I appreciate the tremendous amount of work that has gone into preparing the draft publication and thank you for the opportunity to comment on the draft publication. The following comments relate to the section on radon (32. Radon).
Table C.8 contains effective dose coefficients (in Sv Bq-1) for individual nuclides of the inhaled radon progeny. The table also includes values for the unattached fraction of Bi-214. This differs from ICRP 137, which assigns no activity to the unattached fraction of Bi-214. Are the Po-218:Pb-214:Bi-214 activity ratios used for public exposure in homes different from those used for workplaces? I have not found any information on this question.
My recalculation of dose coefficients for radon progeny using the values in Table C.8 shows considerable differences to the corresponding values in Table 32.7, which are not solely due to rounding differences. I used the activity ratios given in ICRP 137. The unattached fraction of Bi-214 in Table C.8 was not considered.
Assuming that the coefficients in Table 32.7 are correct, the values given in Table C.8 need to be revised to achieve better consistency between the different calculation methods. The activity ratios of Po-218:Pb-214:Bi-214 used for atmospheres in home should be given.
In the draft publication, dose coefficients for radon are also expressed in the unit WLM (Working Level Month). This unit was developed to represent miners' exposure to radon and is commonly used in epidemiological studies on miners. It is a combined quantity that expresses the exposure of a miner when he spends 170 hours (monthly working hours) in an atmosphere with 1 WL (Working Level). 1 Working Level is the potential alpha energy concentration of 100 pCi/l (3700 Bq/m³) Rn-222 in equilibrium with its short-lived decay products (therefrom the transformation 1WLM=3.53 mJ.h.m-3). It should be considered whether this quantity is still up-to-date, especially for the characterization of radon exposure in dwellings. Epidemiological studies on radon in dwellings are rather based on radon concentration expressed in Bq/m3. Furthermore, the quantity WLM was not originally defined for exposure to thoron. Therefore, the quantity WLM is redundant in the context of the draft publication.
In this publication as well as elsewhere it is claimed that radon epidemiology and dosimetry are in good agreement. The ICRP epidemiological approach uses the occupational risk coefficient of 5E-4 per WLM originally derived from mining studies for estimating doses from residential radon in the general population. However, this risk coefficient is higher than that derived from indoor radon studies and appears to overestimate the risk from radon in homes to the general population. For this reason and others, the ICRP approach for radon in residential areas is subject to large uncertainties, and it is questionable whether it can be used for qualified estimates in this area.
Consideration of an example with regard to No. 4:
The arithmetic mean of radon concentration in the USA is 46 Bq.m-3 (WHO Radon Handbook). For a residence time of 7000 hours, this results in a radon exposure of 322 kBq.h.m-3. Using a conversion of about 9E-06 mSv/Bq.h.m-3 (rough value from Table 32.7), the average effective dose from radon in U.S. households is thus 2.9 mSv. With the dose conversion of 6.7E-6 mSv/Bq.h.m-3 (recommended value from paragraph 543), the corresponding average effective dose is about 2.2 mSv.
The U.S. has a population of approximately 332,000,000 people. According to the WHO Radon Manual, 15,400 to 21,800 people die annually from lung cancer caused by radon in homes.
ICRP 103, Table A.4.1, column 2 gives the nominal risk of lung cancer from external radiation as 114 per 10,000 people per Sv (Sv is the equivalent dose to the lung). Based on the values from ICRP 103, Table A.4.2, the lung cancer incidence risk is assumed to be approximately equal to the lung cancer mortality risk (approx. 111 per 10,000 people per Sv). Applied to the entire U.S. population, this results in 3785 cases per mSv equivalent dose. Using the tissue weighting factor for the lung of 0.12, this gives 31,540 lung cancer cases for an effective dose from external radiation of 1 mSv. In contrast, residential radon causes only about 15,400 to 21,800 cases in the United States. Comparing the actual number of cases caused by radon to those caused by external radiation, the average effective dose to the U.S. population from residential radon must be less than 1 mSv. This pattern is not unique to the U.S. population, but applies to other countries as well. The effective dose of 2.9 mSv resulting for the U.S. example with the coefficients from this draft overestimates the health effects of indoor radon. How does ICRP justify these higher dose levels attributed to indoor radon?
Minor Comments:
- Check paragraph 531. It consists only of table 32.6
- Check paragraph 530. The last sentence is incomplete.
- Reference in paragraph 533 not found.