Particle Size Distribution: Implications For Risk Characterization. D. Ager, T. Jarv, and R.Taylor, Ontario Power Technologies, Toronto, Ontario, Canada
The mass concentrations, size distributions and compositions of ambient particles at a rural, transboundary site in southern Ontario (Cheapside) were assessed. For a 24-h period (Aug. 6, 1998), PM10 concentrations ranged between 30-60 ug/m3 with an average daily value of 44 ug/m3. Particle characteristics for this ‘snap-shot in time’ were determined and the ICRP-66 Human Respiratory Tract Model was used to predict particle deposition patterns within the respiratory tract for 4 age/gender classifications. The results suggest that particle uptake, especially in the alveolar-interstitial region, may be substantially greater for males than for females. To examine the impact of different size distributions, lung dosimetry simulations were carried out using previously published data for two additional locations (Philadelphia, Phoenix). To provide a consistent measure for comparison, PM10 exposure levels were fixed at a level of 40 ug/m3. Total particle deposition was predicted to be greatest at the Cheapside location (1.3 mg/day). Lung burdens at Cheapside (Aug. 6, 1998) were 1.4-fold and 2.1-fold greater than values predicted for Phoenix and Philadelphia, respectively. Thus, despite the fact that simulations were performed using identical PM10 mass concentration exposure levels, estimated lung deposition patterns varied significantly from location to location. Because health impacts are expected to be linked to particle deposition patterns within the respiratory tract, this study highlights the difficulties associated with estimating human health impacts solely on the basis of a mass concentration exposure metric. It is crucial that health risk assessment methods incorporate important parameters such as particle size and composition.
Project funded by Ontario Power Generation, Fossil Business Unit Science Program.
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