1. Journal of
Environmental Radioactivity 58 (2002) 1–11
Comparative study of 137
Cs partitioning between
solid and liquid phases in Lakes Constance,
Lugano and Vorsee
A. Konopleva,
*, S. Kaminskib
, E. Klemtb
, I. Konoplevac
,
R. Millerb
, G. Ziboldb
a
Scientific Production Association ‘‘Typhoon’’, Lenin Av., 82, 249038 Obninsk, Kaluga reg., Russia
b
Fachhochschule Ravensburg-Weingarten, University of Applied Sciences, 88250 Weingarten, Germany
c
Institute of Agricultural Radiology and Agroecology, 249020 Obninsk, Kaluga reg., Russia
Received 25 October 2000; received in revised form 5 March 2001; accepted 23 March 2001
Abstract
The methodology for estimating radiocaesium distribution between solid and liquid phases
in lakes is applied for three prealpine lakes: Lake Constance (Germany), Lake Lugano
(Switzerland) and Lake Vorsee (Germany). It is based on use of the exchangeable distribution
coefficient and application of the exchangeable radiocaesium interception potential (RIPex
).
The methodology was tested against experimental data. Good agreement was found between
estimated and measured 137
Cs concentrations in Lake Constance and Lake Lugano, whereas
for Lake Vorsee a discrepancy was found. Bottom sediments in Lake Vorsee are composed
mainly of organic material and probably cannot be described in terms of the specific sorption
characteristics attributed to illitic clay minerals. r 2001 Elsevier Science Ltd. All rights
reserved.
Keywords: Radiocaesium; Prealpine lakes; Sediments; Distribution coefficient
1. Introduction
The distribution coefficient Kd characterising the partitioning of a radionuclide
between solid and liquid phases remains a basic parameter in prediction of
radionuclide behaviour in aquatic ecosystems (IAEA, 1994). The value of the total
*Corresponding author. Tel.: +7-08439-71896; fax: +7-08439-44204.
E-mail addresses: konoplev@obninsk.com (A. Konoplev).
0265-931X/01/$ - see front matter r 2001 Elsevier Science Ltd. All rights reserved.
PII: S 0 2 6 5 - 9 3 1 X ( 0 1 ) 0 0 0 7 5 - 3

2. distribution coefficient Ktot
d , which is the ratio of the total radionuclide concentration
in the solid phase to its concentration in solution, is very sensitive to radionuclide
speciation in the solid phase (Konoplev, Bulgakov, Popov, a Bobovnikova, 1992;
Konoplev a Bulgakov, 2000; Wauters et al., 1996). In the immediate term, only the
exchangeable portion of a radionuclide contributes to solid–liquid interphase
exchange. Therefore, the notion of an exchangeable distribution coefficient Kex
d was
introduced as a ratio of the concentration of the radionuclide in exchangeable form
in the solid phase to its concentration in solution at equilibrium (Konoplev et al.,
1992). The advantage of Kex
d is that its value is governed by ion exchange and can be
calculated on the basis of environmental characteristics such as the capacity of
sorption sites and the cation composition of the solution.
It is well proven now that the high retention of radiocaesium in soil and bottom
sediments is determined by two different processes: fixation and reversible selective
sorption. Fixation describes the ‘‘permanent’’ (or at least long-term) replacement of
interlattice K- by Cs-ions. Reversible selective sorption of radiocaesium occurs on
frayed edge sites (FES), located at the edges of micaceous clay particles (Cremers,
Elsen, De Preter, a Maes, 1988). The ability of a solid to sorb radiocaesium
selectively is characterised by the capacity of the selective sorption sites (FES) or by
the so-called radiocaesium interception potential (RIP), which is the product of the
FES capacity and the selectivity coefficient of radiocaesium in relation to the
corresponding competitive ion (Sweeck, Wauters, Valcke, a Cremers, 1990).
Cremers and co-workers (Cremers et al., 1988; Sweeck et al., 1990) developed a
special method for the quantitative determination of FES capacity ([FES]) and RIP.
The method is based on using silver thiourea Ag(TU)+
as a masking
agent for regular exchange sites (RES), which correspond to the planar and easily
exchangeable sites. RES selectively bind this complex. At the same time Ag(TU)+
does not interact with FES because of the molecule’s large size. Thus, the masking
blocks RES and allows the study of caesium sorption–desorption on FES.
This method, however, ignores Cs fixation during the equilibration time (24 h) and
thus overestimates the amount of reversibly sorbed caesium. In the case of highly
organic soils and bottom sediments, collapse of the interlayers of micaceous clay
does not allow the determination of [FES] using this method. To avoid these
disadvantages, modifications of the procedure were proposed (Konoplev a
Konopleva, 1999), which included
* An additional step of ammonium acetate extraction after the equilibration time.
This step avoids the influence of fast fixation on [FES] or RIP determination.
Moreover, sorbed caesium in this case is measured directly in the ammonium
acetate extraction and the error of such a measurement is lower than the error
generated using Cremers et al. (1988) method, which takes the difference of two
measurements to determine sorbed caesium.
* The [FES] is calculated using the linearised form of the Langmuir isotherm and its
value is given by the intercept on the ordinate of the graph of the inverse
concentration of reversibly sorbed caesium versus inverse equilibrium concentra-
tion of caesium in solution. To obtain the FES capacity for highly organic soils
A. Konoplev et al. / J. Environ. Radioactivity 58 (2002) 1–112

3. and bottom sediments, the range of the isotherm before saturation (or induced
interlayer collapse) can be used;
* Taking the initial range of the isotherm at low caesium concentrations one can
determine the capacity of high affinity sites [HAS] located between layers of
micaceous clay particles. HAS have a much higher selectivity for caesium as
compared to average FES and therefore are occupied by caesium in the first stage.
HAS represent 1–10% of FES.
The objective of this paper is to test the ability of the proposed modified
methodology to predict partitioning of 137
Cs between sediments and water in three
prealpine lakes: Lake Constance (Germany), Lake Lugano (Switzerland) and Lake
Vorsee (Germany). They showed similar deposition levels on the water surface
ranging between 17 and 28 kBq/m2
of 137
Cs originating from Chernobyl on
1.05.1986; however, these lakes have very different limnological characters. A
location map of the lakes is presented in Fig. 1.
2. Materials and methods
2.1. Study sites
2.1.1. Lake Constance
Lake Constance is a large and deep prealpine hardwater lake. It represents a
typical example of a large lake ecosystem with a very high self-purification ability
(Kaminski, Konoplev, Lindner, a Schroeder, 1998). The main tributaries of the
lake are the Alpine Rhine, Bregenzer Ache and Argen. The catchment area of the
Alpine Rhine amounts to 6119 km2
, which is the largest part of the total catchment
area. From all the tributaries, about 11 km3
of water flows into the lake annually.
The only outflow is the Rhine River. Lake Constance is morphologically subdivided
Fig. 1. Location map of the lakes.
A. Konoplev et al. / J. Environ. Radioactivity 58 (2002) 1–11 3

4. into two parts: the deeper Upper Lake Constance and the shallow Lower Lake
Constance in the west. Illite, kaolinite and chlorite represent the typical clay mineral
composition of sediments of the lake, amounting to about 45% of dry sediment in
Upper Lake Constance (Robbins et al., 1992). The mean calcite content in the sediment
is between 20% and 30% in Upper Lake Constance and more than 40% in Lower
Lake Constance. The average value of organic matter in the sediments is about 5%.
2.1.2. Lake Lugano
Lake Lugano is one of the large drinking water reservoirs of southern Switzerland,
situated in the foothills of the southern Alps. Lake Lugano is divided into two parts
by a morainic front (about 5 km south of Lugano) on which an artificial dam was
built. The deeper northern basin with a maximum depth of 288 m close to the village
Gandria has a water residence time of 30 y, whereas the water residence time in the
rest of the lake is only 2–3 y (Niessen, 1987). The main tributaries of Lake Lugano
are the Cassarate, Vedeggio, Magliasina and Cuccio. The outflow leading to Lago
Maggiore is the river Tresa, with a mean outflow rate of 24.2 m3
/s (Hydrologisches
Jahrbuch der Schweiz, 1995), which means that about 0.8 km3
of water flows out of
Lake Lugano per year. The mineralogy of the sediments can be characterised as
follows: the dominant mineral components in all basins are quartz and mica (biotite
and muscovite); in the eastern parts of the basins, carbonates (calcite and dolomite)
are frequent (Niessen, 1987). About 15–20% of the sediment dry mass is of an
organic nature. The removal of radiocaesium from the water column of Lake
Lugano was much slower than in Lake Constance. 137
Cs residence times, calculated
in 1988 (Santschi, Bollhalder, Zingg, Luck, a Farrenkothen, 1990), were 5 months
for Lake Constance, 14 months for the southern basin of Lake Lugano, and 21
months for the northern basin.
2.1.3. Lake Vorsee
Vorsee is situated 40 km north of Lake Constance. It is a glacially- formed,
eutrophic lake. Bottom sediments have a very loose consistency down to a depth of
7 m, with a high water content (still 96% at 60 cm sediment depth); the rest is mainly
organic matter (from 70% at the sediment surface to 55% at 60 cm sediment depth,
percentage of dry sediment). Lake Vorsee shows a slightly higher initial
contamination than Lake Constance, because weather conditions have been very
different for the two lakes on 1.05.1986 due to local thunderstorms resulting in
different amounts of 137
Cs washout.
Table 1 summarises the main characteristics of the lakes under study.
The comparison of 137
Cs behaviour in these three lakes was aimed at verification
of the proposed methodology for the lakes with diverse limnological and
hydrochemical characteristics.
2.2. Sampling
Bottom sediment cores from Lake Constance and Lake Lugano were collected in
1996 using a gravity sampler (Meischner a Rumohr, 1974) with a 5.8 cm inner
A. Konoplev et al. / J. Environ. Radioactivity 58 (2002) 1–114

5. diameter. The sediment cores were split longitudinally and then sliced in layers of 1
or 2 cm thickness. Sediments from Lake Vorsee were taken in 1996 with a gravity
corer specially constructed for soft sediments, which allowed the taking of pore
water and solid material from different sediment depths. After freeze-drying, the
total activity concentrations of 137
Cs and 134
Cs in the sediments were measured by
gamma-spectrometry using HPGe detectors.
Lake and river waters were collected in 1996 and 1999 using ‘‘Midiya’’, a large
volume water sampler developed in SPA ‘‘Typhoon’’ (Makhonko, 1990) and capable
of performing both collection of suspended material and fixation of dissolved 137
Cs.
Water volumes from 1000 to 3000 l were filtered through sets of ‘‘Petryanov-filters’’
(Makhonko, 1990). Dissolved 137
Cs was fixed using columns containing ‘‘Fezhel
sorbent’’ based on wood cellulose coated with ferric ferrocyanide (Remis, 1996). In
October 1996, water samples from four different depths were collected in the central
(deepest) part of Upper Lake Constance to study the vertical distribution of 137
Cs in
the lake water. About 600 l of lake water from the surface layer at the same location
were tangentially filtered using the ‘‘Millipore system’’.
2.3. Physico-chemical analysis
2.3.1. The capacity of the FES (modified method)
Air-dried sediment samples (0.1–1 g) were pre-equilibrated with 30 ml of
a 0.015 mol/l solution of silver thiourea (AgTU+
4 ), shaken overnight, centrifuged
(30 min, 5000 rpm) and the supernatants discarded (the same procedure is
also applicable to soil samples). Caesium sorption isotherms were measured
by equilibrating (24 h) sediment samples with AgTU+
4 solutions (0.015 mol/l)
containing increasing levels of CsNO3 (137
Cs labelled) from 0.2 to 1.6 mmol/l.
Then samples were centrifuged and exchangeable Cs was extracted from
sediment samples with 30 ml of 1 mol/l ammonium acetate solution. 137
Cs was
counted in the extract using an HPGe detector. Results were plotted as the inverse
concentration of exchangeable Cs in the solid phase versus the inverse Cs
concentration in the equilibrium solution. According to a linearised form of the
Langmuir isotherm, which describes the adsorption on homogeneous sites with
saturation at high concentrations, the capacity of FES was taken as the inverse
Table 1
Characteristics of the lakes under study
Lake Constance Lake Lugano Lake Vorsee
Surface area (km2
) 572 48.9 0.09
Mean water depth (m) 85 134 0.6
Maximum water depth (m) 254 288 2.2
Mean residence time (y) 4.1 7 0.24
Drainage basin (km2
) 11,487 615 1.27
Initial Chernobyl 137
Cs fallout (kBq/m2
) 17 24 28
A. Konoplev et al. / J. Environ. Radioactivity 58 (2002) 1–11 5

6. intercept of this linear dependence:
1
Cs½ Šads
¼
1
FES½ Š
þ
const:
FES½ Š
1
Cs½ Šsol
: ð1Þ
2.3.2. Exchangeable radiocaesium interception potential RIPex
(K) and RIPex
(NH4)
0.5 g samples of air-dried sediment were pre-equilibrated with 30 ml of 0.015 mol/l
Ag(TU)4
+
solutions containing different KCl concentrations ranging from 2 to
10 meq/l. Phase separation was made by high speed centrifugation (30 min,
5000 rpm). Liquid phase was then discarded. Sediment samples were then
equilibrated with the same Ag(TU)4
+
/KCl mixtures containing labelled 137
Cs. After
24 h of shaking and centrifugation, exchangeable 137
Cs was extracted from the
sediment by 30 ml of 1 mol/l ammonium acetate solution. After phase separation,
137
Cs was measured in extracts using HPGe detectors. The measured Kex
d was then
multiplied by the appropriate molarity of potassium mk and the product Kex
d Csð Þmk
plotted against mk. The exchangeable radiocaesium interception potential, i.e. the
plateau value of Kex
d Csð Þmk attained at high mk, was then read off from the graph.
The same experimental protocol was followed to obtain RIPex
(NH4) except that
NH4Cl was used instead of KCl. The selectivity coefficient KFES
c NH4=K
À Á
was
calculated as a ratio of RIPex
(NH4) and RIPex
(K).
2.3.3. Measurement of major ions
Major cations Ca2+
, Mg2+
, K+
and Na+
in water and in extracts were measured
by atomic absorption spectroscopy (AAS); ammonium was measured using a
spectrophotometric technique.
3. Results and discussions
Table 2 presents the data on the cation compositions of the lake waters under study.
As can be seen from Table 2, all lake waters have rather similar ionic
compositions. All three lakes are characterised by relatively high concentrations of
calcium and relatively low concentrations of potassium. The substantial difference
between the lakes is the different ammonium concentrations. There are extremely low
concentrations of ammonium in Upper Lake Constance, measurable levels in Lower
Lake Constance, medium concentrations in Lake Lugano and high concentrations in
Vorsee particularly in bottom sediment pore waters (up to 90 mg/1). Ammonium is
the strongest natural competitor of radiocaesium for FES. Taking into account the
relatively low concentrations of potassium in all the lakes, one can expect that
radiocaesium will have the highest mobility in Vorsee, less mobility in Lake Lugano
and Lower Lake Constance and the lowest mobility in Upper Lake Constance.
Cation composition, concentrations of 137
Cs and its exchangeability in bottom
sediments of the lakes under study are presented in Table 3.
As an illustration, isotherms of Cs selective sorption on FES of bottom sediments
from Upper and Lower Lake Constance are presented in Fig. 2.
A. Konoplev et al. / J. Environ. Radioactivity 58 (2002) 1–116

7. For the lakes under study, the highest capacity of FES was found for bottom
sediments from Lake Lugano (7.0 meq/kg) and the lowest for bottom sediments from
Vorsee (1.1 meq/kg), as can be seen in Table 4. It is also interesting to note that the
capacity of FES in Lower Lake Constance is about a factor 2 lower than in Upper
Lake Constance. We think that the main reason for the difference in FES capacity
between the Upper and Lower parts of Lake Constance is the different compositions
of their bottom sediments. In particular, bottom sediments from Lower Lake
Constance contain much more organic material and less micaceous clay minerals.
Table 4 summarises the data obtained on radiocaesium selective sorption
characteristics of bottom sediments. Using the data of Table 4 together with the
data on the cationic compositions of the lake waters (Table 2), it is possible to
estimate the radiocaesium distribution coefficient (Kd) and its concentration in water
using the following equation (Wauters et al., 1996):
Kex
d ¼
RIPex
Kð Þ
mk þ KFES
c NH4=K
À Á
mNH4
; ð2Þ
Table 2
Cation compositions of lake waters under study
Lake [K+
]
(mg/l)
[NH+
4 ]
(mg/l)
[Ca2+
]
(mg/l)
[Mg2+
]
(mg/l)
[Na+
]
(mg/l)
pH
Upper Lake Constance 1.1–1.3 o0.01 48.7–54.1 6.7–9.7 4.4–4.7 7.5–8.1
Lower Lake Constance 0.8–1.2 0.01–0.17 41.3–53.7 6.6–8.3 4.2–4.5 7.5–8.5
Lake Lugano (Agno basin) o0.4 0.23–0.52 25–32 5–8 8–18 7.7
Vorsee 0.9–2.0 0.04–1.0 53–118 6.9–8.6 3.5–5.0 7.4–9.4
Table 3
137
Cs concentration, 137
Cs exchangeability, cation exchange capacity and exchangeable cation composi-
tion of the studied bottom sediments
137
Cs,
(Bq/kg)
aex (%) CEC
(meq/kg)
[Ca]ex
(meq/kg)
[Mg]ex
(meq/kg)
[K]ex
(meq/kg)
[Na]ex
(meq/kg)
Upper Lake Constance
Bottom sediments
(upper 4 cm)
460790 2.971.0 240717 222715 1872 0.270.1 0.5070.07
Lake Lugano (Agno basin)
Bottom sediments
(upper 10 cm)
2800 4.2@1.9 553 6.2 97.5 0.7 0.1
Lake Vorsee (bottom sediments)
Layer 0–10 cm 3110 9 630 540 59 29 2
Layer 10–20 cm 3890 7.7 600 510 61 23 2
Layer 20–30 cm 3210 9.8 600 525 55 14 2
Layer 30–40 cm 860 18.3 710 650 50 6 2
Layer 40–50 cm 650 15.4 640 590 43 5 2
A. Konoplev et al. / J. Environ. Radioactivity 58 (2002) 1–11 7

8. where KFES
c NH4=K
À Á
is the selectivity coefficient of ammonium sorption on FES in
relation to potassium, mk and mNH4
are the molarities of potassium and ammonium
in solution, respectively. The results of these calculations for the lakes under study
are presented in Table 5. To calculate Ktot
d , the measured values of the 137
Cs
exchangeability (Table 3) have been used:
Kex
d ¼ aexKtot
d : ð3Þ
The 137
Cs concentration in water was calculated by assuming that its concentration
in surface sediments is the same as in suspended matter. As can be seen from Table 5,
the 137
Cs concentration in Lower Lake Constance is expected to be 3–10 times higher
than in Upper Lake Constance. There are two main reasons for this difference: (1)
the lower ability of bottom sediments in Lower Lake Constance to selectively bind
radiocaesium (Table 4); (2) the generation of ammonium in eutrophic Lower Lake
Constance during late summer–autumn and radiocaesium remobilisation due to
cation exchange with ammonium.
To test the applicability of the method of estimation of distribution coefficients,
the 137
Cs activity concentrations in water and in suspended matter of both parts of
Fig. 2. Isotherm of Cs selective sorption on FES of bottom sediments from Lower Lake Constance: open
dots, and Upper Lake Constance: filled dots.
Table 4
Characteristics of radiocaesium selective sorption by bottom sediments (upper 10 cm) from lakes under
study
Lake [FES]
(meq/kg)
[HAS]
(meq/kg)
RIPex
(K)
(meq/kg)
RIPex
(NH4)
(meq/kg)
KFES
c
(NH4/K)
Upper Lake Constance 4.1 F 1300 434 3.0
Lower Lake Constance 1.7 F 478 187 2.6
Lake Lugano (Agno basin) 7.0 0.38 224 130 1.7
Vorsee 1.1 0.12 87 60 1.45
A. Konoplev et al. / J. Environ. Radioactivity 58 (2002) 1–118

9. Lake Constance were measured as well as in Rhine river inflowing to and outflowing
from Lake Constance using the ‘‘Mydiya’’ sampling system. The Alpine Rhine River
flows into Upper Lake Constance and the River Rhine flows out from Lower Lake
Constance. These results are presented in Table 6.
To assess the heterogeneity of 137
Cs activity concentration with depth in Lake
Constance, the vertical distribution of 137
Cs in lake water was studied (Fig. 3). The
calculated values agree with the experimental values, which vary depending on the
depth by a factor of 5.
137
Cs concentrations measured in the water of Lake Lugano is 1 mBq/1 for
the surface layer and 5 mBq/1 for the layer close to the bottom (Fig. 3).
The agreement between estimated and measured values for Lake Constance
and Lake Lugano is encouraging, taking into account the possible spatial
heterogeneity of the characteristics of each lake. The values of the distribution
coefficients estimated as described have been used to model the 137
Cs vertical
distribution in bottom sediments of Lake Constance (Konoplev et al., 1996).
Good agreement of the calculated results and observations also confirms the
applicability of the method.
At the same time, for Vorsee there is a factor of 2–3 difference between
the estimated and measured values of 137
Cs concentration. The possible reason
for this discrepancy could be the fact that the bottom sediments in Vorsee mainly
consist of organic matter and water. In this case, the proposed approach for Kd
prediction, based on selective sorption by illitic clay minerals, is probably only
partially valid.
Table 6
Results of measurements of 137
Cs activity concentration in solution and in suspended matter and measured
in situ values of total distribution coefficients in Lake Constance and inflowing Alpine Rhine and
outflowing Rhine River in 1996
Water object 137
Cs in solution
(mBq/1)
137
Cs in suspended matter
(Bq/kg)
Ktot
d
(1/kg)
Alpine Rhine 0.0770.05 1072 1.4 Â 105
Upper Lake Constance 0.2370.04 120730 5.2 Â 105
Lower Lake Constance 1.2170.07 56713 4.6 Â 104
Rhine River 0.2970.06 8007300 2.7 Â 106
Table 5
Results of estimation of distribution coefficients and concentrations of dissolved 137
Cs in waters of the
lakes under study
Lake Kex
d (1/kg) Ktot
d (1/kg) [137
Cs] (mBq/1)
Upper Lake Constance 32,500 106
0.2
Lower Lake Constance 3750–12,000 105
@3*105
0.7–2.0
Lake Lugano 5200 157,000 2–7
Lake Vorsee 1150 8100 380
A. Konoplev et al. / J. Environ. Radioactivity 58 (2002) 1–11 9

10. 4. Conclusions
* Estimated and measured values of Ktot
d for 137
Cs in Upper Lake Constance are
very high (up to 106
1/kg). The main reasons for this are a high content of clay
minerals in the sediments of the lake and very low concentrations of competing
ions (K+
, NH4
+
). A high concentration of Ca2+
in water is favourable for
enhanced fixation of 137
Cs by illitic clay minerals.
* 137
Cs remobilisation is essentially higher in Lower Lake Constance compared
with Upper Lake Constance because of the lower binding ability of the sediments
and the existence of a considerable concentration of ammonium during late
summer and autumn.
* Estimated 137
Cs activity concentrations in Lake Constance and Lake Lugano are
in good agreement with measured data.
* Disagreement by a factor of 2–3 between the measured 137
Cs activity
concentrations and estimated values for Lake Vorsee indicates that the
methodology fails to predict the radiocaesium distributions in lakes with highly
organic sediments.
Acknowledgements
This work was partly supported by the Alexander von Humboldt Foundation
(Germany), which provided a research fellowship to A. Konoplev, and by the CEC
Project IC15 CT98-0205 (AQUASCOPE). The authors would like to thank O.
Voitsekhovich and V. Kanivets from the Ukrainian Hydrometeorological Institute
for their help in water sampling.
Fig. 3. Depth distribution of the 137
Cs activity concentration in Lake Constance and in Lake Lugano.
A. Konoplev et al. / J. Environ. Radioactivity 58 (2002) 1–1110

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