Surface reactivity of metal nanoparticles : - importance of surface active agents and biomolecules from a transformation, mobility and toxicity perspective

Abstract: Metallic nanoparticles possess unique properties due to their size and are widely used in e.g. consumer products. From this follows a need to identify and assess potential risks of human and environmental exposure. Their size facilitates uptake in organisms and disruption of various biological processes. Together with a high reactivity, mainly due to their large surface area in solution, they are both commonly used in different applications and of a potential safety concern. Risk assessment requires hence in-depth knowledge on the particle characteristics and their behavior in solution but also how these properties change with time and exposure conditions and whether these characteristics can be linked to toxicity following nanoparticle exposure. This thesis addresses these aspects with a main focus on metal nanoparticles and elaborates on the importance of characterization, how such measurements can be done, and on interactions with surfactants and biomolecules and toxic effects.Silver nanoparticles are, due to their antibacterial properties, often used in sportswear to prevent sweat odor. During laundry they may be dispersed and interact with surfactants of the washing powder, influencing their properties and stability in solution. These aspects are addressed in Papers I, III and V on silver nanoparticles of different size and surface coatings. The stability was shown to depend on the surface charge and the concentration of the surfactant. The stability and extent of silver release were reduced upon sequential exposure, indicating the importance of the particle history on their bioaccessibility, mobility and potential toxicity. A mechanism was proposed for how silver nanoparticles are stabilized in surfactant solutions.Toxic effects of silver nanoparticles of different size and coatings on cultivated lung cells, Paper II, and effects of copper-containing nanoparticles on different blood cells, Paper IV, were studied in vitro. The smallest particles were most cytotoxic and the “Trojan horse” mechanism played an important role, meaning that the nanoparticles facilitate cellular uptake followed by ion-release.Difficulties in the determination and interpretation of the zeta potential, related to the surface charge, of metal nanoparticles in complex solutions are elucidated in Paper VI. Guidelines are provided on how to accurately assess this property.