Nanoparticles of polytetrafluoroethylene (PTFE), used for the generation of respiratory nanoparticles, were first found to be highly toxic to birds and mammals (Oberdörster et al. 1995), but this was attributed to a different mechanism. The nanoparticles, generated by heating PTFE, were found to be highly toxic to rats (Oberdörster et al. 1995), as previously observed for PTFE fumes (Auclair et al. 1983; Goldstein et al. 1987; Lee et al. 1997; Woo et al. 2001). At the time, this was attributed to the release of toxic gases, such as carbon tetrachloride (Oberdörster et al. 1995), and the inhalation of the nanoparticles was not considered toxic. This was confirmed in a subsequent study by Pabst et al. (2002), who observed that the inhalation of dispersions of PTFE nanoparticles was not toxic to rats. However, it was observed that, after repeated inhalation of these dispersions, the particles were gradually removed from the lungs, and the animals recovered from the acute toxic effects (Pabst et al. 2002). This was attributed to the accumulation of the nanoparticles in the alveoli, but the mechanisms involved were not investigated. It is possible that the nanosized particles were removed from the lungs by the mucociliary clearance mechanism, which is driven by the cilia of the lung, or that they were oxidized and degraded in the lung.
In the examples discussed here, the particle size is about one order of magnitude too small to be readily aerosolized by human breath or by an air cleaner used in the laboratory (such as those used in the studies by Oberdörster et al. 1995 and Johnston et al. 2000).
The AutoCAD Software Ultimate 2017 is a highly advanced and customizable version of AutoCAD that will make your life easier by providing you with a range of new and improved features. The AutoCAD Software Ultimate 2017 is the perfect solution for building complex drawings, navigating BIM and M&A data efficiently and collaborating easily with other users.
But as AutoCAD has matured from a simple 2D drawing and modeling tool into a full blown 3D visualization and design package, it has also become enormously complex, and for many users, it has become an absolute nightmare to learn and use. 827ec27edc