"Celery is well-liked by the health-conscious because it's low in calories -- but the stalky veggie is not low in another health concern: pesticides. Eat conventionally farmed celery, and you're eating the veggie found to have the most pesticide residue, according to green nonprofit Environmental Working Group's latest Shopper's Guide to Pesticides.
 
The updated guide hasn't been officially released yet, but EWG sent out a sneak preview for its members. In this new version, celery displaces the peach as the dirtiest piece of produce -- though both were already on the "Dirty Dozen" list of most tainted produce last time around too. New inductees into the list are blueberries, spinach and potatoes -- which replaced lettuce, carrots and pears."

Siel Ju reports for Mother Nature Network April 28, 2010. [2]

The 1996 Food Quality Protection Act requires EPA to distribute a brochure in supermarkets informing consumers of pesticide residue risks, but supermarket rarely distribute it.