Relationship between Aerosols Exposure and Lung Deposition Dose

We conducted a systematic study to evaluate the relationship of exposure to aerosols with specific focus on airborne ultrafine particles and the effective dose in the lungs of humans or animals. By multiplying particle concentration size distributions with lung deposition curves of the Multiple-Path Particle Dosimetry (MPPD) model, the lung deposition concentrations, which could be directly linked to the effective dose via inhalation rate and exposure time, were estimated. The calculations were performed on a number of representative particle size distributions ex-tracted from measurement data in the literature. Apart from the evaluation of the lung depos-ited particle concentration, we investigated whether and how the lung deposited particle con-centration depended on the diameter of the main mode of the considered size distribution and if there was a potential animal surrogate for human beings in inhalation exposure studies. The average deep-lung deposited fraction (sum of alveolar and trachea-bronchial deposited concentrations divided by the ambient concentration) depended on the inhaled aerosol size distribution and the considered metric (number, surface area or mass). It was slightly higher in terms of number than for surface area and mass. Moreover, the lung deposited particle frac-tion depended also on the diameter of the main mode of the inhaled aerosol size distribution: the smaller the diameter of the main mode, the higher the lung deposited particle fraction. Our study aims at a better understanding of the correlations between the particle parameters meas-ured in exposure studies and the dose metrics in the lung, which in turn facilitates the risk as-sessment of ambient ultrafine particles.