evaluated. After treatment by RAOC for 24 h, approximately 94% of nitrogen derived from the amino and sulfanilamide groups and 39% of sulfur from the sulfanilamide group were mineralized, which indicated that the mineralization behavior of SMT treated by RAOC was different from that treated by TiO₂ powder. These results strongly suggested that the dissociation of the amino group and cleavage of the sulfonamide group and subsequent dissociation of the amino group preferentially proceeded inside the composite sheets.

Transformation of antimicrobial agent sulfamethazine by peroxymonosulfate: Radical vs. nonradical mechanisms

Peroxymonosulfate (PMS) is increasingly used as an oxidant for in situ remediation of organic contaminants in soil and groundwater. In this study we demonstrated that sulfamethazine (SMZ) could be transformed by PMS in the absence of any activators. Such transformation was ascribed to the oxidation by PMS per se, rather than free radicals (SO₄^- or HO), superoxide (O₂^-), or singlet oxygen (¹O₂). The aniline moiety of SMZ molecule was the reactive site for PMS oxidation, leading to the formation of nitrated products. This nitration pathway in fact played a significant role in the removal of SMZ in activated PMS oxidation processes. For instance, it contributed 26% of the total SMZ transformation, while SO₄^- contributed the other 74% during the removal of SMZ, in Co(II)/PMS oxidation process with initial PMS and Co(II) concentrations of 1.0 mM and 0.1 μM, respectively. Similar nitration reaction also occurred to other sulfonamide antibiotics bearing an aniline moiety upon the reaction with PMS. Since nitrated sulfonamide antibiotics appear more persistent than the parent compounds and may cause other environmental problems, such a pathway should not be desired. Therefore, PMS might not be an ideal oxidant for the treatment of sulfonamide antibiotics and other compounds having aniline moieties, especially in subsurface remediation practices where efficient activation of PMS represents a major challenge.

Efficient degradation of sulfamethazine in simulated and real wastewater at slightly basic pH values using Co-SAM-SCS /H2O2 Fenton-like system

The presence of antibiotics in aquatic environments has attracted global concern. Fenton process is an attractive yet challenging method for antibiotics degradation, especially when such a reaction can be conducted at neutral pH values. In this study, a novel composite Fe/Co catalyst was synthesized via the modification of steel converter slag (SCS) by salicylic acid-methanol (SAM) and cobalt nitrate (Co(NO₃)₂). The catalysts were characterized by N₂-Brunauer-Emmett-Teller (BET), X-ray diffraction (XRD), Fourier transform infrared (FT-IR), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS). The results indicated that the Co-SAM-SCS/H₂O₂ Fenton-like system was very effective for sulfamethazine (SMZ) degradation at a wide pH range. At initial pH of 7.0, the degradation rate of SMZ in Co-SAM-SCS/H₂O₂ system was 2.48, 3.20, 6.18, and 16.21 times of that in Fe-SAM-SCS/H₂O₂, SAM-SCS/H₂O₂, Co(NO₃)₂/H₂O₂ and SCS/H₂O₂ system, respectively. The preliminary analysis suggested that high surface area of Co-SAM-SCS sample and synergistic effect between introduced Co and SAM-SCS are responsible for the efficient catalytic activity. During the degradation, three main intermediates were identified by high performance liquid chromatography-mass spectrometry (HPLC-MS) analysis. Based on this, a possible degradation pathway was proposed. The SEM images, XRD patterns and XPS spectra before and after the reactions demonstrate that the crystal and chemical structure of Co-SAM-SCS after five cycles are almost unchanged. Besides, the Co-SAM-SCS presented low iron and cobalt leaching (0.17 mg/L and 2.36 mg/L, respectively). The studied Fenton-like process also showed high degradation of SMZ in river water and municipal wastewater. The progress will bring valuable insights to develop high-performance heterogeneous Fenton-like catalysts for environmental remediation.

Aqueous chlorination of sulfamethazine and sulfamethoxypyridazine: Kinetics and transformation products identification

Sulfonamides (SNs) are synthetic antimicrobial agents. These substances are continually introduced into the environment, and they may spread and maintain bacterial resistance in the different compartments. The chlorination of 2 SNs, namely, sulfamethazine (SMT) and sulfamethoxypyridazine (SMP), was investigated to study their reactivity with chlorine at typical concentrations for water treatment conditions. Experiments conducted in purified water show an acceleration of SMT and SMP degradation of a factor 1.5 by comparison to drinking water matrix. This difference is due to pH variation and competitive reactions between SNs and mineral and organic compounds, with chlorine in drinking water. In the presence of an excess of chlorine (6.7 μmol·L^-1 ) in ultrapure water at pH 7.2, second-order degradation rate constants were equal to 4.5 × 10² M^-1 ·s^-1 and 5.2 × 10² M^-1 ·s^-1 for SMT and SMP, respectively. The structures of transformation products were investigated by liquid chromatography tandem mass spectrometry analyses with equimolar concentrations between chlorine and SNs. SO₂ elimination, cyclization, and electrophilic substitutions were the main pathways of by-products formation. Moreover, the toxicity of the proposed structures was predicted by using toxicity estimation software tool program. The results indicated that most by-products may present developmental toxicity.

Explaining the accelerated degradation of ciprofloxacin, sulfamethazine, and erythromycin in different soil exposure scenarios by their aqueous extractability

Antibiotics are frequently introduced into agricultural soils with the application of sewage sludge or farm organic fertilizers. Repeated exposure of soils to a pollutant can enrich for microbial populations that metabolize the chemical, reducing its environmental persistence. In London, Canada, soils from a long-term field experiment have received different concentrations of antibiotics annually for several years. The purpose of the present study was to assess the bioavailability of sulfamethazine, erythromycin, or ciprofloxacin through aqueous extractions with borax or EDTA solutions and their biodegradation following different soil exposure scenarios. Control soils and soils treated annually in the field with 10 mg antibiotics per kg were sampled, supplemented in the laboratory with radiolabeled antibiotic either added directly or carried in dairy manure. Sulfamethazine and erythromycin were initially more bioavailable than ciprofloxacin, with aqueous extractabilities representing 60, 36, and 8%, respectively. Sulfamethazine and erythromycin were degraded in soils, with a larger fraction mineralized in the long-term exposed soil (20 and 65%, respectively) than in control soil (0.4 and 3%, respectively) after 7 days of incubation. In contrast, ciprofloxacin was not mineralized neither in control nor long-term exposed soils. The mineralized fractions were similar for antibiotics added directly to soil or carried in dairy manure.

Complexation of sulfamethazine with Cd(II) and Pb(II): implication for co-adsorption of SMT and Cd(II) on goethite

This study quantified the complex stability constants of sulfamethazine (SMT) with cadmium (Cd²⁺) and lead (Pb²⁺) under different pH conditions. The UV-Vis spectrophotometer was used for acquiring the complexation data. Results showed that the complex stability constants of SMT with cadmium (Cd²⁺) and lead (Pb²⁺) increased as a function of the solution pH. In the investigated pH range, Cd²⁺ showed stronger complex affinity with SMT than Pb²⁺. It appeared that cation-π interactions might dominate the complex between SMT with Pb²⁺ and Cd²⁺ at acid environment, and the covalent bonding might play a major role at neutral environment. Batch adsorption equilibrium experiment showed that the sorption capacity of Cd²⁺ on goethite increased from 3.83 to 7.64 mg/g along with the addition of 1 mg/L SMT, indicating SMT can impede the transportation of Cd. In general, this study worked out the complexation constants and clarified the complexation mechanism between SMT with lead and cadmium, while sorption experiment indicated that sorption of Cd onto goethite was enhanced with SMT.

Iron doped fibrous-structured silica nanospheres as efficient catalyst for catalytic ozonation of sulfamethazine

Sulfonamide antibiotics are ubiquitous pollutants in aquatic environments due to their large production and extensive application. In this paper, the iron doped fibrous-structured silica (KCC-1) nanospheres (Fe-KCC-1) was prepared, characterized, and applied as a catalyst for catalytic ozonation of sulfamethazine (SMT). The effects of ozone dosage, catalyst dosage, and initial concentration of SMT were examined. The experimental results showed that Fe-KCC-1 had large surface area (464.56 m2 g^-1) and iron particles were well dispersed on the catalyst. The catalyst had high catalytic performance especially for the mineralization of SMT, with mineralization ratio of about 40% in a wide pH range. With addition of Fe-KCC-1, the ozone utilization increased nearly two times than single ozonation. The enhancement of SMT degradation was mainly due to the surface reaction, and the increased mineralization of SMT was due to radical mechanism. Fe-KCC-1 was an efficient catalyst for SMT degradation in catalytic ozonation system.

Aquatic photochemistry of sulfamethazine: multivariate effects of main water constituents and mechanisms

The ubiquity of sulfonamides (SAs) in natural waters requires insight into their environmental fate for ecological risk assessment. Extensive studies focused on the effect of univariate water constituents on the photochemical fate of SAs, yet the multivariate effects of water constituents in environmentally relevant concentrations on SA photodegradation are poorly understood. Here, response surface methodology was employed to explore the integrative effects of main water constituents (dissolved organic matter (DOM), NO₃^-, HCO₃^-, Cu²⁺) on the photodegradation of a representative SA (sulfamethazine). Results showed that besides single factors, interaction of factors also significantly impacted the photodegradation. Radical scavenging experiments indicated that triplet-excited DOM (³DOM*) was responsible for the enhancing effect of DOM on the photodegradation. Additionally, DOM may also quench the ³DOM*-mediated oxidation intermediate of sulfamethazine causing the inhibiting effect of DOM-DOM interaction. We also found that HCO₃^- was oxidized by triplet-excited sulfamethazine producing CO₃˙^-, and the high reactivity of CO₃˙^- with sulfamethazine (second-order rate constant 2.2 × 10⁸ M^-1 s^-1) determined by laser flash photolysis revealed the enhancing photodegradation mechanism of HCO₃^-. This study is among the first attempts to probe the photodegradation of SAs considering the integrative effects of water constituents, which is important in accurate ecological risk assessment of organic pollutants in the aquatic environment.

Application of membrane bioreactor for sulfamethazine-contained wastewater treatment

The presence of antibiotics in wastewater has been widely confirmed. Membrane bioreactor (MBR), as an efficient wastewater treatment technology, has attracted increasing interest in its ability to remove antibiotics in recent years. However, its long-term operation stability and the underlying mechanisms for antibiotics removal are still poorly understood. In this study, a hollow fiber MBR was used to treat low concentration sulfamethazine (SMZ) contained wastewater. The long-term effects of various SMZ concentrations on nutrients removal, SMZ degradation, and sludge characteristics were investigated. During the 244 days operation, the overall SMZ removal efficiency could reach 95.4 ± 4.5% under various SMZ concentrations and hydraulic retention times. The reactor exhibited high chemical oxygen demand and NH₄⁺-N removal efficiencies, which reached 93.0% and 96.2%, respectively. A sludge concentration of 4.1 ± 0.3 g/L was maintained in the system without excess sludge discharge. The dosage of SMZ had obvious effect on sludge characteristics. The contents of extracellular polymeric substances (EPS) in MBR decreased after a long-term operation of the reactor under SMZ pressure. The low sludge concentration and the reduced EPS content were also beneficial for mitigating membrane fouling. Thus, this study provides a low-cost, efficient and simple approach to treat SMZ-contained wastewater.

Removal of the veterinary antimicrobial sulfamethazine in a horizontal-flow anaerobic immobilized biomass (HAIB) reactor subjected to step changes in the applied organic loading rate

A bench-scale horizontal-flow anaerobic immobilized biomass (HAIB) reactor treating synthetic swine wastewater was operated under different applied organic loading rates (OLR) through both variations in feed strength and in hydraulic retention time (HRT). The influence of step changes in OLR on the removal of the veterinary antimicrobial sulfamethazine (SMZ) was assessed. The highest observed SMZ removal efficiency, 75 ± 6%, was achieved with an OLR of 2.7 ± 0.4 kg O₂ m^-3 d^-1 when a significant increase in COD removal rate was observed. The SMZ removal rate was positively correlated (r = 0.899) to the COD removal rate in all of the experimental conditions in which the HRT was kept at 24 h, indicating a cometabolic transformation of the antimicrobial. Decreasing the HRT caused a significant decrease in SMZ removal efficiency without affecting the HAIB reactor performance in terms of stability, COD removal or metabolic intermediates production. Functionally equivalent steady states were observed in four different operational phases with similar operating conditions but with widely different behavior in relation to SMZ removal. The experimental results showed the potential of anaerobic technology in removing environmentally relevant concentrations of SMZ, and the possibility of enhancing reactor performance by controlling operating conditions.

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

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

Sorptive removal of ionizable antibiotic sulfamethazine from aqueous solution by graphene oxide-coated biochar nanocomposites: Influencing factors and mechanism

Significant concerns have been raised over antibiotics pollution in aquatic environments in recent years. In this study, sorption of sulfamethazine (SMT) by novel graphene oxide-coated biochar nanocomposites (GO-BC) based on graphene oxide (GO) with bamboo sawdust biochar (BC) was investigated. In comparison with the original BC, the sorption capacity of GO-BC for SMT increased by 1.14 times. Sorption of SMT onto GO-BC was proved to be dominantly by chemisorption, and Freundlich isotherm described the sorption adequately. It was found that variation of pH and ionic strength obviously affected the sorption of SMT, and GO-BC had a good sorption effect on SMT at pH 3.0-6.0 and lower ionic strength. Obvious enhancement (by 30%) in sorption of SMT on GO-BC was observed, which might be attributed to the increase of functional groups on the surface of GO-BC. Moreover, the main sorption mechanism for SMT was π-π electron-donor-acceptor interaction, while auxiliary sorption mechanisms were inferred as pore-filling, cation exchange, hydrogen bonding interaction and electrostatic interaction. The results indicated that GO-BC sorption was an efficient way for the removal of SMT.

Roles of phytoplankton- and macrophyte-derived dissolved organic matter in sulfamethazine adsorption on goethite

Phytoplankton-derived dissolved organic matter (PDOM) and macrophyte-derived dissolved organic matter (MDOM) exist ubiquitously in eutrophic freshwater lakes. To understand the heterogeneous roles of individual fluorescent DOM components in the adsorption of antibiotics onto sediment minerals, the adsorptive fractionation of DOM on goethite (α-FeOOH) and its interaction with sulfamethazine (SMT) were investigated using fluorescence excitation-emission matrix combined with parallel factor analysis (EEM-PARAFAC). The affinity sequence for goethite of the 4 fluorescent PARAFAC components followed the order of: tryptophan- > tyrosine- > long emission wavelength (LEW) humic- > and short emission wavelength (SEW) humic-like component. This sequence indicated the preferential adsorption of protein-like substances. Meanwhile, tyrosine-like components can strongly form complexes with SMT with a large binding constant, followed by tryptophan- and SEW humic-like components. However, LEW humic-like component did not effectively react with SMT. The main mechanism of fluorescence quenching between DOM and SMT was static quenching. The result indicated that protein-like substances in DOM were favorable to SMT adsorption by acting as a bridge to form complexes with both goethite surface and SMT molecules, whereas humic-like substances played secondary roles in the DOM-goethite-SMT ternary system. Due to its higher content of protein-like substances, PDOM improved the SMT adsorption on goethite more than MDOM. Therefore, the abundant DOM released from phytoplankton and macrophytes affected the transport of antibiotics to sediments and might eventually change their bioavailability and toxicity to organisms.

Combination of the Electro/Fe3+/peroxydisulfate (PDS) process with activated sludge culture for the degradation of sulfamethazine

In this paper, the major factors affecting the degradation and the mineralization of sulfamethazine by Electro/Fe³⁺/peroxydisulfate (PDS) process (e.g. current density, PDS concentration, Fe³⁺ ions concentration and initial sulfamethazine (SMT) concentration) were evaluated. The relevance of this process as a pretreatment prior to activated sludge culture was also examined. Regarding the impact on SMT degradation and mineralization, the obtained results showed that they were significantly enhanced by increasing the current density and the PDS concentrations in the ranges 1-40mAcm^-2 and from 1 to 10mM respectively; while they were negatively impacted by an increase of the initial SMT concentration and the Fe³⁺ concentration, from 0.18 to 0.36mM and from 1 to 4mM respectively. The optimal operating conditions were therefore 40mAcm^-2 current density, 10mM PDS concentrations, 1mM Fe³⁺, and 0.18mM SMT. Indeed, under these conditions the degradation of SMT and its mineralization yield were 100% and 83% within 20min and 180min respectively. To ensure a significant residual organic content for activated sludge culture after Electro/Fe³⁺/PDS pre-treatment, the biodegradability test and the biological treatment were performed on a solution electrolyzed at 40mAcm^-2, 10mM PDS concentrations, 1mM Fe³⁺, and 0.36mM SMT. Under these conditions the BOD₅/COD ratio increased from 0.07 to 0.41 within 6h of electrolysis time. The subsequent biological treatment increased the mineralization yield to 86% after 30days, confirming the relevance of the proposed combined process.

Effect of pH on the adsorption and photocatalytic degradation of sulfadimidine in Vis/g-C3N4 progress

In this study, g-C₃N₄ was synthesized by thermal polycondensation of melamine and was characterized by X-ray powder diffraction, X-ray photoelectron spectroscopy, UV-visible diffuse reflection spectroscopy, and scanning electron microscopy. Results showed that g-C₃N₄ degraded sulfadimidine (SMD) under visible light, in which the adsorption and photocatalytic degradation was influenced by pH. The maximum adsorption capacity was achieved at approximately pH 5. The highest degradation rate constant was obtained at strong acid and alkali. In addition, the degradation mechanism of g-C₃N₄ was evaluated with the help of quencher agents. The intermediates, degradation pathways, and mineralization of SMD were also determined to evaluate the degradation and oxidation ability of g-C₃N₄.

Sorption mechanisms of sulfamethazine to soil humin and its subfractions after sequential treatments

Sorption mechanisms of an antibiotic sulfamethazine (SMT) to humin (HM) isolated from a peat soil and its subfractions after sequential treatments were examined. The treatments of HM included removal of ash, O-alkyl carbon, lipid, and lignin components. The HF/HCl de-ashing treatment removed a large amount of minerals (mainly silicates), releasing a fraction of hydrophobic carbon sorption domains that previously were blocked, increasing the sorption of SMT by 33.3%. The de-O-alkyl carbon treatment through acid hydrolysis greatly reduced polarity of HM samples, thus weakening the interaction between sorbents with water at the interfaces via H-bonding, leaving more effective sorption sites. Sorption of SMT via mechanisms such as van der Waals forces and π-π interactions was enhanced by factors of 2.04-2.50. After removing the lipid/lignin component with the improved Soxhlet extraction/acid hydrolysis, the organic carbon content-normalized sorption enhancement index E_oc was calculated. The results demonstrated that the E_oc-lipid for SMT (16.9%) was higher than E_oc-lignin (10.1%), implying that removal of unit organic carbon mass of lipid led to a higher increase in sorption strength than that of lignin. As each component was progressively removed from HM, the sorption strength and isotherm nonlinearity of the residual HM samples for SMT were gradually enhanced. The K_oc values of SMT by HM samples were positively correlated with their aromatic carbon contents, implying that π-π electron donor-acceptor interactions between the benzene ring of sorbate and the aromatic domains in HM played a significant role in their interactions.