Browsing by Author "Dr. David Danehower, Committee Member"

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    Novel Methods for Monitoring Chlorinated Contaminants in Aquatic Environments
    (2005-04-07) Heltsley, Rebecca Marie; Dr. David Danehower, Committee Member; Dr. Marjorie F. Oleksiak, Committee Member; Dr. Chris Hofelt, Committee Member; Dr. Damian Shea, Committee Chair
    Chemical exposure assessment is a fundamental component of ecological risk assessment. Without proper tools to determine exposure, final decisions regarding risk must be estimated. In this study, novel methods for improving exposure assessment in aquatic ecosystems were evaluated. Methods for rapid extraction, detection, and quantification of two dioxin-like compounds in tissue, sediment, and water were developed and validated. Methods were notably sensitive and reproducible. The methods were applied to fish samples with induced ethoxyresorufin-O-deethylase activity. Although the compounds were not detected, this study demonstrated for the first time the analysis of tetrachloroazobenzenes with low ppb method detection limits. A novel passive sampling device (PSD), a tool used to monitor waterborne concentrations of organic contaminants, consisting of polydimethysiloxane (PDMS) as the polymeric sorption material was developed. Uptake rates were determined for a suite of >50 polychlorinated biphenyls (PCBs) and organochlorine pesticides (OCPs) into PDMS disks in order to investigate the device's potential as an in-situ sampler for hydrophobic organic contaminants. Uptake rates ranged from 0.03 to 0.7 L/g*d. Compounds with log Kow values >4.5 remained in the linear uptake phase, demonstrating the ability of PDMS to function as a time-integrated PSD. Results indicate that PDMS offers great potential to be an effective alternative to conventional sampling and other passive sampling techniques. In the final phase of this project, PDMS samplers were evaluated as mobile PSD attached to flathead catfish. Also, the potential for using adipose fin clips from catfish as a non-lethal sampling technique to estimate concentrations of PCBs and OCPs in muscle tissues was investigated. Results indicated no practical/physical barriers for attaching mobile PSDs to aquatic organisms. Mobile samplers provided accurate estimates of location specific concentrations of waterborne contaminants that fish were exposed to during the sampling period. Adipose fin concentrations were highly correlated (r2 = 0.77) with those found in the muscle, which requires mortality. This study represents the first time mobile PSDs and adipose fin clips have been used for exposure assessment of organic contaminants.
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    Performance of Diclosulam in Conventional and Strip-Tillage Peanut; Physiological Behavior of Flumioxazin in Cotton, Peanut, and Selected Weeds; Peformance of Flumioxazin in Cotton; and Morningglory Reponse to Neighboring Plants and Structure.
    (2003-03-18) Price, Andrew Jennings; Dr. Randy Wells, Committee Member; Dr. David Danehower, Committee Member; Dr. David Monks, Committee Member; Dr. John Wilcut, Committee Chair
    Research evaluated new herbicides to improve weed management in conventional and minimum-tillage production in cotton and peanut, herbicide physiology in cotton, peanut, and selected weeds, and morningglory response to neighboring plants and objects. Diclosulam preemergence plus metolachlor PRE in conventional and strip-tillage peanut production usually controlled common lambsquarters, common ragweed, eclipta, prickly sida, and entireleaf morningglory. Flumioxazin applied preplant at 71 or 105 g ai/ha tank mixed with the isopropylamine salt of glyphosate at 1.12 kg ai/ha, paraquat at 1.05 kg ai/ha, or with the trimethylsulfonium salt of glyphosate at 1.12 kg ai/ha controlled common chickweed, common lambsquarters, common ragweed, Palmer amaranth, and smooth pigweed ≥ 96% at 29 to 43 days after treatment. Differential absorption, translocation, and metabolism at various growth stages, as well as the development of a bark layer, are the bases for differential tolerances of cotton at different growth stages to flumioxazin applied as a postemergence-directed spray. Morningglories initial planting distance from structures as well as the structures spectral reflectance influenced the percentage of ivyleaf morningglory that exhibited climbing growth as well as their final weight. Flumioxazin treatments at 1.4 mmol/L did not influence germination compared to non-treated peanut across all temperature regimes. Peanut treated with flumioxazin PRE and receiving irrigation at emergence and at 2 and 4 d after emergence were injured between 40 and 60%, while peanut treated at 8 and 12 d after emergence were injured between 25 and 15%, respectively. Total 14C absorbed by ivyleaf mornigglory was 57% of applied while sicklepod absorbed 46%, at 72 hours after treatment (HAT). Peanut absorbed > 74% of applied 14C 72 HAT. Ivyleaf morningglory contained 41% of the parent herbicide 72 HAT while sicklepod and peanut contained only 24 and 11% parent compound, respectively. Regression slopes indicated slower metabolism by ivyleaf morningglory compared to sicklepod and peanut.