Theses/Dissertations - Environmental Science
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Browsing Theses/Dissertations - Environmental Science by Author "Cobb, George P."
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Item Interactive effects of copper oxide nanoparticles and arsenic on rice (O.sativa japonica ’Koshihikari’) plant growth and development.(2019-05-02) Liu, Jing, 1987-; Cobb, George P.The emerging applications of nanomaterials (NMs) encompass a wide range of industries, including agriculture (e.g., as fertilizers, pesticides, and biosensors). NMs applied in the crop-field may influence plant growth and uptake of heavy metal(loid)s including arsenic (As). Being ubiquitous in the environment and readily bioavailable in aquatic system, As is taken up by rice plants, causes phytotoxicity and accumulates in rice grains. Classified as a Class I carcinogen and causing many diseases, As in rice grains potentially causes human health effects, particularly for infants who are eating rice to transition from breast milk to solid food, and Asian populations with regular daily rice consumption. Although As in water can be removed dramatically by copper oxide nanoparticles (nCuO) due to their high adsorption capacity for As, the interaction of nCuO and As has not been well elucidated on rice plant growth and As accumulation. This project was the first to investigate the interaction of nCuO and As on rice (Oryza sativa japonica’Koshihikari’) plant growth and development during a life cycle (from seed germination to seed maturation). The effects of nCuO and As were determined, individually and interactively, on rice seed germination and early seedling growth in sand and an artificial soil mixture of clay and topsoil. A greenhouse study on the life cycle growth of rice plants in the artificial soil mixture approximated the real agriculture scenario and identified the nCuO dependent acceleration of heading process of rice plants. Particularly, As accumulation in dehusked rice grains was decreased by nCuO to 128 ng/g, 36% lower than the WHO maximum safe concentration of As in white rice (200 ng/g) for humans. Arsenic distribution and speciation inside the plant growth were also affected by nCuO. Transgenerational effects of nCuO and As were also verified on seed germination and early seedling growth of rice plants in this project. These results contribute to the fundamental database of endpoint effects on rice plants, direct future research about wide-scale application of NMs in crop field as fertilizers or amendments, and provide insightful information to investigate the mechanism of the interaction between nCuO and As on plant growth.Item Quantification of titanium dioxide nanoparticles in environmental matricies(2016-11-21) Watkins, Preston S., 1990-; Cobb, George P.A consistent analytical method incorporating sulfuric acid (H₂SO₄) digestion and ICP-MS quantification for titanium dioxide (TiO₂) was validated for 4 environmentally relevant matrices. The method provided Ti recoveries of 97 ± 2.5%, 91 ± 4.0%, 94 ± 1.8%, and 73 ± 2.6% (mean ± standard deviation) from water, fish tissue, periphyton, and sediment, respectively. Lower recoveries from sediment coincided with the percentage of sand in the sediments used for validation suggesting that unrecoverable Ti may be sequestered in the sand matrix. Our method was then used to quantify Ti in the the four validated matrices along four reaches in the North Bosque River Watershed. Ti concentrations ranged from 0 to 8 μg L^-1 in water, 45 to 526 μg g^-1 in sediment, 276 to 1520 μg g^-1 in periphyton, and 0 to 30 μg g^-1 in fish tissue. Ti concentrations in periphyton were significantly higher (p ˂0.001) than concentrations in other sample types, but were independent of distance from the effluent discharge.Item Spatial and temporal distribution of lead, copper, and zinc in sediments of East Fork Wetland, Seagoville, TX.(2014-10-23) Acharya, Abhilasha, 1988-; Cobb, George P.This study evaluated concentrations of three metals: lead, copper and zinc in sediments of East Fork Wetland, in Seagoville, Texas. Sediments were collected during June 2013, December 2013, and March 2014 from 138 different sites during each sampling event. Analytes were quantified using inductively coupled plasma mass spectrometry following acid digestion of samples. Average lead and zinc concentrations in interval 1 were higher than interval 3. Copper concentrations showed no seasonal variation. Average concentrations of all metals were lower than consensus based sediment quality guideline (SQG) thresholds. SQG consist of threshold effect concentration (TEC), below which harmful effects on benthic organisms are unlikely and probable effect concentration (PEC), above which adverse effects are expected to occur frequently. Approximately 98% of the individual concentrations were below TEC and 42% of data were 50% below TEC. No individual concentrations exceeded PEC levels, therefore sediments can be considered to have low toxicity.