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

Photochemical behaviors of sludge extracellular polymeric substances from bio-treated effluents towards antibiotic degradation: Distinguish the main photosensitive active component and its environmental implication

Activated sludge extracellular polymeric substances (ASEPSs) comprise most dissolved organic matters (DOMs) in the tail water. However, the understanding of the link between the photolysis of antibiotic and the photo-reactivity/photo-persistence of ASEPS components is limited. This study first investigated the photochemical behaviors of ASEPS's components (humic acids (HA), hydrophobic substances (HOS) and hydrophilic substances (HIS)) separated from municipal sludge's EPS (M-EPS) and nitrification sludge's EPS (N-EPS) in the photolysis of sulfadiazine (SDZ). The results showed that 60% of SDZ was removed by the M-EPS, but the effect in the separated components was weakened, and only 24% - 39% was degraded. However, 58% of SDZ was cleaned by HOS in N-EPS, which was 23% higher than full N-EPS. M-EPS components had lower steady-state concentrations of triplet intermediates (3EPS*), hydroxyl radicals (·OH) and singlet oxygen (1O2) than M-EPS, but N-EPS components had the highest concentrations (5.96 ×10-15, 8.44 ×10-18, 4.56 ×10-13 M, respectively). The changes of CO, C-O and O-CO groups in HA and HOS potentially correspond to reactive specie's generation. These groups change little in HIS, which may make it have radiation resistance. HCO-3 and NO-3 decreased the indirect photolysis of SDZ, and its by-product N-(2-Pyrimidinyl)1,4-benzenediamine presents high environmental risk.

Effective photocatalytic inactivation of Microcystis aeruginosa by Ag3VO4/BiVO4 heterojunction under visible light

In recent years, photocatalytic technology has been increasingly used for the treatment of algal blooms in water bodies due to its high efficiency and environmental advantages. However, conventional semiconductor materials suffer from high electron-hole recombination rate, low carrier mobility and weak surface adsorption ability, which made their photocatalytic performance limited. Therefore, the photocatalytic performance of the composites can be improved by coupling another semiconductor material to form a heterojunction to accelerate electron transfer. In this study, a novel composite Ag3VO4/BiVO4 (ABV) photocatalyst was successfully prepared by in-situ deposition method for the photocatalytic inactivation of Microcystis aeruginosa (M. aeruginosa) under visible light. The photocatalyst showed excellent photocatalytic activity, and the degradation rate of M. aeruginosa chlorophyll a was up to 99.8% within 4 h under visible light. During the photocatalytic degradation, the morphology of algae cells, the permeability of cell membrane, the organic matter inside and outside the cells, the antioxidant system and the soluble protein were seriously damaged. Moreover, three cycle experiments showed that the prepared ABV photocatalyst had high reusability. Finally, a possible mechanism of M. aeruginosa inactivation was proposed. In general, the synthesized ABV photocatalyst can effectively inactivate cyanobacteria under visible light and provided a new method for M. aeruginosa removal in water.

Biodegradation, photolysis, and sorption of antibiotics in aquatic environments: A scoping review

The presence of antibiotics in surface waters is a potential driver of antibiotic resistance and thus of concern to human and environmental health. Key factors driving the potential impact of antibiotics are their persistence and transport in rivers and lakes. The goal of this study was to describe the peer-reviewed published literature on the photolysis (direct and indirect), sorption, and biodegradation of a selected group of antibiotic compounds following a scoping review methodology. Primary research from 2000 to 2021 was surveyed to compile information on these processes for 25 antibiotics from 6 classes. After compilation and assessment of the available parameters, the results indicate that information is present to predict the rates of direct photolysis and reaction with hydroxyl radical (an indirect photolysis process) for most of the selected antibiotics. There is insufficient or inconsistent information for including other indirect photolysis processes, biodegradation, or removal via sorption to settling particles for most of the targeted antibiotic compounds. Future research should focus on collecting fundamental parameters such as quantum yields, second-order rate constants, normalized biodegradation rates, and organic carbon or surface area normalized sorption coefficients rather than pseudo-first order rate constants or sorption equilibrium constants that apply only to specific conditions/sites.

Light-dependent enhancement of sulfadiazine detoxification and mineralization by non-photosynthetic methanotrophs

Co-metabolism and photodegradation are two approaches for remediating trace organic compounds (TOrCs), however, interactions between the two with regards to TOrCs degradation have not been elucidated. In this study, sulfadiazine (SDZ) was chosen as a representative TOrC and Methylocystis bryophila as a typical strain. Under light conditions, about 80.6% of SDZ was removed by M. bryophila, but only 7.6% or 28.9% of SDZ was eliminated by either individual photodegradation or by co-metabolism. The SDZ stimulated more extracellular organic matter (EOM) production by M. bryophila. The enhanced SDZ degradation was attributed to indirect photolysis caused by the excited triplet state of EOM (³EOM*) and co-metabolism. The UPLC-QTOF-MS analysis showed that due to co-metabolism, the pyrimidine ring was broken and could further be oxidized into smaller molecules under light conditions, such as formic and acetic acids. The SDZ mineralization ratio increased from 9.9% under the co-metabolic condition alone to 36.5% under co-metabolism coupled with photodegradation. The Ames tests confirmed that the SDZ degradation products by co-metabolism were mutagenic, however, their toxicity was ameliorated by light during co-metabolism. In conclusion, light plays a crucial role in co-metabolic processes of TOrCs.

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.

Heme Protein Binding of Sulfonamide Compounds: A Correlation Study by Spectroscopic, Calorimetric, and Computational Methods

Protein-ligand interaction studies are useful to determine the molecular mechanism of the binding phenomenon, leading to the establishment of the structure-function relationship. Here, we report the binding of well-known antibiotic sulfonamide drugs (sulfamethazine, SMZ; and sulfadiazine, SDZ) with heme protein myoglobin (Mb) using spectroscopic, calorimetric, ζ potential, and computational methods. Formation of a 1:1 complex between the ligand and Mb through well-defined equilibrium was observed. The binding constants obtained between Mb and SMZ/SDZ drugs were on the order of 104 M-1. SMZ with two additional methyl (-CH3) substitutions has higher affinity than SDZ. Upon drug binding, a notable loss in the helicity (via circular dichroism) and perturbation of the three-dimensional (3D) protein structure (via infrared and synchronous fluorescence experiments) were observed. The binding also indicated the dominance of non-polyelectrolytic forces between the amino acid residues of the protein and the drugs. The ligand-protein binding distance signified high probability of energy transfer between them. Destabilization of the protein structure upon binding was evident from differential scanning calorimetry results and ζ potential analyses. Molecular docking presented the best probable binding sites of the drugs inside protein pockets. Thus, the present study explores the potential binding characteristics of two sulfonamide drugs (with different substitutions) with myoglobin, correlating the structural and energetic aspects.

Abiotic transformation and ecotoxicity change of sulfonamide antibiotics in environmental and water treatment processes: A critical review

Sulfonamides (SAs) are among the most widely used antibiotics to treat bacterial infections for humans and animals. They are also used in livestock agriculture to improve growth and feed efficiency in many countries. Recent years, there is a growing concern about the environmental fate and treatment technologies of SAs, in order to eliminate their potential impact on the ecosystem and human health. Additionally, SAs are frequently used as model compounds to evaluate the performance of newly developed advanced water treatment processes. Hence, understanding the chemical reaction features of SAs can provide valuable information for further technological development. In this review, the reaction kinetics, abiotic transformations and corresponding ecotoxicity changes of SAs in natural environments and water treatment processes were comprehensively analyzed to draw critical suggestion and new insights. The •OH-based AOP is proposed as an effective method for the elimination of SAs toxicity, although it is susceptible to water constituent due to low selectivity. The application of biochar or metal-based oxidants in AOPs is becoming a future trend for SA treatment. Overall, this review would provide useful information for the development of advanced water treatment technologies and the control of ecological risks related to SAs.

Phototransformation of Graphene Oxide on the Removal of Sulfamethazine in a Water Environment

Graphene oxide (GO) is widely used in various fields and has raised concerns regarding its potential environmental fate and effect. However, there are few studies on its influence on coexisting pollutants. In this study, the phototransformation of GO and coexisting sulfamethazine (SMZ) under UV irradiation was investigated, with a focus on the role of reactive oxygen species. The results demonstrated that GO promoted the degradation of SMZ under UV irradiation. The higher the concentration of GO, the higher the degradation rate of SMZ, and the faster the first-order reaction rate. Two main radicals, ∙OH and ¹O₂, both contributed greatly in terms of regulating the removal of SMZ. Cl⁻, SO₄²⁻, and pH mainly promoted SMZ degradation by increasing the generation of ∙OH, while humic acid inhibited SMZ degradation due to the reduction of ∙OH. Moreover, after UV illumination, the GO suspension changed from light yellow to dark brown with increasing absorbance at a wavelength of 225 nm. Raman spectra revealed that the I_D/I_G ratio slightly decreased, indicating that some of the functional groups on the surface of GO were removed under low-intensity UV illumination. This study revealed that GO plays important roles in the photochemical transformation of environmental pollutants, which is helpful for understanding the environmental behaviors and risks of nanoparticles in aquatic environments.

Sensitized Photolysis of Thioglycolic Acid in Aquatic Environment

The photochemical transformations of thioglycolic acid using model systems was studied by varying the irradiation sources and the kinetic parameters were determined. It was found that thioglycolic acid undergoes destruction on induced photolysis in the presence of humic substances, and its half-life can be estimated as 10-14 days, depending on weather conditions (cloudiness, time of day, season etc.). Results obtained in the course of this study on model systems were transferred to natural waters, and it was concluded that thioglycolic acid has a positive influence on the chemical self-purification processes of water, in the natural aquatic environment. This is manifested by increasing the self-purification capacity of water, due to the generation of active oxygen species, which lead to the degradation not only of this thiol, but of other pollutants present in aquatic environment, as well. At the same time, the products of the transformations are harmless to the aquatic environment and hydrobionts.

Effect of nitrate on the phototreatment of Triton X-100 simulated washing waste containing 4,4'-dibromodiphenyl ether: Kinetics, products and toxicity assessment

This study aimed to investigate the effects of nitrate on the ultraviolet (UV) treatment of simulated washing wastes containing Trion X-100 (TX-100) surfactant and 4,4'-dibromodiphenyl ether (BDE-15) pollutant. The presence of nitrate accelerated the photodegradation of BDE-15 and TX-100, because they reacted with reactive oxygen species (ROS) produced from conversion between nitrate and nitrite. Due to nitrite having a stronger radical quenching property than nitrate, nitrite hindered TX-100 decay while the photodegradation rate of BDE-15 was similar to that in the presence of nitrate. This indicated that nitrate/nitrite affected BDE-15 photodegradation by photosensitization and TX-100 loss by ROS attack. An increased TX-100 concentration increased the loss of total inorganic nitrogen possibly owing to an increase in organic nitrogen formation through TX-100 nitration reactions. At pH < 7 HOONO rapidly isomerized to NO₃^-, and at pH = 7-9 it homolyzed to ONOO^-, which increased OH production to decay the BDE-15 and TX-100 and also increased NO₂^- formation. BDE-15 mainly underwent debromination, and some rearrangement, ring formation, nitration and hydroxylation products were detected, indicating that the produced OH and NO₂ attacked the BDE-15 and products. Furthermore, broken-chain, carboxylation, hydroxylation and nitro products were detected by Liquid chromatography high resolution mass spectrometry (LC-HRMS). Escherichia coli was used to assess the toxicity of washing waste containing nitrate: the presence of nitrate will increase the wastes' toxicity during UV treatment. Therefore, the presence of nitrate is deleterious to the UV treatment of washing wastes, and it is important to remove nitrates and nitrites from washing waste before UV irradiation.

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

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

Trace amounts of fenofibrate acid sensitize the photodegradation of bezafibrate in effluents: Mechanisms, degradation pathways, and toxicity evaluation

Effluent organic matter (EfOM), which is composed of background natural organic matter (NOM), soluble microbial degradation products, and trace amounts of organic pollutants, can play an important role in the photodegradation of emerging pollutants in the effluent. In this study, the impact of organic pollutants, using fenofibrate acid (FNFA) as a representative, on the photodegradation of emerging contaminants, using bezafibrate (BZF) as a representative, in effluents was investigated. It is found that BZF undergo fast degradation in the presence of FNFA although BZF is recalcitrant to degradation under simulated sunlight irradiation. The promotional effect of FNFA is due to the generation of singlet oxygen (¹O₂) and hydrated electrons (e^-_aq). Based on the structures of the identified intermediates, ¹O₂ initiated oxidation and e^-_aq initiated reduction reactions were the main photodegradation pathways of BZF in the effluents. The toxicity of the main photodegradation intermediates for BZF and FNFA was higher than that of the parent compounds, and the acute toxicity increased during simulated sunlight irradiation. The results demonstrated that trace amounts of organic compounds in EfOM can play an important role in sensitizing the photodegradation of some emerging pollutants in the effluent.