Exposure-Dose Analysis of Various Bimodal Ambient Aerosols in Adult Subjects

Chong Kim (1), Jung-il Choi (2)

(1) U.S. EPA NHEERL, Research Triangle Park, (2) North Carolina State University, Raleigh

     Abstract Number: 758
     Last modified: May 14, 2010

Abstract
Internal dose is a key factor for determining the health risk of inhaled pollutant particles. However, size distribution of ambient aerosols is complex, often with multi-modal peaks in different size ranges. Lung dose analysis of such a complex aerosol is a difficult task. Because ambient aerosols are typically represented by bimodal distribution with peaks in the fine and coarse size ranges, we have attempted to analyze lung deposition of such bimodal aerosols with varying mass ratios between the two distributions: mass median diameter of 0.3 um and 5.0 um with GSD of 1.5-2.0. Mass ratios were varied with an increment of 0.2, thus covering a wide range of distribution pattern. Realistic breathing patterns were used mimicking resting and mild to moderate exercise conditions. During moderate exercise, oronasal breathing was considered for those with compulsory mouth breathers. As the mass size distribution changes, the number and surface area changes drastically. Thus, lung deposition was assessed for mass, surface area and number of particles and relationships between the three dose metrics were analyzed with respect to size distributions using a dynamic transport mathematical model. Results show that polydispersity of size distribution affects lung deposition variably in the different size ranges: there is no consistent trend for different size fractions. For 50:50 mass ratio between the two modes, mass and surface area dose was contributed mainly by coarse and fine particles, respectively, whereas ultrafine particles (diameter <0.1 um) were the major contributor to number dose. In conclusion, different size fractions in the bimodal distribution aerosols can become major contributors of lung dose of different metrics. Because chemical composition may be different for different size fractions, dose metric and chemical composition may have a compounding role in potential health risk of inhaled aerosols.