Nanoparticle properties affecting embryotoxicity: toward a design of safer nano-Zinc oxide

The impact of nano metal-oxides on human and environmental health is predicted to be increasing. Among metal oxides, nano ZnO (nZnO) is retained one of the most dangerous. Recently nZnO has invaded the market for its UV protective and antibacterial properties, that make it suitable for a wide range of application for functional coating formulations to protect wood, plastics, textiles from UV and microbial degradation. Previous data already showed that nZnO has a powerful embryotoxic potential on X. laevis and that it was able to mainly affect gut development. It was clearly demonstrated that nZnO produced severe lesions at the intestinal mucosa and potentially cross the gut barrier reaching the underlying tissues. In this work we used Xenopus laevis embryos to characterize the embryotoxic and teratogenic potential of nZnO according to the modulation of NP size and surface charge, as well as to the irradiation conditions. To optimize the stability of the NP suspensions and to achieve useful NP-surface functionalization, we worked in strict connection with a private nanotech company with both R&D and commercial activities. The purpose was to provide mechanistic data on nZnO ecotoxicology and to suggest criteria to design safer Zinc oxide NPs. We demonstrated that nZnO-induced embryotoxicity was mediated by NPs’ own reactivity rather than ion dissolution and that it is strongly associated with the modality of the biological interactions at the nano-level, which at last depend upon the physical and chemical NP surface properties. These properties are also at the base of the induced oxidative potential by nZNO, which is also very efficiently modulated by light irradiation. Finally NP dimension, and especially surface charge, played a crucial role in determining the embryotoxic potential and the intestinal translocation and lesions of nZnO. The present results showed how a comprehensive knowledge of the nZnO physical and chemical properties, affecting the interactions at the bio-interface, may contribute to make nanotoxicology a predictive science and may help chemists and material scientists in the design of safer NPs.