I will admit...I eat like most 5 year olds. Even though I am 20 years old I still won't touch most vegetables. Sad, but true. Every once in awhile I will enjoy the occasional salad, but if I do I buy organic so I am not incredibly concerned with contamination in the product.
It is a concern even for organic foods because of how it is handled from field to store. Grown your own and you know how it has been handled. Otherwise, do some research to find out how best to wash the lettuce you want to use.