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Article

Estimation of Natural Radionuclides’ Concentration of the Plutonic Rocks in the Sakarya Zone, Turkey Using Multivariate Statistical Methods

by
Fusun Yalcin
1,
Nurdane Ilbeyli
2,*,
Mehmet Demirbilek
3,
Mustafa Gurhan Yalcin
2,
Alper Gunes
2,
Abdullah Kaygusuz
4 and
Suleyman Fatih Ozmen
5
1
Department of Mathematics, Akdeniz University, 07058 Antalya, Turkey
2
Department of Geological Engineering, Akdeniz University, 07058 Antalya, Turkey
3
Department of Geological Engineering, Dumlupinar University, 43100 Kutahya, Turkey
4
Department of Geological Engineering, Gumushane University, 29100 Gumushane, Turkey
5
Department of Physics, Akdeniz University, 07058 Antalya, Turkey
*
Author to whom correspondence should be addressed.
Symmetry 2020, 12(6), 1048; https://doi.org/10.3390/sym12061048
Submission received: 3 May 2020 / Revised: 18 June 2020 / Accepted: 19 June 2020 / Published: 23 June 2020
Browse Figures
Versions Notes

Abstract

:
The study aimed to determine the natural radioactivity levels of 226Ra, 232Th, and 40K by the Gamma-Ray spectrometry method, and radiological hazard parameters of the plutonic rocks in the Western and Central Sakarya Zone and to analyze the data using multivariate statistical methods. The average radiological values of samples were determined as 40K (1295.3 Bq kg−1) > 232Th (132.1 Bq kg−1) > 226Ra (119.7 Bq kg−1). According to the skewness values of the distributions of the examined radionuclides, 226Ra (2.1) and 232Th (0.7) seemed to be positively right-skewed while 40K (−0.2) had a negatively right-skewed histogram. On the other hand, the following kurtosis values were calculated for the distributions: 226Ra (5.8 > 3), 232Th (−0.7), and 40K (−0.8). Kolmogorov–Smirnov and Shapiro–Wilk tests were applied to the data to test their normality. Therefore, Spearman’s correlation coefficient method was performed. The radionuclides of 226Ra and 232Th were found to have a positive correlation with radiological hazard parameters of the samples. 2 (two)-related factors identified, and the cumulative value was calculated to be 98.7% on the basis of the Scree Plot. According to the hierarchical cluster analysis, the samples that are grouped with those from Camlik region are prominent. The average radioactivity values of Camlik, Sogukpinar, Karacabey, and Sogut (except for 232Th) regions were detected to be higher than the world averages while the value of 40K was also found to be higher than the average values of various countries in the world.

1. Introduction

“Natural radioactivity” is observed all around the world, particularly in the geological environment consisting of rocks, soils, plants, fluids, and gas as well as the artificial environment consisting of man-made structures [1,2,3,4,5,6,7,8,9]. People living in environments containing natural radioactivity are exposed to different doses of radiation. People living in the natural environment receive 82% of their average annual dose (2.4 μSv) from natural radiation sources. Therefore, natural radiation sources are important for the health of people [9]. It is also important to learn the decay rates of radionuclides regarding these sources. Radioactive equilibrium is the state in which each radionuclide has the same decay. Understanding the decay chain equilibrium helps estimate the amount of radiation to be emitted in the decay of radionuclide. There are detailed studies on radioactive equilibrium, which is one of the important issues, in the literature [10]. The amount of radium (226Ra), thorium (232Th), and potassium (40K) contents of the materials are measured to define natural radiation rates and to calculate radiological hazard indices. Radium (226Ra), thorium (232Th), and potassium (40K) isotopes can be observed in various levels in plutonic rocks. Plutonic rocks and soils are among rocks with terrestrial and cosmic radiation, with high levels of natural radioactivity. Therefore, exposure to gamma rays may pose health risks for people [11,12,13]. These rocks that we contact in various ways are very crucial in terms of the health of living things.
Many locations in Turkey and around the world have been studied in terms of granitic rocks [14,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29,30,31,32,33,34,35,36,37,38]. In the literature, there are studies on the plutonic rocks in the Northwestern and Western Anatolia (Ilica, Cataldag, Uludag, Eybek, Kozak, Evciler, Orhaneli, Kapidag, Camlik, Topuk, Tepeldag, Gurgenyayla, Egrigoz), which were partially covered by the study area [18,24]. However, no detailed and comprehensive study has been found in the literature on the specified locations in the Sakarya Zone, which is the study area, except for the Camlik region. The findings of the former studies increased the importance of the unstudied regions where the plutonic rocks spread. Therefore, the use of these rocks and the presence of habitats and residential areas in the study area increase the significance of this study.
In this context, the study aimed to measure the radioactivity levels of the plutonic rocks widely observed in the Sakarya Zone to determine the radiation hazard indices, and to interpret all the data obtained by using multivariate statistical analysis. Besides, interpretations were made by comparing the obtained data and the radiogenic levels exposed to living things in the regions with the values of different areas.

2. Materials and Methods

2.1. Description of the Study Area

The study area is located in the Sakarya Zone on which there are a few large and small settlements. The settlements in the study area have different names; therefore, the rock samples taken from different regions were given codes according to their locations. For example, a sample from Ericek was given the code of “ER” and recorded as “Sample No: ER”; similarly, other samples from Karacabey, Camlik, Sogut, Kapanca, and Sogukpinar were given the codes of “KR”, “E”, “F”, ”ST”, “KP”, and “SR”, respectively. The villages where the rock samples were taken, and their vicinity are shown on the site location map (Figure 1).
The region extending from the Biga Peninsula to the Eastern Pontides is called the Sakarya Zone, which is characterized by sedimentary and igneous rocks subjected to intense deformation and metamorphism in different facies [39]. There are igneous rocks of various ages and origins in the Sakarya Zone

2.2. Sampling and Preparation

A total of 30 rock samples were collected from the plutonic rocks in the study area and several locations where the regional rocks dominated. An area of approximately 100 m2 was marked at each sampling location. After removing impurities, such as stones, pebbles, and roots, 50–100 g of rock samples were taken in each corner and center of the marked area to a depth of about 50 cm. Four different samples representing the study area were taken for each sample. The sub-samples obtained were mixed and put in packages of 400–500 g. The samples were packed in polyethylene bags, systematically labeled, and the coordinates of the sample locations were recorded using Global Positioning System (GPS). The samples were homogenized using an agate mortar at the sample preparation laboratory of the Department of Geological Engineering at Akdeniz University (Turkey) and kept under normal conditions in the laboratory environment for a month to achieve secular equilibrium.
All samples were kept tightly closed with gas-tight parafilm and stored for about 30 days to form a radioactive equilibrium between 226Ra and 222Rn and stabilize the Compton region (7 × 3.9 days) [40].

2.3. Radioactivity Measurements Using High-Purity Germanium (HPGe) Detector and Dose Calculations

The gamma spectroscopic measurements of the plutonic rock samples were performed with AMETEK-ORTEC brand, GEM40P4 model, High Purity Germanium (HPGe) detector and Maestro32 software at the Department of Physics at Akdeniz University (Turkey). The relative efficiency of the HPGe detector was 40%. The full width half maximum (FWHM) values at 122 keV (57Co) and at 1332 keV (60Co) were 768 eV and 1.85 keV, respectively. The energy and efficiency calibration of the HPGe gamma spectrometer were made using the mixed source (International Atomic Energy Agency, (IAEA) 1364-43-2) of the same geometry with sample energies ranging from 47 to 1836 keV. IAEA RGU-1, RGTh-1, and RGK-1 standards were used for the quality controls and activity calculations (Table 1). Detailed information about the measurement system is provided by [40,41].
All samples were counted for 50,000 s. Background intensities were also obtained under the same conditions before and after the measurements of the samples. In the gamma spectra of the samples, the activity concentrations of 226Ra were determined by using 352 (214Pb) and 609 keV (214Bi), while the activity concentrations of 232Th were determined by using 911 (228Ac) and 583 keV (208Tl) energy peaks, which were released from product radionuclides in the 238U and 232Th disintegration series. 40K activity concentrations were determined by using the 1461 keV energy peak. Radionuclide activity concentrations were calculated using Equation (1):
A = N / t ε × I γ × m ,
where A stands for the activity of the radionuclide in Bq kg−1, N stands for the total net count in the energy of interest as counting time in seconds, ε stands for the efficiency of the HPGe detector in the gamma energy of interest, Iγ stands for the abundance of the gamma ray, and m stands for the sample mass [40,41].

2.4. Radiation Hazards Parameters

Firstly, the samples of the radioactivity levels of the naturally occurring radionuclide materials (NORMs) collected from the study area were measured. Then, internationally adopted radiological health parameters were calculated using all of the data obtained by the gamma-ray spectrometry method (Table 2). Finally, multivariate statistical analyses were performed on all data obtained and the results were interpreted by comparing them with world averages.
The following radiological health parameters were applied to radioactivity levels: Absorbed dose rate (D), radium equivalent activity (Raeq), alfa index (Iα), gamma index (Iγ), external hazard index (Hex), internal hazard index (Hin), annual effective dose equivalent (AEDEindoor), annual effective dose equivalent (AEDEoutdoor), annual gonadal dose equivalent (AGDE), excess lifetime cancer risk (ELCRoutdoor), and activity utilization index (AUI).

2.5. Statistical Analysis

Multivariate statistical studies on the interpretation of radioactivity data and radiological parameters are quite important [49,50,51]. In this regard, multivariate statistical analyses are useful, and these tools are required to explain the data. In this study, multivariate statistical analyses, such as correlation analysis, factor analysis, cluster analysis, and regression analysis, were performed to interpret the data using the SPSS 23 software package.

2.6. Comparison with Other Countries

This finding of this study were compared with those of similar studies conducted in different parts of the world, and the differences between them were revealed.

3. Findings

3.1. Activity Concentration and Radiological Characterization

Table 3 gives the radiological health parameters calculated for the study area.
The recommended average value of the gamma radiation absorbed dose rate (D) ranges between 10 and 200 nGy hr−1, and the population-weighted gamma radiation absorbed dose rate is 59 nGy hr−1 [14]. D values of the samples were observed to range between 8.7 and 691.6 nGy hr−1 and the mean value was found to be 222 nGy hr−1. The maximum and average absorbed dose rates due to gamma radiation in the air 1 m above the ground level exceeded world limit values. Moreover, these values are well above the limit value that should be taken into account in the settlements.
The limit value for radium equivalent activity (Raeq) ranges between 370 and 740 Bg kg−1 [14]. Raeq values, which were calculated to identify the homogeneous distributions of radionuclides, were observed between 17.5 and 1503.4 Bg kg−1 with an average value of 478.3 Bg kg−1. The maximum and average values were observed to exceed world limits.
The recommended limit value for the alpha index (Iα) is Iα < 1 μRh r−1 [14]. Iα values were calculated to be between 0.02 and 3.8 μRh r−1 with an average value of 0.7 μRh r−1. The maximum value exceeded the recommended limit values. According to the average values, no problems were observed in terms of radon inhalation; however, there seemed a problem according to the maximum value.
While the recommended upper limit for gamma index (Iγ) is Iγ < 1 μRh r−1, the exemption criterion of gamma dosage is Iγ < 0.3 μRh r−1 [14]. In this study, Iγ values were observed to range between 0.07 and 5.3 μRh r−1 with an average of 1.8 μRh r−1. The maximum Iγ value exceeded the recommended upper limit. The samples with a maximum value exceeding Iγ < 0.3 μRh r−1 are not suitable to be used as a building material. The radiological effect must be at least (Iγ < 0.5) to be tolerated.
The external hazard index (Hex) was calculated together with the internal hazard index (Hin) to evaluate the effects of the radioactivity of the surface materials on health. The recommended limit value for the external hazard index (Hex) is (Hex < 1). In the study, Hex values were observed to be between 0.05 and 4.1 with an average of 1.3. The maximum and average values were found to exceed the limit values.
The recommended limit value for the internal alpha radiation (Hin) is Hin < 1 [14]. In the study, Hin values were found to range between 0.07 and 6.1, with an average of 1.7. All values were observed to exceed the limit value. According to these figures, health problems stemming from the inhalation of radon and radon products can be seen. The radiological hazard indices of the samples should be below the limit values (Hex < 1 and Hin < 1) to assume their radiological effects are not significant.
The recommended world average for the annual effective dose equivalent (AEDE) is AEDE < 70 µSv yr−1 [14]. The minimum, maximum, and mean values of AEDEindoor and AEDEoutdoor were calculated to be 42.7–3395.1 µSv yr−1, 1089.7 µSv yr−1 (mean) and 10.7–848.8 µSv yr−1, and 272.4 µSv yr−1 (mean), respectively. The samples were observed to have high AEDEindoor values. The maximum and mean values were found to exceed limit values. The regions seem to have a health problem of inhalation of radon and its products.
The recommended limit for the annual gonadal dose equivalent (AGDE) is AGDE < 300 µSv yr−1 [14]. An active cell’s direct exposure to radiation may damage the reproductive organs, active bone marrow, and bone surface cells; it may even lead to cell mutation or death [14,52,53]. In this study, the AGDE values ranged between 61.6 and 4779.9 µSv yr−1, and the average AGDE was observed to be 1559.3 µSv yr−1. The maximum and average AGDE values were found to exceed the limit values. These findings are significant since the radiation taken by the reproductive organs (gonads) of the population exceeds the recommended annual dose equivalent.
The recommended limit value for the excess lifetime cancer risk (ELCRoutdoor) is ELCRoutdoor < 2.9 × 10−4 µSv yr−1 [14]. The ELCRoutdoor values were found to range between 37.3 and 2970.8 (µSv yr−1) with an average of 953.5. µSv yr−1. All values were observed to be well above the limit value. According to these results, the lifetime cancer risk of the people who live in these regions with anomalies for up to 70 years due to land use is quite high. Therefore, the contact of people living in these regions with these plutonic rocks in their living areas should be reduced.
If the recommended limit value for the activity utilization index (AUI) is AUI ≤ 1, the dose that the individual receives corresponds to 0.3 µSv yr−1. On the other hand, if the limit value is AUI ≤ 3, the dose that the individual receives corresponds to 1 µSv yr−1 [14]. In this study, the AUI values were observed to range between 0.1 and 11.6 µSv yr−1 with an average of 3.3 µSv yr−1. Since the maximum and average values exceeded the limit value (AUI ≤ 3), the regions were found to have excess amounts of external gamma radiation (1 µSv yr−1) due to the surface materials.
The regions in the study area from where the samples with the maximum and average values exceeding the international limit values were taken may pose significant radiological risks to the people living there.

3.2. Multivariate Statistical Analysis and Data Mining

3.2.1. Descriptive Statistics

Descriptive statistical analyses were applied to radiological indices calculated by the radiological analyses and the data obtained from them (Table 4). The mean values of the radionuclides obtained by radiological analyses were ordered as follows: 40K (1532.6 Bq kg−1) > 226Ra (148.5 Bq kg−1) > 232Th (148.1 Bq kg−1). It is noteworthy that the values of 226Ra and 32Th are close to each other, and they show a similar concentration. This indicates that these radionuclides showed similar behavior and that they are not affected by the metamorphism of the rocks. The samples were not taken from the same location. The standard deviation values of radionuclides were found to be high due to the fact that the sample rocks taken from different locations had different chemical contents and differ in terms of their minimum and maximum values. This is an expected case in terms of statistics.
The kurtosis values of the distributions of the radionuclides were found to be 226Ra (5.8 > 3), 232Th (−0.7), and 40K (−0.8) in the descending order. While the distribution of 226Ra had a leptokurtic shape, the distributions of 232Th and 40K had platykurtic shapes (Table 4, Figure 2).
The skewness range of (−2 < skewness < 2) covers 95% of the total area, while the skewness range of (−3 < skewness < 3) covers 99% of the total area. The skewness values of the radionuclides were found to be 226Ra (−3 < 2.1 < 3), 232Th (−2 < 0.7 < 2), and 40K (−2 < −0.2 < 2) in the descending order. While the distribution of 226Ra was found to have a right-skewed and asymmetrical shape, the distributions of 232Th and 40K could be assumed to have a normal distribution.
Figure 3 clearly indicates that the linear correlation coefficient between the effective 226Ra content and 232Th content was 0.9, pointing to the high strong linear dependency between both concentrations in the plutonic rocks.

3.2.2. Correlation Analysis

A correlation analysis was performed to determine the relationship and similarity between all the data obtained. The normality of the data was tested before performing multivariate statistical analyses. The Kolmogorov–Smirnov and Shapiro–Wilk tests were used to test the normality of the distributions (Table 5). The significance values of all the data were calculated to be less than 0.05 (sig. < 0.05). Therefore, Spearman’s correlation coefficient was used in the correlation analysis.
In general, the radionuclides have a positive correlation with the radiological parameters, which were obtained from the analysis of radionuclides (Table 6). In particular, while the radionuclides of 226Ra and 232Th have a positive correlation with the radiological parameters, 40K has a lower positive correlation with these parameters. 40K was observed to have a lower correlation with all other variables compared to the other radionuclides.
Therefore, 226Ra and 232Th were found to have a more significant contribution to the radioactivity in the plutonic rocks. As a result, the variables that showed a positive correlation with the radioactivity parameters were interpreted to behave similarly and were of the same origin.

3.2.3. Factor Analysis

Factor analysis was applied to obtain significantly explained variables from the results of the analyses and calculations. The automatic factor selection tool of SPSS found one (1) factor with an eigenvalue greater than 1. However, the rotation sums of squared loadings method was applied to reveal the variance of the data and particularly 40K, even it was very low; thus, the number of factors was selected as two (2) manually. In this context, two factors were extracted, and the cumulative value of variance explained was determined to be 98.7%. The results showed that the significant variance of the data was calculated very perfectly (Table 7).
Principal component analysis (PCA) was performed after factor analysis. According to the results of the rotated component matrix data, two components were determined (Table 8). The first factor was determined to consist of 226Ra, 232Th, Raeq, D, Iα, Iγ, Hex, Hin, AEDEindoor, AEDEoutdoor, AGDE, ELCR, and AUI, and their total variance was found to be 95.1%. The second factor was determined to consist of 40K with a total variance value of 3.5%. The radionuclide of 40K, which constitutes a separate component, is completely independent of the variables representing the other component. With its percentage of 3.5% in the grand total, 40K has a high effect on the total variance. It has an important place in the statistical evaluation of the data. This finding indicates that 40K has a different effect than 226Ra and 232Th. It is considered that the radionuclides of 226Ra and 232Th are influenced by granitic rocks, as well as 40K being affected by rock alterations, and clayey rocks have more effect on this radionuclide.
After analyzing the Scree Plot of the data used in the factor analysis, it can be seen that the data is flattened after the second factor; therefore, extraction of two factors from these data seems to be appropriate (Figure 4).
According to the principal component analysis, 226Ra and 232Th radionuclides were found to have a very high effect on the radiological parameters; this finding seemed to be compatible with the correlation analysis. 40K showed a different behavior compared to the other radionuclides and indices and seemed to be distant from them (Figure 5).

3.2.4. Cluster Analysis (CA)

The Wards method was used in the hierarchical cluster analysis and the Q-mode cluster showed an arbitrary similarity level of 50%. Two (2) groups were determined in the dendrogram of a total of 30 samples (Figure 6). The samples showing similarities among themselves were determined. The samples of N9-F-29, N11-F-34, and N15-E-18 together with N13-E-3 and N14-E-14, which were connected to them externally, formed the first dendrogram. The second dendrogram consisted of the samples of N27-SR-5, N29-SR-12, N6-KR-3, N16-ST-1, N20-ST-87, N30-SR-18, N18-ST-59, N7-KR-4, N28-SR-11, N23-KP-2, N17-ST-52, N19-ST-80, N5-KR-1, N8-KR-7, and N10-F-31, which were connected to them externally. The samples in the same dendrogram showed similar characteristics.

3.3. Comparison with Other Countries

Before comparing the average values of plutonic rock samples collected from the study area with the world averages, muscovite schist sample (N6-KR-3) as a metamorphic rock, aplite sample (N13-E-3) as a dike, and pegmatite rock samples (N14-E-14, N18-ST-59, N23-KP-2) were excluded from the dataset in the calculation of the average values since they increased the grand mean significantly. The values of 226Ra (148.53), 232Th (148.11), and 40K (1532.59) seemed to have an abnormally negative impact on the grand mean of the region. In particular, the aplite sample No. N13-E-3 collected from the Camlik region had the highest 40K value while the pegmatite rock sample No. N14-E-14 had the highest 226Ra value. All the data about 40K were grouped into four equal classes (10.5–624; 624–1694.9; 1695–2582.4; 2582.4–3569.1), and star figures were created from these new data; then, they were marked on the site location map (Figure 1).
The mean values of granite, metagranite, and chlorite schist samples were taken into consideration to evaluate the situation using similar samples from various countries in the world (Table 9). The average 226Ra (119.7), 232Th (132.1), and 40K (1295.3) values were compared with the world averages of the granite samples in terms of the average natural radioactivity behavior of these rocks. Additionally, the samples were compared with the average values of the natural granite samples from different countries and different regions of Turkey, including the commercial ones and the imported ones.
Considering the average values of granite, metagranite, and chlorite schist samples, 226Ra (119.7), 232Th (132.1), and 40K (1295.3) values were found to exceed the world averages (Table 9). The 226Ra value of the samples seemed to be higher than all other samples except for those from the South Eastern Desert (Egypt), Ezine (Turkey), and commercial ones (China). The 232Th value was determined to be higher than all other samples, except for commercial ones (China). The 40K value showed higher values than all other samples, except for those from Al Madinah (Saudi Arabia) and Juban (Yemen).
Likewise, the average radioactivity values of the plutonic rock samples from Camlik, Sogukpinar, Karacabey, and Sogut (except for 232Th) were found to be higher than the world averages. Particularly, the 40K values in these regions were higher than those of samples from various countries in the world. The average radioactivity values of the plutonic rock samples from Ericek and Kapanca were found to be lower than the world averages and those of samples from other regions (Figure 7).

4. Conclusions

The radiological levels of the plutonic rock samples from various regions in the Sakarya Zone were measured and their radioactivity parameters were calculated; then, all data were interpreted using multivariate statistical methods.
Considering the average radioactivity concentrations of granite and metagranite, which are plutonic rocks, and chlorite schist, which is a metamorphic rock, the abundance order was determined to be 40K (1295.3 Bq kg−1) > 232Th (132.1 Bq kg−1) > 226Ra (119.7 Bq kg−1). Therefore, the plutonic rocks should be identified in similar studies, and dikes should not be taken into consideration in the calculation of the grand mean.
The average values of the absorbed dose rate (D), radium equivalent activity (Raeq), external hazard index (Hex), internal hazard index (Hin), the annual effective dose equivalent values of AEDEindoor and AEDEoutdoor, the annual gonadal dose equivalent (AGDE), excess lifetime cancer risk (ELCRoutdoor), and activity utilization index (AUI) were found to be 222, 478.3, 1.3, 1.7, 1089.7, 272.4, 1559.3, 953.5, and 3.3, respectively. All average values were found to exceed world limit values. The averages of the alpha index (Iα) and gamma index (Iγ) values were found to be 0.7427 and 1.7463, respectively. Therefore, the radiological effect was determined to exceed the value that can be tolerated (Iγ < 0.5). The results of the AUI calculations revealed that there was external gamma radiation from the surface materials.
According to the descriptive statistics applied as part of the multivariate statistical analyses, the skewness values of the radionuclides were found to be 226Ra (−3 < 2.1 < 3), 232Th (−2 < 0.7 < 2), and 40K (−2 < −0.2 < 2). The distribution of 226Ra was found to have a positively right-skewed and asymmetrical shape while the distribution of 232Th had a positively right-skewed symmetrical shape, and 40K had a negatively right-skewed and symmetrical shape. The kurtosis values of the distributions of the radionuclides were found to be 226Ra (5.8 > 3), 232Th (−0.7), and 40K (−0.8) in the descending order. The 226Ra radionuclide had a sharply peaked and the highest distribution.
Kolmogorov–Smirnov and Shapiro–Wilk normality tests were performed, and the significance values were found to be less than 0.05 (sig. < 0.05). Therefore, it was decided that the data did not have a normal distribution, and Spearman’s correlation coefficient method was performed. A positive correlation was found between 226Ra, 232Th, and the radiological parameters. It was interpreted that they had a higher radioactivity effect. However, 40K did not show a similar correlation level. The findings also reveal that the radionuclides of 226Ra and 232Th are geologically affected by granitic rocks. On the other hand, 40K was affected by clayey rocks formed by the alteration of granitic rocks.
Factor analysis resulted in two factors with a cumulative value of 98.7%. While one of the factors represents 40K (3.5%), the other factor represents all remaining variables (95.2%). The diagram clearly shows that 40K is positioned in a different location from other variables. Moreover, the Scree Plot of the variables is flattened after the second component.
Two (2) hierarchical groups were obtained from the Q-mode cluster at the arbitrary similarity level of 50%. While the first group consists of N9-F-29, N11-F-34, N15-E-18, N13-E-3, and N14-E-14, the second group consists of N22-KP-1, N24-KP-8, N21-ST-89, N26-KP-12, N1-ER-2, N3-ER-4, N2-ER-3, N25-KP-11, N4-ER-5, N27-SR-5, N29-SR-12, N6-KR-3, N16-ST-1, N20-ST-87, N30-SR-18, N18-ST-59, N7-KR-4, N28-SR-11, N23-KP-2, N17-ST-52, N19-ST-80, N5-KR-1, N8-KR-7, and N10-F-31. The first group, which showed higher values, is prominent.
The radiological values of the samples from the Sakarya Zone are higher than the world average. The 226Ra value was found to be lower than the values of the samples from the South Eastern Desert (Egypt), Ezine (Turkey), and commercial ones (China). The 232Th value was found to be lower than that of the commercial sample (China), and the 40K value was found to be lower than the values of the samples from Al Madinah (Saudi Arabia) and Juban (Yemen). However, the values were found to be higher than other samples from various regions of the world.
The average radioactivity values of Camlik, Sogukpinar, Karacabey, and Sogut (except for 232Th) were observed to be higher than the world averages. The average 40K value was higher than the world average, as well as the values of samples from various countries in the world.
The samples exceeding the limit values are not suitable for use as a building material. Inhalation of radon and its products may lead to health problems. The AGDE calculations revealed a significant finding that the radiation received by the reproductive organs (gonads) of the population exceeds the annual gonadal dose equivalent. According to the ELCRoutdoor calculations, the lifetime cancer risk for up to 70 years due to land use is high. Therefore, it will be appropriate to carry out a follow-up on the rocks used as products quickly and effectively. The scope of the production of these rocks, their marketing, and use as a building material should be limited.

Author Contributions

Conceptualization, F.Y., N.I. and M.G.Y.; methodology, M.D., S.F.O., A.G.; software, F.Y.; validation, N.I. and M.G.Y.; formal analysis, F.Y., N.I., A.G.; investigation, A.K.; resources, M.G.Y. and A.G.; data curation, F.Y.; writing-original draft preparation, F.Y., N.I. and M.G.Y.; writing-review and editing, M.D. and A.K.; visualization, M.G.Y. and A.G.; supervision, N.I. and M.G.Y.; project administration, N.I.; funding acquisition, N.I. All authors have read and agreed to the published version of the manuscript.

Funding

This research received no external funding.

Acknowledgments

The corresponding author, Nurdane Ilbeyli, extends her appreciation to the Scientific Research Projects Coordination Unit at Akdeniz University for funding the Ra, Th, K analyses of the rocks by the Research Groups Program (Project Number: FBA-2015-652).

Conflicts of Interest

The authors declare no conflict of interest.

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Symmetry 12 01048 g001 550
Figure 1. Site location map of the study area, sample locations, and the distribution of 40K samples.
Figure 1. Site location map of the study area, sample locations, and the distribution of 40K samples.
Symmetry 12 01048 g001
Symmetry 12 01048 g002 550
Figure 2. Frequency distributions of 226Ra, 232Th, and 40K.
Figure 2. Frequency distributions of 226Ra, 232Th, and 40K.
Symmetry 12 01048 g002
Symmetry 12 01048 g003 550
Figure 3. The relation between 226Ra and 232Th concentrations.
Figure 3. The relation between 226Ra and 232Th concentrations.
Symmetry 12 01048 g003
Symmetry 12 01048 g004 550
Figure 4. Scree plot of the principal component analysis.
Figure 4. Scree plot of the principal component analysis.
Symmetry 12 01048 g004
Symmetry 12 01048 g005 550
Figure 5. Component plot in the varimax-rotated space, component 1 (95.1%) and component 2 (3.5%).
Figure 5. Component plot in the varimax-rotated space, component 1 (95.1%) and component 2 (3.5%).
Symmetry 12 01048 g005
Symmetry 12 01048 g006 550
Figure 6. The clustering of radioactive variables.
Figure 6. The clustering of radioactive variables.
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Symmetry 12 01048 g007 550
Figure 7. The activity concentration of 226Ra, 232Th, and 40K in the plutonic rock samples.
Figure 7. The activity concentration of 226Ra, 232Th, and 40K in the plutonic rock samples.
Symmetry 12 01048 g007
Table
Table 1. Summary of the analysis of standard materials.
Table 1. Summary of the analysis of standard materials.
StandardReference Value (Bq kg−1)Measured Value (Bq kg−1)
RGU-14940 ± 304964 ± 72
RGTh-13250 ± 903276 ± 64
RGK-114000 ± 40014240 ± 546
Table
Table 2. Radiological parameters.
Table 2. Radiological parameters.
S/NRadiological ParametersUnitsUsed FormulaReferences
1Absorbed dose rate (D)nGy hr−1DR = (0.462 AU + 0.604ATh + 0.0417 AK) ≤ 80[14,36]
2Radium equivalent (Raeq)Bq kg−1Raeq = (Au + 1.43 ATh + 0.077 AK) ≤ 370[14,36]
3Alfa index (Iα)µRh r−1Iα = AU/200 ≤ 1[42]
4Gamma index (Iγ)-Iγr = AU/300 + ATh/200 + AK/3000 ≤ 1[43]
5External hazard index (Hex)-Hex = AU/370 + ATh/259 + AK/4810 ≤ 1[44]
6Internal hazard index (Hin)-Hin = AU/185 + ATh/259 + AK/4810 ≤ 1[42]
7Annual effective dose equivalent (AEDEindoor)µSv yr−1AEDE(indoor) = DR × 8766 h × 0.7 Sv/Gy × 0.8 × 10−3 ≤ 0.48[14,36,42]
8Annual effective dose equivalent (AEDEoutdoor)µSv yr−1AEDE(outdoor)= DR × 8766 h × 0.7 Sv/Gy × 0.2 × 10−3 ≤ 0.48[14,36]
9Annual gonadal dose equivalent (AGDE)µSv yr−1AGDE= 3.09 AU × 4.18 ATh × 0.314 AK ≤ 300[36,45]
10Excess lifetime cancer risk (ELCRoutdoor)µSv yr−1ELCR(outdoor) = AEDEoutdoor × DL × RF ≤ 0.29[35,46,47]
11Activity utilization index (AUI)-AUI = AU/50 fU + ATh/50 fTh + AK/500 fK ≤ 2[48]
Where AU, ATh, and AK are the activity concentrations of 238U, 232Th, and 40K in (Bq kg−1) present in tar sand soil, respectively. fU (0.462), fTh (0.604), and fK (0.0417) are the fractional contributions to the total dose rate due to γ-radiation from the actual radionuclide of 238U, 232Th, and 40K, respectively. DL and RF is duration of life (70 years) and risk factor (Sv−1), fatal cancer risk per Sievert. For stochastic effects, ICRP 60 uses values of 0.05 for the public.
Table
Table 3. Radiological parameters of the plutonic and metamorphic rock samples of the western and central Sakarya zone.
Table 3. Radiological parameters of the plutonic and metamorphic rock samples of the western and central Sakarya zone.
LocationsNumberLongitudeLatitudeRock Types226Ra (Bq kg−1) ± 232Th (Bq kg−1) ± 40K (Bq kg−1)±DRaeqIαIγHexHinAEDEindoorAEDEoutdoorAGDEELCRAUI
nGy hr−1Bq kg−1µRhr −1µSv yr−1µSv yr−1µSv yr−1µSv yr−1
EricekN1-ER-228.43204309839.676005958Metagranite12.110.819.330.7339.262.0312.8728.470.060.100.080.1163.1615.7988.7455.260.23
N2-ER-328.43175522039.676180693Chlorite schist16.410.9944.393.7418.750.9035.1781.330.080.280.220.26172.6643.17242.13151.080.69
N3-ER-428.43171504239.675928916Metagranite9.840.700.000.0099.353.808.6917.490.050.070.050.0742.6510.6661.5937.320.10
N4-ER-528.43129169139.675753940Metagranite118.368.860.000.0045.941.7656.60121.900.590.410.330.65277.8469.46380.16243.111.10
KaracabeyN5-KR-128.32426980240.273353542Metagranite39.183.3266.843.151982.63111.78141.15287.420.201.130.780.88692.88173.221022.99606.271.33
N6-KR-328.32761938140.278639427Musqovite schist141.978.83126.706.962300.20122.99238.04500.270.711.871.351.731168.51292.131690.571022.453.03
N7-KR-428.33400297740.271881386Metagranite140.2912.19203.2112.242026.3878.34272.05586.910.702.161.591.961335.50333.881919.201168.563.92
N8-KR-728.46767466140.252524554Granite133.3110.46147.1211.331110.4946.14196.76429.200.671.551.161.52965.87241.471375.58845.133.10
CamlikN9-F-2927.14783661139.654970995Granite337.7824.65366.9818.602164.4595.02467.971029.231.693.682.783.692297.25574.313257.372010.097.73
N10-F-3127.16034561439.660657918Dike152.587.67263.7720.581160.8957.31278.22619.170.762.211.672.081365.77341.441938.571195.054.69
N11-F-3427.16040579439.666523519Granite314.2214.91386.8427.142158.8988.00468.851033.641.573.702.793.642301.56575.393265.842013.867.76
N12-F-35A27.15716566839.677241137Granite353.7123.43381.2825.062323.2289.28490.591077.831.773.862.913.872408.26602.073416.202107.238.07
N13-E-327.14168003839.648329069Aplite425.8029.54351.9831.853569.09162.79558.151203.962.134.373.254.402739.93684.983907.712397.448.48
N14-E-1427.15314711839.652747590Pegmatite752.3050.70367.9017.462921.97130.26691.621503.393.765.324.066.093395.14848.794779.932970.7511.64
N15-E-1827.14863206539.650834260Granite295.5315.30285.1218.101689.3985.85379.20833.341.482.972.253.051861.46465.362635.471628.786.32
SogutN16-ST-130.22163182840.034862141Metagranite151.3511.15113.019.741924.67110.23218.44461.150.761.711.251.651072.30268.071544.37938.262.92
N17-ST-5230.58331679640.069253317Granite50.412.5582.255.651694.9381.92143.65298.540.251.140.810.94705.17176.291031.79617.021.60
N18-ST-5930.58857706740.081668280Pegmatite83.984.3399.685.222221.4288.19191.64397.570.421.521.071.30940.74235.191373.68823.152.17
N19-ST-8030.01166074740.093298000Metagranite50.753.9879.356.751569.4678.43136.82285.070.251.090.770.91671.66167.91981.33587.701.56
N20-ST-8730.38339250440.042351196Metagranite140.8312.93117.248.571975.1791.55218.24460.570.701.711.241.621071.34267.841545.44937.432.88
N21-ST-8930.72850136240.137206230Diorite4.360.237.110.40568.2422.0830.0058.280.020.240.160.17147.2836.82221.60128.870.17
KapancaN22-KP-128.97275290439.888305934Metagranite9.700.4830.972.15623.9529.5749.21102.030.050.400.280.30241.5560.39355.34211.350.52
N23-KP-228.97034865539.890517980Pegmatite60.635.08195.2610.362582.37147.27253.63538.690.302.041.451.621245.07311.271814.391089.433.13
N24-KP-828.96530154939.895612630Granite21.781.2914.930.71545.2531.4541.8285.120.110.330.230.29205.2851.32300.92179.620.43
N25-KP-1128.96908827139.889386245Granite41.522.6741.222.5310.470.4744.52101.270.210.350.270.39218.5354.63303.89191.210.88
N26-KP-1228.96797137239.891225020Granite40.112.7050.674.52343.1013.9763.44138.980.200.500.380.48311.4277.86443.45272.491.01
SogukpinarN27-SR-529.10973653740.073022948Metagranite106.139.41153.358.012099.64105.49229.21487.100.531.821.321.601125.20281.301628.25984.553.01
N28-SR-1129.15343219540.122621203Metagranite209.5517.49215.8910.782061.6477.85313.18677.021.052.471.832.391537.39384.352197.291345.224.72
N29-SR-1229.15343219540.122621203Metagranite119.067.29136.839.292134.5385.91226.66479.090.601.791.291.621112.67278.171610.09973.582.93
N30-SR-1829.11867851640.064157408Granite122.318.34104.176.332012.03102.53203.33426.200.611.601.151.48998.14249.531445.16873.372.56
Table
Table 4. Descriptive statistics of radionuclides and radiological indices.
Table 4. Descriptive statistics of radionuclides and radiological indices.
226Ra232Th40KRaeqDIαIγHexHinAEDEindoorAEDEoutdoorAGDEELCRAUI
N3030303030303030303030303030
Minimum4.40.010.517.58.70.020.070.050.142.710.6661.5937.320.10
Maximum752.3386.83569.11503.4691.63.85.34.16.13395.1848.794779.932970.7511.64
Mean ± SEM148.5148.11532.6478.32220.71.71.31.71089.7272.431559.3953.523.28
Std. Deviation161.3125.9969.7384.7175.80.81.41.031.5863.02215.751220.73755.142.95
Kurtosis5.8−0.7−0.80.40.55.80.30.41.60.50.4680.3880.4680.893
Skewness2.10.7−0.21.0.92.10.911.30.90.9290.8890.9291.197
Table
Table 5. Normality tests of all data.
Table 5. Normality tests of all data.
Kolmogorov–Smirnov aShapiro–Wilk
StatisticdfSig.StatisticdfSig.
226Ra0.257300.0000.776300.000
232Th0.150300.0830.889300.005
40K0.190300.0070.912300.017
Raeq0.144300.1140.906300.012
D0.141300.1310.910300.015
Iα0.258300.0000.776300.000
Iγ0.134300.1760.913300.018
Hex0.145300.1110.906300.012
Hin0.190300.0070.878300.003
AEDEindoor0.141300.1310.910300.015
AEDEoutdoor0.141300.1310.910300.015
AGDE0.145300.1100.914300.018
ELCR0.141300.1310.910300.015
AUI0.222300.0010.869300.002
a Lilliefors Significance Correction.
Table
Table 6. Pearson correlation coefficients between the radioactive variables in the samples.
Table 6. Pearson correlation coefficients between the radioactive variables in the samples.
226Ra232Th40KRaeqDIαIγHexHinAEDEindoorAEDEoutdoorAGDEELCRAUI
226Ra1
232Th0.845 **1
40K0.641 **0.729 **1
Raeq0.939 **0.963 **0.804 **1
D0.937 **0.959 **0.817 **1.000 **1
Iα1.000 **0.845 **0.641 **0.939 **0.937 **1
Iγ0.931 **0.962 **0.822 **1.000 **1.000 **0.931 **1
Hex0.939 **0.963 **0.803 **1.000 **1.000 **0.939 **0.999 **1
Hin0.969 **0.941 **0.765 **0.995 **0.994 **0.969 **0.992 **0.995 **1
AEDEindoor0.937 **0.959 **0.817 **1.000 **1.000 **0.937 **1.000 **1.000 **0.994 **1
AEDEoutdoor0.937 **0.959 **0.817 **1.000 **1.000 **0.937 **1.000 **1.000 **0.994 **1.000 **1
AGDE0.933 **0.958 **0.826 **0.999 **1.000 **0.933 **1.000 **0.999 **0.992 **1.000 **1.000 **1
ELCR0.937 **0.959 **0.817 **1.000 **1.000 **0.937 **1.000 **1.000 **0.994 **1.000 **1.000 **1.000 **1
AUI0.958 **0.962 **0.727 **0.993 **0.990 **0.958 **0.989 **0.993 **0.995 **0.990 **0.990 **0.988 **0.990 **1
** Correlation is significant at the 0.01 level (2-tailed). * Correlation is significant at the 0.05 level (2-tailed).
Table
Table 7. Total variance explained.
Table 7. Total variance explained.
ComponentInitial EigenvaluesExtraction Sums of Squared LoadingsRotation Sums of Squared Loadings
Total% of VarianceCumulative %Total% of VarianceCumulative %Total% of VarianceCumulative %
113.32195.15195.15113.32195.15195.1519.07964.84964.849
20.4893.49698.6470.4893.49698.6474.73233.79998.647
Extraction Method: Principal Component Analysis.
Table
Table 8. Rotated factor loadings and explained variance for variables in the samples.
Table 8. Rotated factor loadings and explained variance for variables in the samples.
VariablesComponent
12
226Ra0.9290.325
232Th0.7670.569
40K0.3320.926
Raeq0.8130.582
D0.8020.597
Iα0.9290.325
Iγ0.7940.607
Hex0.8130.582
Hin0.8580.513
AEDEindoor0.8020.597
AEDEoutdoor0.8020.597
AGDE0.7930.609
ELCR0.8020.597
AUI0.8740.483
% of variance explained95.1513.496
Extraction Method: Principal Component Analysis.
Rotation Method: Varimax with Kaiser Normalization. a
a Rotation converged in 3 iterations.
Table
Table 9. Concentrations of 226Ra, 232Th, and 40K in different plutonic rock samples.
Table 9. Concentrations of 226Ra, 232Th, and 40K in different plutonic rock samples.
LocationSpecific activity (Bq kg−1)References
226Ra232Th40K
TurkeyWestern and Central Sakarya Zone 1119.7132.11295.3This Study
World averageGranite samples781111104[14]
Brazilcommercial 282.52271109.5[15]
imported369.675.6580[16]
Chinacommercial 210294632[17]
commercial 2881141270[18]
commercial 290116969[19]
Cypruscommercial 2771431215[20]
EgyptSouth Eastern Desert 1121.382.2840[21]
Abu Dabbab Mine 145.829.8619.7[22]
Greececommercial 27485881[23]
commercial 264811104[25]
Irancommercial 244.577.41017.2[26]
Italyimported 259.892.31141.2[27]
Japancommercial 243721004[28]
JordanAmman 141.558.4497[29]
Nigeriacommercial 251.1881433[30]
Palestinecommercial 271.082780.8[31]
Saudi ArabiaAl Madinah 133.2551.451334[7]
Spaincommercial 284421138[32]
Turkeycommercial 27180965[33]
imported 393.4124.81050[34]
Western Anatolia58901097[24]
commercial 188951055[35]
Kutahya 156.425.9538.4[36]
Ezine 11752051172[54]
Egrigoz 155761111[55]
commercial 26160851[36]
USAcommercial 231611210[37]
YemenJuban 1541271743[38]
1 natural rocks; 2 decorative rocks or ornamental stones; 3 imported granites.

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Yalcin, F.; Ilbeyli, N.; Demirbilek, M.; Yalcin, M.G.; Gunes, A.; Kaygusuz, A.; Ozmen, S.F. Estimation of Natural Radionuclides’ Concentration of the Plutonic Rocks in the Sakarya Zone, Turkey Using Multivariate Statistical Methods. Symmetry 2020, 12, 1048. https://doi.org/10.3390/sym12061048

AMA Style

Yalcin F, Ilbeyli N, Demirbilek M, Yalcin MG, Gunes A, Kaygusuz A, Ozmen SF. Estimation of Natural Radionuclides’ Concentration of the Plutonic Rocks in the Sakarya Zone, Turkey Using Multivariate Statistical Methods. Symmetry. 2020; 12(6):1048. https://doi.org/10.3390/sym12061048

Chicago/Turabian Style

Yalcin, Fusun, Nurdane Ilbeyli, Mehmet Demirbilek, Mustafa Gurhan Yalcin, Alper Gunes, Abdullah Kaygusuz, and Suleyman Fatih Ozmen. 2020. "Estimation of Natural Radionuclides’ Concentration of the Plutonic Rocks in the Sakarya Zone, Turkey Using Multivariate Statistical Methods" Symmetry 12, no. 6: 1048. https://doi.org/10.3390/sym12061048

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