Comparative Dosimetry of Radon in Mines and Homes (1991) / Chapter Skim
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Introduction
Introduction
Pages 9-19
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From page 9... ...
As information on air quality in indoor environments accumulated, it became apparent that radon and its progeny are invariably present in indoor environments and that concentrations vary widely, even reaching in some dwellings levels found in underground mines. The well-documented excess cases of lung cancer among underground miners exposed to radon raised concern that exposure to the gas might also be a cause of lung cancer in the general population.
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Although EPA does not have a statutory basis for regulating concentrations of radon indoors, its action guidelines are the most widely considered national recommendations on acceptable concentrations indoors. In 1988, EPA and the Centers for Disease Control jointly recommended that nearly all homes in the United States be tested for radon and in 1989 the EPA called for testing of schools.
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Excess occurrences of lung cancer have been found in uranium miners in the United States, Czechoslovakia, France, and Canada and in other underground miners exposed to radon decay products, including Newfoundland fluorspar miners, Swedish and U.S. metal miners, British and French iron miners, and Chinese and British tin miners (National Research Council [NRC]
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From page 12... ...
Extrapolation of the lung cancer risks observed in underground miners to the risks for the general population who are exposed to radon indoors is subject to uncertainties related to the differences between the physical environments of homes and mines, the circumstances and temporal patterns of exposure in the two environments, and the potential biological differences between miners and the general population (Table 1-2 and Figure 1-21. With regard to the physical differences between homes and mines, the activity-weighted particle size distributions tend to be different, with there being more activity in the ultrafine mode (unattached fraction)
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INTRODUCTION TABLE 1-2 Potentially Important Differences Between Exposure to Radon in the Mining and Home Environments PHYSICAL FACTORS Aerosol characteristics: Greater concentrations in mines; differing size distributions Attached/unattached fractions: Greater unattached fractions in homes Equilibrium of radon/decay products: Highly variable in homes and mines ACTIVITY FACTORS Amount of ventilation: Probably greater for working miners than for persons indoors Pattern of ventilation: Patterns of oraVnasal breathing not characterized BIOLOGICAL FACTORS Age: Miners have been exposed during adulthood; entire spectrum of ages exposed indoors Gender: Miners studied have been exclusively male; both sexes exposed indoors Exposure pattern: Miners exposed for variable intervals during adulthood; exposure is lifelong for the population Cigarette smoking: The majority of the miners studied have been smokers; only a minority of U.S. adults are currently smokers Exposure ~ · he 13 Activity-aerosol size distribution Ventilation pattern Bronchial morphometry Deposition pattern Clearance rate Mucus thickness Exposure rate Age at exposure Age at risk Sex Smoking Other carcinogens Nonspecific inflammation of airways Addressed by Dosimetric Modeling Response ~ Not Addressed by Dosimetric Modeling FIGURE 1-2 Factors influencing the relationship between radon exposure and the risk of lung cancer.
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From page 14... ...
Thus, further consideration of the relation between exposure to radon and the radiation dose and its biological effectiveness as delivered to the respiratory tract is warranted by the continuing scientific controversy concerning the risks of exposure to indoor radon and by the potential policy implications of risk projections of radon-related lung cancer in the general population. Such risk projections serve as the basis for establishing action guidelines for judging the safety of the nation's homes, schools, and offices and for guiding potentially costly mitigation of unacceptable concentrations (EPA, 19861.
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Because the dose of alpha energy delivered to target cells in the lungs cannot be measured directly, modeling approaches are used to simulate the sequence of events from inhalation of radon progeny to cellular injury by alpha particles. These complex models generally incorporate biological factors, including airway geometry, mucociliaIy clearance, particle deposition, ventilation pattern, and location of the target cells, and physical factors, including the aerosol size distribution and the proportion of progeny not attached to particles.
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From page 16... ...
RISK ASSESSMENT FOR INDOOR RADON To estimate the lung cancer hazard associated with indoor radon, information on exposure levels in dwellings is used in a risk projection equation, or model, that describes the increment in the occurrence of lung cancer per unit exposure. In the principal models in use at present, the risk coefficients describing the relationship between exposure and lung cancer occurrence are derived from studies of miners (NCRP, 1984b; ICRP, 1987; NRC, 1988~.
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At present, the risks of indoor radon can be estimated best by using risk coefficients derived from epidemiological studies of underground miners in risk models. However, application of the evidence from the mining environment to the indoor environment requires assumptions and introduces substantial uncertainty.
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1985. Health hazards associated with elevated levels of indoor radon Pennsylvania.
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A Report of the Surgeon General. Office on Smoking and Health, Center for Chronic Disease Prevention and Health Promotion, Centers for Disease Control, Public Health Service, U.S.
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