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Photocatalytic ROS production and phototoxicity of titanium dioxide nanoparticles is dependent on solar UV radiation spectrum
Citation:
Ma, H., A. Brennan, AND S. Diamond. Photocatalytic ROS production and phototoxicity of titanium dioxide nanoparticles is dependent on solar UV radiation spectrum. ENVIRONMENTAL TOXICOLOGY AND CHEMISTRY. Society of Environmental Toxicology and Chemistry, Pensacola, FL, 31(9):2099-2107, (2012).
Impact/Purpose:
This work is a continuation of a previously submitted manuscript entitled “Phototoxicity of TiO2 nanoparticles under solar radiation to two aquatic species: Daphnia magna and Japanese Medaka” that is currently under review with ET&C. In this work, we investigated the photocatalytic ROS production and its consequent phototoxicity to D. magna under different solar UV spectrum by applying a series of optical filters in a solar simulator. Intracellular ROS production within the test organisms was also examined. We found a linear correlation between ROS production and D. magna immobilization, suggesting that photocatalytic ROS production may be a predictor of phototoxicity for nano-TiO2. Intracellular ROS production within D. magna was consistent with the immobilization of the organism under different solar UV spectrum, indicating that oxidative stress was involved in phototoxicity. We also identified that solar UVA with wavelengths ranging 345 nm ~ 380 nm were most effective in photoactivating nano-TiO2 and cause toxicity. We believe these findings have immediate application in risk assessment of nano-TiO2 in natural environments. The elucidation of a ROS-mediated mechanism of phototoxic action in whole organisms, combined with the strong correlation between simple chemical ROS assays and whole-organism toxicity, provide a means to screen various TiO2 forms for their potential phototoxicity. The identification of critical wavelength ranges and their relative effectiveness at initiating TiO2 phototoxicity provides a means to incorporate realistic estimates of solar radiation levels into TiO2 phototoxicity risk assessment.
Description:
Generation of reactive oxygen species (ROS) by titanium dioxide nanoparticles (nano-TiO2) and its consequent phototoxicity to Daphnia magna were measured under different solar UV radiation spectrum by applying a series of optical filters in a solar simulator. Removing UVB (280-320 nm) from the solar radiation had no significant impact on photocatalytic ROS production of nano-TiO2, whereas further removal of UVA caused significant decrease in ROS production. Removal of all wavelengths below 400 nm resulted in no ROS production. Phototoxicity of nano-TiO2, evaluated by immobilization of D. magna, was in good agreement with ROS production under different solar UV radiation spectra. A linear correlation between ROS production and D. magna immobilization suggests that photocatalytic ROS production may be a predictor of phototoxicity for nano-TiO2. Intracellular ROS production within D. magna was consistent with the immobilization of the organism under different solar UV spectrum, indicating that oxidative stress was involved in phototoxicity. The dependence of nano-TiO2 phototoxicity on environmentally realistic variation in solar radiation suggests that risk assessment of these nanomaterials requires careful evaluation of exposure conditions in the environment.
