MULTI-CRITERIA ANALYSIS OF SOIL RADIOACTIVITY IN ČAČAK BASIN,

M. PAPIĆ1, M. VUKOVIĆ2, I. BIKIT3, D. MRĐA3, S. FORKAPIĆ3, K. BIKIT3, Đ. NIKOLIĆ2 1Faculty of Technical Sciences, Čačak, , Svetog Save 65, Čačak, Serbia, E-mail: [email protected] 2Technical Faculty Bor, University of , Vojske Jugoslavije 12, Bor, Serbia, E-mail: [email protected]; Email: [email protected] 3Faculty of Sciences, University of Novi Sad, Trg Dositeja Obradovića 6, Novi Sad, Serbia, Email: [email protected]; Email: [email protected]; Email: [email protected]; Email: [email protected] Received March 11, 2014

The paper looks at the method of presenting and comparing soil radioactivity on different locations. Activities of natural radionuclides 238U, 226Ra, 232Th, 40K and anthropogenic 137Cs in arable land of Čačak basin were measured. Some 30 soil samples collected from different locations, i.e. the vicinity of the river, both urban and industrial areas of the town and rural region were analysed. Samples were taken from 0–30 cm depth. According to the values of the Shapiro-Wilk’s test (0.05 significance level), contents of 238U, 232Th and 40K were within the limits of normal distribution, while 226Ra and 137Cs were not. As espected, statistically significant positive correlation (p<0.01) was found between all the natural radionuclides. The analysed sites were ranked using the PROMETHEE method, and the results were presented in graph using the GAIA plane. The ranking involved five criteria which represented the overall activities of each of the radionuclides. The ranking inferred that Ljubić Polje location was the one with the lowest radioactivity, while, in contrast, the location of Trnavska showed the highest radioactivity level. As regards presence of radionuclides in soil, the comparative study of urban (industrial) and rural areas did not imply any significant differences among the locations. The results of the present study were discussed and compared with related values from several sources found in the literature. Generally, the study infers that soil in Čačak basin has not showed increased levels of radioactivity. Key words: soil, radioactivity, the absorbed dose rate, multi-criteria analysis, PROMETHEE/ GAIA.

1. INTRODUCTION

Soil is usually defined as the upper layer of the Earth’s crust, formed by mineral particles, organic matter, water, air, and living organisms [1]. Its depth can vary from a few millimeters to several meters, and it is present in the larger part of the Earth’s surface as a narrower or wider layer called the pedosphere [2].

Rom. Journ. Phys., Vol. 59, Nos. 7–8, P. 846–861, Bucharest, 2014 2 Multi-criteria analysis of soil radioactivity in Čačak Basin 847

Soil contamination is one of the most serious problems in the world, with long term consequences on human life [3]. One of the most important aspects of soil contamination is its radioactivity which is based on the presence of radioactive elements or radionuclides. Radioactivity can be distinguished as natural and anthropogenic. Natural radioactivity refers to natural radionuclides which can regularly be found in the earth’s crust. In most places on the earth, the natural radioactivity varies only within narrow margins, but in some places there are wide deviations from normal levels because of the abundance of minerals with high radioactivity [4]. The main contribution to external exposure comes from gamma-emitting radionuclides present in trace amounts in the soil, mainly potassium (40K) and the uranium (238U) and thorium (232Th) families [5]. Radiation energy of the elements above accounts for some 98% of the total radiation of natural radioactive elements. Anthropogenic radioactivity of soil relies on anthropogenic radionuclides of various chemical elements which are the result of human intervention, in terms of the use of nuclear energy for military and apart from military purposes. Of all the anthropogenic radionuclides studied so far, cesium (137Cs) has been the predominant one. It is one of the most widespread and also among the most dangerous radionuclides for both humans and other living organisms, given its long disintegration period (30.2 years) and high energy radiation level. The overall background radiation caused by the natural radionuclides above can be expressed by using the absorbed dose of radiation at 1m above ground (D) which is calculated by coefficients of 0.462, 0.604 and 0.0417 (nGy/h)/(Bq/kg) for the content of 238U (226Ra), 232Th and 40K respectively [5]. However, this method does not provide a more comprehensive insight into the radioactivity of a particular location as it does not include the presence of some other radionuclides. The objective of this paper was to assess and rank the sampling locations in terms of the presence of the most significant natural and anthropogenic radionuclides in the alluvial soil [6–13] on the territory of Čačak. The ranking which involved five criteria (activities of 238U, 226Ra, 232Th, 40K and 137Cs) was done using the PROMETHEE (Preference Organization Method for Enrichment Evaluation) multi-criteria decision making method. The GAIA (Geometrical Analysis for Interactive Assistance) plane was used for the graphical representation of results. A comparative analysis of results of related studies performed by other authors was also provided in the paper so as to obtain a more comprehensive insight into the issue. 848 M. Papić et al. 3

2. MATERIALS AND METHODS

2.1. STUDY AREA

The town of Čačak is located in western part of with the municipalities of to the north, Požega to the west, Lučani to the southwest and south, and Kraljevo and Knić to the east (Figure 1). It is the administrative center of the . The geographic coordinates of the municipality are 20° 07'–20° 38' east longitude and 43° 44'–44° 01' north latitude. Morphologically, the Čačak basin is a tectonic depression formed in the Oligocene by the lowering movement of two longitudinal faults. The surface area of the Čačak basin towards the Kraljevo narrowing is over 270 km2. The basin lies at an elevation of 200 to 300 m. The pedological composition of the Čačak territory is diverse. The most common soil types are alluvial soil, vertisols, cambisols, and parapodzol. Alluvial soil is formed from deposits made by rivers, and it can be found in the Čačak basin all along the West Morava river. It belongs to fertile soils, particularly in mid – and low river courses. It is composed of river sediment, silt, sand and gravel deposited during floods. It is highly rich in organic matter and is easy to work [14].

Fig. 1 – Location of town Čačak, Serbia.

Such soil diversity provides the conditions for highly developed biological diversity. Hence, this is the region with probably the most diverse agricultural production on the territory of entire Serbia. Based on the data of the Republic Institute for Statistics, the surface area of the Čačak municipality is 636 km2, whereby urban, forest and agricultural areas cover 45 km2 (7%), 158 km2 (25%) 4 Multi-criteria analysis of soil radioactivity in Čačak Basin 849 and 433 km2 (68% or 44.060 ha), respectively. Areas covering fields and gardens, orchards, vineyards and pastures follow with 26.935 ha, 6.930 ha, 5.456 ha and 4.609 ha, respectively. Based on the number of people employed in various agricultural activities, agriculture is the primary branch of economy [15]. According to the 2002 census, the town of Čačak (the municipality of Čačak, at the time of census) had the population of 117.072, with 73.152 and 43.920 people living in the urban and rural areas respectively [16]. Favourable geographic and climate setting and fertile West Morava basin allowed for the development of different branches of agriculture. The Čačak region has a long tradition of fruit growing, stock farming, vegetable growing and fruit- planting material production, which ensure a solid foundation for further investment in the development of agriculture. This hilly region is known for fruit production, while in fertile Morava basin vegetable and cereal crops are grown. The glasshouse production is also developed in lowlands [17]. Table 1 shows names of places and coordinates of the sampling sites examined. The exact position of each sampling site was recorded using Global Positioning System (GPS). These locations, extending from Pakovraće and Prijevor in the north west to Mrčajevci and Mršinci in the south east, form the agriculturally important region of central Serbia.

Table 1 Sampling locations Coordinates Altitude Location Place [N] [E] [m] 1. 43° 53' 50.2404" 20° 17' 40.3044" 246 2. Pakovraće 43° 54' 2.361" 20° 15' 58.4238" 253 3. Riđage 43° 53' 50.0526" 20° 16' 45.0942" 281 4. Beljina 43° 53' 37.8018" 20° 19' 22.4106" 243 5. Ljubić Kej 43° 54' 5.2266" 20° 20' 12.7068" 237 6. Prijevor 43° 53' 55.773" 20° 17' 27.7434" 246 7. Prijevor 43° 54' 9.8748" 20° 17' 11.364" 247 8. Prijevor 43° 54' 25.4298" 20° 16' 25.4202" 250 9. Prijevor 43° 54' 2.7396" 20° 16' 22.695" 246 10. Suvi Breg 43° 54' 1.0542" 20° 19' 7.2372" 240 11. Stančići 43° 52' 56.1288" 20° 26' 34.8756" 223 12. 43° 52' 57.648" 20° 27' 40.6044" 228 13. 43° 52' 22.8864" 20° 29' 7.0656" 223 14. Mrčajevci 43° 51' 1.44" 20° 31' 21.36" 212 15. Mrčajevci 43° 49' 50.3394" 20° 30' 7.4874" 211 16. Kukići 43° 49' 56.7726" 20° 28' 23.106" 226 850 M. Papić et al. 5

Table 1 (continued) 17. Mršinci 43° 48' 47.2752" 20° 29' 24.2478" 224 18. Zablaće 43° 50' 18.5742" 20° 27' 23.1084" 226 19. 43° 51' 2.3034" 20° 26' 33.6474" 228 20. Trnavska Baluga 43° 51' 58.8024" 20° 25' 29.4528" 225 21. 43° 51' 52.0698" 20° 23' 57.0798" 231 22. 43° 52' 20.9388" 20° 23' 52.4688" 230 23. Konjevići 43° 53' 35.0946" 20° 23' 47.9934" 231 24. Konjevići 43° 53' 37.6074" 20° 24' 12.7434" 231 25. Konjevići 43° 52' 48.4176" 20° 24' 34.761" 228 26. Konjevići 43° 53' 13.5558" 20° 23' 24.9678" 230 27. Ljubić Polje 43° 53' 24.972" 20° 22' 32.4114" 232 28. Ljubić Polje 43° 53' 50.2434" 20° 22' 1.6314" 236 29. Preljinska Baluga 43° 53' 16.2276" 20° 24' 53.0352" 229 30. Preljinska Baluga 43° 52' 41.8074" 20° 25' 38.6394" 225

2.2. METHOD OF SAMPLING AND MEASUREMENT

Samples were collected in spring 2013. Samples of cultivating soil (1 kg) in the disordered state were taken from depths of 0 cm to 30 cm. The sample material was thoroughly mixed and homogenized to reach the size of the analytical sample. The homogenized soil samples were dried at 105°C to constant mass and transferred to sample holders. Gamma-spectrometric measurements were performed with a high-resolution HPGe gamma-spectrometer made by ORTEC. The nominal detector efficiency exceeds 36%, while the resolution is less than 1.9 keV. The detector has an increased energy range of measurement (GMX-type) and can detect also low-energy γ – and x – radiation. The metallic parts of the detector were made of materials tested for high radio purity. The detector was placed in a special low background protection chamber with iron walls 25 cm thick. The chamber is made of pre-WW II cast iron, so that it does not contain admixtures of man-made radioactivity, thereby reducing about 100 times the background radiation level. The background in the measuring chamber was 1.7 counts/s in the energy range from 30 to 1800 keV. Post radon lines dominate the background spectrum. By ventilation of the measuring room, the background level was kept low and stable. The detection limit for 137Cs (for the 80 ks counting) was 0.5 Bq. The spectra were led through the preamplifier-amplifier chain (the latter of Canberra- type) to the Canberra Series 35+ multi channel analyser with two analog-to-digital converters and with a memory containing 8192 channels. The multichannel analyser was directly connected to a personal computer where the spectra were processed and stored. A modified version of the SAMPO program was used to 6 Multi-criteria analysis of soil radioactivity in Čačak Basin 851 process the spectra, in such a way that, besides the identified gamma-lines, it always presented spectral intensities of 20 selected isotopes. The samples were measured in cylindrical geometry, placed in sample containers with 67 mm diameter and 62 mm height. The detection efficiency for this geometry was determined with primary calibration point sources (Amersham), calibrated voluminous sources (NBS and OMH), as well as a phosphate-ore sample of known activity concentration. The consistency of the calibration results was checked with a modified version of the Solang computer program. The overall statistical uncertainty of the detection efficiency curve was less than 5%. Typical measurement time was 80 ks. The measurement uncertainties were presented at the 95% confidence level. This means that the probability for obtaining a result laying outside the presented limits in a repeated measurement of the same sample is less than 5%. Activity concentrations of fission and corrosion products (except 137Cs) were below the detection limits. Therefore, in the final results only the activity concentrations of 137Cs, the natural radioactive series of 238U and 232Th, and the natural radionuclide 40K are presented.

2.3. MULTI-CRITERIA ANALYSIS

For ranking the sites according to soil radioactivity, seen from the point of presence of the five radionuclides, we have chosen the PROMETHEE multi- criteria decision-making method – MCDM [18, 19]. PROMETHEE methods are widely applied in different areas [20]. PROMETHEE/GAIA method is particularly useful for the selection of sites, ranking of sites and prioritization of remedial actions [21]. The PROMETHEE method is based on determining the positive (Φ+) and the negative flow (Φ-) for each alternative towards outranking relations and in correlation with the acquired weight coefficients for each criterion-attribute [18, 19, 20]. In the case of this research, the alternatives were investigated locations and the ranking criteria were four natural radionuclides: 238U, 226Ra, 232Th, 40K and an anthropogenic 137Cs. Defining appropriate preference function is also necessary when implementing this method. The preference function defines how pairwise evaluation differences are translated into degrees of preference. It reflects the perception of the criterion scale by the decision-maker [19]. The preference functions are crucial because they define how much one object is to be preferred to others [22]. GAIA adds a descriptive complement to the PROMETHEE rankings. It performs Principal Component Analysis (PCA) to reduce the dimensionality of the problem to 2 spatial dimensions (called the GAIA plane) for visual interpretation of the problem [18]. A graphical representation of the multicriteria problem enables the decision maker to better understand the available choices and the necessary compromises he or she will have to make to achieve a best decision. GAIA can also be used to see the impact of the criteria weights on the PROMETHEE rankings. 852 M. Papić et al. 7

The significant advantage of PROMETHEE/GAIA is that it facilitates a rational decision making process which is achieved by virtue of a decision vector that directs the decision makers towards ‘preferred’ solutions [19]. In this paper, the VPSolutions Visual PROMETHEE 1.3 software was used to apply PROMETHEE I for partial – and PROMETHEE II method for complete ranking of the alternatives, as well as to preform the Geometrical Analysis for Interactive Assistance.

2.4. STATISTICAL ANALYSIS

Statistical analysis, such as descriptive statistics, Shapiro-Wilk’s normality test and Pearson correlation coefficient, were performed using SPSS 20.0 software for Windows.

3. RESULTS

3.1. PROMETHEE/GAIA

Table 2 shows activities of radionuclides measured in the locations examined above. Given that the presence of radionuclides in soil is considered as a form of contamination, all the criteria were defined as the undesirable (min). It goes without saying that not all radionuclide exert identical contaminating influence on soil, therefore they are defined by relative severity level of each criterion. The weighing of the criteria is known to play a major role in MCDA. It is thus essential for decision makers to be able to see to what extent changes of the weights of the criteria will impact the rankings provided by the multicriteria method [18, 19]. The significance level depends on radiotoxicity of each of the radionuclide, based on the classification specified in ISO 2919:2004 standard [23]. As stipulated by the classification, 226Ra belongs to a group of excessively toxic elements, 137Cs is defined as a highly toxic element, 40K belongs to the group of moderately toxic elements, whereas 232Th and 238U are classified as the elements exerting low radiotoxicity. On that basis, the elements above are assigned their relative significance or severity coefficients, i.e. 238U, 226Ra, 232Th, 40K and 137Cs were defined to have 14.00, 29.00, 14.00, 19.00 and 24.00 severity coefficients, respectively. In addition, preference functions were determined based on the examination data. Linear functions were chosen for all the criteria owing to their quantitative nature, whereas the indifference and preference thresholds (Q and P) involved the values of 8.97 and 21.22; 5.06 and 12.01; 7.30 and 17.74; 91.40 and 219.52; 28.53 and 56.52, respectively. 8 Multi-criteria analysis of soil radioactivity in Čačak Basin 853

Table 2 Evaluation table Criteria Alternatives 238U 226Ra 232Th 40K 137Cs max/min min min min min Min weight 14.00 29.00 14.00 19.00 24.00 Preference function Linear Linear Linear Linear Linear Q: Indifference 8.97 5.06 7.30 91.40 28.53 P: Preference 21.22 12.01 17.74 219.52 56.52 Unit Bq/kg Bq/kg Bq/kg Bq/kg Bq/kg 1. Parmenac 42±5 24.0±0.9 27.9±1.2 351±11 5.6±0.3 2. Pakovraće 55±10 22.3±1.1 38.3±1.9 483±24 30.9±0.9 3. Riđage 36±5 25.9±1.0 33.8±1.4 417±13 33.9±0.9 4. Beljina 37±7 19.6±1.0 24.8±1.3 353±18 19.0±0.7 5. Ljubić Kej 43±5 22.4±1.0 25.8±1.2 317±11 17.4±0.6 6. Prijevor A 32±5 19.4±1.1 25.1±1.4 320±17 156.2±2.6 7. Prijevor B 60 20±2 34±4 410±30 28.1±2.4 8. Prijevor C 44±8 37.0±2.3 45±4 430±30 56±4 9. Prijevor D 41±10 20±2 16.1±2.0 282±23 48.9±2.5 10. Suvi Breg 28±7 21.5±1.5 20.4±2.1 296±17 21.6±1.1 11. Stančići 42±5 26.5±2.3 38±4 502±23 61.7±2.6 12. Mojsinje 43±10 22.5±2.7 39.9±2.8 500±30 62.0±2.4 13. Donja Gorevnica 53±9 31.2±1.4 44.2±2.0 520±26 30.3±0.9 14. Mrčajevci A 48±6 22.7±1.7 35.7±2.1 446±14 34.2±1.0 15. Mrčajevci B 56±6 26.4±1.5 40±5 597±26 46.5±2.1 16. Kukići 44±9 35.7±1.5 50.7±2.3 416±22 28.2±0.9 17. Mršinci 63±7 37.4±1.4 46.6±1.9 401±13 34.8±1.0 18. Zablaće 60±6 35.7±1.2 44.7±1.8 285±10 5.2±0.3 19. Vapa 48±8 27.9±1.2 39.8±1.8 452±23 23.8±0.7 20. Trnavska Baluga 64±7 34.6±1.3 46.6±1.9 585±19 73.3±1.8 21. Trnava 51±8 33.7±1.4 43.4±2.1 610±30 64.5±1.4 22. Atenica 58±6 35.4±1.3 43.6±1.9 652±21 54.4±1.4 23. Konjevići A 60±6 25.0±1.2 33.4±1.7 538±27 54.8±1.3 24. Konjevići B 45±8 26.6±1.2 32.2±1.6 378±19 37.7±1.0 25. Konjevići C 47±5 24.7±0.9 31.1±1.9 414±13 33.6±0.9 26. Konjevići D 36±4 24.0±1.2 28.6±1.3 328±11 38.4±1.0 27. Ljubić Polje A 20±5 16.2±0.8 19.0±1.1 281±14 21.5±0.7 28. Ljubić Polje B 60±5 24.1±1.0 27.8±2.2 356±18 34.0±0.9 29. Preljinska Baluga A 49±5 27.1±1.4 34.2±2.2 435±12 52.4±1.3 30. Preljinska Baluga B 48±4 33.7±1.4 41±4 658±23 76.7±2.2 854 M. Papić et al. 9

Table 3 shows the values of positive (Ф+) and negative (Ф–) flows of preferences, obtained from the data shown in Table 2. The greater the positive flow, the more important the alternative, while the opposite stands for the negative flow. Therefore, for the alternative to be more important from the perspective of the negative flow, it needs to be as low as possible.

Table 3 Preference flows Location Ф+ Ф– Ф 1. Parmenac 0.2854 0.0141 0.2713 2. Pakovraće 0.1200 0.1024 0.0176 3. Riđage 0.1669 0.0375 0.1294 4. Beljina 0.3178 0.0038 0.3139 5. Ljubić Kej 0.2869 0.0108 0.2762 6. Prijevor A 0.3096 0.2420 0.0677 7. Prijevor B 0.1744 0.0804 0.0941 8. Prijevor C 0.0572 0.2972 -0.2399 9. Prijevor D 0.3426 0.0165 0.3261 10. Suvi Breg 0.3888 0.0003 0.3884 11. Stančići 0.0945 0.1396 -0.0451 12. Mojsinje 0.1283 0.1308 -0.0025 13. Donja Gorevnica 0.0301 0.2281 -0.1980 14. Mrčajevci A 0.1393 0.0545 0.0849 15. Mrčajevci B 0.0557 0.2072 -0.1515 16. Kukići 0.0769 0.2814 -0.2045 17. Mršinci 0.0493 0.3456 -0.2963 18. Zablaće 0.1718 0.2937 -0.1219 19. Vapa 0.0931 0.1003 -0.0072 20. Trnavska Baluga 0.0083 0.5005 -0.4922 21. Trnava 0.0111 0.3808 -0.3697 22. Atenica 0.0083 0.4358 -0.4276 23. Konjevići A 0.0917 0.1728 -0.0811 24. Konjevići B 0.1419 0.0394 0.1025 25. Konjevići C 0.1539 0.0338 0.1202 26. Konjevići D 0.2428 0.0132 0.2296 27. Ljubić Polje A 0.5143 0.0000 0.5143 28. Ljubić Polje B 0.1845 0.0672 0.1173 29. Preljinska Baluga A 0.0928 0.0841 0.0087 30. Preljinska Baluga B 0.0197 0.4443 -0.4246

The complete ranking of the alternatives (locations) is achieved by calculating the NetFlow (Ф) which represents the difference between the positive and negative flow. Thus, in this case, locations were ranked from the location with the lowest radioactivity to the one with the highest radioactivity. Locations were ranked top to bottom, as shown in Figure 2. 10 Multi-criteria analysis of soil radioactivity in Čačak Basin 855

Fig. 2 – PROMETHEE II complete ranking of alternatives. 856 M. Papić et al. 11

The complete ranking of alternatives shows that the location with the lowest soil contamination, in terms of the presence of radionuclides, is Ljubić Polje A (Location 27), whereas the highest radionuclide content in soil was measured in Trnavska Baluga (Location 20) with Net Flows of 0.5143 and –0.4922, respectively. GAIA planes offer a graphical representation of the results which can provide a clearer insight into the results. Figure 3 shows the graphical representation of locations and criteria using the GAIA planes, the value of ∆ being 78.6%. This means that 22.4% of the total data was lost in the projection. Given that the application of such a manner of representation is justified when the value of ∆ is higher than 60%, the validity of the application of the represented results in this investigation is justified [18].

Fig. 3 – GAIA plane for the defined Scenario. 12 Multi-criteria analysis of soil radioactivity in Čačak Basin 857

The closer the alternative (square) to the axis of a given criterion, the more favourable it is from the aspect of the criterion. Generally, the most favourable alternative is the one closest to the axis of decision-making (pi) (marked by the red line). This cannot be clearly observed in the two-dimensional representation of GAIA plane shown in Figure 3, however the 3D software enables us to pinpoint this location as Ljubić Polje A (No 27). The adjacent locations (1, 3, 4, 5, 6, 7, 9, 14, 24, 25, 26, 28 and 29) are grouped into one cluster. Prijevor A (No 6) also belongs to the group of positively ranked locations. The other locations were ranked as negative.

3.2. DESCRIPTIVE STATISTICS AND RADIONUCLIDE CORRELATIONS

Table 4 shows the descriptive statistics for the measured contents of radionuclides. Means and standard deviation used to describe central tendency and variation of the data [24] are given in the table in addition to the minimum and maximum values.

Table 4 Descriptive statistics

Sample 238U 226Ra 232Th 40K 137Cs

Minimum 20±5 16.2±0.8 16.1±2.0 281±14 5.2±0.3

Maximum 64±7 37.4±1.4 50.7±2.3 658±23 156.2±2.6

Average 47.1±6 26.77±1.4 35.06±2.2 433.77±19.6 42.84±1.4

Std. Deviation 10.74 6.08 9.01 111.28 28.26

Skewness -0.435 0.403 -0.339 0.494 2.257

Kurtosis 0.017 -0.997 -0.684 -0.639 8.184

Skewness and kurtosis are also presented which can, to some extent, enable computing of the normality of the distribution which, in this particular case, was calculated using the Shapiro-Wilk’s test (0.05 significance level). It renders the conclusion that 238U, 232Th and 40K can be said to follow normal distribution of the concentrations, while 226Ra and 137Cs don’t. According to the values of Pearson correlation coefficient (Table 5) all the radionuclides, except anthropogenic 137Cs, show statistically significant positive correlation. 858 M. Papić et al. 13

Table 5 The Pearson correlation matrix of radionuclide

238U 226Ra 232Th 40K 137Cs 238U 1 0.544** 0.631** 0.515** -0.044 226Ra 1 0.855** 0.500** 0.044 232Th 1 0.654** 0.067 40K 1 0.322 137Cs 1 **. Correlation is significant at the 0.01 level.

4. DISCUSSION

Given that similar research had not been done on the territory of Cacak in earlier period, measurement results were compared with results obtained by the Agency for Radiation Protection and Nuclear Safety of Serbia dated 2010 [25] and those carried out by individual researchers in the region [6–13]. 238U content was in agreement with results obtained from six measuring points (towns) included in the report on the level of exposure of the population to the environmental ionizing radiation in the Republic of Serbia in 2010. The average contents of 226Ra, 232Th and 40K were around the average values presented in the Report [25] which included the entire territory of Serbia. 137Cs content greatly exceeded the values obtained in all the measurements in Serbia presented in the Report [36], except for Zlatibor which has had the highest quantities of this anthropogenic radionuclide since the Chernobyl disaster. Mean and range values of radionuclide activities (Bq/kg) obtained from all sampling sites along with comparative values from several sources found in the literature are shown in Table 6.

Table 6 Mean and range values of radionuclide activities (Bq/kg) of all sampling sites and related values from various sources Radionuclide activities [Bq/kg] Source Measure 238U 226Ra 232Th 40K 137Cs Min 20±5 16.2±0.8 16.1±2.0 281±14 5.2±0.3 Our research Max 64±7 37.4±1.4 50.7±2.3 658±23 156.2±2.6 Mean 47.1±6 26.77±1.4 35.06±2.2 433.77±19.6 42.84±1.4 14 Multi-criteria analysis of soil radioactivity in Čačak Basin 859

Table 6 (continued)

Min 37.9 20.2 17.6 179 11.9 Pantelić et al. [6] Max 48 34.3 40 606 176.4 Mean 42.6±4.9 27.0±6.6 29.7±9.4 457±192 62±77 Min 24±9 19.7±1.0 22.0±1.5 238±13 5.7±0.9 Bikit et al. [7] Max 72±21 50.9±1.8 64±4 730±40 55±3 Mean 51±9 38±2.3 53±8 554±92 11.7±1.1 Min 11 12 9 98 - Kovacs et al. [8] Max 90 270 170 2600 - Mean 34±19 63±44 77±33 800±520 - Min - 20.49±0.74 31.24±1.22 515.61±17.8 1.26±0.35 Antović et al. [9] Max - 38.26±1.36 56.33±2.52 753.41±25.6 84.20±3.01 Mean - 28.6 43.1 620.08 55 Min 8.31 - 9.34 68 81.4 Dragović et al. [10] Max 71.6 - 33.1 240 410 Mean 27.1 - 17.9 142 232 Min - - - - - Grdović et al. [11] Max - - - - - Mean 47±7 51±5 50±4 608±15 25±2 Min - - - - - Dugalić et al. [12] Max - - - - - Mean 60.4±26.2 33.2±13.4 49.1±18.5 379±108 36.4±23.3 Min 6.5±4.2 5.1±0.5 6.8±0.8 60±6 2.1±0.2 Janković et al. [13] Max 228±53 128±12 72±7 821±82 68±6 Mean 64 47 41 536 26

Mean and range contents of natural radionuclides in cultivating soil on the territory of town of Čačak did not significantly deviate from those obtained in referential papers. The increased activity of 137Cs (156.2±2.6, 73.3±1.8 and 76.7±2.2 Bq/kg) was recorded at 3 sites (6, 20 and 30), hence the higher average content of natural radionuclides, which affects the picture of the actual state. Contents of 137Cs on Zlatibor, measured by Dragović et al. [10], showed however, that its content in Čačak is 5 times lower. According to results of Pantelić et al. [6], the difference in the amount of 137Cs in the soil of central Serbia (62±77 Bq/kg), Western Serbia in particular 860 M. Papić et al. 15

(114±49 Bq/kg), compared to other regions in Serbia is also obvious, rendering the conclusion that the values obtained in the testing on the territory of Čačak (137Cs) did not deviate from the Central Serbia region, where it is located. The comparative analysis of the study results supports the assertion that soil of Čačak basin is agriculturally safe.

5. CONCLUSION

This paper presents a comprehensive method of analysis of soil radioactivity using PROMETHEE/GAIA method of multi-criteria analysis. As compared to the current method, using the data on the absorbed rates, this method of determination and comparison of soil radioactivity on different locations could be applied in other studies on the number of radionuclides, i.e. radionuclides which do not include uranium, radium, thorium and potassium. Analyses of samples taken from 30 locations which are very similar in terms of soil type, were ranked from the most favourable to the least favourable ones from the standpoint of radioactivity based on five criteria (five radionuclide) using the PROMETHEE method. The results suggest that the least radioactive soil is found in Ljubić Polje A site (Location 27) while the highest measured radioactivity was recorded in Trnavska Baluga (Location 20). No significant differences in radionuclide content in soil in both urban and industrial areas of the town (Locations 22–30) were observed compared to the same parameters recorded in rural areas. Comparison of the results with similar studies in the region indicate that the radioactivity of soil in the territory of Čačak is not increased relative to the region.

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