Photodegradation mechanisms of acyclovir in water and the toxicity of photoproducts

Acyclovir eco-geno-toxicity in freshwater organisms

This study explores the eco-geno-toxic impact of Acyclovir (ACV), a widely used antiviral drug, on various freshwater organisms, given its increasing detection in surface waters. The research focused on non-target organisms, including the green alga Raphidocelis subcapitata, the rotifer Brachionus calyciflorus, the cladoceran crustacean Ceriodaphnia dubia, and the benthic ostracod Heterocypris incongruens, exposed to ACV to assess both acute and chronic toxicity. The results indicate that while acute toxicity occurs at environmentally not-relevant concentrations, a significant chronic toxicity for C. dubia (EC50 = 0.03 µg/L, NOEC = 0.02·10-2 µg/L), highlighted substantial environmental concern. Furthermore, DNA strand breaks and reactive oxygen species detected in C. dubia indicate significant increase at concentrations exceeding 200 µg/L. Regarding environmental risk, the authors identified chronic exposures to acyclovir causing inhibitory effects on reproduction in B. calyciflorus at hundreds of µg/L and hundredths of µg/L for C. dubia as environmentally relevant environmental concentrations. The study concludes by quantifying the toxic and genotoxic risks of ACV showing a chronic risk quotient higher than the critical value of 1and a genotoxic risk quotient reaching this threshold, highlighting the urgent need for a broader risk assessment of ACV for its significant implications for aquatic ecosystems.

Ozonation products of purine derivatives, the basic structures of antiviral micropollutants

Purine and its nucleobases adenine and guanine are the basic structures of a large group of antiviral agents such as acyclovir and penciclovir. Hence, their ozonation is of interest with regard to wastewater treatment due to the formation of products that could affect the aquatic environment. In this study, the transformation products of the mentioned substances are investigated under different defined reaction conditions in order to gain insight into the ozonation characteristics of this compound class. Results show that examining related molecules significantly improves product screening by compiling known products and analogues leading to comprehensive candidate lists, for the purines with a total number of >120 candidates (including possible duplicates for several purines) of which 49 were detected for the derivatives studied. One product, cyanuric acid, which was previously postulated for adenine, was tentatively confirmed and quantified for the first time for the reaction of purine and adenine with ozone. In addition, two prioritisation approaches are presented to identify the major products that are either formed under specific reaction conditions or are potentially relevant for structurally related pollutants. First, principal component analysis allowed the prioritisation of the products formed according to reaction conditions. In the analysis of guanine and the two antivirals, this approach showed that at neutral and basic pH the 2-imino-5-oxoimidazoline products dominated while at acidic pH either analogues of 5-amino-2,4-imidazolidinedione or 2,4-diamino-1,3-oxazol-5-(2H)-one were abundant. A second approach prioritising common products in the ozonation of all three basic structures revealed the formation of two products that had not been reported before: C4H8O3 and C3H2N2O3, presumably oxalylurea. Both molecules or their analogues may also be formed from related micropollutants. Overall, examining basic structures and exemplary micropollutants in combination was shown to be a worthwhile approach to gain knowledge on the ozonation of a whole range of compounds.

Photodegradation of the pure and formulated scoparone in liquid solutions: kinetics and mechanism

Scoparone (hereafter SPR) is a prominent candidate of plant-derived acaricide. The photodegradation of the pure SPR was first investigated under different light sources, initial concentrations, pH values, temperatures, organic solvents, aqueous media, and the photolytic characteristics of its formulation in pure water were also studied. The photodegradation rates of pure SPR under different light sources showed the following sequence: 28 W ultraviolet lamp (0.3045 h-1) > 500 W xenon lamp (0.1094 h-1) > 300 W xenon lamp (0.0312 h-1). Under the irradiation of 500 W xenon lamp, the lower initial SPR concentrations, higher pH value, and higher temperatures increased the photodegradation rates of SPR, especially, when the temperature increased higher than 35℃, the degradation rate of SPR increased slowly and maintained at a stable level, the pH and temperatures had small effects on the photodegradation of SPR. The photodegradation rates of pure SPR in organic decreased comparing to in aqueous media. The removal efficiency of 98% SPR technical material (TC) was higher than 5% SPR emulsifiable concentrate (EC) in pure water, indicating that the components present in formulated SPR greatly affected the photodegradation kinetics. Detecting the photoproducts by HPLC/ESI-MS indicated that three main types of reaction including photorearrangement, photohydrolysis, and photooxidation occurred in the photodegradation of SPR at aqueous solution. These results will be helpful for the rational use of SPR and provide a scientific reference for environmental risk evaluation of SPR.

A sustainable approach for the removal methods and analytical determination methods of antiviral drugs from water/wastewater: A review

In the last years, antiviral drugs especially used for the treatment of COVID-19 have been considered emerging contaminants because of their continuous occurrence and persistence in water/wastewater even at low concentrations. Furthermore, as compared to antiviral drugs, their metabolites and transformation products of these pharmaceuticals are more persistent in the environment. They have been found in environmental matrices all over the world, demonstrating that conventional treatment technologies are unsuccessful for removing them from water/wastewater. Several approaches for degrading/removing antiviral drugs have been studied to avoid this contamination. In this study, the present level of knowledge on the input sources, occurrence, determination methods and, especially, the degradation and removal methods of antiviral drugs are discussed in water/wastewater. Different removal methods, such as conventional treatment methods (i.e. activated sludge), advanced oxidation processes (AOPs), adsorption, membrane processes, and combined processes, were evaluated. In addition, the antiviral drugs and these metabolites, as well as the transformation products created as a result of treatment, were examined. Future perspectives for removing antiviral drugs, their metabolites, and transformation products were also considered.

Nanomaterials for Photocatalytic Degradations of Analgesic, Mucolytic and Anti-Biotic/Viral/Inflammatory Drugs Widely Used in Controlling SARS-CoV-2

The COVID-19 pandemic has been transformed into one of the main worldwide challenges, in recent years. For controlling symptoms that are caused by this disease (e.g., chills or fever, shortness of breath and/or difficulty in breathing, cough, sore throat, fatigue, headache, muscle aches, the new loss of tastes and/or smells, congestion or runny nose, nausea, vomiting and/or diarrhea), lots of medicines including analgesics, mucolytics, and anti-biotic/viral/inflammatory drugs have been frequently prescribed. As these medicines finally contaminate terrestrial and aquatic habitats by entering surface waterways through pharmaceutical production and excreting trace amounts of waste after human usage, they have negative impacts on wildlife’s health and ecosystem. Residual drugs in water have the potential to harm aquatic creatures and disrupt their food chain as well as the breeding cycle. Therefore, proper degradation of these broadly used medicines is highly crucial. In this work, the use of nanomaterials applicable in photocatalytic degradations of analgesics (e.g., acetaminophen, aspirin, ibuprofen, and naproxen), mucolytics (e.g., ambroxol), antibiotics (e.g., azithromycin and quinolones including hydroxychloroquine and chloroquine phosphate), anti-inflammatory glucocorticoids (e.g., dexamethasone and cortisone acetate), antihistamines (e.g., diphenhydramine), H2 blockers (e.g., famotidine), anthelmintics (e.g., praziquantel), and finally antivirals (e.g., ivermectin, acyclovir, lopinavir/ritonavir, favipiravir, nitazoxanide, and remdesivir) which widely used in controlling/treating the coronavirus have been reviewed and discussed.

Transformation products of pharmaceuticals in the environment: Their fate, (eco)toxicity and bioaccumulation potential

Nowadays, a huge scientific attention is being paid to the chemicals of emerging concern, which may pose a significant risk to the human and whole ecosystems. Among them, residues of pharmaceuticals are a widely investigated group of chemicals. In recent years it has been repeatedly demonstrated that pharmaceuticals are present in the environment and that some of them can be toxic to organisms as well as accumulate in their tissues. However, even though the knowledge of the presence, fate and possible threats posed by the parent forms of pharmaceuticals is quite extensive, their transformation products (TPs) have been disregarded for long time. Since last few years, this aspect has gained more scientific attention and recently published papers proved their common presence in the environment. Also the interest in terms of their toxicity, bioconcentration and stability in the environment has increased. Therefore, the aim of our paper was to revise and assess the current state of knowledge on the fate and effects resulting from the presence of the pharmaceuticals' transformation drugs in the environment. This review discusses the metabolites of compounds belonging to six major pharmaceutical groups: SSRIs, anticancer drugs, antibiotics, antihistamines, NSAIDs and opioids, additionally discussing other individual compounds for which literature data exist. The data presented in this paper prove that some TPs may be as harmful as their native forms, however for many groups of drugs this data is still insufficient to assess the risk posed by their presence in the environment.

Ecotoxicity and photodegradation of Montelukast (a drug to treat asthma) in water

The present work focuses on the ecotoxicological effects of montelukast sodium (MTL) and its photoproducts, obtained under environmentally-like conditions. Despite of the potential presence in surface waters and the common use of MTL as asthma drug, limited data has been published for its photodegradation, while no information is available for its ecotoxicity. Light-induced degradation is an effective way for drugs to degrade in aquatic environments, and MTL is highly photosensitive, even by exposure to sunlight. In this study, solar-simulated irradiation of the drug in water was investigated. The drug was quickly converted into a series of photoproducts that were spectroscopically characterized. The possible photoreaction pathways were proposed. Ecotoxicity tests were performed on parent compound and mixture of photoproducts towards two bioindicators (Raphidocelis subcapitata and Daphnia magna). Results evidenced that effects of MTL on D. magna (EC50 = 16.4 mg/L) were greater than effects on R. subcapitata (EC50 = 195.7 mg/L). Microscopy observations revealed that MTL had mainly accumulated in the gut of daphnia. Toxicity data on photolysed solutions highlighted the presence of residual toxicity in all samples, evidencing that no complete mineralization occurred. Future research should focus on monitoring of MTL concentrations in the environment and study its effects in bioaccumulation tests.

Natural attenuation characteristics and comprehensive toxicity changes of C9 aromatics under simulated marine conditions

Microcosmic experiments were performed under a simulated marine environment to investigate the natural attenuation of C9 aromatics using nine components (propylbenzene, isopropylbenzene, 2-ethyltoluene, 3-ethyltoluene, 4-ethyltoluene, 1,2,3-trimethylbenzene, 1,2,4-trimethylbenzene, 1,3,5-trimethylbenzene, and indene). This research aims to assess the contribution of biodegradation and abiotic activity to total attenuation of C9 aromatics and ascertain the changes in the comprehensive toxicity of seawater in the natural environment. The process of natural attenuation indicates the agreement with pseudo-first-order kinetics for all nine components in microcosmic experiments. The half-lives of the nine main compounds in C9 aromatics ranged between 0.34 day and 0.44 day under optimal conditions. The experiments showed that the natural attenuation of nine aromatic hydrocarbons mainly occurred via abiotic processes. Seawater samples significantly inhibited the luminescence of P. phosphoreum (the luminescence inhibition ratio reached 100%) at the beginning of the experiment. In addition, the toxicity declined slowly and continued for 25 days. The attenuation kinetics and changes in toxicity could be applied to explore the natural attenuation of C9 aromatics in the marine environment.

Identification of photodegradation product of organophosphorus pesticides and elucidation of transformation mechanism under simulated sunlight irradiation

Organophosphorus pesticides (OPs) are posing great threat to the environment and human health, due to their overuse and persistence in the environment. Photolysis has been established as an effective method to degrade OPs. The influence of pH value, the initial concentration of pesticides and the light source on the photolysis of two OPs, including chlorpyrifos and dimethoate, was investigated. The optimal reaction condition for OPs degradation was under pH 9, with xenon lamp as the light source, in which the photodegradation efficiencies of chlorpyrifos and dimethoate (500 mg/L) were 75.12% and 94.31%, respectively. The photodegradation products of chlorpyrifos and dimethoate were identified by GC-MS. Also, density functional theory (DFT) calculations were used to characterize the molecular properties of chlorpyrifos and dimethoate, as well as predicting potential photolysis reactions. Photodegradation mechanisms of chlorpyrifos and dimethoate were proposed, in which 3,5,6-trichloropyridinol (TCP), O,O-diethyl thiophosphate (DETP), 2,3,5-Trichloro-6-methoxypyridine (TMP) and O,O,S-trimethyl phosphorothioate were identified as the main products of chlorpyrifos degradation. Omethoate, O,O,S-trimethyl thiophosphorothioate, N-methyl-2-sulfanylacetamide, O,O,O-trimethyl thiophosphate, O,O,S-trimethylphosphorothiate, and O,O,O-trimethyl phosphoric ester as the main photodegradation products for dimethoate. The main degradation mechanisms included ring opening, cleavage, oxidation and demethylation. This work demonstrated the feasibility of combining chemical analysis with quantum chemical calculation in unraveling degradation mechanisms of OPs. Also, it is of great significance for evaluating the environmental fate of OPs in aquatic system and further environmental risk assessment.