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  • Did You Know?
    Three new studies confirm that exposures to common insecticides during pregnancy can cut a child’s IQ 4% to 7%  by age 9.
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Cynthia Curl, Boise State University

Apr 23, 2015
Dr. Cynthia Curl

Dr. Cynthia Curl

Your most recent publication links an organic diet with reduced organophosphate (OP) pesticide exposure. Is your study the first to do this? What is special about this research?

It is true that our study demonstrated that among individuals matched on total produce intake, those with organic diets had significantly lower levels of organophosphate pesticide breakdown products in their urine than those with conventional diets. However, while this finding received a lot of attention in the popular media, it was not the central point of this study. Several studies over the past decade have shown, fairly conclusively, that consuming organic food can reduce exposure to many categories of pesticides, including OPs.
To my knowledge, the first study to demonstrate that an organic diet can lead to a marked reduction in exposure was one that we conducted back in 2003. That was just a very small study looking at differences in pesticide metabolite levels in two groups of preschool children in Seattle. This small study (40 kids total) showed that those whose parents reported that they ate primarily conventional diets had approximately 9 times higher levels of OP breakdown products (called “dialkylphosphates”, or DAPs) in their urine than those with organic diets. Since that study was published, many researchers both in the United States and internationally have shown that people with organic diets have reduced pesticide exposures. The most compelling of such investigations were intervention studies where participants began with conventional diets and were then provided organic diets over a period of a few days or weeks. Urinary DAP levels were seen to drop immediately and dramatically with the introduction of organic diets in those individuals.

salad greensSince the relationship between organic food consumption and reduced exposure has been well documented, our recent study had a different purpose. We aimed to develop an inexpensive, non-invasive method to allow us to characterize long-term dietary exposure to OP pesticides. Our method paired self-reported food consumption habits with information from a national database on average pesticide residue levels on specific food items. Using these data sources, we were able to calculate individual-level estimates of total OP pesticide exposure. We then compared the results of our estimation method with measured urinary DAP levels in a subset of 720 participants. We found that the estimates we generated were consistent with the results of the urinary measurements. Specifically, we found that those people who ate organic diets had lower DAP levels. We also found something else that was maybe even more interesting. We found that people with conventional diets who ate greater quantities of food to which OPs are typically applied had higher DAP levels than people who ate less of these foods. For example, someone who reported eating a lot of conventionally grown apples, peaches and green beans had significantly higher DAP levels than someone who didn’t eat those foods but instead ate a lot of cantaloupes and corn.

The bottom line is that by combining the information on dietary habits, organic choices, and pesticide residue levels, we were able to do a good job of predicting pesticide exposure. These predictions were confirmed by urinary bio-monitoring. Essentially – if you tell me what you typically eat and whether or not it is organic, I can do a good job of telling you about your average exposure to OPs.

small plantsWhat are the benefits of being able to estimate pesticide exposure without using biological samples such as urine?

This is a good question, and there are several important benefits. The first is financial—collecting, shipping, storing and analyzing urine samples are far more expensive than collecting dietary survey data. It is also less invasive—there is something much more palatable about answering questions as opposed to collecting and providing a researcher with your urine. But beyond these practical considerations, biological monitoring for OP pesticide exposure is not perfect; it’s not a gold standard. While urinary bio-monitoring for DAPs is considered the current best practice (and it does provide us with a way to do a check of the “face validity” of our method), it certainly has its drawbacks.

First, DAP levels in urine only represent exposure over the past 24-48 hours, but people’s diets vary, so what you ate yesterday and the day before may or may not accurately reflect your average diet. Since diet is a chronic exposure, what we are really interested in is exposure over the long term. By asking people what they typically ate over the past year, as we did in this study, we are probably better able to capture exposure during the most relevant time frame. Second, the OP pesticides we are studying can break down to form DAPs even before they enter our bodies. For example, apples still on trees in the orchard can have measureable levels of these DAPs on them before they are even picked. These breakdown products themselves are non-toxic, and are excreted in the urine unchanged. So it is possible that some of the DAPs we measure in urine samples represent pre-formed breakdown products, rather than the toxic parent compounds. Thus, urinary bio-monitoring may, in some cases, overestimate exposure to OPs. This is avoided with our new method, because USDA measures residues of the toxic parent compounds on fruits and vegetables at the point of sale (e.g., grocery stores), and those measurements are what we use to estimate individual exposures. Finally, there are some OPs that do not break down to form DAPs, and exposures to these compounds are missed when urinary bio-monitoring is used. This could lead to underestimation of exposure by urinary bio-monitoring. Our method can include all OPs registered for use in the United States and internationally.

greenhouseEven though your results suggest that while people who consume organic produce have significantly reduced pesticide exposure compared to those who primarily eat conventional produce, you still detected some pesticide exposure in the urine of participants that primarily consume organic. Where do you think these exposures may be coming from?

I think that, both in general and in our study population in particular, it’s rare to have an entirely organic diet. We asked people to report whether they “often or always,” “sometimes,” or “rarely or never” ate organic fruits and vegetables. It’s true that we did find measureable levels of pesticide metabolites in the urine of people who said that they “often or always” ate organically, but the definition of “often” eating organic is fairly subjective, and we also know that people who “often or always” consume organic produce also tend to eat about twice as many servings of fruits and vegetables each day than those who “rarely or never” consume organic food. If some fraction of the food consumed by “often or always” organic eaters is conventionally grown (which I would expect), and if these people eat a greater quantity of produce in general (which we know to be true), then it really isn’t terribly surprising that they still have some level of pesticide metabolites in their urine. Overall, I think that for most people, diet is the primary source of OP exposure, even among people who do consume “mostly” organic food.

A lot of your research, including your most recent paper, uses data from The Multi-Ethnic Study of Atherosclerosis (MESA). What is MESA? Why collect data from this group of individuals?

The Multi-Ethnic Study of Atherosclerosis is a large, multi-ethnic, prospective cohort study of the factors that are associated with cardiovascular disease. This study, funded by the National Heart, Lung, and Blood Institute, includes 6,814 participants who were originally enrolled between 1999 and 2000 and who have been followed for approximately 15 years at this point. These participants have attended five clinic examinations, which have included extensive medical testing with repeated CT scans, ultrasounds and MRIs, primarily focused on cardiovascular health. These participants also completed repeated food frequency questionnaires and provided multiple urine samples which have been stored at the study’s central laboratory. Our use of this population was essentially opportunistic. The existing availability of the biological samples and dietary information, paired with the large sample size and the fact that participants were recruited from six different cities and provided a diverse sample, made this an ideal setting in which to test our exposure prediction method. Essentially, we were able to conduct this fairly large study relatively inexpensively. We added questions to the existing questionnaire about organic food consumption habits, and funded the biological sample analysis, but otherwise were able to successfully leverage a great deal of existing data.

Dr. Cynthia Curl

Dr. Cynthia Curl

What produce would you recommend purchasing organic to avoid the highest levels of OP pesticides?

Of the 20 different produce items included in our study, those with the highest levels of the most toxic OPs included peaches, nectarines, apples, tomatoes and green beans. However, OPs are just one class of compounds in use. There are many others. I would direct people to a new article published just this month in Consumer Reports ( which I think does a great job of describing which food items are highest in pesticides, with special attention to the country of origin.

What are some of the other research projects your lab is working on?

The next step in this research is to utilize these pesticide exposure estimates to understand the potential health impacts of an organic diet. We plan to evaluate the potential association between dietary exposure to OP pesticides and scores on a suite of neurological and cognitive tests among MESA study participants.

In terms of other projects, we are also interested in understanding whether maternal organic diets during pregnancy result in any measurable health benefits in children, such as reduced ADHD incidence or differences in IQ.

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