The health agency says the effects on humans are inconclusive
In a decision that angered many toxicologists and pesticide experts, the World Health Organization has classified 2,4-D as an agent that “possibly” causes cancer in humans.
The International Agency for Research on Cancer (IARC), a division of the WHO that identifies causes of cancer so preventive action can be taken, reviewed research on 2,4-D at an early June meeting in France.
In late June, IARC members published a summary of their findings, which concluded that 2,4-D, the world’s oldest herbicide, is “possibly” carcinogenic because:
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- There was “limited evidence” that 2,4-D causes cancer in experimental animals.
- There was strong evidence that 2,4-D causes oxidative stress, an im-balance in the production of free radicals and the body’s ability to neutralize the free radicals.
- There was “inadequate evidence” that 2,4-D causes cancer in humans.
IARC completed a similar review of glyphosate in March, which concluded that glyphosate, the most popular herbicide in the world, “probably” causes cancer in humans.
DowAgrosciences, which manufactures 2,4-D, said the IARC decision is inconsistent with decades of research.
“No herbicide has been more thoroughly studied and no national regulatory body in the world considers 2,4-D a carcinogen,” said John Cuffe, global regulatory sciences and regulatory affairs at Dow AgroSciences.
Julie Goodman, an epidemiologist and toxicologist who works for the 2,4-D Task Force, which is funded by Dow and other companies that hold 2,4-D registrations, said IARC uses a hazard assessment rather than a risk assessment.
A risk assessment accounts for real world exposures.
“What’s important is that when you do a risk assessment, there is absolutely no indication that there is a cancer risk to humans,” she said.
“This has been done by over 90 health and safety regulatory agencies around the world, and none of them has concluded that 2,4-D is carcinogenic.”
The IARC classification could be significant for public perception because Dow is expecting farmers to use much more 2,4-D in coming years.
The company has developed and has registered Enlist, a new weed control system for corn and soybeans. The genetically modified technology provides “stacked” herbicide tolerance, which allows soybeans and corn to be sprayed with 2,4-D and glyphosate.
Dow has also registered Enlist Duo, a new formulation of 2,4-D and glyphosate, which is part of the Enlist weed control system.
