Daphnia Magna Toxicity Research Articles

Metabolomic analysis to understand the mechanism of Ti3C2Tx (MXene) toxicity in Daphnia magna

Due to their potential release into the environment, the ecotoxicity of Ti3C2Tx (MXene) nanomaterials is a growing concern. Unfortunately, little is known about the toxic effects and mechanisms through which Ti3C2Tx induces toxicity in aquatic organisms. The aim of this study is thus to investigate the toxic effects and mechanisms of Daphnia magna upon exposure to Ti3C2Tx with different sheet sizes (100 nm [Ti3C2Tx-100] and 500 nm [Ti3C2Tx-500]) by employing conventional toxicology and metabolomics analysis. The results showed that exposure to both Ti3C2Tx-100 and Ti3C2Tx-500 at 10 μg/mL resulted in a significant accumulation of Ti3C2Tx in D. magna, but no effects on the mortality or growth of D. magna were observed. However, the metabolomics results revealed that Ti3C2Tx-100 and Ti3C2Tx-500 induced significant changes in up to 265 and 191 differential metabolites in D. magna, respectively, of which 116 metabolites were common for both. Ti3C2Tx-100-induced metabolites were mainly enriched in phospholipid, pyrimidine, tryptophan, and arginine metabolism, whereas Ti3C2Tx-500-induced metabolites were mainly enriched in the glycerol-ester, tryptophan, and glyoxylate metabolism and the pentose phosphate pathway. These results indicated that the toxicity of Ti3C2Tx to D. magna has a size-dependent effect at the metabolic level, and both sheet sizes of Ti3C2Tx can lead to metabolic disturbances in D. magna by interfering with lipid and amino acid metabolism pathways.

A strategy for the investigation of toxic mechanisms and protection by efflux pumps using Schizosaccharomyces pombe strains: Application to rotenone

Effects not related with the inhibition of complex I of the mitochondrial electron transport chain are studied in S. pombe, which lacks it. This study aims: First, the use of a strategy with S. pombe strains to investigate the toxicity, mechanisms of action, interactions and detoxication by efflux pumps. Second, to investigate the mechanisms of toxic action of rotenone. In the dose-response assessment, the yeast presented a good correlation with the toxicity in Daphnia magna for 15 chemicals. In the mechanistic study, the mph1Δ strain presented marked specificity to the interaction with microtubules by carbendazim. DNA damage caused by hydroxyurea, an inhibitor of deoxynucleotide synthesis, was identified with marked specificity with the rad3Δ strain. The sty1Δ strain was very sensitive to the oxidative and osmotic stress induced by hydrogen peroxide and potassium chloride, respectively, being more sensitive to oxidative stress than the pap1Δ strain. The protection by exclusion pumps was also evaluated. Rotenone presented low toxicity in S. pombe due to the lack of its main target, and the marked protection by the exclusion transporters Bfr1, Pmd1, Caf5 and Mfs1. Marked cellular stress was detected. Finally, the toxicity of rotenone could be potentiated by the fungicide carbendazim and the antimetabolite hydroxyurea. In conclusion, the use of S. pombe strains is a valid strategy to: a) assess global toxicity; b) investigate the main mechanisms of toxic action, particularly spindle and DNA interferences, and osmotic and oxidative stress not related to complex I inhibition; c) explore the detoxication by efflux pumps; and d) evaluate possible chemical interactions. Therefore, it should be useful for the investigation of adverse outcome pathways.

Methylation and Demethylation of Emerging Contaminants Changed Bioaccumulation and Acute Toxicity in Daphnia magna.

Contaminants of emerging concern (CECs) in the environment undergo various transformations, leading to the formation of transformation products (TPs) with a modified ecological risk potential. Although the environmental significance of TPs is increasingly recognized, there has been relatively little research to understand the influences of such transformations on subsequent ecotoxicological safety. In this study, we used four pairs of CECs and their methylated or demethylated derivatives as examples to characterize changes in bioaccumulation and acute toxicity in Daphnia magna, as a result of methylation or demethylation. The experimental results were further compared to quantitative structure-activity relationship (QSAR) predictions. The methylated counterpart in each pair generally showed greater acute toxicity in D. magna, which was attributed to their increased hydrophobicity. For example, the LC50 values of methylparaben (34.4 ± 4.3 mg L-1) and its demethylated product (225.6 ± 17.3 mg L-1) differed about eightfold in D. magna. The methylated derivative generally exhibited greater bioaccumulation than the demethylated counterpart. For instance, the bioaccumulation of methylated acetaminophen was about 33-fold greater than that of acetaminophen. In silico predictions via QSARs aligned well with the experimental results and suggested an increased persistence of the methylated forms. The study findings underline the consequences of simple changes in chemical structures induced by transformations such as methylation and demethylation and highlight the need to consider TPs to achieve a more holistic understanding of the environmental fate and risks of CECs.

Carbon quantum dot-induced developmental toxicity in Daphnia magna involves disturbance of symbiotic microorganisms

With the increasing synthesis and application of carbon quantum dots (CQDs), their prevalence as pollution in water environments has increased. However, the toxic effects of CQDs on aquatic organisms are unclear, and their environmental safety must be evaluated. Herein, Daphnia magna was used as a model organism to explore the developmental toxicity of CQDs under a full life-cycle exposure. It was found that the feeding rate and offing number of D. magna decreased with increasing CQD concentration, and the body length of D. magna showed a trend of first increasing and then decreasing. These results indicated that long-term exposure to CQDs has evident toxic effects on D. magna development. Symbiosis analysis showed that the composition of the symbiotic microbial community of D. magna was disturbed by CQDs. The abundance of microorganisms involved in the immune response of D. magna such as Rhodobacter, decreased; those involved in the inflammation such as Gemmobacter, increased; and those involved in the nitrogen cycle, such as Hydrogenophaga and Paracoccus, decreased. When D. magna was subjected to environmental pressure, host-microflora interactive immune regulation was induced. The abundance of probiotics in D. magna, such as Rhodococcus, increased in response to environmental pressure. The results of KEGG function prediction showed that the abundance of symbiotic microorganisms involved in energy absorption and metabolism was affected by CQDs. In addition, the correlation analysis showed that there was a correlation between the changes in the symbiotic microbial community and the damage to D. magna after exposure to CQDs. Thus, it is appealed that as a potential environmental pollutant, CQDs have aquatic environmental risks, and their safe application deserves attention.

Developmental toxicity in Daphnia magna induced by environmentally relevant concentrations of carbon black: From the perspective of metabolomics and symbiotic bacteria composition

The level of carbon black (CB) pollution in the environment is rapidly increasing, owing to the increase in natural and industrial emissions. The water environment has become an important sink for CB. However, studies on CB mainly focused on its impact on air pollution and phytoremediation applications, and the toxicity mechanism of CB in aquatic organisms is relatively limited. Thus, Daphnia magna was used as a model organism to explore the developmental toxicity of environmentally relevant concentrations of CB under a full life-cycle exposure. The toxicity mechanism of CB in aquatic organisms was investigated based on metabolomic and symbiotic microbial analyses. It was found that compared with the control group, the body length of exposed D. magna decreased, while the mortality and intestinal inflammation increased with increasing concentration of CB. The normal reproductive regularity of D. magna was disturbed, and the deformity and body length of the offspring increased and decreased, respectively, after CB exposure. Metabolomic analysis showed that the urea cycle metabolic pathway of exposed D. magna was increased significantly, suggesting a perturbation of N metabolism. In addition, two eicosanoids were increased, suggesting possible inflammation in D. magna. The levels of seven phospholipid metabolites decreased that might be responsible for offspring malformations. Microbiological analysis showed that the composition of the symbiotic microbial community of D. magna was disturbed, including microorganisms involved in carbon cycling, nitrogen cycling, and biodegradation of pollutants, as well as pathogenic microorganisms. Overall, this study found that the inflammatory related metabolites and symbiotic bacterial, as well as reproductive related metabolites, were disrupted after D. magna exposed to different concentrations of CB, which revealed a possible developmental toxicity mechanism of CB in D. magna. These findings provide a scientific basis for analyzing the risks of CB in aquatic environments.

Influence of ozone microbubble enhanced oxidation on mine effluent mixes and Daphnia magna toxicity

The mining industry often must mix different kinds of water on the mine site during pre-treatment or post-treatment before the final discharge of the treated water to the environment. Microbubble ozonation has proven to be efficient in the removal of contaminants of concern from mine water, such as metals, metalloids, and nitrogen compounds, which can persist in the environment and entail toxicity issues. This study evaluated the efficiency of ozone microbubbles combined with lime precipitation on contaminant removal and its impact on toxicity for Daphnia magna with five different mine effluent mixes from an active mine site located in Abitibi-Témiscamingue, QC, Canada. For the non-acidic mixes, two scenarios were tested: first, pre-treatment of metals using lime precipitation and a flocculant was conducted prior to ozonation; and second, ozonation was conducted prior to metals post-treatment using the same precipitation and flocculation technique. Results showed that the NH3–N removal efficiency ranged from 90% for the lower initial concentrations (1.1 mg/L) to more than 99% for the higher initial concentrations (58.4 mg/L). Moreover, ozonation without metals pre-treatment improved NH3–N treatment efficiency in terms of kinetics but entailed abnormal toxicity issues. Results of bioassays conducted on water with metals pre-treatment did not show any toxicity events but showed abnormal toxicity patterns on the mixes treated without metals pre-treatment (diluted effluents were toxic, while undiluted were not). At 50% dilution, the water was toxic, probably due to the potential presence of metal oxide nanoparticles. The confirmation of the source of toxicity requires further investigation.

Chronic toxicity of broflanilide in Daphnia magna: changes in molting, behavior, and gene expression.

Broflanilide is a novel pesticide used in agriculture that binds to unique receptors on pests; however, the widespread use of broflanilide has led to toxicity in Daphnia magna. At present, little information on the potential threats broflanilide imposes on D. magna is available. Therefore, the present study examined the chronic toxicity of broflanilide in D. magna by comparing changes in molting, neurotransmitter function, and behavior. The results showed that broflanilide caused chronic toxicity in D. magna at a concentration of 8.45μg/L, and growth, development, reproduction, and the development of offspring were affected. In addition, broflanilide affected the molting of D. magna by significantly inhibiting the expression of chitinase, ecdysteroid, and related genes. Broflanilide also affected the expression of γ-glutamic acid, glutamine, gamma-aminobutyric acid, 5-hydroxytryptamine, 5-hydroxytryptophan, dopa, and dopamine. Furthermore, the swimming distance and speed of D. magna were reduced. Taken together, the results demonstrate the chronic toxicity and exposure risk of broflanilide in D. magna.

Phytochemical and biological properties of the water extract from roots and leaves of Lactuca longidentata, an endemic phytoalimurgic (food) species of Central Sardinia (Italy)

Lactuca longidentata is an endemic species present in Sardinia (Italy). The present study aimed to investigate the phytochemical composition and biological properties of leaf and root water extracts obtained from L. longidentata. Phenolic composition, scavenging/reducing, and enzyme inhibition properties were investigated. In vitro studies, namely allelopathy assay, brine shrimp and Daphnia magna toxicity tests, and viability assay on C2C12 myocytes were also conducted for defining the limits of biocompatibility. Antimicrobial properties were studied against Gram + and Gram − bacteria, yeasts, dermatophytes, and fungi isolated as contaminants of public swimming pools. Colorimetric analyses indicated that leaves are richer than roots in total phenols and flavonoids, whereas chromatographic analyses confirmed that leaves are richer in catechins and chicoric acid. The leaf extract was also the most effective as antiradical agent. Within the limits of biocompatibility (concentration <200 µg/mL), the leaf extract was particularly effective in reducing the growth of Escherichia coli and Trichophyton tonsurans (MIC < 10 µg/mL). However, a similar potency was showed by the root extract against the swimming pool fungal species Rhodotorula, Auxarthron ostraviense, and Trichothecium roseum. Overall, the present study suggested new scenarios for this botanical resource, traditionally used as a food, but underestimated as a health-promoting agent.

Pollution Evaluation of the El Pueblito River in Queretaro, Mexico, Using the Water Quality Index

This study evaluated the water pollution of the El Pueblito River by employing physicochemical parameters and biological indicators. Monitoring was conducted weekly during three months at seven sampling sites. To ease the representation of the results of this analysis, the water quality index (WQI) was calculated. The results obtained by the physicochemical analysis show the same trends as those of the analyses performed with bioassays using Daphnia magna and the WQI. The obtained values showed a deterioration of water quality from upstream to downstream due to the discharges into the river that occurred as it went through the city of Corregidora. The WQI values shifted from good water quality (83.00 ± 7.40) upstream to poor water quality (27.00 ± 0.85) downstream. This study also shows the utility of the WQI and how a Daphnia magna toxicity test can be an affordable and fast tool used to indicate high levels of pollution, such as in the case of El Pueblito River.

Water Hardness Alters the Gene Expression Response and Copper Toxicity in Daphnia magna

The influence of water hardness on copper (Cu) toxicity in Daphnia magna was studied using gene expression analysis. Exposing D. magna to Cu in water with increasing levels of hardness decreased the acute toxicity. Hardness did not affect the predicted Cu complexation. After 24 h, D. magna showed an increased level of genes related to metal homeostasis (mt) following exposure to 25 μg Cu/L in hard water. Daphnids in soft and medium water responded to 25 μg Cu/L by upregulation of antioxidant defense and mt genes, revealing oxidative stress as a mechanism of Cu toxicity in D. magna. D. magna exposed to 25 μg Cu/L in soft water did not survive for 96 h. In contrast, those exposed to 25 μg Cu/L in medium and hard water survived for 96 h with significantly higher levels of mt genes. The genes related to oxidative damage (heat shock protein and glutathione S-transferase) in these groups did not deviate from control levels, indicating the protective effect of hardness. Metallothionein genes were upregulated at 17 μg Cu/L at both 24 h and 96 h. The expression of catalase and ferritin increased in this group in soft and hard water at 96 h. The protective effect of hardness (in the tested range) on survival was also observed at a concentration of 25 μg/L. The results suggest metallothionein (A and B), catalase, and ferritin genes, as potential biomarkers for copper exposure in D. magna regardless of hardness.

Modeling and insights into the structural basis of chemical acute aquatic toxicity

It has become a top global regulatory priority to prevent and control pollution from the release of synthetic chemicals, which continues to affect the aquatic communities. In the past decades, computational tools were largely used to significantly reduce the budget and time cost of chemical acute aquatic toxicity assessment. But the structural basis of toxic compounds was rarely analyzed. In the present study, we collected 1438, 485 and 961 chemicals with acute toxicity data records for three representative aquatic species, including Tetrahymena pyriformis, Daphnia magna, and Fathead minnow, respectively. A series of artificial intelligence models were developed using OCHEM tools. For each aquatic toxicity endpoint, a consensus model was developed based on the top performed individual models. The consensus models provided good performance on external validation sets with total accuracy values 96.88 %, 90.63 %, and 84.90 % for Tetrahymena pyriformis toxicity (TPT), Daphnia magna toxicity (DMT), and Fathead minnow toxicity (FMT), respectively. The models can be freely accessed via https://ochem.eu/article/146910. Moreover, the analysis of physical-chemical properties suggested that several key molecular properties of aquatic toxic compounds were significantly different with those of non-toxic compounds. Thus, these descriptors may be associated to chemical acute aquatic toxicity, and may be useful for the understand of chemical aquatic toxicity. Besides, in this study, the structural alerts for aquatic toxicity were detected using f-score and frequency ratio analysis of predefined substructures. A total of 112, 58 and 33 structural alerts were identified responsible for TPT, DMT, and FMT, respectively. These structural alerts could provide useful information for the mechanisms of chemical aquatic toxicity and visual alerts for environmental assessment. All the structural alerts were integrated in the web-server SApredictor (www.sapredictor.cn).

Prediction of acute toxicity to Daphnia magna and interspecific correlation: a global QSAR model and a Daphnia-minnow QTTR model

ABSTRACT Acute toxicity is an important basis for the assessment of hazardous chemicals, but currently there is a huge data gap in chemical toxicity information. The in silico Quantitative Structure Activity Relationship (QSAR) models can use the existing experimental data information to predict the missing chemical toxicity information data and thus reduce animal testing. In the present study, a global QSAR model for the prediction of acute Daphnia magna toxicity has been developed based on the five principles proposed by the Organization for Economic Co-operation and Development (OECD). Moreover, a Daphnia-minnow (referring specifically to the fathead minnow) Quantitative Toxicity–Toxicity Relationship (QTTR) prediction model has been developed based on the present study and our previous work on fathead minnow (Pimephales promelas). Both the QSAR and QTTR prediction models have good goodness-of-fit, robustness, and predictive ability. Finally, the acute toxicity mode of action (MOA) for fathead minnow and Daphnia magna was compared by toxicity ratio based on interspecies toxicity data. By comparison, Daphnia magna was found more sensitive to anilines and phosphorothioates than fathead minnow. The present models can fill the acute toxicity data gap and contribute to the chemicals risk assessment and priority setting.

Correlation analysis of single- and multigenerational endpoints in Daphnia magna toxicity tests: A case-study using TiO2 nanoparticles

Multigenerational toxicity tests provide more sensitive measures of population-level effects than conventional single-generation tests. Particularly for stressors which exhibit slow uptake rates (e.g. nanomaterials), multigenerational tests may also provide a more realistic representation of natural exposure scenarios. To date, the inherently high costs and labor intensity have however limited the use of multigenerational toxicity tests and thereby their incorporation in environmental risk assessment. The aim of the present study was therefore to determine to what extent short(er) term endpoints which are conventionally measured in Daphnia magna toxicity tests hold predictive capacity towards reproduction measured over longer timescales, including multiple generations. To assess this, a case-study was performed in which effects of TiO2 nanoparticles (0, 0.02, 0.2, 2 and 5 mg L−1) on D. magna life-history traits were assessed over five generations. Additionally, it was determined whether offspring derived from exposed parents exhibited sustained adverse effects when rearing them in clean (non-exposed) media after each generation of exposure. The present study showed that although various life-history traits correlate with the total reproductive output in the same- and subsequent generation under non-exposed conditions, these correlations were decoupled in presence of exposure to nTiO2. In addition, it was found that nTiO2 can induce adverse effects on population relevant endpoints at concentrations 1–2 orders of magnitude lower than previously found (i.e. 0.02 mg L−1), and close to the range of concentrations occurring in natural freshwater ecosystems.

Comparative study on ozonation and catalytic ozonation using MgO@Fe3O4 magnetic nanoparticles for the removal of phenylamine from aqueous solutions

ABSTRACT In this research, the performance of catalytic ozonation process (COP) with MgO@Fe3O4 magnetic nanocomposite for phenylamine removal from aqueous solution in a batch environment was evaluated. The features of the catalyst were determined by the FE-SEM, EDS, XRD, VSM and TEM techniques. The effect of several operating parameters such as solution pH, reaction time, catalyst dosage, ozone dose and the initial phenylamine concentrations was investigated in parallel with a single ozonation process (SOP). The effect of the scavengers was assessed. Possible mechanisms, by-products identification and pathway of degradation were also performed. The mineralisation rate was analysed with COD and TOC tests, respectively. The results indicated that the highest efficiency of phenylamine degradation (98.5%) and mineralisation with COD (74%) and TOC (51%) happens in the COP under the optimum conditions (pH = 11.0, reaction time = 30 min, catalyst dosage = 2.0 g/L, ozone dose = 0.38 g/h, phenylamine concentration = 10 mg/L), respectively. The experimental data were in good agreement with pseudo-first-order kinetic model. The toxicity of untreated phenylamine solution revealed that have higher acute toxicity for Daphnia magna than the phenylamine treated solution with COP. The hydroxyl radicals were dominant species during phenylamine degradation. The reusability of the catalyst was evaluated, indicating a 4.7% decrease in performance after six consecutive cycles of the process. As compared to SOP, a significant synergistic effect was observed between ozone and MgO@Fe3O4. It can be concluded that application of MgO@Fe3O4 in catalytic ozonation process is as a successful and promising method for phenylamine degradation of aqueous solutions.

Influence of water hardness on zinc toxicity in Daphnia magna.

Zinc is an essential trace metal required for the maintenance of multiple physiological functions. Due to this, organisms can experience both zinc deficiency and toxicity. Hardness is recognized as one of the main modifying physiochemical factors regulating zinc bioavailability. Therefore, the present study analyzed the effect of hardness on zinc toxicity using Daphnia magna . Endpoint parameters were acute‐toxicity, development, reproduction, and expression data for genes involved in metal regulation and oxidative stress. In addition, the temporal expression profiles of genes during the initiation of reproduction and molting were investigated. Water hardness influenced the survival in response to exposures to zinc. A zinc concentration of 50 μg/l in soft water (50 mg CaCO3/L) caused 73% mortality after 96 h exposure, whereas the same zinc concentration in the hardest water did not cause any significant mortality. Moreover, increasing water hardness from 100 to 200 mg CaCO3/L resulted in a reduced number of offspring. Fecundity was higher at first brood for groups exposed to higher Zn concentrations. The survival data were used to assess the precision of the bioavailability models (Bio‐met) and the geochemical model (Visual MINTEQ). As the Bio‐met risk predictions overestimated the Zn toxicity, a competition‐based model to describe the effects of hardness on zinc toxicity is proposed. This approach can be used to minimize differences in setting environmental quality standards. Moreover, gene expression data showed that using the toxicogenomic approach was more sensitive than the physiological endpoints. Therefore, data presented in the study can be used to improve risk assessment for zinc toxicity.

Applicability of nanomaterial-specific guidelines within long-term Daphnia magna toxicity assays: A case study on multigenerational effects of nTiO2 and nCeO2 exposure in the presence of artificial daylight

In recent years, various ecotoxicological test guidelines and (technical) guidance documents have been evaluated and updated with regard to their applicability to nanomaterials (NMs). Several of these have currently reached official regulatory status. Ensuring their harmonized implementation with previously recognized methods for ecotoxicity testing of chemicals is a crucial next step towards effective and efficient regulation of NMs. In the present study, we evaluated the feasibility of assessing multigenerational effects in the first generation of offspring derived from exposed Daphnia magna whilst maintaining test conditions in accordance with regulatory test guidelines and guidance documents for NMs. To do so, we integrated the recommendations for ecotoxicological testing of NMs as defined in OECD Guidance Document 317 into an extended long-term D. magna reproduction test method (OECD Test Guideline 211) and assessed effects of two poorly soluble NMs (nTiO2 and nCeO2). Our results show adverse effects on life-history parameters of D. magna exposed to the selected nanomaterials within the range of reported environmental concentrations. We argue that conforming to OECD test guidelines and accompanying guidance for nanomaterials is feasible when performing D. magna reproduction tests and can minimize unnecessary duplication of similar experiments, even when extensions to the standardized test setup are added.

Ecotoxicological assessment of amoxicillin trihydrate: Stability, solubility, and acute toxicity for Oreochromis niloticus, Lemna minor, and Daphnia magna

Among the different pharmaceuticals present in water as micro-contaminants, antibiotics are considered an important risk group for the aquatic ecosystem, since their increasing use in human and veterinary medicine could affect the diversity of microorganism communities. This study aims to classify the acute toxicity of amoxicillin trihydrate for organisms of different trophic levels of aquatic biological chains, represented by Oreochromis niloticus (fish), Lemna minor (macrophyte) and Daphnia magna (microcrustacean). For this purpose, amoxicillin trihydrate degradability in water as well as changes in physicochemical characteristics are focused herein. Initial tests were performed to validate the assay, including drug dissolution in M4 medium, drug degradation in various culture media, sensitivity of experimental organisms as well as preliminary drug intoxication test. Upon validation tests, 2.6 g L−1 amoxicillin was determined as the concentration to evaluate the toxicity factor. Static (48 h) and semi-static (168 h) assays were performed. Therefore, amoxicillin trihydrate did not have an acute toxic effect at the concentration of 2.6 g L−1 under the experimental conditions applied to the species Lemna minor, Daphnia magna and Oreochromis niloticus. demonstrating the very low acute toxicity to aquatic organisms at different trophic levels.

Valorization of UWWTP effluents for ammonium recovery and MC elimination by advanced AOPs

The main objective of this study was to generate ready-to-use revalorized irrigation water for fertilization from urban wastewater treatment plant (UWWTP) effluents. The focus was on controlled retention of NH4+ and microcontaminants (MC), using nanofiltration. Retentates generated were treated by solar photo-Fenton at circumneutral pH using Ethylenediamine-N, N′-disuccinic acid (EDDS) iron complexing agent. Solar photo-Fenton degradation efficacy was compared with electrooxidation processes as anodic oxidation, solar-assisted anodic oxidation, electro-Fenton and solar photoelectro Fenton. Finally, phytotoxicity and acute toxicity tests were performed to demonstrate the potentially safe reuse of treated wastewater for crop irrigation. Nanofiltration was able to produce a ready-to-use permeate stream containing recovered NH4+. (valuable nutrient). Solar photo-Fenton treatment at circumneutral pH would only be of interest for rapid degradation of contaminants at less than 1 mg/L in nanofiltration retentates. Other alternative tertiary treatments, such as electrooxidation processes, are a promising alternative when a high concentration of MC requires longer process times. Anodic oxidation was demonstrated to be able to eliminate >80% of microcontaminants and solar-assisted anodic oxidation significantly reduced the electricity consumption. Electro-Fenton processes were the least efficient of the processes tested. Phytotoxicity results showed that irrigation with the permeates reduced germination, root development was mainly promoted and shoot development was positive only at low retention rate (concentration factor = 2). Acute and chronic Daphnia magna toxicity studies demonstrated that the permeate volumes should be diluted at least 50% before direct reuse for crop irrigation.

QSAR modelling of organic dyes for their acute toxicity in Daphnia magna using 2D-descriptors

ABSTRACT The present study reports quantitative structure-activity relationship (QSAR) models for 22 organic dyes spanning a broad chemical domain to predict their toxicity in Daphnia magna [log (1/EC50)]. Only two-dimensional descriptors with clear physicochemical meaning were used to construct the QSAR models. The process of development, validation, and interpretation of models adheres to the stringent recommendations of the Organization for Economic Cooperation and Development (OECD) guidelines. In this study, the multi-layered stepwise regression method and linear discriminant analysis (LDA) method were employed for the deployment of regression – and classification-based models respectively; however, the final regression-based QSAR models were obtained through the partial least squares (PLS) regression. Additionally, the applicability domain of the developed models was verified. The constructed models should be applicable in the absence of toxicity data of new or untested dye structures, particularly when the compounds fall within the developed models’ scope, and also implementable to develop more environmentally friendly alternatives.

Spanish Satureja montana L. hydrolate: Ecotoxicological study in soil and water non-target organisms

Despite the current popularity of herbal and flower hydrolates and the multiple applications found in the food, wood, pharmaceutical, pesticide, perfume, cosmetic, and aromatherapy industries, the effect of hydrolates in the environment is poorly known. This study evaluates the ecotoxicity of the Satureja montana L. hydrolate on water and soil bioindicators and also on the fluvial periphyton mesocosms for a more ecological point of view. The acute toxicity of the fresh water invertebrate Daphnia magna, the bacteria Vibrio fisheri, and the earthworm Eisenia fetida, was quantified as well as the phytotoxic effect on the plant Allium cepa L. Communities of river periphyton were used to study the impact of the hydrolate on the freshwater ecosystems. The taxonomic study of these communities revealed a rich diversity of diatoms. The hydrolate of S. montana showed a high ecotoxicity at very low percentages of hydrolate in all organisms tested and in the periphyton communities. The LC50 varies from 0.05% to 4.25%, with a clear dose-dependent relationship. The effect of the hydrolate in decreasing order was: A.cepa > D. magna > V. fisheri > periphyton > E. fetida. The strong phytotoxic effect on A. cepa allows exploring possible uses of the hydrolate as a bio-herbicide. The Gas Chromatography Mass Spectrometry (GC-MS) characterisation of the hydrolate reveals 1 alcohol and 6 terpenes. Carvacrol (89.03%) and thymol (6.66%) are the volatile compounds found in the highest proportion, products that have multiple biological properties and known synergistic effects, which could explain the high bioactivity of the hydrolate. Our study suggests that S. montana hydrolate could impact different trophic levels of the river ecosystems and can affect the soil functions affecting earthworms due its powerful bioactivity on a wide range of non-target organisms even in complex communities such as the fluvial periphyton. Therefore, although hydrolates can become a good alternative to synthetic products, the use of these products is not free of environmental risks and their release to the environment should be evaluated.