Young brains appear at risk from exposure to popular weed killers

Exposure to two widely used weed killers could be harming the brain function of young people, impacting their memory and learning abilities, according to a study published Wednesday.

The study looked specifically at glyphosate, the active ingredient in Roundup herbicide and scores of other brands, and also at 2,4-D – a long-used, weed-killing chemical that has seen a surge in use in recent years and has increasingly been combined with glyphosate to kill tenacious weeds.

Concerns about impaired brain function were associated with both chemicals, particularly with 2,4-dichlorophenoxyacetic acid (2,4-D), according to the study, which was led by researchers at the Herbert Wertheim School of Public Health and Human Longevity Science at University of California San Diego and published in the journal Environmental Health Perspectives.

“This herbicide (2,4-D) has gone mostly under the radar and more studies aimed at understanding the health effect of herbicide exposures are needed,” said Jose Ricardo Suarez, director of the Climate and Environmental Health Research Program at the University of California San Diego.

“This builds on the growing knowledge that not just insecticides – pesticides that are designed to be neurotoxins – can affect brain processes,” Suarez said. The study showed that as herbicide exposures increased, neurobehavioral performance decreased, he said.

The researchers analyzed urine samples taken from 519 young people ages 11-17 who lived in farming communities in Ecuador where herbicides and other pesticides were sprayed. They then assessed the neurobehavioral performance of the youth, testing them on their attention/inhibitory control, memory/learning, language, visuospatial processing, and social perception.

Glyphosate was detected in the urine of 98.3% of the study participants and 2,4-D in 66.2%. Glyphosate was associated with problems with social perception, while 2,4-D was associated with attention/inhibition, language and memory/learning skills.

The researchers noted in their study that prior research in mice found subchronic and chronic exposure to glyphosate-based herbicides was linked to a range of neurobehavioral changes. And they cited prior research showing that doses of 2,4-D have also been linked to behavioral changes and neurological toxicity in rat studies.

The researchers said that there are a number of different ways in which the herbicides can be impacting human health, including through disruption of the endocrine system, which is “crucial” for the proper development of the central nervous system and human behavior. Both glyphosate and 2,4-D have endocrine disrupting characteristics, the researcher said.

The researchers said that despite the fact that pesticides are widely used around the world, there is a ‘dearth of studies characterizing the associations between these chemical groups and human neurobehavior.” More research is needed, the study authors said.

The study is part of the Secondary Exposures to Pesticides among Children and Adolescents (ESPINA) research, a prospective cohort study that examines the associations of subclinical pesticide exposures on human development.

Glyphosate is the world’s most widely used chemical, but has become controversial in many countries because of scientific research linking it to multiple health concerns, including cancer.

As glyphosate has become less effective, with weeds developing resistance to it, the use of other herbicides has climbed, including 2,4-D. Many farmers spray fields with both glyphosate and 2,4-D. Glyphosate is often sprayed directly onto crops, leaving residues in finished foods that people consume. 2,4-D is often sprayed directly onto certain crops.

European lawmakers are currently considering whether or not to renew the approval for glyphosate use across member states when the current approval expires Dec. 15.

The US Environmental Protection Agency maintains that glyphosate is “not likely” to be carcinogenic, and says there are no human health risks “of concern”. But the agency was forced to withdraw that safety determination last year after a federal appellate court invalidated the EPA’s assessment. The court ruling said that the EPA ignored expert advice from scientific advisers, and used “inconsistent reasoning” with respect to glyphosate safety.

2,4-D also has been linked through scientific research to an array of health concerns, including certain types of cancer, birth defects, immunosuppression and other health impacts in farming communities. More than 1,000 products containing 2,4-D are sold in the US, and 2,4-D is so widespread that residues have been detected in surface and groundwater sources.

(Featured photo credit: damircudic)