Bronchial dose

Both the Weibel A and Yeh-Schum models need to be reduced in scale to represent adult human lung at a normal level of inflation corresponding to 3000 ml functional residual capacity (FRC) (Yu and Diu, 1982). Partial scaling has been included in some dosimetric models (NEA, 1983 James, 1984) but not in others. In all cases the airway sizes used to represent adult lung correspond to a higher level of inflation than the standard FRC, leading to general but relatively small underestimates of bronchial dose. 

Table II lists values of mean bronchial dose obtained by weighting equally the results from all three lung models and clearance assumptions. I propose these as reference values.

Table II. Reference Values of Mean Bronchial Dose from Exposure to 1 WLM Potential Alpha-energy in Homes...

Effective dose equivalent. If it is assumed that the weighting factor for bronchial dose equivalent is 0.06, the unattached fraction of potential alpha-energy in room air is typically about 570, and that the aerosol AMD is typically 0.12 pm (Reineking et al., 1985), the... 

Figure 11. Variation of unattached fraction of potential alpha-energy and equilibrium factor according to a model of room aerosol behaviour and the effect on bronchial dose rate per unit radon gas concentration.

It is important to update the bronchial dosimetry for radon daughters as new information becomes available. It is the purpose of this study to show that there is a potential for either significantly increased bronchial dose in the home per unit exposure if the ambient particle size is artificially reduced due, for example, to open-flame burning or use of kerosene heaters, or a decreased dose if hygroscopic particles dominate the indoor aerosol. 

Table II shows the nominal alpha dose factors for occupational mining exposure. Table III shows the alpha dose factors for the nominal environmental situation. Table IV shows the bronchial dose factors for the smallest sized particles, that dominated by the kerosene heater or 0.03 pm. particles. The radon daughter equilibrium was shifted to a somewhat higher value in this calculation because this source of particles generally elevates the particle concentration markedly with consequent increase in the daughter equilibrium. Table V shows the alpha dose for a 0.12 pm particle, the same as the nominal indoor aerosol particle, but for a particle which is assumed to be hygroscopic and grows by a factor of 4, to 0.5 pm, once in the bronchial tree.

Figure 2. Mean bronchial dose to basal cells, standardized for 1 WLM exposure to free radon 222 daughter atoms for different physical activities (assuming typical indoor exposure with equilibrium factor F = 0.4) ...

Fig. 1.15. Dose rate to alveolar (A) and bronchial (B) regions of lungs by inhalation of radon daughters (James, 1987b). Range of values for bronchial dose reflects uncertainties in breathing pattern, airway size and clearance rates.

The conversion factor for the bronchial dose from both unattached and attached decay products is... 

Since the number of nuclei is usually less in dwellings than in uranium mines, the bronchial dose, per Bq m-3 of 222Rn, is greater in the domestic than in the industrial situation. 

Jacobi Paretzke (1985) estimated that the uranium miners in Colorado accumulated an average exposure of 820 WLM in the years 1950-77. Using the factor 16 mSv per WLM, the average bronchial dose would have been 13 Sv, giving a 20% chance of cancer on the basis of the ICRP (1981) estimate. The BEIR IV report of the US National Research Council (1988) recorded 256 deaths from lung cancer among the Colorado miners. The total exposure was 73 600 person-years, and 58 deaths would have been expected if there were no carcinogenic effects. 

Ihe dosimetric consequence of particle size determination is tiiat a realistic bronchial dose may be calculated (13). In tiiis case, essentially the same dose conversion factor applies at both Femald and at the residential home in New Jersey because the median diameter is identical. UNSCEAR 2000 (14) gives the... 

Harley, N. H. Cohen, B. S. Robbins E. S. The Variability in Radon Decay Product Bronchial Dose. Environ. Int. 1996,22, S959-964. 

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