Synergistic Health Risk Assessment of Aircraft Lubricating Oil Aerosols: Respiratory Deposition Simulation and Cytotoxicity Experiments

Aircraft cabin air quality has emerged as a critical public health concern due to potential contamination from engine lubricating oil through bleed air systems. Despite extensive research on individual pollutants, a comprehensive risk assessment of lubricating oil aerosol mixtures remains limited. This study integrated in vitro cytotoxicity experiments with respiratory deposition modeling to assess health risks of aviation lubricating oil aerosols. Human lung epithelial cells (A549) were exposed to lubricating oil and major components to establish dose–response relationships and elucidate toxicity mechanisms through cell viability, reactive oxygen species (ROS) detection, inflammatory responses, and apoptosis. The multiple-particle-dosimetry (MPPD) model was employed to simulate aerosol deposition patterns across different respiratory regions under three different exposure scenarios. In vitro experiments revealed distinct cytotoxicity profiles among lubricating oil components, with tricresyl phosphate (TCP) showing the strongest toxicity (lowest observed effective concentration, LOEC = 20 μM), followed by N-phenyl-1-naphthylamine (PAN) (80 μM) and tributyl phosphate (TBP) (100 μM), while base stock demonstrated excellent biostability. Actual aviation lubricating oil exhibited a cytotoxicity threshold at 300 μM. MPPD simulations revealed time-dependent deposition patterns: short-term exposure favored tracheobronchial retention, while long-term exposure resulted in preferential alveolar accumulation. Risk assessment using hazard quotients (HQs) showed all exposure scenarios yielded values well below 1.0. Without adjustment of uncertainty factors, the highest HQ was 8.7 × 10–4; even with the uncertainty factors of 300, the highest HQadj reached only 2.6 × 10–1 under 25-year high-end exposure conditions, indicative of acceptable health risks. This combined study provides quantitative evidence that aircraft cabin environments complying with the WHO 24 h and annual air quality guideline values present manageable health risks.