Written By : Terry Turner
Edited By : Kim Borwick
This page features 37 Cited Research Articles

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Roundup is a brand-name herbicide that contains the active ingredient glyphosate. Monsanto, an American agricultural chemical company, first sold the herbicide commercially in 1974. It produced a wide range of weed killers and other products under the Roundup brand. German drug and chemical giant Bayer acquired Monsanto in 2018 and began phasing out the Monsanto company name. But Bayer continues to make and market Roundup.

Originally developed for large-scale farming operations, Roundup is now available in home and garden versions and has become a popular household weed killer among consumers.

In 2015, a United Nations agency listed the active ingredient in Roundup as “probably carcinogenic.” The announcement set off a controversy over whether a link between Roundup and cancer exists. Courts and regulatory agencies have had conflicting reactions to the connection claim.

In 2017, the United States Environmental Protection Agency issued a draft report that concluded glyphosate, the main ingredient in Roundup, is safe and “not likely” to cause cancer in humans. The EPA is still reviewing data on the herbicide to determine whether it is a harmful product.

California courts have taken up Roundup lawsuits over glyphosate exposure, and a jury in 2018 awarded a multimillion-dollar verdict to a man who blamed the chemical for his cancer.

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What Is Glyphosate?

Glyphosate is the most widely used herbicide in global agriculture. And glyphosate-based products are the second most widely used home and garden herbicides. Glyphosate is non-selective, which means it will kill just about any plant it comes into contact with. Once the compound is applied, plants’ leaves absorb it and pass it throughout the plant down to the roots.

It prevents plants from making certain proteins they need to grow. It does this by shutting down the shikimic acid pathway in plants. Without this pathway, plants die in a matter of days or weeks. Some microorganisms have this same pathway, but humans and animals don’t.

Manufacturers mix glyphosate with other chemicals that cause it to stick tightly to the weeds and soil it’s sprayed on. This keeps it from drifting and damaging crops or other desirable plants.

Did you know?
Roundup and other Monsanto glyphosate pesticides are marketed in 130 countries and approved for 100 different kinds of crops.
Source: Monsanto

Monsanto’s patent on glyphosate expired in 2000, which allowed other companies to begin making and marketing herbicides that contain the ingredient. By 2015, more than 750 products made with glyphosate were available in the United States, according to the National Pesticide Information Center.

Though businesses primarily sell the chemical in liquid form, companies also manufacture acid and salt versions of the pesticide. It can be applied at ground level from farm machines or through aerial spraying by crop dusters. It also comes pre-mixed for use in handheld sprayers.

Glyphosate is widely used on fruit, vegetable and cereal crops, and ornamental plantings, but corn and soybean crops account for about two-thirds of the pesticide’s use every year.

Glyphosate infographic

Widespread Use of Roundup Weed Killer

Glyphosate use exploded exponentially in 1996 when Monsanto introduced “Roundup Ready” crops. The genetically modified seeds were immune to glyphosate’s effects. Farmers could spray the herbicide on their fields, and it would only kill weeds, while the crops continued to grow.

Previously, farmers had applied Roundup before their crops emerged from the ground or after harvest to kill lingering weeds. The new seed technology let farmers use glyphosate even as their crops were growing. As a result, farmers used as much as triple the amount of glyphosate.

By 2016, these genetically engineered crops accounted for 56 percent of glyphosate use around the world.

“In the U.S., no pesticide has come remotely close to such intensive and widespread use.”

A 2016 analysis in Environmental Sciences Europe found glyphosate use increased nearly 15-fold in just 18 years. It found while glyphosate had been around since 1974, two-thirds of all glyphosate use in the United States had taken place between 2004 and 2014.

“In the U.S., no pesticide has come remotely close to such intensive and widespread use,” author Charles Benbrook wrote.

The EPA estimated glyphosate use had hit between 280 million and 290 million pounds a year by 2016. An EPA report suggested that while part of the increase was due to more farmers using the herbicide, “it is more likely that individuals already using glyphosate increased their use and subsequent exposure.”

Is Roundup Safe?

The EPA says glyphosate has “low toxicity for humans,” which means in most cases, you would have to be exposed to large amounts of glyphosate for it to become harmful. But other ingredients in glyphosate-based herbicides may make some versions more toxic than others.

It is often difficult for researchers to determine whether added chemicals pose an increased risk or how the chemicals may interact with glyphosate. That’s because manufacturers consider these chemicals to be trade secrets, which means they do not need to name the chemicals in the list of ingredients. As a result, researchers have trouble determining exactly what chemicals are in a particular herbicide and in what amounts.

Even so, the EPA recommends very few precautions when using these products.

EPA Precautions for Safe Glyphosate Use

  • Follow all label directions
  • Use protective eyewear for the few versions that may cause eye irritation
  • Avoid entering sprayed fields for 12 hours after application

You can be exposed to glyphosate if you get it on your skin or in your eyes, or if you breathe it in. The herbicide does not easily vaporize once it’s applied, so it usually stays where you spray it.

It’s hard to absorb glyphosate through the skin. But you should thoroughly wash your hands after using it or after touching plants that have been sprayed with it. You may swallow some of the chemical if you eat or smoke while it is still on your hands.

Short-term exposure can irritate your skin and eyes. Breathing in the chemical can irritate your nose and throat. And swallowing glyphosate can burn your mouth and throat and cause diarrhea, nausea and vomiting. Intentionally swallowing large amounts of the herbicide can be fatal.

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Roundup Risks

International regulators disagree on whether long-term exposure to glyphosate can lead to non-Hodgkin lymphoma, a type of cancer. An agency of the United Nations’ World Health Organization concluded in 2015 that it is “probably carcinogenic.”

But the United States Environmental Protection Agency has not declared a cancer risk. The agency continues to examine potential risks as it conducts a routine review of the herbicide.

A 2019 study in the journal Mutation Research/Reviews in Mutation Research reported a link between long-term, high-use exposure and a 41 percent increase in the risk of developing non-Hodgkin lymphoma.

Monsanto has said “more than 800 rigorous registration studies” required by international regulators have failed to show any cancer risk. The company says Roundup is safe if used according to label directions.

A 2003 internal Monsanto email cautioned executives against saying Roundup is not a carcinogen. A company scientist said Monsanto had not done the necessary testing to back up the claim.

The National Pesticide Information Center says it could not find information that links glyphosate to asthma or other diseases outside of cancer. The center, along with the EPA and the World Health Organization, have looked at the effects of residue on food and in water, and at glyphosate’s potential to cause issues in children, pregnant women, pets and the environment.

Is Glyphosate on Food Dangerous?

Glyphosate on food is unlikely to pose a risk of cancer, according to the World Health Organization.

The organization found food and water are the main ways most people are exposed to glyphosate. But a panel of pesticide experts with the agency concluded in 2016 that people don’t ingest enough of the chemical through their diets to be at risk.

The EPA bases toxicity on exposure over a long period of time, even an entire lifetime. Under the agency’s guidelines, a 200 pound man could ingest almost 159 milligrams, or 0.0056 ounces, of the chemical every day without serious consequences.

Risks to Children and Pregnant Women

The National Pesticide Information Center warns children are more sensitive than adults to the effects of pesticides. But it found no research that shows children have a higher sensitivity specifically to glyphosate-based herbicides.

The center warns infants’ livers and kidneys are still developing and cannot remove pesticides from the body as easily as adults’ livers and kidneys can. Kids also spend time closer to the ground, take more breaths per minute and have more skin surface area compared to their body weight. And children are much more likely to put their hands in their mouths. All these factors can increase pesticide exposure.

The center recommends minimizing children’s exposure to all pesticides, reading label directions carefully and taking practical steps such as washing children’s hands if they’ve been near a place where pesticides are used.

Safety advice for consumers
The National Pesticide Information Center offers a checklist of steps parents can take to protect children from pesticides.

Pregnant rats exposed to high levels of the herbicides became sick and some acquired developmental and reproductive issues. Rat fetuses exposed to high levels of the chemical had problems gaining weight and some suffered skeletal defects. Researchers did not see these problems in rats exposed at lower levels. No major human studies have assessed glyphosate’s effects on pregnancy.

Pets and Other Animals

Glyphosate can cause problems for pets that touch or eat plants that are still wet with the chemical. Most appear to be short-term complications. Not much research looks into long-term problems for pets.

Symptoms of Glyphosate Exposure in Pets

  • Diarrhea
  • Drooling
  • Drowsiness
  • Loss of Appetite
  • Vomiting

The EPA says glyphosate is “no more than slightly toxic” to birds. The agency also says it is “practically non-toxic” to honey bees and aquatic invertebrates, which are small creatures such as insects, worms and shellfish.

Some glyphosate versions are designed specifically to control aquatic plants. Glyphosate is low in toxicity to fish, but some glyphosate-based herbicides may contain other chemicals that can hurt fish. The EPA recommends following label directions to avoid hurting fish and aquatic environments.

Environmental Damage

The National Pesticide Information Center says half of glyphosate in dead leaves breaks down in eight to nine days. But the chemical can remain in soil for up to six months with the right soil and weather conditions. But because it binds so tightly to soil, it is unlikely to get into groundwater.

Increased use of glyphosate has also caused some weed species to develop immunity to the chemical. A 2014 study in Pest Management Science reported at least 24 species were immune to glyphosate and 16 of those had been found in fields planted with Roundup Ready crops, leaving few alternatives to control them.

Alternatives to Roundup

Some alternatives to Roundup for household and even commercial landscaping applications are available. But large-scale farming alternatives are more difficult to find.

Roundup alternatives include:

  • Vinegar
  • Manual removal
  • Flame
  • Steam
  • Hot-foam weeding
  • Alternative commercial herbicides
  • Mechanical farming (plow, no-till methods)

The University of Maryland Extension Service says commercially available alternatives are not as effective as glyphosate. It recommends using alternative herbicides with other gardening practices such as soil health and irrigation methods. The service also reviewed vinegar as a possible alternative.

Alternatives usually work by burning plants.  Agricultural vinegar can quickly burn down plants especially in bright sunlight. The service says vinegar can kill 90 percent of treated weeds within a day. But it also warns that it will kill any plant it touches, including desirable ones.

“Natural” does not always mean “safe.” Most vinegar and natural oil herbicide alternatives are more toxic to human skin than glyphosate or other synthetic pesticides. People should avoid inhaling these alternatives or getting them on their skin or in their eyes.

The North Carolina State Extension Service reviewed several different alternatives to glyphosate in landscape management. It found manual weeding was effective but had to be performed every two weeks. Using flame, steam or hot-foam weeding proved effective but can only be used in non-flammable areas such as cracks or crevices in driveways and sidewalks.

A 2016 German study published in the Julius-Kühn-Archive found mechanical farming practices were the only alternatives that produced similar results to pesticides. These included different ways of tilling farmland and making three passes over the fields.

But the researchers cited potential costs involved in the extra days, manpower and equipment needed for the additional work. They cited a previous study that had estimated the costs could reduce farm profits by 3 percent to 36 percent depending on farm conditions and types of crops in different parts of the country.

Please seek the advice of a qualified professional before making decisions about your health or finances.
Last Modified: August 5, 2022

37 Cited Research Articles

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