Common herbicides found to be harmful to the teenage brain

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Common herbicides found to be harmful to the teenage brain

Common herbicides found to be harmful to the teenage brain.

Herbicides are among the most widely used pesticides worldwide, employed extensively in agriculture, households, and industry.

A study led by researchers from the University of California, San Diego (UCSD) Herbert Wertheim School of Public Health and Human Longevity Science has revealed that exposure to two of the most popular herbicides is associated with poorer cognitive function in adolescents.

In an article published on October 11, 2023, in the Environmental Health Perspectives online journal, researchers reported on measurements of two commonly used herbicides, glyphosate and 2,4-dichlorophenoxyacetic acid (2,4-D), as well as the metabolite concentration of the insect repellent DEET.

Urine samples were collected from 519 adolescents aged 11 to 17, residing in Pedro Moncayo Agricultural County in Ecuador in 2016.

Researchers also assessed neurological behavioral performance in five areas: attention and inhibition control, memory and learning, language, visual-spatial processing, and social perception.

Common herbicides found to be harmful to the teenage brain

The main findings and historical context

“Over the past two decades, there has been an increase in chronic diseases and mental health disorders among adolescents and young people worldwide, and exposure to neurotoxic pollutants in the environment can partially explain this increase,” said senior author Jose Ricardo Suarez, MD, PhD, MPH, Associate Professor at the Herbert Wertheim School of Public Health.

The research revealed the following:

Glyphosate, a non-selective herbicide used in many crops (including corn and soybeans) and for vegetation control in residential areas, was detected in 98% of participants.

2,4-D, a broadleaf herbicide used for lawns, aquatic environments, and crops, was detected in 66% of participants.

Higher concentrations of 2,4-D in urine were associated with lower performance in areas such as attention and inhibition control, memory and learning, and language.

Glyphosate concentration in urine was only significantly correlated with lower social perception scores, while DEET metabolites showed no association with neurological behavioral changes.

Following the introduction of glyphosate-resistant “Roundup Ready” crops in 1996 and the introduction of 2,4-D-resistant crops in 2014, the usage of glyphosate and 2,4-D has significantly increased, making them the most widely used herbicides in the world.

Scholars’ concerns and future research

“Herbicides and pesticides are heavily used in agricultural production in developed and developing countries worldwide, increasing the likelihood of children and adults coming into contact with them, especially if they reside in agricultural areas, but we don’t know how it affects each stage,” said first author Briana Chronister, a doctoral student in the joint UCSD-SDSU Public Health Ph.D. program.

Prior research has indicated that exposure to some of the most commonly used pesticides can alter cognitive function, while other pesticides may affect emotions and brain development. Currently, 20% of adolescents and 26% of young people have diagnosable mental health conditions such as anxiety, depression, impulsivity, aggression, or learning disabilities.

The authors reported that 2,4-D was negatively correlated with performance in all five neurological behavioral domains, with statistically significant associations observed in attention and inhibition control, memory and learning, and language. Glyphosate was only significantly negatively correlated with social perception (a test measuring emotional recognition abilities), while DEET metabolites showed no link to neurological behavioral changes.

“Every year, hundreds of new chemicals are introduced into the market, and over 80,000 chemicals are currently registered for use,” Suarez said. “Unfortunately, we know very little about the safety of most of these chemicals and their long-term effects on humans. More research is needed to truly understand their impact.”

This study is part of the ESPINA (Children and Adolescent Secondhand Pesticide Exposure Study) initiative, a prospective cohort study funded by the National Institute of Environmental Health Sciences (NIEHS), the National Institute for Occupational Safety and Health (NIOSH), and other private sources. ESPINA aims to understand the impact of pesticide exposure on human development from childhood to early adulthood.

In 2022, Suarez and his team completed the 14th-year follow-up of study participants, planning to assess whether the observed associations persist into early adulthood.