About once every decade there is a major oil spill somewhere in the world – the Exxon Valdez in 1989, the Prestige in 2002, and the Deepwater Horizon in 2010 all come to mind. These spills can do tremendous damage to the ecosystem in the area of the spill and can expand over vast regions to affect coastlines and indigenous wildlife hundreds of miles away.
That’s why clean-up is so important. There are three major methods for clean-up, containment and skimming, using dispersants or adding biological agents to speed up the oil breakdown.
“Harbour Buster” high-speed oil containment system (U.S. Navy photo by Mr. Paul Farley)[/caption]The most common oil spill cleanup methods involve trying to contain the spill with floating booms that prevent the spill from getting out of control. These are only possible if the spill is accessible within a few hours of happening, otherwise the area of the spill gets too large to contain with even the largest floating stoppers.
Floats are equipped with skirts that hang down beneath them so oil does not get pushed under the booms by the ocean waves. Unfortunately, if the seas are high or the winds are strong, booms and floats become ineffective.
Once the floats are in place, boats can use skimmers or oil scoops to remove the contaminant for the surface of the water. In addition to boats and skimmers, larger oil slicks may require the use of sorbents. These are large sponges that have been specially designed to pull oil from the water surface.
If the spill happens out at sea, in situ burning might be an option. This is where the oil slick is lit on fire and burned off the surface of the water. Because ocean going freighters usually carry crude oil, the burn creates a highly toxic smoke. This is why oil spills near the coastline are not burned away.
C-130 Hercules dropping an oil-dispersant into the Golf of Mexico following the Deepwater Horizon disaster.[/caption]When the oil spill cannot be contained, the only options available require speeding up the natural breakdown of oil components. The first method for doing this is adding dispersal agents. These are chemicals that allow the oil to chemically bond with water. This prevents the slick from traveling over the water and increases the surface area of each oil molecule.
One of the major problems with dispersants is the creation of tar balls. As the oil combines with water, it also congeals around sand and other particles in the water. This results in large tar balls floating at the surface of the water. They can be scooped up by skimmers, but often eventually find their way back to shore. This was one of the major problems with the cleanup of the Deepwater Horizon.
Dispersants are clearly not the best choice available from an environmental perspective. They introduce oil compounds into the natural environment where they can be absorbed by the aquatic life in the area and enter the food chain. Oil treated with dispersants has been found to be more harmful to coral reefs and sea grass than the crude oil itself. In addition, the chemicals themselves are extremely dangerous to work with.
When money is not an option, the best way how to clean oil spills is with biological agents that break down the oil into fatty acids and carbon dioxide. This process is usually reserved for areas where oil has reached shore, but it has recently been used in river systems in test cases. Phosphorus and nitrogen based fertilizers are dropped into the area to promote the growth of microorganisms that break down the sand bound oil.
The biggest factor in how to clean up an oil spill is where it has happened. Some oil spills, if they happen far out to sea, are left to naturally decompose in the environment. As they get closer to shore we begin to treat them.
The treatments follow this general rule:
- • Outside of 200 nautical miles, no treatment is used.
- • Between 200 nautical miles and shore, booms may be use.
- • Outside of 10 nautical miles from shore, dispersants are used.
- • Biological agents are used on shorelines that have been affected.
These are general rules and can be changed based on the type of oil that has been spilled, the weather conditions near the spill and prevailing ocean currents. No two spills are the same, so each one is evaluated on its own merit.
Thankfully, due to ever increasing safety measures, oil spill frequency has steadily declined since the early 1990s. In fact, there hasn’t been a major tanker related spill since the 2002 Prestige spill off the coast of Spain.
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