Diacetyl Fact Sheet

General Information
Chemical formula: C4H6O2
Butanedione or 2,3-butanedione
Diacetyl is a chemical that imparts a butter flavor to food and beverages. It occurs naturally in butter and fermented beverages, and it is also manufactured as a food additive.

Diacetyl is used in a variety of food products, from butter-flavored microwave popcorn to baked goods, candy, and cake mixes. Diacetyl is rarely mentioned on an ingredient label, but is often included under “artificial flavor.”

Public health scientists and worker advocates are particularly concerned about workers’ exposure to airborne diacetyl, which can occur when diacetyl is heated to the point of producing vapors.

Diacetyl is one of a group of chemicals used in artificial flavorings. While it is difficult to isolate the effects of these different chemicals when they are used together, diacetyl has been tested separately and found to cause adverse health effects in studies on laboratory animals.

Health Factors listed on OSHA's website
Potential symptoms: Eye, mucous membrane, respiratory system, skin irritation; persistent cough, phlegm production, wheezing, dyspnea (shortness of breath); unusual fatigue; episodes of mild fever or generalized aches; severe skin rashes.

Health Effects: Irritation - Eyes, Nose, Throat, Skin (HE15); Suspected cumulative lung damage---bronchiolitis obliterans (HE10)

Affected organs: Eyes, respiratory system, skin

Regulatory Involvement
The Occupational Safety & Health Administration (OSHA) of the US Department of Labor establishes and enforces standards to protect workers from on-the-job hazards. For some health hazards, OSHA has set permissible exposure limits (PELs), which are regulatory limits on the amount or concentration of a substance allowed in the workplace air. OSHA does not have a PEL for diacetyl on the books, but it has other standards, such as the general duty clause, that could be used to protect workers from this respiratory hazard.

In July of 2006, the United Food and Commercial Workers Union and the International Brotherhood of Teamsters petitioned OSHA to issue an Emergency Temporary Standard (ETS) for diacetyl. The ETS would set a PEL that would be in effect for six months; during that time, OSHA would be required to issue a permanent rule for the substance.

The Centers for Disease Control’s National Institute for Occupational Safety and Health (NIOSH) has conducted workplace health hazard evaluations at 10 microwave popcorn plants, as well as animal studies to investigate the effects of diacetyl. On the basis of the findings of these studies, NIOSH issued an interim recommendation for worker diacetyl exposure in 2000 and an official alert (detailing findings and recommendations for employer safety measures and monitoring) in 2003.

Selected Studies
Health Hazard Evaluation at Flavor Plant, conducted by NIOSH in 1985: After two young, previously healthy, non-smoking employees were diagnosed with severe obstructive lung disease (consistent with bronchiolitis obliterans) within a year of beginning employment, NIOSH investigated an Indiana plant that manufactured flavors for bakeries. Investigators did not identify a cause of the disease, though they recommended the facility reduce workers’ dust exposure. Diacetyl was listed as one of 33 chemicals commonly used at the plant.

Diacetyl Animal Toxicology Study, conducted 1993: Rats underwent a single 4-hour exposure to diacetyl vapors, and all of them died at diacetyl concentrations > 23.9 mg/l. (This study, undertaken by German chemical manufacturer BASF, was never reported to the government or published in scientific literature, but its results are similar to those found by NIOSH years later.)

Survey of Health of Microwave Popcorn Workers, published 2002 in the New England Journal of Medicine: NIOSH investigators conducted interviews and lung-function tests for 117 workers at a single microwave popcorn plant and conducted air sampling at the plant. Analysis showed that workers had 2.6 times the expected rates of chronic cough and shortness of breath, according to comparisons with the national data, and twice the expected rates of physician-diagnosed asthma and chronic bronchitis. Workers who had never smoked had 10.8 times the expected rate of airway obstruction, and workers directly involved in the production of microwave popcorn had higher rates of shortness of breath on exertion (that had developed since they started work) than workers in other parts of the plant.
Citation: Kreiss K, et al. (2002). Clinical bronchiolitis obliterans in workers at a microwave-popcorn plant . N Engl J Med 347(5): 330-338.

Artificial Butter Flavor Animal Toxicology Study, published 2002 in Toxicology and Applied Pharmacology: In a study conducted by NIOSH scientists, rats underwent single 6-hour exposure to vapors liberated from heated butter flavorings. Vapors containing 285–371 ppm diacetyl were found to cause bronchitis, and vapors containing 203–371 ppm diacetyl were found to cause necrosuppurative rhinitis.
Citation: Hubbs AF, et al. (2004). Necrosis of nasal and airway epithelium in rats inhaling vapors of artificial butter flavoring . Toxicol Appl Pharmacol 185: 128-135.

Diacetyl Animal Toxicology Study, published 2006 in Toxicology and Applied Pharmacology: NIOSH investigators studied the effects of diacetyl solutions of different concentrations on in vitro preparations of guinea pig trachea. They concluded that “our results suggest that diacetyl exerts toxic effects on airway epithelium, which lead to airway hyperreactivitiy in vitro and degradation of its protective barrier function.”
Citation: Fedan JS, et al. (2006). Popcorn worker's lung: In vitro exposure to diacetyl, an ingredient in microwave popcorn butter flavoring, increases reactivity to methacholine . Toxicol Appl Pharmacol 215(1): 17-22.

Survey of Health of Microwave Popcorn Workers published 2006 in Journal of Occupational and Environmental Medicine: Investigators analyzed data from medical and environmental surveys at six microwave popcorn plants for which NIOSH had received workplace health hazard evaluation requests. They found higher prevalence of respiratory symptoms and airways obstruction in oil and flavorings mixers with longer work histories and in packaging-area workers near non-isolated tanks of oil and flavorings. The NIOSH scientists found workers with occupational lung disease at five of the six plants; one affected worker was employed in a mixing area where mean personal exposure to diacetyl was 0.02 ppm.
Citation: Kanwal R et al. (2006). Evaluation of flavorings-related lung disease risk at six microwave popcorn plants . J Occup Environ Med 48(2): 149-57.