| Stockholm, 13 September 2006
Comments and suggestions for the forthcoming recommendations by the ICRP
The scientific basis
The document should give much more direct references to the underlying scientific basis. The reasons for this includes pedagogical aspects but also those of credibility.
There is a general problem with the uncertainties of most numbers in the draft document: With a numerical estimate follows a severe limitation if no uncertainty is related to the value.
The use of “constraint”
The status of the concept “constraint” is unclear: In some contexts in the present draft it seems
like “constraint” is an alternative dose limit which has probably not been the intention. The confusion arises because of phrases like “…constraint is the fundamental level of protection…”.
Perhaps the origin of this confusion is of linguistic character with different interpretations relating to the word “fundamental” and where non-native English speaking people refer to some “basic thinking and practices” rather than a “limit” (the word “basic” appears somewhere in the draft as a “synonym” to “fundamental”). Regardless of the origin of the problem, the status of the concept of “constraint” is unclear.
§67 Equilibrium between mutation and selection
It is stated that the new approach will leave the equilibrium between mutation and selection and instead truncate at the level of second generation risks. This change is unfortunate as it creates a contradiction with the ambition to radioprotect non-humans at a population level (biodiversity). As the suggested change stands it follows, as an inadvertant understatement, that only human individuals are of interest whereas the gene pool dynamics (many generations into the future) is more or less is irrelevant. This has probably not been the intended message as an induced mutation (harmful or beneficial) theoretically can persist for 10 000 years or longer into the future.
In practice the irrelevance of “far into the future” may in some sense be true but it is clearly in conflict with ambitions such as the Swedish environmental goal which states that biodiversity shall be protected against harmful effects of radiation. It should be noted that ambitions to radioprotect biodiversity requires the concept of evolution driven by mutations and selection.
The bottom-line is that the approach with equilibrium for mutations and selection should be kept. Leaving the previous equilibrium (mutation-selection) approach leads into a dead end where one will find typological thinking and “intelligent design” as the basis for discussing radioprotection of the environment (gene pool dynamics).
§72 Table 2 and §114 Table 4 regarding gonad/genetic weighting
Table 2 gives about 3 % of the total risk as heritable whereas wT (gonads) in table 4 gives a value of 8 %. These two values may indicate an inconsistency but perhaps reflect 5 % being related to cancer risks for testis or ovaries. To avoid any misunderstanding, it would be of value to have a clear statement (footnote is fine) in Table 4 saying something like “In turn 0.05 of this value for wT reflects the corresponding cancer risks”.
In the legend of Table 2 it should also be stated whether “cancer” is referring to incidence or lethality (an understatement of the word “detriment” is not clear enough to many readers).
§86-87 1 Sv vs. 100 mSv
In §86 the text includes ”…at doses of the order of 1 Sv…” and a threshold of around 0.5 Sv is mentioned. Then as a conclusion in §87 the dose level of around 100 mSv is mentioned. This discrepancy is not possible to understand. Perhaps a comment should also be made regarding the time aspect (high vs. low dose and dose-rate)
§104 Radiation weighting factor for neutrons
The function as described by Eq. 4.3 seems to be a clear improvement (but where are the underlying data?) compared to the step function used in ICRP60. It should be noted however that there is a clear discontinuity at the 50 MeV point
As 50 MeV is far above “fission energies”, this observation is probably of minor interest to most readers and at most an esthetic discrepancy. If, however, there indeed is a need (fundamental science) for weighting for 50 MeV energies it should be noted that the related error probably is quite large (20-30 %?). Mathematically the problem can be circumvented in several different ways, for instance by manipulating the derivative at the 50 MeV point (resulting in “uglier looking functions”) or by inserting another function for the interval 50 MeV-500 MeV.
Besides this specific academic aspect of the numbers see also the general comment above relating to numerical uncertainties.
§114-120 Tissue weighting factor for breast (gender problem)
The tissue weighting for breast and the related difference between men and women is strange (wrong?) for several reasons. In §22 it is stated that the Commission uses gender-averaged tissue weighting factors. This is then done in Eqs. 4.5-4.6 but the breast has been included in these equations as if it were being radiologically equivalent for men and women.
This can hardly be the case considering the experiences from Japanese atomic bomb survivors. What was found was that women who had been exposed before puberty had a much higher (a factor of 15 or so) risk for breast cancer later in life compared to women who had been exposed at age 18 or later. The underlying mechanism is certainly related to the cell division that follows with the development of the breast. This has no equivalence in men.
As table 4 gives the same tissue weighting factor (0.12) for men and women the question arises whether this is indeed meant to be the same. As it seems now, instead an average gender (as opposed to gender average) approach has been taken. If this is the case it should be explained because the reader may wonder if the underlying weighting factor actually was 0.24 for women and 0 for men (and the sum then divided by 2). If instead the weighting factor for women indeed was estimated to be 0.12 (and essentially zero for men) the tissue weighting calculation for breast here would be wrong by roughly a factor of 2.
If an average gender approach was taken, consistency would also require an average prostate and uterus weighting factor for both men and women (why then separate the genders at all?).
It is thus important that this gender issue is clarified – especially the references and reasoning relating to the tissue factor for breast.
§157-§158 Types of sources vs. groups of sources
It is clear what is meant by “types of sources” whereas “groups of sources” perhaps could be better explained.
§351-§357 Protection of the environment
This section is philosophically the most dramatic change compared to ICRP Publication 60.
Since the scientific basis for this issue is under development more effort should be taken
in paragraphs 19 and 20 to explain how radioprotection of humans as well as non-humans is to be integrated as a general framework. Clearly no scientifically based recommendations for the radioprotection of the environment can be made at this stage. In order to avoid any misunderstanding (regarding the “recommendation status”), it may therefore be advisable to
place Chapter 10 as a separate appendix or alternatively integrate the text as a separate section of chapter 1.
The ideas expressed above are my own and should not be a burden to the academic background I have (see below). If I misinterpreted certain points - please disregard the corresponding comments.
PhD, Associate Professor (Medical Radiation Biology, Karolinska Institutet)
MSc (Nuclear Chemistry and Biochemistry, Royal Institute of Technology)
Home address: Frejgatan 46A, 4tr, SE-113 26 Stockholm, Sweden