Phototoxicity of TiO2 nanoparticles under solar radiation to two aquatic species: Daphnia magna and Japanese medaka

One target of development and application of TiO2 nanoparticles (nano-TiO2) is photochemical degradation of contaminants and photo-killing of microbes and fouling organisms. However, few ecotoxicological studies have focused on this aspect of nano-TiO2, specifically whether this photoreactivity might significantly increase hazard and risk of the materials in the natural environment. In the present study, we evaluated acute phototoxicity of nano-TiO2 under simulated solar radiation (SSR) to two aquatic speciesDaphnia magna and Japanese medaka, using 48-h and 96-h assays, respectively. A thorough characterization of the exposure system was performed by measuring particle agglomeration and TiO2 concentration in suspension in a time-course manner. Sedimentation and loss of bulk concentration of nano-TiO2 particles occurred at all concentrations above 2?mg/L and was more significant as concentration increased. Phototoxicity of nano-TiO2 under SSR was enhanced by two to four orders of magnitude as compared to toxicity under ambient laboratory light, with a 48-h median lethal concentration (LC50) of 29.8 mu g/L in D. magna and a 96-h LC50 of 2.2?mg/L in medaka. Our results also indicate that these effects are dependent on simultaneous exposure of the organisms to nanoparticles and SSR. This dramatic increase in toxicity of nano-TiO2 at environmentally realistic levels of SSR indicates the need to incorporate this mode of action into risk assessment for nano-TiO2 and other photoreactive nanomaterials. Environ. Toxicol. Chem. 2012; 31: 16211629. (C) 2012 SETAC