Oxidative stress and genotoxicity in Rhinella arenarum (Anura: Bufonidae) tadpoles after acute exposure to Ni-Al nanoceramics

The impact of chemical pollution across major life transitions: a meta-analysis on oxidative stress in amphibians

Among human actions threatening biodiversity, the release of anthropogenic chemical pollutants which have become ubiquitous in the environment, is a major concern. Chemical pollution can induce damage to macromolecules by causing the overproduction of reactive oxygen species, affecting the redox balance of animals. In species undergoing metamorphosis (i.e. the vast majority of the extant animal species), antioxidant responses to chemical pollution may differ between pre- and post-metamorphic stages. Here, we meta-analysed (N = 104 studies, k = 2283 estimates) the impact of chemical pollution on redox balance across the three major amphibian life stages (embryo, tadpole, adult). Before metamorphosis, embryos did not experience any redox change while tadpoles activate their antioxidant pathways and do not show increased oxidative damage from pollutants. Tadpoles may have evolved stronger defences against pollutants to reach post-metamorphic life stages. In contrast, post-metamorphic individuals show only weak antioxidant responses and marked oxidative damage in lipids. The type of pollutant (i.e. organic versus inorganic) has contrasting effects across amphibian life stages. Our findings show a divergent evolution of the redox balance in response to pollutants across life transitions of metamorphosing amphibians, most probably a consequence of differences in the ecological and developmental processes of each life stage.

2,4-D-based herbicide underdoses cause mortality, malformations, and nuclear abnormalities in Physalaemus cuvieri tadpoles

Amphibians are considered bioindicators of the environment due to their high sensitivity and involvement in terrestrial and aquatic ecosystems. In the last two decades, 2,4-D has been one of the most widely used herbicides in Brazil and around the world, as its use has been authorized for genetically modified crops and therefore has been detected in surface and groundwater. Against this background, the aim of this work was to investigate the effects of environmentally relevant concentrations of 2,4-D-based herbicides on survival, malformations, swimming activity, presence of micronuclei and erythrocyte nuclear abnormalities in Physalaemus cuvieri tadpoles. The amphibians were exposed to six concentrations of 2,4-D-based herbicides: 0.0, 4.0, 30.0, 52.5, 75.0, and 100 μg L-1, for 168 h. At concentrations higher than 52.5 μg L-1, significantly increased mortality was observed from 24 h after exposure. At the highest concentration (100 μg L-1), the occurrence of mouth and intestinal malformations was also observed. The occurrence of erythrocyte nuclear abnormalities at concentrations of 30.0, 52.5, 75.0 and 100 μg L-1 and the presence of micronuclei at concentrations of 52.5, 75.0, and 100 μg L-1 were also recorded. These effects of 2,4-D in P. cuvieri indicate that the ecological risk observed at concentrations above 10.35 μg L-1 2,4-D may represent a threat to the health and survival of this species, i.e., exposure to 2,4-D at concentrations already detected in surface waters in the species' range is toxic to P. cuvieri.

Ecotoxicity risk assessment of copper oxide nanoparticles in Duttaphrynus melanostictus tadpoles

In recent years, copper oxide nanoparticles (CONPs) have gained considerable importance in ecotoxicology studies. CONP ecotoxicity studies on amphibians are limited, particularly on Duttaphrynus melanostictus (D. melanostictus) tadpoles, and most CONP ecotoxicity studies have shown developmental effects on amphibians. Therefore, the present study aimed to determine the ecotoxicity of CONPs in D. melanostictus tadpoles by assessing multi-biomarkers including bioaccumulation, antioxidants, biochemical, haematological, immunological and oxidative stress biomarkers. Transmission electron microscopy (TEM) and dynamic light scattering (DLS) were used to characterize the morphology and physicochemical properties of CONPs. After 30 d of the experiment, blood and organs were collected to measure the levels of multiple biomarkers. The dissolution rate of copper ions in exposed media was observed in all studied groups. According to the results, significant (p < 0.05) increase in copper ion bioaccumulation (blood, liver and kidney), oxidative stress and biochemical biomarkers in the blood serum of CONPs exposed tadpoles compared to control tadpoles, which was accompanied by significant variations in morphological and haematological parameters. In contrast to the untreated tadpoles, the CONPs-exposed tadpoles showed statistically significant (p < 0.05) decreases in antioxidants and immunological indices of blood serum. Based on our results, we concluded that the ecotoxicity of CONPs is due to the production of reactive oxygen species (ROS), which can cause oxidative stress in tadpoles, resulting in impairments. According to our knowledge, the present study was the first to use a multi-biomarker ecotoxicity approach on D. melanostictus tadpoles that could be used as an ecological bioindicator to assess aquatic toxicity.

Humane acute testing with tadpoles for risk assessment of chemicals: Avoidance instead of lethality

In spite of the sensitivity of amphibians to contamination, data from fish have been commonly used to predict the effects of chemicals on aquatic life stages. However, recent studies have highlighted that toxicity data derived from fish species may not protect all the aquatic life stages of amphibians. For pesticide toxicity assessment (PTA), EFSA has highlighted that more information on lethal toxicity for the aquatic life stages of amphibians is still needed to reduce uncertainties. The current review aims to propose a test with amphibians based on spatial avoidance, as a more humane alternative method to the lethality tests for chemicals. A review of lethal toxicity tests carried out with amphibians in the period between 2018 and 2021 is presented, then we discuss the suitability of using fish toxicity data as a surrogate to predict the effects on more sensitive amphibian groups. The possible differences in sensitivity to chemicals may justify the need to develop further tests with amphibian embryos and larvae in order to reduce uncertainties. A new test is proposed focused on the avoidance behaviour of organisms fleeing from contamination to replace lethal tests. As avoidance indicates the threshold at which organisms will flee from contamination, a reduction in the population density, or its disappearance, at the local scale due to emigration is expected, with ecological consequences analogous to mortality. Avoidance tests provide an ethical advantage over lethal tests as they respect the concepts of the 3 Rs (mainly Refinement), reducing the suffering of the organisms.