Oil spill

From Open Encyclopedia

Image:PrestigeVolunteersInGaliciaCoast.jpg An oil spill is the intentional or unintentional release of oil (generally, petroleum) into the natural 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 or by-products, oily refuse, oil mixed in waste, or oily ballast. Oil is also released into the environment from natural geologic seeps on the seafloor, as along the California coastline.

The fate, behavior, and and environmental effects of spilled oil can vary depending upon 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 evaporate relatively 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 where stranded on the shoreline for much longer. Oil from the Exxon Valdez and Gulf War oil spills, while weathering over time, have persisted along the shoreline for years after the spill.

1 Behavior of spilled oil
2 Environmental effects
3 Largest oil spills
- 3.1 Other notable spills
4 See also
5 References
6 External links

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Behavior of spilled oil

Most types of oil float on the water surface, because they are less dense than water. These oils types tend to spread out and form slicks which are moved across the water surface by wind, waves, and currents. Depending upon the type of oil, some portion of oil in surface slicks will disperse naturally into the water column.

Oil spilled into the water often reaches the shore. Oil may strand at the high tide line, coating rocks, beaches or vegetation. On saturated sediments such as on mudflats, oil tends to remain on the mud surface if left undisturbed, and be lifted again on the next tide. Where animals have burrowed into the mud, oil may penetrate the surface through these openings. Oil that remains on the shoreline may "weather" physically and chemically, forming a hard asphalt-like substance. In sheltered areas, oil may remain for a long time.

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Environmental effects

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.

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