The long awaited EPA study of chemicals emitted when microwave popcorn is popped has just been published. Its results are not surprising: popping microwave butter flavor popcorn releases a sizable number of chemicals into the air, although not necessarily in large amounts. These chemicals include diacetyl, the primary chemical implicated in the bronchiolitis obliterans (“popcorn lung”) cases seen in popcorn and flavor factories.

The study does not attempt to measure or model the exposure consumers get when they pop microwave popcorn at home. Rather, it simply measures what chemicals are emitted when you pop the stuff, and when you open the bags.

Why did the EPA insist on not sharing these results with anyone (including OSHA) before publication?

The results of the study were fairly predictable. With one exception (methyl ethyl ketone) the same chemicals found in the popcorn factories were emitted from the sampled microwave popcorn bags. The greatest emissions (and 80% of the total) come when you open the bag (not while the bag is being microwaved), and emissions drop off dramatically but continue at low levels for some minutes after opening.

There was a sizable variation between brands and types of popcorn popped. For most brands, popping the butter flavor samples resulted in more diacetyl emissions than popping the “light” samples, but not for all.

What does this tell consumers about the hazards of breathing artificial butter vapors from popcorn microwaved at home? Not much. We have already have exposure (rather than emission) data from the case of the Colorado man who popped and ate two bags of heavy butter microwave popcorn a day and developed popcorn lung. The exposure levels in his home were 0.5-3 parts per million after he popped the bags. This is comparable to levels in popcorn factories and evidently enough to damage his lungs.

The EPA scientists also measured the flourotelemers that are released in the popping. These are chemicals used in the lining of the bags, to keep the oils from seeping out. There is evidence that the body can convert flourotelemers into PFOA, a chemical considered by some scientists to be a likely carcinogen. (For more about PFOA, see this case study at

The Project on Scientific Knowledge and Public Policy FOIA’d these results more than a year ago and were refused by EPA. At its recent stakeholder meeting, OSHA staff said they aksed EPA for the results and were turned down as well.

I cannot explain why the EPA was adamantly opposed to sharing these results with the public or other regulatory agencies. The journal in which the article appeared, Critical Reviews in Food Science and Nutrition, does not prohibit scientists from discussing studies before publication. Perhaps one of our readers can help us understand the EPA’s actions, since it makes little sense to me.