An article about oil spills from Grolier Multimedia Encyclopedia™ (Lexile 1530)
The discharge—either accidental or deliberate—of petroleum or petroleum products, an oil spill may occur naturally, as a seep; as the result of human-consumption activities; from oil wells, oil transport trucks, or pipelines; or on water from ocean-sited oil rigs, oil tankers, or oil-fueled vessels. Many land spills, in addition to fouling the soil, have the potential to reach surface water and move from there to rivers, lakes, and oceans. Thousands of spills of varying magnitudes are reported in the United States each year. Most spills are relatively minor, amounting to less than 3,785 l (1,000 U.S. gal). Catastrophic spills, in which many thousands of liters are lost, occur regularly, however.
About 680 million l (180 million gal) enter the oceans each year through natural seepage processes in the seafloor, which account for approximately 48% of all petroleum that enters the oceans of the world. In the United States, natural seeps occur primarily in the Gulf of Mexico, off the coast of southern California, and in several locations off the northern and southern coasts of Alaska. Although the total amount of petroleum that reaches water through natural seeps is great, it does not tend to have catastrophic adverse effects on ocean environments, and the seeps are studied to learn more about how marine life adapts to the presence of petroleum.
Worldwide, some 530 million l (140 million gal) enter the ocean each year as the result of a range of human activities associated with the consumption of petroleum products, amounting to roughly 37% of the total volume of oil spilled into waters. Such spills occur when these products, in the form of fuels and lubricants, reach water through land runoff, wastewater treatment facilities, the exhaust of two-stroke marine engines, or careless disposal of waste oils. In North America, much of the oil spilled is land-based runoff or comes from airplanes, small boats, and jet skis.
Transportation spills come most commonly from pipelines, seagoing oil tankers, railroad tank cars, and over-the-road tanker trucks and contribute about 166.5 million l (44 million gal), constituting approximately 12% of the total annual global oil-spill volume. Although the size and frequency of oil spills associated with oil tankers has been reduced significantly in recent years, the potential for a large spill remains. As worldwide petroleum consumption continues to increase, the amount of oil moved by oil tankers will also increase, resulting in the continued risk of large oil spills. The switch to double-hulled tankers and improved tanker operations is expected to help reduce the risk of large spills. Growing demand for imported oil in North America, however, will require greater emphasis on tanker safety at loading and off-loading terminals. To manage the risk of pipeline-related spills, enhanced pipeline-maintenance procedures will be required.
As the result of international oil and natural-gas exploration and production, about 41.6 million l (11 million gal) enters the world's oceans each year, constituting roughly 3% of the total annual spill volume. On land and at sea, the processes of extraction may produce spills from accidental well blowouts, from platforms or drill sites, from the disposal of produced water, and from the disposal of rock cuttings created while drilling.
The most catastrophic spill in recent history was caused when the Iraqi army, in its retreat from their occupation of Kuwait in 1991 (see Persian Gulf War), attempted to destroy Kuwait's oil fields. The Iraqis intentionally damaged more than 700 oil wells, creating 300 oil lakes over an area of 978 km2 (378 mi2). As much as 159 million l (42 million gal) of the Kuwaiti crude oil that was spilled on land may have made it to the sea. Another 1.27 billion l (336 million gal) of oil was spilled directly into the Persian Gulf from Kuwaiti oil tankers and production, storage, and tanker-loading facilities. Fortunately, floating booms and favorable winds kept the oil slick away from the desalination plants on the Gulf coast of Saudi Arabia. Nevertheless, the torching of the Kuwaiti oil fields—which spewed untold amounts of oily smoke into the atmosphere—while not the first time oil-field sabotage has been used as an act of war, is certainly the first instance of the deliberate use of oil as a weapon against the environment.
The size of an oil spill may have little bearing on its environmental effects. The 1979 blowout of the Ixtoc I oil well in the Gulf of Mexico released—at a low estimate—about 530 million l (140 million gal), but ocean winds and currents prevented the slicks from drifting inland and the oil was dispersed and presumably disintegrated in the open sea. On the other hand, a far smaller spill (265.4 million l70.1 million gal) from the tanker Amoco Cadiz when it ran aground (1978) in the English Channel fouled hundreds of kilometers of the Brittany coast, creating an ecological disaster whose effects were felt for more than a decade. In a repetition of that disaster, in December 1999 the tanker Erika broke up off the coast of Brittany, fouling more than 320 km (200 mi) of beach with thick crude oil. Crude—unlike the lighter fuel oil spilled by the Amoco Cadiz—does not evaporate over time and presents a serious long-term threat to the economy and environment of Brittany.
The Exxon Valdez tanker spill of March 1989 is ranked as the worst U.S. oil disaster (see Exxon Valdez disaster). More than 41.6 million l (11 million gal) of oil were released from the gashed hull of the ship where it ran aground in Alaska's Prince William Sound. The possibility of such an accident had long concerned environmentalists and the fishing industry, which feared the polluting of the sound, a bountiful fishery and a pristine area rich in wildlife. Government reports released two years after the spill indicated that plants and animals living along the shoreline and in shallow -water areas were most heavily affected by the spill.
Both Spain and France suffered major oil spills in the 1990s—Spain in 1992 when a Greek tanker lost 81 million l (21.5 million gal) off its northern Atlantic coast; and France in 1999, from a spill that polluted 400 km (250 mi) of its coastline.
The 1994 rupture of a corroded pipeline in Komi in the Russian Arctic was a near disaster. The spilled oil was at first confined behind an earth dam, but spring rains broke down the dam and the stored oil—whose estimated volume was some eight times greater than that of the Exxon Valdez spill—was spewed out over about 186 km2 (72 mi2) of Siberian tundra and marsh and then into the Kolva and Usa rivers. Russian and international cleanup efforts were said to have prevented an environmental disaster there, but the potential remains for other huge spills throughout the antiquated and badly maintained Russian oil industry.
In November 2002 the 26-year-old oil tanker Prestige began to founder after having leaked a long trail of heavy crude—almost 7.5 million l (2 million gal)—into the Atlantic Ocean off the coast of northern Spain. As the oil coated about 200 km (125 mi) of Spanish beach and the Spanish navy raced to contain the spill, the tanker broke in two and sank slowly to the ocean bottom, carrying with it the remaining 68 million l (18 million gal) of crude oil. The tanker continued to leak from the ocean floor, dashing the hope that the crude-oil cargo now at the cold bottom of the ocean, would congeal and remain inside the wreck. Both tourism and fishing—the two major industries in this part of Spain—were essentially wiped out by the spill. By early January 2003, oil from the wreck was beginning to wash ashore in coastal towns in the southwest region of France, recalling to residents there the awful effects of the 1999 disaster.
The Prestige catastrophe brought to the forefront several ongoing problems relating to tanker spills. The ship was old and single-hulled; double-hulling is not yet a legal requirement for all tankers. Furthermore, the complex ownership of the ship clouded the issue of responsibility: it flew a Bahamian flag, was registered in Liberia, was managed by a Greek company, and had been inspected and found in compliance with all safety requirements (see shipping; flag of convenience). Finally, the decisions made by the Spanish authorities were questioned by many experts: instead of towing the ship out to sea, they claim it might have been better to tow it into a bay where the seas were less turbulent (thus delaying or preventing the vessel's breakup) and the spill might have been contained.
In addition to the scenic degradation when oil fouls a coastline and to the economic losses borne by fishing, tourist, and other industries dependent on the health of coastal waters, a major effect of spills is the mass killing of waterfowl, whose feathers can no longer hold air or repel water. Oil-coated birds, and furred ocean mammals such as otter, die from drowning, exhaustion, or freezing. Edible mollusks such as shellfish, clams, and oysters ingest oil-impregnated water and become tainted with an oily taste. Commercial shellfish beds must therefore be closed for a number of years following an oil spill. Fisheries have been wiped out when a spill occurs in regions where fish spawn or on fish-migration routes.
Long-term effects may be equally devastating. The soluble fraction of the spilled oil may spread over vast areas, and toxic components may create chronic damage to life. A study of spill effects in the Caribbean found that coral organisms were severely hurt and coastal environments such as mangrove thickets were wiped out along with the creatures that inhabited them. A study of the Brittany coastline in the years following the Amoco Cadiz spill found massive death rates for bottom-dwelling species, the practical elimination of some other species, and the overall reduction of animal numbers.
Experts believe that oil-tainted ocean environments probably recover eventually, although not all species may return to their prespill status. Some oceans are more vulnerable to long-term damage than others, however. The waters of the Mediterranean Sea change relatively slowly, and a massive oil spill there would have incalculable consequences. Even more vulnerable is the Persian Gulf. The highway for the transport of much of the world's petroleum, the Gulf is a shallow, almost completely enclosed body whose waters are entirely renewed only over about 200 years.
In the United States the federal oil-spill laws that are executed through Environmental Protection Agency (EPA) regulations determine reporting and spill-prevention requirements. The reporting of oil spills into natural surface waters is not dependent on the size of the spill but rather on any of three criteria: the presence of a visible sheen on water or on adjoining shorelines; the deposition of a sludge beneath the water surface or on adjoining shorelines; and spills that violate applicable water-quality standards. To help reduce the risk of land-based spills reaching surface waters, the EPA has promulgated an Oil Pollution Prevention regulation that applies to facilities that engage in any aspect of the oil industry, and to other industries that consume oil in quantities considered significant under the regulation, or that are situated close to bodies of water. Such regulated facilities are required to have fully prepared and implemented plans to prevent oil spills from reaching natural surface waters. Similar spill-prevention plans are required for each tanker, all tanker loading and offloading facilities, and all offshore oil production and transportation systems.
These regulations, along with an increased sense of environmental stewardship by commercial enterprises, appear to have been effective in reducing the number of significant oil spills and in reducing the cumulative volume of U.S. spills. For example, 87% of all spills that occurred in U.S. waters from 1973 to 2000 were between 3.8 and 380 l (1 and 100 gal), and there has been a general downward trend in the number of spills over 3,785 l (1,000 gal).
The last spill of more than 3.8 million l (1 million gal) occurred in 1990, and the volumes of spills greater than 378,500 l (100,000 gal) shrank dramatically after 1985.
Cleanup and Control Technology
Techniques for dealing with spills at sea include the use of floating booms to keep the oil contained until it can be collected by pumps or skimmers; spraying chemical dispersants, which break down the oil; and burning surface oil. Pools of spilled oil on land can be contained by dikes or removed by pumps. No method has yet proved effective, however, for cleaning oil-impregnated soil.
The legacy of the Exxon Valdez spill has been a loud public call for spill prevention, and the creation of strong regulations putting comprehensive oil spill cleanup responsibilities and liabilities on spillers, both in the United States and internationally. The U.S. Oil Pollution Act (OPA) of 1990 improved the nation's ability to prevent and respond to oil spills and created a trust fund that is available to fund cleanup expenses of up to $1 billion per spill. The OPA also increased penalties for regulatory noncompliance, broadened the response and enforcement authorities of the federal government, and preserved state authority to establish laws governing spill prevention and response. The OPA further required that U.S.-registered oil tankers have double hulls by the year 2010.
—Reviewed by Gary J. Green