W9 PM Residual Oil and its Effects
Wednesday, 16 November 2005: 1:50 PM - 5:30 PM in 339-340

(BOE-1118-205730) Combined Analytical and Comprehensive Sampling Approaches to Determine Sources of PAHs in Prince William Sound.

Boehm, Paul¹, Page, David², Bence, A. Edward³, ¹ Exponent, Inc., Maynard, MA, USA² Bowdoin College, Brunswick, ME, USA³ ExxonMobil Upstream Research, Houston, TX, USA

ABSTRACT- The NRDA CERCLA Regulation describes how oil spill injury assessment must be performed. They establish the rationale for conducting chemical fingerprinting and considering all hydrocarbon sources other than the just the spill. Fingerprinting methodology is both qualitative (source recognition) and quantitative (source allocation). Here we discuss the evolution of this methodological approach as applied to the Exxon Valdez oil spill (EVOS) investigations. Hydrocarbon fingerprinting was used to recognize the spill oil at various weathering states, to define the pre-existing baseline, and to quantitatively resolve multiple sources contributing to environmental samples. Steps included determining: a) composition of the oil and weathering trends; b) identification of the non-EVOS natural petrogenic background; c) identification of anthropogenic sources not related to the spill. Analysis of hundreds of samples of potential sources and environmental assemblages of PAHs formed the backbone of the effort. Source apportionment methodology (Principal Components Analysis; Partial Least Squares; TOC methodology apportionment from multiple sources) were used to analyze the data. These analyses supported the overall exposure assessment which involved: discrimination of sources of any exposure; evaluation of the bioavailability of the oil compared to background; evaluation the dose-response paradigm (e.g., sediment toxicity); and overall to relate to the biological effects of the spill. Results support the conclusions that weathering and removal rates of oil and the toxic fraction of the PAHs were rapid from the vast majority of shorelines in the Sound; toxicity of any oil residues rapidly declined as the oil weathered and became insignificant; bioavailability of EVOS oil residues decreased rapidly over time and by 1998 the background levels of non-EVOS bioavailable PAHs was the dominant factor in the Sound; any possible chemical exposure from EVOS could not be distinguished from that of the background. These results further support the likely explanation of bile FAC/CYP1A studies as performed by numerous investigators. Such non-source specific measures of exposure can be largely attributed to the non-EVOS background in the Sound and not to the residual minor amounts of buried EVOS oil.

Key words: polycyclic aromatic hydrocarbons, Exxon Valdez, Sources, Effects