This article, just posted online by Environmental Health Perspectives, describes a study in which levels of certain commonly used organophosphate pesticides dropped significantly in urine samples from children who switched to a mostly organic diet for just five days.
Of course, the big chemical companies will counter with "but those children were perfectly healthy even when they ate a pesticide-laden diet, weren't they?"
I'm not so sure. With all the immune-related illnesses these days, and the hundreds of thousands of chemicals we are bombarded with which make it virtually impossible to prove cause-and-effect, I'll err on the side of caution. Last night it was broccoli and potatoes from the garden.