Date of Award

2013-01-01

Degree Name

Doctor of Philosophy

Department

Chemistry

Advisor(s)

Jorge Gardea-Torresdey

Abstract

The rapid growth of nanotechnology is exposing the environment to abnormal concentrations of engineered nanoparticles (NPs). There is concern about the unknown consequences of NPs on the environment and human health. This Dissertation has relied significantly on Synchrotron and other spectroscopic techniques to give insights on the effects, speciation and distribution of two metal oxide nanoparticles (ZnO, CeO2) on two plant species (Mesquite and Soybean). We evaluated the effects of ZnO (10 nm) and CeO2 (8 nm) NPs on a plant species native to the semi-arid regions of North America, Mesquite (Prosopis juliflora velutina). Mesquite plants grown in hydroponic culture with ZnO NPs presented an increased uptake of Zn when compared to control plants. Zn synchrotron μXRF from root transversal sections (30 μm) showed Zn accumulated mainly in the vascular region. Zn μXRF maps obtained from the leaves showed that Zn is mainly concentrated in the veins. Combined Bulk and μXANES synchrotron analysis showed that Zn has different coordination environments compared to the ZnO NPs, and corroborated that ZnO NPs were transformed on/in the root surface and transported as Zn (II) from roots to leaves. Exposure to ZnO NPs increased the specific activity of stress enzymes catalase in root, stem and leaves and ascorbate peroxidase only in stem and leaves. The concentration of Ce in mesquite plants exposed to CeO2 NPs was higher when compared to the control; however Ce μXRF maps showed most of the cerium was adsorbed in the root. Bulk XANES showed that Ce maintained the same coordination as the CeO2 NPs.

Few reports thus far have addressed the entire life cycle of plants grown in NP-contaminated soil. We performed a lifecycle study of ZnO and CeO2 NPs with the fifth largest crop produced in the world and second in the USA, Soybean (Glycine max).We determined the effects of NPs exposure and the potential storage of NPs or their biotransformed products in edible/reproductive organs of the plants in order to study the possible transfer of NPs into the food chain and potentially into the next plant generation.

Soybean (Glycine max) seeds were germinated and grown to full maturity in organic farm soil amended with either ZnO NPs or CeO2 NPs at different concentrations. At harvest, synchrotron μ-XRF and μ-XANES analyses were performed on soybean tissues, including pods, to determine the forms of Ce and Zn in NP-treated plants. The X-ray absorption spectroscopy studies showed no presence of ZnO NPs within tissues. However, μ-XANES data showed O-bound Zn, in a form resembling Zn-citrate, which could be an important Zn complex in the soybean grains. On the other hand, the synchrotron μ-XANES results showed that Ce remained mostly as CeO2 NPs within the plant. Our results also showed that a small percentage of Ce(IV), the oxidation state of Ce in CeO2 NPs, was biotransformed to Ce(III). Our results also showed that the plants exposed to CeO2 diminished in growth but most importantly, nitrogen fixation was stopped at higher exposure concentrations. To our knowledge, this is the first report on the presence and effects of CeO2 and Zn compounds in the reproductive/edible portion of the soybean plant grown in farm soil with CeO2 and ZnO NPs.

Language

en

Provenance

Received from ProQuest

File Size

62 pages

File Format

application/pdf

Rights Holder

Jose Angel Hernandez Viezcas

Download

Share

COinS