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.