The Risks of Consuming Pesticide Residue—and How to Avoid It

To follow the news is to know that there are chemicals in our waterways and carcinogens in our food supply. But what and where and how much? That’s where things get murky. Which is why we tapped Nneka Leiba, the director of healthy living science at Environmental Working Group. In her monthly column, Leiba answers our most pressing concerns about toxicity, the environment, and the health of the planet. Got a question for her? You can send it to [email protected].

Researchers have long linked pesticide exposure, particularly occupational exposure, to myriad health effects, including fertility problems. Now, new research suggests dietary exposure to pesticides may have similar negative effects. But choosing organic versions of the fruits and vegetables that would otherwise carry the largest pesticide loads will lessen your exposure.

If you’re pregnant, trying to get pregnant, or breastfeeding, it’s even more important to eat organic. In January, researchers from the Harvard T.H. Chan School of Public Health found women trying to get pregnant could significantly improve their chances of conceiving by eating fruits and vegetables with fewer pesticide residues. The analysis included 325 women undergoing infertility treatment who completed a dietary questionnaire. The study showed that 26 percent of women who reported eating two or more servings per day of fruits and vegetables with high amounts of pesticide residues had a lower chance of a successful pregnancy than participants who ate fewer servings of these foods.

Men also need to be aware of the pesticides they consume. A previous Harvard study of male participants found a link between exposure to pesticides and semen quality. The authors cautioned that the study should be replicated with other study populations before people rely on the results. (“I am now more willing to buy organic apples than I was a few months ago,” said senior author Jorge Chavarro.)

Both studies’ definition of higher and lower pesticide foods mirrors the Dirty Dozen™ and Clean Fifteen™ lists published in the Environmental Working Group’s annual Shopper’s Guide to Pesticides in Produce™. The EWG guide is based on laboratory tests done by the U.S. Department of Agriculture’s Pesticide Testing Program and the Food and Drug Administration. The USDA found 230 different pesticides in more than 38,000 produce samples.

Since 1995, EWG has listed the fruits and vegetables with the highest and lowest levels of pesticide residues. Higher-residue foods in both Harvard fertility studies included strawberries, apples, grapes, leafy greens, and sweet bell peppers—all on EWG’s Dirty Dozen list. Low-residue foods included avocados, sweet corn, grapefruit, and cabbage. Fruits and vegetables with thick outer peels tend to have less pesticide residue than leafy greens or produce with soft, edible skins. The thick skins provide a barrier between the pesticides and the edible parts of the fruit or vegetable.

When possible, buy organic versions of foods on the Dirty Dozen list. Some botanically derived pesticides are used on organic produce, but in general, there are fewer pesticides on organic produce and at much lower concentrations. If buying organic produce is not an option, the guide will help you choose conventional foods with lower pesticide residues, so you can enjoy the health benefits of a diet rich in fruits and vegetables while limiting your exposure to pesticides.

To be clear, avoiding fruits and vegetables is not a good idea: In fact, it is important for everyone to eat more of them. A variety of plant-based foods are an essential part of a healthy diet, providing vitamins and fiber. There also is compelling research that filling your plate with fruits and vegetables can reduce the risk of heart disease and stroke, lower your risk of type 2 diabetes, lower your blood pressure, and protect against certain cancers. But the fact is many people are unaware that most conventional produce contains residues of synthetic pesticides.

Here are some more key facts about pesticides found on nonorganic produce:

• More than 98 percent of the samples of strawberries, spinach, peaches, nectarines, cherries, and apples tested positive for residue of at least one pesticide.

• A single sample of strawberries showed twenty different pesticides.

• Spinach samples had, on average, 1.8 times as much pesticide residue by weight than any other crop.

• Avocados and sweet corn were the cleanest: Less than 1 percent of samples showed any detectable pesticides.

• More than 80 percent of the samples of pineapple, papaya, asparagus, onions, and cabbage had no pesticide residues.

• No single fruit sample from the Clean Fifteen tested positive for more than four pesticides.

• Multiple pesticide residues are extremely rare on Clean Fifteen vegetables. Only 5 percent of Clean Fifteen vegetable samples had two or more pesticides.

As the director of healthy living science at Environmental Working Group, Nneka Leiba, M.Phil., M.P.H., translates complicated scientific topics, particularly ones dealing with the effects of everyday chemical exposures on our health, into easily accessible tips and advice. Leiba has become an expert in a wide range of issues, including the safety of ingredients in cosmetics and other consumer products, and drinking water quality. She earned graduate degrees in zoology and public health from the University of the West Indies and Johns Hopkins University, respectively.