Is Roundup Dangerous? Can Weed Killer Cause Cancer?

Weeds in Rocks (is Roundup Safe?)

As spring emerges and winter weather gives way to warmer temperatures, ideas about gardening, landscaping, and other types of lawn and flora care start to fill our thoughts. Among those thoughts should not be the word "cancer."

The sad reality, however, is that there could be a risk of developing cancer if part of your gardening or landscaping activities includes using chemicals that contain glyphosate, the active ingredient in Monsanto's Roundup Weed Killer and other herbicide products.

See Why People Are Suing Monsanto Learn About Roundup Lawsuits

Roundup Cancer Risk: Is It Real?

Monsanto and its supporters point to a number of studies that found no evidence of a link between Roundup and any form of cancer. For example, a 2016 study funded by Monsanto "did not find support in the epidemiologic literature for a causal association between glyphosate and [non-Hodgkin lymphoma (NHL)] or [multiple myeloma (MM)]," two types of cancer commonly associated with the substance. Other studies have similarly failed to discover a connection between Roundup and cancer.

Nonetheless, in 2015, the International Agency for Research on Cancer (IARC), the World Health Organization's international agency, classified glyphosate as "probably carcinogenic in humans," even while noting that there was "limited evidence" of a link between glyphosate and non-Hodgkin's lymphoma. There are two primary reasons for why IARC researchers classified the weed killer as a carcinogenic chemical, despite what some have called thin evidence:

  • Animal studies - specifically, studies of mice and rats - demonstrated a possible link between glyphosate and cancerous tumours.
  • Laboratory studies of the damaging effects of glyphosate on DNA showed "mechanistic evidence" that the weed killer can indeed damage DNA in human cells upon exposure.

A French court cited the IARC's decision and several scientific health studies when it enacted an immediate ban of Monsanto's product Roundup Pro 360 earlier this year. Politicians in France have also taken steps to reduce the amount of glyphosate use in the country. Though a complete ban on glyphosate products has been deemed unwise in an effort to protect farmworkers and the country's economy during the change.

Other groups have called the IARC's classification into question, claiming that it ignored various studies. While this is true (scientists at the IARC do not consider studies funded by privately held companies, as well as studies that meet certain other criteria), the IARC has not retracted or changed its classification.

Other regulatory agencies have made their own determinations. For example, both the U.S. Environmental Protection Agency (EPA) and the European Food Safety Authority (EFSA) found that glyphosate was probably not carcinogenic. However, the California Office of Environmental Health Hazard Assessment lists the chemical as a "known carcinogen," largely based on the IARC's classification.

The claim that glyphosate causes cancer has led to the filing of hundreds of Roundup lawsuits in state and federal courts across the United States. So far, two state court juries and one federal court jury found verdicts in favor of the plaintiffs against Monsanto and their parent corporation Bayer. In total, Bayer and Monsanto have been ordered to pay nearly $2.2 billion in damages for these three trials. While the companies continue to file appeals, many more lawsuits are still underway. Though these initial verdicts grant hope to plaintiffs, given the unclear state of scientific evidence, the amount to which Monsanto could be held liable in future cases and appeals remains to be seen.

Earlier this month, following the third American verdict in May, the first Australian plaintiff filed a lawsuit against the herbicide manufacturer.

Non-Cancer Roundup Health Risks

Whether or not Roundup causes cancer, it still could be harmful to human health for other reasons. In fact, there is plenty of evidence that glyphosate has a number of harmful health effects, from mild to severe.

At the most basic level, Roundup herbicide can cause a type of skin irritation known as photocontact dermatitis. In most cases this is limited to contact with uncovered hands, arms, or legs while using the weed killer. However, if used in spray form, it could also get into the nose, mouth, or eyes, where the effects could be more severe.

More dangerous is the ingestion of Roundup, especially for those who may swallow it on purpose. The most common damage from swallowing is burns to the mouth, throat and esophagus. However, more severe injuries can also occur, including permanent liver damage or even death. Some cases of death have been reported within just a few hours of drinking relatively small amounts of Roundup. Needless to say, this potentially deadly chemical should never be swallowed.

While there are some claims linking Roundup (and glyphosate) to other diseases and conditions - such as diabetes, autism, depression and heart disease - there is very little reliable evidence for those claims. The study these claims primarily rely on was a non-systematic review of the literature, and the editors of the journal that published the study issued a statement of concern, noting that the paper relied largely on opinion and speculation. There is also little evidence that glyphosate exposure by women who are pregnant will lead to birth defects, but animal studies suggest they may manifest in grandchildren and great-grandchildren.

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Stay Safe While Using Roundup

While the jury may still be out on whether Roundup and other glyphosate-based weed killers can cause cancer, it's still a good idea to take safety precautions when using it. If you decide to use Roundup, whether you are just doing some work around the house or using it as an industrial herbicide, here are some ways to stay safe:

  • Store it in a safe place, out of reach of children, when not in use.
  • When using it, wear appropriate safety gear, such as long sleeves, pants, gloves, goggles, and a face mask.
  • If you get any on your skin or in your eyes, follow the instructions on the bottle to rinse with water for 15-20 minutes.
  • If you swallow any of it, call a poison control center (1-800-222-1222) or your doctor immediately.

Of course, you can also just kill weeds the old-fashioned way - by pulling them up by the roots!

Authored by Curtis WeyantContributor
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Curtis Weyant has more than 20 years as a writer, editor, and communicator, publishing on a wide variety of topics, especially in the financial, legal, and medical fields. At, Curtis managed the day-to-day publication of all content from 2016-2019.
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