When anthropologist Elizabeth Guillette decided to study the effects of pesticides on children, she faced a daunting task. She suspected that chronic exposure to pesticides could affect a child’s growth and development. To prove this, she needed two groups of children that were identical in every way—except for their exposure to pesticides. In other words, she needed an “experimental group” and a “control group.” She found them in the Yaqui Valley of Mexico.

Beginning in the 1950s, the use of chemical fertilizers and pesticides became widespread in the Yaqui Valley, an agricultural region in northwestern Mexico. At the same time, farming operations grew larger and more mechanized. Families from the nearby mountain foothills moved to the valley for jobs. Meanwhile, some of the valley residents moved into the foothills. Both groups have resisted changes in their social and cultural identity; they remain alike in diet, culture, genetic heritage, and standard of living. The only big difference between the two groups is their exposure to pesticides. In the valley, pesticide use is widespread and continues throughout the year, with pesticides applied up to 45 times per crop between planting and harvesting. By contrast, the families in the foothills are rarely exposed to pesticides. For Guillette, the exposed children in the valley would serve as her experimental group, while the children in the foothills would be her control.

The scientists tested four- and five-year-old children with a handful of exercises: for instance, they measured how long a child could jump in place, and whether he or she could draw a person. The results were significant. Guillette found that the children in the foothills performed better at every task. One difference that was particularly striking was in how children from each group drew a person. Foothills children—the control group—averaged 4.4 body parts per drawing, while valley children—the experimental group—averaged only 1.6 body parts per picture, and often just drew meaningless circles. This doesn’t mean that the valley children were bad artists. All children go through predictable developmental stages when learning to draw; the valley children’s pictures showed that they had significant delays in development.

What does this study mean for children outside the Yaqui Valley? Children in the United States are also exposed to pesticides through agricultural use, household bug sprays, lawn and garden use, and residue on foods. Scientists have found that pesticides known as organophosphates could increase a child’s risk of attention-deficit/hyperactivity disorder (ADHD). Research has suggested that children may also be particularly sensitive to the carcinogenic effects of pesticides.

How can you limit your exposure to pesticides? The Environmental Working Group, a nonprofit research and advocacy organization, has created a list called the “Dirty Dozen,” the 12 fruits and vegetables that consistently have the highest levels of pesticides. They are: peaches, apples, sweet bell peppers, celery, nectarines, strawberries, cherries, pears, imported grapes, spinach, lettuce, and potatoes. When it comes to these items, you should opt for organic. If organic isn’t an option, make sure to wash fruits and vegetables thoroughly before eating them.

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