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, lit-tle 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 sup-pression 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 bioac-cumulation 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 re-vealed 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.

Automated summary

This study aimed to evaluate the potential effects of Physalaemus cuvieri tadpoles exposed to substrates enriched with ZnO nanoparticles (ZnO NPs). Results showed an increase in the frequency of erythrocyte nuclear abnormalities and suppression of antioxidant activity in tadpoles exposed to ZnCl2 and ZnONP. Zn bioaccumulation from ZnO NPs or Zn+2 released from them was associated with the observed changes. The study highlights the need to consider the environmental risks of using these nanomaterials for agricultural purposes for amphibians.