Earlier this month, news broke of a study that found potentially health-harming chemicals in a variety of fast food packaging. Upon hearing such news, the natural inclination is to worry that you’re ingesting those chemicals along with your burger and fries. Study researcher Graham Peaslee says that’s certainly a risk. But perhaps the greater risk, he says, happens after that hamburger wrapper ends up in landfill and the chemicals seep into our environment and water.

The chemicals in question are per- and polyfluoroalkyl substances (PFASs), which are used to make consumer products nonstick, waterproof and stain-resistant. Think carpets, upholstery and weather-resistant clothing. Previous research has found associations between exposures to PFASs and kidney and testicular cancer, low birth weight, thyroid disease, decreased sperm quality, pregnancy-induced hypertension and immunotoxicity in children. The chemicals have become somewhat ubiquitous too, detected worldwide in water, soil, sediment, wildlife and human blood samples. The study that Peaslee co-authored tested hundreds of fast food packaging samples for fluorine, a marker of PFASs, finding the element in about half of paper wrappers and one-fifth of paperboard samples.

The study, published earlier this month in Environmental Science & Technology Letters, ended up being the most comprehensive assessment to date on the presence of fluorinated chemicals in U.S. fast food packaging. However, Peaslee, a professor in the Department of Physics at the University of Notre Dame, told me that the original intent of the study was actually to test out a novel technique he developed for measuring fluorine known as particle-induced gamma-ray emission (PIGE) spectroscopy. The technique is about 10 times faster than more typical methods — in other words, he said, researchers can test a product for fluorine in just three minutes, which means one could potentially test hundreds of samples in a day. And that means researchers could test entire categories of consumer products in relatively short time spans.

So, Peaslee and colleagues decided to try out the new testing method on a large sample of products, choosing fast food packaging because prior research had detected PFASs in such products. Study researchers ended up collecting more than 400 packaging samples from 27 fast food restaurant chains, including McDonald’s, Burger King, Chipotle, Starbucks, Jimmy Johns, Panera and Chick-Fil-A, with the majority of samples coming from western Washington, eastern Massachusetts, western Michigan, northern California and Washington, D.C. Samples were then divided into six groups: food contact paper, like sandwich wrappers; noncontact paper, such as outer bags; food contact paperboard, like pizza boxes; paper cups; other beverage containers, such as milk cartons; and everything else, such as drink lids or applesauce containers.

Using the PIGE method, researchers found that of the 407 samples, 33 percent had detectable fluorine concentrations. Among food contact papers, detection frequencies ranged from 38 percent for sandwich and burger wrappers to about 57 percent for Tex-Mex food packaging and dessert and bread wrappers. Fluorine was more commonly found in grease-proof products than in beverage containers and products not intended for direct food contact. Overall, 46 percent of food contact papers and 20 percent of paperboard samples had detectable fluorine.

To help validate their findings — or to confirm that a positive result for fluorine is a reasonable proxy for PFASs — researchers then picked out a subset of 20 packaging samples to test for specific PFASs. They found that six of those samples had detectable levels of long-chain PFASs perfluorooctanoic acid (PFOA), even though U.S manufacturers had agreed in 2011 to stop using such substances for food contact via a U.S. Food and Drug Administration initiative. In general, researchers found that the subset testing supported the PIGE results, with samples that had tested high in fluorine also containing PFASs.

With results in hand, study authors reached out to the fast food restaurants with some questions. Co-authors Laurel Schaider, Simona Balan, Arlene Blum, David Andrews, Mark Strynar, Margaret Dickinson, David Lunderberg, Johnsie Lang and Peaslee write:

We attempted to investigate the fast food chains’ knowledge of their use of fluorinated food packaging. For each of the fast food chains that we sampled, we submitted questions through Web sites and by phone regarding company use, sourcing, and general policies on fluorinated products. Only two companies provided a substantive response: one stated that they believed none of their food packaging contained fluorinated chemicals, and the other stated that they verified with their suppliers that their food packaging did not contain PFASs. However, we found a substantial portion of fluorinated food contact papers from these two chains. While it is difficult to draw conclusions on the basis of so few responses, this suggests a lack of knowledge in the fast food industry about the use of fluorinated packaging.

The study also noted that while manufacturers did phase out certain PFASs of concern, alternative PFASs still pose an environmental and health risk, which is prompting researchers like Peaslee to call for reducing the use of highly fluorinated compounds and switching to nonfluorinated food packaging alternatives, like wax paper or aluminum foil. In fact, Peaslee said highly fluorinated compounds shouldn’t be used in products that go to landfills, as the chemicals don’t naturally degrade and end up accumulating in the environment as well as in people’s bodies. Indeed, a 2016 study found that drinking water sources for 6 million U.S. residents exceeded federal advisories for PFASs.

But back to fast food packaging — how dangerous is it to our health? According to Peaslee’s study, the extent to which PFASs from food packaging actually migrate into the food depends on a number of variables, such as the type of food, temperature of the food, and how long the food remains in the packaging. It’s also unclear as to how much food packaging is responsible for people’s dietary consumption of PFASs, though the study noted that children may be at heightened risk because they eat significant amounts of fast food and are more vulnerable to negative health impacts. Still, the study states that fast food packaging “can contribute to indirect dietary exposure via migration into food.”

And while no one likes to think of their food being wrapped up in harmful chemicals, Peaslee said the greater risk to human health comes after all those wrappers end up at the landfill, where PFASs can begin seeping into and building up in our soil and water.

“You won’t eat that wrapper, but you will be eating the chemicals off that wrapper when it degrades,” he told me.

Peaslee added that he’s not holding his breath for better chemical safety regulations when it comes to PFASs. Instead, he said consumers can use their voices and dollars to call on companies to stop using fluorinated products. He also noted that after his study hit the newsstands, several fast food companies contacted him to discuss the results.

“We shouldn’t ban this whole class of chemicals, but we should certainly use them sparingly,” Peaslee told me, noting that PFASs are still critical firefighting tools. “For consumers, look for the tag that says it doesn’t contain (perfluorinated chemicals). That will be the loudest voice you have.”

To download a full copy of the fast food study, visit Environmental Science & Technology Letters.

Kim Krisberg is a freelance public health writer living in Austin, Texas, and has been writing about public health for 15 years.