earlier CRP upper limit
DIFFERENT GREEK SOIL TYPES
3. RESULTS AND DISCUSSION 1. Characteristics of soils
3.2. Estimation of radionuclides accumulation by crops from different soils
90Sr and 137Cs in soils and crops were determined. The uptake of radionuclides by crop is reported as the specific activity in crop divided by the specific activity in soil:
TF = (Bq/kg plant)/(Bq/kg soil).
3.2.1. Accumulation of 137Cs by crops from different soils
The results illustrate the influence of soil properties and biological peculiarities of crops on 137Cs TFs.
For the period 1999–2002 the differences in means of TFs 137Cs for different soil types reach 28.1 times for barley and 5.2 times for cabbage (Table 5). The differences between barley and cabbage are from 1.1–7.0 times.
The highest availability of 137Cs is reported for peat (Dystric Histosols and Eutri-Histic Gleysols), Molli-Gleyic Fluvisols and sod-podzolic sandy and sandy loam soil (Umbric Podzols). Soils with higher fertility and higher content of clay retain 137Cs more strongly. The studies have shown that radionuclides are accumulated less by plants from Hapric Kastanozems and different chernozems than from Grey-Luvic Phaeozem, Umbric Podzols and Dystric Histosols.
3.2.2. Accumulation of 90Sr by crops from different soils
Differences of 90Sr TFs for different soil types were 6.4 times for barley and 5.5 times for cabbage.
The differences between barley and cabbage in the accumulation of 90Sr varied from 1.1–2.0 times (Table 6). The highest availability occurred in Dystric Histosols, Eutri-Histic Gleysols, Umbric Podzols, Albic Luvosols, Grey-Luvic Phaeozem and Molli-Gleyic Fluvisols.
The accumulation of 90Sr by crops was higher than that of 137Cs. The differences averaged 2.6–14.3 times for barley and 8.1–32 times for cabbage (Tables 5,6).
The behaviour of 137Cs and 90Sr is different, because of different mechanisms of radionuclide fixation in soil. 137Cs exists in soil mainly in the non-exchangeable form, whereas 90Sr sorption is characterized by a cation exchange.
1 C 39.24 60.76 33.96
TABLE 5. TFs OF 137Cs BY CROPS FROM DIFFERENT SOILS (Bq/kg plant)/(Bq/kg soil), 1999–
2002
Type of soil 1999 2001 2002
Average SD Average SD average SD
Barley. grain
Haplic Kastanozems 0.0072 0.0025 0.0076 0.0013
Calcaric Chernozems 0.0040 0.0010 0.0051 0.0002
Chernic Chernozem 0.006 0.005 0.0117 0.0064 0.0081 0.0015 Haplic Chernozem 0.0043 0.006 0.0093 0.0021 0.0047 0.0036 Luvic Chernozem 0.0111 0.0028 0.0146 0.0065 0.0145 0.0078 Grey-Luvic Phaeozem 0.0074 0.0034 0.0233 0.0133 0.0154 0.0062
Albic Luvosols 0.017 0.004 0.0294 0.0079 0.035 0.0090
Umbric Podzols 0.023 0.0004 0.0450 0.0200 0.0246 0.0137
Dystric Histosols 0.0860 0.0280 0.0228 0.0105
Eutri-Histic Gleysols 0.055 0.019 0.10 0.0033
Cabbage. head
Haplic Kastanozems 0.0080 0.0024 0.0007 0.0001
Calcaric Chernozems 0.0041 0.0027 0.0021 0.0002
Chernic Chernozem 0.005 0.006 0.0054 0.0029 0.0026 0.0017 Haplic Chernozem 0.006 0.005 0.0064 0.0021 0.0021 0.0006 Luvic Chernozem 0.002 0.0012 0.0065 0.0081 0.0027 0.0010 Grey-Luvic Phaeozem 0.0028 0.0006 0.0036 0.0007 0.0014 0.0007 Molli-Gleyic Fluvisols 0.017 0.02 0.0227 0.0044 0.0008 0.0074 Albic Luvosols 0.001 0.0005 0.0120 0.0030 0.0015 0.0010
Umbric Podzols 0.015 0.001 0.0086 0.0028 0.0050 0.0036
Dystric Histosols 0.0101 0.0039 0.0054 0.0036
3.2.3. Influence of soil properties on uptake of 137Cs and 90Sr by the crops
Distinctions in 137Cs and 90Sr accumulation from different soil types result from the influence of soil characteristics, which are responsible for the biological availability of radionuclides.
A preliminary data analysis has shown that 137Cs accumulation is inversely proportional to the contents of exchangeable potassium and calcium, cation exchange capacity, content of particles <0.01 mm (clay) (Figs 1–3,6,7–9,12). There are differences between crops with clear-cut relationships for barley but these are not so well pronounced for cabbage.
There is a trend towards declining in TFs 137Cs to barley and cabbage with the increasing pH (Fig. 4,10). It should be noted that the effect pH depends partly on the response of different crops to pH. Thus, cabbage grows well only with neutral or weak alkaline reaction (pH7-8) but barley grows well only with neutral or weak acidic reaction (pH6-7).
There appeared to be no influence of organic matter (Fig. 5, 11).
average SD Average SD average SD Barley (grain)
Haplic Kastanozems 0.078 0.032 0.0895 0.0474
Calcaric Chernozems 0.054 0.027 0.0765 0.0332
Chernic Chernozem 0.037 0.013 0.059 0.018 0.0540 0.0028
Haplic Chernozem 0.122 0.019 0.053 0.032 0.05 0.024
Luvic Chernozem 0.086 0.011 0.080 0.023 0.073 0.016
Grey-Luvic Phaeozem 0.102 0.03 0.103 0.048 0.125 0.050
Albic Luvosols 0.163 0.038 0.158 0.056 0.219 0.049
Umbric Podzols 0.093 0.039 0.126 0.071 0.141 0.058
Dystric Histosols 0.280 0.144 0.355 0.109
Eutri-Histic Gleysols 0.122 0.034 0.28 0.087 Cabbage (head)
Haplic Kastanozems 0.055 0.032 0.0585 0.0092
Calcaric Chernozems 0.033 0.005 0.032 0.0099
Chernic Chernozem 0.038 0.017 0.046 0.021 0.033 0.0102 Haplic Chernozem 0.0509 0.0011 0.054 0.021 0.0447 0.0021
Luvic Chernozem 0.108 0.050 0.073 0.043 0.041 0.019
Grey-Luvic Phaeozem 0.093 0.026 0.074 0.014 0.086 0.032 Molli-Gleyic Fluvisols 0.0709 0.018 0.143 0.019 0.169 0.034
Albic Luvosols 0.078 0.019 0.090 0.032 0.107 0.021
Umbric Podzols 0.0468 0.0304 0.103 0.038 0.0821 0.0182
Dystric Histosols 0.159 0.062 0.1995 0.0804
For 90Sr, the dependence of the TFs on various soil properties is similar to that of 137Cs but the relation between 90Sr accumulation in crops and pHKCl (Fig. 16, 22) and content of OM (Fig. 17, 23) is weaker.
At the same time, 90Sr TFs tend to decrease with increase in exchangeable potassium (Fig. 13, 19), exchangeable calcium (Fig. 14, 20), cation exchange capacity (Fig. 15, 21) and clay content (Fig. 18, 24).
Thus, soil properties influence the behaviour of 90Sr and 137Cs in the soil-plant system differently.
Statistical methods need to be applied to estimate the effects of individual soil parameters on the radionuclide migration [22].
Exch. K in soil (cmol/kg)
TF Cs-137 in barley
-0,01 0,01 0,03 0,05 0,07 0,09 0,11
0,0 0,4 0,8 1,2 1,6 2,0 2,4
Fig. 1. The relationship between K and the 137Cs TF for barley.
Fig. 2. The relationship between Ca and the 137Cs TF for barley.
Fig. 3. The relationship between CEC and the 137Cs TF for barley.
Fig. 5. The relationship between OM and the 137Cs TF for barley.
Fig. 6. The relationship between the content of particles (<0.01 mm) and the 137Cs TF for barley.
Fig. 7. The relationship between K and the 137Cs TF for cabbage.
Fig. 8. The relationship between Ca and the 137Cs TF for cabbage.
Fig. 9. The relationship between CEC and the 137Cs TF for cabbage.
Fig. 11. The relationship between OM and the 137Cs TF for cabbage.
Fig. 12. The relationship between the content of particles (<0.01 mm) and the 137Cs TF for cabbage.
Fig. 13. The relationship between K and the 90Sr TF for barley.
Fig. 14. The relationship between Сa and the 90Sr TF for barley.
Fig. 15. The relationship between CEC and the 90Sr TF for barley.
pH
TF Sr-90 in barley
0,0 0,1 0,2 0,3 0,4
4,0 4,5 5,0 5,5 6,0 6,5 7,0 7,5 8,0 8,5
Fig. 16. The relationship between pH and the 90Sr TF for barle.y
OM (%)
TF Sr-90 in barley
0,0 0,1 0,2 0,3 0,4 0,5 0,6
-2 2 6 10 14 18 22
Fig. 17. The relationship between OM and the 90Sr TF for barle.y
Content of particles, size<0.01 mm (%)
TF Sr-90 in barley
0,0 0,1 0,2 0,3 0,4 0,5 0,6
5 15 25 35 45 55 65 75
Fig. 18. The relationship between content of particles (<0.01 mm) and the 90Sr TF of barley.
Exch. K in soil (cmol/kg)
TF Sr-90 in cabbage
0,00 0,04 0,08 0,12 0,16 0,20 0,24 0,28 0,32
-0,2 0,2 0,6 1,0 1,4 1,8 2,2 2,6
Fig. 19. The relationship between K and the 90Sr TF for cabbage.
Exch. Ca in soil (cmol/kg)
TF Sr-90 in cabbage
0,00 0,04 0,08 0,12 0,16 0,20 0,24 0,28 0,32
2 6 10 14 18 22 26 30 34
Fig. 20. The relationship between Ca and the 90Sr TF for cabbage.
CEC in soil (cmol/kg)
TF Sr-90 in cabbage
0,00 0,04 0,08 0,12 0,16 0,20 0,24 0,28 0,32
0 20 40 60 80 100
Fig. 21. The relationship between CEC and the 90Sr TF for cabbage.
pH
TF Sr-90 in cabbage
0,00 0,04 0,08 0,12 0,16 0,20 0,24
4,0 4,5 5,0 5,5 6,0 6,5 7,0 7,5 8,0 8,5
Fig. 22. The relationship between pH and the 90Sr TF for cabbage.
OM (%)
TF Sr-90 in cabbage
0,00 0,04 0,08 0,12 0,16 0,20 0,24 0,28 0,32
-2 4 10 16 22 28
Fig. 23. The impact of OM on the 90Sr TF of cabbage.
Content of particles, size<0.01 mm (%)
TF Sr-90 in cabbage
0,00 0,04 0,08 0,12 0,16 0,20 0,24 0,28 0,32
5 15 25 35 45 55 65 75
Fig. 24. The relationship between the content of particles (<0.01 mm) and the 90Sr TF of cabbage.
4. IDENTIFICATION OF QUANTITATIVE RELATIONSHIPS BETWEEN RADIONUCLIDE