It is time to rethink organic. For example, a non-organic celery stick could contain 67 pesticides , according to a new report from the nonprofit Environmental Working Group, reports CNN.

Concerned with public health, the group scrutinized 100,000 produce pesticide reports from the U.S. Department of Agriculture and the U.S. Food and Drug Administration to ascertain which fruits and vegetables have the highest and lowest amounts of chemical residue.

Called the "Dirty Dozen," these fruits and vegetables contain 47 to 67 pesticides per serving, probably because they have soft skins that absorb more pesticides. The group suggests purchasing organic instead.

"It's critical people know what they are consuming," the Environmental Working Group's Amy Rosenthal said. "The list is based on pesticide tests conducted after the produce was washed with USDA high-power pressure water system. The numbers reflect the closest thing to what consumers are buying at the store. You can reduce your exposure to pesticides by up to 80 percent by buying the organic version of the Dirty Dozen," said Rosenthal.

The Dirty Dozen

Celery

Peaches

Strawberries

Apples

Domestic blueberries

Nectarines

Sweet bell peppers

Spinach, kale and collard greens

Cherries

Potatoes

Imported grapes

Lettuce

Some produce have outer layers that are a defense against pesticide contamination.The group says the following non-organic fruits and vegetables, dubbed the "Clean 15," contain little or no pesticides.

The Clean 15

Onions

Avocados

Sweet corn

Pineapples

Mango

Sweet peas

Asparagus

Kiwi fruit

Cabbage

Eggplant

Cantaloupe

Watermelon

Grapefruit

Sweet potatoes

Sweet onions

The Environmental Working Group acknowledges that data from long-term studies aren't available but warns consumers of possible dangers. Also, some doctors say that children's developing brains are the most vulnerable to food pesticides.

"Pesticides are designed to kill things. Why wait for 20 years to discover they are bad for us?" Rosenthal said.

Dr. Philip Landrigan, chairman of the department of preventive medicine at Mount Sinai School of Medicine in New York, said "A kid's brain goes through extraordinary development, and if pesticides get into the brain, it can cause damage," quoted CNN.

All fresh produce should be washed with water to remove dirt and potentially harmful bacteria. Health experts concur that when considering the Dirty Dozen list, choose organic if available.

"To the extent you can afford to do so, [parents] should simply buy organic, because there have been some very good studies that shows people who eat mostly organic food reduce 95 percent of pesticides [in their body] in two weeks," Landrigan said, quoted CNN.