Due to their extensive use, the release of zinc oxide nanoparticles (ZnO NP) into the environment is increasing and may lead to unintended risk to both human health and ecosystems. Access of ZnO NP to the brain has been demonstrated, so their potential toxicity on the nervous system is a matter of particular concern. Although evaluation of ZnO NP toxicity has been reported in several previous studies, the specific effects on the nervous system are not completely understood and, particularly, effects on genetic material and on organism behaviour are poorly addressed. We evaluated the potential toxic effects of ZnO NP in vitro and in vivo, and the role of zinc ions (Zn²⁺) in these effects. In vitro, the ability of ZnO NP to be internalized by A172 glial cells was verified, and the cytotoxic and genotoxic effects of ZnO NP or the released Zn²⁺ ions were addressed by means of vital dye exclusion and comet assay, respectively. In vivo, behavioural alterations were evaluated in zebrafish embryos using a total locomotion assay. ZnO NP induced decreases in viability of A172 cells after 24 h of exposure and genetic damage after 3 and 24 h. The involvement of the Zn²⁺ ions released from the NP in genotoxicity was confirmed. ZnO NP exposure also resulted in decreased locomotor activity of zebrafish embryos, with a clear role of released Zn²⁺ ions in this effect. These findings support the toxic potential of ZnO NP showing, for the first time, genetic effects on glial cells and proving the intervention of Zn²⁺ ions.

Titanium dioxide nanoparticles (TiO₂ NPs) have a wide variety of applications in many consumer products, including as food additives, increasing the concern about the possible hazards that TiO₂ NPs may pose to human health. Although most previous studies have focused on the respiratory system, ingestion must also be considered as an important exposure route. Furthermore, after inhalation or ingestion, TiO₂ NPs can reach several organs, such as the liver, brain or lungs. Taking this into consideration, the present study focuses on the uptake and potential genotoxicity (micronuclei induction) of TiO₂ NPs on four human cell lines of diverse origin: lung cells (A549), liver cells (HepG2), glial cells (A172) and neurons (SH-SY5Y), using flow cytometry methods. Results showed a concentration-, time- and cell-type- dependent increase in TiO₂ NPs uptake but no significant induction of micronuclei in any of the tested conditions. Data obtained reinforce the importance of cell model and testing protocols choice for toxicity assessment. However, some questions remain to be answered, namely on the role of cell culture media components on the agglomeration state and mitigation of TiO₂ NPs toxic effects.