Diacetyl (formally called 2,3-butanedione), with molecular formula C4H6O2, is a natural byproduct of fermentation. It is a yellow-colored vapor with a pungent odor.

Workers involved with the manufacturing of artificial butter flavorings have been diagnosed with a disease called called bronchiolitis obliterans, which is a serious and life-threatening disease of the lungs. Recently, serious incidents of the disease or lung damage have been reported in seven California factories, while another 22 factories have reported abnormal lung tests in its workers—all in factories that produce artificial butter flavorings.

What is unusual in these diagnoses is that most of these workers are young, non-smoking workers without a history of lung problems. The medical community is calling this disease diacetyl-induced bronchiolitis obliterans (DIBO), but it is informally called Popcorn Worker’s Lung, even though the disease can occur in any industry (not just popcorn) that manufactures artificial butter flavorings. Currently, no treatment is available for DIBO, although lung transplantation is available.

Problems associated with diacetyl have been voiced since the mid-1970s, according to U.S. community health professor David Egilman, from Brown University. [New York Times, subscription required]

By the mid-1990s, the chemical industry was aware that diacetyl was highly toxic to laboratory rats. According to Sarah Shipley, with the St. Louis Post-Dispatch, the earliest hazard statement in the flavoring industry database is dated April 1989 when “diacetyl vapor was pronounced to be ‘irritating to throat and lungs’”. Cases of lung disease caused by diacetyl were found in the 1980s and 1990s in Missouri and Illinois artificial butter flavoring factories.

In 2001, the Flavor and Extract Manufacturers Association began providing information on worker health to state and federal authorities about diacetyl. At that time, the U.S. Occupational Safety and Health Administration (OSHA) issued a report linking lung problems with workers in a popcorn packaging plant in Missouri that used diacetyl.

In 2002, a National Institute for Occupational Safety and Health (NIOSH) study performed on rats was published in the journal Toxicology and Applied Pharmacology that was titled “Necrosis of Nasal and Airway Epithelium in Rats Inhaling Vapors of Artificial Butter Flavoring”. [St. Louis Post-Dispatch]

In the study, 19 rats were exposed to vapors from diacetyl for six hours with a concentration of 203 to 371 parts per million (ppm). This concentration is two to four times higher than the average level measured on any given work day inside a factory producing artificial butter flavorings but lower than concentrations that employees might be exposed to during various times of the work day. NIOSH veterinary pathologist Ann Hubbs commented on the study results after exaimining the tissue samples from the rats. She said they found “the most dramatic case of cell death I’ve ever seen” within the airways of the rats. [St. Louis Post-Dispatch]

Two U.S. unions—the United Food and Commercial Workers and the International Brotherhood of Teamsters—asked the OSHA on July 26, 2006 to enact emergency standards to temporarily protect workers from the dangerous effects of inhaling diacetyl vapors while at work.

The Food and Drug Administration (FDA) and the Environmental Protection Agency (EPA) are also involved in the investigation of diacetyl.

Currently, California government officials and legislators are introducing bills to remove diacetyl in the California workplace by 2010.

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