Date of Award

2009-01-01

Degree Name

Master of Science

Department

Environmental Science and Engineering

Advisor(s)

Jorge Gardea-Torresdey

Abstract

The impact of metal nanoparticles (NPs) in biological systems is still not well understood. Little is known about the response of plants, the first trophic level, to NP exposure; consequently, their possible role on the fate and transport of NPs in ecosystems is unknown. The aim of this research was to determine the response of mesquite (Prosopis juliflora-velutina), a native desert plant, to ZnO and CeO2 (nanoceria) NPs. Mesquite seedlings were grown for 15 days in hydroponics with of ZnO (10 nm) and CeO2 NPs (10 nm) at concentrations varying from 500 to 4000 mg L-1. In the present study, cerium and zinc concentrations as well as the concentration of some macro and micro elements in plant tissues were determined by inductively coupled plasma optical emission spectroscopy (ICP OES). Structural and morphological modification in tissues, deposition of Ce and Zn, and plant stress were examined by infra red microspectroscopy (IMS), electron probe micro-analyzer (EPMA), and specific activity of catalase (CAT) and ascorbate peroxidase (APOX), respectively. In addition, the biotransformation of CeO2 and ZnO NPs was determined by using x-ray absorption spectroscopy (XAS). Results showed that none of the NPs reduced plants growth. In addition, at all concentrations the nanoceria increased CAT and APOX in leaves, while ZnO NPs increased CAT in roots stems and leaves, while APOX was increased in stems and leaves. The ICP-OES data showed that mesquite plants differentially absorbed Zn and Ce from the NPs. In the case of Zn, the bioconcentration factors (metal in tissues/metal in medium) were 11, 4, 2, and 0.9 for the 500, 1000, 2000, and 4000 mg L-1 treatments, respectively. While for the nanoceria the bioconcentration factors were 53, 30, 26, 30, and 12 for the 500, 1000, 2000, and 4000 mg L-1 treatments, respectively. However, in all cases the translocation factors were higher for the ZnO NPs. ZnO NPs reduced the accumulation of some micronutrients, mainly in roots and in some cases in stems; but very few changes were observed in leaves. On the other hand, the nanoceria reduced the concentration of Cu, Mn, and Fe, but increased Mo concentration in roots. The IMS analysis of roots treated with the nanoceria at 4000 mg L-1 showed changes in the peaks associated with proteins (1150-1100 cm-1) and lipids (2900-2850 cm-1), whereas in the ZnO NPs treated plants, only the band of aromatic phenolic compounds (845 cm-1) showed changes. The EPMA analysis confirmed the presence of Zn in the vascular system of the ZnO NP treated plants, but the nanoceria treated plants showed Ce only in cortex and epidermis. However the x-ray mapping did not showed evidence of nanoceria agglomeration in the vascular tissue. The XAS study showed clear evidence of the presence of CeO2 NPs within tissues but ZnO NPs were not observed. The data also showed that at the concentration used and the growth stage studied, the nanoceria and ZnO NPs exerted low toxicity on mesquite, suggesting that this desert plant may display some resistance to both the nanoceria and ZnO NPs.

Language

en

Provenance

Received from ProQuest

File Size

82 pages

File Format

application/pdf

Rights Holder

Jose Angel Hernandez Viezcas

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