The outbreak of E-coli in spinach and other vegetables recently put a new spotlight on the way fruits and vegetables are processed in the United States. More and more processing is done in factory-style plants. The vegetables are rinsed in large sluices, then sliced and packaged by machines on conveyor belts. Each leaf, stem or floret comes in contact with many other vegetables and with the same surfaces in the plant. So any contamination, such as fecal material from cattle or wild animals, can easily spread. Peeling and slicing the vegetables in the factory also creates openings for bacteria to get inside the vegetable where you can't rinse it off at home. So you're better off buying whole heads of lettuce or broccoli and unpeeled carrots, then chopping them at home.