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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.
Depending on the particle size, the location and the percentage of deposit of the particles vary during an inspiration/expiration cycle.
The very small particles (1 nm) do not settle in the alveolar area but are stopped in the upper airways. The alveolar fraction deposited is the most important at around 20 nm.
The deposit location determines the future of nanoparticles in the organism.