Thursday, May 27, 2010

What will happen to all this oil? (Oil spill off Changi East)

Work has been terribly hectic the past few weeks so please excuse me for my lack of posts.

But hearing about the oil spill (2500 tonnes of crude oil) off Changi East made me sit up to find out more. As usual, I depended on Ria's blog posts to bring me up to speed on this accident which is the latest in a string of similar accidents (see list compiled by Siva).
  1. Any crude on our shores? (26 May)
  2. Will the oil spill reach Singapore shores? (26 May)
  3. Any crude on our shores? (25 May)
  4. What is being done about the oil spill? (25 May)
  5. 2,000-tonne crude oil spill off Singapore
The oil spill has apparently hit our shores despite earlier comments that it might vaporise before reaching land. The argument was being a light crude, the spill could vaporise easily.

So far, I have not seen any mention of exactly what kind of crude we are dealing with. Different crudes will have different compositions, affecting how a spill will behave and the remediation steps required.

Nevertheless, a crude oil should have the following fractions. Only the percentage of each fraction differs for different crudes.
  1. Light fraction
    This refers to the low molecular weight compounds e.g. benzene which have a tendency to vaporise. Naturally, their vapours led to the petrochemical odour experienced in the eastern part of Singapore. In terms of marine pollution, these guys are of little consequence.
  2. Water soluble fractionYes, some oily compounds are relatively soluble in water e.g. benzene. These are especially worrisome as they do not float on the sea surface but instead disperse both horizontally and vertically. (You are right if you deduce that living in the depths of the sea does not protect against these dangerous components.)

    Being water soluble, they are very bioavailable to marine organisms, easily entering their bodies through inhalation and ingestion. Oil booms have limited effect against them. On the other hand, being bioavailable makes them rather susceptible to decomposition.
  3. Immiscible fraction
    These stuff do not mix with water. However, they can form emulsions (suspension of liquid particles in another liquid). Depending on the sea conditions, an oil-in-water emulsion or a water-in-oil emulsion may form.

    Oil-in-water emulsion means the oil is distributed into tiny droplets in the sea. This allows them to be more readily decomposed. BUT at the same time, these emulsified oil droplets are quite bioavailable and can disperse vertically, hence they are more likely to affect marine life.

    Water-in-oil emulsion commonly appears as yucky patches similar to chocolate mousse. These are tough for microbes to gobble up so they tend to remain in the sea for a long time.
  4. Heavy fraction
    High molecular weight stuff like waxes make up this fraction. No surprise here - they are formidable for microbes to handle. They also tend to form "tar balls" - ugly pieces of black, viscous oil. These balls remain unchanged for a long time in the sea.

    Moreover, certain heavy compounds are literally that - HEAVY. They sink. Bottom feeders take note as the oil spill is no longer just restricted to the sea surface.
All the above considerations do not make oil spill response any easier. A good response will have to identify the kind of oil it is dealing with, accurately model the transport and fate of the oil and effectively manage adequate resources to combat the spill.

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