In a determination that could have far-reaching implications for the agro-chemical giants like Dow Chemical and Monsanto, the research arm of the World Health Organization has declared that glyphosate—the key ingredient of widely-used herbicides such as Roundup—should now be categorized as a “probable carcinogen” for humans.

In a report published on Friday in The Lancet Oncology medical journal, the International Agency for Research on Cancer (IARC), based in France, announced its findings after a meeting of 17 oncology experts from 11 countries met to review the available scientific research exploring the connection between glyphosate, as well as several organophosphate insecticides, and various human cancers.

“Consumers have the right to know how their food is grown and whether their food dollars are driving up the use of a probable carcinogen.” —Ken Cook, EWGAccording to IARC, glyphosate is used in more than 750 different herbicide products and its use has been detected in the air during spraying, in water and in food. The panel of experts concluded that “limited evidence” exists to show the herbicide can cause non-Hodgkins lymphoma in humans and additional “convincing evidence” that it can cause other forms of cancer in both rats and mice. Researchers noted that glyphosate has been found in the blood and urine of agricultural workers, showing the chemical has been absorbed by the bodies of those who work most with it.

As the Associated Press explained, the research agency—which provides academic and scientific research FOR the WHO—has four levels of risks for possible cancer-causing agents: known carcinogens, probable or possible carcinogens, not classifiable and probably not carcinogenic. Glyphosate now falls in the second level of concern.

Though Monsanto immediately and predictably rejected the findings of the IARC, scientists who have long-warned of the public health impacts and wider dangers of glyphosate say the announcement should add urgency to the debate about whether or not such products should be allowed to dominate the world’s agricultural systems.

“The widespread adoption of GMO corn and soybeans has led to an explosion in the use of glyphosate – a main ingredient in Monsanto’s Roundup and Dow’s Enlist Duo,” said Ken Cook, president and co-founder of the Environmental Working Group. “Consumers have the right to know how their food is grown and whether their food dollars are driving up the use of a probable carcinogen.”

Emily Marquez, Ph.D., a staff scientist at the Pesticide Action Network, in a statement on Monday, said, “Given glyphosate’s widespread usage with crops genetically engineered to tolerate herbicides, IARC’s finding comes none too soon.”

“This increasingly dangerous pesticide treadmill calls into question the logic of genetically engineered herbicide technologies that rapidly lose their utility to farmers and put human health at risk.” —Emily Marquez, Pesticide Action Network

Though the IARC’s finding have no regulatory bearing on the U.S. Environmental Protection Agency determinations about glyphosates and the other compounds studied, they do add weight to the body of evidence showing how harmful such chemicals are.

According to Marquez and her colleagues at PAN, since Monsanto’s signature “RoundUp Ready” corn and soy crops were introduced in 1996, more than 500 million additional pounds of glyphosate and other herbicides have been used in the United States.