Revision 1
March 19, 1998
by Radiation, Science, and Health, Inc.,
Edited by J. Muckerheide

1.6
Biological Models

Figure 1 Figure 2

"Lung-cancer mortality (LCM) is elevated in underground miners who chronically inhaIed mutagenic, cytotoxic alpha-decay products of radon gas. Studies of LCM associations with residential radon exposure (RRE) levels remain inconclusive, but indicate at least the plausibility of a negative LCM-RRE association over a restricted exposure range. Recently this possibility was investigated using a ‘cytodynamic 2-stage’ (CD2) cancer model developed at LLNL. (Bogen 1996a) The new model accounts for interrelated killing, regeneration, critical DNA damage, and possibly incomplete exposure of tracheobronchial stem cells; it also presumes non- threshold, low-dose linearity for radon-induced critical DNA damage. This model was fit to combined data on LCM vs. estimated radon exposures for (i) white males in 1601 U.S. counties (Cohen 1995) (considered controversial because these data exhibit a negative ICM-RRE association), and (ii) white male Colorado Plateau uranium miners. (BEIR IV 1988)

"The CD2 fit obtained not only predicts the combined residential/miner data, but also predicts the inverse dose-rate (TDR) effect (i.e., the higher risk for a given total exposure of longer duration) observed for radon-exposed miners, and has parameter estimates that all are realistic when compared to experimental data. (Bogen 1996b)

"As shown in Figure 1, both the nonlinear CD2 and linear BEIR IV risk models predict substantially increased risk above 10 pCi/L, but below this concentration, risks predicted by the two models diverge dramatically. For 20-pCi/L residential radon exposures — the approximate household concentration implied by the efflux design criterion used recently for DOE’s uranium-bearing Nevada Low-level Waste.

"CD2 model plausibility thus bears directly on the scientific basis for risk assessments concerning residential radon exposure and related waste-management issues (e.g., optimal design of uranium-bearing low-level waste sites)."