Germany’s Federal Institute for Occupational Safety and Health (BAuA) has published a report entitled Comparison of Inhalation and Intratracheal Instillation as Testing Methods for Characterisation of Granular Biopersistent Particles (GBP).  In Project F 2364, researchers conducted an in vivo validation study to evaluate the consistency of data with results obtained in the preceding intratracheal instillation study in Project F 2336.  The abstract states that the same test items were used, and similar lung loads were achieved by calculating the target values after inhalation with the Multi-Path Particle Dosimetry (MPPD) model.  This approach served as proof of whether the instillation can be a reliable surrogate instead of the physiological inhalation route while assessing the GBP status of dust samples.  According to the conclusion in the abstract, considering the percentual polymorphonuclear neutrophil (PMN), as well as the absolute PMN concentrations, “the predominant observation is that inhalation induced a smaller PMN influx (with exception of biosoluble μ-BaSO4 and nano-SiO2) at similar doses.  This can be expected because of the physiological dust uptake and deposition by inhalation that is more gentle than intratracheal instillation (bolus effect!).”  The conclusion notes that effects detected after instillation will not always allow a “non inert” statement.  The final setting of maximum tolerable clearance t_1/2 and PMN levels to define the GBP category should include inhalation.  The conclusion states that “[d]oses at instillation testing of nanoparticles should not exceed volumetric values of 0.3 μl (using the correct agglomerate density).”