Toxico-/biokinetics of nanomaterials

Nanomaterials (NM) offer great technological advantages but their risks to human health are still under discussion. For toxicological testing and evaluation, information on the toxicokinetics of NM is essential as it is different from that of most other xenobiotics. This review provides an overview on the toxicokinetics of NM available to date. The toxicokinetics of NM depends on particle size and shape, protein binding, agglomeration, hydrophobicity, surface charge and protein binding. In most studies with topical skin application, unintentional permeation and systemic availability were not observed; permeation for some NM with distinct properties was observed in animals. Upon inhalation, low levels of primary model nanoparticles became systemically available, but many real-world engineered NM aggregate in aerosols, do not disintegrate in the lung, and do not become systemically available. NM are prone to lymphatic transport, and many NM are taken up by the mononuclear phagocyte system (MPS) acting as a depot. Their half-life in blood depends on their uptake by MPS rather than their elimination from the body. NM reaching the GI tract are excreted with the feces, but of some NM low levels are absorbed and become systemically available. Some quantum dots were not observably excreted in urine nor in feces. Some model quantum dots, however, were efficiently excreted by the kidneys below, but not above 5-6 nm hydrodynamic diameter, while nanotubes 20-30 nm thick and 500-2,000 nm long were abundant in urine. NM are typically not metabolized. Some NM cross the blood-brain barrier favored by a negative surface charge.