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Which particles penetrate the respiratory system?
In professional environment, the principal route of entry for nanoparticles in the organism is the inhalation. Particles are inhalable or not depending on their size. When they are inhaled, they can either be exhaled or deposited in different regions of the respiratory track. There are three zones of deposit in the respiratory system: extra thoracic, or upper alveolar (nose, mouth, pharynx, and larynx), tracheo-bronchial (trachea, bronchi), and alveolar (alveoli). The percentage of exhaled particles and the deposit location in the respiratory system vary considerably as a function of the particle size and the aggregation or agglomeration level.
[M. Ricaud et al., INRS ED 6050 (2012)].
Particles greater than 100 microns do not enter the respiratory tract (non-inhalable particles). Particles, with a diameter of more than 10 nm up to 100 nm, deposit mostly in the pulmonary alveoli with a higher proportion than micrometric particles. Those of 10 microns reach the tracheo-bronchial tree, and smaller particles can reach deep into the lung or alveolar area.