A study finds pollutants in the soil where they decompose.

Photo: Lucca Fabian / Getty Images

For eco-conscious consumers getting takeout, taking home doggie bags, or just trying to have a picnic without doing extra damage to the planet, the idea of compostable food containers is compelling. Instead of plastic (which doesn't break down, and isn't always recyclable) or styrofoam (which is really awful for the environment), these containers are made from paper, bamboo or other things that are supposed to degrade into nutrient-rich organic matter, leaving you to feel much better about tossing them in the trash-or even into your backyard composter.

But a recent study finds that many containers marketed as compostable are still made with polyfluoroalkyl substances, also known as PFAS, which end up leaching into the soil and potentially causing long-term environmental and health problems. According to the Environmental Protection Agency, not only can PFAS build up over time in the environment and in the human body, but "there is evidence that exposure to PFAS can lead to adverse human health effects." The effects include increased liver and kidney damage, low infant birth rate, higher rates of cancer and even "increased cholesterol levels among exposed populations."

The study, published in Environmental Science & Technology Letters, analyzed the PFAS in "nine ... commercial composts and one backyard compost." Researchers found higher concentrations of the chemicals in compost where food containers were present.

Why do food containers contain these chemicals? According to a news release by the American Chemical Society, which helped publish the study, "PFAS are widely used in manufacturing because of their flame-retardant and water- and oil-repellent properties," making them ideal for keeping paper cups of soup or boxes holding greasy fries or salads covered in dressing from becoming soaked and disintegrating before you make it home.

And the problem isn't just that they are touching your food. If PFAS end up in compost, they may end up back in your bodies via the food that compost is used to grow. As the press release explains: "Previous research has shown that PFAS in biosolids applied as fertilizer can migrate from soil to plants and then accumulate in humans through the food chain."

As such, it might be best to avoid composting any food containers in your back yard-especially in compost you're using on vegetables. And the safest bet is to purchase reusable BPA-free glass bottles, and plastic-free food containers that you can take with you-and avoid disposable containers altogether.