Oil spill

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Help after an oil spill
Oil slick from the Montara oil spill in the Timor Sea, September 2009

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.

Spilt 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. 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]

Largest oil spills[edit]

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) 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 / TankerLocationDateTonnes of crude oil
(thousands)[a]
Barrels
(thousands)
US Gallons
(thousands)
References
Kuwaiti oil fires[dubious ] [b] KuwaitJanuary 16, 1991 - November 6, 1991136,0001,000,00042,000,000[3][4]
Kuwaiti oil lakes [c] KuwaitJanuary, 1991 - November, 19913,409-6,81825,000-50,0001,050,000-2,100,000[5][6][7]
Lakeview Gusher United States, Kern County, CaliforniaMarch 14, 1910September, 19111,2009,000378,000[8]
Gulf War oil spill [d] Kuwait, Iraq, and the Persian GulfJanuary 19, 1991 - January 28, 1991818–1,0916,000–8,000252,000–336,000[6][10][11]
Deepwater Horizon United States, Gulf of MexicoApril 20, 2010July 15, 2010560-5854,100-4,900172,000-180,800[12][13][14][15][16]
Ixtoc I Mexico, Gulf of MexicoJune 3, 1979March 23, 1980454–4803,329–3,520139,818–147,840[17][18][19]
Atlantic Empress / Aegean Captain Trinidad and TobagoJuly 19, 19792872,10588,396[20][21][22]
Fergana Valley UzbekistanMarch 2, 19922852,09087,780[23]
Nowruz Field Platform Iran, Persian GulfFebruary 4, 19832601,90780,080[24]
ABT Summer Angola, 700 nmi (1,300 km; 810 mi) offshoreMay 28, 19912601,90780,080[20]
Castillo de BellverUnion of South Africa South Africa, Saldanha BayAugust 6, 19832521,84877,616[20]
Amoco Cadiz France, BrittanyMarch 16, 19782231,63568,684[20][23][23][25][26]
  1. ^ One metric ton (tonne) of crude oil is roughly equal to 308 US gallons or 7.33 barrels approx.; 1 oil barrel (bbl) is equal to 35 imperial or 42 US gallons. Approximate conversion factors.[dead link]
  2. ^ 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.
  3. ^ 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.[5]
  4. ^ 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.[9] 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 impact[edit]

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;[27] 80,000 people in Coca, Ecuador,.[28] In 2000, springs were contaminated by an oil spill in Clark County, Kentucky.[29]

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 effects[edit]

A Surf Scoter covered in oil as a result of the 2007 San Francisco Bay oil spill.
A bird covered in oil from the Black Sea oil spill.

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.[30] The majority of birds affected by oil spills die from complications without human intervention.[31][32] Some studies have suggested that less than one percent of oil-soaked birds survive, even after cleaning,[33] although the survival rate can also exceed ninety percent, as in the case of the Treasure oil spill.[34]

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 occurrence[edit]

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.[35] 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.[36] On the other hand, only 5% of the actual spills came from oil tankers, while 51.8% came from other kinds of vessels.[36]

The International Tanker Owners Pollution Federation has tracked 9,351 accidental spills that have occurred since 1974.[37] According to this study, most spills result from routine operations such as loading cargo, discharging cargo, and taking on fuel oil.[20] 91% of the operational oil spills are small, resulting in less than 7 metric tons per spill.[20] 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.[20]

Cleanup and recovery[edit]

A U.S. Air Force Reserve plane sprays Corexit dispersant over the Deepwater Horizon oil spill in the Gulf of Mexico.
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.[1]

Methods for cleaning up include:[38]

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


Equipment used includes:[44]

Prevention[edit]

Spill response procedures should include elements such as;

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

[54]

Environmental Sensitivity Index (ESI) mapping[edit]

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.[55][56] 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.[57]

Shoreline type[edit]

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.[58] 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.[57] 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.[59] 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[edit]

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.[57][59] 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.[60]

Human-use resources[edit]

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.[57][60] Some examples include airports, diving sites, popular beach sites, marinas, natural reserves or marine sanctuaries.

Estimating the volume of a spill[edit]

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.[61]

Film thicknessQuantity spread
Appearanceinmmnmgal/sq miL/ha
Barely visible0.00000150.000038038250.370
Silvery sheen0.00000300.000076076500.730
First trace of color0.00000600.00015001501001.500
Bright bands of color0.00001200.00030003002002.900
Colors begin to dull0.000040.001000010006669.700
Colors are much darker0.00008000.00200002000133219.500

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.[62] 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.[63]

See also[edit]

References[edit]

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Further reading[edit]

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