Biokinetics of inhaled silver, gold, copper oxide, and zinc oxide nanoparticles: a review

The understanding of nanomaterial toxicity is aided by biokinetic information pointing to potential target organs. Silver (Ag), copper oxide (CuO), and zinc oxide (ZnO) are often referred to as soluble materials in the literature. In addition, data suggest gold (Au) nanoparticles to be soluble in the mammalian body. We identified inhalation studies on these materials and extracted data on physicochemical properties, organ distribution, and excretion. Silver and gold were retained in the lung for an extended period (>2,000 and >672 hours, respectively); copper initially increased in lung and then returned to baseline at ∼500 hours. Zinc increased in the lungs after short-term exposure to zinc oxide, but not after prolonged exposure. In blood, silver initially increased after inhalation but then gradually declined over ∼200 hours. Gold was elevated in the blood after exposure to 4, 7, 11, and 13 nm particles (but not particles of 20, 34, and 105 nm) and remained elevated for at least 672 hours after exposure to the 4 and 11 nm particles. Silver increased in the liver and spleen and was still present 2,000 hours post exposure. Gold was elevated in several organs, including the spleen and kidney, for more than 600 hours post exposure, indicating persistence in some organs. Both silver and gold were increased in the brain and olfactory bulb. Overall, we found no large differences in the biodistribution of the four nanomaterials but note that silver and gold were still increased in several organs at the last investigated post-exposure time points.