RADIOLOGICAL ASSESSMENT OF STREAM SEDIMENTS BETWEEN
BĂIŢA-PLAI AND BEIUŞ*
R.-CS. BEGY, H. SIMON, C. COSMA
Faculty of Environmental Sciences and Engineering, Babeș-Bolyai University,
Fântânele Str. 30 Cluj-Napoca, Romania
Received November 15, 2012
This study relies on the measurement activity concentration of stream sediments from
the Băiţa-Plai brook, which is polluted by the spoil-banks of an abandoned uranium
mine. Geologically speaking, the area is mainly formed out of sedimentary rocks,
which are soluble in water, so they can travel large distances in this medium. We
measured several radionuclide activity concentrations along the river using an Ortec
GMX – type HpGe detector with relative efficiency of 34%. The investigated
radionuclides were 238U, 210Pb, 232Th, 226Ra, 137Cs, and 40K. The average activity
concentrations were 260±45 Bq/kg for 238U, 50±4 Bq/kg for 210Pb, 21±2 Bq/kg for
232
Th, 80±4 Bq/kg for 226Ra, 2±0.2 Bq/kg for 137Cs, and 383±15 Bq/kg for 40K. We
observed that the values were much higher at the upper side of the river and at the
regions, where the settlements are and that they were lower at the estuary of the brook.
We also measured limit exceeding levels of 226Ra concentration in the area of the
settlements and the first sample had a much larger activity (546±20 Bq/kg)
concentration than the concentration of a normal soil sample.
Key words: 238U, radionuclides, stream sediment, Băița-Plai.
1. INTRODUCTION
Stream sediments contain measurable radiological properties and it is
advantageous to integrate information from these data sets (Danley et al., 2005). It
is essential to clarify that stream sediment data are point data with irregular pattern
of sample locations and non-uniform sampling density because the samples are
taken by following rivers and that these samples contain various concentrations of
different radioactive elements (Nugraha, 2011).
It is important to assess the nature and extent of the zones that are potential at
high risk from radioactive exposure. Such information is needed for policy makers
to provide sound basis for addressing public concern regarding high natural
radioactivity in some specific areas (Mukherjee et al., 2007). Stream sediments are
good sorbents and in the case of Mountain Rivers and brooks, they are a dynamic,
*
Paper presented at the First East European Radon Symposium – FERAS 2012, September 2-5,
2012, Cluj-Napoca, Romania.
Rom. Journ. Phys., Vol. 58, Supplement, P. S22–S28, Bucharest, 2013
2
Radiological assessment of stream sediments beetween Băiţa-Plai and Beiuş
S23
informative substance. Their chemical and microelement composition is influenced
by many parameters such as the geochemical composition of the nearby soils,
meteorological conditions and technogenic activities in the region (Maslyuk et al., 2012).
Potassium (40K), uranium (238U, 235U) and thorium (232Th) are the principal
radioactive elements in terrestrial materials. These occur in a wide variety of
minerals in various combinations as phosphates, silicates and oxides. Daughter
products of the uranium ant thorium decay-series include radon (222Rn) and radium
(226Ra), whose presence and relative abundance has exposure related health
hazards. Where host minerals occur in usually high concentrations, radon may be a
serious concern when spatially associated with human community (Lima et al.,
2005). If these stream sediment samples are used as construction materials, the
radon can accumulate in closed spaces. Because of the outflow of this radioactive
gas, the air in the houses built from these materials can exceed the limit proposed
by WHO (WHO, 2012). In some cases this value can be ten times higher than the
limit (Alexandra Cucos (Dinu), 2012). Sand and rocks some of the most important
materials used in constructions, therefore it is important to know how high the
radiation exposure is (Ramasamy et al., 2011).
The area of our study was the Băița-Plai brook (Apuseni Mountains,
Romania) and its stream sediment. At the upper side of this river lays a deserted
mine with its spoil-banks. In the beginning of the 20-th century the area witnessed
substantial mining activities for noble metals. From the 1950s to 1989 the mine
was used for uranium exploitation, after which it was closed.
In this paper we attempt to present the distribution and activity concentration
of the radioactive elements in the Băiţa-Plai brook stream sediments. We want to
prove that the absence of the spoil-bank recultivation has a negative impact on the
environment, mainly because the rain washes a considerable amount of
radionuclides in the riverbank. We took samples along the river and used gamma
spectrometry to measure the activity of the uranium and its daughter elements.
2. MATERIAL AND METHODS
2.1. STUDY SITE
Băița-Plai lays at the feet of the Bihar Mountains highest pike, the Curcubăta
Mare (1849 m) and at the spring of the Crișul Negru river. The population in this
area is about 1500–2000.
From a geological point of view the area contains crystalline rocks as well as
sedimentary ones (especially limestone and bauxite). There are many thermal
springs and karst features in the area, therefore there are a variety of caves.
We took 13 samples (Table 1) from Băița-Plai to Beiuș (from the upper of the
river to the estuary) and used a GPS to define the accurate location. The samples
were taken with a measuring spoon and then put into labeled plastic bags.
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R.-Cs. Begy, H. Simon, C. Cosma
3
Table 1
Accurate locations of the sample takings
Sample nr.
1
2
3
4
5
6
7
8
9
10
11
12
13
Northern latitude
46,48621
46,48675
46,48102
46,49015
46,50490
46,51426
46,52735
46,53131
46,54255
46,55552
46,59073
46,62735
46,66006
Eastern longitude
22,61865
22,61413
22,59441
22,55713
22,53488
22,51920
22,49720
22,48401
22,45671
22,44324
22,42807
22,37360
22,34432
Altitude (m)
551
516
468
402
360
333
310
277
270
240
225
193
187
Location
Uranium mine
Băița-Plai
Băița-Plai
Băița-Plai
Nucet
Nucet
Beiuș
The first sampling spot was in Băița-Plai, which is located at approximately
200–300 from the entrance of the mine. The next four samples were taken at
400–500 m distance from each other to cover the upper side of the river as
precisely as possible. The other samples were taken at bigger distances until the
Crișul Pietros brooks flowing into the Arieș river (Figure 1).
Fig. 1 – Sampling sites (via Google Maps)
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Radiological assessment of stream sediments beetween Băiţa-Plai and Beiuş
S25
2.2. ANALYTICAL METHOD
After transporting the samples to the laboratory, each of them was put to dry
into a drying oven at 90°C. After 24 hours they were taken out and homogenized
using a mortar, a pestle and a sieve. We used an ORTEC GMX HpeGe (FWHM
1.92KeV at 1.33MeV with 0.5 mm Be window for low energy) semiconductor
detector to measure the radionuclise content of the samples by gamma
spectrometry. Soil samples were placed into labeled plastic cases. We had to wait 3
weeks for the radium-226 to reach secular equilibrium with its daughter elements
(222Rn) so that we can determine the activity concentration of the radium-226
isotope.
The activity concentration from radionuclides from the sample was
determined using the relative activity measurement method. This means that the
sample spectra were compared with a reference material (IAEA-312) spectrum,
which contained the same radionuclides and had the same geometry as the samples.
The radionuclides concentration were determined by using the folowing
photopeaks: a 238U (uranium) at 1001 keV, 226Ra (radium) at 295; 351; 609 keV,
232
Th (thorium) at 238; 338; 583 keV, 40K (potassium) at 1461 keV and 210Pb (lead)
at 46 keV. In the case of 238U the determination is made by using it’s daughter
234m
Pa (with half live of 1.17m) with a photopeak at 1001 keV. This photopeak has
very low gamma intensity (0.837 %) and due to this, the minimum detectable
activity for 238U is 98 Bq/kg and the critical detectable activity (which corresponds
to critical detection level) is 48 Bq/kg.
3. RESULTS AND DISCUSSION
The results for each sample and its radionuclides are summarized in Table 2.
The first sample has the biggest activities as expected, because it was taken from
near the uranium mine and the rain washed the radionuclides into the riverbank.
Another explanation is that the depth of the water is small at the upper side of the
river, so radionuclides can settle more easily than at the lower sides of the river.
In the rivers or stream sediments near the uranium exploitation the radionuclides
can arrive from two distinct sources, first with rain water (dissolved radionuclides
from uranium waste) and the second with in situ sediment particles. The leaching
factor can influence the concentration of the radionuclides and the radioactive
equilibrium among them. In normal case the equilibrium between U and Ra
remains (Hierro 2012, Cukrov 2009).
The activity of the other samples is decreasing in proportion with the distance
from the mine, though in some cases this is not valid. This can be explained with
the fact that the river does not have a constant velocity and other rivers flow in
bringing sediments with them.
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R.-Cs. Begy, H. Simon, C. Cosma
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Table 2
The radionuclide concentration of the samples
Sample
238
U
210
Pb
232
Th
Bq/kg
1
2
3
4
5
6
7
8
9
10
11
12
13
Average activity
concentration
1
Ra
137
Cs
40
K
737±100
72±351
115±28
71±30
60±201
UDL2
117±50
UDL
UDL
UDL
UDL
UDL
UDL
375±20
34±3
55±4
30±3
29±3
20±3
42±6
19±3
26±3
6±2
8±2
UDL
UDL
34±3
15±2
14±2
20±3
17±2
22±4
31±3
21±3
23±3
18±3
20±8
13±2
15±2
546±25*
57±8
87±7
61±5
52±5
35±4
75±4
31±4
30±2
18±2
22±2
14±2
13±2
5±0.1
2±0.2
2±0.2
3±0.3
2±0.2
7±0.1
7±0.6
1±0.2
1±0.1
0.7±0.2
1±0.2
0.8±0.2
0.3±0.1
754±27
259±10
237±10
396±15
330±13
365±14
369±21
423±16
382±14
378±15
445±16
290±12
355±14
260±45
50±4
21±2
80±4**
2±0.2
383±15
Above Critical activity level
UDL- under detection limit
2
226
* see also possible dis-equilibrium [6]
**Average from all radium values
After comparing the results with the internationally accepted limits, we
noticed, that the activity concentration of the 226Ra is exceeding these (Figure 2).
This is because until the 8-th sampling point there is only inflowing river into the
Băița-Plai brook, which cannot homogenizise and dissolve the radium, and because
the radium concentration is closely related to the four settlements Băița,
Fig. 2 – The measured radium-226 levels in comparison
with the internationally accepted limits.
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Radiological assessment of stream sediments beetween Băiţa-Plai and Beiuş
S27
Nucet, Câmpeni and Fânațe. The people from these areas use building materials
from the mine and bring radium to their living environment. When 226Ra
disintegrates, the result always is an alpha particle and 222Rn. The travelling
distance of these particles depends on the pore sizes of the construction materials
(the traveled distances can vary between 20 and 70 nm).
In the case of 238U (the amount of 235U is negligible, because it is only 1/136
238
of U ), 226Ra, 232Th and 137Cs we can see, that highest values are in the 7-th
sample, so we can deduce that the velocity of the river is lower at this point. The
sediments could settle better and more fine-grained samples could settle.
Radionuclides can accumulate better in these areas. The solubility of thorium is
constant and low, its mobility is low too and it mainly depends on the velocity of
the river.
The activity concentration of lead 210Pb is also small in comparison with its
natural occurrence. The 226Ra cannot generate enough lead because it dissolves and
is transported. To create enough lead, 226Ra would have to spend at least 2 years in
the sediments to reach balance.
The activity concentration of 40K can be taken as normal. Rocks, which reach
the surface by mining, contain lots of potassium, so it can be found in each rock.
Acknowledgments. Authors are grateful to Ervin Farkas for the support given in sample taking
and preparation.
The financial support of the Sectoral Operational Programme “Increase of Economic
Competitiveness” co-financed by The European Regional Development Fund under the project
IRART 586-12487, Contract No. 160/15.06.2010 is highly appreciated.
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