Oil spill

Deepwater Horizon oil spill on June 25, 2010.
A beach after an oil spill
Oil Slick from the Montara oil spill in the Timor Sea, September, 2009.

An oil spill is a release of a liquid petroleum hydrocarbon into the environment due to human activity, and is a form of pollution. The term often refers to marine oil spills, where oil is released into the ocean or coastal waters. Oil spills include 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, and heavier fuels used by large ships such as bunker fuel, or the spill of any oily refuse or waste oil. Spills may take months or even years to clean up.[1]

Oil also enters the marine environment from natural oil seeps.[2] Most human-made oil pollution comes from land-based activity, but public attention and regulation has tended to focus most sharply on seagoing oil tankers.

Contents

Environmental effects

Surf Scoter covered in oil as a result of the 2007 San Francisco Bay oil spill. Less than 1% of oil soaked birds survive, even after cleaning.[3]

The oil penetrates into the structure of the plumage of birds, reducing its insulating ability, thus making the birds more vulnerable to temperature fluctuations and much less buoyant in the water. It also impairs birds' flight abilities to forage and escape from predators. As they attempt to preen, birds typically ingest oil that covers their feathers, causing kidney damage, altered liver function, and digestive tract irritation. This and the limited foraging ability quickly causes dehydration and metabolic imbalances. Hormonal balance alteration including changes in luteinizing protein can also result in some birds exposed to petroleum.[4]

Most birds affected by an oil spill die unless there is human intervention.[5][6] Marine mammals exposed to oil spills are affected in similar ways as seabirds. Oil coats the fur of Sea otters and seals, reducing its insulation abilities and leading to body temperature fluctuations and hypothermia. Ingestion of the oil causes dehydration and impaired digestions. Because oil floats on top of water, less sunlight penetrates into the water, limiting the photosynthesis of marine plants and phytoplankton. This, as well as decreasing the fauna populations, affects the food chain in the ecosystem. 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.

Cleanup and recovery

Clean-up efforts after the Exxon Valdez oil spill.
A US Navy oil spill response team drills with a "Harbour Buster high-speed oil containment system".

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.[7]

Methods for cleaning up include:

Oil slicks on Lake Maracaibo.
Volunteers cleaning up the aftermath of the Prestige oil spill.

Equipment used includes:[11]

Prevention

Environmental Sensitivity Index (ESI) mapping

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.[18][19] 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.[20]

Shoreline type

Shoreline type is classified by rank depending on how easy the garet would be to cleanup, how long the oil would persist, and how sensitive the shoreline is.[21] 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.[20] 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.[22] 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 resources

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.[20][22] Issues 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.[23]

Human-use resources

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.[20][23] Some examples include airports, diving sites, popular beach sites, marinas, natural reserves or marine sanctuaries.

Estimating the volume of a spill

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.[24]

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 0.0000400 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.[25] 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.[26]

Largest oil spills

Oil spills of over 100,000 tons or 30 million US gallons, ordered by tons[a]
Spill / Tanker Location Date *Tons of crude oil Barrels US Gallons References
Kuwaiti oil fires [b]  Kuwait 01991-01-01January 1991 - 01991-11-01November 1991 &0000000136000000000000136,000,000-205,000,000 &00000010000000000000001,000,000,000-1,500,000,000 &000004200000000000000042,000,000,000-63,000,000,000 [27]
Kuwaiti oil lakes [c]  Kuwait 01991-01-01January 1991 - 01991-11-01November 1991 &00000000034090000000003,409,000-6,818,000 &000000002500000000000025,000,000-50,000,000 &00000010500000000000001,050,000,000-2,100,000,000 [28][29][30]
Lakeview Gusher  United States, Kern County, California 01910-05-141910-5-14 – September, 1911 &00000000012000000000001,200,000 &00000000090000000000009,000,000 &0000000378000000000000378,000,000 [31]
Gulf War oil spill [d]  Iraq, Persian Gulf and Kuwait 01991-01-191991-1-19 - 01991-01-281991-1-28 &0000000000818000000000818,000–1,091,000 &00000000060000000000006,000,000–8,000,000 &0000000252000000000000252,000,000–336,000,000 [32][33][34]
Deepwater Horizon  United States, Gulf of Mexico 02010-04-202010-4-2002010-07-152010-7-15 &0000000000560000000000560,000-585,000 &00000000041000000000004,100,000-4,300,000 &0000000172000000000000172,000,000-180,000,000 [35][36][37][38]
Ixtoc I  Mexico, Gulf of Mexico 01979-06-031979-6-3 – March 23, 1980 &0000000000454000000000454,000–480,000 &00000000033290000000003,329,000–3,520,000 &0000000139818000000000139,818,000–147,840,000 [39][40][41]
Atlantic Empress / Aegean Captain  Trinidad and Tobago 01979-07-191979-7-19 &0000000000287000000000287,000 &00000000021050000000002,105,000 &000000008839600000000088,396,000 [42][43][44]
Fergana Valley  Uzbekistan 01992-03-021992-3-2 &0000000000285000000000285,000 &00000000020900000000002,090,000 &000000008778000000000087,780,000 [45]
Nowruz Field Platform  Iran, Persian Gulf 01983-02-041983-2-4 &0000000000260000000000260,000 &00000000019070000000001,907,000 &000000008008000000000080,080,000 [46]
ABT Summer  Angola, 700 nmi (1,300 km; 810 mi) offshore 01991-05-281991-5-28 &0000000000260000000000260,000 &00000000019070000000001,907,000 &000000008008000000000080,080,000 [42]
Castillo de Bellver South Africa South Africa, Saldanha Bay 01983-08-061983-8-6 &0000000000252000000000252,000 &00000000018480000000001,848,000 &000000007761600000000077,616,000 [42]
Amoco Cadiz  France, Brittany 01978-03-161978-3-16 &0000000000223000000000223,000 &00000000016350000000001,635,000 &000000006868400000000068,684,000 [45][45][42][47][48]
MT Haven  Italy, Mediterranean Sea near Genoa 01991-04-111991-4-11 &0000000000144000000000144,000 &00000000010560000000001,056,000 &000000004435200000000044,352,000 [42]
Odyssey  Canada, 700 nmi (1,300 km; 810 mi) off Nova Scotia 01988-11-101988-11-10 &0000000000132000000000132,000 &0000000000968000000000968,000 &000000004065600000000040,656,000 [42]
Sea Star  Iran, Gulf of Oman 01972-12-191972-12-19 &0000000000115000000000115,000 &0000000000843000000000843,000 &000000003542000000000035,420,000 [45][42]
Irenes Serenade  Greece, Pylos 01980-02-231980-02-23 &0000000000100000000000100,000 &0000000000733000000000733,000 &000000003080000000000030,800,000 [42]
Urquiola  Spain, A Coruña 01976-05-121976-5-12 &0000000000100000000000100,000 &0000000000733000000000733,000 &000000003080000000000030,800,000 [42]
Torrey Canyon  United Kingdom, Isles of Scilly 01967-03-181967-3-18 &000000000008000000000080,000–119,000 &0000000000587000000000587,000–873,000 &000000002465400000000024,654,000–36,666,000 [45][42]
Greenpoint Oil Spill  United States, Brooklyn, New York City 01940 1940–1950s &000000000005500000000055,000– 97,000 &0000000000400000000000400,000–710,000 &000000001700000000000017,000,000–30,000,000 [49]

a One ton of crude oil is roughly equal to 308 US gallons or 7.33 barrels approx.; 1 oil barrel is equal to 35 imperial or 42 US gallons.
b Estimates for the amount of oil burned in the Kuwaiti oil fires range from 500,000,000 to nearly 2,000,000,000 barrels. 732 wells were set ablaze, while many others were severely damaged and gushed uncontrolled for several months. The fires alone were estimated to consume approximately 6,000,000 barrels of oil per day at their peak. However, it is difficult to find reliable sources for the total amount of oil burned. The range of 1 to 1.5 billion barrels given here represents frequently-cited figures, but better sources are needed.
c 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 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.[50]
d Estimates for the Gulf War oil spill range from 4,000,000 to 11,000,000 barrels. The figure of 6,000,000 to 8,000,000 barrels 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.[51] 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.

See also

References

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Further reading