Exxon Valdez Shows Oil Spills Have Longer, More Harmful Impact

The ship spilled some 11 million gallons of crude oil into Alaska's Prince William Sound in 1989. The new study finds that the environmental consequences went far beyond the more than 250,000 seabirds, and thousands of marine mammals and other coastal marine species killed in the first days, weeks and months.

The researchers synthesized results of numerous investigations of the Alaskan disaster's impact on various plant and animal species.

This work showed that "that oil has persisted in surprisingly large quantities for years after the Exxon Valdez spill in subsurface reservoirs under course intertidal sediments," said principal investigator Dr. Charles Peterson, a marine sciences professor at the University of North Carolina at Chapel Hill.

"This oil was sequestered in conditions where weathering by wave action, light and bacteria was inhibited, and toxicity remained for a decade or more," Peterson said.

As a result, many species suffered long term loss, he said. For example, chronic exposure to the oil in mouths of streams boosted mortality among incubating pink salmon eggs for at least four years after the spill.

"Earlier experiments incorrectly implied that lower oil concentrations were safe, which the new work clearly showed was not true," Peterson said.

The study by Peterson and his colleagues appears in the December 19 issue of the journal "Science."

ExxonMobil Vice President Frank Sprow criticized the study.

"What science has learned in Alaska and elsewhere is that while oil spills can have acute short term effects, the environment has remarkable powers of recovery," Sprow said.

Sprow says there is ample evidence that oil remnants are only being found where they were known to have existed at the conclusion of the cleanup and where the U.S. Coast Guard concluded there was no net environmental benefit associated with further cleanup 11 years ago.

"The abundance of biology in close association with the remnant oil remaining today refutes the notion that this oil residue has any significant biological effect," Sprow said. "The vast majority of the affected shorelines have no visible oil remnants on the surface or subsurface."

But the new study finds oil lingers in sea bed sediments. Researchers found that marine mammals and sea ducks suffered high mortality for years after the accident in part because they ate invertebrates contaminated by the hidden oil and also because they contacted oil directly while digging up prey.

Species as diverse as sea otters, harlequin ducks and killer whales suffered large, long term losses, Peterson and colleagues report, and oiled mussel beds and other tidal shoreline habitats will take an estimated 30 years to recover.

Peterson said studies of the Exxon Valdez oil spill should lead to a new understanding of how lingering oil deposits affect species over many years, how sublethal, chronic doses compromise health, growth and reproduction and how impaired species interact negatively with one another in "cascade" fashion.

According to the National Academy of Sciences, nearly 11 million gallons of oil -- the equivalent of the Exxon Valdez spill -- runs off streets and driveways into U.S. waters every eight months.