65
dolomite flour, and other reclaiming additives in agriculture leads to additional
amounts of uranium entering the soil. Initially, in the Chernobyl products falling on
the territory of Belarus, uranium was mainly in the composition of oxidized fuel
particles. Over time, the fuel particles were destroyed, and the uranium species
changed as a result of interacting with the components of the environment and gradually approached to the natural uranium species.
The distribution of uranium along the vertical profiles of soils of various types,
differing in geomorphological position, humidification conditions, and the level of
uranium content was analyzed. In general, in the (0–20)-cm layer of undisturbed
soils, 46–57% of the uranium inventory in the soil profile is concentrated.
The fractions of uranium associated with the migratory active (located in pore
solution), exchangeable, mobile, and fixed forms were determined. It was found that
in the soils widely distributed in Belarus, the main amount of uranium (85–96%)
was in the fixed form. It was shown that the fractions of
238
U in the migratory active,
exchangeable, and mobile (conditionally biological available) forms increased from
loamy to sandy loam and to sandy soils. The fraction of U mob in mineral and organic
soils did not exceed 15%.
The values of К d coefficient as ratio between activity concentrations of radionuclide in the solid phase and pore solutions of water-saturated soils were estimated.
Among the mineral soils, the minimum coefficients K d (166–282) were characteristic of sandy soils. The maximum coefficients K d (720–1,400) were found for loamy
soils. The relatively high sorption properties of loamy soils to uranium were due to
the high (20–40 wt. %) content of the “physical” clay (the particle size of less than
1 × 10
−5
m). In organic soils, the K d coefficient varied over the range of 430–2.780
and significantly depended on the ratio of soluble and hardly soluble organic components and the acidity of the soil.
For some species of soil, the effect of temperature and humidity of the soil on the
uranium content in a mobile (conditionally biologically available) form was studied. In general, the genetic type of soil significantly affects the content of U mob in the
soil, as well as the degree of change in U mob content as a function of temperature. In
air-dry conditions, the maximum U mob content in sod-podzolic light loamy and
peaty soils was observed at a temperature of +15 °C. With a subsequent rise in temperature to +30 °C, the content of U mob in both soils was reduced. In water-saturated
soils, the maximum U mob content was observed after soil freezing.
For all the temperature regimes studied, the content of U mob in the sod-podzolic
medium loamy soil increased with an increase in soil moisture from 5.5 to 60% of
the WC. A subsequent increase in soil moisture from 60 to 100% resulted in a
decrease in the U mob content, and the levels reached were practically preserved with
a subsequent increase in humidity to 140% of the WC. From the data obtained, it
follows that freezing the waterlogged soil during the vegetation period can lead to
an increase in U mob content, which contributes to the accumulation of uranium by
terrestrial ecosystem vegetation.
The information on the uranium species in the soils, as well as on the K d values can
be used for parametrization of models for forecasting the redistribution of uranium in
soil media and uranium entering the natural waters and biological communities.
Uranium and Its Distribution in Typical Belarusian Soils
dolomite flour, and other reclaiming additives in agriculture leads to additional
amounts of uranium entering the soil. Initially, in the Chernobyl products falling on
the territory of Belarus, uranium was mainly in the composition of oxidized fuel
particles. Over time, the fuel particles were destroyed, and the uranium species
changed as a result of interacting with the components of the environment and gradually approached to the natural uranium species.
The distribution of uranium along the vertical profiles of soils of various types,
differing in geomorphological position, humidification conditions, and the level of
uranium content was analyzed. In general, in the (0–20)-cm layer of undisturbed
soils, 46–57% of the uranium inventory in the soil profile is concentrated.
The fractions of uranium associated with the migratory active (located in pore
solution), exchangeable, mobile, and fixed forms were determined. It was found that
in the soils widely distributed in Belarus, the main amount of uranium (85–96%)
was in the fixed form. It was shown that the fractions of
238
U in the migratory active,
exchangeable, and mobile (conditionally biological available) forms increased from
loamy to sandy loam and to sandy soils. The fraction of U mob in mineral and organic
soils did not exceed 15%.
The values of К d coefficient as ratio between activity concentrations of radionuclide in the solid phase and pore solutions of water-saturated soils were estimated.
Among the mineral soils, the minimum coefficients K d (166–282) were characteristic of sandy soils. The maximum coefficients K d (720–1,400) were found for loamy
soils. The relatively high sorption properties of loamy soils to uranium were due to
the high (20–40 wt. %) content of the “physical” clay (the particle size of less than
1 × 10
−5
m). In organic soils, the K d coefficient varied over the range of 430–2.780
and significantly depended on the ratio of soluble and hardly soluble organic components and the acidity of the soil.
For some species of soil, the effect of temperature and humidity of the soil on the
uranium content in a mobile (conditionally biologically available) form was studied. In general, the genetic type of soil significantly affects the content of U mob in the
soil, as well as the degree of change in U mob content as a function of temperature. In
air-dry conditions, the maximum U mob content in sod-podzolic light loamy and
peaty soils was observed at a temperature of +15 °C. With a subsequent rise in temperature to +30 °C, the content of U mob in both soils was reduced. In water-saturated
soils, the maximum U mob content was observed after soil freezing.
For all the temperature regimes studied, the content of U mob in the sod-podzolic
medium loamy soil increased with an increase in soil moisture from 5.5 to 60% of
the WC. A subsequent increase in soil moisture from 60 to 100% resulted in a
decrease in the U mob content, and the levels reached were practically preserved with
a subsequent increase in humidity to 140% of the WC. From the data obtained, it
follows that freezing the waterlogged soil during the vegetation period can lead to
an increase in U mob content, which contributes to the accumulation of uranium by
terrestrial ecosystem vegetation.
The information on the uranium species in the soils, as well as on the K d values can
be used for parametrization of models for forecasting the redistribution of uranium in
soil media and uranium entering the natural waters and biological communities.
Uranium and Its Distribution in Typical Belarusian Soils