A widely used farm chemical that is a key ingredient in a new herbicide developed by Dow AgroSciences “possibly” causes cancer in humans, a World Health Organisation research unit has determined.
The classification of the weed killer, 2,4-dichlorophenoxyacetic acid, known as 2,4-D, was made by the WHO’s International Agency for Research on Cancer (IARC).
The IARC said it reviewed the latest scientific literature and decided to classify 2,4-D as “possibly carcinogenic to humans”. That is a step below the more definitive “probably carcinogenic” category but two steps above the “probably not carcinogenic” category.
IARC’s findings on 2,4-D have been awaited by environmental and consumer groups that are lobbying US regulators to tightly restrict its use, as well as by farm groups and others that defend 2,4-D as an important agent in food production that does not need more restrictions. Since its introduction in 1945, 2,4-D has been widely used to control weeds in agriculture, forestry, and urban and residential settings.
In March, IARC said it had found another popular herbicide –glyphosate – was “probably carcinogenic to humans”. Glyphosate is the world’s most widely used weed killer. IARC classifications do not carry regulatory requirements but can influence regulators, lawmakers and the public. Following the glyphosate classification, some companies and government officials moved to limit glyphosate use.
IARC said it decided on the “possibly carcinogenic” classification because there was “inadequate evidence in humans and limited evidence in experimental animals” of ties between 2,4-D and cancer. It said that epidemiological studies provided “strong evidence that 2,4-D induces oxidative stress... and moderate evidence that 2,4-D causes immunosuppression”.
However, “epidemiological studies did not find strong or consistent increases in risk of non-Hodgkin lymphoma (NHL) or other cancers in relation to 2,4-D exposure”.
Some critics of 2,4-D had expected IARC to classify 2,4-D as “probably” cancer-causing. But the classification it did receive still underscores the dangers of 2,4-D and the need for a “much more rigorous regulatory process,” the Pesticide Action Network North America said in a statement.