A New Weed Killer Could Be More Toxic Than Previously Thought

New questions have been raised about Enlist Duo, a herbicide for corn and soybeans made by Dow AgroSciences

Tomassereda / Getty Images

About a year ago, the U.S. Environmental Protection Agency approved a new weed killer for farmers called Enlist Duo, declaring it "safe for the environment, including endangered species." Now, the chemical's safe status is not so clear.

Last week, the EPA motioned to revoke registration of Enlist Duo herbicide after learning that its "two active ingredients could result in greater toxicity to non-target plants," or plants that aren't weeds, according to a statement. The product was developed by Dow AgroSciences, a subsidiary of Dow Chemical, which had sales of $7.3 billion in 2014.

"EPA cannot be sure, without a full analysis of the new information, that the current registration does not cause unreasonable effects to the environment," the agency stated in a court document. The court must now rule on the EPA's proposal.

Dow AgroSciences' herbicide is registered for use in 15 states and had a limited launch in the U.S. and Canada this year (it is waiting for China to approve Enlist corn and soybean for import before fully commercializing). Enlist Duo remains registered for use at this time and will only be vacated if the court orders it, a Dow spokesperson said in an email to BuzzFeed News, "an action that would be unprecedented."

Dow said in a press release it "is working quickly with EPA to provide assurances that our product’s conditions of registered use will continue to protect the environment," and believes it can resolve the issue in time for the 2016 crop growing season.

The two active ingredients in Enlist herbicide are glyphosate and 2,4-D.

Like other agricultural products in the market, Enlist is a seed-and-herbicide system. The Enlist Duo weedkiller was one part; the other was the company's genetically modified Enlist Duo corn and soybean crops, which were engineered to survive exposure to the chemicals as they killed "tough weed species."

Such herbicide-resistant crops are a huge business and Enlist stands to be a big new product. In 2015, about 89% of all corn planted and 94% of all soy planted in the U.S. were herbicide-tolerant, according to the U.S. Department of Agriculture. GMO crops have been available in the U.S. only since the 1990s.

The glyphosate in Enlist Duo is already widely used in weedkillers like Monsanto's Roundup. However, it is becoming less effective as weeds resistant to glyphosate grew in their place (herbicides are not know to cause mutations, however).

To compete with Roundup, Dow AgroSciences developed the Enlist system. It combined glyphosate with 2,4-D — a widely-used but possibly carcinogenic herbicide, according to the World Health Organization — and genetically engineered seeds that could withstand the effects of the new weedkiller.

Before last week's motion, conservation groups had sued the EPA for failing to consider the impact of Enlist on endangered species (like the whooping crane and Indiana bat) in violation of the Endangered Species Act.

Brendan Smialowski / AFP / Getty Images

Whooping cranes


It wasn't until Dow claimed Enlist had “synergistic herbicidal weed control” properties in a patent application, that it got into trouble.

In plainer terms, this means combining the two ingredients may result in greater toxicity than when applied separately, which was not originally disclosed to the EPA.

This triggered the agency to ask the court to vacate and remand the registration of Enlist pesticide. "Dow had not provided this information to EPA prior to EPA issuing the Enlist Duo registration. EPA has not yet completed its review of the new information," the agency said in a statement last week.

Dow said in an email that after review, "the entire data set indicates that synergism does not exist" in the final formulation of Enlist Duo, and that it won't harm "non-target threatened or endangered plant species" if it's applied at the at the labeled use rates.

The review could result in EPA imposing expanded buffer zones to protect other nearby plants, including endangered species.