Do Single-Component and Mixtures Selected Organic UV Filters Induce Embryotoxic Effects in Zebrafish (Danio rerio)?

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.

Alps at risk: High-mountain lakes as reservoirs of persistent and emerging contaminants

Despite their remote locations, high-mountain lakes located in the Alps are vulnerable to chemical pollution. This discussion explores the important aspects of these lakes as repositories of Persistent Organic Pollutants (POPs) and Contaminants of Emerging Concern (CECs), elucidating their sources and implications for both the environment and human health. In terms of the presence of POPs in high-altitude lakes of the Alps, 14 studies have been identified examining the occurrence of polychlorinated biphenyls, dichlorodiphenyltrichloroethane an its metabolites, polybrominated diphenyl ethers, and polycyclic aromatic hydrocarbons. The bulk of research on POPs in high-mountain lakes is concentrated in the Italian Alps (63%), followed by Switzerland (22%), Austria (12%), and France (3%), respectively. Sediment is predominantly investigated (65%), followed by fish (33%) and water (2%). Similarly, in relation to the presence of CECs in high-mountain lakes of the Alps, six studies have been identified investigating the occurrence of musks, perfluorinated compounds, and microplastics. Investigations into CECs predominantly occur in Switzerland (42%), France (33%), and Italy (25%), with fish samples (muscle and liver) being the primary focus (46%), followed by sediment (17%) and water (17%). Other compartments like zooplankton, frog/tadpoles, and snow remain less explored. The discussion also shed light on various pathways through which pollutants reach these remote landscapes, including atmospheric transport, glacial meltwater, and human activities. Protecting these pristine peaks demands concerted efforts encompassing ongoing research, vigilant monitoring, and dedicated conservation initiatives.

Effects associated with exposure to the emerging contaminant octyl-methoxycinnamate (a UV-B filter) in the aquatic environment: a review

Given the increasing concern surrounding ultraviolet (UV) radiation-induced skin damage, there has been a rise in demand for UV filters. Currently, UV-filters are considered emerging contaminants. The extensive production and use of UV filters have led to their widespread release into the aquatic environment. Thus, there is growing concern that UV filters may bioaccumulate and exhibit persistent properties within the environment, raising several safety health concerns. Octyl-methoxycinnamate (OMC) is extensively employed as a UV-B filter in the cosmetic industry. While initially designed to mitigate the adverse photobiological effects attributed to UV radiation, the safety of OMC has been questioned with some studies reporting toxic effects on environment. The aim of this review to provide an overview of the scientific information regarding the most widely used organic UV-filter (OMC), and its effects on biodiversity and aquatic environment.

Acute toxicity assessment of nine organic UV filters using a set of biotests

UV filters in environmental compartments are a source of concern related to their ecotoxicological effects. However, little is known about UV filters' toxicity, particularly those released into the environment as mixtures. Acute toxicity of nine organic UV filters benzophenone-1, benzophenone-2, benzophenone-3, 4-methoxy benzylidene camphor, octocrylene, ethylhexyl methoxycinnamate, 2-ethylhexyl salicylate, homosalate, and butyl methoxydibenzoylmethane was determined. UV filter solutions were tested as single, binary, and ternary mixtures of various compositions. Single solutions were tested using a set of bio tests, including tests on saline crustaceans (Artemia franciscana), freshwater crustaceans (Daphnia magna), marine bacteria (Aliivibrio fischeri), and freshwater plants (Lemna minor). The tests represent different stages of the trophic chain, and hence their overall results could be used to risk assessment concerning various water reservoirs. The toxicity of binary and ternary mixtures was analyzed using the standardized Microtox® method. Generally, organic UV filters were classified as acutely toxic. Octocrylene was the most toxic for Arthemia franciscana (LC50 = 0.55 mg L-1) and Daphnia magna (EC50 = 2.66-3.67 mg L-1). The most toxic against freshwater plants were homosalate (IC50 = 1.46 mg L-1) and octocrylene (IC50 = 1.95 mg L-1). Ethylhexyl methoxycinnamate (EC50 = 1.38-2.16 mg L-1) was the most toxic for marine bacteria. The least toxic for crustaceans and plants were benzophenone-1 (EC50 = 6.15-46.78 mg L-1) and benzophenone-2 (EC50 = 14.15-54.30 mg L-1), while 4-methoxy benzylidene camphor was the least toxic for marine bacteria (EC50 = 12.97-15.44 mg L-1). Individual species differ in their sensitivity to the tested organic UV filters. An assessment of the toxicity of mixtures indicates high and acute toxicity to marine bacteria after exposition to a binary mixture of benzophenone-2 with octocrylene, 2-ethylhexyl salicylate, or homosalate. The toxicity of mixtures was lower than single solutions predicting antagonistic interaction between chemicals.

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Toxic effects of sirolimus and everolimus on the development and behavior of zebrafish embryos

Sirolimus and everolimus have been widely used in children. These mammalian target of rapamycin (mTOR) inhibitors have shown excellent efficacy not only in organ transplant patients as immunosuppressive agents but also in patients with some other diseases. However, whether mTOR inhibitors can affect the growth and development of children is of great concern. In this study, using zebrafish models, we discovered that sirolimus and everolimus could slow the development of zebrafish, affecting indicators such as survival, hatching, deformities, body length, and movement. In addition to these basic indicators, sirolimus and everolimus had certain slowing effects on the growth and development of the nervous system, blood vessels, and the immune system. These effects were dose dependent. When the drug concentration reached or exceeded 0.5 μM, the impacts of sirolimus and everolimus were very significant. More interestingly, the impact was transient. Over time, the various manifestations of experimental embryos gradually approached those of control embryos. We also compared the effects of sirolimus and everolimus on zebrafish, and we revealed that there was no significant difference between these drugs in terms of their effects. In summary, the dose of sirolimus and everolimus in children should be strictly controlled, and the drug concentration should be monitored over time. Otherwise, drug overdosing may have a certain impact on the growth and development of children.

Safety of benzophenone-type UV filters: A mini review focusing on carcinogenicity, reproductive and developmental toxicity

Consumer products containing benzophenone-type ultraviolet (UV) filters (BPs) have been widely accepted by the public, resulting in the widely existence of various BPs in the human body and environment. In recent years, more and more evidences show that BPs are endocrine disruptors. In view of the continuous exposure risk of BPs and their endocrine disrupting characteristics, the carcinogenicity of BPs and their effects on reproduction and development are of particular concern. However, due to the wide varieties of BPs and the scattered toxicity studies on BPs, people have a limited understanding on the safety of BPs. Therefore, this paper systematically reviews the carcinogenicity, reproductive and developmental toxicity of BPs in order to expand people's knowledge on the health risks of BPs and screen for more safe BPs. Although existing toxicological studies are insufficient, it can be determined that BPs have different potentials for carcinogenicity, and reproductive and developmental toxicity. Among those BPs, 2-hydroxyl-4-methoxyl benzophenone needs to be used with caution due to its adverse effects on cancer cell proliferation and migration, reproductive ability, sex differentiation, neurodevelopment, and so on. It is worth noting that functional group substitutions significantly affect the interaction between BPs and biomolecules such as DNA, cancer cells, and seminal fluid, resulting in different levels of toxicity. In short, it is very necessary to evaluate the carcinogenicity, reproductive and developmental toxicity of BPs, which is of great significance for establishing reasonable BPs content standards in cosmetics, water quality treatment standards for BPs, and so on.

Biomarkers activity in Oreochromis niloticus under sub-chronic exposure to a UV filters ternary mixture

The behavior of organic UV filters in aquatic ecosystems and living organisms raises concern. For the first time, biochemical biomarkers were evaluated in the liver and brain of juvenile Oreochromis niloticus exposed to 0.001 and 0.5 mg L^-1 of a benzophenone-3 (BP-3), octyl methoxycinnamate (EHMC), and octocrylene (OC) mixture for 29 days. Before the exposure, the stability of these UV filters was investigated using liquid chromatography. The experiment with aeration in the aquarium showed a high percentage of concentration reduction (%) after 24 h: 62 ± 2 for BP-3, 96 ± 6 for EHMC, and 88 ± 2 for OC versus 5 ± 4 for BP-3, 8 ± 7 for EHMC, and 2 ± 3 for OC when without aeration. These results defined the bioassay protocol. The stability of the filters concentrations after being stored in PET flasks and subjected to freezing and thawing cycles was also verified. In PET bottles, the BP-3, EHMC, and OC presented concentration reductions of 8 ± 1, 28 ± 7 and 25 ± 5 respectively, after 96 h storage and four freezing cycles. In falcon tubes the concentration reductions observed were 47 ± 2 for BP-3, >95 ± 1 for EHMC and 86 ± 2 for OC after 48 h and two cycles. The 29 days of sub-chronic exposure indicated the occurrence of oxidative stress through the enhanced lipid peroxidation (LPO) levels for the groups exposed to both bioassay concentrations. The catalase (CAT), glutathione-S-transferase (GST), and acetylcholinesterase (AChE) activities did not show significant alterations. The genetic adverse effects were analyzed in erythrocytes of fish exposed to 0.001 mg L^-1 of the mixture by comet and micronucleus biomarkers and no significant damage was observed.

First In Vivo Insights on the Effects of Tempol-Methoxycinnamate, a New UV Filter, as Alternative to Octyl Methoxycinnamate, on Zebrafish Early Development

The demand for organic UV filters as active components in sunscreen products has rapidly risen over the last century, as people have gradually realized the hazards of overexposure to UV radiation. Their extensive usage has resulted in their ubiquitous presence in different aquatic matrices, representing a potential threat to living organisms. In this context, the need to replace classic UV filters such as octyl methoxycinnamate (OMC), one of the most popular UV filters reported to be a potential pollutant of aquatic ecosystems, with more environmentally friendly ones has emerged. In this study, using zebrafish, the first in vivo results regarding the effect of exposure to tempol-methoxycinnamate (TMC), a derivative of OMC, are reported. A comparative study between TMC and OMC was performed, analyzing embryos exposed to similar TMC and OMC concentrations, focusing on morphological and molecular changes. While both compounds seemed not to affect hatching and embryogenesis, OMC exposure caused an increase in endoplasmic reticulum (ER) stress response genes, according to increased eif2ak3, ddit3, nrf2, and nkap mRNA levels and in oxidative stress genes, as observed from modulation of the sod1, sod2, gpr, and trx mRNA levels. On the contrary, exposure to TMC led to reduced toxicity, probably due to the presence of the nitroxide group in the compound's molecular structure responsible for antioxidant activity. In addition, both UV filters were docked with estrogen and androgen receptors where they acted differently, in agreement with the molecular analysis that showed a hormone-like activity for OMC but not for TMC. Overall, the results indicate the suitability of TMC as an alternative, environmentally safer UV filter.

Biotransformation, metabolic response, and toxicity of UV-234 and UV-326 in larval zebrafish (Danio rerio)

Benzotriazole ultraviolet stabilizers (BUVSs) are emerging pollutants that are widely detected in aquatic ecosystems. While structure-dependent effects of BUVSs are reported, the relationship between biotransformation and toxicity outcomes remains unclear. In this study, zebrafish embryos were exposed to two common BUVSs (UV-234 and UV-326) at 1, 10, and 100 µg/L for up to 7 days. Comparison of their uptake and biotransformation revealed that the bioaccumulation capacity of UV-234 was higher than that of UV-326, while UV-326 was more extensively biotransformed with additional conjugation reactions. However, UV-326 showed low metabolism due to inhibited phase II enzymes, which may result in the comparable internal concentrations of both BUVSs in larval zebrafish. Both BUVSs induced oxidative stress while decreased MDA, suggesting the disturbance of lipid metabolism. The subsequent metabolomic profiling revealed that UV-234 and UV-326 exerted different effects on arachidonic acid, lipid, and energy metabolism. However, both BUVSs negatively impacted the cyclic guanosine monophosphate / protein kinase G pathway. This converged metabolic change resulted in comparable toxicity of UV-234 and UV-326, which was confirmed by the induction of downstream apoptosis, neuroinflammation, and abnormal locomotion behavior. These data have important implications for understanding the metabolism, disposition, and toxicology of BUVSs in aquatic organisms.

Octinoxate as a potential thyroid hormone disruptor - A combination of in vivo and in vitro data

Ultraviolet filters are commonly used in various cosmetic products. Due to their huge consumption ultraviolet filters become a part of the environment. Octinoxate is a commonly used ultraviolet filter that is widely detected in the aquatic environment. In our study, we investigated whether this ultraviolet filter is able to disrupt thyroid hormone regulation after six weeks of exposure in rainbow trout (Oncorhynchus mykiss). Thyroid hormones play crucial role in development and regulation of the organism and its disruption could cause the whole-body imbalance. Our study includes a compilation of in vivo and in vitro tests. The results of the in vivo experiment revealed a significant increase in thyroxine hormone in plasma for the highest tested dose of octinoxate (i.e. 395.6 μg/kg). We examined selected tissues (liver and cranial kidney) to determine the mRNA expression of genes involved in thyroid hormones regulation. The analysis confirmed downregulation of deiodinase 2 mRNA expression for the highest tested dose (i.e. 395.6 μg/kg) and downregulation of paired box 8 mRNA for medium (96 μg/kg) and the highest octinoxate dose (395.6 μg/kg.) only in cranial kidney. In vitro analysis indicated that octinoxate does not elicit (anti-)thyroid activity via thrβ and does not behave as a transthyretin ligand. Based on our results, octinoxate has a potential to act as a thyroid hormone disruptor, but further research required to better understand the entire regulatory mechanism.

Toxicity of single and combined 4-epianhydrotetracycline and cadmium at environmentally relevant concentrations on the zebrafish embryos (Danio rerio)

The combined pollution of antibiotics and heavy metals has attracted a worldwide attention in the recent years. 4-epianhydrotetracycline (EATC) is the major degradation product of tetracycline (TC), which has been detected frequently in environment and its concentration is even higher than TC under some circumstances. Cadmium (Cd) is a common heavy metal contaminant and has highly toxic to organisms, plants and humans even at low doses. In the present study, zebrafish (Danio rerio) embryo toxicity test was performed to investigate the single and combined effects of EATC and Cd on aquatic organisms. Exposure to EATC and Cd at environmentally relevant concentrations had a series of hazardous impacts on the embryonic development, including lethality, hatching rate, heart rate and teratogenic effects. Compared to the contaminant existed alone, combined pollution produced stronger toxicity, which appeared as the decreasing of heart rate and hatching rate, and the increasing of malformation of zebrafish embryos. After 96 h exposure, the reactive oxygen species (ROS) levels in zebrafish embryos were increased significantly, revealing that EATC-Cd co-exposure resulted in potential oxidative stress-induced damage. Acridine orange (AO) staining showed that combined exposure resulted in stronger cell apoptosis. The potential health risks of the combined pollution of EATC and Cd should be paid more attention to higher level vertebrates and humans.

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.

Freshwater Environmental Risk Assessment of Down-the-Drain Octinoxate Emissions in the United States

Organic ultraviolet (UV) filters are used in a variety of cosmetic and personal care products (CPCPs), including sunscreens, due to their ability to absorb solar radiation. These UV filters can be washed down the drain through bathing, cleansing, or the laundering of clothing, therefore UV filters can enter the freshwater environment via wastewater treatment plant effluent, and so a freshwater risk assessment is necessary to establish the environmentally safe use of these important CPCP ingredients. In the present study, an environmental safety assessment for a UV filter of regulatory concern, octinoxate, was conducted. An established risk assessment framework designed specifically for CPCPs released to the freshwater environment in the United States was used for the assessment. A distribution of predicted environmental concentrations (PECs) representative of conditions across the region was calculated using the spatially resolved probabilistic exposure model iSTREEM. A review of available hazard data was conducted to derive a predicted no-effect concentration (PNEC). The safety assessment was conducted by comparing the PEC distribution to the PNEC. A substantial margin of safety was found between the 90th percentile PEC, which is representative of the reasonable worst-case environmental exposure, and the PNEC. Owing to this finding of negligible risk, further refinement of the risk assessment through the generation of experimental data or refinement of conservative assumptions is not prioritized. These results are critical for demonstrating the environmental safety of UV filters in the US freshwater environment and will help guide future work. Environ Toxicol Chem 2022;41:3116-3124. © 2022 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Gone with sunscreens: Responses of blue mussels (Mytilus edulis) to a wide concentration range of a UV filter ensulizole

Organic UV filters have emerged as a new threat to marine organisms, but ecotoxicological studies have so far focused on only a few substances despite the chemical diversity of these synthetic sunscreen agents. Here we examined the responses of blue mussels Mytilus edulis to ensulizole, a non-lipophilic UV filter commonly found in the Baltic Sea. Mussels were exposed for three weeks to five ensulizole concentrations of 10, 10², 10³, 10⁴, and 10⁵ ng/L. Stress on stress response was evaluated by subjecting mussels to air exposure. A battery of biomarkers related to detoxification and antioxidant defense, oxidative stress damage, energy reserves and metabolism, autophagy, apoptosis, inflammation, and DNA damage was measured in the gills and the digestive gland. In general, ensulizole affected the antioxidant response, energy storage, and cell death-related processes in mussel tissues. Mussels exposed to low, environmentally relevant concentrations of ensulizole had a shorter air survival time than the control. Ensulizole often showed the non-monotonic concentration-response curves, suggesting the complex effects of this UV filter at molecular, biochemical, and organismal levels.

Comparative transcriptome analysis reveals immunotoxicology induced by three organic UV filters in Manila clam (Ruditapes philippinarum)

Benzophenone-3 (BP-3), 4-methyl-benzylidene camphor (4-MBC) and 2-ethyl-hexyl-4-trimethoxycinnamate (EHMC) are commonly used organic ultraviolet (UV) filters and are frequently detected in water environments. In the present study, we studied the potential adverse impacts of UV filter exposures in Ruditapes philippinarum by investigating transcriptomic profiles and non-specific immune enzyme activities. Transcriptome analysis showed that more genes were differentially regulated in EHMC-treated group, and down-regulated genes (2009) were significantly more than up-regulated ones (410) at day 7. Function annotation revealed that pathways "immune system", "cell growth and death" and "infectious diseases" were significantly enriched. Generally, combined qPCR and biochemical analyses demonstrated that short-term exposure to low dose of UV filters could activate immune responses, whereas the immune system would be restrained after prolonged exposure. Taken together, the present study firstly demonstrated the immunotoxicology induced by BP-3, 4-MBC and EHMC on R. philippinarum, indicating their potential threats to the survival of marine bivalves.

Single and combined effects of ultraviolet radiation and triclosan during the metamorphosis of Solea senegalensis

Ultraviolet radiation (UV) and triclosan (TCS) affect the early development of marine fish; however, the corresponding molecular mechanisms are still not fully understood. Therefore, this work aims to study the effects of the single and combined exposure to these stressors during the thyroid-regulated metamorphosis of the flatfish Solea senegalensis. Sub-lethal exposure (5.89 kJ m^-2 UV and/or 0.546 and 1.090 mg L^-1 TCS for 48 h) was performed at the beginning of metamorphosis (13 days after hatching, dah), followed by a period in clean media until complete metamorphosis (24 dah). Malformations, metamorphosis progression, length, behavior and the expression of thyroid axis-related genes were studied. TCS induced malformations, decreased swimming performance, and induced metamorphosis acceleration at 15 dah, followed by a significant metamorphosis delay. Such effects were more noticeable in the presence of UV. The down-regulation of five thyroid axis-related genes occurred after exposure to TCS (15 dah), and after 9 days in clean media two genes were still down-regulated. UV exposure increased the effect of TCS by further down-regulating gene expression immediately after the exposure. Since several effects persisted after the period in clean media, implications of these stressors (mainly TCS) on the ecological performance of the species are suggested.

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.

Effects of plastic particles on aquatic invertebrates and fish - A review

This review summarises the current knowledge on the effects of microplastics and their additives on organisms living in the aquatic environment, particularly invertebrates and fish. To date, microplastics have been recognised to affect not only the behaviour of aquatic animals but also their proper development, causing variations in fertility, oxidative stress, inflammations and immunotoxicity, neurotoxicity, and changes in metabolic pathways and gene expression. The ability of microplastics to bind other xenobiotics and cause combined toxicity along side the effect of other agents is also discussed as well. Microplastics are highly recalcitrant materials in both freshwater and marine environments and should be considered extremely toxic to aquatic ecosystems. They are severely problematic from ecological, economic and toxicological standpoints.

2, 5-dichloro-1, 4-benuinone exposure to zebrafish embryos/larvae causes neurodevelopmental toxicity

2, 5-dichloro-1, 4-benuinone (2, 5-DCBQ) is an emerging disinfection by-product belonging to the class of halobenzoquinones (HBQs). However, there is limited evidence regarding the neurotoxic effects of 2, 5-DCBQ. To better understand the toxicological mechanisms of aquatic organisms, zebrafish embryos were exposed to 0.2 mg/L, 0.4 mg/L, and 0.6 mg/L of 2, 5-DCBQ from 4 h post-fertilization (hpf) to 120 hpf. Developmental defects, such as reduced body length, decreased heart rate, decreased pigmentation, and abnormal motor axon structure was observed. In particular, the locomotor activity of zebrafish larvae reduced with exposure to increasing 2, 5-DCBQ concentrations, and this effect was more pronounced under dark stimulation. The results indicated that the genes associated with neuronal development (gfap, mbp, syn2a, elavl3, ache, and a1-tubulin) were significantly downregulated after treatment with 2, 5-DCBQ. Furthermore, the KEGG result showed the neuroactive ligand-receptor interaction and apoptosis pathways were visibly disrupted, and we found acetylcholinesterase activity was also affected. In summary, the disinfection by-product, 2, 5-DCBQ, exhibits neurodevelopmental toxicity in zebrafish embryos, providing novel evidence for comprehensive analyses of its toxicity.

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.

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.

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.

Effect of benzophenone-3 on the blood cells of zebrafish (Danio rerio)

Benzophenone-3 (BP-3) is a common component of organic sunscreen widely used that can affect especially aquatic ecosystems health, including fish. To verify the biological effects of low concentrations of BP-3 on blood cells, one hundred and forty zebrafish (D. rerio) were used and then randomly divided into five groups: control group (water), solvent group (alcoholic water), and BP-3 group (BP-3 at 7 µg L^-1, BP-3 at 70 µg L^-1, and BP-3 at 700 µg L^-1). The blood slices were stained with Panoptic stain and with Giemsa solution for the hematological analysis. During the exposure to BP-3, no behavioral changes were observed. Although no significant difference in total leukocytes occurred, an increase in neutrophils and a reduction of lymphocytes at the highest concentration on both 7th and 14th days were detected. The total and cytoplasmic area of erythrocytes on the 7th day at the highest concentration were reduced. In addition, alterations on the erythrocyte nuclear morphology in fish exposed to BP-3 were usually visualized, mainly when considered the occurrence of blebbed nucleus and micronucleus, indicating that BP-3 exhibits cytotoxic and mutagenic effects. The results indicate that BP-3 can interfere with the morphophysiology of aquatic organisms.

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.

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.

Environmentally Relevant Concentrations of Triclosan Induce Cyto-Genotoxicity and Biochemical Alterations in the Hatchlings of Labeo rohita

Xenobiotic Triclosan (TCS) is of great concern because of its existence in a variety of personal, household and healthcare products and continuous discharge in water worldwide. Excessive use of TCS-containing sanitizers and antiseptic products during the COVID-19 pandemic further increased its content in aquatic ecosystems. The present study deals with the cyto-genotoxic effects and biochemical alterations in the hatchlings of Labeo rohita on exposure to environmentally relevant concentrations of TCS. Three-days-old hatchlings were exposed to tap water, acetone (solvent control) and 4 environmentally relevant concentrations (6.3, 12.6, 25.2 and 60 µg/L) of TCS for 14 days and kept for a recovery period of 10 days. The significant concentration-dependent decline in cell viability but increase in micronucleated cells, nucleo-cellular abnormalities (NCAs) and DNA damage parameters like tail length, tail moment, olive tail moment and percent of tail DNA after exposure persisted till the end of recovery period. Glucose, triglycerides, cholesterol, total protein, albumin, total bilirubin, uric acid and urea (except for an increase at 60 µg/L) showed significant (p ≤ 0.05) concentration-dependent decrease after 14 days of exposure. The same trend (except for triglycerides, albumin and total bilirubin) continued till 10 days post exposure. In comparison to control, transaminases (alanine and aspartate aminotransferases) increased (p ≤ 0.05) after exposure as well as the recovery period, while a decline in alkaline phosphatase after exposure was followed by a significant increase during the recovery period. The results show that the environmentally relevant concentrations of TCS cause deleterious effects on the hatchlings of L. rohita.

Embryotoxicity of Selective Serotonin Reuptake Inhibitors—Comparative Sensitivity of Zebrafish (Danio rerio) and African Clawed Frog (Xenopus laevis) Embryos

Over the past twenty years, the prescription of antidepressant drugs has increased all over the world. After their application, antidepressants, like other pharmaceuticals, are excreted and enter the aquatic environment. They are dispersed among surface waters mainly through waste water sources, typically at very low concentrations— from a tenth up to hundreds of ng/L. Frequently detected antidepressants include fluoxetine and citalopram—both selective serotonin reuptake inhibitors. The aim of our study was to assess the embryotoxicity of fluoxetine hydrochloride and citalopram hydrochloride on the early life stages of zebrafish (Danio rerio) and the African clawed frog (Xenopus laevis). The embryos were exposed to various concentrations of the individual antidepressants and of their mixtures for 96 h. The tested levels included both environmentally relevant and higher concentrations for the evaluation of dose-dependent effects. Our study demonstrated that even environmentally relevant concentrations of these psychiatric drugs influenced zebrafish embryos, which was proven by a significant increase (p < 0.01) in the embryos’ heart rates after fluoxetine hydrochloride exposure and in their hatching rate after exposure to a combination of both antidepressants, and thus revealed a potential risk to aquatic life. Despite these results, we can conclude that the African clawed frog is more sensitive, since exposure to the highest concentrations of fluoxetine hydrochloride (10,000 μg/L) and citalopram hydrochloride (100,000 μg/L) resulted in total mortality of the frog embryos.

Removal of Aqueous Para-Aminobenzoic Acid Using a Compartmental Electro-Peroxone Process

The presence of emerging contaminant para-aminobenzoic acid (PABA) in the aquatic environment or drinking water has the potential to harm the aquatic ecosystem and human health. In this work, the removal of aqueous PABA by a compartmental electro-peroxone (E-peroxone) process was systematically investigated from the kinetic and mechanism viewpoints. The results suggest that single electrolysis or ozonation was inefficient in PABA elimination, and the combined E-peroxone yielded synergistic target pollutant degradation. Compared to the conventional E-peroxone oxidation, the sequential cathodic reactions, followed by anodic oxidations, improved the PABA removal efficiency from ~63.6% to ~89.5% at a 10-min treatment, and the corresponding pseudo first-order kinetic reaction rate constant increased from ~1.6 × 10−3 to ~3.6 × 10−3 s−1. Moreover, the response surface methodology (RSM) analysis indicated that the appropriate increase of inlet ozone concentration, applied current density, initial solution pH value, and solution temperature could accelerate the PABA degradation, while the excess of these operational parameters would have a negative effect on the treatment efficiency. The comparation tests revealed that the coupling of electrolysis and ozonation could synergistically produce hydroxyl radicals (HO•) and the separation of cathodic reactions and anodic oxidations further promoted the HO• generation, which was responsible for the enhancement of PABA elimination in the compartmental E-peroxone process. These observations imply that the compartmental E-peroxone process has the potential for aqueous micropollutants elimination, and the reaction conditions that favor the reactive oxygen species generation are critical for the treatment efficiency.