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Long-term effects of Exxon Valdez Are there lingering problems from one of the world’s worst oil spills? are free of oil, and the rocky beaches are What lies beneath hen the Exxon Valdez ran almost entirely clean. Many animal speaground in March 1989 at the Government scientists literally uncovered cies, including bald eagles, river otters, northern end of Prince William Sound, the potential missing link between some and several sea birds, have recovered Alaska, and spilled ~11 million gal of the long-term damages and the oil (38,800 t) of Alaska North spill when, in 2001, they Slope crude oil, the impacts found substantial amounts of were all too obvious. The oil buried beneath the surshort-term effects included face of some of the beaches the deaths of ~250,000 sea that had been most heavily birds, up to 2800 sea otters, oiled by the spill. Jeffrey and ~300 harbor seals. Now, Short, a research chemist 17 years later, Prince William with the National Oceanic Sound, with its spectacular and Atmospheric Administraf jords, rugged islands, vivid tion in Auke Bay, Alaska, led tidal pools, and teeming mathe half-million-dollar study rine life, shows no apparent that sent a small army of resigns of the spill. But as a searchers out to 91 beaches court-determined deadline in the western, oiled part of approaches, controversy still the sound. They dug ~9000 clouds the scientific determipits and found subsurface oil. nation of whether any longBefore this finding, oil spills term effects of the spill were generally thought of as linger. short-lived disasters that only Prince William Sound is affected beaches at their easily the best-studied oilsurfaces. spill site in the world. The This buried legacy of the Lingering legacy. Oil that lies under the surface of some of Prince Exxon Valdez Oil Spill Trusspill is the key to the longtee Council has funded reterm effects, Short argues. William Sound’s rocky beaches persists because it is protected from search on the spill’s effects Scientists funded by Exxon sun, wind, waves, and microbes. for more than a decade and disagree. The buried oil is from the effects of the spill. But govern- merely a curiosity because it is not currently spends several hundred thoument scientists believe that some species, bioavailable, they say. sand dollars a year on research into the particularly sea otters and harlequin long-term effects of the spill. Exxon To back their cases, both sides marducks, have not recovered. Scientists Mobil funds parallel studies. The Trusshal analyses of oil sources, the lingering tee Council funding comes from a $900 disagree on the role of the oil spill in subsurface oil, and biomarkers from the the fate of these species. million civil settlement, which left open affected animals. GC/MS is the workSuch disagreement is common in inthe possibility of an additional payment horse for analyses of oil residues. Advestigations of contaminated sediments, of $100 million for restoration of unanvanced techniques, such as comprehensay several environmental scientists who ticipated damages that come to light by sive 2D GC/MS and GC/MS with don’t work on Prince William Sound. May of this year. Trustee-funded scienhydrocarbon biomarker analysis, along In these studies, the strands of evidence tists believe that they have found such with improved statistical analyses, have seldom all point in the same direction. long-term damages. But scientists fundprovided methods to apportion hydroResearchers tend to select from among ed by Exxon disagree. carbon sources. Enzymatic biomarkers the strands based on their opinions, says from affected animals can be measured The two groups agree that the overone outside expert. all picture is good. The sound’s waters directly by analyzing mRNA or indirectNOAA
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ly by measuring the catalytic activity of detoxifying enzymes induced by exposure to contaminants.
dioxins. Combustion-related PAHs have been found to be more potent at inducing the enzyme than petroleum-related PAHs, says Boehm.
Fingerprints and finger-pointing
sources, are not accumulating PAHs. “The clams and mussels show no evidence of PAH levels above the pre-spill baseline level,” he says. “That’s why the government’s story has now turned to theories involving oil on the pelage.”
USGS/BRD
Teasing out the links between the longBring in the otters term effects of the spill and adverse efU.S. Geological Survey wildlife biologist fects on populations of otters or ducks is James Bodkin has been studying a group Clams or fat bags? not easy, but all of the efforts seem to of ~70 sea otters from northern Knight Government scientists don’t dispute the focus on polycyclic aromatic hydrocarIsland, a heavily oiled region that lost clam data. But they counter that what’s bons (PAHs). This is because PAHs are 90% of its sea otter population after the available to the clams may not reflect the usual suspects when it comes to toxic spill. The otters there haven’t recovered what’s available to the otters. They reeffects from an oil spill, according to as rapidly as otter populations at lightly cently finished a study that uses semiJohn Farrington, a senior scientist permeable membrane devices at Woods Hole Oceanographic In(SPMDs) in an attempt to address stitution. These hydrocarbons are this issue. composed of multiple interconSPMDs, also known as fat bags, nected benzene rings, like pieces of are long, flat, plastic tubes filled chicken wire. PAHs are often used with oil that are designed to monito help identify sources. In the tor lipophilic environmental conearly stages of the Exxon Valdez taminants by mimicking the fat in oil-spill investigation, researchers animals, which is the site of biobuilt up fingerprints of characterconcentration. Short and colistic PAH patterns together with leagues deployed partially buried the unique signatures of “chemical SPMDs at various sites. They confossils” (molecules such as steranes centrated the contaminants collectClams in oil sauce, anyone? When sea otters dig underand triterpanes) to match PAH ed by the devices and injected them sources with patterns found in into trout. The samples that came ground for clams, one of their favorite foods, they may get the field, says Paul Boehm, a from oil-spill-affected sediments residual oil on their fur. principal scientist with the enviwere most effective at inducing cyronmental consulting group Exponent. tochrome P450-1A. “It’s the oiled sites oiled sites. Population studies indicate In Prince William Sound, for examthat this is due to a lack of young otters. that induce, not the others,” says Short. ple, oil from the Exxon Valdez spill was But SPMDs were never meant to be Some of these otters show signs of liver just one source of possible exposure. damage, and this group has higher levels put into pits, says Boehm. “SPMDs are Other sources include natural petroleum of cytochrome P450-1A than other otter great, but that’s a misuse of the methseeps, coal and oil shales, old oil from od,” he says. populations. canneries and mines, current inputs The final twist in the tale may come Sea otters don’t have thick layers of from fishing and logging, and even oil from the most recent data on enzyme fat or blubber to keep them warm. Infrom storage tanks ruptured during a levels in the Knight Island sea otters. stead, they have thick fur or pelage. 1964 earthquake. The petroleum-relatAnalysis of data from 2003 and 2005 Bodkin has shown that these otters eat ed sources of PAHs tend to be dominat- clams buried below the surface on the surveys shows that the cytochrome ed by 2– 4 -ring alkylated PAHs. But P450-1A levels of the otters on Knight lower part of the beach. When the combustion-related PAHs from many of beach is covered by the tide, the animals Island are no longer different from these human activities contain more 3– those of other otter populations. This dive down and dig for clams. Govern6-ring unalkylated PAHs, says Boehm. could be very good news, because it ment scientists think that the otters get The distinction between oil- and suggests that oil in sediments is slowly oil on their fur while they are digging combustion-related PAHs is important declining and has reached the tipping and eating and that this is the source of for attempts to tie PAH exposure to point at which the exposure is not the exposure. harm. PAHs are known to induce cytoenough to induce the enzyme. If this is Boehm says that there is no direct chrome P450-1A, an enzyme that plays the case, the otters should be set for reevidence for this notion. “The sea-otter a crucial role in efforts to link PAH excovery. But the results could also mean story is a myth that makes selective use posure to effects. Cytochrome P450-1A of the data,” he says. The otters do not that the oil isn’t the problem and that is not harmful. It is induced by expofavor oiled beaches and mainly dig away something else is affecting the otters— sure to nonpolar aromatic chemicals, perhaps another mystery for analytical from subsurface oil. In addition, the such as PAHs, and other contaminants, chemists to solve. a clams in the sediments and the mussels such as polychlorinated biphenyls and —Rebecca Renner on the beaches, the otters’ major food 2092
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