The Not-So-Dirty Dozen?

Remember the old Westerns? There was always a scene in which an outlaw sees a lone rider appear atop the crest of a hill. Fear mounts. Is it really just the lone rider or will a huge posse soon gallop up behind? Alone, the rider is not much of a threat, but backed by an army, he’ll strike fear into the heart of any outlaw.

It’s a similar situation with pesticides, where the risk has everything to do with numbers. The simple presence of a pesticide doesn’t necessarily pose a health hazard; the risk is tied to the amount of pesti­cide a food contains. “The dose makes the poison,” says Carl K. Winter, PhD, director of the FoodSafe Program at the University of California, Davis and a member of the Institute of Food Technologists.

In 2010, Winter decided to look more closely at the Environmental Working Group’s (EWG) “Dirty Dozen,” a list of fresh fruits and vegetables that the advocacy group claims have the greatest number of pesticide residues and therefore present the greatest chance of being harmful to our health. Apples, celery, strawberries, peaches, spinach, imported nectarines, imported grapes, sweet bell peppers, potatoes, domestic blueberries, lettuce, and kale/collard greens all made the most recent list. The group suggests that consumers can lower their pesticide exposure by nearly 80% by avoiding conventionally grown vari­eties of these “dirty” fruits and vegetables.

This list piqued Winter’s analytical interest, espe­cially in light of the USDA’s new MyPlate recommen­dation to fill half our plates with fruits and vege­tables. He feared this list might cause shoppers to buy and eat less produce if they couldn’t afford the often more costly organic forms. So he examined the EWG’s methods for determining its list to see whether the rankings remained valid after careful examination of the scientific evidence.

“The problem,” Winter says, “is that only one of the EWG’s six indicators of contamination considered the actual amount of pesticide residue detected. Even this indicator failed to relate expo­sures to the residues with risk to health.”

Instead, Winter examined one of the same sources of data the EWG used, namely the USDA’s Program, but with a different set of criteria. Specifically, he looked at how much of a pesticide was actually in or on a food, the pesticide’s toxicity, and how these two factors related to the number of servings of this food a person is likely to eat on average over a lifetime.

His results were surprising. “Our findings conclu­sively demonstrated that consumers’ exposure to the 10 most frequently detected pesticides on the Dirty Dozen commodity list is negligible,” Winter says. “In addition, substituting organic forms of the Dirty Dozen commodities for conventional won’t lead to any measurable consumer health benefit.”

Concern over pesticides is justified. After all, these chemicals are toxic. Their prime purpose is to kill the weeds, insects, rodents, and molds that damage crops and reduce farmers’ yields for market. There are more than 100 cases of pesticide-related illnesses annually, according to the California Department of Public Health’s Occupational Pesticide Illness Preven­tion Program. The majority of these, however, don’t result from eating fresh produce; they’re due to occupational exposure that occurs when individuals pick or pack fruits and vegetables.

Anxiety about the health effects of pesticides in foods has spurred a huge interest in organic foods. Sales of organic foods in the United States reached $24.8 billion in 2009, with organic fruits and vegeta­bles representing 38% of this total—or $9.5 billion—up 11.4% from the year prior. At the same time, organic fruits and vegetables represent only 11.4% of all produce sold in the United States, while 88.6% is conventionally grown. According to the USDA’s National Organic Program, foods can be marketed as organic if they were grown without synthetic pesti­cides, fertilizers, or genetically engineered organisms.

Interestingly, “Eating organic produce doesn’t mean that you’re eating pesticide-free produce,” Winter notes. “Organic produce may contain synthetic pesticides by virtue of drift from nearby conventional fields. In addition, pesticides from natural sources, such as biological pesticides, are approved for use in organic farming.”

This last point hits home in a startling result from the USDA’s 2009 Pesticide Data Program Annual Summary. Residue of the pesticide spinosad was found in 18% of organic lettuce samples tested. Again, the important point here isn’t detectable presence but dose. This USDA report concluded that less than one-third of 1% of food samples tested contained pesticide residues that exceeded safety tolerances set by the Environmental Protection Agency.

While even organically grown fruits and vege­tables may contain pesticides—albeit fewer than 

conventional—the bottom line, Winter says, “is that if you can’t buy organic, this shouldn’t stop you from purchasing conventional fruits and vegetables and eating plenty of them. The health benefits of fresh produce far outweigh any risks from pesticides.”

The Alliance for Food & Farming, a Watson­ville, California-based nonprofit group made up of conventional and organic farmers, has created an online calculator (www.safefruitsandveggies.com/calculator) based on dose-related response meth­odology akin to what Winter used in his research. Consumers can pick their favorite fruits and vegeta­bles, click, and learn how many daily servings they’d need to eat before they’ve swallowed a potentially serious amount of pesticides.

The Dirty Dozen are included in the calculator, and the news is good. For example, you can eat 529 servings of apples daily before worrying about significant pesticide exposure. Then again, maybe the army of nutrients in this orchard-size serving of apples will counteract any health risks from pesticides. That’s the subject Winter has just started to explore.

— Carol M. Bareuther, RD