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

1.2.6
Natural Radiation and Radioactivity

1.2.6.2
Natural Background: Populations

In theory, we thought it might be saved, confining higher expectations to 10 of the 56 Mn types, even though these 10 correspond poorly to those for which human radio-carcinogenesis had been shown in BEIR 1972. In practice, though, even this turned out to be improbable when we examined this unholy decade.

We note that this epidemiological approach possesses some peculiar advantages over less direct studies of radiation effects. It addresses itself directly to the population of interest, in this case that of the U. S., rather than to small, select populations of the war-torn (e.g., Japan), of the ill (e.g., those irradiated for spondylitis, tuberculosis, thyroiditis, malignancies, thymic disorders, etc.), of the young (e.g., irradiation for tinea), or of the occupationally stressed (e.g., uranium miners). Even the smallest population groups are as large and usually much larger than these select irradiated groups. Then, too, the time span of observation is large. Although we have dealt only with an 18-year span here, the data are an 18-year sampling of a continuing procession of cohorts which span the full biblical ‘three score years and ten’. And, of course, the radiation is being delivered over this entire time span, at the very rates of interest, and compounded, so to speak, for effects in utero, on the young, on the general population, and on the aged.

While each malignancy type at 0.003 is within its respective statistical expectation, the consistent string of zero observed deaths, over populations that range from tens of thousands to nearly ten million, is a bit unsettling. Many of the 10 apocalyptic horsemen who refused to show significant groups below 0.3, appear less formidable when viewed in the light of worldwide malignancy mortalities. The fact that cancer is a reportable disease in the Scandanavian countries with their remarkably complete registries, estimates 163 entirely and produces some very low rates for 174 and for some of the ICD types included in 65. The very low rates observed help to dispel the enticing, if mildly parochial, notion that the remaining 7 types somehow constitute "common" malignancies, while the 46 eliminated are ‘rare’. While these 7 do account for perhaps a third of total U. S. malignant mortality, they hardly constitute important malignancies in other lands. Indeed, the only one of these to coincide with the BEIR list of important radiogenic malignancies, ICD 151 (stomach), is dropping so linearly and rapidly in the U. S. that it bids fair to reach zero within the coming two decades.

If these are indeed valid, a goodly fraction of the total radiogenic insult must have been received by age 10 and a significant number of radiogenic mortalities should have appeared by age 30. However, this does not seem to be the case. Here we have isolated those national rates for which we had age-specific data, and for which the rate is zero up to age 30 or beyond. Again, if these ten horsemen were truly riding to the beat of a radiogenic drum, they were certainly riding more slowly than predicted by the linear additive models so far proposed. All in all it appears that even the abandonment of poly-carcinogenesis would do little for the additive model, especially in the long run, and this model will probably have to be abandoned in toto."

Admittedly, radiation at low dose rates does seem to be remarkably ineffective as a complete pancarcinogen, or even as a complete carcinogen of any sort. But it could well be a pan-co-carcinogen, as envisioned by the multiplicative model. If this were the case, one would predict a fair increase of malignant mortality with increasing background, and this prediction has been made quite explicit by the model’s authors, (Gofman 1971; Tamplin 1971) e.g., from 1% to 30% increase at 170 mrem/yr, depending on various assumptions of latency, plateau, and doubling dose. (Gofman 1971; Tamplin 1971; BEIR 1972) With this in mind it was intriguing to note, the resolute insistence on dwelling in regions of high background that seemed to characterize the low mortality groups. At rates of 0.03 and 0.003 only six groups were at the 170 mrem/yr national average, none were below the average, and at least 40 were above 180 mrem/yr. At first we thought this might only be a secondary association with the well-known urban trend of U.S. cancer mortality. Tests failed to substantiate this, however. A white female resident of Dallas, for example (at 140 mrem/yr), simply seems to be about twice as likely to contract leukemia as her counterpart in Denver (at 290 mrem/yr). Since we doubted that anyone was prepared to ascribe oncolytic properties to the radiation background, we felt obliged to search for some other association. Surely there must be some sort of mortality increase with increasing background. (Gofman 1971; Tamplin 1971; BEIR 72)

However, U. S. rates for white, malignant mortality vs. natural background for the 50 states showed, if anything, the reverse. Now, were it not for the insistence of the hypothesis (Gofman 1971; Tamplin 1971) that there must be a correlation between malignant mortality and background, we would be inclined to dismiss this as an example of simple non-correlation. However, of the 14 states above 140 mrem/yr, 12 were very significantly (P<0.01) below the U. S. average, one insignificantly lower, and only one slightly, but significantly, higher. The probability of this occurring by pure chance proved to be <0.001.

The data base is, literally, enormous. Each point represents an average of about 10⁵ deaths, and a coefficient of variability of about 0.3%. Finally, in addition to the negative correlation of rate with background, the ten lowest states in the U. S. all lay at backgrounds >135 mrem/yr. Thus, there seemed to be some real, if hidden, association between high backgrounds and low malignant mortalities. A similar and even more dramatic effect was noted in the non-white population, but we confined ourselves to the white population because of its greater homogeneity, better statistics, the better availability of socioeconomic data, etc.

We discriminated three groups: 1) the seven states of natural background above 165 mrem/yr; 2) the fourteen states of natural background above 140 mrem/yr; 3) the fourteen states with the lowest backgrounds, compared with all 50 U. S. states. We first analyzed the 50 states for each of the 56 (Mn) types to see if the low mortalities of groups A and B could be due to particularly low rates for a few types. These two groups, however, proved to be lower in all categories than the U. S. average, and this premise had to be discarded. The rates for all categories, in fact, tended to decrease with increasing background. Also, if the decedent populations of groups 1) or 2) had significantly large numbers of immigrants from other parts of the U.S., (i.e. , the decedents had not been exposed to the high backgrounds until late in life), one would have expected the rates in groups 1) and 2) to be higher than those of the remaining states, because the Mn rates of the remaining states are much higher. Instead, the reverse was true. Accordingly, if short-term residents are a factor, the true rates for the long-term residents must be even lower. Regardless of which of the suggested values (Gofman 1971; Tamplin 1971; BEIR 1972) we used for D or DD, variability invariably increased, i.e., the results were always the opposite of what would have been expected if the model represented a real factor in U. S. malignant mortality. Furthermore, this increase was found to hold for essentially all U.S. malignancies, even for leukemia, the classic of radiogenic malignancies Thus we seemed to be left without statistical support for a multiplicative model, either for all malignancies (pancarcinogenesis), or even for specific ones.