10 June 2010

Oil spill at Changi East: What impact of dispersants?

Today a Straits Times article discusses the impact of disperants on marine life.
Dispersant applied at sea by the grey boat, soon after the accident.
The damaged orange tanker is in the background,
Reuters videoclip 26 May 10;

According to the article "more than 30 tonnes of dispersant were used in the recent oil spill".

What are dispersants?

(also based on The science of dispersants Nature.com 12 May 10)
Dispersants are chemicals that break up the crude oil into droplets. Those who are involved in producing and using dispersants usual say things like "Dispersants now are much less toxic and are quite similar to dishwashing liquids."

But "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," says Associate Professor Tan Soon Keat of the Division of Environmental and Water Resources Engineering at Nanyang Technological University (NTU).

The Straits Times article says the substances used in dispersants "may be toxic to marine life like mussels, clams, crabs, eels and shrimp." Although no details of the ingredients of the dispersants in our waters were disclosed.

In the US, the components of the dispersant used in the Gulf oil spill has just been publicised after much public pressure. See Ingredients of Controversial Dispersants Used on Gulf Spill Are Secrets No More Elana Schor, The New York Times 9 Jun 10.
Dispersant applied by boats at sea on our oill spill,
Reuters videoclip 26 May 10;

What do dispersants do to crude oil?
Dispersants do not remove oil from the sea. These droplets remain in the water. The idea is that these droplets are easier for naturally occurring sea-living microbes to break down - "biodegrade".

Thus, the crude is 'out of sight' and does not land on the shore in big smelly slicks.

In a way, we are making the pollution appear to disappear by adding more pollution.

What are the effects of dispersants on marine life?
Dispersants may prevent crude from fouling beaches and coating animals. But while surface-dwelling animals may benefit, animals in other parts of the oceans and those at the sea floor will experience MORE pollution.

"You're trading one species for another" says Carys Mitchelmore,a US environmental chemist who specialises in studying the effects of dispersants.

Thus we 'save' charismatic adult sea birds, in exchange for the bottom of the food chain and larvae of all kinds of marine life including our seafood.

In addition, as microbes 'biodegrade' the oil, they might also affect the water quality, for example, reducing oxygen levels. The mass deaths of fish at the fish farms off Pasir Ris and Pulau Ubin earlier in Dec 09 was due to (yet to be explained) low oxygen-levels in the waters there.

There is still a dearth of knowledge about the impact of dispersants. "The long-term effects are really unknown. The dispersant has inherent toxicity. And these oil droplets tend to be the same sort of size as food particles for filter-feeding organisms," says Mitchelmore.

In the Straits Times article: "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.
Worker applying dispersant to oil slick that reached the shore
near the SAF Yacht Club on 26 May.

Is there a better way to deal with crude oil spills?

"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, in the Straits Times article.

The experts note that more efficient, less toxic and more environment-friendly types of dispersants have emerged over the years.

But some experts are beginning to press for more efficient methods to deal with oil spills.

Prof Tan Soon Keat 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". The ozone gas is saturated in water and it is sprayed on oil slicks or bubbled through seawater filled with oil globules.

MPA announced during the cleanup that it had experimented with imbiber beads which are usually used by the Singapore Civil Defence Force (SCDF) to clean up chemical spills on land. Imbiber beads are spherical plastic particles that absorb organic liquids. MPA said results have been encouraging and with support from SCDF, it is deploying more imbiber beads to supplement other efforts.

Dispersion of oil not ideal 'but still best method' Janice Tai Straits Times 10 Jun 10.

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Oil spill: What long-term effects on our marine life?


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