**Read about the BP Deepwater Horizon oil spill in the Gulf of Mexico.**

An oil spill is the accidental petroleum release into the environment. On land, oil spills are usually localized and thus their impact can be eliminated relatively easily. In contrast, marine oil spills may result in oil pollution over large areas and present serious environmental hazards. The primary source of accidental oil input into seas is associated with oil transportation by tankers and pipelines (about 70%), whereas the contribution of offshore drilling and production activities is minimal (less than 1%). Large and catastrophic spills releasing more than 30,000 tons of oil are relatively rare events and their frequency in recent decades has decreased perceptibly. Yet, such episodes have the potential to cause the most serious ecological risk (primarily for sea birds and mammals) and result in long-term environmental disturbances (mainly in coastal zones) and economic impact on coastal activities (especially on fisheries and mariculture).

Public concern over marine oil spills has been clearly augmented since the 1967 Torrey Canyon supertanker accident off the UK coast, when 100,000 tonnes of spilled oil caused heavy pollution of the French and British shores with serious ecological and fisheries consequences. More recently, the highly publicized 1989 spill of the Exxon Valdez in Prince William Sound, Alaska caused unprecedented damage to the fragile Arctic system. Since then, impressive technical, political, and legal experience in managing the problem has been gained in many countries and at the international level, mainly through a number of Conventions initiated by the International Maritime Organization (IMO). As a result of the Exxon Valdez oil spill, the U.S. passed legislation requiring all newly built tankers to have a double hull.

When the oil reaches the shoreline, on rocky shores some components of the oil evaporate, leaving behind the heaviest components and turning the oil into tar. On rocky shores with surf, the tar will erode away from the wave action, and biological communities will return rather quickly. In marshes, however, oil can sink down below the surface and remain for many years. Oil accumulated in marsh sediments undergoes some microbial breakdown, but it is slow. Low-energy environments like marshes are the most vulnerable and show the slowest rates of recovery from oil spills. Effects of a rather small oil spill in Falmouth, MA in the late 1960s were seen to last for a decade by a team of scientists from the nearby Woods Hole Oceanographic Institute. It is seldom that a spill occurs right in an area that has been intensively studied prior to the spill. Fiddler crabs were particularly sensitive, and were still affected after seven years. The oil affected their burrow construction – the burrows did not go straight down, but leveled off to a horizontal plane. While this was not a problem during the summer, when winter came the crabs were not below the freezing zone of the marsh as they should have been and froze to death. Benthic communities took about a decade to return to normal. After 30 years, some abnormalities still are noted in fiddler crab burrows in the oiled areas.

Marshes and sediments in Prince William Sound in Alaska retained oil from the massive oil spill of the Exxon Valdez in 1989 for many years, affecting the development of fish embryos on the bottom. After ten years, pockets of oil remained in these marshes, and mussels, clams, ducks and sea otters showed evidence of harm in some localized areas. Remedial actions after oil spills are controversial, and some of the cures (e.g. aggressive cleaning with large heavy equipment) may be worse than the original problem, as was seen in the attempted clean up after the Exxon Valdez oil spill.

Further Reading

• Patin, Stanislav and Elena Cascio (Translator), 1999. Environmental impact of the offshore oil and gas industry. EcoMonitor Pub, East North Port, N.Y. ISBN: 0-9671836-0-X
• Patin, Stanislav, 2004. Crude Oil Spills, Environmental Impact of, In: Cutler J. Cleveland (Editor), The Encyclopedia of Energy. Elsevier Science, Oxford, pp. 737-748.