This is Complicated, But Important

8/26/2016 10:10 AM

Pesticide metabolites – It is really tempting to just stop reading after those two words but this is important.  Complicated, but important.  And, this is why.  There are often-cited studies which make associations with increased incidence of attention deficit disorders and lower IQ based solely upon pesticide metabolite levels measured one to two times in pregnant women.  The claim is these metabolites are present due to pesticide residues found on foods.  There are also several studies that show switching to all organic diets lower supposed risks from residues again based upon pesticide metabolites measured one to two times in the urine of children. 

But what about the science of measuring pesticide metabolites and the accuracy of those results?  Since this is the foundation of those studies, examination of that methodology would seem important.  A 600-plus page peer reviewed analysis published in the Journal of Critical Reviews in Toxicology did just that and the findings are worth reviewing. 

First, in the studies cited above, potential exposure to organophosphate (OPs) pesticides is what is being measured. Those potential exposures could be environmental or dietary, however, our focus is on studies regarding dietary exposures to OP residues.

Let’s start with the analysis conclusions:  “Based on this analysis, reported associations between exposure and birth and neurodevelopmental outcomes are weak and the measured OP levels in the studies are too low to cause meaningful effect.  At low-level exposures to OPs, clear evidence of adverse birth or neurological outcomes has not been demonstrated in humans.  Further data are needed in order to establish any connections between low-level OP exposure and any resulting birth or neurological effects.

How did the scientists arrive at this conclusion?  Some background:

OPs are metabolized by the body to other compounds, most of which are known as dialkyl phosphates (DAPs).  DAPs do not exert the same effects as OPs and are not considered toxic.  DAPs are excreted in urine, can be measured and are regarded as indicators of exposure to OPs.  DAPs are also formed in the environment and on food, so DAPs measured in urine may reflect exposure to DAPs themselves and not exposure to an OP insecticide.  Finding a measurable level of DAPs in urine does not indicate risk of an adverse health effect.

DAPs are excreted rapidly in the body (within 24 to 48 hours) and thus reflect recent exposures to DAPs.  A single point DAP measurement taken from a pregnant woman at one time during her pregnancy will not reflect her exposure during the entire time she was pregnant.  Variability in DAP measurements is quite high, meaning several samples taken from the same individual over the course of a few days can vary greatly in magnitude.

Limitations to the studies which found associations with pesticide metabolites measured and neurodevelopment limitations and claims that switching to an organic diet reduce “risks” from residues in children include:

  • Limited exposure information was collected.  Most studies measured urinary DAPs in the mother one or two times during pregnancy or one or two times in children, which does not reflect long term exposure or changing levels of exposure.  This severely limits exposure estimation and thus study results.
  • Measurement of maternal or child DAP levels were used to estimate exposure.  As described in bullet point above, DAPs are not specific to a single OP pesticide, DAPs are also present in the environment therefore OP exposure is not the only source of DAPs. Use of DAP levels cannot distinguish the exposure source as an individual could have been exposed to an OP or simply exposed directly to DAPs formed by plants or in the environment.
  • Confounding factors, such as diet, exposure to other chemicals, child nutrition, poverty, were not adjusted, which can influence the responses measured.
  • There is high variability in estimated exposures across the studies, which limits how the results can be compared.

At the Alliance for Food and Farming, whenever we see a study that concerns produce safety, we look to scientists and science to help us better understand the findings and implications.  In this case, we learned of this outcome from the 600-plus page peer reviewed literature analysis:  "Evidence in these human studies does not provide support or demonstrate that low-level maternal or childhood exposure to OPs or DAPs causes adverse birth or neurodevelopmental outcomes in humans."

Back to why this is important.  Many activist groups have used these studies to discourage consumption of conventionally grown produce while promoting organics, especially among pregnant women and children.  These are the very populations where consumption of fruits and veggies is critical for the health and well being of infants and children.  Decades of studies show that women's diets rich in fruits and veggies results in healthier babies.  Numerous studies have also found that children who eat more fruits and veggies actually have improved neurological function, including increased IQ.  This is why critical examination and understanding of these studies and their limitations is of importance.

For those of you who want more information to reach your own conclusions, you can review the peer reviewed literature analysis, “A review of epidemiological studies of low-level exposures to organophosphorus insecticides in non-occupational populations,” here.  If you want to read a seven-page synopsis of the analysis written by the lead author Dr. Richard Reiss, you can find that here.

Read, learn, choose but eat more organic and conventionally grown fruits and veggies every day for better health and a longer life.


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