Problems With Linking ADHD and Organophosphate Insecticides

A recent scientific paper published in the journal, Pediatrics made a tentative link between exposure to an old class of insecticides organophosphates, OPs, average 40 years old) and ADHD (attention deficit hyperactivity disorder). They measured metabolites of OPs in urine samples from children and they interviewed their parents about whether their children’s behavior fit the pattern of ADHD.

The kids “diagnosed” in this fashion tended to have higher levels of the OP metabolites in their urine samples. The authors acknowledged that this study is far from making a solid connection and that there were other possible explanations for the data. Even so, there did seem to be some relationship and it was quickly picked up by many commentators in the popular press.

In a way this connection makes sense. OPs have been widely used on food crops. Their mode of action is to inhibit the important, neurological enzyme, cholinesterase. ADHD is a behavioral syndrome, but a neurological connection would fit. So, is this the explanation for the seeming increasing incidence of ADHD among American kids?

Well, there is one major problem with the linkage. Over the time period that ADHD seems to have been on the rise, the use of OP insecticides has been on the decline having been replaced with better alternatives.

In response to the Pediatrics publication, the EPA released a statement describing their overall regulatory oversight of OPs and pointed out that since the mid 1990s, OP use has declined by 57%, 17 products have been terminated, and 58 specific use patterns that effect foods consumed by children have been ended. California’s EPA does extensive annual pesticide residue testing and has shown that not only OP residues, but also other chemical residues, are mostly undetectable or well under established safety levels. All of this actually raises questions about where the OP metabolites in the Pediatrics study came from. In any case, the trend does not fit the increasing ADHD trend.

The relative “toxic load” of OPs has declined to only 9% of 1992 levels and the “toxic load” of all cholinesterase inhibitors has dropped to 14% of what it was in 1992.

If OPs or cholinesterase inhibitors were the cause of ADHD, that problem should have been declining rapidly over the last decade. That does not seem to be the case, so the connection is in doubt.

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Steve Savage is a scientist (PhD Plant Pathology) with more than thirty years of diverse experience with crops and agricultural technologies.
He has worked on everything from biological controls to chemicals to genetics to biotechnology. He has worked for a university (Colorado State), a large company (Du Pont), a small company (Mycogen) and for the last 13 years as an independent consultant.
He writes about farming both to address widespread myths and to confront the real challenges of sustainably feeding a world population headed to 9 billion in an age of climate change. Steve writes from sunny San Diego county in California in an office with a view of his home vineyard and garden.
Links to his writing can be found at