Three billion pounds of herbicides are sprayed over farmlands every year. Yet, we know very little about their impact on animals and humans. Previous studies have focused on glyphosate—the main herbicide in Roundup—but the adjuvant components of Roundup and other herbicidal formulations are considered trade secrets, creating a huge knowledge gap in mechanistic studies.
In a groundbreaking study focusing on glyphosate and Roundup as a whole, researchers have shown that both increase seizure-like behavior in C. elegans. They also provide significant evidence that glyphosate targets GABA-A receptors, which are essential for animal movement and heavily involved in regulating sleep and mood in humans.
Even though the study, published in Scientific Reports, is the first to link the use of Roundup to convulsions in animals, that’s not even what sets it apart. The researchers examined the herbicides and formulations at a level 300 times less than what is recommended by the EPA and what humans encounter regularly.
“The concentration listed for best results on the Roundup Super Concentrate label is 0.98 percent glyphosate, which is about 5 tablespoons of Roundup in 1 gallon of water,” said Akshay Naraine, research lead and Ph.D. student at Florida Atlantic University. “Our study reveals that just 0.002 percent glyphosate, a difference of about 300 times less herbicide than the lowest concentration recommended for consumer use, had concerning effects on the nervous system.”
For the study, the researchers first tested glyphosate alone, then both the U.S. and United Kingdom formulations of Roundup from two distinct time periods—before and after the U.K.’s 2016 ban on polyethoxylated tallowamine (POEAs). The conditions were very purposely selected to pinpoint which effects are specific to the ingredient glyphosate, Roundup formulations in general, the POEAs surfactants, or any combination.
According to the results, C. elegans that underwent electroshock to mimic seizure behavior recovered in 34.1 seconds, on average, in normal saline conditions. However, when the nematodes were exposed to glyphosate and all Roundup formulations, the convulsion duration spiked to 56.9 seconds or longer—an increase in seizure behavior of at least 66%. The worst offender was the current Roundup formulation in the U.S., which resulted in an average convulsion duration of 65 seconds—an increase of over 90% compared with saline.
The data also indicate there is an important distinction between exposure to glyphosate and Roundup, with Roundup exposure increasing the percentage of C. elegans that did not recover from seizure activity. In saline, less than 5% of worms did not recover within 5 minutes. C. elegans exposure to glyphosate caused that number to jump to 12.9%. In the Roundup conditions, between 19 and 33% of worms did not recover from their seizure-like behavior within the time period. Again, the team discovered the worst results from the current Roundup sold in the U.S.— 33.5% of C. elegans did not recover when exposed to this herbicide formulation.
When sodium valproate, an FDA approved antiepileptic drug, was co-administered with Roundup, every worm recovered to normal locomotion.
“The non-recovery phenotype and prolonged convulsions in C. elegans from this study have helped to set a foundation for understanding nuanced physiological effects of herbicide that occur at concentrations exponentially below neurotoxic levels,” write the researchers in their paper.
Investigating mechanisms behind their findings, the researchers discovered significant evidence that glyphosate targets GABA-A receptors, which control animal movement and affect sleep and mood in humans. Experiments that paired subeffective dosages of glyphosate and a GABA-A antagonist yielded a 24% increase in non-recovery compared with the antagonist alone. This led the team to suggest the GABA-A receptor as a neurological target for the observed physiological changes.
With glyphosate use projected to increase 200-fold in the U.S. and similarly globally, the research team says it is essential to understand the nuanced affects that may be influencing neurotransmission.
“Given how widespread the use of these products is, we must learn as much as we can about the potential negative impacts that may exist,” said Ken Dawson-Scully, study co-author and associate provost in the Division of Research and Economic Development at Nova Southeastern University. “There have been studies done in the past that showed the potential dangers, and our study takes that one step further with some pretty dramatic results.”