Author ORCID Identifier

https://orcid.org/0000-0002-1785-6652

Date Available

6-14-2019

Year of Publication

2018

Degree Name

Doctor of Philosophy (PhD)

Document Type

Doctoral Dissertation

College

Medicine

Department/School/Program

Toxicology and Cancer Biology

First Advisor

Dr. Jason M. Unrine

Abstract

Large quantities of manufactured nanomaterials (MNM) are released into the environment by human activity each year. The entry of MNM into the terrestrial food webs, which has the potential for far-reaching impacts, begins with the uptake by plant species from the soil. These processes can be affected by MNM physico-chemical properties such as size, chemical composition, surface charge, etc., of which our knowledge is still incomplete. To bridge some of the gaps in our understanding of these processes and, specifically, to determine whether the physico-chemical properties of the MNM are predictive of their behavior in terrestrial food chains, we conducted a series of experiments using different MNM and model organisms.

First, we synthesized functionalized CeO2 MNM having different charges and exposed tomato plants (Solanum lycopersicum cv Micro-Tom) to them. We found that plant growth and the rate of root-to-shoot translocation were functions of surface charge and exposure concentration. Mechanisms of entry into roots were examined using recent advances in high-resolution synchrotron X-ray microscopy to show that a combination of apoplastic and symplastic routes was used by the particles to penetrate to the interior of the roots. Our results also illustrate that these particles have drastically different tissue distribution patterns depending on their surface charges.

Second, we exposed tomato plants with these CeO2 MNM and fed the leaves to the tobacco hornworm (Manduca sexta). Differential trophic transfer was observed as a function of the surface charge of the particles. An uptake and elimination study was conducted to obtain a time course of Ce dynamics. Despite no observed overall biomagnification across trophic levels, these differentially charged CeO2 MNMs had higher bioaccumulation factors than that of ionic Ce3+. The uptake-elimination dynamics were influenced by the surface charge of the NPs. Positively charged NPs had higher bioaccumulation factors and assimilation efficiencies but lower elimination rate than neutral and negatively charged CeO2 MNMs.

Finally, to determine if studies conducted with highly purified, lab synthesized materials, were predictive of behavior of commercial nanopesticide formulations, we studied the dietary uptake of Cu(OH)2 MNMs by hornworms feeding on surface-contaminated tomato leaves. We compared lab-synthesized copper hydroxide (Cu(OH)2) nanowire with the widely used fungicide KOCIDE® 3000, whose active ingredient is nano-needles of copper hydroxide (Cu(OH)2). The difference in their toxicity and accumulation/elimination dynamics was found to correlate with the solubility of the materials.

We have shown that the physico-chemical properties of MNM affect the toxicity, bio-distribution and trophic transfer of MNM in terrestrial ecosystems. With the increase of MNM release into the environment as a result of the rapid development of nanotechnology, these results have important implications for the evaluation of environmental risks associated with these MNMs and may help the application of nanotechnology to evolve to be more environmentally friendly.

Digital Object Identifier (DOI)

https://doi.org/10.13023/etd.2018.474

Funding Information

This dissertation was supported by the National Science Foundation under Grants 1530594 and 1266252. This research also used the Hard X-ray Nanoprobe (HXN) Beamline at 3-ID and the Submicron Resolution X-ray Spectroscopy (SRX) Beamline at 5-ID National Synchrotron Light Source II, a U.S. Department of Energy (DOE) Office of Science User Facility operated for the DOE Office of Science by Brookhaven National Laboratory under Contract No. DE-SC0012704. Portions of this work were performed at GSECARS (The University of Chicago, Sector 13), Advanced Photon Source (APS), Argonne National Laboratory. GSECARS is supported by the National Science Foundation – Earth Sciences (EAR-1128799) and Department of Energy – Geosciences (DE-FG02-94ER14466). APS facility is supported by DOE under Contract No. DE-AC02-06CH11357.

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