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The fate of airborne microfibers in the human respiratory tract in different microenvironments
M Triantafyllaki1, E Chalvatzaki1, A Torres-Agullo2
1School of Chemical and Environmental Engineering, Technical University of Crete, Chania, Greece.
Abstract:
Αirborne microplastics (MPs) are considered an important exposure hazard to humans, especially in the indoor environment. Deposition and clearance of MPs in the human respiratory tract (HRT) was investigated using the ExDoM2 dosimetry model, modified to incorporate the deposition and clearance of MPs fibers. Fiber deposition was calculated via the fiber equivalent aerodynamic diameter determined using their properties such as size, density and dynamic shape factor. Scenario simulations were performed for elongated particles of cylindrical (base) diameters 1 μm and 10 μm and aspect ratios (ratio of fiber length to base diameter) 3, 10 and 100. Modelling results showed that the highest fiber deposition occurred in the extra-thoracic region due to large particles (fiber cylindrical diameter dp > 0.1 μm), whereas particle length (via the aspect ratio) had an influence mainly on smaller base-diameter fibers (dp < 0.1 μm) that deposited predominantly in the alveolar region. The ExDoM2 dosimetry model was also used to calculate fiber deposition in the HRT using experimental data for microplastic fiber and fragment concentrations in different microenvironments. The highest deposited number dose (220 fibers) after a 24-hour exposure was calculated in the microenvironment (bus) that had the highest fiber concentration (17.3 ± 2.4 fibers/m3). After clearance, the majority (66.4 %) of the average deposited fiber mass was transferred from the respiratory tract to the esophagus via mucociliary clearance, 32.6 % was retained in the respiratory tract, 1 % passed into the blood, and a very small amount (0.0004 %) was transferred to the lymph nodes.
Insights
Airborne microplastics (MPs) pose an indoor exposure risk. A dosimetry model simulated MP fiber deposition and clearance in the human respiratory tract (HRT), revealing significant deposition in the extra-thoracic region for larger fibers.
Area of Science:
- Environmental Science
- Toxicology
- Respiratory Medicine
Background:
- Airborne microplastics (MPs) are an emerging human exposure concern, particularly indoors.
- The respiratory tract (HRT) is a primary route for MP inhalation and deposition.
- Understanding MP fiber behavior within the HRT is crucial for assessing health risks.
Purpose of the Study:
- To investigate the deposition and clearance of microplastic (MP) fibers in the human respiratory tract (HRT).
- To utilize the ExDoM2 dosimetry model, adapted for MP fiber characteristics.
- To simulate fiber deposition across various particle sizes and aspect ratios.
Main Methods:
- Modified the ExDoM2 dosimetry model to include MP fiber deposition and clearance.
- Calculated fiber deposition using equivalent aerodynamic diameter based on size, density, and shape factor.
- Performed scenario simulations for fibers with varying base diameters (1-10 μm) and aspect ratios (3-100).
- Applied the model to experimental data of MP fiber concentrations in diverse microenvironments.
Main Results:
- Highest fiber deposition occurred in the extra-thoracic region for larger particles (diameter > 0.1 μm).
- Particle length (aspect ratio) significantly influenced deposition of smaller fibers (diameter < 0.1 μm), primarily in the alveolar region.
- The highest deposited dose (220 fibers) was observed after 24-hour exposure in a bus environment with high MP fiber concentration (17.3 fibers/m³).
- Post-clearance, 66.4% of deposited fiber mass transferred to the esophagus, 32.6% was retained in the HRT, 1% entered the bloodstream, and 0.0004% reached lymph nodes.
Conclusions:
- The ExDoM2 model effectively simulates MP fiber deposition and clearance in the HRT.
- Particle size and shape significantly dictate MP fiber deposition location and retention within the respiratory system.
- Mucociliary clearance is the primary pathway for removing deposited MP fibers, with a substantial portion being swallowed.
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