As if we needed another reason to cut back on fatty and high-calorie fast food, now comes this: The packaging that accompanies those super-sized burgers and fries may also be harmful to our health.

Scientists who looked at more than 400 samples from 27 fast food chains around the country found that almost half of all paper wrappers used and 20 percent of the boxes recently tested contain fluorine — a marker of PFASs (per- and polyfluoroalkyl substances) — or PFCs.

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PFCs have been linked to numerous health problems, including cancer, thyroid disease, immune suppression, low birth weight, and decreased fertility.

“Children are especially at risk for health effects because their developing bodies are more vulnerable to toxic chemicals,” Laurel Schaider, an environmental chemist at Silent Spring Institute and the study’s lead author, said in a statement.

Roughly one-third of children in the U.S. consume fast food every day. Tex-Mex food packaging and dessert and bread wrappers, in particular, were most likely to contain fluorine compared with other categories of packaging.

Related: Curing Our Super-Sized Food Hangover

U.S. manufacturers should be phasing out long-chain PFASs in consumer products, but other countries still produce them and some were detected in the study. PFASs from consumer products have been found in multiple studies to accumulate in landfill sites, and can migrate into groundwater, potentially impacting drinking water supplies.