Polycyclic aromatic hydrocarbon (PAH) pollutants that arise from sources such as oil spills, industrial waste, and navigation accumulate in marine sediments. The carcinogenic and mutagenic properties of these pollutants have distinguished them as priority pollutants and rank them second in magnitude only to chlorinated solvents. Microbial biodegradation of PAHs is considered to be a convenient and cost-effective alternative mitigation strategy which exploits the naturally occurring biodegradation potential of microorganisms capable of utilizing and thereby degrading aromatic hydrocarbons. The fate and dissemination of these pollutants in the marine environment depends on their rate of biodegradation and/or physical transport processes, which in turn depend on the physicochemical interactions of the pollutants at the seabed surface.

In our previously ONR research, we successfully demonstrated the value of ¹³C-labeling PAHs with ¹³C-NMR studies to examine and characterize complex chemical processes pertinent to biodegradation, aging, and incorporation of 3, 4, and 5-ring PAHs and PAH metabolites in marine sedimentary organic matter (SOM). By using consortia microcosm studies and several analytical approaches (flash pyrolysis-GC/MS, CPMAS ¹³C-NMR and HPLC), we have demonstrated biologically-mediated sequestration of [¹³C]-pyrene in refractory SOM. A key component of this work was the analytical capability to evaluate molecular interactions of nonextractable PAHs in insoluble sedimentary organic matter by using pyrolysis-GC/MS, ¹³C-NMR, and ¹³C-labeled PAHs.

In the current ONR study we intend to determine the mechanisms by which biological sequestration occurs. Our approach is twofold. First, we examine and characterize PAH associations with field samples (San Diego bay, CA and Chico Bayou, FL) of PAH contaminated SOM in situ by using laser microscopy pyrolysis-GC/MS in tandem with solid state ¹³C-NMR. This microscopic technique will enable us to determine preferential sequestration of ¹³C-labeled PAHs and weathered PAHs in specific macromolecular organic compartments of field sediments during early diagenesis. Secondly, we determine biologically-mediated sequestration mechanisms in controlled laboratory studies using well-characterized fractions of SOM that are amended with ¹³C labeled PAHs and then exposed to different types of biological activity. Both the structural composition of the ¹³C labeled PAH and the SOM fraction will be monitored during incubation by the aforementioned analytical techniques. Our overall research objective is to use these two approaches to assess in situ the biological sequestration of PAHs with specific sedimentary organic macromolecules asa function of sediment depth and diagenesis.

Objectives for the ONR study:

1. Characterize and identify in situ the composition of macromolecular SOM where weathered PAHs predominate in field sediments by laser micropyrolysis GC/MS.
2. Evaluate the extent of biological sequestration of ¹³C PAHs, [¹³C]-pyrene and [¹³C]-benzo(a)pyrene, in whole sediment microcosms from different PAH contaminated sites and a pristine site.
3. Determine specific mechanisms by which biological sequestration occurs in model SOM compartments in the presence or absence of biological activity, i.e., SOM degradation or extracellular enzyme activity.

Recent publication resulting from this study:

1. Guthrie, E.A., J. T. Bortiatynski, K. M. Stewart, E. M. Kovach, M. W. Medlin, J.E. Richman, and P.G. Hatcher. 1999. Organic Matter Degradation and [13C] Pyrene Association with Refractory Organic Matter. Environ. Sci. Technol. 33:119-125.
2. Greenwood P.F., E. A. Guthrie and P.G. Hatcher. 1999. Laser micropyrolysis GC-MS of the different petrographically recognisable entities in a synthetic soil. American Chemical Society, Division of Geochemistry, March 21-26^th, Anaheim, CA.
3. Hatcher P.G., E. A. Guthrie, J. T. Bortiatynski, R. Saunders and E.M. Kovach. Evidence for encapsulation interactions between polycyclic aromatic hydrocarbons and humic substances. American Chemical Society, Division of Environmental Chemistry, August 23-27th, Boston, MA.
4. Greenwood P.F., E. A. Guthrie and P.G. Hatcher. 1999. The in situ pyrolysis of two different organic phases of a synthetic soil doped with [4,9-¹³C] pyrene. Org. Geochem.
5. Greenwood P.F., Patrick G. Hatcher, Jasper D. H. van Heemst, and Elizabeth A. Guthrie. 1999. Laser Micropyrolysis-GC/MS of Lignin. (Submitted to: The J. Anal. Appl. Pyrolysis)
6. Chefetz, B., A. Deshmukh, E. A. Guthrie and P. G. Hatcher. Pyrene Sorption by Natural Soil/Sediment Organic Matter. (Submitted to Environmental Science & Technology)

Last Modified: Wednesday, May 10, 2000
Address all comments and questions about this site to: Bea Solomon <bsolomon@chemistry.ohio-state.edu>