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ANALYSIS OF RESPIRATORY DESPOSITION DOSE OF INHALED AMBIENT AEROSOLS FOR DIFFERENT SIZE FRACTIONS
Citation:
Kim, C. S., S. C. Hu, AND P. Jaques. ANALYSIS OF RESPIRATORY DESPOSITION DOSE OF INHALED AMBIENT AEROSOLS FOR DIFFERENT SIZE FRACTIONS. Presented at Society for Risk Analysis, New Orleans, LA, December 8-11, 2002.
Description:
ANALYSIS OF RESPIRATORY DEPOSITION DOSE OF INHALED AMBIENT AEROSOLS FOR DIFFERENT SIZE FRACTIONS. Chong S. Kim, SC. Hu**, PA Jaques*, US EPA, National Health and Environmental Effects Research Laboratory, Research Triangle Park, NC 27711; **IIT Research Institute, Chicago, IL; *Southern California Particle Center, UCLA, Los Angeles, CA.
Although many epidemiological studies have shown a consistent correlation between observed health effects and mass concentration of airborne particulate matter (PM), some evidence suggest that particle number or surface area may also play an important role in PM associated health effects. However, specific quantitative data are lacking for respiratory dose of heterogeneous ambient aerosols and the relationship between different size fractions vs. their relative contributions to the number (N), surface area (SA) and mass (M) deposition. Using a serial targeted delivery method, we measured total and detailed regional deposition values in healthy young adults (n=10, age = 18-40 years) for a series of monodisperse aerosols in the size range of 0.04 -5 micron in diameter. Using these data, respiratory deposition of a typical bi-modal ambient aerosol (MMD1 = 0.3 micron, MMD2 = 5 micron and GSD = 2.0 for each mode) was calculated for different size fractions (eg, 0.04, 0.06, 0.1, 1, 3 and 5 micron), and deposition dose per the unit surface area of airways was analyzed for M, N and SA of particles in different lung regions. At a tidal volume of 500 ml and breathing frequency of 15 breaths/min the results show that 3 and 5 micron fractions are a dominant contributor for mass deposition. Mass contributions from ultrafine size fractions (< 0.1 micron) were negligible. Number deposition was dominated by ultrafine size fractions. However, surface area deposition peaked at the size fraction of ~0.1 micron, and both 0.04 and 5 micron fractions were notable contributors. The finding was consistent for the tracheobronchial (TB) and alveolar (AL) region as well as the whole lung. However, deposition dose was several time greater in TB than AL regardless of particle size and dose metrics. In summary, for a typical bi-modal ambient aerosol lung deposition dose is dominated by coarse particles for mass and by ultrafine particles for number, but all sizes are important for surface area. The results suggest that from the physical dose metric point of view the particle size itself may have an ambiguous role on causal mechanisms of PM-associated health effects. Chemical compositions and other particle properties may be examined along with particle size to obtain realistic dose-response relationship.
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