Reproductive toxicity of azoxystrobin to adult zebrafish (Danio rerio)

Combined toxic impacts of thiamethoxam and four pesticides on the rare minnow (Gobiocypris rarus)

To examine pesticide mixture toxicity to aqueous organisms, we assessed the single and combined toxicities of thiamethoxam and other four pesticides (chlorpyrifos, beta-cypermethrin, tetraconazole, and azoxystrobin) to the rare minnow (Gobiocypris rarus). Data from 96-h semi-static toxicity assays of various developmental phases (embryonic, larval, juvenile, and adult phases) showed that beta-cypermethrin, chlorpyrifos, and azoxystrobin had the highest toxicities to G. rarus, and their LC₅₀ values ranged from 0.0031 to 0.86 mg a.i. L^-1, from 0.016 to 6.38 mg a.i. L^-1, and from 0.39 to 1.08 mg a.i. L^-1, respectively. Tetraconazole displayed a comparatively high toxicity, and its LC₅₀ values ranged from 3.48 to 16.73 mg a.i. L^-1. By contrast, thiamethoxam exhibited the lowest toxic effect with LC₅₀ values ranging from 37.85 to 351.9 mg a.i. L^-1. Rare minnow larvae were more sensitive than embryos to all the pesticides tested. Our data showed that a pesticide mixture of thiamethoxam-tetraconazole elicited synergetic toxicity to G. rarus. Moreover, pesticide mixtures containing beta-cypermethrin in combination with chlorpyrifos or tetraconazole also had synergetic toxicities to fish. The majority of pesticides are presumed to have additive toxicity, while our data emphasized that the concurrent existence of some chemicals in the aqueous circumstance could cause synergetic toxic effect, leading to severe loss to the aqueous environments in comparison with their single toxicities. Thence, the synergetic impacts of chemical mixtures should be considered when assessing the ecological risk of chemicals.

Molecular mechanism of reproductive toxicity induced by beta-cypermethrin in zebrafish

Beta-cypermethrin, a type II synthetic pyrethroid insecticide, is widely used in pest control. Several studies have demonstrated that beta-cypermethrin can affect the reproductive system of mammals. However, there is still a scarcity of information about the reproductive toxicity to fish induced by beta-cypermethrin and its molecular mechanism. Therefore, this study was conducted to address this scientific question, in which the adult zebrafish were exposed to 0 (blank control), 0 (acetone solvent control), 0.1, 0.5, and 2.5 μg/L of beta-cypermethrin for 21 days. A decrease in cumulative egg production of zebrafish was observed, indicating that beta-cypermethrin had a negative impact on reproductive capacity of zebrafish. Regarding the histomorphological analysis of gonads, the delay of gonadal development was observed after exposure for 21 days. In addition, significant changes in plasma 17β-estradiol (E2) and testosterone (T) were found in zebrafish. Further exploration showed that the transcription levels of hypothalamic-pituitary-gonadal (HPG) axis-related genes were remarkably changed, which corresponded well with the alterations of hormone levels. These results demonstrated that beta-cypermethrin might have an adverse effect on the reproduction system of zebrafish through delaying gonadal development, disturbing sex hormone secretion, and affecting HPG axis gene expression. This study suggests that beta-cypermethrin poses a potential threat to the reproduction of fish populations, and the toxicity assessment of beta-cypermethrin plays a vital role in the environmental risk assessment of pesticides.

Zebrafish (Danio rerio) as an excellent vertebrate model for the development, reproductive, cardiovascular, and neural and ocular development toxicity study of hazardous chemicals

In the past decades, the type of chemicals has gradually increased all over the world, and many of these chemicals may have a potentially toxic effect on human health. The zebrafish, as an excellent vertebrate model, is increasingly used for assessing chemical toxicity and safety. This review summarizes the efficacy of zebrafish as a model for the study of developmental toxicity, reproductive toxicity, cardiovascular toxicity, neurodevelopmental toxicity, and ocular developmental toxicity of hazardous chemicals, and the transgenic zebrafish as biosensors are used to detect the environmental pollutants.

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

Boscalid is a succinate dehydrogenase inhibitor fungicide and is frequently detected in surface water. Due to the frequent detection of boscalid, we evaluated its impact on the reproduction of adult zebrafish following a 21 d exposure to 0, 0.01, 0.1, and 1.0 mg/L. Following exposure to boscalid, the fertility of female zebrafish and fertilization rate of spawning eggs were reduced in a concentration-dependent manner up to a respective 87% and 20% in the highest concentration. A significant 16% reduction in the percentage of late vitellogenic oocytes was noted in ovaries, and a significant 74% reduction in the percentage of spermatids in testis was also observed after treatment with 1.0 mg/L. 17β-Estradiol (E2) concentrations decreased significantly in females (34% decrease) but significantly increased in males (15% increase) following 1.0 mg/L boscalid treatment. The expression of genes (such as era, er2b, cyp19a, and cyp19b) related to the hypothalamus-pituitary-gonad-liver (HPGL) axis was significantly altered and positively correlated with E2 concentrations in female and male zebrafish (p < 0.05). Molecular docking results revealed that the binding modes between boscalid and target proteins (ER and CYP19) of zebrafish were similar to that of the reference compounds and the target proteins. The binding energies indicate that boscalid may have a weak estrogen-like binding effect or CYP19 inhibition, potentially altering the HPGL axis, thereby reducing E2 concentrations and fecundity in females. In contrast, boscalid caused significant induction of E2 steroidogenesis and subsequent feminization of gonads in males, indicating gender-specific adverse outcome pathways.

Ecotoxicology of strobilurin fungicides

Strobilurin fungicides (SFs), a class of new fungicides, use strobilurin A as a lead compound. However, with excessive production and usage, the SF residues in soil and aquatic ecosystems may lead to environmental pollution. The mechanism of action (MOA) of SFs is respiratory inhibition of fungal mitochondria. Specifically, azoxystrobin (AZO), pyraclostrobin (PYR), trifloxystrobin (TRI), fluoxastrobin (FLUO), picoxystrobin (PICO), and kresoxim-methyl (KRE) are considered the most widely used SFs. The toxicities of those six fungicides in the environment are still unclear. The present review summarized the toxicities of the six SFs to terrestrial and aquatic biota, including mice, amphibians, aquatic organisms (fish, daphnia, algae, etc.), apoidea, soil animals (earthworms and Folsomia fimetaria), and soil microorganisms. We also review the residue, fate, and transportation of SFs. The results indicate that SFs are highly toxic to aquatic and soil organisms and pose potential risks to ecosystems. Current toxicology studies are more focused on acute or chronic toxicity, but the underlying mechanisms are still unclear and require further analysis. In addition, a simple and scientific analysis method is needed to compare the toxicity differences of different SFs to the same test organisms or differences in the same SFs to different test organisms.

The effects of a short-term exposure to propiconazole in zebrafish (Danio rerio) embryos

Propiconazole (PCZ) is a widely used fungicide around the world and was frequently detected in surface waters, which would pose risk to aquatic organisms. Previous studies indicated that PCZ has high toxicity to different kinds of fish. However, most of the studies focus on the toxicity and mechanisms of PCZ to adult fish, the potential toxicity mechanism of PCZ to fish embryos is still poorly understood. The present study investigated the effects of PCZ on content of reactive oxygen species (ROS) and malondialdehyde (MDA); activities of superoxide dismutase (SOD), catalase (CAT), and Na⁺-K⁺-ATPase; and expression level of genes related to oxidative stress, cell apoptosis, and innate immune system in zebrafish embryos after 96-h exposure. The results showed that 5.0 mg/L PCZ induced oxidative damage in zebrafish embryos, as indicated by increased ROS and MDA content and alteration of antioxidative enzyme activity. The activity of Na⁺-K⁺-ATPase in zebrafish embryos was significantly inhibited after exposure to 0.5 mg/L PCZ. The expression levels of bax, p53, casp-3, casp-9, and apaf-1 were significantly increased, indicating that cell apoptosis was caused in embryos by 5.0 mg/L PCZ. The expression level of interleukin-1b (IL-1b) and IL-8 increased after exposure to 0.5 mg/L PCZ, but that of IL-1b, IL-8, and cxcl-c1c (chemokine (C-X-C motif) ligand 18b) decreased in 5.0-mg/L PCZ treatment group, indicating an immunotoxicity effect. Our results suggest that oxidative damage, cell apoptosis, and immunotoxicity would be induced in zebrafish embryos after short-term exposure to PCZ.

Pyriproxyfen induced impairment of reproductive endocrine homeostasis and gonadal histopathology in zebrafish (Danio rerio) by altered expression of hypothalamus-pituitary-gonadal (HPG) axis genes

Pyriproxyfen (PPF), a broad-spectrum insecticide known to cause reproductive and endocrine disruption in invertebrates, while the data is scarce in aquatic vertebrates. The goal of this study is to investigate the impact of PPF on reproductive endocrine system of male and female zebrafish along hypothalamus-pituitary-gonadal (HPG) axis. In brain, PPF caused significant alteration in the transcripts of erα, lhβ, and cyp19b genes in male and fshβ, lhβ, and cyp19b genes in female zebrafish. The downstream genes of steroidogenic pathway like, star, 3βhsd, 17βhsd, and cyp19a expression were significantly altered in gonad of both sexes. Subsequent changes in circulatory steroid hormone levels lead to imbalance in hormone homeostasis as revealed from estradiol/testosterone (E₂/T) ratio. Further, the vitellogenin transcript level was enhanced in hepatic tissues and their blood plasma content was increased in male (16.21%) and declined in female (21.69%). PPF also induced histopathological changes in gonads such as, reduction of mature spermatocytes in male and vitellogenic oocytes in female zebrafish. The altered E₂/T ratio and gonadal histopathology were supported by the altered transcript levels of HPG axis genes. Overall, these findings provide new insights of PPF in zebrafish reproductive system and highlights for further investigations on its potential risks in aquatic environment.

Transcriptomic analysis reveals common pathways and biomarkers associated with oxidative damage caused by mitochondrial toxicants in Chironomus dilutus

A variety of chemicals are capable of provoking mitochondrial dysfunction and thereby contribute to metabolic disorder related effects in wildlife and human. For better identifying new mitochondrial toxicants and assessing mitochondria-related risk, an in-depth understanding of toxic mechanisms and biomarkers should be attained. In the current study, a representative mitotoxicant, azoxystrobin, was assessed for lethal and sublethal outcomes in Chironomus dilutus after 96-h exposure and the toxic mechanism was explored. Global transcriptomic profiles by RNA-sequencing revealed that ampk, acc1, atp2a, gsk3b, pi3k, fak, atr, chk1, and map3k5 were the key genes which involved in the toxic action of azoxystrobin and could serve as potential molecular biomarkers. A major network of common toxicity pathways was then developed for mitotoxicants towards aquatic insects. In particular, calcium ion-PI3K/AKT and cAMP-AMPK-lethality pathways were demonstrated, in addition to the well-known mitochondrial electron transfer-oxidative damage-apoptosis pathway. These analyses could help developing adverse outcome pathways that integrate toxicological information at various levels and support more effective risk assessment and management of mitotoxicants.

Uptake, translocation and accumulation of the fungicide benzene kresoxim-methyl in Chinese flowering cabbage (Brassica campastris var. parachinensis) and water spinach (Ipomoea aquatica)

Benzene kresoxim-methyl (BKM) is an important methoxyacrylate-based strobilurin fungicide widely used against various phytopathogenic fungi in crops. Uptake, translocation and accumulation of BKM in vegetables remain unknown. This study was designed to investigate uptake, translocation, and accumulation of ¹⁴C-BKM and/or its potential metabolites in Chinese flowering cabbage and water spinach. ¹⁴C-BKM can be gradually taken up to reach a maximum of 44.4% of the applied amount by Chinese flowering cabbage and 34.6% by water spinach at 32 d after application. The ¹⁴CO₂ fractions released from the hydroponic plant system reached 37.8% for cabbage and 45.8% for water spinach, respectively. Concentrations of ¹⁴C in leaves, stems and roots all gradually increased as vegetables growing, with relative 44.9% (cabbage) and 26.8% (water spinach) of translocated from roots to edible leaves. In addition, ¹⁴C in leaves was mainly accumulated in the bottom leaves, which was visualized by quantitative radioautographic imaging. The bioconcentration factor of ¹⁴C ranged from 7.1 to 38.2 mL g^-1 for the cabbage and from 8.6 to 24.6 mL g^-1 for the water spinach. The translocation factor of BKM ranged from 0.10 to 2.04 for the cabbage and 0.10-0.46 for the water spinach throughout the whole cultivation period, indicating that the cabbage is easier to translocate BKM from roots to leaves and stems than water spinach. In addition, the daily human exposure values of BKM in both vegetables were much lower than the limited dose of 0.15 mg day^-1. The results help assess potential accumulation of BMK in vegetables and potential risk.

Combined toxic effects of fludioxonil and triadimefon on embryonic development of zebrafish (Danio rerio)

Pesticides scarcely exist as individual compounds in the water ecosystem, but rather as mixtures of multiple chemicals at relatively low concentrations. In this study, we aimed to explore the mixture toxic effects of fludioxonil (FLU) and triadimefon (TRI) on zebrafish (Danio rerio) by employing different toxicological endpoints. Results revealed that the 96-h LC₅₀ values of FLU to D. rerio at multiple developmental stages ranged from 0.055 (0.039-0.086) to 0.61 (0.33-0.83) mg L^-1, which were less than those of TRI ranging from 3.08 (1.84-5.96) to 9.75 (5.99-14.78) mg L^-1. Mixtures of FLU and TRI exerted synergistic effects on embryonic zebrafish. Activities of total superoxide dismutase (T-SOD) and catalase (CAT) were markedly altered in most of the individual and pesticide mixture treatments compared with the control. The expressions of 16 genes involved in oxidative stress, cellular apoptosis, immune system and endocrine system displayed that embryonic zebrafish were affected by the individual pesticides and their mixtures, and greater variations of four genes (ERɑ, Tnf, IL and bax) were found when exposed to pesticide mixtures compared with their individual compounds. Therefore, more studies on mixture toxicities among different pesticides should be taken as a priority when evaluating their ecological risk.

Toxicogenomics provides insights to toxicity pathways of neonicotinoids to aquatic insect, Chironomus dilutus

Neonicotinoid insecticides have posed a great threat to non-target organisms, yet the mechanisms underlying their toxicity are not well characterized. Major modes of action (MoAs) of imidacloprid were analyzed in an aquatic insect Chironomus dilutus. Lethal and sublethal outcomes were assessed in the midges after 96-h exposure to imidacloprid. Global transcriptomic profiles were determined using de novo RNA-sequencing to more holistically identify toxicity pathways. Transcriptional 10% biological potency values derived from ranked KEGG pathways and GO terms were 0.02 (0.01-0.08) (mean (95% confidence interval) and 0.05 (0.04-0.06) μg L^-1, respectively, which were more sensitive than those from phenotypic traits (10% lethal concentration: 0.44 (0.23-0.79) μg L^-1; 10% burrowing behavior concentration: 0.30 (0.22-0.43) μg L^-1). Major MoAs of imidacloprid in aquatic species were identified as follows: the activation of nicotinic acetylcholine receptors (nAChRs) induced by imidacloprid impaired organisms' nerve system through calcium ion homeostasis imbalance and mitochondrial dysfunction, which posed oxidative stress and DNA damage and eventually caused death of organisms. The current investigation highlighted that imidacloprid affected C. dilutus at environmentally relevant concentrations, and elucidated toxicity pathways derived from gene alteration to individual outcomes, calling for more attention to toxicity of neonicotinoids to aquatic organisms.

Mummichog (Fundulus heteroclitus) are less sensitive to 17α-ethinylestradiol (EE2) than other common model teleosts: A comparative review of reproductive effects

The environmental estrogen 17α-ethinylestradiol (EE₂) will depress or completely inhibit egg production in many common model teleosts at low concentrations (≤0.5 ng/L; Runnalls et al., 2015). This inhibition is not seen in the estuarine killifish, or mummichog (Fundulus heteroclitus), even when exposed to 100 ng/L EE₂. This relative insensitivity to EE₂ exposure indicates species-specific mechanisms for compensating for exogenous estrogenic exposure. This review compares various reproductive responses elicited by EE₂ in mummichog to other common model teleosts, such as zebrafish (Danio rerio) and fathead minnow (Pimephales promelas), identifying key endpoints where mummichog differ from other studied fish. For example, EE₂ accumulates primarily in the liver/gall bladder of mummichog, which is different than zebrafish and fathead minnow in which accumulation is predominantly in the carcass. Despite causing species-specific differences in fecundity, EE₂ has been shown to consistently induce hepatic vitellogenin in males and cause feminization/sex reversal during gonadal differentiation in larval mummichog, similar to other species. In addition, while gonadal steroidogenesis and plasma steroid levels respond to exogenous EE_2, it is generally at higher concentrations than observed in other species. In mummichog, production of 17β-estradiol (E₂) by full grown ovarian follicles remains high; unlike other teleost models where E₂ synthesis decreases as 17α,20β-dihydroxy-4-prenen-3-on levels increase to induce oocyte maturation. New evidence in mummichog indicates some dissimilarity in gonadal steroidogenic gene expression responses compared to gene expression responses in zebrafish and fathead minnow exposed to EE₂. The role of ovarian physiology continues to warrant investigation regarding the tolerance of mummichog to exogenous EE₂ exposure. Here we present a comprehensive review, highlighting key biological differences in response to EE₂ exposure between mummichog and other commonly used model teleosts.

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

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

Dysregulation of endocrine disruption, apoptosis and the transgenerational toxicity induced by spirotetramat

Spirotetramat (SPT) is a new tetronic acid derivative insecticide used to control scales and aphids; the potential for endocrine disruptor effects in fish could not be finalized with the available data. In this study, zebrafish were selected to assess the endocrine-disrupting effects. Significant decrease of plasma estradiol (E2), testosterone (T) and 11-ketotestosterone (11-KT) were observed in both male and female following the spirotetramat exposure; the vitellogenin (VTG) level in females significantly decreased. The expression of the hypothalamic-pituitary-gonad (HPG) axis genes fshr, lhr and esr1 showed significant increase in the gonads, which expression in males is higher than in females. In addition, the activities of capspase-3 and caspase-9 significantly decreased in both males and females liver, while the capspase-3 and caspase-9 were increased in male testis, the mRNA expression levels of genes expression related to the apoptosis pathway were also significantly altered after the spirotetramat exposure. Additionally, we found the parental zebrafish exposed to spirotetramat induced the development delay of its offspring. Above all, the adverse effects induced by spirotetramat suggesting that spirotetramat is a potential exogenous hazardous agent.

Developmental toxicity in embryo-larval zebrafish (Danio rerio) exposed to strobilurin fungicides (azoxystrobin and pyraclostrobin)

Azoxystrobin and pyraclostrobin are broad spectrum strobilurin fungicides that have been measured in the aquatic environment. Strobilurins inhibit mitochondrial respiration by binding to the mitochondrial respiratory complex III. The goal of this study was to investigate mitochondrial dysfunction and oxidative stress in the developing zebrafish from exposure to azoxystrobin and pyraclostrobin. Exposure studies were performed where zebrafish embryos were exposed to azoxystrobin and pyraclostrobin at 0.1, 10, 100 μg/L from 4 hpf to 48 hpf to measure mitochondrial dysfunction and oxidative stress mRNA transcripts, and 5 dpf to measure movement, growth, oxygen consumption, enzymatic activities, and mRNA transcripts. Results from this study indicated that there was a significant reduction in both basal and maximal respiration at 48 hpf in zebrafish exposed to 100 μg/L of pyraclostrobin. There was no difference in oxidative stress or apoptotic mRNA transcripts at 48 hpf, indicating that the two strobilurins were acting first on mitochondrial function and not directly through oxidative stress. At 5 dpf, standard body length was significantly reduced with exposure to pyraclostrobin and azoxystrobin exposure as compared to the control. These reductions in apical endpoints corresponded with increases in oxidative stress and apoptotic mRNA transcripts in treatment groups at 5 dpf indicating that strobilurins' exposure followed the adverse outcome pathway for mito-toxicants. Our results indicate that strobilurins can decrease mitochondrial function, which in turn lead to diminished growth and movement.

Purification and characterization of the carbonic anhydrase enzyme from horse mackerel (Trachurus trachurus) muscle and the impact of some metal ions and pesticides on enzyme activity

In this paper, the total carbonic anhydrase (CA) enzyme was purified from horse mackerel (Trachurus trachurus) muscle with a specific activity of 23,063.93 EU/mg, purification fold of 551.08, total activity of 1522.22 EU/mL and a yield of 18.50% using sulfanilamide affinity column chromatography. For obtaining the subunit molecular mass and enzyme purity, sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) for this part was performed and a single band was clearly recorded. The molecular mass of this enzyme was found approximately 35 kDa. The optimum temperature and pH values were obtained from Arrhenius plot. In addition, the inhibitory effects of different heavy metal ions (Fe²⁺, Cu²⁺, Co²⁺, Pb²⁺ Hg²⁺ and As³⁺) and some pesticides (thiram, clofentezine, propineb, deltamethrin, azoxystrobin and thiophanate) on horse mackerel (Trachurus trachurus) muscle tissue CA enzyme activities were investigated by utilizing esterase assay activity. The used metal ions and pesticides had IC₅₀ values in the range of 0.21-13.84 mM and 3.78-70.58 mM, respectively.

Short-term developmental toxicity and potential mechanisms of the herbicide metamifop to zebrafish (Danio rerio) embryos

Metamifop is a novel aryloxyphenoxy propionate (AOPP) herbicide that is widely applied in paddy fields, which will inevitably enter aquatic environments and pose a risk to aquatic organisms. However, the potential threat and toxicological mechanisms of metamifop in aquatic organisms are poorly understood. In this study, zebrafish embryos were used to investigate the potential developmental toxicity and mechanisms of metamifop. The results showed that metamifop exhibited high acute toxicity to zebrafish, with 96 h-LC₅₀ values of 0.648 and 0.216 mg/L to embryos and larvae of 72 h post-hatching (hph), respectively. Decreased body lengths, heartbeat number, and hatching rates, and increased malformation rates of embryos were observed after 96 h of exposure to 0.38 mg/L or higher concentration of metamifop. Furthermore, oxidative stress was caused in embryos, with increased contents of reactive oxygen species (ROS) and malondialdehyde (MDA), and altered activities of superoxide dismutase (SOD), catalase (CAT), and glutathione peroxidase (GPx). Metamifop exposure clearly triggered cell apoptosis in embryos, result in the increase of Caspase-3 and Caspase-9 activities and up-regulation of apoptosis-related genes (bax, p53, apaf1, caspase-3, and caspase-9). Additionally, the transcriptions of innate immune-related genes (il-8, il-1b, and ifn) were increased in the groups treated with 0.25 and 0.5 mg/L of metamifop. These results indicate that metamifop induced developmental toxicity in zebrafish, and the potential toxicological mechanisms were related to oxidative stress, cell apoptosis, and the innate immune responses in embryos.

Mitochondrial dysfunction, apoptosis and transcriptomic alterations induced by four strobilurins in zebrafish (Danio rerio) early life stages

Though the toxicity of strobilurins on non-target aquatic organisms has been characterized, the associated toxic mechanisms have not been fully explored. The present study showed that the larval stage was the most sensitive developmental stage in zebrafish, and pyraclostrobin (PY) had the highest acute toxicity to embryos, larvae, juvenile and adult with 96 h-LC₅₀ at 0.048 mg/L, 0.029 mg/L, 0.039 mg/L, 0.031 mg/L respectively, when compared with the toxicity of trifloxystrobin (TR), kresoxim-methyl (KM) and azoxystrobin (AZ) at corresponding developmental stage. Then we investigated the transcriptomics and developmental toxicity of TR, KM, AZ and PY on zebrafish embryos after 72 h exposure. RNA-seq revealed that the pathways related to cell apoptosis and cancer, and cellular components organelle membrane and mitochondrion, were markedly affected after TR, KM, AZ and PY exposure during zebrafish early life stages. The results were further confirmed by the induction of antioxidant enzymes catalase (CAT) and superoxide dismutase (SOD) activities, the elevation of H₂O₂, malondialdehyde (MDA) and reactive oxygen species (ROS) level, as well as the reduction of intracellular calcium ions (Ca²⁺) and mitochondrial membrane potential (MMP), which indicated that strobilurins could cause mitochondrial dysfunction and cell apoptosis. The present study was performed a systematic analysis of strobilurins to zebrafish at multi-levels, which provided suggestions for further investigation of molecular mechanisms underlying the toxicity induced by strobilurins on aquatic organisms.

Using enzyme activities and soil microbial diversity to understand the effects of fluoxastrobin on microorganisms in fluvo-aquic soil

Whether now or in the foreseeable future, agricultural production cannot do without chemical pesticides. Strobilurin fungicides, including mitochondrial inhibitors, can easily enter the soil environment and causing pollution. Fluoxastrobin is one of the top-selling strobilurin fungicides. Limited information can be found in the literature on the environmental toxicity of fluoxastrobin in soil. It is essential to understand the effects of fluoxastrobin on microorganisms in fluvo-aquic soil. The present study used a Biolog-EcoPlate method to analyze the effects of fluoxastrobin on soil microbial diversity in groups exposed to 0.1, 1.0, and 2.5 mg/kg fluoxastrobin and in control groups at exposure and on days 7, 14, 21, 28, and 48. The effects of fluoxastrobin on enzyme activities (β-glucosidase, dehydrogenase, and urease) in the soil were also evaluated. The results indicated that the three tested enzyme activities were lower at each dose to a varying degree than those of the controls. The soil microbial diversity was shown to be affected according to the results of average well color development (AWCD) experiments. The present study aimed to assess environmental risks to terrestrial ecosystems under the stress of pesticide use. These results also enrich the basic data on fungicide toxicity to the soil environment and have a guiding significance for the rational use of pesticides and the sustainable utilization of resources.

Toxic effects of boscalid in adult zebrafish (Danio rerio) on carbohydrate and lipid metabolism

Boscalid as one of the most widely used succinate dehydrogenase inhibitor (SDHI) fungicides has been frequently detected in both freshwater and estuarine environments. Its acute toxic effects on zebrafish and freshwater algae have been reported in our previous studies. To further investigate its chronic toxic effects to aquatic organisms, adult zebrafish were exposed for 28 days to a series of environmentally relevant boscalid concentrations in this study. Growth indicators and histopathology were determined in this study. Results indicated that boscalid inhibited the growth of zebrafish and induced damage in the kidneys and liver. Carbohydrate and lipid metabolism as the key pathways of energy metabolism in growth of zebrafish were also investigated. Results showed boscalid caused an increase in the activity of hexokinase (HK), the content of glycogen, glucose-6-phosphatase (G6Pase), and insulin (INS) in liver and a decrease in blood glucose content and succinate dehydrogenase (SDH) activity. Boscalid reduced the total content of triacylglyceride (TG) and cholesterol (TC) and the activity of fatty acid synthase (FAS) and acetyl coenzyme A carboxylase (ACC) in the liver. Correspondingly, expression of the genes related to carbohydrate and lipid metabolism in liver and intestine was affected by boscalid, especially in the significant upregulation of G6Pase and pparα and downregulation of SGLT-1 and AMY. Results suggested that boscalid could affect carbohydrate metabolism of adult zebrafish via regulation of gluconeogenesis and glycolysis at 0.1 mg/L. Moreover, boscalid might induce an increase in β-oxidation and a decrease in lipid synthesis at 0.01 mg/L. In conclusion, our study identified that carbohydrate and lipid metabolism are the possible biological pathways that mediate boscalid-induced developmental effects.

Developmental toxicity of kresoxim-methyl during zebrafish (Danio rerio) larval development

Kresoxim-methyl (KM) is a broad spectrum strobilurin fungicide that has been used widely on crops around the world. In the present study, we aimed to investigate the toxic effects of KM using various sublethal endpoints during zebrafish (Danio rerio) larval development. Results showed that the LC₅₀ values of KM to zebrafish at multiple life stages (embryo, larvae, juvenile and adult) were 0.340, 0.224, 0.328 and 0.436 mg/L, respectively. The transcription patterns of 45 genes involved in hypothalamic-pituitary-thyroid/gonadal (HPT/HPG) axis, oxidative stress and apoptosis revealed KM could affect zebrafish larval development at multiple pathways. The activities of aromatase, superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPX), caspase 3 (Cas3) and caspase 9 (Cas9), and the levels of estradiol (E₂), vitellogenin (VTG), thyroid hormones (T₃ and T₄), reactive oxygen species (ROS) and ATP after embryos exposed to KM for 3 d, 6 d and 10 d were correlated well with the transcription of the corresponding molecules involved in these pathways. In addition to providing the first description of the toxic effects induced by KM during larval development, the results of present study also provided the potential mechanisms of KM on multi-level biomarker responses in larval zebrafish.

Long-Term Exposure to Environmental Concentrations of Azoxystrobin Delays Sexual Development and Alters Reproduction in Zebrafish ( Danio rerio)

The strobilurin fungicide azoxystrobin (AZO) can induce adverse effects in aquatic organisms, but data are lacking on endpoints associated with sexual development and reproduction following chronic exposure to AZO. In this study, zebrafish embryos (F0) at 2-4 h postfertilization (hpf) were exposed to 0.2, 2.0, and 20.0 μg/L AZO until 120 d postfertilization (dpf). Decreased male ratio and increased intersex ratio were observed by 20.0 μg/L AZO at 42 and 60 dpf, but this effect disappeared at 120 dpf. AZO at 20.0 μg/L inhibited growth, retarded gonadal development, and disrupted sex hormone and vitellogenin in females at 60 and 120 dpf and in males at 42, 60, and 120 dpf. These effects were associated with altered expression of cyp19a, cyp19b, hsd3b, hsd17b, vtg1, and vtg2. Exposure to 2.0 μg/L AZO altered mRNA levels of these transcripts in females at 120 dpf and in males at 60 and 120 dpf. Reproduction ability was reduced by 20.0 μg/L AZO at 120 dpf. Developmental defects were observed after F1 embryos from exposed parents of 20.0 μg/L were reared in AZO-free water at 96 hpf. Overall, these data provide new understanding of fish sexual development and reproduction following chronic exposures to AZO.

Acute toxicity of the fungicide azoxystrobin on the diatom Phaeodactylum tricornutum

Azoxystrobin (AZ) is an effective broad-spectrum fungicide. Due to its extensive application, AZ is detectable in aquatic ecosystems and thus influences aquatic organisms. In this study, the acute toxicity (96 h) of AZ at concentrations of 1.0 mg/L and 5.0 mg/L on the diatom Phaeodactylum tricornutum were examined. At the tested concentrations, AZ significantly inhibited P. tricornutum growth and destroyed its cellular structure. Furthermore, the mechanisms of AZ-induced toxicity on P. tricornutum changed as the exposure time extended. Forty-eight hours after exposure, AZ inhibited P. tricornutum growth primarily via inducing oxidative stress, which increased the activity of two main antioxidant enzymes, superoxide dismutase and peroxidase, and inhibited energy metabolism. However, after 96 h of treatment, the decline in the photosynthetic capacity of P. tricornutum demonstrated that the photosystem was the main AZ target. The pigment content and expression levels of genes related to photosynthetic electron transfer reactions were also significantly decreased. The present study describes AZ toxicity in P. tricornutum and is very valuable for assessing the environmental risk of AZ.

Acute exposure to a commercial formulation of Azoxystrobin alters antioxidant enzymes and elicit damage in the aquatic macrophyte Myriophyllum quitense

Azoxystrobin is a strobilurin of growing concern in aquatic environments because it is the most sold fungicide worldwide, however, the information available about its effect on aquatic non-target organisms is scarce. The objective of the present study was to evaluate potential physiological, biochemical, and genetic effects at environmentally relevant (1-10 μg/L) and elevated (100-500 μg/L) concentrations in the aquatic macrophyte Myriophyllum quitense exposed to the commercial formulation AMISTAR^®. Following an acute 24-h exposure, there were no effects of AMISTAR^® on photosynthetic pigments at any of the concentrations evaluated. Glutathione-S-transferase activity was significantly elevated at 1 and 10 μg/L AZX. Significant decrease of catalase and guaiacol peroxidase activities in plants exposed to 500 μg/L, and to 100 and 500 μg/L, respectively, and an increase in glycolate oxidase activity at 500 μg/L was observed. DNA damage at 100 and 500 μg/L was observed. These data indicate that although environmentally relevant levels of AMISTAR^® did not result cytotoxic, this fungicide was genotoxic, affecting the physiological process of photorespiration and caused oxidative damage at high concentrations. In this sense, it is necessary to explore sub-lethal responses in non-target organisms because some effects could promote further potential long-term biological consequences in a context of repeated pulses of exposure.

Parental exposure to azoxystrobin causes developmental effects and disrupts gene expression in F1 embryonic zebrafish (Danio rerio)

The fungicide azoxystrobin induces reproductive toxicity in adult zebrafish. However, data are lacking regarding the impact of azoxystrobin in the F1 generation after parental exposure. To address this knowledge gap, parental zebrafish (F0) were exposed to 2, 20 and 200 μg/L azoxystrobin for 21 days. Following this, fertilized F1 embryos from the exposed parents were either exposed to the same concentration as their corresponding exposed parents (F0+/F1+) or were reared in clean water (F0+/F1-) for 96 h ("+", exposed; "-" unexposed). Likewise, F1 embryos from the non-exposed parents were either reared in clean water (F0-/F0-) as the control group or were exposed to 2, 20 and 200 μg/L azoxystrobin (F0-/F1+) for 96 h. Mortality, deformities, hatching rate, body length, and the expression of transcripts related to the endocrine system, oxidative stress, and apoptosis were measured. Increased mortality, higher malformation rate, decreased hatching rate, and a shorter total body length, as well as up-regulated cyp19b, vtg1, vtg2, p53, casp3, and casp9 mRNA and down-regulated sod1 and sod2 mRNA were detected in F1 embryos from the F0 and F1 exposure group at 20 and 200 μg/L azoxystrobin (F0+/F1+) when compared with the group from the F0 exposure alone (F0+/F1-). Interestingly, F1 exposure alone (F0-/F1+) did not induce mortality, developmental impairments, nor morphological deformations compared to the control group, but it did increase expression level of sod1, sod2, cat, p53, and casp9 at 200 μg/L azoxystrobin. Taken together, these data suggest that azoxystrobin affects survivability, development, and genes involved in the endocrine system, oxidative stress, and apoptosis in F1 embryos if their parents are initially exposed to this fungicide compared to embryos from non-exposed parents. Moreover, the effects are more severe if the offspring are continuously exposed to azoxystrobin similar to their parents.

Effects of two strobilurins (azoxystrobin and picoxystrobin) on embryonic development and enzyme activities in juveniles and adult fish livers of zebrafish (Danio rerio)

Azoxystrobin and picoxystrobin are two primary strobilurin fungicides used worldwide. This study was conducted to test their effects on embryonic development and the activity of several enzyme in the zebrafish (Danio rerio). After fish eggs were separately exposed to azoxystrobin and picoxystrobin from 24 to 144 h post fertilization (hpf), the mortality, hatching, and teratogenetic rates were measured. Additionally, effects of azoxystrobin and picoxystrobin on activities of three important antioxidant enzymes [catalase (CAT), superoxide dismutase (SOD) and peroxidase (POD)] and two primary detoxification enzymes [carboxylesterase (CarE) and glutathione S-transferase (GST)] and malondialdehyde (MDA) content in zebrafish larvae (96 h) and livers of adult zebrafish of both sexes were also assessed for potential toxicity mechanisms. Based on the embryonic development test results, the mortality, hatching, and teratogenetic rates of eggs treated with azoxystrobin and picoxystrobin all showed significant dose- and time-dependent effects, and the 144-h LC₅₀ values of azoxystrobin and picoxystrobin were 1174.9 and 213.8 μg L^-1, respectively. In the larval zebrafish (96 h) test, activities of CAT, POD, CarE, and GST and MDA content in azoxystrobin and picoxystrobin-treated zebrafish larvae increased significantly with concentrations of the pesticides compared with those in the control. We further revealed that azoxystrobin and picoxystrobin exposure both caused significant oxidative stress in adult fish livers and the changes differed between the sexes. Our results indicated that picoxystrobin led to higher embryonic development toxicity and oxidative stress than azoxystrobin in zebrafish and the male zebrafish liver had stronger ability to detoxify than that of the females.

Biological response of zebrafish after short-term exposure to azoxystrobin

Azoxystrobin (AZ) is a broad-spectrum systemic fungicide that widely used in the world. The present study investigated the toxicity effects on zebrafish after short-term exposure of AZ. Results demonstrated that the larval stage was most susceptible to AZ in the multiple life stages of zebrafish, with 96 h-LC₅₀ value of 0.777 mg/L. Zebrafish larvae were exposed to different AZ concentrations (0, 0.1, 1, 10, 100 μg/L) and examined on 24, 48 and 72 h. It was found that AZ induced ROS accumulation, increased GST, GPX and POD activity and the transcriptions of antioxidant and stress response related genes, while the opposite trend occurred for SOD and CAT activity in 24-h or 48-h exposure period. The increased E₂ and VTG levels in zebrafish larvae, and altered transcription levels of regulatory and steroidogenic genes in the hypothalamus-pituitary-gonad (HPG) axis indicated the endocrine disruption capacity of AZ. The transcripts of mdm2, p53, ogg1, bcl2, bbc3, cas8 and cas9 involved in cell apoptosis, and the mRNA levels of cytokines and chemokines such as cxcl-c1c, ccl, il-1β, il-8, ifn, and tnfα were in accordance with the trends of the examined genes involved in oxidative stress and endocrine system. The results suggested that short-term exposure to AZ might impose ecotoxicological effects on zebrafish larvae, and the information presented here also provide molecular strategies and increase mechanistic understanding of AZ-induced toxic response, and help elucidate the environmental risks of AZ.

Mycotoxin zearalenone induced gonadal impairment and altered gene expression in the hypothalamic-pituitary-gonadal axis of adult female zebrafish (Danio rerio)

In the present study, we aimed to assess the adverse effects of zearalenone (ZEA) at environmentally relevant concentrations (0.5, 1, 5 and 10 μg l^-1 ) on hypothalamic-pituitary-gonadal axis associated reproductive function using zebrafish model. ZEA was exposed to female zebrafish for 21 days to assess growth indices such as condition factor, hepatosomatic index, gonadosomatic index and caspase 3 activity. Further, expression of estrogen receptor (ER) α and CYP19a1b genes in the brain, ERα and vitellogenin (Vtg) genes in the liver and follicle-stimulating hormone receptor, luteinizing hormone receptor, ERα, steroidogenic acute regulatory protein, 3β-hydroxysteroid dehydrogenase (HSD), 17-βHSD and CYP19a1 genes in the ovary were also investigated. Our results showed that there were no significant changes in the condition factor and hepatosomatic index, whereas a significant (P < .05) reduction in the gonadosomatic index, increase in caspase 3 activities and Vtg expression was observed at higher concentration. However, no significant changes were observed at lower treatment levels. Further, we also observed significant (P < .05) upregulation in ERα, Vtg, luteinizing hormone receptor, steroidogenic acute regulatory protein, 3β-HSD, 17β-HSD, CYP19a1 and CYP19a1b genes in treatment groups with higher levels of ZEA. Moreover, in histopathological examination, we observed oocyte atresia and oocyte membrane detachment in ovaries at the highest concentration. In conclusion, the present study revealed the negative impact of ZEA on zebrafish reproductive system by involvement of the hypothalamic-pituitary-gonadal axis-associated reproductive function.

Evaluation of joint effects of cyprodinil and kresoxim-methyl on zebrafish, Danio rerio

Aquatic organisms are usually exposed to a mixture of pesticides instead of individual chemicals. However, risk assessment of pesticides is traditionally based on toxicity data of individual compounds. In this study, we aimed to examine the joint toxicity of two fungicides cyprodinil (CYP) and kresoxim-methyl (KRM) to zebrafish (Danio rerio) using a systematic experimental approach. Results from 96-h semi-static test indicated that the LC₅₀ values of KRM to D. rerio at multiple life stages (embryonic, larval, juvenile and adult stages) ranged from 0.034 (0.015-0.073) to 0.61 (0.39-0.83) mg a.i. L^-1, which were higher than those of CYP ranging from 1.05 (0.88-1.52) to 4.42 (3.24-6.02) mg a.i. L^-1. Pesticide mixtures of CYP and KRM exhibited synergistic effect on embryonic zebrafish. The activities of carboxylesterase (CarE) and cytochrome P450 (Cyp450) were significantly altered in most of the individual and combined exposures compared with the control group. The expressions of seven genes (Mnsod, cyp17, crhr 2, crh, gnrhr 4, gnrhr 1 and hmgrb) were significantly altered upon exposure to combined pesticides compared with their individual pesticides. Collectively, these findings suggested joint effects should be considered in the risk assessment of pesticides and development of water quality criteria for the protection of aquatic environment.

Acute toxicity and associated mechanisms of four strobilurins in algae

Strobilurins have been reported highly toxic to non-target aquatic organisms but few illustrated how they cause toxic effects on algae. This study investigated the acute toxicity of Kresoxim-methy (KRE), Pyraclostrobin (PYR), Trifloxystrobin (TRI) and Picoxystrobin (PIC) on two algae and their toxicity mechanisms. Four strobilurins showed lower toxic effects on Chlorella pyrenoidsa but higher on Chlorella vulgaris. bc1 complex activities in C. vulgaris were significantly inhibited by all strobilurins, suggesting bc 1 complex might be the target of strobilurin toxicity in algae. Moreover, SOD, CAT and POD activities were significantly up-regulated by all doses of KRE, PYR and PIC. In contrast, low concentrations of TRI stimulated SOD and POD activities but highest concentration significantly inhibited those activities. Comet assays showed damaged DNA in C. vulgaris by four strobulirins, suggesting their potential genotoxic threats to algae. The results illustrated acute toxicity by strobulirins on algae and their possible toxicity mechanisms.

Developmental toxicity and potential mechanisms of pyraoxystrobin to zebrafish (Danio rerio)

As a newly developed, highly efficient strobilurin fungicide, pyraoxystrobin has been reported to be highly toxic to some aquatic organisms. However, the toxicity of pyraoxystrobin to different life stages of fish and the potential underlying mechanisms are still unknown. Hence, in the present study, the acute toxicity of pyraoxystrobin to different life stages of zebrafish (embryo, larva, and adult) was assessed. The developmental toxicity of pyraoxystrobin to zebrafish embryos and its effects on gene transcription in the embryo were also investigated. The results showed that the 96-h LC₅₀ values of pyraoxystrobin to embryos [2h post-fertilization (hpf)], 12h post-hatching (hph) larvae (84 hpf), 72 hph larvae (144 hpf), and adult zebrafish were 4.099, 1.069, 3.236, and 5.970µg/L, respectively. This suggests that pyraoxystrobin has very high toxicity to different life stages of zebrafish, while the newly hatched larvae constitute the most sensitive period of zebrafish to pyraoxystrobin. Decreased heart rate, hatching inhibition, growth regression, and morphological deformities were observed in zebrafish embryos after acute exposure to different concentrations of pyraoxystrobin. The rate of malformation increased in a time- and concentration-dependent manner in embryos, and the most pronounced abnormality was pericardial edema and yolk sac edema. Pyraoxystrobin (2 and 4μg/L) significantly altered the mRNA levels of genes related to mitochondrial respiratory chain and ATP synthesis (NDI, uqcrc, and ATPo6), oxidative stress (Mn-Sod, Cat, and Gpx), apoptosis (p53, Bcl2, Bax, and Cas3), and immune system (TNFα, IFN, and IL-1b) in zebrafish embryos. This result indicates that the alteration of these genes is a potential mechanism underlying the toxic effects of pyraoxystrobin on zebrafish.

Evaluation of the toxic response induced by azoxystrobin in the non-target green alga Chlorella pyrenoidosa

The top-selling strobilurin, azoxystrobin (AZ), is a broad-spectrum fungicide that protects against many kinds of pathogenic fungi by preventing their ATP production. The extensive use of AZ can have negative consequences on non-target species and its effects and toxic mechanisms on algae are still poorly understood. In this work, Chlorella pyrenoidosa that had been grown in BG-11 medium was exposed to AZ (0.5-10 mg L^-1) for 10 d. The physiological and molecular responses of the algae to AZ treatment, including photosynthetic efficiency, lipid peroxidation level, antioxidant enzyme activities, as well as transcriptome-based analysis of gene expression, were examined to investigate the potential toxic mechanism. Results shows that the photosynthetic pigment (per cell) increased slightly after AZ treatments, indicating that the photosystem of C. pyrenoidosa may have been strengthened. Glutathione and ascorbate contents were increased, and antioxidant enzyme activities were induced to relieve oxidative damage (e.g., from lipid peroxidation) in algae after AZ treatment. Transcriptome-based analysis of gene expression combined with physiological verification suggested that the 5 mg L^-1 AZ treatment did not inhibit ATP generation in C. pyrenoidosa, but did significantly alter amino acid metabolism, especially in aspartate- and glutamine-related reactions. Moreover, perturbation of ascorbate synthesis, fat acid metabolism, and RNA translation was also observed, suggesting that AZ inhibits algal cell growth through multiple pathways. The identification of AZ-responsive genes in the eukaryotic alga C. pyrenoidosa provides new insight into AZ stress responses in a non-target organism.

Concentration and timing of application reveal strong fungistatic effect of tebuconazole in a Daphnia-microparasitic yeast model

Given the importance of pollutant effects on host-parasite relationships and disease spread, the main goal of this study was to assess the influence of different exposure scenarios for the fungicide tebuconazole (concentration×timing of application) on a Daphnia-microparasitic yeast experimental system. Previous results had demonstrated that tebuconazole is able to suppress Metschnikowia bicuspidata infection at ecologically-relevant concentrations; here, we aimed to obtain an understanding of the mechanism underlying the anti-parasitic (fungicidal or fungistatic) action of tebuconazole. We exposed the Daphnia-yeast system to four nominal tebuconazole concentrations at four timings of application (according to the predicted stage of parasite development), replicated on two Daphnia genotypes, in a fully crossed experiment. An "all-or-nothing" effect was observed, with tebuconazole completely suppressing infection from 13.5μgl^-1 upwards, independent of the timing of tebuconazole application. A follow-up experiment confirmed that the suppression of infection occurred within a narrow range of tebuconazole concentrations (3.65-13.5μgl^-1), although a later application of the fungicide had to be compensated for by a slight increase in concentration to elicit the same anti-parasitic effect. The mechanism behind this anti-parasitic effect seems to be the inhibition of M. bicuspidata sporulation, since tebuconazole was effective in preventing ascospore production even when applied at a later time. However, this fungicide also seemed to affect the vegetative growth of the yeast, as demonstrated by the enhanced negative effect of the parasite (increasing mortality in one of the host genotypes) at a later time of application of tebuconazole, when no signs of infection were observed. Fungicide contamination can thus affect the severity and spread of disease in natural populations, as well as the inherent co-evolutionary dynamics in host-parasite systems.