Ten years ago this month theExxon Valdez tanker crashedinto Bligh Reef, releasing at

least 11 million gallons or so of crude oilinto Prince William Sound in Alaska.The spill had enormous implications notonly for the environment and people ofthe surrounding area but for public per-ceptions of oil pollution and for the fed-eral law governing oil spills as well. Thespill also created a massive experiment.

Despite many scientific conflicts, ongo-ing studies have led to some importantinsights. Researchers now have a betterunderstanding of the impact of cleanupand of how an ecosystem recovers. Theyalso have a clearer picture of how hydro-carbons—the building blocks of oil—af-fect certain species. Of these latter stud-ies, work on pink salmon has recentlyproduced some surprising results that, ifthey hold up, could have widespread im-plications for water-quality standards.

As a commercially critical fish, pinksalmon received much attention after the

spill. For years, biologists have docu-mented the size and health of salmonpopulations returning to oiled and un-oiled sites in the sound and have con-ducted laboratory experiments to deci-pher the precise dangers of hydrocar-bons. Such studies are proving to beeye-opening. “Now we believe that oilpollution has much longer effects atmuch lower concentrations and withdifferent compounds than we hadthought,” says Ronald A. Heintz, a biol-ogist at the National Marine FisheriesService’s Auke Bay Laboratory in Juneau.

Oil is composed of thousands of com-pounds, including polynuclear aromatichydrocarbons, or PAHs. PAHs are notregulated in the aggregate nor for theirimpact on aquatic life. The Environmen-tal Protection Agency issues water-quali-ty recommendations only for humanconsumption of specific PAHs—such asnaphthalene and chrysene—althoughstates can devise their own regulations.

What Heintz and histeam did was to exposepink salmon eggs and em-bryos to different amountsof total PAHs. In previous-ly published papers, the re-searchers reported thatpostspill concentrations ofPAHs—from a high of51.5 parts per billion to alow of 4.4 ppb—can, vari-ously, kill the fish, impairtheir ability to reproduceand lower their growthrates. “Exposing an em-bryo to oil is like taking ashotgun to its DNA,”Heintz describes. It has lotsof different effects, headds, and “over the wholelife cycle, those little effectsreally add up.”

Now Heintz and his colleagues havedetermined that PAH levels as low as 1ppb harm both pink salmon and Pacificherring. In their most recent studies,which appear in this month’s Environ-mental Toxicology and Chemistry, thescientists found that mortality increasedfor both species of fish exposed to 1 ppb.And they discovered that the effects ofvery weathered oil were the same asthose of fresh oil—which means that theold oil persisting under gravel in someparts of Prince William Sound could stillbe harmful.

The fact that 1 ppb is damaging to twospecies suggests that intertidal organismseverywhere may be affected by thechronic pollution brought about by smallspills or leaks. “You’d be hard-pressed tofind any coastal area where you wouldn’tget total PAH concentrations of thatmagnitude,” asserts Judith E. McDowellof the Woods Hole Oceanographic Insti-tution in Massachusetts.

If more researchers determine thatPAHs at 1 ppb are damaging fish andother organisms, new regulations maybe needed to ensure water quality—

which could affect oil exploration off-shore and ballast-water discharges.Even Alaska, which has the strictest cri-teria in the world at 15 ppb, might haveto rethink its standards, observes JeffreyW. Short, a chemist at the Auke BayLaboratory. But it could prove virtuallyimpossible to regulate the many non-point sources of PAHs, such as storm-water runoff and people’s sloppinesswith their motor oil. “The conscious-ness has got to change with the publicand the way that we set standards,”says Usha Varanasi of the NorthwestFisheries Science Center in Seattle. “It isnot always a company.”

For now, as Heintz and both his sup-porters and critics point out, much morework is needed. “You need replication byan outside group,” notes Paul D. Boehm,a petroleum expert at the consulting firmArthur D. Little who has worked in thesound for Exxon. In addition, other spe-cies need to be studied to see if the obser-vations extend beyond salmon and her-ring—although there is some evidence tosupport the Auke Bay findings. For in-stance, a 1991 study from Prince WilliamSound found that growth rates of capelinwere affected at PAH concentrations of 4ppb. And researchers in Puget Sound arefinding similar effects in juvenile salmon,Varanasi remarks.

But in general, low-level PAH analy-ses remain uncharted terrain. Many in-tertidal regions are polluted, and dis-cerning the specific effects of PAHsagainst a background of other contami-nants is difficult. Heintz notes that hisfindings came to light because PrinceWilliam Sound had been a pristinearea. “The Exxon Valdez is the stimu-lus that motivated a new way of look-ing at it for us,” he says. “It has radical-ly changed the way we think about oilpollution.” —Marguerite Holloway

News and Analysis38 Scientific American March 1999

TECHNOLOGY AND BUSINESS

OIL IN WATER

Studies arising from the Exxon

Valdez oil spill suggest that fish aremore sensitive to hydrocarbons

than previously thought

ENVIRONMENT

PRINCE WILLIAM SOUND,a decade after the spill, is still providing scientists

with insights about pollution’s effects.

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Copyright 1999 Scientific American, Inc.