The Role of the Nano-Environmental Interface in ZnO and CeO2 Nanoparticle Ecotoxicology
Walker, Nicholas David Leyland
Thesis or dissertation
University of Exeter
An increase in nanotechnology has seen an associated rise in nanoparticles released into the environment. Their potential toxicity and exposure to humans and the environment, the field of nanoecotoxicology, is not yet well understood. The interactions at the nanoparticle surface will play a fundamental role in the nanoparticle behaviour once released into the environment. This study aims to characterise the particle surface interaction, determining key parameters influential in the nanoparticle fate. Evanescent Wave Cavity Ring Down Spectroscopy techniques have been applied to study molecular interactions at the silica-water charged interface. The adsorption of the electronic spectrum of Crystal Violet has demonstrated the formation of a monolayer with different binding site orientation at the interface. The binding affinity for the chromophore was calculated as 29.15 ± 0.02 kJmol-1 at pH 9 and this was compared with other interface structures involving both inorganic and organic components. The study of the model interface was extended to the properties of CeO2 nanoparticles, where the surface charge density was determined to be 1.6 ± 0.3 e- nm-2.The nanoparticle surface charge controls the suspension stability which was measured for CeO2 nanoparticles giving a stability half-life of 330 ± 60 hours in pure water, and 3.6 ± 0.6 hours in ISOFish water. Studies were extended to the toxicity of ZnO nanoparticles. An assay was developed to quantify the photo-electron production for nanoparticles exposed to UV light both in deionised water and soil suspensions with a photo-radical production yield of 19 ± 2 % and an electron production of 709 e-s-1np-1 for a 100 mgL-1 suspension. The species-specific photo-radical assay was subsequently used to determine the rate of ZnO nanoparticle dissolution in water and soil suspensions. Comparable dissolution rates in complex cell growth media were also measured, detecting total zinc by Inductively Coupled Plasma Atomic Emission Spectroscopy, with comparable dissolution rates derived.
PhD in Biological Sciences