Fast food and takeout items have been a staple for many families during the COVID-19 pandemic. But a new study finds that there could be a hidden danger inside the packaging that the food comes in.

“To our surprise, we found that nearly half of all samples we collected tested positive for elevated levels of fluorine,” says Mike Schade with the organization Safer Chemicals, Healthy Families.

Safer Chemicals, Healthy Families conducted the study along with the Public Interest Research Group. Schade says that chemicals known as PFAs were found in the packaging at McDonald’s, Burger King, Wendy’s and other popular fast food restaurants.

“Unfortunately, they can migrate out of the food packaging and get into the food,” says Schade. “And also, when these food packaging items are disposed of, the chemicals can persist in the environment literally forever.”

PFAs are grease-resistant, which makes them good for food packaging. But studies have associated them with health issues, including thyroid problems and certain forms of cancer.

“One of the strongest associations we see in multiple populations is the ability to suppress the immune system,” says Linda Birnbaum, the former director of the National Toxicology Program. “There’s been a recent study that showed people who ate more fast food…they ate more fast food and they had higher PFA levels in their blood. So, there is a clear correlation between the amount of fast food consumption and the amount of PFAs.”

A few companies like Sweetgreen, Cava and Freshii have committed to stop using PFAs in their packaging. But the chemicals are still fairly widespread. But this seems to be changing.

New York lawmakers have just passed a bill to regulate PFAs in food packaging. Gov. Andrew Cuomo is expected to sign it.

Lawmakers in New Jersey and Connecticut are considering similar bills.

Chemical manufacturers agreed last month to start phasing out the use of certain types of PFAs in food containers starting next month.

“I think the manufacturers want to do the right thing. They want to do the right thing for our health. They just have to know that there's a problem, and they have to know that there are alternatives,” Birnbaum says.