Biokinetics of carbon black, multi-walled carbon nanotubes, cerium oxide, silica, and titanium dioxide nanoparticles after inhalation: a review.

Understanding the biokinetics of nanoparticles will support the identification of target organs for toxicological endpoints. We investigated the biokinetics of poorly soluble nanomaterials carbon black, multi-walled carbon nanotubes (MWCNT), cerium oxide (CeO2), titanium dioxide (TiO2), crystalline silica (SiO2) in inhalation studies in rodents (the soluble amorphous silica was also included). By reviewing research papers on the inhalation of these substances, we collected physico-chemical data and elemental distribution to organs, urine, and feces. Carbon black, MWCNT, cerium, and titanium accumulated during exposure and persisted in the lung post-exposure (still present at >3000 h). For silica, the amorphous form resulted in silicon accumulation in the lungs. Silicon was increased in the blood. Lymph node accumulation was observed for MWCNT, cerium, and titanium. Liver accumulation was observed for cerium and titanium. Cerium and silicon were increased in the spleen. Titanium accumulated and remained in the spleen (>4000 h). MWCNT were increased in several organs, some of which had a persistent presence of this material. In conclusion, we collected data on the biodistribution of five nanomaterials that, except for amorphous silica, are poorly soluble. The poorly soluble materials or their elements were persistent in the lungs but also showed persistence in other organs. In addition, the data on lung content supports Haber's rule, with titanium being deposited to a greater extent at exposure end than the other materials. Lung deposition seems relatively linear for the collected MMAD values, indicating size may be less important than previously suggested regarding alveolar deposition of the sub-2-micrometer size.