Transport and deposition of cigarette microplastics in human respiratory tracts

Recent research has raised significant concerns regarding microplastic (MP) exposure through cigarette smoking. This study investigates the inhalation dynamics and deposition patterns of four types of cigarette smoke MPs, ranging in diameter from 1 to 100 μm, during cigarette smoking. A computed tomography-based respiratory tract model extending from the nasal cavity to the 13th bronchial generation was implemented to ensure anatomical accuracy. To advance the understanding of MP behavior in the respiratory system, computational fluid–particle dynamics modeling was conducted. Specifically, the study utilized the finite volume method, integrating the k–ω shear–stress transport turbulence model and discrete phase model to accurately capture the complexities of airflow turbulence and particle dynamics. Three instantaneous puffing (breathing) profiles (fast, intermediate, and slow) were employed to simulate typical airflow variations encountered during smoking. Additionally, a novel modeling approach for nonspherical, elongated MPs was introduced, incorporating experimentally measured circularity and eccentricity. The results revealed insights into how particle shape, size, and puffing profiles influence transport and deposition within the respiratory tract during smoking. Through the analysis of the deposition patterns and risk contribution fraction of cigarette smoke MPs, this study significantly enhances the understanding of MP inhalation risks, providing valuable information for public  health interventions and regulatory frameworks.