Herbicides Could Impact Brain Function in Teens

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This article originally appeared in the spring 2024 issue of UC San Diego Magazine as “What Lies Beneath.”

Fresh-cut flowers, houseplants and other greenery bring joy and beauty to homes and offices. They’re also big business. In Pedro Moncayo, an agricultural area located in the Ecuadorian Andes, 21% of adults work in the floriculture industry. While economic projections are trending upward across the globe, a concerning reality lurks beneath the surface: herbicides used to grow these vibrant crops may be reducing brain function in adolescents.

“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,” says José Ricardo Suárez, associate professor in the Herbert Wertheim School of Public Health and Human Longevity Science at UC San Diego.

For more than a decade, researchers have been aware of a connection between insecticide exposure and changes in neurocognitive performance in young children. But a recent study in Pedro Moncayo led by Suárez and Briana Chronister, doctoral candidate in the UC San Diego- San Diego State University Joint Doctoral Program in Public Health, shows that exposure to common herbicides may be associated with reduced brain function in adolescents as well.

In Pedro Moncayo, flower crops are subjected to a range of pesticides, including over 50 fungicides (for controlling mold and mildew), more than 20 insecticides (for controlling insects) and two known herbicides (for controlling weeds), although many more may be present.

In urine samples collected from 519 adolescents (ages 11 to 17) residing in Pedro Moncayo, researchers measured metabolite concentrations of glyphosate and 2,4-dichlorophenoxyacetic acid (2,4-D), two of the most widely used herbicides in the world. They also evaluated the neurobehavioral performance of study participants. Both herbicides were detected in a high percentage of participants and exhibited strong associations with decreased cognitive functioning, including attention and inhibitory control, language and social perception.

Glyphosate and 2,4-D are two among the more than 800 pesticides registered for use in the U.S., many of which have been associated with a range of health problems.

“There is considerable use of herbicides and insecticides in agricultural industries in both developed and developing nations around the world, raising exposure potential for children and adults, especially if they live in agricultural areas,” says Chronister.

Yet exposure isn’t just limited to production regions. In 2022, the United States imported $3.3 billion in cut flowers from 81 countries across the globe — with no limit on the amount of pesticide residue they may carry.

“Sadly, very little is known about the safety and long-term effects on humans for most of these chemicals,” says Suárez. “Additional research is needed to truly understand the impact.”

This article originally appeared in the spring 2024 issue of UC San Diego Magazine as “What Lies Beneath.”