N -acetylcysteine inhibits Mancozeb-induced impairments to the normal development of zebrafish embryos

Investigation on the mancozeb toxicity in adult zebrafish (Danio rerio)

Agriculture has gained increasing importance in response to the continuous growth of the world population and constant need for food. To avoid production losses, farmers commonly use pesticides. Mancozeb is a fungicide used in agriculture as this compound is effective in combating fungi that harm crops. However, this fungicide may also produce damage to non-target organisms present in soil and water. Therefore, this study aimed to investigate the influence of exposure to mancozeb on survival rate, locomotor activity, behavior, and oxidative status utilizing adult zebrafish (Danio rerio) as a model following exposure to environmentally relevant concentrations of this pesticide. The experimental groups were negative control, positive control, and mancozeb (0.3; 1.02; 3.47; 11.8 or 40 μg/L). Zebrafish were exposed to the respective treatments for 96 hr. Exposure to mancozeb did not markedly alter survival rate and oxidative status of Danio rerio. At a concentration of 11.8 μg/L, the fungicide initiated changes in locomotor pattern of the animals. The results obtained suggest that the presence of mancozeb in the environment might produce locomotor alterations in adult zebrafish, which subsequently disrupt the animals' innate defense mechanisms. In nature, this effect attributed to mancozeb on non-target organisms might result in adverse population impacts and ecological imbalance.

Investigating the impact of Psidium guajava leaf hydroalcoholic extract in improving glutamatergic toxicity-induced oxidative stress in Danio rerio larvae

Glutamate is one of the predominant excitatory neurotransmitters released from the central nervous system; however, at high concentrations, this substance may induce excitotoxicity. This phenomenon is involved in numerous neuropathologies. At present, clinically available pharmacotherapeutic agents to counteract glutamatergic excitotoxicity are not completely effective; therefore, research to develop novel compounds is necessary. In this study, the main objective was to determine the pharmacotherapeutic potential of the hydroalcoholic extract of Psidium guajava (PG) in a model of oxidative stress-induced by exposure to glutamate utilizing Danio rerio larvae (zebrafish) as a model. Data showed that treatment with glutamate produced a significant increase in oxidative stress, chromatin damage, apoptosis, and locomotor dysfunction. All these effects were attenuated by pre-treatment with the classical antioxidant N-acetylcysteine (NAC). Treatment with PG inhibited oxidative stress responsible for cellular damage induced by glutamate. However, exposure to PG failed to prevent glutamate-initiated locomotor damage. Our findings suggest that under conditions of oxidative stress, PG can be considered as a promising candidate for treatment of glutamatergic excitotoxicity and consequent neurodegenerative diseases.

Network analysis of toxic endpoints of fungicides in zebrafish

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

Assessing the disparity: comparative toxicity of Copper in zebrafish larvae exposes alarming consequences of permissible concentrations in Brazil

Copper (Cu) is a naturally occurring metal with essential micronutrient properties. However, this metal might also pose increased adverse environmental and health risks due to industrial and agricultural activities. In Brazil, the maximum allowable concentration of Cu in drinking water is 2 mg/L. Despite this standard, the impact of such concentrations on aquatic organisms remains unexplored. This study aimed to evaluate the toxicity of CuSO4 using larval zebrafish at environmentally relevant concentrations. Zebrafish (Danio rerio) larvae at 72 hr post-fertilization (hpf) were exposed to nominal CuSO4 concentrations ranging from 0.16 to 48 mg/L to determine the median lethal concentration (LC50), established at 8.4 mg/L. Subsequently, non-lethal concentrations of 0.16, 0.32, or 1.6 mg/L were selected for assessing CuSO4 -induced toxicity. Morphological parameters, including body length, yolk sac area, and swim bladder area, were adversely affected by CuSO4 exposure, particularly at 1.6 mg/L (3.31 mm ±0.1, 0.192 mm2 ±0.01, and 0.01 mm2 ±0.05, respectively). In contrast, the control group exhibited values of 3.62 mm ±0.09, 0.136 mm2 ±0.013, and 0.3 mm2 ±0.06, respectively. Behavioral assays demonstrated impairments in escape response and swimming capacity, accompanied by increased levels of reactive oxygen species (ROS) and lipid peroxidation. In addition, decreased levels of non-protein thiols and reduced cellular viability were noted. Data demonstrated that exposure to CuSO4 at similar concentrations as those permitted in Brazil for Cu adversely altered morphological, biochemical, and behavioral endpoints in zebrafish larvae. This study suggests that the permissible Cu concentrations in Brazil need to be reevaluated, given the potential enhanced adverse health risks of exposure to environmental metal contamination.

Exposure to the environmentally relevant fungicide Maneb: Studying toxicity in the soil nematode Caenorhabditis elegans

Maneb is a manganese-containing ethylene bisdithiocarbamate fungicide and is still commonly used as no cases of resistance have been documented. However, studies have shown that Maneb exposure has neurodegenerative potential in mammals, resulting in symptoms affecting the motor system. Despite its extensive use, structural elucidation of Maneb has only recently been accomplished by our group. This study aimed to examine the bioavailability of Maneb, the quantification of oxidative stress-related endpoints and neurotransmitters employing pure Maneb, its metabolites and structural analogues, in the model organism Caenorhabditis elegans. Exposure to Maneb did not increase the bioavailability of Mn compared to manganese chloride, although Maneb was about 8 times more toxic with regard to lethality. Maneb generated not significantly reactive oxygen and nitrogen species (RONS) but decreased the ATP level while increasing the amount of glutathione and its oxidized form in a dose-dependent manner. Nevertheless, an alteration in the neurotransmitter homeostasis of dopamine, acetylcholine, and gamma-butyric acid (GABA) was observed as well as morphological changes in the dopaminergic neurons upon Maneb exposure, which underlines the assumption of the neurotoxic potential of Maneb. This study showed that Maneb exhibits effects based on a combined interaction of the ligand and manganese.

Effects of curcumin to counteract levodopa-induced toxicity in zebrafish

Parkinson's disease (PD) is a neurodegenerative disorder characterized by motor dysfunction due to the death of dopaminergic neurons in the substantia nigra pars compacta. Currently, treatment of PD has focused on increasing dopamine levels, using a dopamine precursor, levodopa (L-DOPA) or stimulation of dopaminergic receptors. Prolonged use of L-DOPA is associated with the occurrence of motor complications and dyskinesia, attributed to neurotoxic effects of this drug. The aim of this study was to investigate the effects of curcumin (CUR), a lipophilic polyphenol, to counteract L-DOPA induced toxicity. Zebrafish larvae were pre-treated with CUR (0.05 µM) or vehicle dimethyl sulfoxide (DMSO) for 24 hr and subsequently exposed to L-DOPA (1 mM) or vehicle. Immediately and 24 hr after L-DOPA exposure, spontaneous swimming and dark/light behavioral tests were performed. In addition, levels of reactive oxygen species (ROS) and lipid peroxidation products were determined at the end of treatment. CUR significantly improved the motor impairment induced by 24 hr L-DOPA treatment, and reduced levels of ROS and lipoperoxidation products in zebrafish larvae. In conclusion, our results suggest that CUR acts as a neuroprotector against toxicity initiated by L-DOPA. Evidence suggests the observed effects of CUR are associated with its antioxidant properties.

Differential Neuroprotective Effects of N-Acetylcysteine against Dithianon Toxicity in Glutamatergic, Dopaminergic, and GABAergic Neurons: Assessment Using Zebrafish

Despite the widespread agricultural use of dithianon as an antifungal agent, its neurotoxic implications for humans and wildlife have not been comprehensively explored. Using zebrafish embryonic development as our model, we found that dithianon treatment induced behavioral alterations in zebrafish larvae that appeared normal. Detailed quantitative analyses showed that dithianon at ≥0.0001 µgmL-1 induced cytoplasmic and mitochondrial antioxidant responses sequentially, followed by the disruption of mitochondrial and cellular homeostasis. Additionally, dithianon at 0.01 and 0.1 µgmL-1 downregulated the expressions of glutamatergic (slc17a6b), GABAergic (gad1b), and dopaminergic (th) neuronal markers. Contrarily, dithianon upregulated the expression of the oligodendrocyte marker (olig2) at concentrations of 0.001 and 0.01 µgmL-1, concurrently suppressing the gene expression of the glucose transporter slc2a1a/glut1. Particularly, dithianon-induced increase in reactive oxygen species (ROS) production was reduced by both N-acetylcysteine (NAC) and betaine; however, only NAC prevented dithianon-induced mortality of zebrafish embryos. Moreover, NAC specifically prevented dithianon-induced alterations in glutamatergic and dopaminergic neurons while leaving GABAergic neurons unaffected, demonstrating that the major neurotransmission systems in the central nervous system differentially respond to the protective effects. Our findings contribute to a better understanding of the neurotoxic potential of dithianon and to developing preventive strategies.

Neurobehavioral effects of fungicides in zebrafish: a systematic review and meta-analysis

Pesticides are widely used in global agriculture to achieve high productivity levels. Among them, fungicides are specifically designed to inhibit fungal growth in crops and seeds. However, their application often results in environmental contamination, as these chemicals can persistently be detected in surface waters. This poses a potential threat to non-target organisms, including humans, that inhabit the affected ecosystems. In toxicologic research, the zebrafish (Danio rerio) is the most commonly used fish species to assess the potential effects of fungicide exposure, and numerous and sometimes conflicting findings have been reported. To address this, we conducted a systematic review and meta-analysis focusing on the neurobehavioral effects of fungicides in zebrafish. Our search encompassed three databases (PubMed, Scopus, and Web of Science), and the screening process followed predefined inclusion/exclusion criteria. We extracted qualitative and quantitative data, as well as assessed reporting quality, from 60 included studies. Meta-analyses were performed for the outcomes of distance traveled in larvae and adults and spontaneous movements in embryos. The results revealed a significant overall effect of fungicide exposure on distance, with a lower distance traveled in the exposed versus control group. No significant effect was observed for spontaneous movements. The overall heterogeneity was high for distance and moderate for spontaneous movements. The poor reporting practices in the field hindered a critical evaluation of the studies. Nevertheless, a sensitivity analysis did not identify any studies skewing the meta-analyses. This review underscores the necessity for better-designed and reported experiments in this field.

Permissible concentration of mancozeb in Brazilian drinking water elicits oxidative stress and bioenergetic impairments in embryonic zebrafish

Mancozeb (MZ) is widely used as a fungicide in Brazil due to its effectiveness in combating fungal infections in plantations. However, its toxicity to non-target organisms, including aquatic organisms, has been reported in the literature. Recently, Brazilian legislation was updated to allow a concentration of 8 μg/L of MZ in drinking water (Ordinance GM/MS nº 888, of May 4, 2021). However, the safety of this concentration for aquatic organisms has not yet been put to the test. To address this gap, we conducted a study using zebrafish (Danio rerio) embryos at 4 hpf exposed to MZ at the concentration allowed by law, as well as slightly higher sublethal concentrations (24, 72, and 180 μg/L), alongside a control group. We evaluated various morphophysiological markers of toxicity, including survival, spontaneous movements, heart rate, hatching rate, body axis distortion, total body length, total yolk sac area, and total eye area. Additionally, we measured biochemical biomarkers such as reactive oxygen species (ROS) levels, lipid peroxidation, non-protein thiols (NPSH), and mitochondrial bioenergetic parameters. Our results showed that the concentration of 8 μg/L, currently permitted in drinking water according to Brazilian legislation, increased ROS production levels and caused alterations in mitochondrial physiology. Among the markers assessed, mitochondrial bioenergetic function appeared to be the most sensitive indicator of MZ embryotoxicity, as a decrease in complex I activity was observed at concentrations of 8 and 180 μg/L. Furthermore, concentrations higher than 8 μg/L impaired morphophysiological markers. Based on these findings, we can infer that the concentration of MZ allowed in drinking water by Brazilian environmental legislation is not safe for aquatic organisms. Our study provides evidence that this fungicide is a potent embryotoxic agent, highlighting the potential risks associated with its exposure.

Propineb induced notochord deformity, craniofacial malformation, and osteoporosis in zebrafish through dysregulated reactive oxygen species generation

Dithiocarbamate (DTC) fungicides are contaminants that are ubiquitous in the environment. Exposure to DTC fungicides has been associated with a variety of teratogenic developmental effects. Propineb, a member of DTCs, was evaluated for the toxicological effects on notochord and craniofacial development, osteogenesis in zebrafish model. Embryos at 6 hours post-fertilization (hpf) were exposed to propineb at dosages of 1 and 4 μM. Morphological parameters were evaluated at exposure times of 24, 48, 72, and 120 hpf after propineb exposure. The survival and hatching rates as well as body length decreased at 1 and 4 μmol/L groups. Besides, transgenic zebrafish exposed to propineb showed abnormal vacuole biogenesis in notochord cells at the early stage of development. The expression of collagen type 2 alpha 1a (col2a1a), sonic hedgehog (shh), and heat shock protein family B member 11 (hspb11) measured by quantitative PCR and in situ hybridization experiment of col8a1a gene have consolidated the proposal process. Besides, Alcian blue, calcein, and alizarin red staining profiles displayed craniofacial malformations and osteoporosis were induced following propineb exposure. PPB exposure induced the changes in oxidative stress and reactive oxygen species inhibitor alleviated the deformities of PPB. Collectively, our data suggested that propineb exposure triggered bone abnormalities in different phenotypes of zebrafish. Therefore, propineb is a potential toxicant of high priority concern for aquatic organisms.

Glyphosate-based herbicide (GBH) causes damage in embryo-larval stages of zebrafish (Danio rerio)

Glyphosate-Based Herbicides (GBH) show risks to the environment and also to aquatic organisms, such as fish. The present work aimed to evaluate the effects of GBH and Pure Glyphosate (PG) exposure on Danio rerio embryos at drinking water concentrations. Zebrafish embryos were exposed to 250, 500, and 1000 μg L^-1 of Roundup Original DI® and pure glyphosate for 96 h. Glyphosate concentration in water, parameters physicochemical water, survival, hatching rate, heart rate, malformations, behavior, and biomarkers were evaluated. We verified that at 6 h post-fertilization (hpf), animals exposed to GBH 500 showed decreased survival as compared to the control. The hatching rate increased in all groups exposed to GBH at 48 hpf as compared to the control group. The embryos exposed did not present changes in the spontaneous movement and touch response. Exposed groups to GBH demonstrated a higher number of malformations in fish embryos as compared to the control. Most malformations were: pericardial edema, yolk sac edema, body malformations, and curvature of the spine. In heart rate, bradycardia occurred in groups exposed, as predicted due to cardiac abnormalities. As biochemical endpoints, we observed a decrease in Glutathione S-transferase (GBH 250, GBH 500 and PG 250) and Acetylcholinesterase (GBH 250 and PG 250) activity. No differences were found between the groups in the concentration of protein, Total Antioxidant Capacity Against Peroxyl Radicals, Lipid peroxidation, Reactive Oxygen Species, Non-protein thiols, and Catalase. In conclusion, the damage in all evaluated stages of development was aggravated by survival and malformations. Therefore, the large-scale use of GBHs, coupled with the permissiveness of its presence could be the cause damage to the aquatic environment affecting the embryonic development of non-target organisms.

Cardiac developmental toxicity and transcriptome analyses of zebrafish (Danio rerio) embryos exposed to Mancozeb

Mancozeb (MZ), an antibacterial pesticide, has been linked to reproductive toxicity, neurotoxicity, and endocrine disruption. However, whether MZ has cardiactoxicity is unclear. In this study, the cardiotoxic effects of exposure to environment-related MZ concentrations ranging from 1.88 μM to 7.52 μM were evaluated at the larval stage of zebrafish. Transcriptome sequencing predicted the mechanism of MZ-induced cardiac developmental toxicity in zebrafish by enrichment analysis of Kyoto Encyclopedia of Genes and Genomes (KEGG) and Gene Ontology (GO). Consistent with morphological changes, the osm, pfkfb3, foxh1, stc1, and nrarpb genes may effect normal development of zebrafish heart by activating NOTCH signaling pathways, resulting in pericardial edema, myocardial fibrosis, and congestion in the heart area. Moreover, differential gene expression analysis indicated that cyp-related genes (cyp1c2 and cyp3c3) were significantly upregulated after MZ treatment, which may be related to apoptosis of myocardial cells. These results were verified by real-time quantitative RT-qPCR and acridine orange staining. Our findings suggest that MZ-mediated cardiotoxic development of zebrafish larvae may be related to the activation of Notch and apoptosis-related signaling pathways.

Riboceine Rescues Auranofin-Induced Craniofacial Defects in Zebrafish

Craniofacial abnormalities are a common group of congenital developmental disorders that can require intensive oral surgery as part of their treatment. Neural crest cells (NCCs) contribute to the facial structures; however, they are extremely sensitive to high levels of oxidative stress, which result in craniofacial abnormalities under perturbed developmental environments. The oxidative stress-inducing compound auranofin (AFN) disrupts craniofacial development in wildtype zebrafish embryos. Here, we tested whether the antioxidant Riboceine (RBC) rescues craniofacial defects arising from exposure to AFN. RBC rescued AFN-induced cellular apoptosis and distinct defects of the cranial cartilage in zebrafish larvae. Zebrafish embryos exposed to AFN have higher expression of antioxidant genes gstp1 and prxd1, with RBC treatment partially rescuing these gene expression profiles. Our data suggest that antioxidants may have utility in preventing defects in the craniofacial cartilage owing to environmental or genetic risk, perhaps by enhancing cell survival.

N-acetyl-cysteine and the control of oxidative stress during in vitro ovarian follicle growth, oocyte maturation, embryo development and cryopreservation

Oxidative stress is generated by an imbalance between reactive oxygen species (ROS) formation and cellular defense mechanisms. To reduce cellular damage caused by ROS in vivo or in vitro, N-acetyl-cysteine (NAC) is converted into metabolites that have the capacity of stimulating synthesis of glutathione (GSH) which functions directly as free radical scavengers. The NAC antioxidant potential evaluated to the greatest extent is the indirect action of NAC, as a precursor of GSH, with glutathione being the primary antioxidant in cells. During long-term preantral follicle culture, NAC has a synergic action with FSH and an important function in sustaining preantral follicle growth and follicle-cell viability in vitro. The NAC inclusion in in vitro maturation medium for cumulus-oocyte complexes (COC) leads to protection of oocytes from damage induced by heat stress, reductions in ROS, and increases in cumulus cell expansion. Developing embryos are susceptable to oxidative stress because of susceptability to cellular structure damage and not having well-developed defense mechanisms. Results from various indicate there are beneficial effects of NAC on embryonic development by increasing GSH biosynthesis and regulating cell proliferation. In addition, NAC is also an effective antioxidant during cryopreservation of ovarian follicles, oocytes and embryos, because inclusion of NAC in preservation medium leads to improvements in mitochondrial function and cell viability, and reductions in ROS and cellular apoptosis. In this review, there is evaluation of mechanisms of action of NAC and beneficial effects during in vitro culture of preantral follicles, as well as oocyte maturation, embryonic development and cryopreservation.

Establishing a high throughput drug screening system for cerebral ischemia using zebrafish larvae

We previously generated an ischemic stroke in a zebrafish model using N₂ gas perfusion; however, this model was an unsuitable drug screening system due to low throughput. In this study, we examined a zebrafish ischemic stroke model using an oxygen absorber to assess drug effects. Hypoxic exposure more than 2 h using the oxygen absorber significantly induced cell death in the brain and damage to the neuronal cells. To confirm the utility of the ischemic model induced by the oxygen absorber, we treated zebrafish with neuroprotective agents. MK-801, an N-methyl-d-aspartate (NMDA) receptor antagonist, significantly suppressed cell death in the brain, and edaravone, a free radical scavenger, significantly reduced the number of dead cells. These results suggest that the activation of NMDA receptors and the production of reactive oxygen species induce neuronal cell damage in accordance with previous mammalian reports. We demonstrate the suitability of an ischemic stroke model in zebrafish larvae using the oxygen absorber, enabling a high throughput drug screening.

Behavioral changes occur earlier than redox alterations in developing zebrafish exposed to Mancozeb

As agriculture expands to provide food and wellbeing to the world's growing population, there is a simultaneous increasing concern about the use of agrochemicals, which can harm non-target organisms, mainly in the aquatic environment. The fungicide Mancozeb (MZ) has been used on a large-scale and is a potent inducer of oxidative stress. Therefore, there is an urgent need for the development of more sensitive biomarkers designed to earlier biomonitoring of this compound. Here we tested the hypothesis that behavioral changes induced by sublethal MZ concentrations would occur first as compared to biochemical oxidative stress markers. Embryos at 4 h post-fertilization (hpf) were exposed to Mancozeb at 5, 10 and 20 μg/L. Controls were kept in embryo water only. Behavioral and biochemical parameters were evaluated at 24, 28, 72, and 168 hpf after MZ exposure. The results showed that MZ significantly altered spontaneous movement, escape responses, swimming capacity, and exploratory behavior at all exposure times. However, changes in ROS steady-stead levels and the activity of antioxidant enzymes were observable only at 72 and 168 hpf. In conclusion, behavioral changes occurred earlier than biochemical alterations in zebrafish embryos exposed to MZ, highlighting the potential of behavioral biomarkers as sensitive tools for biomonitoring programs.

Orbencarb induces lethality and organ malformation in zebrafish embryos during development

Thiocarbamates are one of the components of pesticides that target weeds by inhibiting adenosine triphosphate (ATP) synthesis. Orbencarb, one of the isomeric thiocarbamates applied to wheat, maize, and soybean, has been found to have toxic effects on mammals and marine ecosystems. Although the toxicity ranges of orbencarb in different organisms are known, specific studies on the environmental contamination and harmful effects of orbencarb on non-target organisms are scarce. In this study, we observed that orbencarb induced embryotoxicity during zebrafish development as well as apoptosis and reactive oxygen species (ROS) production in the intestine. It was further observed that orbencarb decreased the viability of the embryos and simultaneously affected the heart rate and vessel formation. Orbencarb decreased the mRNA levels of ccnd1, ccne1, cdk2, and cdk6 and induced abnormal development of the eyes, brain, yolk sac, and spinal cord in zebrafish embryos. Orbencarb also hampered vasculogenesis in the zebrafish embryos by inhibiting the mRNA expression of flt1, flt4, kdr, and vegfc. Collectively, these results suggested that orbencarb is embryotoxic and disrupts the normal growth of zebrafish embryos by inducing the generation of ROS and hampering vasculogenesis.

Toxic effects of a mancozeb-containing commercial formulation at environmental relevant concentrations on zebrafish embryonic development

The toxicological knowledge of mancozeb (MZ)-containing commercial formulations on non-target species is scarce and limited. Therefore, the objective of this work was to represent a realistic application scenario by evaluating the toxicity of environmental relevant and higher concentrations of a commercial formulation of MZ using zebrafish embryos. Following determination of the 96-h LC₅₀ value, the embryos at the blastula stage (~ 2 h post-fertilisation, hpf) were exposed to 0.5, 5, and 50 μg L^-1 of the active ingredient (~ 40× lower than the 96-h LC₅₀). During the exposure period (96 h), lethal, sublethal, and teratogenic parameters, as well as behaviour analysis, at 120 hpf, were assayed. Biochemical parameters such as oxidative stress-linked enzymes (superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx), and glutathione reductase (GR)), reactive oxygen species (ROS) levels, and glutathione levels (GSH and GSSG), as well as the activity of degradation (glutathione S-transferase (GST) and carboxylesterase (CarE)), neurotransmission (acetylcholinesterase (AChE)), and anaerobic respiration (lactate dehydrogenase (LDH))-related enzymes, were analysed at the end of the exposure period. Exposed embryos showed a marked decrease in the hatching rate and many malformations (cardiac and yolk sac oedema and spinal torsions), with a higher prevalence at the highest concentration. A dose-dependent decreased locomotor activity and a response to an aversive stimulus, as well as a light-dark transition decline, were observed at environmental relevant concentrations. Furthermore, the activities of SOD and GR increased while the activity of GST, AChE, and MDA contents decreased. Taken together, the involvement of mancozeb metabolites and the generation of ROS are suggested as responsible for the developmental phenotypes. While further studies are needed to fully support the hypothesis presented, the potential cumulative effects of mancozeb-containing formulations and its metabolites could represent an environmental risk which should not be disregarded.

Ecological risk of pesticide contamination in a Brazilian river located near a rural area: A study of biomarkers using zebrafish embryos

Aquatic environments are affected by the use of pesticides in agricultural areas near rivers. To assess the impact of pesticide residues on affected environments Danio rerio (zebrafish) embryos have become an alternative model for biomonitoring studies. In the present study, zebrafish embryos were used as bioindicator of water quality in the Vacacaí river, located in the city of Santa Maria, southern Brazil. We hypothesized that it would be possible to observe changes in the biomarkers tested in the embryos. Exposures were performed over a total of eight months during the year 2018 using water collected in a river located near agricultural areas. Twenty-four pesticides were found in river water samples. The most frequently found were atrazine, quinclorac and clomazone. During exposure (96 h) spontaneous movement, the heart rate and hatching rate were evaluated. After the exposure time the embryos were euthanized for biochemical assays. We analyzed biomarkers such as thiobarbituric acid reactive substance (TBARS), acetylcholinesterase (AChE), glutathione S-transferase (GST) and catalase (CAT). We observed increases in GST and TBARS, especially during periods of major water contamination such as January, February, October, and November. Pesticides can affect the development of native species that reproduce during periods of high agricultural production. These results demonstrate the potential use of biochemical parameters combined with developmental and behavioral analyses in zebrafish embryos for biomonitoring studies.

Acute embryonic exposure of zebrafish to permethrin induces behavioral changes related to anxiety and aggressiveness in adulthood

Permethrin (PM) is one of the most used synthetic pyrethroid worldwide. Exposure to this compound during pregnancy and early childhood has been indicated as a risk factor for neurodevelopmental disorders. We evaluated the long-term effects of embryonic PM exposure in different stages of zebrafish development. Briefly, embryos (3 hpf) were exposed to sub-lethal concentrations of PM (25 and 50 μg.L^-1) during 24 h and then behavioral parameters were evaluated during embryonic (28 hpf), eleutheroembryonic (3 dpf), larval (7 dpf), and adult stages (90 dpf). PM exposure decreased spontaneous movement at 28 hpf and decreased thigmotaxis in eleutheroembryos. The long-term effects of PM include changes in non-motor behaviors such as fear and anxiety in larva and adults. Adults embryonically exposed to PM also showed a significant increase in aggressiveness parameters. These results demonstrated that embryonic exposure to PM induces persistent neurotoxic effects in adulthood, which can impair the cognitive and behavioral fitness of non-target species contributing to a rise in neurodevelopmental disorders.