Once best known as half of the formula for the Vietnam War defoliant known as Agent Orange, 2,4-D is now widely used as an agricultural herbicide—and it may cause cancer in humans, says the World Health Organization.
According to WHO’s International Agency for Research on Cancer (IARC), recent studies on the weed killer 2,4-dichlorophenoxyacetic acid led the organization to list it as “possibly carcinogenic to humans”, which is a step below the more definitive “probably carcinogenic” category, but two steps above the “probably not carcinogenic” category, reports Reuters.
The announcement comes just months after the IARC classified glyphosate—the top selling herbicide better known as Monsanto’s Roundup—as “probably carcinogenic to humans.”
But that doesn’t mean 2,4-D is safer than glyphosate. According to Reuters, IARC said it only decided on the “possibly” classification because there was “inadequate evidence in humans and limited evidence in experimental animals” of ties between 2,4-D and cancer. IARC pointed to epidemiological studies that held “strong evidence that 2,4-D induces oxidative stress... and moderate evidence that 2,4-D causes immunosuppression,” noted Reuters.
However, IARC said, “epidemiological studies did not find strong or consistent increases in risk of NHL (non-Hodgkin lymphoma) or other cancers in relation to 2,4-D exposure."
2,4-D is of particular concern, as it is now being employed in combination with or as a replacement for glyphosate in areas where some weeds have developed resistance to glyphosate.
Dow AgroSciences is using a combination of 2,4-D and glyphosate in an herbicide called Enlist Duo, approved by the EPA for use in the U.S. last year. It’s intended for use on seeds genetically modified to withstand heavy applications of the dual herbicides in efforts to kill glyphosate-resistant weeds. But environmental and human health advocacy groups say it's just a matter of time before crops also develop resistance to 2,4-D (and other herbicides). The answer, they say, isn't in heavier applications of the herbicides or using more chemicals.
“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 the Environmental Working Group said in statement. “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.”
“The EPA’s decision means that millions of Americans will be exposed to herbicides with known human health hazards in coming years,” Gary Hirshberg, chairman of the Just Label It campaign and chairman and co-founder of Stonyfield Farm said in a statement. “Unless GMO products are labeled, consumers have no way to know if ingredients in the food they buy were grown in a way that promoted use of these herbicides.”
“Because of the approval of Enlist Duo for use on GMO crops, we expect the use of 2,4-D to increase up to seven-fold by the end of the decade,” said Kustin. “Since the federal government has failed to curb the overreliance of glyphosate and 2,4-D, mandatory GMO labeling is essential so that consumers can know whether they are buying GMO foods that rely heavily on these toxic herbicides.”
Dow and other chemical companies that produce herbicides maintain that weedkillers, including 2,4-D, are safe and effective chemical tools for use in agriculture.
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herbicide spraying image via Shutterstock