Macroscopic to microscopic scales of particle dosimetry: from source to fate in the body

Additional perspective with regards to particle dosimetry is achieved by exploring dosimetry across a range of scales from macroscopic to microscopic in scope. Typically, one thinks of dosimetry as what happens when a particle is inhaled, where it is deposited, and how it is cleared from the body. However, this paper shows a much more complicated picture starting with emissions sources, showing how the source-to-intake fraction (iF) can be used to estimate changes in the inhaled dose due to changes in emissions and then ending with particle-liquid, particle-cellular and subcellular interactions, and movement of ultrafine particles across the lung-blood barrier. These latter issues begin to suggest mechanisms that can lead to adverse health effects; the former can provide guidance to policy decisions designed to reduce the health impact of atmospheric particles. The importance of ultrafine particles, their ability to translocate to other parts of the body, and the potential impact of these particles has advanced significantly over the last decade, including studies that show the movement of ultrafine particles along the olfactory nerves in the nose with direct transport to the brain, the neurological effects of which are still unknown. Incremental advancements continue with regards to understanding particle deposition, including regional and local deposition (including hot spots) and clearance and the factors that affect these variables, in part due to the development and implementation of computational fluid dynamics (CFD) models and digital imaging of the lungs. CFD modeling will continue to provide new information for reducing uncertainty in dosimetric calculations. We understand better today how a number of diseases may develop based on the fate of particles after deposition in the respiratory track and how changes in source emissions might impact that dose. However, a number of uncertainties remain, some of which can be reduced by addressing the research needs stated in this paper.