By Liz Borkowski

While we’re waiting to hear what EPA and ConAgra have learned from studying emissions from microwave popcorn, it’s worth remembering that airborne artificial butter flavoring isn’t the only concern associated with this particular convenience food.

Rebecca Renner reported last year in Environmental Science & Technology about a study by FDA scientists on consumer products that contact food. They were investigating potential sources of the 4-5 ppb of PFOA, a suspected carcinogen, that most Americans carry in their blood, and one of the things they looked at was fluorotelomer coating on paper food packaging, which can degrade into PFOA. (To learn more about PFOA, see this case study at DefendingScience.org.) The packaging with the most fluorotelomer content was microwave popcorn bags.

What matters isn’t just how much PFOA is in consumer products, but how much of the chemical migrates from the product to the food cooked in it. Renner compares the scientists’ findings on microwave popcorn bags to findings on certain nonstick cookware that’s produced by a process that uses PFOA:

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.

What does that mean for consumers? Renner explains:

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,” [University of Alberta biochemist Jonathan] 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, [lead study author Timothy] 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.

In a study published recently in Environmental Science & Technology, scientists from Wadsworth Center, SUNY at Albany, and Consumers Union looked at the vapor angle, measuring gas-phase PFOA and fluorotelomer alcohol released from nonstick pans and bags of microwave popcorn. They found PFOA in the vapors released from both microwave popcorn bags and from nonstick frying pans; one pan released significantly less PFOA after multiple uses, while another did not.

In a voluntary pact with the EPA, eight U.S. companies have agreed to reduce trace amounts of PFOA in consumer products by 95 percent by 2010 and virtually eliminate them by 2015.  Maybe I’ll eventually be able to eat microwave popcorn without feeling a little twinge of worry.

UPDATE 5/30/07: Here are a couple of other articles worth reading on this subject:

Ken Ward’s 11/14/05 Charleston Gazette story details the struggles of Glenn Evers, a former DuPont engineer who was fired after raising questions about C8 leaching from paper food packaging.

Rebecca Renner’s 5/23/07 Environmental Science & Technology article about scientists’ efforts to track the source of PFOA contamination in humans.