Nanoparticles in aqueous environments : a physicochemical and ecotoxicological study of cerium dioxide

摘要

The unique properties which make cerium dioxide (ceria) nanoparticles (NPs) so useful in e.g. catalytic applications, pose a real risk to environmental systems and species alike. Increasing our knowledge of ceria NP characteristics in a range of aquatic systems was a contributing theme of this thesis. Nano-ceria particle sizes (dH) were found to significantly change due to adjustments in media composition. The addition of Suwannee River fulvic acid to an aquatic media decreased dH up to 88%, significantly increased the negative charge measured from zeta potential (ζ) and increased Ce dissolution by 2%. The presence of test biota significantly increased dH up to 80%, further increased the ζ negative charge and increased Ce dissolution up to 63%, predicted as being due to the presence of exudates. Nanotoxicological investigations using P. subcapitata showed a convincing size-dependent toxicity to well-defined synthesized nanoceria particles. EC50 values of 5 nm to 35 nm ceria particles (0.013 mgL to 0.8 mgL respectively) showed between 600 and 10 fold increases in toxic response compared to commercial nano-ceria particles (EC50 8 mgL). EC50 of 5 nm and 35 nm ceria particles showed significant metabolic differences compared to controls indicating a cellular response of P. subcapitata as a function of nano-ceria size and dose. Although metabolomic extraction methods are sensitive to cell density and temperature changes, metabolomic analysis has huge potential in future environmental nanoecotoxicological applications using P. subcapitata. It was evident from this study that further work is still required to help develop methods of NP characterisations under environmental conditions with a necessity for a future NP modelling protocol.