Cs-137 versus stable K in root uptake from radioactively

contaminated soils: field observations

Tatiana Paramonova, Vladimir Belyaev

Soil Science & Geography Faculties of Moscow Lomonosov State University,

Moscow, Russia

Analogies and differences between Cs-137 and stable K (K-39) bioavailability for crops growing on radioactively contaminated lands are still under discussion.

To clarify the peculiarities of Cs-137 and K root uptake and the elements distribution over the parts of plant biomass the field observations within post-Chernobyl Plavsky radioactive hot spot (Tula region, Russia) have been examined.

Outline

137Cs deposition within Eastern Europe after

Chernobyl accident (April 26, 1986)

Outline

Moscow

Atlas of 137Cs depositon on Europe after The Chernobyl accident / M. De Cort et all., 1998

≈350 km

Russian radiation safety standard for 137Cs - 37 kBq/m2

Plavsky radioactive hotspot,

Tula region 137Cs deposition 185-555 kBq/m2

Plavsk

Outline

Landscapes of Plavsky radioactive hotspot

Outline

EU Soil Map by Prof.Dr.H.E. Stremme

A+AB ~60-80 cm

Corg 4.9-7.3%

pHw 6.2-6.7

dV1.1-1.2 g/cm3

loamy texture

Soil cover of Plavsky radioactive hotspot

Objectives:

What are peculiarities of Cs-137 and K root uptake from soils of radioactively contaminated areas – whether they biochemical analogs or not?

Sampling area and plots

Watersheds and low-gradient hillslopes, 213-248 m ASL

Floodplain, 194 m ASL

maize rape potatoes

barley dry meadow wet meadow

Lower parts of hillslopes, 208-211 m ASL

Methodology

4 agricultural crops of field rotation (spring barley, maize, potatoes, and rape) and

semi-natural vegetation of dry and wet meadows were selected for the study.

Soil sampling

Methodology

Above- and belowground parts of biomass

were separated for the detailed examination.

Methodology

Vegetation sampling – aboveground parts

Methodology

Vegetation sampling – belowground parts

Methodology

The control of washing out soil particles with optical microscopy.

Total Cs-137 and stable K (K-39) were

analyzed in aboveground and belowground

biomass of vegetation.

Total Cs-137 and non-exchangeable stable K

(2 n HCl extraction) were analyzed in soils

that resulting in comparability of their

bioavailability for plants.

Methodology

137Cs and K in soils Results

Soil Altitude,

m ASL Cs-137

Bq/kg

Knon-ex,

%

barley 248 486 0.09

maize 248 459 0.41

rape 245 494 0.11

potatoes 213 674 0.10

dry meadow chernozem 208 712 0.12

wet meadow alluvial

calcareous 194 621 0.11

Determined current activities of Cs-137 in arable and native chernozems of the area taking into

account initial level of contamination and the relief position varied from 460 Bq/kg to 710 Bq/kg

(170-280 kBq/m2). The amount of non-exchangeable K in rhizosphere represented 0.09-0.14%

without mineral fertilizers and 0.40% after soil fertilization (for maize).

Profile distribution of 137Cs and K in soil

Results

Cs-137, Bk/kg

0 500 1000 1500 2000

barley

maize

rape

potatoes

dry meadow

wet meadow

0-10 cm

10-20 cm

20-30 cm

Knon-ex , %

0,0 0,2 0,4 0,6

barley

maize

rape

potatoes

dry meadow

wet meadow

0-10 cm

10-20 cm

20-30 cm

137Cs and K in vegetation

Results

Agrosystem /

natural ecosystem Cs-137, Bq/kg K, %

barley 37 0.4

maize 58 2.1*

rape 5 0.9

potatoes 31 1.1

dry meadow 73 0.3

wet meadow 120 0.3

* - mineral fertilizers have been used for maize agrosystem.

To avoid the difference in Cs-137 and K

content in soils of different plots and to

appreciate the biological peculiarities of

individual crops the transfer factor (TF)

values (the ratio of the activities for Cs-137

and concentrations for K between vegetation

and in soil) were calculated.

Results

Transfer factors for 137Cs and K Results

Agrosystem /

natural ecosystem TFCs-137 TFK

barley 0.06 3.8

maize 0.13 5.1

rape 0.01 8.4

potatoes 0.05 12.9

dry meadow 0.10 2.0

wet meadow 0.19 3.0

TFCs-137 : wet meadow > maize, dry meadow > barley, potatoes > rape

TFK : potatoes > rape > maize, barley > wet meadow, dry meadow

As a whole, TFK were several orders more than

TFCs-137 that stressed the biogenic nature of

potassium and the xenophobic nature of caesium.

Among the investigated agricultural crops and

meadow plant communities TFK were minimal for

maize and barley, middle – for rape, dry and wet

meadows, and maximal – for potatoes (17.4).

TFCs-137 were minimal for rape, middle – for wheat,

barley and potatoes, and maximal – for maize, dry

and wet meadows.

Results

Results Transfer factors in above- and belowground parts of

biomass for 137Cs and K

TFK

20

15

10

5

0

5

10

15

20

barle

y

maize

rape

pota

toes

dry

mea

dow

wet

mea

dow

aboveground biomass belowground biomass

TFCs-137

0,25

0,20

0,15

0,10

0,05

0,00

0,05

0,10

barle

y

maize

rape

pota

toes

dry

mea

dow

wet

mea

dow

aboveground biomass belowground biomass

An accounting of Cs-137 and stable K distribution among above- and belowground parts of plant biomass clearly demonstrated the importance of biological characteristics in root uptake of the elements: wheat, barley and maize (Gramíneae family) were characterized by elevated Cs-137 activities in belowground parts (12-14 times higher than in shoots), and rape (Brassicaceae family) and potatoes (Solanaceae family) were characterized by homogenous distribution of the radionuclide over plant biomass, whereas K concentrations in aboveground parts of plants were 1.5-10 times greater than in belowground parts of plants for all investigated crops.

Results

Conclusion

Root uptake of the elements was characterized by different peculiarities. Thus, Cs-137 and stable K were difficult if not impossible to consider as biochemical analogists in root uptake from radioactively contaminated soils.

The study was supported by

the Russian Foundation for Basic Research

(project no. 14-05-00903).

Acknowledgements

Thank you for attention!