Estimation of dietary 14C dose coefficient using 13C-labelled compound administration analysis

Carbon-14 released from nuclear facilities has been assessed to contribute significantly to the radiation dose that people are exposed to through the food chain. However, the current dose coefficient for members of public, which is the ratio of the 50-year committed effective dose to ingested 1Bq C-14, recommended by the International Commission on Radiological Protection (ICRP) is not based on experimental human metabolic data for C-14 in nutrients and diet. Therefore, to validate the coefficient, we administered C-13-labelled nutrients consisting of four amino acids, three fatty acids, and one monosaccharide to volunteers as substitutes for C-14 labelled nutrients and measured the C-13 concentration in various excreta samples. Although metabolic models were constructed from the excretion data, a significant fraction of administered C-13 was not recovered from some nutrients. The dose coefficients of C-14 in uniformly labelled Japanese diet, which were estimated under several assumptions about the unrecoverable fraction, varied from (6.2 +/- 0.9) x 10(-11) to (8.9 +/- 4.4) x 10(-10)SvBq(-1) and were approximately comparable to the current value of 5.8 x 10(-10)SvBq(-1) recommended by the ICRP. Further studies are necessary to elucidate the metabolism of C-14 in various nutrients in the unrecoverable fraction.