Concentration Coefficients of Radioiodine in Different Chemical Forms
from Sea Water to Fishery Products
Masaomi TAKAHASHI, Yuichi TAKAKU, and Shun’ichi HISAMATSU
Department of Radioecology
Abstract
Radioiodine takes various chemical forms in the environment. Ion forms of I- and IO3- were found inocean 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 on thechemical 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 2012, 1) the concentration coefficients of I- and IO3- for green algae (Ulva pertusa) weredecided using an iodine radiotracer and 2) the chemical form of stable iodine in U. pertusa was analyzed byusing X-ray absorption fine structure (XAFS) analysis.
The concentration coefficient of I- or IO3- for U. pertusa was measured with iodine radiotracer (125I).
The seaweed samples were incubated for 3 d at 15C in the seawater with added 125I as I- or IO3-. The
biological activity of the seaweed samples was checked by 13C absorption experiment. Since the biologicalactivity 3 d after the start of the incubation was lower than that before, we used the data for 2 d after the start.
The concentration of 125I in U. pertusa samples increased with the period of incubation in both forms. The125

I concentration in U. pertusa samples exposed to 125I- was much higher than that for 125IO3-. The 125I

concentration in seawater in the incubation bottle decreased during the exposure experiment relative to the125 -I concentration. The concentration factor of 125I- for U. pertusa was estimated to be 140 with a

one-compartment dynamic model considering decline of 125I- concentration in seawater, while that of IO3was ~8. Those results showed that the iodine concentration coefficient of U. pertusa strongly depends on thechemical form of iodine.
Since XAFS analysis of chemical forms of stable iodine in the natural U. pertusa samples was hard todo due to the low iodine concentration, a U. pertusa sample was incubated in seawater with added I- to get aniodine concentration of 5 g g-1 seawater (total iodine concentration in natural seawater is approximately 50ng g-1). The XAFS analysis of the incubated seaweed sample showed that iodine in the sample consisted of34% I- and 66% organic iodine.

IO3-I concentration in Ulva pertusa

I125

10000
5000

1500
1000

102030Times (h)40500

50020010125200I concentration in sea water

2030Times (h)

50125

I

I concentration in sea water

8040150001020304010050050010Times (h)18000

Total concentration of 125I

16000
14000
12000
10000
0102030
Times (h)

2030

4050

Times (h)Total concentration of125
I (Bq)

Total concentration of125
I (Bq)

40-1

Concentration of120(Bq g )

I

125

160

125

2000

00-1

I concentration in Ulva pertusa

2500
-1

Concentration of-1(Bq g )Concentration of15000(Bq g )

125

3000

0Concentration ofb3500(Bq g )

20000

125125

25000

IaI-40Total concentration of20000

125I15000
10000
5000
050

0102030Times (h)4050Fig. 1 Concentration of 125I in Ulva pertusa and seawater samples,
and total content of 125I in seawater.
ヨードフェノール
4-Iodphenol
NaIO3

NaIO3
NaI

NaI
Athena Fitting

Ulvapertusa
アオサスペクトル－：XANES spectrum－：Linear fitting result

33150

33200

33250

33300

X ray energy (eV)Fig. 2 XANES spectrum of Ulva pertusa.