The early 21st century is experiencing a transition of nanotechnology from discovery to commercialization, but the potential risks of engineered nanomaterials (ENMs) as emerging environmental contaminants have not been rigorously evaluated. Herein, we present our study on the bacterial toxicity of nanostructured titania (nano-TiO2), one of the most extensively used ENMs, and its regulating factors, as probed by high-throughput screening conducted in environmental-relevant conditions. Despite of inevitable aggregation in natural aqueous matrices, common commercial nano-TiO2 exhibit significant acute bacterial cytotoxicity that is only observed under simulated solar irradiation. This phototoxicity, however, varies among different exposed bacterial species and is potentially mitigated by UV attenuation and increased concentration of natural organic matter (NOM) in natural water environments. Recently, nano-TiO2 with various morphologies have been tailored and produced to optimize the material structure and function. These newly developed ENMs improve the photocatalytic performance of nano-TiO2 but meanwhile add more uncertainties to their environmental safety. Therefore, the effects of material morphology on nano-TiO2 toxicity are assessed. Results show that morphology plays a critical role in regulating the phototoxicity of nano-TiO2 to bacteria, with low dimensional materials (e.g., nanotubes, nanorods, and nanosheets) less toxic than their spherical counterparts. However, the order of nano-TiO2 phototoxicity is not correlated to that of either acetaldehyde photooxidation or hydroxyl radical production, indicating that factors other than photocatalytic activity control nano-TiO2 phototoxicity. Cryo-scanning transmission electron microscopy results suggest that morphology likely influences the phototoxicity of nano-TiO2 by determining the geometry, density and alignment of nano-TiO2 aggregates at the bacterial surface. Overall, our study demonstrate that combined effects of the intrinsic physicochemical properties of nano-TiO2, exposed organism, as well as environmental factors need to be considered synergistically to evaluate the ecotoxicity of nano-TiO2 accurately.

Ecotoxicological effects of nanostructured titania to bacteria: Mechanistic insights of regulating factors

246th National Meeting (2013)

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