Low-level exposure to pyrethroid insecticides found in common pesticide brands like RAID and ORTHO results in neurodevelopmental damage to laboratory animals, reinforcing evidence of harm found in epidemiological studies on human exposure to these chemicals.
According to research published in April in PNAS Nexus, mice exposed to the pyrethroid deltamethrin displayed atypical behavior similar to humans with developmental disorders.
“We are not saying these mice have autism or that they have ADHD [attention-deficit/hyperactivity disorder]. That’s not the goal here,” said James Burkett, Ph.D., study co-author and assistant professor of neuroscience at the University of Toledo College of Medicine.
“What we are saying is that something in their brain has been altered by this exposure and it’s resulting in the same kinds of behaviors that we see in children with autism.”
Scientists arrived at this determination by exposing a group of mouse mothers to consistently low levels of deltamethrin in their food during preconception, pregnancy and lactation.
The study notes that the amount of pesticide provided was “well below the benchmark dose for regulatory guidance.”
A separate control group was given no pesticide in its food. Offspring from the female mice were then put through behavioral tests on social behavior, restrictive or repetitive behaviors, cognition and communication.
Results found that mouse pups whose mothers were exposed to deltamethrin increased their repetitive behaviors.
In tests, they buried more marbles than control pups and performed more self-grooming than the control group. Male pups exposed to deltamethrin also produced fewer vocalizations when being separated from their mothers.
Pesticide exposure also impaired learning and memory; in a fear conditioning test, exposed mice were less likely to react to a fearful event they encountered before.
In addition to behavior, scientists observed physiological changes in pups whose mothers were pyrethroid-exposed. These mice exhibited significant changes in dopamine levels and transport around the body.
For autistic individuals, the metabolite homovanillic acid is considered the earliest biomarker for the condition, and exposed mice pups displayed increased levels of the substance.
“These are all similar to symptoms human patients with neurodevelopmental disorders might have,” Burkett said.
Synthetic pyrethroids are hazardous pesticides that have flown below even pesticide advocates’ radar for far too long, not receiving nearly as much attention as other dangerous and commonly used pesticides like glyphosate.
“If you have someone who comes and sprays in your house, this is likely what they’re spraying. It’s used in landscaping, it’s what they fog in the streets for mosquitos. It’s everywhere,” said Burkett.
“Our study, however, adds to the evidence that these chemicals might not be as safe for children and pregnant women as we once believed.”
In fact, Beyond Pesticides has never believed these chemicals to be safe for children or pregnant women. The depth of historical reporting on these chemicals in the Daily News Blog bares this out. As far back as 2008, Beyond Pesticides was reporting on the risk these chemicals pose to children’s development.
The research on this class of chemicals has sounded a consistent drumbeat of developmental harm to children.
In 2011, research determined that children exposed to higher levels of synthetic pyrethroids are three times as likely to have mental delay compared to less exposed children.
A study from 2014 associated proximity to pesticide-treated agricultural fields in pregnancy with increased risk of autism in children of exposed mothers.
Data published in 2015 found that deltamethrin increases the risk of ADHD in children, with one study finding impacts specifically on boys.
Studies published two years later determined that synthetic pyrethroid exposure increases the risk of premature puberty in boys, and another associated the chemicals with externalizing and internalizing disorders.
Another study found that aerial mosquito spraying, which is most frequently conducted with synthetic pyrethroids, is linked to elevated autism rates.
The impacts seen are not all developmental.
A 2012 study associates pyrethroid exposure before, during and after pregnancy with an increased risk of infant leukemia.
And a recent study published earlier this year finds that synthetic pyrethroid exposure during mosquito control operations increases the risk of respiratory disease and certain allergies.
Rather than rein in the use of these chemicals, the U.S. Environmental Protection Agency (EPA) in 2019 stripped away protections that reduced children’s exposure to pyrethroids.
In making its decision, the agency allowed a letter from the pesticide industry umbrella group CropLife America to dictate its approach to protecting children from hazardous, neurotoxic pyrethroids.
The model proposed by CropLife America eliminated safety factors for children. In a rare instance, the EPA conducted an outside literature review to buttress its argument but instead ignored those data and prioritized the unprotective model proposed by the pesticide industry.
After selling out children’s health, the agency then took directions from a group referring to themselves as the Pyrethroid Working Group, comprised of major pesticide manufacturers Bayer, FMC, Syngenta, BASF, AMVAC and Valent.
At the request of this working group, the EPA reduced a proposal from EPA staff scientists to implement 66-foot buffer zones between agricultural fields and water bodies down to 10-25 feet.
The agency also agreed that wind speeds up to 15 miles per hour were acceptable for pyrethroid applications, despite previous proposals setting the cut-off at 10 miles per hour.
“We have reduced our exposures to many classes of dangerous pesticides over the past few decades through restrictions and regulations,” said study co-author Gary Miller, Ph.D., vice dean for research strategy and innovation at Columbia University Mailman School of Public Health.
“This study adds to a growing body of literature that the widely used pyrethroids are not without adverse effects and should be further evaluated for their safety.”
While further study is warranted, it should be conducted while this class of chemicals is suspended from public use.
Rather than place the burden of proof on scientists to show harm, chemical manufacturers should be required to provide evidence that these chemicals will not harm children’s health. It is evident that they cannot, and with every new study there is growing awareness from the scientific community that these chemicals do not belong on the market.
Originally published by Beyond Pesticides.
The views and opinions expressed in this article are those of the authors and do not necessarily reflect the views of Children's Health Defense.