The estimation of annual limit on intake for tritiated food

Tritium incorporation into tissues and DNA of mice was studied after daily ingestion of tritiated food or tritiated water. The tritiated food used was a commercial preparation mixed with brine shrimp which had been reared in tritiated sea water. After ingestion of tritiated food or water for up to 22 d, the specific activity of tritium in tissues was measured as tissue-free-water tritium, tissue-bound tritium and DNA-bound tritium. In order to compare the tritium intake from food with that from water, 14C-glucose was added to food and drinking water. The specific activity of tritium of tissues obtained was then corrected by the specific activity of 14C in tissues in order to analyse the tritium incorporation from the same amount of ingested food and water. DNA-bound tritium after the ingestion of tritiated food was 4.6 times higher than that of tritiated water, while tissue-bound tritium was 2.2 times higher. The radiation dose to liver from tritium incorporated through food was two-fold higher than through tritiated water, which was mainly due to the high incorporation of tritium into DNA. Our results demonstrated that the dose calculation based on tissue-free-water tritium alone would underestimate the radiation exposure of the human population exposed to tritiated food. (author)