Whether on social media or in farming circles, many questions linger about glyphosate, better known as Roundup, and a link to cancer.
“It’s hard to know what to believe, but it’s important to make sure the information you receive is based on good science,” said Scott Nolte, Ph.D., Texas A&M AgriLife Extension Service state weed specialist, College Station.
Nolte addressed the issue during the Panhandle Farm Management Symposium in Amarillo recently, providing insight into the “myths and truths” surrounding the issue.
The controversy began with a ruling in 2015 by the International Agency for Research on Cancer, IARC, a subgroup of the World Health Organization tasked with determining the potential of a product to be carcinogenic. IARC indicated there was limited evidence glyphosate is carcinogenic in humans and sufficient evidence in animals.
However, because risk assessment and certain key studies were not considered by this organization, this year the U.S. Environmental Protection Agency released a statement Aug. 8 saying it would no longer approve product labels claiming glyphosate is known to cause cancer. The Agency said it is a false claim that does not meet the labeling requirements of the Federal Insecticide, Fungicide and Rodenticide Act.
Glyphosate use and regulation
Nolte said glyphosate has been in use since the mid-1970s and is the most studied chemical ever.
“Glyphosate, or Roundup, is a very effective herbicide that works on grasses and broadleaf weeds,” he said. “It works by inhibiting an enzyme that prevents plants from making three key amino acids needed to grow. This enzyme is not found in humans or animals, so it does not hurt them.”
Glyphosate was first tested in 1974, and while it worked well, it also killed the crops. Continued work with the chemical included the development of a gene that made crops resistant to the herbicide, so the chemical could be sprayed over a crop and kill the weeds, but not the crop. Roundup Ready soybeans were developed and commercially released for use in 1996.
Pesticides such as glyphosate are regulated by the EPA; the Food and Drug Administration, FDA; and the U.S. Department of Agriculture, USDA. These regulatory agencies determine safe residue levels and regulate tolerances.
They determine exposure risk through residue in food, water, residential use and occupational use, Nolte said. Two criteria they use are lowest observable adverse effect level and no observable adverse effect level. They set the chronic reference dose, which is an estimate of a daily oral exposure for a chronic duration to the human population that is likely to be without an appreciable risk of deleterious effects during a lifetime.
“Studies are conducted to get an observable effect and then they cut it back 100-fold to ensure if you are exposed on a daily basis to a chemical, chronic duration, it is without appreciable risk of effects during a lifetime,” he said.
How do we know Roundup is safe?
“Nothing is guaranteed to be 100% safe,” Nolte said. “But glyphosate is the most studied chemical in use today. None of the scientific studies have been able to definitively tie glyphosate to the cancer risks it’s been tied to.”
He said studies show the relative toxicity of glyphosate is just slightly higher than Vitamin B2 and far lower than Vitamin D3.
“Just about everything can be toxic in sufficient quantity – water, salt, organic pesticides, aspirin, caffeine, even sunscreen approved for babies – so it’s all relative,” he said. “Every day we weigh the risk with the benefits, whether it is driving to work or flying on an airplane.”
Nolte said there’s a scale of low risk to high risk, and sometimes, if something is considered low risk, some people are less careful in their use of that product.
“You are responsible for good stewardship and following the label of all chemicals used,” he said. “So, handle it properly.”
Each chemical is required to have a signal word on it to determine its toxicity:
- “Danger, poison” indicates the product is highly toxic by any route into the body.
- “Danger” means it can cause severe eye damage or skin irritation.
- “Warning” indicates it is moderately toxic orally, dermally or through inhalation. Moderate eye or skin irritation.
- “Caution” means the product is slightly toxic orally, dermally or through inhalation. Slight eye or skin irritation.
“In this ranking system, only the word ‘caution’ is used on Roundup. You have to read and follow the label.”
What does science tell us about Roundup?
When IARC came out with their ruling on glyphosate in 2015, they knew about some additional data that would have been useful in making their decision. However, since it was not printed yet, they did not take it into consideration.
“It’s extremely challenging to talk in absolutes,” Nolte said. “There are too many things at play. But based on scientific evidence at this point, statistically, there is no tie between glyphosate and cancer. It’s usually never one thing that is involved in causing cancer, so that doesn’t mean in an individual situation where someone was predisposed to cancer that the chemical didn’t play a role.”
The piece of missing information was the Agricultural Health Study, funded by the National Cancer Institute and the National Institute of Environmental Health Sciences in collaboration with EPA.
Considered one of the largest human health studies done, it has been following people for 20 years who are chemical applicators using glyphosate or their spouses. The conclusion of this large, prospective cohort study was “no association was apparent between glyphosate and any solid tumors or lymphoid malignancies overall.”
“You can decide if it is right for you to use or not,” Nolte said. “Genetic probability likely has as much or more to do with someone getting cancer as the environment. And science tells us if we use these things properly, the risk is extremely low. The label is the law. Follow it.”