Isotopic Constraints on the Sources and Associations of Organic Compounds on Marine Sediments

Helen White, Ph.D., 2006
Timothy Eglinton, Christopher Reddy, Advisors

To provide a new perspective on the fate of natural organic matter and hydrophobic organic contaminants (HOCs) in marine sediments, we investigated the relationship between radiocarbon age and different modes of association in aquatic sediments. Radiocarbon is a sensitive tracer of OM provenance, with variations in its natural abundance reflecting age and origin of material. The main objective has been to determine the significance of these associations, and to assess their affect on transport, bioavailability, preservation and residence times of organic compounds in the environment.

Our results indicate that the majority of HOCs persisting in marine sediments are solvent-extractable and incorporation into insoluble residues is not quantitatively significant. For pristine sediments, systematic variations in radiocarbon content are observed between different chemically defined sedimentary organic fractions and are dependent on organic matter inputs and/or diagenesis. Our observations also provide evidence for the protection of labile marine carbon by chemical binding. Finally, the persistence of /n/-alkanes from biogenic sources compared to those derived from petroleum indicates the role of protective matrix association in determining a compound’s long-term fate. Overall, it is clear that organic compounds undergo different fates depending on their mode of introduction to, and physical disposition in environmental matrices.