A new study suggests that human exposure to the herbicide glyphosate has increased by 500 percent in the past two decades. The findings, published today in the medical journal JAMA, represent one of the only efforts to figure out how much of this chemical is making its way from food, air, and water into our bodies.

"This study demonstrates something many scientists have been worried about," says Michael Hansen, Ph.D., senior scientist at Consumers Union, the policy and mobilization division of Consumer Reports. "As use of the chemical grows, more of it is getting into our bodies." 

Glyphosate is the key ingredient in Roundup, a pesticide used on a wide range of crops, including wheat and oats and genetically modified soy and corn. The chemical is also found in hundreds of weed-killing products used on suburban lawns and gardens. Previously published data shows that use of the chemical has increased significantly (some fifteenfold) in the past two decades.

And as its use has grown, so have concerns—and debates—over the potential risks to human health. In 2015 the World Health Organization classified glyphosate as a probable carcinogen. Earlier this year, the state of California followed suit with a new requirement that products containing this chemical carry warning labels on their packaging.

More on Glyphosate

But the Environmental Protection Agency (EPA) continues to assert that glyphosate is safe. In 2013 the agency increased the allowable levels so that twice as much of the chemical can now be found on certain crops without penalty.

And despite being the most widely applied pesticide in the world, glyphosate is still not monitored by the Department of Agriculture's pesticide data program or the Centers for Disease Control and Prevention's program on human exposure to environmental chemicals. "It's a huge gap in our safety net," Hansen says. Neither agency responded to a request for comment. 

New Findings

For the current study, researchers measured the urine concentrations of glyphosate in 100 elderly people living in Rancho Bernardo, a large suburb in southern California. The urine samples were collected between 1993 and 1996, and again between 2013 and 2016.

The scientists found a large increase in the proportion of study participants whose exposure levels exceeded the detection limit. In the 1990s, just 12 percent of the samples had detectable levels of glyphosate. By the 2010s, 70 percent did.  

They also found a thirteenfold increase in glyphosate concentrations between the two collection periods. The concentrations they measured were far below the EPA’s daily exposure limit of 1.75 mg/kg and the European Union’s more conservative limit of 0.3 mg/kg. But experts say the increase in exposure levels across time is cause enough for concern.

"We're being exposed to more and more of this chemical,” says Paul J. Mills, Ph.D., a professor at the UC San Diego School of Medicine and the study’s lead author. “Most people don't even realize that they are consuming it through their diet."

The current study didn't look at health outcomes or evaluate urine samples from people in any other part of the country. But Mills and his colleagues are planning several follow-up studies.

Unknown Quantities, Unknown Risks

A 2016 report in the journal Environmental Health that looked at human and animal studies found a link between glyphosate exposure and a number of health problems, including liver and kidney damage, endocrine disruption, and an elevated risk of non-Hodgkin’s lymphoma. But a vast majority of those studies were done with animals.

In fact, very few human studies have been done on the health effects of glyphosate, and no federal agency monitors how much of the chemical makes it from the environment into our bodies. That lack of information makes it difficult to even begin to assess how much glyphosate is potentially harmful to humans and whether current exposure levels are above or below that mark.

Researchers like Mills have begun to piece some information together from isolated studies. Mills says that his new findings coincide with a 2015 review that found similar concentrations in U.S. and European adults. (Together, the findings indicate that U.S. exposure rates are higher than European ones.) But in general, experts including Mills agree that much more data is needed.

The Bottom Line

While the health effects of glyphosate aren't well-understood, many scientists and consumer-safety advocates believe its widespread and growing use are reason enough for closer monitoring and more careful study by federal agencies. 

"The safety limits we have right now are complete guesses," says Bruce Blumberg, a scientist at the University of California at Irvine who has studied glyphosate.  

The fact that pesticide residue on fruits and veggies is generally below those limits sometimes leads people to conclude that there's no risk associated with pesticide exposure from food. But at least some human and animal studies suggest otherwise, and given recent disputes over the authorship of some glyphosate studies, including ones the EPA used in its assessments, some experts say it’s time to revisit those conclusions.