Aspects of the Exxon Valdez oil spill—a forensic study and a toxics controversy

After the Exxon Valdez oil spill in Prince William Sound in March, 1989, much work has been done to track the spilled oil and study its fate and its affect on the environment. Our studies involved developing and applying methods to identify and track the spilled Exxon Valdez oil (EVO) as it weathered, as well as to differentiate it from other petrogenic hydrocarbon input sources in PWS. Application of these methods to the study area has yielded two important findings. First, it was discovered that not all the oil or tar on the beaches was EVO. Instead, tarry residues of oil from the Monterey Formation, Southern California, also were prominent on some of the Prince William Sound beaches along with EVO. Monterey Formation oil was used in the early development of Alaska, before the discovery of North Slope Crude, and most likely was disbursed throughout the Sound from the port of Old Valdez in the Great Alaskan Earthquake of 1964. The second study also involves differentiating petrogenic sources. A third petroleum input source to PWS, namely natural oil seeps in the Gulf of Alaska, has been claimed by others to contribute a substantial, and potentially toxic, polycyclic aromatic hydrocarbon (PAH) background to the Prince William Sound benthic sediments. If this claim is true, it would have the effect of mitigating the long-term effects of the oil spill. Our studies and cooperative work with NOAA provide evidence that it is coal and not oil that contributes this PAH background. Unlike the case with oil, PAHs in coal would not be bioavailable and thus would be considered contaminants but not pollutants capable of causing adverse effects on exposed biota. Resolution of the source of the PAHs is, therefore, an important environmental issue. This work in identifying petroleum sources, both natural and anthropogenic, has a great deal of transfer value to other estuarine systems. The geochemical information obtained in Prince William Sound can be extrapolated and applied to the study of oil residues on the California coastline and in San Francisco Bay. Current studies are attempting to correlate or differentiate spills in these two areas and sort out the origin of the petroleum input sources.