Table 5.1

Annual Weighted Equivalent Dosea to the Lung from 222Rn Gas Exposure

Organ

mSv y-1 per Bq m-3

Reference

Whole lungb

7 × 10-3

ICRP (1981)

Bronchial surfacesc

5 × 10-3

NCRP (1975)

a Weighted using ICRP values of Wr and Wt

b Dose calculated from 222Rn solubility in tissue and radon in airways.

c Dose calculated to bronchial surfaces from 222Rn decay in airways.

Dose to Organs Other than the Lung from Inhaled 222Rn

Any inhaled gas, including radon, is slightly soluble in body tissues. Radon in the lung diffuses to blood and is transported to other organs, where the gas and the decay products that build up in the tissue deliver a radiation dose. Harley and others (1958) in a study of inhaled radon, determined the solubility of radon in the body. Two persons were in a controlled, relatively high-radon atmosphere for about a day. Sequential exhaled-breath samples were used to infer retention times in the five major body-compartments—lung, blood, intracellular and extracellular fluid, and adipose tissue. The data were used in the metabolic modeling of the dose to other organs from inhaled radon (Harley and Robbins 1992). The dose to organs other than the lung had been calculated previously by Jacobi and Eisfeld (1980). The dose per unit exposure for organs other than the lung are shown in table 5.2, where it can be seen that the dose to other organs is lower than the dose to the bronchial epithelium, in most cases by a factor of about 100.

222Rn Decay-Product Dose During Showering

The most important variables in the alpha dose to cell nuclei in the bronchial airways are aerosol size distribution, breathing rate, and location of the target-cell nuclei.

The most extensive activity-weighted size distributions that have been measured in homes were reported by Hopke and others (1995a). Figure 5.1 shows the average values of the activity fractions for each of the decay products and for PAEC for the homes in which no smokers are present; figure 5.2 presents similar data on homes with smokers.

When a home is supplied by radon-bearing groundwater, the radon that is released into the air during water use becomes another source of indoor radon decay products. To evaluate the significance of this contribution to the overall radon risk, it is necessary to examine each instance of water use (such as in the kitchen, bathroom, and laundry room) and to look at both the steady-state (long-



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