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International Agency Deems 2,4-D A Possible Human Carcinogen

Pesticides: Chemical makers dispute the categorization for widely used herbicide

by Britt E. Erickson
June 26, 2015 | A version of this story appeared in Volume 93, Issue 26

The widely used herbicide 2,4-dichlorophenoxyacetic acid (2,4-D) is “possibly carcinogenic to humans,” concludes the World Health Organization’s International Agency for Research on Cancer (IARC).

IARC released its determination this week, based on “strong evidence that 2,4-D induces oxidative stress,” a condition that can lead to chronic inflammation and ultimately cancer. IARC says there is “inadequate evidence” to fully deem 2,4-D a human carcinogen and “limited evidence” of carcinogenicity in laboratory animals.

Chemical manufacturers are strongly disputing the “possibly” classification, saying it is inconsistent with government findings in nearly 100 countries, including the U.S.

“No herbicide has been more thoroughly studied and no national regulatory body in the world considers 2,4-D a carcinogen,” says John Cuffe, global regulatory sciences and regulatory affairs leader at Dow AgroSciences.

The company won approval late last year to market its Enlist Duo herbicide—a mixture of 2,4-D and glyphosate—in the U.S. Many environmental groups are concerned this will cause use of 2,4-D to skyrocket.

Even before IARC’s evaluation, the Natural Resources Defense Council and other environmental organizations filed lawsuits against the Environmental Protection Agency for approving Enlist Duo. They claim the agency did not adequately study the mixture’s effects on human health and endangered species.


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