In silico ecotoxicity assessment of pharmaceutical residues in wastewater following oxidative treatment.

Advanced oxidation processes such as thermal plasma activation and UV-C/H2O2 treatment are considered as applications for the degradation of pharmaceutical residues in wastewater complementary to conventional wastewater treatment. It is supposed that direct oxidative treatment can lower the toxicity of hospital sewage water (HSW). The aim of this study was to predict the ecotoxicity for three aquatic species before and after oxidative treatment of 10 quantified pharmaceuticals in hospital sewage water. With the application of oxidative chemistry, pharmaceuticals are degraded into transformation products before reaching complete mineralization. To estimate the potential ecotoxicity for fish, Daphnia and green algae ECOSAR quantitative structure-activity relationship software was used. Structure information from pristine pharmaceuticals and their oxidative transformation products were calculated separately and in a mixture computed to determine the risk quotient (RQ). Calculated mixture toxicities for 10 compounds found in untreated HSW resulted in moderate-high RQ predictions for all three aquatic species. Compared to untreated HSW, 30-min treatment with thermal plasma activation or UV-C/H2O2 resulted in lowered RQs. For the expected transformation products originating from fluoxetine, cyclophosphamide and acetaminophen increased RQs were predicted. Prolongation of thermal plasma oxidation up to 120 min predicted low-moderate toxicity in all target species. It is anticipated that further degradation of oxidative transformation products will end in less toxic aliphatic and carboxylic acid products. Predicted RQs after UV-C/H2O2 treatment turned out to be still moderate-high. In conclusion, in silico extrapolation of experimental findings can provide useful predicted estimates of mixture toxicity. However due to the complex composition of wastewater this in silico approach is a first step to screen for ecotoxicity. It is recommendable to confirm these predictions with ecotoxic bioassays.

Xenon-lamp simulated sunlight-induced photolysis of pyriclobenzuron in water: Kinetics, degradation pathways, and identification of photolysis products.

Pyriclobenzuron 1(PBU) is a novel molluscicide developed to control Pomacea canaliculate, and little information on its environmental fate has been published. In this study, the photolysis of PBU in an aqueous environment was simulated using a xenon lamp. Results showed that the photolysis of PBU in water followed first-order kinetics, exhibiting a t0.5 of 95.1 h and 83.6 h in Milli-Q water and river water, respectively. Two main photolysis products 2(PPs) were detected by HPLC-UV and identified by UPLC-Q/TOF MS, which were formed via the hydroxylation and photocatalytic hydro-dehalogenation of PBU, respectively. The initial relative abundance of photolysis product 1 3(PP-1) in Milli-Q water was 1.55 times higher than that in river water. PP-1 was detected at 26.5 % and 76.8 % of the maximum relative abundance in the river water and Milli-Q water after 720 h, respectively. Photolysis product 2 4(PP-2) was stable in water because of its weak hydrophilicity. The PP-2 detected after 720 h in Milli-Q water and river water was 93.7 % and 93.5 % of the maximum relative abundance, respectively. Finally, ECOSAR software was used to evaluate the acute aquatic toxicity of PBU and its PPs, revealing that the PPs had lower toxicity levels to non-target aquatic organisms.

AOP-Based Transformation of Abacavir in Different Environments: Evolution Profile of Descyclopropyl-Abacavir and In Silico Toxicity Assessment of the Main Transformation Products.

This study explores the photocatalytic transformation of the antiviral drug abacavir employing different advanced oxidation processes (AOPs) such as UV/TiO2, UV/MOF/H2O2, UV/MOF/S2O82-, UV/Fe2+/H2O2, and UV/Fe2+/S2O82-. All processes appear to be effective in eliminating abacavir within a few minutes, while the evolution profile of the basic transformation product, descyclopropyl-abacavir (TP-247) was also monitored. Moreover, the implementation of the most efficient technologies towards the removal of abacavir in different matrices such as wastewater effluent and leachate was also assessed, revealing that the organic matter present or the inorganic constituents can retard the whole process. Four major transformation products were detected, and their time-evolution profiles were recorded in all studied matrices, revealing that different transformation pathways dominate in each matrix. Finally, the prediction of the toxicity of the major TPs employing ECOSAR software was conducted and showed that only hydroxylation can play a detoxification role in the treated solution.

Eco-toxicological effect of a commercial dye Rhodamine B on freshwater microalgae Chlorella vulgaris.

In this study, the acute toxicity effects of a fluorescent xanthene dye, Rhodamine B (RhB), widely used in textile, paper, and leather industries was investigated on a freshwater microalgae Chlorella vulgaris. The acute toxicity of RhB on C. vulgaris was determined by examining the growth, cell morphology, pigment production, protein content, and the activities of oxidative stress enzymes. Based on the results of the toxicity study of 24-96 h, the median inhibitory concentration (IC50) values ranged from 69.94 to 31.29 mg L-1. The growth of C. vulgaris was conspicuously inhibited by RhB exposure, and the cell surfaces appeared to be seriously shrunk in SEM analysis. The growth of C. vulgaris was hindered after exposure to graded concentrations (10-50 mg L-1) of RhB. A significant reduction in growth rate, pigment synthesis (chlorophyll a, chlorophyll b, and carotenoid), and protein content was recorded in a dose-dependent manner. After 96 h exposure of C. vulgaris to 50 mg L-1 RhB, chlorophyll a, chlorophyll b, carotenoids, and protein contents were reduced by 71.59, 74.90, 65.84, and 74.20%, respectively. The activities of the antioxidant enzymes peroxidase (POD), and catalase (CAT) also increased markedly in the presence of RhB. A notable effect was observed on oxidative enzymes catalase and peroxidase, indicating that oxidative stress may be the primary factor in the inhibition of growth and pigment synthesis. Consequently, the experimental acute toxicity data were compared to the QSAR prediction made by the ECOSAR programme. Results showed that the experimental acute toxicity values were 67.74-fold lower than the ECOSAR predicted values. The study provides convincing evidence for the metabolic disruption in the ubiquitous microalgae C. vulgaris due to the RhB dye toxicity.

Screening and Risk Evaluation of Organic Contaminants in an Urban Wetland Fed with Wastewater Effluents.

Wastewater release in an urban wetland in Mexico City entails discharging complex mixtures of hundreds of chemical substances into the aquatic system. Therefore, in order to identify the most important contaminants, a GC-MS screening method coupled with deconvolution software was used. LC50 values from ECOSAR and Toxic Units were obtained to identify the organic pollutants-of-concern and to pinpoint the most ecotoxic sites. The results showed that, even though the area has intensive farming, agrochemicals are not of concern. Industrial and domestic groups make up from about 30%-66% of the pollutants for all sites. Of the 189 identified substances, 17 were detected 44% of the time and the Toxic Unit showed that terbutol, coprostanol, and hexadecane were capable of generating considerable adverse effects on the aquatic ecosystem. Total Toxic Units for each site exhibited a decreasing trend as they distanced from the urban and agricultural area.

Consensus QSAR modeling of toxicity of pharmaceuticals to different aquatic organisms: Ranking and prioritization of the DrugBank database compounds.

In the present work, quantitative structure-activity relationship (QSAR) models have been developed for ecotoxicity of pharmaceuticals on four different aquatic species namely Pseudokirchneriella subcapitata, Daphnia magna, Oncorhynchus mykiss and Pimephales promelas using genetic algorithm (GA) for feature selection followed by Partial Least Squares regression technique according to the Organization for Economic Co-operation and Development (OECD) guidelines. Double cross-validation methodology was employed for selecting suitable models. Only 2D descriptors were used for capturing chemical information and model building, whereas validation of the models was performed by considering various stringent internal and external validation metrics. Interestingly, models could be developed even without using any LogP terms in contrary to the usual dependence of toxicity on lipophilicity. However, the current manuscript proposes highly robust and more predictive models employing computed logP descriptors. The applicability domain study was performed in order to set a predefined chemical zone of applicability for the obtained QSAR models, and the test compounds falling outside the domain were not taken for further analysis while making a prioritized list. An additional comparison was made with ECOSAR, an online expert system for toxicity prediction of organic pollutants, in order to prove predictability of the obtained models. The obtained robust consensus models were utilized to predict the toxicity of a large dataset of approximately 9300 drug-like molecules in order to prioritize the existing drug-like substances in accordance to their acute predicted aquatic toxicities following a scaling technique. Finally, prioritized lists of 500 most toxic chemicals obtained by respective consensus models and those predicted from ECOSAR tool have been reported.

Novel indazolylchromones: synthesis, fungicidal evaluation, molecular docking and aquatic toxicity prediction.

Fungal diseases cause substantial loss to agricultural crops, affecting both quantities and quality. Although several methods are used for preventing disease incidence, fungicides remain crucial for higher yields and better quality. But in the past, the efficacy of several fungicides has decreased due to increased cases of fungicide resistant. In our pursuit of new effective fungicides, we synthesised a series of twenty 2-Indazol-1-yl-chromen-4-one derivatives (6a- 6t). The characterization of synthesized compounds was performed by several spectroscopic methods including Infrared, Nuclear Magnetic Resonance (1H and 13C) and HRMS. Out of 20 synthesised compounds, 19 (6b- 6t) were found to be novel. All synthesised indazolylchromones showed very good antifungal activity against Sclerotium rolfsii and Fusarium oxysporum. Among the tested compounds, 6t and 6f exhibited very good fungicidal activity against S. rolfsii with an ED50 of 10.10 mg L-1 and 16.18 mg L-1, respectively. In case of Fusarium oxysporum compound 6f displayed good' activity with an ED50 value of 27.82 mg L-1. Molecular docking study was done to predict the binding sites of most active compounds, 6t and 6f with Cytochrome P450 14alpha -sterol demethylase (CYP51) enzyme using molsoft software. The acute toxicity predictions the of synthesized compounds for fish (LC50,96 Hr), daphnid (LC50, 48 Hr) and green algae (EC50, 96Hr) and the chronic toxicity predictions (ChV) were assessed using Ecological Structure Activity Relationship (ECOSAR) model. As per ECOSAR prediction, all the chemicals are inside AD and not missing predictions.

Percarbonate mediated advanced oxidation of irbesartan: A suitable alternative to chlorination?

This study aims to investigate the environmental fate of irbesartan when subjected to activated percarbonate treatment. The investigation delves into the formation of disinfection byproducts (DBPs) and evaluates their toxicity, and it seeks to draw comparisons with outcomes from treatment with sodium hypochlorite, already characterized in previous findings. The proposed treatment indicates the formation of at least 11 DBPs - eight identified for the first time - which have been isolated by various chromatographic techniques, identified by Nuclear Magnetic Resonance and Mass Spectrometry studies and for which a mechanism has been proposed to elucidate their formation. To evaluate irbesartan's biological impact during treatment with sodium percarbonate (SPC), a toxicity study of the DBPs was conducted using Daphnia magna, Aliivibrio fischeri, and Raphidocelis subcapitata, three model organisms. The ecotoxicity was evaluated using the Ecological Structure-Activity Relationships (ECOSAR) computer program and compared with experimental results. Compared to chlorination treatment, a lower mineralization percentage (-43 %) and amount of DBPs at least twice higher were observed. Toxicity assessment highlighted that DBPs formed during SPC treatment were more toxic than those from chlorination. ECOSAR predicted toxicity aligned with experimental findings. Additionally, the DBPs exhibited varying levels of toxicity, primarily attributable to the presence of aromatic and hydroxyl groups in their chemical structure, indicating that SPC treatment is not suitable for treatment of irbesartan polluted waters.

Degradation and detoxification of ribavirin by UV/chlorine/Fe(II) process in water treatment system.

Ribavirin (RBV), which is extensively used to treat viral diseases such as COVID-19, is considered one of the major emerging contaminants due to its long-term existence and health risk in the aqueous environmental system. However, research on effective removal of RBV still remains insufficient. In this study, we investigated the RBV degradation kinetics and mechanism in UV/chlorine/Fe(II) process. The degradation rate constant kobs-RBV of RBV was 2.52 × 10-4 s-1 in UV/chlorine/Fe(II) process, which increased by 1.6 times and 1.3 times than that in chlorine alone and UV/chlorine process, respectively. Notably, trace amount Fe(II) promoted RBV degradation in UV/chlorine system through Fe2+/Fe3+ cycles, enhancing the yield of reactive species such as HO· and certain species reactive chlorine radicals (RCS). The contributions of HO· and RCS toward RBV degradation were 53.91% and 16.11%, respectively. Specifically, Cl·, ClO·, and Cl2·- were responsible for 8.59%, 2.69%, and 4.83% of RBV removal. The RBV degradation pathway indicated that the reactive species preferentially attacked the amide moiety of RBV, which cleaved the ether bond and the hydroxyl group. The toxicity evaluation of RBV degradation products elucidated that UV/chlorine/Fe(II) process was beneficial for RBV detoxification.

Ranking of concern, based on environmental indexes, for pharmaceutical and personal care products: an application to the Spanish case.

A wide range of Pharmaceuticals and Personal Care Products (PPCPs) are present in the environment, and many of their adverse effects are unknown. The emergence of new compounds or changes in regulations have led to dynamical studies of occurrence, impact and treatment, which consider geographical areas and trends in consumption and innovation in the pharmaceutical industry. A Quantitative study of Structure-Activity Relationship ((Q)SAR) was performed to assess the possible adverse effects of ninety six PPCPs and metabolites with negligible experimental data and establish a ranking of concern, which was supported by the EPA EPI Suite™ interface. The environmental and toxicological indexes, the persistence (P), the bioaccumulation (B), the toxicity (T) (extensive) and the occurrence in Spanish aquatic environments (O) (intensive) were evaluated. The most hazardous characteristics in the largest number of compounds were generated by the P index, followed by the T and B indexes. A high number of metabolites has a concern score equal to or greater than their parent compounds. Three PBT and OPBT rankings of concern were proposed using the total and partial ranking method (supported by a Hasse diagram) by the Decision Analysis by Ranking Techniques (DART) tool, which was recently recommended by the European Commission. An analysis of the sensibility of the relative weights of these indexes has been conducted. Hormones, antidepressants (and their metabolites), blood lipid regulators and all of the personal care products considered in this study were at the highest levels of risk according to the PBT and OPBT total rankings. Furthermore, when the OPBT partial ranking was performed, X-ray contrast media, H2 blockers and some antibiotics were included at the highest level of concern. It is important to improve and incorporate useful indexes for the predicted environmental impact of PPCPs and metabolites and thus focus experimental analysis on the compounds that require urgent attention.

Dataset on aquatic ecotoxicity predictions of 2697 chemicals, using three quantitative structure-activity relationship platforms.

Empirical and in silico data on the aquatic ecotoxicology of 2697 organic chemicals were collected in order to compile a dataset for assessing the predictive power of current Quantitative Structure Activity Relationship (QSAR) models and software platforms. This document presents the dataset and the data pipeline for its creation. Empirical data were collected from the US EPA ECOTOX Knowledgebase (ECOTOX) and the EFSA (European Food Safety Authority) report "Completion of data entry of pesticide ecotoxicology Tier 1 study endpoints in a XML schema - database". Only data for OECD recommended algae, daphnia and fish species were retained. QSAR toxicity predictions were calculated for each chemical and each of six endpoints using ECOSAR, VEGA and the Toxicity Estimation Software Tool (T.E.S.T.) platforms. Finally, the dataset was amended with SMILES, InChIKey, pKa and logP collected from webchem and PubChem.

Assisted wet deposition targeted synthesis of Co-N coordination single-atom catalysts for efficient Fenton-like catalytic degradation of micropollutants.

Assisted wet deposition methods to localize the active phase metal on the carrier surface and prevent atomic aggregation during conventional heat treatment are strongly preferred. Herein, single-atom cobalt catalysts (SA-Co-PCN) with different metal-central content were target-prepared using a combination of impregnation and secondary annealing on polymerized carbon nitride (PCN) through reticular confinement. Fitting the coordination configuration of the Co-N pathway within the first coordination shell according to quantitative EXAFS indicated that the ligancy of Co-N was 4. The removal efficiency of representative micropollutants in the SA-Co-PCN/PMS system achieved 100% within 15 min. The outstanding degradation properties of micropollutants were ascribed to the SA-Co-PCN boosts PMS to a 1O2-dominated system. Moreover, the effects of substituents on the degradation behavior and ecotoxicology of sulfonamides (SAs) in PMS-activated systems were investigated in depth. The combination of DFT theoretical calculations and LC-MS further confirmed that the similar electron-rich sites on the SAs molecules allowed for commonality in the degradation pathway. Both S-N bond and C-S bond fragments became the initial attack and cleavage sites in the series of SAs. Ecotoxicity predictions indicated that most intermediates of SAs exhibited lower acute and chronic toxicity, especially acute toxicity, than the parent compounds. ENVIRONMENTAL IMPLICATION: Assisted wet deposition to localize the active phase metal on the carrier surface allows easy target formation of single-atom cobalt catalysts (SA-Co-PCN), which could boost PMS to a 1O2-dominated system for efficient oxidation of typical micropollutants. The degradation behavior and ecotoxicology of sulfonamides in the SA-Co-PCN/PMS system were investigated in depth, revealing that most intermediates of sulfonamides exhibited lower acute and chronic toxicity, especially acute toxicity, than the parent compounds. This work provides a strategy for the development of facilely prepared single-atom catalysts and contributes to the development and application potential of PMS advanced oxidation technology for water pollution control.

Degradation of tartrazine by Oxone® in the presence of cobalt based catalyst supported on pillared montmorillonite - Efficient technology even in extreme conditions.

The catalytic degradation of hazardous organic contaminants in industrial wastewater is a promising technology. Reactions of tartrazine, the synthetic yellow azo dye, with Oxone® in the presence of catalyst in strong acidic condition (pH 2), were detected by using UV-Vis spectroscopy. In order to extend the applicability profile of Co-supported Al-pillared montmorillonite catalyst an investigation of Oxone® induced reactions were performed in extreme acidic environment. The products of the reactions were identified by liquid chromatography-mass spectrometry (LC-MS). Along with the catalytic decomposition of tartrazine induced by radical attack (confirmed as unique reaction path under neutral and alkaline conditions), the formation of tartrazine derivatives by reaction of nucleophilic addition was also detected. The presence of derivatives under acidic conditions slowed down the hydrolysis of tartrazine diazo bond in comparison to the reactions in neutral environment. Nevertheless, the reaction in acidic conditions (pH 2) is faster than the one conducted in alkaline conditions (pH 11). Theoretical calculations were used to complete and clarify the mechanisms of tartrazine derivatization and degradation, as well as to predict the UV-Vis spectra of compounds which could serve as predictors of certain reaction phases. ECOSAR program, used to estimate toxicological profile of compounds to aquatic animals, indicated an increase in the harmfulness of the compounds identified by LC-MS as degradation products from the reaction conducted for 240min. It could be concluded that an intensification of the process parameters (higher concentration of Oxone®, higher catalyst loading, increased reaction time, etc.) is needed in order to obtain only biodegradable products.

Intelligent consensus predictions of bioconcentration factor of pharmaceuticals using 2D and fragment-based descriptors.

Bioconcentration factors (BCFs) are markers of chemical substance accumulation in organisms, and they play a significant role in determining the environmental risk of various chemicals. Experiments to obtain BCFs are expensive and time-consuming; therefore, it is better to estimate BCF early in the chemical development process. The current research aims to evaluate the ecotoxicity potential of 122 pharmaceuticals and identify possible important structural attributes using BCF as the determining feature against a group of fish species. We have calculated the theoretical 2D descriptors from the OCHEM platform and SiRMS descriptor calculating software. The regression-based quantitative structure-property relationship (QSPR) modeling was used to identify the chemical features responsible for acute fish bioconcentration. Multiple models with the "intelligent consensus" algorithm were employed for the regression-based approach improving the predictive ability of the models. To ensure the robustness and interpretability of the developed models, rigorous validation was performed employing various statistical internal and external validation metrics. From the developed models, it can be specified that the presence of large lipophilic and electronegative moieties greatly enhances the bioaccumulative potential of pharmaceuticals, whereas the hydrophilic characteristics have shown a negative impact on BCF. Furthermore, the developed models were employed to screen the DrugBank database (https://go.drugbank.com/) for assessing the BCF properties of the entire database. The evidence acquired from the modeled descriptors might be used for aquatic risk assessment in the future, with the added benefit of providing an early caution of their probable negative impact on aquatic ecosystems for regulatory purposes.

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

Sulfamethoxazole (SMX) is a typical antibiotic in the world, which is frequently detected in the aquatic environment. The current study was aimed to investigate the SMX degradation in secondary treated wastewater using potassium Ferrate [Fe(VI)]. The effects of various experimental conditions, EDTA and phosphate as chelating agents, and toxicity assessment were also considered. Secondary treated effluent was spiked with predefined SMX concentrations, and after desired reaction time with Fe(VI), residual SMX was measured using HPLC. Results indicated that SMX degradation by Fe(VI) was favored under acidic condition, where 90% of SMX degradation was achieved after 120 min. Fe(VI) and SMX reaction obeyed first-order kinetic; meantime, the SMX degradation rate under pH 3 was 7.6 times higher than pH 7. The presence of phosphate (Na2HPO4) and EDTA declined SMX degradation, while Fe (III) effect was contradictory. In addition to promising demolition, 10% TOC removal was achieved. Eighteen major intermediates were identified using LC-MS/MS and the degradation pathways were suggested. Transformation products (TPs) were formed due to hydroxylation, bond cleavage, transformation after bond cleavage, and oxidation reactions. The ECOSAR analysis showed that some of the SMX oxidation products were toxic to aquatic organisms (fish, daphnia and green algae). Supplementary Information: The online version contains supplementary material available at 10.1007/s40201-021-00769-9.

Electrocatalysis degradation of coal tar wastewater using a novel hydrophobic benzalacetone modified lead dioxide electrode.

Coal tar wastewater is hard to degrade by traditional methods because of its toxic pollutant constituents and high concentration of aromatic hydrocarbons, especially phenolic substances. A new type of hydrophobic benzacetone modified PbO2 anode (BA-PbO2 electrodes) was used for the electrocatalytic treatment of coal tar wastewater in a continuous cycle reactor. The surface morphology, structure, valences of elements, hydrophobicity, hydroxyl radical (·OH) produced capacity, electrochemical properties and stability of BA-PbO2 electrodes were characterized by SEM (scanning electron microscopy), XRD (X-ray diffraction), XPS (X-ray photoelectron spectroscopy), contact angle, a fluorescence probe test, an electrochemical workstation and accelerated life test, respectively. The BA-PbO2 electrodes exhibited a compact structure and finely dispersed crystallize size of 4.6 nm. The optimum degradation conditions of coal tar wastewater were as follows: current density of 90 mA cm-2, electrode gap of 1 cm and temperature at 25 °C with flow velocity of 80 L h-1. The chemical oxygen demand (COD) removal efficiency reached 92.39% after 240 min of degradation under the optimized conditions and the after-treatment COD value was 379.51 mg L-1 which was lower than the centralized emission standard (less than 400 mg L-1). These findings demonstrated the feasibility and efficiency of electrocatalytically degrading coal tar wastewater by BA-PbO2 electrodes. The possible mechanism and pathway for phenol a specific pollutant in coal tar wastewater were investigated by quantum chemistry calculations (Multiwfn) and gas chromatography-mass spectrometry (GC-MS). The toxicity of each intermediate was predicted by the ECOSAR program.

Photocatalytic response in water pollutants with addition of biomedical and anti-leishmanial study of iron oxide nanoparticles.

Public health is a major concern globally, owing to the presence of industrial dyes in the effluent. Nanoparticles with green synthesis are an enthralling research field with various applications. This study deals with investigating the photocatalytic potential of Fe-oxide nanoparticles (FeO-NPs) for the degradation of methylene blue dye and their potential biomedical investigations. Biosynthesis using Anthemis tomentosa flower extract showed to be an effective method for the synthesis of FeO-NPs. The freshly prepared FeO-NPs were characterized through UV/Vis spectroscopy showing clear peak at 318 nm. The prepared FeO-NPs were of smaller size and spherical shape having large surface area and porosity with no aggregations. The FeO-NPs were characterized using XRD, FTIR, HRTEM, SEM and EDX. The HRTEM results showed that the particle size of FeO-NPs was 60-90 nm. The antimicrobial properties of FeO-NPs were investigated against two bacterial Staphylococcus aureus 13 (±0.8) and Klebsiella pneumoniae 6(±0.6) and three fungal species Aspergillus Niger, Aspergillus flavus, and Aspergillus fumigatus exhibiting a maximum reduction of 57% 47% and 50%, respectively. Moreover, FeO-NPs exhibited high antioxidant properties evaluated against ascorbic acid. Overall, this study showed high photocatalytic, antimicrobial, and antioxidant properties of FeO-NPs owing to their small size and large surface area. However, the ecotoxicity study of methylene blue degradation products showed potential toxicity to aquatic organisms.

Toxicity of the pharmaceuticals finasteride and melengestrol acetate to benthic invertebrates.

The toxicity of endocrinologically active pharmaceuticals finasteride (FIN) and melengestrol acetate (MGA) was assessed in freshwater mussels, including acute (48 h) aqueous tests with glochidia from Lampsilis siliquoidea, sub-chronic (14 days) sediment tests with gravid female Lampsilis fasciola, and chronic (28 days) sediment tests with juvenile L. siliquoidea, and in chronic (42 days) sediment tests with the amphipod Hyalella azteca and the mayfly Hexagenia spp. Finasteride was not toxic in acute aqueous tests with L. siliquoidea glochidia (up to 23 mg/L), whereas significant toxicity to survival and burial ability was detected in chronic sediment tests with juvenile L. siliquoidea (chronic value (ChV, the geometric mean of LOEC and NOEC) = 58 mg/kg (1 mg/L)). Amphipods (survival, growth, reproduction, and sex ratio) and mayflies (growth) were similarly sensitive (ChV = 58 mg/kg (1 mg/L)). Melengestrol acetate was acutely toxic to L. siliquoidea glochidia at 4 mg/L in aqueous tests; in sediment tests, mayflies were the most sensitive species, with significant growth effects observed at 37 mg/kg (0.25 mg/L) (ChV = 21 mg/kg (0.1 mg/L)). Exposure to sublethal concentrations of FIN and MGA had no effect on the (luring and filtering) behaviour of gravid L. fasciola, or the viability of their brooding glochidia. Based on the limited number of measured environmental concentrations of both chemicals, and their projected concentrations, no direct effects are expected by these compounds individually on the invertebrates tested. However, organisms are exposed to contaminant mixtures in the aquatic environment, and thus, the effects of FIN and MGA as components of these mixtures require further investigation.

Predicting the acute ecotoxicity of chemical substances by machine learning using graph theory.

Accurate in silico predictions of chemical substance ecotoxicity has become an important issue in recent years. Most conventional methods, such as the Ecological Structure-Activity Relationship (ECOSAR) model, cluster chemical substances empirically based on structural information and then predict toxicity by employing a log P linear regression model. Due to empirical classification, the prediction accuracy does not improve even if new ecotoxicity test data are added. In addition, most of the conventional methods are not appropriate for predicting the ecotoxicity on inorganic and/or ionized compounds. Furthermore, a user faces difficulty in handling multiple Quantitative Structure-Activity Relationship (QSAR) formulas with one chemical substance. To overcome the flaws of the conventional methods, in this study a new method was developed that applied unsupervised machine learning and graph theory to predict acute ecotoxicity. The proposed machine learning technique is based on the large AIST-MeRAM ecotoxicity test dataset, a software program developed by the National Institute of Advanced Industry Science and Technology for Multi-purpose Ecological Risk Assessment and Management, and the Molecular ACCess System (MACCS) keys that vectorize a chemical structure to 166-bit binary information. The acute toxicity of fish, daphnids, and algae can be predicted with good accuracy, without requiring log P and linear regression models in existing methods. Results from the new method were cross-validated and compared with ECOSAR predictions and show that the new method provides better accuracy for a wider range of chemical substances, including inorganic and ionized compounds.

Hydroxyl radical-mediated degradation of salicylic acid and methyl paraben: an experimental and computational approach to assess the reaction mechanisms.

Advanced oxidation processes (AOPs) using various energy sources and oxidants to produce reactive oxygen species are widely used for the destruction of recalcitrant water contaminants. The current study is about the degradation of two emerging pollutants-salicylic acid (SA) and methyl paraben (MP)-by high-frequency ultrasonication followed by identification of the oxidation byproducts and modeling of the reaction mechanisms using the density functional theory (DFT). The study also encompasses prediction of the aquatic toxicity and potential risk of the identified byproducts to some aquatic organisms bussing the ECOSAR (Ecological Structure Activity Relationships) protocol. It was found that the degradation of both compounds was governed by •OH attack and the pathways consisted of a cascade of reactions. The rate determining steps were decarboxylation (~ 60 kcal mol-1) and bond breakage reactions (~ 80 kcal mol-1), which were triggered by the stability of the reaction byproducts and overcome by the applied reaction conditions. Estimated values of the acute toxicities showed that only few of the byproducts were harmful to aquatic organisms, implying the environmental friendliness of the experimental method.