It's also one of the most pesticide-contaminated vegetables in the US, according to the nonprofit Environmental Working Group (EWG), which lists kale among its " Dirty Dozen " guide to the most contaminated food products.
Despite not making the list in 2018, kale ranks third this year, behind strawberries and spinach. The news, though potentially worrying for salad fans, could have even greater implications for America's agricultural workers.
Kale samples contained traces of weed-killer
After analyzing 2017 tests from the US Department of Agriculture, the EWG found that the average kale sample contained traces of more than five different pesticides, despite the fact that the samples were thoroughly washed.
More than 90% of the samples showed detectable levels of at least two pesticides, and the most contaminated sample had 18 different pesticide residues.
When it comes to kale, the EWG found that 60% of the samples tested positive for an herbicide called DCPA, which is marketed under the name Dacthal. The chemical was introduced in the US in the late 1950s as a weed-killer for strawberries, vegetables, beans, and cotton. By the 1990s, it was mostly used to tame weeds on golf courses and residential lawns.
Thus far, the EPA has found " suggestive evidence " that Dacthal could cause cancer. The organization has listed the herbicide as a possible carcinogen based on a two-year study that linked DCPA to thyroid and liver tumors in rats, but the effects on humans haven't been tested.
As of 2018, the California Office of Environmental Health Hazard has determined that even a lifetime exposure to Dacthal in drinking water would not present an adverse health effect in humans.
The EWG analysis also found that 30% of the kale samples contained bifenthrin and cypermethrin , two insecticides that have been classified by the EPA as possible human carcinogens based on studies in mice. Excessive exposure to these chemicals could cause nausea, headaches, and neurological issues, such as tingling and numbness.
Pesticides could be even more harmful to farmers
Though contaminated vegetables may wind up at restaurants and grocery stores, farmers are routinely exposed to higher quantities of pesticides.
Workers who grow kale run the risk of coming into direct contact with herbicides like Dacthal. Those spraying pesticides on kale crops may also inhalechemicals that could jeopardize their health.
The EPA states that respiratory and skin contact with Dacthal is "expected among agricultural and horticultural professionals" who work with the chemical, though it doesn't identify the risk of exposure.
A 2017 study found that exposure to certain pesticides may increase farmers' risk of non-Hodgkin's lymphoma, a cancer that develops in the lymphatic system.
By the EPA's own estimates, around 10,000 to 20,000 agricultural workers are diagnosed with pesticide poisoning each year. More than a decade ago, the organization stated that "risks to workers still exceed EPA's level of concern" even with its worker protection standards in place.
Should we be worried about eating kale?
For those still worried about putting kale in their salads or smoothies, there isn't much to fear. There's far more evidence to suggest that the vegetable actually benefits your health.
Some studies even suggest that cruciferous vegetables like kale can protect against certain types of cancer.
In the future, scientists could discover new health risks related to pesticides in food. If that happens, the consequences for farmers may be even more devastating than the effects on consumers.
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