10 Foods That You Should Only Buy Organic (Slideshow)

Conventionally grown apples contain the highest traces of pesticides in supermarkets than any other crop. Even after apples were washed, 48 types of pesticides were discovered by the EWG. Farmers use a wide range of chemicals on apple crops because they're highly susceptible to regional insect infestation and blights. Apple skins absorb these pesticides to fight these environmental problems, but the chemicals remain in the fruit long after harvest. In addition to organic apples not being laden with as many pesticides, their skins have been shown to contain 15 percent more antioxidants than non-organic apples.

Celery has no protective skin, so it is vulnerable to contact with insecticides and pesticides. Celery stocks are also porous, so they retain the pesticides that they're treated with, which can be up to 13 different types.

In the EWG study, a single sample of cherry tomatoes tested positive for 13 different pesticides. Because of the way that they grow in dense clusters, there is more surface area to spray, which results in more chemical product on the fruit. Their thin skins make it easy for chemicals to leach into the flesh of the fruit. 

Non-organic cucumbers were found to contain 69 types of pesticides in the 2013 EWG study. If you can't find organic, peel the cucumbers because the waxes that are used to make them shiny also tend to hold onto chemical treatments.

Grapes ripen quickly, so they are more prone to mold and insects. As a result, grapes are heavily sprayed. Grape crops were found to contain 34 pesticide residues by the U.S. Department of Agriculture Pesticide Data Program, four of which are known to be, or are probably carcinogenic. When tested, imported Chilean grapes contained 17 various chemicals.

In the weeks before harvest, conventional farmers spray peaches with pesticides to guarantee perfect-looking fruits on the shelves. Even if you wash and peel a non-organic peach before eating it, it would be impossible to get rid of all 62 pesticides found by the USDA.

Even root vegetables that grow underground are susceptible to chemical treatment. Potato vines grow above the surface, and are regularly sprayed with pesticides when conventionally grown. The soil is also treated with fungicide to further prevent diseases like potato blight. For this reason, the average potato contains a higher total weight of pesticides than any other edible crop. 

Non-organic salad greens, especially spinach and lettuce, are sprayed with potent pesticides right onto their leaves. Organic farmers combat the insects and worms that like to snack on them by using traps, non-toxic repellents, and mesh nets to keep natural attackers at bay.

Strawberries are a delicate fruit with thin skin that is prone to growing fungus. To combat this, conventional farmers spray them with pesticides that linger when they hit the produce section. The nooks and crannies in strawberries also make for a higher concentration of pesticide compound. Almost 60 different types of pesticides have been detected in washed strawberries.

Peppers, especially sweet bell peppers, are highly susceptible to insect infestation, so when they're grown non-organically, they're generously sprayed with insecticides. Their thin crunchy skins absorb pesticides like a sponge — 50 different pesticides were detected on sweet bell peppers when tested.