Size-dependent toxicity of metal oxide particles—A comparison between nano- and micrometer size

Toxicological studies have shown increased toxicity of nanoparticles (<100 nm) compared to micrometer particles of the same composition, which has raised concern about the impact on human health from nanoparticles. However, if this is true for a wide range of particles with different chemical composition is not clear. The aim of this study was to compare the toxicity of nano- and micrometer particles of some metal oxides (Fe2O3, Fe3O4, TiO2 and CuO). The ability of the particles to cause cell death, mitochondrial damage, DNA damage and oxidative DNA lesions were evaluated after exposure of the human cell line A549. This study showed that nanoparticles of CuO were much more toxic compared to CuO micrometer particles. One key mechanism may be the ability of CuO to damage the mitochondria. In contrast, the micrometer particles of TiO2 caused more DNA damage compared to the nanoparticles, which is likely explained by the crystal structures. The iron oxides showed low toxicity and no clear difference between the different particle sizes. In conclusion, nanoparticles are not always more toxic than micrometer particles, but the high toxicity of CuO nanoparticles shows that the nanolevel gives rise to specific concern.