Photodegradation of sulfamethoxazole in environmental samples: The role of pH, organic matter and salinity

Environmental and toxicological aspects of sulfamethoxazole photodegradation in the presence of oxidizing agents

Sulfamethoxazole (SMX) is a popular active substance, which is extensively applied to treat bacterial infections in humans and animals. Due to its widespread use, SMX enters the natural environment, where it can undergo degradation. Similarly to other emerging contaminants, SMX photodegradation and the use of oxidants in wastewater treatment processes can lead to the formation of potentially adverse transformation products for ecosystems. This study investigated the efficiency of SMX photodegradation in the presence of oxidizing agents (H2O2 and Fenton reagent). The potential environmental consequences of degradation product formation were analyzed based on experimental toxicity characterization. Standardized tests employing diverse organisms were utilized: Alivibrio fischeri (Microtox®), Daphnia magna (Daphtoxkit F®), and Lemna minor (Lemna sp. GIT). The potential environmental impact of the products identified in the reaction mixtures was evaluated using parameters describing aqueous solubility, hydrophobicity, toxicity, bioconcentration, persistence, and mobility. The analysis revealed that photodegradation produces transformation products with higher toxicity than SMX, as confirmed by in vitro tests of the reaction mixtures. Most of the detected compounds were found to have low mobility potential. The formation rates of key environmentally relevant transformation products, such as 1,4-benzoquinone, aniline, and phenol, were also discussed. The changes in total organic carbon (TOC) affected by photodegradation under the influence of the considered oxidizing agents were characterized.

From bacteria to fish: ecotoxicological insights into sulfamethoxazole and trimethoprim

Sulfamethoxazole (SMX) and trimethoprim (TRIM) are two of the most used antibiotics in the last 50 years, to prevent and treat bacterial infections; however, the available literature about toxicity to non-target organisms is quite discrepant and incomplete. This study aims to assess the SMX and TRIM ecotoxicological effects in standard species: Aliivibrio fischeri (bioluminescence inhibition), Escherichia coli ATCC 25922 (growth inhibition), Lemna minor (growth inhibition and biochemical biomarkers), Daphnia magna (immobilization/mortality, life history traits, and biochemical biomarkers), and Danio rerio (survival, hatching, abnormalities, and biochemical biomarkers). The species tested showed different acute sensitivities to SMX (A. fischeri < D. magna < E. coli < L. minor) and TRIM (L. minor < A. fischeri < D. magna < E. coli). Overall, TRIM reveals less toxicity than SMX, except for E. coli (Ecotoxicological approach based on Antimicrobial Susceptibility Testing - EcoAST procedure). Both antibiotics affect individually (e.g., growth and survival) and sub-individually (e.g., antioxidant defenses) L. minor, D. magna, and D. rerio. This study allowed us to generate relevant data and fill gaps in the literature regarding the effects of SMX and TRIM in aquatic organisms. The here-obtained results can be used to (i) complete and re-evaluate the Safety Data Sheet to improve the assessment of environmental safety and management of national and international entities; (ii) clarify the environmental risks of these antibiotics in aquatic ecosystems reinforcing the inclusion in the 4th Watch List of priority substances to be monitored in whole inland waters by the Water Framework Directive; and (iii) combat the development of antimicrobial resistance, as well as supporting the definition of environmental measurements in the context of European One Health Action Plan. However, it is essential to continue studying these antibiotics to better understand their toxicity at ecologically relevant concentrations and their long-term effects under different climatic change scenarios.

Ranitidine degradation in layered double hydroxide activated peroxymonosulfate system: impact of transition metal composition and reaction mechanisms

Ranitidine, a competitive inhibitor of histamine H2 receptors, has been identified as an emerging micropollutant in water and wastewater, raising concerns about its potential impact on the environment and human health. This study aims to address this issue by developing an effective removal strategy using two types of layered double hydroxide (LDH) catalysts (i.e., CoFeLDH and CoCuLDH). Characterization results show that CoFeLDH catalyst has superior catalytic properties due to its stronger chemical bond compared to CoCuLDH. The degradation experiment shows that 100% degradation of ranitidine could be achieved within 20 min using 25 mg/L of CoFeLDH and 20 mg/L of peroxymonosulfate (PMS). On the other hand, CoCuLDH was less effective, achieving only 70% degradation after 60 min at a similar dosage. The degradation rate constant of CoFeLDH was 10 times higher than the rate constant of CoCuLDH at different pH range. Positive zeta potential of CoFeLDH made it superior over CoCuLDH regarding catalytic oxidation of PMS. The catalytic degradation mechanism shows that sulfate radicals played a more dominant role than hydroxyl radicals in the case of LDH catalysts. Also, CoFeLDH demonstrated a stronger radical pathway than CoCuLDH. XPS analysis of CoFeLDH revealed the cation percentages at different phases and proved the claim of being reusable even after 8 cycles. Overall, the findings suggest that CoFeLDH/PMS system proves to be a suitable choice for attaining high degradation efficiency and good stability in the remediation of ranitidine in wastewater.

Aquatic photolysis of high-risk fluorinated liquid crystal monomers: Kinetics, toxicity evaluation, and mechanisms

Despite the frequent detection of fluorinated liquid-crystal monomers (FLCMs) in the environment, the level of understanding of their fate, toxicity, and transformation remains insufficient. Herein, we investigated the degradation kinetics and mechanism of an FLCM (4-cyano-3-fluorophenyl 4-ethylbenzoate, CEB-F) under ultraviolet (UV) photolysis in aquatic environment. Our findings demonstrated that the UV photolysis of CEB-F followed first-order kinetics. Photodegradation products were identified using liquid chromatography with mass spectrometry, and detailed reaction pathways were proposed. It is postulated that through the attack of reactive oxygen species, hydroxylation, and CO/C-F bond cleavage, CEB-F gradually degraded into small molecular compounds, releasing fluorine ions. Acute immobilization tests with Daphnia magna (D. magna) revealed significant acute toxicity of CEB-F, with LC50 values ranging from 1.023 to 0.0536 μM over 24 to 96 h, emphasizing the potential high risk of FLCMs in aquatic ecosystems if inadvertently discharged. Interestingly, we found that the toxicity of CEB-F photolysis reaction solutions was effectively reduced. Through catalase and acetylcholinesterase activities analysis along with molecular docking simulation, we proposed differences in the underlying toxicity mechanisms of CEB-F and its photolysis products to D. magna. These findings highlight the potential harmful effects of FLCMs on aquatic ecosystems and enrich our understanding of the photolysis behavior of FLCMs.

Assessing ecological responses to exposure to the antibiotic sulfamethoxazole in freshwater mesocosms

Antibiotics are a contaminant class of worldwide concern as they are frequently detected in aquatic ecosystems. To better understand the impacts of antibiotics on aquatic ecosystems, we conducted an outdoor mesocosm experiment in which aquatic communities were exposed to different concentrations of the antibiotic sulfamethoxazole (0, 0.15, 1.5, 15 and 150 μg/L). These concentrations include mean (0.15 μg/L) and maximum detected concentrations (15 and 150 μg/L) in aquatic ecosystems worldwide. Sulfamethoxazole was applied once a week for eight consecutive weeks to 1530 L outdoor mesocosms in the Netherlands, followed by an eight-week recovery period. We evaluated phytoplankton-, bacterial- and invertebrate responses during and after sulfamethoxazole exposure and assessed impacts on organic matter decomposition. Contrary to our expectations, consistent treatment-related effects on algal and bacterial communities could not be demonstrated. In addition, sulfamethoxazole did not significantly affect zooplankton and macroinvertebrate communities. However, some effects on specific taxa were observed, with an increase in Mesostoma flatworm abundance (NOEC of <0.15 μg/L). In addition, eDNA analyses indicated negative impacts on the insects Odonata at a sulfamethoxazole concentration of 15 μg/L. Overall, environmentally relevant sulfamethoxazole concentration did not result in direct or indirect impairment of entire aquatic communities and ecological processes in our mesocosms. However, several specific macroinvertebrate taxa demonstrated significant (in)direct effects from sulfamethoxazole. Comparison of the results with the literature showed inconsistent results between studies using comparable, environmentally relevant, concentrations. Therefore, our study highlights the importance of testing the ecological impacts of pharmaceuticals (such as sulfamethoxazole) across multiple trophic levels spanning multiple aquatic communities, to fully understand its potential ecological threats.

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.

Key constructed wetland design features for maximized micropollutant removal from treated municipal wastewater: A literature study based on 16 indicator micropollutants

The removal of micropollutants from wastewater by constructed wetlands (CWs) has been extensively studied and reviewed over the past years. However, most studies do not specifically focus on the removal of micropollutants from the effluent of conventional wastewater treatment plants (WWTP) that still contains micropollutants, but on the removal of micropollutants from raw wastewater. Raw wastewater has a significantly different composition compared to WWTP effluent, which positively or negatively affects micropollutant removal mechanisms. To determine the optimal CW design for post-treatment of WWTP effluent to achieve additional micropollutant removal, this review analyzes the removal of 16 Dutch indicator micropollutants for post-treatment technology evaluation from WWTP effluent by different types of CWs. It was concluded that CW systems with organic enhanced adsorption substrates reach the highest micropollutant removal efficiency as a result of adsorption, but that the longevity of the enhanced adsorption effect is not known in the systems studied until now. Aerobic biodegradation and photodegradation are other relevant removal mechanisms for the studied micropollutants. However, a current knowledge gap is whether active aeration to stimulate the aerobic micropollutant biodegradation results in an increased micropollutant removal from WWTP effluent. Further knowledge gaps that impede the wider application of CW systems for micropollutant removal from WWTP effluent and allow a fair comparison with other post-treatment technologies for enhanced micropollutant removal, such as ozonation and activated carbon adsorption, relate to i) saturation of enhanced adsorption substrate; ii) the analysis of transformation products and biological effects; iii) insights in the relationship between microbial community composition and micropollutant biodegradation; iv) plant uptake and in-plant degradation of micropollutants; v) establishing design rules for appropriate hydraulic loading rates and/or hydraulic retention times for CWs dedicated to micropollutant removal from WWTP effluent; and vi) the energy- and carbon footprint of different CW systems. This review finishes with detailed suggestions for future research directions that provide answers to these knowledge gaps.

Combining environmental, health, and safety features with a conductor like Screening Model for selecting green solvents for antibiotic analyses

Extraction and chromatographic techniques for analyzing pharmaceutically active compounds necessitate large quantities of organic solvents, resulting in a high volume of hazardous waste. The concept of green solvents focuses on protecting the environment by reducing or even eliminating the use of toxic solvents. The main objective of this critical review article is to build a framework for choosing green solvents for antibiotic analyses. The article briefly discusses the chemical properties of ciprofloxacin, sulfamethoxazole, tetracycline, and trimethoprim, and the current state of methodologies for their analyses in water and wastewater. It evaluates the greenness of solvents used for antibiotic analyses and includes insights on the comparison between conventional and green solvents for the analyses. An economic and environmental health and safety analysis combined with a Conductor-like Screening Model for Real Solvent (COSMO-RS) molecular simulation technique for predicting extraction efficiency was used in the evaluation. Methyl acetate and propylene carbonate tied for the greenest solvents from an environmental and economic perspective, whereas the COSMO-RS approach suggests dimethyl sulfoxide (DMSO) as the most suitable candidate. Although DMSO ranked third environmentally and economically, after methyl acetate and propylene carbonate, it would be an ideal replacement of hazardous solvents if it could be manufactured at a lower cost. DMSO showed the highest extraction capacity, as it can interact with antibiotics through hydrophobic interaction and hydrogen bonding. This article can be used as a green solvent selection guide for developing sustainable processes for antibiotic analyses.

The distinct resistance mechanisms of cyanobacteria and green algae to sulfamethoxazole and its implications for environmental risk assessment

Cyanobacteria and green algae are the OECD recommended test organisms for environmental toxicity assessments of chemicals. Whether the differences in these two species' responses to the identical chemical affect the assessment outcomes is a question worth investigating. Firstly, we investigated the distinct resistance mechanisms of Synechococcus sp. (cyanobacteria) and R. subcapitata (green algae) to sulfamethoxazole (SMX). The antioxidant system analysis demonstrated that R. subcapitata mainly relies on enhancing the activity of first line defense antioxidants, including superoxide dismutase (SOD), catalase (CAT) and glutathione peroxidase (GPx), which is the most powerful and efficient response to get rid of ROS, whereas Synechococcus sp. depends upon increasing the activity of glutathione-S-transferase (GST) and GPx to resist oxidative stress. Besides, a total 7 transformation products (TPs) of SMX were identified in R. subcapitata culture medium. The analysis of conjectural transformation pathways and the predicted toxicity indicates that R. subcapitata could relieve SMX toxicity by degrading it to low eco-toxic TPs. Additionally, we summarized numerous exposure data and assessed the environmental risk of various antibiotics, revealing an inconsistent result for the same type of antibiotic by using cyanobacteria and green algae, which is most likely due to the different resistance mechanisms. In the future, modified indicators or comprehensive assessment methods should be considered to improve the rationality of environmental toxicity assessments.

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

Critical role of tetracycline's self-promotion effects in its visible-light driven photocatalytic degradation over ZnO nanorods

Zinc oxide (ZnO), which is widely applied for ultraviolet-light driven photocatalysis, has no activity in visible-light photocatalytic process due to its large band gap of ∼3.2 eV. Herein, however, we demonstrated the multiple self-promotion effects of tetracycline as band adjuster, photo-sensitizer, and charge transfer promoter for ZnO nanorods, realizing its visible-light photocatalytic degradation with an excellent removal efficiency up to 91.1% within only 2 h. Besides, the influence of complex realistic factors on this unique process was evaluated together with tests with realistic water matrices. Furthermore, the active species and degradation products were identified. Both acute and developmental toxicities were found to be reduced as the degradation proceeds. These results pave the path for the brand-new self-driven visible-light photocatalysis.

Global review of macrolide antibiotics in the aquatic environment: Sources, occurrence, fate, ecotoxicity, and risk assessment

The extensive use of macrolide antibiotics (MCLs) has led to their frequent detection in aquatic environments, affecting water quality and ecological health. In this study, the sources, global distribution, environmental fate, ecotoxicity and global risk assessment of MCLs were analyzed based on recently published literature. The results revealed that there are eight main sources of MCLs in the water environment. These pollution sources resulted in MCL detection at average or median concentrations of up to 3847 ng/L, and the most polluted water bodies were the receiving waters of wastewater treatment plants (WWTPs) and densely inhabited areas. Considering the environmental fate, adsorption, indirect photodegradation, and bioremoval may be the main attenuation mechanisms in natural water environments. N-demethylation, O-demethylation, sugar and side chain loss from MCL molecules were the main pathways of MCLs photodegradation. Demethylation, phosphorylation, N-oxidation, lactone ring hydrolysis, and sugar loss were the main biodegradation pathways. The median effective concentration values of MCLs for microalgae, crustaceans, fish, and invertebrates were 0.21, 39.30, 106.42, and 28.00 mg/L, respectively. MCLs induced the generation of reactive oxygen species, that caused oxidative stress to biomolecules, and affected gene expression related to photosynthesis, energy metabolism, DNA replication, and repair. Moreover, over 50% of the reported water bodies represented a medium to high risk to microalgae. Further studies on the development of tertiary treatment technologies for antibiotic removal in WWTPs, the combined ecotoxicity of antibiotic mixtures at environmental concentration levels, and the development of accurate ecological risk assessment models should be encouraged.

SARS-CoV-2 pharmaceutical drugs: a critical review on the environmental impacts, chemical characteristics, and behavior of advanced oxidation processes in water

This review summarizes research data on the pharmaceutical drugs used to treat the novel SARS-CoV-2 virus, their characteristics, environmental impacts, and the advanced oxidation processes (AOP) applied to remove them. A literature survey was conducted using the electronic databases Science Direct, Scopus, Taylor & Francis, Google Scholar, PubMed, and Springer. This complete research includes and discusses relevant studies that involve the introduction, pharmaceutical drugs used in the SARS-CoV-2 pandemic: chemical characteristics and environmental impact, advanced oxidation process (AOP), future trends and discussion, and conclusions. The results show a full approach in the versatility of AOPs as a promising solution to minimize the environmental impact associated with these compounds by the fact that they offer different ways for hydroxyl radical production. Moreover, this article focuses on introducing the fundamentals of each AOP, the main parameters involved, and the concomitance with other sources and modifications over the years. Photocatalysis, sonochemical technologies, electro-oxidation, photolysis, Fenton reaction, ozone, and sulfate radical AOP have been used to mineralize SARS-CoV-2 pharmaceutical compounds, and the efficiencies are greater than 65%. According to the results, photocatalysis is the main technology currently applied to remove these pharmaceuticals. This process has garnered attention because solar energy can be directly utilized; however, low photocatalytic efficiencies and high costs in large-scale practical applications limit its use. Furthermore, pharmaceuticals in the environment are diverse and complex. Finally, the review also provides ideas for further research needs and major concerns.

Enantioselective hydrolysis and photolysis of mandipropamid in different aquatic environments - evaluation of influencing factors

The hydrolysis and photolysis of the chiral fungicide mandipropamid were investigated, and the potential enantioselectivity of mandipropamid in solutions was further assessed. The aqueous solutions were filtered and directly injected into the liquid chromatography with tandem mass spectrometry. In the hydrolysis experiments, mandipropamid enantiomers hydrolyzed slowly in aquatic solutions with half-lives > 200 days; nevertheless, rise of the pH and incubation temperature could increase the hydrolysis rates more than 1.1 times (half-lives decreased from 495.1 to 216.6 days). Compared with the hydrolysis results, photolysis was found to be the main degradation pathway for mandipropamid in different solutions (half-lives < 14 h, except in pH = 5.05 buffer solution). Organic solvents were able to accelerate the photolysis of mandipropamid, but acidic solutions and the addition of flavonoids or inorganic salts significantly inhibited the photolysis of mandipropamid. During the hydrolysis and photolysis processes, the configuration of mandipropamid enantiomers was stable and five possible transformation products were identified by high resolution mass spectrometry. Due to the enantiomeric fraction values > 0.5, the hydrolysis and photolysis of mandipropamid were enantioselective, and S-( +)-mandipropamid preferentially disspated in certain aqueous solutions. The systematic evaluation of the hydrolysis and photolysis of mandipropamid enantiomers may provide more accurate data for better assessment of environmental and ecological risks in aquatic ecosystems.

Straw return in paddy field alters photodegradation of organic contaminants by changing the quantity rather than the quality of water-soluble soil organic matter

Straw return, an important agricultural management practice, is worldwide adopted to enhance soil carbon sequestration and soil fertility. Although water-soluble soil organic matter (WSOM) in paddy field is known to affect the photodegradation of organic contaminants, how straw return regulates the photosensitization of WSOM by changing its properties remain unclear. Here, we determined the temporal variations in the content, chemical characteristics, and photosensitizing ability of WSOM after wheat straw return in a wheat-rice rotation system using optical spectroscopy and steady-state photodegradation tests. After straw return, the WSOM content first increased to a maximum and then gradually decreased to pre-return level at day 90. Nevertheless, the relative abundance of humic-like components in WSOM was not shifted by straw return, and protein-like component in WSOM just showed a slight decrease at day 45. All the WSOM samples inhibited sulfamethoxazole (SMX) photodegradation by light filtering, reactive species quenching and other mechanisms, while promoted diuron (DIU) degradation via reacting with •OH, ¹O₂ and excited triplet WSOM. The photodegradation of SMX and DIU was little affected by straw return changing WSOM composition and photochemical activity. However, straw return could decelerate SMX and DIU photodegradation by elevating WSOM content in a relatively short-term. This study emphasizes that straw return may reduce the photodegradation of organic contaminants by increasing WSOM concentration instead of altering WSOM chemical characteristics.

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.

Intermediates formed during natural attenuation of C9 aromatics under simulated marine conditions: Identification, transformation pathway, and toxicity to microalgae

C9 aromatics - benzene hydrocarbon containing nine carbon atoms among - leakage accident has caused serious damage to the marine ecology near Quangang District, Fujian Province, China. The ecological restoration of the accident sea area is basically realized through natural attenuation. To determine whether the natural attenuation of C9 aromatics in the marine environment will generate highly toxic intermediates, and thus cause more serious harm to marine ecology, the intermediates of C9 aromatics (n-propylbenzene, isopropylbenzene, 2-ethyltoluene, 3-ethyltoluene, 4-ethyltoluene, 1,2,3-trimethylbenzene, 1,2,4-trimethylbenzene, 1,3,5-trimethylbenzene, and indene) in the process of natural attenuation were studied under the marine conditions simulated by a microcosm. The acute toxic effects of 12 intermediates with longer residual time on Phaeodactylum tricornutum were also ascertained. Twenty natural attenuation intermediates of C9 aromatics were identified. These products primarily include the derivatives of phenols, aromatic alcohols, aromatic aldehydes, aromatic ketones, and aromatic acids, as well as an aromatic lactone compound. No intermediates of 1,3,5-trimethylbenzene and indene during the attenuation process were determined. The indirect photooxidation initiated by hydroxyl radical might play an essential role in the formation of intermediates of C9 aromatic. Based on the 96-h EC₅₀ values for P. tricornutum, the toxicity of the 12 intermediates, in descending order, was: 4-ethylphenol, 2-methylacetophenone, 2,3-dimethylbenzyl alcohol, 4-methylacetophenone, 3-methylacetophenone, 1-phenyl-1-propanol, 1-(2-methylphenyl) ethanol, 2-phenyl-2-propanol, 3,4-dimethylbenzoic acid, 2,4-dimethylbenzoic acid, 2,5-dimethylbenzoic acid, then 4-tolylacetic acid. The 96-h EC₅₀ values of the intermediates of C9 aromatics to P. tricornutum ranged from 8.4 to 199.1 mg/L, which were lower than that of their corresponding parent compound. The findings provided essential fundamental insights for the assessment of marine environmental risk of C9 aromatics leakage accidents, and subsequent emergency disposal countermeasures.

Adsorption behavior and mechanism of sulfonamides on controllably synthesized covalent organic frameworks

In this work, four kinds of covalent organic framework (COF) materials (TpPa-1, TpBD, TpDT, and TFBBD) with different pore sizes or functional groups were synthesized by an ultrasonic method for the adsorption of five sulfonamides. Optimization experiments regarding the adsorption time, vortex speed, and pH were carried out to improve adsorption efficiency. In addition, kinetic and thermodynamic experiments were conducted to explore the adsorption mechanism of the sulfonamides on the different COFs. The adsorption processes of the five sulfonamides on the four COFs fit the pseudo-second-order kinetic model and Langmuir adsorption isotherm model. Additionally, pore filling, hydrogen bond interactions, and electrostatic attraction were found to be the main adsorption mechanisms.

Enhanced removal efficiency of sulfamethoxazole by acclimated microalgae: Tolerant mechanism, and transformation products and pathways

This study utilized sulfamethoxazole (SMX) acclimatization to enhance the tolerance and biodegradation capacity of Chlorella vulgaris. Compared to wild C. vulgaris, the growth inhibition and oxidative damage induced by SMX evidently decreased in acclimated C. vulgaris, and meanwhile photosynthetic and antioxidant activities were significantly promoted. The physiological analyses with the aid of principal component analysis revealed the increase of catalase and glutathione reductase activities was the critical tolerant mechanism of acclimated C. vulgaris. As the consequence, the acclimated C. vulgaris exhibited enhanced efficiency and (pseudo-first-order) kinetic rate for removal of SMX. The distribution analysis of residual SMX demonstrated the biodegradation was the major removal mechanism of SMX by C. vulgaris, while bioadsorption and bioaccumulation made pimping contributions. During the degradation process of SMX, nine transformation products (TPs) were identified. Based on the identified TPs, a possible transformation pathway was proposed.

The environmental distribution and removal of emerging pollutants, highlighting the importance of using microbes as a potential degrader: A review

Emerging pollutants (EPs) create a worldwide concern owing to their low concentration and severe toxicity to the receptors. The prominent emerging pollutants categories as pharmaceutical and personal care product, plasticizer, surfactants, and persistent organic pollutants. Typically, EPs are widely disseminated in the aquatic ecosystem and capable of perturbing the physiology of water bodies as well as humans. The primary sources of EPs in the environment include anthropogenic release, atmospheric deposition, untreated or substandard treated wastewater, and extreme weather events. Intensive research has been done covering the environmental distribution, ecological disturbance, fate, and removal of EPs in the past decades. However, a systematic review on the distribution of EPs in the engineered and natural aquatic environment and the degradation of different EPs by using anaerobic sludge, aerobic bacteria, and isolated strains are limited. This review article aims to highlight the importance, application, and future perceptions of using different microbes to degrade EPs. Overall, this review article illustrates the superiority of using non-cultivable and cultivable microbes to degrade the EPs as an eco-friendly approach. Practically, the outcomes of this review paper will build up the knowledge base solutions to remove EPs from the wastewater.

Process enhancing strategies for the reduction of Cr(VI) to Cr(III) via photocatalytic pathway

This discourse aimed at providing insight into the strategies that can be adopted to boost the process of photoreduction of Cr(VI) to Cr(III). Cr(VI) is amongst the highly detestable pollutants; thus, its removal or reduction to an innocuous and more tolerable Cr(III) has been the focus. The high promise of photocatalysis hinged on the sustainability, low cost, simplicity, and zero sludge generation. Consequently, the present dissertation provided a comprehensive review of the process enhancement procedures that have been reported for the photoreduction of Cr(VI) to Cr(III). Premised on the findings from experimental studies on Cr(VI) reductions, the factors that enhanced the process were identified, dilated, and interrogated. While the salient reaction conditions for the process optimization include the degree of ionization of reacting medium, available photogenerated electrons, reactor ambience, type of semiconductors, surface area of semiconductor, hole scavengers, quantum efficiency, and competing reactions, the relevant process variables are photocatalyst dosage, initial Cr(VI) concentration, interfering ion, and organic load. In addition, the practicability of photoreduction of Cr(VI) to Cr(III) was explored according to the potential for photocatalyst recovery, reactivation, and reuse reaction conditions and the process variables.

Photo-mediated and advanced oxidative processes applied for the treatment of effluents with drugs used for the treatment of early COVID-19: Review

The COVID-19 pandemic is proving to be one of the most challenging health and social crises ever faced by humanity. Several drugs have been proposed as potential antiviral agents for the treatment of COVID-19 since the beginning of the health crisis. Among them are chloroquine (CQ), hydroxychloroquine (HCQ), ivermectin (IVM), and the combination of QC or HCQ and azithromycin (AZI). The use of these and several other drugs has grown sharply, even if there is proof of ineffectiveness in the early treatment or mild cases of COVID-19. Thus, there is great concern about the potential environmental impacts of the effluents released with the presence of these drugs. Therefore, this work aimed to carry out a literature review on wastewater treatment processes, focusing on removing these substances through advanced oxidation process. As the conventional effluent treatment processes do not have high efficiency for removal, it was concentrated in the literature that had as scope advanced and photo-mediated techniques to remove CQ, HCQ, IVM, and AZI. It is expected, with this work, to highlight the importance of conducting research that contributes to the control of pollution and contamination.

The adsorption-desorption characteristics and degradation kinetics of ceftiofur in different agricultural soils

Cephalosporins are one of the most widely used antibiotics. When cephalosporins are discharged into the environment, they not only induce the production of antibiotic resistant genes (ARGs) and antibiotic resistant bacteria (ARBs) but also cause toxic effects on animals and plants. Due to their complicated environmental behavior and lack of relevant data, the environmental behavior remains unclear. In this study, the adsorption-desorption and degradation characteristics of the third-generation cephalosporin drug ceftiofur (CEF) were investigated in three agricultural soils (sandy loam, loam and clay). According to the relevant parameters of the Freundlich adsorption isotherm (the K_f range was 57.63-122.44 μg^1-1/n L^1/n kg^-1), CEF was adsorbed moderately in the soils and had the potential to migrate into groundwater. CEF exhibited low persistence in the soils and faster degradation than other antibiotics, such as tetracyclines and fluoroquinolones. The degradation half-lives (DT50) of CEF in soils ranged from 0.76 days to 4.31 days. Adding feces, increasing the water content, providing light and increasing the temperature significantly accelerated the degradation of CEF in soils. The DT50 values of CEF in soils were significantly prolonged when the soils were sterilized, indicating that both physical degradation and biodegradation played important roles in the degradation of CEF in soils. The DT50 values of CEF in soils were significantly prolonged at high concentrations, indicating that the degradability of CEF in soils was affected by the initial concentration. No significant differences were observed in the DT50 values for the different soil types (p > 0.05). This study provides useful information about the environmental behavior of CEF and improves the environmental risk assessment of CEF.

Sulfamethoxazole induced systematic and tissue-specific antioxidant defense in marine mussels (Mytilus galloprovincialis): Implication of antibiotic's ecotoxicity

Sulfamethoxazole (SMX), recognized as emerging pollutant, has been frequently detected in aquatic environment. However, effects induced by SMX and the underneath mechanism on non-target aquatic organisms, marine mussels (Mytilus galloprovincialis), are still largely unknown. In present study, marine mussels were exposed to SMX (nominal concentrations 0.5, 50 and 500 μg/L) for 6 days, followed by 6 days depuration and responses of antioxidant defenses, e.g. superoxide dismutase (SOD), catalase (CAT) and glutathione-S-transferase (GST), etc., at transcriptional, translational and functional levels were evaluated in two vital tissues, gills and digestive glands. Results showed SMX can be accumulated in mussels while the bio-accumulative ability was low under the experimental condition. A systemic but not completely synchronous antioxidant defense at different levels upon SMX exposure. The transcriptional alteration was more sensitive and had the potential to be used as early warning of SMX induced ecotoxicity. Complementary function of antioxidant enzymes with specific alteration of metabolism related gene (gst) suggested that further researches should focused on SMX metabolism and SMX induced effects simultaneously. Significant tissue-specific antioxidant responses were discovered and gills showed earlier and quicker reacting ability than digestive glands, which was closely related to the functional diversity and different thresholds of xenobiotics allowance.

Antibiotics in Aquaculture Wastewater: Is It Feasible to Use a Photodegradation-Based Treatment for Their Removal?

Aquacultures are a sector facing a huge development: farmers usually applying antibiotics to treat and/or prevent diseases. Consequently, effluents from aquaculture represent a source of antibiotics for receiving waters, where they pose a potential threat due to antimicrobial resistance (AMR) induction. This has recently become a major concern and it is expectable that regulations on antibiotics’ discharge will be established in the near future. Therefore, it is urgent to develop treatments for their removal from wastewater. Among the different possibilities, photodegradation under solar radiation may be a sustainable option. Thus, this review aims at providing a survey on photolysis and photocatalysis in view of their application for the degradation of antibiotics from aquaculture wastewater. Experimental facts, factors affecting antibiotics’ removal and employed photocatalysts were hereby addressed. Moreover, gaps in this research area, as well as future challenges, were identified.

Effects of natural colloidal particles derived from a shallow lake on the photodegradation of ofloxacin and ciprofloxacin

Natural colloidal particles (NCPs), which are ubiquitous and abundant in surface waters, may play a crucial role in the sunlight-driven transformation of organic contaminants. This research focused on the effects of NCPs on the photodegradation of two fluoroquinolone antibiotics (FQs), ofloxacin (OFL) and ciprofloxacin (CIP), and assessed the photosensitivity of colloidal organic matter (COM). Results showed that the photodegradation rate constants (k_obs) of OFL and CIP in NCP solutions ranged from 9.28 × 10^-2 h^-1 to 15.98 × 10^-2 h^-1 and 63.88 × 10^-2 h^-1 to 196.59 × 10^-2 h^-1, respectively, and NCPs can significantly accelerate the photodegradation rate of OFL and CIP. Indirect photodegradation (IP) accounted for >50% of the overall observed degradation in most treatments and was the dominant degradation pathway for the two FQs, especially for CIP, for which IP reached 82%-94%. In the IP process, the contributions of triplet states of colloidal organic matter (³COM^⁎) to the photolysis of OFL and CIP were close to 42% and 46%, respectively. The compositions of COM played an important role in the IP of the FQs, among which terrestrial sources of COM tended to have higher photoreactivity than biological sources. This study is essential in predicting the photochemical effect of FQs and also allows for a better understanding of the real environmental fate of antibiotic contaminants.

Layered double hydroxides and related hybrid materials for removal of pharmaceutical pollutants from water

Pharmaceuticals and their by-products are recalcitrant contaminants in water. Moreover, the high consumption of these drugs has many detrimental effects on body waters and ecosystems. In this timely review, the advances in molecular engineering of layered double hydroxides (LDH) that have been used for the removal of pharmaceutical pollutants are discussed. The approach starts from the strategies to obtain homogeneous synthesis of LDH that allow the doping and/or surface functionalization of different metals and oxides, producing heterojunction systems as well as composites with carbon and silica-based materials with high surface area. Adsorption is considered as a traditional removal of pharmaceutical pollutants, so the kinetic and mechanism of this phenomenon are analyzed based on pH, temperature, ionic strength, in order to obtain new insights for the formation of multifunctional LDH. Advanced oxidation methodologies, mainly heterogeneous photocatalysis and Fenton-like processes, stand out as the more efficient even to obtain the mineralization of the drugs. The LDH have the advantage of structural memory that favors regeneration processes. The reconstruction of calcined LDH can be used to improve drug removal, through a combination of adsorption capacity/catalytic activity. A meticulous analysis of the persistence, toxicity and bioaccumulation of the most common pharmaceuticals has allowed us to highlight the ability of the LDH to remove recalcitrant drugs at relatively low concentrations (ppm, ppb), in contrast to other mixed oxide nanostructures and homogeneous oxidation processes. In this sense, the mechanism of drug removal by LDH is discussed based on the importance of the use of composites, scavenger agents, Fenton and electro-Fenton processes, membranes, thin films and coatings, among others. In addition, the ecotoxicity of LDH is also reviewed to indicate that these layered structures can exhibit biocompatibility or high toxicity depending on the adsorbed drug and ions/metals that compose them. Undoubtedly, the LDH have a unique flexible structure with adsorption capacity and catalytic activity, facts that explain the important reasons for their extensive use in the environmental remediation of pharmaceutical pollutants from water.

Photochemical persistence of sulfa drugs in aqueous medium: kinetic study and mathematical simulations

This study aimed at investigating the photochemical behavior of sulfa drugs containing five and six-membered heterocyclic substituents (sulfamethoxazole (SMX) and sulfadiazine (SDZ), respectively), in an aqueous medium. Despite their importance, studies devoted to the use of photochemical models to predict the environmental phototransformation of pollutants in surface waters, by combining laboratory results and natural aquatic systems parameters, are still scarce in the scientific literature. In this work, the second-order reaction rate constants of SDZ and SMX with hydroxyl radicals (^●OH), singlet oxygen (¹O₂), and triplet excited states of chromophoric dissolved organic matter (³CDOM*) were experimentally determined at pH 7, using the competition kinetics approach. The results show that ^●OH and ³CDOM* are the key species involved in sulfonamide degradation, with anionic SMX, most prevalent at pH 6-9, being degraded much slower than the anionic form of SDZ. Moreover, SDZ and SMX photodegradation in natural water samples (spring-fed natural pond, public supply reservoir, and sea water) was significantly enhanced relative to depletion in pure water. Finally, from mathematical simulations of the sunlight-driven sulfonamide degradation, half-life times were predicted for these drugs varying from less than 2 to about 90 days, depending on the water depth, concentration of key species (DOC, HCO₃^-, NO₂^-, CO₃^2-) in natural aqueous systems, as well as on the particular heterocyclic substituent.

Multiple roles of dissolved organic matter released from decomposing rice straw at different times in organic pollutant photodegradation

Rice straw returning causes a considerable amount of dissolved organic matter (DOM) release into aquatic croplands in a relatively short-term. The presence of rice straw-derived DOM in cropland waters may alter the photochemical behaviors of organic pollutants. However, the photochemical activity and photosensitization role of the DOMs are poorly understood. Here, eight DOM samples were extracted from decomposing rice straw at different times in 49 days to explore their photosensitizing capacities toward diuron (DIU), 17β-estradiol (E2), and sulfamethoxazole (SMX). All of the DOMs were photosensitive and mainly composed of tryptophan-, tyrosine- and fulvic-like substances. Over the decomposition period, the amount of photochemically produced reactive intermediates (PPRIs) by the DOMs peaked on days 7 and 14. The evolution of the DOM photosensitizing capacity towards DIU and E2 was consistent with the variations of PPRIs, and HO· was confirmed as a critical factor. However, the influence of the DOMs on SMX photodegradation was opposite to that on DIU and E2. The positive role of the DOMs in SMX photodegradation was attributed to the tryptophan-like components. The results suggest that straw-derived DOM is an important photosensitizer and that its photosensitization towards organic pollutants is dependent on straw decomposing time and pollutant type.

Oxolinic acid in aquaculture waters: Can natural attenuation through photodegradation decrease its concentration?

Quinolones, such as oxolinic acid (OXA), are antimicrobials commonly used in aquaculture. Thus, its presence in the aquatic environment surrounding aquaculture facilities is quite easy to understand. When present in aquatic environment, pharmaceuticals may be subjected to several attenuation processes that can influence their persistence. Photodegradation, particularly for antibiotics, can have significant importance since these compounds may be resistant to microbial degradation. OXA photodegradation studies reported in literature are very scarce, especially using aquaculture waters, but are markedly important for an appropriate risk assessment. Results hereby presented showed a decrease on photodegradation rate constant from 0.70 ± 0.02 h^-1 in ultrapure water to 0.42 ± 0.01 h^-1 in freshwater. The decrease on photodegradation rate constant was even more pronounced when brackish water was used (0.172 ± 0.003 h^-1). In order to understand which factors contributed to the observed behaviour, environmental factors, such as natural organic matter and salinity, were studied. Results demonstrated that dissolved organic matter (DOM) may explain the decrease of OXA photodegradation observed in freshwater. However, a very sharp decrease of OXA photodegradation was observed in solutions containing NaCl and in synthetic sea salts, which explained the higher decrease observed in brackish water. Moreover, under solar radiation, the use of an ¹O₂ scavenger allowed us to verify a pronounced retardation of OXA decay, suggesting that ¹O₂ plays an important role in OXA photodegradation process.

Photodegradation of sulfadiazine in different aquatic environments - Evaluation of influencing factors

The presence of antibiotics, such as sulfadiazine (SDZ), in the aquatic environment contributes to the generation of antimicrobial resistance, which is a matter of great concern. Photolysis is known to be a major degradation pathway for SDZ in surface waters. Therefore, influencing factors affecting SDZ photodegradation in different aquatic environments were here evaluated in order to have a better knowledge about its persistence in the environment. Photodegradation of SDZ was found to be more efficient at higher pH (t_1/2 = 6.76 h, at pH = 7.3; t_1/2 = 12.2 h, at pH = 6.3), in the presence of humic substances (HS) (t_1/2 between 1.76 and 2.42 h), as well as in the presence of NaCl (t_1/2 = 1.00 h) or synthetic sea salts (t_1/2 = 0.78 h). Using ˙OH and ¹O₂ scavengers, it was possible to infer that direct photolysis was the main pathway for SDZ photodegradation in ultrapure water. Furthermore, results under N₂ purging confirmed that ¹O₂ was not relevant in the phototransformation of SDZ. Then, the referred observations were used for the interpretation of results obtained in environmental matrices, namely the final effluent of a sewage treatment plant (STPF), fresh and brackish water (t_1/2 between 2.3 and 3.48 h), in which SDZ photodegradation was found to be much faster than in ultrapure water (t_1/2 = 6.76 h).

Environmental concentrations of sulfamethoxazole increase crayfish Pacifastacus leniusculus susceptibility to White Spot Syndrome Virus

Antibiotics used for humans and livestock are emerging as pollutants in aquatic environments. However, little is known about their effect on aquatic organisms, especially in crustaceans. In the present study, the freshwater crayfish Pacifastacus leniusculus was exposed during 21 days to environmental concentrations of sulfamethoxazole (SMX) (100 ng/L and 1 μg/L). Subsequently, the crayfish susceptibility to infection was evaluated by using White Spot Syndrome Virus (WSSV) challenge, a well-known crustacean pathogen. The median survival time of the infected crayfish exposed to 100 ng/L SMX was one day, whereas the control and the group exposed to 1 μg/L SMX survived for two and three days, respectively. In order to elucidate the effect of SMX upon the crayfish immune response, new sets of crayfish were exposed to the same SMX treatments to evaluate mRNA levels of immune-related genes which are expressed and present in hemocytes and intestine, and to perform total and differential hemocyte counts. These results show a significant down-regulation of the antimicrobial peptide (AMP) Crustin 3 in hemocytes from the 100 ng/L SMX group, as well as a significant up-regulation of the AMP Crustin 1 in intestines from the 1 μg/L SMX group. Semigranular and total hemocyte cell number were observed to be significantly lower after exposure to 100 ng/L SMX in comparison with the control group. The present study demonstrates that environmentally relevant SMX concentrations in the water at 100 ng/L led to an increased WSSV susceptibility, that may have been caused by a reduction of circulating hemocytes. Nevertheless, SMX concentrations of 1 μg/L could marginally and for a few days have an immunostimulatory effect.

Effects of fertilization on the triafamone photodegradation in aqueous solution: Kinetic, identification of photoproducts and degradation pathway

Triafamone is a highly effective, low toxicity sulfonamide herbicide widely used for weeding paddy fields. The triafamone photodegradation in water environment must be explored for its ecological risk assessment. In this work, the effects of chemical fertilizer (urea, diammonium phosphate, potassium chloride, and potassium sulfate), urea metabolites (CO₃^2- and HCO₃^-), and organic fertilizers (unfermented organic fertilizer [UOF] and fermented organic fertilizer [FOF]) on the triafamone photodegradation in aqueous solution under simulated sunlight were evaluated. Results showed that the triafamone photodegradation rate was unaffected by urea. The half-life of triafamone decreased from 106.8 h to 68.4 h with increasing diammonium phosphate concentration. Potassium chloride, potassium sulfate, CO₃^2-, and HCO₃^- could accelerate the triafamone photodegradation at all concentrations, whereas the degradation rate of triafamone decreased when the concentration of potassium sulfate or CO₃^2- was 2000 mg/L. Triafamone photodegradation was promoted by 20-200 mg/L UOF and FOF but decreased to 236.6 and 142.3 h when the concentration reached 2000 mg/L. Twenty-three transformation products were isolated and identified from triafamone by using ultra-performance liquid chromatography with quadrupole time-of-flight mass spectrometry under simulated sunlight irradiation, and the kinetic evolution of these products was explored. Five possible degradation pathways were inferred, including the cleavage of C-N, C-C, and C-O bonds; CO bond hydrogenation; the cleavage of triazine ring; the cleavage of the sulfonamide bridge; hydroxylation; hydroxyl substitution; methylation; demethylation; amination; and rearrangement. In summary, these results are important for elucidating the environmental fate of triafamone in aquatic systems and further assessing environmental risks.

Sulfamethoxazole/Trimethoprim ratio as a new marker in raw wastewaters: A critical review

Global Trimethoprim (TMP) and Sulfamethoxazole (SMX) occurrences in raw wastewaters were systematically collected from the literature (n = 140 articles) in order to assess the relevance of using the SMX/TMP ratio as a marker of the main origin of wastewaters. These two antibiotics were selected due to their frequent use in association (i.e. co-trimoxazole) in a 5:1 ratio (SMX:TMP) for medication purposes, generating a unique opportunity to globally evaluate the validity of this ratio based on concentration values. Several parameters (e.g. sorption, biodegradation) may affect the theoretical SMX/TMP ratio. However, the collected data highlighted the good agreement between the theoretical ratio and the experimental one, especially in wastewater treatment plant influents and hospital effluents. Only livestock effluents displayed a very high SMX/TMP ratio, indicative of the very significant use of sulfonamide alone in this industry. Conversely, several countries displayed low SMX/TMP ratio values, highlighting local features in the human pharmacopoeia. This review provides new insights in order to develop an easy to handle and sound marker of wastewater origins (i.e. human/livestock), beyond atypical local customs.

Antibiotics induced alterations in cell density, photosynthesis, microcystin synthesis and proteomic expression of Microcystis aeruginosa during CuSO4 treatment

Antibiotic contaminants have the potential to interfere with the control of cyanobacterial bloom through generating hormesis in cyanobacteria at current contamination level of ng L^-1. This study investigated the influence of a mixture of four frequently detected antibiotics, amoxicillin, ciprofloxacin, sulfamethoxazole and tetracycline, during the treatment of Microcystis aeruginosa by copper sulfate (CuSO₄) algaecide. CuSO₄ significantly (p <  0.05) inhibited cell density, growth rate, F_v/F_m value, chlorophyll a content and microcystin production ability of M. aeruginosa in a dose-dependent manner at application doses of 0.01-0.05 mg L^-1. Besides, CuSO₄ inhibited oxidation-reduction process, photosynthesis and biosynthesis in M. aeruginosa at the proteomic level. Preventative application of CuSO₄ to a low density (4 × 10⁵ cells mL^-1) of M. aeruginosa effectively prevented the formation of bloom at low CuSO₄ doses, which is a possible route for eliminating the negative effects of CuSO₄ algaecide in aquatic environments. The presence of mixed antibiotics alleviated the toxicity of CuSO₄ in M. aeruginosa, through the downregulation of cation transport proteins and the upregulation of proteins related with chlorophyll a synthesis, photosynthesis, gene expression and oxidation-reduction. Mixed antibiotics also promoted microcystin synthesis in CuSO₄ treated cells through the upregulation of microcystin synthetases. Mixed antibiotics significantly (p <  0.05) increased cell density, growth rate, F_v/F_m value, chlorophyll a content and microcystin production ability in CuSO₄ treated cells at test concentrations of 80 and 200 ng L^-1. A no-impact threshold of 20 ng L^-1 for mixed antibiotics (5 ng L^-1 for each antibiotic) was suggested for eliminating the interference of antibiotic contaminants on cyanobacterial bloom control.

New insight into the substituents affecting the peroxydisulfate nonradical oxidation of sulfonamides in water

The large consumption and discharge of sulfonamides (SAs) have potentially induced antibiotic resistance genes, posing inestimable threats to humans and ecosystems. In the present study, five SAs with different substituents were regarded as target compounds to be degraded using the nonradical dominated peroxydisulfate (PDS) activation process by the combination of ¹O₂ oxidation and direct electron transfer. The degradation rates, toxicities and pathways of SAs largely varied with their substituents. For instance, sulfathiazole with five-membered substituent had the highest degradation rate of 0.19 min^-1, which was 3.8 times as the rate of sulfanilamide (0.05 min^-1) without substituent. Then the theoretical calculation was adopted to further confirm that different substituents on the SAs could influence the molecular orbital distribution and their stability, thus resulting in the different removal rate of SAs. Finally, the products of different SAs were concisely deduced to take insight into the effects of different substituents on SAs degradation pathways. It was demonstrated that the geometrical differences among various SAs caused by the different substituents contributed to the different degradation pathways of SAs. Representatively, the special Smiles-type rearrangement pathway was occurred in the six-membered SAs instead of in the five-membered SAs, which inversely resulted in the slower degradation rate of six-membered SAs than the five-membered SAs. Thus, the present study provides a valuable insight into the effects of substituents on the degradation rate and transformation pathways of SAs in the nonradical PDS activation process.

Spectrum and environmental risks of residual pharmaceuticals in stream water with emphasis on its relation to epidemic infectious disease and anthropogenic activity in watershed

Pharmaceuticals vastly consumed by modern human for health and food might track anthropogenic impacts on aquatic ecosystem via their wide residual spectrum. This study investigated the spectrum of pharmaceutical residuals in stream water at confluence point of each subwatershed with various land use pattern in Jiulong River watershed, southeastern China. Stream water was sampled in both wet and dry seasons of 2016. Results showed that 59 out of the selected 94 compounds from 6 pharmaceutical categories were quantified among these stream water samples, up to 1488 ng L^-1 for caffeine (CAF). Antibiotics and central nervous system drugs (CNs) collectively dominated the quantified instream pharmaceutical residuals. Outbreaks of epidemic infectious diseases for human and livestock partially but significantly matched seasonality of instream pharmaceutical residuals. Anthropogenic impact as land use composition of subwatersheds was significant on instream pharmaceutical loadings, especially urban land use. Cocktail risk of instream pharmaceutical residuals to aquatic organisms was assessed ranging from low to medium among the subwatersheds except high risk for the W-01 subwatershed in the dry season. Evidence from this study indicated that seasonality and wide spectrum of instream pharmaceutical residual determination could reveal anthropogenic impacts to aquatic ecosystem, such as epidemic disease and land use.

Sulfamethoxazole exposure to simulated solar radiation under continuous flow mode: Degradation and antibacterial activity

Among pharmaceuticals, the occurrence of antibiotics in the environment is a subject of special concern due to their environmental impact, namely the development of bacterial resistance. Sulfamethoxazole (SMX) is one of the most commonly used antibiotics and it is regularly found, not only in effluents from sewage treatment plants (STPs), but also in the aquatic environment. Photodegradation appears as an alternative process for the removal of this type of pollutants from contaminated waters. In order to be used for a remediation purpose, its evaluation under continuous flow mode is essential, as well as the determination of the final effluent antibacterial activity, which were assessed in this work. As compared with batch operation, the irradiation time needed for SMX elimination under continuous flow mode sharply decreased, which is very advantageous for the target application. Moreover, the interrelation between SMX removal, mineralization and antibacterial activity was evaluated before and during photodegradation in ultrapure water. Although mineralization was slower than SMX removal, bacterial activity increased after SMX photodegradation. Such increase was also verified in environmental water matrices. Thus, this study has proven that photodegradation is an efficient and sustainable process for both (i) the remediation of waters contaminated with antibiotics, and (ii) the minimization of the bacterial resistance.

The role of photodegradation in the environmental fate of hydroxychloroquine

For many organic pollutants present in surface waters, photolysis is considered as a major abiotic degradation process. The present study aimed to explore the role of photolysis in the environmental fate of hydroxychloroquine (HCQ) for the first time. The photolytic degradation of HCQ was investigated under simulated solar radiation (300-800 nm) in ultrapure, spring, river, and sea water. The effect of pH on the photodegradation rate was substantial and it was observed that degradation was faster at higher pH-values. Obtained half-lives ranged from 5.5 min at pH 9 to 23.1 h at pH 4. Humic acids, nitrate and iron(III) enhanced photodegradation of HCQ due to formation of hydroxyl radicals and its attack on HCQ molecule. In contrast, chloride, sulfate and bromide inhibited photodegradation. Additionally, the humic acids exhibited a dual role, photosensitization and inner filter effect. The study of the reaction kinetics was performed with HPLC-PDA, while the identification of degradation products formed during photolytic degradation was carried out using HPLC-MS/MS and NMR spectroscopy. The hydroxylation was recognized as the dominant path of photoproducts formation. The results of this research reveal the importance of photolytic degradation in environmental fate of HCQ and enable a better understanding of its behavior in the environment. Moreover, the results showing the significant effect of pH on the photodegradation of HCQ can be very useful in water treatment processes.

Effect of PHRs and PCPs on Microalgal Growth, Metabolism and Microalgae-Based Bioremediation Processes: A Review

In this review, the effect of pharmaceuticals (PHRs) and personal care products (PCPs) on microalgal growth and metabolism is reported. Concentrations of various PHRs and PCPs that cause inhibition and toxicity to growths of different microalgal strains are summarized and compared. The effect of PHRs and PCPs on microalgal metabolism (oxidative stress, enzyme activity, pigments, proteins, lipids, carbohydrates, toxins), as well as on the cellular morphology, is discussed. Literature data concerning the removal of PHRs and PCPs from wastewaters by living microalgal cultures, with the emphasis on microalgal growth, are gathered and discussed. The potential of simultaneously bioremediating PHRs/PCPs-containing wastewaters and cultivating microalgae for biomass production in a single process is considered. In the light of reviewed data, the feasibility of post-bioremediation microalgal biomass is discussed in terms of its contamination, biosafety and further usage for production of value-added biomolecules (pigments, lipids, proteins) and biomass as a whole.

Studying the fate of the drug Chlorprothixene and its photo transformation products in the aquatic environment: Identification, assessment and priority setting by application of a combination of experiments and various in silico assessments

Chlorprothixene (CPTX) is an antipsychotic drug of the thioxanthene class. Although it is widely used as a tranquillizer in psychiatry, anesthesiology, pediatrics, and in general medical practice, there is a gap in knowledge regarding its occurrence and fate in the environment. Therefore, we provide for the first-time data on the environmental fate and ecotoxicity of CPTX and its potential photo-transformations products (PTPs). Firstly, two standardized biodegradation tests (Closed Bottle test (CBT) and Manometric Respiratory test (MRT)) were performed to assess CPTX's environmental biodegradability. Then, its photodegradability was studied using Xenon and UV lamps. Effects of different conditions (initial drug concentration, pH, and temperature) were applied during UV-photodegradation. Subsequently, the time courses of CPTX and dissolved organic carbon (DOC) concentrations were monitored throughout the photodegradation tests. After that, high-resolution mass spectrometry was employed to elucidate the structures of the formed photo-transformation products (PTPs). In addition, biodegradation tests were performed for the photolytic mixtures to assess the biodegradability of the PTPs. Finally, the (eco)toxicity assessment for CPTX and its photolytic mixtures was predicted using different (quantitative) structure-activity relationship ((Q)SAR) software. CPTX was found to be not readily biodegradable in CBT and MRT. CPTX was not eliminated by irradiation with the Xenon lamp, however primarily eliminated using the UV-lamp. The CPTX elimination during UV-irradiation was faster at lower concentrations. CPTX UV-photodegradation was affected by pH value, while not affected by the temperature of the irradiated solution. 13 PTPs were detected in UV-photolysis mixtures. One additional product was detected in CPTX standard solution, and it was degraded simultaneously with CPTX during UV-irradiation. On one hand, Biodegradation assays revealed that UV-photolytic mixtures of CPTX, containing its PTPs, were not better biodegradable than CPTX itself. On the other hand, LC-MS analysis showed some PTPs which were eliminated after the biodegradation tests indicating possible biodegradability of these PTPs. This because those PTPs are present in low concentrations in the photolysis mixture and their effect can be hindered by the effect of CPTX and other non-biodegradable PTPs. QSAR analysis revealed that CPTX and some of its PTPs may have some human and/or eco-toxic properties. In conclusion, the release of CPTX into aquatic environments could be harmful. Therefore, further research focusing on CPTX and its PTPs are strongly recommended.