Date of Award

2018-01-01

Degree Name

Doctor of Philosophy

Department

Chemistry

Advisor(s)

Jorge L. Gardea-Torresdey

Abstract

Soil exposure to engineered nanomaterials (NMs) occurs through the intentional use of nano-agrochemicals, incidental contamination from industrial-waste release, irrigation with wastewater and gray water, or amendment with NM-loaded sludge. Although there are several reports about the effects of NMs in terrestrial plants, there is still a lack of knowledge about the effects of NMs in crop plants and their edible portions.

Among the large list of produced NMs, it is estimated that 34,000 tons of ZnO NMs are produced yearly. Due to their growing applications in cosmetics and personal care products, there is a high possibility that the ZnO NMs released into the environment could reach edible crops. Even when research in the implications of ZnO NMs in crop plants is growing, to the best of the author's knowledge, none of the studies have focused on commercial Z-COTE and Z-COTE HP1 ZnO NMs. Z-COTE is an uncoated ZnO NM of hydrophilic nature, while Z-COTE HP1 is hydrophobic due to a surface coating of triethoxycaprylylsilane, both manufactured by BASF.

Amid the crops for human feed, beans are the most consumed legume in the world, with productions over 26 million tons in a large range of environments worldwide. Thus, there is a possibility that the large amounts of commercial ZnO NMs released into the environment could reach bean crops.

This research aimed at evaluating the effects of Z-COTE and Z-COTE HP1 on the development and yield of bean plants (Phaseolus vulgaris L. var. red hawk kidney). In this study, the long-term exposure of Z-COTE and Z-COTE HP1 to common bean (Phaseolus vulgaris) was evaluated through the effects on plant growth, yield, nutritional quality of seeds, and residual effects of these NMs in seeds from the second generation plants. The research was divided into three stages. Stage I was established to evaluate the effects of the ZnO NMs in the plant's physiological, biochemical, and agronomical parameters. Stage II was set to evaluate the effects of the ZnO NMs in mature seeds harvested from two different soils, while the residual effects of the ZnO NMs in seeds of second-generation plants were evaluated in stage III.

In stage I, bean plants were grown for 45 days in natural soil (NS) amended with either Z-COTE, Z-COTE-HP1, bulk ZnO, or ionic ZnCl2 at 0, 62.5, 125, and 500 mg kg-1. Growth parameters and essential elements were determined. Z-COTE did not produce phenotypic changes, while Z-COTE-HP1 increased root and leaf length. Z-COTE increased Zn in nodules, stems, and leaves, while Z-COTE-HP1 increased it in roots, stems, and leaves. At 125 mg kg-1, Z-COTE-HP1 increased S and Mg in root, but Z-COTE increased stem B and Mn. Bulk ZnO and ZnCl2 imposed more toxicity than the NMs, since they reduced root and leaf elongation, respectively, and the concentration of several essential elements in tissues.

In stage II, yield and seed nutrient composition were evaluated in plants grown to maturity in NS or organic matter-enriched soil (ES) amended with ZnO NMs, bulk ZnO or ZnCl2. Results showed an interaction of soil x compounds that reduced the maturation time by 25 days and increased seed yield in ES, compared to NS. Z-COTE HP1 and ZnCl2 produced the highest sugar content in seeds of plants grown in NS and ES, respectively. In addition, seeds from ES + Z-COTE HP1 had less Zn than the rest of the compounds. In comparison to NS, the organic matter enrichment and pH reduction in ES enhanced the accumulation of Zn, K, S, P, Mg, Ca, Fe, and Mn in seeds from all tested compounds, but reduced Mo under Z-COTE HP1 and ZnCl2. In general, Z-COTE and Z-COTE HP1 affected seed nutritional elements in a similar manner. However, results indicate that the effects of ZnO NMs in bean plants vary with soil composition.

In stage III, seeds from plants cultivated in ES amended with 0 - 500 mg kg-1 of the ZnO NMs were cultivated in ES without further exposure to ZnO NMs. At day 45, the activity of antioxidant enzymes in seeds was evaluated. At maturity, the yield and nutritional composition of seeds were assessed. None of the treatments affected the yield, sugar, protein, and the activities of catalase and ascorbate peroxidase. However, superoxide dismutase activity increased in seeds from the 500 mg kg-1 ZnCl2 treatment. There was no residual effect on Zn accumulation; however, Z-COTE and Z-COTE HP1 reduced Ni, compared with control, suggesting epigenetic changes driven by the enhanced Zn accumulation in seeds from the previous generation.

This Dissertation provided valuable insight into the interaction of Z-COTE and Z-COTE HP1 with bean plants. Overall results of this research have shown that, at the evaluated concentrations and growth conditions, Z-COTE and Z-COTE HP1 do not represent a threat to the growth and production of bean plants. These findings open an opportunity for application of ZnO NMs in agriculture.

Language

en

Provenance

Received from ProQuest

File Size

139 pages

File Format

application/pdf

Rights Holder

Illya Aidee Medina Velo

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