a compartment model (the parameter values are not given in the paper) for the distribution of radon in the body based on data from Hursh and others (1965), Harley and others (1994), and Harley and Robbins (1994). They assumed that a fraction of the ingested radon diffuses into the stomach wall but that the vascular structure in the mucosa intercepts the radon before it reaches a depth from which the alpha emissions could irradiate the stem cells (N. Harley personal communication, see appendix A). Sharma and others (1996) used the compartment model of Peterman and Perkins (1988) and the data of Brown and Hess (1992) to estimate the dose from dissolved radon. They make no statements regarding the diffusion of radon into the stomach wall and computed, in a most unusual manner, the stomach dose as the alpha energy emitted within the stomach contents divided by the mass of the stomach wall and contents (C.T. Hess personal communication). The estimates of the dose to the stomach obtained by the various investigators are listed in table 4.4. All authors assumed that the short-lived decay products of radon decayed at the site of the 222Rn decay; that is, the alpha energy of 19.2 MeV (see table 4.1) was associated with each 222Rn decay. Those specifically considering the diffusion of radon within the stomach wall generally associated the first two alpha emissions, 11.5 MeV, with the radon decay in the stomach wall.

The data in table 4.4 indicate that the estimated dose to the stomach depends on the extent to which the investigators considered diffusion as a mechanism by which radon comes into intimate contact with the stomach wall; the highest dose coefficient is about 200 times the lowest (Sharma and others 1996; Harley and Robbins 1994; Brown and Hess 1992; Crawford-Brown 1989; Suomela and Kahlos 1972; Hursh and others 1965; Von Doebeln and Lindell 1964). Except for Harley and Robbins (1994), none of the investigators identified any basis for their assumption regarding the movement or lack of movement of radon into the stomach wall. Harley and Robbins (1994) assumed that the absorption of radon follows that of water which is predominantly from the small intestine, and cited the large countercurrent flow of fluid (1500 mL per day) from the stomach wall as

Table 4.4

Summary of Estimates of Equivalent Dose to Stomach per Unit Activity of 222Rn Ingested

Authors

Diffusion

Dose Coefficient, Sv Bq-1

Hursh and others (1965)

Yes

1.1 × 10-7

Von Doebeln and Lindell (1964)

Yes

1.1 × l0-7

Suomela and Kahlos (1972)

Yes

1.3 × 10-7

Crawford-Brown (1989)

Yes

3.0 × 10-7

Brown and Hess (1992)

See footnotea

8.8 × 10-8

Sharma and others (1996)

See footnotea

8.2 × 10-8

Harley and Robbins (1994)

Yes

1.6 × 10-9

a Dose averaged over the mass of the stomach wall and contents.



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