Implicit in the feasibility study is the question of whether it is worth while to perform a substantially expanded study of all radionuclides. The committee believes that although a more detailed study is technically possible, neither the data nor the consequences appear to justify it. The measurement data on which the dose estimates rest are limited;1 additional dose refinements are unlikely to transform the existing sparse data into precise exposure estimates. Improvements in methods are always possible, but the quality of the data and the very low doses involved do not justify such efforts. To obtain substantially better estimates of exposures from NTS (Nevada Test Site) fallout would require the location of a body of exposure data that is much more extensive and of better quality than the available measurements; it is doubtful that such data exist. However, if extensive additional exposure data are found, the question about performing a more detailed dosimetry and risk assessment should be revisited.

If further dose-reconstruction work were to be proposed, however, it should be evaluated according to specific scientific and public-health criteria. The first would be improvement in the accuracy of exposure estimation at the individual or geographic level (to the extent of making new epidemiologic studies feasible, for example). Given the measurement data available, there is little hope that further dose reconstruction can achieve that; compellingly better estimates of doses are unlikely to be possible unless a substantial new body of dose-measurement data is discovered. A second would be sufficient improvement in the dosimetry to permit substantial risks to be addressed with meaningful studies. There is no evidence that either external or internal fallout exposures other than to 131I (iodine-131) could be large enough to produce detectable increases in individual risk in any feasible epidemiologic study, and fine tuning of the dosimetry will not change that situation. There could be a third criterion: to improve the characterization of the uncertainty of individual exposure estimates. But the ability to make major improvements in that arena also is speculative. The lifetime risk of a death due to cancer is about 20% absent the fallout radiation exposure. The fallout putatively raises that risk to about 20.03% (with a credibility interval of about 20.01% to 20.09%), which is of little health consequence. However, if new exposure data were found to indicate that exposures were substantially higher, this could trigger a need for additional studies. Nevertheless, the committee believes that there is insufficient justification for a more detailed study of the amounts and effects of fallout radionuclides other than 131I.

The committee supports continuation of the identification, cataloging, and preservation of fallout-related documents, that is, the archival work described in the draft report. In addition to its value for evaluating exposure to fallout, the committee believes that such work is well justified as a record of a historically important period in the nation’s history. If substantial new knowledge of radiation biology and markers of radiation injury are developed, data that are of limited current interest may be able to support the testing of new hypotheses that relate low doses of radiation to human-health effects. The ability to collect, document, extract, archive, and effectively use fallout records depends on the knowledge possessed by the diminishing number of scientists from that era who are still available and who can help to identify and interpret the data. It is not that the type of data available cannot be analyzed now, but that the scientists of

1  

The basic limitation occurs because in the 1950s there were fewer than 100 monitoring stations across the United States to make the measurements. Interpolation and extrapolation of such measurements in more than 3000 US counties is necessarily imprecise, given the vagaries of the weather, the principal controlling factor. Only if there had been several thousand monitoring stations with data could exposures be estimated much better.



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