Water disinfection processes change the cytotoxicity of C fullerene: Reactions at the nano-bio interface.

The environmental transformation of nanoparticles results in significant changes in their structure, properties, and toxicity, which are imperative for assessing their environmental impact and health risks. Little is known about the toxicity alteration of fullerene nanoparticles (C) after water disinfection processes considering their potential application in antimicrobial control in water treatment ultimately ending in sewage treatment plants. We showed that C aggregates (nC) were converted to more oxidized forms via commonly used water disinfection processes (i.e., phototransformation and photochlorination treatment). The light-irradiated nanoparticles (UV_nC) exhibited mitigated cytotoxicity relative to nC, whereas photochlorinated nC (UV/Cl_nC) showed an exacerbated outcome. We revealed a distinct toxic mechanism occurring at the nano-bio interface, for which electrons were shuttled by C nanoparticles from membrane-bound NADPH oxidase to extracellular molecular oxygen, resulting in the production of various extracellular reactive oxygen species (ROS). UV/Cl_nC showed the highest electron-shuttling activity due to its high carbonyl content, and more than 2.4-fold higher level of extracellular hydroxyl radicals were detected relative to that in untreated cells. Although UV_nC possessed a somewhat higher carbonyl content than nC, it showed a weaker adhesion to the cell membrane, which compromised the electron-transfer process. The intrinsic ROS generation/quenching capabilities and oxidative potentials of the various nanoparticles were also systematically compared. Overall, this report highlights the importance of understanding environmental transformations in risk assessment and uncovers an overlooked mechanism through which nC/derivatives can modulate the electron transfer process at the nano-bio interface via acting as electron shuttles.