Updated

The calorie count might not be the only thing to be concerned about in that fast-food order.

Toxic chemicals may be coating the wrappers and containers used at popular fast-food restaurants, according to a report titled “Packaged in Pollution: Are food chains using PFAS in packaging?” that was released Thursday by environmental advocacy groups Toxic-Free Future and Mind the Store.

In it, tests revealed toxic levels of PFAS substances, a group of man-made chemicals composed of non-biodegradable linked carbon and fluorine atoms (including perfluoroalkyl and polyfluoroalkyl chemicals) found in the packaging. The tests were said to be conducted by an independent laboratory in February.

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Researchers found the chemicals present in packaging for the Whopper at Burger King and in the packaging used for the chain’s chicken nuggets and cookies. The substances were also found in McDonald’s wrappers for its Big Mac sandwich, fries and cookies, and in the paper bags used at Wendy’s.

A new report found PFAS present in packaging at fast-food chains such as McDonald's and Burger King.

A new report found PFAS present in packaging at fast-food chains such as McDonald's and Burger King. (iStock)

Containers made from molded fiber, said to be environmentally friendly, tested high for PFAS, according to the report. PFAS were also found in bowls and containers used at restaurants that market themselves as healthy and eco-conscious, including Sweetgreen, Freshii and Cava.

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Sweetgreen, the D.C.-based salad chain, recently announced it was phasing out all of its bowls made with PFAS by the end of the year and has since launched PFAS-free bowls in restaurants.

Last week, the FDA agreed to begin eliminating the use of select synthetic chemicals used in food packaging materials in the next few years.

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A spokesperson for Burger King parent company, Restaurant Brands International, told Fox News in a statement: "We are looking forward to extending our safe ingredients policy to include the removal of the short-term PFAS recently identified by the FDA. We will work with our suppliers to remove them from all packaging by or, where feasible, earlier than the three years recommended by the FDA."

A spokesperson for McDonald's said the chain has eliminated a "significant subset classes of PFASs" from McDonald’s food packaging globally.

"We know there is more progress to be made across the industry and we are exploring opportunities with our supplier partners to go further," McDonald's said in a statement.

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The other fast-food chains and restaurants did not immediately return a Fox News request for comment.