Chemical dispersants were sprayed in unprecedented quantities in the Gulf as part of the response to the BP oil spill. The toxic effects of these dispersants on marine life and humans provide yet another illustration of the dangerous environmental impacts of offshore oil drilling and why it must be stopped.

What are dispersants and why are they used in oil-spill response?

Dispersants are chemicals that are sprayed on a surface oil slick to break down the oil into smaller droplets that more readily mix with the water. Dispersants do not reduce the amount of oil entering the environment, but push the effects of the spill underwater. While dispersants make the oil spill less visible, dispersants and dispersed oil under the ocean surface are hazardous for marine life.

Dispersants were being used in the BP oil spill to reduce the chance that the surface oil slick would reach shoreline habitats like marshes and mangroves or come into contact with animals at the surface. However, by mixing the oil below the water surface, dispersants increase the exposure of a wide array of marine life in the water and on the ocean floor to the spilled oil. Dispersants also decrease the ability to skim or absorb oil from the ocean surface.

How much dispersant was used in the BP spill?

More dispersant was used on the BP spill than in any other oil spill in U.S. history. Moreover, for the first time ever, the EPA approved using dispersants not only at the surface but deep underwater at the source of the spill. Approximately 1.84 million gallons of dispersant were applied, with more than 1 million gallons on the surface and 771,000 gallons pumped deep into the water column to dilute the oil.

What are the environmental hazards of dispersants?

Dispersants and dispersed oil have been shown to have significant negative impacts on marine life ranging from fish to corals to birds. Dispersants release toxic break-down products from oil that, alone or in combination with oil droplets and dispersant chemicals, can make dispersed oil more harmful to marine life than untreated oil. Both the short-term and long-term impacts of dispersants on marine life have not been adequately tested. As acknowledged by the EPA, the "long term effects [of dispersants] on aquatic life are unknown."

Dispersants create a toxic environment for fish by releasing harmful oil break-down products into the water. Dispersed oil has been shown to be toxic to fish at all life stages, from eggs to larval fish to adults, according to numerous laboratory studies that have tested a variety of species.

Dispersants and dispersed oil are particularly toxic to corals, leading scientists to call for a ban on dispersant use near coral reefs. Dispersants and dispersed oil harm the early stages of corals by increasing death rates, reducing settlement on reefs, and altering behavior. A formulation of one of the dispersants being used in the BP spill response, Corexit 9527, has been shown to prevent fertilization of mature eggs and hinder the development of young life stages of reef-building corals.

Sea turtles
According to the Minerals Management Service, dispersant components absorbed by sea turtles can affect their organs and interfere with digestion, excretion, and respiration.

Studies have found that dispersed oil, including oil dispersed by Corexit 9527, damages the insulating properties of seabird feathers more than untreated oil, making the birds more susceptible to hypothermia and death. Dispersants and dispersed oil have also been shown to have toxic effects on bird eggs that are similar or worse than from untreated oil. Birds exposed to dispersed oil that return to their nests risk the death of their eggs.

Risks to humans

Dispersants pose significant human health risks as well. One of the dispersants used at the BP spill, Corexit 9527A, contains the toxin 2-Butoxyethanol which "may cause injury to red blood cells (hemolysis), kidney or the liver" with "repeated or excessive exposure," according to the manufacturer's safety data sheet. Corexit 9527 was sprayed on the 11-million gallon oil slick created by the Exxon Valdez spill, and cleanup workers reportedly suffered health problems afterward, including blood in their urine as well as kidney and liver disorders, attributed to 2-Butoxyethanol.

What dispersants were used? Why weren't the least toxic, most effective dispersants used?

BP used two dispersants called Corexit 9500A and Corexit 9527A. These products are significantly more toxic and less effective than other available EPA-approved dispersants. Of the 18 dispersants approved for use by the EPA, seven were found to be less toxic than the Corexit products, and some were 10 times less toxic. Six of seven safer dispersants were found to be more effective on southern Louisiana crude oil than the Corexit products. Two were found to be 100 percent effective compared to the 55 and 63 percent effectiveness of the Corexit products.

Although approved by the EPA, formulations of Corexit 9500 and 9527 were banned from use in the United Kingdom in 1998 because laboratory tests found them harmful to marine life that inhabits rocky shores.

BP's use of the more toxic, less effective Corexit dispersants is under scrutiny since the company that manufactures these dispersants, Nalco Co., has ties to the oil industry. In the 1990s, Nalco formed a joint venture company with Exxon Chemical Company and has board members and executives that have previously worked for Exxon and BP. Nalco has sold millions of dollars of dispersants for the BP spill. Nalco has also refused to disclose all of the ingredients in the Corexit products.

In the first 30 days of the spill, the EPA did not intervene in BP's decision to use the more toxic, less effective dispersants in the spill. The EPA stated that it approves a list of dispersants, and oil companies are allowed to choose which dispersants to use. On May 20 the EPA issued a directive requiring BP to identify and use a less toxic and more effective dispersant. BP refused in a clash with the federal government, but slowed the use of dispersants shortly thereafter.

Are the giant, deep-sea oil plumes in the Gulf of Mexico related to the use of dispersants?

Researchers working in the BP spill zone discovered giant plumes of oil in the deep waters of the Gulf of Mexico, estimated in size at 10 to 15 miles long and four to five miles wide. The plumes raised concerns about the subsea use of dispersants, but researchers were unable to conclusively determine if they were related. Learn more from The New York Times and Reuters.

Deepwater Horizon explosion photo courtesy U.S. Coast Guard