title: Phototoxicity of TiO2 nanoparticles under solar radiation to two aquatic species: Daphnia magna and Japanese medaka.
abstract: One target of development and application of TiO(2) nanoparticles (nano-TiO(2) ) is photochemical degradation of contaminants and photo-killing of microbes and fouling organisms. However, few ecotoxicological studies have focused on this aspect of nano-TiO(2) , 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-TiO(2) 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 TiO(2) concentration in suspension in a time-course manner. Sedimentation and loss of bulk concentration of nano-TiO(2) particles occurred at all concentrations above 2 mg/L and was more significant as concentration increased. Phototoxicity of nano-TiO(2) 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-TiO(2) at environmentally realistic levels of SSR indicates the need to incorporate this mode of action into risk assessment for nano-TiO(2) and other photoreactive nanomaterials.
authors.affiliation: U.S. Environmental Protection Agency, Office of Research and Development, National Health and Environmental Effects Research Laboratory, Mid-Continent Ecology Division, Duluth, Minnesota.
authors.forename: Hongbo
authors.initials: H
authors.lastname: Ma
authors.forename: Amanda
authors.initials: A
authors.lastname: Brennan
authors.forename: Stephen A
authors.initials: SA
authors.lastname: Diamond
mesh_terms: D000818:Animals; D003621:Daphnia / Q000187:drug effects* / Q000254:growth & development; D007814:Larva / Q000187:drug effects; D007928:Lethal Dose 50; D053758:Nanoparticles / Q000633:toxicity*; D009990:Oryzias; D013472:Sunlight; D014025:Titanium / Q000633:toxicity*; D023382:Toxicity Tests, Acute; D014874:Water Pollutants, Chemical / Q000633:toxicity*
chemical_list: D014874:Water Pollutants, Chemical; C009495:titanium dioxide; D014025:Titanium