Buying organic groceries isn't as expensive as it used to be, but it's still a significant price jump from nonorganic meat and produce. If you're going to buy some but not all organic, do so wisely. There are fruits and vegetables more likely to contain pesticides than others, and thus buying pesticide-free versions of them will give you more bang for your organic buck and keep more harmful chemicals off of your dinner plate. 

To help decide which foods you should buy organic and which ones it might be OK not to, food safety nonprofit Environmental Working Group curates a yearly list of the foods most likely to contain pesticides dubbed "The Dirty Dozen." 

To do so, the group analyzed 46,569 samples of 46 fruits and vegetables tested by the US Food and Drug Administration and the Department of Agriculture.

The No. 1 offender of pesticides in the group's latest study? Strawberries. These popular red berries had more instances of farming chemicals found on them than any other fruit or vegetable included in the study.

Fruits and vegetables are billed as some of the healthiest foods, but they're also the most likely to pesticides, which are used to protect them from invasive animals and diseases during cultivation. In fact, nearly three-quarters of all nonorganic produce has detectable levels of pesticides by the time it reaches your supermarket shelves or grocery delivery order, according to the study.

Foods that don't have natural casings or have edible skins such as apples, greens and berries are more likely to contain pesticides. Pieces of produce with commonly removed skin such as avocados and pineapples are far less likely to be tainted. 

Below you'll find the 12 foods most likely to contain pesticides and the 15 foods least likely to be tainted.

The Dirty Dozen

Foods most likely to contain pesticides, according to FDA and USDA data.

1. Strawberries
2. Spinach
3. Kale, collard and mustard greens
4. Peaches
5. Pears
   
6. Nectarines
   
7. Apples
   
8. Grapes
   
9. Bell and hot peppers
   
10. Cherries
    
11. Blueberries
    
12. Green beans

The Dirty Dozen is a good indicator meant to alert consumers to the fruits and vegetables most in need of thorough washing. Even a quick rinse with water or a spritz of produce wash helps. 

You can also sidestep much of the potential risk by buying certified organic fruits and vegetables that are free from the use of farming pesticides. Knowing which foods are more likely to contain pesticides might help you decide where to spend that bit of extra money on organic. And as I learned in an analysis of organic and nonorganic prices, they aren't as expensive as you might think.

More takeaways from the Dirty Dozen study

• More than 90% of samples of strawberries, apples, cherries, spinach, nectarines and grapes tested positive for residues of two or more pesticides.
• A total of 210 different pesticides were found on Dirty Dozen items.
• Of those 210, over 50 different pesticides were detected on every type of crop on the list, except cherries.
• Kale, collard and mustard greens, as well as hot peppers and bell peppers, had the most pesticides detected of any crop -- 103 and 101 pesticides in total, respectively.

Conversely, the EWG found these 15 fruits and vegetables Ieast likely to contain pesticides. 

The Clean 15

These are the fruits and vegetables least likely to contain pesticides, according to the study:

1. Avocados
2. Sweet corn
3. Pineapple
4. Onions
   
5. Papaya
   
6. Sweet peas (frozen)
   
7. Asparagus
   
8. Honeydew melon
   
9. Kiwi
   
10. Cabbage
    
11. Mushrooms
    
12. Mangoes
    
13. Sweet Potatoes
    
14. Watermelon
    
15. Carrots
    

EWG's methodology involves six measures of pesticide contamination. The analysis focuses on which fruits and vegetables are most likely to contain one or more pesticides but does not measure how much of any one pesticide is on a given piece of produce. You can read more on the EWG's Dirty Dozen in the published study here.