August 25, 2001

NCRP
Suite 800
7910 Woodmont Ave.
Bethesda, MD 30814

Re: Comments on NCRP Report No. 136, " Evaluation of the Linear-Nonthreshold Model for Ionizing Radiation"

To: NCRP

On review of this report, it seems apparent that the objective was to defend the status quo. You have, no doubt, received comments from other reviewers criticizing your summary dismissal of the plethora of scientific publications that support the existence of a dose threshold and the validity of hormesis. Although some of this evidence is cited and discussed in the report, no cogent rationale was presented for rejecting its importance in reaching your conclusions.

The main point I would like to make in this letter is to urge you to consider the total spectrum of ionizing radiation effects on biological systems, primarily humans, in assessing the net overall health consequences to dose recipients. As stated in NCRP-136, the study focused on those effects related to chromosome aberration (carcinogenicity, etc). While such effects are certainly important, they may not be of overriding impact at all dose levels and/or for all organs and tissue systems. For example, there is a considerable body of evidence that low-dose ionizing radiation can have a stimulatory affect upon the immune response system. This phenomenon could account for the negative correlation between background radiation levels and various morbidity endpoints observed in studies in the USA, China, and India. If you are not familiar with the body of knowledge on immumological effects of low-dose radiation, I would be happy to supply a list of references. It is noted that the scientific committee preparing NCRP-136 included no immunologists. There is a strong possibility that inclusion of this body of expertise might have significantly influenced the conclusions of the report.

Perhaps what is needed in the evaluation of radiation effects is a new paradigm. Rather than perpetuating an approach that focuses only those effects involving chromosome aberration, it might be in the best interests of public health to consider the complete spectrum of radiation effects that could result from radiation exposure. It is likely that ionizing radiation could simultaneously produce a multiplicity of effects on biological systems, some of which may be harmful, while others may concurrently be beneficial in nature. Determination of the net consequence to the dose receptor should require a quantitative consideration and evaluation of all such effects. Depending upon the dose level, the net consequence might be either detrimental or beneficial in nature. In any case, the simple inference of low-dose effects from observation of certain high-dose consequences seems more an exercise in faith than of science.

Should you be interested, I would be happy to provide any further information that you may request to support the arguments made in this letter. Thank you for your consideration.

Sincerely,