Apples are one fruit you should buy organic whenever possible, according to an environmental group.Worried about pesticides and produce? Wondering if it’s worth it to go organic? The Environmental Working Group has released its 2012 guide to the most- and least-contaminated cropsout there — its “Dirty Dozen” and “Clean 15″ lists — and this year there are a few new items to watch out for, including certain types of baby food.

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Apples, celery, and sweet bell peppers top this year’s “Dirty Dozen,” which has been expanded to the “Dirty Dozen Plus” in order to include green beans and leafy greens like collards and kale. (You can read the entire report here.) Though they don’t meet traditional criteria for the Dirty Dozen, green beans and leafy greens are often contaminated with organophosphate insecticides. “These insecticides are toxic to the nervous system and have been largely removed from agriculture over the past decade,” the EWG said in its report. “But they are not banned and still show up on some food crops.”

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Pesticides aren’t necessarily just on the surface of the food, Chensheng (Alex) Lu, Associate Professor of Environmental Exposure Biology at the Harvard School of Public Health told Yahoo! Shine in an interview. “If you look at apples, for example, they often spray from March to late June. After that they don’t spray anything,” he said, explaining that in many cases the fruit grows with pesticides already in it, thanks to pesticide seed treatment programs where seeds are soaked in pesticides before they’re even planted. “It started with corn, but now is used with a lot of different kinds of produce,” he said.

According to the EWG, 96 percent of celery samples, 96 percent of peach samples, and 88 percent of spinach samples contained residue from one or more pesticides. Up to 15 different pesticides were detected on a single sample of grapes, 93 percent of apple samples had traces of two or more pesticides on them, and samples of lettuce sported 78 different pesticides. Cucumbers, a newcomer to the Dirty Dozen Plus, turned up 10 different pesticides on a single sample.

The group also took a look at commercial baby food for the first time. “Department scientists analyzed about 190 samples each of prepared baby food consisting of green beans, pears, and sweet potatoes,” the report said (it did not name specific brands). Green beans prepared as baby food tested positive for five pesticides, while 92 percent of pear samples had at least one type of pesticide and three samples tested positive for Iprodione, a probable carcinogen which is not registered with the EPA for use on pears. Sweet potatoes, which are long-time members of the “Clean 15″ group, had nearly no pesticide residue at all.

“Federal testing of pesticide residue in baby food was long overdue, as infants are especially vulnerable to toxic compounds,” said Andrew Weil, MD, Founder and Director, Arizona Center for Integrative Medicine. “Now that it has begun, the results are highly disturbing. It is bad enough that baby food contains pesticides at all; the fact that pears contain a likely human carcinogen is an outrage.”

Weil recommends that parents purchase organic baby food if they’re not able to prepare their own. “It is vital that an infant’s developing brain and nervous system receive only uncontaminated, nutrient-dense foods,” he said.

“For baby food, I would probably recommend that parents take the time to prepare their own baby food using either organic produce or produce they buy from a reliable source,” Harvard’s Dr. Lu agreed.

While buying organic produce is often the best way to avoid pesticide contamination, it’s not an option for everyone, especially people who are already struggling to make ends meet. The EWG also notes that “the health benefits of a diet rich in fruits and vegetables outweigh the risks of pesticide exposure.” Still, here are the items that you should try to buy organic (or from local farmers markets, or grow in your own garden) whenever possible:

The Dirty Dozen Plus: