1998 Shoreline Conditions in the Exxon Valdez Oil Spill Zone in Prince William Sound

Abstract

ABSTRACT After the March 24, 1989 grounding of the Exxon Valdez and the release of 258,000 barrels of Alaska North Slope (ANS) crude oil into the marine environment of Prince William Sound (PWS), Alaska, a number of scientific studies were conducted from 1989 to 1998 to assess the fate and effects of the spill. These included the 1990–1991 shoreline ecology program (SEP), which detected little measurable impact of the spill, except at certain heavily oiled sites. In 1998, these 1990 and 1991 studies were updated. The 1998 study found spill small remnants from originally heavily oiled sites represent a minute fraction of the total PWS shoreline area. Any isolated deposits of remaining oil residues from the spill generally were found at the top of the tidal zone and highly weathered and therefore in a form and location unavailable and non-toxic to biota. Between 1991 and 1998, the concentrations of petroleum hydrocarbons at the “worst case” sites studied decreased dramatically. The polycyclic aromatic hydrocarbon (PAH) concentrations measured at these sites in 1998 were at least three times lower than the effects range-low (ER-L) sediment toxicity threshold values of 4,022 ng/g for total PAH. Mussels sampled at heavily oiled “worst case” sites in 1998 also had dramatically lower tissue PAH concentrations compared with samples taken in 1993, indicating low bioavailability of any hydrocarbons present and thus low risk to biota. Natural interannual variability in the structure of the biological infaunal communities is the largest, most consistent signal observed in this study, not any residual oil spill effects. The results of statistical analyses of the data (ANCOVA) indicated no continuing oiling effects in 1998. Consistent differences were observed between oiled and unoiled reference sites, but they were significant in only one analysis. These differences were unrelated to differences in the total PAH present among sites. Any observed differences are more likely related to the fact these “worst case” oiled sites were not selected in an unbiased, random manner.