Ecotoxicity of TiO2 to Daphnia similis under irradiation

Currently, there are a large number of products (sunscreen, pigments, cosmetics, plastics, toothpastes and photocatalysts) that use TiO(2) nanoparticles. Due to this large production, these nanoparticles can be released into the aquatic, terrestrial and aerial environments at relative high concentration. TiO(2) in natural water has the capacity to harm aquatic organisms such as the Daphnia (Cladocera) species, mainly because the photocatalytic properties of this semiconductor. However, very few toxicity tests of TiO(2) nanoparticles have been conducted under irradiation. The aim of this study was to evaluate anatase and rutile TiO(2) toxicity to Daphnia similis exploring their photocatalytic properties by incorporating UV A and visible radiation as a parameter in the assays. Anatase and rutile TiO(2) samples at the highest concentration tested (100 mg L(-1)) were not toxic to D. similis, neither in the dark nor under visible light conditions. The anatase form and a mixture of anatase and rutile, when illuminated by a UV A black light with a peak emission wavelength of 360 nm, presented photo-dependent EC50 values of 56.9-7.8 mg L(-1), which indicates a toxicity mechanism caused by ROS (reactive oxygen species) generation.