If you frequent Chipotle, Sweetgreen, Dig or other restaurants that offer compostable bowls and plates, you’re probably familiar with the beige, cardboard-esque products your food comes in. These molded fiber bowls feel a little thicker than paper and have a go-green, earthy look and feel. They might even make you feel a little better after you’ve cleaned your plate, because you know you’re doing a small part to help save Mother Earth — you can finish your burrito and toss the bowl sans guilt, right?

Not so fast. You’ve been promised your plate is compostable, but there’s a glaring problem with that claim. According to tests by The New Food Economy, all fiber bowls contain per- and polyfluoroalkyl substances (PFAS) — a class of more than 4,000 synthetic toxic chemicals. In addition to these chemicals having the potential to wind up in your food, they are also unable to biodegrade naturally into the environment.

The New Food Economy’s testing included fiber bowls from 14 locations of eight different restaurants in New York City, including Chipotle, Sweetgreen and Dig. Researchers found that all the samples — 100% — tested contained high levels of fluorine — indicating treatment with PFAS compounds. If you’ve ever wondered how your hot, greasy burrito doesn’t soak through your Chipotle bowl like it would on a paper plate, it’s because of PFAS compounds — they’re used to help keep the bowl intact so your food doesn’t end up soaking through.

Not only are fiber bowls not compostable as has been claimed, they’re actually adding to the chemical load and making compost even more toxic. Don’t be fooled into thinking your bowl will gracefully degrade after you toss it. Those PFAS will stick around forever — literally. They’re often referred to as “forever chemicals” because they’re guaranteed to stick around for generations to come.

PFAS can often be found in food packaging, commercial household products and drinking water — especially bottled water. The toxic chemicals do not break down in the environment or in the human body. Studies suggest that exposure to PFAS may affect children’s abilities to grow and learn, reduce fertility in men and women, interfere with hormone levels, alter the immune system and increase the risks of high cholesterol, high blood pressure and certain cancers.