A Review of the Radiological Assessments Corporation's Fernald Dose Reconstruction Report (1997)

The range of cumulative exposures observed in studies of indoor radon exposure is similar to that being discussed here, so an overall, balanced summary of the findings from these studies (including the absolute excess number of lung-cancer cases observed) would be a helpful comparison.

The committee has some additional specific comments:

Page 94, middle paragraph, and table 26: The baseline radiogenic risk of cancer (5%/Sv) that RAC multiplies by 2 for exposures before age 20 years is based on a population of all ages; that is, it includes the population aged 0-19 years. It is more appropriate to multiply by 2 a risk figure for only those aged 20 years and over, which would be 20% lower than what RAC derived.

Page 96: Figure 51, which is reasonable for presenting risk estimates, contains an error. The top left bubble and bracket in the figure incorrectly label the distance from the median to the 95th percentile as the “uncertainty range of additional risk” due to Fernald irradiation. The bracket should instead extend from the 5th percentile to the 95th percentile; the 5th percentile is not even identified on the chart, so there is no place to extend the bracket.

As previously stated, the appendixes to the final Fernald report contain the technical details associated with the dose reconstruction. Because these appendixes are likely to be of interest to others involved in dose-reconstruction projects, the National Research Council committee offers several suggestions.

RAC has chosen to accomplish several things in this appendix, including fitting the cascade-impactor data by exact polynomial equations, simulating mathematically the action of an Andersen impactor by describing the jet configurations and air flows to match the air-sampling process, and comparing this approach to conventional particle-size analysis by using lognormal distribution assumptions and probit analyses to obtain mass median aerodynamic diameters (MMADs). This is an acceptable approach to obtain a more-accurate description of the particles collected on each impactor run, but it is unconventional, and operationally it might be cumbersome or time-consuming.

Several basic statements made in this appendix should be emphasized, as follows.

Page H-2, paragraph 4: “Rather than making the prior assumption that all particle size distributions were lognormal, we fitted cubic polynomials to the log-probability-transformed cumulative sampler data in order to represent the distributions by continuous functions for further calculations. . . . We did not consider possible distortion of the distribution of particles that entered the sampler.”

Page H-1, paragraph 6, and page H-2, paragraph 1: “We have examined the properties of the Andersen Mark II cascade impactor, and we have developed a simulation of the instrument to study its potential for distorting the sampled distribution. We have found no reason to alter our approach to representing particle size distributions. ” This statement indicates that the authors were aware of the “in-field” distortion of particle size distributions that actually occur on sampling, but the theoretical description of the instrument does not indicate such losses, so this theoretical model of the impactor is a proper approach.