(CNN) - Apples and celery are still agriculture's dirtiest pieces of produce, according to the Environmental Working Group's annual "Dirty Dozen" report. The report names the fruits and vegetables ranking highest in pesticide residue.
Cucumbers were added to the 2012 Dirty Dozen, while Kale and collard greens were moved from the list to join green beans in a new "Plus" category.
The category was created this year to highlight crops that did not meet traditional Dirty Dozen criteria but are still commonly contaminated with organophosphate insecticides, which are toxic to the nervous system.
Also included on the Dirty Dozen list are:
3. Sweet bell peppers
6. Imported nectarines
11. Domestic blueberries
And on the "Dirty Dozen Plus" list:
+ Green beans
+ Kale/collard greens
The fruits and vegetables with the least amount of pesticide residue make up a list of the "Clean 15":
2. Sweet corn
6. Sweet peas
11. Domestic cantaloupe
12. Sweet potatoes
Although some switched spots within the ranks, the fruits and vegetables included on the lists stayed fairly consistent from the 2011 report.
The EWG report is based on pesticide residue data collected by the U.S. Department of Agriculture and the Food and Drug Administration, which tested samples as they normally would be eaten -- after being washed or peeled.
The chronic health effects of pesticide intake have not been widely studied, but Chensheng Lu, an associate professor of environmental exposure biology at the Harvard School of Public Health, said the toxins appear to be connected to a prevalence of diseases, including cancer. And some studies suggest pesticide intake, especially in the prenatal stage, can cause neurological developmental problems in infants, Lu said.
"Knowing that this chemical is designed to kill (certain) organisms, you have to be careful ingesting it," he said.
With the release of this list, the EWG suggests consumers reduce their exposure to pesticides as much as possible by purchasing organic versions of the Dirty Dozen. Organic produce is grown using materials of plant or animal origin, instead of chemicals.
Organic produce is often thought of as more expensive than conventionally grown produce, but Lu said an increased demand in recent years has led to lower prices.
"You may want to think about saving money just for buying organic apples and not buying organic other stuff," Lu said. "You switch your resources for the high risk produce and buy organic for those."
For the first time this year, the USDA also collected data on pesticide residue in baby food, finding many of the studied samples to be contaminated with organophosphate pesticides. In its report, the EWG stresses the importance of accelerating testing of baby foods and asks the Environmental Protection Agency to focus on reducing the organophosphate pesticide exposure allowed for Americans, especially infants.