Evaluation of Guidelines for Exposures to Technologically Enhanced Naturally Occurring Radioactive Materials (1999) / Chapter Skim
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8 Indoor-Radon Guidelines and Recommendations
8 Indoor-Radon Guidelines and Recommendations
Pages 157-182
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From page 157... ...
or becquerels per cubic meter (Bq/m3~; and 1 pCi/L is equal to 37 Bq/m3. Concentrations of radon decay products (RDPs)
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From page 158... ...
In SI units, 1 WLM is approximately 3.5 mJh/m3. PATEIWAYS OF HUMAN EXPOSURE Inhalation is the principal route of radon exposure of humans.
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From page 159... ...
The main source of quantitative information on the risks posed by radon exposure is the epidemiologic studies of miners which uses data on thousands of occupationally related lung cancers among many diverse groups of miners. The epidemiologic evidence of the induction of lung cancer after inhalation of radon comes from several cohort and case-control studies of underground miners, particularly uranium miners.
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From page 160... ...
, ICRP assumed that the risk coefficients for residential indoor exposures would be 80% of those for mine exposures. Second, because of potential differences in breathing rate and the unattached fraction between residential and mine exposure conditions, ICRP assumed that the observed dose of alpha radiation per unit of cumulative radon exposure for the general population is only 80% of that for miners.
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From page 161... ...
In the first, age-specific baseline lungcancer mortality was adjusted by eliminating projected deaths due to an average background radon exposure of 0.24 WLM per year, reducing the lifetime risk estimates by about 10%. The second was based on differences in dose to the bronchial epithelium per unit of radon-progeny exposure in mines and homes due to a number of physical and biologic factors that are expected to differ in the two environments.
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From page 162... ...
162 INDOOR-RADON GUIDELINES Table 8.1 Comparison of principal risk-projection models for radon and lung-cancer Feature NCRP ICRP BEIR IV Form of model Attributable-risk Relative-risk Relative-risk Time-dependent Yes; risk declines No exponentially after exposure Lag Sy toy Sy Yes; risk declines as time since exposure lengthens Effect of age at No effect of age at Threefold increased No effect of age at exposure exposure risk for exposures exposure before age of 20 y Age at risk Risk commences at ageof40y Dosimetry Increased risk for adjustment indoor exposure Relative risk does Lower risk at age not change with age of 55 y and older Decreased risk for No adjustment indoor exposure Risk coefficient 10 x 10-6/y per WLM Excess relative risks: Excess relative risk 1.9%/WLM at ages of 2.5%/WLM but 0-20 years and modified by time 0.64%/WLM for since exposure ages 21 years and above Source: National Research Council (1991)
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From page 163... ...
. The assumption underlying the EPA estimates of radon risk by smoking category is that radon risk varies in proportion to smoking risk (radon and smoking act multiplicatively in causing lung cancer)
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From page 165... ...
Among cohorts with tobacco-use information, the slope of the radon exposure-response function for never-smokers was 3 times that for smokers, indicating a much greater risk for never-smokers relative to their background risk of lung cancer from all causes. Assuming that the miner-based findings apply to residential radon exposure, the study estimated that about 9% of all lung-cancer deaths among residents of single-family dwellings in the United States could be attributable to indoor radon exposure.
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From page 166... ...
It also stated that exposures just below the remedial action level might not be acceptable to some individuals, who could of course try to reduce their exposures further. The assumption by NCRP of an excess risk of death from lung cancer of 2% posed by a lifetime exposure of 2 WLM was based on the available underground-miner epidemiologic data at the time and on the attributable-risk projection model (NCRP 1984b)
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From page 167... ...
NCRP (1984c) 300 220a 305b 360C 350 460d 230 130 167 aBased on BEIR IV model adjusted by subtracting projected deaths due to average background radon exposure of 0.24 WLM/y and adjusting risk factor from occupational exposure to general public with a factor of 0.7.
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From page 168... ...
of 0.02 WL. The EPA radon action level of 4 pCiLL (equivalent to 0.02 WL at 50°/O equilibrium of the radon decay products)
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From page 169... ...
EPA has emphasized several priorities regarding indoor radon: target the highest-risk areas first, promote radon-resistant new construction, support testing and mitigation in connection with real-estate transactions, use information and motivation programs to promote public awareness, and develop a coordinated research plan for radon-related issues. As previously discussed, EPA has relied primarily on relative-risk projection models to estimate radon risks to the public (National Research Council 1988~.
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From page 170... ...
. The principle of justification is used to set action levels at which intervention would almost always be justified to reduce radon exposure.
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From page 171... ...
The main IAEA recommendation is that the optimized action level related to chronic exposure involving radon in dwellings should fall within a yearly average 222Rn concentration of 200-600 Bq/m3 in air. For the optimized action levels, account should be taken of the benefits and costs assessed in the remedial action plan.
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From page 172... ...
· To have national authorities provide information to the public on radon exposure, risk, and available remedial measures. Other Various countries' and organizations' current recommendations for action levels for existing houses and for upper limits (bounds)
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From page 176... ...
176 INDOOR-RADON GUIDELINES o C~ |
From page 177... ...
GUIDELINES FOR EXPOSURE TO TENORM o ._ ct =0, ce o ·s ._ ct ~ v, c, ._ o 00 E~ ~q o ._ e.
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From page 179... ...
Although occupancy rates of schools are lower than those of dwellings, some countries have adopted the same action levels for both. In Switzerland, the reference level of 400 Bq/m3 for schools is lower than the legally enforced 1,000 Bq/m3 limit for dwellings but is equal to the level above which remediation of homes is recommended.
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From page 180... ...
b Country or Aboveground Schools Status Organization Workplaces Australia 1,000 1,000 Advisory based on IAEA recommendations Austria 400 400 Existing advisory 200 200 New advisory Canada None 800 Advisory Finland 400 400 Legally enforced Germany None 250 Advisory Ireland None 150 Advisory Luxembourg 150 150 Advisory Netherlands 20 20 Advisory Norway 800 800 Legally enforced Sweden 400 400 Existing advisor 400 400 Legally enforced, new Switzerland 3,000 400 Legally enforced United Kingdom 0.01 WL in any 8-h period Legally enforced US EPA None 150 Advisoly IAEA 1,000 1,000 Advisor ICRP 500-1,500 500-1,500 Advisory aColgan and Gutierrez (1996)
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From page 181... ...
· EPA's current estimates of lung-cancer risk associated with indoor radon exposures are based on the BEIR IV report and later adjustments. EPA risk estimates related to domestic radon exposure are 1.6 x 10-3 for never-smokers and 3 x 10-2 for smokers at 1 WLM (equal to 4 pCi/L, which is recommended as the remedial action level)
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From page 182... ...
182 INDOOR RADON GUIDELINES the age dependence of risk, extrapolation to females, the relationship between radon risk and smoking risk, and the impact of risk extrapolation of the different levels and types of particles in uranium mines and in homes.
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