Evaluation of organ developmental toxicity of environmental toxicants using zebrafish embryos

Abstract

There is increasing global concern about environmental pollutants, such as heavy metals, plastics, pharmaceuticals, personal care products, and pesticides, which have been detected in a variety of environments and are likely to be exposed to nontarget organisms, including humans. Various animal models have been utilized for toxicity assessment, and zebrafish are particularly valuable for studying the toxicity of various compounds owing to their similarity to other aquatic organisms and 70% genetic similarity to humans. Their development is easy to observe, and transgenic models for organs such as the heart, liver, blood vessels, and nervous system enable efficient studies of organ-specific toxicity. This suggests that zebrafish are a valuable tool for evaluating toxicity in specific organs and forecasting the potential impacts on other nontarget species. This review describes organ toxicity caused by various toxic substances and their mechanisms in zebrafish.

INTRODUCTION

There is growing worldwide concern regarding environmental pollutants, including heavy metals, plastics, pharmaceuticals, personal care products (PPCPs), and pesticides. These environmental pollutants have been detected in various aquatic environments, and their potential for human exposure has increased as a result of the ecological cycle (Lee et al., 2024b, Pirsaheb and Moradi, 2020). Various in vitro and in vivo models have been developed to investigate the toxic effects of environmental pollutants.

Zebrafish animal models are widely used to examine the effects of numerous toxicants because of their various advantages. They have comparable reactivities to toxicants in other aquatic organisms and are 70% genetically similar to humans, with 80% similarity in genes associated with disease (Adhish and Manjubala, 2023, Howe et al., 2013). They have transparent embryos, making it easy to observe changes during development and to use various transgenic models to determine toxicity in different organs (Bauer et al., 2021, Hong et al., 2024b, Silva Brito et al., 2022). Numerous organ toxicities, including cardiotoxicity, vascular toxicity, hepatotoxicity, and neurotoxicity, have been examined in zebrafish models (Min et al., 2023a, Park et al., 2023a). Because the structure and physiology of each organ are similar to those of humans, it is possible to predict the toxic effects on aquatic organisms as well as on humans (Bauer et al., 2021, Teame et al., 2019).

This review describes the effects of common environmental contaminants frequently found in aquatic environments on different zebrafish organs. Various transgenic zebrafish models with fluorescent proteins attached to organ-specific markers, such as the heart, blood vessels, liver, and nerves, have been used to investigate abnormal structures and alterations in organ-specific gene expression. Moreover, genes and signaling pathways involved in the development and function of each organ were identified to elucidate the mechanisms of toxicity. This indicates that zebrafish can be effectively used to assess organ-specific toxicity and predict potential effects on other nontarget organisms.

ZEBRAFISH ANIMAL MODEL FOR TOXICITY ASSESSMENT AND ITS DEVELOPMENTAL PROCESS

Zebrafish are small; therefore, they can be bred on a large scale, have a relatively short generation period, and have high fecundity. Additionally, females lay approximately 200 eggs per week through external fertilization, and because the embryos are transparent, the development of internal tissues and organs can be easily monitored (Bacila et al., 2021). Moreover, zebrafish have the advantage of being similar to many aquatic organisms in terms of their reactivity to toxicants (Su et al., 2021). They are 70% genetically similar to humans; therefore, the toxic effects of various toxicants can be predicted in aquatic organisms as well as in humans (Howe et al., 2013). These advantages have led to their widespread use in toxicity assessment.

Primary neurogenesis in zebrafish begins at approximately 3-somite and is completed by 24 hours postfertilization (hpf), with changes in neural and axonal pathways assessed at 48 hpf (Wu et al., 2019). Myelinated Schwann cell precursors in the peripheral nervous system were observed at 2 days postfertilization (dpf), and myelinating oligodendrocytes in the central nervous system (CNS) were observed at 60 hpf (Fig. 1). Myelin loss and dysfunction are pathological features of several neurological diseases (Bin and Lyons, 2016).

Fig. 1.

Graphical illustration depicts the developmental process of the blood vessels, heart, nerves, and liver in zebrafish larvae.

Blood vessels are the first organ system to be created during vertebrate embryonic development through the process of angiogenesis, where vascular endothelial cells coalesce to form vascular cords, and the initial vascular network expands by dividing or elongating existing blood vessels through angiogenesis (Wilkinson and van Eeden, 2014). The cardiovascular system of zebrafish is essential for survival 7 days after fertilization, and the endocardium, the inner lining of the heart, is formed by vascular endothelial cells (Lowe et al., 2021).

The zebrafish heart is the first organ to form during embryonic development and has a simple structure with 1 ventricle and 1 atrium compared to the human heart. The heart precursors are located on the side of the blastocyst, form a linear heart tube at 24 hpf, clearly divide into an atrioventricular structure at 48 hpf, and eventually form a S-shaped heart through cardiac looping (Fig. 1) (Brown et al., 2016, Liu and Stainier, 2012, Tessadori et al., 2021). Endocardial cushions are then formed between the chambers, and the heart valve structure is reshaped to prevent blood from flowing backward (Stainier, 2001). Additionally, zebrafish embryos can progress to the late heart formation stage without circulation, because they receive oxygen through passive diffusion (Beis et al., 2005).

At approximately 30 hpf, hepatic anlagen initially appears as a small protrusion on the left side of the intestinal rod. At 2 dpf, the liver bud was enlarged, indicating a transition from budding to the growth phase and formation of the hepatic duct (Korzh et al., 2008). Additionally, liver growth occurs as blood circulates through the hepatic blood vessels, and its size increases up to 10-fold between 72 and 120 hpf (Korzh et al., 2008). This organ plays an important role in the circulatory system by detoxifying toxic substances and secreting bile to aid digestion. The zebrafish liver first expresses liver-specific factors, such as hhex and prox1 at 24 hpf, and development is complete at 120 hpf (Lu et al., 2011).

ENVIRONMENTAL POLLUTANTS THAT AFFECT AQUATIC ENVIRONMENTS

Many environmental pollutants are emerging as global concerns. We selected and briefly described representative toxic substances that are frequently detected in the aquatic environment and are likely to affect nontarget organisms (Jan et al., 2023, Nallakaruppan et al., 2024).

Heavy Metal

Heavy metals are divided into toxic metals (eg, cadmium and mercury) and essential trace metals (eg, manganese and iron) and pollute the environment through various routes, such as waste disposal and fossil fuel combustion (Pan et al., 2024). They are not biodegradable and remain in the environment for a long time when released into ecosystems, thereby affecting both humans and animals (Kiran et al., 2022). For example, elevated concentrations of total mercury and methylmercury have been reported in rivers and reservoirs in the Atlantic region of the United States and are known to be potent neurotoxins in fish. Additionally, the concentration of Hg in shallow groundwater in a nonurbanized environment was 20 ng/L, whereas in an urbanized environment, the concentration of Hg was as high as 177 ng/L compared with undeveloped wetlands (Barringer et al., 2013).

Plastics

Plastics are essential for a wide range of applications, including healthcare, clothing, and construction. It has been reported that global plastic production increased rapidly from 1950 to 2016, reaching approximately 30 million tons. Due to improper disposal methods, plastics are released into the natural environment (Horton, 2022, Li et al., 2021). Especially during the COVID-19 pandemic, the increased use of masks and disposable packaging to prevent the spread of the virus, along with their inappropriate disposal, has caused serious environmental problems, resulting in increased plastic debris in the ocean (de Sousa, 2020). Plastics have a very long half-life, and their decomposition rate is slow in the deep sea, making it one of the places with the highest concentration of microplastic particles. These particles are likely to be absorbed into the gastrointestinal tract and tissues of fish (MacLeod et al., 2021).

Pharmaceuticals and Personal Care Products

Pharmaceuticals and personal care products (PPCPs) are a variety of chemicals used to prevent and treat human and animal diseases, including medicines (eg, anticancer drugs, antibiotics, and hormones) and personal care products (eg, shampoos, lotions, and sunscreens). PPCPs enter the environment through several routes, such as hospitals, residential areas, and wastewater treatment facilities, and are detected in surface water and groundwater at concentrations ranging from ng/L to mg/L (Wang and Wang, 2016). Humans and animals exposed to PPCPs have been reported to experience various changes, such as endocrine disruption, hormonal function disruption, cellular changes, behavioral effects, and oxidative stress. For example, the risk index for antibiotics and anticancer drugs in aquatic environments is high in regions with high population densities (Cizmas et al., 2015). In particular, amoxicillin, a widely used antibiotic, has been detected at 13,300 ng/L in African surface waters, whereas acetaminophen has been detected at 506 ng/L in surface waters and 25 ng/L in groundwater (Cizmas et al., 2015).

Pesticide

Pesticides with low adsorption to soil particles can be transported far from farmlands and, depending on factors such as temperature, humidity, and air movement, enter various environments (Park et al., 2024, Tudi et al., 2021). Organophosphate insecticides, dinitroaniline herbicides, and triazole fungicides are commonly used in aquatic environments. Organophosphate insecticides, including malathion, parathion, and dimethoate, are used in agriculture for pest control and crop protection (Kumar et al., 2016). This compound was detected at high concentrations in groundwater in China, with levels of 4.86 ng/L for methyl-parathion, 3.88 ng/L for malathion, and 7.14 ng/L for dimethoate. Dinitroaniline herbicides are pre-emerging herbicides detected in various water samples (Chen et al., 2021). For example, pendimethalin was detected at maximum concentrations of 28 ng/L in groundwater in Greece (1996-1997) and 2 µg/L in surface water in Georgia, USA (2015-2016), respectively (Glinski et al., 2018, Papastergiou and Papadopoulou-Mourkidou, 2001). Furthermore, the triazole fungicide, which is widely used worldwide, has also been detected in rivers and agricultural water up to 0.5 μg/L (Huang et al., 2022, Park et al., 2023c).

TOXICOLOGICAL RESEARCH IN THE DEVELOPMENT OF ZEBRAFISH

Cardiotoxicity

Cardiotoxicity damages the heart tissue and muscle, which can induce heart dysfunction, leading to heart rate changes and inadequate blood pumping (Cross et al., 2015). Zebrafish embryos have been widely utilized in cardiotoxicity research because of several advantages (Zakaria et al., 2018). The zebrafish heart has 2 chambers, making it structurally different from the human heart, which has 4 chambers, but it has similar electrophysiological features; it is easy to observe changes in phenotype, and it has a high degree of genetic orthology (Lane et al., 2021, Milan et al., 2006). In zebrafish, cardiotoxicity can be assessed using various indicators, such as hemorrhage, pericardial edema, heart rate, and thrombosis (Zakaria et al., 2018). Moreover, various genes related to cardiac development and function, such as cmlc2, amhc, vmhc, ugt1a6, and rarg, have been examined to investigate cardiotoxicity at the molecular level (Wang et al., 2020, Zakaria et al., 2018). Indeed, our study showed that the triazole fungicide, triadimenol, induces cardiotoxicity in zebrafish larvae. Cardiotoxicity was examined using the transgenic model flk1:EGFP, a green fluorescent protein attached to the endothelial receptor flk1 (Jin et al., 2005, Park et al., 2023c). Changes in cardiac structure due to triadimenol exposure were determined by measuring the change in length between sinus venosus and bulbus arteriosus, which are connected to the atrium and ventricle, respectively (Hu et al., 2000). An alteration in the distance between them indicates abnormal cardiac structure and the possibility of irregular blood circulation (Cui et al., 2016, Lu et al., 2022). Indeed, the abnormal cardiac structure induced by triadimenol resulted in a reduced heart rate in zebrafish larvae. These changes in zebrafish hearts were accompanied by the altered expression of genes involved in cardiac function and development, such as actc1, erbb4a, and erbb4b. Moreover, triadimenol reduced the phosphorylation of PI3K/Akt and MAPK signaling molecules, including ERK, JNK, and p38. The PI3K pathway regulates the cardiac cell state and immune responses within the heart, and anomalies in this pathway can affect the development of cardiomyocytes and cardiac fibroblasts, potentially resulting in apoptosis and heart muscle contraction (Ghafouri-Fard et al., 2022). The ERK, JNK, and p38 signaling pathways are also known to play important roles in cardiac development by regulating fibroblast growth factor and Wnt signaling (Lavine et al., 2005, Romero-Becerra et al., 2020, Rose et al., 2010). Therefore, the downregulation of these pathways by triadimenol could affect cardiac development (Park et al., 2023c). In the previous report, penconazole, a triazole fungicide, has been reported to cause cardiotoxicity in zebrafish (Jiang et al., 2023). myl7:EGFP transgenic zebrafish whose cardiomyocytes were labeled with green fluorescent proteins were used to investigate the cardiotoxicity of penconazole (Fig. 2). It also increases the bulbus arteriosus-sinus venosus distance, indicating an abnormal cardiac structure and altered cardiac development-related genes such as nkx2.5, gata4, and vmhc (Jiang et al., 2023). Furthermore, previous studies have reported other environmental pollutants, such as heavy metals and microplastics (La Pietra et al., 2024, Qiao et al., 2021).

Fig. 2.

Evaluation of cardiotoxicity and vascular toxicity in zebrafish larvae. To evaluate cardiotoxicity, transgenic models, such as flk1:EGFP, myl7:EGFP, and myl7:DsRed are typically used, and structural abnormalities are analyzed by measuring the distance between the bulbus arteriosus (BA) and sinus venosus (SV). To investigate vascular toxicity, transgenic models such as flk1:EGFP, fli1a:EGFP, and gata1a:DsRed are typically used, and vasculature intensity and defects are analyzed. Genes primarily evaluated when identifying both toxicities are shown.

Vascular Toxicity

The development of the heart and the formation of blood vessels are closely linked. In cardiac hypertrophy, cardiomyocyte growth is accompanied by angiogenesis, which expands the coronary vasculature (Mohammed et al., 2015). Therefore, appropriate oxygen and nutrients can be delivered to the heart, affecting normal heart development (Hemanthakumar and Kivela, 2020, Mohammed et al., 2015). In zebrafish larvae, prominent vascular structures near the heart and yolk include the common cardinal vein (CCV) and aortic arch. The CCV links all veins to the heart before the cardiovascular system is fully developed in zebrafish larvae and begins to diminish between 74 and 98 hpf (An et al., 2022, Bello et al., 2004). The aortic arches are crucial for blood circulation in the head and tail regions as they link the ventral and lateral dorsal aortas (Crucke and Huysseune, 2013, Isogai et al., 2001, Park et al., 2023b). Vascular structures such as the posterior cardinal vein (PCV), dorsal aorta (DA), dorsal longitudinal anastomotic vessels, intersegmental vessels (ISV), caudal artery, and caudal vein are present in the bodies and tails of zebrafish larvae (Fig. 2) (Isogai et al., 2001). Arterial blood from the heart flows through the DA in the trunk to the caudal artery in the tail region, and venous blood flows from the caudal vein through the PCV into the heart (Isogai et al., 2001, Lee et al., 2017). ISVs include arterial and venous ISV that connect the DAs and PCVs to the dorsal longitudinal anastomotic vessels (Bussmann et al., 2010, Ellertsdottir et al., 2010). These vasculatures have frequently been investigated to examine the vascular toxicity of various environmental pollutants. Our previous studies showed that the benzimidazole fungicide thiabendazole induces malformation of the vasculature in zebrafish larvae (Park et al., 2023b). In the head region, it reduced the relative intensity of the cerebrovascular and aortic arches, and the CCV area, which should have decreased between 74 and 98 hpf was increased by thiabendazole exposure. Moreover, thiabendazole inhibits the segregation of DA and PCV in the zebrafish trunk. Ethalfluralin, a dinitroaniline herbicide, also induces abnormal development of the vascular structure in zebrafish larvae (Hong et al., 2023b). The vascular toxicity of ethalfluralin was examined using the flk1:EGFP transgenic model, which reduced the relative intensity of the brain and intestinal vasculature. Both toxicants cause vascular toxicity by altering the expression of genes involved in blood vessel development, such as those belonging to the vascular endothelial growth factor (VEGF) family. Moreover, polyvinylpyrrolidone-coated silver nanoparticles could induce hypoxia by disturbing oxygen diffusion in zebrafish eggs, which activated hif1 and VEGF signaling, resulting in bcl2 downregulation. Additionally, the aggregation of nanoparticles in the endoplasmic reticulum inhibits protein synthesis. These changes induced vascular toxicity in zebrafish by disrupting angiogenesis (Gao et al., 2016).

Neurotoxicity

Because zebrafish have a morphology similar to that of the CNS in humans, they are widely used in research of neuroscience (Jeong et al., 2022, Kalueff et al., 2014). Structurally, the zebrafish brain is organized similarly to the mammalian brain, with a forebrain, midbrain, hindbrain, and spinal cord (Guo, 2009, Shenoy et al., 2022). There are many functional similarities between the zebrafish and human brain. The participation of the amygdala and habenula in the emotional behavior of zebrafish is similar to that observed in humans and plays a role in controlling the release of dopamine and serotonin (Kalueff et al., 2014, Mathuru and Jesuthasan, 2013). Moreover, it is easy to observe structural changes in the nervous system through various transgenic models and evaluate behavior; therefore, it is often used for neurotoxicity evaluation and drug evaluation for neurological diseases (Babin et al., 2014, Guo, 2009). In a previous study, the olig2:DsRED transgenic zebrafish model was used to determine the neurotoxicity of the carbamate insecticide, oxamyl (An et al., 2023). It reduces the relative number and length of dorsal axons, and these changes are accompanied by changes in the expression of genes involved in neurodevelopment, such as neurog1, gfap, sox10 (Fig. 3) (An et al., 2023). The same transgenic model was used to investigate the neurotoxicity of mevinphos, an organophosphate insecticide (Lee et al., 2024a). It reduces the length of the ventral axon and induces notochord defects by decreasing the expression of neurogenesis-associated genes. In another study, the neurotoxicity of the herbicide, fluroxypyr-1-methylheptyl ester was determined using the mbp:EGFP transgenic zebrafish model with a fluorescent protein attached to myelin basic protein (An et al., 2021). It induces abnormal myelination by triggering discontinuous expression pattern of Mbp. In a previous study, the hb9:GFP transgenic zebrafish model with a fluorescent protein attached to the motor neuron marker Hb9 was used to examine the neurotoxicity of photoaged polystyrene microplastics (Li et al., 2024). The microplastics reduced the fluorescence intensity of motor neurons in the hb9:GFP transgenic models and altered the levels of neurotransmitters such as acetylcholine and γ-aminobutyric acid (GABA), as well as neurotransmitter-related enzymes, resulting in changes in locomotor activity. Neurotoxicity in zebrafish has also been reported for the macrolide antibiotic, azithromycin. It induced reactive oxygen species (ROS) generation and cell death in the brain and interfered with the VEGF/Notch signaling pathway, which plays an important role in neurodevelopment (Chen et al., 2023, Kim et al., 2020). It also excessively activated vegfaa, kdrl, and flt1, which are involved in the VEGF signaling pathway, while inhibiting Notch signaling, including notch1a, notch1b, notch2, and notch3. These alterations downregulated HuC/D, neuronal markers, acetylcholinesterase, and dopamine activities, resulting in abnormal behavior.

Fig. 3.

Evaluation of hepatotoxicity and neurotoxicity in zebrafish larvae. Hepatotoxicity was analyzed by measuring the intensity and area of the liver in fabp10a:DsRed transgenic model. Transgenic models such as olig2:DsRed, huc:GFP, mbp:GFP, and hb9:GFP are typically used to analyze neurotoxicity in various structures, such as the brain, motor neurons, and myelination. Genes that were mainly assessed when identifying both toxicities are also indicated.

Hepatotoxicity

The liver of zebrafish comprises cell types that are similar in morphology and function to those found in the human liver, including hepatocytes, stellate cells, biliary epithelial cells, and endothelial cells (Kita and Shimomura, 2022, Min et al., 2023b, Shimizu et al., 2023, van der Helm et al., 2018). These conserved orthologous cell types in the zebrafish larvae perform the same functions as those in humans (Oderberg and Goessling, 2023, Shimizu et al., 2023). Unlike humans, who have hepatic lobules, zebrafish have hepatic tubules, indicating a structural difference in the liver. Nevertheless, recent studies have reported that zebrafish exhibit an architecture resembling that of hepatic lobules, which are characterized by polygonal structures (Ota and Shiojiri, 2022, Shimizu et al., 2023). Cytochrome P450 enzymes, which play an important role in metabolizing substances in the liver, are evolutionarily conserved in zebrafish and humans (Goldstone et al., 2010). Moreover, in zebrafish liver development, transcription factors, including prox1, hhex, and foxa2, play crucial roles in hepatic specification, as in mammals (Ober et al., 2003). Although there are structural differences between the human and zebrafish livers, similarities in metabolism, function, and development are often used to determine the hepatotoxicity of toxicants and drugs. The hepatotoxicity of acifluorfen and fluchloralin, which are diphenyl ether and dinitroaniline herbicides, respectively, has previously been investigated using the fabp10a:DsRed transgenic model with liver-specific fluorescently labeled genes (Hong et al., 2023a, Hong et al., 2024a). Both acifluorfen and fluchloralin reduced the intensity and size of the liver, and fluchloralin reduced the expression of genes related to liver function and development, such as prox1, hdac1, and ppp1r12a. Pb, a well-known heavy metal with a high exposure potential toward aquatic organisms, has also been reported to cause hepatotoxicity in zebrafish (Dey et al., 2024). Pb decreases catalase activity and produces ROS in the zebrafish liver, leading to lipid peroxidation. Furthermore, ROS activates the Nrf2-Keap1 pathway, and the activated Nrf2 is translocated to the cell nucleus, stimulating the transcription factor ARE and increasing the expression of ho1, nqo1, and hsp70. These changes lead to structural abnormalities in the liver of zebrafish, as identified by histological analysis. The organ toxicities of these toxicants and their mechanisms of action are summarized in Table 1.

Table 1.

Identifying organ toxicity of various toxicants and their mechanisms using zebrafish.

Affected organ	Toxicant	Transgenic model	Major findings (mechanism)	Reference
Cardiotoxicity	Triadimenol	flk1:EGFP	Change in length between sinus venosus (SV) and bulbus arteriosus (BA) Altered expression of genes, such as actc1, erbb4a, and erbb4b Reduced the phosphorylation of PI3K/Akt and MAPK signaling, including Erk, Jnk, and p38	(Park et al., 2023b)
	Penconazole	myl7:EGFP	Increased the BA-SV distance Altered expression of genes, nkx2.5, gata4, and vmhc	(Jiang et al., 2023)
Vascular toxicity	Thiabendazole	flk1:EGFP	Reduced the relative intensity of the cerebrovascular and aortic arches Reduced common cardinal vein (CCV) area Inhibited the segregation of dorsal aorta (DA) and posterior cardinal vein (PCV) Altered expression of genes, such as those belonging to the VEGF family	(Park et al., 2023a)
	Ethalfluralin		Reduced the relative intensity of the brain and intestinal vasculature Altered expression of genes, such as those belonging to the VEGF family	(Hong et al., 2023b)
	Polyvinylpyrrolidone-coated silver nanoparticles	fli1a:EGFP	Induced hypoxia state by disturbing oxygen diffusion Activated hif1 and VEGF signaling, resulting in bcl2 downregulation Inhibited protein synthesis in endoplasmic reticulum	(Gao et al., 2016)
Neurotoxicity	Oxamyl	olig2:DsRED	Reduced the relative number and length of dorsal axons Altered expression of genes, such as neurog1, gfap, and sox10	(An et al., 2023)
	Mevinphos		Reduced the length of the ventral axon Altered the expression of neurogenesis-associated genes	(Lee et al., 2024a)
	Fluroxypyr-1-methylheptyl ester	mbp:EGFP	Induced abnormal myelination by triggering discontinuous pattern of Mbp	(An et al., 2021)
	Polystyrene microplastics	hb9:GFP	Reduced the fluorescence intensity of motor neurons Altered the levels of neurotransmitters such as acetylcholine and GABA	(Li et al., 2024)
	Azithromycin		Activated VEGF signaling pathway, including vegfaa, kdrl, and flt1 Inhibited Notch signaling, including notch1a, notch1b, notch2, and notch3	(Chen et al., 2023)
Hepatotoxicity	Acifluorfen	fabp10a:DsRed	Reduced the intensity and size of the liver	(Hong et al., 2023a)
	Fluchloralin		Reduced the intensity and size of the liver Altered expression of genes, such as prox1, hdac1, and ppplr12a	(Hong et al., 2023a)
	Pb		Decreased catalase activity and produced ROS Activated Nrf2-Keap1 pathway	(Dey et al., 2024)

ROS, reactive oxygen species.

LIMITATIONS AND FURTHER RESEARCH

Some of the toxicants reviewed in this study have been investigated for their detailed mechanisms of organ toxicity; however, specific mechanisms have not yet been explored. Additionally, while toxicants induce toxicity in various organs, their associations have not been adequately investigated. Therefore, it is necessary to study the toxicity at different stages of zebrafish development to determine the association between different organ toxicities. Zebrafish are widely used as toxicity assessment models owing to their many advantages; however, they also have limitations. Toxicants are added to the water in zebrafish toxicity assessments, making dermal exposure the primary route of action. By contrast, humans are more likely to be exposed to toxic substances through contaminated drinking water, highlighting the differences in exposure routes (Bambino and Chu, 2017). Although zebrafish are genetically similar to humans, significant differences exist, such as differences in their immune systems and a relatively simple CNS. Therefore, the use of humanized models or organoids in conjunction with zebrafish has been proposed (Martinez-Lopez et al., 2023, Wang et al., 2023, Zhao et al., 2024). Thus, future research that considers these limitations is necessary to better predict the toxic effects in aquatic organisms and humans using zebrafish.

CONCLUSION

There is an increasing global concern regarding environmental pollutants, particularly heavy metals, plastics, PPCPs, and pesticides. Recent studies have emphasized the necessity of comprehensive toxicity assessments to understand their impacts on ecosystems and human health. Consequently, ongoing research is focused on developing methodologies for more accurate and reliable toxicity evaluations. This review article presents organ toxicity, including cardiotoxicity, vascular toxicity, hepatotoxicity, and neurotoxicity, in zebrafish caused by representative environmental toxicants and their mechanisms and discusses toxicity assessment methods. Organ toxicity can be easily identified using various transgenic zebrafish models, because the reactivity of zebrafish to toxicants is similar to that of other aquatic organisms, and the anatomical and functional similarities of their organs to those in humans enable the prediction of potential toxic effects. However, there are also limitations to toxicity studies using zebrafish, and future studies will need to take these into account.

Author Contributions

Taeyeon Hong: Writing – original draft, Visualization, Validation, Formal analysis, Data curation. Junho Park: Writing – original draft, Validation, Formal analysis, Data curation. Garam An: Visualization, Validation, Investigation. Jisoo Song: Visualization, Validation, Data curation. Gwonhwa Song: Writing – review & editing, Supervision, Project administration, Data curation, Conceptualization. Whasun Lim: Writing – review & editing, Validation, Supervision, Project administration, Funding acquisition, Conceptualization.

Declaration of Competing Interests

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.