The Unintended Ecological Consequences and Interactions of Nanotitania in Aquatic Environments: From Single- to Multi-Nanomaterial Systems

The transition of nanotechnology from discovery to commercialization raises concerns about the possible environmental and ecological risks of engineered nanomaterials (ENMs). Accordingly, this research investigated the potential ecological impacts of nanotitania (nano-TiO2) in aquatic environments under various scenarios. Since natural ecosystems are likely exposed to ENM mixtures, the chemical interactions and combined toxicity of nano-TiO 2 and nano-ZnO, two extensively used ENMs with overlapping applications, were probed in a natural aqueous medium, expanding nanotoxicity research from single- to multi-nanomaterial systems. Additionally, the average TiO 2 phase composition in environmental samples was characterized by X-ray absorption spectroscopy (XAS) to provide insight into the fate of nano-TiO 2 in real environmental systems.;Despite aggregation in natural aqueous matrices, common commercial nano-TiO 2 exhibit significant acute phototoxicity towards bacteria, which reflects the photoactivity of these spherical materials and is diminished by UV attenuation and natural organic matter in water. When comparing materials with different morphologies, however, nano-TiO2 phototoxicity is not a simple function of photoactivity or reactive oxygen species (ROS) production. Instead, the geometry, density and alignment of nano-TiO2 aggregates at the bacterial surface regulate nano-TiO2 phototoxicity.;When coexisting with nano-ZnO, nano-TiO2 not only influences dissolved zinc concentration released by nano-ZnO but also reduces nano-ZnO toxicity in decreasing bacterial ATP levels under dark conditions, due to the adsorption of Zn2+. Yet, nano-ZnO surprisingly controls the combined phototoxicity of nano-TiO2 and nano-ZnO in damaging bacterial membrane, as nano-ZnO and dissolved zinc alter the extent of bacteria/nano-TiO2 surface contact.;Finally, Ti K-edge XANES analysis quantitatively reveals the average TiO2 phase composition in samples collected from a wastewater treatment plant (WWTP) and nearby sediments. Thus, the annual release of anatase and rutile from the WWTP can be estimated. Although the TiO2 phase composition in WWTP samples was stable among primary sludge, activated sludge, and final effluent over a two-month period, sediments located upstream and downstream of the WWTP both exhibit distinct XANES spectra, reflecting a different TiO2 phase composition with a reversed relative abundance of anatase to rutile. Therefore, XAS provides fingerprints of TiO2 in each sample that are potentially used to follow the sources of TiO2 inputs into natural ecosystems.