WASHINGTON — A Louisiana environmental activist told the Congress on Thursday that workers cleaning up the Gulf of Mexico oil leak are not being given information about the hazards of dispersants being used to break down the oil.

Anne Rolfes, executive director of the Louisiana Bucket Brigade, testified to a Senate subcommittee that cleanup workers are warned about everything from poisonous plants to mosquitoes, but the dispersant chemicals are not addressed.

“What you know that is not on this list is anything about dispersants,” Rolfes said.

The oil leak began on April 20, when the Deepwater Horizon rig being operated by BP exploded, killing 11 workers. Since then, BP has been using dispersants to break up the oil before it rises to the surface.

Rolfes contends that 20 percent of the chemical being used by BP contains material that made workers sick as they worked on cleanup of the Exxon Valdez oil spill in 1989.

She urged the commerce, justice and science and related agencies subcommittee to give the Environmental Protection Agency more power to regulate BP on its use of dispersants.

“BP was allowed to thumb its nose at the administrator of the EPA,” Rolfes said. “It seems that she does not have the legal authority that is needed.”

EPA Administrator Lisa Jackson also testified before the panel. Jackson said she has been working through the Unified Incident Command set up to coordinate response to the disaster.

The EPA was able to get BP to reduce the amount of dispersants it was using, Jackson said. The company is now using 15,000 gallons a day, down from 70,000 gallons, she said.

“That was an alarming number,” Jackson said.

Sen. Frank Lautenberg, D-N.J., said he intends to soon introduce legislation that would require testing of dispersants before they are used.

“We need to do our work in advance and not rely on catch up,” Lautenberg said.

Ken Cook, of the Environmental Working Group, a consortium of environmental organizations, called the BP use of dispersants an experiment. No agencies or groups were prepared for such a catastrophe, he said.

“We walked into this almost completely blind,” Cook said.

The EPA considers the dispersant nontoxic, and it breaks down over a matter or weeks, as opposed to oil, which can take years, the EPA has said.

The testimony Thursday alarmed subcommittee Chairwoman Barbara Mikulski, D-Md.

“I don’t want these dispersants to be the Agent Orange of this oil spill,” Mikulski said, referring to the defoliant used during the Vietnam War that some analysts blame for post-war health problems.