Risk assessment of inhaled diacetyl from electronic cigarette use among teens and adults

Highlights: • Diacetyl as a flavoring compound in e-Cigarettes causes bronchiolitis obliterans. • USEPA/NRC risk framework allowed for exposure and risk characterization. • All Hazard Quotient (HQ) values estimated were greater than 1. • Higher HQ values suggest a higher non-cancer risk from diacetyl in e-Cigarettes. • Our results highlight a need to regulate e-Cigarette use among teens and adults. Diacetyl (C₄H₆O₂) is a toxicant commonly found in electronic cigarettes (e-Cigs) as a flavoring component and an enhancer of e-juices. Lung injury in current and former workers in popcorn manufacturing suggests a possible association with diacetyl inhalation exposure. Although the number of e-Cig users continues to rise steadily among the teens and adults, the potential risk of pulmonary disease has not been characterized. A systematic review of the open literature identified bronchiolitis obliterans—a pathological inflammation resulting in fibrosis of the bronchioles leading to an irreversible limitation to airflow in lungs—as the primary outcome of diacetyl exposures. Following the deterministic United States National Research Council/Environmental Protection Agency's risk assessment framework, that consists of four key steps: hazard identification, dose-response assessment, exposure assessment and risk characterization, we estimated noncarcinogenic (systemic) risks using a Hazard Quotient (HQ) approach upon exposure to diacetyl among teens and adults who use e-Cigs. Based on the NIOSH Benchmark Dose (BMD; 0.0175 mg/kg-day) and modelled Average Daily Doses (ADDs; range 0.11–5.2 mg/kg-day), we estimated 12 different HQ values—a measure of non-carcinogenic risk for diacetyl inhalation exposures—all of which were greater than 1 (range 6.2875–297.1429), suggesting a significantly higher non-carcinogenic risk from diacetyl exposures among the teens and adults who use e-Cigs. These results underscore the need to regulate e-Cigs to protect teens and adults from diacetyl exposures and risk of developing lung injuries, including bronchiolitis obliterans.