A new study led by the Silent Spring Institute revealed that toxic highly fluorinated chemicals remain prevalent in fast food packaging in the U.S.

The study, published in ACS Environmental Science and Technology Letters, found more than two dozens of highly fluorinated chemicals in the packaging used by different fast food companies. Surprisingly, the toxic chemicals discovered during the study include a certain substance that is known to be phased out several years ago.

"These chemicals have been linked with numerous health problems, so it's concerning that people are potentially exposed to them in food," said Laurel Schaider, an environmental chemist at Silent Spring Institute and lead author of the study, in a press release. "Children are especially at risk for health effects because their developing bodies are more vulnerable to toxic chemicals,"

For the study, the researchers tested more than 400 samples of food packaging taken from 27 fast food chains across the U.S. The samples, which include paperboards, paper wrappers and drink containers, were analyzed using particle-induced gamma-ray emission (PIGE) spectroscopy. The PIGE spectroscopy looked for a class of chemicals known as PFASs (per- and polyfluoroalkyl substances) using fluorine as a marker.

The researchers found fluorine in almost half of the paper wrappers and 20 percent of the paperboard samples. Food packaging as well as dessert and bread wrappers of Tex-Mex were discovered to most likely contain fluorine compared to other categories of packaging.

Furthermore, six of the samples with high fluorine also contain a long-chain PFAS called PFOA (perfluorooctanoic acid), also known as C8. Due to the potential health hazards of C8, several major U.S. manufacturers voluntarily agreed to cease the use of the chemical in their food packaging.

PFAS are commonly used in a variety of non-stick, stain-resistant and waterproof products. These products include but are not limited to carpeting, cookware, outdoor apparel and food packaging. Exposure to PFAS has been linked with cancer, immune suppression, decreased fertility, thyroid disease and low birth weight.