The neurodevelopmental impact of common herbicides and pesticides
Herbicides stand as the most widely used class of pesticides across farms, homes, and industrial sites. A recent study links exposure to two of the most common herbicides—glyphosate and 2,4-D—to declines in brain function among adolescents. Researchers from the Herbert Wertheim School of Public Health and Human Longevity Sciences at the University of California, San Diego report these findings.
In a study published in Environmental Health Perspectives, scientists measured the presence of metabolites from glyphosate and 2,4-dichlorophenoxyacetic acid (2,4-D), along with metabolites of the insect repellent DEET, in urine samples. The samples came from 519 adolescents aged 11 to 17 living in Pedro Moncayo, an agricultural canton in Ecuador, collected in 2016. The team evaluated neurobehavioral performance across five domains: attention and inhibitory control, memory and learning, language, visual-spatial processing, and social perception.
“Many chronic diseases and mental health disorders among adolescents and young adults have risen over the past two decades. Environmental exposure to neurotoxic pollutants may help explain part of this trend,” notes lead author José Ricardo Suárez, associate professor at the Herbert Wertheim School of Public Health.
The study highlights several key findings:
• 98 percent of participants showed traces of glyphosate, a non-selective herbicide used to control vegetation in residential areas and on crops such as corn and soybeans.
• 66 percent had detectable 2,4-D, a broadleaf herbicide used on lawns, wetlands, and agricultural crops.
• Higher urinary 2,4-D levels correlated with poorer performance in attention and inhibitory control, memory and learning, and language tasks.
• Glyphosate levels were linked to lower scores in social perception, while DEET metabolites did not show an association with neurobehavioral outcomes.
“Herbicides and insecticides are widely used in agriculture across both developed and developing regions. Exposure risk rises for children and adults living near agricultural areas, but researchers still do not fully understand how different life stages are affected,” explains Briana Chronister of San Diego State University, the study’s first author.
Earlier research has connected exposure to common pesticides with impaired neurocognitive performance, and other chemicals may influence mood and brain development as well.
The mental health landscape is changing
Contemporary data show that about 20 percent of adolescents and 26 percent of young adults meet criteria for diagnosable mental health problems such as anxiety, depression, impulsivity, aggression, or learning disorders.
“Hundreds of new chemical products enter markets each year, and today more than 80,000 chemicals are registered for use,” says José Ricardo Suárez, emphasizing the volume of potential exposure in everyday life.
The authors report that 2,4-D adversely affected performance across all five neurobehavioral domains, with notable impacts on attention, inhibitory control, memory, learning, and language. Glyphosate showed a significant negative effect on social perception, a measure of recognizing emotions, while DEET metabolites did not appear to influence neurobehavioral outcomes. Suárez cautions that much remains unknown about the long-term safety of numerous chemicals in use today and calls for further research to clarify these effects.
Regulatory outlook and ongoing debates
Glyphosate has long sparked debate about safety, especially after classifications by health authorities in previous years. In the European Union, the license for glyphosate has faced extensions and ongoing scrutiny as agencies review data gaps and consumer diet exposure. The extension discussions reflect the tension between market access for agricultural inputs and evidence about potential health risks. In this ongoing regulatory context, researchers and policymakers stress the need for robust, long-term studies to understand real-world impacts.
In response to regulatory developments, commentaries from representatives of scientific and policy communities highlight the limits of current knowledge and the importance of safeguarding public health. Markers of exposure and health outcomes continue to shape discussions about herbicides and related chemicals in modern agriculture.
Reference: This summary draws on a report published in Environmental Health Perspectives.