Your Citation Does Not Say What You Think It Does

Recently, Dr. Oz said some things that certain left-leaning folks have interpreted as condemning organic agriculture. Tom Philpott at Mother Jones wrote a piece about how Dr. Oz got it wrong citing various recent studies about pesticides. I thought most weren’t very convincing citations and he neglected to cite anything that pointed out most conventional food has fairly small or undetectable pesticide residues. But one study he cited completely contradicts the point he was trying to make.

Normally I would just comment on his post but due to how busy I’ve been this week, it’s a few days later and it won’t actually be read (well it won’t be read much here either).

Updated 2012-12-09: Well this is embarassing. Somehow I neglected to actaully link to Philpott’s piece. This is now fixed.


The second study he cites for evidence that organic food helps one avoid pesticide exposures is “Neurobehavioral problems following low-level exposure to organophosphate pesticides: a systematic and meta-analytic review” (sadly pay-walled) about which he writes:

For a paper released in November, UK researchers conducted a "meta-analysis" on the neurological effects of organophosphate pesticides at low levels—that is, they gathered all of the well-designed studies on the topic they could find and analyzed the combined results. They found a "significant association between low-level exposure to OPs [organophosphates] and impaired neurobehavioral function." Specifically, they found that exposure to the pesticides reduced people's memory and their ability to process information quickly. Organophosphates have been "largely withdrawn from use" in the last decade, EWG reports, but the Environmental Protection Agency has not seen fit to ban them, and they are still sprayed on some crops. According to EWG's latest analysis of USDA data, they still turn up in bell peppers, green beans, kale, and collards—again, all foods that authorities like Oz rightly encourage people to eat more of. EWG recommends buying these foods organic if possible.

Philpott’s text, including his referencing the EWG and detection of OP residues on certain foods, implies that this study is relevant to dietary organophosphate exposure levels. If you got the impression that eating conventionally grown kale or collards might mean you’re going to get neurological problems, then I wouldn’t be surprised. However, when I loaded the study, I found that the first sentence of the abstract is: “Meta-analysis was carried out to determine the neurotoxic effects of long-term exposure to low levels of organophosphates (OPs) in occupational settings.” Occupational exposures are rarely relevant to non-occupational conditions so I was a bit skeptical that Philpott’s implication would hold up.

A nice internet person helped me look at the study and unsurprisingly the studies included are ones from workers on farms applying pesticides, pesticide factory production workers, pest control workers, sheep dippers and so forth. In other words, people who work with pesticides either every day or regularly as part of their job which exposes them to much greater amounts than anyone eating food bought from Safeway. Further, this meta-study explicitly excluded studies that didn’t have an control group that wasn’t similarly exposed. One of the exclusion criteria reads: “Animal studies, studies of children, studies of human adults which did not include an unexposed control group, single case reports”. That is, if a study looked at neurological effects in farm workers who apply pesticides, the study would be excluded if it didn’t include a comparison to a similar (probably non-farm worker) control group.

This review did find that most of the included studies supported its title. Occupational exposure to organophosophate pesticides does appear to be linked to neuro-behavioral problems. But, since each of those studies had to have an appropriate non-occupationally exposed control group that didn’t show the neurological effects, that means the non-occupationally exposed people weren’t showing similar effects. Otherwise, they wouldn’t be able to find a difference. Duh. So unless you’re a sheep dipper or a farm worker or one of the other groups studied here, this study just doesn’t apply to you. Your kale is not going to give you mental problems.

To summarize: using this study to justify the idea that you should avoid certain conventionally grown vegetables because the organophosphate residues might cause neurological problems is wrong. It’s a good study to cite for why it’s important to heavily and closely regulate pesticide use to protect workers (including maybe banning some!). However, that’s not what Philpott wrote despite mentioning the issue of workers’ rights elsewhere. This study says nothing whatsoever about dietary intake of pesticides. This citation just doesn’t say what the author is claiming. Period.

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