Bernard Cohen, doctor of science and professor emeritus at Pittsburgh University, is a liberal Democrat. [He mentions this in his terrific book, The Nuclear Energy Option, Plenum Press, New York, 1990, p. 269.] I probably would disagree with everything he believes in politically. But Dr. Cohen is also a scientist. He is convinced that the way mankind can continue to raise itself up from our back-breaking labor and mud huts is through increasing our knowledge about the world we live in. And most important, he is convinced this knowledge is objective. We can find truth. It is verifiable. It can stand on its own.
In by far the largest "ecological" study of low-level radiation ever made, Professor Cohen was attempting to refine the Linear No-Threshold theory. But, in his words, "It came as a great shock to me that my data ran contrary to the LNT, and I didn't fully believe it until about 1993 - when I shut off the $1,200 radon reduction system in my home to save electricity." But he was using the scientific method, which is very clear about hypotheses that have been shown to be false: they are stuffed immediately into the trash can.
Under the LNT theory, cancer rate increases with increasing doses of radiation - even at very low exposures. If you are to plot response (cancer) versus dose, you should have a straight line with a positive slope according to this theory that has been sanctified by the regulators and rule writers. Using data from the American Academy of Sciences' Biological Effects of Ionizing Radiation committee (BEIR), the slope of this line should be an increased cancer risk of 4% per gray for chronic radiation and 8% per gray for acute exposure. By knowing the "whole body" dose given by various radon concentrations, this slope can also be expressed in terms of lung cancer mortality (since that is the only place in the body where significant radon progeny reside) per picocurie per liter of air.The value of this prediction for men, without any consideration of smoking, is 4.5 deaths per 10,000 men per year for each pCi/l increase in airborne radon. Remember this figure.
Cohen's initial study took five years, cost millions of dollars, and accumulated data from homes in 1,729 counties, comprising about 90% of the U.S. population. [Because so many retirees move to California, Florida and Arizona, these data were deleted, reducing the number of counties to 1,601. This deletion, incidentally, had an insignificant effect on the results.] It considered radon data from the EPA, state agencies, and 272,000 measurements made by the University of Pittsburgh. Census data on smoking, rural-urban balance, occupations, education, housing, medical care - a total of fifty-four socioeconomic "confounding" factors (alone and in combinations with each other) were analyzed to determine if and how they affected the lung cancer rate.
The study found - as you may now suspect - a discrepancy between the LNT's prediction of lung cancer and the actual data. This has since been known as "our discrepancy," and Cohen has invited his colleagues to try to find a confounder that would explain it. He notes that unless someone can come up with a reason to put aside "our discrepancy," the LNT must be considered a false and unacceptable theory and discarded as a source for use in regulatory authority. With more than 500 of the suspected confounders and combinations thereof already eliminated, it does not look good for the LNT advocates - most of whom do not address "our discrepancy" but prefer to snub Dr. Cohen as a mere physicist, and not an epidemiologist. (Critics overlook that G.A. Colditz is a world-class epidemiologist and was co-author with Cohen on "Tests of the linear-no-threshold theory for lung cancer induced by exposure to radon" in Environmental Research, 64, 1994.)
Note and source for Figure 33: Effect of Residential Radon Levels on Lung Cancer - Each data point represents an average of eighty-nine U.S. counties. Source: Cohen, B.L. Test of the linear-no-threshold theory of radiation carcinogenesis for inhaled radon decay products. Health Physics, 68, 157, 1995.
Figure 33 is typical of the curves plotted from the University of Pittsburgh data and is one of four similar figures in the report - this one is for males without smoking's begin taken into account. The others are for males with smoking taken into consideration, and similar data on females both considering and not considering smoking. [These are available from his paper, Test of the Linear-No-Threshold Theory of Radiation Carcinogenesis for Inhaled Radon Decay Products," Health Physics, February 1995. All curves give a similar negative correlation between radon and cancer through 6 pCi/l.]
I have deleted the error bars and the "first and third quartile" curves because I don't think they'd mean much to the average reader. Cohen also had indicators of the numbers of counties for each data point on his curves ranging from 4 to 216 with an average of 88.9. These are counties, bear in mind, not individuals.
Remember the increase by 4.5 deaths per pCi/l predicted by the LNT? That is shown graphically by the dashed line on Figure 33. The solid line with a negative slope is the best fit of the collected data. It shows a minus 4.7 deaths per pCi/l. If some hypothetical man (recall our graph is of male data) had a choice between being exposed to, say, 6 pCi of radon in his house, or being exposed to none, what is the significance of this choice? By sealing his house and spending some $3,000 to $4,000 for the government-recommended heat exchangers, he could increase his risk of lung cancer by 7.5%.
Perhaps that doesn't sound like much to you (especially if we're not talking about your lungs), but it is a huge increase in risk compared even with the LNTer's worst chortlings. You may recall the BEIR statistic for chronic radiation exposure predicts an increase in risk of cancer mortality of 8% for exposure to 2 gray, which is 200 cGy or 200,000 mrem. This is far above the risk experienced by all but a small fraction of A-bomb survivors! So if you missed Hiroshima and Nagasaki, just hang in there with the EPA recommendation on radon. They'll help you reach that goal of a significant increase in cancer risk!
I like the way Jay Lehr summed up Cohen's results in an article, "Good News About Radon: The Linear Nonthreshold Model is Wrong":
"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. This is indeed good news."
It would have been even better news if more people knew about it.
[Dr. Lehr is a senior scientist with Environmental Education Enterprises, a provider of high-technology short courses for environmental professionals.]
