An oil spill is the 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. The oil may be a variety of 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 may take months or even years to clean up. Oil also enters the marine environment from natural oil seeps. 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.
* 1 Environmental effects
* 2 Cleanup and recovery
o 2.1 Prevention
* 3 Environmental Sensitivity Index (ESI) mapping
o 3.1 Shoreline type
o 3.2 Biological resources
o 3.3 Human-use resources
* 4 Estimating the volume of a spill
* 5 Largest oil spills
* 6 Gallery
* 7 See also
* 8 References
* 9 Further reading
* 10 External links
Surf Scoter covered in oil as a result of the 2007 San Francisco Bay oil spill.
The oil penetrates up the structure of the plumage of birds, reducing its insulating ability, and so 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. Most birds affected by an oil spill die unless there is human intervention. 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.
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”.
A sheen is usually dispersed (but not cleaned up) with detergents which makes oil settle to the bottom. Oils that are denser than water, such as Polychlorinated biphenyls (PCBs), can be more difficult to clean as they make the seabed toxic.
Recovering the oil is difficult and depends upon many factors, including the type of oil spilled, the temperature of the water (in warmer waters, some oil may evaporate), and the types of shorelines and beaches involved. Methods for cleaning up include:
* Bioremediation: use of microorganisms or biological agents to break down or remove oil.
* Bioremediation Accelerator: Oleophilic, hydrophobic chemical, containing no bacteria, which chemically and physically bonds to both soluble and insoluble hydrocarbons. The bioremedation 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 carbon dioxide, 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..
* Controlled burning can effectively reduce the amount of oil in water, if done properly. But it can only be done in low wind, and can cause air pollution.
Oil slicks on Lake Maracaibo.
Volunteers cleaning up the aftermath of the Prestige oil spill.
* Dispersants act as detergents, clustering around oil globules and allowing them to be carried away in the water. This improves the surface aesthetically, and mobilizes the oil. Smaller oil droplets, scattered by currents, may cause less harm and may degrade more easily. But the dispersed oil droplets infiltrate into deeper water and can lethally contaminate coral. Recent research indicates that some dispersants are toxic to corals.
* 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. 
* Dredging: for oils dispersed with detergents and other oils denser than water.
* Skimming: Requires calm waters
* Solidifying.
Equipment used includes:
* 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 equipments: typically used to clean up oil on beaches
* 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.
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. 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.
Shoreline type is classified by rank depending on how easy the oil would be to cleanup, how long the oil would persist, and how sensitive the shoreline is. 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. 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. 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.
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 and 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. 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.
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. Some examples include airports, diving sites, popular beach sites, marinas, natural reserves or marine sanctuaries.
Estimating the volume of a spill
Bottsand class oil recovery ship of the German Navy.
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.
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.
Largest oil spills
Main article: List of oil spills
Note: the extent of the Deepwater Horizon oil spill has not been well determined as of this writing.
Oil spills of over 100,000 tonnes or 30 million US gallons, ordered by tonnes[a] Spill / Tanker? Location?
a One tonne of crude oil is roughly equal to 308 US gallons or 7.33 barrels approx.; 1 oil barrel is equal to 42 US gallons.