There is very little tritium-specific data and the risk assessments are taken from calculations based on data on the hereditary effects of ionising radiation in general. Thus, based on the fact that there is no cell division in oocytes from the foetal period until fertilisation, British researchers calculated the risk of a woman passing on a radiation-induced anomaly 30 years after her mother ate Cardiff Bay fish containing OBT during pregnancy. The oocyte dose was estimated to by 2.7-5.4 mGy and the calculated risk value was an undetectable increase in risk. The handful of experimental studies performed in the USA on induced mutations (spermatogenesis) following chronic exposure to HTO gave results that were similar to those obtained with X-ray or gamma radiation exposure. However, reservations should be expressed as to the validity of cross-species extrapolation based on these experimental studies. Data regarding the potential induction of hereditary effects should be critically assessed and with great care. New approaches should be investigated, in light of the latest advances in biology. New tools in the fields of genetics and cellular imaging can be used to analyse the transmission of lesions and their consequences (by studying recessive mutations, non-coding regions that are important for verifying genome integrity, gene expression, etc.). In addition, genomics tools can be used to identify the transmission of a hereditary characteristic (not spontaneously apparent) through several generations of a family. In utero exposure The former Chairman of German radiation protection commission SSK presented and discussed experimental data on the effects of embryo exposure to tritiated thymidine and tritiated arginine (histone precursor) at the pre-implantation stage of pregnancy (in vitro experiments). Given the heterogeneous distribution and specific incorporation into DNA, tritiated thymidine is 1,000 to 5,000 times more effective than tritiated water in inducing harmful effects at the same level of applied activity. The effect is even more marked with tritiated arginine (factor of 10,000) and can be observed at lower levels of activity. Given mechanisms at work, this observation could be relevant to other cell types and systems with regard to mutagenicity. However, it should be noted that these in vitro studies performed at high levels of specific activities are not necessarily representative of in vivo situations. The CEA (Life Sciences Department) presented a summary of work into the in utero effects of tritium. Tritium (HTO or tritiated organic molecules) crosses the placental barrier fairly easily. As for other ionising radiations, beta radiation from tritium causes local apoptosis and mutagenesis, which can lead to tumours or functional consequences by negatively affecting organogenesis (the mechanisms of cell proliferation, migration and differentiation that are closely linked in an embryo). The central nervous system seems to be a particularly vulnerable target. Tritium concentration in this system is 3 to 20 times higher than in other organs, and at values of just a few cGy (roughly 1 GBq.L-1 of tritium), deterioration of cognitive functions can be observed, along with a reduction in the number of neural cells. Transfer of tritiated organic molecules to the foetus is a process of active transport and the molecules are preferentially incorporated into the DNA of cells that are actively multiplying. The CEA has concluded that the studies currently available are difficult to analyse because of their disparate nature and that further in-depth study is required into the effects of tritium (HTO and tritiated organic molecules) after exposure during in utero development. All members of the group agree that further research is vital in order to improve knowledge of the effects of tritium exposure on embryos and foetuses. Recommendations from the “Tritium Impact” working group The various recommendations issued by the group are summarised below. Clearly, the one key word that comes up repeatedly is (further) “research”. With respect to the environment, the group recommends the following (in order of priority): 1. Current work to validate and standardise measurement and sampling methods and protocols (“to be sure of what is measured”) should be continued and carried out within an international framework; 2. Appropriate environmental measurement campaigns should be used, with a scientific approach to clear up doubts and 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
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