120
above- ground mass of cotton and wheat and the estimation of the amount of radionuclide in the root system require the information on the biomass of crops. Data on
the sizes of the root system remaining in the soil after harvesting cotton and wheat
and the balance of the above-ground biomass could not be found.
3 Mechanisms of Transfer of
238
U from Soil to Plants
The role of biogenic migration of
238
U, when it moves in the biosphere, is very significant, although its ability to be absorbed by plants is characterised as weak
(Alexakhin 1982). Nevertheless, the accumulation of
238
U in agricultural plants and
the subsequent entrance of a radionuclide into the human body can be a source of its
irradiation from the natural radiation background.
The properties of the soil-forming rock determine the content of
238
U in the soil;
profile differentiation depends on the genetic features of soil formation (Alexakhin
et al. 1990). It is noted both an accumulation of
238
U in the upper horizons enriched
with organic substances (Sultanbaev and Grigoryev 1979) and relatively uniform
distribution in the soil profile. Under pollution conditions,
238
U is mainly fixed by
clay minerals and organic matter in the upper soil horizons (Taskaev 1979; Alexakhin
et al. 1990). The initial chemical form of the element and the presence of macrocomponents have an effect on the sorption behaviour of the radionuclide from technogenic pollution sources. Due to the fixation (isomorphic entry into the crystal
lattice of minerals, diffusion into the internal cavities of the mineral structure by its
defects, precipitation or co-precipitation, complexation with nonmobile fractions of
organic matter), the biological availability of the radionuclide in contaminated soils
may be lower than in the background ones. A similar fact has been established for
the mountain taiga soils of Yakutia, altered as a result of exploration and development of
238
U deposits (Sobakin 1998). It was found that the biological absorption
coefficient (BAC) of
238
U correlates most closely with the content of the acid- soluble
form of the element.
The main factors determining the intake of
238
U from soil to plants are:
• The concentration of
238
U
• Biological features of plants
• Physical and chemical indicators of soils
• The content of
238
U mobile forms in the soil
• The chemical composition of soils and plants, soil moisture, the granulometric
and mineralogical composition of the soil, the time of interaction with the soil
and the forms of deposition of
238
U on the soil and vegetation cover
The quantitative characteristics of radionuclide intake from soil to plants are:
• Accumulation coefficient AC (Alexakhin and Korneyev 1992)
AC
Radionuclide concentration in the plant dry weight
Radionucl
=
(
)
i ide concentration in the soil
A. N. Ratnikov et al.
above- ground mass of cotton and wheat and the estimation of the amount of radionuclide in the root system require the information on the biomass of crops. Data on
the sizes of the root system remaining in the soil after harvesting cotton and wheat
and the balance of the above-ground biomass could not be found.
3 Mechanisms of Transfer of
238
U from Soil to Plants
The role of biogenic migration of
238
U, when it moves in the biosphere, is very significant, although its ability to be absorbed by plants is characterised as weak
(Alexakhin 1982). Nevertheless, the accumulation of
238
U in agricultural plants and
the subsequent entrance of a radionuclide into the human body can be a source of its
irradiation from the natural radiation background.
The properties of the soil-forming rock determine the content of
238
U in the soil;
profile differentiation depends on the genetic features of soil formation (Alexakhin
et al. 1990). It is noted both an accumulation of
238
U in the upper horizons enriched
with organic substances (Sultanbaev and Grigoryev 1979) and relatively uniform
distribution in the soil profile. Under pollution conditions,
238
U is mainly fixed by
clay minerals and organic matter in the upper soil horizons (Taskaev 1979; Alexakhin
et al. 1990). The initial chemical form of the element and the presence of macrocomponents have an effect on the sorption behaviour of the radionuclide from technogenic pollution sources. Due to the fixation (isomorphic entry into the crystal
lattice of minerals, diffusion into the internal cavities of the mineral structure by its
defects, precipitation or co-precipitation, complexation with nonmobile fractions of
organic matter), the biological availability of the radionuclide in contaminated soils
may be lower than in the background ones. A similar fact has been established for
the mountain taiga soils of Yakutia, altered as a result of exploration and development of
238
U deposits (Sobakin 1998). It was found that the biological absorption
coefficient (BAC) of
238
U correlates most closely with the content of the acid- soluble
form of the element.
The main factors determining the intake of
238
U from soil to plants are:
• The concentration of
238
U
• Biological features of plants
• Physical and chemical indicators of soils
• The content of
238
U mobile forms in the soil
• The chemical composition of soils and plants, soil moisture, the granulometric
and mineralogical composition of the soil, the time of interaction with the soil
and the forms of deposition of
238
U on the soil and vegetation cover
The quantitative characteristics of radionuclide intake from soil to plants are:
• Accumulation coefficient AC (Alexakhin and Korneyev 1992)
AC
Radionuclide concentration in the plant dry weight
Radionucl
=
(
)
i ide concentration in the soil
A. N. Ratnikov et al.