Wednesday, May 26, 2010

You keep using that word. I do not think it means what you think it means

This hit the news last week: Study: A Link Between Pesticides and ADHD

Within days, parents were asking how to get their children's urine tested for OP metabolites.

Major Annoyance #1: One of the researchers interviewed in the above article tells the media, "I was quite surprised to see an effect at lower levels of exposure."

Effect? Effect?! What we have here folks is a correlation (which, to be fair, is the language used in the actual publication. But who reads the actual study?) Enough of this talk of effects, and causes, and the wringing of hands, and oh, what shall we do about it?!

Major Annoyance #2: The confounding of all "pesticides" (a huge, diverse group of chemicals) with organophosphates (one type pesticide). OPs have been in the process of being phased out since the 1990's. A few of the OPs (mainly malathion and chlorpyrifos) are still being used on food, but as a group, OPs aren't that common anymore. Unfortunately, there's a trend among researchers who want to study "pesticides" to pick OPs as a representative for all. There are several reasons for this - OPs are well-studied and well-known and they actually produce nice, recognizable metabolites in the urine as a biomarker of exposure (surprisingly few chemicals do this). As OPs are used less and less in the real world, it makes research like this, which is supposed to represent all "pesticides", less and less relevant.

Huge Study Weakness #1: The residues of pesticides on fruits and vegetables varies a lot. Even if a child's diet remains the same, they could have zero metabolites in the urine one week, and higher levels the next, depending on the batch of food. For example, look at the residues of malathion in corn in 2008. Two thirds of the samples had zero detectable residues. This is one thing that is true for all pesticides: most of the time, there are no residues at all on food crops in the US.

Huge Study Weakness #2: OPs break down so quickly in the human body, you will only find metabolites in the urine for a day or two after exposure (sometimes longer, often even shorter).

Everyone seems to be making the assumption that these kids a) have had the same diet their entire lives and b) have been getting the same, consistant OP exposure. It's inappropriate to make those assumptions.

Is there a significant correlation that warrants further investigation? Yes.

Should parents get their kids urine tested or switch to an all organic diet (or really, take any action at all)? No.

The majority of research still tells us only this: that it's far more important for human health to eat as many, and as varied a selection, of fruits and vegetables as you can than it is to avoid low levels of pesticide residues that MAY be on food. Again, most of the time, non-organic food doesn't even have detectable pesticide residues. Switching to an all-organic diet MAY reduce exposure to an OP, (or may not, if there was no exposure in the first place), and even if it does, clear health effects from such a reduction in exposures are unclear. But what that will likely do, because of higher expense, is result in eating fewer or less varied selection of fruits and vegetables, which is a clear and well-known detriment to short and long-term health.

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