A Canadian toxicologist says the World Health Organization made a critical scientific error in its decision to classify glyphosate as a probable carcinogen.
A panel of experts with the WHO’s International Agency for Research on Cancer released a report March 20 on five pesticides, including glyphosate, the most widely used herbicide in the world.
After reviewing the scientific literature, the experts classified glyphosate, which is the active ingredient in Roundup, as Group 2A: probably carcinogenic to humans.
In a brief statement explaining the new designation, the scientists cited a number of research papers, such as a study on rural Colombians who were exposed to a spray of Roundup.
IARC said the study demonstrated that glyphosate can cause genotoxicity, or DNA damage, and cause cellular mutations that may result in cancer.
“One study (of) community residents reported increases in blood markers of chromosomal damage (micronuclei) after glyphosate formulations were sprayed nearby,” the report said.
Keith Solomon, a University of Guelph professor emeritus and a globally recognized authority on pesticides, said the conclusion is “totally wrong.”
Solomon should know because he wrote the Colombian study.
“They stated there was evidence of genotoxicity and they quoted one paper to support that statement,” Solomon said.
“There’s no evidence that glyphosate is genotoxic.”
Solomon and an international team of scientists conducted a study on glyphosate in Colombia in the early 2000s as part of a Colombian government program to destroy illegal coca fields in the countryside.
Coca is used to produce cocaine.
Solomon and his colleagues were asked to do a risk assessment of the human health and environmental risks associated with the coca eradication program.
The scientists took blood samples from Colombian volunteers who were exposed to glyphosate when government planes sprayed coca fields.
To assess the likelihood of DNA damage, they tested for the presence of “genotoxicity biomarkers” in the volunteers’ blood, known as micronuclei.
“All we were interested in was, does the spraying of the coca cause increased micronuclei,” Solomon said.
The scientists took blood samples four months later because that’s approximately how long it would take to replace the white blood cells exposed to glyphosate. Solomon and his team then compared the results to a group of rural residents who weren’t exposed to the airplane spray.
“When we looked at the differences in the micronuclei between those two groups, we found no difference,” he said.
“They (IARC) got this totally wrong. They said the study showed there was a relationship…. It’s certainly a different conclusion than the one we came to.”
Solomon isn’t the only scientist to speak out against the IARC decision. A number of toxicologists and pesticide experts have criticized the United Nations agency for a lack of balance.
They said the report ignored an abundance of papers showing that glyphosate is not carcinogenic. Instead, it focused on a few marginal studies showing that glyphosate promotes tumours in mice and epidemiological studies linking the herbicide to non-Hodgkin’s lymphoma.
Aaron Blair, a scientist emeritus at the National Cancer Institute who led the IARC group of 17 experts, told Reuters that the classification is scientifically appropriate.
He said there might be hundreds of studies on glyphosate, but concern about the herbicide are mounting.
“We looked at, ‘is there evidence that glyphosate causes cancer?’ and the answer is ‘probably.’ That is different than yes.”
Solomon said the conclusion contradicts scientific consensus. National regulatory agencies around the globe have evaluated glyphosate and concluded the weed killer is not a human health risk. As an example, a recent German report concluded that glyphosate is probably not a carcinogen.
Solomon said he would reserve final judgment until IARC publishes a comprehensive report on its decision, which will be released in about a year.
The International Agency for Research on Cancer classifies substances and agents into five groups according to cancer risk:
- Group 1: Carcinogenic to humans.
- Group 2A: Probably carcinogenic to humans.
- Group 2B: Possibly carcinogenic to humans.
- Group 3: Not classifiable as to its carcinogenicity to humans.
- Group 4: Probably not carcinogenic to humans.
Examples of agents in Group 1 are asbestos, alcoholic beverages and working as a painter.
Examples of agents in Group 2A are working as a hair stylist and burning wood in a fireplace.