Some samples contained as many as 18 different pesticides.
According to the EWG's analysis of test data from the Department of Agriculture, 70 percent of the produce sold in the USA comes with pesticide residues, and surprisingly, kale is among the most contaminated fruits and vegetables that Americans consume.
The findings came in an annual report from the Environmental Working Group (EWG), the Shopper's Guide to Pesticides in Produce.
In USDA's most recent round of tests, more than 92 percent of conventionally grown kale samples had at least two or more pesticide residues.
Avocados were ranked the "cleanest" fruit on EWG's "Clean 15" list, followed by sweet corn, pineapples, frozen sweet peas, and onions.
Additionally, recent EWG-commissioned tests of kale from grocery stores found that on two of eight samples, Dacthal residues "were comparable to the average level reported by the USDA".
"We were surprised kale had so many pesticides on it, but the test results were unequivocal", Alexis Temkin, the group's toxicologist, said in a statement.
What is so surprising about kale being number three on the Dirty Dozen list? The latest report on kale found traces of Dacthal, which the Environmental Protection Agency classified as a possible human carcinogen.
Numerous pesticides detected by EWG have always been banned in the European Union and have been the subject of concern at the EPA-but the USA has failed to take the chemicals off the market.
USDA's tests found a total of 225 different pesticides and pesticide breakdown products on popular fruits and vegetables Americans eat every day. "That's largely because residues are so low, if present at all", she said. Before testing, all produce was thoroughly washed and peeled, just as consumers would prepare food at home, showing that simple washing does not remove all pesticides. People are exposed to pesticides through the food they eat due to their broad use.
Fear shouldn't be a part of the decision whether to buy foods on the pesticide list, said Teresa Thorne, executive director of the Alliance for Food and Farming, a non-profit that represents organic and conventional farmers of fruits and vegetables.
Still, while EWG recommends that consumers buy organic versions of produce on its Dirty Dozen list when possible, it still advises eating fresh produce even if conventionally grown when organic is not available or too expensive.
The report found that less than one percent of avocado and sweet corn samples had any detectable pesticides. DCPA was the most commonly-found pesticide in USA produce.
Multiple pesticide residues are extremely rare on Clean Fifteen vegetables. Kale and spinach samples had, on average, 1.1 to 1.8 times as much pesticide residue by weight than any other crop, says the EWG. "Data supports the fact that pesticides can have adverse health effects, especially for children, so reducing pesticide residue in the diet is a good way to reduce exposure and lower those risks", says Temkin.