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BIOACCUMULATION OF Tc-99,
Pu-239 AND Np-237 BY
BOTTOM SEDIMENTS OF
FRESH WATER LAKES OF
MOSCOW REGION
German K.E., Firsova E.V., Peretrukhin V.F.,
Khijnyak T.V., Simonoff M.*
- Institute of Physical Chemistry of Russian
Academy of Sciences, Moscow, Russia
* - UMR 5084 - Chimie NuclГ©aire Analytique et
Bioenviron., Le Haut Vigneau, Gradignan, France
Two typical lakes of different
trophic types:
Moscow region map
Eutrophic Lake
“Beloe” (Kosino)
systematically
characterized
since 1896
Dystrophic Lake
“Peaty” (Shatura)
the typical of peatbogs
After the treatment of literature
data on the lakes of Moscow reg.
we have chosen the sampling sites
at l. Beloe, Kosino (depth 9 m):
l. Beloe, Kosino
Expedition to lake Beloe
(Assembling the boat and the
research team)
Expedition to lake Beloe (autumn )
Temperature of air (day) = 12 oC
Temp. surface water = 11 oC
Temp. of sediment
= 8 oC
Sampling the lake sediment
and bottom water
Sampling
instrumentation
designed by Molchanoff
Permits to control
- Temperature & Depth
- No air contact
- Min. layer mixing
Solid : Liquid = 1:3 by volume
Solid : Liquid = 1:33 by dry weight
Eutrophic lake sediment was
mainly
formless
organic
detritus, gray colored, H2S
odoriferous.
Dystrophic lake sediment
was 98% organic peat and
humics, 2% sand.
Samples transported to the IPC
RAS for characterization and
model experiments
M icroorganism
M icroalgae
B acteria:
S ulphate reducing
M ethanogenic
N itrifying
D enitrifying
C ells’
num ber
N /m l
6
10
4
10
4
5
10 – 10
3
4
10 - 10
5
10
C om m ents
R atio in batch: V sedim ent : V liquid = 1:3; M solid : M liquid = 1:30
9
T otal = 2 * 10 bacteria/g, pH = 7.0 (stable); E h = -0.20V
N H E (inner sedim ent part); w ater phase: [H C O 3 ] = 1 –
4 m g-C /l; [H S O 4 ] = 0 – 50 m g/l, [C l ] = 35 m g/l.
sum m er - autum n: sedim ent rich in organic easy for
assim ilation by m icroorganism s
w inter-spring : sedim ent rich in ferm entated organic
Two equilibration modes were modeled
- overhead agitation
- hypolimnionic Tc transfer to sediment
(diffusion+microbial)
L g [([M e ] 0 -[M e ])/[M e ]]
Model experiments of radionuclides uptake
by eutrophic lake bottom sediment,
[Tc]0 , [Np]0 , [Pu]0 ~ 10-5M
2
1
0
Tc
Np
- Centrifuge MPW-210 (1500 g, 15
-1
Pu
min), and microfilterfuge tubes
-2
10,000 - 30,000 NMWL Polysul0
20
40
60
phone (RAININ Instr. Co., Inc) were
T im e, days
used for microphase separation
Hypolimnionic uptake of Tc, Np and Pu
(colloids and microbes).
пЃ®More than 95% of Tc 99 were truly dissolved species of TcO4- in water phase all time
through the experiment.
The kinetics’ analysis of data has shown that the half-time values of the initial content
removal from the water-phase form 400h for Tc, 10h for Np and less than 1h for Pu.
пЃ®Two different uptake rates were characteristic for plutonium and neptunium sorption:
fast uptake during the first hour when 60% and 50% of initial input was sorbed by
sediment of eutrophic and dystrophic lakes, and a slow bioaccumulation period when
neptunium uptake was completed in 1 and 2 months for eutrophic and dystrophic lakes
respectively
The microflora of lake
played important role
in the accumulation
and reduction of
radionuclides.
[T c] in w ater phase, % .
Substrates (additions of sulfate and nitrate) effect
on the kinetics of Tc-99 uptake by eutrophic lake
sediment (t = 20oC; [Tc]0 = 10-5M)
100
N a tu ra l w a te r (N W )
N W + S u lfa te 8 0 m g /l
80
N W + N itra te 8 0 m g /l
60
40
20
0
0
10 20 30 40 50 60 70
T im e , d a ys
Some microorganisms being able of anaerobic respiration had
competition relationships between SO42- or NO3- and TcO4-. Addition
of SO42- or NO3- decreases the rate of Tc accumulation by sediment.
Concentration factors were 1700 ml/g (eutrophic) and 56 ml/g (dystrophic)
after 1550 hours of equilibration of the lake sediment with spiked water phase.
N p a ccu m u la t ion by dy st r oph y c la k e bot t om se dim e n s
10000
8000
N o1
A c ti v i ty
N o2
6000
N o3
N o4
N o5
4000
N o6
N o7
2000
0
0
20
40
60
80
100
120
140
Tim e , h ou r
No1& No2 - natural (silt+water), t=15oC
No3 & No4 - natural (silt+water), t=6oC
No 5 - natural (silt+water), t=15oC + 0.02 M H2CO
No 6 - humine water from the pond; t=15oC
No 7 - humine water from the pond + 0.02 M H2CO; t=15oC
Temperature effect
[T c ] i n w a te r p h a s e , %
100
22 C
18 C
75
15 C
6C
50
25
0
0
10
20
30
Tim e, days
40
50
Very small increase of
uptake rate for contact
time 10-20 days was found
for cold weather.
This observation correlates
with the hypothesis that
sulfate-reducing bacteria
(dominating
at
this
temperature if no artificial
aeration was applied) are
the most active microbial
species
toward
Tc
reduction among these
present
in
the
lake
sediment.
[T c ] in w ater phas e, %
of total ac c um ulated
ac tiv ity
Desorption tests
H 2O 2
90
(1 0 0 % )
60
30
H 2O
(5 % )
HCl
(5 % )
N a C lO 4
(8 % )
0
The desorption of Tc
was carried out with H2O,
1M HCl, 1M NaClO4 or
15% H2O2 and gave the
desorption factors of 0.05,
0.05, 0.08 and more 0.99
thus indicating the reduction
of technetium to be the main
mechanism of its uptake.
D e s o rp tio n a g e n t
п‚­
п‚­
The sediments from freshwater lakes have a
considerable sorption capacity.
4 consecutive sorption runs have demonstrated only
small decrease of Tc uptake rate.
Mechanism of radionuclide uptake by
fresh water lake sediment
• At the actual TcO4- and S2- concentrations the
reduction of pertechnetate with hydrosulfide is
inhibited.
• Tc(VII) reduction and further uptake by the lake
sediment is due to microbial activity of the sediment
components, most probably to sulfate-reducing bacteria
• Reduction of Np, Pu and Tc to Me(IV) oxidation state
and sorption of hydrolyzed species are the main
mechanisms for Np, Pu and Tc accumulation in this
biosystem
• The difference in the uptake rate is associated with the
higher chemical stability of TcO4
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