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ANALYSIS OF RESPIRATORY DEPOSITION OF INHALED AMBIENT AEROSOLS FOR DIFFERENT DOSE METRICS
Citation:
Kim, C. S., S. C. Hu, AND P. Jaques. ANALYSIS OF RESPIRATORY DEPOSITION OF INHALED AMBIENT AEROSOLS FOR DIFFERENT DOSE METRICS. Presented at American Association for Aerosol Research Conference, Charlotte, NC, October 7-11, 2002.
Description:
ANALYSIS OF RESPIRATORY DEPOSITION OF INHALED AMBIENT AEROSOLS FOR DIFFERENT DOSE METRICS.
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 suggests 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, surface area and mass deposition.
Using the serial bolus delivery method, we measured total as well as 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 m in diameter. Using these data, respiratory deposition of a typical bi-modal ambient aerosol (MMD1 = 0.3 m, MMD2 = 5 m and GSD = 2.0 for each mode) was calculated for six different size fractions (eg, 0.04, 0.06, 0.1, 1, 3 and 5 m), and deposition dose per the unit surface area of airways was analyzed for the mass, number and surface area 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 m fractions are a dominant contributor for mass deposition. Mass contributions from ultrafine size fractions (< 0.1 m) were negligible. Number deposition was dominated by ultrafine size fractions. However, surface area deposition peaked at the size fraction of ~0.1 m, and both 0.04 and 5 m fractions were notable contributors. The finding was consistent for the tracheobronchial and alveolar region as well as the whole lung. However, deposition dose was several times greater in the trachebronchial than alveolar region regardless of particle size and dose metrics. In summary, for a typical bi-modal ambient aerosol lung deposition 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 should be examined along with particle size to find realistic dose-health effects relationships.
This is an abstract of a proposed presentation and does not necessarily reflect EPA policy.