by Klaus Becker, Berlin

Radon may be one of mankind’s oldest therapies: Close to the source with the highest radon concentration in Gastein/Austria, 5.000-6.000 y old votive offerings have been found: the ancient Romans and other old civilizations appreciated radon spas; and in Japan, the springs on Misasa, with up to 160.000 Bq/l of radon, have been used for 800 years (for a review ref.. 1). Currently about 75.000 patients annually are treated in German or Austrian radon spas and many more in other countries, in particular in Russia mostly for painful joint or backbone diseases such as rheumatic arthritis and spondilytis ankylosans (Morbus Bechterew), either by inhaling high radon concentrations (in the Bad Gastein „Heilstollen", for example, about 170.000 Bq/m³, or more than 1000 times of the current EPA residential radon limits), by drinking, or by bathing in radon water. The expenses (e. g. in Bad Gastein about $ 500 for 10 h) are mostly paid by the health insurance systems. Even in the more radiophobic USA, a „Free enterprise radon health mine" has been operating successfully for half a century (B. Erickson, loc. cit. 3, p. 269-277).

Many clinical studies, some of them randomized double-blind studies, clearly demonstrated the superior effect of radon in comparison with an otherwise identical treatment lasting for several months after the end of the treatment (1, 2). Various mechanisms have been suggested for such effects involving radiation doses in the order of only one mGy, including stimulation of repair or radical scavenger enzymes, or the production of neuropeptides, but there are still many open questions. However, considering the practical success and acceptance of radon treatments by the patients suffering from severe pains, radon balneology has recently been accepted (similar to other treatments for which there is not yet a profound scientific explanation) even by the extremely cautious and occasionally almost radiophobic German authorities. Thus it is not surprising that the radon spa in Bad Schlema (Saxony), which has been famous up the end of WW II (slogan: „Schlema’s waters perform miracles!") has been officially reopened about three years ago and is again popular, with the conventional monitoring for the staff.

However, this reopening occurred in the center of one of the world’s largest U mining areas, where the former Soviet Union extracted 220.000 t of U between 1945 and 1990, and about 6 bill. $ U.S. are being spent by the German government on mostly overground remediation and radon reduction programs. It was in this area where Paracelsus (famous for his statement: „It is the dose which makes the poison") first described in 1537 the high rate of lung cancers among miners, which was first related in 1913 by a local physician not only to As, but also to the extremely high radon concentrations in the mines, exceeding in some cases 2 mill. Bq/m³, corresponding to several Sv/y according to ICRP. Such concentrations probably contributed - in combination with other factors such as the inhalation of high concentrations of toxic mineral dusts including quartz, U and As, diesel exhaust fumes, nitrous gases, substantial external gamma exposures, heavy smoking, etc. - to several thousand additional lung cancers among the hundreds of thousands of post-war miners. Even such an effect is, however, not conclusive according to a new retrospective analysis of 1945-1955 miners in this area, showing a dominating effect of other inhaled agents.

In some houses of this region, radon concentrations exceeding 100.000 Bq/m³ have been measured, and 12 % of all homes exceed the EPA limits by a factor of more than 100. However, contrary to the LNT approach of ICRP (and consequently also of IAEA, EU, NCRP, BEIR VI, etc.) of extrapolating from very high and complex miner’s data orders of magnitude down to completely different current mining conditions, residential radon doses and dose-rates, and a multitude of other confounding factors, even very careful epidemiological studies could not demonstrate any cancerogenic radon effects up to levels around 1000 Bq/m³, or ca. 7 times the EPA limit (3, 4). While one German case control study appears to indicate a slight increase in residential lung cancer, another shows a slight decrease around 500 Bq/m³ and a threshold around 1000 Bq/m³.

The reason for this difference probably has a simple explanation: The second study (4) is restricted to never-smoking women in high-radon areas, and thus excludes the crucial confounder in radon studies. Actually, it seems from 20.000 autopsies performed in the Dresden area, where German cigarette production started in 1862, that lung cancer was an extremely rare disease among non-miners before the large-scale smoking impact occurred, with lung cancer steadily increasing from only 0.06 % between 1852 and 1876 (5) up to currently a hundred-fold level. Furthermore, it is known that smokers, in particular after the diagnosis of lung cancer, dramatically underestimate their past smoking habits, and even differences by a few cigarettes per day can falsify epidemiological lung cancer studies.

But there are other good reasons to question the power and significance of some of the frequently quoted recent case control residential radon studies, in which out of nine studies in seven countries almost as many data points are below as above the zero line, with only a single Swedish point slightly above the error bars at 450 Bq/m (incidentally: the author of this study recently stated that no lung cancer increase has been found among non-smokers) Among the reasons are poor epidemiological practice; questionable retrospective radon dosimetry; problems with the actual lung dose estimates which may be wrong by a factor of five; data indicating an alpha radiation RBE for lung cancer induction of 2 instead of 20; a threshold of 2 Gy for lung cancer induction due to external low-LET exposures; etc. (for ref. 2). It is, therefore, unlikely that a new meta-analysis, which is currently in progress in the U. K., will provide much substantial clarification in this hotly disputed field. There are additional serious questions, e.g. whether the dose-rate instead of dose determines the effect, and about basic differences in the biological response to high and low doses (see G. Monchaux and J.P. Morlier; S. Z. Liu; and others in the Proceed. ref. 3).

Moreover, there are also recent studies which indicate that not only lung cancer, but also other cancers including childhood leukemia are substantially lower in high natural background and radon than in low-dose areas (6). Similar effects have also been recently observed in Kerala/India, Russia, etc. - usually with the explanation that it is not the radiation level, but other factors such as industrial pollution and living habits, which far outweigh any possible small detrimental radiation effects beyond statistical detection - if they should exist at all. Regarding overground radon, it may be concluded that:

1. Despite substantial and expensive efforts (the „German Radon Study" involved almost 70 persons at a cost of about 8 mill. US $), there are no reliable epidemiological data clearly establishing negative health effects up to about 1000 Bq/m³, but a likely reduction of lung cancer as well as other types of cancer, in the region around 500 Bq/m³. Early miners data cannot be transferred to residential situations.
2. Residential radon reduction programs are, with possibly very few rare exceptions such as heavy smokers in very high radon environments , not required from a public or individual health, as well as from a cost/benefit point of view, for the tax-payer as well as for the individual home-owner.
3. Radon balneology remains an important therapy against painful joint diseases, etc., with a hypothetical minor negative radiation effect certainly negligible compared to the benefits.
4. Restrictive new E. U. radon regulations (max. 200 Bq/m³ for new and 400 Bq/m³ for old buildings, somewhat higher for the working place) would, if enforced, create serious social, economic, and other problems not only for private homes (in particular considering new regulations about better thermal insulation in order to save energy, thus increasing indoors radon levels), but also for many important industries such as phosphate, metallurgy, mineral and coal mining, oil production, etc., in various countries around the world.
5. Obviously, the question of bionegative or biopositive radon effects remains , considering the large contribution of radon to the total natural radiation exposure and the wide range of regional fluctuations, an interesting test case for the LNT hypothesis, and all its regulatory implications and expensive consequences.
6. Last but perhaps not least, the radon debate became an example for the techniques of selective quoting, and the suppression of "inconvenient" data and opinions, which can to a large part be explained with vested personal and commercial interests of the radon research and remediation „industry". This complicates an unbiased judgment in the good vs. bad radon discussion even more.

1. H. G. Pratzel et al., Schmerzstillender Effekt durch Radonbäder..., in: Radon und Gesundheit - Radon and Health, P. Deetjen and A. Falkenbach, Ed., P. Land, Frankfurt 1999 (ISBN 3-631-35532-7), p. 163-182.
2. L. Reiner et al., Radonbäder unterstützen den Hafteffekt...., ibid. P. 139-162
3. K. Becker: Residential radon and the LNT hypothesis. Proceed. 5^th Conf. High Levels of Natural Rad. & Radon Areas, Munich, Int. Congr. Ser. 1225, Elsevier/Amsterdam, in print
4. J. Conrady et al., The true extent of the lung cancer risk from indoor radon: Hidden behind a smoke screen? Ibid.
5. W. Schüttmann, Bewertung des Lungenkrebsrisikos durch Wohnungsradon, Strahlenschutzpraxis 5, No. 4, 35-40, 1999
6. J. Conrady et al., Vergleichende Analyse der räumlichen und zeitlichen Verteilung von Krebserkrankungsfällen, Staatsminist. f. Umwelt etc., Freistaaat Sachsen, Dresden 1997 ; also presented at Ann. Meet. Germ. Nucl. Soc., Munich 1998.