As well as being one of the world's most widely used commercial herbicides, Roundup is also a household name and a surefire first choice for killing weeds. But a new report out last week from a World Health Organization (WHO) agency concluded that the popular product can "probably" cause cancer in humans.

According to scientists gathered by the WHO's France-based International Agency for Research on Cancer (IARC), the active ingredient in Roundup––a chemical called glyphosate––can be "classified as probably carcinogenic to humans." For the report, scientists cobbled together findings from three recent studies which suggest that workers who were regularly exposed to glyphosate could have "increased risks for non-Hodgkin lymphoma that persisted after adjustment for other pesticides" and that the chemical by itself and in mixtures "induced DNA and chromosomal damage in mammals, and in human and animal cells in vitro" as well as in workers in nearby farm communities.

Roundup is a herbicide product that has been produced by the U.S. agrochemical giant Monsanto since the 1970s and is sprayed across millions of acres of U.S. crops each year. According to the company's 2014 annual report, herbicides brought in about a third of the total $15.8 billion in sales, growing by 13 percent that year. Despite long-standing opposition to the chemical formula from environmental and health advocacy groups, the product has gained worldwide popularity becoming especially popular in the 1990s with the release of Monsanto's "Roundup Ready" seed line, which included soy, corn, and cotton genetically altered to withstand Roundup's deleterious effects. It's believed that more than 90 percent of soy and almost 90 percent of corn grown domestically are herbicide tolerant––if not certified "Roundup Ready."  

Roundup, and other herbicides that contain glyphosate, such as Ultra, Rodeo, TouchDown Pro, and Accord, are sanctioned for use by the Environmental Protection Agency (EPA), though concern over their safety has grown in recent years. Activists made headlines last year when a group of mothers, scientists, and environmentalists met with the EPA after a five-day phone "blitz" over worries about traces of Roundup found in breast milk. 

"This is a poison, and it's in our food. And now they've found it in breast milk," Zen Honeycutt, founder of Moms Across America told Reuters. "Numerous studies show serious harm to mammals. We want this toxic treadmill of chemical cocktails in our food to stop."   

The IARC report is not the first of its kind to suggest that Roundup chemicals carry carcinogenic potentials, though its timing comes serendipitously as the EPA is set to review the safety of glyphosate sometime this year. Opponents of the chemical hope that the findings will only add to years of protest efforts and lawsuits aimed at limited the chemical's use. 

"The WHO [report] is not the first to link Monsanto's glyphosate to cancer," Katherine Paul, associate director of the Organic Consumers Association, told ATTN: in an email. "However, it is one of the more incriminating, and it comes at an opportune moment when glyphosate is under review by the EPA."

For its part, Monsanto called the report's conclusions too dramatic and cited numerous shortcomings in IARC's scientific rigor during a media call Tuesday. Company representatives cited numerous sources, including the American Council on Science and Health (ACSH), a science watchdog group that claimed that "IARC's ruling on glyphosate ignores the science" shortly after the report's release. But according to leaked ACSH financial reports, the company is on the payroll of big industry groups like Chevron, Coca Cola, McDonald's, and Procter & Gamble and has pursued financial contributions from Monsanto since July 2012. Moreover, according to a 1985 ACSH document, funders included Dow Chemical and Monsanto. (Read more about ACSH here.)

Monsanto's claims of junk science aside, glyphosate (and Roundup) isn't just profitable––it's become an incredibly useful tool for farmers. In 2007, over 2 billion pounds of various herbicides were used globally, with 531 million pounds of that total used in the U.S., according to the EPA.

But there are some consequences to rampant herbicide use. Although new numbers have not been released, reports indicate that some farmers could be second-guessing their use of herbicides with the rise of chemical-resistant "super weeds," which reportedly cover some 11 million acres. 

Skeptics are hesitant to accept IARC's findings at face value, pointing to the lack of groundbreaking new data on the chemicals in question. The "probably carcinogenic to humans" IARC classification known as "2A", critics point out is, susceptible to the "dose makes the poison" argument––in other words, that glyphosate and Roundup is dangerous to humans only in extreme exposure situations. Interestingly, there are numerous articles and studies pointing to the conclusion that glyphosate poses no proved threat to human health. 

The discrepancy clearly points to the need for more research on the subject, but the considerable outpouring of concern over the use of chemicals like glyphosate in products that are increasingly, perhaps more troubling, deeply ingrained into the fabric of our environment, is at the very least notable.