what is now known about this problem. From this review, the committee makes the following observations:

  • The literature on inert gases in the stomach clearly supports an assumption that movement into the stomach wall occurs, and diffusion is the probable mechanism.
  • Physiologic processes and histologic structures prevent gastric acids from digesting the stomach, and it is reasonable to assume that they restrict to some degree the movement of gases into the wall.
  • The basic input data for the calculations of stomach-cancer risk are based on risk factors derived from the Japanese atomic-bomb survivors, and a high background of stomach cancer among the Japanese population is well established. Thus, the Japanese data are transported to the US population with a relative-risk projection model that considers the background rate of stomach cancer in the United States. The incidence of stomach cancer in the US population involves a number of cofactors and has been declining in recent years.

It is the judgment of the committee that the risk of cancer posed by an absorbed dose in the stomach is probably not greater than 2.3 times the best estimate of 1.6 × 10-9 per Bq m-3 and it is probably greater than this value divided by 5; that is, it is probably between 3.8 × 10-10 to 4.4 × 10-9 per becquerel per m3. Assuming that these bounding values represent the 80% confidence interval—that is, a 3.3 standard-deviation range of risk, the committee estimates that the uncertainty in this risk factor has a GSD of 2.1, which is lower than the EPA-estimated GSD of 2.4. Thus, the proposed committee model gives an estimate of risk that is about a factor of 3 lower than the EPA median risk estimate and has a lower GSD that reflects uncertainty. Variations in ingestion are incorporated into this estimate of risk, but uncertainties in the nature and magnitude of diffusion processes in the stomach are dominant contributors to overall uncertainty.

Uncertainty and Variability with Regard to Mitigation

A key issue of uncertainty is quantification of the reduction in the level of radiation dose achieved by various mitigation technologies and how this reduction is distributed among the populations at risk. The actual performance of these technologies, compared with what it is assumed to be, is probably an important uncertainty. Variations in performance and reliability might be large and difficult to quantify.

Communication Of Uncertain Risk Information

The decision to expend societal resources to identify, estimate, and manage risk implies a valuation of the risk being controlled. Because of the inherent



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