Nano-sized CuO, TiO₂ and ZnO affect Xenopus laevis development

The teratogenic potential of commercially available copper oxide (CuO), titanium dioxide (TiO2) and zinc oxide (ZnO) nanoparticles (NPs) was evaluated using the standardized FETAX test. After characterization of NP suspensions by TEM, DLS and AAS, histopathological screening and advanced confocal and energy-filtered electron microscopy techniques were used to characterize the induced lesions and to track NPs in tissues. Except for nCuO, which was found to be weakly embryolethal only at the highest concentration tested, the NPs did not cause mortality at concentrations up to 500 mg/L. However, they induced significant malformation rates, and the gut was observed to be the main target organ. CuO NPs exhibited the highest teratogenic potential, although no specific terata were observed. ZnO NPs caused the most severe lesions to the intestinal barrier, allowing NPs to reach the underlying tissues. TiO₂ NPs showed mild embryotoxicity, and it is possible that this substance could be associated with hidden biological effects. Ions from dissolved nCuO contributed greatly to the observed embryotoxic effects, but those from nZnO did not, suggesting that their mechanisms of action may be different.