When oil spills from a tanker, its behavior and impact can depend on several factors: proximity of the spill to shore, tides, currents, weather, and fuel type. If a spill occurs in the open ocean, little can be done to contain and remove the spilled oil. What doesn't evaporate on its own will generally coalesce and sink to the seafloor, where it will remain in the sediment for years, or form tar balls that will float with the currents for many years.

In near-shore environments, spilled oil is carried in and out with the tides and moved laterally along a coastline by currents. In the short term, many organisms die from direct or indirect exposure to the oil. Over the long term, oil spills can greatly impact shorelines, plant and animal life, the marine ecosystem, and the local economy. In Alaska's Prince William Sound, the site of the 1989 Exxon Valdez tanker accident, most of the spilled oil has either evaporated, decomposed, or settled into the coastline. However, pockets of pollution persist.

Oil contaminates shorelines and other sensitive coastal areas, leaving a coating that can suffocate animals and plants on contact or destroy their natural oils, making them susceptible to disease and hypothermia. Deciding whether or not to clean up a coastline is a complex matter, as intensive cleanup activities can damage coastal ecosystems. After human efforts have been exhausted, natural processes—in particular evaporation and the cleansing action of waves breaking on shore—disperse what remains, but nature does not make it disappear rapidly.

Conventional wisdom held that residual oil wasn't particularly harmful to animals that inhabit spill zones because most of the volatile compounds such as benzene and ethylene had evaporated. But the non-volatile hydrocarbons that remain are known to be toxic to fish at levels as low as one part per billion. While salmon harvests are back to pre-spill levels, herring continue to exhibit signs of disease that may or may not be related to residual oil. Moreover, sedentary animals, such as filter-feeding oysters, mussels, and clams, are likely to accumulate oil components in their tissues. While these components may not be dangerous to the animals' own health, a strong odor may make them unsuitable for human consumption. Even more worrying is that organisms that accumulate toxins may pass them through the food chain.

Both the subsistence and commercial fishing lifestyles of the Alutiiq that inhabit Chenega Bay in Prince William Sound have been adversely affected by the Exxon Valdez spill. Salmon, shellfish, and certain marine mammals remain important components of the Alutiiq subsistence diet. The concentration of pollutants in these food species jeopardizes the healthfulness of the Alaska Native diet.

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