earlier CRP upper limit
SOUTHWEST CHINA
2. MATERIALS AND METHODS 1. Experimental field
2.4. Sampling procedures
At harvest time, plant and soil samples were collected simultaneously. Soil samples were randomly taken. Only the edible parts of the crops were sampled. Potato, spinach, Chinese cabbage and radish were washed to remove soil contamination. Maize and wheat grains were not washed. For each TF measurement five replicate crop and soil samples were taken.
and then passed through a 2 mm sieve, ready for analysis.
For 137Cs plant samples were dried at 105 oC and then ground into powder for analysis. Soil samples were treated as for 90Sr.
3. RESULTS AND DISCUSSION
TABLE 3. SOIL CHARACTERISTICS AND OTHER PARAMETERS OF THE EXPERIMENT
Parameters Unit 1999* 2000* 2001* 2002
pH(water) 7.4 7.5 7.5 7.5
Exch K+ Cmol/kg 25.9* 17.9* 20.5* 16.0*
Exch Ca2+ Cmol/kg 8.0* 7.8* 10.0* 7.0*
CEC Cmol/kg 41.1* 23.3* 37.2* 27.5*
Org. carbon % 4.3 5.7 6.9 3.6
Rooting depth cm 18 18 18 18
Bulk density (kg/m3) 1650 1650 1650 1650
Crop yield
Maize (kg/m2) 0.33 0.53 0.62
Potato (kg/m2) 0.47
Spinach (kg/m2) 0.43
Chinese cabbage (kg/m2) 0.3 2.85 9.28
Wheat (kg/m2) 0.25 0.25
Radish (kg/m2) 1.4
Tomato (kg/m2) 0.5 0.63 0.27
Lettuce (kg/m2) 0.65 1.81
Broad bean (kg/m2) 0.52
Moisture content of crop
Maize % 54.5 57.4 44.5
Potato % 79.8
Spinach % 94.2
Chinese cabbage % — 92.1 95.4
Wheat % — — —
Radish % — 92.4
Tomato % — 92.9 95.4 94.7
Lettuce % 93.7 96.1
Broad bean %
Soil properties, pH (in water), organic carbon content, exchangeable K in soil (cmol(+)/kg), exchangeable Ca in soil ( cmol(+)/kg) and CEC were determined yearly by the methods described in [3]. Other parameters related to the experiments were measured, including moisture content of crop before drying, rooting depth (estimate, cm), bulk density at sampling times (kg/m3), crop yield (kg/m2).
These soil characteristics and the parameters concerned are given in Table 3.
The concentrations of 90Sr and 137Cs in soil and crop samples are given in Tables 4 and 5.
TABLE 4. THE CONCENTRATION OF 90Sr AND 137Cs IN SOIL SAMPLES (Bq/kg dry soil)
Crop N 90Sr 137Cs
1999
Maize 5 5.50E+02±1.21E+02 6.16E+02±2.59E+02 Potato 5 6.59E+02±1.09E+02 3.91E+02±4.79E+01 Spinach 5 7.50E+02±1.50E+02 5.33E+02±2.75E+02 2000
Wheat 5 4.52E+02±1.19E+02 4.92E+02±1.70E+02 Chinese Cabbage 5 4.03E+02±1.46E+02 5.41E+02±2.77E+02
Tomato 5 5.50E+02±1.16E+02 3.86E+02±1.45E+02 Radish 5 5.10E+02±1.28E+02 4.21E+02±9.73E+01 2001
Lettuce 5 3.91E+02±2.08E+02 7.86E+02±3.93E+02 Tomato 5 3.58+E02±6.11E+01 4.95E+02±2.06E+01 Maize 5 5.58E+02±1.67E+02 7.20E+02±2.42E+02 Chinese cabbage 5 5.01E+02±1.24E+02 3.98E+02±1.20E+02
Broad bean 5 4.33E+02±1.24E+02 3.75E+02±8.92E+01 2002
Maize 5 2.98E+02±1.13E+02 3.45E+02±1.33E+02 Tomato 5 3.36E+02±4.67E+01 2.76E+02±4.02E+01 Chinese 5 3.50E+02±7.21E+01 2.76E+02±8.59E+01 Wheat 5 2.75E+02±９.73E+01 3.99E+02±7.07E+01 Lettuce 5 1.68E+02±４.04E+01 3.27E+02±4.96E+01 N.B. The data are the average±SD.
TABLE 5. CONCENTRATION OF RADIONUCLIDE IN EDIBLE PARTS OF CROPS*
(Bq/kg dry crop)
Crop N 90Sr 37Cs
1999
Maize 5 1.59E+00±6.01E-01 1.16E+00±6.57E-01 Potato 5 4.97E+00±7.31E-01 8.80E- 01±1.41E-01 Spinach 5 1.84E+01±1.09E+0 6.06E+01±3.86E+01 2000
Wheat 5 2.91E+00±1.08E+00 5.23E-01±2.12E-01 Chinese cabbage 5 5.69E+02±2.02E+02 1.67E+01±8.34E+00
Tomato 5 2.17E+01±1.13E+01 8.88E+00±7.90E-01 Radish 5 3.88E+02±6.07E+01 3.80E+00±1.07E+00 2001
Lettuce 5 1.65E+01±9.95E+00 1.74E+01±8.93E+00 Tomato 5 9.58E+00±3.24E+00 1.21E+01±1.10E+00 Maize 5 7.05E-01±1.73E-01 1.25E+00±8.19E-02 Chinese cabbage 5 4.13E+02±6.73E+01 6.56E+00±2.35E+00
Broad bean 5 4.40E+00±1.39E+00 5.50E+00±1.89E+00 2002
Maize 5 2.47E-01±2.16E-02 1.29E+00±5.72E-02 Wheat 5 3.00E+00±4.94E-01 3.55E-01±2.83E-03 Tomato 5 7.25E+00±6.31E-01 4.14E+00±4.26E-01 Chinese cabbage 5 2.86E+02±6.15E+01 2.35E+01±6.63E+00 Lettuce 5 1.10E+01±2.61E+00 6.29E+00±1.90E+00
* See note of Table 4.
TF values of 90Sr, 137Cs for experimental crops (average and standard deviation) are given in Table 6.
Crops N 90Sr N 137Cs 1999
Maize 5 2.97E-03±1.31E-03 5 2.27E-03±1.79E-03 Potato 5 7.64E-03±1.11E-03 5 2.25E-03±2.56E-04 Spinach 5 2.34E-02±1.22E-02 5 6.74E-03±2.72E-03 2000
Wheat 5 6.50E-03±2.28E-03 5 1.18E-03±4.48E-04 Chinese cabbage 5 1.47E+00±4.04E-01 5 3.90E-02±2.74E-02 Radish 5 7.80E-01±1.12E-01 5 8.93E-03±5.75E-04 Tomato 5 4.26E-02±2.00E-02 5 2.61E-02±1.73E-02 2001
Lettuce 5 5.32E-02±5.05E-02 5 2.30E-02±5.50E-03 Tomato 5 2.79E-02±1.19E-02 5 2.45E-02±2.63E-03 Maize 5 1.29E-03±1.76E-04 5 1.97E-03±8.81E-04 Chinese cabbage 5 8.57E-01±2.36E-01 5 1.79E-02±9.04E-03 broad bean 5 1.10E-02±5.02E-03 5 1.49E-02±4.74E-03 2002
Maize 5 9.08E-04±2.64E-04 5 4.16E-03±1.39E-03 Wheat 5 1.17E-02±3.81E-03 5 9.17E-04±2.68E-04 Tomato 5 2.21E-02±4.78E-03 5 1.53E-02±2.92E-03 Chinese cabbage 5 8.69E-01±3.21E-01 5 9.27E-02±3.98E-02 Lettuce 5 6.65E-02±1.24E-02 5 1.91E-02±4.19E-03 For 90Sr, Chinese cabbage and radish (only one harvest year) have the highest TFs while maize has the lowest TF. For 137Cs, maize, wheat, potato and spinach have the lowest TFs.
As mentioned above, maize, Chinese cabbage and tomato were grown for three harvest years. The comparison of 90Sr and 137Cs TF data for these crops in different years are shown in Figs 1–6. Figure 1 shows that uptake of 90Sr by maize decreased yearly whereas uptake of 137Cs by maize increased in 2002 (Fig. 2).
Figure 3 shows TF of 90Sr for Chinese cabbage in 2000 is higher than those for 2001 and 2002 while Fig. 4 shows that 137Cs TF for Chinese cabbage is highest in 2002. We noticed that the yields of Chinese cabbage increased during the years of the experiment so the higher TFs might be differences in plant development.
There are individual samples in the first year with relatively high TF values (see Figs 1, 2, 5 and 6), that might indicate higher variation in the first year of the study but Figs 1–6 also show that TFs for the same type of crop and the same radionuclide in different harvest years are generally of the same order. Mean values of 90Sr and 137Cs TF are presented in Tables 7 and 8.
0.0000
FIG.1. Comparison of Sr-90 TFs for maize in 1999, 2001 and 2002.
FIG. 2. Comparison of Cs-137 TFs for maize in 1999, 2001, 2002. Sr-90 TF for Chinese cabbage Bq/kg dry crop/(Bq/kg dry soil)
2000 2001 2002
FIG. 3. Comparison of Sr-90 TFs for Chinese Cabbage in 2000, 2001 and 2002.
0. 000
Cs-137 TF for Chinses cabbage Bq/kg dry crop/(Bq/kg dry soil) 2000
2001 2002
FIG. 4. Comparison of Cs-137 TFs for Chinese cabbage in 2000, 2001 and 2002.
0
FIG. 5. Comparison of Sr-90 TFs for tomato in 2000, 2001 and 2002.
FIG. 6. Comparison of Cs-137 TFs for tomato in 2000, 2001 and 2002.
Wheat 10 1.05E-02 1.35E-02±1.30E-02 5.04E-03 4.89E-02
Maize 15 3.14E-03 5.58E-03±5.53E-03 5.72E-04 1.55E-02
Broad bean 5 1.00E-02 1.10E-02±5.02E-03 5.02E-03 1.64E-02
Spinach 5 3.37E-01 4.16E-01±2.94E-01 1.47E-01 8.52E-01
Chinese cabbage 15 9.88E-01 1.07E+00±4.24E-01 4.48E-01 2.04E+00
Potato 5 7.57E-02 7.64E-03±1.11E-03 6.13E-03 8.77E-03
Radish 5 7.73E-01 7.80E-01±1.12E-01 6.17E-01 9.01E-01
Tomato 15 2.82E-02 3.09E-02±1.55E-02 1.46E-02 7.68E-02
Lettuce 10 5.03E-02 5.99E-02±3.52E-02 1.49E-02 1.38E-01
TABLE 8. TFs OF 137Cs (Bq/kg dry crop)/(Bq/kg dry soil)
Crops N Geo mean Average±SD Range
Wheat 10 1.00E-03 1.05E-03±3.68E-04 6.19E-04 1.89E-03
Maize 15 2.34E-03 2.83E-03±1.64E-03 7.55E-04 5.59E-03
Broad bean 5 1.39E-02 1.49E-02±5.12E-03 9.34E-03 2.14E-02
Spinach 5 1.06E-01 1.24E-01±5.49E-02 2.96E-02 1.71E-01
Chinese cabbage 15 3.49E-02 4.99E-02±4.18E-02 8.61E-03 1.39E-01
Potato 5 2.24E-03 2.25E-03±2.54E-04 1.91E-03 2.53E-03
Radish 5 8.92E-03 8.93E-03±5.75E-04 8.19E-03 9.60E-03
Tomato 15 2.03E-02 2.20E-02±1.07E-02 1.30E-02 5.69E-02
Lettuce 10 2.05E-02 2.11E-02±5.06E-03 1.47E-02 2.97E-02
90Sr TFs for maize, wheat, broad bean and potato are generally lower in than those of Chinese cabbage, radish and lettuce. 137Cs TFs for wheat, maize and potato are usually lower than those of vegetables.
Chinese cabbage showed the highest ability to accumulate 137Cs.
0.0E+00 2.0E-01 4.0E-01 6.0E-01 8.0E-01 1.0E+00 1.2E+00
TF (Bq/kg dry crop)/(Bq/dry soil)
Maize Wheat Spinach Lettuce Chinese
cabbage
Crops
FIG. 7. Soil to plant TF of 90Sr for crops in Calcaric Cambisol in China.
The ranges of 90Sr and 137Cs mean TF values for different crops are shown in Figs 7 and 8.
FIG. 8. Soil to plant TF of 137Cs for Crops in Calcaric Cambisol in China.
4. CONCLUSION
The variability of the 90 Sr and 137Cs TFs is rather wide. The year-to-year variations suggest climatic factors may be important. For both radionuclides, the TFs to cereals were close to, or below, the bottom of the range predicted on the basis of IUR data and the previous CRP. There was no clear trend for TF to change with time for either 90 Sr or 137Cs.
REFERENCES
[1] PAN, Z. Q. et al., The nuclear environmental quality assessment of Chinese nuclear industry for 30 years, Beijing, Atomic Energy Press, 1990 (in Chinese).
[2] INTERNATIONAL ATOMIC ENERGY AGENCY, Handbook of parameter values for the prediction of radionuclide transfer in temperate environments, Technical Report Series No. 364, IAEA, Vienna, 1994.
[3] JACKSON, M.L., Soil Chemical Analysis, Constable and Company Ltd., London, U.K., 1985.
0. 0E+00 5. 0E- 03 1. 0E- 02 1. 5E- 02 2. 0E- 02 2. 5E- 02 3. 0E- 02 3. 5E- 02 4. 0E- 02 4. 5E- 02 5. 0E- 02
TF (Bq/dry kg crop)/(Bq/kg dry soil)
Wheat Pot at o Mai ze Spi nach Radi sh br oadbean Let t uce Tomat o Chi nese cabbage
Cr ops