Identification and characterization of photodegradation products of metoprolol in the presence of natural fulvic acid by HPLC-UV-MSn

Wastewater disinfection with photodynamic treatment and evaluation of its ecotoxicological effects

Research has demonstrated the presence of viruses in wastewater (WW), which can remain viable for a long period, posing potential health risks. Conventional WW treatment methods involving UV light, chlorine and ozone efficiently reduce microbial concentrations, however, they produce hazardous byproducts and microbial resistance that are detrimental to human health and the ecosystem. Hence, there is a need for novel disinfection techniques. Antimicrobial Photodynamic Inactivation (PDI) emerges as a promising strategy, utilizing photosensitizers (PS), light, and dioxygen to inactivate viruses. This study aims to assess the efficacy of PDI by testing methylene blue (MB) and the cationic porphyrin TMPyP as PSs, along a low energy consuming white light source (LED) at an irradiance of 50 mW/cm2, for the inactivation of bacteriophage Phi6. Phi6 serves as an enveloped RNA-viruses surrogate model in WW. PDI experiments were conducted in a buffer solution (PBS) and real WW matrices (filtered and non-filtered). Considering the environmental release of the treated effluents, this research also evaluated the ecotoxicity of the resulting solution (post-PDI treatment effluent) on the model organism Daphnia magna, following the Organisation for Economic Cooperation and Development (OECD) immobilization technical 202 guideline. Daphnids were exposed to WW containing the tested PS at different concentrations and dilutions (accounting for the dilution factor during WW release into receiving waters) over 48 h. The results indicate that PDI with MB efficiently inactivated the model virus in the different aqueous matrices, achieving reductions superior to 8 log10 PFU/mL, after treatments of 5 min in PBS and of ca. 90 min in WW. Daphnids survival increased when subjected to the PDI-treated WW with MB, considering the dilution factor. Overall, the effectiveness of PDI in eliminating viruses in WW, the fading of the toxic effects on daphnids after MB' irradiation and the rapid dilution effect upon WW release in the environment highlight the possibility of using MB in WW PDI-disinfection.

Drought impact on pharmaceuticals in surface waters in Europe: Case study for the Rhine and Elbe basins

Hydrological droughts are expected to increase in frequency and severity in many regions due to climate change. Over the last two decades, several droughts occurred in Europe, including the 2018-drought, which showed major adverse impacts for nature and different sectoral uses (e.g. irrigation, drinking water). While drought impacts on water quantity are well studied, little understanding exists on the impacts on water quality, particularly regarding pharmaceutical concentrations in surface waters. This study investigates the impact of the 2018-drought on concentrations of four selected pharmaceuticals (carbamazepine, sulfamethoxazole, diclofenac and metoprolol) in surface waters in Europe, with a major focus on the Elbe and Rhine rivers. Monitoring data were analysed for the period of 2010-2020 to estimate the spatiotemporal patterns of pharmaceuticals and assess the concentration responses in rivers during the 2018-drought compared to reference years. Our results indicate an overall deterioration in water quality, which can be attributed to the extremely low flow and higher water temperatures (∼ + 1.5 °C and + 2.0 °C in Elbe and Rhine, respectively) during the 2018-drought. Our results show an increase in the concentrations of carbamazepine, sulfamethoxazole, and metoprolol, but reduced concentrations of diclofenac during the 2018-drought. Significant increases in carbamazepine concentrations (+45 %) were observed at 3/6 monitoring stations in the upstream part of the Elbe, which was mainly attributed to less dilution of chemical loads from wastewater treatment plants under drought conditions. However, reduced diclofenac concentrations could be attributed to increased degradation processes under higher water temperatures (R2 = 0.60). Moreover, the rainfed-dominated Elbe exhibited more severe water quality deterioration than the snowmelt-dominated Rhine river, as the Elbe's reduction in dilution capacity was larger. Our findings highlight the need to account for the impacts of climate change and associated increases in droughts in water quality management plans, to improve the provision of water of good quality for ecosystems and sectoral needs.

Fulvic acid-like substance-Ca(II) complexes improved the utilization of calcium in rice: Chelating and absorption mechanism

Water-soluble chelated calcium has been widely used in agriculture as a fertilizer to improve the absorption and utilization of calcium by plants. This paper prepared a new organic mineral fertilizer, based on fulvic acid-like substance chelated calcium (PFA-Ca²⁺ complex), using optimal parameters (i.e., pH, time, temperature, and Ca²⁺ concentration) to achieve a high chelation efficiency. The absorption, utilization, and distribution of the PFA-Ca²⁺ complex in rice roots were analyzed using laser scanning confocal microscopy (LSCM). Our results demonstrated that the optimal PFA-Ca²⁺ complex chelating efficiency (87%) was achieved at an initial Ca²⁺ concentration of 0.1 mol L^-1, an equilibration time of 120 min, a pH of 5.0, and a temperature of 40 °C. The chelating reaction of a fulvic acid-like substance with Ca²⁺ primarily occurred on phenol hydroxyl, alcohol hydroxyl, and carboxyl groups. The PFA-Ca²⁺ complex was primarily enriched in the roots' pericycle, cortical, and epidermis cells, in both chelating and non-chelating forms. To our knowledge, this is the first report investigating how the PFA-Ca²⁺complex affects transformation in plants, which has significant implications for research on plant nutrition and nutrient distribution.

Organic dyes supported on silicon-based materials: synthesis and applications as photocatalysts

The most important advance in photocatalysis in the last decade has been the synthesis and application of organic compounds to promote this process.

Catalytic ozonation for metoprolol and ibuprofen removal over different MnO2 nanocrystals: Efficiency, transformation and mechanism

Manganese dioxide has been widely recognized as catalyst in catalytic ozonation for organic pollutants removal from wastewater in recent decades. However, few studies focus on the structure-activity relationship of MnO₂ and catalytic ozonation mechanism in water. In the present study, the oxidative reactivity of three different crystal phases of MnO₂ corresponding to α-MnO₂, β-MnO₂ and γ-MnO₂ towards metoprolol (MET) and ibuprofen (IBU) were evaluated. α-MnO₂ was found to contain the most abundant oxygen vacancy and readily reducible surface adsorbed oxygen (O^2-, O^-, OH^-), which facilitated an increase of ozone utilization and the highest catalytic performance with 99% degradation efficiency for IBU and MET. α-MnO₂ was then selected to investigate the optimum key operating parameters with a result of catalyst dosage 0.1 g/L, ozone dosage 1 mg/min and an initial pH 7. The introduction of α-MnO₂ promoted reactive oxygen species (O^2-, O^-, OH^-) generation which played significant roles in IBU degradation. Probable degradation pathways of MET and IBU were proposed according to the organic intermediates identified and the reaction sites based on density function theory (DFT) calculations. The present study deepened our understanding on the MnO₂ catalyzed ozonation and provided reference to enhance the process efficiency.

Antimicrobial Photodynamic Approach in the Inactivation of Viruses in Wastewater: Influence of Alternative Adjuvants

Pathogenic viruses are frequently present in marine and estuarine waters, due to poor wastewater (WW) treatments, which consequently affect water quality and human health. Chlorination, one of the most common methods used to ensure microbiological safety in tertiarily treated effluents, may lead to the formation of toxic chemical disinfection by-products on reaction with organic matter present in the effluents. Antimicrobial photodynamic therapy (aPDT) can be a promising disinfecting approach for the inactivation of pathogens, without the formation of known toxic by-products. Additionally, some studies have reported the potentiator effect on aPDT of some compounds, such as potassium iodide (KI) and hydrogen peroxide (H2O2). In the present study, the aPDT efficiency of a PS formulation constituted of five cationic porphyrins (Form) in the inactivation of E. coli T4-like bacteriophage, a model of mammalian viruses, in different aqueous matrices with different organic matter content, was evaluated. Photoinactivation studies were performed at different concentrations of Form and in the presence of the adjuvants KI and H2O2. The results showed that the efficiency of bacteriophage photoinactivation is correlated with the Form concentration, the amount of the organic matter in WW, and the adjuvant type. Form can be an effective alternative to controlling viruses in WW, particularly if combined with H2O2, allowing to significantly reduce PS concentration and treatment time. When combined with KI, the Form is less effective in inactivating T4-like bacteriophage in WW.

Metoprolol and Its Degradation and Transformation Products Using AOPs-Assessment of Aquatic Ecotoxicity Using QSAR

Pharmaceuticals are found in waterbodies worldwide. Conventional sewage treatment plants are often not able to eliminate these micropollutants. Hence, Advanced Oxidation Processes (AOPs) have been heavily investigated. Here, metoprolol is exposed to UV irradiation, hydrogen peroxide, and ozonation. Degradation was analyzed using chemical kinetics both for initial and secondary products. Photo-induced irradiation enhanced by hydrogen peroxide addition accelerated degradation more than ozonation, leading to complete elimination. Degradation and transformation products were identified by high-performance liquid-chromatography coupled to high-resolution higher-order mass spectrometry. The proposed structures allowed to apply Quantitative Structure-Activity Relationship (QSAR) analysis to predict ecotoxicity. Degradation products were generally associated with a lower ecotoxicological hazard to the aquatic environment according to OECD QSAR toolbox and VEGA. Comparison of potential structural isomers suggested forecasts may become more reliable with larger databases in the future.

Persulfate activation by nano zero-valent iron for the degradation of metoprolol in water: influencing factors, degradation pathways and toxicity analysis

In this study, nano zero-valent iron (nZVI) was utilized to activate persulfate (PS) for the degradation of metoprolol (MTP), a commonly used drug for curing cardiovascular diseases, in water. Quenching tests indicated that both the sulfate radical (SO₄˙⁻) and hydroxyl radical (˙OH) contributed to the degradation of MTP, while SO₄˙⁻ seemed to play a large role under natural pH conditions. Batch tests were conducted to investigate the effects of several influencing factors, such as PS concentration, initial MTP concentration, pH, temperature and common anions, on the degradation performance of MTP. Generally, lower MTP concentration and pH values, and higher PS concentration and temperature favoured MTP degradation. HCO₃⁻, NO₃⁻ and SO₄²⁻ were found to inhibit MTP degradation, while Cl⁻ enhanced MTP degradation. Several corrosion products of nZVI, including Fe₃O₄, Fe₂O₃ and FeSO₄, were formed during the reaction, which was reflected by the combined XRD and XPS analysis. Degradation pathways of MTP were proposed according to the identified transformation products, and the peak areas of the major products along with the time were also monitored. Finally, the toxicity of the reaction solution was assessed by experiments using Aliivibrio fischeri. Overall, it could be concluded that nZVI/PS might be a promising method for the rapid treatment of MTP-caused water pollution.

The influencing factors, mechanism and toxicity of MTP degradation by nZVI activated persulfate were investigated.

Comparing non-targeted chemical persistence assessed using an unspiked OECD 309 test to field measurements

Previous research has shown that unspiked OECD 309 tests can be used to quantify chemical biodegradation in surface waters, relying on chemical residues already present in the water. Here we test the hypothesis that unspiked OECD 309 tests can quantitatively predict chemical persistence in the environment by comparing chemical half-lives assessed in the laboratory against those measured in the field. The study object was a Swedish lake heavily impacted by treated municipal wastewater. Half-lives in the field were measured by mass balance over 12 weeks. In parallel, half-lives in the lab were determined with an unspiked OECD 309 test run for 60 days. Chemical analysis was conducted using a non-target screening approach. The field study yielded a half-life <100 days for 38 chemicals for which the dominant source was wastewater; 32 of these were also detected in the lab test, whereby 18 had half-lives with a well-constrained uncertainty that did not intersect infinity. For 14 of the 18 chemicals, the field and lab half-lives agreed within a factor 3. In summary, the lab test predicted chemical attenuation in the field well. Limitations of the approach include the need for measurable chemical concentrations in the water body and failure to account for some attenuation mechanisms like phototransformation.

Photochemical degradation of nebivolol in different natural organic matter solutions under simulated sunlight irradiation: Kinetics, mechanism and degradation pathway

Nebivolol (NEB) is widely used for the treatment of hypertension and chronic heart failure and has become an ubiquitous emerging organic pollutant. It has been shown to undergo direct photolysis, but the role of DOM in its degradation kinetics and mechanism is not well understood. In this study, we studied the photochemical behavior of NEB in the presence of seawater DOM (SW-DOM) and freshwater DOM (SRNOM) under simulated sunlight irradiation. SW-DOM had a promotion effect on NEB photodegradation, whereas SRNOM retarded its photolytic transformation. After eliminating the influence of light screening, we found that the indirect photodegradation rate of NEB in the presence of SRNOM was lower than that in the presence of SW-DOM. Results show that the indirect photodegradation pathway occurred by reaction with triplet-excited DOM (³DOM*). The second-order rate constants for ³SW-DOM* and ³SRNOM* reaction with NEB are 3.7 × 10⁹ M^-1 s^-1 and 3.7 × 10⁸ M^-1 s^-1, respectively. The electron donating capacity of SRNOM is higher than that of SW-DOM, indicating that SRNOM may contain more activated phenolic moieties. SRNOM may thus have higher antioxidant activity, leading a higher inhibitory effect on NEB photodegradation. A total of six degradation products were identified in the absence and presence of DOM by HPLC-ESI-MS/MS. The substitution of F by OH-groups and further oxidation a OH-group in the lateral chain to a ketone, and cleavage of N-C bond by the attack of ³DOM* are here proposed as the main degradation pathways.

Photodegradation of metoprolol in the presence of aquatic fulvic acids. Kinetic studies, degradation pathways and role of singlet oxygen, OH radicals and fulvic acids triplet states

Metoprolol is a pharmaceutical used for the treatment of cardiovascular diseases and disorders, whose frequent detection in surface waters raises concern. Indirect photodegradation is an important degradation pathway in waters and dissolved organic matter has a major role as photosensitizer. In this study, metoprolol photodegradation, in the absence and in the presence of fulvic acids extracted from the Vouga River (Portugal) (VRFA), was assessed under simulated sunlight. While metoprolol direct photodegradation was deniable, indirect photolysis occurred under the presence of VRFA. It followed a pseudo-first order kinetics and after 72 h of irradiation there was a decrease of metoprolol concentration of ∼80 %. The OH radical (OH) was verified to be the main reactive species (RS) responsible for the photosensitized degradation of metoprolol, but other RS are also involved, probably triplet excited states of FA (³FA*) and singlet oxygen (¹O₂), as demonstrated by the higher inhibition of the photodegradation in presence of sodium azide than in presence of 2-propanol. Based on a previous identification of photoproducts, tentative degradation mechanisms were here proposed. Photoproducts analysis after 24 h irradiation in the absence and presence of scavengers, shown that different RS are involved in the formation of different products/intermediates.

Quantifying photo-production of triplet excited states and singlet oxygen from effluent organic matter

The organic matter present in wastewater effluents (EfOM), is likely to have different properties than the organic matter present in the receiving water. The properties of EfOM will affect the fate of contaminants of emerging concern because EfOM is a source of photochemically produced reactive intermediates (PPRIs) capable of transforming contaminants. Effluent water samples were taken seasonally from sixteen wastewater treatment plants in Minnesota and two effluent dominated rivers in California and Arizona. Samples (n = 94) were tested for water chemistry, light absorption characteristics, and excited state triplet organic matter (³EfOM^∗) and singlet oxygen (¹O₂) production. Based on analysis of spectral parameters, EfOM had higher molecular weight and lower aromatic content than organic matter present in stormwaters from Minnesota, which are representative of human-impacted natural organic matter (NOM) containing waters. The second order rate constant for the reaction of the ³EfOM^∗ probe 2,4,6-trimethylephenol (k_T,TMP) for the effluents was 7.79 (±3.03) × 10⁸ M^-1s^-1, and this value was used to calculate apparent quantum yields for ³EfOM^∗ production, which ranged from 0.006 to 0.114. The quantum yield for the production of singlet oxygen ranged from 0.007 to 0.064. Processes in the wastewater treatment train, season, and water chemistry parameters did not serve as predictors of ³EfOM^∗ or ¹O₂ production. Among the parameters measured, Spearman rank correlations were strongest between quantum yields of ¹O₂ and ³EfOM^∗ and E2/E3 (absorption at 250 nm/absorption at 365 nm). This relationship, however, is weaker than that previously observed for NOM. The efficiency of ¹O₂ production from ³EfOM^∗ was 54%. Results indicate that 2,4,6-trimethylphenol samples nearly all of the triplets in EfOM that have sufficient energy to produce ¹O₂, which may not be the case for NOM.

Photodegradation of metoprolol using a porphyrin as photosensitizer under homogeneous and heterogeneous conditions

Porphyrins are known as effective photosensitizers and can be an interesting key in phototreatment of water contaminated with micropollutants such as pharmaceuticals. They already showed to be efficient photocatalysts for the degradation of dyes, chlorophenols and other pollutants. This work demonstrates the applicability of 5,10,15,20-tetrakis(pentafluorophenyl)porphyrin (H₂TF₅PP) as photosensitizer for treatment of water contaminated with metoprolol, a highly prescribed β-blocker, which is not completely removed in sewage treatment plants. Studies were firstly developed under homogeneous conditions with simulated solar radiation and porphyrin was found to be efficient in the photodegradation of metoprolol, following a pseudo-first order kinetics with ca. 90% metoprolol degradation after 12 h. Experiments in presence of scavengers confirmed the mechanism of degradation via singlet oxygen. Appearance of several new peaks in HPLC chromatograms indicates the formation of products, identified by HPLC-MSⁿ. Furthermore, the porphyrin was immobilized on a silica support and used as heterogeneous photocatalyst in degradation of metoprolol. Experiments using this heterogeneous photocatalyst under real solar irradiation were also performed, and similar results were obtained. Kinetic comparison of metoprolol photodegradation in buffer solution and in real wastewater treatment plant effluent showed that the efficiency of the immobilized porphyrin was not decreased by the complex matrix of the effluent.

Wastewater chemical contaminants: remediation by advanced oxidation processes

Approximately 70% of the terrestrial area is covered with water, but only a small water fraction is compatible with terrestrial life forms. Due to the increment in human consumption, the need for water resources is increasing, and it is estimated that more than 40% of the population worldwide will face water stress/scarcity within the next few decades. Water recycling and reuse may offer the opportunity to expand water resources. For that, the wastewater treatment paradigm should be changed and adequately treated wastewater should be seen as a valuable resource instead of a waste product. It is easily understandable that the exact composition and constituent concentration of wastewater vary according to its different sources (industrial, agricultural, urban usage of water). Consequently, a variety of known and emerging pollutants like heavy metals, antibiotics, pesticides, phthalates, polyaromatic hydrocarbons, halogenated compounds and endocrine disruptors have been found in natural water reservoirs, due to the limited effectiveness of conventional wastewater treatment. The conventional approach consists of a combination of physical, chemical and biological processes, aiming at the removal of large sediments such as heavier solids, scum and grease and of organic content in order to avoid the growth of microorganisms and eutrophication of the receiving water bodies. However, this approach is not sufficient to reduce the chemical pollutants and much less the emerging chemical pollutants. In this review, after some considerations concerning chemical pollutants and the problematic efficiency of their removal by conventional methods, an update is presented on the successes and challenges of novel approaches for wastewater remediation based on advanced oxidation processes. An insight into wastewater remediation involving the photodynamic approach mediated by tetrapyrrolic derivatives will be underlined.

Transformation products formation of ciprofloxacin in UVA/LED and UVA/LED/TiO2 systems: Impact of natural organic matter characteristics

The role of natural organic matter (NOM) in contaminants removal by photolysis and photocatalysis has aroused increasing interest. However, evaluation of the influence of NOM characteristics on the transformation products (TPs) formation and transformation pathways of contaminants has rarely been performed. This study investigated the decomposition kinetics, mineralization, TPs formation and transformation pathways of antibiotic ciprofloxacin (CIP) during photolysis and photocatalysis in the presence of three commercial NOM isolates (Sigma-Aldrich humic acid (SAHA), Suwannee River humic acid (SRHA) and Suwannee River NOM (SRNOM)) by using UVA light emitting diode (UVA/LED) as an alternative light source. NOM isolates insignificantly affected CIP photolysis but strongly inhibited CIP photocatalysis due to competitive radical quenching. The inhibitory effect followed the order of SAHA (49.6%) > SRHA (29.9%) > SRNOM (21.2%), consistent with their •OH quenching abilities, SUVA₂₅₄ values and orders of aromaticity. Mineralization rates as revealed by F^- release were negatively affected by NOM during CIP photocatalysis. TPs arising from hydroxylation and defluorination were generally suppressed by NOM isolates in UVA/LED and UVA/LED/TiO₂ systems. In contrast, dealkylation and oxidation of piperazine ring were promoted by NOM. The enhancement in the apparent formation kinetics (k_app) of TP245, TP291, TP334a, TP334b and TP362 followed the order of SRNOM > SRHA > SAHA. k_app values were positively correlated with O/C ratio, carboxyl content, E2/E3 and fluorescence index (FI) of NOM and negatively related with SUVA₂₅₄ values. The observed correlations indicate that NOM properties are important in determining the fate and transformation of organic contaminants during photolysis and photocatalysis.

Nitrogen-containing organic compounds: Origins, toxicity and conditions of their photocatalytic mineralization over TiO2

Sustainable water management remains a global concern to meet the food needs of industrial and agricultural activities. Therefore, pollution abatement techniques, cheap and environmentally, are highly desired and recommended. The present review is devoted to the origin and the toxicity of nitrogen-containing organic compounds in water. The progress made in removing these pollutants, in recent years, is addressed. However, a prominent place is given to the photocatalytic degradation process using the TiO₂ as a semiconductor, the conditions for good mineralization and especially the factors influencing it. The parameters that impact the performance of this method are the pH, the temperature, the reactor used, the light, the concentration of the pollutant, the amount of catalyst, etc. Up to now, the importance of one parameter relative to another has not been established because in the context of the photocatalytic degradation, certain parameters are often tightly coupled. Consequently, the mineralization is dependent on the initial degree of oxidation of nitrogen atom contained in the pollutant to be degraded. The hydroxyl nitrogen is primarily converted into nitrate ions (NO₃^-), while the amides and the primary amines are converted into ammonium ions (NH₄⁺).