Nano form of titanium dioxide can be toxic to marine organisms

www.physorg.co Nano-titanium dioxide is highly reactive to sunlight and other forms of ultraviolet radiation (UVR), the authors write, adding that TiO2's property of generating reactive oxygen species (ROS) when exposed to UVR makes it useful in antibacterial coatings and wastewater disinfection, and potentially valuable as an anti-cancer agent.
Until now, they say, no research has demonstrated that photoactivity causes environmental toxicity of TiO2 under natural levels of UVR.

Sunscreen concern reaches into the school grounds – Features – ABC Environment (Australian Broadcasting Corporation)

ABC Environment (Australian Broadcasting Corporation): Both the government and the industry lobby group Accord point to a 2009 TGA study stating, "The potential for titanium dioxide (TiO2) and zinc oxide (ZnO) nanoparticles in sunscreens to cause adverse effects depend primarily upon the ability of the nanoparticles to reach viable skin cells. To date, the current weight of evidence suggests that TiO2 and ZnO nanoparticles do not reach viable skin cells, rather, they remain on the surface of the skin and in the outer layer (stratum corneum) of the skin that is composed of non-viable, keratinised cells."