The International Atomic Energy Agency welcomes very much the efforts of the ICRP to include considerations on Protection of the Environment into the Radiation Protection System. It is very much appreciated that ICRP provides the opportunity to comment on the “Draft Report for Consultation: Protection of the Environment under Different Exposure Situations”. The following comments are made:
ICRP recommends DCRLs for benchmarking exposures to Reference Animals and Plants. DCRLs were derived in ICRP 108 as “bands of dose within which certain effects have been noted, or might be expected, and then to select a band to serve as what is termed a derived consideration reference level”. The DCRLs have been largely derived on an analysis of deterministic radiation effects; such effects are usually characterized by a threshold. This suggests that, if at all, only negligible radiation effects below the lower band of the DCRL can be expected and that the lower band of the DCRL can be considered as a kind of threshold.
The document suggests the optimisation of exposures to RAPs even below the lower end of the DCRL. However, optimisation in the sense of radiation protection is only applicable, if the underlying dose-effect relationship is linear and has no threshold (as it is assumed for humans). If a threshold exists, efforts to further reduce exposures below the threshold will not result in a benefit with regard to the reduction deleterious effects.
Environmental Reference Level (ERL)
The document suggests the ERL, which is below the lower band of the DCRL: this is understood as an equivalent to the dose constraint that is applied for humans.
It is questionable whether this additional level is really needed. The bands of the DCRLs have been derived in a way that below the lower value of the DCRL, no or only negligible effects have to be expected. Further reduction of doses rate would then not result in fewer effects.
To consider exposures from more than one source, it could be simply recommended that multiple sources should be taken into account when estimating dose rates.
Reference animals and plants (RAP) and representative organisms (RO)
In the radiation protection system, the concept of the reference persons is applied to define characteristics (age, size, breathing rates, metabolism of radionuclides, etc.) that are needed to estimate external and internal exposures. Similarly, Reference Animals and Plants define the factors (mass, size and concentration ratios) needed to estimate exposures to biota.
However, whereas the representative person defines living habits of exposed persons (intake rates, location of residence, shielding factors, etc.), the definition of representative organism remains ambiguous. Obviously, ROs are defined through the function of species in a specific ecosystem. In so far, the definition of ROs is based on assumptions on the importance or relevance of an organism type for an ecosystem. Criteria to decide on the representativeness of organisms in ecosystem have not been achieved yet, so it remains unclear how this could be applied in practice.
In view of the enormous variability of ecosystems and habitats, it is believed that the definition of ‘Representative Organisms” requires further efforts to achieve an approach that can be smoothly integrated into the radiation protection system.
A way out might be to define the reference animals and plants in a broader way so that they cover a wider range of species rather than well-defined RAPs (e.g. deer, rat).
Representative areas for estimating dose rates
Populations, communities and ecosystems – the objects of protection - may occupy large areas. Therefore, it would be useful to discuss in more detail how to average in space and time in order to derive representative environmental concentration for the use of estimating dose rates to RAPs.
It could be considered to give also reference to the IAEA Safety Fundamentals (IAEA: Fundamental Safety Principles, IAEA Safety Standards Series No. SF-1, Vienna, 2006) where Principle 7 (Protection of present and future generations) says: “People and the environment, present and future, must be protected against radiation risks”.
Inside Figure 3, the term “potential dose” is used for planned exposure situations. This term might be confused with the term “potential exposure” which is used in ICRP 103 for exposures that are not planned, but that can be anticipated under e.g. accidental situations. However, this is probably not the meaning in Figure 3. The meaning in Figure 3 is understood as “Expected dose under normal operation”.
In planning for emergencies, this paragraph suggests the “examination of protective strategies” (704/705) for the purpose of optimization. This term may be easily confused with “protective actions” that may have to be taken to prevent undue exposures to humans in emergency situations.
It is felt that the document would benefit from some numerical examples that provide exposures to humans as well as for RAPs for the same activity concentrations in the environment. This could help to put exposures into a common context.