TORONTO, Ontario, Canada - Chemicals used to keep grease from leaking through fast food wrappers and microwave popcorn bags are migrating into food, being ingested by people and showing up as contaminants in blood, according to new research at the University of Toronto.

The contaminants are perfluoroalkyls, stable, synthetic chemicals that repel oil, grease, and water. They are used in surface protection products such as carpet and clothing treatments and coating for paper and cardboard packaging.

Earlier research by University of Toronto environmental chemists Scott Mabury and Jessica D'eon, established in 2007 that the wrappers are a source of these chemicals in human blood. Their new study shows that perfluorinated chemicals can migrate from wrappers into food.

The specific chemicals studied are polyfluoroalkyl phosphate esters, or PAPs, breakdown products of the perfluorinated carboxylic acids, or PFCAs, which are used in coating the food wrappers.

"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, a graduate student in the University of Toronto's Department of Chemistry.

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

In their latest study, D'eon and Mabury exposed rats to PAPs either orally or by injection and monitored for a three-week period to track the concentrations of the PAPs and PFCA metabolites in their blood.

The researchers used the PAP concentrations previously observed in human blood together with the PAP and PFCA concentrations observed in the rats to calculate human exposure to the chemical perflurooctanoic acid, PFOA.

"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," said Mabury, the lead researcher and a professor in the university's Department of Chemistry.

Elevated levels of PFOA in blood have been associated with changes in sex hormones and cholesterol, according to the U.S. Agency for Toxic Substances. Exposure to PFOA also has resulted in early death and delayed development in mice and rat pups, the agency says.

Rats that ingested PFOA for a long time developed tumors. However, based on differences between rats and humans, scientists have not determined for certain whether this could also occur in humans, the agency says.

"We found the concentrations of PFOA from PAP metabolism to be significant and concluded that the metabolism of PAPs could be a major source of human exposure to PFOA, as well as other PFCAs," said Mabury.

"This discovery is important because we would like to control human chemical exposure, but this is only possible if we understand the source of this exposure," Mabury said.

"In addition," he said, "some try to locate the blame for human exposure on environmental contamination that resulted from past chemical use rather than the chemicals that are currently in production."

The study is published today in the journal "Environmental Health Perspectives," published by the U.S. National Institute of Environmental Health Sciences. Research was funded by the Natural Sciences and Engineering Research Council of Canada.

"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," Mabury said.

The researchers concluded that due to the long time that PFOA remains in human blood, even low-level PAP exposure could, over time, result in significant exposure to PFOA.

Although humans are exposed directly to PFCAs in food and dust, the University of Toronto researchers said that because of the way the human body processes these chemicals, "PAP exposure should be considered as a significant indirect source of human PFCA contamination."

Regulatory interest in human exposure to PAPs has been growing. Governments in Canada, the United States and Europe have signaled their intentions to begin extensive and longer-term monitoring programs for these chemicals.

Regulators have made three assumptions, said Mabury, releasing the results of his 2007 study. "That the chemicals wouldn't move off paper into food, they wouldn't become available to the body and the body wouldn't process them. They were wrong on all three counts."