WASHINGTON, June23, 2015 – The International Agency for Research on Cancer (IARC) says that after reviewing the latest available scientific literature, it has classified the herbicide 2,4-D as “possibly carcinogenic to humans,” based on “limited evidence in experimental animals.” The classification was made by a working group of 26 experts from 13 countries, IARC said.

“There is strong evidence that 2,4-D induces oxidative stress, a mechanism that can operate in humans, and moderate evidence that 2,4-D causes immunosuppression, based on in vivo and in vitro studies,” according to IARC, the specialized cancer agency of the World Health Organization. “However, “epidemiological studies did not find strong or consistent increases in NHL (non-Hodgkin lymphoma) or other cancers in relation to 2,4-D exposure,” IARC said in a press release. A summary of IARC’s evaluation can be found in The LANCET Oncology.

IARC noted that since the introduction of 2,4-D, the herbicide has been widely used in agriculture, forestry and urban and residential settings. Occupational exposures to 2,4-D can occur during manufacturing and application, and the general population can be exposed through food, water, dust or residential application, and during spraying.

The Environmental Working Group said the classification “underscores the risk” posed by the U.S. government’s recent approval of 2,4-D for crops made with genetically engineered crops, those made with modified organisms (GMOs).

“We have known for decades that 2,4-D is harmful to the environment and human health, especially for the farmers and farm workers applying these chemicals to crops,” Mary Ellen Kustin, senior policy analyst for EWG, said in a release. “Now that farmers are planting 2,4-D-tolerant GMO crops, this herbicide is slated to explode in use much the way glyphosate did with the first generation of GMO crops. And we know from experience – and basic biology – that weeds will soon grow resistant to these herbicides, making GMO crop growers only more dependent on the next chemical fix.”  

2,4-D is one of the two active ingredients in Enlist Duo, a herbicide marketed by Dow AgroSciences, which the Environmental Protection Agency recently approved for use in 15 states. The other herbicide in Enlist Duo is glyphosate, which the international cancer agency had previously classified as “probably carcinogenic.”

When the EPA approved Enlist Duo for use on GMO crops, the agency did not consider the effects the two defoliants may have on human health when mixed together, EWG said, noting that exposure to both chemicals has separately been linked to non-Hodgkin lymphoma.

An industry task supported by Dow AgroSciences and other companies holding technical 2,4-D registrations said the IARC classification – in its 2B grouping --“is at odds with comprehensive cancer reviews completed by health and safety regulators worldwide.”

“No regulatory agency in the world considers 2,4-D to be a carcinogen,” Dr. Julie Goodman, an epidemiologist, board certified toxicologist, and consultant to the 2,4-D Research Task Force, said in a release. “

“This ranking does not mean that 2,4-D causes or is even likely to cause cancer in people. IARC ranks substances based on potential hazards, but it is important to look at how they are used to assess real-world risk. IARC has assigned its 2B grouping to many other common products including aloe vera, coffee and pickled vegetables." Goodman was an observer throughout the IARC meeting, which took place in France earlier this month.

The task force also said that the studies that IARC considered have previously been reviewed by health and safety regulators around the world.

“Based on published, ongoing and continually updated scientific studies, health and safety authorities in more than 90 countries – including US Environmental Protection Agency, Health Canada, the European Food Safety Authority and the World Health Organization – continue to find that 2,4-D meets modern safety standards,” the task force said.

It also noted that in 2014, the EPA stated: "…[B]ased on weight of evidence consideration of the available data, 2,4-D would be classified as 'Not Likely to be Carcinogenic to Humans.’”

The Agricultural Retailers Association also criticized IARC’s action, saying the agency had once again mislabeled “safe and effective pesticides.”

“Farmers use these proven tools to protect crops from weeds," Daren Coppock, ARA’s president and CEO, said in a release. “They have passed through intense regulatory analysis and have been in use, in the case of 2,4-D, for more than 70 years."

“Ag retailers understand consumers have questions about how their food is produced; unfortunately, IARC's report only serves to cause confusion," Coppock said. "IARC analysis does not actually identify whether a compound is a carcinogen. It should not be the basis to ban useful crop protection tools.”

(This story was updated at 10:40 a.m.)