Just three months after the International Agency for Research on Cancer (IARC) labeled glyphosates as "probably carcinogenic", the group has determined there is a potential link between another weed killer and the disease.

In The Lancet Oncology, a working group from the World Health Organization (WHO) affiliated agency described the chemical 2,4-D as "possibly carcinogenic to humans".

The group's consensus was that there was inadequate evidence in humans for the carcinogenicity of the herbicide, and their meta-analysis of 11 studies showed no association of non-Hodgkin lymphoma with overexposure to the ingredient.

However, a historical cohort study of 2,4-D manufacturing workers gave some indication of increased risk in the highest categories of estimated exposure.

Additionally, the group highlighted mechanistic studies provided "strong evidence" the chemical induced oxidative stress in humans, while in-vivo and in-vitro studies showed there was "moderate evidence" it caused immunosuppression.

The authors also reported the injections of the chemical led increased the incidence of reticulum-cell sarcoma in female mice, while 2,4-D in the diet induced a positive trend in the incidence of rare brain astrocytomas in male rats.

"The Working Group concluded that there was limited evidence in experimental animals for the carcinogenicity of 2,4-D due to methodological concerns regarding the positive studies, although a substantial minority judged the evidence to be sufficient," the group said in The Lancet Oncology.

Dow AgroSciences, which uses the chemical in its crop protection products, slammed the finding and accused the agency for investigating whether a substance "could be" a carcinogen rather than whether it is a carcinogen under "real-world circumstances".

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

"In fact, IARC stated that there is ‘inadequate evidence’ for human carcinogenicity. IARC’s findings on 2,4-D are not the last word even within the WHO, whose JMPR [Joint Meeting on Pesticide Residues] does not consider the handling and use of approved 2,4-D herbicides to pose a cancer risk."

Dow said the IARC's classification was inconsistent with with government findings n nearly 100 countries, including the U.S., Canada, U.K., Germany, France, Japan, Brazil and China.

"IARC has classified only one of about 1,000 agents and activities it has reviewed as 'probably not carcinogenic to humans,'" Cuffe said.

"IARC has classified products we use as potential carcinogens, including coffee, aloe vera, and pickled vegetables."

Ken McCauley, Kansas grower and past president of the National Corn Growers Association, said in the release he was very concerned classifications like this could be misinterpreted by the general public.

"Herbicides like 2,4-D are essential to modern farming, helping us produce more food, control weeds, use less resources and reduce our costs, which ultimately helps the consumer," McCauley said.

"Based on all the studies and government reviews, we believe 2,4-D herbicides are safe or we wouldn't be using them."

Photo: Rama, via Wikimedia Commons

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