Polyvinyl chloride microplastics in the aquatic environment enrich potential pathogenic bacteria and spread antibiotic resistance genes in the fish gut.

Microplastics and antibiotics coexist in aquatic environments, especially in freshwater aquaculture areas. However, as the second largest production of polyvinyl chloride (PVC) in the world, the effects of co-exposure to microplastics particles and antibiotics on changes in antibiotic resistance gene (ARG) profiles and the microbial community structure of aquatic organism gut microorganisms are poorly understood. Therefore, in this study, carp (Cyprinus carpio) were exposed to single or combined PVC microplastic contamination and oxytetracycline (OTC) or sulfamethazine (SMZ) for 8 weeks. PVC microplastics can enrich potential pathogenic bacteria, such as Enterobacter and Acinetobacter, among intestinal microorganisms. The presence of PVC microplastics enhanced the selective enrichment and dissemination risk of ARGs. PVC microplastics combined with OTC (OPVC) treatment significantly increased the abundance of tetracycline resistance genes (1.40-fold) compared with that in the OTC exposure treatment, revealing an obvious co-selection effect. However, compared with those in the control group, the total abundance of ARGs and MGEs in the OPVC treatment groups were significantly lower, which was correlated with the reduced abundances of the potential host Enterobacter. Overall, our results emphasized the diffusion and spread of ARGs are more influenced by PVC microplastics than by antibiotics, which may lead to antibiotic resistance in aquaculture.

Effects of four antibiotics on the photosynthetic light reactions in the green alga Chlorella pyrenoidosa.

Antibiotics are ubiquitously present in aquatic environments, posing a serious ecological risk to aquatic ecosystems. However, the effects of antibiotics on the photosynthetic light reactions of freshwater algae and the underlying mechanisms are relatively less understood. In this study, the effects of 4 representative antibiotics (clarithromycin, enrofloxacin, tetracycline, and sulfamethazine) on a freshwater alga (Chlorella pyrenoidosa) and the associated mechanisms, primarily focusing on key regulators of the photosynthetic light reactions, were evaluated. Algae were exposed to different concentrations of clarithromycin (0.0-0.3 mg/L), enrofloxacin (0.0-30.0 mg/L), tetracycline (0.0-10.0 mg/L), and sulfamethazine (0.0-50.0 mg/L) for 7 days. The results showed that the 4 antibiotics inhibited the growth, the photosynthetic pigment contents, and the activity of antioxidant enzymes. In addition, exposure to clarithromycin caused a 118.4 % increase in malondialdehyde (MDA) levels at 0.3 mg/L. Furthermore, the transcripts of genes for the adenosine triphosphate (ATP) - dependent chloroplast proteases (ftsH and clpP), genes in photosystem II (psbA, psbB, and psbC), genes related to ATP synthase (atpA, atpB, and atpH), and petA (related to cytochrome b6/f complex) were altered by clarithromycin. This study contributes to a better understanding of the risk of antibiotics on primary producers in aquatic environment.

Surface functional groups on nanoplastics delay the recovery of gut microbiota after combined exposure to sulfamethazine in marine medaka (Oryzias melastigma).

Nanoplastics can interact with antibiotics, altering their bioavailability and the ensuing toxicity in marine organisms. It is reported that plain polystyrene (PS) nanoplastics decrease the bioavailability and adverse effects of sulfamethazine (SMZ) on the gut microbiota in Oryzias melastigma. However, the influence of surface functional groups on the combined effects with SMZ remains largely unknown. In this study, adult O. melastigma were fed diet amended with 4.62 mg/g SMZ and 3.65 mg/g nanoplastics (i.e., plain PS, PS-COOH and PS-NH2) for 30 days (F0-E), followed by a depuration period of 21 days (F0-D). In addition, the eggs produced on the last day of exposure were cultured under standard protocols without further exposure for 2 months (F1 fish). The results showed that the alpha diversity or the bacterial community of gut microbiota did not differ among the SMZ + PS, SMZ + PS-COOH, and SMZ + PS-NH2 groups in the F0-E and F1 fish. Interestingly, during the depuration, a clear recovery of gut microbiota (e.g., increases in the alpha diversity, beneficial bacteria abundances and network complexity) was found in the SMZ + PS group, but not for the SMZ + PS-COOH and SMZ + PS-NH2 groups, indicating that PS-COOH and PS-NH2 could prolong the toxic effect of SMZ and hinder the recovery of gut microbiota. Compared to plain PS, lower egestion rates of PS-COOH and PS-NH2 were observed in O. melastigma. In addition, under the simulated fish digest conditions, the SMZ-loaded PS-NH2 was found to desorb more SMZ than the loaded PS and PS-COOH. These results suggested that the surface -COOH and -NH2 groups on PS could influence their egestion efficiency and the adsorption/desorption behavior with SMZ, resulting in a long-lasting SMZ stress in the gut during the depuration phase. Our findings highlight the complexity of the carrier effect and ecological risk of surface-charged nanoplastics and the interactions between nanoplastics and antibiotics in natural environments.

[Effects of Combined Stress of Polyethylene and Sulfamethazine on Seed Germination, Seedling Growth, and Physiological Characteristics of Soybean].

The combined pollution of antibiotics adsorption by microplastics has become inevitable in soil ecosystems; moreover, the plant biological effects under combined stress remain unclear. This study used soybean variety Jindou 21 as the material and conducted seed germination test and soil-potted seedling experiment to study the effects of different single and combined treatments of polyethylene (PE) and sulfamethazine (SMZ) on seed germination, seedling growth, photosynthetic parameters, chlorophyll fluorescence parameters, and nitrogen metabolism. The results showed that single PE treatment at low levels promoted soybean seed germination and seedling growth physiology; however, inhibited them at a high level. A lower-level PE treatment[10 mg·L-1 (or mg·kg-1)] could promote soybean seed germination, seedling growth, photosynthesis, and nitrogen metabolism, whereas a higher level PE treatment[100 mg·L-1 and 200 mg·L-1 (or mg·kg-1)] had significant inhibition. The single SMZ treatment had different degrees of inhibition on soybean seed germination and seedling growth physiology, and the inhibition degree increased with the increase in SMZ treatment level. Under the different levels of combined treatments of PE and SMZ, adding the lower level PE treatment could alleviate the inhibition of the single SMZ treatment on soybean, with 10 mg·L-1(or mg·kg-1) PE+1 mg·L-1(or mg·kg-1) SMZ treatment having the best comprehensive mitigation effect, which could increase soybean seed germination potential, germination rate, germination index, vigor index, plant height, root length, shoot and root fresh weight, Pn, Gs, Tr, chlorophyll contents, Fv/Fm, ΦPSⅡ, ETR, qP, and key enzyme activities for nitrogen metabolism such as NR and decrease the average germination time, Ci, NPQ, and NO3--N and NH4+-N contents compared with those in the single SMZ treatment. Adding the higher level PE treatment enhanced the inhibition of SMZ on soybean, and the inhibition degree increased with the increase in SMZ treatment level, in which 200 mg·L-1(or mg·kg-1) PE+50 mg·L-1(or mg·kg-1) SMZ treatment yielded the greatest inhibition. In summary, the lower level PE treatment could alleviate the inhibition of SMZ on soybean seeds and seedlings to a certain extent; however, the higher level PE treatment could produce a synergistic effect with SMZ, thus aggravating the toxic effect of the single stress treatment.

Incomplete recovery of gut microbiota in marine medaka (Oryzias melastigma) during the depuration phase, after exposure to sulfamethazine/nanoplastics.

The persistence of antibiotics and nanoplastics in aquatic environment poses a great threat to aquatic organisms. In our previous study, significant decreases of bacterial richness and changes of bacterial communities in the Oryzias melastigma gut after sulfamethazine (SMZ) and polystyrene nanoplastics (PS) exposure were observed. Here, the O. melastigma dietary exposed to SMZ (0.5 mg/g, LSMZ; 5 mg/g, HSMZ), PS (5 mg/g, PS) or PS + HSMZ were depurated for 21 days to assess the extent of which these effects were reversible. Our results revealed that most diversity indexes of bacterial microbiota in the O. melastigma gut from the treatment groups were insignificantly different from the control, suggesting a large recovery of bacterial richness. Although the sequence abundances of a few genera remained significantly changed, the proportion of dominant genus was recovered. Exposure to SMZ affected the complexity of the bacterial networks, and the cooperation and exchange events of positively associated bacteria were enhanced during this period. After depuration, increases in the complexity of networks and intense competitions among bacteria were observed, which was beneficial for the robustness of networks. However, the gut bacterial microbiota was less stable, and several functional pathways were dysregulated, relative to the control. In addition, higher occurrence of pathogenic bacteria was found in the PS + HSMZ group relative to the signal pollutant group after depuration, indicating a greater hazard for the mixture of PS and SMZ. Taken together, this study contributes to a better understanding of the recovery of bacterial microbiota in fish gut after individual and combined exposure to nanoplastics and antibiotics.

Enhanced sulfamethazine detoxification by a novel BiOCl (110)/NrGO/BiVO4 heterojunction.

The emerging contaminants removal from the environment has recently been raised concerns due to their presence in higher concentrations. Over usage of emerging contaminant such as sulfamethazine poses serious threat to the aquatic and human health as well. This study deals with rationally structured a novel BiOCl (110)/NrGO/BiVO4 heterojunction which is used to detoxify sulfamethazine (SMZ) antibiotic efficiently. The synthesised composite was well characterized and the morphological analysis evidenced the formation of heterojunction consisted of nanoplates BiOCl with dominant exposed (110) facets and leaf like BiVO4 on NrGO layers. Further results revealed that the addition of BiVO4 and NrGO tremendously increased the photocatalytic degradation efficiency of BiOCl with the rate of 96.9% (k = 0.01783 min-1) towards SMZ within 60 min of visible light irradiation. Furthermore, heterojunction energy-band theory was employed to determine the degradation mechanism of SMX in this study. The larger surface area of BiOCl and NrGO layers are believed to be the reason for higher activity which facilitates the excellent charge transfer and improved light absorption. In addition, SMZ degradation products identification was carried out by LC-ESI/MS/MS to determine the pathway of degradation. The toxicity assessment was studied using E. coli as a model microorganism through colony forming unit assay (CFU), and the results indicated a significant reduction in biotoxicity was observed in 60 min of degradation process. Thus, our work gives new methods in developing various materials that effectively treat emerging contaminants from the aqueous environment.

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), SO42- 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.

Influence of co-exposure to sulfamethazine on the toxicity and bioaccumulation kinetics of chlorpyrifos in zebrafish (Danio rerio).

Pesticides and antibiotics are frequently present in aquatic environment which may pose potential risks to aquatic organisms. However, the interaction of pesticides and antibiotics in co-exposure model remains unclear. Here, the effects of the co-exposure of sulfamethazine (SMZ) on the toxicity and bioaccumulation of the organophosphorus insecticide chlorpyrifos (CPF) in zebrafish (Danio rerio) were explored. The 96-h LC50 of chlorpyrifos to zebrafish was 1.36 mg/L and sulfamethazine at 1 mg/L slightly increased the acute toxicity with the 96-h LC50 of 1.20 mg/L which was not significant. The 30-day co-exposure of chlorpyrifos with sulfamethazine at 1 mg/L aggravated the oxidative stress, decreased CarE and AChE activity, and increased CYP450 activity significantly. Furthermore, the co-exposure reduced the accumulation of chlorpyrifos and sulfamethazine while prolonged their depuration duration. The results demonstrated the exposure risk of chlorpyrifos to zebrafish may be enhanced in the presence of sulfamethazine.

Toxicological and transcriptomic-based analysis of monensin and sulfamethazine co-exposure on male SD rats.

Antibiotic residue has become an emerging environmental contaminant, while the toxicological effects and underlying mechanisms caused by the co-exposure to multiple veterinary antibiotics were rarely studied. In this study, male Sprague Dawley rats were exposed to monensin (M) (1, 2, 10 mg/(kg·body weight (BW)) combined with sulfamethazine (S) (60, 120, 600 mg/(kg·BW)) or single drugs for 28 consecutive days. The body weight, hematological and blood biochemical parameters, organ coefficients, and histopathology were analyzed to discover their combined toxicity effect. Transcriptomic analysis was used to reveal the possible mechanisms of their joint toxicity. Compared with the control group, the weight gain rate was significantly reduced in the H-M+S and H-S, and alkaline phosphatase in H-M+S was significantly increased. Furthermore, relative liver and kidneys weight was significantly increased, and the liver of H-M+S showed more severe lesions in histopathological analysis. For H-M+S, H-M and H-S, transcriptomic results showed that 344, 246, and 99 genes were differentially expressed, respectively. The Gene Ontology terms mainly differ in sterol biosynthetic process and steroid hydroxylase activity. The Kyoto Encyclopedia of Genes and Genome pathways showed abnormal retinol metabolism, metabolism of xenobiotics by cytochrome P450, and drug metabolism-cytochrome 450; the common 30 genes were screened from the network of protein-protein interaction. The results showed that mixed contamination of M and S produces hepatotoxicity by interfering with linoleic acid metabolism, retinol metabolism and CYP450 enzyme-dominated drug metabolism. Further analysis showed that Cyp1a2, Cyp2c61, Ugt1a3, and Ugt1a5 might be the key genes. These findings could provide more evidence for investigating the toxic effects and metabolism of mixed antibiotics contamination in mammals.

UV/Chlorination of sulfamethazine (SMZ) and other prescription drugs: kinetics, transformation products and insights into the combined toxicological assessment.

The UV/chlorination of three prescription drugs, sulfamethazine (SMZ), gemfibrozil (GEM) and antipyrine (ANT) were studied by the investigation of kinetics, transformation products and combined toxicological assessment. The degradation followed pseudo-first-order kinetics, with half-lives significantly affected by chlorine dosage, without being greatly influenced by pH value and bromide concentration. Based on the Frontier Orbital Theory, the structures of products by hydroxylation or chlorine substitution were proposed and the transformation pathways were introduced, with two, two and one never-before-reported products identified for SMZ, GEM and ANT, respectively. Compared to the results of the experiments with artificial water sample, the degradation kinetics of the three prescription drugs was observed with a prolonged half-lives in both Yangtze River and Taihu Lake water, suggesting that aromatic containing transformation products (TPs) may also exist in UV/chlorine treated natural waters. The results of combined toxicity on E. coli showed that the antagonism effect predominated in most binary and ternary combinations. However, the synergistic toxicity of combinations at low concentrations of prescription drugs subjected to UV/chlorine should be cautioned, which was more close to the natural concentration of prescription drugs in waters.

Parental exposure to sulfamethazine and nanoplastics alters the gut microbial communities in the offspring of marine madaka (Oryzias melastigma).

The individual and combined toxicity of antibiotics and nanoplastics in marine organisms has received increasing attention. However, many studies have been mostly focused on the impacts on the directly exposed generation (F0). In this study, intergenerational effects of sulfamethazine (SMZ) and nanoplastic fragments (polystyrene, PS) on the growth and the gut microbiota of marine medaka (Oryzias melastigma) were investigated. The results showed that parental exposure to dietary SMZ (4.62 mg/g) alone and PS (3.45 mg/g) alone for 30 days decreased the body weight (by 13.41% and 34.33%, respectively) and altered the composition of gut microbiota in F1 males (two months after hatching). Interestingly, parental exposure to the mixture of SMZ and PS caused a more modest decrease in the body weight of F1 males than the PS alone (15.60% vs 34.33%). The hepatic igf1 level and the relative abundance of the host energy metabolism related phylum Bacteroidetes for the SMZ + PS group were significantly higher than those for the PS group (igf1, increased by 97.1%; Bacteroidetes, 2.876% vs 0.375%), suggesting that the parentally derived mixture of SMZ and PS might influence the first microbial colonization of gut in a different way to the PS alone. This study contributes to a better understanding of the long-term risk of antibiotics and nanoplastics to marine organisms.

Subchronic toxicity of dietary sulfamethazine and nanoplastics in marine medaka (Oryzias melastigma): Insights from the gut microbiota and intestinal oxidative status.

Antibiotics and nanoplastics are two prevalent pollutants in oceans, posing a great threat to marine ecosystems. As antibiotics and nanoplastics are highly bioconcentrated in lower trophic levels, evaluating their impacts on marine organisms via dietary exposure route is of great importance. In this study, the individual and joint effects of dietborne sulfamethazine (SMZ) and nanoplastic fragments (polystyrene, PS) in marine medaka (Oryzias melastigma) were investigated. After 30 days of dietary exposure, 4.62 mg/g SMZ decreased the Chao1 index (60.86% for females and 26.85% for males) and the Shannon index (68.95% for females and 65.05% for males) and significantly altered the structure of gut microbial communities in both sexes. The female fish exposed to 4.62 mg/g SMZ exhibited higher intestinal sod (43.5%), cat (38.5%) and gpx (39.6%) transcripts, indicating oxidative stress in the gut. PS alone at 3.45 mg/g slightly altered the composition of the gut microbiota. Interestingly, the mixture of SMZ and PS caused more modest effects on the gut microbiota and intestinal antioxidant physiology than the SMZ alone, suggesting that the presence of PS might alleviate the intestinal toxicity of SMZ in a scenario of dietary co-exposure. This study helps better understand the risk of antibiotics and nanoplastics to marine ecosystems.

Polystyrene microplastics alleviate the effects of sulfamethazine on soil microbial communities at different CO2 concentrations.

Microplastics were reported to adsorb antibiotics and may modify their effects on soil systems. But there has been little research investigating how microplastics may affect the toxicities of antibiotics to microbes under future climate conditions. Here, we used a free-air CO2 enrichment system to investigate the responses of soil microbes to sulfamethazine (SMZ, 1 mg kg-1) in the presence of polystyrene microplastics (PS, 5 mg kg-1) at different CO2 concentrations (ambient at 380 ppm and elevated at 580 ppm). SMZ alone decreased bacterial diversity, negatively affected the bacterial structure and inter-relationships, and enriched the sulfonamide-resistance genes (sul1 and sul2) and class 1 integron (intl1). PS, at both CO2 conditions, showed little effect on soil bacteria but markedly alleviated SMZ's adverse effects on bacterial diversity, composition and structure, and inhibited sul1 transmission by decreasing the intl1 abundance. Elevated CO2 had limited modification in SMZ's disadvantages to microbial communities but markedly decreased the sul1 and sul2 abundance. Results indicated that increasing CO2 concentration or the presence of PS affected the responses of soil microbes to SMZ, providing new insights into the risk prediction of antibiotics under future climate conditions.

Biochemical Toxicity and Potential Detoxification Mechanisms in Earthworms Eisenia fetida Exposed to Sulfamethazine and Copper.

The present study investigated the biochemical toxicity and potential detoxification mechanisms in earthworms Eisenia fetida exposed to sulfamethazine (SMZ) (7.5, 15 and 30 mg kg-1) either alone or in combination with Copper (Cu) (100 mg kg-1) in soil. The results showed that increasing concentrations of SMZ in soil activated superoxide dismutase, catalase and glutathione peroxidase isozymes, suggesting reactive oxygen species (ROS) burst in earthworms. Treatment with SMZ and Cu separately or in combination caused protein oxidation and damage, elevating the synthesis of ubiquitin, the 20S proteasome, cytochrome P450 (CYP450), and heat shock protein 70 (HSP70). Such treatments also induced the activities of proteases, endoproteinase (EP) and glutathione S-transferases (GSTs). The results suggested that the ubiquitin-20S proteasome, proteases, EP and HSP70 were involved in degradation or remediation of oxidatively damaged proteins. Elevated levels of CYP450 and GSTs also participated in the detoxification of the earthworms.

Electro-Fenton and photoelectro-Fenton degradation of sulfamethazine using an active gas diffusion electrode without aeration.

A novel superhydrophobic gas diffusion electrode based on carbon black (CB)- polytetrafluoroethylene (PTFE) modified graphite felt cathode was prepared to increase oxygen mass transfer efficiency and produce hydrogen peroxide at the gas-liquid-solid three-phase interface without aeration. The gas diffusion electrode system was further tested for the degradation of sulfamethazine (SMT) by electro-Fenton (EF) and photoelectro-Fenton (PEF). In the EF process, SMT was removed effectively, but the mineralization degree was not high due to the generation of organic acids which were difficult to be further degraded. While in the PEF process, organic contaminant can be destroyed by the combined action of Fe2+/H2O2, UV/H2O2 and UV radiation, and more efficient mineralization (>83.5%) at low current (50 mA) was attained, which might be attributed to the high H2O2 utilization (70-90%), rapid regeneration of Fe2+ and photolysis of intermediates. In addition, it was verified that the PEF system had a good adaptability to pH and pollutant concentration. Compared with aeration system, the use of this active gas diffusion cathode in electrochemical advanced oxidation processes significantly reduced energy consumption.

Dose and time-dependent response of single and combined artificial contamination of sulfamethazine and copper on soil enzymatic activities.

The widespread contamination of antibiotics and heavy metals results in imbalance in the ecosystem. However, the effect of the interaction between sulfamethazine (SM2) and copper (Cu) on soil enzymatic activities is unclear. Therefore, this study investigated the effect of single and combined artificial contamination of SM2 and Cu (0, 1.6 mmol kg-1 Cu and 0, 0.05, 0.2, 0.8 mmol kg-1 SM2) on soil enzymatic activities (urease, sucrose, phosphatase, and RubisCO). A single application of Cu at a concentration of 1.6 mmol kg-1 inhibited the urease, phosphatase and sucrase activities, while a stimulating effect on RubisCO activity was observed on day 7, 21, and 28 of incubation. The individual application of SM2 at higher concentration exhibited significant inhibition of sucrase, phosphatase, and urease activities while a stimulatory effect on RubisCO activity was observed on day 14 and 21 of incubation. The combined contamination of SM2 and Cu significantly inhibited the activities of urease, sucrase, and phosphatase. The effect of combined contamination of SM2 and Cu on the activity of RubisCO was different. The analysis results of interaction types show that there are synergistic or antagonistic effects between Cu and SM2, and these effects can amplify or reduce the effect of Cu or SM2 on soil enzyme activities. Integrated biological responses version 2 (IBRv2) analysis showed that the combined contamination of Cu and SM2 had a greater inhibitory or stimulatory effect on soil enzyme activities than the single contamination of Cu and SM2, depending upon dose and time.

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.

Combined effects of sulfamethazine and sulfamethoxazole on a freshwater microalga, Scenedesmus obliquus: toxicity, biodegradation, and metabolic fate.

This study investigated the environmental effects of two common emerging contaminants, sulfamethazine (SMZ) and sulfamethoxazole (SMX), and their mixture using a green microalga, Scenedesmus obliquus. The calculated EC50 values of SMZ, SMX, and their mixture (11:1 wt/wt) after 96 h were 1.23, 0.12, and 0.89 mg L-1, respectively. The toxicity of the mixture could be better predicted using a concentration addition model than an independent action model. The risk quotients of SMZ, SMX, and their mixture were >1 during the experiment, indicating their high potential risks on aquatic microorganisms. Despite their toxicity, S. obliquus exhibited 17.3% and 29.3% removal of 0.1 mg L-1 and 0.2 mg L-1 after 11 days of cultivation. The changes of SMZ and SMX removal were observed when combined, which showed a significantly improved removal of SMZ (up to 3.4 folds) with addition of SMX (0.2 mg L-1). The metabolic pathways of SMZ and SMX were proposed according to mass spectroscopic analysis, which showed six metabolites of SMX and seven intermediates of SMZ, formed as a result of ring cleavage, hydroxylation, methylation, nitrosation, and deamination.

Toxicity of sulfamethazine and sulfamethoxazole and their removal by a green microalga, Scenedesmus obliquus.

A comprehensive ecotoxicological evaluation of a sulfamethazine (SMZ) and sulfamethoxazole (SMX) mixture was conducted using an indicator microalga, Scenedesmus obliquus. The toxicological effects of this mixture were studied using microalgal growth patterns, biochemical characteristics (total chlorophyll, carotenoid, carbohydrate, fatty acid methyl ester), and elemental and Fourier-transform infrared spectroscopy analyses. The 96-h half maximal effective concentration (EC50) of the SMZ and SMX mixture was calculated to be 0.15 mg L-1 according to the dose-response curves obtained. The chlorophyll content decreased with elevated SMZ and SMX concentrations, while the carotenoid content initially increased and then decreased as concentration raised. The unsaturated fatty acid methyl esters (FAMEs) content was enhanced with higher SMZ and SMX concentrations, while that of saturated FAMEs simultaneously decreased due to SMZ and SMX stress. Elemental analyses showed an improved percentage of nitrogen and sulfur in the microalgal biomass as SMZ and SMX concentrations increased. The microalga S. obliquus was shown to biodegrade the chemicals tested and removed 31.4-62.3% of the 0.025-0.25 mg SMZ L-1 and 27.7-46.8% of the 0.025-0.25 mg SMX L-1 in the mixture after 12 days of cultivation. The greater biodegradation observed at higher SMZ and SMX concentrations indicates that microalgal degradation of SMZ and SMX could act as an efficient adaptive mechanism to antibiotics.

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.