A coalition of health and environmental organizations on Monday challenged the U.S. Environmental Protection Agency's (EPA) decision to expand the use of a new herbicide in nine states, which the groups say could endanger wildlife and public health.

The lawsuit (pdf) is the most recent step in a fight to push back against the use of the weed killer, Dow's Enlist Duo, which combines glyphosate, found in Monsanto's Roundup, and 2,4-D, the key ingredient in the infamous warfare herbicide Agent Orange.

As the coalition points out in a press release following its lawsuit, 2,4-D "has been linked to serious illnesses like Parkinson's disease, non-Hodgkin's lymphoma and reproductive problems. It also threatens endangered species that reside in the approved states, like the whooping crane, the Louisiana black bear, and the Indiana bat."

In March, the research arm of the World Health Organization declared that glyphosate was a "probable" source of cancer in humans and should be considered a carcinogen.

The EPA first approved use of Enlist Duo in six states in October, but recently widened that list to include an additional nine. The 15 total states where Enlist Duo may now be used are Arkansas, Illinois, Indiana, Iowa, Kansas, Louisiana, Minnesota, Missouri, Mississippi, Nebraska, North Dakota, Ohio, Oklahoma, South Dakota, and Wisconsin.

"Our federal regulators have again unlawfully bowed to the chemical industry, rather than protect our communities, land, and farms," said George Kimbrell, senior attorney for the Center for Food Safety, one of the groups challenging the EPA's decision. "We will continue to defend them vigorously."

Also in the coalition are Earthjustice, the Center for Biological Diversity, and Pesticide Action Network North America. The groups initially sued the EPA in October in response to its first approval, charging that the agency violated the Endangered Species Act by allowing the use of those chemicals, but the case was dismissed.

"In expanding its approval for this super-toxic chemical cocktail, EPA has shown an utter disregard for human health, our drinking water, and endangered species like the iconic whooping crane," said Lori Ann Burd, environmental health director at the Center for Biological Diversity, on Monday. "EPA has left us with no choice but to go to court."

As the coalition points out, the EPA approved Enlist Duo to address the rash of glyphosate-resistant "super weeds" infesting tens of millions of acres of U.S. farmland. But using 2,4-D to kill the weeds is nothing more than a "quick fix," the coalition said.

"Independent and USDA scientists... predict that the Enlist Duo 'crop system' will only foster resistance to 2,4-D in addition to glyphosate, continuing the GE crop pesticide treadmill," the Center for Food Safety said in a statement.

Marcia Ishii-Eiteman, senior scientist at the Pesticide Action Network North America, added, "Rural communities rely on EPA to take its job seriously... Communities across the Midwest are furious, knowing that they now face unprecedented levels of 2,4-D drift each summer."