INTRODUCTION AND SUMMARY OF SECTION 5: RADON AND HEALTH
Robert A. Michaels*
This section addresses three issue areas relating to radon and health, only the first of which is central to the science of environmental toxicology:
Risk Assessment, or the measure of how much risk is associated with given exposures,
Risk Management, the attempt to control the degree of risk, and
Acceptable Risk, or how much risk does society choose to tolerate.
Each of these can be summarized in turn. RISK ASSESSMENT
Risk assessment encompasses assessment of exposure and health risks. In "The Association between Radon Daughter Exposure and Lung Cancer: Evidence and Implications from Studies of Miners," Geoffrey Howe (Professor of Preventive Medicine, University of Toronto) and Kristan L'Abbe review available data relating radon exposure to its principal health effect, lung cancer, as well as evidence of incremental stomach cancer risk. In addition, they present findings of Howe's own research into the lung cancer issue. In all, some six epidemiological investigations have contributed to elucidating a dose-response relationship describing lung cancer risk following radon exposure. Each investigation focused upon a significantly large population of hard-rock miners (ores included uranium, fluorspar, and iron), who were occupationally exposed to elevated levels of
radon gas--the principal radioactive hazard even in uranium mines.
Lung cancer rates among the mining populations were compared with rates in comparable non-mining populations, yielding relative risk ratios of from 1.9 to 6.7; that is, the mining populations exhibited lung cancer rates of from 1.9 to 6.7 times those of control populations selected for
*Robert A. Michaels, Co-Chairman of the Radon and Health
Session, is a principal of Ramtrac, a consulting firm dealing with environmental toxicology and risk assessment.
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comparison, The relative risk ratios were found to be related to independently calculated levels of radon exposure, measured in working level months (WLM), where one working level is roughly equivalent to a radon radioactivity level of 200 picocuries per liter (pCi/l) of air inhaled. Lung cancer risks associated with residential radon exposure, when quantified by extrapolating the dose-response curve to lower radon exposure levels, are overestimated. In "Updating Radon Daughter Risk Projections," Naomi Harley, (Professor of Environmental Medicine, New York University), documents this overestimation, and attempts to explain it. She concludes that children appear not to constitute a particularly sensitive population group, and that lung
cancer risk appears to decline gradually once radon exposure is discontinued.
RISK MANAGEMENT
In "Comments on the Heath Presentations," Judith Klotz, (Coordinator of Environmental Epidemiology, New Jersey Department of Health), notes the significance of Harley's conclusions with respect to the issue of mitigation. Mitigation of excessive radon levels will not only decrease future lung cancer risk in proportion to reduction of future radon exposure. As a bonus, mitigation of future radon exposure is also likely to decrease the lung cancer risk incurred by past exposure to radon. In this context, it is unfortunate that, as Howe observed, radon and smoking appear to contribute to lung cancer risk in an additive rather than a multiplicative (synergistic) manner. Were the contributions multiplicative, reduction of either risk would accomplish a disproportionately large reduction in lung cancer risk posed by the other.
ACCEPTABLE RISK
Acceptable risk is not decided by scientific principles, but by regulatory agency decisions, which should reflect each agency's role in promoting the values embraced by our society. In "Overview of Federal Planning and Guidance," Christie Eheman, (Health Physicist, Centers for Disease Control, Atlanta), discusses the basis for federal agencies recommending mitigation of residential radon levels exceeding 4 pCi/l. Radon at this level is acknowledged to pose a worst-case incremental lifetime lung cancer risk in the range of about 1 to 3 percent (10,000 to 30,000 per million), assuming continuous exposure over 70 years. The federal recommendations were clearly based upon cost-benefit considerations, in particular, the high cost and diminishing returns of mitigating residential radon levels which are intially as low as 4 pci/l or lower.
Robert Michaels (Consultant in Environmental Toxicology and Risk Assessment, Long Island City, NY) notes in the discussion that confusion has resulted from the failure of
160 Radon and the Environment
health agencies to separate concepts of risk assessment, acceptable risk, and economic factors, all of which may limit risk management. For example, one company which analyzes radon samples of residential air interprets results for clients as follows: “The maximum safe level for radon in homes tentatively recommended by EPA is approximately 4 pci/l" (emphasis added). In fact, the worst-case incremental cancer risks associated with this radon level appear to be some 10,000 to 30,000 times the one-per-million level that, in other circumstances, would trigger EPA action to reduce then.
A second effect of the federal recommendations may be to inhibit investment of venture capital toward development technologies to improve the economics of radon mitigation. Such investment requires unequivocal federal agency commitment to achieving lower levels as they become technically feasible. Michaels suggests that federal agencies can drive radon mitigation technology by establishing mitigation targets, just as automobile engine efficiency is driven by miles-per-gallon targets which become more demanding over the years. Until action is taken to reduce average residential radon exposure instead of just extreme levels, which exert little effect upon average exposure, Klotz notes, no appreciable reduction of the radon contribution to rising lung cancer rates in the U.S. can be anticipated.
Publication citation
Michaels, RA. Introduction and Summary of Section 5: Radon and Health, pages 158-60 in: Makofske, William J.; and Michael R. Edelstein. Radon and the Environment. Proceedings of a conference sponsored by the Institute for Environmental Studies at Ramapo College of New Jersey on 8-10 May 1986. William Andrew, Inc.; ISBN 0815511612, 9780815511618, 465 pages, 1988;