Grande-Bretagne: Review of Risks from Tritium
(104 pages)

     The independent Advisory Group on Ionising Radiation has published a report reviewing the risks of exposure to tritium, a radioactive isotope of hydrogen. Tritium is used in scientific and medical research and it also has various industrial applications. Following an extensive review of scientific evidence on the risks from exposure to tritium, the Advisory Group suggests that the International Commission on Radiological Protection (ICRP) should consider increasing its radiation weighting factor for tritium from 1 to 2. Radiation weighting factors are used to calculate doses and risks from radiation exposures.
     Tritium is a radioactive isotope of hydrogen that decays by beta emissions with a maximum energy of 18.6 keV and a half-life of 12.3 years. It is formed through several processes, both natural and artificial, including nuclear fission and fusion power generation.
     The Advisory Group has examined biological evidence from published laboratory experiments with tritium in cell cultures (in vitro) and from animal experiments (in vivo). They have also reviewed the published evidence for effects on human health (epidemiology). The evidence indicates that tritium has a larger impact on biological systems than gamma rays or x-rays and its relative biological effectiveness (RBE) is greater than 1.
     This is the basis for the Advisory Group's recommendation that the RBE value for tritium should be taken as 2 and its suggestion that ICRP should consider increasing its radiation weighting factor for tritium from 1 to 2.
     Epidemiological data on risks associated with tritium exposure are not strong because most of the studies conducted worldwide involved small numbers of people. The report therefore recommends that consideration is given to an international collaborative epidemiological study of tritium exposed populations.
     In reviewing biokinetic models for tritium the report notes a wide range of animal and human data support the current ICRP models for radiation exposure and that models for tritiated compounds are under development. The report concludes by welcoming the development of new tritium models by ICRP and recommends that they be adopted for routine dose assessments when available.
     Professor Bryn Bridges, Chairman of the Advisory Group said, "A lot of work has gone into this report and I hope the International Commission on Radiological Protection will consider our suggestion. Tritium is not highly radioactive but it can become widely dispersed in the environment and we felt a special review of the evidence was necessary."
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