Environmental application and implication of engineered nanomaterials in soil, water, and plant systems
Nanotechnology is promising to develop novel engineered nanomaterials (ENMs) for industrial and consumer products, environmental engineering, and agricultural production. Specifically, ENMs can be used to remove contaminants from wastewater and to produce plant care agrochemicals (e.g., nanopesticides). The rapidly growing use of nano-enabled products is leading to increased release of ENMs into agroecosystems and their uptake by organisms and crop plants, thus posing potential threats to environmental and human health. To maximize environmental benefits and minimize potential risks of ENMs, this dissertation research focused on both environmental application and implication of ENMs in soil, water, and plant systems.The first study systematically investigated the photodegradation of antibiotic cephalexin (as an emerging contaminant in water) by novel ZnO nanowires under simulated sunlight through a combination of experimental and theoretical techniques including kinetic batch degradation, free radical trapping experiments, degradation product identification by mass spectrometry, and molecular computation. The ZnO nanowires substantially increased the degradation efficiency of cephalexin, especially under circumneutral and alkaline conditions (pH of 7.2-9.2). Anions (HCO3-) and natural organic matter inhibited the photodegradation of cephalexin by scavenging radical species (2022OH and 2022O2-). Finally, cephalexin photodegradation pathways included hydroxylation, demethylation, decarboxylation, and dealkylation. Overall, the ZnO nanowires can be potentially used for removing antibiotics from contaminated water.The second study examined the effect of biochar amendments on soil sorption of Ag NPs and Ag+, their soil-bound fractions, and their uptake and translocation by radishes grown in a loamy sand soil spiked with 1 mg kg-1 Ag NPs or Ag+. Biochar amendment had no significant effect on Ag uptake by radishes, which also did not differ with and without Ag addition. Results of Ag sorption, soil-bound fractions, and soil pore water concentrations showed that the bioavailable Ag at the environmentally-relevant concentration (1 mg/kg) was low, which may partially explain the non-significant effect of biochar amendment on the Ag uptake. This study demonstrated that the accumulation risk of Ag NPs and Ag+ ions in vegetable crops at environmentally-relevant concentrations is very low.The third study addressed the role of stomata in the internalization of Ag NPs using abscisic acid (ABA)-responsive ecotypes (Ler and Col-7) and ABA-insensitive mutants (ost1-2 and scord7) of Arabidopsis thaliana in batch sorption experiments. The sorbed amount of Ag NPs was much lower in the leaves of the Ler and Col-7 ecotypes treated with 10 M ABA than that in the ABA-free control, mainly due to ABA-induced stomatal closure. However, sorption of Ag NPs by the leaves of the ost1-2 and scord7 mutants did not change with and without ABA. Microscopic images showed that internalized Ag NPs were located in the cell membrane, cytoplasm and plasmodesmata. Clearly stomata play an important role in the internalization of ENMs in plants, which has broader implications in foliar application of nanopesticides and minimizing ENMs contamination of food crops. Overall, the sustainable use of nanotechnology will depend on improved knowledge on and proper management of its benefits and potential risks.
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- In Collections
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Electronic Theses & Dissertations
- Copyright Status
- In Copyright
- Material Type
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Theses
- Authors
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He, Jianzhou
- Thesis Advisors
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Zhang, Wei
- Committee Members
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Li, Hui
Ryser, Elliot
He, Sheng Yang
- Date
- 2020
- Subjects
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Nanotechnology--Research
Nanostructured materials
Risk assessment
Emerging contaminants in water
- Degree Level
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Doctoral
- Language
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English
- Pages
- xiii, 147 pages
- ISBN
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9798664760293
- Permalink
- https://doi.org/doi:10.25335/r9e9-jc39