WASHINGTON (October 15, 2014)—The Natural Resources Defense Council today filed suit to block the use of a powerful, newly approved weed killer that will wreak further destruction on monarch butterfly populations already devastated by agricultural chemicals and poses risks to human health.

The suit was filed in the D.C. Circuit court immediately after the Environmental Protection Agency approved the use of “Enlist Duo,” a combination of two herbicides: glyphosate (initially marketed as Roundup) and 2,4-D, an older, toxic herbicide. Enlist Duo is intended for use on corn and soybeans genetically modified to be resistant to this chemical cocktail. Glyphosate, the most widely used weed killer in the country, is the chief cause of the decline of the monarchs, and scientists have raised serious questions about 2,4-D’s impact on human health.

“This weed killer is more bad news for monarch butterflies, whose migrating population has dropped by more than 90 percent in recent years because glyphosate has wiped out the milkweed they need to survive,” said Sylvia Fallon, a senior scientist at NRDC. “EPA completely ignored the impact on monarchs when it granted this new approval, and seriously underestimated the toxicity for people.”

Citing the devastating impact on monarchs, NRDC earlier this year filed an emergency petition with EPA to restrict glyphosate, which has soared ten-fold in use since biotech giant Monsanto’s introduction of glyphosate-resistant “Roundup Ready” crops in the 1990s. These crops have been widely adopted and as a result, farmers can drench their fields with the weed killer, in the process destroying vast amounts of native milkweed, the only food that monarch larvae can eat.

The heavy use over the years has resulted in the rise of glyphosate-resistant “super weeds” (not including milkweed, however). Chemical maker Dow AgroSciences responded by developing new corn and soybeans resistant to both glyphosate and 2,4-D. The Agriculture Department predicts Enlist Duo could result in as much as a six-fold increase in the use of 2,4-D, a herbicide developed in the 1940s that has been linked to health impacts in humans, including decreased fertility, birth defects and thyroid problems. Dow won approval to use Enlist Duo over more of the growing season than has been authorized for 2,4-D alone, which could mean wider human exposure.

“Because of its documented impacts on the thyroid, a critical organ for brain development, infants and children are at especially high risk from adverse impacts of 2,4-D exposure,” said Kristi Pullen, an NRDC staff scientist. People can be exposed to 2,4-D in numerous ways, including contaminated food, drinking water, or breast milk (for nursing infants), and through inhalation of pesticide particles released during use on nearby fields.

“Solving one pesticide’s problem by adding another puts us on a completely unsustainable path,” Fallon said. “EPA has started a snowballing effect of more and more powerful pesticides that threaten both wildlife and human health.”

The monarch butterfly, which makes a unique annual migration from Mexico through the Midwest and eastern U.S. to Canada and back, has been in decline since Monsanto introduced transgenic crops. Where once as many as a billion were recorded at their winter refuge in the Mexican mountains, this year only about 33 million returned, a record low. Deforestation and climate change have contributed to the crisis, experts say, but the massive loss of milkweed habitat is the main culprit.

In addition to seeking restrictions on the use of herbicides that destroy milkweed, NRDC is working to develop “butterfly highways” by promoting the planting of milkweed along the monarchs’ migration routes.

For background on monarchs and herbicides, see Sylvia’s blog: http://switchboard.nrdc.org/blogs/sfallon/epa_approves_new_pesticide_com.html

For background on 2,4-D, see Kristi Pullen’s blog: http://switchboard.nrdc.org/blogs/kpullen/question_answered_epa_approves.html