An oil spill is the release of a liquid petroleum hydrocarbon into the environment, especially marine areas, due to human activity, and is a form of pollution. The term is usually applied to marine oil spills, where oil is released into the ocean or coastal waters, but spills may also occur on land. Oil spills may be due to releases of crude oil from tankers, offshore platforms, drilling rigs and wells, as well as spills of refined petroleum products (such as gasoline, diesel) and their by-products, heavier fuels used by large ships such as bunker fuel, or the spill of any oily refuse or waste oil.

Oil spills penetrate into the structure of the plumage of birds and the fur of mammals, reducing its insulating ability, and making them more vulnerable to temperature fluctuations and much less buoyant in the water. Cleanup and recovery from an oil spill is difficult and depends upon many factors, including the type of oil spilled, the temperature of the water (affecting evaporation and biodegradation), and the types of shorelines and beaches involved.[1] Spills may take weeks, months or even years to clean up.[2]

Oil spills can have disastrous consequences for society; both economically, environmentally, and socially. As a result of these consequences oil spill accidents can initiate intense media attention and political uproar. Multiple kinds of actors in society can become involved in a political struggle on how government should respond to oil spills and what actions prevent them from happening.[3] Despite substantial national and international policy improvements on preventing oil spills adopted in recent decades, large oil spills keep occurring.

Largest oil spillsEdit

Main article: List of oil spills

Crude oil and refined fuel spills from tanker ship accidents have damaged natural ecosystems in Alaska, the Gulf of Mexico, the Galapagos Islands, France and many other places. The quantity of oil spilled during accidents has ranged from a few hundred tons to several hundred thousand tons (e.g., Deepwater Horizon Oil Spill, Atlantic Empress, Amoco Cadiz)[4] but is a limited barometer of damage or impact. Smaller spills have already proven to have a great impact on ecosystems, such as the Exxon Valdez oil spill because of the remoteness of the site or the difficulty of an emergency environmental response.

Oil spills at sea are generally much more damaging than those on land, since they can spread for hundreds of nautical miles in a thin oil slick which can cover beaches with a thin coating of oil. This can kill sea birds, mammals, shellfish and other organisms it coats. Oil spills on land are more readily containable if a makeshift earth dam can be rapidly bulldozed around the spill site before most of the oil escapes, and land animals can avoid the oil more easily.

Largest oil spills.
Spill / Tanker Location Date Tonnes of crude oil
(thousands)[lower-alpha 1]
US Gallons
Kuwaiti oil firesScript error [lower-alpha 1] Template:KWT Error in Template:Dts: 'January 16, 1991' is an invalid date - Error in Template:Dts: 'November 6, 1991' is an invalid date 136,000 1,000,000 42,000,000 [1][2]
Kuwaiti oil lakes [lower-alpha 2] Template:KWT Error in Template:Dts: 'January, 1991' is an invalid date - Error in Template:Dts: 'November, 1991' is an invalid date 3,409-6,818 25,000-50,000 1,050,000-2,100,000 [3][4][5]
Lakeview Gusher
, Kern County, California
Error in Template:Dts: 'March 14, 1910' is an invalid dateError in Template:Dts: 'September, 1911' is an invalid date 1,200 9,000 378,000 [6]
Gulf War oil spill [lower-alpha 3] Template:KWT, Iraq, and the Persian Gulf Error in Template:Dts: 'January 19, 1991' is an invalid date - Error in Template:Dts: 'January 28, 1991' is an invalid date 818–1,091 6,000–8,000 252,000–336,000 [4][8][9]
Deepwater Horizon
, Gulf of Mexico
Error in Template:Dts: 'April 20, 2010' is an invalid dateError in Template:Dts: 'July 15, 2010' is an invalid date 560-585 4,100-4,900 172,000-180,800 [10][11][12][13][14]
Ixtoc I Template:MEX, Gulf of Mexico Error in Template:Dts: 'June 3, 1979' is an invalid dateError in Template:Dts: 'March 23, 1980' is an invalid date 454–480 3,329–3,520 139,818–147,840 [15][16][17]
Atlantic Empress / Aegean Captain Template:TTO Error in Template:Dts: 'July 19, 1979' is an invalid date 287 2,105 88,396 [18][19][20]
Fergana Valley Template:UZB Error in Template:Dts: 'March 2, 1992' is an invalid date 285 2,090 87,780 [21]
Nowruz Field Platform Template:IRN, Persian Gulf Error in Template:Dts: 'February 4, 1983' is an invalid date 260 1,907 80,080 [22]
ABT Summer Template:AGO, 700 nmi (1,300 km; 810 mi) offshore Error in Template:Dts: 'May 28, 1991' is an invalid date 260 1,907 80,080 [18]
Castillo de Bellver Template:Country data Union of South Africa South Africa, Saldanha Bay Error in Template:Dts: 'August 6, 1983' is an invalid date 252 1,848 77,616 [18]
Amoco Cadiz Template:FRA, Brittany Error in Template:Dts: 'March 16, 1978' is an invalid date 223 1,635 68,684 [18][21][21][23][24]
  1. Estimates for the amount of oil burned in the Kuwaiti oil fires range from 500,000,000 barrels (79,000,000 m3) to nearly 2,000,000,000 barrels (320,000,000 m3). Between 605 and 732 wells were set ablaze, while many others were severely damaged and gushed uncontrolled for several months. It took over ten months to bring all of the wells under control. The fires alone were estimated to consume approximately 6,000,000 barrels (950,000 m3) of oil per day at their peak.
  2. Oil spilled from sabotaged fields in Kuwait during the 1991 Persian Gulf War pooled in approximately 300 oil lakes, estimated by the Kuwaiti Oil Minister to contain approximately 25,000,000 to 50,000,000 barrels (7,900,000 m3) of oil. According to the U.S. Geological Survey, this figure does not include the amount of oil absorbed by the ground, forming a layer of "tarcrete" over approximately five percent of the surface of Kuwait, fifty times the area occupied by the oil lakes.[3]
  3. Estimates for the Gulf War oil spill range from 4,000,000 to 11,000,000 barrels (1,700,000 m3). The figure of 6,000,000 to 8,000,000 barrels (1,300,000 m3) is the range adopted by the U.S. Environmental Protection Agency and the United Nations in the immediate aftermath of the war, 1991–1993, and is still current, as cited by NOAA and The New York Times in 2010.[7] This amount only includes oil discharged directly into the Persian Gulf by the retreating Iraqi forces from January 19 to 28, 1991. However, according to the U.N. report, oil from other sources not included in the official estimates continued to pour into the Persian Gulf through June, 1991. The amount of this oil was estimated to be at least several hundred thousand barrels, and may have factored into the estimates above 8,000,000 barrels (1,300,000 m3).

Human impactEdit

An oil spill represents an immediate fire hazard. The Kuwaiti oil fires produced air pollution that caused respiratory distress. The Deepwater Horizon explosion killed eleven oil rig workers. The fire resulting from the Lac-Mégantic derailment killed 47 and destroyed half of the town's centre.

Spilled oil can also contaminate drinking water supplies. For example, in 2013 two different oil spills contaminated water supplies for 300,000 in Miri, Malaysia;[25] 80,000 people in Coca, Ecuador,.[26] In 2000, springs were contaminated by an oil spill in Clark County, Kentucky.[27]

Contamination can have an economic impact on tourism and marine resource extraction industries. For example, the Deepwater Horizon oil spill impacted beach tourism and fishing along the Gulf Coast, and the responsible parties were required to compensate economic victims.

Environmental effectsEdit

File:Oiled bird 3.jpg
File:Oiled Bird - Black Sea Oil Spill 111207.jpg

Oil penetrates into the structure of the plumage of birds and the fur of mammals, reducing its insulating ability, and making them more vulnerable to temperature fluctuations and much less buoyant in the water.

Animals who rely on scent to find their babies or mothers cannot due to the strong scent of the oil. This causes a baby to be rejected and abandoned, leaving the babies to starve and eventually die. Oil can impair a bird's ability to fly, preventing it from foraging or escaping from predators. As they preen, birds may ingest the oil coating their feathers, irritating the digestive tract, altering liver function, and causing kidney damage. Together with their diminished foraging capacity, this can rapidly result in dehydration and metabolic imbalance. Some birds exposed to petroleum also experience changes in their hormonal balance, including changes in their luteinizing protein.[28] The majority of birds affected by oil spills die from complications without human intervention.[29][30] Some studies have suggested that less than one percent of oil-soaked birds survive, even after cleaning,[31] although the survival rate can also exceed ninety percent, as in the case of the Treasure oil spill.[32]

Heavily furred marine mammals exposed to oil spills are affected in similar ways. Oil coats the fur of sea otters and seals, reducing its insulating effect, and leading to fluctuations in body temperature and hypothermia. Oil can also blind an animal, leaving it defenseless. The ingestion of oil causes dehydration and impairs the digestive process. Animals can be poisoned, and may die from oil entering the lungs or liver.

There are three kinds of oil-consuming bacteria. Sulfate-reducing bacteria (SRB) and acid-producing bacteria are anaerobic, while general aerobic bacteria (GAB) are aerobic. These bacteria occur naturally and will act to remove oil from an ecosystem, and their biomass will tend to replace other populations in the food chain.

Sources and rate of occurrenceEdit

A VLCC tanker can carry 2 million barrels (320,000 m3) of crude oil. This is about eight times the amount spilled in the widely known Exxon Valdez incident. In this spill, the ship ran aground and dumped 10,800,000 US gallons (41,000 m3) of oil into the ocean in March 1989. Despite efforts of scientists, managers, and volunteers over 400,000 seabirds, about 1,000 sea otters, and immense numbers of fish were killed.[33] Considering the volume of oil carried by sea, however, tanker owners' organisations often argue that the industry's safety record is excellent, with only a tiny fraction of a percentage of oil cargoes carried ever being spilled. The International Association of Independent Tanker Owners has observed that "accidental oil spills this decade have been at record low levels—one third of the previous decade and one tenth of the 1970s—at a time when oil transported has more than doubled since the mid 1980s."

Oil tankers are only one source of oil spills. According to the United States Coast Guard, 35.7% of the volume of oil spilled in the United States from 1991 to 2004 came from tank vessels (ships/barges), 27.6% from facilities and other non-vessels, 19.9% from non-tank vessels, and 9.3% from pipelines; 7.4% from mystery spills.[34] On the other hand, only 5% of the actual spills came from oil tankers, while 51.8% came from other kinds of vessels.[34]

The International Tanker Owners Pollution Federation has tracked 9,351 accidental spills that have occurred since 1974.[35] According to this study, most spills result from routine operations such as loading cargo, discharging cargo, and taking on fuel oil.[18] 91% of the operational oil spills are small, resulting in less than 7 metric tons per spill.[18] On the other hand, spills resulting from accidents like collisions, groundings, hull failures, and explosions are much larger, with 84% of these involving losses of over 700 metric tons.[18]

Cleanup and recoveryEdit

File:C-130 support oil spill cleanup.jpg
File:Exxon Valdez Cleanup.jpg
File:Harbour Buster high-speed oil containment system.jpg

Cleanup and recovery from an oil spill is difficult and depends upon many factors, including the type of oil spilled, the temperature of the water (affecting evaporation and biodegradation), and the types of shorelines and beaches involved.[36]

Methods for cleaning up include:[37]

  • Bioremediation: use of microorganisms[38] or biological agents[39] to break down or remove oil; such as the bacteria Alcanivorax[40] or Methylocella Silvestris.[41]
  • Bioremediation Accelerator: Oleophilic, hydrophobic chemical, containing no bacteria, which chemically and physically bonds to both soluble and insoluble hydrocarbons. The bioremediation accelerator acts as a herding agent in water and on the surface, floating molecules to the surface of the water, including solubles such as phenols and BTEX, forming gel-like agglomerations. Undetectable levels of hydrocarbons can be obtained in produced water and manageable water columns. By overspraying sheen with bioremediation accelerator, sheen is eliminated within minutes. Whether applied on land or on water, the nutrient-rich emulsion creates a bloom of local, indigenous, pre-existing, hydrocarbon-consuming bacteria. Those specific bacteria break down the hydrocarbons into water and CO2, with EPA tests showing 98% of alkanes biodegraded in 28 days; and aromatics being biodegraded 200 times faster than in nature they also sometimes use the hydrofireboom to clean the oil up by taking it away from most of the oil and burning it.[42]
  • Controlled burning can effectively reduce the amount of oil in water, if done properly.[43] But it can only be done in low wind,Script error and can cause air pollution.[1]
File:Close-up of Lake Maracaibo, Venezuela.jpg
  • Dispersants can be used to dissipate oil slicks.[2] A dispersant is either a non-surface active polymer or a surface-active substance added to a suspension, usually a colloid, to improve the separation of particles and to prevent settling or clumping. They may rapidly disperse large amounts of certain oil types from the sea surface by transferring it into the water column. They will cause the oil slick to break up and form water-soluble micelles that are rapidly diluted. The oil is then effectively spread throughout a larger volume of water than the surface from where the oil was dispersed. They can also delay the formation of persistent oil-in-water emulsions. However, laboratory experiments showed that dispersants increased toxic hydrocarbon levels in fish by a factor of up to 100 and may kill fish eggs.[3] Dispersed oil droplets infiltrate into deeper water and can lethally contaminate coral. Research indicates that some dispersants are toxic to corals.[4] A 2012 study found that Corexit dispersant had increased the toxicity of oil by up to 52 times.[5]
  • Watch and wait: in some cases, natural attenuation of oil may be most appropriate, due to the invasive nature of facilitated methods of remediation, particularly in ecologically sensitive areas such as wetlands.[6]
  • Dredging: for oils dispersed with detergents and other oils denser than water.
  • Skimming: Requires calm waters at all times during the process.
  • Solidifying: Solidifiers are composed of dry hydrophobic polymers that both adsorb and absorb. They clean up oil spills by changing the physical state of spilled oil from liquid to a semi-solid or a rubber-like material that floats on water. Solidifiers are insoluble in water, therefore the removal of the solidified oil is easy and the oil will not leach out. Solidifiers have been proven to be relatively non-toxic to aquatic and wild life and have been proven to suppress harmful vapors commonly associated with hydrocarbons such as Benzene, Xylene, Methyl Ethyl, Acetone and Naphtha. The reaction time for solidification of oil is controlled by the surf area or size of the polymer as well as the viscosity of the oil. Some solidifier product manufactures claim the solidified oil can be disposed of in landfills, recycled as an additive in asphalt or rubber products, or burned as a low ash fuel. A solidifier called C.I.Agent (manufactured by C.I.Agent Solutions of Louisville, Kentucky) is being used by BP in granular form, as well as in Marine and Sheen Booms at Dauphin Island and Fort Morgan, Alabama, to aid in the Deepwater Horizon oil spill cleanup.
  • Vacuum and centrifuge: oil can be sucked up along with the water, and then a centrifuge can be used to separate the oil from the water - allowing a tanker to be filled with near pure oil. Usually, the water is returned to the sea, making the process more efficient, but allowing small amounts of oil to go back as well. This issue has hampered the use of centrifuges due to a United States regulation limiting the amount of oil in water returned to the sea.[7]
  • Beach Raking: coagulated oil that is left on the beach can be picked up by SURF RAKE beach cleaning machines by H. Barber and Sons.[8]
File:Valdez Trash Pile.jpg

Equipment used includes:[9]

  • Booms: large floating barriers that round up oil and lift the oil off the water
  • Skimmers: skim the oil
  • Sorbents: large absorbents 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 equipment: typically used to clean up oil on beaches

Prevention Edit

  • Secondary containment - methods to prevent releases of oil or hydrocarbons into environment.
  • Oil Spill Prevention Containment and Countermeasures (SPCC) program by the United States Environmental Protection Agency.
  • Double-hulling - build double hulls into vessels, which reduces the risk and severity of a spill in case of a collision or grounding. Existing single-hull vessels can also be rebuilt to have a double hull.
  • Thick-hulled railroad transport tanks[10]

Spill response procedures should include elements such as;

  • A listing of appropriate protective clothing, safety equipment, and cleanup materials required

for spill cleanup (gloves, respirators, etc.) and an explanation of their proper use;

  • Appropriate evacuation zones and procedures;
  • Availability of fire suppression equipment;
  • Disposal containers for spill cleanup materials; and
  • The first aid procedures that might be required.


Environmental Sensitivity Index (ESI) mappingEdit

Environmental Sensitivity Index (ESI) maps are used to identify sensitive shoreline resources prior to an oil spill event in order to set priorities for protection and plan cleanup strategies.[12][13] By planning spill response ahead of time, the impact on the environment can be minimized or prevented. Environmental sensitivity index maps are basically made up of information within the following three categories: shoreline type, and biological and human-use resources.[14]

Shoreline typeEdit

Shoreline type is classified by rank depending on how easy the garet would be to clean up, how long the oil would persist, and how sensitive the shoreline is.[15] The floating oil slicks put the shoreline at particular risk when they eventually come ashore, covering the substrate with oil. The differing substrates between shoreline types vary in their response to oiling, and influence the type of cleanup that will be required to effectively decontaminate the shoreline. In 1995, the US National Oceanic and Atmospheric Administration extended ESI maps to lakes, rivers, and estuary shoreline types.[14] The exposure the shoreline has to wave energy and tides, substrate type, and slope of the shoreline are also taken into account—in addition to biological productivity and sensitivity. The productivity of the shoreline habitat is also taken into account when determining ESI ranking.[16] Mangroves and marshes tend to have higher ESI rankings due to the potentially long-lasting and damaging effects of both the oil contamination and cleanup actions. Impermeable and exposed surfaces with high wave action are ranked lower due to the reflecting waves keeping oil from coming onshore, and the speed at which natural processes will remove the oil.

Biological resourcesEdit

Habitats of plants and animals that may be at risk from oil spills are referred to as "elements" and are divided by functional group. Further classification divides each element into species groups with similar life histories and behaviors relative to their vulnerability to oil spills. There are eight element groups: Birds, Reptiles, Amphibians, Fish, Invertebrates, Habitats and Plants, Wetlands, and Marine Mammals and Terrestrial Mammals. Element groups are further divided into sub-groups, for example, the ‘marine mammals’ element group is divided into dolphins, manatees, pinnipeds (seals, sea lions & walruses), polar bears, sea otters and whales.[14][16] Problems taken into consideration when ranking biological resources include the observance of a large number of individuals in a small area, whether special life stages occur ashore (nesting or molting), and whether there are species present that are threatened, endangered or rare.[17]

Human-use resourcesEdit

Human use resources are divided into four major classifications; archaeological importance or cultural resource site, high-use recreational areas or shoreline access points, important protected management areas, or resource origins.[14][17] Some examples include airports, diving sites, popular beach sites, marinas, natural reserves or marine sanctuaries.

Estimating the volume of a spillEdit

By observing the thickness of the film of oil and its appearance on the surface of the water, it is possible to estimate the quantity of oil spilled. If the surface area of the spill is also known, the total volume of the oil can be calculated.[18]

Film thickness Quantity spread
Appearance in mm nm gal/sq mi L/ha
Barely visible 0.0000015 0.0000380 38 25 0.370
Silvery sheen 0.0000030 0.0000760 76 50 0.730
First trace of color 0.0000060 0.0001500 150 100 1.500
Bright bands of color 0.0000120 0.0003000 300 200 2.900
Colors begin to dull 0.00004 0.0010000 1000 666 9.700
Colors are much darker 0.0000800 0.0020000 2000 1332 19.500

Oil spill model systems are used by industry and government to assist in planning and emergency decision making. Of critical importance for the skill of the oil spill model prediction is the adequate description of the wind and current fields. There is a worldwide oil spill modelling (WOSM) program.[19] Tracking the scope of an oil spill may also involve verifying that hydrocarbons collected during an ongoing spill are derived from the active spill or some other source. This can involve sophisticated analytical chemistry focused on finger printing an oil source based on the complex mixture of substances present. Largely, these will be various hydrocarbons, among the most useful being polyaromatic hydrocarbons. In addition, both oxygen and nitrogen heterocyclic hydrocarbons, such as parent and alkyl homologues of carbazole, quinoline, and pyridine, are present in many crude oils. As a result, these compounds have great potential to supplement the existing suite of hydrocarbons targets to fine-tune source tracking of petroleum spills. Such analysis can also be used to follow weathering and degradation of crude spills.[20]

See alsoEdit


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  4. Barry, Carolyn (2007). Slick Death: Oil-spill treatment kills coral, Science News vol. 172, p. 67.
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  6. Pezeshki, S. R., Hester, M. W., Lin, Q. & Nyman, J. A. (2000). The effects of oil spill clean-up on dominant US Gulf coast marsh macrophytes: a review. Environmental Pollution. 108: 129-139.
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  14. 14.0 14.1 14.2 14.3 NOAA (2002). Environmental Sensitivity Index Guidelines, version 3.0. NOAA Technical Memorandum NOS OR&R 11. Seattle: Hazardous Response and Assessment Division, National Oceanic and Atmospheric Administration, 129p.
  15. Gundlach, E.R. and M.O. Hayes (1978). Vulnerability of Coastal Environments to Oil Spill Impacts. Marine Technology Society. 12 (4): 18-27.
  16. 16.0 16.1 NOAA (2008). Introduction to Environmental Sensitivity Index maps. NOAA Technical Manual. Seattle: Hazardous Response and Assessment Division, National Oceanic and Atmospheric Administration, 56p.
  17. 17.0 17.1 IMO/IPIECA (1994). Sensitivity Mapping for Oil Spill Response. International Maritime Organization/ International Petroleum Industry Environmental Conservation Association Report Series, Volume 1. 22p.
  18. Metcalf & Eddy. Wastewater Engineering, Treatment and Reuse. 4th ed. New York: McGraw-Hill, 2003. 98.
  19. Anderson, E.L., E. Howlett, K. Jayko, V. Kolluru, M. Reed, and M. Spaulding. 1993. The worldwide oil spill model (WOSM): an overview. Pp. 627–646 in Proceedings of the 16th Arctic and Marine Oil Spill Program, Technical Seminar. Ottawa, Ontario: Environment Canada.
  20. Wang, Z., M. Fingas, and D.S. Page. 1999. Oil spill identification. Journal of Chromatography A. 843: 369-411. doi:10.1016/S0021-9673(99)00120-X.

Further readingEdit

16x16px Media related to Oil spills at Wikimedia Commons

  • The World Almanac and Book of Facts, 2004
  • Oil Spill Case Histories 1967-1991, NOAA/Hazardous Materials and Response Division, Seattle WA, 1992
  • Nelson-Smith, Oil Pollution and Marine Ecology, Elek Scientific, London, 1972; Plenum, New York, 1973
  • Oilspill Data set

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