The fruits and vegetables in the dirty dozen list are the ones that have the highest concentration of toxic pesticides and chemicals in and on them, you are far better off buying these in organic to avoid exposure especially if you consume their skins.
The Dirty Dozen:
Apples, strawberries, grapes, peaches, nectarines, tomatoes, celery, spinach, bell peppers, cucumber, peas and potatoes.
It is also best to buy leafy greens as organic.
The clean fifteen are the fruits and vegetables that have lower to no pesticide traces found in or on them.
It is still recommended that you wash your produce before consuming.
The Clean Fifteen:
Sweet potato, cabbage, grapefruit, pineapple, sweet peas, cantaloupe, mango, sweet corn, papaya, eggplant, kiwi, onions, mushrooms, asparagus and avocado.