In case you missed it, check out this post for context.

August seems to be turning into a month of popcorn toxicology. While doing a bit of house blogkeeping this morning, I ran across a release about a new study on a diacetyl substitute.

After manufacturers started reducing and removing diacetyl from their fake butter recipes, they switched to a series of closely related compounds, simple extensions of the carbon chain. National Institute of Environmental Health & Safety and National Institute of Occupational Safety & Health have now assessed the toxicity of one substitute, 2,3-pentanedione, in rodents. Given the structural similarity to diacetyl, both groups thought the respiratory effects of 2,3-pentanedione should be explored. The NIOSH study, published online today, also looks at neurological effects because a related compound, 2,4-pentanedione is neurotoxic.

I won’t go into the detail that I did for the diacetyl Alzheimer’s post, because I am not a pathologist, and pathology is the meat of these papers. But here’s the gist: Inhaling 2,3-pentanedione injures the respiratory epithelium of rats and mice. Based on the NIOSH results, acute respiratory toxicity is comparable for diacetyl and 2,3-pentanedione.

However, 2,3-pentanedione creates some other major problems in rats. It damages to olfactory neurons, inducing degeneration and apoptosis. The compound also increases mRNA expression* of inflammatory genes – in the brain. Presumably it’s crossing the blood-brain barrier and dispersing throughout the brain; the authors observed changes in mRNA expression in the olfactory bulb, hippocampus, striatum, and cerebellum.

* The changes for the inflammatory genes IL6 and NOS2 are significant… but I suspect Alejandro would yell at them for using only one reference gene for their RT-qPCR

As is typical for early stage toxicology studies, concentrations of 2,3-pentanedione used were moderate to high – 200+ ppm (or 200 mg/L air) administered continuously –  but both neural and respiratory effects were observed within 6 hours of continuous exposure. Although rats are not humans, these studies highlight the importance of establishing exposure limits and proper engineering and personal protection controls for industry workers.

What does this mean for the consumer? Like diacetyl, the FDA lists 2,3-pentanedione as GRAS, “general recognized as safe” under normal consumption conditions. If 2,3-pentanedione levels in food are comparable to diacetyl, then a single bag of microwave popcorn emits less than 1 mg, with about 80%  immediately upon opening.

I, for one, would continue to enjoy my popcorn. But it might be wise to adapt example of a former U.S. president: Pop but don’t inhale.

References

Daniel L. Morgan, Micheal P. Jokinen, Herman C. Price, William W. Gwinn, Scott M. Palmer, & Gordon P. Flake (2012): Bronchial and bronchiolar fibrosis in rats exposed to 2,3-pentanedione vapors: implications for bronchiolitis obliterans in humans. Toxicological Pathology. DOI: 10.1177/0192623311431946

Ann F. Hubbs, Amy M. Cumpston, W. Travis Goldsmith, Lori A. Battelli, et al. (2012): Respiratory and Olfactory Cytotoxicity of Inhaled 2,3-Pentanedione in Sprague-Dawley Rats. The American Journal of Pathology. DOI: 10.1016/j.ajpath.2012.05.021

Jacky A. Rosati, Kenneth A. Krebs & Xiaoyu Liu (2007): Emissions from Cooking Microwave Popcorn, Critical Reviews in Food Science and Nutrition. DOI: 10.1080/10408390701638951