Identification of Hydrocarbon Sources in the Benthic Sediments of Prince William Sound and the Gulf of Alaska Following the Exxon Valdez Oil Spill

Abstract

Advanced hydrocarbon fingerprinting methods and improved analytical methods make possible the quantitative discrimination of the multiple sources of hydrocarbons in the benthic sediments of Prince William Sound (PWS) and the Gulf of Alaska. These methods measure an extensive range of polycyclic aromatic hydrocarbons (PAH) at detection levels that are as much as two orders of magnitude lower than those obtained by standard Environmental Protection Agency methods. Nineteen hundred thirty six (1 936) subtidal sediment samples collected in the sound and the eastern Gulf of Alaska in 1989, 1990, and 1991 were analyzed. Fingerprint analyses of gas chromatography-mass spectrometry data reveal a natural background of petrogenic and biogenic PAH. The petrogenic background is derived largely from oil seeps in the eastern Gulf of Alaska. Age-dated (210pb) sediment cores indicate that significant input of seep hydrocarbons into Prince William Sound has been going on for at least 160 years and probably for thousands of years. Superimposed on this natural background are locally elevated concentrations of anthropogenic hydrocarbons from sources such as diesel fuel and pyrogenic PAH that are found primarily adjacent to active or historical sites of human use. Exxon Valdez crude, its weathering products, and diesel fuel refined from Alaska North Slope crude are readily distinguished from the natural seep petroleum background and from each other because of theirdistinctive PAH distributions. Mixing models were developed to calculate the PAH contributions from each source to each sediment sample. These calculations show that most of the seafloor in PWS contains no detectable hydrocarbons from the Exxon Valdez spill, although elevated concentrations of PAH from seep sources are widespread. In those areas where they were detected, spill hydrocarbons were generally a small increment to the natural petroleum hydrocarbon background. Low levels of Exxon Valdez crude residue were present in 1989 and again in 1990 in nearshore subtidal sediments off some shorelines that had been heavily oiled. By 1991 these crude residues were heavily degraded and even more sporadically distributed.

Chemical characterization of naturally weathered oil residues in the sediment from Yellow River Delta, China

“…Polycyclic aromatic hydrocarbons (PAH) can provide more detailed compositional data that can be used to identify both the source and extent of degradation of released oils (Page et al, 1995;Douglas et al, 1996;Hegazi et al, 2004), Which largely because PAHs are more complex and more resistant to biodegradation than alkanes. The GC-MS analytical results indicated that the aromatic hydrocarbons of the weathered petroleum residues consist primarily of five families of PAH compounds: naphthalenes, phenanthrenes, dibenzothiophenes, fluorenes, and chrysenes.…”

“…The relative abundance of the PAH alkyl homologue ratios, C 2 -DBTs/C 2 -PHENs and C 3 -DBTs/C 3 -PHENs, vary among oils having different sulfur contents. Furthermore, they were previously shown to remain relatively constant as oil weathers and prove useful in distinguishing and correlating hydrocarbon inputs to heavily weathered oil residues (Page et al, 1995;Barakat et al, 2001;Wang and Fingas, 2003).…”

Use of Data on Contaminant/Sediment Interactions to Streamline Sediment Assessment and Management

“…More detailed examination of contaminant signatures, such as the relative distribution of individual compounds in an organic mix, the isotopic signature of metals or organic compounds, or the presence or absence of various markers, can help elucidate these questions. For instance, while total PAH (tPAH) numbers are needed to compare to potential sediment quality criteria or benchmarks, the PAH fingerprint (the relative distribution of individual PAHs) can provide a significant amount of information on source, background, weathering patterns, potential toxicity, and the potential for natural attenuation (e.g., Page et al, 1995). Literature in environmental forensics is rich (e.g., see Morrison [2000] and his references).…”

“…Examination of changes in contaminant fingerprints over time or space, indicative of biological, as opposed to physical, processes. In this approach, ratios or trends between components that have very similar physical behavior but differ in their amenability to biodegradation are compared to distinguish biodegradation from abiogenic processes such as physical weathering, volatilization, and leaching (Blumer, Ehrhardt, and Jones, 1973;Kennicutt, 1988;Pritchard et al, 1992;Page et al, 1995;Apitz and Meyers-Schulte, 1996). In such an approach, changes in contaminant fingerprints from the source into and through the contaminated region can provide insight into whether and how further microbial processes should be examined.…”

Radionuclides, Metals, and Hydrocarbons in Oil and Gas Operational Discharges and Environmental Samples Associated with Offshore Production Facilities on the Texas/Louisiana Continental Shelf with an Environmental Assessment of Metals and Hydrocarbons.

“…Besides being critical to assessing biological effects and toxicological relationships of dose and response , PAHs are extremely valuable in identifying and differentiating sources of hydrocarbons in an impacted environment (Youngblood and Blumer, 1975;Wakeham et al, 1980;Sauer and Uhler, 1994;Page et al, 1995b).…”