IARC: Possible 2,4-D Cancer Link

Classification Unlikely to Affect 2,4-D's Registration, IARC Observer Says

Todd Neeley
By  Todd Neeley , DTN Staff Reporter
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The International Agency for Research on Cancer classified the herbicide 2,4-D as possibly carcinogenic to humans on Tuesday. (Logo courtesy of the World Health Organization's International Agency for Research on Cancer)

OMAHA (DTN) -- The International Agency for Research on Cancer has classified the herbicide 2,4-D as possibly carcinogenic to humans. However, the classification likely will not affect the chemical's registration in the United States or elsewhere, an expert observer of the IARC said during a press conference Tuesday following the announcement.

Dr. Julie Goodman, epidemiologist, board-certified toxicologist, IARC observer and consultant to the 2,4-D Research Task Force, said the public should be reassured by the classification.

"This classification does not mean 2,4-D causes cancer," she said. "It is very reassuring IARC found no association of cancer in humans. Based on the science, if anything, it should be a '3.'"

A "3" classification would mean the chemical is not classifiable as carcinogenic to humans. "This category is used most commonly when the evidence of carcinogenicity is inadequate in humans and inadequate or limited in experimental animals," IARC said in a Q&A on the classification system. "Limited evidence in experimental animals means that the available information suggests a carcinogenic effect but is not conclusive."

A working group of 26 experts from 13 countries meeting in Lyon, France, classified 2,4-D in the '2B' category, meaning its possible link to human cancers is the same as that of coffee and aloe vera, for example.

As a result, Goodman said she doesn't expect the IARC's classification will have any effect on 2,4-D's registration.

The latest IARC classification is the second time in three months the World Health Organization group has taken aim at an agricultural chemical. Back in March, the IARC classified glyphosate as a "probable carcinogen" to humans.

"The herbicide 2,4-D was classified as possibly carcinogenic to humans (Group 2B), based on inadequate evidence in humans and limited evidence in experimental animals," the IARC said in a news release Monday. "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. However, epidemiological studies did not find strong or consistent increases in risk of NHL (non-Hodgkin's lymphoma) or other cancers in relation to 2,4-D exposure."

The chemical is used to control noxious and invasive weeds.

Environmental groups and others have tried to make a connection between the use of 2,4-D today and Agent Orange during the Vietnam War. The component of that jungle herbicide mix connected to health issues of Vietnamese and U.S. soldiers was 2,4,5-T, not 2,4-D. Regulators banned 2,4,5-T decades ago.

New formulations of 2,4-D are the foundation of the latest genetically engineered corn and soybean crops aimed at combatting weeds that have evolved to be resistant to glyphosate. Those and similar seed-herbicide packages, which are just coming to market, have increased the debate over the safety of older, growth-regulator herbicides.


Dow AgroSciences said in a news release Tuesday that the IARC's latest classification runs contrary to the body of science.

"The classification of the herbicide 2,4-D by the International Agency for Research on Cancer is inconsistent with government findings in nearly 100 countries, including the U.S., Canada, U.K., Germany, France, Japan, Brazil and China, which have for decades affirmed the safety of 2,4-D when used according to approved labeling," Dow said in the news release. "Government reviews were based on rigorous hazard and risk evaluations of more than 4,000 scientific studies. In sharp contrast to the government reviews, IARC, an agency of the United Nations World Health Organization, reviews an incomplete set of information to focus solely on whether a substance or activity could be a carcinogen, not whether it is a carcinogen when used under real-world circumstances.

"The IARC classification, which is unchanged from the previous IARC review of chlorophenoxy herbicides, should not be mischaracterized in ways that are misleading and harmful to farmers and consumers."

John Cuffe, global regulatory sciences and regulatory affairs at Dow AgroSciences, said in a news release the IARC's view runs contrary to all other evaluations conducted.

"IARC's findings on 2,4-D are not the last word even within the WHO, whose JMPR (Joint FAO-WHO Meeting on Pesticide Residues) does not consider the handling and use of approved 2,4-D herbicides to pose a cancer risk," he said.

An October 2014 review of health and safety data by the U.S. Environmental Protection Agency affirmed 2,4-D is not a carcinogen. Health Canada in 2009 found the chemical does not pose a cancer risk and can be used safely by following label directions.

Also in 2014, the European Food Safety Authority concluded it was unlikely 2,4-D posed a carcinogenic risk.

"IARC has classified only one of about 1,000 agents and activities it has reviewed as 'probably not carcinogenic to humans,'" Cuffe said in the news release. "IARC has classified products we use as potential carcinogens, including coffee, aloe vera and pickled vegetables."

Ken McCauley, Kansas farmer and past president of the National Corn Growers Association, said in the Dow news release that he's concerned the latest classification will hurt the way the general public views agriculture.

"Herbicides like 2,4-D are essential to modern farming, helping us produce more food, control weeds, use less resources and reduce our costs, which ultimately helps the consumer," he said.

Todd Neeley can be reached at todd.neeley@dtn.com

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