Guidelines for the use of dispersants for combating oil pollution at sea in the Mediterranean region
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- Figure 13: Under water blowout in ultradeep environment during Deep Water Horizon incident (source SINTEF)
- What would be the impact of the pollution when treated with dispersant and when non treated with dispersant
Guidelines for the use of dispersants for combating oil pollution at sea in the Mediterranean region Part II: Basic information on dispersants and their application – Page 18
mammals to oil can lead to changes in the ability of animals to deal with the uptake, storage and depuration of hydrocarbons whilst acute exposures can result in mortality in particular with young mammals which are more susceptible to the toxicological effects of oil.
Oiling causes reduction in fur insulating capacity and dispersants have been experimentally used for the removal of crude oil attached to fur. These experiments resulted in the removal of natural skin oils together with crude thus destroying the fur's water-repellency. Surfactants can increase the wettability of fur or feathers, allowing cold water penetration and subsequent increase of the thermal conductance. This is particularly dangerous to animals that are buoyed or insulated by their fur or feathers. Records of animal deaths due to direct ingestion of oil during grooming also exist. Extremely limited information on the influence of dispersants or dispersed oil on marine mammals exists, nevertheless the use of dispersants may not reduce the physical threat of spilled oil to some fur-insulated sea mammals.
7.4
The use of dispersant on underwater oil releases (e.g. blow out)
Dispersant can be used to disperse under water releases such as blow out coming from sub sea well head.
This technique has been used recently during the “Deep Water Horizon” incident , in the Gulf of Mexico in 2010, where large quantities of oil were released at sea (high pressure / high shear rate). Large quantities of dispersants have been injected directly at the source of the spillage at the sea bottom (1300 m depth) into the damaged riser to disperse the oil just released (fresh), in order to:
reduce the amount of volatile in the atmosphere close to the damaged well (for security reason);
reduce the amount of oil liable to be drifted to the sensitive Louisiana shoreline (environmental issue).
The formation of a large plume of dispersed oil between 1100 and 1300 m, with low oil concentrations has been observed. At the time this text has written there was still debate on the effects (efficiency and impact) of this peculiar dispersant application.
In terms of efficiency, uncertainties remain on the real effect of dispersants (e.g. what was really dispersed by the dispersant and what would have been naturally dispersed).
Waiting for further investigations, the preliminary feeling of the scientists community is “that the use of dispersants and the effects of dispersing oil into the water column has generally been less environmentally harmful than allowing the oil to migrate on the surface into the sensitive wetlands and near shore coastal habitats” (“Deep Water Horizon” Dispersant Use Meeting Report –
It should be highlighted that the usual recommendations for regular dispersant application on surface slicks may not be suitable to the sub-sea application of dispersant on a sub-sea blowout plume. In sub-sea application the oil is fresh with its light ends, (the most toxic fractions) while surface slicks are usually partly weathered. However, considering ultra-deep environment the environmental conditions are so different (temperature, ecological sensitivity and diversity, temperature… etc.) in comparison with surface water (photic zone) that the usual way to assess the possible impact of chemical dispersion (as described in Part II and Part III of these Guidelines) is not applicable as they are (e.g. regular NEBA process as described in the next chapter 8).
Guidelines for the use of dispersants for combating oil pollution at sea in the Mediterranean region Part II: Basic information on dispersants and their application – Page 19
If required, this chapter on sub-sea dispersant application could be further expended in a future edition of the Guidelines when the results of the ongoing studies on the Deep Water Horizon incident and its consequences will be made available.
during Deep Water Horizon incident (source SINTEF)
8. NET ENVIRONMENTAL BENEFIT ANALYSIS (NEBA)
As the aim of the spill response is to minimise the overall environmental impacts on natural and economic resources, the decision on the use of dispersants should be based on the following comparison: “ What would be the impact of the pollution when treated with dispersant and when non treated with dispersant? ”.
This comparison is named: the NEBA 2 (the Net Environmental Benefit Analysis). The NEBA should:
stream, speed of dilution of the plume) and of the non treated oil (drift according to the stream and the wind);
the treated oil or by the surface oil;
assess the sensibility of the different resources at concern towards the dispersed oil and toward the surface oil (non dispersed);
impacted.
These analyses assist decision makers when considering whether or not the use of dispersants is appropriate, to minimize the environmental/economic damage.
Often, the NEBA can lead to compare the damage of the oil dispersed at sea with the damage of the slick drifted on the shoreline.
In most cases, the damages at sea caused by the dispersed oil are less than those generated by the oil weathered (often persistent) and stranded on the shoreline. However, the closer it affects the shoreline, the more difficult is the NEBA, as depending on the response strategy,
2 The concept of NEBA can be found in the literature under different names : NEEBA (Net Environmental & Economic Benefit Analysis, or NEDRA (Net Environmental Damage Risk Assessment), etc….
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