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article imageEffects of dispersants in the Gulf of Mexico oil spill

By Bart B. Van Bockstaele     May 13, 2010 in Environment
Dispersants are part of the arsenal used in the battle against the oil spill in the Gulf of Mexico. No one knows what the effect will be on the environment, but there are some clues.
When the Deepwater Horizon oil rig exploded and sank in April, a small oil leak began. That oil leak has been growing and because it does not stop, it may turn out into an environmental disaster without equal.
According to the scientific journal Nature, several weapons are being used in the battle against the oil, mechanical as well as chemical.
Attempts to stop the oil from spilling by capping the well have been unsuccessful so far, but efforts are ongoing and will have to be successful eventually since the alternative is too hideous to contemplate: waiting until the spill stops on its own. Eight hundred thousand litres of oil (5,000 barrels) are spilling out every day at the moment.
In order to protect the coastline beaches and wetlands, floating booms are used to physically prevent the oil floating on the sea from reaching them. This is at best a temporary measure, for choppy seas or a minor storm is all that is needed to all but annihilate this protection.
Another measure are so-called controlled burns. This gets rid of only part of the oil since the water it is floating on helps extinguish the flames, and it causes environmental problems of its own since crude oil as it is spilling from the well contains large amounts of natural contaminants that are bad news for the environment and burning only helps to spread this pollution over both air and water, and over larger areas and volumes, leading to higher dilutions and therefore to less nasty results.
Crude petroleum tends to form large globs that are very hard to break down and that have detrimental effects on the environment. These globs are broken down into smaller ones by spraying so-called surfactants or dispersants on the affected areas.
In this oil spill, two dispersants are being used: Corexit 9500 and Corexit EC9527A, one is better for fresh oils and the other one is better for weathered oils. More than 1,000,000 litres have been used so far.
Dispersants are not a miracle solution. It is known, for example, that -depending on the type- they must be applied within hours to days to have any efficacy. That is in and of itself a reason why dispersants are not always used. Dispersants are chemical concoctions with unpleasant effects. Using them does not make the oil disappear; they merely disperse it. The advantage of using dispersants is that smaller globs of oil are easier to digest by micro-organisms and that the oil will therefore disappear faster.
The total effects on the environment are less clear. While it is true that dispersants will lead to less disastrous effects in animals and plants that live on or close to the surface, such as seabirds and mangroves, they will lead to more disastrous effects on plants and animals that live in deeper layers, such as seagrass and coral reefs.
Application of dispersants is not unlike chemotherapy for cancer. In chemotherapy, highly toxic products are applied, but because they are more toxic for the cancer cells than for the body, they often lead to a full recovery of the patient, while getting rid of the cancer. Not an ideal situation, but it is the best we have at the moment. This is really how the application of dispersants in oil spills has to be viewed. It is, in effect, a lesser of two evils. Best is to avoid spills altogether, but this is highly unlikely in any human endeavour.
Dispersants are normally sprayed on the surface, but now, for the first time, the EPA has approved a test for underwater application. While surface spraying is a lot easier, scientists think that underwater application at the source may have distinct advantages.
The response to the Deepwater Horizon incident is the start of a giant long-term experiment on the use of dispersants.
More about Dispersants dispersant, Gulf of Mexico, Deepwater horizon oil rig
 
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