Relationship between Aerosols Exposure and Lung Deposition Dose

We systematically evaluated the relationship between exposure to aerosols-specifically, ultrafine airborne particles-and the effective dose in the lungs of humans and animals. By multiplying particle concentration size distributions with lung deposition curves generated by the Multiple-Path Particle Dosimetry (MPPD) model, the lung deposition concentrations, which can 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 extracted from measurement data in the literature. In addition to determining the lung deposited particle concentration, we investigated its possible relationship with the diameter of the main mode for the size distribution. We also examined the potential use of animal surrogates for human beings in inhalation exposure studies. The average concentration of the deep-lung deposited fraction (the sum of the alveolar and trachea-bronchial deposited concentrations divided by the ambient concentration) depended on the size distribution of the inhaled aerosol and the specific metric (particle number, surface area or mass), being slightly higher when the particle number instead of the surface area or mass was measured. It was also affected by the diameter of the aerosol size distribution's main mode: the smaller the diameter, the larger the lung deposited particle fraction. Our study aims at a better understanding of the correlations between the particle parameters measured in exposure studies and dose metrics in the lung, thereby facilitating an accurate risk assessment of ultrafine ambient particles.