This is a copy of the slides presented at the meeting but not formally written up for the volume.

The unique and diverse physico-chemical properties of nanoscale materials suggest that their toxicological properties may differ from materials of similar composition but larger size. Studies suggest that particle size, surface area and surface chemistry of engineered nanoscale materials can impact toxicity equally, if not more so, than chemical composition. The National Toxicology Program (NTP) (ntp.niehs.nih.gov) is a multi agency program headquartered at the NIEHS that coordinates toxicology research and testing programs within the federal government and conducts research to provide information about potentially toxic chemicals to health, regulatory, and research agencies, scientific and medical communities, and the public. The NTP is currently engaged in a research program that is evaluating the toxicological properties of current major nanoscale materials classes. These materials represent a cross-section of composition, size, surface coatings, and physico-chemical properties. The studies are designed to investigate fundamental questions concerning how nanoscale materials are absorbed and distributed in vivo and whether they can adversely impact biological systems. Some of these fundamental questions include: What are the appropriate methods for detection and quantification of nanoscale particles in tissues? How are nanoscale materials absorbed, distributed in the body and taken up by cells? Are there novel toxicological interactions? The NTP's nanotechnology safety initiative (http://ntp.niehs.nih.gov/go/nanotech) is focusing research with respect to specific types or groups of nanoscale materials: Non-medical, commercially relevant/available nanoscale materials to which humans are intentionally being exposed, e.g., cosmetics and sunscreens; Nanoscale materials representing specific classes (e.g., fullerenes and metal oxides) so that information can be extrapolated to other members of those classes; Subsets of nanomaterials to test specific hypotheses about a key physiochemical parameter (e.g., size, composition, shape, or surface chemistry) that might be related to biological activity. Ongoing research activities are addressing (1) the fate and distribution of nanoscale metal oxides and quantum dots in the body following their dermal application to rodents with attention given to the role of surface coating, size, polarity, vehicle, and skin condition on the ability of nanoscale TiO2 to penetrate the skin; (2) whether nanoscale TiO2 and ZnO applied dermally to mice in combination with UVA-containing light affects cell signaling, and (3) the potential for TiO2 applied dermally to haired and hairless mice in combination with UV-containing light to cause skin cancer.