Good News About Radon:
The Linear Nonthreshold Model Is Wrong
Jay Lehr, Ph.D.
Environmental Education Enterprises
May 1996The cancer risk from low-level radiation is normally estimated by use of a linear no-threshold theory which is a logical consequence of the view that a single particle of radiation hitting a single biological cell can initiate a cancer. The number of these initiating events would then be proportional to the number of particles of radiation and hence the dose. This theory however ignores the obvious biological defense mechanisms that prevent numerous initiating events from developing into cancers each day of our lives.
There is now a substantial body of evidence which has been previously presented by Luckey(1), Sugahara(2) and Calabrese(3) indicating that low level radiation actually stimulates our biological defense mechanisms to work on our behalf. An early hint of this phenomenon came with detailed studies of those living near World War II atomic bomb blasts. At points distant from the blasts where radiation was minimal but existent, leukemia deaths among A-bomb survivors was below normal, while as expected, closer to the blast where radiation was high, leukemia deaths rose well above normal.
The most persuasive evidence of this reverse phenomenon now appears in the report of the nations most comprehensive radon study which appears in the February 1995 issue of Health Physics (Vol.68, No. 2) presented by Bernard L. Cohen of the University of Pittsburgh. Cohen used radon data from 1601 counties covering more than 80% of the US population. Data was derived either directly from measurements by a University of Pittsburgh research team or by USEPA or from data bases compiled by individual states.
With or without corrections for variations in smoking prevalence, the data clearly shows that there is a strong tendency for lung cancer rates to decrease with increasing radon exposure. The actual radiation/cancer relationship indicating a decline in cancer with an increase in low level radon radiation is in sharp contrast to the reverse relationship which coincides with the prevailing no threshold theory.
The discrepancy in slope between the measured and theoretical relationship is about 20 standard deviations. If the theory is correct, the only reasonable explanation for the discrepancy is that there are one or more confounding factors that correlate strongly and with opposite signs with both lung cancer mortality and radon exposure. They thereby introduce a strong negative correlation between lung cancer mortality and radon exposure which is not due to a direct causal relationship. Smoking was the obvious candidate because of its known strong correlation with lung cancer but it was considered in great detail and found not to explain the discrepancy.
In all, variations in 54 socio-economic factors as well as geography, altitude and climate were considered by stratifying the data accordingly. No significant change in the relationship between radon level and lung cancer was observed. That is to say, when Cohen considered only completely rural counties, or only the poorest counties, or only the richest counties, or only the counties with the best medical care, or those with the worst medical care, and so forth, for 54 socio-economic variables plus climate, altitude and geography, the very same decline in cancer mortality occurred when increased airborne radon existed.
Thus, in spite of extensive efforts to find a flaw in the obvious results indicated by the observed data, no potential explanation for the discrepancy between theory and reality could be found. It therefore appears that the linear no-threshold theory for carcinogenesis from inhaled radon decay products is invalid. That is indeed good news.
References: 1- Luckey, T.D. Radiation Hormesis. CRC PRESS, Boca Raton,FL. 1991
2- Sugahara,T; Sagan,L.A.; Aoyama, T. Low dose irradiation and biological defense mechanisms. Amsterdam: Excerpta Medica: 1992.
3- Calabrese, E.J.Biological effects of low level exposures to chemicals and radiation. CRC Lewis Publishers, Boca Raton, FL. 1994.
4- Cohen, B.L. Test of the linear-no threshold theory of radiation carcinogenesis for inhaled radon decay products. Health Phys 1995;68:157-174.
Jay Lehr, Ph.D. is a senior scientist with Environmental Education Enterprises, 2764 Sawbury Blvd., Columbus, Ohio 43235 (tel 614-792-0005; fax 614-792-0006; email firstname.lastname@example.org). Environmental Education Enterprises, a leading provider of high technology short courses for environmental professionals, will be happy to send readers reprints of Dr. Cohen's paper upon request free of charge.
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