The sun, wave action and weather all contribute to the breakdown of oil in water. Eventually, the oil will evaporate. Because of this, experts leave some oil spills alone. If the slick doesn't threaten wildlife, business or civilization, cleanup agencies may choose to let the natural processes handle it. Oil always floats in salt water, and most of the time in fresh water. In fresh water, though, the heaviest crude oil may sink. Often, as it breaks down, oil will mix with water -- along with particulate matter like sand -- and become tar balls. These balls tend to harden on the outside and stay soft in the middle. Since they are separate and scattered, tar balls and other degraded forms of oil in the sea don't pose the same kind of environmental threat as concentrated oil slicks do.
Often, oil spills in tropical areas are handled with dispersants -- chemicals which break down oil much more quickly than the elements can alone. Dispersants break the oil slick apart, allowing oil droplets to mix with water and be absorbed into the aquatic system more quickly. These chemicals pose their own danger, however. This broken-down oil can be absorbed by marine life and into the food chain. A 2007 Israeli study also reported that the combination of dispersants and broken-down oil are actually more toxic to tropical coral reefs than raw crude oil [source: Science Daily].
When a slick threatens to infiltrate coastal areas -- or worse, an oil spill occurs near a coastal area, as when a tanker runs aground or a refinery leaks -- the situation becomes even more dire. Cleaning the spill becomes trickier as well, and methods to deal with the oil must also be more delicate.
One method for dealing with oil spills that have reached shore is to employ biological agents. Fertilizers like phosphorus and nitrogen are spread over the oil-slicked shoreline to foster the growth of microorganisms, which break down the oil into natural components like fatty acids and carbon dioxide. Other forms of biological agents can also be used in marine -- or open sea -- spills.
But spills on the shore are most likely to affect wildlife habitats.
The severity of the spill and its proximity to wildlife habitats have an effect on the numbers of aquatic wildlife hurt or killed. Waterfowl and other animals like seals and otters can become covered in oil, which breaks down the water-resistant properties of the birds' feathers, as well as the insulation provided by sea mammals' fur. Animals can be poisoned by the oil they ingest while licking themselves clean [source: NOAA].
Oil cleanup agencies use floating dummies and balloons to scare wildlife away from spill areas, but it doesn't prevent animals from being affected. Experts have techniques to help minimize the mortality rate among animals that become polluted by oil, but rescuing birds and sea mammals like walruses and otters present challenges. One thing is encouraging: Since the Exxon Valdez ran aground, the experts are having to clean up spills less often. The U.S. Coast Guard reports that by 2004 there was a 58 percent decrease in oil spills in American waters from 1989.
No matter how successful and extensive the recovery effort, oil spills leave an indelible mark on the environment they impact. In 2007, 18 years after the Exxon Valdez spill, areas along Prince William Sound are still polluted from oil that has yet to completely biodegrade [source: Science Daily].
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