Doctor of Philosophy (PhD)
The main purpose of the research presented in this dissertation was to further understand the intricate and convoluted interactions between natural organic material, biological entities, and pollutants. This was achieved by utilizing humic acids (HAs) from differing sources, chemically modified humic acid, two biological entities (model biomembranes and Artemia Franciscana), and three types of pollutants (cations, surfactants, and carbon nanotubes). Fluorescence spectroscopy and model biomembranes were used to measure the change in HA’s ability to interact with the biomembranes in the presence of cations. Three differently sourced HAs, chemical modified HAs, and a range of cations were studied to elucidate specific interactions that can occur in the environment. It was determined that the cations limited the ability of humic acids to interact with the biomembranes, which was attributed to humic acid conformation changes in the presence of cations, and the protection capacity increased as the softness of the cation increased. Artemia Franciscana (Artemia) was utilized as an analytic tool to determine the changes in toxicity of surfactants in the presence of humic acid. Artemia were exposed to three different surfactants, Triton X-100 (Tx-100), cetylpyridinium chloride (CPC), and sodium dodecyl sulfide (SDS), for both hatching studies and in vivo 31P NMR. It was determined by hatching assays that Tx-100 caused mortality after hatching while CPC and SDS inhibited hatching. 31P NMR corroborated these findings by showing an increase in phosphodiester bonds in saline water and in the Tx-100 exposure while there was no increase in the presence of the other two surfactants. HAs from three different sources were added to the surfactant exposures which showed that HAs played a mediation role in terms of toxicity and the extent of mediation was dependent on the type of HA and surfactant. Artemia was also utilized to measure the toxicity of carbon nanotubes under a variety of conditions. Both single-walled and multi-walled carbon nanotubes that were either in the presence of humic acid or had been sonicated were studied. Overall, there was no significant carbon nanotube toxicity to the Artemia.
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Deese, Rachel Dawn, "Fundamental Studies of Humic Acid's Influence on Pollutant Toxicity to Aquatic Organisms" (2016). LSU Doctoral Dissertations. 4319.
Cook, Robert L.
Available for download on Saturday, February 23, 2019