Until now, TiO₂ was regarded as an innocuous compound whose use has been approved in drugs, toothpastes, food and cosmetics.
Concern about atmospheric particles and the growing development of nanoparticles has generated new research on the effects of fine particles upon health. The main questions addressed were whether these particles can go through the biological barriers, be transported by blood, be excreted or accumulated in the body, and what damage they can cause. The results have clearly pointed out a danger. Furthermore, on the basis of new in vitro experiments, TiO₂ is now classified as potentially carcinogenic.
To assess the ensuing risk, there is a lack of measurements about the release of particles from photocatalytic materials under appropriate conditions. It does not seem that commercialized self-cleaning glass can release significant daily amounts of TiO₂ particles because the coating is only ca. 100 nm thick and the adhesion is high. However, in cement-based materials, 0.3-3 wt% of TiO₂ is simply mixed. According to a manufacturer, no loss of TiO₂ was found for concrete after several years. However, to more satisfactorily respond to the new concern about fine particles, laboratory experiments and on-site evaluations must be performed.
Because the concentration of particles in air regarded as harmless is gradually lowered considering new information about health effects (cf. asbestos), these data are essential even if, given the durability of most photocatalytic materials, the daily release of TiO₂ particles is probably very low compared to the emissions of other particles, e.g. from combustions.