Celery also made a repeat appearance in the guide: It’s the second most likely produce item to turn up with pesticide residues. In fact, annual tests conducted by the US Dept. of Agriculture and the US Food and Drug Administration between 2000 and 2010, which were analyzed by the Environmental Working Group (EWG) for the annual report, found 13 different pesticides on one celery sample. The tests turned up pesticides in about 98 percent of conventional apples.

But there were changes on the list over the past year: Some produce items moved up the list to a less auspicious location and one, the cucumber, made its debut on the list at number 10. Others moved down the list to improve their status—if only in comparison to some others moving up. Sweet bell peppers helped them along, bumping off strawberries from the number 3 spot to become one of the dirtiest of the dozen.

No matter where they are on the list, these food items are targeted by EWG as produce people should buy organic because they’re otherwise quite likely to contain pesticide residue. For example, the domestic blueberry’s status among the Dirty Dozen improved slightly in 2012 (from 9th in 2011 to 10th this year), but 42 different kinds of residual pesticide was found on samples tested. Nectarines maintained their number-6 slot after 100 percent of the samples tested by the USDA had measurable pesticide residues.

While the Dirty Dozen list focuses on likelihood of pesticide residues, it also singled out two food items that didn’t make the top 12 but still concerned EWG because they could contain unhealthy levels of neurotoxic organophosphate insecticides.

EWG reminds consumers that they should buy organic versions of these items if they want to avoid pesticides, but not to let the list deter them from eating lots of fruits and veggies.

“The health benefits of a diet rich in fruits and vegetables outweigh the risks of pesticide exposure,” EWG said in a summary of the report. “Use EWG's Shopper's Guide to Pesticides to reduce your exposures as much as possible, but eating conventionally grown produce is far better than not eating fruits and vegetables at all.”

Sweet corn is considered one of EWG’s “clean 15,” but it’s important to note that most feed corn and some sweet corn is genetically modified (GM). It can be hard to know, since producers aren’t required to label GM foods. The Non-GMO Project has some tools at www.nongmoproject.org to help shoppers, or if a question about corn remains, buying certified organic corn ensures it isn’t GM.

You can read the complete guide summary here.