Published online 20 March 2009 | Nature | doi:10.1038/news.2009.176

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Lasting legacy of the Exxon Valdez

Twenty years on, the iconic oil spill remains an expensive ecological disaster.

Exxon ValdezThe Exxon Valdez: pollution icon.NOAA | U.S. Department of Commerce

When people think of big oil spills, they think of the Exxon Valdez. Twenty years ago, the oil tanker spilled its load off the coast of Alaska, and images of oil-slicked birds hit the news at a time when environmental awareness was quickly rising in the United States.

The accident became a lightening rod for green groups and lawmakers, but has also prompted hundreds of scientific studies looking at the implications of the disaster on local people, the ecosystem, remediation practices and oil spill response. Nature takes a look back at the disaster, and finds out what the situation is today.

What happened?

Shortly after midnight on 24 March 1989, the Exxon Valdez grounded on a reef in Prince William Sound in the Gulf of Alaska. Despite calm weather in the following days, the clean-up was not well organized, and a storm on 27 March helped to spread heavy crude oil across nearly 2,000 kilometres of shoreline, hundreds of kilometres away.

The nearly 40 million litres of oil that spilled from the Exxon Valdez may seem rather small in comparison to earlier spills, such as the Amoco Cadiz off the French coast in 1978 (260 million litres) or the Prestige off Spain in 2002 (76 million litres). But size isn't everything. The combination of the spill's location — in Alaska's relatively cold and pristine subarctic waters — and the timing — as the ecosystem was gearing up for spring — made it particularly devastating.

What were the effects and how's the ecosystem doing now?

Ten years after the spill, ecologists estimated that between 100,000 and 700,000 birds had died because of oil exposure, based on an extrapolation of the number of oiled carcasses collected on beaches and from the water1. While many species are now back up to pre-spill levels, or are recovering well, two have not recovered at all: pigeon guillemots and Pacific herring.

On 31 December 2008, the Exxon Valdez Oil Spill Trustee Council submitted a recovery plan for the herring, an economically important fish in the region. But some argue that the oil spill may not have been responsible for the demise of the herring fishery. Overfishing or other ecosystem shifts, such as an increase in disease or decline in available food sources for the fish, may have contributed.

What was done to clean up the beaches and the oil slicks?

beachOil deposits from the Exxon Valdez have been found along Herring Bay, Prince William Sound.Capt. David Janka

The clean-up was particularly difficult because of the remote location of the spill. The US Coast Guard and other responders tested every type of boom available to contain the oil, as well as dispersants. Volunteers trapped and cleaned birds, otters and other animals. Some experimental use of microbes in the Sound led scientists to develop groundbreaking bioremediation methods, husbanding Pseudomonas aeruginosa strains to break down oil in situ2.

The Exxon Mobil Corporation spent more than $2 billion to finance some of these efforts, and has disbursed over $900 million to individuals, the state of Alaska and the Exxon Valdez Oil Spill Trustee Council for research on the impacts of the spill.

How long will it take for the oil to disappear?

Exxon Valdez oil that settled on active shorelines, where wave action or microbes could break it down, disappeared fairly fast. But surface puddles of crude oil from the Valdez are still found, and pockets of undegraded oil rest just below the surface of some beaches3.

This has fuelled the ongoing debate over whether sea otters digging for food on a beach could still be exposed to Exxon Valdez oil. Exxon consultants say that sea otters and other animals are not at risk of exposure at toxic levels any more, and that natural processes will either sequester away any remaining oil or soon take care of whatever background levels are left4.

Did anything good come from this disaster?

A century of mining for copper, oil drilling and fishing had already impacted Prince William Sound. One challenge researchers faced was how to identify the molecular fingerprint of oil from the spill, to distinguish it from oil released by other human activities from decades past. In response to the legal wrangling surrounding issues of the clean-up and responsibility, scientists have taken the art of fingerprinting oil hydrocarbons to a new level of accuracy. Analytical contract labs can now get "bulletproof" identification of an oil sample's provenance, says Chris Reddy of the Woods Hole Oceanographic Institution, Massachusetts.

Prompted by difficulties in tackling the spill, the US Coast Guard clarified its chains of command and retrained its clean-up teams for oil spills. The US Congress passed the Oil Pollution Act of 1990, which laid out responsibility for fiscal damage and clean-up.

Most spills now come from single-hull ships, comments Dennis Nixon, an environmental law professor at the University of Rhode Island, Kingston. The single-hulled Exxon Valdez — which was repaired, then sold and renamed Mediterranean — is actually still in service in east Asia. Single-hulled tankers are now barred from using US ports, while European countries such as France and Spain do not allow then within 200 miles of their coast.

What about the people of Alaska?

The Exxon Valdez Oil Spill Trustee Council continues to categorize "human services" — such as fishing, recreation and subsistence use — as "'recovering" until the resources that they depend on return to normal5.

And in 2008, a US Supreme Court decision dramatically decreased the amount to be paid to local people in punitive damages from $2.5 billion to $507.5 million, judging the initial award as excessive under maritime law. The Exxon Mobil Corporation has started to disburse those damages. 

  • References

    1. Piatt, J. F. & Ford, R. G. American Fisheries Society Symposium 18, 712-719 (1996). | ChemPort |
    2. Harvey, S. et al. Nat. Biotechnol. 8, 228-230 (1990). | Article | ChemPort |
    3. Short, J. W. et al. Environ. Sci. Technol. 41, 1245–1250 (2007). | Article | PubMed | ChemPort |
    4. Boehm, P. D. et al. Environ. Sci. Technol. 41, 6860–6867 (2007). | Article | PubMed | ChemPort |
    5. Legacy of an Oil Spill — 20 Years After the Exxon Valdez Exxon Valdez Oil Spill Trustee Council; available online at www.evostc.state.ak.us/Universal/Documents/Publications/20th%20Anniversary%20Report/2009%20Status%20Report%20(Low-Res).pdf (2009).
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