Comparative Dosimetry of Radon in Mines and Homes (1991) / Chapter Skim
Currently Skimming:
Extrapolation of Doses and Risk per Unit Exposure from Mines to Homes
Extrapolation of Doses and Risk per Unit Exposure from Mines to Homes
Pages 31-51
The Chapter Skim interface presents what we've algorithmically identified as the most significant single chunk of text within every page in the chapter.
Select key terms on the right to highlight them within pages of the chapter.
From page 31... ...
More specifically, the aim is to compare values of the exposure-dose conversion coefficient that apply to subjects exposed in the home with those applicable to underground miners, for the purpose of extrapolating to 31
|
From page 32... ...
m (3-2) The dose conversion coefficients (Dose/W~M)
|
From page 33... ...
The corresponding values of the unattached fraction and radon progeny aerosol size that are assumed to represent these various exposure scenarios in the home are given in Table 3-1. In both mine and home atmospheres, unattached radon progeny are considered to have a characteristic diffusion coefficient of 0.035 cm2/s (see Chapter 6~.
|
From page 34... ...
In order to derive exposure-dose conversion coefficients for a population of underground miners, the committee calculated the individual time-weighted doses for mining and haulageway work. The corresponding average doseweighted minute volume corresponds to a minute volume of 28 liters/mint To represent overall exposure in the home, the committee used a time-weighted average of individual values of the exposure-dose conversion coefficient calculated for the normal living room and normal bedroom.
|
From page 35... ...
The committee used the model to calculate doses received by target cells in each generation and then averaged the results to express an exposure-dose conversion coefficient for bronchial epithelium as a whole. The exposure-dose conversion coefficients calculated for a miner and for an adult male exposed to radon progeny at home are shown in Figure 3-1.
|
From page 36... ...
~ ~ 0 U) ~ > Secretory Cells / Insoluble Rn-progeny: Basal Cells / Insoluble Rn progeny: Secretory Cells / Partially Soluble Rn-progeny: Basal Cells / Partially Soluble Rn-progeny: K=0.81 K=0.77 K=0.72 K=0.60 11 FIGURE 3-l Comparison of dose conversion coefficients for a miner and for a man exposed to radon progeny at home.
|
From page 37... ...
Figure 3-1 shows that the corresponding values of the K factor, which represent the ratios of dose conversion coefficients from exposure in the home to that in a mine, vary from 0.81 to 0.60 for secretory cell and basal cell targets, respectively. As noted earlier, the K factor is derived by averaging the exposure-dose conversion coefficients calculated for the normal living room and bedroom and comparing the result with the average value calculated for mining and haulageway work.
|
From page 38... ...
o en .= . _ 0 cat O ~ Secretor + Basal Cells in All Bronchi: Secretory + Basal Cells in Lobar/Segmental Bronchi: Secretory Cells in Bronchioles: Epithelial Cells in the Alveoli: K=0.73 K=~.69 K=0.99 K=0.47 FIGURE 3-2 Comparison of dose conversion coefficients calculated for sensitive cells in venous tissues of the lung.
|
From page 39... ...
The lower exposure-dose conversion coefficients implied by the data of Cheng et al.'s result from corresponding
|
From page 40... ...
The effect on calculated exposure-dose conversion coefficients by using bronchial deposition efficiencies based on empirical observations made from experiments with bronchial casts (Cohen et al., 1990) , rather than a purely theoretical analysis, is shown in Figure 3-4 (see Chapter 9 for a discussion of the data and theoretical deposition models)
|
From page 41... ...
The sensitivities of calculated exposure-dose conversion coefficients and the K factor to the assumption made by the committee that the attached radon progeny aerosol grows in the respiratory tract to double its size in ambient air are examined in Figure 3-5. In this case, the values shown in Figure 3-5 are averages of dose conversion coefficients calculated for secretory and basal cell targets.
|
From page 42... ...
If the attached radon progeny aerosols in both mines and homes were, in fact, stable in the respiratory tract, the K factor would increase to 1.16, which is significantly higher than the committee's estimate of 0.73. DOSES TO ADULT FEMALES Bronchial exposure-dose conversion coefficients calculated for a female exposed to radon progeny in the home (a female homemaker)
|
From page 43... ...
cell targets and 0.62 for basal cells in a female compared with 0.76 and 0.69, respectively, for a male. DOSES TO CHILDREN AND INFANTS L;xposure-dose conversion coefficients calculated for children and infants exposed to radon progeny in the home are compared in Figure 3-7 with those for adult males and females.
|
From page 44... ...
The K factors are given in Tables 3-4 and 3-5, for normal subjects and for nose and mouth breathers, respectively. - -r VARIABILITY OF THE DOSE CONVERSION COEFFICIENT IN HOMES The dose conversion coefficients shown in Figure 3-7 apply to exposure conditions in living rooms and bedrooms that are assumed to represent normal (or typical)
|
From page 45... ...
+SD refers to the standard deviation of the calculated K factor for the five home environments and three mine environments shown in Figure 3.1. conversion coefficients calculated for each subject exposed to radon progeny in a living room in the presence of an active cigarette smoker (where the unattached fraction of potential alpha energy, Up, is assumed to be only 1%, and the AMD of the attached aerosol is 0.25 Am)
|
From page 46... ...
and is devoid of secretory cells. Basal cell nuclei, which are assumed to be the sensitive targets, are located in an abnormally thick layer (30-,~bm thick)
|
From page 47... ...
The principal targets are assumed to be the nuclei of secretory cells. Comparison of the conversion coefficients calculated for miners under these assumed conditions of disease with values calculated for healthy subjects yields the somewhat complex effects shown in Figure 3-9.
|
From page 48... ...
Dose conversion coefficients calculated on the assumption that radon progeny are insoluble (i.e., that they remain in mucus) are shown separately from the corresponding values calculated if part of the progeny activity is assumed to be taken up by the bronchial epithelium.
|
From page 49... ...
COMPARATIVE DOSES FROM RADON AND THORON PROGENY The dose conversion coefficients calculated for exposure to thoron progeny in a mine or a home are compared in Figure 3-10 with the values applicable for an adult male exposed to radon progeny. For thoron progeny, the unattached fraction of potential alpha energy, Up, is assumed to be 0.1% during active mining, 1% in an underground haulageway, and normally, 2% indoors in the home.
|
From page 50... ...
The exposure-dose conversion coefficients shown in Figure 3-10 were obtained by averaging the values calculated for both types of assumed clearance behavior. It is seen from the data in Figure 3-10 that, for unit exposure to thoron progeny in a mine or in the home, secretory cell nuclei are expected to receive only about 20% of the dose that they receive from the same exposure to radon progeny.
|
From page 51... ...
for extrapolating the observed risk of radon progeny exposure in mines to domestic settings that were derived in this chapter for various reference target tissues and different subjects are summarized in Table 3-4. K factors derived with respect to miners and subjects in the home who breath habitually through both the mouth and nose are summarized in Table 3-5.
|
Key Terms
This material may be derived from roughly machine-read images, and so is provided only to facilitate research.
More
information on Chapter Skim is available.