Exposure to acetochlor impairs swim bladder formation, induces heat shock protein expression, and promotes locomotor activity in zebrafish (Danio rerio) larvae

Occurrence of current-use pesticides in sediment cores from lakes and peatlands in pristine mountain areas of Brazilian national parks

This study assessed the occurrence of current-use pesticides in sediment cores from six lakes and peatlands in high-altitude (1952-2374 m) pristine areas within two southeastern Brazilian National Parks: Itatiaia National Park (IT-NP) and Serra dos Órgãos National Park (SO-NP). We sampled three sediment cores from lakes at IT-NP and three from peatlands at SO-NP, totaling 60 subsamples. Among the 38 current-use pesticides assessed, 17 were found in at least one sample, with 14 - including herbicides, insecticides, fungicides, and acaricides - identified in both parks. The most frequently detected pesticides were carbendazim and carbaryl (75-95%), followed by acetochlor, chlorpyrifos, diuron, metolachlor and tebuconazole (40-70%) and, to a lesser extent, terbuthylazine and malathion (10-30%). The organophosphates disulfoton (6.83 ± 20.18 ng g-1 dry weight) and chlorpyrifos (4.34 ± 6.81 ng g-1 dw) registered the highest concentrations across all compounds in the sediment layers, with chlorpyrifos showing the greatest relative abundance (65.9-92.8%) in four out of six sites. Risk characterization results revealed highest risk quotient (RQ) values (416-14,589) for chlorpyrifos, indicating potential ecological risks. High RQs were also obtained for acetochlor (5.76-94.6), carbaryl (0.4-4.08), carbendazim (0.09-3.46), diazinon (2048), disulfoton (34-569), diuron (1.45-35.0) and malathion (10.94). These results highlight the threat posed by long-range pesticide transport to pristine areas at National Parks. Urgent regulatory measures are needed to mitigate their impact and safeguard these ecosystems from degradation.

GPR120 exacerbates the immune-inflammatory response in chicken liver by mediating acetochlor induced macrophage M1 polarization

Acetochlor is a widely used and highly effective herbicide. Its overuse poses significant threats to biosecurity and ecological integrity, particularly affecting free-ranging birds. Data on its impact, especially mechanisms of liver toxicity in chickens, are lacking. Thus, we established an animal-cell-animal model to explore intrinsic mechanisms at multiple levels. We found that acetochlor exposure caused liver cell swelling, inflammatory cell accumulation, and lipid deposition. Transcriptomic analyses revealed that differential gene were mainly enriched in hepatic immune, inflammatory, and programmed cell death pathways. We next focused on the gene GPR120, conducting transfection and agonism experiments in LMH, HD11, and co-cultured cells. Acetochlor significantly increased ROS accumulation, activated the NLRP3 inflammasome, and which induced PANoptosis. HD11 cells exhibited M1 polarization with upregulated pro-inflammatory factors. Silencing GPR120 exacerbated cellular damage and immune responses, whereas its agonist, GSK7A, dramatically reduced macrophage M1 polarization and mitigated immune damage to LMH cells. Finally, we returned to animal studies, adding Omega-3-a known GPR120 agonist-to the diet. Omega-3 effectively reversed acetochlor-induced hepatitis and PANoptosis. Given that acetochlor residues pose potential threats to ecosystems and avian health, it is crucial to strengthen residue control, conduct risk assessments, and explore targeted pathways and nutritional supplementation to counteract these negative impacts.

Polystyrene microplastics exacerbate acetochlor-induced reproductive toxicity and transgenerational effects in zebrafish

Microplastic (MPs) can adsorb co-existing pollutants, and alter their behavior and toxicity. Meanwhile, amide herbicides like acetochlor (ACT) are widely used in agriculture, with potential endocrine-disrupting effects that raise ecological concerns. The aim of this research was to examine the effects of MPs on the reproductive endocrine disruption caused by ACT and the effects of maternal transmission. Zebrafish were employed in this study to assess the reproductive toxicity of ACT alone and in combination with polystyrene microplastics (PS-MPs) of different sizes (200 nm and 2 μm) and concentrations (0.1 and 1 mg/L) over a 63-day exposure experiment. The results indicated that ACT was concentrated in zebrafish tissues in the order: intestine > liver > gill > brain > gonad > muscle. PS-MPs increased ACT bioaccumulation, worsened gonadal damage, led to abnormalities in hormone levels, and caused disruptions in HPG axis gene expression, further exacerbating the reproductive toxicity. Maternal transfer of ACT affected offspring growth, thyroid function, and HPT axis gene expression, with nanoplastics (NPS) amplifying these adverse effects. This study offers crucial insights into the ecological hazards posed by ACT and PS-MPs, emphasizing the increased toxicity due to PS-MPs.

Impact of sub-lethal Aclonifen intoxication on biochemical and stress markers on Oncorhynchus mykiss: an integrative assessment of multi-biomarker responses

Aclonifen is a diphenyl ether herbicide being included in the list of priority substances. Nevertheless, the data related to its sublethal effects on fish are limited. Therefore, the present study has been carried out to investigate the toxic effects of aclonifen in juvenile Oncorhynchus mykiss following 24, 48, 72 and 96 hours of application to sublethal concentrations of 12.7, 63.5 and 127 μg/L. The application resulted in altered blood biochemistry appearing as hyperglycemia, decreased cholesterol and induced activities of transaminases of ALT and AST. The inhibition of AChE in brain, gill and liver was unimportant revealing its weak potential as anticholinesterase. The induction recorded for SOD, CAT, GPx and GST activities was accompanied with sustained elevation in TBARS and PC levels. It demonstrates both the pro-oxidant potential of aclonifen and oxidation of lipid and proteins resulting in the loss of membrane integrity and protein function. Hyperglycemic condition and decreased protein levels in gill and liver might be proposed as general adaptive responses to compensate increased energy demand. The integrative assessment of multi-biomarker responses shows concentration and duration related rise in calculated indexes. CAT, PC and SOD achieved the maximum scores for brain, gill and liver, respectively. Considering the results, oxidative stress inducing potential and weak anticholinesterase activity along with its disturbing impact on blood biochemistry were evidenced. Moreover, adverse affects observed after short term application on O. mykiss, present the potential risk aclonifen may cause at population level in aquatic ecosystems emphasizing the importance of pesticide regulations to avoid adverse impacts on non-target species.

The herbicide acetochlor causes lipid peroxidation by inhibition of glutathione peroxidase activity

Metabolic syndrome is increasing worldwide, particularly in rural communities, where residents have a higher risk of exposure to pesticides. We investigated whether six commonly used agricultural pesticides on corn and soy fields possess adipogenic and metabolic disruption activity. Exposure to two of these pesticides, the herbicides acetochlor and metolachlor, induced adipogenesis in vitro in mouse 3T3-L1 preadipocytes. The most potent compound, acetochlor, was selected for further studies in zebrafish. Acetochlor exposure induced morphological malformations and lethality in zebrafish larvae with an EC50 of 7.8 µM and LC50 of 12 µM. Acetochlor exposure at 10 nM resulted in lipid accumulation in zebrafish larvae when simultaneously fed a high-cholesterol diet. To decipher the molecular mechanisms behind acetochlor action, we performed transcriptomic and lipidomic analyses of exposed animals. The combined omics results suggested that acetochlor exposure increased Nrf2 activity in response to reactive oxygen species, as well as induced lipid peroxidation and ferroptosis. We further discovered that acetochlor structurally shares a chloroacetamide group with known inhibitors of glutathione peroxidase 4 (GPX4). Computational docking analysis suggested that acetochlor covalently binds to the active site of GPX4. Consistent with this prediction, Gpx activity was efficiently repressed by acetochlor in zebrafish, whereas lipid peroxidation was increased. We propose that acetochlor disrupts lipid homeostasis by inhibiting GPX activity, resulting in the accumulation of lipid peroxidation, 4-hydroxynonenal, and reactive oxygen species, which in turn activate Nrf2. Because metolachlor, among other acetanilide herbicides, also contains the chloroacetamide group, inhibition of GPX activity may represent a novel, common molecular initiating event of metabolic disruption.

Transcriptome networks and physiology related to cardiac function and motor activity are perturbed in larval zebrafish (Danio rerio) following exposure to the antidepressant citalopram

Citalopram is a selective serotonin reuptake inhibitor (SSRI) used to treat depression and is often detected in aquatic environments. Here, we measured the acute toxicity of citalopram at environmentally relevant concentrations to zebrafish embryos/larvae and utilized RNA-seq to reveal potential mechanisms of toxicity. We also assessed behavioral outcomes in larval zebrafish. Zebrafish embryos were exposed continuously to embryo rearing medium (ERM), or one concentration of 0.1, 1, 10, 100, and 1000 μg/L citalopram for 7 days post-fertilization (dpf). No acute toxicity was noted for citalopram over 7-days in developing zebrafish, nor were there any effects on hatch rates; however, exposure resulted in a dose-dependent decrease in heart rate at 2 dpf. Reactive oxygen species were also increased in 7-day old larvae zebrafish exposed to 100 μg/L citalopram. There were 29 genes differentially expressed in fish exposed to 10 μg/L citalopram [FDR <0.05] and 79 genes differentially expressed in fish exposed to 1000 μg/L citalopram [FDR <0.05]. In the 1000 μg/L citalopram treatment, there were several transcripts downregulated related to muscle function, including myhz2, myhz1, and myom1. Twenty-five gene set pathways were shared between exposure concentrations including 'IL6 Expression Targets', 'Thyroid Stimulating Hormone (TSH) Resistance in Congenital Hypothyroidism', and 'GFs/TNF - > Ion Channels.' Enrichment of KEGG pathways revealed that 1000 μg/L citalopram altered processes related to the proteosome and cardiac muscle contractions. Larval zebrafish at 7 dpf showed hypoactivity with exposure to ≥10 μg/L citalopram. This may be related to the downregulation of transcripts involved in muscle function. Overall, our results show that citalopram as a pharmaceutical pollutant may have an adverse influence on aquatic species' ability to survive by reducing their abilities to elude predators (e.g. cardiac output, locomotor activity). This study improves mechanistic understanding of the potential harm citalopram may cause fish and contributes to environmental risk assessments for SSRIs in aquatic species.

Neurotoxicity assessment of the herbicide pethoxamid in zebrafish (Danio rerio) embryos/larvae

Pethoxamid, a member of the chloroacetamide herbicide family, is a recently approved chemical for pre- or post-emergence weed control; however, toxicity data for sublethal effects in aquatic organisms exposed to pethoxamid are non-existent in literature. To address this, we treated zebrafish embryos/larvae to pethoxamid over a 7-day period post-fertilization and evaluated several toxicological endpoints associated with oxidative stress and neurotoxicity. Continuous pethoxamid exposure did not affect survival nor hatch success in embryos/larvae for 7 days up to 1000 μg L-1. Exposure to pethoxamid did not affect embryonic ATP-linked respiration, but it did reduce non-mitochondrial respiration at the highest concentration tested. We also noted a significant increase in both apoptosis and levels of reactive oxygen species (ROS) in larvae zebrafish following exposure to pethoxamid. Increases in apoptosis and ROS, however, were not correlated with any altered gene expression pattern for apoptotic and oxidative damage response transcripts. To assess neurotoxicity potential, we measured behavior and several transcripts implicated in neural processes in the central nervous system. While locomotor activity of larval zebrafish was affected by pethoxamid exposure (hyperactivity was observed at concentrations below 1 μg L-1, and hypoactivity was noted at higher exposures to 10 and 100 μg L-1 pethoxamid), there were no effects on steady state mRNA abundance for neurotoxicity-related transcripts tested. This data contributes to knowledge regarding exposure risks for chloroacetamide-based herbicides and is the first study investigating sublethal toxicity for this newly registered herbicide.

Assessment of the impact of chemical pollution on endangered migratory fish in two major rivers of France, including spawning grounds

Water pollution is a one of the most contributors to aquatic biodiversity decline. Consequently, ecological risk assessment methods have been developed to investigate the effects of existing stresses on the environment, including the toxic effects of chemicals. One of the existing approaches to quantify toxic risks is called "Potentially Affected Fraction of species" (PAF), which estimates the potential loss of species within a group of species studied. In this study, the PAF method was applied to the Garonne catchment (southwest France) due to the limited information available on the involvement of water pollution in the decline of diadromous fish populations. This approach was used to quantify the potential toxic risk associated with chemical contamination of water for fish species. The objectives were to quantify this risk (1) in the Garonne and Dordogne rivers and (2) in the spawning grounds of two endangered anadromous fish species: the allis shad and the European sturgeon during the development period of their early life stages. Environmental pollution data was provided for 21 sites within the Garonne catchment between 2007 and 2022, and toxicity data was obtained specifically from freshwater toxicity tests on fish species. Then, for each site and each year, the potential toxic risk for a single substance (ssPAF) and for a mixture of substances (msPAF) was calculated and classified as high (>5 %), moderate (>1 % and < 5 %) or low (<1 %). Potential toxic risks were mostly moderate and mainly associated with: metals > other industrial pollutants and hygiene and care products > agrochemicals. In summary, this study highlights the probable involvement of water contamination on the decline, fate and restoration of diadromous fish populations in the Garonne catchment, focusing notably on the toxic effects on early life stages, a previously understudied topic.

Exposure to the antineoplastic ifosfamide alters molecular pathways related to cardiovascular function, increases heart rate, and induces hyperactivity in zebrafish (Danio rerio)

Ifosfamide is an alkylating antineoplastic drug used in chemotherapy, but it is also detected in wastewater. Here, the objectives were to (1) determine teratogenic, cardiotoxic, and mitochondrial toxicity potential of ifosfamide exposure; (2) elucidate mechanisms of toxicity; (3) characterize exposure effects on larval behavior. Survival rate, hatch rate, and morphological deformity incidence were not different amongst treatments following exposure levels up to 1000 µg/L ifosfamide over 7 days. RNA-seq reveled 231 and 93 differentially expressed transcripts in larvae exposed to 1 µg/L and 100 µg/L ifosfamide, respectively. Several gene networks related to vascular resistance, cardiovascular response, and heart rate were affected, consistent with tachycardia observed in exposed embryonic fish. Hyperactivity in larval zebrafish was observed with ifosfamide exposure, potentially associated with dopamine-related gene networks. This study improves ecological risk assessment of antineoplastics by elucidating molecular mechanisms related to ifosfamide toxicity, and to alkylating agents in general.

Assessing and mitigating foodborne acetochlor exposure induced ileum toxicity in broiler chicks: The role of omega-3 polyunsaturated fatty acids supplementation and molecular pathways analysis

Excessive acetochlor residues present ecological and food safety challenges. Here, broiler chicks were exposed to varied acetochlor doses to first assess its effects on the gut. Subsequent dietary supplementation with omega-3 was used to assess its anti-contamination effects. Pathologically, acetochlor induced notable ileal lesions including inflammation, barrier disruption, tight junction loss, and cellular anomalies. Mechanistically, acetochlor stimulated the TNFα/TNFR1 and TLR4/NF-κB/NLRP3 pathways, promoting RIPK1/RIPK3 complex formation, MLKL phosphorylation, NLRP3 inflammasome activation, Caspase-1 activation, and GSDMD shearing with inflammatory factor release. These mechanisms elucidate ileal cell death patterns essential for understanding chicken enteritis. Omega-3 supplementation showed promise in mitigating inflammation, though its precise counteractive role remains unclear. Our findings suggest early omega-3 intervention offered protective benefits against acetochlor's adverse intestinal effects, emphasizing its potential poultry health management role. Harnessing dietary interventions' therapeutic potential will be pivotal in ensuring sustainable poultry production and food safety despite persistent environmental contaminants.

Exposure to the pharmaceutical buspirone alters locomotor activity, anxiety-related behaviors, and transcripts related to serotonin signaling in larval zebrafish (Danio rerio)

Buspirone is a pharmaceutical used to treat general anxiety disorder by acting on the dopaminergic and serotoninergic system. Buspirone, like many human pharmaceuticals, has been detected in municipal wastewater; however, the environmental exposure risks are unknown for this psychoactive compound. We studied the effects of buspirone on the behavior of zebrafish, focusing on locomotor and anxiolytic behavior. We also measured transcripts associated with oxidative stress, neurotoxicity, and serotonin signaling to identify potential mechanisms underlying the behavioral changes. Concentrations ranged from environmentally relevant (nM) to physiologically active concentrations typical of human pharmaceuticals (μM). Buspirone treatment did not impact survival, nor did it induce deformities in zebrafish treated for 7 days up to 10 μM. There was a positive relationship between locomotor activity and buspirone concentration in dark periods of the visual motor response test. In the light-dark preference test, both the average time per visit to the dark zone and the percent cumulative duration in the dark zone were increased by 1 μM buspirone. Transcript levels of ache, manf, and mbp were decreased in larvae, while the expression of gap43 was increased following exposure to buspirone, indicating potential neurotoxic effects. There was also reduced expression of serotonin-related genes encoding receptors, transporters, and biosynthesis enzymes (i.e., 5ht1aa, sertb, and tph1a). These data increase understanding of the behavioral and molecular responses in zebrafish following waterborne exposure to neuroactive pharmaceuticals like buspirone.

The novel insecticide broflanilide dysregulates transcriptional networks associated with ion channels and induces hyperactivity in zebrafish (Danio rerio) larvae

Broflanilide is a novel insecticide that is classified as a non-competitive γ-aminobutyric acid (GABA) receptor antagonist. However, indiscriminate use can have negative effects on non-target species. The objective of this study was to determine the sub-lethal toxicity potential of broflanilide in early staged zebrafish. Embryos/larvae were assessed for multiple molecular and morphological endpoints following exposure to a range of concentrations of broflanilide. The insecticide did not affect hatch rate, the frequency of deformities, nor did it impact survival of zebrafish at exposure concentrations up to 500 μg/L over a 7-day period from hatch. There was also no effect on oxidative consumption rates in embryos, nor induction of reactive oxygen species in fish exposed up to 100 μg/L broflanilide. As oxidative stress was not prominent as a mechanism, we turned to RNA-seq to identify potential toxicity pathways. Gene networks related to neurotransmitter release and ion channels were altered in zebrafish, consistent with its mechanism of action of modulating GABA receptors, which regulate chloride channels. Noteworthy was that genes related to the circadian clock were induced by 1 μg/L broflanilide exposure. The locomotor activity of larval fish at 7 days was increased (i.e., hyperactivity) by broflanilide exposure based on a visual motor response test, corroborating expression data indicating neurotoxicity and motor dysfunction. This study improves the current understanding of the biological responses in fish to broflanilide exposure and contributes to risk assessment strategies for this novel pesticide.

Toxicity assessment of carvacrol and its acetylated derivative in early staged zebrafish (Danio rerio): Safer alternatives to fipronil-based pesticides?

Fipronil is a broad-spectrum pesticide presenting high acute toxicity to non-target organisms, particularly to aquatic species. Natural compounds stand out as promising alternatives to the use of synthetic pesticides such as fipronil. Thus, our study aimed to compare the toxicity of carvacrol (natural), acetylcarvacrol (semisynthetic), and fipronil (synthetic) to early staged zebrafish. We conducted a series of toxicity assays at concentrations ranging from 0.01 μM to 25 μM for fipronil and 0.01 μM to 200 μM for carvacrol and acetylcarvacrol, depending on the assay, after 7-days post-fertilization (dpf). The potency (EC50) of fipronil was ∼1 μM for both deformities and mortality at 7 dpf, whereas EC50 was >50 μM for carvacrol and >70 μM for acetylcarvacrol. Fipronil at 0.1 and 1 μM caused a decrease in body length and swim bladder area of larvae at 7dpf, but no difference was observed for either carvacrol or acetylcarvacrol. Based upon the visual motor response test, fipronil induced hypoactivity in larval zebrafish at 1 μM and acetylcarvacrol induced hyperactivity at 0.1 μM. Anxiolytic-type behaviors were not affected by any of these chemicals. All chemicals increased the production of reactive oxygen species at 7 dpf, but not at 2 dpf. Genes related to swim bladder inflation, oxidative stress, lipid metabolism, and mitochondrial activity were measured; only fipronil induced upregulation of atp5f1c. There were no changes were observed in oxygen consumption rates of fish and apoptosis. Taken together, our data suggest that carvacrol and its derivative may be safer replacements for fipronil due to their lower acute toxicity.

Evidence for neurotoxicity and oxidative stress in zebrafish embryos/larvae treated with HFPO-DA ammonium salt (GenX)

"GenX" [ammonium perfluoro (2-methyl-3-oxahexanoate] was developed as a replacement chemical for toxic perfluorinated compounds to be used in product manufacturing. Here, we assessed developmental, mitochondrial, and behavioral toxicity endpoints in zebrafish embryos/larvae exposed to GenX. GenX exerted low toxicity to zebrafish embryos/larvae up to 20 mg/L. GenX did not affect mitochondrial oxidative phosphorylation nor ATP levels. ROS levels were reduced in larvae fish exposed to 10 and 100 µg/L, indicative of an antioxidant defense; however, ROS levels were elevated in fish exposed to 1000 µg/L. Increased expression of cox1 and sod2 in GenX exposed 7-day larvae was noted. GenX (0.1 or 1 µg/L) altered transcripts associated with neurotoxicity (elavl3, gfap, gap43, manf, and tubb). Locomotor activity of larvae was reduced by 100 µg/L GenX, but only in light periods. Perturbations of anxiety-related behaviors in larvae were not observed with GenX exposure. These data inform risk assessments for long-lived perfluorinated chemicals of concern.

A lateral flow immunoassay method for the rapid detection of acetochlor and alachlor in vegetable oil by sensitivity enhancement by using dimethyl-β-cyclodextrin

Acetochlor is an endocrine disruptor. The acetochlor residue is strongly lipophilic and can be enriched into products during the manufacturing process. In this study, we found that dimethyl-β-cyclodextrin (DM-β-CD) solution could decrease the apparent oil/water partition coefficient (Koil-w) of acetochlor and increase the sensitivity of fluorescence lateral flow immunoassay (LFIA) for acetochlor simultaneously. Based on this, a simple LFIA method for the determination of acetochlor and alachlor residues in vegetable oil was established. The detection process only involves vortex mixing of an oil sample and dimethyl-β-cyclodextrin solution in a 1 : 3 (V/V) ratio, loading the water phase onto the immunoassay strips and reading the results. Under optimized conditions, the LOD for acetochlor in oil was 3.53 ng g-1, and the working range was 12.03-2000.00 ng g-1. The recoveries of spiked samples ranged from 91.69% ± 1.12% to 112.23% ± 2.20%. Meanwhile, the cross reactivity for alachlor was 108.22%, while for other investigated acetochlor analogues it was less than 1%, and the recoveries of alachlor were from 92.90% ± 8.03% to 113.53% ± 3.40%, which indicate that this method can detect acetochlor and alachlor simultaneously. Compared with the traditional detection method, the pre-treatment process of the proposed method is "green" and simple, and can be applied to the on-site rapid detection of acetochlor and alachlor in vegetable oil and can provide inspiration for the detection of other lipophilic pollutants.

Effects of microplastics, pesticides and nano-materials on fish health, oxidative stress and antioxidant defense mechanism

Microplastics and pesticides are emerging contaminants in the marine biota, which cause many harmful effects on aquatic organisms, especially on fish. Fish is a staple and affordable food source, rich in animal protein, along with various vitamins, essential amino acids, and minerals. Exposure of fish to microplastics, pesticides, and various nanoparticles generates ROS and induces oxidative stress, inflammation, immunotoxicity, genotoxicity, and DNA damage and alters gut microbiota, thus reducing the growth and quality of fish. Changes in fish behavioral patterns, swimming, and feeding habits were also observed under exposures to the above contaminants. These contaminants also affect the Nrf-2, JNK, ERK, NF-κB, and MAPK signaling pathways. And Nrf2-KEAP1 signalling modulates redox status marinating enzymes in fish. Effects of pesticides, microplastics, and nanoparticles found to modulate many antioxidant enzymes, including superoxide dismutase, catalase, and glutathione system. So, to protect fish health from stress, the contribution of nano-technology or nano-formulations was researched. A decrease in fish nutritional quality and population significantly impacts on the human diet, influencing traditions and economics worldwide. On the other hand, traces of microplastics and pesticides in the habitat water can enter humans by consuming contaminated fish which may result in serious health hazards. This review summarizes the oxidative stress caused due to microplastics, pesticides and nano-particle contamination or exposure in fish habitat water and their impact on human health. As a rescue mechanism, the use of nano-technology in the management of fish health and disease was discussed.

Molecular and behavioral toxicity assessment of tiafenacil, a novel PPO-inhibiting herbicide, in zebrafish embryos/larvae

Tiafenacil is a newly registered herbicide and a protoporphyrinogen IX oxidase inhibitor. However, sub-lethal effects of PPO-inhibitors in aquatic species are unknown. Embryos or larvae were exposed to 0.1 µg/L up to 10 mg/L tiafenacil for 7-days post-fertilization. Decreased survival (> 50%) and deformities were noted at concentrations > 1 mg/L. Potency (EC50) of tiafenacil for 5- and 7-day larvae were 818.1 µg/L and 821.7 µg/L, respectively. Pericardial and yolk sac edema were the most frequent deformities observed. Heartbeat frequency at 3 dpf was decreased in zebrafish exposed to > 10 µg/L tiafenacil, coinciding with increased reactive oxygen species. Oxygen consumption rates were not affected by tiafenacil, nor did we detect differences in indicators of apoptosis. The abundance of eighteen transcripts related to oxidative stress and mitochondrial complexes I through V were unchanged. Larval activity was decreased with exposure to 1000 µg/L tiafenacil. These data contribute to risk assessment for a new class of herbicide.

Sulfamethoxazole (SMX) Alters Immune and Apoptotic Endpoints in Developing Zebrafish (Danio rerio)

Sulfamethoxazole (SMX) is a broad-range bacteriostatic antibiotic widely used in animal and fish farming and is also employed in human medicine. These antibiotics can ultimately end up in the aquatic ecosystem and affect non-target organisms such as fish. To discern the effect of SMX on developing zebrafish embryos and larvae, we investigated a broad range of sub-lethal toxicity endpoints. Higher concentrations of SMX affected survivability, caused hatch delay, and induced malformations including edema of the yolk sac, pericardial effusion, bent tail, and curved spine in developing embryos. Lower levels of SMX provoked an inflammatory response in larvae at seven days post fertilization (dpf), as noted by up-regulation of interferon (ifn-γ) and interleukin 1β (il-1β). SMX also increased the expression of genes related to apoptosis, including BCL2-Associated Agonist of Cell Death (bad) and BCL2 Associated X, Apoptosis Regulator (bax) at 50 µg/L and decreased caspase 3 (casp3) expression in a dose-dependent manner. SMX induced hyperactivity in larval fish at 500 and 2500 µg/L based upon the light/dark preference test. Collectively, this study revealed that exposure to SMX can disrupt the immune system by altering host defense mechanisms as well as transcripts related to apoptosis. These data improve understanding of antibiotic chemical toxicity in aquatic organisms and serves as a baseline for in-depth environmental risk assessment of SMX and antibiotics.

Prostaglandin Metabolome Profiles in Zebrafish (Danio rerio) Exposed to Acetochlor and Butachlor

Prostaglandins (PGs) are critically important signaling molecules that play key roles in normal and pathophysiological processes. Many endocrine-disrupting chemicals have been found to suppress PG synthesis; however, studies about the effects of pesticides on PGs are limited. The effects of two known endocrine disrupting herbicides, acetochlor (AC) and butachlor (BC), on PG metabolites in zebrafish (Danio rerio) females and males were studied using widely targeted metabolomics analysis based on ultraperformance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS). In total, 40 PG metabolites were detected in 24 zebrafish samples, including female and male samples, with and without exposure to AC or BC at the sub-lethal concentration of 100 μg/L for 96 h. Among them, 19 PGs significantly responded to AC or BC treatment, including 18 PGs that were upregulated. The enzyme-linked immunosorbent assay (ELISA) test in zebrafish showed BC could cause significant upregulation of an isoprostane metabolite, 5-iPF2a-VI, which is positively related to the elevated level of reactive oxygen species (ROS). The present study guides us to conduct a further study to determine whether PG metabolites, including isoprostanes, could be potential biomarkers for chloracetamide herbicides.

Developmental and mitochondrial toxicity assessment of perfluoroheptanoic acid (PFHpA) in zebrafish (Danio rerio)

The potential toxicity of several perfluoroalkyl and polyfluoroalkyl substances (PFASs) to aquatic species are not well understood. Here, we assessed the sub-lethal toxicity potential of perfluoroheptanoic acid (PFHpA) to developing zebrafish. PFHpA was not acutely toxic to fish up to 50 µM and there was > 96% survival in all treatments. Exposure to 200 µM PFHpA decreased ATP-linked respiration of embryos. There was no evidence for ROS induction in 7-day-old larvae fish exposed to 0.1 µM or 1 µM PFHpA. Twenty-four transcripts related to mitochondrial complexes I through V were measured and atp06, cox4i1, and cyc1 levels were decreased in larval zebrafish in a concentration-dependent manner by PFHpA exposure. Locomotor activity was reduced in fish exposed to 0.1 µM PFHpA based on a visual motor response test. Anxiolytic-type behaviors were not affected by PFHpA. This study contributes to environmental risk assessments for perfluorinated chemicals.

Perfluorotetradecanoic Acid (PFTeDA) Induces Mitochondrial Damage and Oxidative Stress in Zebrafish (Danio rerio) Embryos/Larvae

Industrial and consumer products, such as pesticides, lubricants, and cosmetics, can contain perfluorinated compounds (PFCs). Although many short-chain PFCs have been linked to physiological and behavioral changes in fish, there are limited data on longer-chain PFCs. The objective of this study was to determine the potential impact of perfluorotetradecanoic acid (PFTeDA) exposure on zebrafish (Danio rerio) during early developmental stages. We measured several endpoints including gene expression, mitochondrial bioenergetics, and locomotor activity in zebrafish. Survival, timing of hatching, and deformity frequency were unaffected by PFTeDA at the concentrations tested (0.01, 0.1, 1, and 10 µM) over a 7-day exposure period. The expression levels of mitochondrial-related genes (cox1 and mt-nd3) and oxidative stress-related genes (cat, hsp70, and hsp90a) were increased in larval fish with exposure to 10 µM PFTeDA; however, there was no change in oxidative respiration of embryos (i.e., basal respiration and oligomycin-induced ATP-linked respiration). Reactive oxygen species were reduced in larvae treated with 10 µM PFTeDA, coinciding with the increased transcription of antioxidant defense genes. Both the visual motor response test and light-dark preference test were conducted on 7 dpf larvae and yielded no significant findings. This study improves current knowledge regarding toxicity mechanisms for longer-chain PFCs such as PFTeDA.

Fish Behavior as a Neural Proxy to Reveal Physiological States

Behaviors are the integrative outcomes of the nervous system, which senses and responds to the internal physiological status and external stimuli. Teleosts are aquatic organisms which are more easily affected by the surrounding environment compared to terrestrial animals. To date, behavioral tests have been widely used to assess potential environmental risks using fish as model animals. In this review, we summarized recent studies regarding the effects of internal and external stimuli on fish behaviors. We concluded that behaviors reflect environmental and physiological changes, which have possible implications for environmental and physiological assessments.

Investigating mitochondria-immune responses in zebrafish, Danio rerio (Hamilton, 1822): A case study with the herbicide dinoseb

The dinitrophenol herbicide dinoseb is an uncoupler of mitochondrial oxidative phosphorylation (OXPHOS). Studies in fish demonstrate impaired OXPHOS is associated with altered immune system responses and locomotor activity in fish. The objective of this study was to determine the effect of dinoseb on zebrafish (Danio rerio) during early stages of development. We measured oxygen consumption rates of embryos, transcripts related to OXPHOS, growth, and the immune system (cytokines and immune-signaling transcripts), and locomotor activity. We hypothesized that OXPHOS of fish would be impaired in vivo, leading to altered basal immune system expression and locomotor activity. Oxidative respiration assessments in embryos revealed that dinoseb decreased both mean basal respiration and oligomycin-induced ATP-linked respiration. Expression levels of cytochrome c oxidase complex IV, 3-hydroxyacyl-COA dehydrogenase and superoxide dismutase 1 were decreased in larvae following exposure to dinoseb while succinate dehydrogenase complex flavoprotein subunit A, insulin growth factor 1 (igf1) and igf2a mRNA were increased in abundance. Immune-related transcripts chemokine (C-X-C motif) ligand 1 and matrix metallopeptidase 9 (MMP-9) were decreased in expression levels while toll-like receptor 5a and 5b were increased in expression. In addition, a visual motor response test was conducted on both 6 and 7 dpf larvae to determine if dinoseb impaired locomotor activity. Dinoseb decreased locomotor activity in 7 dpf larvae but not 6 dpf. This study improves knowledge of toxicity mechanisms for dinoseb in early stages of fish development and demonstrates that mitochondrial toxicants may disrupt immune signaling in zebrafish.

Developmental and behavioral toxicity assessment of glyphosate and its main metabolite aminomethylphosphonic acid (AMPA) in zebrafish embryos/larvae

The relative toxicity of glyphosate (GLY) and its metabolite aminomethylphosphonic acid (AMPA) to zebrafish were compared. Embryos/larvae were exposed to one dose of either GLY (0.1, 1, or 10 μM), AMPA (0.1, 1, or 10 μM), or a 1 μM mixture for 7-days post-fertilization. Survival, success of hatch, and deformity frequency were not different from controls. Neither chemical induced reactive oxygen species in larval fish. GLY increased superoxide dismutase 2 mRNA in larvae while AMPA increased catalase and superoxide dismutase 1 in a concentration-specific manner. GLY increased cytochrome c oxidase subunit 4 isoform 1 and citrate synthase mRNA in larvae while AMPA decreased cytochrome c oxidase I and increased 3-hydroxyacyl CoA dehydrogenase transcripts. Hyperactivity was noted in fish treated with GLY, but not AMPA nor the mixture. Anxiety-like behaviors were absent with exposure to GLY or AMPA. GLY and AMPA may exert different effects at the molecular and behavioral level.

Acetochlor Affects Bighead Carp (Aristichthys Nobilis) by Producing Oxidative Stress, Lowering Tissue Proteins, and Inducing Genotoxicity

Acetochlor is persistently used in the agroproduction sector to control broadleaf weeds. Due to frequent and continuous applications, this herbicide can reach nearby water bodies and may induce deleterious changes in aquatic life. Therefore, investigation of harmful impacts of different environmental pollutants, including herbicides, is vital to knowing the mechanisms of toxicity and devising control strategies. The current experiment included bighead carp (n = 80) to estimate adverse impacts. Fish were randomly placed in 4 different experimental groups (T0-T3) and were treated for 36 days with acetochlor at 0, 300, 400, and 500 μg/L. Fresh blood without any anticoagulant was obtained and processed for nuclear and morphological changes in erythrocytes. At the same time, various visceral organs, including the gills, liver, brain, and kidneys, were removed and processed on days 12, 24, and 36 to determine oxidative stress and various antioxidant biomarkers. Comet assays revealed significantly increased DNA damage in isolated cells of the liver, kidneys, brain, and gills of treated fish. We recorded increased morphological and nuclear changes (P ≤ 0.05) in the erythrocyte of treated fish. The results on oxidative stress showed a higher quantity of oxidative biomarkers and a significantly (P ≤ 0.05) low concentration of cellular proteins in the gills, liver, brain, and kidneys of treated fish compared to unexposed fish. Our research findings concluded that acetochlor renders oxidative stress in bighead carp.

Molecular and behavioral assessment in larval zebrafish (Danio rerio) following exposure to environmentally relevant levels of the antineoplastic cyclophosphamide

Antineoplastics treat cancers and enter aquatic ecosystems through wastewater and hospital effluent. Risks associated with antineoplastics are not well characterized in aquatic organisms. We conducted zebrafish embryo/larvae toxicity assays to evaluate responses to cyclophosphamide (0.01-50 µM). Zebrafish survival was affected by 5 µM cyclophosphamide and deformities were noted at > 1 µM. Oxidative respiration remained unchanged in embryos with exposure up to 200 µM. Reactive oxygen species were not increased by 50 µM cyclophosphamide exposure. More than 15 oxidative stress and immune-related transcripts were measured. Superoxide dismutase 2 and heat shock protein 70 and 90a were induced in larvae by cyclophosphamide. Immune-related transcripts were assessed due to immunosuppressive properties of cyclophosphamide, and mmp9 and myd88 levels were altered in expression. Hyperactivity of larvae was noted following 5 µM cyclophosphamide exposure. There was no change in anxiety-related endpoints (light-dark preference). Risks for larval fish exposed to cyclophosphamide in the environment may be low.