Single and combined chronic toxicity of cadmium and titanium dioxide nanoparticles in Aquarana catesbeiana (Anura: Ranidae) tadpoles

•TiO2 NPs and Cd can cause adverse effects in developing amphibians.•TiO2 NPs and Cd increased the mortality of Aquarana catesbeiana tadpoles.•TiO2 NPs and Cd induced histophalogical changes in the gills epithelium.•Combined exposure caused malformations in the chondrocranium of the tadpoles.•Co-exposure reduced the body length and altered the anatomical proportions. The rising production and improper disposal of titanium dioxide nanoparticles (TiO2 NPs) into aquatic systems present considerable environmental challenges, especially when these particles interact with other contaminants such as cadmium (Cd). Thus, the current study aimed to evaluate the potential toxic effects on the gills, chondrocranium, body growth, and mortality of Aquarana catesbeiana tadpoles. The tadpoles were exposed to environmentally relevant concentrations of TiO2 NPs (10 µg L-1), and CdCl2 (10 µg L-1), both individually and in combination, for 30 days (chronic exposure), along with a control group. Our results indicate that the co-exposure to TiO2 NPs and Cd induced a higher mortality rate. In the gills, TiO2 NPs led to epithelial simplification, while Cd exposure resulted in stratified epithelium formation. Additionally, there were notable changes in the index of degenerative alterations for the co-exposed group and the overall organ index for the groups exposed to Cd and the mixture. The viscerocranium showed significant malformations in the ceratobranchials and reticular processes, indicating the mixture's toxicological potential during the skeletal system's development. Morphometric analysis also revealed reduced body length and abnormal body ratios in tadpoles from the co-exposure group. In conclusion, TiO2 NPs and Cd, both alone and in combination, exhibit toxicological effects in A. catesbeiana tadpoles, indicating a potential ecological risk associated with releasing these contaminants into aquatic environments. [Display omitted]