Exposure to Boscalid Induces Reproductive Toxicity of Zebrafish by Gender-Specific Alterations in Steroidogenesis

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.

Temperature dependent cholinergic synapse induced by triphenyl phosphate and tris(1.3-dichloroisopropyl) phosphate via thyroid hormone synthesis in Cyprinus carpio

Triphenyl phosphate (TPHP) and tris(1.3-dichloroisopropyl) phosphate (TDCIPP) are emerging contaminants that pervade diverse ecosystems and impair the thyroid and neural signaling pathways. The intricate interactions between thyroid and neurodevelopmental effects mediated by TPHP and TDCIPP remain elusive. This study integrates in vivo, in vitro, and in silico approaches to elucidate these mechanisms in Cyprinus carpio at varying temperatures. It showed that TPHP and TDCIPP hindered fish growth, particularly at low temperatures, by interfering with thyroid hormone synthesis and transport processes. Both compounds have been identified as environmental hormones that mimic thyroid hormone activity and potentially inhibit acetylcholinesterase, leading to neurodevelopmental disorders characterized by brain tissue damage and disrupted cholinergic synapses, such as axon guidance and regeneration. Notably, the bioaccumulation of TPHP was 881.54 % higher than that of TDCIPP, exhibiting temperature-dependent variations with higher levels of TDCIPP at low temperatures (20.50 % and 250.84 % above optimum and high temperatures, respectively), suggesting that temperature could exacerbate the toxicity effects of OPEs. This study sheds new light on the mechanisms underlying thyroid endocrine disruption and neurodevelopmental toxicity in C. carpio. More importantly, these findings indicate that temperature affects the environmental fate and effects of TPHP and TDCIPP, which could provide an important basis for ecological environmental zoning control of emerging contaminants in the future.

Fluopyram SDHI pesticide alters fish physiology and behaviour despite low in vitro effects on mitochondria

Pollution from pesticides is an increasing concern for human health and biodiversity conservation. However, there is lack of knowledge about some emerging molecules such as SDHI fungicides (succinate dehydrogenase inhibitors) that are widely used but potentially highly toxic for vertebrates. Boscalid, fluopyram, and bixafen are 3 frequent SDHI molecules commonly detected in surface waters, which may pose risks to aquatic species. This study aimed to (1) test the in vitro effects of SDHI on mitochondrial activities (inhibition of succinate dehydrogenase SDH, also named respiratory chain complex II) and (2) assess the in vivo effects of sublethal SDHI concentrations on fish physiology and behaviour over 96 hours of exposure, using Carassius auratus fish as a model species. Results show that bixafen and boscalid inhibited complex II activities in vitro as expected (bixafen > boscalid), while fluopyram had no in vitro effects. In contrast, in vivo studies showed that fluopyram strongly altered fish behaviour (enhanced activity, social and feeding behaviours), likely explained by reduced AChE enzymatic activity. In addition, fluopyram increased muscle lipid content, suggesting metabolic disruption. These findings raise serious concern about the toxic effects of SDHI pesticides, especially fluopyram, although its underpinning molecular mechanisms remain to be explored. We thus encourage further research on the long-term impacts of SDHI pesticides to improve existing regulation and prevent adverse effects on wildlife.

Female zebrafish are more affected than males under polystyrene microplastics exposure

Microplastics are ubiquitous in freshwater and can be absorbed into fish skin and gills, accumulate in the gut, and be transported to other tissues, thus posing a risk to fish health. Further studies are needed, however, to investigate effects such as endocrine disruption and multi-tissue toxicity. In this study, zebrafish were exposed to polystyrene (PS) microplastics and health-related indicators were measured, including skin mucus, gut damage, oxidative stress, stable isotope composition and reproduction as well as an assessment of changes to metabolites using a metabolomics approach. Results showed that concentrations of PS microplastics were higher in gills than those in the gut. Minimal impact to immunoglobulin M level and lysozyme activity in mucus indicated, however, that microplastic toxicity primarily stemmed from ingestion rather than disruption of skin mucus immunity. Female zebrafish were more affected by PS microplastics. Gut microbiota dysbiosis was induced, especially in females. Significant alterations in pathways associated with lipid and energy metabolism were observed in the liver of female fish. PS microplastics also induced sex steroid hormone disorder and reduced female egg production, possibly linked to the alteration of gut microbiota and hepatic metabolism. Combined, these results highlight the gender-specific toxicity of PS microplastics to zebrafish health, potentially harming their population.

Hexafluoropropylene oxide trimer acid (HFPO-TA) disrupts sex differentiation of zebrafish (Danio rerio) via an epigenetic mechanism of DNA methylation

Hexafluoropropylene oxide trimer acid (HFPO-TA), an alternative to perfluorooctanoic acid, has been shown to have estrogenic effects. However, its potential to disrupt fish sex differentiation during gonadal development remains unknown. Therefore, this study exposed zebrafish to HFPO-TA from approximately 2 hours post fertilization (hpf) to 60 days post fertilization (dpf) to investigate its effects on sex differentiation. Results indicated that HFPO-TA disrupted steroid hormone homeostasis, delayed gonadal development in both sexes, and resulted in a female-skewed sex ratio in zebrafish. HFPO-TA exposure up-regulated gene expressions of cyp19a1a, esr1, vtg1 and foxl2, while down-regulated those of amh, sox9a and dmrt1. These suggested that HFPO-TA dysregulated the expressions of key genes related to sex differentiation of zebrafish, promoted the production and activation of estrogen, and further induced the feminization. Interestingly, we observed promoter hypomethylation of cyp19a1a and promoter hypermethylation of amh in male zebrafish, which were negatively associated with their gene expressions. These suggested that HFPO-TA dysregulated these key genes through DNA methylation in their promoters. Therefore, the HFPO-TA disrupted the sex differentiation of zebrafish through an epigenetic mechanism involving DNA methylation, ultimately skewing the sex ratio towards females. Overall, this study demonstrated adverse effects of HFPO-TA on fish sex differentiation and provided novel insights into the underlying epigenetic mechanism.

Long-term exposure of metamifop affects sex differentiation and reproductive system of zebrafish (Danio rerio)

The extensive use of herbicide metamifop (MET) in rice fields for weeds control will inevitably lead to its entering into water environments and threaten the aquatic organisms. Previous researches have demonstrated that sublethal exposure of MET significantly affected zebrafish development. Yet the long-term toxicological impacts of MET on aquatic life remains unknown. Herein, we investigated the potential effects of MET (5 and 50 μg/L) on zebrafish during an entire life cycle. Since the expression level of male sex differentiation-related gene dmrt1 and sex hormone synthesis-related gene cyp19a1b were significantly changed after 50 μg/L MET exposure for only 7 days, indicators related to sex differentiation and reproductive system were further investigated. Results showed that the transcript of dmrt1 was inhibited, estradiol content increased and testosterone content decreased in zebrafish of both sexes after MET exposure at 45, 60 and 120 dpf. Histopathological sections showed that the proportions of mature germ cells in the gonads of male and female zebrafish (120 dpf) were significantly decreased. Moreover, males had elevated vitellogenin content while females did not after MET exposure; MET induced feminization in zebrafish, with the proportion of females significantly increased by 19.6% while that of males significantly decreased by 13.2% at 120 dpf. These results suggested that MET interfered with the expression levels of gonad development related-genes, disrupted sex hormone balance, and affected sex differentiation and reproductive system of female and male zebrafish, implying it might have potential endocrine disrupting effects after long-term exposure.

Effects of whole life-cycle exposure to carbaryl on reproduction of female marine medaka (Oryzias melastigma) and their offspring

Carbaryl is widely used as a highly effective insecticide which harms the marine environment. This study aimed to assess the reproductive toxicity of chronic carbaryl exposure on female marine medaka and their female offspring. After a 180-day exposure from embryonic period to adulthood, females exhibited reduced attraction to males, decreased ovulation, increased gonadosomatic index and a higher proportion of mature and atretic follicles. These reproductive toxic effects of carbaryl may stem from changes in hormone levels and transcription levels of key genes along the HPG axis. Furthermore, maternal carbaryl exposure had detrimental effects on the offspring. F1 females showed the reproductive disorders similar to those observed in F0 females. The significant changes in the transcription levels of DNA methyltransferase and demethylase genes in the F0 and F1 generations of ovaries indicate changes in their DNA methylation levels. The changes in DNA methylation levels in F1 female marine medaka may lead to changes in the expression of certain reproductive key genes, such as an increase in the transcription level of cyp19a, which may be the reason for F1 reproductive toxicity. These findings indicate that maternal exposure may induce severe generational toxicity through alterations in DNA methylation levels. This study assesses the negative impacts of whole life-cycle carbaryl exposure on the reproductive and developmental processes of female marine medaka and its female offspring, while offering data to support the evaluation of the ecological risk posed by carbaryl in marine ecosystems.

Gender-specific effects of polystyrene nanoplastic exposure on triclosan-induced reproductive toxicity in zebrafish (Danio rerio)

Nanoplastics (NPs) and triclosan (TCS) are ubiquitous emerging environmental contaminants detected in human samples. While the reproductive toxicity of TCS alone has been studied, its combined effects with NPs remain unclear. Herein, we employed Fourier transform infrared spectroscopy and dynamic light scattering to characterize the coexposure of polystyrene nanoplastics (PS-NPs, 50 nm) with TCS. Then, adult zebrafish were exposed to TCS at environmentally relevant concentrations (0.361-48.2 μg/L), with or without PS-NPs (1.0 mg/L) for 21 days. TCS biodistribution in zebrafish tissues was investigated using ultra-performance liquid chromatography coupled with triple quadrupole mass spectrometry. Reproductive toxicity was assessed through gonadal histopathology, fertility tests, changes in steroid hormone synthesis and gene expression within the hypothalamus-pituitary-gonad-liver (HPGL) axis. Transcriptomics and proteomics were applied to explore the underlying mechanisms. The results showed that PS-NPs could adsorb TCS, thus altering the PS-NPs' physical characteristics. Our observations revealed that coexposure with PS-NPs reduced TCS levels in the ovaries, livers, and brains of female zebrafish. Conversely, in males, coexposure with PS-NPs increased TCS levels in the testes and livers, while decreasing them in the brain. We found that co-exposure mitigated TCS-induced ovary development inhibition while exacerbated TCS-induced spermatogenesis suppression, resulting in increased embryonic mortality and larval malformations. This co-exposure influenced the expression of genes linked to steroid hormone synthesis (cyp11a1, hsd17β, cyp19a1) and attenuated the TCS-decreased estradiol (E2) in females. Conversely, testosterone levels were suppressed, and E2 levels were elevated due to the upregulation of specific genes (cyp11a1, hsd3β, cyp19a1) in males. Finally, the integrated analysis of transcriptomics and proteomics suggested that the aqp12-dctn2 pathway was involved in PS-NPs' attenuation of TCS-induced reproductive toxicity in females, while the pck2-katnal1 pathway played a role in PS-NPs' exacerbation of TCS-induced reproductive toxicity in males. Collectively, PS-NPs altered TCS-induced reproductive toxicity by disrupting the HPGL axis, with gender-specific effects.

Development of a Portable Cell-Based Biosensor for the Ultra-Rapid Screening for Boscalid Residues in Lettuce

Fungal plant pathogens have posed a significant threat to crop production. However, the large-scale application of pesticides is associated with possible risks for human health and the environment. Boscalid is a widely used fungicide, consistently implemented for the management of significant plant pathogens. Conventionally, the detection and determination of boscalid residues is based on chromatographic separations. In the present study, a Bioelectric Recognition Assay (BERA)-based experimental approach combined with MIME technology was used, where changes in the electric properties of the membrane-engineering cells with anti-boscalid antibodies were recorded in response to the presence of boscalid at different concentrations based on the maximum residue level (MRL) for lettuce. The membrane-engineering Vero cells with 0.5 μg/mL of antibody in their surface were selected as the best cell line in combination with the lowest antibody concentration. Furthermore, the biosensor was tested against another fungicide in order to prove its selectivity. Finally, the BERA cell-based biosensor was able to detect the boscalid residue, below and above the MRL, in spiked lettuce leaf extracts in an entirely distinct and reproducible manner. This study indicates that the BERA-based biosensor, after further development and optimization, could be used for the routine, high-throughput detection of boscalid residue in lettuce, and not only that.

From cradle to grave: Deciphering sex-specific disruptions of the nervous and reproductive systems through interactions of 4-methylbenzylidene camphor and nanoplastics in adult zebrafish

4-methylbenzylidene camphor (4-MBC) and micro/nanoplastics (MNPs) are common in personal care and cosmetic products (PCCPs) and consumer goods; however, they have become pervasive environmental contaminants. MNPs serve as carriers of 4-MBC in both PCCPs and the environment. Our previous study demonstrated that 4-MBC induces estrogenic effects in zebrafish larvae. However, knowledge gaps remain regarding the sex- and tissue-specific accumulation and potential toxicities of chronic coexposure to 4-MBC and MNPs. Herein, adult zebrafish were exposed to environmentally realistic concentrations of 4-MBC (0, 0.4832, and 4832 μg/L), with or without polystyrene nanoplastics (PS-NPs; 50 nm, 1.0 mg/L) for 21 days. Sex-specific accumulation was observed, with higher concentrations in female brains, while males exhibited comparable accumulation in the liver, testes, and brain. Coexposure to PS-NPs intensified the 4-MBC burden in all tested tissues. Dual-omics analysis (transcriptomics and proteomics) revealed dysfunctions in neuronal differentiation, death, and reproduction. 4-MBC-co-PS-NP exposure disrupted the brain histopathology more severely than exposure to 4-MBC alone, inducing sex-specific neurotoxicity and reproductive disruptions. Female zebrafish exhibited autism spectrum disorder-like behavior and disruption of vitellogenesis and oocyte maturation, while male zebrafish showed Parkinson's-like behavior and spermatogenesis disruption. Our findings highlight that PS-NPs enhance tissue accumulation of 4-MBC, leading to sex-specific impairments in the nervous and reproductive systems of zebrafish.

Cardiac and neurobehavioral impairments in three phylogenetically distant aquatic model organisms exposed to environmentally relevant concentrations of boscalid

Boscalid (2-Chloro-N-(4'-chlorobiphenyl-2-yl) nicotinamide), a pyridine carboxamide fungicide, is an inhibitor of the complex II of the respiration chain in fungal mitochondria. As boscalid is only moderately toxic for aquatic organisms (LC50 > 1-10 mg/L), current environmental levels of this compound in aquatic ecosystems, in the range of ng/L-μg/L, are considered safe for aquatic organisms. In this study, we have exposed zebrafish (Danio rerio), Japanese medaka (Oryzias latipes) and Daphnia magna to a range of concentrations of boscalid (1-1000 μg/L) for 24 h, and the effects on heart rate (HR), basal locomotor activity (BLA), visual motor response (VMR), startle response (SR), and habituation (HB) to a series of vibrational or light stimuli have been evaluated. Moreover, changes in the profile of the main neurotransmitters have been determined. Boscalid altered HR in a concentration-dependent manner, leading to a positive or negative chronotropic effect in fish and D. magna, respectively. While boscalid decreased BLA and increased VMR in Daphnia, these behaviors were not altered in fish. For SR and HB, the response was more species- and concentration-specific, with Daphnia exhibiting the highest sensitivity. At the neurotransmission level, boscalid exposure decreased the levels of L-aspartic acid in fish larvae and increased the levels of dopaminergic metabolites in D. magna. Our study demonstrates that exposure to environmental levels of boscalid alters cardiac activity, impairs ecologically relevant behaviors, and leads to changes in different neurotransmitter systems in phylogenetically distinct vertebrate and invertebrate models. Thus, the results presented emphasize the need to review the current regulation of this fungicide.

Combined Effects of Polystyrene Nanosphere and Homosolate Exposures on Estrogenic End Points in MCF-7 Cells and Zebrafish

BACKGROUND

Micro- and nanoplastics (MNPs) and homosalate (HMS) are ubiquitous emerging environmental contaminants detected in human samples. Despite the well-established endocrine-disrupting effects (EDEs) of HMS, the interaction between MNPs and HMS and its impact on HMS-induced EDEs remain unclear.

OBJECTIVES

This study aimed to investigate the influence of MNPs on HMS-induced estrogenic effects and elucidate the underlying mechanisms in vitro and in vivo.

METHODS

We assessed the impact of polystyrene nanospheres (PNSs; 50  nm , 1.0 mg / L ) on HMS-induced MCF-7 cell proliferation (HMS: 0.01 - 1 μ M , equivalent to 2.62 - 262 μ g / L ) using the E-SCREEN assay and explored potential mechanisms through transcriptomics. Adult zebrafish were exposed to HMS (0.0262 - 262 μ g / L ) with or without PNSs (50  nm , 1.0 mg / L ) for 21 d. EDEs were evaluated through gonadal histopathology, fertility tests, steroid hormone synthesis, and gene expression changes in the hypothalamus-pituitary-gonad-liver (HPGL) axis.

RESULTS

Coexposure of HMS and PNSs resulted in higher expression of estrogen receptor α (ESR1) and the mRNAs of target genes (pS2, AREG, and PGR), a greater estrogen-responsive element transactivation activity, and synergistic stimulation on MCF-7 cell proliferation. Knockdown of serum and glucocorticoid-regulated kinase 1 (SGK1) rescued the MCF-7 cell proliferation induced by PNSs alone or in combination with HMS. In zebrafish, coexposure showed higher expression of SGK1 and promoted ovary development but inhibited spermatogenesis. In addition, coexposure led to lower egg hatchability, higher embryonic mortality, and greater larval malformation. Coexposure also modulated steroid hormone synthesis genes (cyp17a2, hsd17[Formula: see text]1, esr2b, vtg1, and vtg2), and resulted in higher 17 β -estradiol (E 2 ) release in females. Conversely, males showed lower testosterone, E 2 , and gene expressions of cyp11a1, cyp11a2, cyp17a1, cyp17a2, and hsd17[Formula: see text]1.

DISCUSSION

PNS exposure exacerbated HMS-induced estrogenic effects via SGK1 up-regulation in MCF-7 cells and disrupting the HPGL axis in zebrafish, with gender-specific patterns. This offers new mechanistic insights and health implications of MNP and contaminant coexposure. https://doi.org/10.1289/EHP13696.

Exposure levels and health implications of fungicides, neonicotinoid insecticides, triazine herbicides and their associated metabolites in pregnant women and men

Exposure to pesticides can pose a series of advance effects on human health. However, the exposure levels and health implications of the current use pesticides and their metabolites in both men and pregnant women remain unclear. In this study, an analytical method was developed to quantify fungicides, neonicotinoid insecticides, triazine herbicides, and their metabolites in the human serum. Fifty of the 73 target pesticides and metabolites were detected in the human serum of men and pregnant women from Wuxi, China, which included 11 triazine herbicides and metabolites, 17 neonicotinoid insecticides and metabolites, and 22 fungicides. Fungicides had the highest cumulative concentration (49.5 ng/mL), followed by neonicotinoid insecticides and metabolites (6.38 ng/mL), and triazine herbicides and metabolites (5.10 ng/mL). Moreover, the estimated daily intake (EDI) of fungicides was 10.4 and 12.7 times higher than that of triazine herbicides (included their metabolites) and neonicotinoid insecticides (included their metabolites), respectively. Of the three categories of pesticides, exposure to fungicides contributed to the highest exposure risk within the hazard quotient in the range of 5.1 × 10-3-0.17. Correlation analysis revealed that the pesticide exposure levels in human serum were correlated with their maximum residue levels in vegetables and fruits. Pesticide exposure has also been correlated with the weight and Body Mass Index (BMI) of humans based on structural equation modeling. This study provides new insights into the exposure of men and pregnant women to a cocktail of fungicides, neonicotinoid insecticides, triazine herbicides and their metabolites.

Embryonic Exposure to the Benzotriazole Ultraviolet Stabilizer 2-(2H-benzotriazol-2-yl)-4-methylphenol Decreases Fertility of Adult Zebrafish (Danio rerio)

Benzotriazole ultraviolet stabilizers (BUVSs) are emerging contaminants of concern. They are added to a variety of products, including building materials, personal care products, paints, and plastics, to prevent degradation caused by ultraviolet (UV) light. Despite widespread occurrence in aquatic environments, little is known regarding the effects of BUVSs on aquatic organisms. The aim of the present study was to characterize the effects of exposure to 2-(2H-benzotriazol-2-yl)-4-methylphenol (UV-P) on the reproductive success of zebrafish (Danio rerio) following embryonic exposure. Embryos were exposed, by use of microinjection, to UV-P at <1.5 (control), 2.77, and 24.25 ng/g egg, and reared until sexual maturity, when reproductive performance was assessed, following which molecular and biochemical endpoints were analyzed. Exposure to UV-P did not have a significant effect on fecundity. However, there was a significant effect on fertilization success. Using UV-P-exposed males and females, fertility was decreased by 8.75% in the low treatment group and by 15.02% in the high treatment group relative to control. In a reproduction assay with UV-P-exposed males and control females, fertility was decreased by 11.47% in the high treatment group relative to the control. Embryonic exposure to UV-P might have perturbed male sex steroid synthesis as indicated by small changes in blood plasma concentrations of 17β-estradiol and 11-ketotestosterone, and small statistically nonsignificant decreases in mRNA abundances of cyp19a1a, cyp11c1, and hsd17b3. In addition, decreased transcript abundances of genes involved in spermatogenesis, such as nanos2 and dazl, were observed. Decreases in later stages of sperm development were observed, suggesting that embryonic exposure to UV-P impaired spematogenesis, resulting in decreased sperm quantity. The present study is the first to demonstrate latent effects of BUVSs, specifically on fish reproduction. Environ Toxicol Chem 2024;43:385-397. © 2023 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Chemical occurrence of pesticides and transformation products in two small lentic waterbodies at the head of agricultural watersheds and biological responses in caged Gasterosteus aculeatus

Recent monitoring campaigns have revealed the presence of mixtures of pesticides and their transformation products (TP) in headwater streams situated within agricultural catchments. These observations were attributed to the use of various agrochemicals in surrounding regions. The aim of this work was to compare the application of chemical and ecotoxicological tools for assessing environmental quality in relation to pesticide and TP contamination. It was achieved by deploying these methodologies in two small lentic water bodies located at the top of two agricultural catchments, each characterized by distinct agricultural practices (ALT: organic, CHA: conventional). Additionally, the results make it possible to assess the impact of contamination on fish caged in situ. Pesticides and TP were measured in water using active and passive samplers and suspended solid particles. Eighteen biomarkers (innate immune responses, oxidative stress, biotransformation, neurotoxicity, genotoxicity, and endocrine disruption) were measured in Gasterosteus aculeatus encaged in situ. More contaminants were detected in CHA, totaling 25 compared to 14 in ALT. Despite the absence of pesticide application in the ALT watershed for the past 14 years, 7 contaminants were quantified in 100 % of the water samples. Among these contaminants, 6 were TPs (notably atrazine-2-hydroxy, present at a concentration exceeding 300 ng·L-1), and 1 was a current pesticide, prosulfocarb, whose mobility should prompt more caution and new regulations to protect adjacent ecosystems and crops. Regarding the integrated biomarker response (IBRv2), caged fish was similarly impacted in ALT and CHA. Variations in biomarker responses were highlighted depending on the site, but the results did not reveal whether one site is of better quality than the other. This outcome was likely attributed to the occurrence of contaminant mixtures in both sites. The main conclusions revealed that chemical and biological tools complement each other to better assess the environmental quality of wetlands such as ponds.

Assessment of reproductive toxicity in adult zebrafish (Danio rerio) following sublethal exposure to penthiopyrad

Penthiopyrad (PO), a succinate dehydrogenase inhibitor (SDHI) fungicide, poses a potential risk to fish. Here, we investigated the adverse effects of PO on endocrine regulation and reproductive capacity in zebrafish during a 21-d sublethal exposure to PO concentrations ranging from 0.02 to 2.00 mg/L. Following exposure to PO (0.20 and 2.00 mg/L), female-specific effects including follicle necrosis, structural disturbance of the yolk follicle, fusion of cortical follicles appeared in ovarian tissue of adult females, which led to a significant reduction in fertility. Correspondingly, 0.20 and 2.00 mg/L PO led to a marked reduction in the GSI values of females, and 2.00 mg/L PO caused a 31% decline in the proportion of perinucleolar oocytes (PCO) in oocytes. In addition, testosterone (T) level was obviously suppressed and 17β-estradiol (E2) level was increased in females after exposure to 2.00 mg/L PO. Male zebrafish treated with 0.20 and 2.00 mg/L of PO exhibited significant interstitial enlargement, edema in the testes, and reduced diameter of seminiferous tubules, along with a thinner basement membrane. The effects of PO on males were associated with significant increase in E2 level, suggesting that PO has an estrogenic effect on male fish. Greater E2 levels in serum were further supported by increased transcription levels of genes linked to the hypothalamic-pituitary-gonad-liver (HPGL) axis. Notably, transcription levels of cyp19a, er2b, era, and cyp19b was remarkably increased, exhibiting a clear link with variations in E2 levels. Overall, the present study demonstrates that PO induces reproductive impairment in zebrafish by promoting steroidogenesis.

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.

Polystyrene microplastics disrupt female reproductive health and fertility via sirt1 modulation in zebrafish (Danio rerio)

Microplastics (MPs) pollution poses an emerging threat to aquatic biota, which could hinder their physiological processes. Recently various evidence has demonstrated the toxic impacts of MPs on cellular and organismal levels, but still, the underlying molecular mechanism behind their toxicity remains ambiguous. The hypothalamic-pituitary-gonadal (HPG) axis regulates the synthesis and release of sex steroid hormones, and SIRT1 plays a vital role in this process. The current study aimed to elucidate the harmful effects of MPs on female reproduction via SIRT1 modulation. Healthy female zebrafish were exposed to different concentrations (50 and 500 µg/L) of polystyrene microplastics (PS-MPs). The results revealed a significant change in the gonadosomatic index (GSI) after exposure to PS-MPs. In addition, the decreased fecundity rate displayed an evident dosage effect, indicating that exposure to PS-MPs causes deleterious effects on fertilization. Furthermore, significantly enhanced levels of reactive oxygen species (ROS) and apoptotic signals through the TUNEL assay were evaluated in different treated groups. Moreover, morphological alterations in the gonads of zebrafish exposed to MPs were also observed through H&E staining. The subsequent change in plasma steroid hormone levels (E2/T ratio) showed an imbalance in hormonal homeostasis. Meanwhile, to follow PS-MPs' effects on the HPG axis via SIRT1 modulation and gene expression related to steroidogenesis, SIRT1/p53 pathway was evaluated through qPCR. The altered transcription levels of genes indicated the plausible interference of PS-MPs on the HPG axis function. Our in-silico molecular docking study proves that PS-MPs efficiently bind and inhibit endocrine receptors and SIRT1. Thus, these findings add to our understanding of the probable molecular mechanisms of reproductive impairment caused by PS-MPs in zebrafish.

The role of miRNA-26a-5p and target gene socs1a in flutolanil induced hepatotoxicity of zebrafish at environmental relevant levels

Flutolanil has been detected worldwide in aquatic environment and fish, which has become an undeniable stressor on ecosystem and human health. Flutolanil has been reported to be toxic to aquatic organisms. However, the pathophysiological and molecular mechanism behind the detrimental effects remains obscure. Here we reported hepatotoxicity induced by flutolanil in HepG2 cells and zebrafish, as revealed by toxicokinetic, HE staining, miRNAs-mRNAs sequencing, molecular dynamic simulations and dual luciferase reporter assays. Collectively, our results indicated that flutolanil could be absorbed by and accumulated in the liver of zebrafish, causing hepatic vacuolar degeneration, steatosis and nuclear condensation and abnormal liver function, where its exposure at environmental levels disrupted the expressions of miRNA-26a-5p and its target gene socs1a by mediating JAK-STAT signaling pathway, which was partially responsible for hepatotoxicity, correlated with oxidative stress, cell apoptosis, inflammation, cell cycle disorder and mitochondrial dysfunction. These findings suggest that miRNA-26a-5p/socs1a can serve as potential biomarkers of hepatotoxicity in zebrafish following exposure to flutolanil. This uncovered route will provide a new tool for the risk assessment of flutolanil and a guide to proper use of flutolanil and environmental remedy, and open up a new horizon for liver disease assessment.

Chronic Paternal/Maternal Exposure to Environmental Concentrations of Imidacloprid and Thiamethoxam Causes Intergenerational Toxicity in Zebrafish Offspring

Imidacloprid (IMI) and thiamethoxam (THM) are ubiquitous in aquatic ecosystems. Their negative effects on parental fish are investigated while intergenerational effects at environmentally relevant concentrations remain unclear. In this study, F0 zebrafish exposed to IMI and THM (0, 50, and 500 ng L-1) for 144 days post-fertilization (dpf) was allowed to spawn with two modes (internal mating and cross-mating), resulting in four types of F1 generations to investigate the intergenerational effects. IMI and THM affected F0 zebrafish fecundity, gonadal development, sex hormone and VTG levels, with accumulations found in F0 muscles and ovaries. In F1 generation, paternal or maternal exposure to IMI and THM also influenced sex hormones levels and elevated the heart rate and spontaneous movement rate. LncRNA-mRNA network analysis revealed that cell cycle and oocyte meiosis-related pathways in IMI groups and steroid biosynthesis related pathways in THM groups were significantly enriched in F1 offspring. Similar transcriptional alterations of dmrt1, insl3, cdc20, ccnb1, dnd1, ddx4, cox4i1l, and cox5b2 were observed in gonads of F0 and F1 generations. The findings indicated that prolonged paternal or maternal exposure to IMI and THM could severely cause intergenerational toxicity, resulting in developmental toxicity and endocrine-disrupting effects in zebrafish offspring.

Putative adverse outcome pathways of the male reproductive toxicity derived from toxicological studies of perfluoroalkyl acids

Adverse outcome pathway (AOP) as a conceptual framework is a powerful tool in the field of toxicology to connect seemingly discrete events at different levels of biological organizations into an organized pathway from molecular interactions to whole organism toxicity. Based on numerous toxicological studies, eight AOPs for reproductive toxicity have been endorsed by the Organization for Economic Co-operation and Development (OECD) Task Force on Hazard Assessment. We have conducted a literature survey on the mechanistic studies on male reproductive toxicity of perfluoroalkyl acids (PFAAs), a class of global environmental contaminants with high persistence, bioaccumulation and toxicity. Using the AOP development strategy, five new AOPs for male reproductive toxicity were proposed here, namely (1) changes in membrane permeability leading to reduced sperm motility, (2) disruption of mitochondrial function leading to sperm apoptosis, (3) decreased gonadotropin-releasing hormone (GnRH) expression in hypothalamus leading to reduced testosterone production in male rats, (4) activation of the p38 signaling pathway leading to disruption of BTB in mice, (5) inhibition of p-FAK-Tyr407 activity leading to the destruction of BTB. The molecular initiating events in the proposed AOPs are different from those in the endorsed AOPs, which are either receptor activation or enzyme inhibition. Although some of the AOPs are still incomplete, they can serve as a building block upon which full AOPs can be developed and applied to not only PFAAs but also other chemical toxicants with male reproductive toxicity.

Chronic diflubenzuron exposure causes reproductive toxic effects in female marine medaka (Oryzias melastigma)

Diflubenzuron, an insecticide commonly used in marine fish farming, has been detected in various marine environments. However, its potential impact on marine fish remains largely unknown. This study investigated the reproductive toxicity of chronic diflubenzuron exposure in female marine medaka (Oryzias melastigma). Marine medaka were exposed continuously to environmentally relevant concentrations of diflubenzuron (0.1, 1, and 10 μg/L) or a solvent control from the fertilized egg to adulthood. In exposed female marine medaka, the gonadosomatic index (GSI) and the number of laid eggs were significantly reduced. Moreover, diflubenzuron-exposed female marine medaka showed altered ovarian histopathology, with an increased relative proportion of immature oocytes and atretic follicles and a decreased relative proportion of mature oocytes. Maternal exposure to diflubenzuron also inhibited the development of the F1 generation, significantly reducing the hatching rate of F1 embryos and significantly increasing the malformation rate of F1 larvae. Furthermore, changes in hormone levels and expression of genes along the hypothalamus-pituitary-gonad-liver (HPGL) axis were observed, which may be the fundamental reason for all the reproductive toxic effects mentioned above. These results provide new insights into the impact of diflubenzuron on the female marine medaka reproductive system and underscore the importance of investigating the potential environmental risks of diflubenzuron in the marine environment.

Exposure to tris(2,6-dimethylphenyl) phosphate interferes with sexual differentiation via estrogen receptors 2a and 2b in zebrafish

Tris(2,6-dimethylphenyl) phosphate (TDMPP), an emerging organophosphate flame retardant, is frequently detected in multiple environmental media. Although TDMPP has been proven as a compound with estrogenic activity, its feminizing effects on reproductive system remain unclear. This study investigated the adverse effects of TDMPP on gonadal development by exposing zebrafish for 105 days from 15 days post-fertilization. Exposure to TDMPP (0.5 and 5 μM, corresponding to about 200 and 2000 μg/L) induced ovarian formation in aromatase mutant (cyp19a1a-/-) line which normally presents all-male phenotype for deficiency of endogenous estrogen (E2), suggesting its feminizing effect on sexual differentiation. In addition, TDMPP also interfered with other aspects of reproduction by delaying puberty onset, retarding sexual maturation, impairing gametogenesis and subfertility. Molecular docking and reporter gene assay indicated that all three nuclear estrogen receptors (nERs) can be binded to and activated by TDMPP. Using a series of nERs mutant lines, we confirmed the indispensable role of esr2a and esr2b in mediating the feminizing effects of TDMPP. Further analysis revealed that the prominent effects of TDMPP on sexual differentiation correlated to upregulation of female-promoting genes and downregulation of male-promoting genes. Taken together, the present study provided unequivocal genetic evidence for estrogenic effects of TDMPP on reproductive system and its molecular mechanisms of action.

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.

Chronic toxic effects of isoflucypram on reproduction and intestinal energy metabolism in zebrafish (Danio rerio)

The intestine is a vital organ involved in chemical and nutrient uptake and biotransformation. Intestinal dysfunction can impair energy and material supply for reproduction. Isoflucypram, a new succinate dehydrogenase inhibitor fungicide, is highly toxic to aquatic systems. However, the chronic toxic effects of isoflucypram on intestinal differentiation in aquatic organisms remain unknown. In this study, zebrafish (F0, 4-month-old) were exposed to 0, 0.008, or 0.08 μM isoflucypram for 120 days. After 90 days of exposure, F0 generations of adult zebrafish were paired, and the corresponding F1 generation embryos were obtained and observed. After 120 days of exposure, the gut of F0 generation zebrafish was collected, and intestinal histopathology and mitochondrial morphology were analyzed. Exposure to 0.08 μM isoflucypram resulted in significant death, hatching delay, and malformation (blood clot clustering, pericardial edema, and microphthalmia) of F1 embryos and larvae. Exposure to isoflucypram caused irregular and swollen villi in the zebrafish gut, accompanied by alterations in the intestinal mitochondrial ultrastructure. In addition, the differentially expressed genes involved in mitochondrial energy metabolism were significantly enriched. Overall, our data suggest that chronic exposure to isoflucypram is associated with reproductive and intestinal dysfunction in adult zebrafish.

Reproductive toxicity of long-term exposure to environmental relevant concentrations of cyprodinil in female zebrafish (Danio rerio)

In recent years, the widespread use of the pesticide cyprodinil has attracted attention due to its harmful effects on aquatic organisms. The purpose of this study was to evaluate the adverse effects of long-term exposure to cyprodinil on the reproductive system of female zebrafish. After the embryos had been treated with 0.1, 1 and 10 μg/L cyprodinil for 180 days, we observed that female fish treated with 1 and 10 μg/L cyprodinil showed decreased sexual attractiveness, a decreased proportion of primordial follicles in the ovary, an increased proportion of mature follicles, and increased egg production. Moreover, exposed females that mated with normal males produced offspring with increased rates of mortality and deformity (the F1 generation). In addition, the levels of gonadotropin and testosterone (T) were increased in females after cyprodinil exposure, especially in the 10 μg/L treated group. After cyprodinil treatment, some key genes in the hypothalamic-pituitary-gonad axis underwent significant changes. For example, gene expression of brain gonadotropin-releasing hormone receptors (gnrhr1, gnrhr2 and gnrhr4) was significantly downregulated after cyprodinil treatment. The study found that expression of the aromatase (cytochrome P450 family 19 subfamily A polypeptide 1a, cyp19a1a) responsible for converting T into estradiol was significantly downregulated after cyprodinil treatment, consistent with elevated T levels in the ovaries and muscles. In summary, these data provide a more comprehensive understanding of the toxicity of cyprodinil and may inform evaluation of the ecotoxicity of cyprodinil to female reproduction at environmentally relevant concentrations.

Deciphering the diversity, composition, function, and network complexity of the soil microbial community after repeated exposure to a fungicide boscalid

Boscalid is a novel, highly effective carboximide fungicide that has been substantially and irrationally applied in greenhouses. However, little is known about the residual characteristics of boscalid and its ecological effects in long-term polluted greenhouse soils. Therefore, actual boscalid pollution status in greenhouse soils was simulated by repeatedly introducing boscalid into the soil under laboratory conditions. The degradation characteristics of boscalid, and its effects on the diversity, composition, function, and co-occurrence patterns of the soil microbial community were systematically investigated. Boscalid degraded slowly, with its degradation half-lives ranging from 31.5 days to 180.1 days in the soil. Boscalid degradation was further delayed by repeated treatment and increasing its initial concentration. Boscalid significantly decreased soil microbial diversity, particularly at the recommended dosage. Amplicon sequencing analysis showed that boscalid altered the soil microbial community and further stimulated the phylum Proteobacteria and four potential boscalid-degrading bacterial genera, Sphingomonas, Starkeya, Citrobacter, and Castellaniella. Although the network analysis revealed that boscalid significantly reduced the microbial network complexity, it enhanced the vital roles of Proteobacteria by increasing its proportion and strengthening the relationships among the internal bacteria in the network. The soil microbial function in the boscalid treatment were simulated at the recommended dosage and two-fold recommended dosage but showed an inhibition-recovery-stimulation trend at the five-fold recommended dosage with an increase in treatment frequency. Moreover, the expression of nitrogen cycling functional genes, nifH, AOA amoA, AOB amoA, nirK, and nirS in all boscalid treatments displayed an inhibition-recovery-stimulation trend during the entire experimental period, and the effects were more pronounced at the five-fold recommended dosage. In conclusion, repeated boscalid treatments delayed degradation, reduced soil microbial diversity and network complexity, disturbed soil microbial community, and interfered with soil microbial function.

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

Difenoconazole (DCZ) is a triazole fungicide that negatively affects aquatic organisms and humans. However, data regarding the reproductive toxicity of DCZ are insufficient. In this study, we used zebrafish (from 2 h post-fertilization [hpf] to adulthood) as a model to evaluate whether DCZ at environmentally relevant concentrations (0.1, 1.0, and 10.0 μg/L) induces reproductive toxicity. After exposure to DCZ, egg production and fertilization rates were reduced by 1.0 and 10.0 μg/L. A significant decrease in gamete frequency (late vitellogenic oocytes and spermatozoa) was observed at 10.0 μg/L. The concentrations of 17β-estradiol (E2), testosterone (T), and vitellogenin (VTG) were disrupted in females and males by 1.0 and 10.0 μg/L. Exposure to 10.0 μg/L DCZ significantly inhibited the contact time between female and male fish, which was mainly achieved by affecting male fish. The transcription of genes involved in the hypothalamus-pituitary-gonad (HPG) axis was significantly changed after treatment with DCZ. Overall, these data show that the endocrine-disrupting effect of DCZ on the zebrafish HPG axis inhibited gamete maturation and disrupted reproductive behavior, reducing fertility.

Sub-lethal concentration of metamifop exposure impair gut health of zebrafish (Danio rerio)

Previous studies have demonstrated that sublethal metamifop exposures induce hepatic lipid metabolism disorder in zebrafish. Whether metamifop will cause adverse effects in zebrafish gut is unknown. In the present study, effects of metamifop on gut heath of zebrafish were investigated after sublethal concentration (0.025, 0.10 and 0.40 mg/L) exposure. Histopathology analysis showed that metamifop induced inflammation and reduction of goblet cells in the gut, indicating that gut health may be impaired. Metamifop exposure could reduce activities of digestive enzymes (lipase and alkaline phosphatase), indicating the capacity of lipid absorption were impaired. Meanwhile, the content of fatty acid-binding protein 2 (FABP2) and mRNA levels of related genes (apoa-1a, apoe-b, fatp4, lpl and fabp2) were reduced in zebrafish gut after exposure to metamifop, suggesting the lipid transportation were decreased. The transcripts of genes associated with inflammation (il-17c, tnf-α and nf-kb) were significantly increased in 0.40 mg/L metamifop treatment group, which were 1.90-, 1.53- and 2.77-fold of the control group, respectively, confirming that metamifop induced inflammatory response in zebrafish gut. Moreover, reduction of mRNA levels of cldn-15 and elevation of lipopolysaccharides (LPS) content were observed in metamifop-treated groups, which suggested that metamifop exposure increased the intestinal permeability. Furthermore, metamifop exposure decreased the relative abundance of beneficial bacteria (Psychrobacter and Aeromonas) and elevated the abundance of pathogenic bacteria (Rhodobacter and Ralstonia) in zebrafish intestine. These results indicated that metamifop exposure at sublethal concentrations would impair zebrafish gut health, via reduction of lipids absorption, inflammatory response, elevation of permeability and microbiota disorder.

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.

Life Cycle Exposure to Cyhalofop-Butyl Induced Reproductive Toxicity in Zebrafish

Cyhalofop-butyl (CyB) is a herbicide widely used in paddy fields that may transfer to aquatic ecosystems and cause harm to aquatic organisms. In this study, zebrafish (Danio rerio) were exposed to CyB at environmental concentrations (0.1, 1 and 10 µg/L) throughout their adult life cycle, from embryo to sexual maturity. The effects of CyB on zebrafish growth and reproduction were studied. It was found that female spawning was inhibited, and adult male fertility decreased. In addition, we examined the expression of sex steroid hormones and genes related to the hypothalamus-pituitary-gonad-liver (HPGL) axis. After 150 days of exposure, the hormone balance in zebrafish was disturbed, and the concentrations of 17β-estradiol (E2) and vitellogenin (VTG) were decreased. Changes in sex hormone were regulated by the expression of genes related to the HPGL axis. These results confirmed that long-term exposure to CyB at environmental concentrations can damage the reproductive capacity of zebrafish by disrupting the transcription of genes related to the HPGL axis. Overall, these data may provide a new understanding of the reproductive toxicity of long-term exposure to CyB in zebrafish parents and offspring.

Insights into toxicity of polychlorinated naphthalenes to multiple human endocrine receptors: Mechanism and health risk analysis

This study explored the combined disruption mechanism of polychlorinated naphthalenes (PCNs) on the three key receptors (estrogen receptor, thyroid receptor, and adrenoceptor) of the human endocrine system. The intensity of PCN endocrine disruption on these receptors was first determined using a molecular docking method. A comprehensive index of PCN endocrine disruption to human was quantified by analytic hierarchy process and fuzzy analysis. The mode of action between PCNs and the receptors was further identified to screen the molecular characteristics influencing PCN endocrine disruption through molecular docking and fractional factorial design. Quantitative structure-activity relationship (QSAR) models were established to investigate the toxic mechanism due to PCN endocrine disruption. The results showed that the lowest occupied orbital energy (E_LUMO) was the most important factor contributing to the toxicity of PCNs on the endocrine receptors, followed by the orbital energy difference (ΔE) and positive Millikan charge (q⁺). Furthermore, the strategies were formulated through adjusting the nutritious diet to reduce health risk for the workers in PCN contaminated sites and the effectiveness and feasibility were assessed by molecular dynamic simulation. The simulation results indicated that the human health risk caused by PCN endocrine disruption could be effectively decreased by nutritional supplementation. The binding ability between PCNs and endocrine receptors significantly declined (up to -16.45%) with the supplementation of vitamins (A, B₂, B₁₂, C, and E) and carotene. This study provided the new insights to reveal the toxic mechanism of PCNs on human endocrine systems and the recommendations on nutritional supplements for health risk reduction. The methodology and findings could serve as valuable references for screening of potential endocrine disruptors and developing appropriate strategies for PCN or other persistent organic pollution control and health risk management.

Microplastics increase the accumulation of phenanthrene in the ovaries of marine medaka (Oryzias melastigma) and its transgenerational toxicity

Microplastics (MPs) are considered to exacerbate the impacts of hydrophobic organic pollutants on aquatic organisms through the carrier function, but whether MPs affect the transgenerational toxicity of pollutants is unclear. This study exposed adult female marine medaka to phenanthrene (Phe)-adsorbed MPs for 60 days to investigate the effects of MPs on the bioaccumulation, reproductive and transgenerational toxicity of Phe. Compared to Phe alone, co-exposure to Phe and 200 μg/L MPs significantly increased Phe bioaccumulation in the intestines and ovaries. Phe alone and Phe combined with MPs disrupted the regulation of the hypothalamus-pituitary-gonadal axis, and reduced vitellogenin levels and reproductive capacity of female fish. In particular, co-exposure to 200 μg/L MPs and Phe increased the rate of follicular atresia, inhibited ovarian maturity, and aggravated reproductive toxicity. Notably, maternal uptake of Phe could be transferred to the offspring, and embryonic accumulation increased with the concentrations of MPs. Moreover, MPs aggravated Phe-induced bradycardia in embryos, suggesting that MPs exacerbated the transgenerational toxicity of Phe. These findings reveal that the growing number of MPs in the ocean might amplify the adverse effects of organic pollutants on the health and population stability of marine fishes, and this problem merits more attention.

Sex-Dependent Environmental Health Risk Analysis of Flupyradifurone

Pesticides are used in agricultural production worldwide, resulting in widespread environmental pollution. Many diseases are closely related to exposure to pesticide residues. In this study, the association between exposure to the pesticide flupyradifurone (FPF), a substitute for neonicotinoids, and sex-dependent thyroid dysfunction was explored for the first time. Exposure using rat models revealed that the FPF metabolism is sex-dependent, with males preferring N-dealkylation and hydrolytic metabolism and females preferring hydroxylation. In particular, novel chloropyridine-site hydroxylation I and II metabolic pathways of FPF were discovered. More importantly, differential metabolic pathways of FPF induced sex-based dysregulation of the hypothalamic-pituitary-thyroid axis, in which females exhibited subclinical hyperthyroidism, while males displayed abnormal hypothyroidism. This may be attributed to the potential agonistic or antagonistic effect of FPF sex-dependent metabolites on liver thyroid hormone receptors. Furthermore, FPF exposure further mediated sex-specific dysregulation of cellular lipid homeostasis, with abnormal fatty acid β-oxidation and excessive energy expenditure in females and the risk of excessive accumulation of triglycerides in males. These results illustrate the potential risk of sex-related thyroid metabolic diseases caused by FPF and provide an important basis and support for further studies of FPF on human health and as an environmental pollutant.

Decabromodiphenyl Ethane Mainly Affected the Muscle Contraction and Reproductive Endocrine System in Female Adult Zebrafish

The novel brominated flame retardant decabromodiphenyl ethane (DBDPE) has become a widespread environmental pollutant. However, the target tissue and toxicity of DBDPE are still not clear. In the current study, female zebrafish were exposed to 1 and 100 nM DBDPE for 28 days. Chemical analysis revealed that DBDPE tended to accumulate in the brain other than the liver and gonad. Subsequently, tandem mass tag-based quantitative proteomics and parallel reaction monitoring verification were performed to screen the differentially expressed proteins in the brain. Bioinformatics analysis revealed that DBDPE mainly affected the biological process related to muscle contraction and estrogenic response. Therefore, the neurotoxicity and reproductive disruptions were validated via multilevel toxicological endpoints. Specifically, locomotor behavioral changes proved the potency of neurotoxicity, which may be caused by disturbance of muscular proteins and calcium homeostasis; decreases of sex hormone levels and transcriptional changes of genes related to the hypothalamic-pituitary-gonad-liver axis confirmed reproductive disruptions upon DBDPE exposure. In summary, our results suggested that DBDPE primarily accumulated in the brain and evoked neurotoxicity and reproductive disruptions in female zebrafish. These findings can provide important clues for a further mechanism study and risk assessment of DBDPE.

The research progress in and perspective of potential fungicides: Succinate dehydrogenase inhibitors

Succinate dehydrogenase inhibitors (SDHIs) have become one of the fastest growing classes of new fungicides since entering the market, and have attracted increasing attention as a result of their unique structure, high activity and broad fungicidal spectrum. The mechanism of SDHIs is to inhibit the activity of succinate dehydrogenase, thereby affecting mitochondrial respiration and ultimately killing pathogenic fungi. At present, they have become popular varieties researched and developed by major pesticide companies in the world. In the review, we focused on the mechanism, the history, the representative varieties, structure-activity relationship and resistance of SDHIs. Finally, the potential directions for the development of SDHIs were discussed. It is hoped that this review can strengthen the individuals' understanding of SDHIs and provide some inspiration for the development of new fungicides.