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Modeling TiO2 nanoparticle phototoxicity: The importance of chemical concentration, ultraviolet radiation intensity, and time
Citation:
Li, S., R. Erickson, L. Wallis, S. Diamond, AND D. Hoff. Modeling TiO2 nanoparticle phototoxicity: The importance of chemical concentration, ultraviolet radiation intensity, and time. ENVIRONMENTAL POLLUTION. Elsevier Science Ltd, New York, NY, 205:327-332, (2015).
Impact/Purpose:
One of the biggest obstacles for future risk assessment of nanomaterials is how to address the dosimetry of nanomaterials in the environment. For phototoxicity of nanomaterials, this issue involves both UV and nanomaterial dosimetry. The present study demonstrated that models for the phototoxicity of nanomaterials should be formulated differently than past models for chemical phototoxicity. A model framework was proposed that was consistent with experimental data and that should be useful in further efforts to address the phototoxicity of nano-TiO2.
Description:
Toxicity of TiO2 nanoparticles (nano-TiO2) to aquatic organisms can be greatly increased upon the exposure to ultraviolet radiation (UV). This phenomenon has received some attention for pelagic species, however, investigations of nano-TiO2 phototoxicity in benthic organisms are still limited. In this study, a series of 48-h bioassays of benthic organisms were conducted to evaluate nano-TiO2 phototoxicity. Species-specific phototoxicity was observed when benthic organisms were exposed to 20 mg/L nano-TiO2. For example, when nano-TiO2 was spiked into thin sand matrix (0.5 mL), the calculated median lethal dose for Hyalella azteca, Lumbriculus variegatus, and Chironomus tentans was 40.7 (95% CI, 36.3-44.7) Wh/m2, > 240 Wh/m2, and 147.9 (95% CI, 123.0-177.8) Wh/m2, respectively. Among these three species, H. azteca is the most sensitive species and hence a potential model organism in future toxicological guidelines for photoactive nanomaterials to benthos. The exposure scenario could also serve as a determining factor in the ultimate phototoxicity. For different exposure scenarios with the same amount of nano-TiO2 (0.6 mg), the one with less bioavailable amounts led to a lower mortality. Surface attachment of nano-TiO2 on benthic organisms was also investigated by Scanning Electron Microscope (SEM). The surface attachment varied among species and exposure scenarios. For H. azteca, an increased surface attachment of nano-TiO2 led to a higher phototoxicity. C. tentans had a minimal surface attachment for all exposure scenarios. For L. variegatus, nano-TiO2 could attach on the surface while no phototoxicity was observed. A set of bioassays was also performed with various nano-TiO2 concentrations (0-50 mg/L) and UV intensities (2.2-9.4 W/m2). Photochemical Bunsen-Roscoe Law was applicable to the phototoxicity of nano-TiO2, but could be complicated by factors such as biological defense and repair mechanisms.
