Thank you for the opportunity to comment on this draft document. While the bulk of this work is welcomed and likely to prove beneficial we do have one major concern and also several minor suggestions.
The principal concern relates to the practical implications for the use of “reference biokinetic models” and how this is incorporated into the definition of “effective dose” and the use of the concept of “dose of record”. It is recognised that these concepts were discussed in ICRP publication 103; however, they were not mentioned within ICRP publication 60, which is the basis of the currently used system of dosimetry. This perceived change of emphasis or tone could have potentially significant, confusing and detrimental consequences for operational dosimetry.
In particular we are concerned about the situation when monitoring data obviously conflicts with the expectations from reference models. Some of these concerns are illustrated below:
(You will appreciate that we are suffering considerable confusion as to the reasons, purpose and value of these proposals, which will inhibit their practical implementation.)
The current practice is to refer to ICRP dosimetry-models and anthropomorphic-models as fixed references with no associated uncertainty; latest published ICRP biokinetic models are used as default references; these are only departed from if there is evidence to indicate they are invalid for a specific investigation and more appropriate alternatives are available (either from published sources or by local investigation). The use of non-ICRP models are subject to standard scientific scrutiny and peer-review processes. The results of this process are recorded as “effective dose”. It is not clear how the latest proposals would improve on this arrangement. It is also unclear why the quantity “effective dose” now seems to be unusable if non-ICRP Reference Biokinetic models are used.
Para 207: Wounds: what would be the dose quantity recorded for intakes via wounds? How would this be compared to dose limits and estimates of “effective dose” from other exposures?
Para 229: Medical Intervention: The same questions as for wounds apply for dose assessments post medical interventions.
Para 245(a) selection of sex-specific biokinetic model: it is not clear why a sex-specific model is recommended to calculate intake, which is then compared to a sex-averaged dose coefficient.
Para 260: include ‘nose blow samples’ as well as ‘nasal smears’.
Paras 263 – 266: air samples: while published studies (and experience) have reported poor correlations between intake estimates based on PAS and those based on bioassay it is noted that these studies have not appeared to have considered the relative uncertainties in any detail. The estimate of uncertainty in bioassay-based estimates for low or chronic doses is difficult and their significance cannot be discounted. For this reason it would be an overly strong comment to state that bioassay should be preferred to PAS at low level doses. It would be more reasonable to state that the relative reliability and accuracy between these techniques for low doses is not well known, and this lack of knowledge should be taken into account when planning monitoring programmes.
Para 313: Detailed evaluation of doses: “At installations where workers have the potential to be exposed to doses higher than 1 mSv… information should be gathered on the physical and chemical characteristics of the inhaled or ingested radionuclide…” It is noted that most facilities – particularly those handling actinides – will have a potential for doses > 1 mSv. While it would be nice to have detailed information for all such facilities it is very unlikely to be practicable or cost effective in practice. This paragraph could be re-drafted to be applicable where doses are likely to be > 1 mSv; or to give greater clarity as to the level of detail required of the materials, and to how this level of detail changes with expected levels of dose.
Para 329: correction for dietary intakes in excreta: we would urge caution in this – excretion rates from dietary contributions are highly variable, subtracting the presumed contribution from bioassay measurements should only be done when there is clear evidence to support it.