Transfer of radionuclides from soil to grass in Northern Taiwan

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Appl. Radiat. lsot. Vol. 48, No. 2, pp. 301 303. 1997 Copyright '.(~, 1997 Elsevier Science Ltd Printed in Great Britain. All rights reserved 0969-8043/97 $17.00 + 0.00 PII: S0969-8043(96)00178-9

Pergamon

Analytical method: soil pH and moisture content The pH values of the soil solution were measured b y a pH meter. The moisture contents of the soil were obtained by the gravimetric method (The Chinese Society of Soil and Fertilizer Sciences, 1993).

Transfer of Radionuclides from Soil to Grass in Northern Taiwan CHIH-JUNG WANG, SHU-YING LAI, JENG-JONG WANG and Y U - M I N G LIN

Analytical method: total potassium content O! soil and o] radionuclides of both soil and grass samples

Taiwan Radiation Monitoring Center, Atomic Energy Council, Executive Yuan, Kaohsiung 833, Taiwan, R.O.C.

The total potassium content of the soil were obtained by y-ray spectrometry of 4°K. The ash samples of soil and grass were analyzed using 7-ray spectrometry to determine the concentrations of radionuclides +°K, ~TCs, +"Co and 54Mn in the soil and igrass samples (The Science and Technology Agency, J~pan, 1993). The detector used for counting had a resolution of 1.86 keV full width at half maximum at 1.33 MeV. Spectral data from the detector were accumulated in a computerbased, 4096-channel, pulse-height analyzer system. The counting time was 80,000 s. The U.S. National Bureau of Standards (now the National Institute of Standard~ and Technology) reference material 4353 of Rocky Flats soil was used to calibrate the Ge(Li) detector. For the grass samples, a mixed )' calibration source blended with agar was Used.

(Received 30 January 1996: ret,ised 4 April 1996) The transfer factors of radionuclides, such as 4°K, L'TCs,6°Co and saMn, from soil to grass in northern Taiwan area were studied. The results showed that the transfer factors were much influenced by the contents of potassium and the pH values of the soils. The transfer factors of4°K, ~':Cs, 6°Co and '+Mn from soil to grass were estimated to be about 0.67-2.84, 0.06-0.63, 0.044).92 and 0.4(~3.30, respectively. Copyright ¢~, 1997 Elsevier Science Ltd

Cah'ulation of tran,~'fer.]aetors (IAEA, Protocol 1994) Definition of TF (transfer factor):

Introduction

TF .....

The absorption of radionuclides into plants from atmospheric deposition via leaves and from soil via roots have two possible pathways. These absorptions are affected by various parameters, such as the chemical and physical properties of soil, temperature, rainfall, sunlight etc. Therefore, the transfer factors of radionuclides from soil to crops, fruits, and from soil to grass and then to animals, and from water to fish, are very important for dose assessment. Besides the transfer factors of radionuclides from soil to grass in the grasslands of northern Taiwan, we have also tried in this study to find out to what extent the Cs transfer to grass is affected by the different types soil parameter, pH. moisture and total potassium content. The results seem to be in agreement with other studies (Kuhn et al., 1984).

R.I. activity concentration of grass = R.I. activity concentration of soil Bq kg ~ dry grass = B q kg ~ dry soil in upper 10cm

Results and Discussion Table 1 shows the analytical results of soil pl-[ and moisture content of grassland in northern Taiwan arid the concentrations of 4°K, ~7Cs, 6"Co and S4Mn of the soil and grass samples. The range of the soil pH and moisture

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Materials and Method Sampling and pretreatment Two kinds of grass were sampled from the areas around the Nuclear Power Plant No. 1 of the Taiwan Power Company in northern Taiwan. Soil (1.5 kg) and grass (I kg) samples were collected from each site of the selected locations shown in Fig. l--spacious and flat areas without past surface disturbance caused by duststorms, inflow and outflow due to precipitation, etc. Places located under trees, in forests and in stony areas inside river banks were avoided. Soil samples were taken from a depth of 10 cm. The soil lumps were crushed, dried, separated from pebbles and plant roots, then ground to powder and sieved to pass through a 2-mm (10-mesh) sieve. The varieties of grass samples include Eleusine indica (L.) Gaerm. sampled at point A and Miscanthus floridulus (Labill.) Warb. ex Schum. & Laut. sampled at points B, C, D, E and F. Each sample was oven-dried at 105°C to get the dry weight, then ashed below 450°C, and measured in a cylindrical plastic container that was placed directly on the

Nuclear Power

i

o

1oom

A

B• I

detector.

Fig. I. Map of sampling sites. 301

+2

11.0

11.6

3.54

18.2

C

D

E

F

5.21

7.29

6.90

1994.01.03 1994.04.01 1994.07.13 1994.10.13 1995.01.17 1995.04.25 1994.01.03 1994.04.01 1994.07.13 1994.10.13 1995.01.17 1995.04.25 1994.01.03 1994.04.01 1994.07.13 1994.10.13 1995.01.17 1995.04.25 1994.01.03 1994.04.0t 1994.07.13 1994.01.03 1994.04.01 1994.07. t 3 1994.10.13 1995.01.17 1995.04.25 1994.01.03 1994.04.01 1994.07.13 1994.10.13 1995.01.17 1995.04.25

Sampling date

376 440 511 443 465 453 404 428 550 367 462 508 560 783 532 456 254 486 517 245 792 569 547 685 382 618 416 508 309 648 608 498 498

Grass

2. T.F.~,,,, = R.I. activity concentration of grass Bq kq ' dry grass R.I. activity concentration of soil = B~ kg dry soil in upper 10 cm"

I. Unit of activity concentration: Bq/kg-dry.

4.18

17.9

B

4.83

5.15

pH 526 348 211 251 230 225 331 456 41 I 291 298 304 419 311 278 362 381 392 422 357 307 364 327 362 342 405 453 290 238 228 448 199 291

Soil

4°K

0.72 1.27 2.42 1.77 2.02 2.01 1.22 0.94 1.34 1.26 1.55 1.67 1.34 2.52 1.91 1.26 0.67 1.24 1.22 0.69 2.58 1.56 1.67 1.89 1.12 1.53 0.92 1.75 1.30 2.84 1.36 2.54 1.70

T.F.

8.79 7.15 8.12 5.11 2.56

4.72

1.01 0.55 0.43 0.92 1.10 0.76

2.39

2.01 5.56 10.0 8.02 5.13 3.06 27.0 13.0 7.0 14.0 18.0 14.0 2.14 1.48 6.00 6.23 6.92 2.19 3.55 22.0 8.03

Soil

]3VCs

0.55

1.22 1.59 2.45 2.26 1.47 1.41 17.12 0.80 3.36 3.49 5.17 1.62 1.28 0.82 1.50 2.45 0.92 1.28 1.07 1.19 0.61

Grass

0.06 0.06 0.11 0.21 0.30

0.21

0.23

0.61 0.29 0.25 0.28 0.29 0.46 0.63 0.06 0.47 0.25 0.29 0.12 0.60 0.56 0.25 0.39 0.13 0.59 0.30 0.06 0.08

T.F

1.67 1.19 3.61 2.82

2.90 1.50

0.89 0.89 0.37 1.93

1.41 0.61

0.49 1.93 0.67

7.44 7.79 4.30

28.0 12.0

2.17 1.47 20.0 1.94

0.43 0.89 1.19 0.73

7.92 0.46

1.20 10.0

Soil

6°Co

1.10 1.38

Grass

Table 1. Transfer factors of radionuclides from soil to grass around Nuclear Power Plant No.l, northern Taiwan

9.80

H_,O (%)

Soil char.

A

Sampling location

0.07 0.25 0.16

0.28 0.04

0.49 0.41

0.53 0.75 0.10 0.68

0.20 0.60 0.05 0.38

0.92 0.14

T.F.

1.16 3.00

0.61

0.61

Grass

0.48 0.91

0.61

1.52

Soil

54Mn

2.42 3.30

1.00

0.40

T.F.

Z o

o~

,-q

t,~

Technical Note 101

A 40K 0 60Co

[] 137Cs

T I0 °

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10-2 3

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4

5

6

8

9

pH Fig. 2. Transfer factors of radionuclides from soil to grass around Nuclear Power Plant No. I, northern Taiwan.

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O West G e r m a n forest clearings • West G e r m a n g r a s s l a n d A Northern T a i w a n g r a s s l a n d

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303

8.01 + 6.25, 6.47 _+ 7.49 and 0.63 + 0.77 for ~K, "TCs, 6°Co and 54Mn, respectively. The ranges of the concentrations of 4°K, 137Cs, 6°Co and ~4Mn of grass on the dry weight basis are 245-792, 0.43-17.12, 0.37-7.92 and 0.61 3.00, respectively. Their average values are 494 + 125, 2.09 + 3.13, 1.37 4- 1.76 and 1.35 + 1.92 for 4°K, n37Cs, 6°Co and ~4Mn, respectively. Because the radioactivity of the atmospheric fallout was low enough to be neglected we assumed that the radioactivity of the plants was mostly through the root absorption from the soil. Hence. the ranges of the transfer factors of ~"K. ~TCs. ~°Co and ~Mn from; soil to grass on a dry weight basis are estimated tO be 0.67-2.84. 0.06~0.63. 0.04~0.92. and 0.403.30, respectively. Their average values are 1.56+_ 0.55. 0.28 + 0.19, 0.35 + 0.27 and 1.78 4-_ 1.32 for ~°K, ~'Cs, ~"Co and '4Mn, respectively. Figure 2 shows the correlation between the transfer factors of radionuclides and pH value of soil. Within the range of pH 3-8, there is no obvious variation for the transfer factors of radionuclide 4°K. But, just as m KUhn's study, the transfer factors of radionuclides ~TCs and 6'~Co seem to appear to decrease as the soil pH values increase for both grasslands. Because of the similar chemical properties of potassium and cesium and the high content of potassium in soil the soil's cesium may be replaced by potassium and absorbed by the plants. The correlation between the transfer factors of ~VCs and total potassium content of soil is shown in Fig. 3. For a comparison, the data from Kfihn eta/. (1984) is depicted in the same figure. Although the total potassium content of soil in Germany and northern Taiwan are quite different, both of them appear to have a similar trend in that the total potassium content of the soil increased, and the transfer factors of radionuClide '37Cs from soil to grass decreased to reach a constant ualue when the total potassium content of soil was > 7 g kg ' dry soil. They were found to be in the same order, compared with the data 0.1.0.4 and 0.3 for the transfer factors of ~37Cs.S'Co and 5"Mn from soil to grass, respectively (IAEA, 1982), and 0.14 for the transfer factor of "3Cs from soil to hay [Ng, 1982).

18

Total potassium contents (g/kg.dry soil) Fig. 3. Transfer factors of grass in northern Taiwan's grassland and German grassland and forest clearings in relation to the total potassium content of 0-10 cm soil layer.

content of the grassland in northern Taiwan are 4.18-7.29 and 3.54-18.2%, respectively. The ranges of the concentrations of 4°K, UTCs, 6°Co and 54Mn of soil on the dry weight basis are 199-526, 1.48-27.0, 1.19-28.0, and 0.48-1.52, respectively. Their average values are 335 _+ 81,

References

The Chinese Society of Soil and Fertilizer Sciences (1993) Handbook of Soil Ana(vsis, pp. 6.1-6.2 and 9.7 9.8~ IAEA (1982) General models and parameters for assessing the environmental transfer of radionuclides from routine releases. IAEA, Sq]'ety Series 57, 61-65. K/.ihn W., Schuller P. and Schuller J. (1984) The influence of soil parameters on ~3VCs-uptake by plants from long-term fallout on forest clearings and grassland. HIth Phys. 46, 1083 1093. Ng Y. C. (1982) A review of transfer factors for assessing the dose from radionuclides in agricultural products. Nucl. Safety 23, 1, 57-71.