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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 species–Daphnia 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 µg/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: 1621–1629. © 2012 SETAC