2,4-D Deemed a “Possible” Carcinogen, But Without Clear Evidence

(Debra Murphy/RealAgriculture)

The World Health Organization’s International Agency for Research on Cancer has moved to categorize 2,4-D as a “possible” carcinogen, while simultaneously stating clearly it doesn’t have sufficient evidence to say the commonly used herbicide causes cancer in humans.

The decision is drawing criticism from companies that sell products containing 2,4-D and agricultural groups, as the risk associated with the weed-killer may be misinterpreted.

In sharing the 2,4-D assessment on June 23rd, the IARC said it found inadequate evidence linking 2,4-D with cancer in humans and limited evidence in experimental animals. “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 non-Hodgkin’s lymphoma or other cancers in relation to 2,4-D exposure,” noted the IARC.

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Regulatory agencies around the world, including the U.S. Environmental Protection Agency, Health Canada, and the European Food Safety Authority, still consider 2,4-D to be safe to use if applied properly.

“This ranking does not mean that 2,4-D causes or is even likely to cause cancer in people,” said Julie Goodman, an epidemiologist, toxicologist and consultant with the 2,4-D Research Task Force, a group of companies that hold 2,4-D registrations. “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.”

Dow AgroSciences, one of the members of the 2,4-D Research Task Force,  said the IARC classification “is inconsistent with government findings in nearly 100 countries.” The company noted the IARC focuses solely on whether a substance or activity could be a carcinogen, not whether it is a carcinogen in reality, adding the classification “should not be mischaracterized in ways that are misleading and harmful to farmers and consumers.”

“No other herbicide in the world has been more thoroughly studied than 2,4-D. Every health and safety regulator in the world, including Health Canada, has concluded that 2,4-D does not pose an unacceptable risk to human health,” says Ted Menzies, president of CropLife Canada.

IARC ranks things based on their potential hazard, not the actual risk that something will cause cancer. IARC panelist, Aaron Blair, clarified the limitations of IARC’s assessment by stating, “We look at ‘could it potentially’ cause cancer, but we don’t look at whether it ‘will or is likely to’ cause cancer in real world use.”

“Every pest control product registered in Canada goes through a thorough scientific, evidence-based risk assessment, which assesses any hazards associated with the product and determines the relevant risks to users, consumers and the environment,” says Menzies.

The 2,4-D classification coincided with the classification of insecticides DDT and lindane as “probable” carcinogens. It also follows the IARC’s controversial decision to apply the more definitive “probable” label to glyphosate back in March.

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