It may look like an apple, peach, strawberry, cherry tomato or celery, but there is something else lurking there. Something invisible. And icky. When you eat that sweet strawberry or crunchy celery, you're also eating a mouthful of pesticides, according to the Washington, D.C.-based Environmental Working Group (EWG).

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What is the harm of pesticides? Pesticides are toxic by design and created expressly to kill living organisms--insects, plants and fungi that are considered "pests." While some pesticides are benign, others have been linked to brain and nervous system toxicity, cancer, hormone disruption, skin and eye and lung irritation.

Strawberries top the 2016 "Dirty Dozen" list, displacing apples which headed the list for the last five years. Fully 98 percent of the strawberries tested by the U.S. Department of Agriculture and analyzed by EWG for the 2016 Shopper's Guide contained pesticide residues, a surprising finding in the face of soaring consumer demand for food without agricultural chemicals. In addition, 40 percent of strawberries had residues of 10 or more pesticides and some had residues of 17 different pesticides.

Why are strawberries so rife with pesticides? Strawberries were once a seasonal, limited crop, but heavy use of pesticides has increased yield and stretched the growing season. In California, where most U.S. strawberries are grown, each acre is treated with an astonishing 300 pounds of pesticides. More than 60 pounds are conventional chemicals that may leave post-harvest residues but most are fumigants, which are considered volatile poison gases.

You can lower your pesticide consumption by nearly four-fifths by avoiding the most contaminated fruits and vegetables and instead eating the least contaminated produce, according to calculations made by EWG.

To rank the produce items, EWG analysts used six metrics, including the total number of pesticides detected on a crop and the percent of samples tested with detectable pesticides. They first washed or peeled the samples prior to testing so the rankings would reflect the amounts of the crop chemicals likely present on the food when it is typically eaten by U.S. consumers.

The Dirty Dozen (It's best to buy organic):
1. Strawberries
2. Apples
3. Nectarines
4. Peaches
5. Celery
6. Grapes
7. Cherries
8. Spinach
9. Tomatoes
10. Sweet bell peppers
11. Cherry tomatoes
12. Cucumbers

The Clean Fifteen (The lowest in pesticides):
1. Avocadoes
2. Sweet corn
3. Pineapples
4. Cabbage
5. Sweet peas (frozen)
6. Onions
7. Asparagus
8. Mangoes
9. Papayas
10. Kiwi
11. Eggplant
12. Honeydew melon
13. Grapefruit
14. Cantaloupe
15. Cauliflower

What can you do to protect yourself? The Environmental Working Group recommends buying organic produce to reduce the chance of ingesting pesticide residue. But even organic does not mean pesticide-free.

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