When oil is “dispersed” from a spill, where does it go?

The conditions of oil spills are always different, and will determine if oil is best removed manually, like we saw in the Cape Moreton, or broken down by chemical dispersants and left to dissolve into the ocean. In March this year, the oil spilled from the Pacific Adventurer container ship, off Cape Moreton in Queensland, was mostly washed onto the coastline south of the cape. The sand was taken to a decontamination centre where the oil was extracted. It’s likely the sand would have been sold for re-use and the oil sent into industrial processes.

How are other spills “cleaned up”?

Co-ordinated by The Australian Maritime Safety Authority, The National Plan to Combat Pollution of the Sea by Oil and other Noxious and Hazardous Substances, lays out a few options for cleaning up oil spills:

  • Chemical dispersants. The use of detergents to break up, or distil, oil in water. When applied to oil, it forms small particles that dissolve into the ocean. However, the longer oil is left untouched, the less effective dispersants can be, as the slick will weather under the force of wind and waves, to become thicker and less dispersible. So immediate testing and assessment of dispersants is necessary, to see if they’re appropriate.
  • Leave alone, but monitor. Sometimes the natural process of dispersion and biodegradation can be enough, if the oil isn’t threatening shores or sensitive areas.
  • Containment and recovery. Oil can be contained by mechanical barriers called booms and collected from the surface by skimmers. Another alternative is sorbents, made from materials such as peat and cotton. These are generally used to absorb or adsorb smaller spills.
  • Biodegradation. A natural process where bacteria and other micro-organisms in the sea break down spilled oil. This can occur at different rates and is dependent on a range of factors such as temperature, oxygen and nutrient levels.
  • Bioremediation. A process where fertilisers or other nutrient materials are used to accelerate the natural biodegradation process. Research continues in this field.
  • In-situ burning. The in-situ burning of spilt oil hasn’t been used in Australia. Its limited use overseas is being monitored.

Are chemical dispersants any more environmentally friendly than the oil they’re combating?

We need to be extremely careful about the use of dispersants, as they wouldn’t work well in rough weather conditions or against some types of oils. That’s why we have a set of specific protocols that deal with how, why and when they can be used. It is a risk to use them, and that’s what these protocols take into account: whether the risk would be greater or smaller than the potential success.

Dr Poiner is also vice-chair of the International Scientific Steering Committee of the Census of Marine Life, and recently was part of an independent scientific panel overseeing the impact of the south-east Queensland oil spill.

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