A proposal for a safe exposure level for diacetyl.

Diacetyl is a naturally occurring compound that has been used in concentrated form as a food additive, particularly in butter flavorings. Inhalation of diacetyl and butter flavoring fumes has caused a variety of respiratory diseases in workers and consumers including bronchiolitis obliterans (BO), a relatively rare, severe, and irreversible lung disease. A safe level of exposure to diacetyl has not been established. We review the literature on diacetyl and flavoring toxicity and critique a recent proposal for an occupational exposure limit (OEL) of 0.2 ppm for diacetyl. We present unpublished data and novel analyses in support of our proposal for a safe level of exposure. Our findings indicate that a safe level of exposure exists around or below a time-weighted average of 1 ppb for an eight-hour workday. The levels of exposure we found to be unsafe include ranges that popcorn consumers may potentially be exposed to, indicating a risk of severe lung disease (including BO) for some consumers.