Artificial Butter Flavorings (ABF) Components

In 2000, eight employees at a microwave popcorn packaging plant were diagnosed with bronchiolitis obliterans—a rare lung disease characterized by fibrotic obstruction of the small airways. A subsequent NIOSH health hazard evaluation found that diacetyl and acetoin were the major volatile components of the artificial butter flavoring vapor to which microwave popcorn packaging workers were exposed. Diacetyl is a naturally occurring substance that gives butter its characteristic flavor and aroma, and is often a component of artificial flavoring formulations. Acetoin, a closely related chemical, also occurs naturally and is an ingredient in many flavoring formulations, perfumes and essences. Diacetyl and acetoin are present in almost all alcoholic beverages as fermentation products.

In 2007, artificial butter flavoring (ABF) and two major volatile constituents, diacetyl and acetoin, were nominated by the United Food and Commercial Workers Union for long-term inhalation testing for respiratory toxicity, general toxicity, and carcinogenicity. Because NIOSH was conducting studies of an artificial butter flavoring formulation, NTP research focused on diacetyl, acetoin, and related flavorings components.

NTP prepared a research concept in 2007. NTP studies on artificial butter flavorings and their components were designed to provide animal toxicity data needed by regulatory agencies to set inhalation exposure limits that will protect workers. The toxicity data were provided to NIOSH and OSHA as they became available.

NTP published the results of a number of short-term two-week inhalation studies of butter flavoring components (see NTP Laboratory Studies). Initial studies demonstrated that inhalation of diacetyl vapors for two weeks caused significant injury to the respiratory tract of rats and mice. Rats developed bronchiolitis obliterans-like lesions similar to those found in workers following two-week exposure to diacetyl. Acetyl propionyl, a potential replacement for diacetyl, was also found to cause bronchiolitis obliterans in rats. Acetyl butyryl (2,3-hexanedione), a structurally-related flavoring, did not cause bronchiolitis obliterans in rats, and was shown to be less toxic than diacetyl and acetyl propionyl at the same exposure concentrations.

Three-month inhalation studies of diacetyl, acetyl propionyl, and acetoin were conducted in rats and mice at concentrations below those shown to cause bronchiolitis obliterans in two-week studies. Exposure to diacetyl and acetyl propionyl for three months caused significant toxicity for the respiratory tract in rats and mice, whereas acetoin did not cause toxicity at significantly higher concentrations. Diacetyl was selected for study in a two-year chronic toxicity and carcinogenicity study.

Inhalation exposure to diacetyl for two years caused a low incidence of rare nasal cavity tumors in male and female rats. A low occurrence of adenocarcinoma of the nose of female mice may be attributed to diacetyl exposure. Diacetyl also caused a spectrum of nonneoplastic lesions of the nose, larynx, trachea, and lung of male and female rats and mice.

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