Janice Tai Straits Times 10 Jun 10;
MORE than 30 tonnes of dispersant were used to break up oil into globules in the recent oil spill off the Changi coast.
In the Gulf of Mexico, experts have deployed about five million litres of the substance on a massive slick that has been gushing out of a ruptured undersea well for the past two months.
But some experts are beginning to press for more efficient methods to deal with oil spills. They argue that the dispersion method, which has been in use for decades, drives some of the oil undersea and threatens marine life.
'Chemical dispersants merely visually 'remove' oil from the water because we cannot see the smaller oil particles. The oil still remains in the water column or on the seabed,' Associate Professor Tan Soon Keat of the Division of Environmental and Water Resources Engineering at Nanyang Technological University (NTU) told The Straits Times.
Dispersants are chemicals with an active ingredient called surfactants.
Surfactants bind well with either water or oil, reducing the tension between them and breaking up oil into droplets.
The application of dispersants is one of the four main ways used to clean up oil spills, the others being soaking up, scraping off and burning.
Dispersion is the only method that uses chemicals, and the substances may be toxic to marine life like mussels, clams, crabs, eels and shrimp.
Furthermore, dispersants do not get rid of all the oil.
Some of it will remain in the water. Plumes can also form undersea, depleting the water's oxygen content - which some scientists say is what is happening in the tainted waters in the Gulf of Mexico.
'I'm afraid that a lot of damage is being done below the surface where the majority of oil is,' said Assistant Professor Prosanta Chakrabarty of Louisiana State University, an expert on fish and marine life.
While the dispersion method is far from ideal, there are few alternatives.
'The strategy to combat oil spills has remained largely unchanged over the last 30 to 40 years. The oil is either dispersed, collected or burned,' said Mr Ho Yew Weng, operations manager of Oil Spill Response.
The Singapore-based company has been involved in the clean-up of the spills in both Changi and the Gulf of Mexico.
Still, the experts note that more efficient and environment-friendly types of dispersants have emerged over the years.
Prof Tan cites the use of gases like ozone instead of the usual chemical dispersants.
'The oil is removed in an environmentally friendly manner as the ozone converts the oil into carbon dioxide and water,' he said.
The ozone gas is saturated in water and it is sprayed on oil slicks or bubbled through seawater filled with oil globules.
Less toxic dispersants have also been developed.
'Dispersants now are much less toxic and are quite similar to dishwashing liquids,' said Mr Ho.
