mollusc, crustacean and fish samples. ARCO highlights the fact that measurements performed on marine organisms in Cardiff Bay suggest that algae are a poor indicator for monitoring tritium contamination in marine fauna, since tritium concentrations were significantly higher (by a factor of over 10) in fish than in algae. Its position is that the choices made by IRSN and AREVA to take measurements in algae for monitoring purposes is not the most appropriate method for identifying concentration phenomena in marine organisms. ACRO also points to the very limited number of measurements taken around La Hague between 2000 and 2009 on edible marine produce (flat fish, crustaceans, molluscs etc.). With regard to the terrestrial environment, the French Atomic Energy Commission (CEA) presented the mechanisms by which tritiated water is incorporated into plants, based on work performed by the International Atomic Energy Agency. The CEA also reported the results of monitoring measurements performed at the Valduc site by the CEA and, in parallel but independently, by SEIVA, a local association. The levels of radioactivity in water produced in combustion of organic plant matter were found to be between the activity in airborne water vapour and the activity in groundwater. In the CEA’s view, these results do not reveal any phenomenon of concentration in the organic matter. According to the CEA, the IAEA calculations could be excessively conservative, by overestimating the free water concentration in plants. Finally, high concentrations of organic tritium have been measured in the sediment of water courses affected by discharges from the watchmaking industry, with the organically bound tritium (OBT) content varying with respect to HTO content in the river water by factors of between 1,000 and 10,000. By way of conclusion, the group considers that the only way to clear up doubts, assess the effect of the various factors at stake, in particular regarding the distribution of tritium in the different compartments (including organic matter in sediment) and to better define the free and organically-bound tritium components in living species is to use appropriate environmental measurement campaigns, with a scientific approach. In the marine environment, these campaigns must focus on a large enough number of edible marine produce samples from various trophic levels (flat fish, crustaceans, molluscs etc.). Some old publications drawing on environmental data (from the 1970s and 1980s) suggest that tritium could bioamplify in some aquatic trophic chains and that the nutritional pathway is predominant with respect to the direct pathway (water). Research has since become rather rare on this subject. International studies were recently analysed in a summary report by the IAEA (EMRAS programme 20062009) and a calculation model has been proposed (TRS No. 472 and Tecdoc No. 1616). These models now explicitly take into account tritiated organic matter formed from tritiated water (by tritium-labelling food), leading to no increase in concentration at higher trophic levels. However this does not prejudice any transfers and incorporation following the discharge of specific tritiated organic molecules. Summary report IRSN DEI 2009-05 states that “on the basis of currently available knowledge and with “normal” environmental activities, no phenomenon has been identified as liable to cause significant “bioaccumulation” over the long term and no measurement has pointed to this.” The same report does however mention that “for animal organisms, there is little data with respect to the complexity of the issue (number of processes involved, interactions and variability according to species, age and diet)”. The group wishes to highlight the still fragmentary nature of current knowledge on remanence and on tritium behaviour in sediment, and the need to use targeted multidisciplinary studies with rigorous protocols to provide experimental verification of the hypotheses put forward in older studies, in particular regarding the possible influence of the activity of microorganisms in aquatic sediments when organic tritium is remobilised in aquatic animal organisms. In general, the scientific data regarding the conversion of tritiated water into organic tritium along the food chain should be enhanced. Reliable quantitative estimates are required. Measurements In discussing tritium, it is essential to state what form it is in (HTO, HT, OBT) and when talking about OBT, it must be clearly specified whether we are talking about the food chain or a molecule that has been labelled for research purposes. One of the reasons for divergences in the measurement results and in the interpretation thereof comes from difficulties related to metrology and the representative nature of measurements and the lack of a standardised protocol. Methodological clarification is required in
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