Concentration Coefficients of Radioiodine in Different Chemical Forms
from Seawater to Fishery Products
Toshihiro SHIBATA, Yoshio ISHIKAWA, Yuichi TAKAKU, and Shun’ichi HISAMATSU
Department of Radioecology
Abstract
Radioiodine takes various chemical forms in the environment. Ion forms of both I- and IO3- were foundin the ocean for 129I discharged from the first Japanese commercial nuclear fuel reprocessing plant located inRokkasho. Since the concentration factor of iodine from seawater to marine products strongly depends onthe chemical form of iodine, it is necessary for realistic assessment of radiation dose from the discharged
radioiodine via marine products to use the concentration factor of each chemical form of iodine. This study
aims to establish the concentration factor of radioiodine in I- and IO3- for marine products (seaweed, shellfishand benthos). In FY 2014, 1) the concentration factors of I- and IO3- for shellfish (abalone, Haliotis discus
hannai) were measured using an iodine radiotracer and 2) the chemical form of stable iodine in abalone wasanalyzed by using X-ray absorption fine structure (XAFS) analysis.
The abalone samples were exposed to 125I- or 125IO3- in seawater using air-tight chambers. Exposures to125

I were carried out for 24, 48 and 72 h. Three abalone samples were used for each exposure, after which

each was dissected to obtain muscle and hepatopancreas tissues. The tissue samples were measured for 125I
concentration by using a NaI detector. The seawater in the chamber was also collected at the time of abalone
sampling, and 125I- and 125IO3- in it were separated by an anion exchange column followed by theradioactivity measurement. Concentration of 125I in both kinds of tissues was monotonically increased during
the expose and did not reach the equilibrium condition with that in seawater. Therefore, only the transfer rate
constant of 125I- or 125IO3- from seawater into each tissue was obtained by fitting experimental data to acompartment model, under the assumption that excretion rate constant from abalone into seawater wasnegligibly small. Excretion rate constant from the tissues to seawater was obtained by using the stable iodine
concentration in seawater and the tissues under the assumption that the stable iodine concentration did notdepend on the iodine in the food which abalone consume. The results showed that the concentration factor of125 -I to muscle tissue was comparable with that of 125IO3-. The concentration factor of 125I- to hepatopancreas

tissue was twice that of muscle tissue, and that of 125IO3- was quite small.
The analysis of chemical forms of stable iodine in hepatopancreas tissue of abalone samples by XAFS
showed that most of the iodine in this tissue was in an organic iodine form similar to seaweeds which are theprimary food for abalone.

4000

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100000010203040506070300

5000

4000

200

3000
2000

100

1000

00080

1020

Measured 125I concentration in abalone andseawater during
circlesandconcentrations

125 -I

openinFig. 250607080

circles

abaloneshow

muscle125

Measured 125I concentration in abalone andseawater during 125IO3- exposure. Open blue

exposure. Open blue

red

40

Exposed time (h-1)

Exposed time (h-1)

Fig. 130

125I concentration in seawater (Bq mL-1)

5000

6000
125I concentration in abalone (Bq g-1)

300

125I concentration in seawater (Bq mL-1)

125I concentration in abalone (Bq g-1)

6000

circles

Iandconcentrations

andopenin

red

circles

abaloneshow

muscle125

Iandhepatopancreas, respectively. Solid blue and red

hepatopancreas, respectively. Dashed blue andlines show estimated concentrations in muscle

red lines show estimated concentrations inand hepatopancreas, respectively. Green solidmuscle and hepatopancreas, respectively. Greensquares and yellow solid triangles showsolid squares and yellow solid triangles show

concentrations of 125I- and 125IO3- in seawater,concentrations of 125I- and 125IO3- in seawater,

respectively.

respectively.

NaIO3
NaI
Iodophenol
hepatopancreas of abalone

33150

Fig. 3

33170

33190
33210
X ray energy (eV)

33230

33250

Measured XAFS spectrums of NaIO3, NaI,
indophenol, and hepatopancreas of abalone.