Deposition and clearance of airborne microplastics in the human respiratory tract.

Αirborne microplastics (MPs) comprise an important exposure pathway to humans and an emerging health hazard. Published MP concentrations and size distributions were applied to a dosimetry model to determine their deposition and clearance in the human respiratory tract (HRT). Inhaled MPs deposited primarily in the extra-thoracic region with smaller MPs accumulated in the tracheobronchial and alveolar regions. The retained mass after exposure of one day was estimated to range from 5.2×10-4 to 9.48 μg based on different exposure concentrations. Moreover, after one day, approximately 60 % of the deposited MP mass was transferred from the respiratory tract to the esophagus, 28 % was retained in the respiratory tract, 0.4 % passed into the blood, and a very small amount was transferred to the lymph nodes. Evaluating the long-term response of the dose accumulated in the HRT was governed by a steady-state condition where the accumulated dose reached a fixed value. Constant exposure conditions drove this observation yet in real world MP exposure is not constant and varies across environments and individuals. Analysis of different environments showed that higher dose is received indoors due to the higher measured MP concentrations. Further research is needed to unravel the impact of varying exposure conditions and inclusion of targeted MPs clearance kinetics to improve human body response to MP intake.