The active ingredient in Roundup, one of the world’s most popular weed-killers — and the most commonly used one in the United States — has been declared a “probable carcinogen” by the World Health Organization. The International Agency for Research on Cancer, an arm of the WHO, released the results of its review of five herbicides and pesticides on Friday.
The French-based agency announced its assessment of glyphosate after convening a meeting this month of 17 cancer experts from 11 countries. They looked at the available scientific evidence on five different pesticides, including glyphosate, to determine whether to classify them as carcinogens. Carcinogens are substances that can lead to cancer under certain levels of exposure.
IARC ranks cancer-causing agents on four levels: known carcinogens, probably or possible carcinogens, not classifiable and probably not carcinogenic. The herbicide glyphosate, the active ingredient in Roundup, was classified by IARC as “probably carcinogenic to humans.”
Glyphosate caused DNA and chromosomal damage in mammals, and in human and animal cells studied in laboratories, the report said. Studies of workers who had been exposed to the chemical in the U.S. Canada, and Sweden found “increased risks for non-Hodgkin lymphoma that persisted after adjustment for other pesticides,” the report said. “In addition, there is convincing evidence that glyphosate also can cause cancer in laboratory animals.”
But the classification is not binding, said the IARC. “It remains the responsibility of individual governments and other international organizations to recommend regulations, legislation or public health intervention,” the agency said in a statement. According to the Associated Press, the United States Environmental Protection Agency said it would consider the IARC’s evaluation.
The IARC did clarify that the new ruling is mostly directed at the industrial use of the herbicide, and that use by home gardeners does not fall under the same classification. Glyphosate, employed in more than 750 herbicide products, is usually used on crops, including corn and soybeans, that are genetically modified to survive it. The herbicide has been detected in food water, and in the air after it has been sprayed, according to the IARC report. “Its use has increased sharply with the development of genetically modified glyphosate-resistant crop varieties,” the report said.
A summary of the agency’s findings was published in the British journal Lancet Oncology Friday.
The determination is sure to alarm the agro-chemical industry and particularly Monsanto, the agribusiness giant that is the leading producer of glyphosate. Worldwide annual sales of the chemical are estimated at $6 billion. The company put out its own statement Friday objecting to the findings: “All labeled uses of glyphosate are safe for human health,” said Monsanto’s Phil Miller, global head of regulatory and government affairs.
“We don’t know how IARC could reach a conclusion that is such a dramatic departure from the conclusion reached by all regulatory agencies around the globe,” said Miller. Monsanto requested an urgent meeting with the World Health Organization to clarify the scientific basis of the ruling.
Glyphosate was originally used as a descaling agent to clean out mineral deposits from pipes because of its ability to avidly bind to heavy metals. The chemical bonds to arsenic, cadmium and other heavy metals found in groundwater.
Scientists and farmers elsewhere have raised other concerns over glyphosate and tried to ban its use.
Channa Jayasumana, with Rajarata University of Sri Lanka, published a study in the International Journal of Environmental Research and Public Health in 2014 on a possible link between glyphosate and chronic kidney disease in farmworkers. His research found that excessive heat and dehydration may weaken the workers’ bodies, making them more susceptible to pesticides and heavy metals, which can lead to kidney disease.
Based on that research, the Sri Lankan government moved to ban glyphosate in spring of 2014. But Monsanto raised objections to the report’s findings, and the ban was lifted. The chemical was, and continues to be, widely used on farms in the country.
The research also suggested a link between glyphosate and a mysterious kidney disease that has killed thousands of farmworkers in Central America. At least 20,000 farm workers have died of chronic kidney disease in Nicaragua in the last two decades, The Guardian reported in February. Researchers who have studied the disease in Central America say that it mainly affects agricultural laborers working under conditions of excessive heat and dehydration, but other factors, including pesticides, may play a role.