Testing Metal-Oxide Nanomaterials for Human Safety

Nanomaterials can display distinct biological effects compared with bulk materials of the same chemical composition. The physico‐chemical characterization of nanomaterials and their interaction with biological media are essential for reliable studies and are reviewed here with a focus on widely used metal oxide and carbon nanomaterials. Available rat inhalation and cell culture studies compared to original results suggest that hazard potential is not determined by a single physico‐chemical property but instead depends on a combination of material properties. Reactive oxygen species generation, fiber shape, size, solubility and crystalline phase are known indicators of nanomaterials biological impact. According to these properties the summarized hazard potential decreases in the order multi‐walled carbon nanotubes >> CeO2, ZnO > TiO2 > functionalized SiO2 > SiO2, ZrO2, carbon black. Enhanced understanding of biophysical properties and cellular effects results in improved testing strategies and enables the selection and production of safe materials. The novel properties of engineered nanomaterials may alter their interaction with the human body, especially for inhalation of unintentionally released biopersistent material. We discuss the characterization of nanoparticles in interaction with biological media and we review animal inhalation and cell culture studies in comparison to original results. We establish that an intrinsic size‐specific toxicity does not exist and identify material‐specific indicators of concern that help to select safe uses.