Breath of pollutants: How breathing patterns influence microplastic accumulation in the human lung

Humans are likely exposed to indoor and outdoor microplastics due to increased plastic degradation processes in the last decade. When inhaled, these microplastics could lead to inflammatory and respiratory disorders. Recent studies have advanced our understanding of microplastic transport in the respiratory system; however, they often overlook the various breathing patterns, effects of particle shape and specific accumulation patterns in the tracheobronchial airways. This study uniquely investigates how microplastics of various shapes accumulate under different breathing flow rates and frequencies, providing new insights into their behavior within these critical airways. The key findings show that microplastic deposition is minimal at a low flow rate of 7.5 LPM and a cycle frequency of 0.5 Hz but increases significantly when the frequency drops to 0.25 Hz, especially in the main bronchus. Higher inhalation flow rates, such as 40 LPM, lead to greater microplastic deposition in the early generations of the tracheobronchial airways, including generations 1–8, with notable differences between the inhalation and exhalation phases. Smaller flow rates result in higher microplastic deposition in distal airways beyond generation 8. The risk of microplastic inhalation is higher in the right bronchi, with larger particles (4–10 $\mu m$) depositing more in the main bronchi at lower flow rates and smaller particles (1–3 $\mu m$) in the initial airways at higher flow rates. The findings of this study, including case-specific microplastic deposition hotspots, will contribute to the up-to-date knowledge on pollutant exposure and relevant preventive measures.