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The use of chemical dispersants in the Gulf of Mexico during the BP Deepwater Horizon disaster began during the early weeks of the oil spill.

Markey's extensive oversight while serving in the House into the response to the oil spill included an investigation into (1) the concern that the application of dispersants proceeded in the absence of comprehensive scientific information about its potential impacts, and (2) that despite the joint May 26 United States Coast Guard (USCG) and Environmental Protection Agency (EPA) Directive that use of surface dispersants be allowed only on “rare” occasions, they were allowed virtually every day.

Below is a timeline of events and letters related to Markey's investigation into the use of unprecedented volumes of chemical dispersants to mitigate the impacts of the oil spill in the Gulf of Mexico.


• May 10:  The EPA USCG authorized BP to begin a trial to determine whether subsurface use of dispersants would be effective in reducing the amount of raw crude oil reaching the surface.
• May 15: USCG and EPA authorized BP to use dispersants sub-surface at the wellhead.  EPA Administrator Lisa Jackson stated that “We believe that the underwater use of dispersants could lessen the overall impact of the spill.” The statement can be found HERE.
• May 17: Rep. Markey sent a letter to EPA raising concerns that BP had selected the least effective and most toxic dispersant available to be used.
• May 20: USCG and EPA directed BP to identify a less toxic dispersant and begin to use it within 72 hours. The statement can be found HERE.
• May 22: EPA released BP's response to the May 20 directive which stated that there was no less toxic dispersant that was available in the quantities needed to respond to the spill. 
• May 25:  Rep. Markey sent a letter to the FDA related to the potential impacts of dispersant use on seafood safety.
• May 26: USCG and EPA issued a new directive to BP, saying that it “shall eliminate the surface application of dispersant” except in the “rare cases” where it would have to seek an exemption which would require the approval of the Federal On-Scene Coordinator (FOSC), and limit subsurface applications to 15,000 gallons per day.
• May 27: EPA responded to Rep. Markey's May 17 letter.
• June 24: Rep. Markey sent letters to EPA and the USCG asking why BP had been regularly exceeding the dispersant limits set in the May 26 directive. Copies of the letter can be found here: to the EPA , to the USCG.
• July 12: The USCG responded to Rep. Markey's June 24 letter.
• August 5: The EPA responded to the June 24 letters sent by Rep. Markey on chemical dispersants.
• September 27: Reps. Markey and Miller requested information from GAO on research on and the use of chemical dispersants.