Advice On Risks From Tritium
Theindependent Advisory Group on Ionising Radiation has published a reportreviewing the risks of exposure to tritium, a radioactive isotope of hydrogen. Tritiumis used in scientific and medical research and it also has various industrialapplications. Following an extensive review of scientific evidence on the risksfrom exposure to tritium, the Advisory Group suggests that the InternationalCommission on Radiological Protection (ICRP) should consider increasing itsradiation weighting factor for tritium from 1 to 2. Radiation weighting factorsare used to calculate doses and risks from radiation exposures.
Tritium isa radioactive isotope of hydrogen that decays by beta emissions with a maximumenergy of 15.6 keV and a half-life of 12.3 years. It is formed throughseveral processes, both natural and artificial, including nuclear fission andfusion power generation.
The Advisory Group has examined biological evidence frompublished laboratory experiments with tritium in cell cultures (in vitro) andfrom animal experiments (in vivo). They have also reviewed the publishedevidence for effects on human health (epidemiology). The evidence indicatesthat tritium has a larger impact on biological systems than gamma rays orx-rays and its relative biological effectiveness (RBE) is greater than 1. Thisis the basis for the Advisory Group's recommendation that the RBE value fortritium should be taken as 2 and its suggestion that ICRP should considerincreasing its radiation weighting factor for tritium from 1 to 2.
Epidemiologicaldata on risks associated with tritium exposure are not strong because most ofthe studies conducted worldwide involved small numbers of people. Thereport therefore recommends that consideration is given to an internationalcollaborative epidemiological study of tritium exposed populations.
In reviewing biokinetic models for tritium the report notesa wide range of animal and human data support the current ICRP models forradiation exposure and that models for tritiated compounds are underdevelopment. The report concludes by welcoming the development of new tritiummodels by ICRP and recommends that they be adopted for routine dose assessmentswhen available.
ProfessorBryn Bridges, Chairman of the Advisory Group said, " A lot of work has goneinto this report and I hope the International Commission on RadiologicalProtection will consider our suggestion. Tritium is not highlyradioactive but it can become widely dispersed in the environment and we felt aspecial review of the evidence was necessary."