ENVIRONMENTAL HEALTH SCIENCES RESEARCH CENTER A National Institute of Environmental Health Sciences Center of Excellence |
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Contacts: To Order a Radon Test Kit: Jim Doolittle
IA Department of Public Health http://www.idph.state.ia.us/eh/radon.asp
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Exposure to Residential Radon and Lung Cancer Radon gas is an important environmental lung carcinogen with extensive exposure occurring in the rural Midwest. A review conducted by The National Research Council on risks of radon exposure concluded that it was the second leading risk factor for lung cancer and may be responsible for up to 20,000 excess lung cancer deaths per year in the United States. Three independent radon surveillance surveys have established that radon is an important residential exposure in Iowa. A U.S. EPA survey of 25 states conducted during the winter of 1989 found that 71% of Iowa's homes exceeded the recommended health advisory level of 4 pCi/L making Iowa the state with the highest radon levels among all states tested. The second survey, that included 2,100 short-term, first-time radon screening test levels, found 70% of Iowa residences to have radon levels greater than the 4 pCi/L level. A third survey conducted by EHSRC investigator Burton Kross, tested 590 homes in rural Iowa and also found that 70% of the rural homes exceeded the 4 pCi/L radon advisory level, that the mean concentration was 10.1 pCi/L and that 11% of these homes exceeded 20 pCi/L. The most recent EHSRC study of radon concentrations in Iowa and Minnesota found unusually high annual average radon concentrations. Between 1990 and 1994, seven large-scale case-control studies of indoor radon and lung cancer reported mixed results of the effects of radon inhalation. As a result, a debate ensued as to whether residential radon exposure posed a serious risk for lung cancer. The lack of definitive results from these studies may have been due to several limitations including: 1) low mean radon levels and limited ranges of exposure, 2) misclassification of exposure from the use of contemporary radon measurements to estimate exposures in years past, 3) high mobility of subjects, 4) alterations in houses, and 5) measurements in only one or two areas of the home, ignoring other sources of exposure inside and outside the home. EHSRC investigators conducted a study of residential radon in Iowa which addressed each of these limitations. The Iowa Radon Lung Cancer Study reported excess risk related to odds ratios two to six times higher than the combined summary excess odds from a recently published meta-analysis of eight previous studies. The study obtained radon measurements from all levels of a home, in contrast to previous studies that obtained their measurements from basement or bedroom and living room areas. More complete exposure assessment was shown to yield higher odds ratios and higher excess risks. In addition, EHSRC investigators measured radon (222Rn) concentrations in Iowa and Minnesota and found that unusually high annual average radon concentrations occur outdoors in portions of central North America. In some areas, particularly western Iowa, outdoor concentrations exceed the national average indoor radon concentration. Implications and Public Health Impact These EHSRC investigators concluded that more thorough radon exposure assessments contribute to higher risk estimates for radon-associated lung cancer. Investigators have recently developed new retrospective radon detectors. Initial work compared the track rate densities produced by two different glass-based retrospective detectors used in the Iowa Radon Lung Cancer Study and the Missouri Radon Lung Cancer Study. Further work examined the contemporary monitoring capabilities of the glass-based retrospective radon detector to assess the contemporary radon equilibrium in the Iowa Radon Lung Cancer Study Homes. These contributions from EHSRC investigators have clearly extended our understanding of the relationship between radon exposure and cancer risk. Center Contribution The EHSRC Pulmonary Biology Research Core brought these investigators together on this line of investigation. Drs. Kross and Lynch were introduced through the EHSRC and Dr. Field was trained as a doctoral student within the EHSRC. The Environmental Measurements Facility (later renamed the Exposure Assessment Facility) provided the equipment for several of the studies described in this highlight. Together, Drs. Kross and Field received an EHSRC pilot grant in 1991 for studies of radon. Key Researchers and NIEHS Support R. William Field, Research Scientist, Department of Epidemiology, P30ES005605, 1R01CA085942; References Field RW, Becker K. Does exposure to residential radon increase the risk of lung cancer? Radiation Protection Dosimetry, 95 (1): 75-78, 2001. |
Environmental Health Sciences Research Center, The University of Iowa, 100 Oakdale Campus, #178 IREH, Iowa City, IA 52242 |