Brit Salbu, UMB, Bergen June 2008
UNIVERSITETET FOR MILJØ- OG BIOVITENSKAP
Risø NKS November 16, 2009
Speciation of radionuclides
Brit Salbu
Isotope Laboratory
Norwegian University of Life Sciences
UMB
[email protected]
Brit Salbu, UMB, Risø, 2009
UNIVERSITETET FOR MILJØ- OG BIOVITENSKAP
Take home message
• Radionuclides can be present in different
physico-chemical forms influencing
transport/mobility and bioavailability
• Radionuclide species depend on sources and
release conditions and transformation processes
occurring in the environment.
• Speciation/fractionation techniques are needed
to distinguish between radionuclides species.
[email protected]
Brit Salbu, UMB, Risø, 2009
UNIVERSITETET FOR MILJØ- OG BIOVITENSKAP
UMB archive
Kurday
Kadji-say
Tabushar
Digmai
Nuclear weapon tests -filters
Semipalatinsk
Thule, Greenland
Palomares, Spain
Novaya
Zemlya
Kara Sea
NW Russia
Kuwait
Kosovo
Chernobyl, Ukraine
Windscale/Sellafield, UK
Dounray, UK
La Hague, France
Mayak, Krashnoyarsk, Russia
Savannah River Site, USA
Oscarshamn,
Forsmark, Sweden
[email protected]
Brit Salbu, UMB, Risø, 2009
UNIVERSITETET FOR MILJØ- OG BIOVITENSKAP
Outline
• Definitions
• Speciation/fractionation techniques applied
•
•
•
In water
In soils/sediments
In biological materials
• Relevance in radioecology
[email protected]
Brit Salbu, UMB, Risø, 2009
UNIVERSITETET FOR MILJØ- OG BIOVITENSKAP
Definition: radionuclide species
Radionuclide species are defined according to
their physico-chemical properties;
9 Molecular mass
9 Charge properties
9 Oxidation state – valence
9 Structure
9 Complexing ability
9 etc.
e.g. ions, molecules, complexes, colloids, particles
Modified after IUPAC (excluded isotopic composition)
(Salbu, JER, 2009)
[email protected]
Brit Salbu, UMB, Risø, 2009
UNIVERSITETET FOR MILJØ- OG BIOVITENSKAP
Definition: Speciation of radionuclides
Speciation of radionuclides is defined as the
distribution of radionuclide species in a system
In accordance with IUPAC 2000
[email protected]
Brit Salbu, UMB, Risø, 2009
UNIVERSITETET FOR MILJØ- OG BIOVITENSKAP
Definition: Speciation analysis
IUPAC 2000: “The analytical activities of identifying
and/or measuring the quantities of one or more
individual chemical species in a sample”
Revised: Application of analytical techniques to identify
and quantify one or more individual radionuclide
species in a sample ( i.e. application of in situ, at site, on
line, at lab. fractionation techniques prior to
measurements).
[email protected]
Brit Salbu, UMB, Risø, 2009
UNIVERSITETET FOR MILJØ- OG BIOVITENSKAP
Definition: Radioactive particles
(IAEA, 2001 and 2009)
• Radioactive particles in the environment are
defined as localised aggregates of radioactive
atoms that give rise to inhomogeneous distribution
of radionuclides significantly different from that of
the matrix background
[email protected]
Brit Salbu, UMB, Risø, 2009
UNIVERSITETET FOR MILJØ- OG BIOVITENSKAP
Definition: Particles (IAEA, 2001 and 2009)
In water/sediment/soil/biota
• Fragments – larger than 2 mm
• Particle size range: 0.45 µm – 2mm (includes
sand+silt fraction)
• Colloidal (nanoparticle) size range: 1 nm - 0.45 µm
• Low molecular mass species: less than 1 nm
In air:
• Particles (submicrons in aerosols to fragments) are
classified according to their aerodynamic diameters.
• Particles less than 10 μm are considered respiratory.
[email protected]
Brit Salbu, UMB, Risø,2009
UNIVERSITETET FOR MILJØ- OG BIOVITENSKAP
Speciation of radionuclides
Diameter
1 nm
10 nm
0.1 µm
Molecular
mass
x 102
x 104
x 106
0.45 µm
1 µm
10 µm
x 108
Category
simple compounds
hydrolyzates/colloids
polymers / pseudocolloids
suspended particles
Cases
inorganic, organic ions,
complexes, molecules etc.
nanoparticles
polyhydroxo complexes
polysilicates
fulvic acids
fatty acids
metal hydroxides
clay minerals
humic acids
proteins
inorganic mineral particles
organic particles
microorganisms
Methods,
Determination of total activity concentration of radionuclides in acidified samples.
Dissolved radionuclides, determination of total in 0.45 µm
filtered sampled and acidified
LMM species
Size
fractionation
techniques
Diffusion
rate
measurement
Ultrafiltration
ultracentrifug.
dialysis
Charge
fractionation
techniques
Ion chromatography – undefined fractions
Complexation – undefined fractions
[email protected]
Filtration
Sedimentation
Brit Salbu, UMB, Risø, 2009
UNIVERSITETET FOR MILJØ- OG BIOVITENSKAP
Fractionation/speciation techniques
Size fractionation
Charge fractionation
Solid state speciation
Electronmicroscopy
Exchange
techniques
chromatography
Tangential
(SEM,
(cation,
anion,
Low activity
concentrations
– noTEM)
flow/hollow-fibre
adsorption)
X-ray induced
ultra filtration
direct specie-specific techniques
spectroscopy
Liquid-liquid
Continousare
flowavailable
(μ-XRD, μ-XAS, μ-XANES,
extraction
centrifugation
EXAFS)
Sequential
Techniques must be combined to
In situ dialysis
Laser-induced
extractions
(small volumes)
provide specie characteristics
spectroscopy
Electrochemical
(LIPAS, LITLS, LAMMA)
Ultra
methods
Advanced techniques within
other
centrifugation
Electron energy loss
Crown
ether
increasingly
needed
spectroscopy
Density disciplines
chromatography
centrifugation
Raman spectroscopy
Filtration
Dialysis
Nuclear magnetic
resonance spectroscopy
Gel
chromatography
[email protected]
Brit Salbu, UMB, Risø, 2009
UNIVERSITETET FOR MILJØ- OG BIOVITENSKAP
Size and charge distribution pattern
Recommended
Total
activity concentration
1. Fractionation according to size
1i.e.
nm particles
10 nm
0.1 µm
1 µm
and colloids
Diameter
2. Fractionation according to charge
i.e. charged
LMM species Particles
Species Low molecular
Colloids
mass species
To avoid analytical problems
Mobile and
Inert
species
bioavailable
species
LMM positively/ negatively
charge or neutral species
[email protected]
Brit Salbu, UMB, Risø, 2009
UNIVERSITETET FOR MILJØ- OG BIOVITENSKAP
Fractionation of radionuclides in rivers
under high flow conditions
For identification of radionuclide species in the
environment – during events - we need in situ
fractionation techniques – avoid storage effects
Fractionation in the field
[email protected]
Brit Salbu, UMB, Risø, 2009
UNIVERSITETET FOR MILJØ- OG BIOVITENSKAP
Size and charged
interfaced system
Charge
fractionation
peristaltic
pump
ultrafiltrate
waste
Hollow-fibre
10 kDa
Hollow fibres
exchange
resins
(Amberlite)
cation
Filters
Size fractionation
membrane filter
0.45μm
peristaltic
pump
in situ
sampling
Cation
resins
[email protected]
Brit Salbu, UMB, Risø, 2009
UNIVERSITETET FOR MILJØ- OG BIOVITENSKAP
Colloids in effluents from reprocessing
plants – Transmission Electron microscopy
(TEM) reflect the presence of colloids.
Effluents contain: ions, colloids, particles
S IX E P
La Hague
SE A TA N K
2 0 0n m
Sellafield
[email protected]
Brit Salbu, UMB, Risø, 2009
UNIVERSITETET FOR MILJØ- OG BIOVITENSKAP
Case: size fractionation of effluent from La Hague
La Hague effluent
Ultrasentrifugation
100 %
90 %
80 %
70 %
60 %
LMW < 1E+3 Da
Colloidal 1E+3-1E+4 Da
Colloidal 1E+4Da-0,45um
Particles >0,45 um
50 %
40 %
30 %
20 %
10 %
0%
Mn-54
Co-60
Sb-125
Cs-134
[email protected]
Cs-137
Brit Salbu, UMB, Risø, 2009
Lind, OC., Oughton, DH., Salbu, B., Skipperud, L., et. al., (2006) Earth and Planetary Science Letters
Pycnocline
24,3 psu
8
68
51
Near
6
21
bottom
32,9 psu
82
70
73
Pycnocline
28 psu
61
61
31 36
36
31
33
33
P articu late (> 0,45 u m )
CISOTOPE
o llo id al (8kD
a-0,45u m )
LABORATORY
DEPARTMENT PLANT AND
LM
M (<8kD a)
ENVIRONMENTAL
SCIENCES
19
11
13 9
78
72
Surface
0 psu
52
52
19 29
19
29
Yenise
y
41
41
Ob
UNIVERSITETET FOR MILJØ- OG BIOVITENSKAP
Fractionation water+ AMS: Trace of
weapon grade Pu in colloidal phase in
Jenisey, all the way into Kara Sea
Total sample = fallout
4
8
[email protected]
32
32
Surface
23,8 psu
77
19
52 29
Pycnocline
28 psu
Surface
0,1 psu
25 45
30
16 Near bottom
36
0 psu
48
Brit Salbu, UMB, Risø, 2009
UNIVERSITETET FOR MILJØ- OG BIOVITENSKAP
Speciation of radionuclides
Diameter
1 nm
10 nm
0.1 µm
Molecular
mass
x 102
x 104
x 106
0.45 µm
1 µm
x 108
Category
simple compounds
hydrolyzates/colloids
polymers / pseudocolloids
suspended particles
Cases
inorganic, organic ions,
complexes, molecules etc.
nanoparticles
polyhydroxo complexes
polysilicates
fulvic acids
fatty acids
metal hydroxides
clay minerals
humic acids
proteins
inorganic mineral particles
organic particles
microorganisms
Proccesses Molecular mass
growth mechanisms:
•hydrolysis
•complexation
•polymerisation
•colloid formation
•aggregation
[email protected]
10 µm
Mobilization mechanisms:
•desorption
•dissolution
•dispersion
Brit Salbu, UMB, Risø, 2009
UNIVERSITETET FOR MILJØ- OG BIOVITENSKAP
Case: Autoradiography using P imaging –
soils contaminated with Chernobyl fallout
Chernobyl soil (Western trace)
[email protected]
Brit Salbu, UMB, Risø, 2009
UNIVERSITETET FOR MILJØ- OG BIOVITENSKAP
Sorption mechanisms – important
for mobility
Physical sorption
Consecutive layers
reversible
Electrochemical
sorption
Monolayer
reversible
Chemisorption
Monolayer
irreversible
Inert
electrolyte
Ionexchange
pH
red/ox
Strategy: sequential extractions
Increased dissolution power of agent
[email protected]
Brit Salbu, UMB, Risø, 2009
UNIVERSITETET FOR MILJØ- OG BIOVITENSKAP
Sequential extraction
– processes, models, agents and reagents
Processes
Model
Agents
Reagents
Physical sorption Consecutive layers,
reversible reaction
Indifferent (inert)
electrolyte
H2O
Electrostatic
sorption
Monolayer,
Reversible
reactions
Ion-exchangeble
species, increased
acidity (pH)
pH<soil/sediment
Chemisorption
Monolayer,
Irreversible
reaction
Red/ox agents,
increase in
temperature
Weak reducing:
NH2OH•HCl
NH4OAc, soil/ sediment
pH
NH4OAc, pH5
Weak oxidizing: H2O2,
pH 2
Strong oxidizing: 7 M
HNO3, 80°C
[email protected]
Brit Salbu, UMB, Risø, 2009
UNIVERSITETET FOR MILJØ- OG BIOVITENSKAP
Sequential Extraction of Radionuclides and
Stable Analogues from Chernobyl contaminated
Soil - Caesium
Weathering – predict decreased
mobility and decreased doses
Oughton et al., Analyst 1992
[email protected]
Brit Salbu, UMB, Risø, 2009
UNIVERSITETET FOR MILJØ- OG BIOVITENSKAP
Sequential Extraction of Radionuclides and
Stable Analogues from Chernobyl contaminated
Soil - Strontium
Weathering – predict increased
mobility and increased doses
Oughton et al., Analyst 1992
[email protected]
Brit Salbu, UMB, Risø, 2009
UNIVERSITETET FOR MILJØ- OG BIOVITENSKAP
Case: Chernobyl fallout. Repeated extractions with
water, NH4Ac (soil pH), and NH4Ac (pH 5).
Differentiate between reversible and irreversible
sorption processes
Sr-90
Cs-137
Reversible: 1 extraction gives 50 %
[email protected]
Brit Salbu, UMB, Risø, 2009
UNIVERSITETET FOR MILJØ- OG BIOVITENSKAP
Pu in the environment – model experiments
PuO2 xH2O
Reducing
Higher pH
Lower pH
Pu(III)
Pu3+
Hydrolysis
Complexation
Sorption
Pu(IV)
Pu4+
Oxidizing
Lower pH
Higher pH
Pu(V)
PuO2+
Pu(VI)
PuO22+
Redoxreactions
Precipitation
[email protected]
Hydrolysis
Complexation
Sorption
Brit Salbu, UMB, Risø, 2009
Soil solution
k2
Easily
exchangeable
(NH4Ac)
”Mobile fraction”
Amorphous
”Bound fraction”
k3
k4
Irreversibly bound
“Fixed fraction”
0,00 10,00 20,00 30,00 40,00 50,00 60,00 70,00 80,00
Mobile (%)
100
H2O
NH4AcpHSoil
Fractions
UNIVERSITETET FOR MILJØ- OG BIOVITENSKAP
Tracer experiments: Pu-species in soil/sediment – water
systems
k1
Redox sensitive/
NH4AcpH=5
Bound
Fixed
Mobile
80
1h
24h
60
168h
NH2OHHCl
720h
2160h
H2O2
HNO3
40
20
0
0
500
[email protected]
1000
1500
Time (hour)
2000
2500
100000,00
Pu-V,VI
Pu-III,IV
Pu-III ,IV+ EDTA
Pu-III,IV + Citrat
10000,00
KD (mg/ml)
Brit Salbu, UMB, Risø, 2009
UNIVERSITETET FOR MILJØ- OG BIOVITENSKAP
-water systems
Kd for Pu species as f(t
f(t)) in a soil
soil-water
1000,00
100,00
o
4C
Soil : Water
1: 10
10,00
1,00
0
500
1000
1500
2000
2500
Contact time (hours)
Pu-species
T1/2 (d)
T1/2 (d)
Associated
Fixation
PuIII,IV
0.4 ± 1 %
34 ± 7 %
PuV,VI
0.8 ± 10 %
40 ± 5 %
PuIII,IV-organic
0.8 ± 1 %
39 ± 6 %
Skipperud, L., Oughton, D. H. and Salbu, B., (2000) "The impact of Pu speciation
on the distribution coefficients
in Mayak soil" Science of the Total Environment
[email protected]
Brit Salbu, UMB, Risø, 2009
UNIVERSITETET FOR MILJØ- OG BIOVITENSKAP
Modelling Doses to humans
Dose from 1 GBq release
Skipperud,
L., Oughton,
D. H., and
Salbu, B.,
(2000)
Health
Physics
[email protected]
Brit Salbu, UMB, Risø, 2009
UNIVERSITETET FOR MILJØ- OG BIOVITENSKAP
Radioactive particles are present in most
contaminated areas. Identifying single U
particles: autoradiography – SEM/BEI mode
P-imaging
BE
I
[email protected]
Brit Salbu, UMB, Risø, 2009
UNIVERSITETET FOR MILJØ- OG BIOVITENSKAP
SEM - XRMA
Localization, Isolation and Characterization of U
containing particles (UMB)
SEM and XRMA
SEI
SEI-mode
•characterization
of particle surface
structure.
BEI-mode
•localization of
particles
containing heavy
elements
X-ray mapping
•localization of
particles
containing
radionuclides.
XRMA
•element analysis
Counts
U
200
U
150
100
U
50
U
U
U
U
U
U
0
0
5
10
15
20
Energy (keV)
[email protected]
Brit Salbu, UMB, Risø, 2009
UNIVERSITETET FOR MILJØ- OG BIOVITENSKAP
X-ray Absorption Spectroscopy - ESRF
•µ-XRF- element
•µ-XANES-ox state
•µ-XRD-structure
•EXAFS – fine structure
[email protected]
• Photons ->
•
exitation ->
•
deexitation
K, L, M electrons
• Emittance
•
X-ray fluorescence
(XRF)
•
Auger electrons
•
Transmission of the
beam – absorption
UNIVERSITETET FOR MILJØ- OG BIOVITENSKAP
Particle characterization methods
1. Digital autoradiography to identify heterogeneities and
sample splitting/gamma measurements
2. ESEM/TEM with XRMA
Surface structure and elemental composition
3. SR-based 2D and 3 D µ-XRF (micro X-ray fluorescens)
Subsurface/volume elemental composition
4. SR-based 2D µ-XANES (micro X-ray absorption near edge
structure spectrometry)
Oxidation state determination, and confirmed by
5. SR-based µ-XRD (micro X-ray diffraction)
Crystallographic forms
6. µ-XAS tomography
Spatial distribution
7. Source identification of isotope ratios by MS techniques
8. Leaching experiments to identify mobilisation potential
[email protected]
UNIVERSITETET FOR MILJØ- OG BIOVITENSKAP
Complex 3D aggregates of different phases
• Absorption X-ray microtomography: 3D density distribution
excellent tool for overall 3D sample exploration
> 0.5 μm resolution
• Confocal μ-XRF: 3D elemental distribution
elemental tomograms in selected planes within
the sample
ROI imaging possible
major elements to trace constituents
combination with confocal μ-XANES
> ~ 5-10 μm resolution (secondary polycapillary
optics)
• Tomographic μ-XRD: 3D structure distribution
phase-tomograms in selected planes within the
sample
minimization of self-absorption
> ~ 10 μm resolution
better resolution possible via KB, CRL, optics
[email protected]
Brit Salbu, UMB, Risø, 2009
UNIVERSITETET FOR MILJØ- OG BIOVITENSKAP
Synchrotron radiation 2D μ-XRF
mapping at HASYLAB, Germany
Ar
K
Ca
Ti
Cr
Mn
Fe
Zn
Sr
Zr
Mo
Ru
Sn
Ba
Pb
U
Chernobyl particles contain while inclusion Ru+Mo
Corresponding distribution: U, Zr, Sr
[email protected]
Brit Salbu, UMB, Risø, 2009
UNIVERSITETET FOR MILJØ- OG BIOVITENSKAP
Synchrotron radiation μ-XANES for determination
of oxidation states of U in a Chernobyl U particle
(ESRF) – should be combined with μ-XRD.
oxidation
state
+4 ±0.5
N
oxidation
state +5±0.5
W
[email protected]
100
% Residual FP
90
2
80
•Two different release scenarios
•Different particle
characteristics
North
•Different ecosystem behaviour
70
60
50
40
30
20
10
2050
2046
2042
2038
2034
2030
2026
2022
2018
2014
2010
2006
2002
1998
1994
1990
0
1986
Brit Salbu, UMB, Risø, 2009
UNIVERSITETET FOR MILJØ- OG BIOVITENSKAP
Explosion: inert U fuel particle, low weathering rate,
low soil-plant transfer.
Fire: Oxidized U fuel, high weathering rate, high
soil-plant transfer.
North:
West: Initial
Weathering of
Subsequent
release
particles at pH6
release (fire)
(explosion)
West – UO
•Same source
Year
Oxidation state +4 ±
0.5 – UO2
Oxidation state +2.5 ± 0.5 Oxidation state +5 ± 0.5
U3O8
U-O-Zr, [email protected]
Brit Salbu, UMB, Bergen June 2008
UNIVERSITETET FOR MILJØ- OG BIOVITENSKAP
Radioactive particles released during ”all” types of severe
nuclear events. The source determines the composition,
the release scenarios dictate particle properties
Nuclear test
Semipalatinsk
Thule
Dounrey
Sellafield
Particle deposition?
•HotKuwait
spots – problems with representative
Aggregate from the
Chernobyl explosion
sampling
•Partial leaching – analytical errors - transuranics
•May underestimate the inventories
XRMA
Adds significantly to the overall uncertainties
Corrosion product
Waste in Kara Sea
[email protected]
Krasnoyarsk U particle
Brit Salbu, UMB, Risø, 2009
UNIVERSITETET FOR MILJØ- OG BIOVITENSKAP
Biological relevance of particles
• Transfer of nano-particles through skin of earthworms.
Accumulation of Co-60 labelled nanoparticles in
spermatogonetic cells and cocoons (Oughton et al)
Male reproductive organs
Smeer of spermatogenic cells
Clitellum
Cocoons
• Retention of micrometer particles in GI tract (Salbu et al)
Effects from particle exposure – IAEA 2008
[email protected]
Brit Salbu, UMB, Risø, 2009
UNIVERSITETET FOR MILJØ- OG BIOVITENSKAP
Case: DU particles from Kosovo and Kuwait
Source
U-Ti alloy
Release
scenario
Weathering
conditions
Solid state
speciation
Dissolution
behaviour
Fire
High temp.
Desert
Arid
XANES: +6
XRD: UO3·x H2O
83% in 2 hrs,
96% in 1 week
Impact
Initially very high,
subsequently
moderate temp.
Mountainous
Humid
XANES: +4 - +5.3
XRD: UO2, UO2.34,
UC, metallic U
25% in 2 hrs,
87% in 1 week
Corrosion
Low temp.
Desert
Arid
XANES:+4.6 - +6
XRD: n.a.
24% in 2 hrs,
73% in 1 week
Linking source and release scenarios to
particle characteristics and remobilization
potential (0.1 M HCl extractions)
[email protected]
Brit Salbu, UMB, Risø, 2009
UNIVERSITETET FOR MILJØ- OG BIOVITENSKAP
Radionuclide species in biological material
•Extraction with agents – poor analytical control
•Separations – size exclusion techniques –proteins etc
•Low level detection
•On line systems – corresponding signals from radionuclides and
proteins
Juice from
human stomach
Milk from
Norwegian
goat
Heat
treatment
pH
adjusted
to 2,5
Juice from
duodenum
human
Digestion
STEP 1
Digestion
STEP 2
37 °C
min.
37 °C
min.
30
30
Digested
Milk
pH
adjusted to
7,5
pH is measured every
minute during this step
Milk from
Norwegian
cow
Human gastric juice (HGJ) and Human duodenal juice (HDJ)
[email protected]
Brit Salbu, UMB, Risø, 2009
UNIVERSITETET FOR MILJØ- OG BIOVITENSKAP
In vitro extraction with Human gastric juice
(HGJ) and Human duodenal juice (HDJ)
Mimicking the degradation of food samples in GI tract
One MBq particle: 2 % released in HGJ, 5 % in HDJ
2 D electrophoresis of milk from different animals
Challenges – sufficient activity to be registered by
autoradiography. Still restricted to tracer experiments.
G. E. Vegarud, UMB
[email protected]
Brit Salbu, UMB, Risø, 2009
Extraction of proteins
from a biological sample
Intensity, counts (77Se)
SEC purification of biomolecule fraction
Challenges
4
6 x10
Need relative high activity
concentrations to obtain
signals above detection limits
4
A
2
0
16
18
20
C
B
22
24
26
tryptic
digestion
28
Time, min
80
Se
3.0
2.5
SeMet
SEC purification (2D gel electrophoresis) of biomolecules
Intensity, counts
UNIVERSITETET FOR MILJØ- OG BIOVITENSKAP
Fractionation/speciation of biomolecules in the future
x103
Identification
2.0
Low level detection
1.5
1.0
0.5
10
80
1
15
2 3 4
20
5
25
Se
6
Time, min
30
35
[email protected]
After Szpunar et al
Brit Salbu, UMB, Risø, 2009
UNIVERSITETET FOR MILJØ- OG BIOVITENSKAP
Challenges in radioecology: Linking radionuclide
species in sources to impact and risk assessment
Sources
Sources
Sources
Transport in different
ecosystems
Climate
Pathogens/virus
conditions
Processes in
soil / water / sediments
Bioavailability
Biological
membrane
Uptake/effect
Exposure
[email protected]
Impact/risks
Brit Salbu, UMB, Risø, 2009
UNIVERSITETET FOR MILJØ- OG BIOVITENSKAP
Conclusions: Take home message
• Radionuclides can be present in different
physico-chemical forms influencing
transport/mobility and bioavailability
• Radionuclide species depend on sources and
release conditions and transformation processes
occurring in the environment.
• Speciation/fractionation techniques are needed
to distinguish between radionuclides species.
[email protected]
Brit Salbu, UMB, Risø, 2009
UNIVERSITETET FOR MILJØ- OG BIOVITENSKAP
Thank you
Acknowledgement to a series of collaborators
[email protected]
Foto: UMBs fotoarkiv
[email protected]