Journal of Nuclear and Radiochemical Sciences, Vol. 6, No. 3, pp. 261-264, 2005

Soil-to-Plant Transfer Factors of Technetium-99 for Various Plants Collected in the
Chernobyl Area
Keiko Tagami and Shigeo Uchida*
Office of Biospheric Assessment for Waste Disposal, National Institute of Radiological Sciences, Anagawa
4-9-1, Inage-ku, Chiba-shi, Chiba 263-8555, Japan
Received: July 31, 2005; In Final Form: September 30, 2005
Technetium-99 is thought to be highly soluble and rarely adsorbed onto soil, however, its mobility under naturalenvironment is not well known because its scarcity and low levels in environmental samples has limited the available data. In this study, we determined 99Tc contents in 27 plant samples collected in three forest sites in 1994
and 1995 around the Chernobyl area to obtain transfer factors (TFs) of Tc in the soil-plant system under environmental conditions. The samples were leaves of raspberry, strawberry and pink plants, black alder, birch, cowberry
and oak trees, and ferns. After chemical separation, 99Tc in the sample was measured by ICP-MS. Tc-95m wasused as a yield tracer and the total recovery ranged from 0.48 to 0.92 with an average of 0.76. The determined99
Tc concentrations in plants ranged from < 0.006 to 6.0 mBq g−1 (dry weight basis). TF values ranged from< 0.006 to 0.47, based on the 99Tc contents of the soil organic layers. The highest TF was found in the leaves ofraspberry plants. The observed TFs were much lower than the values of 8.1–2600 compiled by IAEA for grass,fodder and leafy vegetables.

1. Introduction
Technetium belongs to the Mn group and it has no stable isotopes. Among its radioactive isotopes, 99 Tc is of potential longterm importance in the environment like 137Cs. Technetium-99
is a pure beta emitter (E max = 0.29 keV) and its radiologicalhalf-life is 2.11 × 105 y. It is produced in the fissions of 235U and239
Pu at relatively high r.atios of ca. 6%, which is similar to thevalues for 137Cs and 90Sr. Technetium-99 is widely distributed in
the environment as a result of fallout from nuclear weapons testing and discharges from nuclear facilities. Nuclear medical useof 99m Tc (half-life: 6.01h) which decays directly to 99Tc is anothersource though the 99Tc introduced into the environment via thisroute is negligible.
For a realistic long-term radiological assessment of the radionuclide, it is necessary to obtain transfer parameters, such as
soil-to-plant transfer factors (TFs, concentration in plant/concentration in soil), under natural conditions. Generally, Tc is
expected to be mobile in the surface soil environment becauseof its chemical form, TcO4 −, which is the most stable chemical
form under natural surface water conditions.1 This chemical
form is highly soluble in water, rarely adsorbed onto soil particle
surfaces, and has a high availability for plants. Indeed, a TF of 5in the edible parts of common plants (on a wet weight basis) was
recommended by the International Atomic Energy Agency(IAEA) for Tc when assessing its behaviour.2 Moreover, in
Reference 3, soil to grass transfer factor for Tc was reported as
78 (on a dry weight basis), while those for Sr and Cs were 0.34–
1.7 and 0.11 –0.53, respectively. This highly mobile chemical
form, TcO4−, however, changes with environmental conditions,4−7
consequently, TF values would also change. Unfortunately, TF
data observed under natural conditions have been limited due tothere being only trace levels of 99Tc. Obtaining TFs using global
fallout 99 Tc in agricultural fields is difficult, because the concentration of 99 Tc is very low.8 Therefore, we focused on the
Chernobyl site where 99 Tc concentration levels have alreadybeen shown to be higher than those from global fallout Tc.9
*Corresponding author. E-mail: s_uchida@nirs.go.jp. FAX:
+81-43-206-3267.

In this study, we determined the concentrations of 99 Tc inplant leaves collected near the Chernobyl site to investigate thetransfer of the nuclide in soil-plant systems under natural conditions. The samples were leaves of raspberry, strawberry andpink plants, black alder, birch, cowberry and oak trees, andferns. Details of 99 Tc and 137Cs data for soil samples collected
at the same time were reported previously,9 thus, the data wereused in this study to obtain TFs. Since TFs are usually high inleafy vegetables and grass as reported in Reference 3, leaves ofraspberry, strawberry and pink plants are of the most interestin this study for comparison purposes.
2. Experimental
2.1. Reagents. Nitric acid used was ultra pure grade (TamaChemicals, AA-100). A Tc-selective chromatographic resin(Eichrom Industries Inc., TEVA resin) was used for Tc purification. The grain size of the resin was 100–150 µm and thevolume of the resin in the column was about 2 mL. Deionizedwater (> 17.6 MΩ) was used throughout the work. Technetium95 m, which was obtained from an Nb foil using the reaction
93
Nb (α, 2n) 95m Tc, was applied to determine the recovery of99
Tc in the samples during the chemical separation procedure.
The 95m Tc was made at Cycrotron and Radioisotope Center,
Tohoku University. In our previous work, we found that thisreaction could not produce other long-lived Tc isotopes.10 A
standard 99 Tc solution available from Amersham (Solution
TCZ.44) was used for calibrating the ICP-MS.
2.2. Plant Samples. Twenty seven plant samples were collected at the Chernobyl site in 1994 and 1995 by the Federal
Office for Radiation Protection, Germany, assisted by Moscow
State University, Russia, and the Research and Industrial
Association “Pripyat”, Ukraine. The sampling was carried out
in three forests, D1, D3 and K2, around the Chernobyl Nuclear
Power Plant. Forests D1 and D3 were 28.5 km and 26 km to
the south of the reactor, respectively, while forest K2 was 6 km
to the southeast. The sites D1 and D3 were mixed forests (D1:
50% oak, 30% pine, 20% birch; 55 – 60 years old; and D3:
50% alder, 40% birch, 10% pine; 50–75 years old), while K2
was a pine forest (about 50 years old).11 Soil samples were

© 2005 The Japan Society of Nuclear and Radiochemical Sciences
Published on Web 12/28/2005

262 J. Nucl. Radiochem. Sci., Vol. 6, No. 3, 2005

Tagamialso collected at the same sampling sites and the details werereported previously.9
The plant samples were leaves of various plants grown in
the forests (Table 1). They were separated into three groups,that is, Fern, Herb (raspberry, strawberry and pink), and Tree
(black alder, birch, cowberry and oak). After the samples wereoven dried at 110 ˚C, they were thoroughly milled. Then they
were transferred to plastic bottles and stored at room temperature.
TABLE 1: Chemical Recovery and Concentration of 99Tc
in Plant Samples Collected in Forests within the 30-km
Zone Around the Chernobyl Nuclear Power Plant
Group
Fern

Herb

Tree

Sampling
Sample
site

Plan

Dry
Technetium-99
weight Recovery(mBq g-dry−1)(g)K2

94F-1a*94F-1b*94F-1c*
95F-1
95F-2

1.01
1.01
2.61
4.04
2.00

0.847
0.895
0.884
0.829
0.749

D3

94F-1
95F-1
95F-2

7.02
9.06
4.03

0.661 < 0.040
0.483 < 0.031
0.844 < 0.069

K2

94G-1
Raspberry
94G-2a* Strawberry
94G-2b*
95G-1
Pink
95G-2
Raspberry

4.04
4.03
2.07
3.99
17.0

0.599
0.747
0.852
0.739
0.762

4.04 ± 0.42
1.30 ± 0.17
1.57 ± 0.16
6.02 ± 0.52
3.61 ± 0.33

D1

94G-1a* Strawberry
94G-1b*
94G-2
Raspberry
95G-1
Raspberry

6.98
2.22
25.1
35.3

0.596
0.824
0.563
0.901

0.254 ± 0.022
0.451 ± 0.090
0.222 ± 0.017
0.257 ± 0.021

D3

94G-1a*94G-1b*94G-1c*
94G-2
94G-3
95G-1

Raspberry
Raspberry
Raspberry

10.2
1.82
2.81
20.0
4.02
16.2

0.868
0.844
0.823
0.706
0.553
0.915

0.215 ± 0.016
0.231 0.025
0.192 0.029
0.094 ± 0.008
0.128 ± 0.011
0.016 ± 0.003

D1

94T-1
95T-1

Oak
Oak

45.4
25.2

0.898
0.883

< 0.006
0.013 ± 0.001

D3

94T-1
94T-2
94T-3
94T-4
95T-1
95T-2
95T-3
95T-4

Birch
Oak
Cowberry
Black alder
BirchBlack alder
Oak
Cowberry

7.99
7.00
5.04
10.0
10.0
12.1
10.1
8.06

0.878
0.652
0.850
0.633
0.685
0.543
0.856
0.843

< 0.035< 0.040< 0.056< 0.028< 0.028< 0.023< 0.0280.094 ± 0.011

Strawberry

2.42 ± 0.18
2.37 ± 0.29
2.31 ± 0.26
0.603 ± 0.045
3.79 ± 0.35*: Replicates.

The activities of 137Cs in the samples were measured with a
Ge detector (Seiko EG&G Ortec) coupled with a multi channel analyzer (Seiko EG&G, Model 7800) before the chemical
separation for 99 Tc.
2.3. Chemical separation. A simple wet digestion method
in combination with an extraction chromatographic resin separation method was applied for 99 Tc. About 1−45 g portions of
the plant samples were incinerated at 450 ˚C in an electricaloven for 2 h to decompose organic matter. Then, in order toobtain the recoveries of 99 Tc, a certain amount of 95m Tc wasadded and they were mixed uniformly. Next Tc was extractedwith 4 M HNO3 while heating the samples at 100 ˚C in a glass
beaker covered with a watch glass. The residue was removed
by filtration and the solution was diluted to obtain the acidityof ca. 0.1M HNO3 and passed through a TEVA resin column topurify and concentrate Tc isotopes. Because ICP-MS cannot
differentiate between 99Ru and 99 Tc, it is necessary to remove
all Ru from the final sample solution prior to ICP-MS mea-

surement. Ruthenium present in the sample solution is noteffectively retained on the TEVA resin and passes directly
through the resin, while almost all Tc is extracted on the resin.12
The column was then washed with 2 M HNO3 to remove any
remaining trace Ru and other matrix elements which interferedwith 99 Tc measurement by ICP-MS. Technetium adsorbed on theresin was eluted with 5 mL of 8 M HNO3 solution. The volumeof the 99 Tc fraction from the TEVA column solution was reduced
to near dryness (< 70 ˚C) and then dissolved in 5 mL of 2%
HNO3 solution. Details of this method are in the literature.13
2.4. Measurements. Radiochemical recoveries of Tc plant
samples were monitored with 95mTc activities in the final 2%
HNO3 solutions before ICP-MS measurements. The gammarays (204 keV), was measured with a NaI (Tl) scintillation
counter (Aloka, ARC-380) for 20 min. Then the solution was
introduced into an ICP-MS (Yokogawa, PMS-2000) to measure 99 Tc for 10 min. The typical detection limit in solutions,calculated as three times the standard deviation of the blank,
was 0.03 mBq mL −1.
3. Results and Discussion
3.1. Technetium-99 concentrations in plant samples. Total
chemical recoveries throughout the method with 95m Tc arelisted in Table 1, and they ranged from 0.48 to 0.92 with anaverage of 0.76. No relation was found between sample amountand recovery. Three replicates of samples K2-94F-1 and D394G-1 were used in amounts of 1−2.6 g and 1.8−10.2 g, respectively, and there were no differences between their recoveries.
However, the recoveries of two sub-samples of K2-94G-2 andD1-94G-1 differed by about 0.1 and 0.2, respectively; whensample amounts increased, the recoveries decreased. Possibly,plant matrices, such as K, Ca and Cl, would affect the 99Tc
recovery, especially at the TEVA resin separation steps.
Technetium-99 concentrations in all samples are also listed
in Table 1 and they ranged from < 0.006 to 6.0 mBq g−1. For
11 samples, especially in the Tree group, it was hard to determine 99Tc, because of its low concentration. Since K2 wascloser to the reactor than the other 2 sites were, Fern and Herbgroups showed higher 99Tc concentrations in K2 than in D1
and D3. No Tree group samples were available from K2; however, we expected 99Tc concentrations in tree leaves would behigher at K2 than at the other 2 sites as well, although the concentrations should be much lower than those of Fern and Herbgroups.
Then, by calculating activity ratios of 99Tc to 137Cs in plant
samples, we were able to compare uptake behavior of these elements. The results are shown in Figure 1. Previously, it wasreported that the soil organic layer in these sites had 99Tc/137Cs
activity ratios of between (0.37−1.24) × 10−4.9 These data werebased on total activity ratio; the bioavailability of 137Cs should
be much smaller than that of 99TcO4− due to their different chemistries and fixation mechanisms by soils. Consequently, higher
activity ratios in the plants than in the soils were expected if Tc
was in TcO4−. At K2, the activity ratios for the Fern group werelower than that for the soils, while the Herb group showed higher
activity ratios than soils did. It is well known that fern plants
can adsorb much more Cs than more highly evolved plants can,and this could be the reason for their low activity ratios. For
the samples at D1 and K2, the ratios for the Herb group wereusually about 5−10 times higher than those for the soils, thatis, bioavailability of Tc at D1 and K2 sites was 5 − 10 times
higher than that of Cs. However the Tc bioavailability was
smaller than expected from their reported TFs3 since TF of Tc
was 150−800 times higher than that of Cs. There was no clear
magnitude difference for the Tree group and soils. On theother hand, the ratios at D3 were usually lower than those insoils for Herb and Tree groups which implied that 99Tc bioavailability there was much lower than expected. The results

J. Nucl. Radiochem. Sci., Vol. 6, No. 3, 2005 263

10

-3

10

-4

Tc/137Cs in soil

0

10

-1

10

-2

10

-3

SampleFigure 1. Activity ratio of 99Tc to 137Cs in plant samples collected inforests within the 30-km zone around the Chernobyl Nuclear Power
Plant. Bars show counting error (1 sigma).

suggested that most part of the Tc was not pertechnetate form.
3.2. Transfer factor for 99Tc. In general, TF is defined as
the ratio of activity concentration in plant (in Bq g−1 dry weight(DW)) to activity concentration in soil (in Bq g−1 DW). It has
been noted that forest under story plants are expected to takeup radionuclides mainly from organic layers9 and therefore,
concentration of 99Tc in organic soil would be important for
estimation of its uptake. For this reason, we calculated TFs interms of activity concentration in a plant relative to activity
concentration in organic soil. In the soils, as reported previously,9 concentrations of 99Tc were 8.6 ± 0.3 Bq g−1 in 1994 and13.4 ± 0.2 Bq g−1 in 1995 for K2 site, 1.1 ± 0.02 Bq g−1 (combined sample from 1994 and 1995) for D1 and 2.4 ± 0.01 Bq g−1
in 1994 and 1.72 ± 0.05 Bq g−1 in 1995 for D3 site.
Figure 2 shows the TFs of Tc for all the samples. They
ranged from < 0.016 to 0.28 for Fern, 0.009 to 0.47 for Herband < 0.006 to 0.05 for Tree groups based on the 99Tc contentsof the organic layers. The highest TF was found in the leavesof raspberry. The observed-TFs were lower than the IAEAcompiled values of 8.1−2600 for leafy vegetables, fodder andgrass3; other reported values are as listed in Table 2. Comparing
TABLE 2: Transfer Factors for Tc Reported for Various
Plants Grown in Soil
Crop

TF

Conditions

Reference

Soybean, Leaves
Wheat, Blade85 –186
312 – 476

Silt loam, Pot

14

Herbaceous
vegetation

6.7–22

Silt loam, Field

15

Radish2.1, 9.5
9.5, 14.2

pH = 5.7
pH = 6.7

Chard

2.6
6.3

pH = 5.7
pH = 6.7

Turnip4.5
7.4

pH = 5.7
pH = 6.7

4> 10y aged, Field
Grass pasture mixture

6

3 y Lysimeter

5

Grass

0.91–3.02

Reclaimed land, Field

16

Green vegetables

1.2

Reclaimed land, Field

17

Rye grass44 –371

Cambisol, Pot

18

Herbaceous
vegetation

0.009 – 0.47

Podzol, Peat-gley, Field

This study

D1 -9 4 T -1
D 1 - 9 5 T -1
D 3 - 9 4 T- 1
D3 - 94 T -2
D3-94T-3
D 3-9 4 T - 4
D3 -95 T -1
D 3 - 9 5 T- 2
D 3-9 5 T - 3
D 3 - 9 5T - 4

K2-94G-1
K2-94G-2
K2-95G-1
K2-95G-2
D1-94G-1
D 1- 9 4 G - 2
D1-95G-1
D 3 - 94 G - 1
D 3 - 9 4 G- 2
D3-94G-3
D3-95G-1-6

K2-94F-1
K2-95F-1
K2-95F-2
D3-94F-1
D3-95F-1
D3-95F-2-5

D1-95T-1
D3-95T-4

1099

K2-94G-1
K2-94G-2
K2-95G-1
K2-95G-2
D1-94G-1
D1-94G-2
D1-95G-1
D3-94G-1
D3-94G-2
D3-94G-3
D3-95G-1

10

10

99

-2

Transfer Factor for Tc

10

K2-94F-1
K2-95F-1
K2-95F-2

99

137
Activity ratio of Tc to Cs

Soil-to-plant Transfer Factors of Technetium-99

SampleFigure 2. Soil-to-plant transfer factor of 99Tc in plant samples. The
99
Tc concentration data are from reference 5. Error bars show counting error (1 sigma). Arrows indicate that TFs are lower than the values estimated from the detection limit for 99Tc.

the TF for Tc reported for various plants grown in soil, the present results were almost the same as the data observed inreclaimed land,16 although the data from pot experiments14, 18
were much higher.
From these results, we concluded Tc bioavailability in thenatural environment would be lower than the bioavailabilities
obtained from laboratory studies that used TcO4 − to obtain Tc
TFs. Previously, we observed that there are three main paths
for TcO4 − uptake by plants.19 However, no clear path has beenreported for the other Tc chemical forms. It is known that themost plant-available form of Tc is TcO4 −, and other forms, suchas Tc-cysteine, have less availability to plants.20 Thus, as written above, TcO 4 − was not the only Tc chemical from in these
forests. Possibly most Tc was in less soluble form, such asorganically bound forms, sesquioxide bound and lower oxidation forms.6
Concerning the Herb group, the TFs were 0.17−0.47 at K2,
0.20 − 0.32 at D1 and 0.009 − 0.086 at D3. The TFs for the
samples collected at D3 were lower than those at D1 and K2.
This might be due to the fact that D3 was a so-called wet forest
and reducing conditions might possibly exist. The bioavailable
Tc was presumably influenced by the soil redox conditions.
Since the anaerobic condition was established by waterlogging
and activity of microorganisms, Tc would be transformed fromto a lower oxidation and less available form such as TcO 2 ,TcO(OH)2 or TcS2 under a relatively low redox condition. Dueto the relatively low redox conditions of the D3 site, the TFs
were lower than those in K2 and D1 sites.
Thus, the low TFs we observed in this study implied that 8−
9 years after 99Tc release from the Chernobyl Nuclear Power
Plant, Tc should have been transformed to insoluble or lessplant-available forms. Technetium would not be in readily
available form to plants in the environment.
Acknowledgements. We are grateful to Dr. W. Rühm, Ludwig
Maximilians University Munich, Germany, Dr. M. Steiner,
BfS·Institute of Radiation Hygiene, Germany and Dr. E. Wirth,
Institute for Atmospheric Radioactivity, Germany, for providing
us with the plant samples. We would like to express our deep
gratitude to Dr. T. Sekine, Tohoku University, Japan, for his help
in the generation of 95mTc.
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