Date of Award

2014-01-01

Degree Name

Doctor of Philosophy

Department

Environmental Science and Engineering

Advisor(s)

Jorge L. Gardea-Torresdey

Abstract

The production and use of numerous engineered nanomaterials (ENMs) have increased exponentially over the past decade. Nanoparticles (NPs), ENMs possessing diameter between 1-100 nm, (NPs), are widely used in many applications. Worldwide consumption of NPs has increased their possible release into the environment. This, in turn, has elevated the extent of the potential impacts of NP exposure to living and non-living organisms. This is why the assessment of the impact of NPs on different environmental components, especially on plants, the producer in the food web, has become a very important aspect of nano-ecotoxicology. However, studies focusing on phytotoxicity and effects on plant life-cycle are very limited. To evaluate the long and short-term phyto-toxicological effects of NPs, we have chosen green peas (Pisum sativum L.), corn (Zea mays), and zucchini (Cucurbita pepo) as the test plants for their worldwide consumption. Different zinc oxide [bare (bare-ZnO), alumina doped (Al2O3@ZnO), iron doped (Fe@ZnO), and KH550 coated (ZnO@KH550)] and silver [(AgNP and PVP coated (Ag@PVP)] NPs have been chosen due to their enormous global consumption in different industries, e.g., paint, cosmetics, and drug, among others. This project was completed in four phases. In Phase I, the green pea plants (P. sativum L.) were exposed to 0, 125, 250, and 500 mg kg−1 of 10 nm bare ZnO NPs and bulk ZnO for 25 days in organic matter enriched soil (native soil: potting soil= 1:1) in a growth chamber. Toxicological effects were investigated in terms of plant growth, chlorophyll production, zinc accumulation in different tissues, reactive oxygen species/ROS (H2O2) generation, stress enzyme activity (catalase/CAT and ascorbate peroxidase/APOX), and lipid peroxidation. Root elongation reduction (48-52%) was observed in all ZnO NP concentrations (p ≤ 0.05); however, stem lengths were unaffected compared to control. Chlorophyll in leaves decreased, compared to the control, by 61%, 67%, and 77% in plants treated with 125, 250, and 500 mg kg−1 ZnO NPs, respectively. Bulk ZnO treatments also showed similar results. In roots and leaves, APOX activity decreased in both nano and bulk treatments. However, in leaves, CAT activity decreased in NP treatments but remained unaltered with addition of bulk ZnO. In leaves, there was a 61% increase in H2O2 production with a twofold increase in lipid peroxidation. From this study, it may be concluded that the nano form of ZnO is more toxic than the bulk form under the growth conditions of this study. Phase II was designed to evaluate the toxicological effects of 10% Fe@ZnO NPs on green peas at 0, 125, 250, and 500 mg kg−1 concentrations for 25 days in similar soil type and similar growth conditions. Results were compared with that of Phase I. At 500 mg kg−1, zinc bioaccumulation was increased in both root (200%) and stem (31-48%), compared to control, without affecting the iron uptake (p ≤ 0.05). Chlorophyll content and H2O2 production decreased by 27% and ~50%, respectively (p<0.05), compared to control. Fe@ZnO showed less toxicity than that of bare-ZnO NPs under the applied growth conditions as indicated by zinc bioaccumulation, chlorophyll production, and H2O2 production. Therefore, iron doping can be considered as a safer approach to reduce toxicity of ZnO NPs in terrestrial plants. Phase III was focused on phyto-toxicological studies of bare-ZnO NPs, alumina@ZnO NPs, and ZnO@KH550 NPs on green pea plant, its life-cycle, and seeds. The plants were grown in a greenhouse with continuous supply of nutrients (fertilizer) in the similar 1:1 organic matter enriched soil for 65 days. Upon harvest, different physiological and biochemical parameters, e.g., fresh and dry weights, leaf chlorophyll a, b, leaf carotenoids, zinc bioaccumulation, protein and carbohydrate profiles were measured in different parts of the plant, as applicable. No change in plant fresh and dry weights with treatments were observed, except with ZnO@KH550 at 1000 mg kg−1 treatment, which showed about one fold (95%) increase in plant fresh weight compared to control. Plant roots showed a significant increase in Zn accumulation of 5.7x, 5.7x, and 8x treated with 250 mg kg−1 bulk ZnO, bare ZnO NP, and Al2O3@ZnO NP respectively, compared to controls. Similarly, at 1000 mg kg−1, bare ZnO NP and Al2O3@ZnO NP treatments showed significant increases in zinc uptake up to 16x and 36x times compared to controls. Green pea stems showed higher level of Zn accumulation, except with the ionic zinc treatment. The Zn accumulation was in this order: [at 250 mg kg−1: bulk (5x), bare (7x), doped (4.7x) and coted (7x); at 1000 mg kg−1: bulk (9x), bare (11x), doped (20x) and coted (9x)] compared to control. In leaves, all the treatments (bulk and coated) showed significant increase in zinc uptake (4.6x to 5.3x) except at 250 mg kg−1 and 500 mg kg−1 treatments. The1000 mg kg−1 treatments (bulk, bare, and doped) also showed significant increase in zinc uptake (5.5x to 11x) except for coated and ionic treatments. The aluminum and silicon uptake did not change with one exception at 1000 mg kg−1. Amount of chlorophyll-a (Chl-a) was significantly increased at 250 mg kg−1 alimina doped treatment (4.5x) and in all the treatments at 1000 mg kg−1 [bulk (3.2x), bare (2.7x), doped (3.6x), coted (2.5x), and ionic (2.4x)] compared to control. However, there was no difference in the amount of chlorophyll-b (Chl-b) was observed. The total carotenoid was increased significantly at 250 mg kg−1 to 10x in doped and 7x times in ionic treatment. The increase was 7.6x in bulk and 8.6x in case of doped NPs at 1000 mg kg−1 treatments. The NP treatments also altered seed quality of the pea. The pod lengths, pod weights, and number of seeds per pod did not change among treatments with the exception of alumina doped 250 mg kg−1 treatment where the number of seeds per pod decreased by 33% compared to that of bare ZnO NP treatment. In seed (pea), zinc accumulation at 1000 mg kg−1 was increased in all the treatments ranging from1.8x to 2.5x, compared to control, except for the ionic treatment. A threefold (3x) increase in aluminum, silicon, and iron content was recorded in all treatments, except with the 250 and 1000 mg kg−1 coated treatment. However, copper, magnesium, phosphorus (except 1000 mg kg−1 coated treatment increased 35%), manganese (except 1000 mg kg−1 coated treatment increased 2x), potassium bioaccumulation did not change with changing treatments. In carbohydrate profile, formation of non-reducing sugar (sucrose) was increased nearly two folds (1.8x) at 1000 mg kg−1 doped treatment, compared to control. The amount of total sugar, starch, reducing sugar, and protein profile remain unaltered. Considering our Phase III results, the Al2O2@ZnO NP treatments was found to be more toxic to green pea compared to all other different NP treatments. The comparative phyto-toxicity of different AgNPs on monocot (corn) and two dicot (green peas, zucchini) plants were studied in Phase IV. Plants were treated with bare silver NPs (Ag NPs, 20 nm), 0.2 weight percent PVP coated AgNPs (Ag-PVP-L with 30-50 nm and Ag-PVP-S with 20 nm diameters), bulk silver, and silver sulfate (Ag-ions) at 500, 1000, and 2000 mg kg−1treatments [ionic treatments were set at 5(Ion-5), 10 (Ion-10), and 20 (Ion-20) mg kg−1]. The experiments were done in small glass jars with 50 g soil, 20 ml vermiculite, and 20 ml 25% Hoagland solution for 20 days. Seeds were germinated in a non-contaminated environment (in vermiculite) and then transferred in the test media. In nano-Ag at 1000 mg kg−1 and in all 2000 mg kg−1 treatments, the fresh weight (FW) was reduced, except with the ionic one. However, the dry weight (DW) remained unaffected in all the treatments. In roots, silver uptake increased in a concentration dependent manner in all the treatments (except the ionic treatment) compared to control. At 2000 mg kg−1, all the treatments (except the ionic) increased shoot silver, compared to control. Chlorophyll-a increased in Ag-PVP-L treatments at 500 and 2000 mg kg−1 treatments. The amount of carotenoid decreased in 500 and 1000 AgNP mg kg−1 and same trend was observed in Ag-PVP-S at 2000 mg kg−1) treatments, compared to control. In zucchini, dry weight decreased in all the NP treatments except with 500 mg kg−1 Ag-PVP-S and AgNP 2000 mg kg−1, compared to control. However, the dry weight decreased in all the NP treatments at all concentrations. At 500 and 1000 mg kg−1, root uptake of Ag increased in a concentration dependent manner. On the other hand, only at 500 mg kg−1 Ag-PVP-L treatment showed an increase in the shoot silver. Ag-PVP-S treatment increased chlorophyll by 2.25x and carotenoid by 2.6x compared to control. In corn, the fresh and dry weights were not affected by any of the treatments. Root uptake of silver was increased (by15x to 26x) with silver treatments. However, the shoot uptake increased only with Ion-10 treatment. Chlorophyll and carotenoid amounts were not affected by any of the treatments (except 1000 and 2000 mg kg−1 Ag-PVP-S treatment). These comparative phyto-toxicological studies of bare, coated, and doped NPs on different higher plants may help to shine light on the mechanism of zinc and NP toxicity.

Language

en

Provenance

Received from ProQuest

File Size

141 pages

File Format

application/pdf

Rights Holder

Arnab Mukherjee

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