Deepwater Horizon: A Dispersant Discussion

Part 2 of a 3 part series on the Deepwater Horizon oil spill (part 1 here) by Joana Tavares-Reager, oceanographer and marine policy expert.  As with all things we classify as disasters, it is sometimes hard to find the silver lining.  The aim of the series is to discuss the broader impacts of the spill and make a connection to each of our daily lives.

Out of sight, out of mind?

Dispersants are chemical products used to accelerate the removal of oil from the surface of the sea by breaking it down into small droplets of oil that sink into the upper zones of the water column. These products have been used to control oil spills with various levels of success, depending on the physical characteristics of the affected area, the types of organisms that inhabit the region and the size of the spill. Thus, knowing how much oil is being released through the gush is fundamental to calculate the appropriate amount of dispersant to apply.

The logic behind the application of dispersants to respond to oil spills is that, although they do not actually reduce the amount of oil, they decrease the potential for a surface slick to contaminate shoreline habitats and come into contact with birds, marine mammals, or other organisms. In general, most marine organisms around the world inhabit and reproduce near the coast, thus the special need to protect nursery areas, such as wetlands and marshes.  Also, “dispersed oil” is expected to be more rapidly biodegraded by naturally occurring microorganisms that consume oil.

Another reason why oil companies want to apply dispersants is, of course, minimizing the evidence of the spill. You throw this stuff on the water, the oil sinks into the ocean and voilà, the mess is gone, right?  Well, not quite.

The problem with using dispersants to deal with oil spills is two-fold. First, the fact that dispersants force the oil to sink represents an increase in the risks to plant and animal life in the water column and on the seafloor, such as plankton, corals, crustaceans and some bottom fish.  This is of special concern in the Gulf Mexico.

According to scientists from the Marine Geology & Geophysics division of the University of Miami (UM), who study deep-see corals and reef ecosystems in the Gulf of Mexico and Straits of Florida, the oil that sinks from the surface remains in suspension in the water column, due to natural stratification patters in the water of the Gulf. The oil suspended between the surface and the bottom forms what is called an oil plume, which poses a serious risk for the sealife throughout the region. Deep, cold-water corals are the foundation of a diverse ecosystem that includes over 1,300 marine species, including economically valuable deep-sea fish such as grouper, snapper and amberjack off the coast of Florida at depths of about 1000 to 5000 feet. These corals feed on organic matter that sinks down from the surface layers.  The large oil plumes formed by natural water stratification and the use of dispersants block and contaminate the particles of food that these deep-water corals depend on, creating cascading impacts to the whole ecosystem.

In addition, much controversy related to the use of dispersants is associated to the fact that the products themselves can be toxic to marine life and humans, especially when applied in large quantities. BP has applied an unprecedented amount of dispersants in the Gulf of Mexico.According to the official reports some 800,000 gallons of dispersants have been sprayed over and injected under the water surface, and at the source of the leak.

The composition of dispersant products has evolved a long way in the last 20 years. Early generations of dispersants were either water-based surfactant systems or nonaromatic hydrocarbon solvent-based systems. These generally required high application rates, and additional mechanical agitation, such as by ship propellers, fire monitors or ‘breaker boards.’ Modern dispersants use solvent systems that allow much higher surfactant content. These modern concentrate dispersants therefore are effective at lower application rates, but the actual compositions of the specific dispersant products can differ significantly, and will represent different levels of environmental side-effects.

Image from Eberli,Grasmueck & Correa, Resenstiel School

Between a rock and a hard place

In the Gulf of Mexico, BP has used two variations of a dispersant called Corexit.  The Corexit series of dispersants has been used on oil spills since 1978, and until now had been generally accepted as a viable alternative to disperse oil spills.  Various versions of Corexit are currently approved by the USEPA for use in oil spill response efforts, and are listed in the National Contingency Plan, maintained by the Agency. In the year 2000, scientists from Exxon Biomedical Sciences published a study in the scientific journal Chemosphere, in which they reviewed published literature and unpublished reports containing Corexit aquatic toxicity data and concluded that the two Corexit dispersants used in the Gulf of Mexico, Corexit 9500 and Corexit® 9527, have low to moderate toxicity to most aquatic species in laboratory tests.  The study cites a number of toxicity studies published in the 1980’s and 90’s, the most relevant ones being those that applied the “spiked, declining exposure” methods, which according to the authors are more reflective of actual dispersant use conditions. Test organims included different life stages of some crustaceans, molluscs, fish, macroalgae, seagrass and bacteria.

However, in the mist of responding to the Deepwater Horizon spill, various scientists and activists voiced their concern over the potential collateral effects that massive applications of Corexit could impose to people and marine organisms in the Gulf of Mexico.

On May 20th, in what could be considered a delayed attempt at diligence, the USEPA issued a directive requiring BP to look “for more effective, less toxic alternative to their current dispersant”, Corexit 9500 and 9527. Too bad EPA’s directive had not teeth. BP claimed they had been properly authorized by the Coast Guard and the EPA to use Corexit from the start, and that there was nothing better in the market anyway- tough luck for the EPA.

Then, on May 26th, the Agency finally took a firmer position regarding the use of dispersants. It determined BP to eliminate the surface application of dispersants and limit subsurface application of dispersant of not more than 15,000 gallons in a single calendar day.  Surface applications could only be done in rare cases when there may have to be an exemption, and BP must make a request in writing providing justification which will include the volume, weather conditions, mechanical or means for removal that were considered and the reason they were not used, and other relevant information to justify the use of surface application.

On May 26th and 27th, the UNH Coastal Response Research Center, NOAA, EPA and Coast Guard held a meeting with some 50 scientists, engineers and spill response practitioners from numerous organizations to clarify the use of dispersants in response to the Deepwater Horizon spill and identify possible new monitoring protocols in the event of continuing aerial and subsurface dispersant application.

A report for this meeting was published in early July and stated that it is the consensus of that group that “up to this point, 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”.

AP Photo

Where do we go from here?

In the last three months, we have witnessed BP fumbling around with a number of frustrated attempts to shut off the Deepwater Horizon gush.

We held our breath with the containment dome, naively cut our hair and shipped our stockings to the Gulf to help soak up the oil from the ocean water, watched a number of spokespersons advertise revolutionary oil response inventions, and by the time BP announced the top kill and junk shot plan, we were all but too tired to get our hopes up for a real solution.

The fact of the matter is that there is no ready-to-go immediate solution. Nobody did their homework in advance, at least not well enough, and now we are trying possible solutions as we go.  While much has been discussed and published about oil spill response techniques in the last 20 years, this field of knowledge remains much more as an art of trial and error than as an exact science.

Please join us for the conclusion of the 3 part series on the Deepwater Horizon oil spill next week, which will discuss the roles of decision making, government and society.

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