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Ms. H. O'Leary 3. Chromosome Aberrations and Human Cancer: It is well established that most human cancers have an abnormal chromosome constitution with a remarkable diversity of karyotypes (Sandberg, "The Chromosomes in Human Cancer and Leukemia," Elsevier, 1980) and those of highest malignancy are characterized by their more deviant chromosome patterns (Wolman, Cancer Genef Cytogenet. 19, 129-140, 1986). What is less widely recognized is that alpha- and beta-particle-emitting radionuclides are, by far, the most effective agents for the induction of chromosome aberrations. Induction of chromosome aberrations requires substantial energy deposition: about 100 eV for induction of a single-strand break in DNA and about 280 eV for double-strand breaks (Bauchinger, M., in Ishihara T. and Sasaki, M. J. (eds) Radiation-Induced Chromosome Damage in Man, Alan Liss, New York, pp. 1-22, 1983). The yield of aberrations by alpha particle interactions shows a nearly linear dependence on radiation dose. Beta particle emitters are not only very effective in producing single strand breaks, but also can induce double-strand breaks by several mechanisms. Based on the energy required for strand breakage it is evident that chromosome aberrations do not occur spontaneously and cannot be induced by chemical mutagens. However, a very large number of primordial, cosmogenic, and manmade radionuclides are present in the food chain, in drinking water, and in indoor air. Inhaled and ingested radionuclides are distributed nonuniformly in mammals and man at concentrations which may very well account for most spontaneous mutations, spontaneous aberrations, and spontaneous tumors. By minimizing or ignoring the adverse health risks of natural background radiation components, the AEC/ERDAIDOE has found it much easier to justify the added human exposure to man-made sources of ionizing radiation. It is now recognized (with no initial help from the AEC/ERDA/DOE) that indoor radon and its decay products are major contributing sources of natural background radiation exposure to the lung, bronchial epithelium, soft tissue, bone surfaces, and bone marrow (see NCRP Report No. 93, 1987, Tables 2.1 and 2.2). However, this is only the tip of the iceberg. Human exposures to inhaled and ingested radionuclides of natural origin vary widely, the tissue distribution of some radionuclides is highly nonuniform, the radiation doses at hotspots are orders of magnitude higher than average tissue and organ doses, and radionuclides other than radon decay products are important at other critical tissue sites. Thus, for example, what are the concentrations and distributions of bone-seeking radionuclides in human atherosclerosis plaques (see discussion of radiation-induced atherosclerosis, below)? There are a myriad of natural and man-made radionuclides in the food we eat and in the air we breathe. A striking example of the radioactivity of vegetation is provided by Russell et al. (J. Ceophys. Rues. 86, 5347-5363, 1981). Figure I of this study (copy attached) shows the spectrum of gamma ray-emitting radionuclides on maple leaf, Framingham, Massachusetts, October 1968. Alpha- and beta-emitting radionuclides also are present in comparable numbers. Leafy vegetables and cereal grains have added radioactivity due to selective plant uptake of radionuclides from soils and fertilizers. We are all exposed to the inhalation and ingestion of a very large number of radionuclides which are effective as mutagens and carcinogens. For more than 40 years, assessment of the health risks of radionuclides has been controlled by a vested interest establishment that has contrived to minimize or ignore adverse effects of all sources of human exposure to ionizing radiation. Clearly it is time for a change. The assessment of radiation health risks must be completely divorced from any influence and control by the nuclear energy establishment.
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