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ЭКОЛОГИЯ ПОЧВ
!'2Otarov A., *Ibraeva M., *Ustemirova A.
ACCUMULATION OF RADIONUCLIDES BY PLANTS AND THEIR BIOLOGICAL CIRCULATION CAPACITY
1Kazakh Research Institute of Soil Science and Agrochemistry after U.U. Uspanov, 050060, Almaty, 75 V al-Farabi avenue, Kazakhstan, e-mail: azimbay@bk.ru 2Scientific-Research Center for Ecology and Environment of Central Asia, 050060, Almaty, 75 V al-Farabi avenue, Kazakhstan Abstract. The research results on accumulative ability of main dominating types of vegetation in the low reaches of the river Ili, are presented. It is determined that all explored types of plants mainly accumulate Sr90 rather than Cs137. Classification of crops is performed according to radionuclides accumulation ability. The degree of radionuclides, involved into biological cycle, is very significant and ranges within hundredths, thousandth share of percentage of their level in soil.
Key words: ancient Akdala-Bakanas delta, soil-plant, accumulation rates, ratio 137Cs:90Sr, removal of radionuclides.
INTRODUCTION
Among the large number of artificial radionuclides, which form in fission of heavy nuclei, 90Sr and 137Cs, being chemical analogous of such biologically important elements as Ca and K, in large quantity are concentrated in plants. Accumulation coefficients 90Sr and 137Cs can reach 20, and 134Cs and 137Cs - 2 [1].
In the soil-plant system, 90Sr has great biological mobility in comparison with 137Cs [2]. One of major reasons for this difference is the process of "aging" of radionuclides, which is most specific for 137Cs. The "aging" process represents a complex of crystal-chemical reaction with possible entry of radionuclide into crystal cell of secondary clay minerals [3, 4]. There is no consensus on fixation mechanisms of 137Cs in soil. Preference is given to possible entry of 137Cs into inter-packet spaces of layered clay secondary minerals [5, 6], though other types of crystal-chemical reaction of 137Cs in soil are not excluded, when application of muscovite in soil and increased contact time of mineral with radionuclide solution has not affected the strength of sorption of 137Cs with soil [7]. However, quite a lot of works [8-10] testify in favor of the theory of crystal-chemical sorption of 137Cs.
In regard to the above mentioned, the assessment of radionuclide accumulat-
ing ability by main types of vegetation in the lower reaches of the Ili river and calculation of values of their radionuclide accumulation coefficients is one of the urgent problems.
OBJECTS AND METHODS
The research object is soil-vegetation cover of the lower reaches of Ili river that occupies the southwestern part of Balkhash-undrainage depression. The main part of the research object begins at the foot of Tasmurun mountain near the Bakbakty village. In the northeast, it has boundary with sandy massif Sary-Ishik-Otrau, in the north-west with sandy area Taukum and in the north - with water area of the lake Balkhash (Figure 1).
Formation of soil-plant cover of ancient delta is closely linked with the history of formation of the river delta. A number of researchers [11, 12] believe that initially the whole Balkhash depression looked like a sandy desert, and then later Ili river has been introduced, and as a consequence of increased moisture in the cavity water-marsh and meadow terrains have formed. The combination of desert regime and high humidity created an exceptional contrast and diversity of soil and vegetation cover of the downstream.
The choice of this region is justified by the fact that it is the object in the whole Ili-Balkhash basin, which is most heavily
exposed to anthropogenic impact. The lower reaches of the rivers are almost always the final area of geochemical flow, and natural complexes are environmentally very vulnerable. In addition, Akdala rice growing area is located in the ancient Akdala-Bakanas delta. It is known that the
increased rates of fertilizers, herbicides, pesticides, and other crop protection chemicals are applied on rice due to its biological features. All of them as impurities constantly, unfortunately, contain a considerable amount of heavy metal salts, radionuclides and other pollutants.
Figure 1 - Research object scheme of the lower stream of Ili river
In addition, due to large volume and high salinity there is a sharp problem of polluted return water, which often exceed the design standards both in composition and in volume. The return drainage sewage water becomes more polluted due to the increasing pressures on the environment. In addition, there is another negative natural factor - a factor of almost wide spread saline soils in the lower reaches of Ili river.
In this regard, we are consider the lower stream of the Ili river as anthropogenic and natural source, significantly influencing on ecological well-being of southern Balkhash area and Balkhash lake.
Artificial radionuclides have been determined by radiochemical method. The essence of radiochemical analysis method, in general, is as follows. To extract radio-chemically pure 90Sr and 137Cs from solution, their stable inactive isotopes, so-called "isotope carriers" are used. It is necessary to observe the following conditions: - first, the quantity of carrier must be sufficient for complete extracting of the element - second, for reducing self-absorption and self-scattering effect in measuring the activity of the extracted element, the quantity of carrier should be minimal, especially in low activeness. To determine 90Sr and 137Cs in plant and soil
samples were used methodological developments, which allow determining 90Sr and 137Cs from one sample. 137Cs has been determined by antimony-iodine method and 90Sr by oxalate method. In both cases, methods of deposition of radionuclides with carrier have been used. 137Cs was deposited with a saturated solution of antimony trichloride in presence of ammonium iodide, and then the activeness of deposit was measured. Chemical output of carrier was determined by gravimetric method. 90Sr was deposited by concentrated ammonia in presence of oxalic acid. Then, after separation of Fe, La and Y (separation time was recorded) 90Y daughter product of 90Sr and activeness was determined by it.
Table 1 - Accumulation coefficients (AC) of the lower reaches of the Ili river
Activeness of preparations was measured on device of small background UMF-1500 with counter the SBT-13.
Method of determination of 90Sr and 137Cs in plant samples after ashing is similar to method of determining soil samples.
RESULTS AND DISCUSSION In order to assess accumulation capacity of main types of vegetation in lower reaches of the Ili river with respect to ra-dionuclides, their accumulation rates were calculated, which are expresses by ratio between radionuclide content in dry plant mass unit and their content in soil (Table 1).
adionuclides by main types of vegetation in
Soils Plants AC
90 Sr 137 Cs
Alluvial- meadow-tugai Meadow grass 0,3 0,1
Licorice «Glycyrrhfza» 0,4 0,1
Brunets «Poterium» 0,4 0,04
Alluvial- meadow Meadow grass 2,8 2,2
Chingil «Halimodendron» 0,2 0,8
Swamp- meadow Reed «Phragmites» 0,06 0,09
Licorice «Glycyrrhfza» 0,6 0,09
Swamp- meadow- drying Reed «Phragmites» 0,1 0,4
Meadow-swamp Reed «Phragmites» 0,4 0,1
Meadow grass 4,5 1,1
Peat-swamp Reed «Phragmites» 0,06 0,2
Saline meadow Tamarisk «Tamarix» 1,1 0,6
Reed «Phragmites» 0,04 0,01
Camel-thorn «Alhagi» 3,5 0,4
Sweda «Suaeda» 0,5 0,03
Saline crust-puffy Black saxaul «Haloxylon aphyllum» 0,6 0,1
Biyurgun «Anabasis salsa» 2,3 0,2
Sarsazan «Halocnemum» 0,8 0,4
Karabarak «Halostachys belangeriana» 0,2 0,1
Continuation tab. 31
Takyr like Biyurgun «Anabasis salsa» 1,8 0,7
Keireuk «Salsola orientals» 3,4 0,3
Dust- sandy Wormwood «Artemisia» 1,1 0,1
Teresken «Ceratoides» 1,0 0,1
Kokpek «Atriplex alba» 0,4 0,2
White saxaul «Haloxylon persicum» 1,3 0,3
Results of analyzes of accumulation coefficient values indicate the presence of significant differences between radionuclides and between plants. Almost all explored plants largely accumulate Sr90 rather than Cs137. In most cases, the accumulation rates of Sr90 are higher than AR Cs137. The largest accumulation ability in relation to Sr90 was shown by meadow grass (4.5), camel thorn (3.5), keireuk (3.4), and the lowest - reed with accumulation rate 0.06.
In relation to Cs137 it was found only one plant (meadow grass) which has accumulation coefficient greater than one. It has been also revealed that accumulation capacity depends on soil conditions of plant habitat. For example, meadow herbs which grow on different soils have different accumulation coefficients - on alluvial-meadow tugai soils 0.3, on alluvial-meadow soils 2.8 and on meadow-marsh soils 4.5.
From the above facts it can be concluded that the removal of radionuclides by plants in lower reaches of Ili river depends on plant biological characteristics and soil physical and chemical properties as well as radionuclides themselves. Consequently, radionuclides accumulation coefficient value also depends on soil and plant properties and properties of radio-nuclide itself. The obtained data on concentration of radionuclides in soil, plants and accumulation coefficients may be used to evaluate radio-ecological situation of the lower reaches of Ili river and forecasting estimates.
Correlations between 137Cs : 90Sr in atmospheric precipitation, which have been observed or long-term period in different parts of the globe, are relatively constant and estimated by figure 1.6 [13]. After falling on the earth surface this ratio depending on terrain-geochemical, soil and other conditions may vary in one or another direction, and can serve as a measure of evaluation of migration ability of these radionuclides in certain terrain components.
In comparing ratio 137Cs : 90Sr in soils and by certain plant species, it can be seen that in transition of radionuclides from soil to plants, this ratio is greatly disturbed, and in most cases becomes narrow, i.e. plants more intensively remove 90Sr rather than 137Cs. It was also determined that the ratio 137Cs : 90Sr in plants, as well as in case with soil, fluctuates quite widely reaching 55.5 multiple values. The maximum value of this ratio was typical for reed as a leading dominant of meadow vegetation and is estimated by figure 11.1, and minimum value 0.2 belongs to brunts as representative of meadow vegetation. Consequently, in transition from soil to plants in relation to these radionuclides, selective ration is shown from various plant species.
Furthermore, it was determined that this ratio also depends on soil conditions of plant habitat. For example, range of ratio 137Cs : 90Sr in aboveground mass of reed, depending on soil conditions is 6.5 times of value, while in meadow grass this range is 1.8 (Table 2).
Table 2 - The ratio 137Cs : 90Sr in main soil types and plant species of the lower reaches of Ili river
Soils 137Cs : 90Sr In soil Plants 137Cs : 90Sr In plants
Alluvial- meadow-tugai 1,59 Meadow grass 0,9
Licorice «Glycyrrhiza» 0,4
Brunets «Poterium» 0,2
Alluvial- meadow 1,9 Meadow grass 0,9
Chingil «Halimodendron» 3,8
Swamp- meadow 1,7 Reed «Phraqmites» 5,5
Licorice «Glycyrrhiza» 0,5
Swamp- meadow- drying 3,8 Reed «Phraqmites» 11,1
Meadow-swamp 4,7 Reed «Phraqmites» 1,7
Meadow grass 1,6
Peat-swamp 2,9 Reed «Phraqmites» 7,5
Saline meadow 3,9 Tamarisk «Tamarix» 1,8
Reed «Phraqmites» 8,0
Camel-thorn «Alhagi» 0,4
Sweda «Suaeda» 0,6
Saline crust-puffy 3,4 Black saxaul «Haloxylon aphyllum» 0,9
Biyurgun «Anabasis salsa» 0,3
Sarsazan «Halocnemum» 1,5
Karabarak «Halostachys belangeriana» 1,6
Takyr like 2,0 Biyurgun «Anabasis salsa» 1,2
Keireuk «Salsola orientalis» 0,3
Dust- sandy 3,6 Wormwood «Artemisia» 0,2
Teresken «Ceratoides» 0,4
Kokpek «Atriplex alba» 1,64
White saxaul «Haloxylon persicum» 0,6
On this basis, it can be concluded that the removal and accumulation of radionuclides by plants, along with other factors, also largely depends on specific features of plant, soil conditions of their habitats and properties of radionuclides.
By magnitude of this ratio the explored dominant vegetation types in the lower reaches of Ili river, it can be conditionally divided into the following groups:
- plants, preferably accumulating 137Cs -reed, chingil, tamarisk, karabarak kokpek;
- plants which accumulate almost same quantity of 137Cs and 90Sr - meadow grass, sweda, saksaul; - plants, preferably accumulating 90Sr - brunets, licorice, wormwood, keireuk, teresken and camel thorn.
Currently radionuclides accumulated in soil are fully involved in biogeochem-ical cycles of circulation of substances and reach humans through food chain. Currently, artificial radionuclides, particularly
90Sr and 137Cs are found in organism of all inhabitants of the planet, including humans. The migration intensity rate, active involvement in food chain depends on properties, vegetation cover characteristics, geochemical activity of radionuclides and depending on "optimal" combination of these factors, their content in foods can vary by hundreds or thousands times. In this regard, the issue of exploring the degree of their involvement into substance biogeochemical cycle is one of topical issues of soil-plant cover radiation ecology.
The survey results show that in the lower reaches of Ili river, despite the significant content of radionuclides in soil and plant dry matter, the degree of their involvement in biological cycle is very small and is ranging in hundredths and thousandths share of a percent of their content in soil (Table 3).
Table 3 - Removal of radionuclides by main types of vegetation in the lower reaches of Ili river
Soils Plants Removal by plants from 1 ha
90Sr 137Cs
EK % Ek %
Alluvial- meadow-tugai Meadow grass 1974 0,012 1690 0,006
Licorice «Glycyrrhiza» 462 0,003 176 0,001
Brunets «Poterium» 480 0,003 80 0,0003
Alluvial- meadow Meadow grass 29800 0,187 3892 0,021
Chingil «Halimodendron» 364 0,002 1372 0,007
Swamp- meadow Reed «Phraqmites» 262 0,002 1441 0,004
Licorice «Glycyrrhiza» 462 0,004 242 0,001
Swamp- meadow- drying Reed «Phraqmites» 1260 0,006 13986 0,016
Swamp- meadow Reed «Phraqmites» 2035 0,027 3515 0,007
Meadow grass 14125 0,188 22875 0,046
Peat-swamp Reed «Phraqmites» 758 0,007 5685 0,024
Saline meadow Tamarisk «Tamarix» 1210 0,008 2112 0,004
Reed «Phraqmites» 138 0,001 1104 0,002
Camel-thorn «Alhagi» 3111 0,020 1139 0,002
Saline crust-puffy Biyurgun «Anabasis salsa» 646 0,004 437 0,001
Sarsazan «Halocnemum» 440 0,003 660 0,001
Karabarak «Halostachys bel-angeriana» 154 0,001 252 0,0004
Takyr like Biyurgun «Anabasis salsa» 840 0,008 980 0,003
Keireuk «Salsola orientalis» 1332 0,013 360 0,001
Dust- sandy Wormwood «Artemisia» 300 0,004 70 0,0003
Teresken «Ceratoides» 336 0,004 96 0,0005
Kokpek «Atriplex alba» 595 0,007 374 0,002
Despite this, in analysis of their absolute value expressed in Becquerel, logical dependence of the amount of radionu-clides involved in biological cycle on plant species features and soil conditions of their habitat has been determined.
For example, among explored plant species maximum capacity of biological cycle of radionuclides, representatives of meadow formations, especially meadow grass have been outlined. Moreover, grasses which grow in alluvial soils group have higher capacity. Also, general tendency of more migration ability in 90Sr is observed rather than in 137Cs.
CONCLUSIONS Results of analyses of accumulation coefficient values indicate the presence of significant differences both between radio-
nuclides and between plants. Almost all explored plants largely accumulate Sr90 rather than Cs137. In most cases, accumulation coefficients of Sr90 are higher than AC Cs137.
Degree of involvement of explored radionuclides in small biological cycle depends on plant species features, soil conditions of their habitats and radionuclides properties.
Both 90Sr and 137Cs have low degree of participation in small biological cycle.
The obtained data on concentration of radionuclides in soils, plants and accumulation coefficients may be used to evaluate radio-ecological situation of the lower reaches of Ili river and in forecasting calculations.
REFERENCES
1 Gulyakin I.V., Yudintseva E.V. Agricultural Radiobiology. - Moscow: Publishing House of the "Kolos", 1973. - 272 p.
2 Feodorov E.A., Smirnov F.G., Martyushov V.Z. et al. Migration of 90Sr and 137Cs in the system soil-vegetation of grasslands and pastures // Abstract of 2nd All-Union. Conf. - Obninsk, 1984. - S. 107-108.
3 Aliev D.A., Abdullaev M.A. Strontium-90 and Cesium-137 in soil and vegetation cover on Azerbaijan. - Moscow: Publishing House "Science", 1983. - 102 p.
4 Alexakhin R.M. Some topical issues of soil chemistry of artificial radionuclides and their accumulation in crops // Soil Science. - 1975. - № 11. - S. 32-39.
5 Russell R.S. Radioactivity and human food. Trans. from English. Ed. V.M. Klechkovskiy. - Moscow: Publishing House 'Atomizdat", 1971. - 375 p.
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TYmH
1 2Отаров А., Щбраева М., ^стемирова А.
0СМД1КТЕРДЩ РАДИОНУКЛИДТЕРД1 БОИЫНА ЖИНАУ БЕЛСЕНД1Л1П ЖЭНЕ
биологияльщ аИналым сыИымдыль^ы
19.О. Оспанов атындагы К,азац топырацтану жэне агрохимия гылыми-зерттеу институты, 050060, Алматы ц., эл-Фараби дацгылы, 75 В, К,азацстан,
e-mail: azimbay@bk.ru 2Орта Азия цоршаган ортасы жэне экология гылыми-зерттеу орталыгы (Алматы), 050060, Алматы ц., эл-Фараби дацгылы, 75 В, Цазацстан
Ма;алада 1ле езеншщ теменп агысындагы доминантты еймджтердщ радионуклидтердi боиына жинауын зерттеудщ нэтижелерi кел^рыген. Барлы; зерттелген еймджтердщ Cs137-re Караганда бг90-ды кеп жинак;тайтындьны аньщталган, еймджтер радионуклидтердi боиына жина;тау ;абыет боиынша топтастырылган. Радионуклидтердщ биологиялы; аИналымга ;атысу мелшерi ете аз, топыра; к^рамындагы мелшершщ жYз жэне мыц паиызындаи рана.
TyuiMdi свздер: А;дала-Ба;анас есга сагасы, топырак;-еймдж, жина;талу жылдамдыгы, 137Cs : 90Sr ;атынасы, радионуклидтердщ жоиылуы.
РЕЗЮМЕ
1 2Отаров А., Щбраева М., ^стемирова А. ИНТЕНСИВНОСТЬ НАКОПЛЕНИЯ РАДИОНУКЛИДОВ РАСТЕНИЯМИ И ЕМКОСТЬ ИХ
БИОЛОГИЧЕСКОГО КРУГОВОРОТА 1Казахский научно-исследовательский институт почвоведения и агрохимии имени У.У. Успанова, 050060, г. Алматы, проспект аль-Фараби, 75, Казахстан, e-mail:
azimbay@bk.ru
2Научно-исследовательский центр экологии и окружающей среды Центральной Азии, 050060, г. Алматы, проспект аль-Фараби, 75, Казахстан Приведены результаты исследования накопления радионуклидов основными доминантными видами растительности нижнего течения р. Или. Установлено, что все изученные виды растения в большои мере накапливают Sr90 чем Cs137, произведено группировка растении по накопительнои способности радионуклидов. Степень вовлечения радионуклидов в биологическии круговорот очень незначительная и колеблется в пределах сотых и тысячных долеи процента от их содержания в почве.
Ключевые слова: древняя дельта Акдала-Баканас, почва-растение, скорость накопления, отношение 137Cs : 90Sr, удаление радионуклидов.
