Long-Term Fate and Persistence of Oil from the Exxon Valdez Oil Spill: Lessons Learned or History Repeated?

Abstract

ABSTRACTFor over 20 years, scientists have studied the shorelines of Prince William Sound (PWS) to understand the distribution, fate, persistence, and bioavailability of Exxon Valdez oil residues that stranded on the shore in 1989. Shoreline surveys in 1989 found that approximately 783 km (16%) of the 4,800 km of the shoreline in PWS, Alaska, and another 1,300 km (13%) of the roughly 10,000 km of shoreline in the western Gulf of Alaska were oiled to varying degrees. The remaining buried subsurface oil (SSO) has been observed on the shorelines in the middle and upper tide zones of a small fraction of the shores where it was originally documented in 1991. Few locations remain with any significant SSO, but the presence of these SSO residues (SSORs) continues to support the hypothesis of continuing harm to wildlife. Our most recent surveys, from 2007–2009, found SSOR in only isolated patches on a very small percentage of shoreline. They were sequestered and largely isolated from the natural weathering processes that would result in their complete and rapid removal. The SSORs are highly weathered and are not accessible or bioavailable to wildlife that forage on the shore. These findings confirm the lessons learned from all previous crude oil spills: 1) weathered SSOR can be sequestered for decades in intertidal sediments at locations where the subsurface water flow required for erosion, dissolution, and biodegradation of the oil is low 2) sequestration limits the exposure of biota to the potentially harmful fractions of the SSO.