Compound in Microwave Popcorn May Cause Severe Lung Damage

Bethesda, MD -- Daniel Morgan and his colleagues are reporting that a chemical called diacetyl, which is commonly used as an artificial butter flavoring (especially in microwave popcorn), is harmful to the lungs and airways of laboratory mice, and may also be the causative agent of a serious lung disease called obliterative bronchiolitis (OB). The study was done at and reported by the National Institute of Environmental Health Sciences, which is part of the National Institutes of Health, and in collaboration with Duke University. It has also been published online in the journal Toxicological Sciences.

Diacetyl, a component of artificial butter flavoring, has been postulated as a potential etiologic agent of obliterative bronchiolitis (OB), a rare but serious lung disease. OB is characterized by fixed airway obstruction as well as inflammation and scarring. Severe shortness of breath and dry cough result due a reduction of lung capacity to 16-21% of lung usage (normal lung usage is 80%). In severe cases of OB, lung transplantation is the only viable treatment.

A higher than normal incidence of OB had been reported in microwave popcorn packaging plant workers, leading to the NIH/Duke study.

Daniel and his colleagues evaluated the respiratory toxicity of diacetyl by having mice inhale diacetyl fumes at several concentrations and lengths of time. Exposure to diacetyl at 200 or 400 parts per million (ppm) over 5 days resulted in death, massive destruction of nasal passages and the larynx, and bronchitis. At lower diacetyl concentrations (100, 200, and 400 ppm) mice exposed for 1 hour per day for 4 weeks straight showed less lung damage and no mortality, but had bronchial tissue breakdown and inflammation. Even at a concentration of 100 ppm for 6 hours per day for 12 weeks straight, mice showed lung damage accompanied by inflammation.

The symptoms evidenced in mice exposed to diacetyl mimic early stages of human OB. All the diacetyl concentrations tested were the same as those to which microwave popcorn plant workers would be exposed during the course of a normal working day.