“The Dirty Dozen”: Fact, Fiction, or a bit of both?

Printed with permission from the Cooper Institute.

The Environmental Working Group (EWG) is a United States-based environmental advocacy group. For the past 15 years or so, the EWG has published an annual list of fruits and vegetables which supposedly have the greatest risk for contamination with the 10 most frequently detected pesticide residues. This list, commonly known as “the dirty dozen” is met with great fanfare by the news media each year. The EWG recommends that consumers avoid conventional forms of the dirty dozen and recommends that consumers purchase these fruits and vegetables in organic form instead. In fact, the EWG has stated that “consumers can lower their pesticide consumption by nearly four-fifths by avoiding conventionally grown varieties of the 12 most contaminated fruits and vegetables”.1 The 2010 dirty dozen list included celery, peaches, strawberries, apples, blueberries, nectarines, bell peppers, spinach, cherries, kale, potatoes, and imported grapes. However, before you run out to buy much more expensive organic versions of these and other fruits and veggies, let’s ‘peel back the layers’ of the EWG recommendations.

First, the EWG annual lists are derived from findings of the U.S. Department of Agriculture (USDA) Pesticide Data Program (PDP) and the U.S. Food and Drug Administration (FDA) Pesticide Program Residue Monitoring Program. In a recent paper  published in the Journal of Toxicology2 (a peer-reviewed medical journal), Drs. Carl Winter and Josh Katz from the University of California Department of Food Science and Technology used PDP data collected over a 5-year period (2004-2008) to estimate consumer exposure to pesticide residues in the dirty dozen. The researchers analyzed the PDP data to identify the ten most common pesticides on each of the food items in the dirty dozen. Furthermore, they used the data to determine the amount of pesticide residue present on each food item. This is critical, since the EWG recommendations are not primarily based on the amount of pesticide residue exposure, but whether or not the pesticide residues are present.

Before I present the findings of Drs. Winter and Katz, let me give you an important definition from the United States Environmental Protection Agency (EPA). A Chronic Reference Dose (RfD) is an estimate of the amount of a chemical a person could be exposed to an a daily basis throughout the person’s lifetime that is likely to be without an appreciable risk of harm.3 Here is a summary of the major findings on the dirty dozen that were published in the Journal of Toxicology.2 After rinsing the foods with water:

  • 40.8% of all possible pesticide residue combinations were present in amounts one hundred thousand times lower than the RfD.
  • 75% of all possible pesticide residue combinations were present in amounts ten thousand times lower than the RfD.
  • 94.2% of all possible pesticide residue combinations were present in amounts one thousand times lower than the RfD.
  • Only one pesticide residue exposure (methamidophos on bell peppers) was present in amounts greater than 1% of the RfD.  This residue was present in an amount that was 2% of the RfD (i.e. 50 times lower than the RfD).
  • For blueberries, cherries and kale, all possible pesticide residue combinations were present in amounts 30,000 times lower than the RfD.

Additionally, the PDP data showed that 23% of organic versions of the dirty dozen tested positive for pesticide residues (surprise!). So, what does all of this mean? Drs. Winter and Katz concluded that 1) exposures to the most commonly detected pesticides on the dirty dozen pose negligible risks to consumers, 2) substitution of organic forms for conventional forms does not result in any appreciable reduction of consumer risks, and 3) the methodology used by the EWG to rank foods with respect to pesticide risks lacks scientific credibility.2 In other words, to achieve maximize health benefits, eat fruits and veggies frequently, don’t worry whether they are organic or conventional, and don’t assume that organic trumps conventional!

1Environmental Working Group Shoppers Guide to PesticidesTM. Environmental Working Group, Washington, DC, USA, 2010.
2Winter CK, Katz, JM. Dietary Exposure to Pesticide Residues From Commodities   Alleged to Contain the Highest Contamination Levels. J Toxicol. 2011;e-pub ahead of print.
3Winter CK, Francis FJ. Assessing, Managing and Communicating Chemical Food Risks. Food Technology. 1997;51(5):85-92.

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