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Oil Spills

Ecological Damages Of Oil Spills

Even small oil spills can cause important change in ecologically sensitive environments. For example, a small discharge of oily bilge washings from the tanker Stylis during a routine cleaning of its petroleum-storage compartments caused the deaths of about 30,000 seabirds, because the oil was spilled in a place where the birds were abundant. This is a regrettably common occurrence. Even relatively small operational spillages of petroleum can have significant though, perhaps temporary, ecological impact, especially to seabirds and marine mammals. An ecosystem is dynamic—ever changing—and continues its natural cycles and fluctuations at the same time that it struggles with the impact of spilled oil. As time passes, separated natural change from oil-spill impacts becomes more and more difficult.

Studies made after large oceanic spills have shown that the ecological damage can be intense. After the Torrey Canyon spill in 1967, hundreds of kilometers of the coasts of southern England and the Brittany region of France were polluted by oily mousse. The oil pollution caused severe ecological damage, due to the physical and toxic effects of fouling of organisms with petroleum residues. Those direct ecological damages were made much worse by some of the cleanup methods, because of the highly toxic detergents and dispersants that were used. As is the case with many oil spills, seabirds were among the most tragic victims of the Torrey Canyon incident. This accident caused the deaths of at least 30,000 birds, causing a substantial decrease in their breeding populations in subsequent years.

The damage caused by detergents and dispersants during the cleanup of shorelines polluted by the Torrey Canyon spill were an important lesson. Subsequent cleanups of oil spills involved a much more judicial use of less toxic chemicals. In addition, their use became largely restricted to offshore locations and places of high value for industrial or recreational purposes, rather than natural habitats.

In 1978, the Amoco Cadiz was wrecked in the same general area as the Torrey Canyon. Considerable ecological damage was also caused by this accident. However, the damage was less intense than that caused by the Torrey Canyon because less-toxic detergents and dispersants were used during the cleanup, in much smaller quantities, and only in high-value places such as harbors.

The most damaging oil spill ever to occur in North American waters was the Exxon Valdez accident of 1989. More than most tanker accidents, this one was very preventable. It was caused when an intoxicated captain gave temporary command of the supertanker to an unqualified and inexperienced subordinate, who quickly erred in his navigation and ran the ship aground onto a well known reef. The spilled oil affected about 1,200 mi (1,900 km) of shoreline of Prince William Sound and its vicinity, causing especially great ecological damages in tidal and subtidal habitats. Large numbers of sea mammals and birds were also affected in offshore waters. An estimated 5,000-10,000 sea otters (Enhydra lutris) were present in Prince William Sound, and at least 1,000 of these charismatic mammals were killed by oiling. About 36,000 dead seabirds of various species were collected from beaches and other places, but the actual number of killed birds was probably in the range of 100,000-300,000 birds. At least 153 bald eagles (Haliaeetus leucocephalus) died from poisoning when they scavenged the carcasses of oiled seabirds.

Great efforts were expended in cleaning up the oiled shoreline, almost entirely using manual and physical methods, rather than dispersants and detergents. In total, about 11,000 people participated in the cleanup, and about $2.5 billion was spent by the ship owners and $154 million by the U.S. federal government. This was by far the most expensive cleanup that has ever been undertaken after an oil spill. Within a year of the spill, the combined effects of the cleanup and winter storms had removed most of the residues of the Exxon Valdez spill from the environment. However, in August 2002 the Exxon Valdez Trustee Council released a report stating that while it is clear that many fish and wildlife species injured by the spill have not fully recovered, it is less clear what role oil plays in the inability of some populations to recover. Bald eagles, black oystercatchers, common murre, pink salmon, river otter and sockeye salmon have recovered. Wilderness area intertidal communities, killer whale, marbled murrelet, sea otters, clams and sediments are recovering but the common loon, three species of cormorants, harbor seals, harlequin duck, Pacific and pigeon guillemot have shown little or no recovery.

See also Fossil fuels.

Resources

Books

Freedman, B. Environmental Ecology. 2nd ed. San Diego: Academic Press, 1994.

GESAMP. Impact of Oil and Related Chemicals and Wastes in the Marine Environment. Joint Group of Experts on the Scientific Aspects of Marine Pollution (GESAMP). Report 50, London: International Marine Organization, 1993.

Keeble, J. Out of the Channel: The Exxon Valdez Oil Spill in Prince William Sound. Eastern Washington University Press, 1999.


Periodicals

U.S. Environmental Protection Agency. "Oil spills." January 28, 2003 [cited February 20, 2003] <http://www.epa.gov/oil-spill/>.


Bill Freedman
William J. Engle

KEY TERMS

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Bilge washings

—Hydrocarbon-contaminated water that results from cleaning of the petroleum-holding compartments of a tanker, and that may be discharged to the environment.

Bunker fuel

—A relatively viscous, liquid hydrocarbon mixture, also known as bunker-C fuel oil, that remains after lighter hydrocarbons are distilled from petroleum during refining. Bunker C is used as a fuel by oil-fired generating stations, heating plants, and ships.

Detergent

—A chemical used as a cleaning agent because it encourages the formation of an oil-in-water emulsion.

Dispersant

—A chemical agent that reduces the surface tension of liquid hydrocarbons, encouraging the formation of an oil-in-water emulsion. This reduces the volume of residual oil on shorelines or the water surface after a spill.

Mousse

—A water-in-oil emulsion that is formed by turbulence of the surface water after a petroleum spill to the aquatic environment.

Petroleum

—A naturally occurring, liquid mixture of hydrocarbons that is mined and refined for energy and the manufacturing of chemicals, especially plastics. Also known as crude oil.

Additional topics

Science EncyclopediaScience & Philosophy: Octadecanoate to OvenbirdsOil Spills - Characteristics Of Petroleum, Oil Pollution, Ecological Damages Of Oil Spills