In a study published in the August 1 issue of the New England Journal of Medicine, a team of researchers from the National Institute for Occupational Safety and Health (NIOSH) led by Kathleen Kreiss, M.D., medically evaluated 117 current employees at the Glister-Mary Lee microwave popcorn plant in Jasper, Mo. Back in May 2000, eight former employees at the facility were diagnosed with bronchiolitis obliterans, a severe, chronic lung disease. At that time, no recognized cause was identified in the plant, although a team of NIOSH researchers reported earlier this year they suspected diacetyl, a ketone used in the butter flavoring, might be the culprit.
Kreiss and her team evaluated the relationship between exposures to diacetyl and health-related symptoms. Overall, the workers had 3.3 times the expected rate of airway obstruction. Those workers who had never smoked had 10.8 times the expected rate.
Unsurprisingly, workers directly involved in the production of microwave popcorn had higher rates of shortness of breath on exertion and skin problems that developed since they started work than workers in other parts of the plant. There was a strong relationship between the estimated cumulative exposure to diacetyl and the frequency and extent of airway obstruction.
Kreiss et al reported that in laboratory studies, levels of diacetyl at 352 parts per million (ppm) damaged the cells in the respiratory tract of rats. They noted that some workers at the Glister-Mary Lee plant were exposed to levels as much as three and four times higher than 352 ppm.
"The excess rates of lung disease and lung-function abnormalities and the relation between exposure and outcomes in this working population indicate that they probably had occupational bronchiolitis obliterans caused by the inhalation of volatile butter-flavoring ingredients," concluded the research team, who were from NIOSH's Division of Respiratory Disease Studies in Morgantown, W.Va., and the Office of Epidemiology, Missouri Department of Health and Senior Services, Jefferson City.
An editorial in the New England Journal of Medicine that accompanied the article noted, "Bronchiolitis obliterans results in irreversible obstruction of the small airways and has known environmental and occupational causes… This study provides convincing evidence that occupational exposure to a substance in microwave popcorn, presumably diacetyl, can lead to severe and irreversible airway obstruction."
For further information about the cases of bronchiolitis obliterans turning up at popcorn factories, see "Popcorn Packer's Lung found in Iowa" and "NIOSH: Emergence of Possible New Occupational Disease."