An oil spill is the release of a liquid petroleum hydrocarbon into the environment as a result of human activity (can be both intentional and unintentional). The term often refers to marine oil spills, where oil is released into the ocean or coastal waters. Oil can refer to many different materials, including crude oil, refined petroleum products (such as gasoline or diesel fuel) or by-products, ships' bunkers, oily refuse or oil mixed in waste. Spills take months or even years to clean up.
Oil is also released into the environment from natural geologic seeps on the sea floor . Most man-made oil pollution comes from land-based activity, but public attention and subsequent regulation has tended to focus most sharply on seagoing oil tankers .
Studies of the Exxon Valdez oil spill have shown that the environmental damage caused by oil spills can be greater than was previously thought. Petroleum-based hydrocarbons can negatively impact marine life at concentrations as low as one part per billion.
Birds killed as a result of oil from the Exxon Valdez spill
The lighter fractions of oil, such as benzene and toluene, are highly toxic, but are also volatile and evaporate quickly.[ citation needed Heavier components of crude oil, such as polycyclic aromatic hydrocarbons (PAHs) appear to cause the most damage; while they are less toxic than the lighter volatiles, they persist in the environment much longer. A heavy oil spill can also blanket estuaries and shoreline ecosystems such as salt marshes and , preventing gas exchange and blocking light. The oil can mix deeply into pebble, shingle or sandy beaches, where it may remain for months or even years.
Seabirds are severely affected by spills as the oil penetrates and opens up the structure of their plumage, reducing the insulating ability of their feathers, making the birds more vulnerable to temperature fluctuations and much less buoyant in the water. The oiled feathers also impairs birds' flight abilities, making it difficult or impossible to forage and escape from predators. As they attempt to preen, birds typically ingest oil that coats their feathers, causing kidney damage, altered liver function, and digestive tract irritation. The limited foraging ability coupled with the ingestion of the oil quickly causes dehydration and metabolic imbalances. Most birds affected by an oil spill will die without human intervention.
Marine mammals exposed to oil spills are affected in many of the same ways as seabirds. Oil coats the fur of Sea otters, seals, reducing their furs natural insulation abilities, leading to body temperature fluctuations and hypothermia. Ingestion of the oil also causes dehydration, and impaired digestion.
A sheen is usually dispersed (but not cleaned up) with detergents which makes oil settle to the bottom. Cleaning up oils that are denser than water could prove difficult as they settle to the bottom making the seabed toxic; PCBs are an example of such a pollutant.
Some of the equipment used in cleaning up include:
Booms: floating barriers that rounds up oil
Skimmers: skim the oil
Sorbents: large sponges that absorb oil
Chemical and biological agents: helps to break down the oil
Vacuums: remove oil from beaches and water surface
Shovels and other road equipments: typically used to clean up oil on beaches
Some of the methods used include:
Bioremediation: use of microorganisms  or biological agents to break down or remove oil
Burning: Controlled burning if conducted properly can effectively reduce the amount of oil in water. However, it can be done only when it is not windy[ citation needed ], and could cause air pollution.
Dispersants: Dispersants act as detergents, clustering around oil globules and allowing it to be carried away in the water. While this improves the surface aesthetically, it only serves to mobilise the oil. This may be beneficial since smaller oil droplets, scattered with currents, may cause less harm and may be easier to degrade. However, the dispersed oil droplets increases infiltration into deeper water and can lethally contaminate coral. Moreover, recent research indicates that some dispersants are toxic to corals.
Watch and Wait: In some cases, allowing nautral attentuation of oil may be the most appropriate choice due to the invasive nature of facilitated methods of remediation, particularly in ecologically sensitive areas.[ citation needed ]
Dredging: for oils dispersed with detergents and other oils denser than water.
Long-Term Ecosystem Response to the Exxon Valdez Oil Spill, Science, v.302, 19 December 2003, pp.2082-2085
Dunnet, G., Crisp, D., Conan, G., Bourne, W. (1982) "Oil Pollution and Seabird Populations [and Discussion]" Philosophical ransactions of the Royal Society of London. B 297(1087): 413–427
Untold Seabird Mortality due to Marine Oil Pollution, Elements Online Environmental Magazine.
George Draffan. Major Oil Spills (HTML) (English). Endgame . Retrieved on 2007-07-29.
a b c d e History (HTML) (English). The Mariner Group .
John S. Patton, Mark W. Rigler, Paul D. Boehm & David L. Fiest (1981-03-19). Ixtoc 1 oil spill: flaking of surface mousse in the Gulf of Mexico (HTML) (English). NPG (Nature Publishing Group) . Retrieved on 2007-07-29.
a b c d e f g h i j Statistics (HTML) (English). ITOPF . Retrieved on 2007-07-29.
Atlantic Empress/Aegean Captain (HTML) (English). Cedre (2006-04). Retrieved on 2007-07-29.
Oil Spills and Disasters (HTML) (English). infoplease . infoplease. Retrieved on 2007-07-29.
Metcalf & Eddy. Wastewater Engineering, Treatment and Reuse. 4th ed. New York: McGraw-Hill, 2003. 98.
a b http://response.restoration.noaa.gov/topic_subtopic_entry.php?RECORD_KEY(entry_subtopic_topic)=entry_id,subtopic_id,topic_id&entry_id(entry_subtopic_topic)=184&subtopic_id(entry_subtopic_topic)=8&topic_id(entry_subtopic_topic)=1
Detergent and Oil Spills (HTML) (English). NEWTON BBS (2002-10-12). Retrieved on 2007-07-29.