2,4-D plays an important role in protecting crops, improving agricultural yields, reducing the risk of invasive and noxious species, protecting wildlife habitats, and protecting infrastructure. While improving food production and reducing food costs are what 2,4-D is best known for, there are also environmental benefits that include decreased soil erosion and decreased greenhouse gases through reduced soil tillage.

It is used by farmers to maximize crop growth and produce more food per acre, public works operators to improve safety along highways and rail lines, foresters to control competing growth to new seedlings, and homeowners to manage weeds on their lawns.

70 Years of Ongoing Research and Review

There have been more than seven decades of ongoing and continuous research on 2,4‑D. It is the world’s most studied chemical, totalling more than 40,000 studies and allowing it to be used in over 90 countries with more than 100 label uses. 2,4-D is such a well-known substance that scientists use it as a standard to judge the performance of their own evaluation methods and practices.

Based on continually updated scientific studies, health and safety authorities around the world find that 2,4-D meets modern safety standards. Regulators such as the US Environmental Protection Agency, Health Canada, and European Food Safety Authority are just some of the 90+ organizations that join the WHO/FAO in stating 2,4-D can be used safely according to label instructions.

Regulatory authorities charged with protection of public health can typically spend more than 15 years conducting thorough, risk-based evaluations of all of the data. For each review, regulators require new studies be conducted, adding to the impressive amounts of studies conducted on 2,4-D.

What is IARC?

The International Agency for Research on Cancer (IARC) creates Working Groups to periodically consider lifestyles, workplaces, and compounds that may have carcinogenicity potential. From June 2nd to 9th, the IARC met to classify 2,4-D, DDT, and lindane. IARC is an agency under the World Health Organization (WHO) but is not responsible for regulating pesticides. The body responsible for conducting risk assessments of pesticides for regulatory purposes is the Joint FAO/WHO Meeting on Pesticide Residues (JMPR).

IARC Working Groups are comprised of academics and researchers with diverse backgrounds who meet to discuss a selection of published literature about several compounds over the course of seven days. The IARC Working Group does not conduct any new research, but rather reviews a selection of studies previously reviewed by health and safety regulators, then scores the compounds.

IARC still retains what is called a hazard-based assessment to chemicals. What the ‘hazard-based’ approach means is they simply look for the potential cause and effect in the absence of any consideration of dose and exposure. They acknowledge, in these hazard-based approaches, that they do ignore dose and exposure, and if exposure was taken into consideration, it might mean the chemical isn’t presenting the risk they say from their hazard-only classification.

IARC’s Conclusion of 2,4-D

After specifically examining many health studies, the IARC Working Group concluded the body of literature on 2,4-D shows “inadequate evidence of carcinogenicity” in humans.

In considering animal studies conducted at doses thousands of times higher than actual 2,4-D exposure, IARC concluded there was “limited evidence of carcinogenicity” in animals. In voting, the IARC Working Group classified the potential hazard as a 2B – “possible” human carcinogen. Other substances in this group include aloe vera, coffee, and pickled vegetables.

Exposure and dosage are critical when determining if a substance is a human carcinogen. For example, IARC acknowledges that if exposure were factored into the equation, a different result could be reached. Aaron Blair, a previous IARC Panel Chair explained:

“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.”

Fortunately, the US EPA does consider real world use. In considering the same data last year after a much longer review than IARC’s seven day glimpse at the data, it determined: “…[B]ased on weight of evidence consideration of the available data, 2,4-D would be classified as ‘Not Likely to be Carcinogenic to Humans’.”