Modeling TiO2 nanoparticle phototoxicity: The importance of chemical concentration, ultraviolet radiation intensity, and time

Abstract As a semiconductor with wide band gap energy, TiO 2 nanoparticles (nano-TiO 2 ) are highly photoactive, and recent efforts have demonstrated phototoxicity of nano-TiO 2 to aquatic organisms. However, a dosimetry model for the phototoxicity of nanomaterials that incorporates both direct UV and photo-activated chemical toxicity has not yet been developed. In this study, a set of Hyalella azteca acute toxicity bioassays at multiple light intensities and nano-TiO 2 concentrations, and with multiple diel light cycles, was conducted to assess how existing phototoxicity models should be adapted to nano-TiO 2 . These efforts demonstrated (a) adherence to the Bunsen-Roscoe law for the reciprocity of light intensity and time, (b) no evidence of damage repair during dark periods, (c) a lack of proportionality of effects to environmental nano-TiO 2 concentrations, and (d) a need to consider the joint effects of nano-TiO 2 phototoxicity and direct UV toxicity.