Biodegradation of sulfamethoxazole photo-transformation products in a water/sediment test

Enhancing the removal of sulfamethoxazole and microalgal lipid production through microalgae-biochar hybrids

The use of microalgae for antibiotic removal has received increasing attention due to its many advantages. However, challenges such as limited removal rates and the complexity of algae cell recovery persist. In this study, chitosan and FeCl3 modified peanut shell biochar (CTS@FeBC) was prepared for the immobilization of Chlorella pyrenoidosa. The results showed that CTS@FeBC effectively adsorbed and immobilized microalgal cells to form microalgae-biochar hybrids, resulting in higher sulfamethoxazole removal rate (45.7 %) compared to microalgae (34.4 %) or biochar (20.0 %) alone, and higher microalgal lipid yield (11.6 mg/L d-1) than microalgae alone (10.1 mg/L d-1). More importantly, the microalgae-biochar hybrids could be rapidly separated from the wastewater within 10 min by applying a magnetic field, resulting in a harvesting efficiency of 86.3 %. Overall, the microalgae-biochar hybrids hold great potential in overcoming challenges associated with pollutants removal and microalgal biomass recovery.

Adsorptive Removal of Cd(II) Ions from Water by a Cheap Lignocellulosic Adsorbent and Its Reuse as a Catalyst for the Decontamination of Sulfamethoxazole

The work reports the removal of cadmium from water by applying an efficient low-cost lignocellulosic adsorbent, rooibos tea waste. The cadmium-loaded rooibos tea waste was used for the photocatalytic abatement of sulfamethoxazole to cater to the setback of secondary pollution mostly associated with the adsorption technique. The rooibos tea waste adsorbent displayed a high removal efficiency of about 90.63% for 10 mg/L Cd(II) ions at 45 °C, 180 min agitation time, pH 7, and a dosage of 500 mg. The process of Cd(II) adsorption was endothermic and spontaneous. Also, the spent adsorbent was found to be efficient toward the photocatalytic breakdown of 10 mg/L sulfamethoxazole with a degradation efficiency of 69% after 150 min. In addition, the extent of mineralization of the sulfamethoxazole by the spent adsorbent as obtained from the total organic carbon data was found to be 53%. Therefore, based on the results obtained from this work, rooibos tea waste lends itself as a cheap, eco-friendly, easily sourced, and viable adsorbent for the removal of toxic ions like Cd(II). Also, the successful reuse of the spent adsorbent is a promising approach to cater to the major setback of secondary pollution associated with adsorption technology.

Direct Phototransformation of Sulfamethoxazole Characterized by Four-Dimensional Element Compound Specific Isotope Analysis

The antibiotic sulfamethoxazole (SMX) undergoes direct phototransformation by sunlight, constituting a notable dissipation process in the environment. SMX exists in both neutral and anionic forms, depending on the pH conditions. To discern the direct photodegradation of SMX at various pH levels and differentiate it from other transformation processes, we conducted phototransformation of SMX under simulated sunlight at pH 7 and 3, employing both transformation product (TP) and compound-specific stable isotope analyses. At pH 7, the primary TPs were sulfanilic acid and 3A5MI, followed by sulfanilamide and (5-methylisoxazol-3-yl)-sulfamate, whereas at pH 3, a photoisomer was the dominant product, followed by sulfanilic acid and 3A5MI. Isotope fractionation patterns revealed normal 13C, 34S, and inverse 15N isotope fractionation, which exhibited significant differences between pH 7 and 3. This indicates a pH-dependent transformation process in SMX direct phototransformation. The hydrogen isotopic composition of SMX remained stable during direct phototransformation at both pH levels. Moreover, there was no variation observed in 33S between the two pH levels, indicating that the 33S mass-independent process remains unaffected by changes in pH. The analysis of main TPs and single-element isotopic fractionation suggests varying combinations of bond cleavages at different pH values, resulting in distinct patterns of isotopic fractionation. Conversely, dual-element isotope values at different pH levels did not significantly differ, indicating cleavage of several bonds in parallel. Hence, prudent interpretation of dual-element isotope analysis in these systems is warranted. These findings highlight the potential of multielement compound-specific isotope analysis in characterizing pH-dependent direct phototransformation of SMX, thereby facilitating the evaluation of its natural attenuation through sunlight photolysis in the environment.

How data on transformation products can support the redesign of sulfonamides towards better biodegradability in the environment

Sulfonamide antibiotics (SUAs) released into the environment can affect environmental und human health, e.g., by accelerating the development and selection of antimicrobial resistant bacteria. Benign by Design (BbD) of SUAs is an effective risk prevention approach. BbD principles aim for fast and complete mineralization or at least deactivation of the SUA after release into the aquatic environment. Main objective was to test if mixtures of transformation products (TPs) generated via photolysis of SUAs can be used as an efficient way to screen for similarly effective but better biodegradable SUA alternatives. Six SUAs were photolyzed (Hg ultraviolet (UV) light), and generated UV-mixtures analysed by high performance liquid chromatography coupled to an UV and tandem mass spectrometry detector. UV-mixtures were screened for antibiotic activity (luminescence bacteria test, LBT, on luminescence and growth inhibition of Aliivibrio Fischeri) and environmental biodegradability (manometric respirometry test, MRT, OECD 301F) using untreated parent SUAs in comparison. Additionally, ready environmental biodegradability of three commercially available hydroxylated sulfanilamide derivatives was investigated. SUA-TPs contributed to acute and chronic bacterial luminescence inhibition by UV-mixtures. LBT's third endpoint, growth inhibition, was not significant for UV-mixtures. However, it cannot be excluded for tested TPs as concentrations were lower than parents' concentrations and inhibition by most parental concentrations tested was also not significant. HPLC analysis of MRT samples revealed that one third of SUA-TPs was reduced during incubation. Three of these TPs, likely OH-SIX, OH-SMX and OH-STZ, were of interest for BbD because the sulfonamide moiety is still present. However, hydroxylated sulfanilamide derivatives, tested to investigate the effect of hydroxylation on biodegradability, were not readily biodegraded. Thus, improving mineralization through hydroxylation as a general rule couldn't be confirmed, and no BbD candidate could be identified. This study fills data gaps on bioactivity and environmental biodegradability of SUAs' TP-mixtures. Findings may support new redesign approaches.

Transformation products of antibacterial drugs in environmental water: Identification approaches based on liquid chromatography-high resolution mass spectrometry

In recent years, the presence of antibiotics in the aquatic environment has caused increasing concern for the possible consequences on human health and ecosystems, including the development of antibiotic-resistant bacteria. However, once antibiotics enter the environment, mainly through hospital and municipal discharges and the effluents of wastewater treatment plants, they can be subject to transformation reactions, driven by both biotic (e.g. microorganism and mammalian metabolisms) and abiotic factors (e.g. oxidation, photodegradation, and hydrolysis). The resulting transformation products (TPs) can be less or more active than their parent compounds, therefore the inclusion of TPs in monitoring programs should be mandatory. However, only the reference standards of a few known TPs are available, whereas many other TPs are still unknown, due to the high diversity of possible transformation reactions in the environment. Modern high-resolution mass spectrometry (HRMS) instrumentation is now ready to tackle this problem through suspect and untargeted screening approaches. However, for handling the large amount of data typically encountered in the analysis of environmental samples, these approaches also require suitable processing workflows and accurate tandem mass spectra interpretation. The compilation of a suspect list containing the possible monoisotopic masses of TPs retrieved from the literature and/or from laboratory simulated degradation experiments showed unique advantages. However, the employment of in silico prediction tools could improve the identification reliability. In this review, the most recent strategies relying on liquid chromatography-HRMS for the analysis of environmental TPs of the main antibiotic classes were examined, whereas TPs formed during water treatments or disinfection were not included.

Spatial trends and ecotoxic risk assessment of selected pharmaceuticals in sediments from Lake Victoria, Uganda, East Africa

Pharmaceutical residues in the aquatic environment are an emerging issue of global concern because of their effects on ecosystems including; antibacterial resistance development and endocrine disruption. Lake Victoria is the largest freshwater lake in Africa, and the second largest lake in the world. It is also the main source of the White Nile River, arguably the longest river in the world, flowing through South Sudan, Sudan, Ethiopia and Egypt, discharging into the Mediterranean Sea. However, its ecology is threatened by rapid industrialisation, urbanization, and increased agricultural activities, which have led to increased pollution via polluted runoffs. In this study, the occurrence of twenty-five pharmaceutical compounds (14 antibiotics, four anti-epileptic and antidepressant drugs, three analgesic and anti-inflammatory drugs, three beta-blockers, and one lipid regulator) was studied in 55 sediment samples obtained from the Ugandan sector of Lake Victoria, and their ecotoxic risk assessed. All the target compounds were quantifiable with levofloxacin (2-120 ng g-1 dm; dry mass), ciprofloxacin (3-130 ng g-1 dm) enoxacin (9-75 ng g-1 dm), ibuprofen (6-50 ng g-1 dm), metoprolol (1-92 ng g-1 dm) and propranolol (1-52 ng g-1 dm) being predominant. Murchison Bay, being the chief recipient of sewage effluents, municipal and industrial waste from Kampala city and its suburbs, had the highest levels. Ecotoxic risk assessment revealed that ciprofloxacin, levofloxacin, sulfamethoxazole, sulfamethazine, oxytetracycline, tetracycline, erythromycin, norfloxacin, ibuprofen, diclofenac, carbamazepine, atenolol, and metoprolol posed high toxic risks to sediment-dwelling organisms (risk quotients, RQ >1). This is the first study reporting concentrations and ecotoxic risks of pharmaceuticals in sediments of Lake Victoria, Uganda, and the whole of East Africa. Detection, identification and quantification of pharmaceuticals in Lake Victoria sediments is essential for gaining knowledge on their occurrence and fate which can ultimately be used to assist in constructing relevant policy and management recommendations.

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.

Experimental and numerical elucidation of the fate and transport of antibiotics in aquatic environment: A review

This review highlights various experimental and mathematical modeling strategies to investigate the fate and transport of antibiotics that elucidate antimicrobial selective pressure in aquatic environments. Globally, the residual antibiotic concentrations in effluents from bulk drug manufacturing industries were 30- and 1500-fold greater than values reported in municipal and hospital effluents, respectively. The antibiotic concentration from different effluents enters the waterbodies that usually get diluted as they go downstream and undergo various abiotic and biotic reactive processes. In aquatic systems, photolysis is the predominant process for antibiotic reduction in the water matrix, while hydrolysis and sorption are frequently reported in the sediment compartment. The rate of antibiotic reduction varies widely with influencing factors such as the chemical properties of the antibiotics and hydrodynamic conditions of river streams. Among all, tetracycline was found to more unstable (log Kow =  - 0.62 to - 1.12) that can readily undergo photolysis and hydrolysis; whereas macrolides were more stable (log Kow = 3.06 to 4.02) that are prone to biodegradation. The processes like photolysis, hydrolysis, and biodegradation followed first-order reaction kinetics while the sorption followed a second-order kinetics for most antibiotic classes with reaction rates occurring in the decreasing order of Fluoroquinolones and Sulphonamides. The reports from various experiments on abiotic and biotic processes serve as input parameters for an integrated mathematical modeling to predict the fate of the antibiotics in the aquatic environment. Various mathematical models viz. Fugacity level IV, RSEMM, OTIS, GREAT-ER, SWAT, QWASI, and STREAM-EU are discussed for their potential capabilities. However, these models do not account for microscale interactions of the antibiotics and microbial community under real-field conditions. Also, the seasonal variations for contaminant concentrations that exert selective pressure for antimicrobial resistance has not been accounted. Addressing these aspects collectively is the key to exploring the emergence of antimicrobial resistance. Therefore, a comprehensive model involving antimicrobial resistance parameters like fitness cost, bacterial population dynamics, conjugation transfer efficiency, etc. is required to predict the fate of antibiotics.

Mesocosm experiment to determine the contribution of adsorption, biodegradation, hydrolysis and photodegradation in the attenuation of antibiotics at the water sediment interface

To understand the fate of antibiotics in the aquatic environment, we need to evaluate to which extent the following processes contribute to the overall antibiotic attenuation: adsorption to river sediment, biodegradation, hydrolysis and photodegradation. A laboratory scale mesocosm experiment was conducted in 10 L reactors filled with river sediment and water. The reactors were spiked with four classes of antibiotics (fluoroquinolones, macrolides, sulfonamides, tetracyclines), as well as clindamycin and trimethoprim. The experimental-set-up was designed to study the attenuation processes in parallel in one mesocosm experiment, hence also considering synergetic effects. Our results showed that antibiotics belonging to the same class exhibited similar behavior. Adsorption was the main attenuation process for the fluoroquinolones and tetracyclines (44.4 to 80.0 %). For the sulfonamides, biodegradation was the most frequent process (50.2 to 65.1 %). Hydrolysis appeared to be significant only for tetracyclines (12.6 to 41.8 %). Photodegradation through visible light played a minor role for most of the antibiotics - fluoroquinolones, sulfonamides, and trimethoprim (0.7 to 24.7 %). The macrolides were the only class of antibiotics not affected by the studied processes and they persisted in the water phase. Based on our results, we propose to class the antibiotics in three groups according to their persistence in the water phase. Fluoroquinolones and tetracyclines were non-persistent (half-lives shorter than 11 d). Chlorotetracycline, sulfapyridine and trimethoprim showed a moderate persistence (half-lives between 12 and 35 d). Due to half-lives longer than 36 d sulfonamides and clindamycin were classified as persistent.

A kinetic study of the photolysis of sulfamethoxazole with special emphasis on the photoisomer

Abstract

The previously not studied photochemical degradation of sulfamethoxazole (SMX) to the isomer of SMX (ISO) was measured via a polychromatic (Xe) and a monochromatic (Hg) light source and accompanied by quantum chemical DFT calculations. In addition to the $$\mathrm{p}K_\mathrm{a} = \;7.0 \pm 0.1$$ p K a = 7.0 ± 0.1 of ISO, tautomer-dependent properties such as the $$K_\mathrm{OW}$$ K OW were measured and theoretically confirmed by DFT. The kinetics in solutions below and above the $$\mathrm{p}K_\mathrm{a} = 5.6$$ p K a = 5.6 of SMX were studied for the available and quantifiable products SMX, ISO, 3-amino-5-methylisoxazole (AMI), 2-amino-5-methyloxazole (AMO), and sulfanilic acid (SUA). The quantum yields of the neutral ($$\Phi _\mathrm{N}$$ Φ N ) and anionic $$\Phi _\mathrm{A}$$ Φ A ) forms of SMX ($$\Phi _\mathrm{A} = 0.03 \pm 0.001$$ Φ A = 0.03 ± 0.001 , $$\Phi _\mathrm{N} = 0.15 \pm 0.01$$ Φ N = 0.15 ± 0.01 ) and ISO ($$\Phi _\mathrm{A} = 0.05 \pm 0.01$$ Φ A = 0.05 ± 0.01 and $$\Phi _\mathrm{N} = 0.06 \pm 0.02$$ Φ N = 0.06 ± 0.02 ) were found to be wavelength-independent. In a competitive reaction to the formation of ISO from SMX, the degradation product TP271 is formed. Various proposed structures for TP271 described in the literature have been studied quantum mechanically and can be excluded for thermodynamic reasons. In real samples in a northern German surface water in summer 2021 mean concentrations of SMX were found in the range of 120 ng/L. In agreement with the pH-dependent yields, concentrations of ISO were low in the range of 8 ng/L.

Graphical abstract

Fate and impact of wastewater-borne micropollutants in lettuce and the root-associated bacteria

The reuse of water for agricultural practices becomes progressively more important due to increasing demands for a transition to a circular economy. Treated wastewater can be an alternative option of blue water used for the irrigation of crops but its risks need to be evaluated. This study assesses the uptake and metabolization of pharmaceuticals and personal care products (PPCPs) derived from treated wastewater into lettuce as well as the impact on root-associated bacteria under a realistic and worst-case scenario. Lettuce was grown in a controlled greenhouse and irrigated with water or treated wastewater spiked with and without a mixture of fourteen different PPCPs at 10 μg/L or 100 μg/L. After harvesting the plants, the same soil was reused for a consecutive cultivation campaign to test for the accumulation of PPCPs. Twelve out of fourteen spiked PPCPs were detected in lettuce roots, and thirteen in leaves. In roots, highest concentrations were measured for sucralose, sulfamethoxazole and citalopram, while sucralose, acesulfame and carbamazepine were the highest in leaves. Higher PPCP concentrations were found in lettuce roots irrigated with spiked treated wastewater than in those irrigated with spiked water. The absolute bacterial abundance remained stable over both cultivation campaigns and was not affected by any of the treatments (type of irrigation water (water vs. wastewater) nor concentration of PPCPs). However, the irrigation of lettuce with treated wastewater had a significant effect on the microbial α-diversity indices at the end of the second cultivation campaign, and modified the structure and community composition of root-associated bacteria at the end of both campaigns. Five and fourteen bacterial families were shown to be responsible for the observed changes at the end of the first and second cultivation campaign, respectively. Relative abundance of Haliangium and the clade Allorhizobium-Neorhizobium-Pararhizobium-Rhizobium was significantly affected in response to PCPPs exposure. Caulobacter, Cellvibrio, Hydrogenophaga and Rhizobacter were significantly affected in microcosms irrigated with wastewater.

Transformation products of sulfonamides in aquatic systems: Lessons learned from available environmental fate and behaviour data

Sulfonamides (SUAs) and their transformation products (TPs) contribute to environmental pollution. Importance of research on TPs' properties has been emphasised, e.g. allowing a comprehensive environmental risk assessment of their parent compounds. However, TPs' properties have been discussed in reviews on SUAs only marginally, if at all. For the first time, a scientific literature review aims to discuss the current state of knowledge on SUA-TPs including research gaps, and commonalities of SUA-TPs and TPs in general. Literature on SUA-TPs was consulted systematically to collect data on occurrence, physicochemical properties, degradability, and (eco)toxicity. TPs of 14 SUAs were reviewed, and aspects applicable for TPs in general were identified to guide future handling of TPs as a complex category of compounds. The data of sulfamethoxazole (SMX), the main representative, was analysed in more detail to discuss insights on a chemical level. Literature search resulted in 607 SUA-TPs reported in 222 publications. Only for 4%, 31%, and 35% of these TPs, data on occurrence in aquatic systems, on degradation, and (eco)toxicity, respectively, was found. Several mixtures of SUA-TPs were more ecotoxic than their parent compounds, e.g. 10 of 15 mixtures of SMX-TPs. Only few TPs were tested as single substance. Although several TPs could be eliminated experimentally, their mineralisation rate remained often unknown. Thus, further transformation to persistent TPs could not be ruled out. Standardised biodegradability tests of individual TPs would monitor their mineralisation rate, but are almost completely lacking. Reasons are likely poor availability of TPs, but also the focus on abiotic water treatment. Data assessment demonstrated that data of high significance according to standard methods, e.g. OECD methods for chronic (eco)toxicity and ready biodegradability, is needed to assess environmental risks of prioritised TPs, but also to redesign their parent pharmaceutical for complete environmental mineralisation in a long-term (Benign by Design).

Oxidative degradation of sulfamethoxazole from secondary treated effluent by ferrate(VI): kinetics, by-products, degradation pathway and toxicity assessment

Sulfamethoxazole (SMX) is a typical antibiotic in the world, which is frequently detected in the aquatic environment. The current study was aimed to investigate the SMX degradation in secondary treated wastewater using potassium Ferrate [Fe(VI)]. The effects of various experimental conditions, EDTA and phosphate as chelating agents, and toxicity assessment were also considered. Secondary treated effluent was spiked with predefined SMX concentrations, and after desired reaction time with Fe(VI), residual SMX was measured using HPLC. Results indicated that SMX degradation by Fe(VI) was favored under acidic condition, where 90% of SMX degradation was achieved after 120 min. Fe(VI) and SMX reaction obeyed first-order kinetic; meantime, the SMX degradation rate under pH 3 was 7.6 times higher than pH 7. The presence of phosphate (Na₂HPO₄) and EDTA declined SMX degradation, while Fe (III) effect was contradictory. In addition to promising demolition, 10% TOC removal was achieved. Eighteen major intermediates were identified using LC-MS/MS and the degradation pathways were suggested. Transformation products (TPs) were formed due to hydroxylation, bond cleavage, transformation after bond cleavage, and oxidation reactions. The ECOSAR analysis showed that some of the SMX oxidation products were toxic to aquatic organisms (fish, daphnia and green algae).

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s40201-021-00769-9.

Effect of chlorination on the characteristics of effluent organic matter and the phototransformation of sulfamethoxazole in secondary wastewater

Chlorination is the most common disinfection technology used to treat wastewater effluent discharged into receiving aquatic environments. Effluent organic matter (EfOM) abundant in wastewater is a well-known photosensitizer and it greatly affects phototransformation of antibiotics in water. However, effects of chlorination on the characteristics and photochemical properties of EfOM have not been studied in sufficient detail. This paper investigated effects of chlorination on the characteristics of EfOM, and its impact on the phototransformation of sulfamethoxazole (SMX). Correlations between the EfOM characteristics and steady-state concentrations of reactive intermediates (RI) formed in the system were established. Chlorination was shown to preferentially remove the aromatic protein-like substances in EfOM, and the incorporation of chlorine into followed by the cleavage of the aromatic rings in EfOM molecules led to the formation of low molecular aliphatic organic matter. Both unaltered and chlorinated EfOM promoted the photodegradation of SMX whose rate constant in the wastewater was 1.32-1.65 times higher than that in pH 8 phosphate buffer. However, the rate of SMX photodegradation decreased at higher chlorination concentrations. The photodegradation of SMX was found to proceed through direct photolysis and oxidation by the RIs generated from EfOM and the self-sensitization of SMX. The steady-state concentrations of ·OH, ¹O₂ and ³EfOM* were 2.15-5.50 × 10^-16, 0.42-1.51 × 10^-13, and 2.54-5.82 × 10^-14 M in unaltered and chlorinated wastewater. The steady-state concentrations of ·OH were well correlated with the removal of the fluorescence regional integration (ΔFRI) for humic-like and soluble microbial products (SMPs), while the photodegradation rate constant of SMX and the steady-state concentration of ¹O₂ and ³EfOM* showed good correlations with ΔFRI for tryptophan and fulvic-like substances. Six transformation products (TPs) of SMX were identified. These findings provide new insights into the photochemical properties of chlorinated EfOM in the aquatic environments and its roles in the degradation of antibiotics and other trace-level pharmaceuticals.

Bibliometric analysis of microbial sulfonamide degradation: Development, hotspots and trend directions

Microbial sulfonamide degradation (MSD) is an efficient and safe treatment in both natural and engineered ecosystems. In order to systematically understand the research status and frontier trends of MSD, this study employed CiteSpace to conduct a bibliometric analysis of data from the Web of Science (WoS) and the China National Knowledge Infrastructure (CNKI) published from 2000 to 2021. During this time, China, Germany, Spain, the United States and Australia played leading roles by producing numerous high impact publications, while the Chinese Academy of Sciences was the leading research institution in this interdisciplinary research category. The Chemosphere was the top journal in terms of the number of citations. MSD research has gradually progressed from basic laboratory-based experiments to more complex environmental microbial communities and finally to deeper research on molecular mechanisms and engineering applications. Although multi-omics and synthetic community are the key techniques in the frontier research, they are also the current challenges in this field. A summary of published articles shows that Proteobacteria, Gammaproteobacteria, Burkholderiales and Alcaligenaceae are the most frequently observed MSD phylum, class, order and family, respectively, while Bacillus, Pseudomonas and Achromobacter are the top three MSD genera. To our knowledge, this study is the first to investigate the development and current challenges of MSD research, put forward future perspective, and form a relatively complete list of sulfonamide-degrading microorganisms for reference.

Antibiotic accumulation, growth performance, intestinal diversification, and function of Nile tilapia (Oreochromis niloticus) feed by diets supplemented with different doses of sulfamethoxazole

To comprehensively investigate the effects of exposure to legal doses of sulfamethoxazole (SMZ) in Nile tilapia (Oreochromis niloticus), fishes were exposed to diets supplemented with different doses of SMZ (NS, normal feed; LS, 20 mg/kg·day; MS, 200 mg/kg·day; and HS, 1000 mg/kg·day) for 4 weeks and then fed with normal feed for 4 weeks. General SMZ accumulation, growth performance, intestinal short-chain fatty acids, intestinal flora diversity, composition, and function were systemically evaluated. Results indicated that the SMZ accumulation in O. niloticus muscles, intestinal contents, and aquaculture environment positively correlated to the exposure dose. The growth performance, measured by weight increase, was MS>LS>NS, while HS antibiotics retarded the growth. SMZ-exposed O. niloticus had an increased number of fat particles in the liver and a change in the content of intestinal SCFAs. Moreover, SMZ exposure changed the biological diversity of the intestinal flora and subsequently induced microbiota dysbiosis, primarily inhibiting the growth of Fusobacteria, especially in HS group. Overall, exposure to higher SMZ doses than the recommended ones impair general intestinal functions and provokes health risk in fish. This study highlights the importance of rational and regulated use of SMZ in aquaculture.

Performance and mechanism of sulfamethoxazole removal in different bioelectrochemical technology-integrated constructed wetlands

Sulfamethoxazole (SMX) has a high concentration and detection frequency in aquatic environments due to the poor removal efficiency of traditional biological treatment processes. Bioelectrochemical technology-integrated constructed wetlands (CWs) have great potential for SMX removal; however, the process of SMX removal in different bioelectrochemical technology-integrated CWs (microbial fuel cell (MFC) and direct current (EC)) remains unclear. To address this, we examined the mechanism of SMX removal in MFCCW and ECCW. The results revealed that the SMX removal efficiency can reach 96.0 ± 2.4% in the ECCW and 97.2 ± 2.2% in the MFCCW. The enhancement of MFC for SMX removal in CW was slightly better than that in direct current (p > 0.05). It was found that the adsorption process of SMX in the substrate promoted by EC was more enhanced than that by MFC. Furthermore, bioelectrochemical technology improved plant activity, including root and enzymatic (superoxide dismutase, peroxidase, and catalase) activities, and fluorescence parameters (photochemical quenching coefficient, non-photochemical quenching coefficient, and quantum efficiency of PS II). Significant differences were found between CW and ECCW (p < 0.05), while no significant differences were found between CW and MFCCW (p > 0.05). The microbial activity and abundance in CW were improved by bioelectrochemical technology, and the microbial community structure was optimised to be simpler and more stable. However, EC tended to promote microbial and plant activity in CW, whereas MFC tended to optimise the microbial community and improve the tightness and stability of the module. The enhanced difference might also account for the changes in the SMX degradation pathway. 4-aminobenzenesulfonic acid (TP174), 3-amino-5-methylisoxazole (TP99) and 5-methylisoxazole (TP84) were all common products in the three reactors, whereas TP99 underwent further ring-opening in MFCCW and TP174 underwent further hydrolysis in ECCW. This study provided an important reference for the targeted regulation of plants and microorganisms in constructed wetlands via different bioelectrochemistry to enhance characteristic pollutants degradation.

Biodegradation and metabolic pathway of sulfamethoxazole by Sphingobacterium mizutaii

Sulfamethoxazole (SMX) is the most commonly used antibiotic in worldwide for inhibiting aquatic animal diseases. However, the residues of SMX are difficult to eliminate and may enter the food chain, leading to considerable threats on human health. The bacterial strain Sphingobacterium mizutaii LLE5 was isolated from activated sludge. This strain could utilize SMX as its sole carbon source and degrade it efficiently. Under optimal degradation conditions (30.8 °C, pH 7.2, and inoculum amount of 3.5 × 10⁷ cfu/mL), S. mizutaii LLE5 could degrade 93.87% of 50 mg/L SMX within 7 days. Four intermediate products from the degradation of SMX were identified and a possible degradation pathway based on these findings was proposed. Furthermore, S. mizutaii LLE5 could also degrade other sulfonamides. This study is the first report on (1) degradation of SMX and other sulfonamides by S. mizutaii, (2) optimization of biodegradation conditions via response surface methodology, and (3) identification of sulfanilamide, 4-aminothiophenol, 5-amino-3-methylisoxazole, and aniline as metabolites in the degradation pathway of SMX in a microorganism. This strain might be useful for the bioremediation of SMX-contaminated environment.

Steroid hormones in the aquatic environment

Steroid hormones are extremely important natural hormones in all vertebrates. They control a wide range of physiological processes, including osmoregulation, sexual maturity, reproduction and stress responses. In addition, many synthetic steroid hormones are in widespread and general use, both as human and veterinary pharmaceuticals. Recent advances in environmental analytical chemistry have enabled concentrations of steroid hormones in rivers to be determined. Many different steroid hormones, both natural and synthetic, including transformation products, have been identified and quantified, demonstrating that they are widespread aquatic contaminants. Laboratory ecotoxicology experiments, mainly conducted with fish, but also amphibians, have shown that some steroid hormones, both natural and synthetic, can adversely affect reproduction when present in the water at extremely low concentrations: even sub-ng/L. Recent research has demonstrated that mixtures of different steroid hormones can inhibit reproduction even when each individual hormone is present at a concentration below which it would not invoke a measurable effect on its own. Limited field studies have supported the conclusions of the laboratory studies that steroid hormones may be environmental pollutants of significant concern. Further research is required to identify the main sources of steroid hormones entering the aquatic environment, better describe the complex mixtures of steroid hormones now known to be ubiquitously present, and determine the impacts of environmentally-realistic mixtures of steroid hormones on aquatic vertebrates, especially fish. Only once that research is completed can a robust aquatic risk assessment of steroid hormones be concluded.

Ecotoxicological risk assessment of wastewater irrigation on soil microorganisms: Fate and impact of wastewater-borne micropollutants in lettuce-soil system

The implementation of the new Water Reuse regulation in the European Union brings to the forefront the need to evaluate the risks of using wastewater for crop irrigation. Here, a two-tier ecotoxicological risk assessment was performed to evaluate the fate of wastewater-borne micropollutants in soil and their ecotoxicological impact on plants and soil microorganisms. To this end, two successive cultivation campaigns of lettuces were irrigated with wastewater (at agronomical dose (not spiked) and spiked with a mixture of 14 pharmaceuticals at 10 and 100 µg/L each) in a controlled greenhouse experiment. Over the two cultivation campaigns, an accumulation of PPCPs was observed in soil microcosms irrigated with wastewater spiked with 100 μg/L of PPCPs with the highest concentrations detected for clarithromycin, hydrochlorothiazide, citalopram, climbazole and carbamazepine. The abundance of bacterial and fungal communities remained stable over the two cultivation campaigns and was not affected by any of the irrigation regimes applied. Similarly, no changes were observed in the abundance of ammonium oxidizing archaea (AOA) and bacteria (AOB), nor in clade A of commamox no matter the cultivation campaign or the irrigation regime considered. Only a slight increase was detected in clade B of commamox bacteria after the second cultivation campaign. Sulfamethoxazole-resistant and -degrading bacteria were not impacted either. The irrigation regimes had only a limited effect on the bacterial evenness. However, in response to wastewater irrigation the structure of soil bacterial community significantly changed the relative abundance of Acidobacteria, Chloroflexi, Verrucomicrobia, Beta-, Gamma- and Deltaprotebacteria. Twenty-eight operational taxonomic units (OTUs) were identified as responsible for the changes observed within the bacterial communities of soils irrigated with wastewater or with water. Interestingly, the relative abundance of these OTUs was similar in soils irrigated with either spiked or non-spiked irrigation solutions. This indicates that under both agronomical and worst-case scenario the mixture of fourteen PPCPs had no effect on soil bacterial community.

Coupling of spectrometric, chromatographic, and chemometric analysis in the investigation of the photodegradation of sulfamethoxazole

A workflow is proposed for the study of the photodegradation process of the sulfamethoxazole (SMX) based on the combination of different experimental techniques, including liquid chromatography, mass spectrometry, UV-Visible spectrophotometry, and the treatment of all the analytical data with advanced chemometric methods. SMX, which is one of the most widely used antibiotics worldwide and has been found at remarkable concentrations in various rivers and effluents over all Europe, was degraded in the laboratory under a controlled source of UV radiation, which simulates the environmental solar radiation (Suntest). Kinetic monitoring of the photodegradation process was performed using UV-Visible spectrophotometric measurements and by further Liquid Chromatography with Diode Array Detector and Mass Spectrometry analysis (LC-DAD-MS). Additionally, the acid-base properties were also investigated to see how the pH can affect the speciation of this substance during the photodegradation process. Based on the Multivariate Curve Resolution-Alternating Least Squares (MCR-ALS) application, the proposed chemometric method coped with the large amounts of data generated by the different analytical techniques used to monitor the evolution of the photodegradation process. Their simultaneous analysis involved applying a data fusion strategy and an advanced MCR-ALS constrained analysis, which allowed and improved the description of the complete degradation process, detecting the different species of the reaction, and identifying the possible transformation products formed. A total number of six species were resolved in the degradation process of SMX. In addition to the initial SMX, a second species corresponded to a conformational isomer, and the other four species represented different photoproducts, which have also been identified. Furthermore, three different acid-base species of SMX were obtained, and their pK_a values were estimated.

Antibiotics: An overview on the environmental occurrence, toxicity, degradation, and removal methods

Antibiotics, as antimicrobial drugs, have been widely applied as human and veterinary medicines. Recently, many antibiotics have been detected in the environments due to their mass production, widespread use, but a lack of adequate treatment processes. The environmental occurrence of antibiotics has received worldwide attention due to their potential harm to the ecosystem and human health. Research status of antibiotics in the environment field is presented by bibliometrics. Herein, we provided a comprehensive overview on the following important issues: (1) occurrence of antibiotics in different environmental compartments, such as wastewater, surface water, and soil; (2) toxicity of antibiotics toward non-target organisms, including aquatic and terrestrial organisms; (3) current treatment technologies for the degradation and removal of antibiotics, including adsorption, hydrolysis, photodegradation and oxidation, and biodegradation. It was found that macrolides, fluoroquinolones, tetracyclines, and sulfonamides were most frequently detected in the environment. Compared to surface and groundwaters, wastewater contained a high concentration of antibiotic residues. Both antibiotics and their metabolites exhibited toxicity to non-target organisms, especially aquatic organisms (e.g., algae and fish). Fluoroquinolones, tetracyclines, and sulfonamides can be removed through abiotic process, such as adsorption, photodegradation, and oxidation. Fluoroquinolones and sulfonamides can directly undergo biodegradation. Further studies on the chronic effects of antibiotics at environmentally relevant concentrations on the ecosystem were urgently needed to fully understand the hazards of antibiotics and help the government to establish the permissible limits. Biodegradation is a promising technology; it has numerous advantages such as cost-effectiveness and environmental friendliness.

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.

Biosynthesized Schwertmannite@Biochar composite as a heterogeneous Fenton-like catalyst for the degradation of sulfanilamide antibiotics

Schwertmannite was successfully loaded onto biochar (Sch@BC) using a biosynthetic method. The physicochemical properties and structural morphology of Sch@BC were explored using XRD, SEM, BET, and XPS. The results showed that introducing biochar can effectively prevent the agglomeration of Sch. The catalytic activity of Sch@BC in the Fenton-like degradation of sulfamethoxazole (SMX) was also systematically investigated under different reaction conditions. Under optimum conditions ([SMX] = 10 mg L^-1, [H₂O₂] = 2.0 mM, Sch@BC = 1.0 g L^-1 and initial pH = 3.0), the removal efficiencies of the SMX and total organic carbon (TOC) were 100% and 45.9%, respectively, within 60 min of the reaction. The results of the radical scavenger effect and ESR studies suggested that the SMX degradation in the Sch@BC/H₂O₂ system was dominated by a heterogeneous Fenton-like reaction. The repeated use of Sch@BC for SMX degradation demonstrated its reusability and stability in Fenton-like reactions. There was also speculation about the degradation mechanism and pathways of SMX. Furthermore, under the same conditions, the removal efficiencies of sulfadiazine (SD) and sulfisoxazole (SIZ) under Fenton-like degradation in the Sch@BC system were 91% and 93%. The results provide a theoretical basis and practical guidance for the creation of a new catalyst using biochar as a support material for the degradation of sulfanilamide antibiotics.

Fate and toxicity of pharmaceuticals in water environment: An insight on their occurrence in South Asia

Pharmaceutically active compounds are newly recognized micropollutants which are ubiquitous in aquatic environment mainly due to direct discharge of treated and untreated wastewater from wastewater treatment plants. These contaminants have attracted mounted attention due to their toxic effects on aquatic life. They disrupt biological processes in non-target lower organisms upon exposure. Biodegradation, photo-degradation, and sorption are key processes which determine their fate in the environment. A variety of conventional and advanced treatment processes had been extensively investigated for the removal of pharmaceuticals from wastewater. However, due to structural complexity and varying operating parameters, complete removal seems ideal. Generally, due to high energy requirement of advanced treatment technology, it is considered cost ineffective. Transport of pharmaceutical compounds occurs via aquatic channels whereas sediments and aquatic colloids play a significant role as sinks for these contaminants. The current review provides a critical understanding of fate and toxicity of pharmaceutical compounds and highlights their vulnerability and occurrence in South Asia. Antibiotics, analgesics, and psychiatric drugs were found predominantly in the water environment of South Asian regions. Despite significant advances in understanding pharmaceuticals fate, toxicity, and associated risks since the 1990s, still substantial data gaps in terms of monitoring, human health risks, and legislation exist which presses the need to develop a more in-depth and interdisciplinary understanding of the subject.

Isolation and characterization of a marine bacterium Vibrio diabolicus strain L2-2 capable of biotransforming sulfonamides

Sulfonamides (SAs) have attracted much attention because of their high detection rates in natural water. In this study, a marine bacterium Vibrio diabolicus strain L2-2 was isolated which could metabolize 9 SAs to a different extent. Compared with SAs and their analogs, SAs with N-oxides of heterocyclic structure were easier to be transformed to their N⁴-acetylated metabolites or their isoxazole ring rearrangement isomers by strain L2-2. And, gene vdnatA and vdnatG were likely to be the key genes in SAs acetylation process, which might code Arylamine N-acetyltransferase. The biotransformation rates of sulfathiazole(STZ), sulfamonomethoxine(SMT), sulfadiazine(SDZ), sulfamethoxazole(SMX) and sulfisoxazole(SIX) could reach 29.39 ± 5.63, 24.97 ± 4.45, 79.41 ± 4.05, 64.64 ± 1.71, 32.82 ± 4.46% in 6 days, respectively. Besides, the overall optimal conditions for SAs biotransformation were less than 100 mg/L for total SAs in neutral or weakly alkaline medium with the salinity of 10-20‰ and additional nutrients like glucose, sucrose or glycerine. Furthermore, toxicity was demonstrated to be significantly reduced after biotransformation. Together, this study introduced a strategy to use V. diabolicus strain L2-2 to realize simultaneous removal and detoxification of multiple SAs in freshwater and seawater, and revealed SAs removal pathways and relevant molecular mechanism.

Efficient degradation of sulfamethoxazole by catalytic wet peroxide oxidation with sludge-derived carbon as catalysts

Sulfamethoxazole (SMX) is a commonly used antibiotic for both human and animals. The frequent detection of SMX in natural water bodies and sediment has become an issue of great environmental concern due to its potential risk to induce antibiotic resistance in pathogenic bacteria. In the present work, the catalytic wet peroxide oxidation (CWPO) was investigated to remove SMX with sludge-derived carbon (SC) as a cheap alternative catalyst. Different acids were used to modify SC. It was found that SC modified with sulphuric acid (SC-H₂SO₄) demonstrated the best catalytic activity. The removal efficiency of SMX and TOC was 97.7% and 65.7%, respectively, after 260 min, at pH 5 with a dosage of 220 mg/L H₂O₂. The effects of temperature, initial pH and H₂O₂ dosage were also investigated. The study demonstrated that the increase of temperature could significantly improve the degradation of SMX from 10.0% at 20°C to 94.7% at 60°C.

Occurrence, distribution, and ecotoxicological risk assessment of selected pharmaceutical compounds in water from Lake Victoria, Uganda

The occurrence of 24 pharmaceuticals (including 15 antibiotics, three analgesic/anti-inflammatory drugs, three anti-epileptic/antidepressant drugs, two beta blockers, and one lipid regulator) was investigated in 75 water samples collected from four bays in the Ugandan part of Lake Victoria. In addition, the potential environmental risk of the target pharmaceutical compounds to aquatic organisms in the aquatic ecosystem of Lake Victoria was assessed. Water samples were extracted using solid phase extraction and analyzed for pharmaceuticals using high-performance liquid chromatography coupled with triple quadrupole mass spectrometry (LC/MS/MS). Eighteen of the 24 pharmaceuticals occurred at quantifiable concentrations. Sulfamethoxazole (1-5600 ng L^-1), trimethoprim (1-89 ng L^-1), tetracycline (3-70 ng L^-1), sulfacetamide (1-13 ng L^-1), and ibuprofen (6-780 ng L^-1) occurred at quantifiable concentrations in all water samples. Sulfamethazine (2-50 ng L^-1), erythromycin (10-66 ng L^-1), diclofenac (2-160 ng L^-1), and carbamazepine (5-72 ng L^-1) were only quantifiable in water samples from Murchison Bay. The highest concentrations of pharmaceuticals were found in Murchison Bay, the main recipient of sewage effluents, industrial and municipal waste from Kampala city via the Nakivubo channel. Ecotoxicological risk assessment showed that sulfamethoxazole, oxytetracycline, erythromycin, and diclofenac pose a high toxic risk to aquatic organisms in the lake, while ciprofloxacin, norfloxacin, and ibuprofen pose a medium risk. This study is the first of its kind to report the levels and ecotoxic risks of pharmaceutical compounds in Lake Victoria waters, of Uganda, and East Africa as a whole.

Degradation of Sulfamethoxazole Using Iron-Doped Titania and Simulated Solar Radiation

This work examined the photocatalytic destruction of sulfamethoxazole (SMX), a widely used antibiotic, under simulated solar radiation using iron-doped titanium dioxide as the photocatalyst. Amongst the various iron/titania ratios examined (in the range 0%–2%), the catalyst at 0.04% Fe/TiO2 molar ratio exhibited the highest photocatalytic efficiency. The reaction rate followed pseudo-first-order kinetics, where the apparent kinetic constant was reduced as the initial concentration of SMX or humic acid increased. The photodecomposition of SMX was favored in natural pH but retarded at alkaline conditions. Unexpectedly, the presence of bicarbonates (in the range of 0.125–2 g/L) improved the removal of SMX, however, experiments conducted in real environmental matrices showed that process efficiency decreased as the complexity of the water matrix increased. The presence of sodium persulfate as an electron acceptor enhanced the reaction rate. However, only a small synergy was observed between the two individual processes. On the contrary, the addition of tert-butanol, a well-known hydroxyl radical scavenger, hindered the reaction, indicating the significant contribution of these radicals to the photocatalytic degradation of SMX. The photocatalyst retained half of its initial activity after five successive experiments.

Fate of Trace Organic Compounds in the Hyporheic Zone: Influence of Retardation, the Benthic Biolayer, and Organic Carbon

The fate of 28 trace organic compounds (TrOCs) was investigated in the hyporheic zone (HZ) of an urban lowland river in Berlin, Germany. Water samples were collected hourly over 17 h in the river and in three depths in the HZ using minipoint samplers. The four relatively variable time series were subsequently used to calculate first-order removal rates and retardation coefficients via a one-dimensional reactive transport model. Reversible sorption processes led to substantial retardation of many TrOCs along the investigated hyporheic flow path. Some TrOCs, such as dihydroxy-carbamazepine, O-desmethylvenlafaxine, and venlafaxine, were found to be stable in the HZ. Others were readily removed with half-lives in the first 10 cm of the HZ ranging from 0.1 ± 0.01 h for iopromide to 3.3 ± 0.3 h for tramadol. Removal rate constants of the majority of reactive TrOCs were highest in the first 10 cm of the HZ, where removal of biodegradable dissolved organic matter was also the highest. Because conditions were oxic along the top 30 cm of the investigated flow path, we attribute this finding to the high microbial activity typically associated with the shallow HZ. Frequent and short vertical hyporheic exchange flows could therefore be more important for reach-scale TrOC removal than long, lateral hyporheic flow paths.

Reducing aquatic micropollutants - Increasing the focus on input prevention and integrated emission management

Pharmaceuticals and many other chemicals are an important basis for nearly all sectors including for example, food and agriculture, medicine, plastics, electronics, transport, communication, and many other products used nowadays. This comes along with a tremendous chemicalization of the globe, including ubiquitous presence of products of chemical and pharmaceutical industries in the aquatic environment. Use of these products will increase with population growth and living standard as will the need for clean water. In addition, climate change will exacerbate availability of water in sufficient quantity and quality. Since its implementation, conventional wastewater treatment has increasingly contributed to environmental protection and health of humans. However, with the increasing pollution of water by chemicals, conventional treatment turned out to be insufficient. It was also found that advanced effluent treatment methods such as extended filtration, the sorption to activated charcoal or advanced oxidation methods have their own limitations. These are, for example, increased demand for energy and hazardous chemicals, incomplete or even no removal of pollutants, the generation of unwanted products from parent compounds (transformation products, TPs) of often-unknown chemical structure, fate and toxicity. In many countries, effluent treatment is available only rarely if at all let alone advanced treatment. The past should teach us, that focusing only on technological approaches is not constructive for a sustainable water quality control. Therefore, in addition to conventional and advanced treatment optimization more emphasis on input prevention is urgently needed, including more and better control of what is present in the source water. Measures for input prevention are known for long. The main focus though has always been on the treatment, and measures taken at the source have gained only little attention so far. A more effective and efficient approach, however, would be to avoid pollution at the source, which would in turn allow more targeted treatment to meet treated water quality objectives globally. New developments within green and sustainable chemistry are offering new approaches that allow for input prevention and a more targeted treatment to succeed in pollution elimination in and at the source. To put this into practice, engineers, water scientists and chemists as well as microbiologists and scientists of other related disciplines need to cooperate more extensively than in the past. Applying principles such as the precautionary principle, or keeping water flows separate where possible will add to this. This implies not minimizing the efforts to improve wastewater treatment but to design effluents and chemicals in such a way that treatment systems and water environments can cope successfully with the challenge of micropollutants globally (Kümmerer et al., 2018). This paper therefore presents in its first part some of the limitations of effluent treatment in order to demonstrate the urgent need for minimizing water pollution at the source and, information on why source management is urgently needed to improve water quality and stimulate discussions how to protect water resources on a global level. Some principles of green and sustainable chemistry as well as other approaches, which are part of source management, are presented in the second part in order to stimulate discussion.

Veterinary pharmaceutical residues from natural water to tap water: Sales, occurrence and fate

Veterinary pharmaceuticals (VPs) increasingly used in animal husbandry have led to their presence in aquatic environments -surface water (SW) or groundwater (GW) - and even in tap water. This review focuses on studies from 2007 to 2017. Sixty-eight different veterinary pharmaceutical residues (VPRs) have been quantified worldwide in natural waters at concentrations ranging from nanograms per liter (ng L^-1) to several micrograms per liter (μg L^-1). An extensive up-to-date on sales and tonnages of VPs worldwide has been performed. Tetracyclines (TCs) antibiotics are the most sold veterinary pharmaceuticals worldwide. An overview of VPRs degradation pathways in natural waters is provided. VPRs can be degraded or transformed by biodegradation, hydrolysis or photolysis. Photo-degradation appears to be the major degradation pathway in SW. This review then reports occurrences of VPRs found in tap water, and presents data on VPRs removal in drinking water treatment plants (DWTPs) at each step of the process. VPRs have been quantified in tap water at ng L^-1 concentration levels in four studies of the eleven studies dealing with VPRs occurrence in tap water. Overall removals of VPRs in DWTPs generally exceed 90% and advanced treatment processes (oxidation processes, adsorption on activated carbon, membrane filtration) greatly contribute to these removals. However, studies performed on full-scale DWTPs are scarce. A large majority of fate studies in DWTPs have been conducted under laboratory at environmentally irrelevant conditions (high concentration of VPRs (mg L^-1), use of deionized water instead of natural water, high concentration of oxidant, high contact time etc.). Also, studies on VPRs occurrence and fate in tap water focus on antibiotics. There is a scientific gap on the occurrence and fate of antiparatic drugs in tap waters.

Biodegradation of sulfamethoxazole by a bacterial consortium of Achromobacter denitrificans PR1 and Leucobacter sp. GP

In the last decade, biological degradation and mineralization of antibiotics have been increasingly reported feats of environmental bacteria. The most extensively described example is that of sulfonamides that can be degraded by several members of Actinobacteria and Proteobacteria. Previously, we reported sulfamethoxazole (SMX) degradation and partial mineralization by Achromobacter denitrificans strain PR1, isolated from activated sludge. However, further studies revealed an apparent instability of this metabolic trait in this strain. Here, we investigated this instability and describe the finding of a low-abundance and slow-growing actinobacterium, thriving only in co-culture with strain PR1. This organism, named GP, shared highest 16S rRNA gene sequence similarity (94.6-96.9%) with the type strains of validly described species of the genus Leucobacter. This microbial consortium was found to harbor a homolog to the sulfonamide monooxygenase gene (sadA) also found in other sulfonamide-degrading bacteria. This gene is overexpressed in the presence of the antibiotic, and evidence suggests that it codes for a group D flavin monooxygenase responsible for the ipso-hydroxylation of SMX. Additional side reactions were also detected comprising an NIH shift and a Baeyer-Villiger rearrangement, which indicate an inefficient biological transformation of these antibiotics in the environment. This work contributes to further our knowledge in the degradation of this ubiquitous micropollutant by environmental bacteria.

Small and large-scale distribution of four classes of antibiotics in sediment: association with metals and antibiotic resistance genes

Antibiotic chemicals and antibiotic resistance genes enter the environment via wastewater effluents as well as from runoff from agricultural operations. The relative importance of these two sources, however, is largely unknown. The relationship between the concentrations of chemicals and genes requires exploration, for antibiotics in the environment may lead to development or retention of resistance genes by bacteria. The genes that confer resistance to metal toxicity may also be important in antibiotic resistance. In this work, concentrations of 19 antibiotics (using liquid chromatography tandem mass spectrometry), 14 metals (using inductively coupled plasma-mass spectrometry), and 45 metal, antibiotic, and antibiotic-resistance associated genes (using a multiplex, microfluidic quantitative polymerase chain reaction method) were measured in 13 sediment samples from two large rivers as well as along a spatial transect in a wastewater effluent-impacted lake. Nine of the antibiotics were detected in the rivers and 13 were detected in the lake. Sixteen different resistance genes were detected. The surrounding land use and proximity to wastewater treatment plants are important factors in the number and concentrations of antibiotics detected. Correlations among antibiotic chemical concentrations, metal concentrations, and resistance genes occur over short spatial scales in a lake but not over longer distances in major rivers. The observed correlations likely result from the chemicals and resistance genes arising from the same source, and differences in fate and transport over larger scales lead to loss of this relationship.

Contribution of biotic and abiotic factors in the natural attenuation of sulfamethoxazole: A path analysis approach

Sulfamethoxazole (SMX) is a sulfonamide antibiotic, widely used as curative and preventive drug for human, animal, and aquaculture bacterial infections. Its residues have been ubiquitously detected in the surface waters and sediments. In the present study, SMX dissipation and kinetics was studied in the natural water samples from Jiulong River under simulated complex natural conditions as well as conditions to mimic various biotic and abiotic environmental conditions in isolation. Structural equation modeling (SEM) by employing partial least square technique in path coefficient analysis was used to investigate the direct and indirect contributions of different environmental factors in the natural attenuation of SMX. The model explained 81% of the variability in natural attenuation as a dependent variable under the influence of sole effects of direct photo-degradation, indirect photo-degradation, hydrolysis, microbial degradation and bacterial degradation. The results of SEM suggested that the direct and indirect photo-degradation were the major pathways in the SMX natural attenuation. However, other biotic and abiotic factors also play a mediatory role during the natural attenuation and other processes. Furthermore, the potential transformation products of SMX were identified and their toxicity was evaluated.

Hierarchical magnetic petal-like Fe3O4-ZnO@g-C3N4 for removal of sulfamethoxazole, suppression of photocorrosion, by-products identification and toxicity assessment

Herein, a petal-like photocatalyst, Fe₃O₄-ZnO@g-C₃N₄ (FZG) with different g-C₃N₄ to ZnO ratios was synthesized with hierarchical structure. The FZG1 photocatalyst, having the weight ratio of 1:1 for the initial urea and Fe₃O₄-ZnO (Fe-ZnO), presented the highest sulfamethoxazole (SMX) degradation rate of 0.0351 (min^-1), which was 2.6 times higher than that of pristine ZnO. Besides the facile separation, the performance of photocatalyst was improved due to the function of iron oxide as an electron acceptor that reduced the electron/hole recombination rate. The coating of g-C₃N₄ on the Fe-ZnO surface not only acted as a protective layer for ZnO against photocorrosion, but it also enhanced the photocatalytic activity of the catalyst for SMX degradation through the heterojunction mechanism. By using the FZG1 photocatalyst, 95% SMX removal was obtained after 90 min reaction, while 47% COD and 30% TOC removal were achieved after 60 min treatment under a low energy-consuming UV lamp (10 W). Moreover, a substantial reduction in the solution toxicity was shown after the treatment, as compared with the SMX solution before treatment. The LC-HR-MS/MS analysis results showed that the concentration of most detected by-products produced after 90 min reaction by FZG1 was considerably lower than those obtained using other synthesized photocatalysts. By performing radical scavenging experiments, OH^° radical was found to be the major reactive species. The FZG1 photocatalyst also displayed excellent reusability in five cycles and the leaching of zinc and iron ions was reduced by 54% and ∼100%, respectively, after coating Fe-ZnO with g-C₃N₄.

Antibiotics in the aquatic environments: A review of lakes, China

The potential threat of antibiotics to the environment and human health has raised significant concerns in recent years. The consumption and production of antibiotics in China are the highest in the world due to its rapid economic development and huge population, possibly resulting in the high detection frequencies and concentrations of antibiotics in aquatic environments of China. As a water resource, lakes in China play an important role in sustainable economic and social development. Understanding the current state of antibiotics in lakes in China is important. Closed and semi-closed lakes provide an ideal medium for the accumulation of antibiotics and antibiotic resistance genes (ARGs). This review summarizes the current levels of antibiotic exposure in relevant environmental compartments in lakes. The ecological and health risks of antibiotics are also evaluated. This review concludes that 39 antibiotics have been detected in the aquatic environments of lakes in China. The levels of antibiotic contamination in lakes in China is relatively high on the global scale. Antibiotic contamination is higher in sediment than water and aquatic organisms. Quinolone antibiotics (QNs) pose the greatest risks. The contents of antibiotics in aquatic organisms are far lower than their maximum residual limits (MRLs), with the exception of the organisms in Honghu Lake. The lakes experience high levels of ARG contamination. A greater assessment of ARG presence and antibiotic exposure are urgent.

Direct Photolysis of Sulfamethoxazole Using Various Irradiation Sources and Wavelength Ranges-Insights from Degradation Product Analysis and Compound-Specific Stable Isotope Analysis

The environmental micropollutant sulfamethoxazole (SMX) is susceptible to phototransformation by sunlight and UV-C light which is used for water disinfection. Depending on the environmental pH conditions SMX may be present as neutral or anionic species. This study systematically investigates the phototransformation of these two relevant SMX species using four different irradiation scenarios, i.e., a low, medium, and high pressure Hg lamp and simulated sunlight. The observed phototransformation kinetics are complemented by data from compound-specific stable isotope and transformation product analysis using isotope-ratio and high-resolution mass spectrometry (HRMS). Observed phototransformation kinetics were faster for the neutral than for the anionic SMX species (from 3.4 (LP lamp) up to 6.6 (HP lamp) times). Furthermore, four phototransformation products (with m/z 189, 202, 242, and 260) were detected by HRMS that have not yet been described for direct photolysis of SMX. Isotopic fractionation occurred only if UV-B and UV-A wavelengths prevailed in the emitted irradiation and was most pronounced for the neutral species with simulated sunlight (ε_C = -4.8 ± 0.1 ‰). Phototransformation of SMX with UV-C light did not cause significant isotopic fractionation. Consequently, it was possible to differentiate sunlight and UV-C light induced phototransformation of SMX. Thus, CSIA might be implemented to trace back wastewater point sources or to assess natural attenuation of SMX by sunlight photolysis. In contrast to the wavelength range, pH-dependent speciation of SMX hardly impacted isotopic fractionation.

Occurrence of pharmaceuticals and UV-filters in riverine run-offs and waters of the German Baltic Sea

The occurrence of pharmaceuticals and personal care products (PPCPs) in the marine environment is of great concern. This study was done to determine the emergence of eight pharmaceuticals and eleven ultraviolet filters (UV-Filters) in 5 rivers/streams discharging into the Baltic Sea. Furthermore, a focus was put on the influence of wastewater treatment plant as indirect source and the occurrence of the PPCPs in close beach proximity. Two pharmaceuticals (sulfamethoxazole, salicylic acid) and two UV-filters (2-phenylbenzimidazole-5-sulfonic acid, octocrylene) were detected in all analyzed water samples, with concentration ranging from 0.6ng/L to 836.3ng/L. In all rivers the PPCP concentration decreases towards the Baltic Sea. Sulfamethoxazole was detected at comparable concentration along the coast, which leads to the assumption of stable concentration in beach proximity. Along the coast UV-filters appeared in varying concentrations, leading to the conclusion that the direct input into the marine environment plays a bigger role than the indirect input.

Degradation of sulfonamides as a microbial resistance mechanism

Two of the main mechanisms of bacterial resistance to sulfonamides in aquatic systems, spread of antibiotic resistance genes (ARG) among the microbial community and in-situ bacterial sulfonamide degradation, were studied in mesocosms experiments using water and cobble biofilms from upstream (pristine waters) and downstream (polluted waters) from the Llobregat river, NE Iberian Peninsula. Mesocosms were prepared at two different concentrations (5000 ng/L and 1000 ng/L) of sulfonamides antibiotics (sulfamethazine and sulfamethoxazole). Concentrations of ARG, nutrients, sulfonamides and their degradation products were measured during the time course of the experiments. Sulfonamides were efficiently degraded by the biofilms during the first four weeks of the experiment. The abundance of ARG in biofilms sharply decreased after addition of high concentrations of sulfonamides, but this was not observed in the mesocosms treated with low concentrations of sulfonamides. Sulfonamide degradation was faster in polluted waters and at high concentrations of sulfonamide (and lower ARG abundances), suggesting that both degradation and ARG are two complementary resistance strategies employed by the microbial community. This study shows that microbial degradation of antibiotics is an efficient resistance mechanism coupled with the presence of ARG, and suggests that in situ degradation prevails at high concentrations of antibiotics whereas physiological adaptation by ARG spread would be more important under relatively lower concentrations of antibiotics.

Occurrence and attenuation of pharmaceuticals and their transformation products in rivers impacted by sewage treatment plants

Pharmaceuticals and transformation products were attenuated in the wastewater-impacted river, and environment conditions influenced the attenuation process.

Effects of halide ions on photodegradation of sulfonamide antibiotics: Formation of halogenated intermediates

The occurrence of sulfonamide antibiotics (SAs) in estuarine waters urges insights into their environmental fate for ecological risk assessment. Although many studies focused on the photochemical behavior of SAs, yet the effects of halide ions relevant to estuarine and marine environments on their photodegradation have been poorly understood. Here, we investigated the effects of halide ions on the photodegradation of SAs with sulfapyridine, sulfamethazine, and sulfamethoxazole as representative compounds. Results showed that halide ions did not significantly impact the photodegradation of sulfapyridine and sulfamethoxazole, while they significantly promoted the photodegradation of sulfamethazine. Further experiments found that ionic strength applied with NaClO4 significantly enhanced the photodegradation of the SAs, which was attributed to the decreased quenching rate constant of the triplet-excited SAs ((3)SA(∗)). Compared with ionic strength, specific Cl(-) effects retarded the photodegradation of the SAs. Our study found that triplet-excited sulfamethazine can oxidize halide ions to produce halogen radicals, subsequently leading to the halogenation of sulfamethazine, which was confirmed by the identification of both chlorinated and brominated intermediates. These results indicate that halide ions play an important role in the photochemical behavior of some SAs in estuarine waters and seawater. The occurrence of halogenation for certain organic pollutants can be predicted by comparing the oxidation potentials of triplet-excited contaminants with those of halogen radicals. Our findings are helpful in understanding the photochemical behavior and assessing the ecological risks of SAs and other organic pollutants in estuarine and marine environment.

Fate of Pharmaceuticals and Their Transformation Products in Four Small European Rivers Receiving Treated Wastewater

A considerable knowledge gap exists with respect to the fate and environmental relevance of transformation products (TPs) of polar organic micropollutants in surface water. To narrow this gap we investigated the fate of 20 parent compounds (PCs) and 11 characteristic TPs in four wastewater-impacted rivers. Samples were obtained from time-integrated active sampling as well as passive sampling using polar organic chemical integrative samplers (POCIS). Seventeen out of the 20 PCs were detected in at least one of the rivers. All the PCs except acesulfame, carbamazepine, and fluconazole were attenuated along the studied river stretches, with the largest decrease found in the smallest river which had an intense surface water-pore water exchange. Seven TPs were detected, all of which were already present directly downstream of the WWTP outfall, suggesting that the WWTPs were a major source of TPs to the recipients. For anionic compounds, attenuation was the highest in the two rivers with the lowest discharge, while the pattern was not as clear for neutral or cationic compounds. For most compounds the results obtained from active sampling were not significantly different from those using POCIS, demonstrating that the cost and labor efficient POCIS is suitable to determine the attenuation of organic micropollutants in rivers.