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Fig. 1. Change of 137Cs TF to various crops on chernozem after HM adding and countermeasures application.

So increased HM concentration in soil leads to 137Cs TF increase. Moreover, HM weakens countermeasures effect for radiocaesium accumulation in plants. Probably, it can be connected with increase of radionuclide mobility due to competition of elements for sorbing sites. The largest affect of heavy metals on radiocaesium behaviour was found on the peat-bog soil, the lowest one – on chernozem due to agrochemical properties of soil. Grasses were more sensitive to interaction of technogenic pollutants in comparison to potatoes tubers.

4. References

1.Grigorjev V.L., Plishko A.A. Microelements in soils of Ukraine. Khimizaciya selskogo hozyaistva (in Russian), 1989, 3, c. 7-8

THE BRILLIANT BLUE METHOD FOR WATER SOLUBLE CHERNOBYL137Cs BEHAVIOUR ESTIMATION IN SOILS OF SOUTH BELARUS

N. GONCHAROVA, K. KALINKEVICH, V. PUTYRSKAYA.

International Sakharov Environmental University, Dolgobrodskaya str.23, Minsk, 220009,BELARUS

A. ALBRECHT

Swiss Federal Institute of Technology, Institute of Plant Sciences, Postfach 185,Eschikon 33,CH-8315 Lindau, SWITZERLAND

1. Introduction

The radionuclides distribution in forest and agricultural soils depends on soil structure, hydromorphity, and hydrological features, in combination with root distribution, caesium mobility and characteristics. The interaction between 137Cs, soil matrix and root distribution is important in radionuclide transfer processes assessment. The study of radionuclides distribution is necessary for estimating plant root uptake and for evaluating dose rate. Migration of 137Cs and its forms is delineated by flow patterns in the soil. A field experiment was carried out on tilled agricultural and forest soils in the South of Belarus affected by the Chernobyl accident. The distinction in accumulation of 137Cs in preferential flow and matrix zones was determined. Brilliant Blue FCF was used to dye flow lines and to determine the activity of Chernobyl 137Cs (deposited in April 1986) as a function of dye presence and absence. The experiment was carried out on the soddy-podzolic soils of forest and agrocoenosis of “Sudkovo” farm, Khoiniki district, Gomel region.

2. Water flow in soils (saturated and unsaturated)

Fluxes of water in soils change their magnitudes and directions depending on spatial variability of the hydraulic properties of soils. When hydraulic properties vary continuously with position in soils, the directions of streamlines may by curved. When hydraulic properties vary discontinuously with position in soils, the streamlines may be refracted at the boundaries between regions of different hydraulic properties. These curvings and refractions of streamlines occur not only in saturated soils but also in unsaturated soils.

Thus refraction of fluxes influences several kinds of soil-hydrological processes: lateral flow of water during vertical percolation in layered soils, surface and subsurface water flow in slopes, and anisotropy of flow in saturated or unsaturated soils [1].

3. Classification of the preferential flow

Classification of preferential flows based on their phenomenological features as proposed by Kung [2-3]. Taking account of his classification, preferential flows in soils are classified into three types:

ξ By-passing flow

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ξ	Fingering flow
ξ	Funnelled flow
	By-passing flow is local flow in such highly permeable zones as a macropore

(right-hand side) and a crack (left-hand side) in heterogeneous soil. This flow takes place either when the macropores and cracks are open to the atmosphere or when the water pressure within the macropores and cracks are positive. When, for example, pounded water infiltrates a soil matrix whose macropores are open to the land surface, water will infiltrate the macropores faster than the soil matrix, water can infiltrates into the soil matrix across the boundary between macroand micropores. Under certain conditions, this type of flow will occasionally be transformed into pipe flows. On the other hand, when pounded water infiltrates a soil matrix within which micropores or cracks are buried, and when the soil matrix is under suction, water will not infiltrate the buried micropores but will infiltrate only the soil matrix. In this case, micropores are not preferential for the flow of water but are obstacles to such flow.

Fingering flow takes place mainly in relatively coarse layers overlain with finer soils. Fingering flow occurs under both pounded and unsaturated condition at the land surface.

Funnelled flow is another type of partial flow accumulated along the inclined bottom of a fine layer overlaying a coarse sublayer. The pressure of funnelled flow is initially negative, and due to the accumulation of infiltrated water, increases with distance along the inclined interface between the fine top layer and the coarse sublayer. The quantity of funnelled flow also increases with distance along the inclined interface. When the pressure of funnelled flow exceeds a critical value, fingering flow will be generated in the coarse sublayer.

4. General features of Brilliant Blue FCF dye

Dyes are widely used to stain the travel path of water and solutes in soils. Brilliant Blue FCF – bright greenish blue food dye – effective indicator for visualizing the flow paths of water in soil. Brilliant Blue FCF – triphenilmethane with formula C37H34N2Na2O9–S3. Chemical structure of dye is shown on the fig.1.

Brilliant Blue FCF is mobile, distinctly visible, non-toxic, chemical stable. So it is a good reagent for field So it is a good reagent for field experiments

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5. Brilliant Blue FCF methods (30-km zone, South Belarus)

The experimental plot was situated on the Poles’e lowland, Sudkovo farm, v. Novosiolki, Hoiniki district. It is a monotonous waterlogged flat plain. For our experiment we took 2 plots (100 υ 100 cm) with the same characteristics. Soil type is podsoluvisols on sandy loam underlying moraine. The difference between plots was in the tillage. One plot was situated on the repeated tillage field; another plot was in a forest. The soil of the second plot has been untouched since April, 1986. Plots were situated close to each other. The first plot was tilled and harvested two times per year. During our experiment (October, 2001) the field plot was under motley grass.

On forest plot we moved off all litter and cut plants at the 5 cm level. Plants were packed into plastic for further laboratory analysis.

Brilliant Blue FCF concentration – 1 g per 1 l of water. Irrigation was 6 times every 15 minutes with 5 litres of dye.

6. Vertical profile observation and soil sampling

We cut the soil every 20 cm on the 25 cm depth. Every slice was indicated by Latin letters (Fig.2). First slice - À1, second - Â1, next 20 cm– slice Ñ1, then – D1 and E1. Thus, we obtained 5 vertical slices: A1, B1, C1, D1, E1. Another 5 vertical slices were obtained at a depht of 20 cm: A2, B2, C2, D2, E2.

All samples of plants and soils were air-dried in laboratory till constant weight. Then samples were weighted (repeated 3 times) and their radioactivity measured (Bq/kg). The root density has been calculated from those root measurements, which included handpicking. The average activity at each depth is based on soil measurements and estimated distribution of individual samples (Table 1, 2).

7. Discussion

The fast passage of the tracer solution through the repacked monolith and the appearance of colour and radionuclide tracers indicate a type of bypass flow, which is generally termed fingering flow [5].

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Table 1. 137Cs specific activity distribution in Sudkovo farm agrocoenosis (October, 2001)

	Slice	Depth, cm	¹¹ʋ	Specific activity 137Cs, Bq/kg
			spot		M	PF
			1	993,1	ρ 22,1	1000,8 ρ 21,8
	A1	0-10	2	927,7	ρ 16,7	254,4	ρ	12,5
			3	1508,3 ρ 19,4		698,8	ρ	16,1
		20-25	4	0 ρ 9,5		0,4 ρ 5,6
	B1	20-25	1	2,9 ρ 6,4		14,8	ρ	3,5
	B2	25-40	1	0 ρ 6,0		1,9 ρ 5,7
	C1	0-10	1	898,6	ρ 13,3	1340,0 ρ 25,1
		10-25	2	981,2	ρ 15,3	731,7	ρ	14,8
	C2	25-40	1	19,8	ρ 4,2	0 ρ 6,3
	D1	0-20	1	920,1	ρ 15,2	946,9	ρ	13,0
		0-10	2	1068,6 ρ 15,1		367,6 ρ 8,3
	D2	25-40	1	3,7 ρ 4,6		0 ρ 5,1
	E1	0-10	1	1178,9 ρ 17,2		n.d.

We have found significant differences in 137Cs specific activity in zones belonging to the same soil horizon. In both plots, 137Cs were enriched in dyed preferential flow zones compared to the soil matrix. We have no data yet on the difference in root density between these zones. There is literature evidence on enhanced rooting along macropores, an important soil structure that triggers preferential flow. Whiteley and Dexter [6] studied the ability of seminal roots of pea, rape and safflower growing along cracks to penetrate the soil matrix. In their analysis of 137Cs transfer factor, Ehlken and Kirchner [7] recognized the importance of the depth distribution of grass roots and developed a code that combines a diffusion model with a root distribution model assuming exponential root decline with depth. With the incorporation of root architecture, they were able to reproduce the change in transfer factors as a function of time to a much better degree than with a model based on meteorological results (soil moisture).

8. Conclusions

During our experiment, we were not able to carry out root and 137Cs tracing to such an extent that both could be fully associated with the different flow compartments within the soil. This is related to the choice of Brilliant Blue as a flow tracer during the irrigation experiment. Brilliant Blue is relatively mobile The distribution of surface applied 137Ñs in the soil profile is delineated by flow patterns in the soil and therefore by soil structure. Tracer experiments in the forest and in the field have shown that 137Cs concentrations between zones of preferential flow (several hundreds Bq/kg) and matrix (in cases below the detection limit) dramatically. In soils without bioturbation, such as acidic forest soils these differences prevail even after 16 years of application

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(Chernobyl NPP). In permanent meadows with high biological activity, reduced aggregate stability and fast turnaround of organic matter, the horizontal differences fade away with time, whereas vertical variation prevails. In the ploughed layer of agricultural

fields both the horizontal and vertical distinction vanishes. Roots develop their architecture also depending on soil structure, zone of enhanced bioaccumulation

therefore develop.

Table 2. 137Cs specific activity distribution in Sudkovo farm forest coenosis (October, 2001)

	slice	Depth, cm	¹			Specific activity 137Cs, Bq/kg
			spot		M			PF
			1	4,6	ρ	6,4	19,9		ρ		9,3
	A1	0-10	2	4,6	ρ	6,4	27,2		ρ		6,9
			3	4,6 ρ 6,4			9,9	ρ		6,0
		20-25	4	2,4	ρ	5,5	0 ρ 7,2
		0-10	1	209,3 ρ 15,3			87,2	ρ		11,2
	B1	0-20	2	66,2	ρ	10,8	12,2		ρ		6,4
			3	66,2	ρ	10,8	270,6		ρ		10,4
	B2	25-40	1	2,7	ρ	4,7	4,8	ρ		5,4
			2	6,1	ρ	4,3	18,1		ρ		5,6
			1	302,1 ρ 17,7			17,1		ρ		7,6
	C1	0-20	2	301,9 ρ 8,5			13,5		ρ		6,8
			3	23,9 ρ 9,0			14,3		ρ		6,7
		25-40	1	6,2	ρ	4,2	8,9	ρ		5,1
	C2		2	2,8	ρ	4,3	4,6	ρ		4,6
		>50	2	n. d.			0,7	ρ		3,1
	D1	0-10	2	n.d.			54,7		ρ		9,1
		0-20	1	35,6 ρ 5,6			24,3		ρ		5,7
	D2	25-40	1	0 ρ 4,3			3,8	ρ		3,6
	E1	0-10	2	59,6 ρ 5,6			110,3 ρ 8,2
		0-20	1	10,9 ρ 4,7			63,5		ρ		5,4
	E2	25-40		0 ρ 5,2			n.d.

9. Acknowledgements

The Swiss National Science Foundation (SNSF) funded SCOPES JRP.

10. References

1. T .Miyazaki Water flow in soils. in: Marcel Dekker,1993 Inc. New York pp.9395.

2. K-J.S. Kung.Preferential flow in a sandy vadose soil: 1. Field observations. in: Geoderma, 1990, 46,

pp.51–58.

3.K-J.S. Kung,Preferential flow in sandy vadose zone 1. Mechanism and implications, in: Geoderma, 1990, 46, pp. 59-71.

4.M.Flury, H. Fluhler H. Tracer characteristics of Brilliant Blue FCF.in: Soil Science Society of

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America Journal,1995, 59(1), pp. 22–27.

5.A. Albrecht., U. Schultze, M. Leidgens, H. Fluhler, E. Frossard. Incorporated soil structure and root distribution into plant uptake models for radionuclides: toward a more physically based transfer model. in: J. Environmental Radioactivity,2001(submitted for publication).

6.D. Whiteley, A. Dexter. Behaviour of roots in cracks between soil peds. in: Plant and Soil, 1983.74.pp 153-162.

7.S. Ehlken, G.Kirchner Seasonal variations in soil-to-grass transfer of fallout strontium and cesium and of potassium in North German soils. In Journal of Environmental Radioacctivity, 1996, 33(2), pp.147-181.

AQUATIC ECOSYSTEMS WITHIN THE CHERNOBYL NPP EXCLUSION ZONE: THE LATEST DATA ON RADIONUCLIDE CONTAMINATION AND ABSORBED DOSE FOR HYDROBIONTS

D.I. GUDKOV, M.I. KUZMENKO

Institute of Hydrobiology, NASU, Geroyev Stalingrada Ave. 12, Kiev, 04210, UKRAINE,

[e-mail]

V.V. DEREVETS, A.B. NAZAROV

State Specialised Scientific Enterprise “Ecocentre” of the Ministry of Ukraine on the Emergency and Affairs of Population Protection Against the Consequences of the Chernobyl Catastrophe, Kirova Str. 17, Chernobyl, 07270, UKRAINE

1. Radionuclides in components of aquatic ecosystems

The territories of the Chernobyl NPP (ChNPP) exclusion zone are characterised by significant heterogeneity of radionuclide contamination, which is significantly reflected by the radioactive substances contents in aquatic ecosystem components. Primarily this is due to the composition and the dynamics of radionuclide emissions into the environment as a result of accident in 1986, as well as to the subsequent processes of radioactive substances transformation and biogeochemical migration in the soils of a catchment basin and bottom sediments of reservoirs. Relatively low contents of radioactive substances are found in the river ecosystems. Due to high water change rate the river bottom sediments have undergone decontamination processes (especially during floods and periods of high water) and over the years that passed since the accident have ceased to play the essential role as a secondary source of water contamination. The main sources of radionuclides in rivers are currently the washout from the catchment basin, the inflow from more contaminated water bodies, as well as the groundwater. On the other hand, the closed reservoirs, and in particular the lakes in the inner exclusion zone, have considerably higher levels of radioactive contamination caused by limited water change and by relatively high concentration of radionuclides deposited in the bottom sediments. Therefore, for the majority of standing reservoirs the level of radionuclide content is determined mainly by the rates of mobile radionuclide forms exchange between bottom sediment and water, as well as by the external wash-out from the catchment basin.

Our research was carried out during 1998–2001 on Azbuchin Lake, Yanovsky (Pripyatsky) Backwater, the cooling pond of the ChNPP, the lakes of the left-bank flood plain of Pripyat River – Glubokoye Lake and Dalekoye-1 Lake and also on Uzh River and Pripyat River. The sampling station on Uzh River is situated near the river mouth (Cherevach village), on Pripyat River – near the town Chernobyl (Figure 1).

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Fig. 1. Map of reservoirs within the Chernobyl NPP exclusion zone.

The radionuclide content in biological tissues was measured for 28 higher aquatic plant species, 6 species of molluscs and 18 species of fish. The results of the radionuclide content measurements in hydrobionts are expressed in Bq kg-1 of wet weight at natural humidity. The tendency of the aquatic organisms to accumulate radionuclides, traditionally expressed as the concentration factor (CF), which is determined by calculating the ratio of the specific activity of radionuclides in tissue to the average annual content (for molluscs and fish) or to the average content in the environment water during the vegetation period (for higher aquatic plants). The estimation of the absorbed dose rate for hydrobionts was carried out according to the method described in literature reference [1].

1.1. WATER AND BOTTOM SEDIMENT

The highest radionuclide activity in water among the studied objects was found in the Azbuchin Lake. During 1998–2001, the average content of 90Sr and 137Cs in lake water reached 120–190 and 18–43 Bq l-1 respectively. The

radionuclide contamination density values found in the lake bottom sediments for 90Sr, 137Cs, 238+239+240Pu and 241Am averaged at 6.70, 11.50, 0.24 and 0.22 TBq km-2

respectively, with the maximum values of 33.30, 14.40, 1.10 and 0.29 TBq km-2.

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The 90Sr and 137Cs content in the water of Glubokoye Lake come to 99–120 and 13–14

Bq l-1 respectively. The average values of contamination density in the bottom sediments by 90Sr, 137Cs, 238+239+240Pu and 241Am in 1998 were 2.6, 5.6, 0.07 and 0.06

TBq km-2, with the maximum values being 10.0, 13.7, 0.22 and 0.23 TBq km-2 respectively. In Dalekoye-1 Lake the average content of 90Sr and 137Cs in the research period reached 82.5 and 11.8 Bq l-1 respectively. The maximum value of radionuclide

contamination density in the bottom sediments by 90Sr in 1999 was 18.9, by 137Cs – 15.2, by 238+239+240Pu – 0.6 and by 241Am – 0.4 TBq km-2. The average values were,

accordingly, 4.0, 3.1, 0.08 and 0.08 TBq km-2.

The average specific activity values for 90Sr and 137Cs in water of Yanovsky Backwater for the period 1998–2001 were 75.2 and 5.6 Bq l-1 respectively. The radionuclide contamination of the bottom sediments of reservoir is extremely heterogeneous, which is obviously caused by the non-uniform character of the nuclear

fall-out and by the absence of wind-induced turbulence in deep water. The average content of 90Sr, 137Cs, 238+239+240Pu and 241Am in bottom sediments was, respectively,

16.3, 14.8, 0.4 and 0.3 TBq km-2. At the same time, within the bounds of silt sediment

deposition, some sites with abnormally high density of contamination by 90Sr, 137Cs and 238+239+240Pu (307.1, 251.6 and 5.3 TBq km-2 respectively, which is 20 times higher than

the average values in the backwater), were found.

The cooling pond of the ChNPP has undergone the highest radionuclide contamination in comparison with other reservoirs of exclusion zone. In the course of time, after the cessation of radioactive emissions into the atmosphere and due to disintegration of short-lived isotopes, 90Sr and 137Cs have become the main radioactive contaminants of the cooling pond water. During 1998–2001, the specific activity of 90Sr in the cooling pond water was found to be within the range of 1.7–1.9, with the range being 2.7–3.1 Bq l-1 for 137Cs. The heterogeneity of the bottom sediment contamination in the cooling pond is currently determined by the nature of the silt accumulation processes. The height of silt layers at the depth of over 11 m (for up to 35 per cent of the bottom area) reaches up to 100 cm., with the density of contamination by 137Cs at 18.5– 133.2 TBq km-2. The bottom at the depth of 3–11 m consists of primary soils, which are covered, with a 1–6 cm layer of silt, with the contamination density by 137Cs in the range of 1.5–5.9 TBq km-2 [2].

Uzh River is the main tributary of Pripyat River within the exclusion zone and the runoff of its inflow covers the southern part of a zone with a rather low level of 90Sr

contamination. The contents of 90Sr and 137Cs in water of Uzh river during 1998–2001 averaged at 0.11 and 0.31 Bq l-1. The specific activity of 90Sr and 137Cs in water of

Pripyat River during 1998–2001 was found in the ranges of 0.22–0.50 and 0.11–0.14 Bq l-1 respectively. The radionuclide content in the bottom sediment of main riverbed sites of Uzh River and Pripyat River is currently only slightly in excess of the preaccident levels. Considerably higher activity in the bottom sediments is still observed in the backwaters, the old riverbeds and other slow-running sites of the rivers.

1.2. HIGHER AQUATIC PLANTS

The radionuclide contents in higher aquatic plants (macrophytes) in the studied water bodies were largely determined by the nature of radionuclide contamination of the water objects and nearby territories, as well as by the