Working Report 2014-28
Sampling and Characterisation of Groundwater
Colloids in ONKALO at Olkiluoto, Finland, 2013
Sari Luste
Mikael Takala
Pentti Manninen
Ramboll Finland Oy
June 2014
Working Reports contain information on work in progress
or pending completion.
SAMPLING AND CHARACTERISATION OF GROUNDWATER COLLOIDS IN
ONKALO AT OLKILUOTO, FINLAND, 2013
ABSTRACT
The purpose of this study was to estimate the concentration of groundwater colloids and
to compare the results with the previous ones. The water samples were collected from
groundwater stations ONK-PVA1, ONK-PVA5 and ONK-PVA10 in August 2013.
The colloid concentrations were determined from scanning electron microscopy (SEM)
micrographs taken from the filters in which the groundwater was run through. The
particle calculations were performed with computer software ImageJ 1.47. In addition,
field flow fractionation (FFF) measurements were performed from the unfiltered water
samples.
The colloid concentration (Ø 0 – 1 µm) determined by the single particle analysis of
SEM micrographs in ONK-PVA1 was 300 µg/l while the colloid concentration in
ONK-PVA5 was 30 µg/l and ONK-PVA10 40 µg/l. FFF measurements supported the
results of single particle analyses with a difference that an extra peak was found from
ONK-PVA1 sample. The peak, which showed no evidence in single particle analyses,
was suspected to contain humic substances.
Keywords: colloids, ONKALO, single particle analysis.
OLKILUODON ONKALON POHJAVEDEN KOLLOIDIEN NÄYTTEENOTTO
JA KARAKTERISOINTI 2013
TIIVISTELMÄ
Työn tarkoitus oli arvioida pohjavedessä esiintyvien kolloidien määrää ja verrata
tuloksia aiempiin tuloksiin. Näytteet haettiin pohjavesiasemilta ONK-PVA1, ONKPVA5 ja ONK-PVA10 elokuussa 2013.
Kolloidien pitoisuus määritettiin pyyhkäisyelektronimikroskoopilla otetuista
mikrografeista suodattimilta, joiden läpi pohjavettä laskettiin. Partikkelilaskenta
suoritettiin ohjelmaa ImageJ 1.47 apuna käyttäen. Sen lisäksi käytettiin
kenttävirtausfraktiointimenetelmää (FFF) suodattamattomille vesinäytteille.
Kolloidien konsentraatio (halkaisija 0 – 1 µm) SEM kuvista tehtyjen laskentojen
perusteella pisteen ONK-PVA1 vedessä oli 300 µg/l. Konsentraatiot pisteissä ONKPVA5 ja ONK-PVA10 olivat 30 µg/l ja 40 µg/l. FFF menetelmä tuki tuloksia sillä
erolla, että FFF tuloksissa havaittiin näytteen ONK-PVA1 osalta ylimääräinen piikki.
Kyseiselle piikille ei SEM kuvista tehdyissä laskennoissa ollut vastaavaa havaintoa ja
sen arveltiin esittävän humusyhdisteitä.
Avainsanat: kolloidit, ONKALO, single particle analysis.
LIST OF SYMBOLS AND ABBREVIATIONS
DLS
Dynamic light scattering
FFF
Field-flow fractionation
HDPE
High density polyethylene
LC
Liquid chromatography
PSS
Polystyrene sulphonate
PTFE
Polytetrafluoroethylene
RI
Refractive index
RPD
Relative percentage difference
RSD
Relative standard deviation
SEM
Scanning electron microscopy
SLS
Static light scattering
UV
Ultraviolet
1
TABLE OF CONTENTS
ABSTRACT
TIIVISTELMÄ
LIST OF SYMBOLS AND ABBREVIATIONS
1 INTRODUCTION .................................................................................................... 2 2 EXPERIMENTAL .................................................................................................... 3 2.1 Preparations .................................................................................................... 3 2.2 Sampling ......................................................................................................... 3 2.3 Single particle analysis ................................................................................... 5 2.4 FFF measurements ......................................................................................... 7 3 RESULTS AND DISCUSSION ............................................................................... 8 3.1 Single particle analysis ................................................................................... 8 3.1.1 ONK-PVA1 results ...................................................................................... 8 3.1.2 ONK-PVA5 results ...................................................................................... 9 3.1.3 ONK-PVA10 results .................................................................................. 10 3.1.4 Discussion ................................................................................................. 11 3.1.5 Reliability evaluation ................................................................................. 11 3.1.6 Other observations .................................................................................... 14 3.1.7 Comparison with the previous results ....................................................... 14 3.2 FFF measurements ....................................................................................... 15 4 RECOMMENDATIONS......................................................................................... 18 5 CONCLUSIONS.................................................................................................... 19 REFERENCES ............................................................................................................. 20 2
1 INTRODUCTION
ONKALO is the underground rock characterisation facility that is currently being
constructed by Posiva for spent nuclear fuel disposal research purposes. For long-term
safety evaluation, characterisation of groundwater colloids is essential owing to the fact
that groundwater colloids may transport radionuclides released from a failed spent fuel
canister. Colloids are generally referred to as particles that do not appear to be
sedimented even after a long period of time. The sizes of colloid particles are usually
from 1 nm to 1 000 nm. Colloids in natural groundwaters consist of inorganic material
(e.g. clay, oxides and carbonates) and organic material (mainly humic and fulvic acids).
Owing to their small size, nano-micrometer particles may be transported along fractures
in the bedrock. The transportation is controlled by groundwater movement, attachmentdetachment kinetics and sedimentation rates. Colloid formation and stability is
dependent on the surrounding hydrogeochemical conditions e.g. pH, EC and redox.
Generally colloids tend to form agglomerates in saline conditions and therefore the
colloid concentrations are lower in saline waters than in fresh waters.
The water samples were collected from groundwater stations ONK-PVA1, ONK-PVA5
and ONK-PVA10. The experiments were done for the first time in ONK-PVA5 and
ONK-PVA10. The colloids of interest are colloids that reflect the in-situ conditions.
During the sampling the in-situ conditions are tried to maintain at the sampling
locations by avoiding sudden changes in flow rates and keeping the flow rates steady.
The colloid concentrations were determined by single particle counting of scanning
electron microscopy (SEM) micrographs taken from the filters. The particle calculations
and size distribution determinations were performed with the assistance of ImageJ, an
image analysis program. In addition, field-flow fractionation (FFF) was used in colloid
particle distribution determinations. FFF is an elution method which have similar
application possibilities as liquid chromatography (LC) (Baalousha, 2011).
The purpose of this study was to analyse the colloid content and to compare the results
with the previous ones. Enhancements in the procedure and new supporting analytical
methods were expected to increase the reliability of the results.
3
2 EXPERIMENTAL
2.1 Preparations
The colloid samples were collected on a Nuclepore polycarbonate 0.05 µm filter. The
sampling assembly had three filter holders with sample containers. The sample
containers were tared before sample collection.
The sample lines were (polytetrafluoroethylene) PTFE ¼ in. (inner diameter) lines and
the valves as well as the fittings were Swagelock’s (PTFE). The sample containers were
made of plastic (high density polyethylene, HDPE). The filter holders were made of
polycarbonate. The filters and filter holders were cleaned by pre-treatment with ultra
clean Millipore water with an ultrasonic mixer to remove any particles from the filter
surface (Nuclepore 0.05 µm) and filter holders before sampling. Further, before the
sampling the filtering lines were flushed with the site water. The filter holders were
assembled at the laboratory of Ramboll Analytics and sealed before the sampling to
avoid any contamination by aerosol particles.
2.2 Sampling
The sampling of colloid samples was performed on 20th and 21st of August 2013. The
samples were taken from the groundwater stations ONK-PVA1 (depth about 14.6 m
b.s.l), ONK-PVA5 (depth about 228.7 m b.s.l) and ONK-PVA10 (depth about 336.5 m
b.s.l). Figure 1 illustrates the locations of the groundwater stations in ONKALO. The
water yields in ONK-PVA1, ONK-PVA5 and ONK-PVA10 were 700, 110 and 50
ml/min. The parallel samples were taken simultaneously. Nuclepore 0.05 µm filters
were used to capture the colloids from the sample stream. The filtration of parallel water
samples took around 3 hours at ONK-PVA1, 1.5 hours at ONK-PVA5 and 2 hours at
ONK-PVA10. Departing from the previous studies, the filter holders were vacuumdried after the sampling and sealed until the SEM-analyses. The water run through the
filters was weighed (Table 1). No analyses were made from the filtered water.
4
Figure 1. The groundwater stations in ONKALO, Olkiluoto (figure made by Pöyry
Finland Oy).
5
Table 1. Volume (ml) of the filtered water.
Volume of water
run through filter (ml)
277.4
1 017.9*
175.5
1 004.3
1 001.2
888.4
1 018.1
1 022.7
1 012.6
Sample
ONK-PVA1 a
ONK-PVA1 b
ONK-PVA1 c
ONK-PVA5 a
ONK-PVA5 b
ONK-PVA5 c
ONK-PVA10 a
ONK-PVA10 b
ONK-PVA10 c
*Discarded since the filter was probably leaking.
One filter sample from ONK-PVA1 was discarded, because the filter holder was
probably leaking. The filtered volumes were taken into account in result calculations.
Samples were taken for FFF-measurements as well. The sampling sites were the same
and the amount of non-filtered water samples were around 1 l. The sampling of each
sample at ONK-PVA1 and ONK-PVA5 took about 10 min while the sampling of one
sample took around 30 min at ONK-PVA10.
2.3 Single particle analysis
The particle concentrations were calculated by counting single particles from the SEM
micrographs. When taking the SEM micrographs, particles in the filters were found to
be more homogenously divided compared to the previous studies. Thus, it can be noted
that the drying phase was beneficial.
The particle calculation was done with computer software ImageJ 1.47, which has been
originally developed for microbiological studies for bacteria enumeration. In the
previous study (Takala et al., 2011) software proved to be useful for the calculation of
colloidal particles from SEM images. The program appeared to work well also for
colloid enumeration from SEM micrographs. The size distribution (number of particles
in size group/l) was produced for selected filter membranes. The distribution was
calculated by the following equation 1:
d [coll ]

dØ
 dN  dØ
s
i
-1

s
V
(1)
where Σ corresponds to the sum of the various micrographs examined, dN/dØ is the
number of detected particles in size group dØ (µm), s (µm2) is the active surface area of
the filter, si (µm2) is the surface area of the micrograph, and V is the filtered volume (l).
The mass concentration (mg/l) for different size intervals was determined by the
following equation 2:
d [coll ]     Ø 3 d [coll ]


dØ
6
dØ
(2)
6
where ρ is the particle density (mg/mm3) and Ø is the particle diameter (µm). The
density of the particles was assumed to be 2 (mg/mm3) and the shape was assumed to be
spherical. The particles on the micrographs are rarely spherical, and so the mass
concentration is overestimated. A correction factor was not used.
The micrographs were taken randomly from the filter surface with magnification factors
of 1 000, 4 000 and 8 000. SEM micrographs were taken from the filters at Mikrofokus
Oy in Helsinki by Simo Lehti.
The number of the micrographs taken is shown in Table 2.
Table 2. The samples and number of micrographs.
Sample
Magnification
Number of micrographs
ONK-PVA1
1 000
12
(three parallel filters, one
discarded*)
4 000
24
8 000
24
ONK-PVA5
1 000
12
(three parallel filters)
4 000
24
8 000
24
ONK-PVA10
1 000
12
(three parallel filters)
4 000
24
8 000
24
* three parallel filters, of which sample “b” was discarded; double pictures from sample “c”.
The computer aided particle calculation process initiated with a step of making a binary
image of the SEM micrograph. The binary was needed for the software being able to
detect the particles. The calculation boundaries were set so that particles smaller than
5x5 pixel were not calculated. The upper boundary was set to 100x100 pixel. The
circularity factor was set to 0.01 – 1, where 1 is a perfectly round particle and when the
value gets closer to 0 it indicates increasingly elongated shape.
The circularity factor is calculated as following (equation 3):
4 (3)
The image sizes were 1 000x750 pixels and resolution was 72 dpi. The scales of the
images for each magnification are presented in the following table 3.
Table 3. Scaling pixels to µm in different magnifications.
Magnification
Scale: 1 pixel to µm
1 000
1 pixel = 0.124 µm
4 000
1 pixel = 0.031 µm
8 000
1 pixel = 0.016 µm
7
ImageJ divides the particles by particle area. The diameter of the particles was thus
calculated by equation 4. Particles, with diameter less than 2 µm were explored.
2
(4)
2.4 FFF measurements
The FFF measurements were conducted at the University of Helsinki by Matti Jussila.
The analyses were performed by Postnova AFFF equipment using regenerated cellulose
membrane and 10 mM phosphate buffer as an eluent (pH 7). The tests were performed
by three different molecular weight series (MW cut off): 30 000 g/mol, 5 000 g/mol and
1 000 g/mol. The membrane with 5 000 g/mol cut off was selected. The used detector
was ultraviolet (UV; 254 nm) detector. Refractive index (RI) and dynamic light
scattering (DLS) detectors were not suitable for these studies. With static light
scattering (SLS) –detector visible peaks were found but they suffered from
interferences. Peaks were, however, similar than with UV detector. Thus, results
obtained with UV detector were selected for further examination.
Since the low concentration, high sample volumes were needed to be used. The sample
volume was 48 ml and it was injected to the channel with the 0.2 ml/min flow rate
during 4 h. Injection was followed by a 30 min focusing phase and finally the sample
run. The flow rate for the detector was 0.5 ml/min.
Polystyrene sulphonate (PSS) standards were used for estimation of molecular weights.
PSS standards were 15 000 g/mol, 30 000 g/mol and 1 000 000 g/mol.
8
3 RESULTS AND DISCUSSION
3.1 Single particle analysis
According to the SEM micrographs and the analyst, the particles were rather equally
distributed in all filters. This might be due to the filter drying phase readily after the
sampling. Since the water was removed, it did not flush and move the content settled in
the filters, as was suspected to have occurred in the previous studies. The results are
presented and discussed for each sampling point in the following sections.
3.1.1
ONK-PVA1 results
SEM micrographs were similar with all magnifications. An example of a micrograph
(ONK-PVA1, 8 000 -fold magnification) and the binary figure of the micrograph are
presented in the figure 2.
Figure 2. SEM micrograph from ONK-PVA1 filter with magnification 8000 and its
binary figure.
The colloid particle concentration and the colloid mass concentration distributions are
presented in the figure 3. The particle total concentration was 2.0 · 109 pt/l with mode
particle size 0.2 µm. The mass concentration was calculated assuming the particles to be
spherical and the particle density to be 2 mg/ml. The total mass concentration was 1.3
mg/l. The particle and mass concentration of particles with a diameter equal or less than
1 µm was 1.7 · 109 pt/l and 0.3 mg/l.
9
0,12
5,00E+08
4,50E+08
0,1
4,00E+08
3,50E+08
0,08
0,06
2,50E+08
mg/l
pt/l
3,00E+08
2,00E+08
0,04
1,50E+08
1,00E+08
0,02
5,00E+07
0
0,00E+00
0
0,5
1
1,5
2
d (µm)
Particle concentration (pt/l)
Mass concentration (mg/l)
Figure 3. Colloid particle (pt/l) and mass (mg/l) concentration distributions of ONKPVA1 water.
3.1.2
ONK-PVA5 results
SEM micrographs were similar with all magnifications. An example of a micrograph
(ONK-PVA5, 8 000 -fold magnification) and the binary figure of the micrograph are
presented in the figure 4.
Figure 4. SEM micrograph from ONK-PVA5 filter with magnification 8000 and its
binary figure.
The colloid particle concentration and the colloid mass concentration distributions are
presented in the figure 5. The particle total concentration was 3.3 · 108 pt/l with mode
particle size 0.2 µm. The mass concentration was calculated assuming the particles to be
spherical and the particle density to be 2 mg/ml. The total mass concentration was 0.070
mg/l. The particle and mass concentration of particles with a diameter equal or less than
1 µm was 3.2 · 108 pt/l and 0.030 mg/l.
10
1,40E+08
0,008
1,20E+08
0,007
0,006
0,005
8,00E+07
0,004
6,00E+07
mg/l
pt/l
1,00E+08
0,003
4,00E+07
0,002
2,00E+07
0,001
0,00E+00
0
0
0,5
1
1,5
2
d (µm)
Particle concentration (pt/l)
Mass concentration (mg/l)
Figure 5. Colloid particle (pt/l) and mass (mg/l) concentration distributions of ONKPVA5 water.
3.1.3
ONK-PVA10 results
SEM micrographs were similar with all magnifications. An example of a micrograph
(ONK-PVA10, 8 000 -fold magnification) and the binary figure of the micrograph are
presented in the figure 6.
Figure 6. SEM micrograph from ONK-PVA10 filter with magnification 8000 and its
binary figure.
The colloid particle concentration and the colloid mass concentration distributions are
presented in the figure 7. The particle total concentration was 3.8 · 108 pt/l with mode
particle size 0.2 µm. The mass concentration was calculated assuming the particles to be
spherical and the particle density to be 2 mg/ml. The total mass concentration was 0.11
mg/l. The particle and mass concentration of particles with a diameter equal or less than
1 µm was 3.6 · 108 pt/l and 0.040 mg/l.
11
1,20E+08
0,01
0,009
1,00E+08
0,008
0,007
8,00E+07
0,005
6,00E+07
mg/l
pt/l
0,006
0,004
4,00E+07
0,003
0,002
2,00E+07
0,001
0
0,00E+00
0
0,5
1
1,5
2
d (µm)
Particle concentration (pt/l)
Mass concentration (mg/l)
Figure 7. Colloid particle (pt/l) and mass (mg/l) concentration distributions of ONKPVA10 water.
3.1.4
Discussion
The colloid particle concentration distributions were more or less equal within all
sampling points. The amount of colloids was somewhat higher in ONK-PVA1 water
compared to ONK-PVA5 and ONK-PVA10 water, which had similar concentrations.
The colloid mass concentration distribution was different in ONK-PVA1 water
compared to the ONK-PVA5 and ONK-PVA10 water. With particle size above one
micrometer in diameter the colloid mass concentration in ONK-PVA1 water increased.
Instead, in case of ONK-PVA5 and ONK-PVA10 water, the mass concentration was the
highest somewhat below one micrometer in diameter and decreased with larger
particles. Some differences were found also in visual appearance of SEM micrographs
(figure 2 vs. figures 4 and 6).
The peak in colloid particle concentration distribution between 0.6 – 1 µm was assumed
to be erroneous and possibly being caused by the selected magnifications in SEM
analysis. It is possible that the 1 000 and 4 000 –fold magnifications had too wide gap
diminishing some of the particles in the range. Without this gap, the particle
concentration distribution might have been more uniform with one peak only
(maximum in 0.2 µm).
3.1.5
Reliability evaluation
The reliability of the colloid concentrations measured with different magnification was
attempted to be evaluated by calculating the expected number of colloids in a specified
size group based on the observed number of colloids in the specified size group from
the image with a small magnification factor.
The expected number of colloids in a specified size group for a higher magnification
factor can be calculated by the following equation (equation 5):
12
,
(5)
Where nimgi is the number of images taken with magnification factor ximgi and ncoll,imgi is
the total number of colloids in the specified size group from images img i. img i are the
images with the higher magnification factor (f.ex 4 000) and img j are the images with
the lower magnification factor (f.ex 1 000).
The relative percentage difference (RPD) can be calculated based on the expected
number of colloids in the specified size group and the observed number of colloids as
presented in the following equation.
|
|
(6)
The expected numbers of colloids for size groups from 0.7 – 0.8, 0.8 – 0.9 and 0.9 –
1.0 µm were calculated from SEM images taken from filter ONK-PVA5 (sample a).
The results are summarized in table 4. The detection limit for magnification factor 1 000
is 0.7 µm, that is why the evaluation was not performed for smaller size groups.
Table 4. Summary of calculated differences from expected number of colloid and
observed number of colloids from SEM images taken from ONK-PVA5 (parallel
samples a, b and c).
1 000
x
166
876
652
377
µ
42
219
163
94
4 000
x
215
106
85
35
RPD
418%
52%
48%
63%
µ
10
55
41
24
8 000
x
43
26
19
14
RPD
314%
53%
53%
41%
x is the observed number of colloids and µ is the expected number of colloids, calculated with equation 5. The images
taken with magnification factor 1000 were used as reference.
Based on the results the RPD ranges from 63% to 41%, except for size group 0.7 – 0.8,
where the observed number of colloids is actually higher in the images with
magnification factor 4 000 and 8 000 than in the images taken with a 1 000
magnification. This is probably due to image background noise which disturbs the
detection of colloids that are just above the detection size, resulting in a lower count of
colloids in this size group.
The colloids are not evenly distributed onto the filter surface. The heterogeneity caused
by the uneven distribution increases as the magnification factor increases i.e. the sample
size reduces. To attempt to understand the uncertainty to the analysis caused by the
distributional heterogeneity, the calculated colloid amount of size group 0.5 to 0.6 µm
was calculated from individual images taken from filters ONK-PVA5(a), ONKPVA5(b) and ONK-PVA5(c). From each filter eight images were taken. The average
number of colloids and the relative standard deviation (RSD) were calculated. This
relative standard deviation represents the short scale (less that 1 cm) distributional
heterogeneity as the images are collected from the same filter sample. The results are
13
summarized in table 5. The long scale distributional heterogeneity (5 to 10 cm) is
further evaluated by comparing results from filters ONK-PVA5 (a), (b) and (c).
Table 5. Summary of colloids (0.5 to 0.6 µm) and relative standard deviations (RSD)
from images taken from filters ONK-PVA 5 (samples a, b and c). Magnification factor
4 000.
Filter (ONK-PVA 5-)
Average
RSD
(a)
42
34
27
9
37
20
44
22
29
41%
(b)
1
2
0
0
1
1
0
4
1.1
121%
(c)
16
18
18
37
23
6
1
2
15
80%
The short scale distributional heterogeneity ranges from 41% to 121%. The long scale
distributional heterogeneity can be calculated from the RSD of results from filters by
counting the square root of the RSD square sums. The long scale distributional
heterogeneity is 150%. This evaluation demonstrates that it is essential to not only
analyze several images from a filter but also take the images evenly from around the
filter.
The Poisson distribution can be used to evaluate the sampling variability based on the
number of particles detected using equation 7.
√
(7)
The Poisson distribution does not take into account the distributional heterogeneity,
therefore the variation estimate obtained from equation 7 should be considered as a
minimum variability. In figure 8 is illustrated the error calculated with equation 7 and
the observed variability from filters ONK-PVA5 (a) to (c) magnifications 4 000 and
8 000.
Figure 8. Dashed line is the RSD estimate using the Poisson model. The green and blue
markers are RSD:s calculated from ONK-PVA5 filter images (Size 0.5 – 0.6 µm, x4000
and x8000).
14
The total variability of the colloid concentration analysis is difficult or even impossible
to quantify with the available data. The variability is a function of among others the
colloid concentration, sample size, analysis error and physical and temporal changes in
the sample stream. The total portion of the sample analysed is proportional to the total
size of the SEM images and the filter size. The total area of the SEM images is ca. 0.1
mm2 and the total surface area of the three filters is 4 770 mm2. This means that only
0.002% of the filtered volume is analysed.
3.1.6
Other observations
During SEM analysis it was observed, that two samples from the station ONK-PVA5
contained some microbes. The microbes were present in filtered material. Also some
salt crystals were observed. Neither microbes nor salt crystals affected the SEM
analyses.
3.1.7
Comparison with the previous results
The colloid particle concentrations and mass concentrations during years 2006 to 2013
are presented in the table 4. The results from 2006 are not comparable, owing to the
differences in the sampling procedures and interpretations of results. Concentrations in
ONK-PVA1 were the highest at 2013. Concentrations have showed significant variation
which might be due to the unevenly spread particles in the filter. In 2013 studies, the
particles were found to be evenly distributed compared to the previous years.
Table 6. Colloid concentrations (Ø 0 – 1 µm) in 2006 – 2013.
Date
ONK-PVA1
18 April 2006
3 Oct. 2007
29 Oct. 2008
21 Dec. 2009
13 Oct. 2011
20.-21. Aug. 2013
ONK-PVA3
19 Nov. 2007
29 Oct. 2008
12 Oct. 2011
ONK-PVA5
20.-21. Aug. 2013
ONK-PVA10
20.-21. Aug. 2013
Sodium fluorescein
[coll] pt/l
[coll] µg/l
~20 µg/l
<1 µg/l
<1 µg/l
<1 µg/l
<1 µg/l
<1 µg/l
2.7 · 109
1.6 · 104
3.5 · 108
1.7 · 106
6.9 · 107
1.7 · 109
200
0.001
200
0.5
6
300
~20 µg/l
<1 – 2 µg/l
<1 µg/l
8.2 · 107
7.8 · 108
7.4 · 107
10
700
7
<1 µg/l
3.2 · 108
30
<1 µg/l
3.6 · 108
40
The sodium fluorescein concentrations were below detection limits in the all
groundwater stations indicating that water used during drilling was not present.
15
3.2 FFF measurements
The results of the preliminary FFF measurements showed significant differences
between the samples from ONK-PVA1 compared to samples from ONK-PVA5 and
ONK-PV10. In ONK-PVA1 samples, two peaks were found, whereas in ONK-PVA5
and ONK-PVA10 samples only one peak was visible. There was no corresponding
observation in single particle analysis from SEM micrographs.
Concentrations were estimated to be somewhat higher in the ONK-PVA1 sample
compared to other samples. Even though the injected sample volume was kept constant,
it was assumed that the amount of sample in the injection channel varied. Thus, the
responses varied also. The standards are presented at the figure 9 and the results at the
figure 10. In FFF measurements it should be noted that in general the retention time is
dependent of the particle size (i.e. the higher the particle size the longer the retention
time).
Figure 9. FFF analyses from PSS standards.
16
ONK‐PVA1
UV absorbance
PVA1a
PVA1b
PVA1c
0
10
20
30
40
50
Retention time (min)
ONK‐PVA5
UV absorbance
PVA5a
PVA5b
PVA5c
0
10
20
30
Retention time (min)
40
50
ONK‐PVA10
UV absorbance
PVA10a
PVA10b
PVA10c
0
10
20
30
40
50
Retention time (min)
Figure 10. Results of the FFF analyses of ONK-PVA1, ONK-PVA5 and ONK-PVA10
water.
17
According to the analyses, the peak found from the ONK-PVA1 samples in the
retention time of 4 to 5 min could represent humic substances. The pore size of the used
membrane is not suitable for retaining humics. However, since the electrostatic
repulsion, a portion of the humic substances were suspected to retain in the channel in
case of ONK-PVA1. The effect is somewhat dependent of the salt concentration, which,
according to previous studies, has been lower in ONK-PVA1 water compared to ONKPVA5 and ONK-PVA10 water (Penttinen et al., 2011). With increasing salt
concentration the particle size of humics decreases. Small particles tend to agglomerate
and be removed from the water by settling in the bottom. This might be the reason that
the peak conceivably representing humics was not found in the ONK-PVA5 and ONKPVA10 samples. The presumed content might be responsible for the visual difference
found in SEM micrographs between ONK-PVA1 vs. ONK-PVA5 and ONK-PVA10.
The latter peak in FFF analysis found from each sample (around 17 min) could
represent the colloids, with mode particle size of 0.2 µm. According to PSS standards,
the molecular size would be >1 000 000 g/mol. Generally speaking, it can be estimated
that 0.1 µm corresponds roughly 1 000 000 g/mol, even though there is no direct
correlation between the size and mass. When analysing the results it should be noted,
that the molecular weight is not a linear function of retention time.
No small peaks were observed on the right side of the peak from FFF analyses
suggesting that there might be a sort of error in analysing the SEM micrographs or
particle calculations. Even so, the shape of especially ONK-PVA1 curve seems to be
elongated to the right in FFF results.
18
4 RECOMMENDATIONS
In SEM analysis, the micrograph magnifications need to be selected so, that there is no
significant gaps in the range of noticeable particles. In the future, SEM samples will be
analysed at more regular magnification intervals (e.g. 2000x) to help bridge the gap
between the 1000 and 4000 magnifications.
In the future FFF studies, the samples are suggested to be preconcentrated e.g. with
cross flow filtration. This would result in significantly shorter analysis time and the
method development would be much faster. In addition, if the concentrations would
become high enough and there would be knowledge of the features of the
molecules/particles, also SLS or DLS detectors could be employed.
19
5 CONCLUSIONS
Colloids (Ø 0 – 1 µm) were calculated to be present at concentrations of 300 µg/l in
ONK-PVA1, 30 µg/l in ONK-PVA5 and 40 µg/l in ONK-PVA10. The mode particle
size was 0.2 µm, as in the previous study. Compared to previous studies the colloids
were found to be more uniformly distributed in the samples (filters) and thus the results
were considered to be somewhat more representative. Nevertheless, the area for particle
calculation is very low compared to the total area of the filter.
FFF studies from the unfiltered groundwater showed similar particle distribution as the
single particle analysis. However, there was an exception in ONK-PVA1 sample in
which an extra peak was found representing material of small particle sizes (possibly
humic substances).
According to both methods, the amount of colloids was defined to be higher in ONKPVA1 compared to ONK-PVA5 and ONK-PVA10. Also indications of differences in
the colloid content were found in ONK-PVA1 vs. ONK-PVA5 and ONK-PVA10
samples.
20
REFERENCES
M. Baalousha, B. Stolpe, J. Lead, (2011); Flow field flow fractionation for the analysis
and characterization of natural colloids and manufactured nanoparticles in
environmental systems: a critical review, Journal of Chromatography A, 1218, 40784103.
C. Degueldre, H. R. Pfeiffer, W. Alexander, B. Wernli, and R. Breutsch, (1996/I);
Colloid properties in granitic groundwater systems, I: Sampling and characterisation,
Applied Geochemistry, Vol 11, pp, 677-695, Elsevier Science Ltd.
ImageJ, Image Processing and Analysis in Java. http://rsbweb.nih.gov/ij/ (6.9.2013).
E. Järvinen, P. Manninen, M. Takala, and S. Vilhunen, (2011); Sampling and
Characterisation of Groundwater Colloids in ONKALO at Olkiluoto, Finland, 20092010. Posiva Working Report 2011-29.
T. Penttinen, S. Partamies, A-M. Lahdenperä, T. Lamminmäki, A. Lehtinen and S.
Sireeni (2011); Results of Monitoring at Olkiluoto in 2010, Hydrogeochemistry, Posiva
Working report 2011-44.
M. Takala, S. Ojala, E. Järvinen, M. Manninen, (2012); Sampling and Characterisation
of Groundwater Colloids at ONKALO, Olkiluoto Finland, 2011. Posiva Working
Report 2012-61.
M. Takala, E. Järvinen, and S. Vilhunen, (2009); Sampling and Characterisation of
Groundwater Colloids in ONKALO at Olkiluoto, Finland, 2008. Posiva Working
Report 2009-108.
M. Takala, and P. Manninen, (2008); Sampling and Characterisation of Groundwater
Colloids at ONKALO, Olkiluoto Finland, 2007. Posiva Working Report 2008-32.
M. Takala, and P. Manninen, (2007); Sampling and Characterisation of Groundwater
Colloids at ONKALO, Olkiluoto Finland, Posiva Working Report 2006-98.