Considerations

• Pesticide residue doesn't disappear once it hits your digestive system. The authors of a 2006 study in "Environmental Health Perspectives" looked at the effects of changing a conventional diet to organic on 23 children, noting that a conventional diet left detectable traces of pesticides such as malathion in the children's urine, while an organic diet did not.
  
  

Highest and Lowest

• The Environmental Working Group issues lists of "Dirty Dozen" and "Clean 15" fruits and vegetables that consumers should buy as organic, or can buy as conventional, respectively. Their list that incorporates 2008 data places the ever-absorbent celery at the top of the list to buy organic, though in previous lists peaches came in first. The cleanest item in terms of pesticide residue was onion.
  
  

The List

• The Environmental Working Group's top 12 items to buy organic to avoid pesticide residues are celery, peaches, strawberries, apples, blueberries, nectarines, bell peppers, spinach, cherries, kale and collard greens, potatoes and imported grapes. The cleanest 15 items on the list are onions, avocado, sweet corn, pineapple, mangoes, sweet peas, asparagus, kiwi, cabbage, eggplant, cantaloupe, watermelon, grapefruit, sweet potato, and honeydew melon.