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In Vitro Phototoxicity and Hazard Identification of Nano-scale Titanium Dioxide
SANDERS, K., L. DEGN, W. R. MUNDY, R. M. ZUCKER, K. L. DREHER, B. Zhao, J. E. Roberts, AND W. K. BOYES. In Vitro Phototoxicity and Hazard Identification of Nano-scale Titanium Dioxide. TOXICOLOGY AND APPLIED PHARMACOLOGY. Academic Press Incorporated, Orlando, FL, 258(2):226-36, (2012).
These experiments demonstrate that TiO2 nanoparticles become phototoxic when exposed to UVA radiation, with potency related to the interdependent properties of reactivity, size, and surface area.
Nano-titanium dioxide (nano-Ti02) catalyzes many reactions under UV radiation and is hypothesized to cause phototoxicity. A human-derived line of retinal pigment epithelial cells (ARPE-19) was treated with six different samples of nano-Ti02 and exposed to UVA radiation. The Ti02 nanoparticles were independently characterized to have mean primary particle sizes and crystal structures of 22 nm anatase/rutile, 25 nm anatase, 31 nm anatase/rutile, 59 nm anatase/rutile, 142 nm anatase, and 214 nm rutile. Particles were suspended in cell culture media, sonicated, and assessed for stability and aggregation by dynamic light scattering. Cells were treated with 0, 0.3, 1, 3, 10, 30, or 100 ug/ml nano-Ti02, in media for 24 hrs and then exposed to UVA (2 hrs, 7.53 J/cm2) or kept in the dark (control condition). Viability was assessed 24 hrs after the end of UVA exposure by microscopy with a live/dead assay (calcein-AM/propidium iodide). Cells exposed to higher concentrations of nano-Ti02 with UVA showed lower viability, but the degree of response varied among the samples. The 25 nm anatase and 31 nm anatase/rutile were the most phototoxic (LC50 with UVA < 5 ug/ml), while the 142 nm anatase and 214 nm rutile were the least phototoxic. An acellular assay was employed to screen and rank Ti02 nanoparticles for their inherent and UVA photocatalytic reactivities. Ti02 nanoparticles were found to be capable of generating thiobarbituric acid reactive substances (TBARS) under UVA radiation. Flow cytometry showed that nano-Ti02 with UVA decreased cell viability and increasedgeneration of reactive oxygen species(ROS, as measured by Mitosox).UnderUVA radiation, LCso values correlated with TBARS reactivity, particle size, and surface area. These experiments demonstrate that TiO2 nanoparticles become phototoxic when exposed to UVA radiation, with potency related to the interdependent properties of reactivity, size, and surface area.