Embryotoxicity of atrazine and its degradation products to early life stages of zebrafish (Danio rerio)

Chemical contaminants and environmental stressors induced teratogenic effect in aquatic ecosystem - A comprehensive review

Aquatic environments, including marine and freshwater ecosystems, are vital for ecological balance and biodiversity. The rising global demand for aquaculture products necessitates increased production, with intensified aquaculture practices posing significant environmental risks. This review explores the pathways through which chemical pollutants, heavy metals, pharmaceuticals, and environmental stressors induce teratogenic effects in aquatic species. The review highlights the impact of pesticide include triazine herbicides, organophosphate and organochlorine insecticides, and carbamates on aquatic life, emphasizing their interference with endocrine systems and developmental processes. Heavy metals like mercury, lead, cadmium, arsenic, and chromium are noted for their persistence and bioaccumulative properties, disrupting cellular and hormonal functions. Pharmaceuticals, including NSAIDs, antibiotics, and chemotherapeutic agents, exert teratogenic effects by disrupting physiological and developmental pathways. Environmental stressors includes temperature fluctuations, salinity variations, pH changes, and oxygen level imbalances exacerbate the teratogenic impact of pollutants. This review highlights the importance of comprehensive environmental management and understanding these complex interactions is essential for formulating efficient strategies to safeguard the effective measures to protect aquatic ecosystems and the biodiversity.

Appraisal of a synthetic preservative, Quaternium - 15, effect on three model organisms: new insight on environmental risks

After the COVID-19 pandemic, the use of quaternary ammonium compounds increased exponentially due to their efficacy as antimicrobials, stabilizers and disinfectants. Among these, Quaternium-15 is a preservative used in the formulation of a variety of personal care products. The increased use of this substance and the resulting persistence in wastewater treatment systems, which are unable to completely remove the Quaternium-15 from the water, is of increasing environmental concern. Using embryotoxicity analyses, this study aimed to investigate the effects of exposure to Quaternium-15 on non-target species and the resulting risks to the environment. Embryotoxicity endpoints such as mortality, hatching, presence of malformations, altered heartbeat and animal length were used to assess the effects on three model organisms (Cyprinus carpio, Danio rerio, Xenopus laevis) were evaluated during a 96-hour exposure to six different concentrations of Quaternium-15 (1, 5, 10, 15, 20 and 25 mg/L). The results obtained from the analyses highlighted: significant mortality for all three model organisms in the highest concentrations tested in which all the embryos died after 96 hpf, a delay in hatching of C. carpio and D. rerio compared to the control group, the insurgence of malformations in all the model organisms chosen and a significant decrease in heartbeat rate for the fish models. Each of these observations underlies the negative interaction between the Quaternium-15 and aquatic organisms making necessary further investigation to prevent damage to ecosystems and non-target species.

Does the atrazine increase animal mortality: Unraveling through a meta-analytic study

Atrazine is one of the most used herbicides in the world, although it is banned in several countries. Pollution of terrestrial and aquatic ecosystems represents a threat to non-target organisms, with various damages already reported in different species. However, there is controversy in studies on atrazine. The question of whether atrazine increases animal mortality is not yet clearly resolved. In this context, this study aimed to carry out a meta-analytic review, focusing on studies on environmental concentrations of the herbicide atrazine to evaluate its lethal effects on various animal species. We identified and analyzed 107 datasets through a selection process that used the Scopus, PubMed, and Web of Science (WoS) databases. A significant increase in the mortality rate of animals exposed to environmental concentrations of atrazine was observed. Nematodes, amphibians, molluscs, insects, and fish showed increased mortality after exposure to atrazine. Animals in the larval and juvenile stages showed greater susceptibility when exposed to different concentrations of atrazine. Furthermore, both commercial and pure formulations resulted in high mortality rates for exposed animals. Atrazine and other pesticides had a synergistic effect, increasing the risk of mortality in animals. There are still many gaps to be filled, and this study can serve as a basis for future regulations involving atrazine.

Simulated climate change and atrazine contamination can synergistically impair zebrafish testicular function

Elements that interfere with reproductive processes can have profound impacts on population and the equilibrium of ecosystems. Global warming represents the major environmental challenge of the 21st century, as it will affect all forms of life in the coming decades. Another coexisting concern is the persistent pollution by pesticides, particularly the herbicide Atrazine (ATZ), which is responsible for a significant number of contamination incidents in surface waters worldwide. While it is hypothesized that climate changes will significantly enhance the toxic effects of pesticides, the actual impact of these phenomena remain largely unexplored. Here, we conducted a climate-controlled room experiment to assess the interactive effects of the projected 2100 climate scenario and environmentally realistic ATZ exposures on the reproductive function of male zebrafish. The gonadosomatic index significantly decreased in fish kept in the extreme scenario. Cellular alterations across spermatogenesis phases led to synergic decreased sperm production and increased germ cell sloughing and death. ATZ exposure alone or combined with climate change effects, disrupted the transcription levels of key genes involved in steroidogenesis, hormone signaling and spermatogenesis regulation. An additive modulation with decreased 11-KT production and increased E2 levels was also evidenced, intensifying the effects of androgen/estrogen imbalance. Moreover, climate change and ATZ independently induced oxidative stress, upregulation of proapoptotic gene and DNA damage in post-meiotic germ cell, but the negative effects of ATZ were greater at extreme scenario. Ultimately, exposure to simulated climate changes severely impaired fertilization capacity, due to a drastic reduction in sperm motility and/or viability. These findings indicate that the future climate conditions have the potential to considerably enhance the toxicity of ATZ at low concentrations, leading to significant deleterious consequences for fish reproductive function and fertility. These may provide relevant information to supporting healthcare and environmental managers in decision-making related to climate changes and herbicide regulation.

Toxicity of water-soluble polymers polyethylene glycol and polyvinyl alcohol for fish and frog embryos

Personal Care Products (PCPs) have been one of the most studied chemicals in the last twenty years since they were identified as pseudo-persistent pollutants by the European Union in the early 2000s. The accumulation of PCPs in the aquatic environment and their effects on non-target species make it necessary to find new, less harmful, substances. Polyethylene glycol (PEGs) and polyvinyl alcohol (PVAs) are two polymers that have increased their presence in the composition of PCPs in recent years, but little is known about the effect of their accumulation in the environment on non-target species. Through embryotoxicity tests on two common models of aquatic organisms (Danio rerio and Xenopus laevis), this work aims to increase the knowledge of PEGs and PVAs' effects on non-target species. Animals were exposed to the pollutant for 96 h. The main embryotoxicity endpoint (mortality, hatching, malformations, heartbeat rate) was recorded every 24 h. The most significant results were hatching delay in Danio rerio exposed to both chemicals, in malformations (oedema, body malformations, changes in pigmentation and deformations of spine and tail) in D. rerio and X. laevis and significant change in the heartbeat rate (decrease or increase in the rate) in both animals for all chemicals tested.

Adsorption behavior of triazine pesticides on polystyrene microplastics aging with different processes in natural environment

The presence of microplastics in the ecological environment, serving as carriers for other organic pollutants, has garnered widespread attention. These microplastics exposed in the environment may undergo various aging processes. However, there is still a lack of information regarding how these aged microplastics impact the environmental behavior and ecological toxicity of pollutants. In this study, we modified polystyrene microplastics by simulating the aging behavior that may occur under environmental exposure, and then explored the adsorption behavior and adsorption mechanism of microplastics before and after aging for typical triazine herbicides. It was shown that all aging treatments of polystyrene increased the adsorption of herbicides, the composite aged microplastics had the strongest adsorption capacity and the fastest adsorption rate, and of the three herbicides, metribuzin was adsorbed the most by microplastics. The interactions between microplastics and herbicides involved mechanisms such as hydrophobic interactions, surface adsorption, the effect of π-π interactions, and the formation of hydrogen bonds. Further studies confirmed that microplastics adsorbed with herbicides cause greater biotoxicity to E. coli. These findings elucidate the interactions between microplastics before and after aging and triazine herbicides. Acting as carriers, they alter the environmental behavior and ecological toxicity of organic pollutants, providing theoretical support for assessing the ecological risk of microplastics in water environments.

Deep degradation of atrazine in water using co-immobilized laccase-1-hydroxybenzotriazole-Pd as composite biocatalyst

The efficient and green removal technology of refractory organics such as atrazine in water has been an important topic of research in water treatment. A novel membrane composite biocatalyst Lac-HBT-Pd/BC as prepared for the first time by co-immobilizing laccase, mediator 1-hydroxybenzotriazole (HBT) and metal Pd on functionalized bacterial cellulose (BC) to investigate the removal of atrazine and degradation of its intermediates under mild ambient conditions. It was found that atrazine could be completely degraded in 5 h by the catalysis of Lac-HBT-Pd/BC, and the removal rate of degradation intermediates from atrazine was about 85% after continuous catalysis, which achieved deep degradation of atrazine. The effect of electrochemical activity and radical stability of the membrane composite biocatalysts loaded with Pd was investigated. The possible degradation pathways were proposed by identifying and analyzing the deep degradation products of atrazine. The Lac-HBT-Pd/BC demonstrated deep degradation of atrazine and favorable reusability as well as considerable adaptability to various water qualities. This work provides an important reference for preparing new kinds of biocatalysts to degrade refractory organic pollutants in water.

The use of integrative tools and multiple models for aquatic environmental quality assessment: a case study of the Mirim Lagoon, Southern Brazil

This study performed toxicity assays with microalgae, microcrustaceans, and fish as well as evaluated biochemical and behavioral biomarkers in fish and microcrustaceans to assess the quality of the surface water of Mirim Lagoon, which belongs to one of the largest hydrographic basins in the world, located in southern Brazil. Three distinct sampling periods were chosen (January, March, and June 2022) based on the rice plantation dynamics which is the main activity surrounding the lagoon. In January, the plantation is irrigated; in March, the water is drained into the Mirim Lagoon, and July is the off-season. Concerning toxicity tests, there was significant inhibition in microalgae growth when exposed to water collected in March, but no mortality was observed for Ceriodaphia dubia, Daphnia magna, and Danio rerio. Regarding biomarkers, behavioral variables contributed more to the higher values of the Integrated Biomarker Response (IBR) index for both D. magna and D. rerio, in March. The Redundancy Analysis (RDA) indicated a correlation between the biomarkers for both organisms and abiotic parameters, mainly nutrients (total phosphorus and total nitrogen), thermotolerant coliforms, total solids, and turbidity. Spatially, there was no difference during monitoring, but the most significant ecotoxicological effects were observed in March. Multivariate analysis and the IBR index proved to be useful tools for monitoring of water bodies such as Mirim Lagoon.

Ecotoxicological insights: Effects of pesticides on ionic metabolism regulation in freshwater catfish, Mystus keletius

Fish maintain their body fluid ionic and osmotic homeostasis using sophisticated iono-/osmoregulation mechanisms through gills ionocytes. Pesticide-induced ionic imbalance in fish has been recognized as a valuable tool to determine its toxic effects. Acute exposure to synthetic and organo-chemical pesticides on the regulation of ionic (Na+, Ca2+, P) metabolism in freshwater catfish Mystus keletius was evaluated. Fish were exposed to sub-lethal concentrations (mg/l) of selected pesticide for a period of 7, 14, 21 and 28 days. Results indicated that chemical pesticides - Impala and Ekalux - evoked adverse toxic effects on selected tissues compared to organo-chemical pesticide tested. Statistical analysis of the summative data using two-way ANOVA was significant (p-value<0.001). Variations in the cellular parameters analysed were attributed to the physiological acclimatization of fish to the pesticide exposed. Based on the results it is concluded that organic pesticides may be preferred for rice field application considering safety aspects.

Delivering on sustainable development goals in wastewater reuse for agriculture: Initial prioritization of emerging pollutants in the Tula Valley, Mexico

Wastewater reuse for agricultural irrigation is a widespread beneficial practice, in line with the sustainable development goals. However, contaminants of emerging concern (CECs) present in wastewater, such as pharmaceuticals, pose an environmental risk. The Tula Valley in Mexico is one of the world's largest agricultural areas reusing wastewater for agriculture. However, no untargeted CEC monitoring has been undertaken there, limiting the information available to prioritise local environmental risk assessment. Furthermore, CEC environmental presence in the Global South remains understudied, compared to the Global North. There is a risk that current research efforts focus on CECs predominantly found in the Global North, leading to strategies that may not be appropriate for the Global South where the pollution profile may be different. To address these knowledge gaps, a sampling campaign at five key sites in the Tula Valley was undertaken and samples analysed using multi-residue targeted and untargeted liquid chromatography mass spectrometry methods. Using the targeted data, ten CECs were found to be of environmental risk for at least one sampling site: 4‑tert-octylphenol, acetaminophen, bezafibrate, diclofenac, erythromycin, levonorgestrel, simvastatin, sulfamethoxazole, trimethoprim and tramadol as well as total estrogenicity (combination of three steroid hormones). Six of these have not been previously quantified in the Tula Valley. Over one hundred pollutants never previously measured in the area were identified through untargeted analysis supported by library spectrum match. Examples include diclofenac and carbamazepine metabolites and area-specific pollutants such as the herbicide fomesafen. This research contributes to characterising the presence of CECs in the Global South, as well as providing site-specific data for the Tula Valley.

Biochemical and histopathological alterations in freshwater fish, Labeo rohita (Hamilton, 1822) upon chronic exposure to a commonly used hopper insecticide, triflumezopyrim

The present study has been carried out to see the long-term effects of triflumezopyrim in an Indian major carp, Labeo rohita. Fishes were exposed to sub-lethal concentrations triflumezopyrim insecticide, 1.41 ppm (Treatment 1), 3.27 ppm (Treatment 2) and 4.97 ppm (Treatment 3), respectively for 21 days. The liver, kidney, gills, muscle, and brain tissues of the fish were examined for physiological parameters and biochemical parameters such as catalase (CAT), superoxide dismutase (SOD), lactate dehydrogenase (LDH), malate dehydrogenase (MDH), alanine aminotransaminase (ALT), aspartate aminotransaminase (AST), acetylcholinessterase (AChE), and hexokinase. After 21 days of exposure, the activity CAT, SOD, LDH, MDH and ALT got increased and a drop in the activity of total protein was found in all treatment groups in comparison to the control group. Long-term triflumezopyrim exposure increased ROS production, ultimately leading to oxidative cell damage and inhibiting the antioxidant capabilities of the fish tissues. Histopathological analysis showed alteration in different tissues structures of pesticide treated fishes. Fishes exposed to highest sublethal concentration of the pesticide showed higher damage rate. The present study demonstrated that chronic exposure of fish to different sublethal concentration of triflumezopyrim exerts detrimental effect on the organism.

Glyphosate-induced liver and kidney dysfunction, oxidative stress, immunosuppression in Nile tilapia, but ginger showed a protection role

The water-borne herbicides are involved in the toxicity of aquatic animals resulting in impaired health status and low productivity. Dietary medicinal herbs present a practical solution to relieve the impacts of herbicides toxicity on the performances of aquatic animals. Herein, we investigated the toxicity of commercial glyphosate-induced oxidative stress, immunosuppression, liver and kidney dysfunction, and the protective role of ginger or ginger nanoparticles in Nile tilapia. Fish were allocated into four groups: the first group presented the control without glyphosate toxicity and ginger feeding, the second group intoxicated with glyphosate at 0.6 mg/L and fed ginger free diet, the third group intoxicated with glyphosate and fed ginger at 2.5 g/kg, and the fourth group intoxicated with glyphosate and fed ginger nanoparticles at 2.5 g/kg. Fish were kept under the experimental conditions for four weeks, and the samples of blood and tissues were collected after 2 and 4 weeks. Markedly, fish exposed to glyphosate showed the highest ALT and AST activities, glucose and cortisol levels, and malondialdehyde levels (MDA) in gills and tissues. While fish in the control and fish intoxicated with glyphosate and fed ginger nanoparticles had the lowest ALT and AST activities, glucose and cortisol levels, and MDA levels after 2 and 4 weeks (P < 0.05). Fish fed dietary ginger had lower ALT and AST activities, glucose and cortisol levels, and MDA levels than the glyphosate intoxicated group after 2 and 4 weeks (P < 0.05). Interestingly, fish-fed ginger nanoparticles showed lower urea and creatinine levels and higher total protein, albumin, and globulin than the glyphosate intoxicated group (P < 0.05) and similar to the control (P > 0.05). Further, fish intoxicated with glyphosate and fed ginger nanoparticles had the highest GSH, lysozyme activity, and immunoglobulin levels after 2 and 4 weeks (P < 0.05). In conclusion, ginger nanoparticles are superior to the standard ginger form in enhancing the antioxidative and immune responses of Nile tilapia exposed to glyphosate.

Evaluation of single and combined effects of mancozeb and metalaxyl on the transcriptional and biochemical response of zebrafish (Danio rerio)

Mancozeb and metalaxyl are fungicidal agents frequently used in combination to control fungi in crops that may affect non-target organisms when entering ecosystems. This study aims to evaluate the environmental effects of Mancozeb (MAN) and Metalaxyl (MET), alone and in combination, on zebrafish (Danio rerio) as an experimental model. The oxidative stress biomarkers and the transcription of genes involved in detoxification in zebrafish (Danio rerio) were assessed after co-exposure to MAN (0, 5.5, and 11 μg L^-1) and MET (0, 6.5, and 13 mg L^-1) for 21 days. Exposure to MAN and MET induced a significant increase in the expression of genes related to detoxification mechanisms (Ces2, Cyp1a, and Mt2). Although Mt1 gene expression increased in fish exposed to 11 μg L^-1 of MAN combined with 13 mg L^-1 of MET, Mt1 expression was down-regulated significantly in other experimental groups (p < 0.05). The combined exposure to both fungicides showed synergistic effects in the expression levels that are manifested mainly at the highest concentration. Although a significant (p < 0.05) increase in alkaline phosphatase (ALP) and transaminases (AST and ALT), catalase activities, the total antioxidant capacity, and malondialdehyde (MDA) contents in the hepatocytes of fish exposed to MAN and MET alone and in combination was detected, lactate dehydrogenase (LDH), gamma-glutamyl transferase (GGT) activities, and hepatic glycogen content decreased significantly (p < 0.05). Overall, these results emphasize that combined exposure to MET and MAN can synergistically affect the transcription of genes involved in detoxification (except Mt1 and Mt2) and biochemical indicators in zebrafish.

Sodium valproate exposure influences the expression of pparg in the zebrafish model

Valproic acid (VPA) is an anti-epileptic drug used alone or in combination with other medications to treat seizures, mania, and bipolar disorder. VPA recognized as a teratogenic chemical can cause severe birth defects mainly affecting the brain and spinal cord when administered during pregnancy. However, the potential mechanisms of developmental toxicity are still less studied, and in the present study, the influence of VPA exposure was evaluated on zebrafish early-life stages. Zebrafish were exposed to two sublethal concentrations of sodium valproate (SV) (0.06 mM and 0.15 mM) from 24 hours post-fertilization (hpf) to 96 hpf and the SV teratogenic potential was investigated through morphometric analysis of zebrafish larvae combined with the evaluation of cartilage profile. Moreover, the effect of SV on the transcription level of pparg was also performed. The results of the study showed the teratogenic potential of SV, which disrupts the morphometric signature of the head and body. The marked distortion of cartilage structures was paralleled to a malformation of telencephalon and optic tectum in both concentrations suggesting a high teratogen effect of SV on the brain. These data were further confirmed by the increased expression of pparg in the zebrafish head. Overall, the present study confirms the teratogenic activity of SV in the zebrafish model and, for the first time, points out the potential protective role of pparg in the SV dose-dependent toxicity.

Sublethal effects of the herbicides atrazine and glyphosate at environmentally relevant concentrations on South American catfish (Rhamdia quelen) embryos

The objective of this work was to evaluate the effects following exposure (96 h) of South American catfish (R. quelen) embryos to active ingredients and commercial formulations from atrazine and glyphosate, isolated and in mixtures, at environmentally relevant concentrations. While the survival rates were not affected, sublethal effects were evidenced after exposure. The most frequent deformities were fin damage and axial and thoracic damage. The mixture of active ingredients caused an increase in SOD and GST, differing from the treatment with the mixture of commercial formulations. The activity of AChE was significantly reduced following the treatment with the active ingredient atrazine and in the mixture of active ingredients. In general, herbicide mixtures were responsible for causing more toxic effects to R. quelen embryos. Therefore, these responses showed to be suitable biomarkers of herbicides' exposure, in addition to generating more environmentally relevant baseline data for re-stablishing safety levels of these substances in aquatic bodies.

Synergistic effect of environmental food pollutants: Pesticides and marine biotoxins

Emerging marine biotoxins such as ciguatoxins and pyrethroid compounds, widely used in agriculture, are independently treated as environmental toxicants. Their maximum residue levels in food components are set without considering their possible synergistic effects as consequence of their interaction with the same cellular target. There is an absolute lack of data on the possible combined cellular effects that biological and chemical pollutants, may have. Nowadays, an increasing presence of ciguatoxins in European Coasts has been reported and these toxins can affect human health. Similarly, the increasing use of phytosanitary products for control of food plagues has raised exponentially during the last decades due to climate change. The lack of data and regulation evaluating the combined effect of environmental pollutants with the same molecular target led us to analyse their in vitro effects. In this work, the effects of ciguatoxins and pyrethroids in human sodium channels were investigated. The results presented in this study indicate that both types of compounds have a profound synergistic effect in voltage-dependent sodium channels. These food pollutants act by decreasing the maximum peak inward sodium currents and hyperpolarizing the sodium channels activation, effects that are boosted by the simultaneous presence of both compounds. A fact that highlights the need to re-evaluate their limits in feedstock as well as their potential in vivo toxicity considering that they act on the same cellular target. Moreover, this work sets the cellular basis to further apply this type of studies to other water and food pollutants that may act synergistically and thus implement the corresponding regulatory limits taking into account its presence in a healthy diet.

Sub-lethal acute effects of environmental concentrations of inorganic mercury on hematological and biochemical parameters in walking catfish, Clarias batrachus

The acute toxicity of mercury to the air-breathing fish Clarias batrachus (Linn.) was determined in this study using hematological (including hemoglobin, hematocrit, total erythrocyte count, total leukocyte count, and mean corpuscular hemoglobin concentration) and biochemical (including total serum protein, serum glucose, triglyceride, cholesterol, albumin) biomarkers at predetermined exposure concentrations (0.069 and 0.139 mg/L). Although significant differences were observed between exposure groups for all hematological and biochemical variables, a distinctive reduction in hemoglobin levels, hematocrit, and total erythrocyte count in the mercury-exposed fish compared to the control was observed from 24 h-96 h. Similarly, marked differences in serum globulin, total serum protein and cholesterol levels were observed across exposure groups from 24 h-96 h. While the marked hematological responses strongly suggestive of toxicant-related anemia, the marked biochemical responses suggest immune-modulation and metabolic disruption. The magnitude of toxic effects under graded toxicant exposures for weighted scores of combined biomarker response index (IBR) indicated an approximately 3-fold deterioration in overall health of mercury-exposed fish compared to control group. Depictions of hematological and biochemical effects in hardy species like Clarias batrachus indicate an imminent onset of anemia, immune-modulation and metabolic disruption within 24hs of exposure to inorganic mercury. Such observations for portends greater deleterious effects to less hardy aquatic biota under acute inorganic mercury environmental exposures.

Ecogenotoxicity of environmentally relevant atrazine concentrations: A threat to aquatic bioindicators

Atrazine (ATZ) is a herbicide that is frequently present in surface waters and may result in damage to the health of various organisms, including humans. However, most scientific literature reports injuries caused by ATZ at high concentrations, which are not found in the environment. Therefore, the scope of this study was to investigate the impacts of realistic concentrations of ATZ found in surface waters (1, 2, 5, 10, 15 and 20 μg/L) using the bioindicators Allium cepa, Daphnia magna and zebrafish (Danio rerio). ATZ elicited a genotoxic effect in A. cepa, manifested by the induction of chromosomal aberrations, and a mutagenic effect with increased incidence of micronuclei formation, promotion of cell death and reduction in nuclear size revealed by flow cytometry analysis. D. magna exposed to 10, 15 and 20 μg/L of ATZ showed significant reduction in body size after 21 days, delayed first-brood release, decreased egg production and total offspring, as well as swimming behavioral changes. ATZ exposure promoted physiological and developmental alterations in zebrafish embryos, including an increased spontaneous movement rate, which led to premature hatching at all concentrations investigated. Increase in total body length, decrease of the yolk sac area, pericardial edema and higher heart rate were also detected in ATZ-treated zebrafish. In summary, environmentally relevant concentrations of ATZ can induce substantial alterations in the three bioindicators investigated. This study evidences the deleterious effects of ATZ on three aquatic bioindicators employing established and current techniques, and may contribute to elucidate the risks caused by this widely used herbicide even at low concentrations and short-to-medium-term exposure.

Potential biomarker of phenol toxicity in freshwater fish C. mrigala: Serum cortisol, enzyme acetylcholine esterase and survival organ gill

In this modern industrialized era of large-scale production of agrochemicals, various emerging contaminants form the main components of waste water and sludge in most of the developing countries of the world. In this concern, phenol- an inevitable and alarming chemical pollutant in aquatic ecosystem, gains a speedy access into the water bodies as an industrial by-product. Though the detrimental effects of phenol have been studied in various aspects of aquatic life, current study is an initiative to unravel the toxic effects of phenol at molecular level in Cirrhinus mrigala. Plasma cortisol level and acetylcholine esterase activity in fish was estimated by Chemiluminescent immunoassay technique and Ellman assay respectively. Scanning electron microscopic studies were carried out to unravel the gill histopathological alterations in exposed fish. It was observed that phenol (22.32 mg/l) inhibits 50 % of acetylcholine esterase activity in brain thereby affecting the locomotion of the targeted carp. Cortisol elevated during the 7th day in exposed fish, but declined progressively on the forthcoming 21st and 28th days. Manifestations in gill encompass curling, fusion, aberrations, sloughing of gill epithelium, wider inter filamentary space and mucus coating in the primary gill filament. It concludes that the discernable deviations produced in both biochemical parameters and key organ gill can be used as a biomarker and bio-indicator respectively for assessing the existence of emerging toxicants in aquatic ecosystem.

Abamectin promotes behavior changes and liver injury in zebrafish

The indiscriminate use of pesticides is a worldwide concern due to the environment contamination since it can cause deleterious effects to non-target organisms including the fishes. The effects of abamectin, a pesticide from the avermectin family, were evaluated in adult zebrafish (Danio rerio) after exposure to a commercial formula commonly used in Brazil. The animals were submitted to acute (96 h) and to a short-term chronic exposure (15 days) of distinct concentrations of abamectin. LC50 was determined and a histological study followed by an immunohistochemistry analysis for P-gp and HSP70 identification were performed on livers of the animals submitted to the acute and chronic treatment, respectively. Moreover, behavior patterns were observed daily in both trials. A LC50 value of 105.68 μg/L was determined. The histological analysis revealed a morphological alteration of the hepatocytes, glycogen accumulation, degeneration, and disorganization of the cytoplasm, and a pyknotic, irregular, and laterally located nuclei. The immunohistochemistry for HSP70 and P-gp showed strong staining in the hepatocytes of the control groups and progressive decrease as the concentration of abamectin increased. Changes were observed in body posture, movement around the aquarium, opercular activity, body color and search for food in the groups treated with abamectin. The results presented suggest that abamectin can affect the behavioral pattern of the animals, promote morphological changes, and decrease the expression of HSP70 and P-gp in zebrafish liver.

Ultimate fate and possible ecological risks associated with atrazine and its principal metabolites (DIA and DEA) in soil and water environment

Atrazine (AT) is a triazine herbicide widely used to control weeds in several crops. De-isopropylatrazine (DIA) and de-ethylatrazine (DEA) are two of the eight primary metabolites produced by AT breakdown in soil and water. The physico-chemical properties of the soil determine their final fate. So, this study aimed to assess the function of clay loam and sandy loam soils in determining their ultimate fate and the potential ecological risks to non-target species during their persistence in soil and transportation to water bodies. The soil in pots was spiked with standard solutions of AT, DEA, and DIA at 0.3 and 0.6 mg/kg for the persistence study. The leaching potential was determined by placing soils in Plexi columns and spiking them with 50 and 100 µg standard solutions. Liquid-liquid extraction was used to prepare the samples, which were then analyzed using GC-MS/MS. The dynamics of dissipation were first-order. AT, DEA and DIA disappeared rapidly in sandy loam soil, with half-lives ranging from 6.2 to 8.4 days. AT and its metabolites had a significant amount of leaching potential. In sandy loam soil, leaching was more effective, resulting in maximal residue movement up to 30-40 cm soil depth. The presence of a notable collection of residues in leachate fractions suggests the potential for surface and groundwater contamination. In particular, DEA and DIA metabolites caused springtail Folsomia candida and earthworm Eisenia fetida to have longer and greater unacceptable risks. If the residues comparable to the amount acquired in leachate fractions reach water bodies, they could cause toxicity to a variety of freshwater fish, aquatic arthropods, amphibians, and aquatic invertebrates. Future studies should take a more comprehensive approach to evaluate ecological health and dangers to non-target species.

Adverse effects of herbicides in freshwater Neotropical fish: A review

Although herbicides have been developed to act on the physiological processes of plants, they are responsible for causing deleterious effects on animals. These chemical compounds are widely used throughout the world, but especially in countries that export agricultural products such as Central and South America, their use has increased in recent years. Aquatic environments are natural reservoirs of herbicides, which after being applied on crops, run off through the soil reaching rivers, lakes, and oceans. Fish are among the many organisms affected by the contamination of aquatic environments caused by herbicides. These animals play an important ecological role and are a major source of food for humans. However, few studies address the effects of herbicides on fish in this region. Thus, in the present review we discuss the morphophysiological and molecular consequences of herbicide exposure in Neotropical fish systems as well as how the environmental and land use characteristics in this region can influence the toxicity of these pollutants. A toxicity pathway framework was developed summarizing the mechanisms by which herbicides act and endpoints that need to be further investigated.

Exposure to levonorgestrel-based birth control pill in early life and its persistent effects in zebrafish

The consumption of progestins has increased considerably in recent decades, as has their disposal into the environment. These substances can negatively affect the reproduction, physiology, and behavior of non-target organisms, such as fish. We aimed to evaluate the effects of exposure to environmentally relevant concentrations of levonorgestrel-control birth based (1.3, 13.3, 133, and 1330 ng/L) on the development and behavior of zebrafish (Danio rerio) in terms of mortality, hatching, spontaneous movement, and larval and adult behavioral tests. Exposure caused anxiogenic-like behavior in larvae, which persisted in adults, as demonstrated by the light-dark test. In contrast, it caused anxiolytic-like behavior in the novel tank test. There was a high mortality rate at all tested concentrations and increases in the hormone cortisol at 13.3 ng/L that affected the sex ratio. These changes may lead to an ecological imbalance, emphasizing the risk of early exposure to progestins in the environment.

Impact of pharmaceutical products on zebrafish: An effective tool to assess aquatic pollution

Overuse of pharmaceuticals products (PPs) and sometimes ineffective wastewater purification systems have led to the accumulation of these residues in aquatic systems. Raising concerns about the likely harmful effects of these substances both to ecosystems and to human health. Animals as model organisms are nowadays increasingly used to track the health of environmental system around the world. They can be used to understand biological processes, to obtain information on the health status of the environment, and to better understand the effects of xenobiotics on organisms. Among model organisms, the zebrafish (Danio rerio) is one of the best models for studying evolution biology, cancer, toxicology, drug discovery, and genetics. This fish is a multipurpose model organism, due to its easy of maintenance and keeping and the transparency of the embryo during the early stages of development. In this paper, the toxicological effects of typical PPs, and their effects on zebrafish are reviewed. Many PPs have been found to be toxic or even fatal to zebrafish. Showing how these pharmaceuticals compound can affect zebrafish from the larval stage and even in the adult stage. Zebrafish is thus a model for how we can better understand how medications affect not only individual fish but the entire aquatic ecosystem, bringing about perturbations in their behaviour and putting their survival at risk.

Are BPA-free plastics safe for aquatic life? - Fluorene-9-bisphenol induced thyroid-disrupting effects and histopathological alterations in adult zebrafish (Danio rerio)

Fluorene-9-bisphenol (BPFL) is used as an alternative compound for bisphenol A, an endocrine disruptor compound which is present in various materials including plastic bottles and packaging. Although it is used extensively in products that are labelled BPA-free, its effect on wildlife and humans have not been fully studied. Therefore, this study aimed to investigate the effects of BPFL in adult zebrafish. In the preliminary experiments of the study, the median lethal concentration value (LC₅₀) of BPFL was 0.25 mg/L (95 % confidence interval 0.15-0.41) for 96 h. Following exposure to three different sublethal concentrations of BPFL after 96 h and 15 days, T4 hormone levels, expression levels of genes involved in thyroid metabolism and histopathological alterations were assessed. T4 hormone levels were found to be significantly higher in females at the lowest BPFL concentration following 96 h exposure (P < 0.05). Expression levels of trh, tshba and trhrb genes were upregulated following 96 h exposure at 0.025 mg/L concentration and crh was upregulated following 15 days exposure at 0.025 mg/L concentration in female zebrafish (P < 0.05). The most prominent histopathological findings in zebrafish exposed to 0.025 and 0.125 mg/L of BPFL were observed in the gill, liver, kidney and testis tissues. The gill tissues showed some hyperemia, lamellar fusion, hyperplasia, epithelial lifting, and telangiectasis, while passive hyperemia, hydropic degeneration, and necrosis were observed in the liver tissues. The BPFL is highly toxic to zebrafish even in sublethal concentrations according to the molecular and histopathological responses.

Impacts of cetylpyridinium chloride on the behavior and brain neurotransmitter levels of juvenile and adult zebrafish (Danio rerio)

Cetylpyridinium chloride (CPC) is a cationic surfactant that has been widely used as an antibacterial ingredient in pharmaceutical and personal care products. Due to its high residue in surface waters, there is increasing concern over the potential risk of CPC to aquatic ecosystems. However, knowledge of its impacts on fish is still limited. Therefore, this study exposed juvenile and adult zebrafish to CPC (0, 10, and 40 μg/L) for four days. Subsequently, changes in their behavioral traits and brain levels of several neurotransmitters were investigated. The behavioral assay showed that CPC exposure significantly decreased the locomotor activity and social interaction of zebrafish at both life stages, and juveniles were more sensitive to CPC exposure than adults. In the control groups, the brain neurotransmitters concentrations increased with age in zebrafish. However, CPC exposure tended to increase the brain neurotransmitter levels of juveniles but decreased their levels in adults. Correlation analysis revealed that the brain monoamine neurotransmitters and their turnover might play important roles in the life stage-dependent behavioral response to CPC. In particular, the DOPAC/DA ratio was significantly associated with CPC-induced hypoactivity and reduced social interactions in juveniles but not adults. Our findings demonstrated that CPC exposure could cause abnormal behavior in juvenile and adult zebrafish and disturb their brain neurotransmitters, even at environmentally relevant concentrations, and thus highlighted the necessity for further assessing its potential risks to aquatic ecosystems.

Transcriptome profiling reveals toxicity mechanisms following sertraline exposure in the brain of juvenile zebrafish (Danio rerio)

Sertraline (SER) is one of the most commonly detected antidepressants in the aquatic environment that can negatively affect aquatic organisms at low concentrations. Despite some knowledge on its acute toxicity to fish, the effects of chronic SER exposure remain poorly understood along with any underlying mechanisms of SER-induced toxicity. To address this knowledge gap, the effects of chronic exposure to three SER concentrations from low to high were investigated in zebrafish. Juvenile zebrafish were exposed to three concentrations of 1, 10, or 100 μg/L of SER for 28 d, after which indicators of oxidative stress and neurotoxicity in the brain were measured. Superoxide dismutase (SOD) activity was significantly enhanced by SER at 1 up to 100 μg/L, and catalase (CAT) activity was significantly induced by SER at 1 or 10 μg/L. The activity of acetylcholinesterase (AChE) was significantly induced by 10 and 100 μg/L of SER, and the serotonin (5-HT) level was significantly increased by all three concentrations of SER. To ascertain mechanisms of SER-induced toxicity, transcriptomics was conducted in the brain of zebrafish following 100 μg/L SER exposure. The molecular signaling pathways connected with circadian system and the immune system were significantly altered in the zebrafish brain. Based on transcriptomic data, the expression levels of six circadian clock genes were measured, and three genes were significantly altered in relative abundance in fish from all experimental treatments with SER, including cryptochrome circadian regulator 2 (cry2), period circadian clock 2 (per2), and period circadian clock 3 (per3). We hypothesize that the circadian system may be related to SER-induced neurotoxicity and oxidative stress in the central nervous system. This study reveals potential mechanisms and key events (i.e., oxidative stress and neurotoxicity) associated with SER-induced toxicity, and improves understanding of the molecular and biochemical pathways putatively perturbed by SER.

Antioxidant enzyme activity and pathophysiological responses in the freshwater walking catfish, Clarias batrachus Linn under sub-chronic and chronic exposures to the neonicotinoid, Thiamethoxam®

The hydrophilic nature and resultant persistence of neonicotinoids in aquatic systems increase the exposure duration for non-target organisms. The sublethal toxicity of the neonicotinoid Thiamethoxam® spanning sub-chronic and chronic durations was investigated in Clarias batrachus, a non-target freshwater fish species. 96 h LC₅₀ value of Thiamethoxam® on Clarias batrachus was 138.60 mg L^-1. Pre-determined exposure concentrations of Thiamethoxam® (6.93 and 13.86 mg L^-1) were used and effects were assessed at days 15, 30, and 45 exposure intervals. Biomarker effects were evaluated using antioxidant enzyme responses (CAT, SOD) neurotransmission (acetylcholinesterase activity), haematological and serum biochemistry changes (including haemoglobin content, total erythrocyte count, and serum albumin total leukocyte count, total serum protein, serum globulin, triglyceride, cholesterol, high-density lipoprotein, very low-density lipoprotein, low-density lipoprotein, phospholipid, and total serum glucose), histopathological alterations (gill and liver). Thiamethoxam®-exposed fish showed a marked reduction in haemoglobin content, total erythrocyte count, and serum albumin levels compared to control fish. Similarly, gill and liver antioxidant enzyme activity (CAT, SOD) and neurotransmission (acetylcholinesterase) also showed altered responses between sub-chronic exposure on day-15 and chronic responses on day-45. Histopathological observations in gill tissue revealed alterations ranging from vacuolation, hypertrophy, disruption of primary lamellar architecture, haemorrhage, the fusion of secondary lamella, and sloughing of outer epithelia. For liver tissue of exposed fish histopathological observations included increased sinusoidal spaces (ISS), necrosis of hepatocytes (NOH), nuclear degeneration (ND), disruption of architecture (DOA), macrophage infiltration of the central vein, vacuolation (V), hypertrophied hepatocytes, and haemorrhages. The gradients of toxic responses across exposure concentrations and depictions of impaired fish health with increasing thiamethoxam® exposure duration portend lowered physiological capacity for survival in the wild.

Ecotoxicological Effects of Pesticides on Hematological Parameters and Oxidative Enzymes in Freshwater Catfish, Mystus keletius

Hematological parameters and changes in stress-induced functionalities of cellular enzymes have been recognized as valuable tools for monitoring fish health and determining the toxic effects of pesticides. The present study was conducted to evaluate the toxic effect of selected pesticides viz., Ekalux (EC-25%), Impala (EC-55%), and Neemstar (EC-15%) on freshwater catfish Mystus keletius. Fish were exposed to sub-lethal concentrations (mg/L) of the selected pesticide for a period of 7, 14, 21, and 28 days. Hematological parameters viz., total erythrocyte (RBC), hemoglobin (Hb), and hematocrit (Ht) packed cell volume values decreased with an increase in exposure time to pesticides, whereas the values for parameters viz., leucocytes (WBC), mean corpuscular hemoglobin concentration (MCHC), mean corpuscular volume (MCV), and mean corpuscular hemoglobin (MCH) increased significantly. A decrease in packed cell volume (PCV) and hemoglobin values coupled with decreased and deformed erythrocytes as signs of anemia were also observed. The effect of pesticides on RBC content was 1.43 (million/mm3) on day 7 and reduced to 1.18 (million/mm3) on days 14 and 21. A similar trend was found for Impala on RBC, which had an initial value of 1.36 (million/mm3) on day 7 and reached a value of 1.10 (million/mm3) on day 28. In contrast, the value of Neemstar decreased from 1.59 (million/mm3) on day 7 in control to 1.02 (million/mm3) on day 28. Data indicates that the order of toxic effect of pesticides recorded a maximum for Impala followed by Ekalux and Neemstar in the selected fish model. Likewise, the overall pattern of pesticidal activity on cellular enzymes (GDH, MDH, and SDH) recorded a maximum toxic effect for Impala followed by Ekalux and Neemstar. Results indicate that Chlorpyrifos pesticide-Impala evoked maximum toxic effect on selected tissues compared to the other two pesticides tested. Statistical analysis of the summative data using two way ANOVA was statistically significant (p-value < 0.001). The differences in the hematological parameters analyzed are attributed to the physiological acclimatization of the fish to the local conditions, which influences the energy metabolism and consequently determines the health status of the fish. Overall, Impala exhibited the highest pesticidal activity on cellular enzyme, followed by Ekalux and Neemstar. Results suggest that natural pesticides may be preferable for rice field application in terms of environmental safety.

Effects of environmentally relevant concentrations of atrazine and glyphosate herbicides, isolated and in mixture, on two generation of the freshwater microcrustacean Daphnia magna

The herbicides atrazine and glyphosate are used worldwide and their excessive usage results in the frequent presence of these pesticides in environmental compartments. We evaluated the effects of environmentally relevant concentrations of analytical standards and commercial formulations of atrazine (2 µg L-1) and glyphosate (65 µg L-1), isolated and in mixture (2 + 65 µg L-1) on the microcrustacean Daphnia magna. Through chronic exposure (21 days) of two generations, we observed effects on survival, reproductive capacity and responses of the antioxidant defense system (catalase) and biotransformation system (glutathione S-transferase). The survival of organisms was affected in the second generation (F1) with a mortality of 17% in the mixture of commercial formulations treatments. In the evaluation of the first generation (F0) we observed only effects on sexual maturation of organisms, while in the F1, changes were observed in all parameters evaluated. A statistical difference (p < 0.05) was also observed between the analytical standards and the commercial formulations for all parameters evaluated, indicating that other components present in the formulations can change the toxicity of products. We suggest that atrazine can modulate toxicity when mixed with glyphosate, as the standard analytical atrazine and mixture of analytical standards results were similar in most parameters. Given the difficulty in estimating effects of mixtures and considering that various stressors are found in the environment, our results support the need to carry out long-term studies and, above all, to verify what are the impacts across generations, so that the toxicity of products is not underestimated. Graphical abstract.

Evaluation of toxicity of Personal Care Products (PCPs) in freshwaters: Zebrafish as a model

Personal care products (PCPs) are part of the large and growing family of emerging contaminants (ECs). Many daily products such as sunscreens, toothpaste, make-up products, perfume, and others, fall under this definition, and their use is increasing exponentially. Furthermore, the degradation of some components of these products is limited. Indeed, they are able to easily reach and accumulate in aquatic systems, representing a new class of contaminants. Moreover, due to their chemical properties, they can interfere at different biological levels, and for this reason, they need to be thoroughly investigated. We have reviewed the literature on PCPs, with a special focus on the adverse effects on the freshwater zebrafish (Danio rerio). The aim of this work is to provide a careful assessment of the toxicity of these compounds, in order to raise awareness for more conscious and responsible use.

Protective effect of protexin concentrate in reducing the toxicity of chlorpyrifos in common carp (Cyprinus carpio)

The present study aimed to evaluate the protective effect of protexin supplementation against chlorpyrifos-induced oxidative stress and immunotoxicity in Cyprinus carpio. After 21 days, the activity of superoxide dismutase (SOD), glutathione peroxidase (GPx) and glutathione reductase (GR), and total antioxidant levels significantly decreased in hepatocytes of fish exposed to chlorpyrifos, while malondialdehyde (MDA) increased. Treatment with protexin was able to reverse the decrease in SOD and GR and significantly reduce MDA levels. Exposure to chlorpyrifos also induced alterations in blood biochemical parameters and caused immunosuppression. Dietary protexin return some parameters (aspartate aminotransferase, lactate dehydrogenase, and γ-glutamyltransferase activities, and glucose, cholesterol, total protein, creatinine, and complement C4 levels) to values similar to those of the control group. Based on the results, it can be concluded that protexin exerted protective effects against chlorpyrifos exposure in C. carpio reducing oxidative damage, and ameriorating blood biochemical alterations and the immunosuppression.

Effects of Diazinon on the Survival, Blood Parameters, Gills, and Liver of Grass Carp (Ctenopharyngodon idella Valenciennes, 1844; Teleostei: Cyprinidae)

Diazinon (DZN) is a widely used pesticide that can affect the vital organs of non-target aquatic animals—mainly fish. This study evaluated the acute toxicity (LC50) of six DZN concentrations (0.5, 0.75, 1.5, 2, 2.5, and 3 mg·L−1) and, based on its evaluation after 24 h, 48 h, 72 h, and 96 h, two sublethal concentrations for chronic toxicity testing (0.01 and 0.05 mg·L−1) for 21 days of exposure to DZN on grass carp fingerlings (Ctenopharyngodon idella Valenciennes, 1844). The median lethal concentrations of DZN at 24, 48, 72, and 96 h were 1.83, 1.57, 1.35, and 1.12 mg·L−1, respectively. Next, histological observations after 96 h LC50 showed oedema of the primary lamellae of the gills at low pesticide concentrations (0.5 to 1 mg·L−1) and extensive necrosis of primary lamellae of the gills at higher concentrations (1.5 to 3 mg·L−1). Moreover, cytoplasmic vacuolation and extensive necrosis were observed in liver tissue. Increased skin mucus, unbalanced swimming on the water surface, and increased gill opercula movements were noted during chronic exposure. Haematological parameters such as haematocrit, red blood cell count, white blood cell count, haemoglobin, and mean corpuscular volume were significantly reduced after 21 days of exposure to 0.05 mg·L−1 of DNZ (p < 0.05). The present study shows that DZN has various toxic effects on grass carp, which may pose a potential risk for other fish species.

Atrazine and Diuron Effects on Survival, Embryo Development, and Behavior in Larvae and Adult Zebrafish

Atrazine and Diuron are widely used herbicides. The use of pesticides contaminates the aquatic environment, threatening biodiversity and non-target organisms such as fish. In this study, we investigated the effects of acute exposure for 96 h hours to atrazine and diuron commercial formulations in zebrafish (Danio rerio, wild-type AB) embryos and larvae and adult stages. We observed a significant concentration-dependent survival decrease and hatching delays in animals exposed to both herbicides and in the frequency of malformations compared to the control groups. Morphological defects included cardiac edema, tail reduction, and head malformation. At 7 days post-fertilization (dpf), atrazine exposure resulted in a reduction in the head length at 2, 2.5, and 5 mg/L and increased the ocular distance at 1, 2, 2.5, and 5 mg/L atrazine when compared to controls. At the same age, diuron increased the ocular distance in animals exposed to diuron (1.0 and 1.5 mg/L) and no effects were observed on the head length. We also evaluated a behavioral repertoire in larvae at 7 dpf, and there were no significant differences in distance traveled, mean speed, time in movement, and thigmotaxis for atrazine and diuron when animals were individually placed in a new environment. The cognitive ability of the larvae was tested at 7 dpf for avoidance and optomotor responses, and neither atrazine nor diuron had significant impacts when treated groups were compared to their corresponding controls. Adults’ behavior was evaluated 7 and 8 days after the end of the acute herbicide exposure. Exploration of a new environment and associated anxiety-like parameters, social interaction, and aggressiveness were not altered. Our results highlight the need for further studies on the sublethal effects of both herbicides and the consideration of the effects of commercial formulas vs. isolated active ingredients. It also emphasizes the need to take sublethal effects into consideration when establishing the environmental limits of residues.

Historical exposure to chemicals reduces tolerance to novel chemical stress in Daphnia (waterflea)

Until the last few decades, anthropogenic chemicals used in most production processes have not been comprehensively assessed for their risk and impact on wildlife and humans. They are transported globally and usually end up in the environment as unintentional pollutants, causing long‐term adverse effects. Modern toxicology practices typically use acute toxicity tests of unrealistic concentrations of chemicals to determine their safe use, missing pathological effects arising from long‐term exposures to environmentally relevant concentrations. Here, we study the transgenerational effect of environmentally relevant concentrations of five chemicals on the priority list of international regulatory frameworks on the keystone species Daphnia magna. We expose Daphnia genotypes resurrected from the sedimentary archive of a lake with a known history of chemical pollution to the five chemicals to understand how historical exposure to chemicals influences adaptive responses to novel chemical stress. We measure within‐ and transgenerational plasticity in fitness‐linked life history traits following exposure of “experienced” and “naive” genotypes to novel chemical stress. As the revived Daphnia originate from the same genetic pool sampled at different times in the past, we are able to quantify the long‐term evolutionary impact of chemical pollution by studying genome‐wide diversity and identifying functional pathways affected by historical chemical stress. Our results suggest that historical exposure to chemical stress causes reduced genome‐wide diversity, leading to lower cross‐generational tolerance to novel chemical stress. Lower tolerance is underpinned by reduced gene diversity at detoxification, catabolism and endocrine genes in experienced genotypes. We show that these genes sit within pathways that are conserved and potential chemical targets in other species, including humans.

Persistent impact of amitriptyline on the behavior, brain neurotransmitter, and transcriptional profile of zebrafish (Danio rerio)

Discontinuation of amitriptyline (AMI) has been demonstrated to induce long-term withdrawal syndromes in mammals. However, no studies have focused on the persistent impacts of short-term AMI exposure on teleosts. Here, following exposure to AMI (2.5 and 40 μg/L) for 7 days (E7), zebrafish were transferred into AMI-free water to recover for 21 days (R21). The behavior, brain neurotransmitters, and brain transcriptional profiles were investigated on E7 and R21. AMI exposure induced persistent hypoactivity (2.5 and 40 μg/L) and abnormal schooling behavior (40 μg/L). AMI also induced long-term impacts on the brain serotonin (5-HT), 5-hydroxyindoleacetic acid, norepinephrine, and acetylcholine levels, several of which showed significant correlations with the locomotor activity or schooling behavior. Transcriptional analysis revealed persistent dysregulation in the pathways involved in the circadian rhythm, glycan biosynthesis and metabolism, and axon guidance in brain samples. Twelve genes were predicted as key driver genes in response to AMI exposure, and their significantly differential expression may direct changes across the related molecular networks. Moreover, upregulated brain 5-HT may serve as the central modulator of the persistent AMI pathogenesis in zebrafish. Considering AMI residues in natural waters may temporarily exceed μg/L, corresponding persistent adverse effects on teleosts should not be ignored.

Biomolecular alterations in the early life stages of four food fish following acute exposure of Triclosan

We investigated the effect of acute concentrations of triclosan (TCS; 96 h exposure and 10d post exposure) on the free amino acid, primary (SDS-PAGE) and secondary (FT-IR) structure of proteins in the embryos/larvae of Cyprinus carpio, Ctenopharyngodon idella, Labeo rohita and Cirrhinus mrigala. A concentration dependent increase in free amino acids, upregulation of polypeptides (100 and 70 kDa in C. carpio, C. idella and L. rohita, 55, 45, 36 kda in C. idella and L. rohita and 22 kDa in all the fish) and a decline in percent area of all the selected peaks of the FT-IR spectra was observed after exposure and recovery period. The decline in percent area was greatest for L. rohita at peak 1080 - 1088 cm^-1 (-75.99%) after exposure and at peak 2854 - 2855 cm^-1 (-53.59%) after recovery. Curve fitting analysis revealed a decrease in α-helices and increase in β-sheets in all fish after exposure and recovery period. The results suggest that TCS elicits alterations in biomolecules of fish embryos.

Commonly used surfactants sodium dodecyl sulphate, cetylpyridinium chloride and sodium laureth sulphate and their effects on antioxidant defence system and oxidative stress indices in Cyprinus carpio L.: an integrated in silico and in vivo approach

The present study evaluated the homology modelling, in silico prediction and characterization of Cyprinus carpio cytochrome P450, as well as molecular docking experiments between the modelled protein and the surfactants sodium dodecyl sulphate (SDS), sodium laureth sulphate (SLES) and cetylpyridinium chloride (CPC). Homology modelling of cytochrome P450 was performed using the best fit template structure. The structure was optimized with 3D refine, and the ultimate 3D structure was checked with PROCHEK and ERRATA. ExPASy's ProtParam was likewise used to analyse the modelled protein's physiochemical and stereochemical attributes. To establish the binding pattern of each ligand to the targeted protein and its effect on the overall protein conformation, molecular docking calculations and protein-ligand interactions were performed. Our in silico analysis revealed that hydrophobic interactions with the active site amino acid residues of cytochrome p450 were more prevalent than hydrogen bonds and salt bridges. The in vivo analysis exhibited that exposure of fish to sublethal concentrations (10% and 30% of 96 h LC₅₀) of SDS (0.34 and 1.02 mg/l), CPC (0.002 and 0.006 mg/l) and SLES (0.69 and 2.07 mg/l) at 15d, 30d and 45d adversely affected the oxidative stress and antioxidant enzymes (CAT, SOD, GST, GPx and MDA) in the liver of Cyprinus carpio. As a result, the study suggests that elicited oxidative stress, prompted by the induction of antioxidant enzymes activity, could be attributable to the stable binding of cytochrome P450 with SDS, CPC and SLES which ultimately leads to the evolution of antioxidant enzymes for its neutralization.

Effects of different pharmaceutical residues on embryos of fish species native to Central Europe

Environmental concentrations of pharmacologically active substances are increasing dramatically throughout the world, to the point where they are now considered a serious threat to the aquatic environment. This high occurrence of pharmaceutical residues in the aquatic environment is due to an increase in i) the prescription and consumption of drugs, and ii) their subsequent discharge into wastewater and its imperfect purification in wastewater treatment plants. Recent surveys have clearly shown that such substances can have serious negative effects on non-target organisms. In the present study, we tested the effects of several commonly used pharmaceuticals, such as antidepressants, analgesics and antibiotics, on the embryonic stages of different fishes. Specifically, we applied concentration ranges of tramadol, enrofloxacin and nortriptylined on a common toxicological model organism, the zebrafish (Danio rerio), and other species native to Central European freshwaters, i.e. common carp (Cyprinus carpio), catfish (Silurus glanis) and tench (Tinca tinca). Our results show that, though malformation and negative impacts on hatching and mortality were only observed at the highest test concentrations, gene expression indicated that even low environmentally relevant concentrations (0.1 μg/L) can cause significant changes in early development of embryo.

Induction of lipid metabolism dysfunction, oxidative stress and inflammation response by tris(1-chloro-2-propyl)phosphate in larval/adult zebrafish

As an important organophosphate flame retardant, tris(1-chloro-2-propyl)phosphate (TCPP) is ubiquitous in the environment leading to inevitable human exposure. However, there is a paucity of information regarding its acute/chronic effects on obesity, lipid homeostasis, and hepatocellular carcinoma, especially regarding the underlying molecular mechanisms in humans. Herein, we investigated the effects of TCPP exposure (5-25 mg/L) on lipid homeostasis in larval and adult zebrafish (Danio rerio). TCPP exposure caused remarkable lipid-metabolism dysfunction, which was reflected in obesity and excessive lipid accumulation in zebrafish liver. Mechanistically, TCPP induced the over-expression of adipogenesis genes and suppressed the expression of fatty-acid β-oxidation genes. Consequently, excess lipid synthesis and deficient expenditure triggered oxidative damage and an inflammation response by disrupting the antioxidant system and over-expressing proinflammatory cytokine. Based on high-throughput transcriptome sequencing, we found that TCPP exposure led to enrichment of several pathways involved in lipid metabolism and inflammation, as well as several genes related to pathways of cancer. Notably, increasing expressions of Ki-67 and 53BP1 proteins, which are reliable biomarkers for recognition and risk prediction of cellular proliferation in cancer cells, were observed in liver tissues of adult zebrafish. These results imply that chronic TCPP exposure triggers a potential risk of hepatocellular carcinogenesis (HCC) progression. Collectively, these findings offer new insights into our mechanistic understanding for the health effects of organophosphorus flame retardants on humans.

Isatis phytogenic relieved atrazine induced growth retardation, hepato-renal dysfunction, and oxidative stress in Nile tilapia

The influence of herbicides causes health and economic loss, which requires innovative solutions to sustain the aquaculture industry. In this regard, dietary isatis is included in Nile tilapia diets to relieve atrazine (ATZ)-induced growth retardation, hepato-renal dysfunction, and oxidative stress. The first and second groups offered the control diet (control), while the third and fourth groups offered the isatis supplemented diet (1%). Meantime, half of the water was replaced and mixed with ATZ (1.39 mg/L) in the second and fourth groups for 30 days. The group of fish delivered isatis had significantly enhanced FBW, WG, and SGR, while fish intoxicated with ATZ had meaningfully impaired growth behavior (p < 0.05). Further, the FCR was improved by isatis, and ATZ resulted in the worst FCR among the groups. Interestingly fish fed isatis and exposed with ATZ (88.89%) had a higher survival rate than fish exposed with ATZ without isatis feeding, and both are lower than the control (97.78%) (p < 0.05). The histological structure in the isatis-treated groups showed distinguished enhancement and branching of the intestinal villi. The intestine of ATZ-treated fish revealed damage and inflammatory cell infiltration in the intestinal mucosa with separation of lining epithelium. Generally, fish fed isatis and intoxicated with ATZ had lower uric acid, urea, creatinine, ALT, and AST and higher total protein, globulin, and albumin than fish exposed with ATZ without feeding with isatis (p < 0.05). Markedly, fish-fed isatis had the highest SOD, CAT, GPx, and the lowest MDA level compared to the other groups (p < 0.05). Meanwhile, fish exposed with ATZ had the worst SOD, CAT, GPx, and the highest MDA level compared to the other groups (p < 0.05). In summary, dietary isatis relieved ATZ induced growth retardation, hepato-renal dysfunction, and oxidative stress in Nile tilapia.

Effect of petroleum wastewater treated with gravity separation and magnetite nanoparticles adsorption methods on the blood biochemical response of mrigal fish (Cirrhinus cirrhosus)

Drainage of treated wastewater to surface water is a severe threat to the health of aquatic organisms. This study aimed to evaluate the effects of 0.5 and 1% water-soluble fractions of crude oil (WSFO), WSFO treated with magnetic nanoparticles of Fe₃O₄ (TWSFO-Fe₃O₄) and with the gravity separation method (TWSFO-GSM) on Cirrhinus cirrhosis for 21 days. The rate of erythrocyte hemolysis in fish exposed to untreated 0.5 and 1% WSFO were significantly high. The activities of alanine aminotransferase (ALT), gamma-glutamyl transferase (GGT), alkaline phosphatase (ALP) were significantly increased in the groups exposed to TWSFO-GSM compared to the control group, while lactate dehydrogenase (LDH) was reduced. No significant differences in LDH, ALT, ALP, and GGT activities were observed in the fish treated with TWSFO-Fe₃O₄. The aspartate aminotransferase activity was significantly increased after exposure to TWSFO-Fe₃O₄ (1%) and TWSFO-GSM. The levels of triglyceride were decreased, whereas glucose, cholesterol, and cholinesterase activity increased in fish after both treatments. The total protein and albumin contents significantly decreased in fish under exposure to both doses of TWSFO-Fe₃O₄ and TWSFO-GSM. The globulin level decreased in fish exposed to TWSFO-Fe₃O₄ (1%) and TWSFO-GSM. Glutathione peroxidase, catalase, glucose-6-phosphate dehydrogenase activities, and total antioxidant levels were significantly reduced in the hepatocytes of fish exposed to TWSFO-Fe₃O₄, TWSFO-GSM, and WSFO, while superoxide dismutase activity and malondialdehyde content were increased. This study showed that despite removing oil drips from the WSFO, the xenobiotics present in the effluent treated by gravitational or nano-magnetite methods caused changes in biochemical parameters and induced oxidative stress. Therefore, it is recommended to prevent the discharge of treated effluent from the oil and petrochemical industries to aquatic ecosystems.

Acute toxicity of methomyl commercial formulation induces morphological and behavioral changes in larval zebrafish (Danio rerio)

The use of pesticides has continue grown over recent years, leading to several environmental and health concerns, such as the contamination of surface and groundwater resources and associated biota, potentially affecting populations that are not primary targets of these complex chemical mixtures. In this work, we investigate lethal and sublethal effects of acute exposure of methomyl commercial formulation in zebrafish embryo and larvae. Methomyl is a broad-spectrum carbamate insecticide and acaricide that acts primarily in acetylcholinesterase inhibition (AChE). Methomyl formulation 96 h-LC₅₀ was determined through the Fish Embryo Acute Toxicity Test (FET) and resulted in 1.2 g/L ± 0.04. Sublethal 6-day exposure was performed in six methomyl formulation concentrations (0.5; 1.0; 2.2; 4.8; 10.6; 23.3 mg/L) to evaluate developmental, physiological, morphological, behavioral, biochemical, and molecular endpoints of zebrafish early-development. Methomyl affected embryo hatching and larva morphology and behavior, especially in higher concentrations; resulting in smaller body and eyes size, failure in swimming bladder inflation, hypolocomotor activity, and concentration-dependent reduction of AChE activity; demonstrating methomyl strong acute toxicity and neurotoxic effect.

Environmentally relevant concentrations of arsenic induces apoptosis in the early life stage of zebrafish

Arsenic (As) in the aquatic environment is a considerable environmental issue, previous studies have reported the toxic effects of low concentrations (≤ 150 μg/L) of As on fish. However, limited information is available regarding the impact of low levels of As on apoptosis. To evaluate this, zebrafish embryos were exposed to different concentrations (0, 25, 50, 75, and 150 μg/L) of As (arsenite [AsIII] and arsenate [AsV]) for 120 h. Our results indicated that low concentrations of AsIII exposure significantly inhibited the survival of zebrafish larvae, and significantly increased the transcription of Caspase-9 and Caspase-3, the ratio of Bax/Bcl-2 transcription, and protein levels of Caspase-3. In contrast, AsV decreased the ratios of Bax/Bcl-2 transcription and protein levels, as well as protein levels of Caspase-3. Our data demonstrated that AsIII and AsV exert different toxic effects, AsIII induced apoptosis via the mitochondrial pathway and the extrinsic pathway, while AsV induced apoptosis only via the mitochondrial pathway.

Transcriptome aberration associated with altered locomotor behavior of zebrafish (Danio rerio) caused by Waterborne Benzo[a]pyrene

Waterborne Benzo[a]pyrene (B[a]P) pollution is a global threat to aquatic organisms. The exposure to waterborne B[a]P can disrupt the normal locomotor behavior of zebrafish (Danio rerio), however, how it affect the locomotor behavior of adult zebrafish remains unclear. Herein, B[a]P at two concentrations (0.8 μg/L and 2.0 μg/L) were selected to investigate the molecular mechanisms of the affected locomotor behavior of zebrafish by B[a]P based on transcriptome profiling. Adverse effects of B[a]P exposure affecting locomotor behavior in zebrafish were studied by RNA sequencing, and the locomotion phenotype was acquired. The gene enrichment results showed that the differentially highly expressed genes (atp2a1, cdh2, aurka, fxyd1, clstn1, apoc1, mt-co1, tnnt3b, and fads2) of zebrafish are mainly enriched in adrenergic signaling in cardiomyocytes (dre04261) and locomotory behavior (GO:0007626). The movement trajectory plots showed an increase in the locomotor distance and velocity of zebrafish in the 0.8 μg/L group and the opposite in the 2.0 μg/L group. The results showed that B[a]P affects the variety of genes in zebrafish, including motor nerves, muscles, and energy supply, and ultimately leads to altered locomotor behavior.

Imperative role of electron microscopy in toxicity assessment: A review

Electron microscope (EM) was developed in 1931 and since then microscopical examination of both the biological and non-biological samples has been revolutionized. Modifications in electron microscopy techniques, such as scanning EM and transmission EM, have widened their applicability in the various sectors such as understanding of drug toxicity, development of mechanism, criminal site investigation, and characterization of the nano-molecule. The present review summarizes its role in important aspects such as toxicity assessment and disease diagnosis in special reference to SARS-COV2. In the biological system, EM studies have elucidated the impact of toxicants at the ultra-structural level in various tissue in conformity to physiological alterations. Thus, EM can be concluded as an important tool in toxicity assessment and disease prognosis.

Transformation of copper oxide nanoparticles as affected by ionic strength and its effects on the toxicity and bioaccumulation of copper in zebrafish embryo

This study aimed to investigate the transformation of copper oxide nanoparticles (CuO NPs) in aquatic environments under different ionic strength and further examine its effects on copper toxicity and bioaccumulation by monitoring the responses and uptake behaviours of zebrafish embryo. Ionic strength (IS) was simulated according to surface water (1.5 mM), groundwater (15 mM), and wastewater (54 mM), representing low-, mid-, and high-IS water, respectively. At the highest exposure of 10 mg CuO/L, zebrafish larvae mortality was increased from 21.3% to 33.3%, when IS decreased from 54 to 1.5 mM. Low-IS solution also caused the highest numbers of delayed hatching embryo (81.3%) and opaque yolk deformation (36.3%). Copper bioaccumulation markedly increased when larvae were exposed to low-IS water (35%) relative to high-IS water (15%). Exposing to low-IS particularly enhanced copper uptake (~15 ng Cu/g inside embryo), facilitating the copper accumulation in the heart of larvae, whereas aggregated CuO NPs (>500 nm) in mid- and high-IS water were blocked from the embryo and found abundantly in the body axis and tail. Results indicate that CuO NPs in low-IS solutions rapidly form the relatively small CuO NP aggregates with a high copper dissolution, which would pose great concern for aquatic organisms.

Integrative effects based on behavior, physiology and gene expression of tritiated water on zebrafish

Tritium is a water-soluble hydrogen isotope that releases beta rays during decay. In nature, tritium primarily exists as tritiated water (HTO), and its main source is nuclear power/processing plants. In recent decades, with the development of nuclear power industry, it is necessary to evaluate the impact of tritium on organisms. In this study, fertilized zebrafish embryos are treated with different HTO concentrations (3.7 × 10³ Bq/ml, 3.7 × 10⁴ Bq/ml, 3.7 × 10⁵ Bq/ml). After treatment with HTO, the zebrafish embryos developed without evident morphological changes. Nevertheless, the heart rate increased and locomotor activity decreased significantly. In addition, RNA-sequencing shows that HTO can affect gene expressions. The differentially expressed genes are enriched through many physiological processes and intracellular signaling pathways, including cardiac, cardiovascular, and nervous system development and the metabolism of xenobiotics by cytochrome P450. Moreover, the concentrations of thyroid hormones in the zebrafish decrease and the expression of thyroid hormone-related genes is disordered after HTO treatment. Our results suggest that exposure to HTO may affect the physiology and behaviors of zebrafish through physiological processes and intracellular signaling pathways and provide a theoretical basis for ecological risk assessment of tritium.

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.