“…Particles with a diameter of 20 nm are expected to be deposited in the alveoli to a particularly large extent. According to Rehn et al (2003), there are, however, no free ultrafine titanium dioxide particles present in commercial products (P25, untreated hydrophilic surface, and T805, silanized hydrophobic surface), but only agglomerates and aggregates, which are considerably larger than the primary particles and, in the opinion of Rehn et al (2003), could not be destroyed even by ultrasound in an aqueous phospholipid lecithin suspension. The authors conclude from this that the agglomerates and aggregates therefore do not disintegrate into primary particles in the alveoli.…”