A new study counters a long-held claim by Exxon that oil seeping from the ground is a natural part of the Prince William Sound environment. Discounting natural oil as a contaminant in the Sound, the new work suggests that signs of oil pollution in sea otters and ducks is due to the 1989 spill.
''It puts Exxon back on the hook,'' said Bob Spies, chief scientist for the Exxon Valdez Oil Spill Trustee Council, the group that funded the study.
The new study is a step toward answering one of the big questions about Prince William Sound: Where have high levels of chemical compounds in the sea floor come from?
A scientific study funded by Exxon reported in 1996 that the compounds, known as hydrocarbons, come from natural oil seeps in the Gulf of Alaska. That study invited the idea that Prince William Sound had natural ability to process oil and that, perhaps, slight contamination in marine species was normal in the Sound.
But the new work by federal scientists in Juneau, which was published last month, finds that coal from the sprawling deposits on the Bering River is the source of hydrocarbons. Because coal hydrocarbons are not easily absorbed into the food chain, the work suggests that any contamination found today therefore comes from the 1989 spill.
The debate resurrects questions over the pollution caused by the 11 million-gallon Exxon Valdez spill, the biggest environmental disaster in Alaska's financially lucrative history of oil production. The new work also comes as scientists wrestle over what is causing persistent stress among marine animals. Sea otters and two species of ducks in western Prince William Sound have been found with an enzyme only produced when exposed to oil. What petroleum source could be responsible?
''By ruling out natural oil, it gives greater weight that these problems are linked to the Valdez spill rather than any other source,'' said Stan Senner, science coordinator with the spill trustee council.
Exxon referred questions to the authors of the 1996 study it funded. David Page, a chemistry professor at Bowdoin College in Maine, and Paul Boehm, a geochemist in Cambridge, Mass., stand by their finding that thousands of tons of oil sweep into the Sound each year.
''Trying to find a signal of the spill today is like trying to tune in PBS from Mars,'' Page said. Too many potential oil sources -- fishing boats, recreation, oil seeps and old spills -- cloud the picture. Stress among marine animals could as easily be blamed on the warm summers of El Nino as on the spill, Page said.
But Jeff Short, author of the new study, said the amount of oil leaking into the ocean near Prince William Sound is negligible.
''Maybe one or two quarts a day. You could scrape more oil off a Wal-Mart parking lot than comes out of those seeps,'' said Short, a NOAA scientist in Juneau.
Besides this disagreement, both scientific teams accuse each other of faults in sampling and in the technique of identifying the source of hydrocarbons.
The focus of their argument is the Sound's seabed.
Following the 1989 spill, scientists found high levels of hydrocarbons in the seabed. Hydrocarbons are the building blocks of coal, oil and other fossil fuels. The findings sparked fears that spilled oil settled to the bottom of the Sound.
Page and Boehm traced the compounds to oil seeps in the Gulf of Alaska off Yakataga and to seeps at Katalla, about 200 miles east of the Sound. The structure or fingerprint of the hydrocarbons from the seeps matched the hydrocarbons from the sediments exactly, Boehm said. They saw no signs of coal in the river drainages and did no fingerprint tests.
''When you find the criminal whose fingerprints match perfectly, you don't go looking for other suspects,'' Boehm said.
Short said that ignoring coal was a mistake.
The Bering River area also holds a massive exposed bed of coal about 100 miles east of the Sound. Short said his work has identified the coal as having an exact fingerprint to the hydrocarbons in the Sound. Waves and wind moved coal sediment into the Sound.
''I trust the abilities of both scientists, but I'm convinced by the new study that coal is the likely source of the hydrocarbons,'' said Susan Saupe, science director at the Cook Inlet Regional Citizens Advisory Council. The council monitors oil shipping in Cook Inlet.
Bruce Wright, a National Marine Fisheries Service representative to the spill trustee council, said the study raises doubts about Exxon's claims that seep oil explains contamination in the Sound.
''It's just unbelievable that they are not backing off their story,'' Wright said. ''This establishes coal as the source. Oil is a contaminant.''