Exposure to difenoconazole induces reproductive toxicity in zebrafish by interfering with gamete maturation and reproductive behavior

Long-term exposure to 2,4-di-tert-butylphenol impairs zebrafish fecundity and affects offspring development

As a widely used antioxidant, 2,4-di-tert-butylphenol (2,4-DTBP) has been frequently detected in the environment and biota. Although a few studies reported its hormone-like activity in vitro, the endocrine disrupting potential of 2,4-DTBP and its effect on reproduction are not yet elucidated. In this study, adult zebrafish were exposed to 5 and 50 nM 2,4-DTBP for 60 days. Reduction in cumulative egg production was observed after 45 days of exposure. Gonadal maturation was also delayed in both female and male zebrafish following 2,4-DTBP exposure. The impaired fecundity was attributed to an imbalance of 17β-estradiol/testosterone ratio (E2/T) and altered transcripts involved in the hypothalamic-pituitary-gonadal (HPG) axis. Upon exposure, aromatase (CYP19) and E2 levels were significantly decreased in females, but were increased in males. Additionally, molecular docking revealed potential binding of 2,4-DTBP to estrogen receptors and CYP19, highlighting molecular initiating events that may interfere with steroid hormone synthesis. We also showed that 2,4-DTBP can be transferred to offspring, affecting their development and compromising immunity. The expression of triiodothyronine (T3) and hatching-related genes (esr2α, esr2β, and zhe2) were altered, suggesting that parental exposure to 2,4-DTBP resulted in intergenerational toxicity in F1 larvae. Taken together, these findings provide novel insight into the reproductive toxicity of 2,4-DTBP, contributing to its ecological risk assessment.

Fabrication of self-defense enzymic biocatalyst for harmless degradation of difenoconazole through post-synthesis infiltration and modification

Difenoconazole (DIF) non-point source pollution presents significant eco-environmental challenges. In the present study, an efficient self-defensive biocatalytic system (D4/enzyme-PDA-MOFs@Sponge) was constructed for the first time through post-synthesis infiltration and cold-plasma discharge modification. The system exhibits strong antibacterial capabilities, achieving 93.39 % and 99.02 % inhibition against Escherichia coli and Staphylococcus aureus, respectively, demonstrating its outstanding self-defense ability against external organism invasion. For DIF degradation, immobilized extracellular and intracellular enzymes achieve 73.2 % and 66.9 % removal rates within 48 h, with total organic carbon removal of 81.3 % and 86.3 %, respectively, indicating efficient mineralization. The "birdcage trapping-enzymatic" mechanism enables rapid substrate adsorption and in-situ catalysis, generating low-toxicity transformation products. Notably, the biocatalyst maintains over 45.7 % degradation efficiency after five reuse cycles, showcasing robust reusability. This work provides a promising, environmentally friendly approach for mitigating DIF pollution through efficient, harmless degradation.

Stereoselective cardiovascular toxicity of difenoconazole stereoisomers in zebrafish larvae (Danio rerio) through thyroid hormone disruption

Difenoconazole (DIF) is a typical chiral triazole fungicide extensively detected in the environment. This study aimed to explore the stereoselective cardiovascular toxicity of DIF and its four stereoisomers (2S,4S-, 2S,4R-, 2 R,4R-, and 2 R,4S-DIF) in zebrafish. Zebrafish embryos were exposed to DIF and its isomers at environmentally relevant concentrations (0.3, 0.6 and 1.2 mg/L) from 4 to 96 hours post fertilization (hpf) and cardiovascular development was systematically evaluated. Our results revealed that Rac-DIF, 2S,4S-DIF and 2 R,4R-DIF significantly decreased the survival rate, hatching rate and body length, and increased the malformation rate at 96 hpf. DIF isomers mainly produced severe stereoselective cardiovascular defects, manifesting as bradycardia, abnormal cardiovascular structure, intersegmental vessel defects, and altered expression of cardiovascular-related genes. Notably, 2 R,4R-DIF displayed the strongest cardiovascular toxicity, followed by 2S,4S-DIF and Rac-DIF. Transcriptome analysis showed that 2 R,4R-DIF and 2S,4S-DIF affected the thyroid hormone signaling pathway, which was validated by altered thyroid hormone levels and hypothalamus-pituitary-thyroid axis-related gene expression. Molecular docking indicated that 2 R,4R-DIF had the strongest binding to the active pockets of zebrafish thyroid hormone receptor β, followed by 2S,4S-DIF, 2S,4R-DIF and 2 R,4S-DIF. Fascinatingly, these adverse outcomes were partially recovered after T3 supplementation, indicating the importance of thyroid disruption in DIF isomers-induced stereoselective cardiovascular toxicity. Overall, this study revealed that DIF and its isomers induced stereoselective developmental and cardiovascular toxicity (ranked as 2 R,4R-DIF > 2S,4S-DIF > Rac-DIF > 2S,4R-DIF ≈ 2 R,4S-DIF) through thyroid hormone disruption, providing favorable information on the environmental risks of chiral DIF in aquatic organisms.

Neurotoxicity induced by difenoconazole in zebrafish larvae via activating oxidative stress and the protective role of resveratrol

Difenoconazole (DIF) is a typical triazole fungicide detected in the aquatic ecosystem and organisms. However, the neurotoxic effects of DIF remain largely unknown. This study aimed to investigate the neurotoxicity of DIF in zebrafish and the underlying neuroprotective properties of resveratrol (RES, an antioxidant polyphenol). Zebrafish embryos/larvae were treated with 0.6 and 1.2 mg/L DIF from 4 to 96 h post fertilization (hpf) and neurodevelopment was systematically assessed. DIF induced developmental toxicity and aberrant neurobehaviors, including decreased movement time, swimming distance and clockwise rotation times. DIF suppressed the neurogenesis of the central nervous system (CNS) in HuC:egfp transgenic zebrafish and the length of motor neuron axon in hb9:egfp transgenic zebrafish. DIF inhibited cholinesterase activities and downregulated neurodevelopment related genes. DIF also increased oxidative stress via excessive production of reactive oxygen species and decreased activities of antioxidant enzymes, subsequently triggering neuronal apoptosis in the brain. RES partially reinstated DIF-induced neurotoxicity and developmental toxicity by inhibiting excessive oxidative stress and apoptosis, suggesting the involvement of oxidative stress in DIF-induced neurotoxicity. Overall, this study identified the potential mechanisms underlying DIF-induced neurotoxicity and suggested RES as a promising therapeutic strategy.

Exposure of Parental Zebrafish to Difenoconazole throughout Their Life Cycle May Lead to Developmental Toxicity in the F1 Generation through Epigenetic Changes in Gametes, Impaired Nutrient Supply from the Ovum, and Maternal Transfer of Difenoconazole

Difenoconazole is a widely used agricultural fungicide that has been frequently detected in aquatic environments. Given its stable presence in aquatic environments, long-term exposure of wild fish may pose a risk to offspring embryonic development. This study demonstrated that exposure of zebrafish to environmental concentrations of difenoconazole throughout their life cycle resulted in abnormal development of offspring embryos/larvae, including decreased heart rate, delayed hatching, increased malformation rate, shortened body length, and increased mortality. These changes were significantly correlated with the affected apoptosis, autophagy, energy metabolism and MAPK signaling pathways in F1 generation. This transgenerational toxic effect results from epigenetic alterations in gametes, impaired nutrient supply from the ovum, and maternal transfer of difenoconazole. After exposure to difenoconazole, the development of female fish offspring was affected more than that of male fish offspring, which was mainly caused by the impaired nutrient supply from the ovum and the maternal transfer of difenoconazole. Because this transgenerational developmental toxicity was observed at environmental levels, difenoconazole may pose a threat to the survival of wild larvae and therefore a risk to wild fish populations.

Immobilization of Acinetobacter sp. A-1 and Applicability in Removal of Difenoconazole from Water-Sediment Systems

Difenoconazole, as a systemic triazole fungicide, is a broad-spectrum, highly effective agent that has been widely used for controlling fungal diseases in 46 different crops (or crop categories), including rice, wheat, and corn. Due to the improper use of difenoconazole, concerns about its environmental residues and toxicity to non-target organisms have drawn significant attention from researchers. In response to this issue, this study aimed to isolate microbial strains capable of degrading difenoconazole from the environment. A novel difenoconazole-degrading strain, Acinetobacter sp. A-1, was screened and identified, demonstrating the ability to degrade 62.43% of 50 mg/L difenoconazole within seven days. Further optimization of the degradation conditions was conducted using single-factor experiments and response surface methodology experiments. The results showed that the optimal degradation conditions for strain A-1 were a difenoconazole concentration of 55.71 mg/L, a pH of 6.94, and an inoculation volume of 1.97%, achieving a degradation rate of 79.30%. Finally, strain A-1 was immobilized using sodium alginate, and its stability and bioremediation efficiency were evaluated. The results indicated that the immobilized strain A-1 exhibited high stability and significantly reduced the half-life of difenoconazole in the water-sediment contamination system. In the sterilized water-sediment system, the degradation rate of difenoconazole by the immobilized strain A-1 reached 65.26%. Overall, this study suggests that Acinetobacter sp. A-1 is a promising candidate for difenoconazole degradation, and immobilization technology can effectively enhance its removal efficiency in water-sediment systems.

The effect of abamectin exposure on gametogenesis in zebrafish

Today, pesticides are widely used to enhance agricultural yield mixed with soil and water, creating significant environmental pollution. The extensive use of insecticides for pest control has made this issue more pronounced. Abamectin, a key member of the avermectin family, is used as an insecticide and an antihelminthic agent in agriculture. It is an active and effective agricultural pesticide, particularly preferred for combating pests such as aphids and red spider mites. The dosage and frequency of its use vary depending on the target plant species and pest organism. For example, abamectin-based products with an 18 g/L EC formulation in apple orchards are typically recommended at 10 ml/100 L of water to control red spider mites. Although significantly below agricultural application levels, the low dose of 0.75 µg L⁻1 used in our study has demonstrated effects that cannot be overlooked. However, it can contaminate aquatic environments, posing harmful effects on organisms. Studies indicate that abamectin exposure may lead to serious health issues, showing toxic and reproductive toxicity effects in aquatic species. Examining abamectin's effects on testicular tissue revealed hypertrophy of Sertoli cells in the group exposed to 0.75 µg L⁻1 of abamectin. Apoptotic cells were observed in the groups exposed to 0.75 µg L⁻1 and 1.5 µg L⁻1. At the same time, pyknotic structures, disruption of seminiferous tubules, interstitial fibrosis, and atrophic appearance were identified across all dose groups, with severity increasing dose-dependently. Analysis of ovarian tissue demonstrated distortion of the zona radiata in groups exposed to 0.75 µg L⁻1 and 1.5 µg L⁻1 of abamectin. Moreover, in all dose groups, thickening of the zona radiata, vacuolization, formation of degenerated follicles, and nuclear disruption were observed, with these pathological alterations exacerbating in a dose-dependent manner. Like many studies involving zebrafish, this research is crucial for assessing potential toxic effects that may pose risks to human health. This study examined the histopathological effects of varying doses of abamectin (0.75 µg L⁻1, 1.5 µg L⁻1, and 3 µg L⁻1) on zebrafish gonads after 96 h of exposure. Using standard histological techniques, the samples prepared were stained with H&E and observed under a light microscope. Statistical analyses were conducted using SPSS 23. The normality of the data was assessed with the Shapiro-Wilk test. One-way ANOVA and Tukey post-hoc tests were used for normally distributed groups, while the Kruskal-Wallis and Dunnett's T3 tests were applied for non-normally distributed groups. All analyses were performed with a 95% confidence interval and a significance level of p > 0.05.

Long-term exposure to Emamectin benzoate impairs reproductive health in adult zebrafish and alters neurodevelopment in their offspring

Emamectin benzoate (EMB) is a widely used insecticide that can accumulate in aquatic environments under specific conditions of high application intensity or improper management, posing potential risks to aquatic organisms and human health. This study aimed to evaluate the reproductive toxicity of long-term EMB exposure in zebrafish (Danio rerio) and neurodevelopmental toxicity in their offspring. Zebrafish embryos were exposed to various concentrations of EMB (0, 0.1, 1, and 10 μg/L) for up to 120 days. The results revealed a significant decrease in reproductive capacity and gonadal tissue damage in the F0 generation zebrafish. Additionally, the increased oxidative stress levels induced by EMB exposure further exacerbated reproductive toxicity. The F1 generation of zebrafish exhibited a high rate of deformities, reduced body length, decreased swim bladder area, and abnormal swimming behavior. Compared to the control group, zebrafish larvae in the 1 and 10 μg/L EMB exposure groups showed a significant reduction in distance travelled of 18.3 % and 36.9 % and a significant increase in dwell time of 6.1 % and 17.1 %. Analysis of neurodevelopment and gene expression in the F1 generation revealed that EMB exposure diminished the development of the central nervous system and further aggravated developmental toxicity through pathways such as oxidative stress, inflammatory response, apoptosis. Notably, maternal exposure to EMB exerted a more significant impact on developmental and neurotoxic effects in the offspring. This study demonstrated that long-term EMB exposure causes significant parental reproductive and offspring neurodevelopmental toxicity in aquatic organisms, thus highlighting the importance of environmental risk assessment and pollution control.

Pathway Elucidation and Key Enzymatic Processes in the Biodegradation of Difenoconazole by Pseudomonas putida A-3

The extensive agricultural use of the fungicide difenoconazole (DIF) and its associated toxicity increasingly damage ecosystems and human health. Thus, an urgent need is to develop environmentally friendly technological approaches capable of effectively removing DIF residues. In this study, strain Pseudomonas putida A-3 was isolated for the first time which can degrade DIF efficiently. After optimization of the degradation conditions, the degradation rate reached 75.98%. Moreover, a new DIF degradation pathway, including hydroxylation, hydrolysis, dechlorination, and ether bond breaking. The acute and chronic toxicity of DIF degradation products assessed using ECOSAR software showed lower toxicity than the parent compound. Furthermore, strain A-3 remarkably accelerated the degradation of DIF in contaminated water-sediment systems. We successfully predicted six potential key enzymes for DIF degradation based on the results of whole genome sequencing, RT-qPCR, and molecular docking. Overall, the results revealed novel pathways for DIF biodegradation and provide a strong candidate for bioremediation of DIF residue-polluted environments.

Insights into organophosphorus insecticide malathion induced reproductive toxicity and intergenerational effect in zebrafish (Danio rerio)

The reproductive and transgenerational effects of malathion, a widely utilized low-toxicity organophosphorus insecticide, were explored using zebrafish as model animal. Adult zebrafish (F0) were exposed to malathion at 0.1-1.0 mg/L for 60 days for exploring the reproductive toxicity in sex differences and the potential mechanisms, and development and transcription levels in F1 offspring were assessed. Malathion significantly suppressed the fertility of zebrafish as evidenced by reduced spawning and lower fertilization rates in F1 offspring. Abnormal gonadal development and steroid hormone disorders were observed in F0 zebrafish, which was associated with the alterations in the transcription of core genes (such as cyp11a, cyp19a, vtg1, era) along the hypothalamus-pituitary-gonad-liver (HPGL) axis. The expression level of vtg1 played a key role in the malathion-induced sex dependence on E2 and VTG levels. The reduction of E2 and VTG could disrupt ovarian capability in females. E2 excess would cause feminization in males. Molecular docking indicated that reproductive disorders induced by malathion in zebrafish mainly through estrogen-like effects and CYP11A antagonism. Parental exposure to malathion abnormalized embryonic development in F1 offspring, comprising heartbeats decrease, deformities and body length reduction. Transcriptomics suggested that malathion-induced reproductive toxicity could be transmitted across generations, which may adversely affect fish populations.

Recent advances in the toxicological effects of difenoconazole: A focus on toxic mechanisms in fish and mammals

The toxicological study of pesticides at sub-lethal and environment-relevant concentrations has become increasingly crucial for human and environmental health. Toxic mechanisms of agrochemicals contribute to discovering green pesticides, assessing the hazards of pesticides comprehensively, and supporting legitimate regulatory decisions. However, the toxicological effects of difenoconazole are not yet fully understood despite being frequently detected in fruits, vegetables, waters, and soils and posing hazards to humans and the environment. This lack of knowledge could lead to flawed risk assessment and administrative oversight. Thus, the review aimed to provide some investigation perspectives for clarifying the toxicological effects of difenoconazole by synthesizing the toxic data of difenoconazole on various organisms, such as bees, Daphnia magna, fish, earthworms, mammals, and plants and summarizing the toxicological mechanisms of difenoconazole, especially in fish and mammals from peer-reviewed publications. Evidence revealed that difenoconazole caused multiple toxicological effects, including developmental toxicity, reproductive toxicity, endocrine disruption effects, neurotoxicity, and transgenerational toxicity. The toxic mechanisms involved in metabolic disturbance, oxidative stress, inflammation, apoptosis, and autophagy by activating reactive oxygen species-mediated signaling pathways and mitochondrial apoptosis routes, disturbing amino acids, lipid, and nucleotide metabolism, and regulating gene transcription and expression in mammals and fish. Based on the review, further studies better focus on the toxic differences of difenoconazole stereoisomers, the toxicological effects of transformation products of difenoconazole, and the mechanism of action of difenoconazole on sex-specific endocrine disruption effects, intestinal damage, and gut dysbacteriosis for its hazard assessment and management synthetically.

Novel Insights into Stereoselective Reproductive Toxicity Induced by Mefentrifluconazole in Earthworms (Eisenia fetida): First Report of Estrogenic Effects

Widespread use of the new chiral triazole fungicide mefentrifluconazole (MFZ) poses a threat to soil organisms. Although triazole fungicides have been reported to induce reproductive disorders in vertebrates, significant research gaps remain regarding their impact on the reproductive health of soil invertebrates. Here, reproduction-related toxicity end points were explored in earthworms (Eisenia fetida) after exposure for 28 d to soil containing 4 mg/kg racemic MFZ, R-(-)-MFZ, and S-(+)-MFZ. The S-(+)-MFZ treatment resulted in a more pronounced reduction in the number of cocoons and juveniles compared to R-(-)-MFZ treatment, and the expression of annetocin gene was significantly downregulated following exposure to both enantiomers. This reproductive toxicity has been attributed to the disruption of ovarian steroidogenesis at the transcriptional level. Further studies revealed that MFZ enantiomers were able to activate the estrogen receptor (ER). Indirect evidence for this estrogenic effect is provided by the introduction of 17β-estradiol, which also induces reproductive disorders through ER activation.

Genetic algorithm multiple linear regression and machine learning-driven QSTR modeling for the acute toxicity of sterol biosynthesis inhibitor fungicides

Sterol Biosynthesis Inhibitors (SBIs) are a major class of fungicides used globally. Their widespread application in agriculture raises concerns about potential harm and toxicity to non-target organisms, including humans. To address these concerns, a quantitative structure-toxicity relationship (QSTR) modeling approach has been developed to assess the acute toxicity of 45 different SBIs. The genetic algorithm (GA) was used to identify key molecular descriptors influencing toxicity. These descriptors were then used to build robust QSTR models using multiple linear regression (MLR), support vector regression (SVR), and artificial neural network (ANN) algorithms. The Cross-validation, Y-randomization test, applicability domain methods, and external validation were carried out to evaluate the accuracy and validity of the generated models. The MLR model exhibited satisfactory predictive performance, with an R2 of 0.72. The SVR and ANN models obtained R2 values of 0.7 and 0.8, respectively. ANN model demonstrated superior performance compared to other models, achieving R2 cv and R2 test values of 0.74 and 0.7, respectively. The models passed both internal and external validation, indicating their robustness. These models offer a valuable tool for risk assessment, enabling the evaluation of potential hazards associated with future applications of SBIs.

Occurrence and risk assessment of azole fungicides during the urban water cycle: A year-long study along the Yangtze River, China

Azole fungicides (AFs) play an important role in the prevention and treatment of fungal diseases in agricultural crops. However, limited studies are addressing the fate and ecological risk of AFs in the urban water cycle at a large watershed scale. To address this gap, we investigated the spatiotemporal distribution and ecological risk of twenty AFs in the lower reaches of the Yangtze River across four seasons. Carbendazim (CBA), tebuconazole (TBA), tricyclazole (TCA), and propiconazole (PPA) were found to be the dominant compounds. Their highest concentrations were measured in January (188.3 ng/L), and November (2197.1 ng/L), July (162.0 ng/L), and November (1801.9 ng/L), respectively. The comparison between wastewater treatment plants (WWTPs) effluents and surface water suggested that industrial WWTPs are major sources of AFs in the Yangtze River. In particular, TBA and PPA were found to be the most recalcitrant AFs in industrial WWTPs, while difenoconazole (DFA) was found to be the most potent pollutant in municipal WWTPs, with an average removal rate of less than 60%. The average risk quotient (RQ) for the entire AFs was 6.45 in the fall, which was higher than in January (0.98), April (0.61), and July (0.40). This indicates that AFs in surface water posed higher environmental risks during the dry season. Additionally, the exposure risk of AFs via drinking water for sensitive populations deserves more attention. This study provides benchmark data on the occurrence of AFs in the lower reaches of the Yangtze River, and offers suggestions for better reduction of AFs.

Network analysis of toxic endpoints of fungicides in zebrafish

Zebrafish being the best animal model to study, every attempt has been made to decipher the toxic mechanism of every fungicide of usage and interest. It is important to understand the multiple targets of a toxicant to estimate the toxic potential in its totality. A total of 22 fungicides of different classes like amisulbrom, azoxystrobin, carbendazim, carboxin, chlorothalonil, difenoconazole, etridiazole, flusilazole, fluxapyroxad, hexaconazole, kresoxim methyl, mancozeb, myclobutanil, prochloraz, propiconazole, propineb, pyraclostrobin, tebuconazole, thiophanate-methyl, thiram, trifloxystrobin and ziram were reviewed and analyzed for their multiple explored targets in zebrafish. Toxic end points in zebrafish are highly informative when it comes to network analysis. They provide a window into the molecular and cellular pathways that are affected by a certain toxin. This can then be used to gain insights into the underlying mechanisms of toxicity and to draw conclusions on the potential of a particular compound to induce toxicity. This knowledge can then be used to inform decisions about drug development, environmental regulation, and other areas of research. In addition, the use of zebrafish toxic end points can also be used to better understand the effects of environmental pollutants on ecosystems. By understanding the pathways affected by a given toxin, researchers can determine how pollutants may interact with the environment and how this could lead to health or environmental impacts.

Mechanistic Insights into 1,2-bis(2,4,6-tribromophenoxy)ethane-Induced Male Reproductive Toxicity in Zebrafish

The novel brominated flame retardant, 1,2-bis(2,4,6-tribromophenoxy)ethane (BTBPE), has increasingly been detected in environmental and biota samples. However, limited information is available regarding its toxicity, especially at environmentally relevant concentrations. In the present study, adult male zebrafish were exposed to varying concentrations of BTBPE (0, 0.01, 0.1, 1, and 10 μg/L) for 28 days. The results demonstrated underperformance in mating behavior and reproductive success of male zebrafish when paired with unexposed females. Additionally, a decline in sperm quality was confirmed in BTBPE-exposed male zebrafish, characterized by decreased total motility, decreased progressive motility, and increased morphological malformations. To elucidate the underlying mechanism, an integrated proteomic and phosphoproteomic analysis was performed, revealing a predominant impact on mitochondrial functions at the protein level and a universal response across different cellular compartments at the phosphorylation level. Ultrastructural damage, increased expression of apoptosis-inducing factor, and disordered respiratory chain confirmed the involvement of mitochondrial impairment in zebrafish testes. These findings not only provide valuable insights for future evaluations of the potential risks posed by BTBPE and similar chemicals but also underscore the need for further research into the impact of mitochondrial dysfunction on reproductive health.

Frontier of toxicology studies in zebrafish model

Based on the 87 original publications only from quartiles 1 and 2 of Journal Citation Report (JCR) collected by the major academic databases (Science Direct, Web of Science, PubMed, and Wiley) in 2022, the frontier of toxicology studies in zebrafish model is summarized. Herewith, a total of six aspects is covered such as developmental, neurological, cardiovascular, hepatic, reproductive, and immunizing toxicities. The tested samples involve chemicals, drugs, new environmental pollutants, nanomaterials, and its derivatives, along with those related mechanisms. This report may provide a frontier focus benefit to researchers engaging in a zebrafish model for environment, medicine, food, and other fields.

Aquatic and sediment ecotoxicity data of difenoconazole and its potential environmental risks in ponds bordering rice paddies

Difenoconazole has a widespread agricultural use to control fungal diseases in crops, including rice. In edge-of-field surface waters the residues of this lipophilic fungicide may be toxic to both pelagic and benthic organisms. To allow an effect assessment we mined the regulatory and open literature for aquatic toxicity data. Since published sediment toxicity data were scarce we conducted 28 d sediment-spiked toxicity test with 8 species of benthic macroinvertebrates. Ecotoxicological threshold levels for effects were assessed by applying the species sensitivity distribution approach. Based on short-term L(E)C50's for aquatic organisms from water-only tests an acute Hazardous Concentration to 5% of the species (HC5) of 100 µg difenoconazole/L was obtained, while the HC5 based on chronic NOEC values was a factor of 104 lower (0.96 µg difenoconazole/L). For benthic macroinvertebrates the chronic HC5, based on 28d-L(E)C10 values, was 0.82 mg difenoconazole/kg dry weight sediment. To allow a risk assessment for water- and sediment-dwelling organisms, exposure concentrations were predicted for the water and sediment compartment of an edge-of-field pond bordering rice paddies treated with difenoconazole using the Chinese Top-Rice modelling approach, the Chinese Nanchang exposure scenario and the Equilibrium Partitioning theory. It appeared that in the vast majority of the 20 climate years simulated, potential risks to aquatic and sediment organisms cannot be excluded. Although the HC5 values based on laboratory toxicity data provide one line of evidence only, our evaluation suggests population- and community-level effects on these organisms due to chronic risks in particular.

Immunoprotective effect of silybin through blocking p53-driven caspase-9-Apaf-1-Cyt c complex formation and immune dysfunction after difenoconazole exposure in carp spleen

As a broad-spectrum and efficient triazole fungicide, difenoconazole is widely used, which not only pollutes the environment but also exerts toxic effects on non-target organisms. The spleen plays an important role in immune protection as an important secondary lymphoid organ in carp. In this study, we assessed the protective impact of silybin as a dietary additive on spleen tissues of carp during exposure to difenoconazole. Sixty carp were separated into four groups for this investigation including control group, difenoconazole group, silybin group, and silybin and difenoconazole group. By hematoxylin-eosin staining, dihydroethidium staining, immunohistochemical staining, terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling assay, quantitative real-time PCR assay, Western blot analysis, biochemical assays, and immune function indicator assays, we found that silybin could prevent difenoconazole-induced spleen tissue damage, oxidative stress, and immune dysfunction, and inhibited apoptosis of carp spleen tissue cells by suppressing the formation of p53-driven caspase-9-apoptotic protease activating factor-1-cytochrome C complex. The results suggested that silybin as a dietary additive could improve spleen tissue damage and immune dysfunction induced by difenoconazole in aquaculture carp.

Long-term tralopyril exposure results in endocrinological and transgenerational toxicity: A two-generation study of marine medaka (Oryzias melastigma)

This study aims to investigate the impact of tralopyril, a newly developed marine antifouling agent, on the reproductive endocrine system and developmental toxicity of offspring in marine medaka. The results revealed that exposure to tralopyril (0, 1, 20 μg/L) for 42 days resulted in decreased reproductive capacity in marine medaka. Moreover, it disrupted the levels of sex hormones E2 and T, as well as the transcription levels of genes related to the HPG axis, such as cyp19b and star. Sex-dependent differences were observed, with females experiencing more pronounced effects. Furthermore, intergenerational toxicity was observed in F1 offspring, including increased heart rate, changes in retinal morphology and cartilage structure, decreased swimming activity, and downregulation of transcription levels of relevant genes (HPT axis, GH/IGF axis, cox, bmp4, bmp2, runx2, etc.). Notably, the disruption of the F1 endocrine system by tralopyril persisted into adulthood, indicating a transgenerational effect. Molecular docking analysis suggested that tralopyril's RA receptor activity might be one of the key factors contributing to the developmental toxicity observed in offspring. Overall, our study highlights the potential threat posed by tralopyril to the sustainability of fish populations, as it can disrupt the endocrine system and negatively impact aquatic organisms for multiple generations.

Integrated Studies on Male Reproductive Toxicity of Bis(2-ethylhexyl)-tetrabromophthalate: in Silico, in Vitro, ex Vivo, and in Vivo

Bis(2-ethylhexyl)tetrabromophthalate (TBPH) has been widely detected in the environment and organisms; thus, its toxic effects on male reproduction were systematically studied. First, we found that TBPH can stably bind to the androgen receptor (AR) based on in silico molecular docking results and observed an antagonistic activity, but not agonistic activity, on the AR signaling pathway using a constructed AR-GRIP1 yeast assay. Subsequently, we validated the adverse effects on male germ cells by observing inhibited androgen production and proliferation in Leydig cells upon in vitro exposure and affected general motility and motive tracks of zebrafish sperm upon ex vivo exposure. Finally, the in vivo reproductive toxicity was demonstrated in male zebrafish by reduced mating behavior in F0 generation when paired with unexposed females and abnormal development of their offspring. In addition, reduced sperm motility and impaired germ cells in male zebrafish were also observed, which may be related to the disturbed homeostasis of sex hormones. Notably, the specifically suppressed AR in the brain provides further evidence for the antagonistic effects as above-mentioned. These results confirmed that TBPH affected male reproduction through a classical nuclear receptor-mediated pathway, which would be helpful for assessing the ecological and health risks of TBPH.

Environmental impacts of chlorpyrifos: Transgenerational toxic effects on aquatic organisms cannot be ignored

Chlorpyrifos (CPF) has been extensively used in the world and frequently found in natural environments, might cause a range of environmental issues and pose a health risk to aquatic species. However, investigation of its toxic effects on offspring after parental exposure has been neglected, especially for aquatic organisms such as fish. In the current study, the effects of chronic CPF exposure (3 and 60 μg/L) on adult zebrafish (F0) was investigated to determine its influence on adult reproductive capacity and offspring (F1 and F2). The results showed the existence of CPF both in F0 ovaries and F1 embryos and larvae, indicating that CPF could be transferred directly from the F0 adult fish to F1 offspring. After 90 d exposure, we observed that F0 female fish showed increased proportion of perinucleolar oocyte in the ovaries, decreased proportion of mature oocyte, and decreased egg production, but not in F1 adult. The transcriptomic analysis revealed that the disruption of metabolism during oocyte maturation in the CPF treatment zebrafish might interfere with F0 oocytes development and quality and ultimately influence offspring survival. For the larvae, the parental CPF exposure distinctly inhibited heart rate at 72 and 120 hpf and increased the mortality of F1 but not F2 larvae. The changes of biochemical indicators confirmed a disturbance in the oxidative balance, induced inflammatory reaction and apoptosis in F1 larvae. Furthermore, the changing profiles of mRNA revealed by RNA-seq confirmed an increased susceptibility in F1 larvae and figured out potential disruptions of ROS metabolism, immune system, apoptosis, and metabolism pathways. Taken together, these results show that chronic CPF treatment can induce reproductive toxicity, and parental transfer of CPF occurs in fish, resulting in transgenerational alters in F1 generation survival and transcription that raising concerns on the ecological risk of CPF in the natural environment.

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.

Enantioselective activity and toxicity of chiral acaricide cyflumetofen toward target and non-target organisms

Cyflumetofen (CYF), a novel chiral acaricide, exert enantiomer-specific effects on target organisms by binding to glutathione S-transferase. However, there is limited knowledge regarding the response of non-target organisms to CYF, including enantioselective toxicity. In this study, we investigated the effects of racemic CYF (rac-CYF) and its two enantiomers (+)-CYF and (-)-CYF on MCF-7 cells and non-target (honeybees) and target (bee mites and red spider mites) organisms. The results showed that similar to estradiol, 1 μM (+)-CYF promoted the proliferation and disturbed the redox homeostasis of MCF-7 cells, whereas at high concentrations (≥100 μM) it exerted a negative effect on cell viability that was substantially stronger than that of (-)-CYF or rac-CYF. (-)-CYF and rac-CYF at 1 μM concentration did not significantly affect cell proliferation, but caused cell damage at high concentrations (≥100 μM). Analysis of acute CYF toxicity against non-target and target organisms revealed that for honeybees, all CYF samples had high lethal dose (LD₅₀) values, indicating low toxicity. In contrast, for bee mites and red spider mites, LD₅₀ values were low, whereas those of (+)-CYF were the lowest, suggesting higher toxicity of (+)-CYF than that of the other CYF samples. Proteomics profiling revealed potential CYF-targeted proteins in honeybees related to energy metabolism, stress responses, and protein synthesis. Upregulation of estrogen-induced FAM102A protein analog indicated that CYF might exert estrogenic effects by dysregulating estradiol production and altering estrogen-dependent protein expression in bees. Our findings suggest that CYF functions as an endocrine disruptor in non-target organisms in an enantiomer-specific manner, indicating the necessity for general ecological risk assessment for chiral pesticides.

Developmental defects and potential mechanisms in F1 generation of parents exposed to difenoconazole at different life stages of zebrafish (Danio rerio)

As a typical triazole fungicide, difenoconazole is extensively used to control plant diseases; however, its residue in environmental waters poses a risk to aquatic organisms. In this study, we investigated the acute toxicity of different life stages and sub-lethal toxicity in embryonic yolk sac stage of difenoconazole to zebrafish, and the developmental toxicity in F1 generation of parents exposed to difenoconazole at different life stages of zebrafish. Furthermore, we used transcriptomics to explore the potential mechanisms of difenoconazole on the F1 larvae of parents exposed to the chemical at the embryonic stage. The results of this study showed that developmental defects were observed in the F1 embryo/larvae of parents exposed to 3, 30, and 300 μg/L of difenoconazole at different (embryo, larval, juvenile, and adult) life stages, and exposure to difenoconazole at the embryonic stage caused more severe developmental toxicity than those at other life stages. Developmental defects (malformation, inhibition of heartbeat and body length) were observed in the F1 embryos and larvae of parents exposed to difenoconazole at the embryonic stage. In addition, the total cholesterol and triglyceride contents were significantly reduced in the F1 larvae, and RNA-seq analysis revealed significant alterations in the expression of nine genes (msmo1, hsd17b7, sc5d, tm7sf2, ebp, cyp2r1, lss, cyp51, and cyp27b1) in the steroid synthesis pathway. This is suggested that F1 larvae of parents exposed to difenoconazole at the embryonic stage show abnormalities in the steroid biosynthetic pathway. These results reveal the differences in toxicity of difenoconazole to zebrafish at different life stages, improve studies on difenoconazole toxicity to zebrafish, and provide a new perspective for assessing the risk of contaminants to aquatic organisms.

Mechanisms regarding respiratory toxicity triggered by accumulation of ROS in carp exposed to difenoconazole

Difenoconazole is a widely used but difficult-to-degrade fungicide that can directly affect aquatic ecosystems. Here, two doses (0.488 mg/L, 1.953 mg/L) of difenoconazole were used to study the toxicity to the respiratory system of carp at an exposure time of 96 h. The results showed that difenoconazole exposure resulted in severe structural damage to carp gill tissue with extensive inflammatory cell infiltration. Mechanistically, difenoconazole exposure led to excessive accumulation of ROS in carp gill tissue, which induced an inflammatory response in the gill tissue. Meanwhile, the activities of SOD and CAT were reduced and the NRF2 signaling pathway was activated to regulate the imbalance between oxidation and antioxidation. In addition, difenoconazole exposure further activated the mitochondrial pathway of apoptosis by upregulating cytochrome C, BAX, cleaved-caspase 9, and downregulating Bcl-2. More interestingly, exposure to difenoconazole increased autophagosomes, but lysosomal dysfunction prevented the late stages of autophagy from proceeding smoothly, resulting in a protective autophagic response that is not properly initiated. In summary, difenoconazole exposure caused respiratory toxicity including inflammation response, oxidative stress, apoptosis, and autophagy in carp through the accumulation of ROS. The present study expanded our understanding of the toxic effects of difenoconazole on organisms and its possible threat to the aquatic environment.

Embryonic benzophenone-3 exposure inhibited fertility in later-life female zebrafish and altered developmental morphology in offspring embryos

Benzophenone-3 (BP3), an organic UV filter widely used in personal care products, is ubiquitous in aquatic environments. Previous studies have shown that BP3 can interfere with oocytes development in the ovary. The current study was conducted to evaluate the effects of embryonic BP3 exposure on reproductive outcomes in later life. Zebrafish embryos were exposed to different concentrations of BP3 (0, 1, 10, 100 μg/L) for 5 days in the developmental stage and subsequently fed for 4 months without any toxins. The body length, body weight, and ovary weight in F0 female adult zebrafish and morphology indices in F1 offspring embryos were measured. The reproductive behaviors of adult zebrafish were recorded by a digital camera. HE staining was used to estimate the development of oocytes and the proportion of different phases was calculated. qPCR was used to detect the expression levels of reproduction-related genes of the hypothalamic-pituitary-gonadal (HPG) axis. Our findings revealed that the body length and body weight were not changed with embryonic BP3 exposure, but BP3 exposure inhibited the development and maturation of ovaries in later-life female zebrafish, accompanied by an increased proportion of follicles in the primary growth and early vitellogenic stages, and a decline in the full-growth stage in ovaries. Meanwhile, reduced egg production, delayed hatching rate, altered somite count and increased mortality rate were observed at 100 μg/L in offspring embryos. Behavioral results showed that BP3 exposure reduced the frequency of chasing, touching, entering the spawning area, and the duration of fish entering the spawning area later in life, qPCR analysis showed that the expression levels of reproduction-related genes of the HPG axis were downregulated in females, following a decreasing trend in plasma E2 and 11-KT levels. These results suggested that embryonic BP3 exposure negatively affected the fertility of fish and the development of their offspring embryos, which may cause potential risks to aquatic ecosystems and human health.

Spatial assessment of triazole organic compounds in surface water from the coastal estuaries to the East China sea

Triazole is widely used in the synthesis of pharmaceuticals, pesticides, and fungicides. However, triazole organic compounds are often a source of toxicity in the water environment due to the presence of chlorobenzene. This study reported on the occurrence and distribution of 15 TrOCs in the surface waters of estuaries and the East China sea, and identified the influences of TrOCs originating from the estuarine environment on the ocean. The results showed that the total concentrations of ∑TrOCs in the surface water of estuaries along the coasts of Jiangsu (JS), Zhejiang (ZJ), and Shanghai (SH), China ranged from 0.020 to 104 ng L^-1 (7.49 ± 18.2 ng L^-1), whereas they ranged from 0.235 to 1.25 ng L^-1 (mean 0.711 ± 0.235 ng L^-1) in the East China sea. Difenoconazole and tebuconazole were the dominant TrOCs in the estuaries, whereas fenbuconazole and hexaconazole dominated in the ocean. TrOCs in surface water of estuaries showed a continuous spatial distribution and presented regional characteristics mainly related to agricultural activities. In contrast, TrOCs in the East China Sea showed a low spatial variation and dispersion, which may be related to complex disturbance by currents and dilution. The low levels of estuarine TrOCs measured in SH estuaries (<0.5 ng L^-1) indicates that the Yangtze River may only pose a low-level TrOC contamination risk to the East China Sea. Moreover, estuary transport in the estuaries of ZJ may have influenced the occurrence of TrOCs in the offshore East China Sea area, although they may have also undergone a filter process in the estuary turbid zone; whereas it had little influence on the open sea. This study can act as a critical reference for the presence of TrOCs in surface water both estuaries and the ocean.

Intergenerational reproductive toxicity of parental exposure to prothioconazole and its metabolite on offspring and epigenetic regulation associated with DNA methylation in zebrafish

Prothioconazole (PTC) is a widely used agricultural fungicide, and its parent and metabolite prothioconazole-desthio (dPTC) have been detected in diverse environmental media. This study was aimed at investigating the gender-dependent effects on adult zebrafish reproduction and intergenerational effects on offspring development following parental exposure to PTC and dPTC. The results showed that after the adult zebrafish (F0) was exposed to 0.5 and 10 μg/L PTC and dPTC for 21 days, the fertility and gametogenesis of female zebrafish were decreased more significantly than that of male zebrafish. After that, three fecundity tests were conducted in the exposure period to explore the development endpoints of F1 embryos/larvae without further treatment with PTC and dPTC exposure. However, PTC and dPTC exposure did lead to abnormal development of F1 embryos, including delayed hatching, shortened body length, abnormal development and significant changes in locomotor behavior. These changes were related to the abnormal expression of sex hormones and the regulation of DNA methylation in F0 fish. In a word, the results of this study showed that parental PTC and dPTC interference have sex-dependent reproductive toxicity on F0 zebrafish, which may be passed on to the next generation through epigenetic modification involving DNA methylation, resulting in alternations in growth phenotype of offspring.

"Fishcide" effect of the fungicide difenoconazole in freshwater fish (Labeo rohita): A multi-endpoint approach

Difenoconazole is widely used to protect crops, fruits, and vegetables. However, this fungicide can enter aquatic environments and cause harmful effects to non-target organisms and induce little-known biological disorders. Thus, aiming to expand our knowledge about the ecotoxicity of difenoconazole on freshwater ichthyofauna, we aimed to determine the median lethal concentration (LC₅₀) of difenoconazole and evaluate its possible impacts from different toxicity biomarkers, using freshwater fish Labeo rohita as a model system. Using the probit analysis method, the 96 h LC₅₀ value of difenoconazole in the fish was calculated as 4.5 mg L^-1. Posteriorly, fish were exposed to two sublethal concentrations (0.45 mg L^-1 1/10th and 0.9 mg L^-1 1/5th LC₅₀ value) for 21 days. A significant reduction of superoxide dismutase (SOD) and catalase (CAT) activity was noted in the gill, liver, and kidneys of fish compared to the control groups. The level of glutathione-S-transferase (GST) and lipid peroxidation (LPO) activity was higher in all vital tissues of difenoconazole-treated fish. Histological alterations in the gill include epithelial lifting, lamellar fusion, hypertrophy, and epithelial necrosis. At the same time, the liver showed pyknotic nucleus, vacuolation, cellular edema and tubular necrosis, shrinkage of glomeruli, vacuolation, and pyknotic nuclei in the kidney. DNA damage was increased significantly with tail formation based on the concentration and time-dependent manner. Therefore, our study confirms that the exposure of L. rohita to difenoconazole induces negative biological consequences and sheds light on the danger of this fungicide for freshwater fish species. We believe that studies like ours can support actions and strategies for the remediation/mitigation of aquatic pollution by difenoconazole and for the conservation of freshwater ichthyofauna.

Highly efficient in-situ cleaner degradation of difenoconazole by two novel dominant strains: Microflora diversity, monoclonal isolation, growth factor optimization, intermediates, and pathways

The non-point source pollution of difenoconazole (DIF) has become a serious environmental issue, increasingly causes indelible damages to eco-environment and human health due to its toxicity, persistence, and biomagnification. An eco-friendly, cost-effective, and efficient control technology is imperative towards a cleaner and sustainable agricultural production. Herein, a dominant microflora of efficiently degrading DIF was successfully screened, and its microbial diversity was investigated. Two novel degrading strains were isolated and identified as Phyllobacterium sp. (T-1) and Aeromonas sp. (T-2). The results of growth factor optimization indicated that the degradation rates of DIF (C₀ = 20 mg/L) by strain T-1 and T-2 were up to 96.32% and 97.86% within 14 d, respectively, under the optimal conditions. Moreover, there no obvious synergy between strain T-1 and strain T-2. From catalytic kinetics of enzymes, the intracellular enzyme of strain T-1 dominated the degradation of DIF (C₀ = 20 mg/L) entirely with the degradation rate of 82.4% (48 h), the extracellular enzyme showed little catalytic activity. However, the degrade rates of DIF (C₀ = 20 mg/L) by both intracellular and extracellular enzymes of strain T-2 were 77.99% and 26.73% within 48 h, respectively. Moreover, these enzymes remained an undiminished catalytic activity within 48 h. DIF was degraded by strain T-1 to three main transformation products (DIF-TPs 406, DIF-TPs 216, and DIF-TPs 198) undergoing hydroxyl substitution, hydrolysis, cleavage of ether bond between benzene rings, and rearrangement, while two additional products (DIF-TPs 281 and DIF-TPs 237) were generated with the biodegradation of strain T-2, excepting for DIF-TPs 406 and DIF-TPs 216, involving hydrolysis, hydroxylation, and ether bond cleavage between benzene rings. Moreover, QSAR simulation showed that the by-products were almost much lower toxicity or even non-toxic to three typical aquatic organisms (fish, daphnia, and green algae) than DIF. This study not only provides an in depth understanding of DIF bioelimination, but also be instrumental in cleaner management of DIF-contaminated soil. This study can promote the sustainable development of agriculture.