3 Reasons Aerial Pesticides Are Not Causing Autism

By Hank Campbell — May 02, 2016
There are bad studies, and worse studies. This one could be either: Pyrethroid pesticides, which have been used for 50 years, are all of a sudden causing autism? We think not.
shutterstock_248074444 Photo credit: Shutterstock

Steven Hicks, M.D. PhD, pediatrician at Penn State Milton S. Hershey Medical Center in Hershey, Pennsylvania, looked at autism rates in a swampy region of New York and saw higher developmental delay and autism diagnoses in some areas and thinks he knows why; pyrethroid pesticides being sprayed by airplanes to kill mosquitoes.

Scientists, toxicologists, and public health officials certainly appreciate some attention being drawn to killing mosquitoes as the season — and Zika concern — approaches, but chemically it just can't be true, for three reasons:

1. Pyrethroids are less toxic than the popular home-use repellent DEET. DEET is even applied directly to the skin, where it is readily absorbed into the blood. It still isn't harmful, meaning pyrethroids are even safer.

2. There is no plausible biological mechanism for this correlation and none is proposed; it is simply two curves that happen to show an association, real or otherwise. It could just be a spurious correlation. For example, organic food sales have also increased with autism(1), which is obviously ridiculous. Furthermore, there are many reasons why people who live near swampland may seem to have more diagnosed developmental delays — a broadening of the definition of autism, and better reporting in areas that were not as well serviced before.

3. Pyrethroids have been used for 50 years, so they can't suddenly be causing autism. In the zip codes that were analyzed, 1 in 120 children was diagnosed with autism spectrum disorder or a developmental delay, while the same class of pesticides without aerial spraying was 1 in 172. Yet the prevalence nationwide for autism spectrum disorder is 1 in 68. From these data, it could be argued that pyrethroids lower the chances of autism, which is no more or less valid than these claims.

Hicks does not say he knows this correlation to be causative, he wants it "studied" more, but his supporting information is sketchy — he invokes a California paper regarding pregnant women and autism being linked to pesticides using proxies the same way, without noting that the paper was widely discredited because it did not measure any pesticides(2), it simply matched two curves as is being done with aerial spraying. The author also did not disclose two conflicts of interest— she is both an autism and an anti-pesticide activist.

Hicks' work has not been peer-reviewed yet (preliminary findings, presented at the Pediatric Academic Societies 2016 Meeting), so it is sadly both unfortunate and predictable that environmental groups are already exploiting developmentally disabled children and their parents by promoting this finding to raise money — and that publications like Newsweek are enabling them without any critical thinking.


(1) It's a serious issue, I don't want to be glib about it, but since every environmental group is glib about their curve matching when dialing for dollars:

(2) Other flawed uses of proxies published as fact:

(1) Zebras evolved stripes due to flies

(2) Famous paintings are proof of climate change

(3) Bicep size correlates to political conservatism.

(4) A lack of vitamins is linked to more autism