Chemicals used in fast food wrappers and microwave popcorn bags to prevent grease from seeping through are being absorbed by food, ingested by people, and showing up as contaminants in their blood, research at the University of Toronto has found.

The study was published in the open-access journal Environmental Health Perspectives Monday and led by environmental chemists Scott Mabury and Jessica D’eon from the University of Toronto.

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The contaminants investigated by the study are perfluoroalkyls, synthetic chemicals that repel oil, grease, and water. The chemicals are used in a number of products such as carpeting and coating for paper and cardboard packaging.

Previous research led by Mabury and D’eon, published in 2007, found that fast food wrappers are a source of these chemicals in the human blood stream.

Their new study shows that perfluorinated chemicals can migrate from wrappers into food.

The specific chemicals they investigated were perfluorinated carboxylic acids (PFCAs), which are produced by the break down of polyfluoroalkyl phosphate esters (PAPs).

“We suspected that a major source of human PFCA exposure may be the consumption and metabolism of polyfluoroalkyl phosphate esters, or PAPs,” said D’eon.

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“PAPs are applied as greaseproofing agents to paper food contact packaging such as fast food wrappers and microwave popcorn bags,” she explained.

PFCAs such as perfluorooctanoic acid (PFOA) are associated with changes in sex hormones and cholesterol levels, according to the US Agency for Toxic Substances. In addition, studies have found rats exposed to high levels of PFOA tend to develop tumors.

“In this study we clearly demonstrate that the current use of PAPs in food contact applications does result in human exposure to PFCAs, including PFOA,” says Mabury. “We cannot tell whether PAPs are the sole source of human PFOA exposure or even the most important, but we can say unequivocally that PAPs are a source and the evidence from this study suggests this could be significant.