Indoor illumination: A possible pitfall in toxicological assessment of photo-active nanomaterials

Standardization of the experimental protocols used in the hazard assessment of nanomaterials (NMs) is strongly required to reduce inconsistency among data deriving by different laboratories. The parameters that are known to modify the toxic response of cells to NMs are in fact higher than for soluble toxicants. Among them illumination, that may induce activation of some semiconducting NMs, has been poorly investigated. The present study, conducted within the FP7 EU project SETNanoMetro, has been designed to assess the effect of indoor illumination on the oxidative potential and dispersion degree of nano-TiO2. The generation of Reactive Oxygen Species (ROS) by four nanometric anatase or rutile-anatase TiO2 specimens under ordinary laboratory illumination has been evaluated by means of Electronic Paramagnetic Resonance (EPR) spectroscopy, while their ability to damage DNA has been measured by agarose gel electrophoresis using plasmid DNA as model. The effect of illumination on nanoparticles dispersion has been evaluated by Dynamic Light Scattering (DLS). The results show the occurrence of photo-activation of TiO2 under indoor illumination that leads to the generation of ROS and slight plasmid DNA damage. Furthermore, significant differences in the amount of ROS generated were found for small variation of the intensity of the illumination. A small effect on the size distribution of TiO2 agglomerates in water was observed. The present findings suggest that illumination should be included among the parameters that have to be controlled during toxicological assessment of photo-active nanomaterials.