Particulate distribution of TiO
particles by size through different regions of the respiratory tract. This diagram was derived from an explanation of particulate distribution after inhalation given by Simko and Mattsson . Arrows represent downward movement of particles through the respiratory tract. Most particles in the size range of 1–5 nm are distributed throughout the three regions. 1 nm and 20 nm particles are mostly distributed in the nasopharyngeal region and alveolar regions respectively. 0.5-10 μm particles remain on the epithelial surface of the airways and alveoli.