RADIONUCLIDE TRANSFER IN FIELD EXPERIMENTS IN ACCORDANCE WITH THE PROGRAM FOR 2000-2002)

Kiev Ivankov, Poljesskoje 4.5¬5.9 0.5¬0.9 6.2¬18.1 6.4¬8.4 5.0¬7.1 Podzolu-

visols Sod-podzolic sandy

Chernigov Kozelets, Сhernigov, 5.2¬5.6 0.6¬0.8 6.0¬8.0 4.8¬6.0 6.3¬7.2 Podzolu

visols

Sod-podzolic gleic

Zhitomir Narodichi 5.4¬6.6 0.9¬1.7 6.2¬15.9 3.2¬8.4 17.6¬19.3 Kiev Borodjanka,

Vyshgorod, Brovary, Makarov

4.7¬6.2 0.5¬1.1 6.1¬15.5 3.2¬9.2 8.2¬11.6 Podzolu-

visols Sod-light podzolic sandy sand

Rivno Dubrovitsa 4.5¬6.0 0.5¬0.9 6.0¬16.3 4.0¬9.2 6.2¬8.4 Podzolu

visols - Sod-light podzolic sandy

Chernigov Repki 4.8¬5.5 0.7¬0.9 10.5¬13.2 6.0¬7.6 6.8¬7.8

Arenosols Sod sandy sand gleic

Rivno Sarny, Zarechnoje 5.6¬6.5 0.7¬1.2 17.1¬18.1 9.6¬10.0 13.8¬14.2 Arenosols Sod clay

sandy Rivno Rokitnoje 5.8¬6.7 1.0¬1.2 17.1¬18.3 8.4¬9.6 14.5¬16.1 Chernozem Chernozem

podzolised Kiev Kiev-Svjatoshin 6.2¬7.3 1.7¬2.7 16.3¬25.3 9.2¬20.4 25.7¬32.4 Rivno Dubrovitsa 3.8¬5.6 2.3¬9.3 6.0¬12.6 Histosols Peat-bog

Zhitomir Narodichi 4.6¬5.4 4.0¬12.5 4.5¬13.0

3. RADIONUCLIDE TRANSFER IN FIELD EXPERIMENTS IN ACCORDANCE WITH THE PROGRAM FOR 2000-2002)

3.1. Radionuclides transfer from various types of soil to crops

Concentrations of ¹³⁷Cs and ⁹⁰Sr in soil and crops was determined as earlier. Data on radionuclide content in components of the chain and calculated TF_ag and TF (accumulation) values are presented in Tables 5–7. All calculations were based on fresh weight of plants.

Soil contamin.

* - name of soil classification accepted in CIS

**-name of soil according to FAO-UNESCO classification

137Cs and ⁹⁰Sr soil to plant transfer factors (TF) depend on soil pH, humus, potassium and calcium contents, and biological peculiarities of crops. Increases of pH from 4.7–6.5 and potassium content in soil solution from 9.3 to 20.1 mg-eq/100 g (see Table 1) lead to decreases of ¹³⁷Cs accumulation in oats up to 7.2–122 times, in potatoes to 5.2–52 times and beet to 5–32 times (see Tables 5–7).

TABLE 6. RADIONUCLIDE TRANSFER FROM SOIL TO BEETROOT^†, 2002

(Podzoluvisol)** 3 150.1 7.51 25.52 6.68 0.17 0.89 0.05 0.24 Average, M±m^§ 172.4

TABLE 7. RADIONUCLIDE TRANSFER FROM SOIL TO POTATO TUBERS^†, 2002 Soil contamin.

by humus content. When calcium content changes from 2.9 (sod-podzolic) to 23.3 (chernozem) meq/100 g, and humus content from 1 to 1.8%, ⁹⁰Sr accumulation in oats decreases from 2.9 to 6.7 times, in potatoes from 3.4 to 10 times and in beet from 2.1 to 2.5 times (see Tables 5–7)

Analysis of the data allows some general conclusions to be drawn. According to data obtained during studies carried out in 1999–2002 both ¹³⁷Cs and ⁹⁰Sr transfer depended on climatic conditions, and agrochemical characteristics of soil. It should be noted that variation of TF reaches 10–20% in all cases but does not exceed 30% of the average. That allows the data to be used for prediction and the creation of analytical functions.

Data on the dynamics of radionuclide TFs during the period of study are presented in Table 8 and show that the minimum accumulation of ¹³⁷Cs in potatoes and beetroot occurred in 2000 and 2002.

These years are characterised by optimum values of temperature and moisture in the period vegetative growth (June–July), that lead to high yields (see Table 2 and 3) and a lower radionuclide accumulation by 1.3 times (peat), 2.8–3.0 (sod-podzolic) and 2–3 times (chernozem).

TABLE 8. CHANGES IN RADIONUCLIDE TFs WITH TIME

137Cs and ⁹⁰Sr TF (mean±SD)

Peat-bog Sod-podzolic Chernozem Years

137Cs ⁹⁰Sr ¹³⁷Cs ⁹⁰Sr ¹³⁷Cs ⁹⁰Sr

Grain of oats (moisture 15%)

1999 0.11±0.002 0.03±0.001 0.04±0.01 0.36±0.01 0.005±0.0002 0.06±0.002 2000 0.09±0.001 0.02±0.002 0.04±0.001 0.31±0.01 0.004±0.0001 0.05±0.002 2001 0.08±0.004 0.02±0.001 0.05±0.004 0.26±0.02 0.005±0.0004 0.032±0.003 2002 0.10±0.002 0.03±0.002 0.03±0.001 0.17±0.01 0.002±0.0004 0.03±0.0004

Beetroot (moisture 86%)

1999 0.15±0.001 0.04±0.001 0.11±0.004 0.28±0.01 0.03±0.0001 0.15±0.003 2000 0.11±0.001 0.06±0.002 0.04±0.002 0.32±0.003 0.01±0.001 0.14±0.003 2001 0.11±0.01 0.05±0.004 0.05±0.004 0.29±0.01 0.02±0.004 0.15±0.01 2002 0.12±0.002 0.06±0.001 0.05±0.002 0.27±0.01 0.01±0.004 0.11±0.002

Potato tubers (moisture 79%)

1999 0.08±0.003 0.03±0.002 0.12±0.005 0.10±0.002 0.007±0.001 0.03±0.001 2000 0.05±0.001 0.01±0.0003 0.03±0.001 0.11±0.001 0.005±0.001 0.02±0.001 2001 0.06±0.004 0.01±0.001 0.04±0.004 0.12±0.007 0.006±0.001 0.03±0.0001 2002 0.06±0.002 0.01±0.001 0.03±0.002 0.11±0.002 0.003±0.001 0.02±0.0001 A similar effect was observed for oats on chernozem in 2002 and on peat soil in 1999. Meteorological characteristics were optimum for the crop growth on peat in 1999 and on sod-podzolic soil and chernozem in 2002. Studies of radiocaesium transfer to various crops confirmed this trend.

It is clear that values of caesium TF are lower for all crops investigated on more fertile soils. Using the decrease of caesium TF to experimental plants as the criterion, soils can be put in a following order:

peat>sod-podzolic>chernozem. Cs transfer is dependent on exchangeable potassium content in a soil solution and pH (see Table 1).

A different picture is observed for strontium TF. Ca and organic matter content in soil determine strontium transfer—the higher these values, the lower strontium TF figures. It should be noted that this dependence is correct at Ca concentrations below 25 meq/100 g. Based on these characteristics soils

can be arranged in the following order: chernozem>peat>sod-podzolic. Precipitation rate did not affect values of strontium TF.

Crops can be put in the following order of ¹³⁷Cs TF: beetroot>oats>potatoes. Differences of TF are explained by biological peculiarities of crops in terms of vegetation and physiological development.

As seen in Table 8 our data belong to the tail-end of curves characterising the dynamics of caesium and strontium TF.

There is a clear inverse proportional relationship between agrochemical properties and TF of ⁹⁰Sr and

137Cs for all three crops grown on podzoluvisol and chernozem. TF values decrease in the order beetroot > oat grain >potato tubers. ⁹⁰Sr TF values are significantly higher than ¹³⁷Cs TF values. In contrast, ¹³⁷Cs TF values on the organic peat-bog soil are higher than those for ⁹⁰Sr, as the latter makes stable complexes with fulvic acids. Complex formation in a peat soil is a more important factor then soil pH in determining radionuclides migration. Probably the formation of radionuclide-organic complexes determines differences of ⁹⁰Sr TF between podzolic soil and chernozem.

The data permit at least two groups of soil properties determining absorption capacity to be defined, i.e. CEC, OM, pH, and complexation ability. It was shown earlier that hydrological regime (automorphous and hydromorphous) and soil particle size composition can be considered as principal characteristics. The last determines the availability of absorbing surface and its quality, and correlates with the exchangeable cations.

Evidently, the quantitative relationship between radionuclide TF value and soil properties requires the use the use of a complete estimate of soil properties accounting for the characteristics of the main phases.

4. DEPENDENCE OF RADIONUCLIDES ACCUMULATION IN PLANTS ON LEVEL OF SOIL