order to be able to compare environmental tritium measurements. The Commission d’ETAblissement des Méthodes d’Analyse (CETAMA), a French working group whose role is to improve the quality of measurements by organising collaborations between laboratories, has done some review work on tritium measurements. In practice, routine environmental monitoring in France currently only focuses on measurements of free tritium (HTO). CETAMA is now working to validate measurement methods for total organically bound tritium (intercomparison exercise 2009-2010). Measurements of nonexchangeable OBT (NE-OBT) are unlikely to be validated until at least 5 years from now. This type of routine measurement still raises metrological problems (the E-OBT and NE-OBT separation test is still unreliable, and analysis takes several days) and unanimous agreement has not been reached. In the opinion of CETAMA, further research is required to improve this measurement in order to better understand the various transfer factors in the environment. The working group agreed on the need to continue this work to validate and standardise measurement and sampling methods and protocols (“to be sure of what is measured”), and that this work should be carried out within an international framework. Nature of releases There is another open question – are there sources of tritium releases in organic form other than those from industries that synthetically create labelled molecules? The aforementioned IRSN report highlights the gaps that exist in knowledge regarding the presence of labelled molecules with high levels of specific activity, their behaviour and the consequences in terms of tritium accumulation. The IRSN feels that a key priority is to carry out metrology studies into the various physicochemical forms (speciation) in which organic tritium is liable to affect humans. For its part, AREVA considers that after more than 10 years operating with solvent in its plants, no tritium transfer has been observed from tritiated zones to nontritiated zones via the solvent. It further concludes, on the basis of concentration factors observed in algae, molluscs, crustaceans and fish, that the chemical form of tritium discharges is principally HTO. 6 IRSN, “Eléments de réflexion sur le risque sanitaire posé par le tritium”, 2009 Given the major diversity of tritiated organic molecules, the group agrees on the need for caution in conclusions and extrapolations and on the need to characterise the chemical speciation of discharges from potentially relevant sites. Health effects of tritium Relevance of “mean organ dose” Should the effects of beta radiation from tritium be reassessed? This question is raised by the fact that the tritium isotope has certain specific features. The electron path is very short (less than the diameter of a cell and even of a cell nucleus) and the ionisation density is high, which can cause cluster damage to DNA if the tritiated molecules get into the cell nucleus. Two further phenomena contribute to locally enhancing the effects of tritium – its in situ transmutation into helium and enrichment of water in the DNA hydration shell, converting it to tritiated water (referred to as “buried tritium” or the “isotope effect”). All these physicochemical effects cause lesions, which can in turn lead to DNA mutations. Although the dose distribution is relatively homogenous when the tritium takes the form of tritiated water, it isheterogeneous when it is incorporated in DNA or histones. The issue of the relevance of themean organ dose concept as a risk indicator therefore arises. In other words, doses calculated according to the conventional method (using the ICRP’s Sv/Bq conversion factors) could lead to an incorrect estimate of the risk. In comparing the studies on the biological and health effects, it would be useful to harmonise the methods used to estimate the dose at different scales (cells and organs), according to the form of the tritium, the exposure pathway, the length of exposure and the time before analysis. Further research into the biological effectiveness of tritium, in particular during various stages of pregnancy, is required in order to clear up these uncertainties and gaps in knowledge. In recent report6, the IRSN stated that “the dosimetric approach to risk is deemed to be robust and lists tritium as one of the least radiotoxic radionuclides,” but nevertheless suggested that “data is lacking on the metabolism and biological effects associated with
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