Exxon Valdez Oil Spill Impacts Lasting Far Longer Than Expected, Scientists Say

Oil's negative effects last far longer, scientists now say, and the findings should be a wake-up call for better environmental research and protection.

The study, conducted by a University of North Carolina at Chapel Hill researcher and colleagues, involved synthesizing results of numerous more specialized but revealing investigations of the Alaskan disaster's impact on various plant and animal species.

"These simply astounding findings have extremely important implications for environmental management," said principal investigator Dr. Charles H. Peterson, Alumni Distinguished professor of marine sciences at the University of North Carolina at Chapel Hill. "They show the environmental consequences of the Exxon Valdez oil spill went far beyond the more than 250,000 seabirds, thousands of marine mammals and countless numbers of other coastal marine organisms killed in the first days, weeks and months."

A report on the work appears in the Dec. 19 issue of the journal Science.

Besides Peterson, authors are Drs. Stanley D. Rice and Jeffrey W. Short of the National Marine Fisheries Service's Auke Bay Laboratory at the Alaska Fisheries Science Center in Juneau; Dr. Daniel Esler of Canada's Simon Fraser University in Burnaby, B.C.; Drs. James L. Bodkin and Brenda E. Ballachey of the U.S. Geological Survey's Alaska Science Center in Anchorage; and Dr. David B. Irons of the U.S. Department of the Interior's Fish and Wildlife Service in Anchorage.

"Studies we reviewed and synthesized showed that oil has persisted in surprisingly large quantities for years after the Exxon Valdez spill in subsurface reservoirs under course intertidal sediments," Peterson said. "This oil was sequestered in conditions where weathering by wave action, light and bacteria was inhibited, and toxicity remained for a decade or more."

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.

"Higher mortality was induced by concentrations of polycyclic aromatic hydrocarbons of only a few parts per billion," Peterson said. "These results require a complete reconsideration of the foundations of ecological risk assessment and ecotoxicology because acute mortality from oil involves concentrations perhaps 1,000 times greater. Earlier experiments incorrectly implied that lower oil concentrations were safe, which the new work clearly showed was not true."

Beyond their acute losses, 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 contacted oil directly while digging up prey. Species as diverse as sea otters, harlequin ducks and killer whales suffered large, long-term losses. Oiled mussel beds and other tidal shoreline habitats will take an estimated 30 years to recover.

"Long-term declines also were observed in pink salmon as sublethal effects of oil exposure early in their life history led to stunted growth and indirect increases in mortality while they were in the ocean phase of their lives," he said.

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.

"Recognition that chronic exposures of fish eggs to oil concentrations as low as a few parts per billion lead indirectly to higher mortality shows the critical need to better control stormwater runoff of petroleum hydrocarbons and other toxins," he said. "In a developed country like the United States, an amount of petroleum equal to the Exxon Valdez oil spill is spilled annually for every 50 million people."

Revising and enforcing water quality standards and stormwater rules can help restore fisheries production lost to pollution, the scientist said.

Peterson works at the Institute of Marine Sciences, a part of UNC's College of Arts and Sciences located in Morehead City, N.C.