Browsing by Subject "Membrane association"

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    An Investigation of Nanoparticle Toxicity Mechanisms against Environmentally Relevant Bacteria and the Potential for Sustainable Agriculture Applications
    (2019-05) Buchman, Joseph
    Due to the unique physicochemical properties of nanoparticles, largely due to their high surface area-to-volume ratio, they are being increasingly used in consumer products. At any time during the manufacture, use, and ultimately, disposal of these products, there is a reasonable likelihood of nanoparticle release into the environment. Once released, their impact on the environment are less well-understood. Therefore, there is a growing emphasis to understand the impacts of nanoparticles on the environment, by understanding how the nanoparticles interact with ubiquitous organisms that have important ecological roles. Beyond looking solely at whether nanoparticle introduction will kill these organisms, the molecular-level mechanisms of their toxicity have been studied. By understanding the mechanisms, the goal is to be able to predict the toxicity of nanoparticles prior to their mass production, and to inform a more sustainable design and use of nanomaterials. Chapter One of this work reviews the understanding of molecular-level toxicity mechanisms to organisms in the environment, with an emphasis on beneficial bacteria. It also describes different strategies that have been employed to redesign nanoparticles that reduce the impact of these toxicity mechanisms. Chapter Two illustrates the importance of using more than one organism when doing studies of nanoparticle toxicity. Not all organisms respond equally, and there are some that are not impacted by a given nanoparticle type, so use of multiple species that cover a range of complexities improves the chances that a nanoparticle will not be incorrectly labeled as “nontoxic”. By using multiple organisms, those that are most impacted can also be identified for follow-on research to investigate the mechanism of toxicity. Chapter Three assesses the toxicity mechanism of an important nanomaterial often used in energy storage applications that is made of the complex oxide, lithium nickel manganese cobalt oxide, across a range of industrially-relevant stoichiometries. While for equimolar stoichiometries of this material, the importance of nickel and cobalt release has been implicated as the main toxicity driver to Shewanella oneidensis MR-1, this work demonstrates that even at increased nickel concentrations in the material, the toxicity remained the same due to increased material stability leading to a similar dissolution profile. For another important environmental organism, Daphnia magna, the toxicity did increase with increasing nickel content, indicating that a material redesign will not necessarily have the same impact on different organisms. Chapter Four investigates the impact of iron oxide nanoparticles to S. oneidensis, which showed that these nanoparticles improved bacterial survival, mostly due to the release of beneficial iron ions. Since changing bacterial populations can perturb an environment, a mesoporous silica coating was applied to the iron oxide nanoparticles to reduce their dissolution and their impact on the bacteria. While more understanding of the mechanisms by which nanoparticles can exhibit toxicity is being gained, there are many nanoparticles for which there is a low toxicity to organisms. In Chapter Five, we apply silica nanoparticles, which have been found to be largely nontoxic, to our plant model, Citrullus lanatus. Through dissolution, silica nanoparticles are capable of serving as a source of silicic acid, an important micronutrient, for plants. These nanoparticles benefit healthy plants by increasing their biomass and improving the overall fruit yield. This work demonstrates a way to apply nanoparticle toxicity knowledge to proactively utilize nanoparticles to improve sustainability in agriculture.