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Experts on clean-up, use of dispersants
Experts on clean-up, use of dispersants
11 October 2011
Maritime New Zealand continues to lead an effort to stabilise the stranded cargo ship Rena, but has been hampered by bad weather, which has prevented the removal of fuel oil from the stricken ship.
The authority said this morning that "130-350 tonnes" is estimated to have leaked from the ship so far.
The SMC gathered the following comments from international experts with experience of oil spills. Feel free to use these quotes - contact the SMC for further information or to speak to the authors.
University of Southampton lecturer in oceanography Dr Simon Boxall, who has experience of the Erika oil spil on France's Brittany coast in 1999, and the MV Braer oil spill in the Shetland Islands in 1993, comments:
"There is nothing positive about an oil spill, they shouldn't happen. A ship going aground and spilling its fuel oil is inexcusable. So far it is a relatively small volume. The stormy weather is both a pro and a con. The bad news is that it hampers the clean up and access to the stricken vessel. The good news is that it helps the oil disperse naturally. A good example of this was the Braer spill off the Shetlands ... very large volumes dispersed very quickly by heavy storms. Tides and currents will also help.
"Microbe activity will act quickly and break the oil that is naturally dispersed in about 4-6 weeks given current temperatures and increasing daylight. Add to that a team of beach clean-up personnel and the impact of the (estimated) 30 tonnes will be minimal. There will be some distressing sights of some sea birds killed and of oil on beaches but it will be short-term.
"Some experts disagree on the dispersants. Dispersants do have a role to play but only in a few cases (but) there is a tendency to use them regardless.
"Contrary to what is coming out, they are more harmful than the oil itself and they are NOT less toxic than dishwashing liquid! Fairy dishwashing liquid doesn't carry hazchem advice and you don't wear protective clothing and masks to do the washing up. In their raw form some dispersants can be very toxic and I believe will do more harm than good. Most of the Corexit dispersants were banned from use by the UK Government in 1998 for rocky shore areas and can only be used offshore after consultation with govt., and if no alternatives are available. Sweden has a blanket ban on all dispersants in the marine environment. In this case - with limited knowledge of the region - I'd advise caution on use of dispersants.
"Nature did a lovely job of Braer and very little human intervention took place (no dispersants). The Erika involved substantial mechanical beach clean up but we did a study 5 months after the spill and levels of hydrocarbons on the beaches of France that had been impacted were below background levels (and in fact were better than one or two control beaches). The Rena spill needs containment as first priority, booming where possible to contain the marine based oil. Beach clean-up will be important and the oil breaks down more slowly on the beach than at sea. At sea, nature will disperse and break the oil down very quickly, without use of chemicals.
CSIRO research scientist Professor Nic Bax, who leads the Biodiversity Hub at the University of Tasmania, comments:
"Responding to oil spills is a very complex, high pressure situation requiring decisions to be made based on whatever data are available at the time. One of the difficulties in assessing the environmental impacts of oil spills is the lack of environmental baselines against which to measure the changes. Hydrocarbons impact the environment and plants and animals through several different pathways - physically through smothering or the external oiling of birds and marine mammals, and chemically through the toxicity of the compounds entering the animal itself causing different levels of short and long-term poisoning. The most visible impact of oil spill is through smothering and this is often the one that gets most attention. The chemical impacts are harder to quantify being less visible, although tainting in commercial species (or the perception of tainting) can have immediate commercial impacts". "While the impacts of oil spills are visually alarming with high local impact, far more oil enters the global oceans through other mechanisms. Local environmental impacts of oil spills will continue after the obvious tarry oil has been removed or dispersed. This is at least in part because some oil seems to usually remain hidden at depth in the sediments. The time this oil remains depends on the environment, with cold, low energy environments being the slowest to recover".
"Dispersants when applied on reasonably fresh oil can disperse the oil though the water column. Dispersants do not change the amount of oil but they redistribute it. They can be used to alter the parts of the environment that are affected from surface creatures and sensitive shorelines to the water column and bottom creatures. Where they are used in deep water and high energy environments they also serve to spread the oil over a wider area (or volume), diluting it and reducing its immediate impact. Dispersants used to be quite toxic but now are considered to be much less toxic than the oil itself, so the main environmental decision regarding their use is determining where the oil will have least harm i.e. concentrated at the surface and on sensitive shorelines, or dispersed through the water column. There does not seem to be much evidence to indicate that dispersing oil leads to greater uptake by organisms, although this would be very hard to measure".
"It seems that oil will eventually be broken down by natural processes including microbial activity. Microbial activity may be especially important after oil has entered habitats such as sub-surface sediments where physical weathering can no longer occur. It seems to be a long-term process as oil has been detected in sediments a decade after oil spills have occurred. The more volatile components of the oil are typically considered to be the most toxic, but they are also the components that will boil off or evaporate most rapidly. Typically heavier crudes hang around longer are harder to disperse and have a greater visual and aesthetic impact. Evaporation of the oil will be increased in warmer temperatures thus reducing impacts. Dispersion in the water column will be increased in high energy environments (such as high wave action) which will dilute the oil ... reducing its local impact".
"In low energy environments, such as there is little opportunity for physical processes to operate. Areas of high tidal energy will again serve to spread and dilute the oil, but may make it harder to prevent the oil reaching sensitive areas. Spilt oil that remains at the surface will gradually be dispersed by natural physical processes at least in high energy environments. Oil that reaches low energy environments or gets buried in sediments may persist for several years".
More on oil dispersants:
Last month, a project based out of the University of Houston in Texas was launched to research new types of oil dispersants that would be friendlier to the environment and appropriate for use in deep sea oil releases - such as that experience in the Deepwater Horizon spill in the Gulf of Mexico.
Ramanan Krishnamoorti Professor of Chemistry at the University of Houston is leading the research. He said:
"Safety has been a big issue in dispersant technology. We already know they can be highly toxic, so the challenge is to make them less so. We hope to make safer and more efficient dispersants.
"My efforts
will be focused on coming up with novel, particle-based and
biological dispersants," Krishnamoorti said. "I'll be
working on developing dispersants that we can use less of
and are more biocompatible with the water, plant life and
wildlife."
ends
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