(CNN) -- BP plans to continue using a controversial subsea dispersant to break up a plume of oil gushing into the Gulf of Mexico, saying that the leading alternative could pose a risk over the long term, the EPA indicated Saturday.





The EPA issued a directive on Thursday, ordering BP to find, within 24 hours, a less toxic but equally effective chemical than its current product, Corexit 9500 -- and one that is available in sufficient quantities. The directive also gave the company 72 hours to stop applying it to the undersea gusher.





Corexit has been rated more toxic and less effective than many others on the list of 18 EPA-approved dispersants, according to testimony at a congressional hearing Wednesday.





The EPA released BP's response to the mandate on Saturday.





The response, which BP submitted late Thursday night, said that the oil company identified the only other effective, less toxic alternative available in mass quantities as Sea Brat 4. However, BP said the Sea Brat product "contains a small amount of a chemical that may degrade to a nonylphenol."





Nonylphenol is an organic chemical that is toxic to aquatic life and may persist in the environment for years.





Corexit, however, "does not contain chemicals that degrade into NP [and] the manufacturer indicates that Corexit reaches its maximum biodegradeablility within 28 days of application" and does not persist in the environment, BP's response said.





"Based on the information that is available today, BP continues to believe that Corexit was the best and most appropriate choice at the time when the incident occurred, and that Corexit remains the best option for subsea application," BP said.





Despite the continuing use of Corexit, BP is not in violation of the EPA directive, which said that should the company not be able to identify alternative products, "BP shall provide ... a detailed description of the products investigated [and] the reason the products did not meet the standards" required by the agency.





"We will continue to review and discuss the science through the end of the 72-hour window on Sunday, and then we will reach a decision," an EPA spokesman said Saturday.





John Sheffield, president of Alabaster Corp., which manufactures Sea Brat, took issue with BP's response, saying Saturday that the company is "nitpicking my product because they want to use what they've always used."





Sheffield told CNN that he discussed the nonylphenol issue with EPA officials earlier this week, saying the chemical makes up less than 1 percent of the Sea Brat dispersant.





"I've already diffused this issue with the EPA," he said, adding the agency "accepted that response days ago."





The EPA has not yet publicly issued a formal response to BP's letter. EPA officials met with BP executives on Friday to discuss the issue and to explore alternatives.





The EPA said Saturday that it "will continue to work over the next 48 hours to ensure BP is complying with the directive," but did not respond to requests for additional comment.





Meanwhile, the Department of Homeland Security announced Saturday that Interior Secretary Ken Salazar and Homeland Security Secretary Janet Napolitano will lead a bipartisan Senate delegation to inspect the Louisiana coastline after globs of thick, heavy oil began washing into some of the state's marshlands this week.





The delegation will meet with federal officials and BP representatives to discuss the ongoing response efforts.





CNN's Ed Lavandera contributed to this report.
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