A study conducted by Pennsylvania State University and Temple University has found that several cold water coral species found in the deep marine environment of the Gulf of Mexico are more seriously affected by exposure to the dispersant Corexit9500A®, used during the Deepwater Horizon event, than by exposure to oil alone or a combination of oil and dispersant.
During the prolonged spill following that Deepwater incident approximately seven million liters of dispersants were used, much of that applied at depth, near the leak. This was the first time dispersant had been used at depth and potential impacts were unknown.
Researchers developed the recent coral study after finding damaged coral populations post-spill. They were unable to determine whether the oil, dispersant, or the combination of the two caused the problem. To learn more, they exposed three common cold water corals to three conditions: oil alone, dispersant alone and a combination of the two, at varying concentrations. Perhaps the most interesting finding was that dispersant alone resulted in death of all three species at a lower concentration than that of oil or the oil/dispersant combination.
In addition, findings by University of Western Australia and University of Miami scientists suggested that the pressure of the Deepwater blowout would likely have resulted in much smaller droplets of oil being released, droplets the size that dispersants would create. This may help explain why so little oil made it to the surface, as drops that small would not have the buoyancy to rise that high against ocean currents.
National policies on dispersant use in European countries vary. Of the 25 countries included in the European Maritime Safety Agency (EMSA) report National Policies Regarding the use of Oil Dispersants in the EU Member States 2014, nine use dispersants only as last resort or prohibit their use and eight will only consider it as a secondary response option. In countries where it may be considered for primary response, authorization from a national agency is required.
Resources:
DeLeo, DM, Ruiz-Ramos, DV, Baums, IB, and Corde, EE. 2015. Response of deep-water corals to oil and chemical dispersant exposure. Deep Sea Research Part II: Tropical Studies in Oceanography. Accessed online 15.April 2015
Aman, ZM, Paris, CB, May, EF, Johns, ML, and Lindo-Atichati, D. 2015 High-pressure visual experimental studies in oil-in-water dispersion droplet size. Chemical Engineering Science. 127: 392-400. Accessed online 15 April 2015.
European Maritime Safety Agency. 2014. Inventory of National Policies Regarding the use of Oil Spill Dispersants in the EU Member States. Accessed online 15 April 2015