The World Health Organization, the U.N.'s public health agency, said on Friday that glyphosate, an herbicide widely used on genetically modified crops such as corn and soybeans, likely causes cancer.

Released by the WHO's cancer arm, the International Agency for Research on Cancer (IARC), the report presents the findings of 17 biochemists, toxicologists, epidemiologists, molecular biologists and environmental scientists from 11 countries, who evaluated the carcinogenicity of glyphosate as well as the insecticides tetrachlorvinphos, parathion, malathion and diazinon. A summary of the evaluation has been published online by the Lancet Oncology.

Glyphosate, which is the active ingredient in Monsanto's popular home and garden weed killer Roundup, was classified by IARC as "probably carcinogenic to humans." The scientists found that the chemical "induced DNA and chromosomal damage in mammals, and in human and animal cells in vitro." They concluded that there was "sufficient evidence" that the herbicide causes cancer in non-human animals and "limited evidence" that it also causes non-Hodgkin's lymphoma in humans.

The agency, headquartered in Lyon, France, said glyphosate "has been detected in the air during spraying, in water and in food," noting that primary exposure to the chemical is through diet, home use and living near sprayed areas.

The researchers reviewed studies on the effect of the herbicide on healthy male workers in the agricultural and forestry sectors since 2001. They also highlighted a study of community residents that reported "increases in blood markers of chromosomal damage after glyphosate formulations were sprayed nearby."

Glyphosate is part of a group of biochemicals called organophosphates, which includes insecticides and nerve agents like sarin that irreversibly inactivate acetylcholinesterase, an enzyme essential for nervous system functionality in insects, humans and many other animals.

Monsanto released a statement Friday disagreeing with IARC's findings.

"There is no new research or data that was used; the most relevant, scientific data was excluded from review; the conclusion is not supported by scientific data; and there is no link between glyphosate and an increase in cancer when the full data set is included in a rigorous review," said Philip Miller, Monsanto’s vice president of global regulatory 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."

On Monday, Monsanto’s chief technology officer Robert Fraley followed up with an encapsulation of the biotech giant's feelings on the matter: "We are outraged with this assessment."

Evidence of health risks mounting; so is revenue

While glyphosate may be most known among consumers for being the key ingredient in Roundup, the IARC report noted that it is also used in more than 750 different agricultural, industrial and residential products.

Its wide range of applications includes weed control in forests, rivers, lakes, parks, grass pastures, lawns, turf, gardens, greenhouses, fruit orchards, vineyards and olive groves. In the U.S., its largest agricultural use is on hay/pasture, soybeans and field corn. According to IARC, glyphosate "currently has the highest global production volume of all herbicides."

The herbicidal properties of glyphosate were first discovered and marketed by Monsanto in 1974. In 2001, it became the most used pesticide in the U.S. agricultural market and the second most used pesticide in the home and garden market.

While the debate surrounding its effect on health continues, sales of glyphosate are chugging right along, no doubt aided by Monsanto's release of Roundup Ready, genetically modified crops that are resistant to the herbicide. In 2012, the global glyphosate market was valued at $5.46 billion. By 2019, it is expected to swell to $8.79 billion.

While glyphosate-driven revenues continue to grow, so does evidence of the chemical's health risks. The IARC assessment builds on existing studies indicating the potential health hazards of glyphosate, including cancer and renal disease.

A 2013 paper published in the journal Food and Chemical Toxicology found that glyphosate induces the growth of human breast cancer cells. The environmental toxicologists at Bangkok's Chulabhorn Graduate Institute who conducted the study concluded "low and environmentally relevant concentrations of glyphosate possessed estrogenic activity."

In February 2014, the International Journal of Environmental Research and Public Health published a paper by researchers from Rajarata University in Sri Lanka and California State University in Long Beach that investigated the potential role of glyphosate in Sri Lanka's chronic kidney disease (CKD) epidemic. Though glyphosate was ruled out as the lone causative factor, the authors said that when mixed with hard water or metals like arsenic and cadmium, the chemical "seems to have acquired the ability to destroy the renal tissues of thousands of farmers."

One thing is certain: It will be decades before scientists fully comprehend all the things that can go wrong when humans and wildlife are exposed to glyphosate. A 2014 study published in the Journal of Organic Systems found a stunning correlation between the rise of glyphosate-sprayed GMO crops and 22 diseases.

No agreement

IARC's conclusions contradict the official stance of the EPA, which maintains that glyphosate is safe. The agency originally classified it as "possibly carcinogenic to humans" in 1985, based on a study in which mice developed tumors after exposure. Then in 1991, the EPA changed its classification to "evidence of non-carcinogenicity" after a re-evaluation of that study.

"EPA's worst case risk assessment of glyphosate's many registered food uses concludes that human dietary exposure and risk are minimal," the agency said in a 1993 glyphosate fact sheet. "Existing and proposed tolerances have been reassessed, and no significant changes are needed to protect the public."

Some governments aren't waiting for another study. In September 2013, the legislature of El Salvador approved a glyphosate ban, following the deaths of thousands of agricultural workers along Central America's Pacific Coast.

It only took a few weeks after the 2014 glyphosate paper on Sri Lanka's CKD epidemic was published for Sri Lanka to ban glyphosate.

Also last year, the Dutch parliament announced a federal ban on non-commercial sales of glyphosate that went into effect in 2015.

"In garden centers Roundup is promoted as harmless, but unsuspecting customers have no idea what the risks of this product are," said Dutch MP Esther Ouwehand, who brought the motion to Holland's legislative body. "Especially children are sensitive to toxic substances and should therefore not be exposed to it."

Monsanto and EPA: Perfect together, not for kids

So Dutch kids gained some protection from glyphosate. What about in the United States?

In February 2012, the EPA said in its Budget in Brief that it would "continue to emphasize the protection of potentially sensitive groups, such as children," asserting that the federal pesticide program would "minimize exposure to pesticides [and] maintain a safe and affordable food supply."

Just three months later, on May 2, 2012, Monsanto challenged this mandate and filed a petition with the EPA to increase the allowable amount of glyphosate on oilseed, sunflowers and a number of fruits and vegetables, including grapes, cranberries, strawberries, carrots, sweet potatoes and citrus fruits.

Environmental and public health activists rallied against the request. The nonprofit Food & Water Watch responded with its own petition with more than 33,000 signatures, saying: "The EPA is failing to protect human health and the environment by neglecting to regulate the excessive use of herbicides; instead, it is just changing its own rules to allow the irresponsible and potentially dangerous applications to continue. Tolerance levels are put in place to protect human health—not the biotech industry."

One might think that, given the research pointing to health problems tied to glyphosate exposure, the EPA would take the time necessary to perform an extensive and thorough evaluation before amending the law. But that didn’t happen.

Instead of increasing protections against glyphosate's potential negative health effects, the EPA went in the opposite direction. On May 1, 2013, it approved Monsanto's request to increase glyphosate tolerance levels, in effect letting more of the chemical enter the American food supply.

The coziness between the EPA and Monsanto is concerning. Just six weeks after the EPA's pro-Monsanto ruling, the Gulf of Mexico Program awarded Monsanto with the First Place 2013 Gulf Guardian Award. This program—a non-regulatory consortium of state and federal government agencies and corporate representatives from the agricultural and fishing industries—is underwritten by, you guessed it—the EPA.

It is difficult to understand how Monsanto can be considered a "Gulf Guardian" considering the company's central role in the acidification of the Gulf: Synthetic nitrogen fertilizer, the major cause of the more than 400 oceanic dead zones around the world, including the Gulf of Mexico, is used on Monsanto's GMO corn more than any other crop.

Timing is everything

What is more puzzling is the fact that the agency awarded the glyphosate tolerance victory to Monsanto after only conducting preliminary reviews of the studies it was provided, blaming "the timing of the submission." In its ruling, the EPA said it "does not believe that further review will result in different conclusions concerning the neurotoxic or immunotoxic potential of glyphosate."

The EPA is hoping the American public will believe that an agency which earmarked $129 million of its 2013 fiscal year budget specifically to "support the EPA pesticide review processes" received a request from Monsanto to raise glyphosate tolerance levels and one year later, it was only able to conduct a preliminary review.

EPA also said it didn't believe that a further review would turn up different results. Isn't that another way of saying it's not absolutely sure?

The EPA also seems to have forgotten that a "different conclusion" is exactly what it came to back in 1991 when it changed its original 1985 glyphosate classification as "possibly carcinogenic to humans" to "evidence of non-carcinogenicity"—precisely because it made a re-evaluation of a single mouse study.

Clearly one year isn't enough time for EPA to conduct more than a preliminary review. Give it seven years and it can conduct a re-evaluation that brings it to a different conclusion. Seven years is also a long time to make sales of—and be exposed to—glyphosate.

The EPA has a fresh opportunity to reach yet another different conclusion, as the agency is currently conducting a scheduled glyphosate review with its Canadian counterpart.

"We will give full consideration to the IARC study and all the other information we have before we reach a final decision," an EPA spokeswoman said.

Side of glyphosate to go with that GMO corn?

With Vermont and Maine passing America’s first mandatory GMO labeling laws in 2014 (and 22 other states considering it), consumers are increasingly concerned about how food is affected by herbicides like glyphosate. This concern may grow along with the increased use of glyphosate-resistant GMO crops.

But it's not just the potential negative health effects of glyphosate that are worrisome. Its massive use on U.S. crops has given rise to glyphosate-resistant "superweeds.

"More than half of all U.S. farms have some Roundup resistant 'superweeds'…that now infest 70 million acres of U.S farmland, an area the size of Wyoming," said Andrew Kimball, founder and executive director of the nonprofit Center for Food Safety.

"It's long past due that our government required real and rigorous science when regulating GE crops," he said. "It's time for them to say 'no' to these herbicide-promoting crops, and prevent the looming agronomic disaster they will inevitably bring with them."

With GMOs present in 80% of processed foods in the U.S., Monsanto, as a primary producer of both GMO crop seeds and pesticides, has become a main target for environmental and public health activists. The average consumer also plays a central role in this rapidly evolving drama, not only by purchasing Roundup and foods sprayed with glyphosate, but also by ingesting the chemical.

In addition to glyphosate's links to cancer and other deadly diseases, it may also play a role in not-so-often-deadly ailment that has nevertheless become a major health concern in recent years: gluten sensitivity. Stephanie Seneff, a senior research scientist at MIT, has co-authored two papers proposing a connection between glyphosate and gluten sensitivity. She and her colleagues found that glyphosate binds to gluten, "causing the gluten to stay in the form that is known to be more allergenic."

Cancer, chronic kidney disease, gluten sensitivity and agronomic disaster. The complex glyphosate-fueled web Monsanto has spun over the world's food system for the past four decades may take another four decades for scientists to untangle. But while the debate on glyphosate's numerous potential health effects rages on, one thing is fairly certain: It is a part of most Americans' diets.

Ronnie Cummins, the national director of the nonprofit Organic Consumers Association, put it bluntly: "If you eat foods that contain genetically modified organisms, you are consuming glyphosate."

[May 28, 2015. Editor's Note: The nonprofit group Beyond Pesticides has launched a public petition urging the EPA to stop the use of glyphosate and take immediate action to reevaluate its widespread use and registration status. To learn more and add your name, click here.]