organic tritium in situations of environmental exposure” and that experimental radio-biological studies should be carried out on various forms of OBT, using a specially adapted technical set-up, in the context of Europe-wide cooperation. The group agrees on the need to use up-to-date methods to gather further knowledge on the effects of tritium, in order to comprehensively characterise the physico-chemical forms used (covering a concentration scale that would include industrial discharges) and the biological mechanisms at work, focusing not only on aspects relating to carcinogenesis, and looking at age at the time of exposure and at differences between accident-related and chronic exposure. WR and RBE For reference, the radiation weighting factor (wR) is used in health physics to take into account the effect of radiation type in inducing long-term stochastic effects such as cancer or hereditary effects. Opinions were divided within the group with regard to the need to increase the value for tritium (currently 1). In opposition to the findings of the 2007 AGIR report in the UK and the EURATOM treaty “Article 31 experts” (cf. 2007 Scientific Seminar), the ICRP recently confirmed its choice of a radiation weighting factor of 1 for tritium and low-energy beta emitters, taking into account on the one hand the uncertainties around the issue and on the other hand, purely forward-looking objectives for the radiation protection system and the priority to be placed on optimisation and dose constraints. The IRSN is of the opinion that the RBE of tritium for stochastic effects, on which the weighting factor wR is based, is closer to 2 than 1, but considers that choosing a weighting factor wR of 2 rather than 1 would only have a minor significance in routine situations and should only be used in assessing individual risks. This opinion is not shared by the associations ACRO and ANCLI, which are arguing for a weighting factor of 5 for the sake of precaution. No consensus was reached on this issue within the group. Epidemiological studies A literature review shows that studies on exposed workers reveal that risk of cancer is not increased. However, the studies are limited in their robustness due to the insufficient statistical power and/or lack of information on tritium dose. It should be noted that the tritium doses logged were of the order of ten mSv, which implies that very large cohorts would be needed to demonstrate a statistically significant difference between the exposed group and control group. A coordinated international approach based on standardised dosimetric assessments would be required in order to make progress in this field. Within France, a vital first step would be to set up a tritium database to enable tritium to be taken into account in epidemiological studies. Furthermore, there have been very few studies into the effects of tritium on the population. The studies that do exist are geographical and not very informative. In general terms, international multi-centre studies would be the only potential way to achieve statistical power that is large enough to offer a relevant response to the epidemiological questions. For populations living close to nuclear facilities, the issue of statistical power in the epidemiological studies is more acute when the doses are lower. The issue of the epidemiological detectability of tritium risk is raised and this highlights the potentially relevant role that molecular studies with biomarkers could play. Currently, the existing epidemiological studies on tritium in populations have been shown to be of no practical relevance. This does not mean that epidemiological monitoring is unnecessary – it is essential, as for any site posing an industrial hazard. The group agrees on the importance of assessing the feasibility of epidemiological studies in French workers, since it would be useful to gather data on tritium exposure and to process this data in a coordinated manner alongside other ongoing studies around the world. Hereditary effects No increase in hereditary effects have been observed to date in the human race, either in the descendents of people exposed to radiations (Hiroshima and Nagasaki survivors; radiation-treated patients or workers exposed to ionising radiation) or in regions with high natural background radioactivity. Quantitative risk assessments are therefore based on indirect data – firstly, on the frequency of spontaneous mutations in the germline of the human race and secondly, on experimental studies tracking the descendants of radiation-exposed rodents.
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