[Effects of nanoparticles on humans].

Methods and end-points used in assessing the hazards of fibrous materials, whose hazards have been assessed, are often employed in studies on the hazards of nanoparticles. Since a possible route of exposure to nanoparticles in work environments is inhalation, data from animal inhalation and intratracheal instillation studies are thought to provide useful insights for assessing the hazards of such particles. Persistent inflammation and fibrosis in the chronic phase and their related factors are particularly important indicators of lung injury. On the other hand, there are some differences in the results of hazard assessment studies due mainly to a lack of detailed physiochemical characterizations of the nanoparticles evaluated. Dispersion properties in the chambers just before exposure in inhalation studies and those in the suspension to be injected in intratracheal instillation studies need to be determined. The number of hazard assessment studies in which characterization of nanoparticles is conducted, while small at present, is increasing and this could consequently yield reliable hazard assessment and risk assessment.