Detrimental Effects of Zinc Oxide Nanoparticles on Amphibian Life Stages

Metal nanoparticle-induced effects on green toads (Amphibia, Anura) under climate change: conservation implications

The toxicity of aluminum oxide (Al2O3), copper oxide (CuO), iron oxide (Fe3O4), nickel oxide (NiO), zinc oxide (ZnO), and titanium dioxide (TiO2) nanoparticles (NPs) on amphibians and their interaction with high temperatures, remain unknown. In this study, we investigated the survival, developmental, behavioral, and histological reactions of Bufotes viridis embryos and larvae exposed to different NPs for a duration of 10 days, using lethal concentrations (LC25%, LC50%, and LC75% mg/L) under both ambient (AT: 18 °C) and high (HT: 21 °C) temperatures. Based on LC, NiONPs > ZnONPs > CuONPs > Al2O3NPs > TiO2NPs > Fe3O4NPs showed the highest mortality at AT. A similar pattern was observed at HT, although mortality occurred at lower concentrations and Fe3O4NPs were more toxic than TiO2NPs. The results indicated that increasing concentrations of NPs significantly reduced hatching rates, except for TiO2NPs. Survival rates decreased, abnormality rates increased, and developmental processes slowed down, particularly for NiONPs and ZnONPs, under HT conditions. However, exposure to low concentrations of Fe3O4NPs for up to 7 days, CuONPs for up to 72 h, and NiO, ZnONPs, and TiO2NPs for up to 96 h did not have a negative impact on survival compared with the control group under AT. In behavioral tests with larvae, NPs generally induced hypoactivity at AT and hyperactivity at HT. Histological findings revealed liver and internal gill tissue lesions, and an increase in the number of melanomacrophage centers at HT. These results suggest that global warming may exacerbate the toxicity of metal oxide NPs to amphibians, emphasizing the need for further research and conservation efforts in this context.

Potential ecotoxicity of substrate-enriched zinc oxide nanoparticles to Physalaemus cuvieri tadpoles

Although the ecotoxicological effects of ZnO nanoparticles (ZnO NPs) have already been reported in different taxa, little is known about their impacts on amphibians. Thus, we aimed to evaluate the potential effects of exposure of Physalaemus cuvieri tadpoles to substrates enriched with ZnO NPs (and with its ionic counterpart, Zn+2, ZnCl2 - both at 100 mg/kg) previously used in the cultivation of Panicum maximum (Guinea grass). We showed that although exposure for 21 days did not impact the survival, growth, and development of tadpoles, we noted an increase in the frequency of erythrocyte nuclear abnormalities in the "ZnCl2" and "ZnONP" groups, which was associated with suppression of antioxidant activity in the animals (inferred by SOD and CAT activity and DPPH free radical scavenging capacity). In the tadpoles of the "ZnONP" group, we also noticed a reduction in creatinine and bilirubin levels, alpha-amylase activity, and an increase in alkaline phosphatase activity. But the treatments did not alter the activity of the enzymes lactate dehydrogenase and gamma-glutamyl-transferase and total protein and carbohydrate levels. On the other hand, we report a cholinesterase and hypotriglyceridemic effect in the "ZnCl2" and "ZnONP" groups. Zn bioaccumulation in animals, from ZnO NPs, from Zn+2 released from them, or both, has been associated with causing these changes. Finally, principal component analysis (PCA) and the values of the "Integrated Biomarker Response" index revealed that the exposure of animals to substrates enriched with ZnO NPs caused more pronounced effects than those attributed to its ionic counterpart. Therefore, our study reinforces the need to consider the environmental risks of using these nanomaterials for agricultural purposes for amphibians.

Assessment of multiple biomarkers in Lithobates catesbeianus (Anura: Ranidae) tadpoles exposed to zinc oxide nanoparticles and zinc chloride: integrating morphological and behavioral approaches to ecotoxicology

The ecotoxicological risk to vertebrates posed by zinc oxide nanoparticles (ZnO NPs) is still poorly understood, especially in animals with a biphasic life cycle, which have aquatic and terrestrial phases, such as amphibians. In the present study, we investigated whether acute exposure (7 days) to ZnO NPs and zinc chloride (ZnCl₂) at three environmentally relevant concentrations (0.1, 1.0, and 10 mg L^-1) induces changes in the morphology, chondrocranium, and behavior of the tadpoles of Lithobates catesbeianus (Anura: Ranidae). Tadpoles exposed to both forms of Zn did not undergo any morphological or behavioral changes at the lowest concentrations (0.1 and 1.0 mg L^-1). However, the animals exposed to the highest concentration (10 mg L^-1) lacked oral disc structures, were smaller in size, had a longer tail, and presented changes in the position and coiling of the intestine and malformations of the chondrocranium in comparison with the control group. This indicates that ZnO NPs and ZnCl₂ altered the development of the tadpoles, causing delays in their metamorphosis and even reducing individual fitness. The tadpoles exposed to both forms of Zn at 10 mg L^-1 also had reduced mobility, especially in the presence of conspecifics. Based on these findings, we emphasize the importance of studying morphological, skeletal, and behavioral biomarkers to evaluate the toxic effects of metal-based nanoparticles in amphibians.

Assessment of toxicity in the freshwater tadpole Polypedates maculatus exposed to silver and zinc oxide nanoparticles: A multi-biomarker approach

Nanoparticles (NPs), especially silver nanoparticles (Ag NPs) and zinc oxide nanoparticles (ZnO NPs), are widely used in various industrial applications and are released into the surrounding environment through industrial and household wastewater. They have enormous toxic effects on aquatic animals and amphibians. In the current study, a multi-biomarker approach was used to assess toxicity on Polypedates maculatus (P. maculatus) tadpoles collected from a freshwater pond and exposed to sub-lethal concentrations of Ag-NPs (1, 5 and 10 mg L^-1) and ZnO-NPs (1, 10 and 50 mg L^-1). A significant bioaccumulation of silver (Ag) and Zinc (Zn) was observed in the blood, liver, kidney and bones in comparison to control tadpoles. Blood parameters (Red blood cells (RBC), Hematocrit (Htc), White blood cells (WBC), monocytes, lymphocytes and neutrophils), immunological markers (ACH50, lysozyme, total Ig, total protein, albumin, and globulin), biochemical markers (glucose, cortisol, cholesterol, triglycerides, alanine transaminase (ALT), asparatate transaminase (AST), alkaline phosphatase (ALP), urea and creatinine) and the oxidative stress marker (LPO) of serum were increased significantly (p < 0.05) in Ag/ZnO-NPs exposed groups when compared to the control groups. The levels of mean corpuscular haemoglobin (MCH), mean corpuscular haemoglobin concentration (MCHC), mean corpuscular volume (MCV) and haemoglobin (Hb) in the ZnO NP-exposed groups were significantly different from those in the control group. Antioxidant (SOD and CAT) levels were significantly declined in the treatment groups. Based on the results, Ag/ZnO-NPs are toxic to aquatic organisms and amphibians at sub-lethal concentrations. The species P. maculatus can be used as a bioindicator for the nanomaterial (NM) contamination of freshwater systems.

Influence of nano and bulk copper on agile frog development

Nanotechnology, as one of the fastest-growing industries, offers many benefits in various fields. However, properties that contribute to its positive effects, in other context, can cause adverse effects to various organisms, such as amphibians. Identifying possible negative effects on its survival is crucial since amphibians are the most threatened group of vertebrates. In that context, we investigated the influence of both nano and bulk copper on embryonic development of agile frog, Rana dalmatina. The embryos were exposed to various concentrations (0.01 mg/L, 0.075 mg/L, 0.15 mg/L or 0.3 mg/L) of either nano (CuO, declared size 40-80 nm) or bulk form (CuSO₄·5H₂O) for 16 days. Upon the experiment, tadpoles were measured and weighted, then homogenized and their protein, lipid, and carbohydrates content determined, as well as the activity of LDH. Our results suggest stronger negative influence of nano copper to size and weight of tadpoles, and bulk copper on lipid content, while both had strong negative effect on carbohydrates content, and LDH activity. In addition, our results suggest agile frog to be more susceptible to negative influence of both, nano and bulk copper, than commonly used Xenopus laevis.

Postnatal distribution of ZnO nanoparticles to the breast milk through oral route and their risk assessment for breastfed rat offsprings

Various studies in rodents have shown that nanoparticles are transferred to the breast milk. Under the present study, lactating Wistar rats were repetitively gavaged 5, 25, and 50 mg/kg bw of zinc oxide nanoparticles (ZnO-NPs) and 50 mg kg^-1 bw of bulk zinc oxide (bZnO) for 19 days after parturition. The results showed that ZnO-NPs were absorbed in the small intestine of dams and distributed to the liver. Furthermore, ZnO-NPs were distributed to the intestine and liver of rat pups through dam's milk. No significant change in body weight was observed in the dams treated with ZnO-NPs or bZnO and their offsprings as compared to the control group. The spleen weight significantly increased in the rat dams treated with 50 mg kg^-1 of ZnO-NPs. ZnO-NPs were mostly excreted through feces. The levels of liver cytochrome P450 reductase and serum total antioxidant capacity significantly decreased in the rat dams treated with ZnO-NPs (50 mg kg^-1) and their offsprings. The levels of serum cytokines (tumor necrosis factor-alpha and interleukin-1 beta) and liver injury marker enzymes (alanine aminotransferase and aspartate aminotransferase) significantly increased in the rat dams treated with ZnO-NPs (25 and 50 mg kg^-1) and their offsprings. The level of immunoglobulin A secretion in the intestinal fluid of rat dams and their offsprings is significantly increased by increasing the dose of ZnO-NPs. Histopathology of intestine and liver of offsprings whose rat dams were treated with ZnO-NPs (50 mg kg^-1) showed gross pathological changes. These results provide information for the safety evaluation of ZnO-NPs use during lactation. In conclusion, a dose-dependent postnatal transfer of ZnO-NPs is hazardous to the breastfed offsprings.

Ecotoxicity of nanomaterials in amphibians: A critical review

Nanomaterials (NMs) have been used in a growing number of commercial products, and their rapid expansion could lead to their release into the aquatic environments. However, there is limited knowledge about the impact of NMs in the biota, especially the amphibians. The present study revised the historical use of amphibian species as a model system for nanoecotoxicological studies and summarized the data available in the scientific literature about the genotoxic, mutagenic, histopathological, embryotoxic and reproductive effects of NMs in different groups of amphibians. The interaction, bioaccumulation, mode of action (MoA) and ecotoxicity of NMs on amphibians were also revised. The nanoecotoxicological studies were conducted with 11 amphibian species, being eight species of the order Anura and three species of the order Caudata. Xenopus laevis was the most studied species. The studies were conducted mainly with inorganic NMs (72%) compared to organic ones. The nanoecotoxicity depends on NM behavior and transformation in the environment, as well as the developmental stages of amphibians. The known effects of NMs in amphibians were mainly reported with reactive oxygen species (ROS) production, oxidative stress, and genotoxic effects. Results emphasize the need for further studies testing the ecotoxicity of different NMs, concentrations and exposure periods at environmentally relevant approaches. Furthermore, standard protocols for nanoecotoxicological tests using amphibians are required. Revised data showed that amphibians are suitable organisms to assess the environmental impact of NMs and indicated significant research gaps concerning the ecotoxicity of NMs on freshwater ecosystems and recommendations for future researches.

An insight on the mutagenicity and cytotoxicity of zinc oxide nanoparticles in Gallus gallus domesticus (Phasianidae)

Although the toxicity of zinc oxide (ZnO) nanoparticles (NPs) is known in several experimental models, little is known about their effects on bird representatives. Therefore, the aim of the current study is to evaluate the mutagenic and cytotoxic potential of ZnO NPs in chicks belonging to species Gallus gallus domesticus, as well as to analyze the role played by nuclear and erythrocyte morphological changes as biomarkers of the toxicity of these nanopollutants. Two doses of ZnO NPs (0.245 mg k^-1 and 245.26 mg kg^-1) were herein tested; they were determined based on the predictive environmental concentration of these NPs (760 μg L-1), on the body biomass of the analyzed animals and on the mean daily water intake/bird. Birds were subjected to two intraperitoneal applications (one per day) of solution containing ZnO NPs; they were euthanized 48 h after the first application. The herein collected data have shown that NPs were capable of inducing the formation of different types of erythrocyte nuclear abnormalities, such as micronucleus, binucleate erythrocytes, blebbed, reniform and multilobulated nuclei, as well as symmetric and asymmetric constriction. In addition, changes in the size and shape of erythrocytes were observed in birds exposed to ZnO NPs. Zn bioaccumulation analysis conducted in brain tissues confirmed the association between these changes and animal exposure to ZnO NPs. Thus, besides confirming the toxicological potential of ZnO NPs, to the best of our knowledge, the current study is the first report on the mutagenic and cytotoxic effects of these NPs on bird representatives.

Exposure to Alumina Nanoparticles in Female Mice During Pregnancy Induces Neurodevelopmental Toxicity in the Offspring

Alumina nanoparticles (AlNP) have been shown to accumulate in organs and penetrate biological barriers which lead to toxic effects in many organ systems. However, it is not known whether AlNP exposure to female mice during pregnancy can affect the development of the central nervous system or induce neurodevelopmental toxicity in the offspring. The present study aims to examine the effect of AlNP on neurodevelopment and associated underlying mechanism. ICR strain adult female mice were randomly divided into four groups, which were treated with normal saline (control), 10 μm particle size of alumina (bulk-Al), and 50 and 13 nm AlNP during entire pregnancy period. Aluminum contents in the hippocampus of newborns were measured and neurodevelopmental behaviors were tracked in the offspring from birth to 1 month of age. Furthermore, oxidative stress and neurotransmitter levels were measured in the cerebral cortex of the adolescents. Our results showed that aluminum contents in the hippocampus of newborns in AlNP-treated groups were significantly higher than those in bulk-Al and controls. Moreover, the offspring delivered by AlNP-treated female mice displayed stunted neurodevelopmental behaviors. Finally, the offspring of AlNP-treated mice demonstrated significantly increased anxiety-like behavior with impaired learning and memory performance at 1 month of age. The underlying mechanism could be related to increased oxidative stress and decreased neurotransmitter levels in the cerebral cortex. We therefore conclude that AlNP exposure of female mice during pregnancy can induce neurodevelopmental toxicity in offspring.