Date of Award
Doctor of Philosophy
Cerium Oxide Nanoparticles (CeO2-NPs) are commonly used in polishing, engine enhancement agents and many other commercial products. Increased applications and accidental release have raised concerns on the potential impact of CeO2-NPs on the environment. Most previous studies focused on the short term effect of CeO2-NPs. Information is severely lacking on the long-term impact of CeO2-NPs at environmentally relevant concentrations. The main goal of the current dissertation was to investigate the chronic phytotoxicity of CeO2-NPs on two plant species, tomato (Solanum lycopersicum L.) and Turnip mustard (Brassica rapa L.) fast growing variety, and the physiological and biochemical responses of these two plant species to CeO2-NPs. Four specific objectives were established. The first objective was to investigate the effects of combined CeO2-NPs and TiO2-NPs exposure on tomato plant growth and oxidative stress. The second objective was to investigate the impact of a lifecycle exposure to CeO2-NPs on wild type tomato growth and fruit yield and to evaluate the transgenerational effects of CeO2-NPs exposure on plant growth and the oxidative stress of the second generation tomato seedlings. The third objective was to compare the influence of CeO2-NPs and bulk CeO2 particles on plant growth and oxidative stress of standard fast growing Brassica rapa. The final objective was to evaluate the risks of CeO2-NPs exposure over three generations on Brassica plant growth, oxidative stress and reproduction. The results suggested that firstly, CeO2-NPs pre-exposure at concentrations of 4 and 40 mg/kg dry soil followed by 1000 mg/L of TiO2-NPs post-treatment increased H2O2 content and antioxidant proteins activities compared with CeO2-NPs alone and TiO2-NPs alone, and reduced biomass of the tomato plants compared with CeO2-NPs alone. Secondly, irrigation of CeO2-NPs at concentrations up to 10 mg/L stimulated wild type tomato plant growth, but exposure to CeO2-NPs over a lifecycle harmed plant growth and induced higher H2O2 content in tomato seedlings of the second generation. Thirdly, bulk CeO2 exposure at irrigation concentrations of 10, and 100 mg/L were more beneficial for Brassica rapa plant growth than CeO2-NPs at equivalent concentrations. CeO2-NPs irrigation at 10 and 100 mg/L increased H2O2 content and antioxidant proteins activities than bulk CeO2 at equivalent concentrations. However, the mustard plants treated by CeO2-NPs or bulk CeO2 showed changes of H2O2 content in different growth stages, which illustrated that CeO2-NPs and the bulk counterpart induced the change of H2O2 content differently. Finally, irrigating mustard plants with 10 to 1000 mg/L CeO2-NPs over three generations resulted in an inhibited plant growth, stronger oxidative stress, less seed yield and poorer reproduction of offspring plants. To our knowledge, this is the first report on the chronic (multigenerational) effects of CeO2-NPs on plant growth and oxidative stress of tomato and mustard plants grown in soil.
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