Chiral bioaccumulation behavior of tebuconazole in the zebrafish (Danio rerio)

Stereoselective In Vitro Metabolism, Hepatotoxicity, and Cytotoxic Effects of Four Enantiomers of the Fungicide Propiconazole

Propiconazole (PRO) is a chiral triazole fungicide that has been widely used for several years. However, its metabolic characteristics and hepatotoxicity in the chiral level environment remain unclear. In this study, the stereoselective behavior of PRO was investigated by using liver microsome incubation, cell viability assay, inhalation exposure, and molecular docking. Our results demonstrated that the isomers trans (-)-2R,4R-PRO and cis (+)-2R,4S-PRO exhibited slower metabolic rates in rat liver microsomes. The cytochrome P450 family 1 subfamily A polypeptide 2 enzyme was found to play a key role in the metabolism of PRO, contributing to its stereoselective behavior. Histopathological and cell viability results showed that exposure to rac-PRO could induce severe hepatotoxicity in mice. This effect might be related to the accumulation of cis (+)-2R,4S-PRO in the liver, which has a slow metabolism and is highly toxic. Our findings indicate that avoiding the application of cis (+)-2R,4S-PRO in agriculture can significantly reduce adverse effects on nontarget organisms.

Elucidating enantioselective fate and sensitive biomarkers in zebrafish of chiral pesticide fenpropidin: Insights into metabolic pathways and hazard assessment

Fenpropidin (FPD), a widely utilized chiral fungicide, has been detected in aquatic environments. This study systematically evaluated the bioaccumulation, depuration, biotransformation, and sensitive biomarkers of FPD enantiomers in zebrafish to assess their environmental risks. Compared with S-FPD, R-FPD demonstrated a higher rate of enrichment and an increased level of bioaccumulation. The half-lives of R-FPD and S-FPD were 0.49 ± 0.01 and 0.91 ± 0.02 days at 0.05 mg/L and 1.65 ± 0.01 and 1.85 ± 0.03 days at 0.5 mg/L. Nontarget metabolism analysis identified nine metabolites, primarily formed through hydroxylation, oxidation, dehydration, glutathione conjugation, and glucuronidation pathways. Some metabolites exhibited high toxicity, underscoring the necessity for continuous monitoring of their toxicological effects and environmental fate in risk assessments. The toxicity of S-FPD in zebrafish was 1.21 times greater than that of R-FPD. Furthermore, this study identified sensitive markers for the enantiomers at both protein and transcriptional levels using an integrated biomarker response approach. S-FPD exhibited increased sensitivity to apoptosis and metabolic gene expression, while R-FPD showed greater sensitivity to antioxidant kinase activity. These findings facilitate timely monitoring of environmental pollution caused by FPD enantiomers. This study provides critical insights for assessing potential risks associated with pesticide exposure to human health.

Synthesis of a novel β-cyclodextrin chiral stationary phase and its application to the evaluation of the enantioselective bioaccumulation and elimination behavior of tebuconazole in Rana nigromaculata tadpoles

BACKGROUND

The increased production and use of chiral pesticides will enhance their exposure in the environment. Chiral pesticides typically exhibit varied biological effects among these enantiomers. Therefore, it is very essential to develop and validate chiral analytical methods to investigate their potential ecological risks from a stereoselective perspective. Current separation of pesticides enantiomers relies extensively on chiral stationary phases (CSPs), while the development of β-Cyclodextrin derivatives CSPs become the research focus due to their great modifiability and excellent chiral recognition capabilities.

RESULTS

A novel chiral stationary phase, 3,5-dichlorophenylaminomethyl-6-phenylenediamine-β-cyclodextrin chemically bonded silica gel (MPDCDA), was successfully prepared. Based on that, a stereoselective HPLC-MS/MS method was developed and validated for the determination of tebuconazole enantiomers in Rana nigromaculata tadpoles. After extraction by QuEChERS, the tebuconazole enantiomers were completely separated with the resolutions of 1.63 using the mobile phase of methanol-water (70/30, v/v). Good linearity (r > 0.9990) for both enantiomers over a concentration range of 0.20-500.0 ng/mL was obtained with the accuracy ranged from 6.7 % to 9.3 % and the intra-day and inter-day precisions below 6.2 % at three quality control levels. The proposed method was successfully applied in evaluating the enantioselective bioaccumulation and elimination profiles of tebuconazole in tadpoles. At the tested conditions, there was no significantly enantioselective difference in the bioaccumulation process for S- tebuconazole and R-tebuconazole. However, the elimination process of tebuconazole enantiomers was enantioselective with R-tebuconazole preferentially degraded.

SIGNIFICANCE

This work provided an accurate risk assessment of chiral pesticides to non-target aquatic organisms from a stereoselective perspective. These findings would deepen our understanding of the potential ecological risks of chiral pesticides on aquatic organisms and provide scientific support for the protection of aquatic organisms and their ecological environments, as well as sustainable development.

High-efficient removal of tebuconazole from aqueous solutions using P-doped corn straw biochar: Performance, mechanism and application

Due to the serious threat posed by tebuconazole to the aquatic ecosystem, it is imperative to develop a highly efficient adsorbent material for the sustainable remediation of tebuconazole-contaminated water. Herein, a phosphorus (P)-doped biochar from corn straw and H3PO4 was fabricated by one-step pyrolysis for tebuconazole adsorption. Results showed that the P-doped biochar produced at 500℃ (PBC500) possesses a large specific surface area (SSA=869.6 m2/g), abundant surface functional groups, and the highest tebuconazole adsorption capacity (429.6 mg/g). The adsorption of tebuconazole on PBC500 followed pseudo-second-order kinetics and Langmuir adsorption isotherm models. Thermodynamic calculations indicated that the adsorption of tebuconazole by PBC500 was a spontaneous, endothermic process with a random increase. Adsorption mechanism mainly involves pore filling, π-π interactions, hydrogen bonding, and hydrophobic interaction. Moreover, PBC500 demonstrated robust anti-interference capabilities in adsorbing tebuconazole from diverse water sources and exhibited excellent reusability, underscoring its potential for a broad array of practical applications.

Computational simulations uncover enantioselective metabolism of chiral triazole fungicides by human CYP450 enzymes: A case study of tebuconazole

Tebuconazole (TEB), a prominent chiral triazole fungicide, has been extensively utilized for plant pathogen control globally. Despite experimental evidence of TEB metabolism in mammals, the enantioselectivity in the biotransformation of R- and S-TEB enantiomers by specific CYP450s remains elusive. In this work, integrated in silico simulations were employed to unveil the binding interactions and enantioselective metabolic fate of TEB enantiomers within human CYP1A2, 2B6, 2E1, and 3A4. Molecular dynamics (MD) simulations clearly delineated the binding specificity of R- and S-TEB to the four CYP450s, crucially determining their differences in metabolic activity and enantioselectivity. The primary driving force for robust ligand binding was identified as van der Waals interactions with CYP450s, particularly involving the hydrophobic residues. Mechanistic insights derived from quantum mechanics/molecular mechanics (QM/MM) calculations established C2-methyl hydroxylation as the predominant route of R-/S-TEB metabolism, while C6-hydroxylation and triazol epoxidation were deemed kinetically infeasible pathways. Specifically, the resulting hydroxy-R-TEB metabolite primarily originates from R-TEB biotransformation by 1A2, 2E1 and 3A4, whereas hydroxy-S-TEB is preferentially produced by 2B6. These findings significantly contribute to our comprehension of the binding specificity and enantioselective metabolic fate of chiral TEB by CYP450s, potentially informing further research on human health risk assessment associated with TEB exposure.

A review on the enantioselective distribution and toxicity of chiral pesticides in aquatic environment

Chiral pesticides account for about 40% of the total pesticides. In the process of using pesticides, it will inevitably flow into the surface water and even penetrate into the groundwater through surface runoff and other means, as a consequence, it affects the water environment. Although the enantiomers of chiral pesticides have the same physical and chemical properties, their distribution, ratio, metabolism, toxicity, etc. in the organism are often different, and sometimes even show completely opposite biological activities. In this article, the selective fate of different types of chiral pesticides such as organochlorine, organophosphorus, triazole, pyrethroid and other chiral pesticides in natural water bodies and sediments, acute toxicity to aquatic organisms, chronic toxicity and other aspects are summarized to further reflect the risks between the enantiomers of chiral pesticides to non-target organisms in the water environment. In this review, we hope to further explore its harm to human society through the study of the toxicity of chiral pesticide enantiomers, so as to provide data support and theoretical basis for the development and production of biochemical pesticides.

Insights into the role of FoxL2 in tebuconazole-induced male- biased sex differentiation of zebrafish

Tebuconazole (TEB) is a commonly used fungicide that inhibits the aromatase Cyp19A and downregulates the transcription factor forkhead box L2 (FoxL2), leading to male-biased sex differentiation in zebrafish larvae. However, the specific mechanism by which FoxL2 functions following TEB exposure remains unclear. In this study, the phosphorylation sites and kinase-specific residues in zebrafish FoxL2 protein (zFoxL2) were predicted. Subsequently, recombinant zFoxL2 was prepared via prokaryotic expression, and a polyclonal rabbit-anti-zFoxL2 antibody was generated. Zebrafish fibroblast (ZF4) cells were exposed to 100-μM TEB alone for 8 h, after which changes in the expression of genes involved in the foxl2 regulatory pathway (akt1, pi3k, cyp19a1b, c/ebpb and sox9a) were detected. When co-exposed to 1-μM estradiol and 100-μM TEB, the expression of these key genes tended to be restored. Interestingly, TEB did not affect the expression of the foxl2 gene or protein but it significantly suppressed the phosphorylation of FoxL2 (pFoxL2) at serine 238 (decreased by 43.64 %, p = 0.009). Co-immunoprecipitation assays showed that, following exposure to 100-μM TEB, the total precipitated proteins in ZF4 cells decreased by 17.02 % (p = 0.029) and 31.39 % (p = 0.027) in the anti-zFoxL2 antibody group and anti-pFoxL2 (ser238) antibody group, respectively, indicating that TEB suppressed the capacity of the FoxL2 protein to bind to other proteins via repression of its own phosphorylation. The pull-down assay confirmed this conclusion. This study preliminarily elucidated that the foxl2 gene functions via post-translational regulation through hypophosphorylation of its encoded protein during TEB-induced male-biased sex differentiation.

Chemoenzymatic Asymmetric Synthesis of Chiral Triazole Fungicide (R)-Tebuconazole in High Optical Purity Mediated by an Epoxide Hydrolase from Rhodotorula paludigensis

Tebuconazole is a chiral triazole fungicide used globally in agriculture as a racemic mixture, but its enantiomers exhibit significant enantioselective dissimilarities in bioactivity and environmental behaviors. The steric hindrance caused by the tert-butyl group makes it a great challenge to synthesize tebuconazole enantiomers. Here, we designed a simple chemoenzymatic approach for the asymmetric synthesis of (R)-tebuconazole, which includes the biocatalytic resolution of racemic epoxy-precursor (2-tert-butyl-2-[2-(4-chlorophenyl)ethyl] oxirane, rac-1a) by Escherichia coli/Rpeh whole cells expressed epoxide hydrolase from Rhodotorula paludigensis (RpEH), followed by a one-step chemocatalytic synthesis of (R)-tebuconazole. It was observed that (S)-1a was preferentially hydrolyzed by E. coli/Rpeh, whereas (R)-1a was retained with a specific activity of 103.8 U/g wet cells and a moderate enantiomeric ratio (E value) of 13.4, which was remarkably improved to 43.8 after optimizing the reaction conditions. Additionally, a gram-scale resolution of 200 mM rac-1a was performed using 150 mg/mL E. coli/Rpeh wet cells, resulting in the retention of (R)-1a in a 97.0% ees, a 42.5% yields, and a 40.5 g/L/d space-time yield. Subsequently, the synthesis of highly optical purity (R)-tebuconazole (>99% ee) was easily achieved through the chemocatalytic ring-opening of the epoxy-precursor (R)-1a with 1,2,4-triazole. To elucidate insight into the enantioselectivity, molecular docking simulations revealed that the unique L-shaped substrate-binding pocket of RpEH plays a crucial role in the enantioselective recognition of bulky 2,2-disubstituted oxirane 1a.

A comprehensive review on toxicological mechanisms and transformation products of tebuconazole: Insights on pesticide management

Tebuconazole has been widely applied over three decades because of its high efficiency, low toxicity, and broad spectrum, and it is still one of the most popular fungicides worldwide. Tebuconazole residues have been frequently detected in environmental samples and food, posing potential hazards for humans. Understanding the toxicity of pesticides is crucial to ensuring human and ecosystem health, but the toxic mechanisms and toxicity of tebuconazole are still unclear. Moreover, pesticides could transform into transformation products (TPs) that may be more persistent and toxic than their parents. Herein, the toxicities of tebuconazole to humans, mammals, aquatic organisms, soil animals, amphibians, soil microorganisms, birds, honeybees, and plants were summarized, and its TPs were reviewed. In addition, the toxicity of tebuconazole TPs to aquatic organisms and mammals was predicted. Tebuconazole posed potential developmental toxicity, genotoxicity, reproductive toxicity, mutagenicity, hepatotoxicity, neurotoxicity, cardiotoxicity, and nephrotoxicity, which were induced via reactive oxygen species-mediated apoptosis, metabolism and hormone perturbation, DNA damage, and transcriptional abnormalities. In addition, tebuconazole exhibited apparent endocrine-disrupting effects by modulating hormone levels and gene transcription. The toxicity of some TPs was equivalent to and higher than tebuconazole. Therefore, further investigation is necessary into the toxicological mechanisms of tebuconazole and the combined toxicity of a mixture of tebuconazole and its TPs.

Effects of acute exposure to environmentally realistic tebuconazole concentrations on stress responses of kidney and digestive gland of Lymnaea stagnalis

This study aimed to investigate the effects of 24 and 72 h exposure to environmentally relevant concentrations of tebuconazole (TEB) (10, 100 and 500 µg/L) fungicide on the freshwater snail Lymnaea stagnalis. The focus was induction of oxidative stress, alteration of gene expressions and histopathological changes in the kidney and digestive gland. TEB treatment induced a time- and concentration-dependent increase in intracellular reactive oxygen species (ROS) and malondialdehyde (MDA) levels, while the total antioxidant capacity (TAC) was decreased. The activities of glutathione peroxidase (GPx), glutathione reductase (GR), and catalase (CAT) also increased in a time- and concentration-dependent manner in both tissues. TEB exposure significantly increased the mRNA levels of CAT, GPx, GR, heat shock proteins HSP40 and HSP70. Histological analysis revealed nephrocyte degeneration and disrupted digestive cells. The study concludes that acute exposure to TEB induces oxidative stress, alters antioxidant defense mechanisms, and leads to histopathological changes in L. stagnalis.

Exposure of embryos to fenbuconazole causes persistent neurotoxicity in adult zebrafish

In this study, the persistent effects of embryonic exposure to fenbuconazole (FBZ), a triazole fungicide, on neurobehaviour in zebrafish were investigated. After exposure of fertilized eggs to FBZ for 72 h (h), the larvae were cultured to adulthood in clean water. In adult zebrafish embryonically exposed to 50 and 500 ng L-1 FBZ, the ratio of brain weight/body weight was significantly decreased, and the number of apoptotic cells in the brain was significantly increased, accompanied by upregulated protein levels of P53 and downregulated levels of BCL2. The novel tank test showed a significant reduction in the moved distance and speed, and a longer period of adaptation to new environments in the 500 ng L-1 group. The social preference experiment showed impaired social interaction behaviour and reduced time of aggregation in the 500 ng L-1 group. Increased dopamine and norepinephrine levels in the brain might be responsible for this anxiety-like behaviour. In addition to upregulated protein levels of tyrosine hydroxylase and β2-adrenoceptor, the transcription of genes related to dopamine and norepinephrine synthesis in the brain such as th1, th2, ddc, drd1b, dat, and dbh, was increased. The methylation levels of related genes were reduced, which were matched with their increased transcriptional levels. These results demonstrate that embryonic FBZ exposure might cause persistent neurotoxicity in adulthood, which suggests the rational cautious use of FBZ.

Comprehensive Stereoselectivity Assessment of Toxicokinetics, Tissue Distribution, Cytotoxicity, and Environmental Fate of Chiral Pesticide Propiconazole

Propiconazole (PRO) has been widely used in the treatment of fungal infection in fruits, vegetables, cereals, and seeds. In this study, a newly established chiral liquid chromatography tandem mass spectrometry method was applied to the systemic stereoselectivity evaluation of PRO enantiomers, including toxicokinetics, tissue distributions, cytotoxicity, accumulation, and degradation. Our results showed that both trans (+)-2S,4S-PRO and cis (-)-2S,4R-PRO had lower Cmax and AUC0-∞ and higher CLz/F values in plasma and lower accumulation concentrations in the liver, heart, and brain. In cytotoxic assays, cis (-)-2S,4R-PRO exhibited the lowest cytotoxicity in PC12 neuronal, N9 microglia, SH-SY5Y neuroblastoma, and MRC5 lung fibroblast cell lines. Moreover, the Eisenia fetida incubation experiment revealed that the accumulations of both trans (+)-2S,4S-PRO and cis (-)-2S,4R-PRO were higher than those of their antipodes in E. fetida. In summary, our findings first suggested that the application of cis (-)-2S,4R-PRO for agriculture would hugely reduce the environmental risk.

Identification of metabolites generated in the biotransformation process by the Danio rerio (zebrafish) exposed to the fungicide tebuconazole

Tebuconazole is a triazole fungicide widely used in agricultural crops for control of multiple fungal, mainly foliar and soil-borne diseases. Due to its intense use, this pesticide has been detected on aquatic matrices in different countries, which makes it necessary to identify metabolites capable to be used in its exposure monitoring. The aim of this work was to evaluate tebuconazole metabolites in zebrafish water tanks using liquid chromatography coupled to a high-resolution mass spectrometer (LCHRMS) to highlight analytical targets to monitor tebuconazole exposure in aquatic environments. Two Phase I metabolites, TEB-OH and TEB-COOH, and one Phase II metabolite, TEB-S, were identified. Target metabolomics pointed TEB-S as the most important metabolite for discrimination between treatment and negative control group and potential surrogate for detection and monitoring of tebuconazole exposure in aquatic environments. To the best of our knowledge, this is the first study to suggest the sulphation of tebuconazole (TEB-S) by zebrafish metabolism. Moreover, the use of water samples proved to be a promising approach when compared to the usual biological matrices (e.g. plasma) for evaluating the exposure of aquatic animals to tebuconazole because it is a clean and easy to obtain matrix. Water samples presented a higher concentration of metabolites when compared to plasma samples. The results suggest the applicability of this assay model for the identification of potential biomarkers for monitoring the presence of xenobiotics in water.

Enantioselective effect of the chiral fungicide tebuconazole on the microbiota community and antibiotic resistance genes in the soil and earthworm gut

Tebuconazole, consisting of two enantiomers, has a high detectable rate in the soil. The residue of tebuconazole in the soil may cause risk to microbiota community. Antibiotic resistance genes (ARGs) are considered as emerging environmental contaminants, and they can be transferred vertically and horizontally between microbiota community in the soil. Until now, the enantioselective effect of tebuconazole on the microbiota community and ARGs in the soil and earthworm gut has remained largely unknown. Tebuconazole enantiomers showed different bioconcentration behaviors in earthworms. The relative abundances of bacteria belonging to Actinobacteriota, Crenarchaeota and Chloroflexi in R-(-)-tebuconazole-treated soil were higher than those in S-(+)-tebuconazole-treated soil at same concentrations. In the earthworm gut, bacteria belonging to Proteobacteria and Bacteroidota exhibited different relative abundances between the S-(+)-tebuconazole and R-(-)-tebuconazole treatments. The numbers and abundances of ARGs in the soil treated with fungicides were higher than those in the control. In earthworm gut, the diversities of ARGs in all treatments were higher than that in the control, and the relative abundances of Aminoglycoside, Chloramphenicol, Multidrug resistance genes and mobile genetic elements (MGEs) in R-(-)-tebuconazole-treated earthworm gut were higher than those in S-(+)-tebuconazole-treated earthworm gut. Most of ARGs showed a significantly positive correlation with MGEs. Based on network analysis, many ARGs may be carried by bacteria belonging to Bacteroidota and Proteobacteria. These results provide valuable information for understanding the enantioselective effect of tebuconazole on the microbiota community and ARGs.

Toxicity effects of pesticides based on zebrafish (Danio rerio) models: Advances and perspectives

Pesticides inevitably enter aquatic environments, posing potential risks to organisms. The common aquatic model organism, zebrafish (Danio rerio), are widely used to evaluate the toxicity of pesticides. In this review, we searched the Web of Science database for articles published between 2012 and 2022, using the keywords "pesticide", "zebrafish", and "toxicity", retrieving 618 publications. Furthermore, we described the main pathways by which pesticides enter aquatic environments and the fate of their residues in these environments. We systematically reviewed the toxicity effects of pesticides on zebrafish, including developmental toxicity, endocrine-disrupting effects, reproductive toxicity, neurotoxicity, immunotoxicity, and genotoxicity. Importantly, we summarized the latest research progress on the toxicity mechanism of pesticides to zebrafish based on omics technologies, including transcriptomics, metabolomics, and microbiomics. Finally, we discussed future research prospects, focusing on the combined exposure of multiple pollutants including pesticides, the risk of multigenerational exposure to pesticides, and the chronic toxicity of aquatic nanopesticides. This review provides essential data support for ecological risk assessments of pesticides in aquatic environments, and has implications for water management in the context of pesticide pollution.

The fungicide tebuconazole modulates the sodium current of human NaV1.5 channels expressed in HEK293 cells

The fungicide Tebuconazole is a widely used pesticide in agriculture and may cause cardiotoxicity. In our present investigation the effect of Tebuconazole on the sodium current (INa) of human cardiac sodium channels (NaV1.5) was studied using a heterologous expression system and whole-cell patch-clamp techniques. Tebuconazole reduced the amplitude of the peak INa in a concentration- and voltage-dependent manner. At the holding potential of -120 mV the IC50 was estimated at 204.1 ± 34.3 μM, while at -80 mV the IC50 was 0.3 ± 0.1 μM. The effect of the fungicide is more pronounced at more depolarized potentials, indicating a state-dependent interaction. Tebuconazole caused a negative shift in the half-maximal inactivation voltage and delayed recovery from fast inactivation of INa. Also, it enhanced closed-state inactivation, exhibited use-dependent block in a voltage-dependent manner. Furthermore, Tebuconazole reduced the increase in late sodium current induced by the pyrethroid insecticide β-Cyfluthrin. These results suggest that Tebuconazole can interact with NaV1.5 channels and modulate INa. The observed effects may lead to decreased cardiac excitability through reduced INa availability, which could be a new mechanism of cardiotoxicity to be attributed to the fungicide.

Bioactivity of the DMI fungicide mefentrifluconazole against Sclerotium rolfsii, the causal agent of peanut southern blight

BACKGROUND

Sclerotium rolfsii, the causal agent of peanut southern blight, has become increasingly prevalent and harmful in China, causing serious economic losses to the peanut industry. To effectively manage peanut southern blight, this study evaluated the bioactivity of the new-generation sterol demethylation inhibitor (DMI) fungicide mefentrifluconazole against peanut S. rolfsii.

RESULTS

In this study, the DMI fungicide mefentrifluconazole exhibited excellent inhibitory activity against the mycelial growth of S. rolfsii, with a mean EC₅₀ value of 0.21 ± 0.11 mg L^-1 and a range of 0.02 to 0.55 mg L^-1 for 261 isolates collected from Hebei, Henan and Shandong provinces. Mefentrifluconazole significantly reduced the biomass of mycelia and affected the morphology of hyphae. Although sclerotia were more tolerant to mefentrifluconazole than mycelial growth, mefentrifluconazole greatly inhibited the formation and germination of sclerotia. In addition, sclerotia produced by mefentrifluconazole-treated mycelia were deficient in nutrients (e.g., protein, carbohydrate and lipid). These results indicated that mefentrifluconazole may reduce the population of S. rolfsii in the following year. In greenhouse experiments, mefentrifluconazole showed control efficacy and good persistence against peanut S. rolfsii. The preventative and curative activities of mefentrifluconazole at 200 mg L^-1 against southern blight still reached 95.36% and 60.94%, respectively, after 9 days of application. No correlation was observed for the sensitivity of S. rolfsii to mefentrifluconazole and the tested DMI, quinone outside inhibitor and succinate dehydrogenase inhibitor fungicides.

CONCLUSION

All data indicated that mefentrifluconazole could provide favorable control efficacy against S. rolfsii from peanuts and reduce the infection and population of S. rolfsii in the following year. © 2023 Society of Chemical Industry.

Metabolomic approach of azole fungicides in radish (Raphanus sativus): Perspective of functional metabolites

Azole fungicides is one of the major fungicides in agricultural field. In this study, toxic effects of diniconazole (DIN), metconazole (MET), and tebuconazole (TEB) to radish leaves and roots were investigated using targeted metabolomics with gas chromatography-mass spectrometry (GC-MS/MS). Especially, the changes of functional chemicals, including phytosterols and glucosinolates evaluated. Radish leaves and roots were harvested after 7 days and 14 days from last exposure. In multivariate analysis, the experimental groups showed clear separation in PCA and PLS-DA score plots. Phytosterols and glucosinolates were significantly changed by azole fungicide. Six metabolic pathways which are affected by fungicides were selected and showed similar patterns regardless of the type of azole fungicide used. As a result, azole fungicide induces the defense mechanisms of plants and affects both primary and secondary metabolism.

Widespread triazole pesticide use affects infection dynamics of a global amphibian pathogen

The sixth mass extinction is a consequence of complex interplay between multiple stressors with negative impact on biodiversity. We here examine the interaction between two globally widespread anthropogenic drivers of amphibian declines: the fungal disease chytridiomycosis and antifungal use in agriculture. Field monitoring of 26 amphibian ponds in an agricultural landscape shows widespread occurrence of triazole fungicides in the water column throughout the amphibian breeding season, together with a negative correlation between early season application of epoxiconazole and the prevalence of chytrid infections in aquatic newts. While triazole concentrations in the ponds remained below those that inhibit growth of Batrachochytrium dendrobatidis, they bioaccumulated in the newts' skin up to tenfold, resulting in cutaneous growth-suppressing concentrations. As such, a concentration of epoxiconazole, 10 times below that needed to inhibit fungal growth, prevented chytrid infection in anuran tadpoles. The widespread presence of triazoles may thus alter chytrid dynamics in agricultural landscapes.

Maternal exposure to chiral triazole fungicide tebuconazole induces enantioselective thyroid disruption in zebrafish offspring

Pesticides could induce long-term impacts on aquatic ecosystem via transgenerational toxicity. However, for many chiral pesticides, the potential enantioselectivity of transgenerational toxicity has yet to be fully understood. In this study, we used zebrafish as models to evaluate the maternal transfer risk of tebuconazole (TEB), which is a chiral triazole fungicide currently used worldwide and has been frequently detected in surface waters. After 28-day food exposure (20 and 400 ng/g) to the two enantiomers of TEB (S- and R-TEB) in adult female zebrafish (F0), increased malformation rate and decreased swimming speed were found in F1 larvae, with R-TEB showing higher impacts than S-enantiomer. Additionally, enantioselective effects on the secretion of thyroid hormones (THs) and expression of TH-related key genes along the hypothalamic-pituitary-thyroid (HPT) axis were found in both F0 and F1 after maternal exposure. Both the two enantiomers significantly disrupted the triiodothyronine (T3) and thyroxine (T4) contents in F0 with different degrees, whereas in F1, significant effects were only found in R-TEB groups with decreasing of both T3 and T4 contents. Most of the HPT axis related genes in F0 were upregulated by TEB and more sensitive to R-TEB than to S-TEB. In contrast, most of the genes in F1 were downregulated by both R- and S-TEB, especially the genes that are primarily responsible for thyroid development and growth (Nkx2-1), TH synthesis (NIS and TSHꞵ) and metabolism (Deio1). Findings from this study highlight the key role of enantioselectivity in the ecological risk assessment of chiral pesticides through maternal transfer.

Systematic Stereoselectivity Evaluations of Tetramethrin Enantiomers: Stereoselective Cytotoxicity, Metabolism, and Environmental Fate in Earthworms, Soils, Vegetables, and Fruits

Tetramethrin is a widely applied type I chiral pyrethroid insecticide that exists as a mixture of four isomers. In the present study, its stereoselective cytotoxicity, bioaccumulation, degradation, and metabolism were investigated for the first time at the enantiomeric level in detail by using a sensitive chiral high-performance liquid chromatography-tandem mass spectroscopy (HPLC-MS/MS) method. Results showed that among rac-tetramethrin and its four enantiomers, the trans (+)-1R,3R-tetramethrin had the strongest inhibition effect on the PC12 cells. In the earthworm exposure trial, the concentration of trans (-)-1S,3S-tetramethrin was 0.94-8.92 times in earthworms (cultivated in natural soil) and 1.67-5.01 times (cultivated in artificial soil) higher than trans (+)-1R,3R-tetramethrin, respectively. In the greenhouse experiment, the trans (+)-1R,3R-tetramethrin and cis (+)-1R,3S-tetramethrin were preferentially degraded. Furthermore, for rat liver microsome in vitro incubation, the maximum metabolism rate of cis (-)-1S,3R-tetramethrin was 1.50 times higher than its antipodes. Altogether, the aim of this study was to provide a scientific and reasonable reference for the possibility of developing a single enantiomer to replace the application of rac-tetramethrin, which could possess better bioactivity and lower ecotoxicity, and thus permit more reliable and accurate environmental monitoring and risk assessment.

Stereoselective toxicity, bioaccumulation, and metabolic pathways of triazole fungicide cyproconazole in zebrafish

Cyproconazole (CPZ) is a broad-spectrum fungicide that is widely used around the world. CPZ can persist in water which raised concerns about its potential adverse effects on aquatic life. In this study, the stereoselective toxicity, bioaccumulation, elimination, and kinetic biotransformation in zebrafish were investigated. The LC₅₀ of 96 h acute toxicity was 15.88, 19.68, 26.99, and 17.10 mg/L for SR-, SS-, RS-, and RR-CPZ, respectively. The uptake and elimination experiment showed the bioconcentration factor in order of SR- > RR- > SS- > RS-CPZ at the exposure concentration of 0.1 and 1 mg/L. In the depuration stage, CPZ isomers were rapidly eliminated by 99% within 24 h. Moreover, the oxidative stress responses (POD, SOD, and CAT) were stereoselectively induced by CPZ stereoisomers, the activity of POD was significantly increased in all CPZ treatment groups compared to the control while the activity of CAT exhibited a concentration-dependent decrease in the CPZ treatment group. Multiple metabolic pathways of CPZ in zebrafish were proposed for the first time and 7 phase I metabolites and 25 phase II conjugates were found. This study determined the potential toxicity of CPZ to zebrafish and provided a strategy for the risk evaluation of CPZ stereoisomers in aquatic ecosystems.

Accumulation, metabolites formation and elimination behavior of rac-glufosinate-ammonium and glufosinate-P in zebrafish (Danio rerio)

•

Zebrafish samples were purified with diatomaceous earth, CH₂Cl₂ and Oasis PRiME HLB SPE column.

•

The bioaccumulation of glufosinate in zebrafish is enantioselective.

•

The accumulation of glufosinate-P in zebrafish was greater than that of rac-glufosinate.

•

The elimination half-life of glufosinate in zebrafish is less than 2.3 d.

•

NAG and MPP produced in fish was not over 4% of the parent culture concentration.

An efficient trace detection method for the determination of residues of the glufosinate enantiomers and metabolites in zebrafish by HPLC–Q-Exactive Orbitrap Mass Spectrometry was developed. After the purification of dichloromethane and Oasis PRiME HLB SPE column, the recovery ranges from 77% to 104%, with RSD < 10.03%. The limits of quantitation in zebrafish were 0.006–0.02 mg/kg. The results revealed zebrafish absorbed glufosinate slowly, reaching a steady state in 10–14 days, and the bioaccumulation factor (BCF) of D/L-glufosinate-ammonium was less than 0.3. L-glufosinate-ammonium accumulated preferentially in zebrafish. The residue of the metabolite N-acetyl glutamate (NAG) was smaller than that of 3-methyl phosphonic acid (MPP). D/L-glufosinate-ammonium had an elimination half-life of less than 2.3 days during the elimination phase. The bioaccumulation and elimination behavior of glufosinate-ammonium in zebrafish aquatic system was shown in this work, which offered scientific data for assessing the food safety of rac-glufosinate-ammonium and glufosinate-P (pure L-glufosinate-ammonium) in fish.

Comprehensive study of pydiflumetofen in Danio rerio: Enantioselective insight into the toxic mechanism and fate

Pydiflumetofen (PYD) is primarily used to control fungal disease. The potential risks posed by PYD enantiomers to the aquatic ecosystem are currently unclear. In this study, the enantioselective toxicity and fate of PYD in Danio rerio were investigated, and the enantioselective toxic mechanism and metabolic pathway were explored. The acute toxicity of R-PYD was 10.7-14.7-fold than that of S-PYD against Danio rerio embryos, larvae, and adults. Meanwhile, R-PYD presented a stronger effect on embryo hatching and abnormalities, adult tissue damage and oxidative stress. R-PYD inhibited the succinate dehydrogenase (SDH) activity more than S-PYD because of its better interaction with SDH with a lower binding free energy (-59.35 kcal/mol), explaining the mechanism of enantioselective toxicity. Remarkable enantioselectivity was observed in uptake, distribution, and elimination. R-PYD showed preferential uptake with the higher uptake rate constants and slow metabolism with a longer half-life, resulting in the bioaccumulation of R-PYD with higher BCF_k (7.37 at 0.05 mg/L and 14.69 at 0.2 mg/L). Besides, muscle is an important tissue for PYD accumulation, existing potential food risk. Eleven PYD metabolites were qualitatively identified, and the metabolic pathway was proposed, including hydroxylation, N-demethylation, demethoxylation, hydrolysation (phase Ⅰ), and acetylation and glucuronidation (phase Ⅱ). The predicted toxicity of the metabolite indicated that several highly toxic metabolites need to be considered in the future. This study provides a new perspective for evaluating the ecological and human health risks of chiral pesticides.

Enantioselective aquatic toxicity and degradation in soil of the chiral fungicide oxathiapiprolin

Oxathiapiprolin is an efficient and chiral fungicide for peronosporomycetes. The enantioselective environmental behavior and ecotoxicity of oxathiapiprolin are still unclear. The enantioselectivity of oxathiapiprolin enantiomers was explored, including their acute toxicity toward aquatic plants (Auxenochlorella pyrenoidosa and Soirodela polyrhiza) along with their influence on photosynthetic pigment production, the acute toxicity and morphological differences for the embryos, larvae and adult stages of zebrafish (Danio rerio), and the degradation in four typical soils (aerobic, anaerobic and sterilized conditions). The enantioselective toxicity of oxathiapiprolin showed that the toxicity of R-oxathiapiprolin was 1.8-2.1 times higher than that of S-oxathiapiprolin toward the two aquatic plants. In particular, the content of photosynthetic pigments decreased significantly stronger after exposure to R-oxathiapiprolin compared with S-oxathiapiprolin. The LC₅₀ values of R-oxathiapiprolin in zebrafish in the different life stages were 1.6-2.1 times higher than those of S-oxathiapiprolin. The zebrafish embryos were most sensitive to the oxathiapiprolin enantiomers. After exposure to R-oxathiapiprolin, zebrafish embryos showed noticeable hatching delays, inhibition or deformation. R-oxathiapiprolin degraded preferentially in all four soils, with an enantiomeric fraction (EF) ranging from 0.28 to 0.42 under aerobic conditions. Enantioselective degradation was not found under anaerobic and sterilized conditions. The enantioselectivity of new chiral pesticides should be fully considered in risk assessments to provide a basis for the development and preparation of pure optical enantiomers.

Enantioselective bioaccumulation, oxidative stress, and thyroid disruption assessment of cis-metconazole enantiomers in zebrafish (Danio rerio)

Chiral triazole pesticides may cause enantioselectively adverse effects to non-target organisms. In this work, we employed zebrafish as an aquatic organism model to explore stereoselective acute toxicity, bioaccumulation, oxidative stress, and thyroid disruption of cis-metconazole enantiomers. The median lethal concentration values of (1S, 5R)-metconazole, (1R, 5S)-metconazole, and the mixture of them against zebrafish were 4.01, 2.61 and 3.17 mg⋅L^-1, respectively. (1R, 5S)-Metconazole was preferentially bioaccumulated in zebrafish than (1S, 5R)-metconazole, and the bioconcentration factor of (1R, 5S)-metconazole was 1.28-fold larger than that of (1S, 5R)-metconazole. Then, the activity order of catalase, superoxide dismutase, and glutathione-S transferase enzymes in zebrafish was expressed as (1S, 5R)-metconazole > the mixture > (1R, 5S)-metconazole, while the order of malondialdehyde content in zebrafish was (1R, 5S)-metconazole > the mixture > (1S, 5R)-metconazole. Moreover, cis-metconazole exhibited enantioselective regulation effects on the levels of triiodothyronine and thyroxine in zebrafish, and (1R, 5S)-metconazole possessed stronger thyroid disruption ability to zebrafish than the others. By virtue of molecular docking methodology, the binding affair and docking energy results supported that interactions between (1R, 5S)-metconazole and thyroid hormone receptors were much stronger than those between (1S, 5R)-metconazole and same receptors. This study of enantioselective evaluation of cis-metconazole in zebrafish can provide favorable information for risk assessments of chiral pesticides toward environment and health of aquatic organisms.

Multi-walled carbon nanotubes impact on the enantioselective bioaccumulation and toxicity of the chiral insecticide bifenthrin to zebrafish (Danio rerio)

The effects of different multi-walled carbon nanotubes on the enantioselective bioaccumulation and toxicity of the chiral pesticide bifenthrin to zebrafish were investigated in this work. The results showed that MWCNTs and MWCNTs-COOH did not affect the preferential bioaccumulation of 1R-cis-BF in zebrafish following exposure to cis-BF enantiomers for 28 days, but which increased cis-BF accumulation amount by 1.03-1.48 times. Further research demonstrated that the genes related to immunity, endocrine activity and neurotoxicity showed enantioselective expression in different zebrafish tissues, and sex-specific differences were observed. The levels of c-fos, th, syn2a, 17β-hsd and cc-chem were expressed as 1.09-2.84 times higher in females and males treated with 1R-cis-BF than in the 1S-cis-BF-treated groups. However, in the presence of MWCNTs or MWCNTs-COOH, c-fos, th, syn2a, 17β-hsd and cc-chem levels were expressed as 1.53-14.92 times higher in females and males treated with 1S-cis-BF than in 1R-cis-BF-treated groups, which indicated that enantioselective expression was altered. The effects of different types of MWCNTs on the enantioselective bioaccumulation and toxicity of BF in zebrafish have little difference. In summary, the presence of MWCNTs or MWCNTs-COOH increased the impact of BF on zebrafish. Therefore, the risks posed by coexisting nanomaterials and chiral pesticides in aquatic environments should be considered.

Zebrafish larvae acute toxicity test: A promising alternative to the fish acute toxicity test

Aquatic toxicity is a mandatory component in risk assessment of chemicals. The currently recommended used acute fish toxicity (AFT) test requires a large test system, bringing onerous experimental operation and discharge of much experimental wastewater. In this study, we established a more convenient and efficient test defined as the zebrafish larvae acute toxicity (FLT) test, which employed zebrafish larvae at four days post fertilization as the test organisms and implemented a 48-hour exposure in 6-well plates. Based on validated reproducibility, we applied this test to evaluate the acute toxicity of 35 chemicals. By comparing the results with the existing acute toxicity data reported in the literature, we found that most chemicals exhibited highly positive correlated LC₅₀ in the FLT and the AFT test, with the same or similar toxicity grade. The FLT test showed more comparable sensitivity with the current AFT test than the previously recommended fish embryo acute toxicity test (FET). Moreover, the FLT test is easier to implement than the FET test which requires microscopic observation to identify the fertilization and development status of the embryos. Despite a limitation similar to the FET test in terms of detecting neurotoxicants, the FLT test could be a more promising alternative to the AFT test relative to the FET test.

Behavioural impairment and oxidative stress by acute exposure of zebrafish to a commercial formulation of tebuconazole

Tebuconazole is a systemic follicular fungicide known to cause diverse problems in non-target organisms namely associated to the pure active ingredient. As such, the objective of this work was to evaluate developmental changes induced by a tebuconazole commercial formulation to a non-target animal model. Zebrafish embryos at ± 2 h post-fertilization were exposed to tebuconazole wettable powder concentrations (0.05, 0.5 and 5 mg L^-1) for 96 h with developmental toxicity assessed throughout the exposure period and biochemical parameters evaluated at the end of the exposure. Behavioural assessment (spatial exploration and response to stimuli) was conducted 24 h after the end of the exposure. While no developmental and physiological alterations were observed, exposure to tebuconazole resulted in an increased generation of reactive oxidative species at the 0.05 and 0.5 mg L^-1 concentrations and a decreased GPx activity at the 0.5 mg L^-1 concentration suggesting a potential protection mechanism. There was also a change in the avoidance-escape behaviour supporting an anxiolytic effect suggesting possible alterations in the central nervous system development demanding further studies.

Stereoselective metabolomic and lipidomic responses of lettuce (Lactuca sativa L.) exposing to chiral triazole fungicide tebuconazole

In this study, non-targeted and targeted metabolomics/lipidomics studies based on UPLC-QTOF-MS and UPLC-MS/MS were carried out to clarify the effects of tebuconazole and its different enantiomers on lettuce metabolites and lipids. Slight enantioselective degradation of tebuconazole was observed and six degradation metabolites were tentatively identified. The endogenous metabolites involved in carbohydrate metabolism, amino acid metabolism, nucleic acid metabolism, phenylpropanoid and flavonoid metabolism, vitamins, and lipid metabolism were significantly affected with enantioselectivity by tebuconazole exposure. Nucleotide metabolism and nicotinic acid metabolic network were significantly activated by the stimulation of tebuconazole. Rac- and (-)-R-tebuconazole caused the down-regulation of soluble sugars and subsequent amino acids and organic acids. Overall, lettuce exposed to tebuconazole was shown to have a significant impact on plant metabolism and lipid metabolism, with notable stereoselectivity. The results showed stereoselective toxicity of tebuconazole and provided a better understanding of its metabolomic and lipidomic effects on lettuce.

A comprehensive review of 1,2,4-triazole fungicide toxicity in zebrafish (Danio rerio): A mitochondrial and metabolic perspective

In this critical review, we synthesize data from peer-reviewed literature reporting on triazole fungicide exposures in the zebrafish model. Based on their mode of action in plants (potent inhibitors of ergosterol synthesis), we focused attention on mechanisms related to cellular, lipid, and steroid metabolism. Evidence from several studies reveals that zebrafish exposed to triazoles present with impaired mitochondrial oxidative phosphorylation and oxidative stress, as well as dysregulation of lipid metabolism. Such metabolic disruptions are expected to underscore developmental delays, deformity, and aberrant locomotor activity and behaviors often observed following exposure. We begin by summarizing physiological and behavioral effects observed with triazole fungicide exposure in zebrafish. We then discuss mechanisms that may underlie adverse apical effects, focusing on mitochondrial bioenergetics and metabolism. Using computational approaches, we also identify novel biomarkers of triazole fungicide exposure. Extracting and analyzing data contained in the Comparative Toxicogenomics Database (CTD) revealed that transcriptional signatures responsive to different triazoles are related to metabolism of lipids and lipoproteins, biological oxidations, and fatty acid, triacylglycerol, and ketone body metabolism among other processes. Pathway and sub-network analysis identified several transcripts that are responsive in organisms exposed to triazole fungicides, several of which include lipid-related genes. Knowledge gaps and recommendations for future investigations include; (1) targeted metabolomics for metabolites in glycolysis, Krebs cycle, and the electron transport chain; (2) additional studies conducted at environmentally relevant concentrations to characterize the potential for endocrine disruption, given that studies point to altered cholesterol (precursor for steroid hormones), as well as altered estrogen receptor alpha and thyroid hormone expression; (3) studies into the potential role for lipid peroxidation and oxidation of lipid biomolecules as a mechanism of triazole-induced toxicity, given the strong evidence for oxidative damage in zebrafish following exposure to triazole fungicides.

Developmental toxicity of fenbuconazole in zebrafish: effects on mitochondrial respiration and locomotor behavior

Triazole fungicides are used to control the disease of cereal crops but may also cause adverse effects on non-target organisms. There is a lack of toxicity data for some triazoles such as fenbuconazole in aquatic organisms. This research was conducted to evaluate the toxicity of fenbuconazole at environmentally relevant concentrations with attention on the mitochondria, antioxidant system, and locomotor activity in zebrafish. Zebrafish were exposed to one concentration of 5, 50, 200 or 500ng/L fenbuconazole for 96h. There was no effect on survival nor percentage of fish hatched, but exposure to 200 and 500ng/L fenbuconazole resulted in malformation and hypoactivity in zebrafish. Oxygen consumption rates (OCR) of embryos were measured to determine if the fungicide impaired mitochondrial respiration. Exposure to 500ng/L fenbuconazole reduced basal OCR and oligomycin-induced ATP linked respiration in exposed fish. Fenbuconazole reduced mitochondrial membrane potential and reduced the activities of mitochondrial Complex II and III. Transcript levels of both sdhc and cyc1, each related to Complex II and III, were also altered in expression by fenbuconazole exposure, consistent with mitochondrial dysfunction in embryos. Fenbuconazole activated the antioxidant system, based upon both transcriptional and enzymatic data in zebrafish. Consistent with mitochondrial impairment, molecular docking confirmed a strong binding capacity of the fungicide at the Q_i site of Complex III, revealing this complex is susceptible to fenbuconazole. This study reveals potential toxicity pathways related to fenbuconazole exposure in aquatic organisms; such data can improve risk assessments for triazole fungicides.

Potential neurotoxicity, immunotoxicity, and carcinogenicity induced by metribuzin and tebuconazole exposure in earthworms (Eisenia fetida) revealed by transcriptome analysis

Metribuzin and tebuconazole have been widely used in agriculture for several decades. Apart from endocrine disruption, little is known about their toxicological effects on organisms without thyroid organs, at the transcriptional level. To explore this toxicity, model earthworm species Eisenia fetida, hatched from the same cocoon and cultured under identical environmental conditions, were independently exposed to the two chemicals at non-lethal concentrations in OECD artificial soil for 48 h after exposure. RNA-seq technology was used to analyze and compare the gene expression profiles of earthworms exposed to metribuzin and tebuconazole. The functions of differentially expressed genes and their standard response patterns of upregulated and downregulated expression for both pesticides were verified. The findings demonstrated that metribuzin and tebuconazole are both potentially toxic to earthworms. Toxicological effects mainly involved the nervous system, immune system, and tumors, at the transcriptional level, as well as the induction of cytochrome P450-dependent detoxification and oxidative stress. In addition, the mitogen-activated protein kinase kinase kinase gene was identified as a biomarker, and the mitogen-activated protein kinase signaling pathway was verified to be a part of the adverse outcome pathway of metribuzin and tebuconazole and their structural analogs.

Health risks of sulfentrazone exposure during zebrafish embryo-larvae development at environmental concentration

Knowledge about the negative effects and mechanism of sulfentrazone (SUL) on aquatic early life stages is still limited. Here we investigated the lethal and sub-lethal effects of SUL during zebrafish embryo-larvae development. Results demonstrated that the 96 h and 120 h-LC₅₀ of SUL to embryonic zebrafish was 2.02 mg/L, and the 30 d-LC₅₀ was 0.899 mg/L after embryos exposed to SUL for 30 d. High concentrations of SUL delayed yolk sac absorption, disordered the hatching and heart rate during zebrafish embryonic stage, while 0.0100-0.100 mg/L SUL had no phenotypic changes on embryonic development, but decreased the body weight of larvae after 30 d exposure. RNA-seq identified 321, 394 and 727 differentially expressed genes in larvae after embryos exposed to 0.0100 mg/L, 0.0400 mg/L and 0.400 mg/L SUL for 30 d, found that the transcriptional profiles involved in heart development and endocrine disruption were simultaneously influenced by different concentrations of SUL, such as adrenergic signaling in cardiomyocytes, cardiac muscle contraction, cell adhesion molecules and steroid biosynthesis. Biochemical analysis showed that SUL increased the levels of E₂, T₃ and TSH, induced the activities of mitochondrial complex IV, cytochrome c oxidase, Ca²⁺-ATPase, total Na⁺K⁺-ATPase and Ca²⁺Mg²⁺-ATPase, and decreased ATP formation after embryos exposed to SUL for 5 d and 30 d. Further comprehensive analysis demonstrated that SUL caused more significantly alteration on the transcript, level or activity of the key elements involved in heart development and endocrine disruption after 30 d exposure, indicated long-term SUL exposure might cause more negative effects on zebrafish at doses below the presumed no-observed-adverse-effect level during early life development. The results inferred the environmental concentration of SUL might cause potential cardiac and endocrine health risk in zebrafish later life stages, also facilitated a better understanding of the sub-lethal effects and molecular mechanism of SUL on aquatic organism.

Combined lethal toxicity, biochemical responses, and gene expression variations induced by tebuconazole, bifenthrin and their mixture in zebrafish (Danio rerio)

Pesticides commonly occur as mixtures in an aqueous environment, causing deleterious effects on human health and the environment. However, the mechanism underlying the combined effects on aqueous organisms remains largely unknown, especially at low concentrations. In the current study, we inspected the interactive toxicity of tebuconazole (TEB), a triazole fungicide, and bifenthrin (BIF), a pyrethroid insecticide, to zebrafish (Danio rerio) using various toxicological assays. Our data revealed that the 96 h-LC50 (lethal concentration 50) values of BIF to fish at different life periods (embryonic, larval, juvenile, and adult periods) ranged from 0.013 (0.011-0.016) to 0.41 (0.35-0.48) mg a.i. L-1, which were lower than that of TEB ranging from 1.1 (0.88-1.3) to 4.8 (4.1-5.7) mg a.i. L-1. Combination of TEB and BIF induced synergetic acute toxicity to embryonic fish. Activities of T-SOD, POD, and GST were distinctly altered in most individual and joint administrations. Expressions of 16 genes associated with oxidative stress, cellular apoptosis, immune system, and endocrine system at the mRNA level were evaluated, and the information revealed that embryonic zebrafish were impacted by both individual compounds and their combinations. Six genes (cas9, P53, gr, TRα, IL-8, and cxcl-clc) exhibited greater changes when exposed to pesticide mixtures. Therefore, the joint effects induced by the pesticides at low concentrations should be considered in the risk assessment of mixtures and regulated as priorities for mixture risk management in the aqueous ecosystem. More research is needed to identify the threshold concentrations of the realistic pesticide mixtures above which synergistic interactions occur.

Enantioselective toxic effects of mefentrifluconazole in the liver of adult zebrafish (Danio rerio) based on transcription level and metabolomic profile

Mefentrifluconazole, a new type of chiral triazole fungicide, is widely applied to control a variety of fungal diseases in crops. However, the toxicological effects of mefentrifluconazole on aquatic organisms are unknown, especially at the enantiomer level. In the present study, zebrafish were selected as a typical model for mefentrifluconazole enantiomer exposure. Metabolomic and transcription analyses were performed with 0.01 and 0.10 mg/L mefentrifluconazole and its enantiomers (i.e., rac-mfz/(-)-mfz/(+)-mfz) at 28 days. The ¹H nuclear magnetic resonance (NMR)-based metabolomics analysis showed that 9, 10 and 4 metabolites were changed significantly in the rac-mfz, (+)-mfz and (-)-mfz treatment groups compared with the control group, respectively. The differential metabolites were related to energy metabolism, lipid metabolism and amino acid metabolism. The qRT-PCR analysis revealed that the expression of lipid metabolism-, apoptosis- and CYP-related genes in the livers of female zebrafish in rac-mfz and (+)-mfz was 1.61-108.92 times and 2.37-551.34 times higher than that in (-)-mfz, respectively. The results above indicate that exposure to mefentrifluconazole induced enantioselective liver toxicity in zebrafish. Our study underlined the importance of distinguishing different enantiomers, which will contribute to environmental protection.

Bioaccumulation, metabolism and endocrine-reproductive effects of metolachlor and its S-enantiomer in adult zebrafish (Danio rerio)

The aim of the present study was to evaluate the enantioselective bioaccumulation, metabolism, and toxic effects of metolachlor and S-metolachlor in zebrafish. Five-month-old zebrafish were exposed to metolachlor and S-metolachlor for 28 days, then transferred to clean water and purified for 7 days. In the uptake phase, S-metolachlor was preferentially accumulated at low concentrations, while metolachlor was preferentially accumulated at high concentrations. The two chemicals were metabolized by >70% in zebrafish on the first day and showed same metabolic process. At the accumulation endpoint, S-metolachlor had no significant inhibitory effect on the enzymes activities of superoxide dismutase (SOD), catalase (CAT) and glutathione S-transferase (GST) and developmental indicators of zebrafish. However, 300 μg/L metolachlor significantly inhibited the enzymes activities of SOD, CAT and GST and affected the liver development. The preferential enrichment of metolachlor at the high concentration may be the reason for its higher toxicity to zebrafish. Further research demonstrated that metolachlor significantly altered the expression of hypothalamic-pituitary-gonadal (HPG) axis-related genes, including gnrh2, gnrh3, lhβ, 17βhsd and cyp19a, thereby reducing the levels of testosterone (T) in females and sex hormones (estradiol and testosterone) in males. S-metolachlor increased the levels of estradiol (E2) in females by altering the expression of HPG axis-related genes such as fshβ, cyp17, 17βhsd and cyp19a. The mechanism of metolachlor and S-metolachlor on the endocrine disrupting effects of zebrafish is different, which may be sex-specific. 7 days after transferring the exposed zebrafish to clean water, most of the enzymes activities, sex hormone levels and related gene expression levels returned to normal, which may be related to the rapid metabolism of the two chemicals.

Enantioselective bioaccumulation and toxicity of the novel chiral antifungal agrochemical penthiopyrad in zebrafish (Danio rerio)

Succinate dehydrogenase inhibitor (SDHI) fungicides has been extensively used in agricultural production, which are not easily degrade in the environment and have various toxic effects on aquatic organisms. However, the toxic effects information to non-target organisms were mostly at the racemate level, which were poorly understood at the enantiomers level. Thus, this study aimed to investigate the enantioselective bioaccumulation behavior and toxic effects of penthiopyrad in zebrafish. Significant enantioselective bioaccumulation was observed when exposed to penthiopyrad at two dose levels: S-(+)-penthiopyrad was preferentially accumulated. Moreover, S-(+)-penthiopyrad caused oxidative stress in zebrafish liver. The results of real-time RT-PCR analyses revealed that exposure to penthiopyrad also enantioselectivity interfered with the expression of mitochondrial respiratory complexes, mtDNA synthesis, lipid metabolism and apoptosis-related genes. S-(+)-penthiopyrad significantly decreased most of the expression of the above gene, which showed higher toxic effects. We inferred that the toxicity mechanism of penthiopyrad was caused by lipid metabolism disorder and mitochondrial dysfunction in zebrafish, and further leads to apoptosis even DNA damage. This study provides more accurate data to investigate the environmental impact of penthiopyrad at the enantiomer level.

Simultaneous determination of penthiopyrad enantiomers and its metabolite in vegetables, fruits, and cereals using ultra-high performance liquid chromatography-tandem mass spectrometry

Penthiopyrad is a novel succinate dehydrogenase inhibitor that has one chiral center and exists a metabolite, 1-methyl-3-trifluoromethyl-1H-pyrazole-4-carboxamide in its residue definition. An efficient analytical method for the simultaneous determination of penthiopyrad enantiomers and its metabolite in eight matrices were developed using modified quick, easy, cheap, effective, rugged, safe method, coupled with chiral stationary phase and ultra-high performance liquid chromatography-tandem mass spectrometry. The absolute configuration of penthiopyrad enantiomers was confirmed by polarimetry and electronic circular dichroism. Eight polysaccharide-based chiral stationary phases were evaluated in terms of the enantioseparation of penthiopyrad and separation-related factors (the mobile phase, flow rate and the column temperature) were optimized. To obtain an optimal purification, different sorbent combinations were assessed. The linearities of this method were acceptable in the range of 0.005 to 1 mg/L with R²  > 0.998, while the limits of detection and quantification were 0.0015 mg/kg and 0.01 mg/kg for two enantiomers and its metabolite. The average recoveries of R-(-)-penthiopyrad, S-(+)-penthiopyrad and the metabolite ranged from 75.4 to 109.1, 69.5 to 112.8, and 70.0 to 108.5%, respectively. The intra-day and inter-day relative standard deviations were less than 18.8%. The analytical method was accurate and convenient, which can support their further research on stereoselective degradation, residual monitoring and risk assessment.

In vitro enantioselective inhibition of the main human CYP450 enzymes involved in drug metabolism by the chiral pesticide tebuconazole

Tebuconazole (TEB) is a chiral triazole fungicide worldwide employed to control plant pathogens and preserve wood. People can be exposed to TEB either through diet and occupational contamination. This work investigates the in vitro inhibitory potential of rac-TEB, S-(+)-TEB, and R-(-)-TEB over the main cytochrome P450 enzymes (CYP450) using human liver microsomes to predict TEB in vivo inhibition potential. The IC₅₀ values showed that in vitro inhibition was enantioselective for CYP2C9, CYP2C19, and CYP2D6, but not for CYP3A4/5. Despite enantioselectivity, rac-TEB and its single enantiomers were always classified in the same category. The inhibition mechanisms and constants were determined for rac-TEB and it has shown to be a mixed inhibitor of CYP3A4/5 (K_i = 1.3 ± 0.3 μM, αK_i = 3.2 ± 0.5 μM; K_i = 0.6 ± 0.3 μM, αK_i = 1.3 ± 0.3 μM) and CYP2C9 (K_i = 0.7 ± 0.1 μM, αK_i = 2.7 ± 0.5 μM), and a competitive inhibitor of CYP2D6 (K_i = 11.9 ± 0.7 μM) and CYP2C19 (K_i = 0.23 ± 0.02 μM), respectively, suggesting that in some cases, rac-TEB has a higher or comparable inhibitory potential than well-known strong inhibitors of CYP450 enzymes, especially for CYP2C9 and CYP2C19. In vitro-in vivo extrapolations (IVIVE) were conducted based on the results and data available in the literature about TEB absorption and metabolism. R₁ values were estimated based on the Food and Drug Administration guideline and suggested that in a chronic oral exposure scenario considering the acceptable daily intake dose proposed by the European Food and Safety Authority, the hypothesis of rac-TEB to inhibit the activities of CYP3A4/5, CYP2C9, and CYP2C19 in vivo and cause pesticide-drug interactions cannot be disregarded.

Tebuconazole Fungicide Induces Lipid Accumulation and Oxidative Stress in HepG2 Cells

Tebuconazole (TEB), a triazole fungicide, is frequently applied to agriculture for the increase of food production. Although TEB causes liver toxicity, its effects on cellular lipid accumulation are rarely investigated. Therefore, this study aimed to study the effects of TEB on lipid metabolism and accumulation in HepG2 cells. HepG2 cells were exposed to 0-320 µM TEB for 1-24 h. TEB (20-80 µM, 24 h)-treated cells showed lipid accumulation. Further, TEB (20-80 µM, 1-12 h) increased the nuclear translocation of peroxisome proliferator-activated receptors and the expression of lipid uptake and oxidation-related markers such as cluster of differentiation 36, fatty acid transport protein (FATP) 2, FATP5, and carnitine palmitoyltransferase 1. Oxidative stress levels in TEB-treated cells (20-80 µM, 24 h) were higher, compared to those in the control. TEB (20-80 µM, 24 h) also induced the loss of mitochondrial membrane potential and lower levels of microsomal triglyceride transfer protein in the cells. Thus, TEB can induce lipid accumulation by altering the expression of lipid-metabolizing molecules and can therefore impair lipid metabolism. Our data suggest that human exposure to TEB may be a risk factor for non-alcoholic fatty liver disease.

Enantioselective Bioaccumulation of the Chiral Insecticide Indoxacarb in Zebrafish (Danio rerio)

Indoxacarb is a typical chiral insecticide widely used in agricultural pest control. In the present study, zebrafish was used as a model animal to explore the enantioselective bioaccumulation behavior of indoxacarb to nontarget species in aquatic environments. Zebrafish were exposed to 0.025 and 0.1 mg/L rac-indoxacarb solution for 12 d under the semistatic method, and the bioconcentration factor (BCF) and enantiomeric fraction of zebrafish were investigated. The results showed that the (-)-R-indoxacarb preferentially accumulated in zebrafish. The BCF values at 0.025 mg/L exposure levels were 1079.8 and 83.4 L/kg for (-)-R-indoxacarb and (+)-S-indoxacarb after 12 d, respectively. The BCF values at 0.1 mg/L exposure levels were 1752.1 and 137.0 L/kg for (-)-R-indoxacarb and (+)-S-indoxacarb after 10 d, respectively. The half-life values of (-)-R-indoxacarb and (+)-S-indoxacarb were 3.47 and 2.05 d for 0.025 mg/L concentration exposure and 4.95 and 2.66 d for 0.1 mg/L concentration exposure, respectively. The enantiomeric fraction values were in the range of 0.48 to 0.55 and 0.89 to 1.00 for water and zebrafish samples, respectively. Studies on the enantioselective bioaccumulation behavior of indoxacarb will provide data for assessing the environmental fate and potential toxic effects of indoxacarb on aquatic organisms. Environ Toxicol Chem 2021;40:1007-1016. © 2020 SETAC.

Influence of multi-walled carbon nanotubes on enantioselective bioaccumulation and oxidative stress toxicity of indoxacarb in zebrafish(Danio rerio)

Carbon nanotubes (CNTs) have been widely used in various fields with the rapid development of nanotechnology. Pesticides have an irreplaceable role in agricultural production, which leads to their massive utilization and their inevitably penetrate into the aquatic environment. However, limited information is available regarding the impact of CNTs on the toxicity and enrichment of chiral compounds to organisms. Using zebrafish as a model to study whether the enantioselective bioaccumulation and oxidative stress of chiral pollutants may be altered in the presence of MWCNTs. Significant enantioselective bioaccumulation was observed in zebrafish with the preferential accumulation of R-(-)-indoxacarb during the 28-day bioaccumulation. The combined exposure of MWCNTs does not affect the enantioselectivity of zebrafish bioaccumulation, but increase the bioaccumulation amount of R-(-)-indoxacarb by 65%. Moreover, the average degradation half-life of indoxacarb enantiomers was 1.30 days. The indoxacarb causes oxidative stress toxicity in zebrafish liver and exhibited enantioselectivity, while the addition of MWCNTs did not significantly change the enantioselectivity of oxidative stress toxicity of indoxacarb, but enhanced the toxicity 20% with increased MWCNTs concentrations. This study suggests that the risk of the co-presence of nanomaterials and chiral pesticides in aquatic environments should be taken into consideration.

A review on the stereospecific fate and effects of chiral conazole fungicides

The production and use of chiral pesticides are triggered by the need for more complex molecules capable of effectively combating a greater spectrum of pests and crop diseases, while sustaining high production yields. Currently, chiral pesticides comprise about 30% of all pesticides in use; however, some pesticide groups such as conazole fungicides (CFs) consist almost exclusively of chiral compounds. CFs are produced and field-applied as racemic (1:1) mixtures of two enantiomers (one chiral center in the molecule) or four diastereoisomers, i.e., two pairs of enantiomers (two chiral centers in the molecule). Research on the stereoselective environmental behavior and effects of chiral pesticides such as CFs has become increasingly important within the fields of environmental chemistry and ecotoxicology. This is motivated by the fact that currently, the fate and effects of chiral pesticides such as CFs that arise due to their stereoselectivity are not fully understood and integrated into risk assessment and regulatory decisions. In order to fill this gap, a summary of the state-of-the-art literature related to the stereospecific fate and effects of CFs is needed. This will also benefit the agrochemistry industry as they enhance their understanding of the environmental implications of CFs which will aid future research and development of chiral products. This review provides a collection of >80 stereoselective studies for CFs related to chiral analytical methods, fungicidal activity, non-target toxicity, and behavior of this broadly used pesticide class in the soil environment. In addition, the review sheds more light on mechanisms behind stereoselectivity, considers possible agricultural and environmental implications, and suggests future directions for the safe use of chiral CFs and the reduction of their environmental footprint.

Stereoselective uptake and metabolism of prothioconazole caused oxidative stress in zebrafish (Danio rerio)

Prothioconazole (PTA) is a novel, broad-spectrum, chiral triazole fungicide that is mainly used to prevent and control the disease of cereal crops. However, the adverse effects of PTA and its major metabolite on nontarget organisms have aroused wide concern. In the present work, the acute toxic of the metabolite prothioconazole-desthio (PTA-desthio), with an LC₅₀ of 1.31 mg L^-1, was 3.5-fold more toxic than the parent compound, indicating that the metabolism of PTA in zebrafish was toxic. The stereoselective uptake and metabolism of PTA and PTA-desthio in zebrafish was firstly investigated using LC-MS/MS. Remarkable enantioselectivity was observed: S-PTA and S-PTA-desthio were preferentially uptake with the uptake rate constants of 8.22 and 8.15 d^-1 at exposure concentration of 0.5 mg L^-1, respectively, and the R-PTA-desthio were preferentially metabolized. PTA-desthio was rapidly formed during the uptake processes. The antioxidant enzyme activities in the zebrafish changed significantly, and these effects were reversible. A metabolic pathway including 13 phase I metabolites and 2 phase II metabolites was firstly proposed. A glucuronic acid conjugate and sulfate conjugate were observed in zebrafish. The results of this work provide information that highlights and can help mitigate the potential toxicity of PTA to the ecological environment and humans health.

Oxidative stress, DNA damage and apoptosis induced by tebuconazole in the kidney of male Wistar rat

Tebuconazole (TEB) is a broad-spectrum conazole fungicide that has been used in agriculture in the control of foliar and soil-borne diseases of many crops. The present study has investigated the adverse effects of subchronic exposure to TEB on the kidney of male rats. Animals were divided into four equal groups and treated with TEB at increasing doses 0.9, 9 and 27 mg/kg body weight for 28 consecutive days. The results showed that TEB induced oxidative stress in the kidney demonstrated by an increase in malondialdehyde (MDA), protein carbonyl (PC), advanced oxidation protein product (AOPP) levels and DNA damage, as compared to the controls. Furthermore, superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx) activities were increased in the renal tissue of treated rats. Moreover, significant decrease in reduced glutathione (GSH) content in TEB-treated rats was observed, while oxidized glutathione (GSSG) levels were increased, thus a marked fall in GSH/GSSG ratio was registered in the kidney. Glutathione reductase (GR) activity showed a significant increase after TEB exposure. Moreover, TEB down-regulated the expression of Bcl2 and up-regulated the expression of Bax and caspase 3, which triggered apoptosis via the Bax/Bcl2 and caspase pathway. Also, TEB administration resulted in altered biochemical indicators of renal function and varying lesions in the overall histo-architecture of renal tissues. Taken together, our findings brought into light the renal toxicity induced by TEB, which was found to be significant at low doses.

Etoxazole stereoselective determination, bioaccumulation, and resulting oxidative stress in Danio rerio (zebrafish)

An environmentally-friendly and fast analytical method for the stereoselective determination of etoxazole was developed and then applied to estimate stereoselective bioaccumulation and elimination in zebrafish using SFC-MS/MS. Optimal enantioseparation conditions were determined using a Chiralpak IG-3 column and CO₂/MeOH mobile phase (80/20, v/v), at 3.0 mL/min within 1 min, 30°Me and 18 MPa. A modified QuEChERS method was developed for zebrafish sample pretreatment, and mean recoveries were 88.43-110.12% with relative standard deviations ranging from 0.32 to 5.34%. The enantioselectives of etoxazole enantiomers in zebrafish during uptake and depuration phases were evaluated. Significant enantioselective bioaccumulation was observed, with preferential accumulation of (-)-R-etoxazole compared to its antipode, during uptake at both low and high exposure concentrations. The toxic effects of etoxazole on zebrafish were further explored, and activities of antioxidant enzymes were determined in liver of zebrafish. Significant changes were observed in the SOD and GST activities and in the MDA levels, which indicated the occurrence of oxidative stress in liver of zebrafish. The toxic effects exhibited time- and dose-dependent properties. These results can facilitate the accurate risk evaluation of etoxazole and provide basic knowledge for further study of biotoxicity mechanisms.

Combined toxicity of imidacloprid, acetochlor, and tebuconazole to zebrafish (Danio rerio): acute toxicity and hepatotoxicity assessment

Compound pollution refers to two or more kinds of pollutants with different properties, a pollutant from different sources, or the simultaneous existence of two or more different types of pollutants in the same environment. In this study, we aimed to investigate the individual and combined toxicity of the insecticide imidacloprid (IMI), the herbicide acetochlor (ACT), and the fungicide tebuconazole (TBZ) to zebrafish. The acute toxicity test results showed that the 96-h LC₅₀ values of IMI, ACT, and TBZ were 276.84 (259.62-294.35) mg active ingredient (a.i.) L^-1, 1.52 (1.34-1.74) mg a.i. L^-1, and 8.16 (7.7-8.6) mg a.i. L^-1, respectively. The combinations of IMI, ACT, and TBZ with toxicity ratios of 1:2:2, 1:4:4, 2:4:1, and 4:1:4 displayed synergistic toxic effects on zebrafish, while the toxicity ratios of 1:1:1, 1:1:2, 2:1:2, 2:2:1, and 4:2:1 of IMI, ACT, and TBZ, respectively, exhibited antagonistic toxic effects on zebrafish. The following experiments were performed with a toxicity ratio of 1:4:4 (IMI:ACT:TBZ). The activities of four enzyme biomarkers related to oxidative stress in the liver, catalase (CAT), superoxide dismutase (SOD), glutathione S-transferase (GST), and malondialdehyde (MDA) content were evaluated in each exposure group on days 7, 14, 21, and 28. Compared with those of the control group, the activities of CAT, SOD, and GST and the MDA content were significantly altered at different time points in the individual and combined exposure groups. Additionally, the activities of CAT, SOD, and GST and the MDA content were significantly altered in the combined group compared with those of the individual group after 14 days or 21 days of exposure. Therefore, it was confirmed that combined toxicity studies are indispensable in risk assessment. Graphical abstract .

Toxicity testing of pesticides in zebrafish-a systematic review on chemicals and associated toxicological endpoints

The use of zebrafish (Danio rerio) has arisen as a promising biological platform for toxicity testing of pesticides such as herbicides, insecticides, and fungicides. Therefore, it is relevant to assess the use of zebrafish in models of exposure to investigate the diversity of pesticide-associated toxicity endpoints which have been reported. Thus, this review aimed to assess the recent literature on the use of zebrafish in pesticide toxicity studies to capture data on the types of pesticide used, classes of pesticides, and zebrafish life stages associated with toxicity endpoints and phenotypic observations. A total of 352 articles published between September 2012 and May 2019 were curated. The results show an increased trend in the use of zebrafish for testing the toxicity of pesticides, with a great diversity of pesticides (203) and chemical classes (58) with different applications (41) being used. Furthermore, experimental outcomes could be clustered in 13 toxicity endpoints, mainly developmental toxicity, oxidative stress, and neurotoxicity. Organophosphorus, pyrethroid, azole, and triazine were the most studied classes of pesticides and associated with various toxicity endpoints. Studies frequently opted for early life stages (embryos and larvae). Although there is an evident lack of standardization of nomenclatures and phenotypic alterations, the information gathered here highlights associations between (classes of) pesticides and endpoints, which can be used to relate mechanisms of action specific to certain classes of chemicals.