Date of Award

December 2016

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Department

Freshwater Sciences

First Advisor

Rebecca Klaper

Committee Members

Laodong Guo, Julia Oliver, Hongbo Ma, Michael Carvan

Keywords

Acute, Chronic, Daphnia, Environmental Toxicology, Nanomaterials, Nanotechnology

Abstract

Nanomaterials (NMs) are being developed for a variety of industrial, biomedical, and environmental applications. Initially these materials consisted of simple metal oxides or carbon based NMs. More recently NMs have become increasingly complex consisting of multiple transition metals and surfaces functionalized with polymers, surfactants and ligands that have the ability to alter their physiochemical properties and enhance performance. As manufactured NM production increases, so does the concern about their release into the environment and potentially harmful effects. The focus of toxicology has largely been on first generation materials and we have comparatively less information about the potential impacts of complex NMs. In order to create environmentally friendly nanotechnologies, the properties that govern NM toxicity need to be better elucidated. In addition, understanding mechanisms for toxicity and impacts to molecular and apical endpoints will greatly aid in the rapid assessment and design of current and future nanotechnologies. In this dissertation my central hypothesis is: altering the core chemical composition and surface functionalization impacts the toxicity of nanomaterials to Daphnia magna. To determine whether to accept or refute this hypothesis I used the environmentally relevant model organism, Daphnia magna, and chemically tailored NMs. My results indicated that acute and chronic impacts to Daphnia upon exposure to functionalized gold NMs are strongly dependent on initial surface charge and the ligand used in the functionalization process; depending on the ligand, negative impacts are explained by the ligand choice, however with others the NM-ligand combination are required for a negative impact indicating a nanospecific effect. Positively charged gold NMs functionalized with polyallylamine hydrochloride are more toxic than negatively charged particles functionalized with citrate or mercaptopropionic acid, impacting daphnid reproduction and mortality at low part per billion concentrations. Gene expression results from Daphnia acutely and chronically exposed to these same materials show that each NM-ligand combination has a unique molecular fingerprint and that for most of the genes I explored the NM-ligand combination induces similar responses in the Daphnia as its respective ligand. Lastly, my studies demonstrate that altering the core chemical composition of complex NMs to decrease toxicity. In addition, this study indicated a nanospecific impact, as the dissolved metals found in solution could not reproduce the chronic endpoint impacts and daphnid gene expression response. Collectively, this work assisted in the development of fundamental knowledge for the factors that regulate NM toxicity and identified novel molecular pathways and responses triggered by specific alterations to complex NM surface and core properties.

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