What does science say about health risks from widely used glyphosate on U.S. farms? An expert weighs in.

Unlike soybean and corn farmers, wheat growers don't
 routinely use glyphosate. (Photo by H. Shedrow, Unsplash)

Despite thousands of lawsuits and some scientific studies linking glyphosate, the active ingredient in the herbicide Roundup, to serious human diseases, the compound remains the most popular herbicide for farmers worldwide.

In the U.S., where Roundup is the most commonly used herbicide, many consumers have questions about the health risks glyphosate may pose. According to epidemiologist Dr. Katelyn Jetelina, writing for Your Local Epidemiologist on Substack, the most pressing questions are: "Does glyphosate cause cancer? And how much exposure is actually risky?" She provides some background and details about what "the scientific evidence actually says."

Like many chemicals, natural and synthetic, the dose determines toxicity. "So, at what dose is glyphosate poisonous? The LD50 in rats (the dose that kills half the test animals) is around 5,600 mg/kg body weight," Jetelina explains. "Table salt is roughly 3,000 mg/kg. By that classic measure, glyphosate is less acutely toxic than salt."

Still, many people who work on farms or live near farms may be regularly exposed to "a lot of glyphosate," Jetelina writes. "Among the general public, there are many questions about low-dose, cumulative exposure from multiple sources over long periods."

Correlation maps that show the number of non-Hodgkin lymphoma cases in counties that spray the most glyphosate seem to point to a relationship between the two. Jetelina adds, "But correlation alone doesn’t establish cause, which is why animal and human studies matter."

Food and Water Watch graph via Your Local Epidemiologist

Tests on rats, which have often been cited as the most alarming, and observation testing on humans, indicate the same thing: "At very high exposure levels, there may be some cancer risk," Jetelina explains. "But that’s about as far as the science currently takes us."

The U.S. EPA, the European Food Safety Authority, Health Canada, and regulatory agencies in Australia and Japan have "all concluded that glyphosate is 'unlikely to be carcinogenic to humans' at realistic exposure levels," Jetelina writes. Those regulatory bodies looked at "how much glyphosate people actually encounter and asked what is the probability of harm? Your actual exposure is what determines your actual risk."

In daily life, an average American would be hard-pressed to consume enough glyphosate to do any harm. To exceed EPA's herbicide residue limits, a "150-pound adult would need to eat roughly 50 pounds of oats every day," Jenelina writes. Organic certification doesn't allow synthetic herbicides, so in practice, most herbicides can be avoided by purchasing organic foods.

For farm workers who mix and apply glyphosate, Jenelina advises using personal protective equipment consistently to prevent unnecessary exposure. People who live near farms can help protect themselves from spray drift by "knowing your local agricultural calendar and keeping windows closed during application are the first steps."