The latest claims about organic food and pesticide residues

A new paper insisting that organic foods leave fewer pesticide residues in the human body than conventional diets.

What the pesticides in our urine tell us about organic food

A study helps answer a question many of us ask when deciding whether to buy organic food: does it really make a difference?

The full paper is here.

In the interests of reducing narrative tension the answer is no.

One detail in the paper is that they don’t in fact measure the levels of the residues. Instead they note movement across the level of detection. So, for example, malathion residues can be detected down to 0.02 ng/mL 87.5% of the urine samples on the conventional had above this level, only 43.04 % on the organic did. Moving one way or the other across the detectability boundary might not be thought to be all that important.

For, as Paracelsus pointed out, it is the dose that is the poison.

Which is where we get to the larger point abut this paper - dosage. So, what do we think is an amount of malathion exposure that is important? The EPA tells us “ 0.1 mg/L for lifetime exposure of adults “. That’s not an entirely useful number because that’s going into the body, not what’s present in urine coming out. But still a useful enough guide to orders of magnitude and so on.

We’ve then got that problem of comparing ng/mL to mg/L, most of us can’t track all those zeros in our head. Fortunately, there’s a converter out there. The level we’ve said we shouldn’t be exposed to - in itself a number of orders of magnitude reduction from what we know does harm - is thus 100 parts per billion. The level this paper is measuring to is 0.02 ng/mL, or 0.02 parts per billion.

We are this, umm, fingers and toes out, at least 4 orders of magnitude below the limit we think reasonable to impose. Nearly 5 in fact.

Does this make any difference? No, of course it doesn’t. This is a story about how much better analytical work in the lab has become, nothing else. Well, OK, a little bit else:


This work was funded by Friends of the Earth U.S, United States.

Oh, right.

Which is why the paper hasn’t gone on to do the only comparison we are really interested in. Organic food costs more than conventionally pesticided stuff. It uses more land too. Cheaper food means, obviously enough, that we all have the ability to eat more and better of it. What is the addition to human health of that as compared to this movement across the detectability barrier of pesticide residues?

No, really, that is the only interesting question. What are the costs - and or benefits - of these residues as against the costs - and or benefits - of not having them?