Doctor of Philosophy (PhD)
This work was done in order to deepen our molecular level understanding of how soil organic matter (SOM) is assembled in a whole soil and to provide further insight on the effect of SOM assembly on the uptake and release of hydrophobic organic compounds. Various techniques, including ultraviolet absorbance, fluorescence, and total carbon analysis, demonstrate that hydration/solvation of SOM is kinetically controlled. Initial wetting of a soil releases the hydrophobic moieties that are located at the outer surface of SOM, and longer wetting times exfoliate more hydrophobic quinone type moieties that are present in the middle layer, which in turn exposes the previously protected hydrophilic moieties. The results of 2-Dimensional 1H-13C Heteronuclear NMR affords for the first time direct molecular level insight into the molecular assembly of SOM in a whole soil. The application of Lee-Goldberg and Ramped CP techniques in the 1H-13C HETCOR NMR experiments enabled the observation of intramolecular and intermolecular connectivities within the SOM. As a result, a model of SOM assemblage in its native matrix is forwarded: the first domain consists of alkyl moieties that are spatially isolated; and the second domain consists of aromatic moieties that are strongly associated with O-alkyl moieties over 0.4 nm and up to 0.8 nm distances, probed in this study. It is envisioned that this SOM assembly affects the uptake and release of HOCs. Sorption of HOCs to a soil also show at least two stages: a region of fast uptake and a second region where sorption is generally slow. Flutolanil showed the highest sorption, followed by norflurazon and then acifluorfen in all soils investigated. The sorption of norflurazon, described in terms of organic carbon-normalized Freundlich sorption capacity (KFOC), indicates that it is predominantly sorbed to organic matter. On the other hand, KFOC of flutolanil or acifluorfen not only is due to organic matter, but is also affected by sand and clay content, because KFOC was greatest in Mandeville soil, followed by Pahokee Peat and then Elliot soil. Finally, it was demonstrated that sorption KFOCs were generally higher on a dry soil compared to a wet soil, with few exceptions, especially on the less organic-rich, high silt containing Elliot soil.
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Lattao, Charisma Vinarao, "Studies on the Effect of Natural Organic Matter and Hydration on the Sorption and Desorption of Trifluorinated Pesticides" (2009). LSU Doctoral Dissertations. 2737.