Metabolic and Dosimetric Study to Estimate an Annual Limit on Intake for Organic Tritium

A series of experimental investigations in rats on metabolism and dosimetry of tritium in various chemical forms(water, amino acids, monosaccharide, fatty acids and nucleoside) have been performed in our laboratory. Based on these experimental results, the relative radiotoxicity of each tritiated compound was assessed. An average radiation dose to various tissues was used as an index to assess their relative radiotoxicity. The average doses were, respectively, higher by a factor of 2.3 – 5.2 for tritiated amino acids, 1.4 – 3.2 for tritiated fatty acids, 1.3 for tritiated glucose, 1.7 for tritiated thymidine, than those from tritiated water. Thus, it was estimated that the tritiated organic compounds is about 1.3 to 5.2 times more radiotoxic than tritiated water. From the result of present study, we propose that an Annual Limit on Intake(ALI) for organic tritium should be 5 times smaller than that for tritiated water currently recommended by the ICRP.