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A potentially cancer-causing chemical is sprayed on much of America’s farmland. Here is where it is used the most.

Weedkillers containing glyphosate are sprayed on nearly half of all corn and soybeans grown in the U.S. Use is highest in parts of Iowa, Illinois and Indiana.
Green corn maize field in early stage.
Herbicides containing glyphosate are used on nearly half of all planted acres of corn, cotton and soybeans in the U.S.oticki / Getty Images / iStockphoto

Every day, farms across the country use a potentially cancer-causing chemical that is in the world’s most common weedkillers. And data shows that it’s most used in the Midwest and parts of the South.

Glyphosate, the active ingredient in many herbicides, has been in use for nearly 50 years.The chemical’s health impacts have for years been heavily debated in studies, U.S. and international regulatory filings and in lawsuits filed after the the World Health Organization’s International Agency for Research on Cancer concluded in a 2015 report that the chemical “is probably carcinogenic to humans.” The Environmental Protection Agency has maintained that there is no risk to human health based on current uses and that there is no evidence glyphosate causes cancer. Bayer, the pharmaceutical company that sells the most widely used glyphosate herbicide, says it stands by the safety of the chemical.

Glyphosate’s main use is in agriculture. Weedkillers containing it are used on nearly half of all planted acres of corn and soybeans in the U.S., though much of those are not grown for human consumption. They’re also used on acres of farmland where wheat, oats, fruits and cotton are grown. Pesticide residue testing from the FDA found glyphosate residues on a wide variety of crops, including oats, soybeans, cranberries, grapes, raisins, oranges, apples, cherries and beans. Data from the U.S. Geological Survey shows several counties across the country with higher than average glyphosate usage. 

An NBC News analysis of 2019 USGS agricultural glyphosate usage data found: 

  • An average of almost 130 pounds of glyphosate herbicides were sprayed per square mile in U.S. counties. 
  • Nueces County, Texas, had the single highest glyphosate usage rate of U.S. counties, with more than 1,100 pounds sprayed per square mile. 
  • Iowa and Illinois, where the most corn and soy crops are grown, accounted for 15% of national usage.
  • Southwestern and Northeastern states used the least glyphosate per square mile.

Being in a county with higher than average glyphosate use does not necessarily lead to increased exposure. A 2020 Department of Health and Human Services report notes that the greatest potential exposure is among farm workers and gardeners that use glyphosate-based herbicides and those who live near farms, manufacturing plants where glyphosate products are produced and hazardous waste disposal sites that contain it.

For the general public, the report notes that exposure to glyphosate typically comes by touching or eating food or water containing residues or inhaling mists or spray while using it. For those only exposed through food, the EPA says that glyphosate residues on food are safe up to certain thresholds

Some studies have found a link between increased cancer rates and higher levels of exposure, though other researchers say limited data on the glyphosate exposure levels in humans makes it difficult to parse a relationship between exposure and disease. Other studies have concluded that it is not carcinogenic. 

The chemical giant Monsanto introduced glyphosate in its product Roundup in 1974. Bayer acquired Monsanto in 2018.

“Glyphosate is the most widely used chemical weedkiller in human history because of genetic engineering,” said Dave Murphy, the founder of Food Democracy Now, an advocacy group that tests glyphosate in food. “It’s sprayed ubiquitously and Monsanto has, for decades, just maintained that it’s the safest agricultural chemical ever made.”

The EPA’s safety limits for glyphosate exposure from food are twice the levels allowed in the European Union. Its runoff is recognized by the agency as a drinking water contaminant at levels that correspond to approximately 1 gallon of Roundup in an Olympic sized pool, according to an NBC News calculation.

Much of the debate about glyphosate’s health implications revolves around a potential link to non-Hodgkin lymphoma. A 2019 analysis conducted by former EPA science review board members indicated a “compelling link” to the disease. Several peer-reviewed studies have also suggested that herbicides containing glyphosate may disrupt hormones and alter the gut microbiome

The 2015 IARC report, which stated that “a positive association has been observed for non-Hodgkin lymphoma,” kicked off a wave of lawsuits that cost Bayer more than $10 billion in settlements, though the company won five consecutive personal-injury trials through September 1. 

Bayer has continued to defend glyphosate’s safety. The company repeatedly disputed the validity of the IARC and other studies, some supported by organic food groups, that have linked the chemical to cancer. The company pointed NBC News to other studies — including some that it has sponsored —  that either refuted a link to cancer or challenged the relationship between acres sprayed and exposure levels.

In California, glyphosate is on a list of chemicals known to cause cancer, a designation that requires manufacturers to print warning labels on products sold in the state. However, after Monsanto and the EPA challenged the requirement, a judge found “almost all other regulators have concluded that there is insufficient evidence that it causes cancer,” preventing such warnings.

Litigation is ongoing. In a statement to NBC News, Bayer said it continues to oppose California’s classification and requirement because it conflicts with “the longstanding consensus of leading health regulators worldwide supporting the safety and non-carcinogenicity of glyphosate-based products.” 

Glyphosate’s use in the U.S. has skyrocketed since 1996, the year Monsanto introduced genetically engineered seeds that could survive being sprayed with higher quantities of herbicides.

Today, almost 90% of corn, cotton and soybean crops are modified to be tolerant to glyphosate and other chemical treatments used by farmers, U.S. Department of Agriculture data shows.

A 2017 study from researchers at the University of California, San Diego showed that the amount of glyphosate in urine samples taken from a group of 100 adults rose between 1993 and 2016. Glyphosate residues have also been detected in air and rain samples, according to a study from the University of Minnesota. 

A national health survey released in June by the Centers for Disease Control and Prevention observed detectable levels of glyphosate in 80% of urine samples tested.

Bayer said that finding traces of glyphosate in urine does not mean there’s a health risk. The company told NBC News in a statement that the highest value found in the CDC’s survey “corresponds to exposures that are less than 0.14% of the U.S. Environmental Protection Agency’s safety threshold” — a measurement that works out to 16 millionths of an ounce per pound of bodyweight.

“The CDC’s data confirms that human exposures to glyphosate are well below these levels, confirming glyphosate can be used safely when following label instructions,” the statement said.

But Robin Mesnage, a toxicologist at King’s College London — who has researched the health effects of environmental contaminants for more than a decade and has been a consultant on glyphosate litigation against Bayer in the U.S. — has questioned whether the current safety thresholds are too high.

His own research, he said, has found glyphosate can induce DNA damage and changes in liver metabolism at doses up to 100 times lower than the permitted levels — which was still higher than any value found in the CDC study. He added that combining glyphosate with the other ingredients in herbicides can lead the final product to be more toxic than its active ingredient alone. In a statement, Bayer objected to Mesnage’s research methodologies.” 

The EPA concluded in 2020 that glyphosate posed “no risks to human health” and was not likely to cause cancer. But a federal appeals court rejected that determination in June, stating that the EPA did not adequately assess the risks to endangered species and human health. The court also pointed out inconsistencies in the agency’s 2016 evaluation of potential links to non-Hodgkin lymphoma. The EPA withdrew its decision in September. 

An internal EPA advisory panel also found inconsistencies in that 2016 evaluation, including that some tumor responses in animals had been discounted. The panel recommended that the EPA obtain updated data in order to make a conclusion about non-Hodgkin lymphoma risk.

“Animals did get tumors and they got more tumors at high doses,” said Bill Freese, the science director at the Center for Food Safety, a nonprofit environmental advocacy organization that was one of the groups that challenged the EPA’s glyphosate review in court. 

“Their cancer conclusion just did not make sense,” Freese said.

EPA spokesperson Melissa Sullivan said in an email that the agency plans to revisit and better explain its evaluation of glyphosate’s carcinogenic potential by 2026, as well as to consider whether to assess other impacts it may have on human health. Until that review is completed, products containing glyphosate can continue being sold.

When it comes to residue in food, the EPA has said traces are fine as long as they don’t exceed its safety thresholds. But environmental and organic advocates note that these thresholds have increased in the past two decades. In 2013, following a Monsanto petition, the EPA raised the permitted levels of glyphosate residues on certain foods, doubling the allowable limit for oilseeds and raising it to more than 15 times the previous level for sweet potatoes and carrots. 

Bayer plans to replace glyphosate in some versions of Roundup by next year. The company said in its statement that the move was made “exclusively to manage litigation risk in the U.S. and not because of any safety concerns.” The current formula will still be available to farmers, pest control companies and other professional services. 

CORRECTION (Oct. 28, 2:57 p.m, ET): A previous version of this article and map miscalculated the rate of glyphosate herbicide use for 41 counties in Colorado and incorrectly asserted that Lake County, Colo., had the highest rate in the country. Nueces County, Texas, had the highest usage rate, while Lake County was among the lowest.

CLARIFICATION: This article has been updated to clarify how people can be exposed to glyphosate. It was also updated to draw the distinction between use and exposure — that not everyone in a high usage area is necessarily exposed or at a health risk. It also clarifies where and what types of crops that glyphosate residues have been found on. It also includes updated statements from Bayer. It also includes additional information about the court decision halting the California labeling requirements. And information about Robin Mesnage’s consulting work for plaintiffs suing Bayer was also added.