Seventeen years after the Exxon Valdez ran aground in Alaska's Prince William Sound, compelling new evidence suggests that remnants of the worst oil spill in U.S. history extend farther into tidal waters than previously thought, increasing the probability that the oil is causing unanticipated long-term harm to wildlife. The finding appears today on the Web site of the American Chemical Society's journal, Environmental Science & Technology.
The study, by research chemist Jeffrey Short and colleagues at the National Marine Fisheries Service in Juneau, Alaska, is also scheduled to appear in the June 15 print issue of the journal.
"This study shows that it is very plausible that exposure to Exxon Valdez oil is having a material impact on many shore-dwelling animals and is contributing to their slow recovery in some parts of Prince William Sound," Short says. "Sea otters, for instance, have yet to re-inhabit Herring Bay, the most oiled bay we studied, and the population of otters elsewhere around northern Knight Island continues to decline. Unfortunately, because much of this oil is buried in beach sediments and not exposed to weathering and other elements that might degrade it, it could remain hazardous to wildlife for decades."
The Exxon Valdez stuck an underwater rock formation on March 24, 1989, spilling 11 million gallons of heavy crude oil into the Sound over the next several days. Despite massive clean-up efforts, Short estimates about six miles of shoreline is still affected by the spill and as much as 100 tons of oil lingers in the Sound.
In their study, Short and his colleagues found significant amounts of Exxon Valdez oil buried in sand and silt that only becomes dry during the lowest tides. This biologically diverse zone is a prime feeding ground for sea otters, ducks and other wildlife.
Previously, scientists believed most of the oil was deposited on beaches at higher tide levels.
The researchers randomly dug 662 pits along 32 stretches of shoreline on northern Knight Island, one of the earliest and worst affected areas during the spill. They found Exxon Valdez oil at 14 of the 32 sites. Although oil was spread throughout the tidal range, about half of it was found in the low tide zone, where predators could encounter it while searching for prey. More than 90 percent of the surface oil and all of the subsurface oil was from the Exxon Valdez, Short says.
Based on these findings, the researchers estimated that in a given year, a sea otter -- digging three pits a day searching for clams and other prey -- would probably come into contact with Exxon Valdez oil at least once every two months. However, sea otters dig thousands of pits a year, and Short suspects they actually could be encountering oil far more often than estimated.
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