In Silico Inhalation Exposure Analysis of Indoor Microplastics/Microfibers Using Two-Year-Old Child Respiratory Tract Model

Children are vulnerable to exposure to airborne microplastics (MPs) because of their developing lungs and prolonged time spent indoors. Therefore, this study employed a computational fluid–particle dynamics framework to simulate the posture-dependent transport and deposition of MPs in a realistic airway model of a 2-year-old child extending to the 8th bronchial generation. A steady inhalation breathing flow rate of 5 L/min was used for both postures. Subsequently, a discrete-phase model was used to predict the transportation and deposition of MPs, which employed an appropriate drag coefficient model. MP configurations were selected from the field survey, identifying the diameters of 4.785, 9.797, and 15.731 µm with aspect ratios of 3, 5, and 10. The results showed that posture significantly altered the deposition patterns of small- and low-aspect-ratio MPs. Specifically, the total deposition fraction was higher in the upright position than in the supine position. Local deposition analyses revealed that hotspots of deposited MPs varied across the airways under the effects of posture, especially in the upper respiratory tract. These findings provide mechanistic insights into how posture shapes regional fiber deposition in children and highlight the need to consider body orientation in pediatric inhalation exposure assessments.