Numerical Analysis of Inhalation Exposure to Indoor Microplastics/Microfibers in a Realistic Human Respiratory Tract Down to 16th Terminal Bronchioles

ABSTRACT

Indoor airborne microplastics, especially in fibrous form, pose significant respiratory health risks due to their widespread distribution and persistence. This study employed computational fluid–particle dynamics (CFPD) simulations to investigate the inhalation, transport, rotation, and deposition behaviors of fibrous microplastics in the human respiratory tract. Because full DEM simulations in realistic airways are computationally demanding, DEM was first applied in a simplified geometry to assess drag and torque closures for nonspherical particles, thereby supporting the accurate and efficient application of the DPM framework in the realistic airway model. This verification confirmed that the Tran‐Cong (TC) and Ganser (GS) drag laws accurately predict fiber motion. Subsequently, a comprehensive airway model, extending from the nostrils to the 16th bronchial bifurcation, was developed to quantify deposition patterns of fibrous microplastics with three diameters (4.785, 9.797, 15.731 μm) × three aspect ratios (AR = 3, 5, 10), yielding nine distinct size groups. The results revealed size‐dependent deposition behaviors, with fibers having an aerodynamic equivalent diameter larger than 20 μm predominantly depositing in the upper respiratory regions owing to inertial impaction, whereas smaller fibers (10–20 μm) penetrated deeper, notably accumulating around the 5th–7th bronchial generations, especially within the right lower lung lobe.