The USDA tests a selection of 10-15 produce items every year for pesticide residues. Items tested are both domestic and imported, and conventionally and organically grown. Health and science journalist Catherine Roberts analyzed seven years of USDA data for Consumer Reports to see which fruits and vegetables had the highest amount of pesticide residue.
The fruits and vegetables tested fall into five categories ranging from very low to very high, depending on how many pesticides are found and their quantity levels. Risk assessments are based on how many pesticides showed up on that food, how often each pesticide was found, and the levels of each of those pesticides. Chemical toxicity is also factored into the algorithm, which computes into how much of a fruit or vegetable can be safely eaten each day.
The USDA conducts its tests by washing the produce in water and removing any peels and seeds that wouldn't normally be eaten. The riskiest foods include watermelon, where pesticides were found in the flesh of the fruit with the rind removed, bell peppers, hot peppers, green beans, kale, mustard greens, potatoes, and canned and frozen spinach. The good news is that broccoli, carrots, cauliflower, cucumbers, asparagus, onions, peas, squash, sweet potatoes, tomatoes, mushrooms, and lettuce had lower levels of pesticide residue.