Study reveals lasting effects of common weed killer on brain health
Glyphosate, one of the most widely used herbicides, is sprayed on crops worldwide. A new study suggests glyphosate can accumulate in the brain, causing damaging effects linked with Alzheimer's disease. Graphic by Jason Drees/ASU
Environmental exposure to toxins in the air, water or certain chemicals can increase the risk of ill health effects, including to the human brain.
Now, new research has shown even brief exposure with a common weed killer can cause lasting damage to the brain, which may persist long after any direct exposure ends.
In the new study, Arizona State University researcher Ramon Velazquez and his team demonstrate that exposure to an active ingredient in weed and grass killers, called glyphosate, can result in significant brain inflammation, and increase the risk of neurodegenerative disease and Alzheimer’s-like effects.
“Our work contributes to the growing literature highlighting the brain’s vulnerability to glyphosate,” Velazquez says. “Given the increasing incidence of cognitive decline in the aging population, particularly in rural communities where exposure to glyphosate is more common due to large-scale farming, there is an urgent need for more basic research on the effects of this herbicide.”
The research was published in the Journal of Neuroinflammation. Velazquez is a researcher with the ASU-Banner Neurodegenerative Disease Research Center at the ASU Biodesign Institute and an assistant professor with the School of Life Sciences.
Velazquez’s team performed the work in collaboration with the Translational Genomics Research Institute, or TGen, part of City of Hope, and used mice to model glyphosate exposure. They showed that brains may be much more susceptible to the damaging effects of the herbicide than previously thought. Glyphosate is the most common chemical herbicide used in the global market.
The study tracked both the presence and impact of glyphosate’s byproducts in the brain long after exposure ends, showing an array of persistent, damaging effects on brain health.
Glyphosate exposure also resulted in neuroinflammation, Alzheimer’s-like symptoms, and premature death and anxiety-like behaviors, replicating others studies.
The researchers tested two levels of glyphosate exposure: a high dose, similar to levels used in earlier research, and a lower dose that is close to the limit used to establish the current acceptable dose in humans. Furthermore, the scientists discovered these symptoms persisted long after a six-month recovery period in which exposure was discontinued.
This lower dose still led to harmful effects in the brains of mice, even after exposure ceased for months. While reports show that most Americans are exposed to glyphosate daily, these results show that even a short period could potentially cause neurological damage.
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By proxy, the study raises serious concerns about the chemical’s safety for human populations.
According to the Centers for Disease Research, farm laborers, landscape workers and others employed in agriculture are more likely to be exposed to glyphosate through inhalation or skin contact. Additionally, the new findings suggest that ingestion of glyphosate residues on foods sprayed with the herbicide potentially poses a health hazard. Most people living in the U.S. have been exposed to glyphosate during their lifetime.
“My hope is that our work drives further investigation into the effects of glyphosate exposure, which may lead to a reexamination of its long-term safety and perhaps spark discussion about other prevalent toxins in our environment that may affect the brain,” said Samantha Bartholomew, an ASU PhD candidate and first author on the paper.
The team’s findings build on earlier ASU research that demonstrates a link between glyphosate exposure and a heightened risk for neurodegenerative disorders. The earlier study showed that glyphosate was able to cross the blood-brain barrier, a protective layer that typically prevents potentially harmful substances from entering the brain. Once glyphosate breaches this barrier, it can interact with brain tissue and contribute to neuroinflammation and other harmful effects on neural function.
Current regulations allow for the use of a pesticide on food crops. The U.S. Environmental Protection Agency sets a tolerance or limit on how much pesticide residue can legally remain on food and feed products. The EPA considers certain levels of glyphosate safe for human exposure, asserting that the chemical is minimally absorbed into the body and is primarily excreted unchanged.
However, recent studies, including this one, may change that perception and raise questions about existing safety thresholds, and whether glyphosate use is safe at all.
“Herbicides are used heavily and ubiquitously around the world,” said co-author Patrick Pirrotte, an associate professor in TGen’s Early Detection and Prevention Division, director of the Integrated Mass Spectrometry Shared Resource at TGen and City of Hope, and senior author of the paper.
“These findings highlight that many chemicals we regularly encounter, previously considered safe, may pose potential health risks. However, further research is needed to fully assess the public health impact and identify safer alternatives,” he said.
“Our goal is to identify environmental factors that contribute to the rising prevalence of cognitive decline and neurodegenerative diseases in our society,” Velazquez said. “By unveiling such factors, we can develop strategies to minimize exposures, ultimately improving the quality of life for the growing aging population.”
The human brain is an incredibly adaptable organ, often able to heal itself, even from significant trauma. Yet for the first time, new research shows even brief contact with a common herbicide can cause lasting damage to the brain, which may persist long after direct exposure ends.
The National Institutes on Aging, National Cancer Institute of the National Institutes of Health and ASU Biodesign Institute funded this study.
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