Some foods contain pesticides and other contaminants. The best way to avoid these is by purchasing organic, but organic can be more expensive. The Dirty Dozen, or the 12 fruits and vegetables most likely to contain pesticide residue, include: apples, celery, sweet bell peppers, peaches, strawberries, nectarines, grapes, spinach, lettuce, cucumbers, blueberries, and potatoes. When buying these items, choose organic.