Tritium Metabolism in the Human Body
Tsuyoshi MASUDA, Kensaku MATSUSHITA, Yasuhiro TAKO, Yuji NAKAMURA
Department of Environmental Simulation
Abstract
In the radiation safety assessment prior to the construction of the first commercial spent nuclear fuelreprocessing plant in Rokkasho, Japan, the internal radiation dose to the public due to tritium was estimated using
the dose conversion factors based on the ICRP metabolic model of hydrogen in the human body. The ICRP
metabolic model is very simple and is comprised of a free water tritium and organically bound tritium (OBT)compartments having biological half-lives of 10 and 40 d, respectively.
Although the biological half-time of tritium water (HTO) in the human body was examined in several casessuch as accidental intakes or experimental administrations, actual data on the metabolism of OBT are quite limited.
The objective of this research program is to establish experimentally the metabolism of tritium including OBT in
the human body for more realistic dose estimation. In the experiment, the stable isotope of hydrogen, deuterium(D), was used as a substitute for tritium.
In FY 2011, urine, breath and serum samples were collected from volunteers administered with D-labeled
glucose or D2O up to 16 weeks after the administration, and analyzed for the isotopic ratios (D/H) with a mass
spectrometer. Since D resulted from decompose of the D-labeled glucose in the human body entered to free water
which is a relatively large pool of hydrogen, the decomposition rate of glucose is not directly monitored from thosesamples collected. To obtain decomposition rate of the administered glucose, 13C-labeled glucose was also
administered to the same volunteers, and 13C isotopic ratios in their urine and breath samples were analyzed.
The D isotopic ratios in the urine and breath samples increased after the administrations, and then decreased
with an exponential function, while the 13C isotopic ratios decreased with two exponential components with thefirst short half-time and the second long one. Since the range of D isotopic ratio between increasing level just after
the administration and background one was one order of magnitude narrower than that of 13C isotopic ratio, thelong component was not observed for the case of D. Half-times of the D isotopic ratios in urine and breath after
D-labeled glucose administration were 6.4 and 6.0 d, which were similar with 7.4 and 7.2 d after D2O
administration, respectively. The half-times for D2O intake were comparable with 5-13 d in the literature, andslightly shorter than 10 d in the ICRP model. The observed short and long half-times of the 13C isotopic ratios afteradministration of 13C-labeled glucose were 1.3 d and 2.1×102 d for urine and 1.1 d and 1.4×102 d for breath,respectively. All procedures of the experiment were approved by the IES Review Board for Human Subject
Experiments, and written informed consents were obtained from all volunteers.

Table 1 Half-life of D ratio (day)Table 2 Half-life of 13C ratio (day)Administration
13
D, C labeled glucose
D2 OComponent
1st
2nd

Urine
6.4

Breath
6.0

7.4

7.2

Urine
1.3
2
2.1×10Breath1.1
2
1.4×10

A

B

C

D

Time after administration (day)Time after administration (day)Fig. 1 D concentration (D/H) after D labeled glucose and D2O administration
A, B: D and 13C labeled glucose administration．
C, D: D2O administration
A, C: urine, B, D: breath．Inserted panels: enlargement of data from day 0 to 7.

A

B

Time after administration (day)Fig. 2Time after administration (day)13

C concentration after 13C labeled glucose
A: urine, B: breath. Inserted panels: enlargement of data from day 0 to 7.