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Weedkiller Chemical and Cancer: Study Finds a Link Between the Two

The study adds to cancer concerns about the widespread use of the herbicide glyphosate.

A new study finds signs of a widely used herbicide in the urine of farmers that may be associated with increased risk of developing blood cancers.

The study found evidence of glyphosate, which is found in products such as Roundup, Rodeo Aquatic Herbicide and Eraser, among others.

"Glyphosate is the most widely applied herbicide worldwide, and its use has been associated with increased risks of certain hematopoietic cancers in epidemiologic studies," according to the study in the Journal of the National Cancer Institute. "Animal and in vitro experiments suggest that glyphosate may induce oxidative stress, a key characteristic of carcinogens; however, evidence in human populations remains scarce."

The study, authored by researchers at the U.S. National Institutes of Health and the Centers for Disease Control and Prevention, is only the latest to look at the consequences of glyphosate use, its links to oxidative stress in humans and the herbicide's carcinogenic potential, which is inconclusive, though evidence is mounting.

"Among farmers reporting recent glyphosate use (last 7 days), use in the previous day was also associated with significantly increased 8-OHdG and MDA levels," according to the study. "Compared with non-farmers, we observed elevated 8-isoprostane levels among farmers with recent, high past 12-month, or high lifetime glyphosate use."

Here's what you need to know.


What Is Glyphosate?

Glyphosate is one of the most widely used herbicides in the United States and the world, according to the National Pesticide Information Center, a cooperative agreement between Oregon State University and the U.S. Environmental Protection Agency. "It is applied to the leaves of plants to kill both broadleaf plants and grasses," the center says. "The sodium salt form of glyphosate is used to regulate plant growth and ripen specific crops."

Monsanto, now a subsidiary of German pharmaceutical and biochem company Bayer, manufactures Glyphosate, which was first registered for use in the U.S. in 1974. 

It is now used in agriculture and forestry, on lawns and gardens and to control weeds in industrial areas. Some products containing glyphosate control aquatic plants, the center reports.


How Does Glyphosate Enter the Body?

Handling glyphosate can introduce it into the body. "You can be exposed to glyphosate if you get it on your skin, in your eyes or breathe it in when you are using it," according to  the National Pesticide Information Center. "You might swallow some glyphosate if you eat or smoke after applying it without washing your hands first. You may also be exposed if you touch plants that are still wet with spray. Glyphosate isn't likely to vaporize after it is sprayed."

Glyphosate has also been found in food and is the main source of exposure in children 18 and younger, according to the CDC. About 87 percent of 650 children tested had detectable levels of glyphosate in their urine, according to a CDC analysis.

Glyphosate was also found in chickpeas and hummus made from them, according to the Environmental Working Group, an advocacy organization. Its tests also found glyphosate in other dry and canned beans, dry lentils and garbanzo flour.

Glyphosate that is absorbed or ingested will pass through the body relatively quickly, the National Pesticide Information Center says. "The vast majority of glyphosate leaves the body in urine and feces without being changed into another chemical," it says.


Signs and Symptoms of Glyphosate Exposure

young woman with nausea in all denim outfit sitting on bed
Shutterstock / New Africa

Glyphosate itself has low toxicity, according to the National Pesticide Information Center

But other ingredients in products containing the herbicide may be toxic and cause irritation of the eyes, skin, nose and throat. Swallowing such products could cause excess saliva; burn the mouth and throat; trigger nausea, vomiting and diarrhea; and even lead to death, the center warns. 

Products containing glyphosate may also be toxic to pets and other animals. They may drool, vomit, have diarrhea, lose their appetite or seem sleepy after ingesting such products.


Cancer Risk of Glyphosate

skin cancer screening

Bayer maintains that glyphosate is a "safe and efficient weed control tool" and is not carcinogenic. 

Under President Donald Trump, the U.S. Environmental Protection Agency said that glyphosate "is not likely to be carcinogenic to humans." But the California-based 9th U.S. Circuit Court of Appeals ordered the EPA to reexamine its 2020 finding that glyphosate did not pose a health risk to people and rejected its finding that it is not likely to cause cancer in humans, The Associated Press reported. 

The World Health Organization's International Agency for Research on Cancer in 2015 classified glyphosate as "probably carcinogenic to humans." 

Hundreds have sued Monsanto and Bayer, alleging that glyphosate exposure caused their cancers. Some have won, some have lost. But the suits led Bayer to announce in 2021 that it will stop selling glyphosate-based weedkillers to nonprofessional gardeners in the U.S.

A 2009 study in the Journal of Environmental Science and Health found evidence that oxidative damage to cellular membranes, proteins and DNA "is one of the predominant forms of free radical-induced oxidative lesions, and has therefore been widely used as a biomarker for oxidative stress and carcinogenesis."


What to Do if You're Exposed to Glyphosate

risk of cancer

The National Pesticide Information Center has a list of resources for more information on glyphosate. 

You can also call the center with questions and concerns between 8 a.m. to 12 p.m. Pacific time, Monday through Friday, at 800-858-7378.

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