Oil spill

An oil spill or oil slick is the unintentional release of liquid petroleum hydrocarbon into the environment as a result of human activity. 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.

Oil is also released into the environment from natural geologic seeps on the seafloor, as along the California coastline. 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.

The fate, behavior and environmental effects of spilled oil can vary, depending upon the type and amount of material spilled. In general, lighter refined petroleum products such as diesel and gasoline are more likely to mix in the water column and are more toxic to marine life, but tend to evaporate more quickly and do not persist long in the environment. Heavier crude or fuel oil, while of less immediate toxicity, can remain on the water surface or stranded on the shoreline for much longer. Oil from the Exxon Valdez and Gulf War oil spills, while weathering over time, has persisted along the shoreline for years after the spill. By contrast, the Braer spill off the Shetland Islands in 1993 and the Sea Empress spill off Milford Haven in 1996 left almost no long-term environmental damage, despite both being twice as large as Exxon Valdez.

With large numbers of people living and depending on coastal areas for fishing and tourism throughout the world, the consequences of oil spills can be serious. Such possibilities have caused outcries for oil companies, ship owners, and shipbuilders to share the responsibility of preventing such a disaster. As oil is lighter than water, and does not quickly decompose, it can remain on the surface for a long time. As it is also flammable, oil spills can fuel ocean fires.

Ships today are better equipped and built than ever before, with all new-build large tankers having double hulls. Ship-source pollution, which averaged over 400,000 tons a year at its peak in the late 1970s, averaged 27,000 tonnes per year from 2000-05, a fall of 93%[1].

Another way to mitigate the effects of an oil spill is through being able to contain and effectively treat spilled oil. A new vital step being developed in preventing oil damage is through installations of systems made for Fast Oil Recovery (FOR) of oil from wrecked ships.

1 Environmental effects
2 Largest oil spills
3 Calculating amount of oil spilled
4 Methods of cleaning an oil spill
5 References
6 See also
7 External links

[edit] Environmental effects

Volunteers cleaning up the aftermath of the Prestige oil spill

Studies of the Exxon Valdez oil spill have shown that the environmental damage caused by oil spills can be greater than was previously thought. It is now thought that the impacts to marine life can be evident at less than one part per billion petroleum hydrocarbons. The lighter fractions of petroleum, such as benzene and toluene, are more toxic, but are more volatile and evaporate quickly. Heavier components of crude oil, such as polynuclear aromatic hydrocarbons (PAHs) appear to cause the most damage; while they are less toxic, they persist in the environment much longer than volatile components. A heavy oil spill across the shore blankets rock-pools etc, preventing gas exchange and eliminating light as well as directly leaching toxins into the water; it can also become mixed deeply into pebble, shingle or sandy beaches, where it may remain for months or even years. Well-weathered heavy oil on intertidal rocks doesn't retain serious toxicity - for example, it will be grazed off by limpets without apparent ill-effect.

Seabirds are adversely affected as the oil penetrates and opens up the structure of their plumage, so they become chilled, lose the ability to fly, and lose their buoyancy in water. They are thus unable to feed normally, but ingest the oil as they attempt to preen. They will almost inevitably die unless rescued and professionally cleaned.

Oil spills cause the air pockets of sea otters to break so they can't keep warm, and cause lesions of some of their organs.

[edit] Largest oil spills

oiled birds

Main article: List of oil spills

**Oil Spills of over 100,000 tonnes or 30 million US gallons, ordered by Tonnes**
Spill / Tanker	Location	Date	*Tonnes of crude oil	link
Gulf War oil spill	Persian Gulf	1991 January 23	780,000 - 1,500,000	[2] [3]
Ixtoc I oil well	Gulf of Mexico	1979 June 3 - 1980 March 23	454,000 - 480,000	[4] [5]
Atlantic Empress / Aegean Captain	Trinidad and Tobago	1979 July 19	287,000	[6] [7]
Fergana Valley	Uzbekistan	1992 March 2	285,000	[8]
Nowruz oil field	Persian Gulf	1983 February	260,000	[9]
ABT Summer	700 nautical miles off Angola	1991	260,000	[10]
Castillo de Bellver	Saldanha Bay, South Africa	1983 August 6	252,000	[11]
Amoco Cadiz	Brittany, France	1978 March 16	223,000	[12] [13]
Amoco Haven tanker disaster	Mediterranean Sea near Genoa, Italy	1991	144,000	[14]
Odyssey	700 nautical miles off Nova Scotia, Canada	1988	132,000	[15]
Sea Star	Gulf of Oman	1972 December 19	115,000	[16] [17]
Torrey Canyon	Scilly Isles, UK	1967 March 18	80,000 - 119,000	[18] [19]
Irenes Serenade	Navarino Bay, Greece	1980	100,000	[20]
Urquiola	A Coruña, Spain	1976 May 12	100,000	[21]

*) One tonne of crude oil is roughly equal to 308 US gallons, or 7.33 barrels.

[edit] Calculating amount of oil spilled

The following empirical values are used to calculate amount of oil spilled if the area of the oil spill is known

The spill thickness is estimated by the color of the sheen.

Silvery sheen .0000315 gal/sq yd
First colors .0000630 gal/sq yd
Bright rainbow .000126 gal/sq yd
Dull colors .000378 gal/sq yd
Dark colors .001134 gal/sq yd

[edit] Methods of cleaning an oil spill

A sheen can not be cleaned up. Also it is very difficult to clean up oils denser than water as they settle to the bottom. PCBs are an example of such a pollutant.

Some of the equipment used in cleaning up include:

Absorbent Boom, Sausage
Pads, Diapers, Wipes
Skimmers
Containment Boom (except for Gasoline where confinement can cause dangerous levels of fume buildup)
Snare

Some of the methods used include:

Breaking down
Skimming: It can't be done if there is a rough sea.
Solidifying
Burning: It can be done only when it is not windy, the oil has not dispersed and there is a calm sea.
Dredging for oils denser than water.
Detergent This is never advised. It just makes the oil settle to the bottom and is not a clean up method.
Do nothing. Sometimes it is better to do nothing and let the oil evaporate or break down on its own than make matters worse by attempting to clean up.

[edit] References

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