Distribution of Strontium in Soil: Interception, Weathering, Speciation, and Translocation to Plants

Abstract

Sr is characterized by rather high mobility in soils, and therefore it is included actively into migration pathways. The migration rate of strontium in the soil profile depends on the physicochemical and mineralogical characteristics of the soil. Thus, during the recent decades the concentration of ⁹⁰Sr mobility in Chernobyl zone soils has increased significantly due to the radionuclide leaching from the hot particles matrix and poor in humus and nutrients sod-podzolic sandy soils of this region. Migration rate of ⁹⁰Sr in plants has also increased.

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33© Springer International Publishing AG 2018
D.K. Gupta, C. Walther (eds.), Behaviour of Strontium in Plants and the
Environment, DOI10.1007/978-3-319-66574-0_3
Distribution ofStrontium inSoil: Interception,
Weathering, Speciation, andTranslocation
toPlants
SergiyDubchak
S. Dubchak (*)
State Ecological Academy of Postgraduate Education and Management,
V.Lypkivsky Str. 35, Building 2, Kyiv 03035, Ukraine
e-mail: sergiy_w@yahoo.com
Introduction
Strontium (Sr) is the element of the II group of the periodic system. Natural
strontium belongs to microelements and consists of a mixture of four stable isotopes
84Sr (0.56%), 86Sr (9.96%), 87Sr (7.02%), and 88Sr (82.0%). According to its physical
and chemical properties, strontium is analogous to calcium being its companion in
geochemical processes. Its estimated clarke content the earth’s crust is 340mgkg−1.
Strontium is contained in all plant and animal organisms in an amount of 10−2 to
10−3% of dry mass (Annenkov and Yudintseva 2002). The organism of adult human
contains about 0.3g of strontium. Almost all of strontium is localized in the skele-
ton, while all other organs contain only 3.3mg of this element. The release of radio-
active isotopes of strontium into the environment began in the middle of the last
century. The most important strontium radioisotope is long-lived 90Sr
(T1/2=29.12year). It was widely dispersed to the environment due to fallouts from
atmospheric testing of nuclear weapons and accidents at the nuclear fuel cycle facil-
ities and nuclear reactors (Prister 1998).
90Sr is a pure beta emitter with a maximum energy of 0.54MeV.Upon decay, it
forms a daughter radionuclide 90Y with a half-life of 64h. 90Sr has a long biological
half-life in the human body estimated to be about 18years. Due to its chemical simi-
larity to calcium, it is accumulated in bones and irradiates the bone marrow, causing
its high radiotoxicity (Prister 1998). Another radiologically signicant strontium
radioisotope is beta-emitting 89Sr (T1/2=51days). However, due to the shorter half-
life, it poses the radiological importance only for relatively short period (about 1
year) till further complete decay.

34
Release ofStrontium Radioisotopes totheEnvironment
The total amount of 89Sr and 90Sr released in the atmosphere is estimated about
90·1018 and 600·1015Bq correspondingly (Pavlockaya 1997). The rst signicant
release of strontium-90 from nuclear facility into the environment (about 2·1015Bq
according to various estimates) occurred in 1957 as a result of a nuclear accident at
the “Mayak” factory in the Southern Ural, USSR.
The accident at the Chernobyl and Fukushima nuclear power plants also intro-
duced a large amount of 90Sr into the environment, at that the largest part of the
radionuclide was deposited in the relative vicinity of these NPPs. The release of 90Sr
after the Chernobyl accident in 1986 is estimated at 8.2·1015Bq (about 4% of the
total inventory). After the accident at the Fukushima nuclear power plant, the rela-
tively small amount of radiostrontium (0.1·1015Bq) was released into the environ-
ment (Fukushima Daiichi accident: Report 2015).
The contamination of land territories with 90Sr has more local character as com-
pared with 137Cs. Thus, the most of 90Sr released after Chernobyl catastrophe
(approximately 3· 1015Bq) was deposited in form of fuel particles within 30-km
Exclusion zone (Kashparov etal. 2008). Except of the Chernobyl NPP industrial
site and radioactive waste disposal sites, the inventory of radiostrontium in soils of
the 30-km Exclusion zone is estimated at about 0.5 ·1015Bq. This value corre-
sponds to 0.7–0.8% of 90Sr total activity in the fourth block of Chernobyl NPP. Half
of radiostrontium inventory contained in the upper 0–30cm soil layer is localized
within only 2% of the territory of Chernobyl zone, and nearly 80% of its inventory
is concentrated within 11% of this area (Table1, Kashparov etal. 2008).
The analysis of data on the migration ability of 90Sr in the soils of Chernobyl
zone demonstrated that three decades after the accident the most of soils have the
main inventory of radiostrontium (more than 95% of its activity) in the upper
10–20cm layer (Kashparov etal. 1999). The intensive vertical migration of 90Sr is
Table 1 Distribution of 90Sr contamination in Chernobyl exclusion zone as of year 2007
Soil contamination (kBqm−2) Area (km2) Area percentage with level (%)
0–20 422 21.3
20–40 393 19.8
40–75 384 19.4
75–200 321 16.2
200–400 143 7.2
400–750 96 4.8
750–2000 143 7.2
2000–4000 43 2.2
4000–7500 20 1
7500–20,000 11 0.6
>20,000 6.6 0.3
Total 1982.6 100
S. Dubchak

35
observed only in weakly humied, unmatted sand, where radiostrontium inventory
in the upper 30-cm layer can be only 30–50% (Ivanov etal. 1996).
Speciation andMigration ofStrontium inSoil
Usually 90Sr has higher mobility in soils as compared to 137Cs. Like 137Cs, 90Sr can
be in water-soluble and water-insoluble forms. Absorption of 90Sr in soils is mainly
caused by the ion exchange. The greater part of strontium is retained in the upper
soil horizons. The rate of its migration in the soil prole depends on the physico-
chemical and mineralogical characteristics of the soil. In the presence of humus
horizon in soil prole located under the litter or sod layer in soil prole, 90Sr is
concentrated in this horizon. In soils such as sod-podzolic sandy, humus-peaty-gley
loam on sand, chernozem-meadow podzolized and leached chernozem, the certain
increase of the radionuclide content in the upper part of the illuvial horizon is
observed (Kashparov 1998). In saline soils, a second maximum appears which is
associated with a lower solubility of strontium sulfate and its mobility. In the upper
horizon of this soil 90Sr is efciently retained by the salt crust. The concentration of
strontium in the humus horizon is explained by the high content of humus, the large
cation absorption capacity and the formation of inactive compounds with organic
matter of soils.
In the model experiments with introduction of 90Sr to different soils in vegetation
vessels, it was found that the rate of its migration under the experimental conditions
increases with an increase of exchangeable calcium content. An increase of 90Sr
migration ability in the soil prole with an increase of the calcium content was also
observed in the eld conditions. It was also found that migration of strontium
increases with raising the acidity and organic matter content (Lazarevich and
Chernukha 2007).
The accumulation coefcient of 90Sr by different plant cultures varies in a rather
wide range, from 0.02 to 12, while for 137Cs it varies from 0.02 to 1.1 (Ageets 2001).
The accumulation of strontium by plant biomass can reach 10–40 kBq per
10MBqm−2. In particular, 90Sr is accumulated in large quantities in legumes, root
crops, and, to a lesser extent (3–7 times less), cereals(Tieplyakov 2010)(Table 2).
According to the classication of radionuclides by type of behavior in the soil–
plant system, Sr2+ has the following basic characteristics:
• Type of behavior—exchangeable;
• Main mechanism of xation in the soil—ion exchange;
Table 2 Accumulation factors of 90Sr in aboveground parts of wheat (Bqkg−1/kBqm−2)
Isotope Leaves Stems Spikelets Grains
Sr-90 57.70 10.50 5.70 3.40
Distribution ofStrontium inSoil: Interception, Weathering, Speciation…

36
• The most important factor of migration—the presence of other cations in the
solution (Sanzharova 2005).
The xation and distribution of 90Sr in the soil are mainly determined by the
behavior of its isotopic carrier—stable strontium, as well as the chemical analogue
of the non-isotope carrier—stable calcium (Ca2+).
When considering 90Sr ions, one can distinguish three following groups:
1. Ions in the soil solution;
2. Exchange ions on the surface of mineral and organic particles;
3. Ions belonging to practically insoluble compounds (Sanzharova 2005).
The rate of strontium migration increases with raising the moistening degree of
soils. It was found that the vertical migration of 90Sr proceeds more intensively than
137Cs in the prole of automorphous fallow soils. In some unprocessed lands, the
main amount of 90Sr (58–61%) and 137Cs (70–85%) is concentrated in the upper part
of 0–5cm of the root layer. The increased 90Sr transfer to plants is explained by its
much greater mobility in the soil than in 137Cs. Thus, about 85–98% of 137Cs is
rmly xed by soil compounds, while for 90Sr this value is only 7–12% (Ministry of
Agriculture and Food: Rules 2002).
According to observations data, it was found that the effective half-life of 90Sr in
0–5cm layer of fallow automorphous sod-podzolic soils is 14.3–15.0years, while
for 137Cs this value is 15.3–21.5years. With an increase in the hydromorphism degree
of soils, the intensity of vertical migration of radionuclides is being increased.
Accordingly, for sod-podzolic gleyey sandy-loam soil the effective half-life of radio-
nuclides is reduced (90Sr– to 10.5years, 137Cs– to 13.8years; Sanzharova 2005).
90Sr belongs to the group of mobile radionuclides, since it is not involved in the
ion exchange reactions with the ions of the clay particles of the soil-absorbing com-
plex and is found in the soil mainly in a mobile state. This radionuclide is character-
ized with the predominance of easily accessible forms for plants, which amount to
53–87% of its total content and tend to increase with time. 90Sr has an oxidation state
+2, and it is found in form of cations in the soil solution. The solubility of 90Sr bicar-
bonate is higher than that of calcium bicarbonate; therefore strontium is more mobile
in the soil than calcium (Kabata-Pendias and Mukherjee 2007). Thus, more than 80%
of 90Sr is being in the exchangeable and water-soluble forms. With the lapse of time,
the destruction of hot particles containing cesium, strontium and plutonium takes
place (Kashparov 1998). With time radiostrontium is being xed by clay minerals. It
is a part of the soil solution in a mobile form, thus increasing the content of water-
soluble and exchangeable forms (Lazarevich and Chernukha 2007).
The degree of strontium accumulation by plants from the soil depends on its
chemical form, the physiological needs of plants and the physicochemical proper-
ties. The stronger the radioisotope is xed in the soil, the smaller its amount is
transferred the plant. Thus, oats cultivated on sand accumulated several times more
90Sr than plants grown on heavy loam. Thus, 8–10% of strontium was transferred to
plants from clayey sand, while plants grown on heavy loam accumulated only 1%
of the total 90Sr introduced into the soil. Likewise, strontium is accumulated by
S. Dubchak

37
plants in relatively high degree as compared to other chemical elements according
to the following sequence (Kashparov etal. 2005):
Sr>I >Ba>Cs, Ru>Ce>Y, Pm, Zr, Nb>Pu
It was found that 90Sr relatively easily penetrates through the root system into all
parts of the plant, while the radioisotopes of cerium, ruthenium, zirconium, yttrium,
and plutonium are accumulated mainly in the plant’s root system. The essential role
in sorption processes of 90Sr by soil is related to the isomorphous replacement in
minerals containing calcium and magnesium, in particular calcite and limestone
(CaCO3), gypsum (CaSO4·2H2O), and dolomite (CaMg(CO3)2) (Sanzharova 2005).
The ion exchange is a predominant mechanism of 90Sr absorption by solid phase
of the soils that is analogous to the adsorption of stable Sr and Ca. Therefore, the
sorption of 90Sr by the solid phase of soils depends on the presence of macro con-
centrations of cations in the solution. The following sequence of inuence of com-
peting cations on sorption of 90Sr by solid phase of soils is revealed: Al3+>Fe3+>B
a2+>Ca2+>Mg2+>K+>NH4+>Na+ (Sanzharova 2005).
The composition and the mineral content of soils have a considerable inuence on
the state and xation of 90Sr in the soil-absorbing complex. 90Sr is more rmly xed
in soils with a high content of silt particles. The clayey soil minerals can sorb up to
99% of this radionuclide. 90Sr is sorbed more preferably by such minerals as ascanite,
bentonite, vermiculite, phlogopite, and humbrin, and to a much lesser extent—by
hydromuscovite and hydrogrogite. Minerals of the montmorillonite group absorb
92.0–99.9% of 90Sr, while minerals of the kaolinite group—40–68%, micas—71–
87%, and hydromicas—80–88%. Minerals of the calcite group, feldspars, quartz,
and gypsum absorb about 10–50% of 90Sr (Vasilenko and Vasilenko 2002).
The behavior of 90Sr is also affected by the organic matter of the soil. The distri-
bution and mobility of 90Sr in soils is largely determined by the quantity and qualita-
tive composition of humus. The radionuclide is present in soils mainly not in the
form of individual compounds with organic substances of a nonspecic nature and
actually humic acids, but in the form of complex compounds, which also contain
Ca, Fe, and Al (Kashparov etal. 2005). The adsorption mechanisms of 90Sr are dif-
ferent in comparison with 137Cs. Radiostrontium is characterized by a simple and
almost complete exchange at surface exchange sites of clay particles. The yield of
the radionuclide in the soil solution also increases with the gain of Ca yield, since
Sr and Ca are present in the solution in a certain ratio. However, the distribution of
90Sr between the soil solution and the absorbing complex differs from the analogous
distribution for Ca. The 90Sr/Ca ratio in the soil solution varies from 0.49 to 0.78 of
the ratio of these ions in the soil, which is related to a stronger 90Sr sorption com-
pared to Ca (Sanzharova 2005).
Since 90Sr in transferred to plants from the soil solution, it can be assumed that
the concentration of the radionuclide in the plant is directly proportional to its con-
centration in the soil solution (other things being equal).
The value indicating the change of 90Sr/Ca ratio upon its transfer from soil to
plant is called the discrimination coefcient. The effect of 90Sr discrimination is a
stronger xation of this radionuclide in the soil as compared to calcium. Usually, the
Distribution ofStrontium inSoil: Interception, Weathering, Speciation…

38
discrimination coefcient varies depending on the degree of soil saturation with
stable calcium, plant species, and the period of plant development. For the most
plant species the discrimination coefcient of 90Sr is 0.8–1.0 (Yudintseva and
Gulyakin 1998).
90Sr2+ is absorbed by plants via transport systems of its macro analogue Ca2+. The
transport of Ca2+ is mainly conducted in the apoplast by free diffusion accelerated
by transpiration in the cell wall, where one part of the ions are in a solution identical
to the outer soil solution, and another part of ions is bound by xed charged centers
in the cell walls of the root exchange complex (Kutlakhmetov etal. 2003).
Translocation ofStrontium toPlant Species
(Factors Inuencing theRadionuclide Transfer)
After their absorption, the ions of 90Sr2+ easily penetrate into the “free space” of the
root hair tissues due to the diffusion. Further the ions enter the conductive tissues of
the root by active transfer and penetrate into the conductive tissues of the plant.
Thus, an upward movement of strontium ions along the vascular tissue is carried out
(Ministry of Agriculture and Food: Rules 2002).
Radioactive isotopes of Sr are analogues of Ca, have much similar in their intake
into plants and distribution across its various organs. Thus, 90Sr ions after their
uptake by roots are accumulated to large extent in aboveground organs of plants
(Kashparov etal. 2005).
The regularity of strontium activity distribution in plant organs is that 90Sr, enter-
ing the aboveground part of the plant, is mainly concentrated in straw (leaves and
stems), less in chaff (spikelets, wisps without grains) and relatively little in grains.
The absorption of 90Sr by plants lags behind the increase of aboveground mass.
Accordingly, the accumulation of radionuclide per unit of dry weight decreases with
the growth of the plant, but it increases during the maturation of plant. The intake of
90Sr into plants increases, as a rule, with an increase in its concentration in solution.
The maximum absorption of radiostrontium is observed at a pH close to neutral
(Kashparov etal. 2005).
The accumulation of 90Sr by plants is also inuenced by their various biological
features, among which the evolutionary origin of plants or phylogenesis. Plants of
early origin accumulate more radiostrontium than plants originated in later periods
(Konoplya 1996). According to the accumulation of strontium, some ora divisions
are arranged in the following descending order: lichens>mosses>ferns>gymno-
sperms > angiosperms (Shkolnik 2012). The differences in the accumulation of
radionuclides are revealed within the classes, families and species. The interspecic
differences can reach up to 5–100 times. The content of radiostrontium per dry mat-
ter of individual crops can differ up to 30 times with the same radionuclide inven-
tory in the soil (Prister 1998). The varietal differences in the accumulation of
radiostrontium are much smaller (up to 1.5–3 times), but they must also be taken
S. Dubchak

39
into account when selecting crops for cultivation under conditions of radioactive
contamination (Shkolnik 2012). According to accumulation of 90Sr, plants are clas-
sied as high-accumulating (legumes), medium-accumulating (cereals) and weakly
accumulating cultures (grains). The accumulation of 90Sr in the commodity part of
some plant cultures could be presented in the following descending order: root
crops >beans> potatoes > groats >cereals and vegetable crops (Vasilenko and
Vasilenko 2002).
The sequence of cultures descending by 90Sr accumulation differs signicantly
from that of 137Cs. The highest accumulation 90Sr in grain was revealed for the spring
rape, followed by descending order: lupine > peas > vetch > barley > spring
wheat>oats>winter wheat and winter rye (Lazarevich and Chernukha 2007).
The largest amount of 90Sr is transferred into straw of barley, followed by straw
of spring and winter wheat, oats and winter rye. According to the accumulation of
radiostrontium in the biomass, the cultures are arranged in the following descending
order: clover>lupine> pea > perennial grasses in oodplain lands > perennial
cereal–bean mixtures > vetch > spring rape > pea–oat and vetch–oat mixtures
>herbs in natural hayelds > grasses on drained lands > grasses on arable
lands>corn (Lazarevich and Chernukha 2007).
The transfer factors of 90Sr in plant biomass depend both on the density of pollu-
tion and on the soil type, the degree of soil moistening, the granulometric composi-
tion and the agrochemical properties. Therefore the transfer factors need periodic
rectication. The indexes of soil fertility also have a signicant impact on the accu-
mulation of radionuclides by all crops.
The high degree of 90Sr mobility in the soil determines the increased transfer fac-
tors of this radioisotope from soil to plants, which are on average an order of mag-
nitude higher than in 137Cs. In general, radiostrontium is transferred to plants from
acidic soils more intensively than from weakly acidic, neutral or slightly alkaline
soils. The sod-podzolic soils are characterized by high initial acidity and weak
alkali saturation. With increase of soil acidity, the xation strength of 90Sr and 137Cs
by soil absorbing complex is reduced and, accordingly, the intensity of their intake
to plants is increased. In case when pH is raised, a number of radionuclides are
transformed from the ionic form into various hydrolysis complex compounds that
reduces their availability for plants (Sanzharova 2005).
Depending on the soil type, the transfer factors of 90Sr can vary for the same
inventory of this radionuclide in the soil up to 2–5 times. For example, the accumula-
tion factor of 90Sr for potatoes on sod-podzolic sandy soil is 0.33, while on sod-
podzolic loamy soil it is 0.17. Polissya is the region of Ukraine most contaminated
with radiostrontium. It has mainly sandy-loamy light sod-podzolic and peaty-bog
soils (Kashparov etal. 2005). The transfer coefcients of 90Sr into plants are 4–5
times higher in this region compared to other types of soils, because in case of clay
minerals deciency, the radiostrontium is found in these soils mostly in water- soluble
and exchange forms. The accumulation of radionuclides in peaty-bog soils depends
on the cultivation of the soil, the mineralization and composition of soil ash, the
thickness of the peat layer, the botanical composition of peat-forming plants, the
Distribution ofStrontium inSoil: Interception, Weathering, Speciation…

40
acidity of the soil solution, the presence of exchangeable cations, the soil moisture as
well as depth and mineralization of groundwater (Kutlakhmetov etal. 2003).
With the same level of contamination, the intake of 90Sr into plants and its accu-
mulation in the crop will be unequal on different soils. The recent studies have
shown that reduced intake of 90Sr into plants and, correspondingly, its accumulation
in food products is observed on fertile soils characterized by high sorption capacity
(Table3, Klekovkin 2004).
A negative dependence between the content of exchangeable calcium, the acidity
level of the soil solution and the intake of 90Sr to plants was found. That is, the
higher the concentration of exchangeable calcium in the soil and the lower acidity
of the soil solution, the smaller the transfer factors of 90Sr to plants (Kutlakhmetov
etal. 2003).
Application ofCountermeasures forReduction ofStrontium
Transfer toPlants
As the content of exchangeable calcium increases from 550 to 2000mg CaO per kg
of soil, the transfer factors are decreased in 1.5–2 times. The change of acidity of the
soil solution from the acidic interval (pH=4.5–5.0) to the neutral interval (pH=6.5–
7.0) reduces 90Sr transfer to plants by 2–3 times. Further saturation of soil with
calcium shifts the pH to the alkaline range, but this is not accompanied with a
decrease of transfer factors (Table4, Konoplya 1996).
Table 3 Average values of 90Sr accumulation factor for agricultural crops (Bqkg−1/kBqm−2)
Culture/organs Sandy loam Medium loam Chernozem Heavy loam
Wheat (grain) 0.70 0.20 0.12 0.06
Potato (tubers) 0.35 0.10 0.06 0.03
Table beetroot (root crop) 1.20 0.34 0.20 0.10
Cabbage (head) 0.90 0.22 0.16 0.07
Cucumber (fetus) 0.35 0.10 0.06 0.03
Tomato (fetus) 0.14 0.04 0.02 0.01
Clover (hay) 20.00 6.00 4.00 2.00
Timothy grass (hay) 7.00 2.00 1.20 0.60
Table 4 90Sr transfer factors of crops depending on the acidity of sod-podzolic loamy soil (Bqkg−1
(plant)/Bqkg−1 (soil) d.w.)
Culture
Acidity value of soil, pH (KCl)
<4.5 4.6–5.0 5.1–5.5 5.6–6.0 6.1–7.0 >7.0
Oats 1.71 1.35 1.25 1.21 1.18 1.10
Barley – 1.45 1.38 1.32 1.28 1.16
Peas – 1.31 1.55 1.44 1.37 1.33
Potatoes 0.36 0.27 0.21 0.15 0.13 0.12
S. Dubchak

41
The practical application of the above research results is the soil liming. This is
one of the most important ways to increase the productivity of agricultural land.
When lime is applied to acidic soil, the content of mobile calcium and magnesium
increases sharply, which affects the biological availability of some radionuclides,
especially 90Sr (Yudintseva and Gulyakin 1998).
When introducing lime fertilizers to acidic soil, the concentration of hydrogen
ions decreases in the soil solution, while the content of mobile calcium decreases.
This effect strengthens 90Sr binding in the soil, thereby reducing its availability to
plants. The liming of acidic soils not only limits 90Sr accumulation in the crops har-
vest, but also increases the fertility of the soil, but also increases the soil fertility and
crop yield, as well as contributes to “dilution” of the radionuclide per unit of plant
biomass (Aleksakhin and Korneev 2001).
It was found that the application of lime in a concentration corresponding to
complete hydrolytic acidity reduces the content of radiostrontium in crop produc-
tion by 1.5–3 times (sometimes up to 10 times), depending on the soil type and
initial acidity. The intake of 90Sr in the crop of plants can be reduced under the inu-
ence of lime depending on the biological features and individual parts of the crop in
3–20 times (Kutlakhmetov etal. 2003). The liming of acid soils reduces the accu-
mulation of 90Sr in the harvest of legumes (peas, vetch, and clover) more than in the
harvest of cereals (oats, barley, timothy grass, and meadow grassland). When lime
is applied in an amount equivalent to 100% of the cation exchange capacity of the
soil, the content of 90Sr in the tops and roots of sugar beet decreases by 7.5 and 20
times respectively, in peas and clover—by 6–8 times, in straw of barley and oats as
well as in hay of timothy grass—by 3–4 times (Aleksakhin and Korneev 2001).
It has been found that the greater the soil saturation with exchange alkali, the
lower 90Sr transfer factors to plants. The peat bog soils are typical acidic soils poor
in potassium, calcium, and magnesium. Therefore 90Sr transfer factors on these soils
are 5–20 times higher than on sod-podzolic ones (Prister 2005).
A considerable impact on the 90Sr accumulation by plants has a moistening
regime of soils. It is known that the amount of strontium cations displaced from the
soil into the solution increases with the gain of humidity(Gerzabek etal. 1999). It
is related to the complex nature of the mutual inuence of moisture, soil properties
and biological characteristics of plants on the migration processes of radiostrontium
in the soil-plant chain. With gain of the soil moisture, the fraction of water-soluble
and exchangeable 90Sr increases, so the transfer factors and radiostrontium content
in vegetation increase as well.
The transfer of Sr to plants is affected by the organic matter of the soil. Humus
acids, especially humic acid, form complex compounds with radiostrontium called
humates. Therefore the availability of strontium from the organic complexes is
reduced a factor of 2–4. The increased bioavailability of 90Sr in peat-bog soils is
associated with the ability of organic matter to x radionuclide ions on the surface
of organic colloids (Gudkov etal. 2013). Therefore the strong sorption of radio-
strontium is not ensured and its availability to plants is increased. In addition, the
acidity of the soil solution in peaty-marsh soils is usually increased, that ensures
good solubility of radiostrontium salts and their accessibility to plants. Thus, the
Distribution ofStrontium inSoil: Interception, Weathering, Speciation…

42
factors of soil fertility can have a signicant impact on the accumulation of
radiostrontium by agricultural crops.
Conclusion
Radioactive strontium is referred to as biologically signicant radionuclides being
characterized with high toxicity. It role in soil contamination and population expo-
sure has remained considerable due to accidental releases. 90Sr that deposits onto the
surface is under the inuence of natural factors in the migration processes. After
atmosphere, soil is the most important depot of 90Sr. The migration of radiostron-
tium in the soil is signicantly inuenced by the physicochemical properties of the
radionuclide and the soil, climatic conditions, landscape, soil type, hydrological
regime, vegetation, agrochemical features of agriculture, etc.
90Sr is predominantly found in easily accessible forms for plants, and the total
content of these forms tends to increase over time. The uptake of radiostrontium
from soil is primarily determined by its bioavailability, solubility, agrochemical soil
properties, and cultivated plant species. Therefore, the understanding of 90Sr specia-
tion in the environment represents a vital tool for tracing transport mechanisms,
distribution pathways, and radionuclide bioavailability.
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