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, estimation of the internal radiation dose to the public due to tritium
was done using the dose conversion factors for the ingestion of HTO and organically bound tritium (OBT),
which were derived based on the ICRP metabolic model of hydrogen in the human body.

The ICRP

metabolic model is very simple and comprised of 2 compartments having biological half-lives of 10 and 40days, respectively.

Although the biological half-life of tritium water (HTO) in humans was examined inseveral cases such as accidental intakes or experimental administrations, actual data on the metabolism of
OBT are quite limited both experimentally and observationally. The objective of this research program isto reexamine experimentally the behavior of tritium 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.
The isotopic ratios (D/H) in breath air, blood serum and urine of participants administered D-labeled
glucose or D2O, together with controls, were determined by a mass spectrometer during one week.

The

temporal changes in (D/H) ratios in breath air of participants who ingested D-glucose were largely different
from those in 13C isotopic ratios in breath air after administration of 13C-labeled glucose in a previous study.
This implied probable differences in the behavior of carbon and hydrogen even in the same organic material.
The observed half-times of the excretion of D in both serum and urine in a short-term observation were 7.7-9.9 days, which were consistent with the reference values previously reported and also with the ICRP model
results.

Longer half-lives exceeding 1 month will be studied hereafter.

All procedures of the experimentwere approved by the IES Review Board for Human Subject Experiments and written informed consents
were obtained from all participants.
Table 1 Half-life of D concentration in breath (day)Administration

Half-life 1D2O

3.5×10-3D-labeled Glucose

2.6×10stHalf-life 21nd

Table 3 Half-life of D concentration in urine (day)Administration

Half-life

5.4

D2O

7.7

-D-labeled Glucose

9.9

Ingested tritium

Table 2 Half-life of D concentration in serum (day)Administration

Half-life

D2O

8.0

D-labeled Glucose

9.7

90% of FWT,

10% of FWT,

50% of OBT

50% of OBT

Compartment 1Compartment 2

C1

C2

Fig. 1 ICRP tritium metabolic model
C1: FWT compartment (T1/2=10 days)
C2: OBT compartment (T1/2=40 day).

1000

10001000

BAC100100

100

1010012345678100123Time (day)45678012345Time (day)Time (day)678Fig. 2 D concentrations in human breath, urine and serum, after oral administration of D2O and D-labeled glucose.
A: breath, B: serum, C: urine. ○: D2O, ×: D-labeled glucose.
40

1A35

B

0.9
0.8

30

0.7

25

0.6

20

0.5
0.4

15

0.3

100.2

50.1

00

123456700123Time (day)4567Time (day)Fig. 3 D and 13C concentrations in human breath, after oral administration of D- and 13C-labeled glucose
A: D-labeled glucose, B: 13C-labeled glucose.

1000

1000

AB

100

100

1010110510Time (day)15200102030

405060Time (day)Fig. 4 D concentrations after oral administrations of D2O and D-labeled glucose in serum and liver ofexperimental rats.

A: serum, B: liver. ○: D2O, ×: D-labeled glucose.