Document Type

Thesis - Open Access

Award Date

2004

Degree Name

Doctor of Philosophy (PhD)

Department

Chemistry

Abstract

Natural organic matter (NOM) is one of the most abundant forms of organic matter on the earth's surface. Because of its agricultural and environmental implications, it is essential to have a basic understanding of the structure and composition of NOM. This dissertation is an attempt to look how the studies of soil / sediment interaction with hydrophobic organic contaminants contribute to understanding the structure of NOM. The potential of polyaromatic hydrocarbon (PAH) and its metabolite to form bound residues was quantified. The formation of bound residues by naphthalene and its metabolite, cis-na phthalene-1,2-dihydrodiol, in a sediment, a silty loam soil and a peat under both sterile and nonsterile conditions was examined. The results showed that bound residue formation is low for naphthalene and between 5 and 20 times higher for the metabolite. The formation of naphthalene bound residues is probably due mainly to noncovalent interactions between the contaminant and natural organic matter. The formation of the diol bound residue is primarily the result of the covalent binding of the contaminant molecules to parts of organic matter. Noncovalent interactions between NOM and PAHs were also investigated. This investigation proceeded through thermodynamical analysis of the sorption of PAHs on whole and lipid-extracted geosorbents. Removal of the lipids was found to increase the sorption capacity of the samples as well as the exothermicity of the process. The entropy changes were small and positive for the whole geosorbent samples, but smaller and more negative when the lipids were removed. This indicated that the interaction of PAHs with soils and sediments in the absence of extractable lipids is stronger and the mechanisms involved may be different, changing from a partitioning-like mechanism to specific adsorption. Because of the competition between lipids and PAHs for the same sorption sites, the lipids can be viewed as an "implicit sorbate". This conclusion points to an alternative explanation for sorption behavior of NOM that does not make any specific assumptions about the structure of NOM. The final part of the dissertation deals with the glass transition of NOM, considered proof of a polymeric nature, that have been inferred from sorption studies. Both thermal analysis and variable temperature solid-state NMR were unable to give a definitive answer concerning the existence of a geosorbent glass transition. However, the data do show the presence of a thermal event in geosorbent. This was identified as being due to the melting of the crystallites present in the geosorbents and not to a glass transition. Based on the findings of this research, this dissertation has shown that NOM models derived exclusively from sorption studies should be very cautiously applied until supported by direct experimental verification.

Library of Congress Subject Headings

Humas

Soil structure

Soil absorption and absorption

Format

application/pdf

Number of Pages

175

Publisher

South Dakota State University

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