Oct 22 (Reuters) - A coalition of U.S. farmer and environmental groups filed a lawsuit on Wednesday seeking to overturn regulatory approval granted last week for a herbicide developed by Dow AgroSciences.

The lawsuit, filed in the U.S. Court of Appeals for the Ninth Circuit in California, argues that the Environmental Protection Agency (EPA) did not adequately analyze the impact of one of the new herbicide’s active ingredients, 2,4-D, before granting approval on Oct. 15 to Dow’s Enlist Duo herbicide.

The groups are asking the court to set aside the EPA’s approval.

Widespread use of 2,4-D carries a range of risks to human health, animals, and the environment, the groups allege. They claim the EPA’s approval violated both the Endangered Species Act and the Federal Insecticide, Fungicide, and Rodenticide Act.

“They did not do an adequate job,” said Andrew Kimbrell, an attorney with the Center for Food Safety, a plaintiff in the case. “This was a rubber stamp. They acted illegally in approving this.”

The National Resource Defense Council filed a similar action on Oct. 16 against the EPA to block Enlist Duo, saying the new weed killer will be destructive to monarch butterfly populations and pose risks to humans.

The herbicide developed by Dow AgroSciences, a unit of Dow Chemical Co, is to be used with new genetically modified corn and soybean crops developed by Dow to tolerate treatments of the herbicide.

The Enlist crops were approved by the U.S. Department of Agriculture last month. When used in combination with the new herbicide, the Dow products should help farmers combat severe weed problems hurting U.S. crop production, according to Dow and government officials.

Millions of acres of U.S. farmland have been infested with weeds resistant to glyphosate-based Roundup herbicide, developed by Dow rival Monsanto Co and used widely by cotton, corn and soybean farmers. Critics say use of Enlist will make weed problems worse.

But the EPA said last week it had thoroughly evaluated the risks, and was requiring many restrictions on use of the herbicide.

Dow AgroSciences said last week it is “confident that EPA thoroughly reviewed” Enlist Duo and that the EPA will prevail in court.

Neither the agency nor Dow had an immediate comment Wednesday.

The EPA has recently been inundated with calls for the agency to deny approval of Enlist Duo, including warnings from a group of physicians and scientists who said 2,4-D can be linked to health problems that include suppressed immune function and greater risk of Parkinson’s disease.

The lawsuit was filed by the Center for Food Safety and by Earthjustice, a nonprofit environmental law firm, on behalf of Beyond Pesticides, Center for Biological Diversity, the Environmental Working Group, the National Family Farm Coalition, and Pesticide Action Network North America.

Initially, EPA approved Enlist Duo only for Illinois, Indiana, Iowa, Ohio, South Dakota and Wisconsin. EPA is considering approving it for use in 10 more states. (Reporting by Carey Gillam in Kansas City, Mo.; editing by Matthew Lewis)