W. Hofmann

Appendix B Analysis of Results of the Nuclear Track Detector Exposure at PTB in View of Cross Sensitivity to Radon/Thoron and the Determination of Decision Threshold and Detection Limit

This appendix describes a computational method for the analysis of the results of the exposure of nuclear track detectors at PTB to a mixture of radon and thoron activity concentrations. Both types of detectors (radon and thoron) were exposed to a series of Rn exposures (102, 500, 1500, 3000 kBq m h), some of these detectors were additionally exposed to one Rn level (1250 kBq m h). An additional background is assumed for all detectors: nR0 (for the radon detectors) and nT0 (for the thoron detectors). By using the formula

2. Health Effects of Radon Exposure

Radon has long been identified as a cause of lung cancer at higher activity concentrations and it was recognized as a human lung carcinogen by the National Institute for Occupational Safety and Health (NIOSH, 1971), the World Health Organization (WHO, 1986; 2009), and by the National Research Council (NA/NRC, 1999a). The main source of information on risks of radon-induced lung cancer has been epidemiological studies of underground miners (ICRP, 1993a), and more recent studies have provided informative data on risks at lower levels of exposure (Darby et al., 2005; 2006; Hunter et al., 2013; Lubin et al., 1997; NA/NRC, 1999a; Tomášek et al., 2008a; Walsh et al., 2010). These studies have shown significant associations between cumulative radon exposure and lung cancer mortality at lower radon activity concentrations found in homes. In the BEIR VI report (NA/NRC, 1999a), risk models that take account of effect modifying factors such as time since exposure, age, and exposure rate have been derived from the joint analysis of 11 cohorts of miners from China, Czech Republic, USA, Canada, Sweden, Australia, and France. Also more recently, a risk model has been derived from the joint analysis of the French and Czech miner cohorts associated with low levels of exposure (Tomášek et al., 2008a). Tomášek et al. (2008b) used these risk models to calculate the lifetime excess absolute risk (LEAR) for reference populations defined by the International Commission on Radiological Protection (ICRP, 2010). Considering a chronic exposure during adulthood, recent estimates of LEAR are significantly greater (by about a factor of 2) compared with previous estimates. As a result, ICRP now recommends a detriment-adjusted nominal risk coefficient for a mixed adult population of non-smokers and smokers of 8 10 per Bq h m for exposure to Rn in equilibrium with its progeny, i.e., 5 10 per WLM or 14 10 per mJ h m (ICRP, 2010). This new value is approximately double the previous nominal risk coefficient given in ICRP Publication 65 (ICRP, 1993a). It should be noted, however, that the LEAR estimate is dependent upon the background lung cancer rates assumed for the reference population and this strongly depends on the prevalence of smoking. In the joint analysis of underground miners described in the BEIR VI report (NA/NRC, 1999a), 6 out of the 11 cohorts had some smoking information. The analysis of these data showed that the relative risk (RR) of lung cancer with cumulative exposure to radon was linear for lifelong non-smokers and for current and ex-smokers. Assuming a RR model, the excess relative risk (ERR) per unit increase in radon exposure was higher among lifelong non-smokers compared with current and ex-smokers, although the confidence intervals overlapped. This suggests sub-multiplicative interaction between radon and smoking in causing lung cancer (i.e., less than the product of the individual risks from the two agents but more than the sum of the risks). However, the absolute risk of lung cancer per unit increase in radon exposure is much greater in smokers than in nonsmokers as smokers have much higher rates of lung cancer than non-smokers in the absence of radon exposure. Recently, a joint analysis of European epidemiological studies on uranium miners with smoking information was carried out (Hunter et al., 2013; Leuraud et al., 2011). As expected, the carcinogenic effect of radon exposure was confirmed even after adjustment for smoking. The results from analyzing the joint effects of radon and smoking indicated a sub-multiplicative interaction; the ERR WLM was greater for non-smokers compared with current or ex-smokers, although there was no statistically significant variation in the ERR WLM associated with smoking status. This is in agreement with the BEIR VI analyses (NA/ NRC, 1999a) and with the results from an updated analysis of the Colorado Plateau miner cohort (Schubauer-Berigan et al., 2009). In contrast, a recent nested case–control study of Czech uranium miners indicated that the combined effect from radon and smoking was closer to an additive than to a multiplicative interaction (Tomášek, 2013). This was shown only when a modifying effect of time since exposure was used. If the interaction is additive as opposed to multiplicative then this would lead to higher estimates of lifetime risks for the nonsmoking population. Journal of the ICRU Vol 12 No 2 (2012) Report 88 doi:10.1093/jicru/ndv005 Oxford University Press

Glossary: Definitions, Quantities, and Units

In contrast to other radiation measurements, the metrology of radon involves several rather sophisticated definitions, quantities, and units. Since these are rather uncommon, this glossary gives an overview about these special terms used in international standards and recommendations, technical descriptions, and scientific papers. General terms of statistics, metrology, and physics are not part of this glossary. The following definitions, quantities, and units are used in agreement with ICRU 85a, ICRP 103 (definition given in Annex B of ICRP 103, not from the glossary), ICRP 32, IEC 61577, and ISO 11665. In the special case that the definitions given in the above documents are not totally consistent or have need of further specification, e.g., modernization, this ICRU report aims to attempt to do so. The quantities describing the movement of air from the environment toward buildings are used in compliance with ISO 9972 and EN 13829:2000. Several more quantities, terms, or definitions are taken from ISO Nuclear Energy Vocabulary (Parts 1 and 2), the IAEA Glossary, the IEC’s International Electrotechnical Vocabulary (IEC 60050), the BIPMs International Vocabulary of Metrology, and also the ISO 17025. Nuclear data are taken from Monographie BIPM-5, while fundamental constants are based on CODATA evaluations. Note: The symbol Rn is used in the following text to refer to both, Rn and Rn. If a special isotope is named, it is done by purpose and the definition is only valid in this configuration.