Joint toxic effects of triazophos and imidacloprid on zebrafish (Danio rerio)

Immunotoxicity of thyroid hormone system disrupting compounds in fish

Endocrine disrupting compounds (EDCs) are among the most studied environmental pollutants in the field of (eco)toxicology, and different fish species are commonly used as model organisms, especially for studying reprotoxic effects. Despite the scientific and regulatory importance of EDCs, little attention has been given to their immunotoxic effects in fish. Basic knowledge and test systems for immune-related outcomes in fish are limited. For example, while the impact of estrogenic EDCs on the fish immune system has raised some attention in the last decade, thyroid hormone system disrupting compounds (THSDCs) and their impact on the fish immune system are less well studied. Thus, this literature review is aimed at describing the immunomodulatory roles of thyroid hormones (THs), as well as summarizing the existing research on the immunotoxicity of THSDCs in fish. A simplified potential adverse outcome pathway (AOP) was created, explaining the key events between THSD and lowered survival of fish experiencing pathogen infections along with chemical exposure. This AOP demonstrates that THSDCs can alter immune system functioning on a molecular, cellular, and organism level and, therefore, lead to reduced survival by lowering pathogen resistance of fish. However, available data were mainly limited to molecular analyses of immune-related biomarkers and included only few studies that conducted experiments demonstrating immunotoxic effects at organism level that can inform about population-relevant outcomes. Our putatively developed and simplified AOP can support the incorporation of immune-related endpoints in EDC testing guidelines and aid the development of risk assessments for THSDCs for human and environmental health.

Unraveling the complexity of organophosphorus pesticides: Ecological risks, biochemical pathways and the promise of machine learning

Organophosphorus pesticides (OPPs) are widely used in agriculture but pose significant ecological and human health risks due to their persistence and toxicity in the environment. While microbial degradation offers a promising solution, gaps remain in understanding the enzymatic mechanisms, degradation pathways, and ecological impacts of OPP transformation products. This review aims to bridge these gaps by integrating traditional microbial degradation research with emerging machine learning (ML) technologies. We hypothesize that ML can enhance OPP degradation studies by improving the efficiency of enzyme discovery, pathway prediction, and ecological risk assessment. Through a comprehensive analysis of microbial degradation mechanisms, environmental factors, and ML applications, we propose a novel framework that combines biochemical insights with data-driven approaches. Our review highlights the potential of ML to optimize microbial strain screening, predict degradation pathways, and identify key active sites, offering innovative strategies for sustainable pesticide management. By integrating traditional research with cutting-edge ML technologies, this work contributes to the journal's scope by promoting eco-friendly solutions for environmental protection and pesticide pollution control.

Enzymatic activity and gene expression changes in the earthworms induced by co-exposure to beta-cypermethrin and triadimefon

Pesticides often exist as complex mixtures in soil environments, yet the toxicity of these combinations has not been thoroughly investigated. In light of this, the current study aimed to assess the enzymatic activity and gene expression responses in the earthworm Eisenia fetida when exposed to a mixture of beta-cypermethrin (BCY) and triadimefon (TRI). The findings revealed that co-exposure to BCY and TRI triggered acute synergistic toxicity in E. fetida, emphasizing the potential risk they pose to soil health. Significant elevations in MDA, Cu/Zn-SOD, and CAT levels were observed across most individual and combined treatments. Additionally, the expression of crt was notably upregulated under most exposure conditions, while the expression levels of tctp and sod were significantly downregulated. These changes suggested the occurrence of oxidative stress and potential carcinogenic effects upon exposure to BCY, TRI, and their combination. Notably, the activities of CAT, caspase-9, and CarE, along with the transcriptional levels of mt, displayed more pronounced variations in response to the pesticide mixture compared to individual exposures. These results indicated that the combined exposure to BCY and TRI intensified oxidative stress, promoted cellular apoptosis, and disrupted detoxification processes more than exposure to either chemical alone. Molecular docking results showed that these two pesticides could interact with CAT, SOD, and GST. These data provided critical insights into the biochemical and molecular toxicity caused by BCY and TRI on E. fetida, offering a deeper understanding of the ecological risks posed by chemical mixtures to soil organisms. This study shed light on the toxicological implications of BCY and TRI co-occurrence and underscored the importance of evaluating the environmental impact of pesticide mixtures to safeguard soil ecosystems.

Impacts of neonicotinoids on biodiversity: a critical review

Neonicotinoids are the most widely used class of insecticides in the world, but they have raised numerous concerns regarding their effects on biodiversity. Thus, the objective of this work was to do a critical review of the contamination of the environment (soil, water, air, biota) by neonicotinoids (acetamiprid, clothianidin, imidacloprid, thiacloprid, thiamethoxam) and of their impacts on terrestrial and aquatic biodiversity. Neonicotinoids are very frequently detected in soils and in freshwater, and they are also found in the air. They have only been recently monitored in coastal and marine environments, but some studies already reported the presence of imidacloprid and thiamethoxam in transitional or semi-enclosed ecosystems (lagoons, bays, and estuaries). The contamination of the environment leads to the exposure and to the contamination of non-target organisms and to negative effects on biodiversity. Direct impacts of neonicotinoids are mainly reported on terrestrial invertebrates (e.g., pollinators, natural enemies, earthworms) and vertebrates (e.g., birds) and on aquatic invertebrates (e.g., arthropods). Impacts on aquatic vertebrate populations and communities, as well as on microorganisms, are less documented. In addition to their toxicity to directly exposed organisms, neonicotinoid induce indirect effects via trophic cascades as demonstrated in several species (terrestrial and aquatic invertebrates). However, more data are needed to reach firmer conclusions and to get a clearer picture of such indirect effects. Finally, we identified specific knowledge gaps that need to be filled to better understand the effects of neonicotinoids on terrestrial, freshwater, and marine organisms, as well as on ecosystem services associated with these biotas.

Non-invasive recording of heartbeats in Danio rerio and Daphnia magna to assess the toxicity of imidacloprid and glyphosate

Non-invasive optical registration and subsequent analysis of heart rate (HR) and heart rate variability (HRV) in transparent aquatic animals have recently been proposed as convenient toxicological endpoints, well-suited for automation data acquisition and processing. This approach was evaluated in experiments involving juvenile Daphnia magna and zebrafish (Danio rerio) embryos exposed to glyphosate solutions (20 mg/L, 2 mg/L, 0.2 mg/L, and 0.02 mg/L) and imidacloprid solutions (30 mg/L, 3 mg/L, 0.3 mg/L, and 0.03 mg/L). The findings indicate that cardiac performance assessment is a promising approach for short-term toxicity evaluation. However, the sensitivity of this physiological endpoint to various external factors may limit its broader application. Results from the two model species highlight their differing sensitivities to the tested substances, emphasizing the need for thorough preliminary studies before establishing this method as a standardized toxicological tool. The potential development and improvement of techniques for assessing heart rate in zebrafish and daphnids are discussed.

Honey Enriched with Additives Alleviates Behavioral, Oxidative Stress, and Brain Alterations Induced by Heavy Metals and Imidacloprid in Zebrafish

Environmental concerns have consistently been a focal point for the scientific community. Pollution is a critical ecological issue that poses significant threats to human health and agricultural production. Contamination with heavy metals and pesticides is a considerable concern, a threat to the environment, and warrants special attention. In this study, we investigated the significant issues arising from sub-chronic exposure to imidacloprid (IMI), mercury (Hg), and cadmium (Cd), either alone or in combination, using zebrafish (Danio rerio) as an animal model. Additionally, we assessed the potential protective effects of polyfloral honey enriched with natural ingredients, also called honey formulation (HF), against the combined sub-chronic toxic effects of the three contaminants. The effects of IMI (0.5 mg·L-1), Hg (15 μg·L-1), and Cd (5 μg·L-1), both individually and in combination with HF (500 mg·L-1), on zebrafish were evaluated by quantifying acetylcholinesterase (AChE) activity, lipid peroxidation (MDA), various antioxidant enzyme activities like superoxide dismutase and glutathione peroxidase (SOD and GPx), 2D locomotor activity, social behavior, histological and immunohistochemical factors, and changes in body element concentrations. Our findings revealed that all concentrations of pollutants may disrupt social behavior, diminish swimming performances (measured by total distance traveled, inactivity, and swimming speed), and elevate oxidative stress (OS) biomarkers of SOD, GPx, and MDA in zebrafish over the 21-day administration period. Fish exposed to IMI and Hg + Cd + IMI displayed severe lesions and increased GFAP (Glial fibrillary acidic protein) and S100B (S100 calcium-binding protein B) protein expression in the optic tectum and cerebellum, conclusively indicating astrocyte activation and neurotoxic effects. Furthermore, PCNA (Proliferating cell nuclear antigen) staining revealed reduced cell proliferation in the IMI-exposed group, contrasting with intensified proliferation in the Hg + Cd group. The nervous system exhibited significant damage across all studied concentrations, confirming the observed behavioral changes. Moreover, HF supplementation significantly mitigated the toxicity induced by contaminants and reduced OS. Therefore, the exposure to chemical mixtures offers a more complete picture of adverse impacts on aquatic ecosystems and the supplementation with bioactive compounds can help to reduce the toxicity induced by exposure to environmental pollutants.

Cocktail effects of clothianidin and imidacloprid in zebrafish embryonic development, with high and low concentrations of mixtures

There is growing concern that sprayed neonicotinoid pesticides (neonics) persist in mixed forms in the environmental soil and water systems, and these concerns stem from reports of increase in both the detection frequency and concentration of these pollutants. To confirm the toxic effects of neonics, we conducted toxicity tests on two neonics, clothianidin (CLO) and imidacloprid (IMD), in embryos of zebrafish. Toxicity tests were performed with two different types of mixtures: potential mixture compounds and realistic mixture compounds. Potential mixtures of CLO and IMD exhibited synergistic effects, in a dose-dependent manner, in zebrafish embryonic toxicity. Realistic mixture toxicity tests that are reflecting the toxic effects of mixture in the aquatic environment were conducted with zebrafish embryos. The toxicity of the CLO and IMD mixture at environmentally-relevant concentrations was confirmed by the alteration of the transcriptional levels of target genes, such as cell damage linked to oxidative stress response and thyroid hormone synthesis related to zebrafish embryonic development. Consequently, the findings of this study can be considered a strategy for examining mixture toxicity in the range of detected environmental concentrations. In particular, our results will be useful in explaining the mode of toxic action of chemical mixtures following short-term exposure. Finally, the toxicity information of CLO and IMD mixtures will be applied for the agricultural environment, as a part of chemical regulation guideline for the use and production of pesticides.

Comprehensive multi-omics investigation of sub-chronic toxicity induced by Cadmium and Triazophos Co-exposure in hook snout carps (Opsariichthys bidens)

The coexistence of heavy metals and pesticides poses a critical challenge in agricultural ecosystems. Traditional toxicity assessments often focus only on the individual impacts of either pesticides or heavy metals. Here, the untargeted metabolomics and 16 S rRNA sequencing were used to assess the individual and combined effects of cadmium (Cd) and triazophos (TRI) on hook snout carps (Opsariichthys bidens). Cd caused much more serious impacts on hepatic metabolism and gut microbiota than those in TRI. Combined Cd and TRI exposure synergistically affected hepatic metabolism, causing mitochondrial dysfunction and even oxidative damage. Simultaneously, 16 S rRNA sequencing highlighted significant variations in the composition and abundance of gut microbiota. A noteworthy connection emerged between these distinct microbiota profiles and disruptions in energy metabolism, ultimately leading to disorders in metabolites. These findings enhanced the understanding of risks posed by heavy metals and pesticides, providing insights for better environmental risk assessments of aquatic organisms.

Effects of Insecticide and Herbicides on Thyroid Disturbances in Zebrafish

Thyroid cancer usually begins with thyroid dysfunction and nodules and has become the most common cancer globally, especially in women. Although the causes of thyroid dysfunction are complex, the presence of environmental pollutants, especially certain pesticides as established mutagens, has been widely accepted. Zebrafish (Danio rerio) have similar toxic reactions and signal transduction pathways to humans and are very similar to humans in physiology, development, and metabolic function. Here, the direct toxicity effects and mechanisms of different insecticides and herbicides on zebrafish thyroid functions and indirect toxicity effects originating from thyroid dysfunction were summarized and compared. The overall toxicity of insecticides on the zebrafish thyroid was greater than that of herbicides based on effective concentrations. Penpropathrin and atrazine were more typical thyroid disruptors than other pesticides. Meanwhile, chiral pesticides showed more sophisticated single/combined toxicity effects on both parental and offspring zebrafish. Besides thyroid hormone levels and HPT axis-related gene expression alteration, developmental toxicity, immunotoxicity, and oxidative damage effects were all observed. These data are necessary for understanding the thyroid interference effect of pesticides on humans and for screening for thyroid disruptors in surface water with zebrafish models for the pre-assessment of human health risks and ecological risk control in the future.

Co-exposure to cadmium and triazophos induces variations at enzymatic and transcriptional levels in Opsariichthys bidens

Heavy metals and pesticides are significant pollutants in aquatic environments, often leading to combined pollution and exerting toxic effects on aquatic organisms. With the rapid growth of modern industry and agriculture, heavy metal cadmium (Cd) and pesticide triazophos (TRI) are frequently detected together in various water bodies, particularly in agricultural watersheds. However, the combined toxic mechanisms of these pollutants on fish remain poorly understood. This experiment involved a 21-day co-exposure of Cd and TRI to the hook snout carp Opsariichthys bidens to investigate the toxic effects on liver tissues at both enzymatic and transcriptional levels. Biochemical analysis revealed that both individual and combined exposures significantly increased the content or activity of caspase-3 (CASP-3) and malondialdehyde (MDA). Moreover, the impact on these parameters was greater in the combined exposure groups compared to the corresponding individual exposure groups. These findings suggested that both individual and combined exposures could induce mitochondrial dysfunction and lipid peroxidation damage, with combined exposure exacerbating the toxicological effects of each individual pollutant. Furthermore, at the molecular level, both individual and combined exposures upregulated the expression levels of cu-sod, cat, and erβ, while downregulating the expression of il-1. Similar to the patterns observed in the biochemical parameters, the combined exposure group exhibited a greater impact on the expression of these genes compared to the individual exposure groups. These results indicated that exposure to Cd, TRI, and their combination induced oxidative stress, endocrine disruption, and immunosuppression in fish livers, with more severe effects observed in the combined exposure group. Overall, the interaction between Cd and TRI appeared to be synergistic, shedding light on the toxic mechanisms by which fish livers responded to these pollutants. These findings contributed to the understanding of mixture risk assessment of pollutants and were valuable for the conservation of aquatic resources.

Metabolic perturbations in zebrafish (Danio rerio) larvae exposed to sulfentrazone and imidacloprid

The intensive and widespread application of pesticides in agroecosystems can lead to the simultaneous exposure of non-target aquatic organisms to insecticides and herbicides. However, the underlying mechanisms through which aquatic organisms undergo metabolic reprogramming to withstand the combined effects of the insecticide imidacloprid (IMI) and herbicide sulfentrazone (SUL) remain poorly elucidated. This study employs metabolomics to investigate the effects of individual and combined exposures to IMI and SUL on zebrafish (Danio rerio), aiming to simulate complex environmental conditions. Metabolomics analysis revealed extensive metabolic reprogramming in larvae induced by the selected agrochemicals. Both individual and combined exposures disrupted nucleotide metabolism, inhibited glycolysis, and led to the accumulation of acetylcholine through the shared modulation of differential metabolites. Notably, individual exposure exhibited a unique mode of action. Larvae exposed to IMI alone showed mitochondrial dysfunction, potentially stemming from interference with the electron transport chain, while SUL-induced disruptions were associated with glycerophospholipid accumulation, marking it as a critical target. Additionally, calculations of the metabolic effect level index indicated antagonistic interactions between SUL and IMI mixtures at an overall metabolic level. The results obtained through investigating the lethal and sub-lethal effects also revealed that the simultaneous application of SUL and IMI may have the potential to diminish acute and developmental toxicity in zebrafish. This study underscores the significance of metabolomics as a valuable and effective strategy for deciphering the toxicity and interactions of agrochemical mixtures.

Pesticide-induced alterations in zebrafish (Danio rerio) behavior, histology, DNA damage and mRNA expression: An integrated approach

To assess the impact of glyphosate and 2,4-D herbicides, as well as the insecticide imidacloprid, both individually and in combination, the gills of adult zebrafish were used due to their intimate interaction with chemicals diluted in water. Bioassays were performed exposing the animals to the different pesticides and their mixture for 96 h. The behavior of the fish was analyzed, a histological examination of the gills was carried out, and the genotoxic effects were also analyzed by means of the comet assay (CA) and the change in the expression profiles of genes involved in the pathways of the oxidative stress and cellular apoptosis. The length traveled and the average speed of the control fish, compared to those exposed to the pesticides and mainly those exposed to the mixture, were significantly greater. All the groups exposed individually exhibited a decrease in thigmotaxis time, indicating a reduction in the behavior of protecting themselves from predators. Histological analysis revealed significant differences in the structures of the gill tissues. The quantification of the histological lesions showed mild lesions in the fish exposed to imidacloprid, moderate to severe lesions for glyphosate, and severe lesions in the case of 2,4-D and the mixture of pesticides. The CA revealed the sensitivity of gill cells to DNA damage following exposure to glyphosate, 2,4-D, imidacloprid and the mixture. Finally, both genes involved in the oxidative stress pathway and those related to the cell apoptosis pathway were overexpressed, while the ogg1 gene, involved in DNA repair, was downregulated.

Comparing the effects of three neonicotinoids on embryogenesis of the South African clawed frog Xenopus laevis

Neonicotinoids (NEOs) are widely used insecticides that are ubiquitous in agricultural use. Since NEOs are found in natural waters as well as in tap water and human urine in regions where NEOs are widely used, NEOs pose a potential hazard to non-target organisms such as animals and humans. Some of the commonly detected NEOs are imidacloprid (IMD), thiamethoxam (TMX), and its metabolite clothianidin (CLO). Although previously published scientific information, including an assessment of the environmental risks, particularly for bees, had resulted in a ban on the outdoor use of these three NEOs in the EU - their use is now only permitted in closed greenhouses - these NEOs continue to be used in agriculture in many other parts of the world. Therefore, a detailed study and comparison of the effects of NEOs on the embryonic development of non-target organisms is needed to further define the risk profiles. Embryos of the South African clawed frog Xenopus laevis, a well-established aquatic model, were exposed to different concentrations of IMD, TMX, or CLO (0.1-100 mg/L) to study and compare the possible effects of a single contaminant in natural water bodies on early embryogenesis. The results included a reduced body length, a smaller orbital space, impaired cranial cartilage and nerves, and an altered heart structure and function. At the molecular level, NEO exposure partially resulted in an altered expression of tissue-specific factors, which are involved in eye, cranial placode, and heart development. Our results suggest that the NEOs studied negatively affect the embryonic development of the non-target organism X. laevis. Since pesticides, especially NEOs, pollute the environment worldwide, it is suggested that they are strictly controlled and monitored in the areas where they are used. In addition, the question arises as to whether pesticide metabolites also pose a risk to the environment and need to be investigated further so that they can be taken into account when registering ingredients.

Combined toxicity of trifloxystrobin and fluopyram to zebrafish embryos and the effect on bone development

Trifloxystrobin (TRI) is a methacrylate fungicide, and fluopyram (FLU) is a new pyridylethylbenzamide fungicide and nematicide. Both are often detected in water bodies and may be highly toxic to many aquatic organisms. Unfortunately, the aquatic biological risks of single FLU or a mixture of trifloxystrobin and fluopyram have not been reported. In this study, zebrafish was selected as the test organism to investigate the combined toxicity of trifloxystrobin and fluopyram to zebrafish. After zebrafish embryos exposed to three pesticide solutions, Alcian-blue staining, Alizarin-red staining and quantitative PCR (qPCR) were performed. The results indicated that 96h-LC50 of TRI was 0.159 mg·L-1 to zebrafish embryo, which was highly toxic. The 96h-LC50 of FLU to zebrafish embryos was 4.375 mg·L-1, being moderately toxic. The joint toxicity to zebrafish embryos(FLU at 96h-LC50 and TRI at 96h-LC50 in a 1:1 weight ratio to form a series of concentration treatment groups) was antagonistic. Both trifloxystrobin and fluopyram also inhibited the skeletal development of zebrafish and showed to be antagonistic. The results of qPCR indicated upregulations of different genes upon three different treatments. TRI mainly induced Smads up-expression, which may affect the BMP-smads pathway. FLU mainly induced an up-expression of extracellular BMP ligands and type I receptor (Bmpr-1a), which may affect the BMP ligand receptor pathway. The 1:1 mixture (weight ratio) of trifloxystrobin and fluopyram induced a reduction of the genes of extracellular BMP ligand (Smads) and type I receptor (Bmpr1ba), which may down-regulate BMP signaling and thus attenuating cartilage hyperproliferation, hypertrophy and mineralization. The results warren an interest in further studying the effect of the two fungicides in a mixture on zebrafish.

Pesticides exposure and compromised fitness in wild birds: Focusing on the reproductive endocrine disruption

Exposure of pesticides to wildlife species, especially on the aspect of endocrine disruption is of great concern. Wildlife species are more at risk to harmful exposures to the pesticides in their natural habitat through diet and several other means. Species at a higher tropic level in the food chain are more susceptible to the deleterious effects due to sequential biomagnifications of the pesticides/metabolites. Pesticides directly affect fitness of the species in the wild causing reproductive endocrine disruption impairing the hormones of the gonads and thyroid glands as reproduction is under the influence of cross regulations of these hormones. This review presents a comprehensive compilation of important literatures on the impact of the current use pesticides in disruption of both the hypothalamic-pituitary-gonadal and hypothalamic-pituitary-thyroid axes particularly in birds addressing impacts on the reproductive impairments and overall fitness. In addition to the epidemiological studies, laboratory investigations those provide supportive evidences of the probable mechanisms of disruption in the wild also have been incorporated in this review. To accurately predict the endocrine-disruption of the pesticides as well as to delineate the risk associated with potential cumulative effects, studies are to be more focused on the environmentally realistic exposure dose, mixture pesticide exposures and transgenerational effects. In addition, strategic screening/appropriate methodologies have to be developed to reveal the endocrine disruption potential of the contemporary use pesticides. Demand for adequate quantitative structure-activity relationships and insilico molecular docking studies for timely validation have been highlighted.

Assessment of imidacloprid induced genotoxicity in Pethia conchonius (Rosy barb), a common freshwater fish of India

Imidacloprid is one of the highly efficient, globally used neonicotinoid groups of insecticides. The indiscriminate use of imidacloprid is contaminating large water bodies affecting not only the target organisms but also non-target organisms including fish. The present study aimed to assess the extent of nuclear DNA damage by imidacloprid in Pethia conchonius a freshwater fish in India using comet and micronucleus assays. The LC50 value of imidacloprid was estimated to be 227.33 mg L-1. Based on the LC50-96 h value, three sub-lethal concentrations of imidacloprid, SLC I -18.94 mg L-1, SLC II -28.41 mg L-1 and SLC III -56.83 mg L-1 were used to detect its genotoxic effect at DNA and cellular level. The imidacloprid exposed fishes exhibited higher DNA damage and nuclear abnormalities (p < 0.05) than the control. The %head DNA, %tail DNA, tail length and the frequency of micronuclei with other nuclear abnormalities like blebbed and notched nuclei were significantly higher than the control in a time and concentration-dependent manner. The DNA damage parameters such as %head DNA (29.107 ± 1.843), %tail DNA (70.893 ± 1.843), tail length (361.431 ± 8.455) micronucleus (1.300 ± 0.019), notched (0.844 ± 0.011) and blebbed (0.811 ± 0.011) nuclei were found to be highest for SLC III (56.83 mg L-1) at 96 h. The findings indicate that IMI is highly genotoxic in fish and other vertebrates leading to mutagenic/clastogenic effects. The study will be helpful in optimization of the imidacloprid use.

Biochemical and gene expression alterations due to individual exposure of atrazine, dichlorvos, and imidacloprid and their combination in zebrafish

In environmental toxicology, combined toxicity has emerged as an important concern. Atrazine (ATZ), dichlorvos (DIC), and imidacloprid (IMD) are the major pesticides, extensively used to control insect, flies, mosquitoes, and weed. Here, we investigate whether the exposure to three different types of pesticides individually and in combination for 24 h alters antioxidant enzyme responses in zebrafish (Danio rerio). Oxidative stress parameters (biochemical and mRNA expression), acetylcholinesterase (AChE) activity, and Metallothionein-II (MT-II) mRNA expression levels were measured. Present work includes toxicological assessment of individual and combined (CMD) exposure of ATZ (185.4 µM), DIC (181 µM), IMD (97.8 µ), and CMD (ATZ 92.7 µM + DIC 90.5 µM + IMD 48.9 µM), in the liver, kidney, and brain of adult zebrafish. Lipid peroxidation (LPO), glutathione (GSH) content, AChE, superoxide dismutase (SOD), catalase (CAT), and glutathione peroxidase (GPx) activity along with mRNA expression of SOD, CAT, GPx, and MT-II were evaluated. Briefly, LPO, GSH content, the activity of AChE, and all antioxidant enzymes enhanced significantly in individual exposure, which was further altered in the CMD group. The mRNA expression of SOD, CAT, GPx, and MT-II in the liver and kidney showed significant down-regulation in all exposed groups. In the brain, significant upregulation in mRNA expression of SOD, CAT, GPx, and MT-II was observed in DIC and IMD groups, while ATZ and CMD showed significant downregulation except for GPx. Findings postulate that the CMD group exhibits synergistic toxic manifestation. The present study provides the baseline data on the combined toxic effects of pesticides and suggests regulating the use of pesticides.

Triazophos exposure on maternal Daphnia magna at environmental-related concentrations revealed toxic effects to its offspring

Due to chemical and photochemical stability, triazophos has been frequently detected in rivers and oceans over the years with extensive use for pest control in agriculture, and it has become a worldwide ecological concern to the aquatic environment. Until now, fewer data are available regarding the potential long-term adverse effects of triazophos on aquatic invertebrates, which plays an essential role in aquatic food webs, as a key group for water ecosystems. In this experiment, the F1- and F2 progenies of Daphnia magna were recovered when daphnias (F0) exposure to triazophos at environmental-related concentrations (0.1 and 1.0 μg/L) for 21 d; and the indexes related to phenotypic traits, reproduction and gene expression were measured in tested animals. The results showed that heart rate and total number of neonates in exposed F0-daphnias were significantly lower than those of control group, and the detoxification genes (HR96 and P-gp) were up-regulated while genes related reproduction (Vtg) and molting (Nvd and Shd) were significantly down-regulated. The heart rate and individual size of F1-daphnias (<24 h) were significantly reduced in the treatment group. After 21-d recovery, the heart rate and expression of HR96, P-gp, Vtg, Nvd and Shd were declined in F1-daphnias. There was no obvious difference of morphological traits and heart rate between treatment and control in F2-daphnias (<24 h). In summary, daphnias (F0) exposure to triazophos with environmental dose could raise toxic effects on its offspring (F1), which is mainly manifested by reduced heart rate, the accumulated number and individual size of offspring and decreased expression of genes related to molting and reproduction.

Using proteomics, q-PCR and biochemical methods complementing as a multiapproach to elicit the crucial responses of zebrafish liver exposed to neonicotinoid pesticide

Pesticides enter the environment through runoff and leaching and this raises public concern about effects on non-target organisms. Imidacloprid (IMI) a synthetic pesticide, has an unstable half-life, metabolized in minutes to weeks in the water. To evaluate the effects of IMI on the zebrafish liver, we conducted proteomic, molecular and biochemical analysis in a multi-level approach, to highlight the complementary features regarding the results of each method. Adult zebrafish were exposed to 60 mg/L IMI for 48 h and were evaluated using nLC-MS/MS for proteins, q-PCR analysis for expression of cat, gpx, pxr, ache, along with CAT and AChE enzyme activities and GSH and MDA assays. Based on proteomics, the regulation of antioxidant and immune responses, as well as gene transcription were significant processes affected. Apoptosis and ER stress pathways were upregulated and there was a down-regulation of cat and gpx genes. There was also elevated CAT activity and GSH and decreased MDA. Additionally, elevated AChE activity and up regulation of ache expression was observed. The multi-approach results included regulators of antioxidant, xenobiotic response and neuro-protective related proteins (genes and enzymes), which overall reflected harmful effects of IMI. Consequently, this study highlights the effects of IMI on zebrafish liver and reveals new potential biomarkers. In this respect, evaluated outcomes reveal the complementary features emphasizing the importance of studying chemicals using several methods. Our study provides deeper insights for future work in ecotoxicological studies regarding IMI and contribute to existing toxicity literature.

Developmental toxicity, immunotoxicity and cardiotoxicity induced by methidathion in early life stages of zebrafish

Methidathion is a highly effective organophosphorus pesticide and is extensively utilized for the control of insects in agricultural production. However, there is little information on the adverse effects and underlying mechanisms of methidathion on aquatic organisms. In this work, embryonic zebrafish were exposed to methidathion at concentrations of 4, 10, and 25 mg/L for 96 h, and morphological changes and activities of antioxidant indicators alterations were detected. In addition, the locomotor behavioral abilities of zebrafish exposed to methidathion were also measured. To further explore the mechanism of the toxic effects of methidathion, gene expression levels associated with cardiac development, cell apoptosis, and the immune system were tested through qPCR assays. The findings revealed that methidathion exposure could induce a decrease in survival rate, hatchability, length of body, and increase in abnormality of zebrafish, as well as cardiac developmental toxicity. The LC50 value of methidathion in zebrafish embryos was determined to be about 30.72 mg/L at 96 hpf. Additionally, methidathion exposure triggered oxidative stress in zebrafish by increasing SOD activity, ROS, and MDA content. Acridine orange (AO) staining indicated that methidathion exposure led to apoptosis, which was mainly distributed in the pericardial region. Furthermore, significant impairments of locomotor activity in zebrafish larvae were induced by methidathion exposure. Lastly, the expression of pro-inflammatory factors including IFN-γ, IL-6, IL-8, CXCL-clc, TLR4, and MYD88 significantly up-regulated in exposed zebrafish. Taken together, the results in this work illustrated that methidathion caused developmental toxicity, cardiotoxicity, and immunotoxicity in embryogenetic zebrafish.

Sex-specific metabolic dysregulation in digestive glands of green mussels following exposure to triazophos

As a ubiquitous environmental pollutant in China, triazophos (TP) is known to have neurotoxicity, oxidative stress, and reproductive toxicity to mussels. To investigate the molecular mechanisms of TP toxicity, metabolic changes in the digestive glands of Perna viridis in different sexes were examined after treated with 35 μg/L TP. Notably, 158 significant different metabolites (SDMs) were detected in TP-treated mussels and more than half of the SDMs were lipids and lipid-like molecules, which suggested that TP disturbed the lipid metabolism of P. viridis. In addition, metabolites associated with neurotoxicity and reproductive disturbance were also detected in female and male mussels. Moreover, a larger number of SDMs were found in male mussels (120 SDMs) than females (99 SDMs), and 60 common metabolites exhibited consistent variation tendency and similar magnitude in both sexes. The metabolic alternations in female and male mussels displayed similar protective mechanisms and also sex-specific responses, male mussels were more sensitive to TP exposure. This research provided new data about the molecular mechanisms of TP toxicity and the gender specific changes in mussels after treated by chemicals.

Ability of Lactobacillus brevis 47f to Alleviate the Toxic Effects of Imidacloprid Low Concentration on the Histological Parameters and Cytokine Profile of Zebrafish (Danio rerio)

In the present article, the possible mitigation of the toxic effect of imidacloprid low-concentration chronic exposure on Danio rerio by the probiotic strain Lactobacillus brevis 47f (1 × 108 CFU/g) was examined. It was found that even sublethal concentration (2500 µg/L) could lead to the death of some fish during the 60-day chronic experiment. However, the use of Lactobacillus brevis 47f partially reduced the toxic effects, resulting in an increased survival rate and a significant reduction of morphohistological lesions in the intestines and kidneys of Danio rerio. The kidneys were found to be the most susceptible organ to toxic exposure, showing significant disturbances. Calculation of the histopathological index, measurement of morphometric parameters, and analysis of principal components revealed the most significant parameters affected by the combined action of imidacloprid and Lactobacillus brevis 47f. This effect of imidacloprid and the probiotic strain had a multidirectional influence on various pro/anti-inflammatory cytokines (IL-1β, TNF-α, IL-6, IL-8). Therefore, the results suggest the possibility of further studying the probiotic strain Lactobacillus brevis 47f as a strain that reduces the toxic effects of xenobiotics. Additionally, the study established the possibility of using imidacloprid as a model toxicant to assess the detoxification ability of probiotics on the kidney and gastrointestinal tract of fish.

Prolonged darkness attenuates imidacloprid toxicity through the brain-gut-microbiome axis in zebrafish, Danio rerio

The present study investigated the toxic effects of IMI on brain and gut of zebrafish (Danio rerio) by a combination of transcriptome and microbiome analysis. In addition, the involvement of light/dark period was also evaluated. An acute toxic test was conducted on adult zebrafish weighing 0.45 ± 0.02 g with 4 experimental groups (n = 15): 1) IMI group (Light: Dark = 12: 12 h), 2) prolonged light group (Light: Dark = 20: 4 h), 3) prolonged darkness group (Light: Dark = 4: 20 h) which received 20 mg/L of IMI, and 4) control group, which was not treated with IMI (Light: Dark = 12: 12 h). The results showed that prolonged darkness improved the survival rate of zebrafish upon IMI exposure for 96 h. In the sub-chronic test, zebrafish were divided into the same 4 groups and exposed to IMI at 1 mg/L for 14 d (n = 30). The results showed that IMI induced oxidative stress in both IMI and prolonged light groups by inhibition of antioxidant activities and accumulation of oxidative products. Transcriptome analysis revealed a compromise of antioxidation and tryptophan metabolism pathways under IMI exposure. Several genes encoding rate-limiting enzymes in serotonin and melatonin synthesis were all inhibited in both IMI and LL groups. Meanwhile, significant decrease (P < 0.5) of serotonin and melatonin levels was observed. However, there's remarkable improvement of biochemical and transcriptional status in prolonged darkness group. In addition, microbiome analysis showed great alteration of gut bacterial community structure and inhibition of tryptophan metabolism pathway. Similarly, the gut microbiota dysbiosis induced by IMI was alleviated in prolonged darkness. In summary, sub-chronic IMI exposure induced neurotoxicity and gut toxicity in zebrafish by oxidative stress and impaired the brain-gut-axis through tryptophan metabolism perturbation. Prolonged darkness could effectively attenuate the IMI toxicity probably through maintaining a normal tryptophan metabolism.

Co-exposure of polycarbonate microplastics aggravated the toxic effects of imidacloprid on the liver and gut microbiota in mice

The joint toxicity of microplastics (MPs) and pesticides may be different from MPs or pesticides individually, however, the information about the combined toxicity of MPs and pesticides is not well understood. Herein, we investigated the joint toxicity of polycarbonate (PC) MPs and imidacloprid (IMI) on mice. After orally exposure for 4 weeks, PC and/or IMI lowered the body weight gain of mice. Single exposure of IMI induced the tissue damage in liver by disturbing the redox homeostasis, and PC significantly aggravated the imbalance of redox homeostasis by facilitating the accumulation of IMI in liver. Additionally, compared to single exposure of PC or IMI, PC+IMI exposure caused more severe damage to the gut microstructure and microbial diversity. Several key metabolic pathways, especially the lipid metabolism, were significantly affected. Overall, these findings provide new insight into understanding the potential risk of co-exposure of microplastics and pesticides to animal and human health.

Do environmentally relevant concentrations of the neonicotinoid insecticide imidacloprid induce DNA damage and oxidative stress on Cnesterodon decemmaculatus (Jenyns, 1842)?

Lethal and sublethal effects of imidacloprid (IMI) were assessed on Cnesterodon decemmaculatus (Pisces: Poeciliidae) by acute exposure to environmentally relevant concentrations of the commercial formulation Punto 35® (Gleba S.A.) under laboratory conditions. Specimens were exposed for 96 h to 1, 10, 20, 25, 35, 75, 100, 125, 150 and 175 mg IMI L^-1 from which an LC₅₀ 96 h value of 35.59 mg IMI L^-1 was calculated. Moreover, sublethal concentrations 0.175, 0.35 and 1 mg IMI L^-1 for 96 h were employed for the evaluation of the comet assay and the variation of activities of catalase (CAT) and glutathione content (GSH). Result demonstrated an increased genetic damage index and activity of CAT was observed. Conversely, no significant variation was observed in GSH activity. Total protein content decreased in treated organisms. These results represent the first report of acute effects induced by IMI on C. decemmaculatus exposed under laboratory conditions.

Sublethal effects of chlorantraniliprole on growth, biochemical and molecular parameters in two chironomids, Chironomus kiiensis and Chironomus javanus

Pesticide residues have serious environmental impacts on rice-based ecosystems. In rice fields, Chironomus kiiensis and Chironomus javanus provide alternative food sources to predatory natural enemies of rice insect pests, especially when pests are low. Chlorantraniliprole is a substitute for older classes of insecticides and has been used extensively to control rice pests. To determine the ecological risks of chlorantraniliprole in rice fields, we evaluated its toxic effects on certain growth, biochemical and molecular parameters in these two chironomids. The toxicity tests were performed by exposing third-instar larvae to a range of concentrations of chlorantraniliprole. LC₅₀ values at 24 h, 48 h, and 10 days showed that chlorantraniliprole was more toxic to C. javanus than to C. kiiensis. Chlorantraniliprole significantly prolonged the larval growth duration, inhibited pupation and emergence, and decreased egg numbers of C. kiiensis and C. javanus at sublethal dosages (LC₁₀ = 1.50 mg/L and LC₂₅ = 3.00 mg/L for C. kiiensis; LC₁₀ = 0.25 mg/L and LC₂₅ = 0.50 mg/L for C. javanus). Sublethal exposure to chlorantraniliprole significantly decreased the activity of the detoxification enzymes carboxylesterase (CarE) and glutathione S-transferases (GSTs) in both C. kiiensis and C. javanus. Sublethal exposure to chlorantraniliprole also markedly inhibited the activity of the antioxidant enzyme peroxidase (POD) in C. kiiensis and POD and catalase (CAT) in C. javanus. Expression levels of 12 genes revealed that detoxification and antioxidant abilities were affected by sublethal exposures to chlorantraniliprole. There were significant changes in the expression levels of seven genes (CarE6, CYP9AU1, CYP6FV2, GSTo1, GSTs1, GSTd2, and POD) in C. kiiensis and ten genes (CarE6, CYP9AU1, CYP6FV2, GSTo1, GSTs1, GSTd2, GSTu1, GSTu2, CAT, and POD) in C. javanus. These results provide a comprehensive overview of the differences in chlorantraniliprole toxicity to chironomids, indicating that C. javanus is more susceptible and suitable as an indicator for ecological risk assessment in rice ecosystems.

Single and mixed exposure to distinct groups of pesticides suggests endocrine disrupting properties of imidacloprid in zebrafish embryos

Due to their selective toxicity to insects, nicotinoid compounds have been widely used to control pests in crops and livestock around the world. However, despite the advantages presented, much has been discussed about their harmful effects on exposed organisms, either directly or indirectly, with regards to endocrine disruption. This study aimed to evaluate the lethal and sublethal effects of imidacloprid (IMD) and abamectin (ABA) formulations, separately and combined, on zebrafish (Danio rerio) embryos at different developmental stages. For this, Fish Embryo Toxicity (FET) tests were carried out, exposing two hours post-fertilization (hpf) zebrafish to 96 hours of treatments with five different concentrations of abamectin (0.5-11.7 mg L^-1), imidacloprid (0.0001-1.0 mg L^-1), and imidacloprid/abamectin mixtures (LC₅₀/2 - LC₅₀/1000). The results showed that IMD and ABA caused toxic effects in zebrafish embryos. Significant effects were observed regarding egg coagulation, pericardial edema, and lack of larvae hatching. However, unlike ABA, the IMD dose-response curve for mortality had a bell curve display, where medium doses caused more mortality than higher and lower doses. These data demonstrate the toxic influence of sublethal IMD and ABA concentrations on zebrafish, suggesting that these compounds should be listed for river and reservoir water-quality monitoring.

Effect of temperature and dietary pesticide exposure on neuroendocrine and olfactory responses in juvenile Chinook salmon (Oncorhynchus tshawytscha)

Projected water temperature increases based on predicted climate change scenarios and concomitant pesticide exposure raises concern about the responses of aquatic organisms. To better understand the effect of pesticide mixtures and influence of water temperature to fish, juvenile Chinook salmon (Oncorhynchus tshawytscha) were dietarily exposed to a mixture of legacy and current use pesticides (p,p'-DDE, bifenthrin, chlorpyrifos, esfenvalerate, and fipronil) at concentrations detected from field-collected prey items in the Sacramento-San Joaquin Delta, California (Delta) and exposed under current and predicted future water temperature scenarios, 11, 14, or 17 °C, for 14 days. The expression of a subset of genes (deiodinase 2-dio2, gonadotropin releasing hormone 2-gnrh2, and catechol-o-methyltransferase-comt) involved in neuroendocrine, dopaminergic, and olfactory function previously shown to be altered by individual pesticide exposures germane to this study were determined and olfactory function assessed using a Y-maze behavioral assay. When total body burdens of pesticides were measured, a significant decrease in dio2 expression was observed in Chinook salmon exposed at 14 °C compared to fish kept at 11 °C. Increases in gnrh2 expression were also observed in fish exposed to 14 °C. Similarly, increases in comt expression was noted at 14 and 17 °C. Additionally, altered expression of all transcripts was observed, showing interactions between temperature and individual pesticide concentrations. Chinook salmon spent significantly more time actively avoiding the odorant arm at baseline conditions of 11 °C in the Y-maze. At higher temperatures, Chinook spent significantly more time not making a choice between the odorant or clean arm following exposure to the low pesticide mixture, relative to 11 °C. These results suggest that dietary exposure to pesticide mixtures can potentially induce neuroendocrine effects and behavior. Impaired olfactory responses exhibited by Chinook salmon could have implications for predator avoidance in the wild under increased temperature scenarios and impact populations in the future.

Acute thiamethoxam exposure induces hepatotoxicity and neurotoxicity in juvenile Chinese mitten crab (Eriocheir sinensis)

The similar nervous system structure between crustaceans and insects and the high-water solubility of thiamethoxam can lead to the more severe toxicity of thiamethoxam to crustaceans. However, the effects of thiamethoxam on crustaceans are unclear. Therefore, a 96-h acute toxicity test was performed to explore the hepatotoxicity and neurotoxicity effects of thiamethoxam on Chinese mitten crab (Eriocheir sinensis) at concentrations 0 µg/L, 150 µg/L and 300 µg/L. The antioxidant and detoxification systems (including phases I and II) were significantly activated after exposure of juvenile crabs to thiamethoxam for 24 h in 300 µg/L group, whereas the toxic activation effect in 150 μg/L group was delayed. Moreover, a similar pattern was observed for the transcription levels of immune-related genes. Further analysis of inflammatory signaling pathway-related genes showed that thiamethoxam exposure with 300 µg/L for 24 h may induce a pro-inflammatory response through the NF-κB pathway. In contrast, the gene expression levels in 150 µg/L group were significantly upregulated compared with 0 µg/L group after 96 h. In addition, although the acute exposure of 150 μg/L thiamethoxam did not seem to induce significant neurotoxicity, the acetylcholinesterase activity was significantly decreased in 300 μg/L group after thiamethoxam exposure for 96 h. Correspondingly, thiamethoxam exposure with 300 µg/L for 24 h resulted in significantly downregulated transcriptional levels of synaptic transmission-related genes (e.g. dopamine-, gamma-aminobutyric acid- and serotonin-related receptors). Therefore, thiamethoxam may be harmful and cause potential toxic threats such as neurotoxicity and metabolic damage to crustaceans.

Predicting and assessing the toxicity and ecological risk of seven widely used neonicotinoid insecticides and their aerobic transformation products to aquatic organisms

Neonicotinoid insecticides (NIs) are widely used worldwide, accounting for 25 % of the global insecticide market, and are easily transported into surrounding aquatic ecological environments after application. At present, >80 % of surface water is contaminated by NIs globally. Some transformation products (TPs) of NIs can exhibit greater toxicity to aquatic organism than their parent products. However, few studies have evaluated the toxicity and ecological risk of the TPs of NIs. In this study, we aimed to assess the toxicity and ecological risk of seven widely used NIs and their aerobic TPs to aquatic organisms using a prediction method. We found that partial aerobic TPs of NIs have greater toxicity to aquatic organisms than their parent products, and some of them could severely damage aquatic ecosystems. Meanwhile, acetamiprid, thiacloprid, and several other TPs of NIs with a chlorinated ring structure showed strong bioconcentration abilities, which could potentially harm aquatic organisms through the food chain. Moreover, the widespread use of NIs has certain aquatic ecological risks, which should be controlled and limited. This study comprehensively evaluated the ecological risk of seven widely used NIs and their aerobic TPs to aquatic organisms for the first time. Our results could provide an important reference for assessment of the aquatic environmental risk posed by NIs and pollution control.

Cumulative Risk Assessment of Dietary Exposure to Pesticide Residues in Brown Rice (Oryza sativa L.) from the Three Main Rice-Growing Regions in China during 2016–2020

The residual levels of 25 monitored pesticides in 6,229 brown rice samples obtained from the 17 provinces of the three main rice-growing regions in China during 2016–2020 were analyzed, and the cumulative risks of chronic and acute exposure to pesticides for the Chinese population were assessed. The QuEChERS extraction coupled with liquid chromatography-mass spectrometry for simultaneous determination of 25 pesticide residues in brown rice was developed and validated with good accuracy and precision (recoveries of 70%–120% and RSD ≤20%). The overall detection rate and over the maximum residue limit (MRL) rate of pesticides in brown rice decreased from 39.15% and 3.59% in 2016 to 34.11% and 1.53% in 2020, respectively. The Yangtze River basin had a higher detection rate and over MRL rate (43.14% and 2.88%, respectively) compared with the Southeast Coastal region (37.28% and 2.77%) and the Northeast Plain (11.28% and 0.17%). Isoprothiolane (13.57%) and carbendazim (8.32%) were the most frequently detected in rice samples. Pesticide residues exceeding the MRLs were found most often in triazophos (0.75%) and isocarbophos (0.51%). The risk ranking of pesticide residues based on the ranking matrix showed that carbofuran, methamidophos, and isocarbophos had the highest residual risk scores of 25.09, 25.01, and 25.00, respectively. 17.7% of rice samples contained two or more pesticide residues. The cumulative risk assessments based on the relative potency factor (RPF) approach revealed that the cumulative risks of chronic and acute dietary exposure to organophosphorus, neonicotinoid insecticides, and triazole fungicides from rice ranged from 7.43 × 10−4 to 3.36 × 10−2, which were not considered of health concern. The study provides national-scale information on the contamination levels and health risks of pesticide residues in rice, which can help develop continuous monitoring programs for pesticide residue contamination in rice in China.

Diflubenzuron Induces Cardiotoxicity in Zebrafish Embryos

Diflubenzuron is an insecticide that serves as a chitin inhibitor to restrict the growth of many harmful larvae, including mosquito larvae, cotton bollworm and flies. The residue of diflubenzuron is often detected in aquaculture, but its potential toxicity to aquatic organisms is still obscure. In this study, zebrafish embryos (from 6 h to 96 h post-fertilization, hpf) were exposed to different concentrations of diflubenzuron (0, 0.5, 1.5, 2.5, 3.5 and 4.5 mg/L), and the morphologic changes, mortality rate, hatchability rate and average heart rate were calculated. Diflubenzuron exposure increased the distance between the venous sinus and bulbar artery (SV-BA), inhibited proliferation of myocardial cells and damaged vascular development. In addition, diflubenzuron exposure also induced contents of reactive oxygen species (ROS) and malondialdehyde (MDA) and inhibited the activity of antioxidants, including SOD (superoxide dismutase) and CAT (catalase). Moreover, acridine orange (AO) staining showed that diflubenzuron exposure increased the apoptotic cells in the heart. Q-PCR also indicated that diflubenzuron exposure promoted the expression of apoptosis-related genes (bax, bcl2, p53, caspase3 and caspase9). However, the expression of some heart-related genes were inhibited. The oxidative stress-induced apoptosis damaged the cardiac development of zebrafish embryos. Therefore, diflubenzuron exposure induced severe cardiotoxicity in zebrafish embryos. The results contribute to a more comprehensive understanding of the safety use of diflubenzuron.

Ecological risk of imidacloprid on the Brazilian non-target freshwater organisms Chironomus sancticaroli and Poecilia reticulata

Imidacloprid (IMI) is a neonicotinoid insecticide widely used in agriculture worldwide. This pesticide has been found in freshwater ecosystems, including Brazilian freshwaters. For this reason, studies are being conducted to detect the presence of IMI in freshwater and understand its effects on the aquatic biota. In the present study, the acute toxic effect of the imidacloprid commercial formulation (ICF) Galeão^® on the Brazilian non-target aquatic organisms Chironomus sancticaroli and Poecilia reticulata was evaluated. Enzymatic activities (glutathione S-transferase (GST), catalase (CAT), and ascorbate peroxidase (APX)) were also determined. Moreover, we considered 11 studies that detected IMI concentrations up to 3.65 µg.L^-1 in 28 different Brazilian freshwaters to evaluate the acute ecological risk of IMI in these environments. From the ecotoxicological assays, we determined the LC₅₀ values for C. sancticaroli (LC_50-48 h 1.52 µg.L^-1) and P. reticulata (LC_50-96 h 122.65 mg.L^-1). The high sensitivity of C. sancticaroli demonstrates that this species could be used as a bioindicator in studies investigating the contamination of freshwater by IMI. Enzymatic activity changes were observed in both organisms and offered sublethal responses to the effects of the pollution by IMI on aquatic biota. Our results suggest that the presence of IMI in Brazilian aquatic ecosystems can represent a potential ecological risk for the aquatic insect populations and, consequently, cause an imbalance in these ecosystems. The present study provides relevant and comparable toxicity information that may be useful to develop public policies to protect the Brazilian aquatic ecosystem from IMI contamination.

RETRACTED: Environmental Impact of Pharmaceutical Pollutants: Synergistic Toxicity of Ivermectin and Cypermethrin

Veterinary antiparasitic pharmaceuticals as well as pesticides have been detected in surface waters, and they may cause several toxic effects in this environmental compartment. In the present study, we evaluated the toxicity after exposure of different concentration of ivermectin (IVM; 50, 100, and 200 μg L-1) and cypermethrin (CYP; 5, 10, and 25 μg L-1) and the combination of these two compounds at non-toxic concentration (IVM 100 + CYP 5 μg L-1) in zebrafish embryos. Combination of IVM at 100 μg L-1 with CYP at 5 μg L-1 exposure induced hatching delay and malformations at 96 hpf in zebrafish larvae as well as significant induction of cell death in zebrafish larvae. At the same time, the two single concentrations of IVM and CYP did not show a toxic effect on zebrafish development. In conclusion, our study suggests that IVM and CYP show a synergistic effect at common, ineffective concentrations, promoting malformation and cell death in fish development.

Transcriptome analysis reveals sex-specific alterations in gonads of green mussel exposed to organophosphorus insecticide triazophos

Triazophos (TP) is a widespread pollutant in aquatic environments. A sex-specific metabolic response in green-lipped mussel Perna viridis to TP exposure was observed in our previous study, and this led us to investigate the mechanisms associated with its toxicity. P. viridis were subjected to chronic exposure (15 days) to TP at 35 μg/L to compare the sex-biased transcriptomic profiles in the gonads of male and female mussels. We identified 632 differentially expressed genes (DEGs) (348 up-regulated and 284 down-regulated) in TP-exposed males, and only 61 DEGs (9 up-regulated and 52 down-regulated) in TP-exposed females. Many DEGs were found to be involved in the nervous, reproductive endocrine, oxidative stress, and immune systems of P. viridis. Additionally, enzymatic activity analysis indicated TP induced neurotoxic effects and oxidative damage to the mussels. Our results demonstrate that the stress response and molecular mechanisms of TP toxicology are different between female and male mussels.

RETRACTED: Combined Effects of Potassium Perchlorate and a Neonicotinoid on Zebrafish Larvae (Danio rerio)

Imidacloprid (IMI) is part of the neonicotinoids family, insecticides widely used by humans and also found in wastewater. This class of compounds, if present in the environment, can cause toxicity to different species such as bees and gammarids, although little is known about vertebrates such as fish. In addition, several substances have been reported in the environment that can cause damage to aquatic species, such as potassium perchlorate (KClO4), if exposed to high concentrations or for long periods. Often, the co-presence of different contaminants can cause a synergistic action in terms of toxicity to fish. In the present study, we first analyzed different concentrations of IMI (75, 100 and 150 mg/L) and KClO4 (1, 1.5 and 5 mM) to highlight the morphological effects at 96 hpf and, subsequently, chose two nontoxic concentrations to evaluate their co-exposure and the pathway involved in their co-toxicity. Morphological alteration, mucus production, messenger RNA (mRNA) expression related to intestinal function and oxidative stress were measured. These results suggest that co-exposure to IMI and KClO4 could affect zebrafish embryo development by increasing gut toxicity and the alteration of antioxidative defense mechanisms.

Toxicogenomic profiling after sublethal exposure to nerve- and muscle-targeting insecticides reveals cardiac and neuronal developmental effects in zebrafish embryos

For specific primary modes of action (MoA) in environmental non-target organisms, EU legislation restricts the usage of active substances of pesticides or biocides. Corresponding regulatory hazard assessments are costly, time consuming and require large numbers of non-human animal studies. Currently, predictive toxicology of development compounds relies on their chemical structure and provides little insights into toxicity mechanisms that precede adverse effects. Using the zebrafish embryo model, we characterized transcriptomic responses to a range of sublethal concentrations of six nerve- and muscle-targeting insecticides with different MoA (abamectin, carbaryl, chlorpyrifos, fipronil, imidacloprid & methoxychlor). Our aim was to identify affected biological processes and suitable biomarker candidates for MoA-specific signatures. Abamectin showed the most divergent signature among the tested insecticides, linked to lipid metabolic processes. Differentially expressed genes (DEGs) after imidacloprid exposure were primarily associated with immune system and inflammation. In total, 222 early responsive genes to either MoA were identified, many related to three major processes: (1) cardiac muscle cell development and functioning (tcap, desma, bag3, hspb1, hspb8, flnca, myoz3a, mybpc2b, actc2, tnnt2c), (2) oxygen transport and hypoxic stress (alas2, hbbe1.1, hbbe1.3, hbbe2, hbae3, igfbp1a, hif1al) and (3) neuronal development and plasticity (npas4a, egr1, btg2, ier2a, vgf). The thyroidal function related gene dio3b was upregulated by chlorpyrifos and downregulated by higher abamectin concentrations. Important regulatory genes for cardiac muscle (tcap) and forebrain development (npas4a) were the most frequently ifferentially expressed across all insecticide treatments. We consider the identified gene sets as useful early warning biomarker candidates, i.e. for developmental toxicity targeting heart and brain in aquatic vertebrates. Our findings provide a better understanding about early molecular events in response to the analyzed MoA. Perceptively, this promotes the development for sensitive and informative biomarker-based in vitro assays for toxicological MoA prediction and AOP refinement, without the suffering of adult fish.

Quercetin antagonizes imidacloprid-induced mitochondrial apoptosis through PTEN/PI3K/AKT in grass carp hepatocytes

Imidacloprid (IMI) is widely used in agriculture, and is toxic to non-target aquatic species. Quercetin (Que) is a flavonoid abundant in fruits and vegetables that exhibits anti-oxidant activity. In the present study, we treated grass carp hepatocytes (L8824) with 0.1 μM Que and/or 1 mM IMI for 24 h to explore the effect of Que on IMI-induced mitochondrial apoptosis. We found that IMI exposure enhanced reactive oxygen species (ROS) generation, inhibiting the activities of SOD, CAT and T-AOC, exacerbating the accumulation of MDA, aggravating the expression of mitochondrial apoptosis pathway (Cyt-C, BAX, Caspase9 and Caspase3) related genes and decreased the expression of anti-apoptosis gene B-cell lymphoma-2 (Bcl-2). In addition, Que and IMI co-treatment significantly restored the activity of anti-oxidant enzymes, downregulated ROS level and apoptosis rate, thereby alleviating the depletion of mitochondrial membrane potential (ΔΨm) and the expression of cytochrome c (Cyt-C), Bcl-2-associated X (BAX), and cysteinyl aspartate specific proteinases (Caspase9 and 3), increasing the Bcl-2 level. Furthermore, we elucidated that Que could inhibit the expression of phosphatase and tensin homolog deleted on chromosome 10 (PTEN), thus activating phosphatidylinositol 3-kinase/protein kinase B (PI3K/AKT) pathway to attenuate IMI-induced apoptosis. Molecular docking provides assertive evidence for the interaction between Que ligand and PTEN receptor. Consequently, these results indicate that Que effectively antagonizes IMI-induced mitochondrial apoptosis in grass carp hepatocytes via regulating the PTEN/PI3K/AKT pathway.

Vitamin C Mitigates Oxidative Stress and Behavioral Impairments Induced by Deltamethrin and Lead Toxicity in Zebrafish

Environmental contamination from toxic metals and pesticides is an issue of great concern due to their harmful effects to human health and the ecosystems. In this framework, we assessed the adverse effects when aquatic organisms are exposed to toxicants such as deltamethrin (DM) and lead (Pb), alone or in combination, using zebrafish as a model. Moreover, we likewise evaluated the possible protective effect of vitamin C (VC) supplementation against the combined acute toxic effects of the two toxicants. Juvenile zebrafish were exposed to DM (2 μg L^-1) and Pb (60 μg L^-1) alone and in combination with VC (100 μg L^-1) and responses were assessed by quantifying acetylcholinesterase (AChE) activity, lipid peroxidation (MDA), some antioxidant enzyme activities (SOD and GPx), three-dimension locomotion responses and changes of elements concentrations in the zebrafish body. Our results show that VC has mitigative effects against behavioral and biochemical alterations induced by a mixture of contaminants, demonstrating that it can be used as an effective antioxidant. Moreover, the observations in the study demonstrate zebrafish as a promising in vivo model for assessing the neuroprotective actions of bioactive compounds.

Thiacloprid Induced Developmental Neurotoxicity via ROS-Oxidative Injury and Inflammation in Chicken Embryo: The Possible Attenuating Role of Chicoric and Rosmarinic Acids

Simple Summary

The current study was designed to evaluate the negative impact of thiacloprid (TH) on the brain tissue of developing chicken embryo models and to evaluate the modulatory effects of chicoric (CA) and rosmarinic (RA) acids. The eggs were injected in ovo with different doses of TH (0.1, 1, 10, and 100 μg/egg). TH significantly increased the oxidative damage in the brain of exposed embryos in a dose-dependent manner (p < 0.001). TH significantly elevated the oxidative stress markers; protein carbonyl, malondialdehyde (MDA) content, and DNA damage (p < 0.001). Myeloperoxidase (MPO) activity and NO significantly increased with overexpression of the pro-inflammatory cytokines (IFN-γ; interferon gamma, TNF-α; tumor necrosis factor alpha, and IL-1β; interleukin-1 beta), stress-related and apoptotic genes (NF-KB, Caspase-3) in the brain tissue on both a biochemical and molecular levels (p < 0.05), while downregulating the expression of antiapoptotic Bcl-2. Co-treatment of CA and RA with TH markedly decreased the insecticide-induced toxicity with a prominent synergistic effect (p < 0.05). In conclusion, TH is suggested to be a possible neurotoxic to embryos of vertebrates and possibly humans. The study also revealed the antioxidant, anti-inflammatory, genoprotective, and antiapoptotic properties of CA and RA against TH toxicity.

Abstract

Insecticides are widely employed in agriculture to control pests and as major factors for enhancing crop productivity. Thiacloprid (TH) is one of the most-used insecticides worldwide. In this study, the negative impact of TH on the brain tissue of developing chicken embryo models and the modulatory effect of chicoric (CA) and rosmarinic (RA) acids were investigated. The eggs were injected in ovo with different doses of TH (0.1, 1, 10, and 100 μg/egg). TH significantly increased the oxidative damage in the brain of exposed embryos in a dose-dependent manner (p < 0.05). TH significantly elevated the oxidative stress markers; protein carbonyl, malondialdehyde content, and DNA damage (p < 0.05). Myeloperoxidase activity and nitric oxide significantly increased with overexpression of the pro-inflammatory cytokines (interferon gamma, tumor necrosis factor alpha, and interleukin-1 beta) and stress-related and apoptotic genes (NF-KB, Caspase-3) in the brain tissue on both biochemical and molecular levels (p < 0.05), while downregulating the expression of antiapoptotic Bcl-2. Co-treatment of CA and RA with TH markedly decreased the insecticide-induced toxicity with a prominent synergistic effect (p < 0.05). In conclusion, TH is suggested to be a possible neurotoxic to embryos of vertebrates including human. The study also revealed the antioxidant, anti-inflammatory, genoprotective, and antiapoptotic property of CA and RA against TH toxicity.

Combined hepatotoxicity of imidacloprid and microplastics in adult zebrafish: Endpoints at gene transcription

Microplastics (MPs) and pesticides are two kinds of ubiquitous pollutants that can pose a health risk to aquatic organisms. However, researches about the combined effects of MPs and pesticides are very limited. A simple combined exposure model was established in this study, adult zebrafish were exposed to 100 μg/L imidacloprid (IMI), 20 μg/L polystyrene microplastics (PS), and a combination of PS and IMI (PS + IMI) for 21 days. The results demonstrated that exposure to PS and IMI inhibited the growth of zebrafish and altered the levels of glycolipid metabolism and oxidative stress-related biochemical parameters. While gene expression analysis revealed that, compared with PS or IMI treatment group, combined exposure caused a greater change in gene expression levels involving the process of glycolipid metabolism (Gk, Hk1, Aco, PPar-α, Cpt1, Acc, Fas, PPar-γ, Apo) and inflammatory response (IL-1β, IL-6, IL-8, TNF-α, IL-10). The results demonstrated that even combined exposure of low concentrations of PS and IMI could cause more severe hepatotoxicity in zebrafish, especially in terms of gene transcription. And more combined toxicity studies are essential for MPs and pesticides risk assessment.

Joint toxicity assessment reveals synergistic effect of chlorpyrifos and dichlorvos to common carp (Cyprinus carpio)

Common carp (Cyprinus carpio) is an important aquaculture species. However, their production and health is sometimes threatened by pesticides. In common carp, extensive studies have been done for exposures of single pesticides, but effects of mixtures such as those of the commonly used chlorpyrifos and dichlorvos, are still unknown for this species. In the first phase of this work, an acute lethal exposure experiment was conducted to estimate 24 h to 96 h lethal concentrations (LC_10-90) of chlorpyrifos, dichlorvos and their mixture. Compared to dichlorvos, chlorpyrifos was found to be highly toxic to the tested species. Joint toxicity assessment of these pesticides in binary mixtures was dominated by synergism. In the second experimental phase, common carp were exposed to sub-lethal concentrations (LD-10% and HD-50% 96 h-LC₅₀) of individual pesticides and their mixture. General fish behaviors, buccal movements and feeding attempts by fish were recorded after 1 h, 24 h, 48 h, 72 h and 96 h whereas aerobic metabolism of fish was recorded for 0-24 h, 24-48 h 48-72 h and 72-96 h of exposure. All pesticide treatments elevated buccal movements and oxygen uptake in a dose dependent manner. Feeding depression was also observed by pesticide exposure. The augmented deleterious effect of these pesticides in a mixture suggests that joint toxicity assessment is critical to develop more realistic water quality standards and monitoring guidelines.

Biochemical and Behavioral Responses in Zebrafish Exposed to Imidacloprid Oxidative Damage and Antioxidant Responses

Imidacloprid (IMI) is an insecticide used worldwide, a neonicotinoid that could cause toxicity in non-target organisms. Zebrafish (Danio rerio) is a model organism widely used in different fields of research such as behavioral studies, biochemical parameters as well as neurotoxicity research. Here, we investigate whether the exposure to three concentrations (0.15, 15, and 45 μg/L) of IMI for 96 h alters responses in zebrafish. Oxidative stress parameters and acetylcholinesterase activity (AChE) as well as the behavioral responses of locomotion were measured. IMI exposure decreased distance traveled in fish exposed to the 45 μg/L. In the exploratory activity, time spent and transitions to the top area of the water column decreased in fish exposed to all concentrations of IMI. In addition, exposures to 45 and 15 μg/L of IMI decreased episodes of erratic movement in the zebrafish. Exposures to IMI at a concentration of 45 μg/L decreased the time spent in erratic movements and increased the time spent with no movement (i.e., "freezing"). Glutathione S-transferase (GST) activity was increased in the brain of zebrafish exposed for 96 h to concentrations of 0.15 and 45 μg/L. Brain AChE activity was reduced and the levels of carbonyl protein (CP) increased in brain of zebrafish at concentrations of 15 and 45 μg/L. Lipid peroxidation measured by TBARS and, also non-protein thiols (NPSH) did not show any variation in the brain of zebrafish exposed to IMI. Changes in the activity of cholinergic neurotransmitters in the brain tissues of zebrafish indicate IMI toxicity. Exposures of fish over 96 h to IMI at a nominal concentration of 45 μg/L caused more extensive sublethal responses in zebrafish, but this concentration is well above those expected in the aquatic environment. Studies are warranted to evaluate the effects on behavior and biomarker responses in fish exposed over longer periods to IMI at environmentally relevant concentrations.

Comparison of the toxicity of pure compounds and commercial formulations of imidacloprid and acetamiprid on HT-29 cells: Single and mixture exposure

Neonicotinoids, which are widely used worldwide, including in Turkey, are an insecticide group that are synthetic derivatives of nicotine. Recently, they have attracted attention due to their toxic effects on non-target organisms, especially bees. Numerous studies have shown that neonicotinoids have been found in detectable levels in the environment and cause various undesirable effects on living organisms, including humans and other mammals. In this study, the possible toxic effects of imidacloprid and acetamiprid, commonly used neonicotinoids, are investigated by their pure forms and commercial formulations on HT-29 cells with individual and combined exposures. According to our results, imidacloprid and acetamiprid induced cytotoxicity by caspase-mediated apoptosis, mitochondrial membrane depolarization, DNA damage, and oxidative stress under these experimental conditions. It is worth mentioning low doses of DNA damage, mixture exposure causes toxic effects at lower concentrations than individual exposure, and formulation groups are at the forefront of toxicity formation, though this varies depending on the parameters.

Endocrine-Disrupting Compounds: An Overview on Their Occurrence in the Aquatic Environment and Human Exposure

Endocrine-disrupting compounds (EDCs) as emerging contaminants have accumulated in the aquatic environment at concentration levels that have been determined to be significant to humans and animals. Several compounds belong to this family, from natural substances (hormones such as estrone, 17-estradiol, and estriol) to synthetic chemicals, especially pesticides, pharmaceuticals, and plastic-derived compounds (phthalates, bisphenol A). In this review, we discuss recent works regarding EDC occurrence in the aquatic compartment, strengths and limitations of current analytical methods used for their detection, treatment technologies for their removal from water, and the health issues that they can trigger in humans. Nowadays, many EDCs have been identified in significant amounts in different water matrices including drinking water, thus increasing the possibility of entering the food chain. Several studies correlate human exposure to high concentrations of EDCs with serious effects such as infertility, thyroid dysfunction, early puberty, endometriosis, diabetes, and obesity. Although our intention is not to explain all disorders related to EDCs exposure, this review aims to guide future research towards a deeper knowledge of EDCs’ contamination and accumulation in water, highlighting their toxicity and exposure risks to humans.

Quantitative characterization of toxicity interaction within antibiotic-heavy metal mixtures on Chlorella pyrenoidosa by a novel area-concentration ratio method

Toxicity interaction, synergism and antagonism, may occur when multiple pollutants are exposed to the environment simultaneously, which limits the utility of some standard models to assess toxicity hazards and risks. The development and application of models which can provide an insight into the combined toxicity of pollutants becomes necessary. Therefore, a novel model, area-concentration ratio (ACR) method, was developed to characterize the toxicity interaction within mixtures of three aminoglycoside antibiotics (AGs), kanamycin sulfate (KAN), paromomycin sulfate (PAR), tobramycin (TOB) and one heavy metal copper (Cu) in this study. The inhibition toxicity of single contaminants and mixtures designed by direct equilibration ray method and uniform design ray method to Chlorella pyrenoidosa (C. pyrenoidosa) was determined by the microplate toxicity analysis (MTA). The results showed that the novel method ACR could be used for quantitative characterization of combined toxicity. According to the ACR, all the binary AG antibiotic mixture systems display obvious synergism and weak antagonism. The addition of the heavy metal Cu into binary AG antibiotic mixtures can obviously change toxicity interaction, but toxicity interaction changing trend varies greatly in different ternary mixture systems. Toxicity interaction in the six mixture systems has component concentration-ratio dependence. ACR can be suggested as an effective novel method to quantitatively characterize toxicity interaction when assessing the hazards and risks of the combined pollution.

Assessing the combined toxicity of carbamate mixtures as well as organophosphorus mixtures to Caenorhabditis elegans using the locomotion behaviors as endpoints

Carbamate pesticides (CMs) and organophosphorus pesticides (OPs) have been widely used in agriculture and toxicologically affect non-target organisms. Although there are many reports about their toxicities, the combined behavioral toxicities of CM/OP mixtures on Caenorhabditis elegans have rarely been studied. In this study, body bend inhibition (BBI), head thrash inhibition (HTI), and swimming speed inhibition (SSI) by CMs and OPs were chosen as the toxicity endpoints. The locomotion behavioral toxicities of individual pesticides (carbofuran (CAR), methomyl (MET), chlorpyrifos (CPF), and triazophos (TAP)) and their binary mixtures on C. elegans were determined systematically and the toxicological interaction profiles of various CM/OP mixture rays constructed using the combination index. It was shown that four pesticides and their binary mixture rays have significant inhibitory effects on the locomotion behavior of C. elegans; that is, they produce locomotion behavioral toxicities and the toxicity of two OPs is higher than those of two CMs. The toxicological interactions in the binary CM and OP mixtures are different from each other. For example, one mixture ray (CAR-MET-R1) in the CM system on the SSI endpoint exhibits synergism at all concentration levels, another ray (CAR-MET-R3) displays low-dose synergism and high-dose additive action on BBI and HTI endpoints, and weak synergism at high-dose on SSI, and other rays perform additive action. Two rays (CPF-TAP-R1 and CPF-TAP-R2) in the OP mixture system display low-dose additive action and high-dose antagonism on the three endpoints. Another ray (CPF-TAP-R3) shows the additive action at all concentration levels. It can be concluded that it is not sufficient to evaluate the combined toxicity of binary CM/OP mixtures using only one concentration ratio ray and that it is necessary to examine multiple concentration ratios.

Combined endocrine disruptive toxicity of malathion and cypermethrin to gene transcription and hormones of the HPG axis of male zebrafish (Danio rerio)

Cypermethrin (CYP) and malathion (MAT) have been widely used and are frequently detected in surface waters. The purpose of the present study was to investigate the endocrine disrupting toxicity of CYP, MAT, and CYP + MAT to 5-month-old male zebrafish (Danio rerio). After exposure, the hepatosomatic index (HSI) and gonadosomatic index (GSI) did not change significantly. Following exposure to the combination of 0.1 μg/L CYP +25 μg/L MAT, the E2 and VTG levels of male zebrafish were significantly increased compared to those after individual pesticide treatments. The molecular level of the hypothalamic-pituitary-gonadal (HPG) axis in zebrafish was studied; it was found that the expression of the estrogen-related genes, especially the vtg1 gene, was significantly altered in 0.1 μg/L CYP + 25 μg/L MAT. Overall, our observation indicated that CYP or MAT could disturb the hormonal balance, and their combination of 0.1 μg/L CYP +25 μg/L MAT could significantly enhance the estrogenic effect.