Nanoplastics under the charge effects: Unveiling the potential threats to amphibian (Rana nigromaculata) growth, intestinal damage and microbial ecology

Nanoplastics (NPs) are contaminants that may be found in charged forms in the environment, capable of accumulating in aquatic organisms and affecting their health. This study compared the effects of positively charged Polystyrene-NPs (PS-NH₂, 30 nm) and negatively charged Polystyrene-NPs (PS-COOH, 30 nm) at 6 and 60 mg/L on the growth and development of black-spotted frog tadpoles (Rana nigromaculata), as well as on intestinal damage and microbial ecology. The results demonstrated that exposure to both types of NPs significantly reduced the survival rate of tadpoles, while significantly increased their body weight and body length. Compared to PS-COOH, PS-NH₂ exposure resulted in more adverse intestinal tissue damage, manifested by more severe intestinal oxidative stress. Furthermore, exposure to PS-NH₂ significantly reduced the abundance and diversity of the microbiome associated with gut function and nutrient absorption, thereby indirectly causing more severe intestinal damage and growth changes. In addition, functional prediction and gene transcription analysis showed that exposure to charged PS-NPs caused changes in genes associated with glycolysis and lipid metabolism, indicating that the glucose-lipid metabolism of tadpoles is impacted. This study revealed the effects of different charged NPs exposure on the growth of tadpoles and their intestinal toxicity, clarified the potential connections between gut microbiota and glucose-lipid metabolism, and provided a new perspectives on the health risks of NPs in amphibians.