Pesticides with a Side of ADHD: The Saga Continues

The Claim: Pesticides might contribute to the development of ADHD in school-aged children.

You might have missed a study out of Harvard's esteemed School of Public Health, the Environmental Health and Epidemiology wing to be exact:

Children with higher concentrations of a certain organophosphate - breathe, it's a scary word but hey, it looks so much more benign in lavender - basically a by-product of a pesticide - were more likely to exhibit ADHD behavior.   Actually, more likely to have their parents report incidences of the usual ADHD suspects.  Inattention, hyperactivity, a dash of impulsivity.  But you get the idea.

Pretty good study with 1,139 kids aged 8 to 15.  Researchers pulled data from the National Health and Nutrrition Examination Survey, a nationally representative survey.  Collected urine samples then interviewed parents on the telephone.  The higher the concentrations of dimethyl thiophosphate in the pee, the more likely the parents reported behavior issues.

Sounds convincing.  But before you run out and re-stock the fridge, consider these not so small caveats:

One urine sample. 
That's right, the researchers looked at only a single potty break.  It's hard to argue a chemical triggered a complex neurological disorder when all you're holding is the clinical equivalent of a Dixie cup. Especially when it's known the suspected toxin leaves the body in a matter of days.  Repeated, continual exposure, okay, we can start talking but then again, we don't have evidence that it sticks around in the body and does damage to developing brains.

Remember the authors are suggesting that this complicated set of symptomatology that arises early in childhood, perhaps even earlier, is linked to exposure to a pesticide that they've only just found in their bodily fluids at a much later age and that the body dumps pretty readily.  Sure, there's some newer research linking prenatal levels of organophosphates to later child development (e.g., IQ, attention problems) but it's equally inconclusive (some culled from this very survey) and often involves kids exposed to lots of pesticides. 

A better study would have urine samples over a long time period.  Years.  I'm sure someone is working the data right now.  We will wait.

ADHD via parental report. 
There were no professional diagnoses here but moms and dads and maybe even grammy answering questions over the telephone about children's behavior.  It's not clear if any of these kids really exhibited ADHD or even if their "caregivers" thought they did. 

On a side note of interest to over-medication theorists, although 119 kids met the criteria in the phone interview, another 30 took ADHD prescription meds though they failed to meet the diagnostic criteria. 

In any event, the better study would include professional assessments, maybe some undergrad scouring medical records for independent verification of ADHD.   

Need I even mention this is correlational evidence, hardly causal in nature? No, you are savvy readers

Here's the silver lining.  Many kids failed to demonstrate "detectable" levels of pesticides.  In other words, too little in the pee to be measured accurately (35% to 80% depending on the pesticide).  For the organophosphate that was linked to ADHD behavior, 63% of kids had detectable levels. 

Very good journal article too - it's free if you wanna give it a go.  I'm happy to report the authors don't plump up the conclusions and thankfully laid out their methods, calculations, and limitations in pretty clear details.  Could have mentioned the little parental self-report problem as a weakness but they didn't declare pesticides the grand culprit in ADHD.  Nor did they suggest you go out and buy only organic produce. 

That's progress in my opinion.  Reasonable, measured, backed by evidence.  My goodness, sometimes researchers do restrain their ambitious conclusions. 

It's even published in the premier journal, Pediatrics back in July....July of 2010. That's right.  Just read about it on a story online at this week as if there weren't any more recent studies to startle parents. 

The Bottom Line:
One more report linking pesticides and children's poor behavior/developmental outcomes.  Some meaningful limitations, especially the limited time frame and lack of verifiable ADHD diagnosis. 

Taken in content with existing studies, I will try to better remember The Dirty Dozen next time I'm strolling between the berries and bananas.  But seeing as this is no smoking gun I very well may slip the pesticide-ridden grapes into my shopping cart. 


scienceofmom said...

Nice post. I really like your blog, and I'm trying to do some similar sciency posts on my own blog to satisfy my craving for a good journal article now and again. Can I just say that I am so grateful for the dirty dozen list!? I am a little scared about pesticides, but I just balk at some of the prices for organic produce. One thing I've been wondering but have never gotten around to looking up - what about grain products like bread and pasta? Is it worth buying organic for those foods? Maybe you have run across something on this in your research?

Polly Palumbo, Ph.D. said...

Hi SciMom,

Thanks! Glad to find your new blog too! As for the pesticides...I've often read that the refined products, like the grains, don't tend to have much if any pesticide residue.

As for dairy, I understand it's not so much the organic part but the hormones that are cause for concern. You can buy non-organic hormone-free. Still, I buy organic milk because my kids seem to like the taste better and more important, I can store extra gallons for what seems weeks. I think the date on the last carton was the end of October!

scienceofmom said...

I'm torn about milk, actually. I buy rBST-free milk, but I don't usually choose organic. I worked in the dairy industry for a few years, and the thing that bothers me about organic milk is that organic cows can't be treated with antibiotics if they get an infection, and mastitis is fairly common even with the best management. Having had one clogged milk duct during my own lactation, I don't even want to think about how painful untreated mastitis would be. I think it is great that organic dairy farms are supporting the organic feed industry and have standards about having their cows outside for a certain percentage of the year, but I get hung up on the antibiotic issue. (Antibiotic residue in conventional milk is very low, because if a cow is being treated for an infection, her milk is not sold until it is clear of antibiotics.) My two cents. It is hard to argue with taste, though! That's probably an effect of the cows being on pasture more.

Polly Palumbo, Ph.D. said...

So you're the dairy expert! Excellent! Many thanks and now I can rest easily when the organic is not available. I'm not convinced about the taste difference but I'm not arguing with the little people at the dinner table.