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ES&T News
It’s in the microwave popcorn, not the Teflon pan
Results of a study by the U.S. Food and Drug Administration (FDA) published in October reveal that compounds known to break down into the suspected carcinogen PFOA (perfluorooctanoic acid) may be served up to millions of unwitting consumers in bags of microwave popcorn. The family treat could account for >20% of the average PFOA levels now measured in the blood of U.S. residents.
Most Americans carry 4–5 ppb of PFOA in their blood, according to the U.S. EPA’s draft PFOA risk assessment, but its source has been unknown. Products used in the home are thought to play a role, including nonstick cookware such as Teflon pans, which are produced by a process that uses PFOA. But several studies, including this one, suggest that nonstick cookware is not a major source.
The FDA team investigated consumer products that contact food—nonstick pans, food wraps, and papers—as potential sources, says FDA chemist Timothy Begley, the study’s lead author. Some of the papers used for packaging food are treated with grease-repelling fluorotelomer coatings. Microwave popcorn bags have the most of any food wrappers—about 4000 mg/kg in the coating or 25 mg per square decimeter (dm) of paper, the authors note.
Many fluorotelomer paper coatings contain mixtures of C6, C8, C10, and C12 fluorochemicals. Previous research suggests that the C8 and higher fluorotelomers can degrade to PFOA, Begley and colleagues write in Food Additives & Contaminants (2005, 22, 1023–1031).
The scientists found that a significant percentage of the fluorotelomers migrated from the bags to the popcorn oil, resulting in levels of 3–4 mg/kg (11 µg/dm2). These concentrations are hundreds of times higher than the amount of PFOA that could migrate from nonstick cookware the first time it is heated >175 °C. Because the surface area of a microwave popcorn bag is ~1000 cm2, a person consuming a bag’s worth could take up to 110 µg of fluorotelomers, according to three toxicologists who performed these calculations on the condition of anonymity.
Toxicologists commonly convert such an exposure into a human dose by dividing by the average adult body weight, 65 kg. This means that the average dose of fluorotelomers from each bag of popcorn is 1.7 µg/kg. Children would get a higher dose.
Scientists don’t currently know how readily humans can metabolize fluorotelomers to PFOA, says University of Alberta (Canada) biochemist Jonathan Martin. But he has found that rat liver cells can directly convert 1.4% of fluorotelomer alcohol to PFOA. Another 7% is metabolized to intermediate acids that are also expected to eventually degrade to PFOA (Chem. Biol. Interact. 2005, 155, 165–180). So a conservative estimate for the conversion from fluorotelomers to PFOA is 1%. This means that a person eating a whole bag of popcorn could take up 0.017 ppb of PFOA.
A person would have to eat about 300 bags of microwave popcorn over 5–10 years (about a bag a week) if the average 4 ppb of PFOA in their blood came from the snack. Toxicologists say that 5–10 years is an appropriate timescale because PFOA is reported to have a half-life in humans of ~4 years. Consumption of just 10 bags of microwave popcorn a year could contribute about 20% of the average blood PFOA levels, say the scientists interviewed anonymously for this article.
“This dose is certainly not insignificant,” Martin says. “Scientists should be, and are, considering polyfluorinated precursors [such as the fluorotelomers] as a potential human exposure pathway to perfluorinated acids, including PFOA,” he adds.
Microwave popcorn bags probably represent the worst-case scenario for getting PFOA precursors into foods, Begley notes. This is because the amount of fluorotelomers in the coatings is high and because popcorn bags heat up to >200 °C in just a minute or two. However, fluorotelomer coatings are not used in all microwave snack-food packaging, according to Begley, who is still researching other papers and coatings.
