Herbicides May Harm Brain Function in Adolescents

Exposure to commonly used herbicides, including glyphosate and 2,4-dichlorophenoxyacetic acid, appears to negatively impact attention, impulse control, and learning and language scores in young people.

In a new study published on October 11 in Environmental Health Perspectives, scientists at the Herbert Wertheim School of Public Health and Human Longevity Science at the University of California San Diego found significant links between exposure to commonly used herbicides and lower neurobehavioral performance in young people ages 11 to 17.

The scientists measured metabolite concentrations of commonly used herbicides glyphosate and 2,4-dichlorophenoxyacetic acid (2,4-D) and the insect repellent DEET in urine samples from 519 adolescents in Pedro Moncayo, Ecuador — an agricultural community.

Glyphosate is found in weed killers like Roundup, and 2,4-dichlorophenoxyacetic acid (2,4-D) is an ingredient in other widely used herbicides. DEET is a compound used in several bug repellent brands.

The researchers also assessed the adolescents’ neurobehavioral performance in areas such as memory and learning, attention and inhibitory control, visuospatial processing, social perception, and language.

Among the participants, 98% had detectable levels of glyphosate, 66% had measurable amounts of 2,4-D, and 33-63% showed DEET metabolites in their urine.

When the investigators compared herbicide levels to neurobehavioral performance, they found statistically significant associations between elevated 2,4-D levels and lower attention, inhibitory control, memory, learning, and language scores.

Still, glyphosate was only associated with lower social perception performance. Moreover, the scientists did not detect neurobehavioral performance issues in participants with DEET metabolites in their urine.

Despite the widespread use of herbicides, the research team says the long-term impact on brain function is largely unknown.

"Many chronic diseases and mental health disorders in adolescents and young adults have increased over the last two decades worldwide, and exposure to neurotoxic contaminants in the environment could explain a part of this increase," said senior author Jose Ricardo Suarez, M.D., Ph.D., M.P.H., an associate professor in the Herbert Wertheim School of Public Health.

For example, in previous research, scientists have found associations between pesticides and autism.

Although the study used hundreds of participants, urine samples can only measure herbicide exposure at a single point in time, which might not provide information on how long a person has been exposed to the compounds.

Still, the study’s authors say that these findings are the first to show links between urinary concentrations of 2,4-D and glyphosate and lower neurobehavioral performance. They suggest more research is needed using a larger number of adult and child participants to make definitive conclusions about whether herbicides harm brain function or influence neurobehavioral symptoms.