Just minutes after midnight on March 24, 1989, the 986-foot Exxon Valdez oil tanker struck Bligh Reef in the Gulf of Alaska, sending some 11 million gallons of crude oil toward the pristine shores of Prince William Sound.
Twenty years later, oil still remains on some of the sound's beaches, which has taught the scientific community a lot about the long-term effects of oil spills, says the dean of Duke University's Nicholas School of the Environment.
"People may assume that because the spill happened 20 years ago, the effects are long gone. But they persist -- and may continue for years to come," said William L. Chameides, who is also the author of the environmental issues blog, The Green Grok, www.thegreengrok.com.
During the first few years of cleanup, studies showed the oil was dissipating at a pretty good clip -- about 58 percent a year, Chameides said. At that rate, little oil was expected to remain past 1992. However, follow-up surveys in 2001 and 2005 revealed much lower rates of dissipation -- 4 percent a year or less. At that rate, Chameides said, the oil will remain on Prince William Sound's beaches for decades, perhaps a century.
"The oil has proven to be remarkably persistent. Some has been pounded by the surf into a recalcitrant, emulsified, mousse-like substance that resists chemical degradation," Chameides said. "Other oil has seeped into subsurface sediments isolated from the elements that would otherwise promote degradation. The long-term impact of the spill might continue to be deliberated, but one thing is clear: the oil is still there. Dip a pail into the sand and you may very likely pull up a black oozy oleo of sand and oil."
In some places, oil on the sound's shore "is nearly as toxic as it was the first few weeks after the spill," according to the Exxon Valdez Oil Spill Trustee Council, set up as part of the court settlement between the United States and Alaska governments and Exxon to oversee the sound's restoration. Some species, including sea otters and Harlequin ducks, have yet to fully recover.
A silver lining from the Exxon Valdez spill, if there can be one, has been the intense scientific research that followed it, Chameides said.
As a result of this research, he said, "we have a much keener understanding of oil spills. Before the Exxon Valdez, oils spills were widely thought to present an acute, short-term environmental threat that would rapidly disperse and subside. Now we know it's not that simple. The oil lingers, just beneath the surface, threatening wildlife and transforming the lives of area residents." _ _ _ _
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