Titanium dioxide induced cell damage: A proposed role of the carboxyl radical

Titanium dioxide (TiO2) nanoparticles have been shown to be genotoxic to cells exposed to ultraviolet A (UVA) radiation. Using the technique of electron spin resonance (ESR) spin trapping, we have confirmed that the primary damaging species produced on irradiation of TiO2 nanoparticles is the hydroxyl (OH) radical. We have applied this technique to TiO2-treated fish and mammalian cells under in vitro conditions and observed the additional formation of carboxyl radical anions (CO2−) and superoxide radical anions (O2−). This novel finding suggests a hitherto unreported pathway for damage, involving primary generation of OH radicals in the cytoplasm, which react to give CO2− radicals. The latter may then react with cellular oxygen to form O2− and genotoxic hydrogen peroxide (H2O2).