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| Forbes Magazine science contributor, Emily Willingham |
An anti-pesticide manifesto [PDF] from the Pesticide Action Network North America (PANNA) has recently made a few headlines in big papers and nabbed a feature on an NPR member station with claims that “children today are sicker than they were a generation ago” and that pesticides are a “key driver” of the increase in childhood disorders such as “childhood cancers … autism, birth defects, and asthma.” The news reports almost invariably describe the tome in scientific terms without mentioning that it’s self published and not peer reviewed and contains no new data or information. The stories do not fail, however, to mention autism and to mention it early.
The PANNA authors pin their autism claim in part on the much written-about “autism epidemic.” While environmental factors might play some role in a small portion of the increase in autism, as I argue here, the general consensus appears to be that diagnostic substitution and enhanced awareness and recognition are the main drivers. Regardless of whether a genuine increase exists and what environmental factors are key to it, very little published evidence suggests a link between autism diagnoses and pesticide exposures. Yet the two keep popping up together in articles that sensationalize a relationship or posit one from research that doesn’t address autism at all.
Autism, though, sells. It sells stories, it gets attention, it attracts clicks. So let’s take a look at what they’re selling you.
The PANNA report mentions autism 58 times but focuses on it only in one short section of its 40 pages. In this section, called “The Science,” the authors cite a handful of published reports, not all of them studies. One paper is a scientific op-ed of sorts that gained fame for asserting that “10 chemicals”–gotta love numbered lists–need attention in the context of autism, which sounds great except…hardly any of them had been linked to autism in any way. Against the backdrop of this editorial, the authors of the PANNA report then go on to list eight other studies they claim support an autism-pesticide link (I note here that the term “pesticide” is used loosely to encompass herbicides, fungicides, and insecticides). In four of eight cases, they simply mischaracterize the studies they cite.
Among the eight studies, an original research study they reference is a 2006 report assessing links between a pesticide, chlorpyrifos , and developmental delays (not diagnosed autism) in urban-dwelling families. Chlorpyrifos was introduced in 1965 and widely used in households until it was banned in 2001 for home use. It remains in wide use in agriculture. A second study the PANNA authors cite was a 2007 article describing prenatal agricultural exposure to several compounds, including chlorpyrifos. Those investigators found no link between chlorpyrifos and endpoints that were similar to those of 2006 study, but did identify an association between another chemical and pervasive developmental disorders (again, not diagnosed autism). So far, we’ve got two reports with conflicting results that don’t involve diagnosed autism.
The PANNA group then lists what they call a “trio of US studies” from 2012 that “examined links between environmental exposures among parents (including but not limited to pesticides) and the incidence of autism among their children.” The studies in question didn’t examine those links at all and don’t mention pesticides or even environment; the authors of those reports might be surprised to see how their work has been described. All three are genetics studies. One group described finding a greater rate of spontaneous mutations passed along from fathers compared to mothers and that accumulation of these mutations was associated with the dad’s age. Another found an association between an epilepsy-related gene variant and autism. The third identified two other gene variants that are risk factors for autism. These studies weren’t about pesticides and autism and they did not “examine links” in the way described. A fourth study the PANNA authors cite, also from 2012, was another genetics study that confirmed an association between father’s age and accumulated mutations and was not a study of pesticides.
Finally, the PANNA report cites, as its last pillar in its “pesticides as key drivers of autism” argument, a 2012 paper proposing a hazy network between autism and a mishmash of high-fructose corn syrup consumption, mercury, organophosphates, and a host of other chemophobia bugbears. But that paper was a review and contained no new data. At the time of its publication, I analyzed its rationales and conclusions and found that the arguments fell apart from the word go. The authors’ response to that critique and my response to them are here.
In sum, the section from this PANNA report asserting that pesticides are a “key driver” of an autism increase contains eight citations of what they call “The Science.” Two contain no original research, four aren’t related to pesticide assessment at all but are misleadingly described as such, and two address intense pesticide exposure and pervasive developmental disorders and delays but not autism specifically. The case they build to link autism and pesticides is not a compelling one. Why did they build it? I’m guessing because autism gets attention.
They could have built it better, at any rate. They did cite one other relevant research paper in the report, but for some reason, they failed to include it in “The Science.” That 2007 study suggested that maternal residence in the vicinity of pesticide application in the central valley of California might be associated with diagnosed autism, although the work had some pretty significant confounders and limitations that its authors note.
Another citation the PANNA authors included outside of “The Science” was a 2012 review in a peer-reviewed journal, “Tipping the Balance of Autism Risk: Potential Mechanisms Linking Pesticides and Autism.” This review offers up a kitchen sink of animal and cell research–ranging from sea urchins to voles–to weave a plausibility argument associating autism and pesticides. One report its authors highlight describes, ironically, a beneficial effect of chlorpyrifos in “restoring behaviors” in a mouse model (ETA: I don’t know what the specific behaviors were, just that the chlorpyrifos treatment restored them to “normal”). Yet in spite of a host of references, based on a quick assessment, only about seven of the 130+ citations might directly address autism and pesticide exposure, three of them already discussed here.
The authors of the “Tipping the Balance” review argue that we need more studies looking at whether or not our pesticide exposures interact with genes to result in autism, using animals with “autism-like” behaviors and evaluating large numbers of people. That may be the case, although because of the nature of scientific publication, we may not know about negative results researchers have already found. Regardless, current studies–animal or human–showing a link are vanishingly rare, even though six years have passed since the chlorpyrifos/urban families report first appeared. This lack of data again leads to the question: Why bring up autism in the PANNA report at all, much less 58 times, asserting that pesticides are a “key driver” of the condition? And why misrepresent half of the studies cited that pertain to it?
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