Introduction

The substances in the world contain radioactive elements, even in a very little amount. The earth’s crust, the air we breathe, the water we drink, and the radioactive elements in the food we eat, the cosmic rays, nuclear weapons, and the accidents at the nuclear power plants cause a significant increase in the level of radiation. The height above the sea level, the topographic and geological structure, and the mineral formations may also increase the radiation level of any location. The annual mean dose taken by a person living in any where through the natural pathways is around 2.4 mSv [1,2,3,4]. Approximately 82% of this annual dose is generated by the natural radiation sources. For this reason, it is very important to know natural radiation sources for human health. In order to determine the radiation level of an area or a terrain, the radioactivity level in the soil, water, and air on that location have to be measured at first [5].

The densities of the elements on the Earth’s surface are different from each other and each contains radionuclides. The concentration levels of the radionuclides depend on the geological structure and environment of the region. During the formation of the earth’s crust, uranium, thorium, and potassium are released. There are ophiolites in the study area which is one of the important tourism centers in Turkey. There has been no scientific study on the level of natural radioactivity in Tekirova, Kemer, and Kumluca regions which are in the western part of Antalya. Therefore, the study to be made in this area is important for tourism and the health of the people living in this region.

The aim of this study is to determine the natural radioactivity levels of the ophiolites outcropped in Tekirova, Kemer and Kumluca regions, to calculate dose values, dose rates, Radium Equivalent Activity, Radiation Risk, Annual Gonadal Dose Equivalent, and excess lifetime cancer risk, and to reveal their effects on human health by comparing the results to the average figures for other countries.

Materials and methods

Regional geology

The units in Antalya complex, which are covered by the study area, are Beydagları, Kumluca, Godene, Kemer, and Tekirova (Fig. 1). The platform of Beydagları is the western column of Isparta geological region and it is composed of carbonate rocks whose ages range between the upper Triassic and the Eocene. Kumluca region is composed of sediments from the period between the late Triassic age and late Cretaceous age [6]. Godene geological region consists of ophiolites, deep-sea sediments, and shallow water limestones from the periods between late Triassic and late Cretaceous. Mesozoic shallow carbonate rocks on the Paleozoic sediments are predominant in Kemer region. There have been late Cretaceous ophiolites formed in the southern Neotethyan ocean basin in Tekirova region [7,8,9] (Fig. 1).

Fig. 1
figure 1

Research area and map of samples

Full size image

HPGe gamma spectrometry

Gamma spectrometric measurements made with high resolution (HPGe) Detectors are frequently used in environmental studies. During preparation of the samples for the analysis, physical processes are carried out before any chemical treatment. During the analysis, gamma-ray emission in the samples, radionuclides (qualitative), and their specific activities (quantitative) can be determined. Necessary precautions are taken to reduce the severity of high-energy cosmic rays during the analyses by gamma spectrometry. Samples prepared for the analysis have to wait for a period of one (1) month in the laboratory in order to facilitate their radioactive equilibrium. In this period, the radioactive equilibrium between the 226Ra, 228Ra and 222Rn decay series is ensured. The HPGe with a relative efficiency of 40% and resolution (FWHM) for 1.85 keV for 60Co at 1332 keV and 0.768 keV for 57Co at 122 keV has been used to measure the activity concentrations of the natural radionuclides in the samples. The calibration of the gamma spectrometer has been carried out by using eleven radionuclides (113Sn, 109Cd, 139Ce, 241Am, 137Cs, 88Y, 203Hg, 57Co, 85Sr, 210Pb, and 60Co) in 1.3 g/cc epoxy matrix. In order to have better values to get at least 20000 counts for each energy peak, the spectrum has been measured as 350000 s for the calibration [10,11,12,13,14].

Dose calculations

50 ophiolite samples have been collected from Tekirova, Kemer, and Kumluca regions in the western part of Antalya and then the activity concentrations of 226Ra, 232Th, and 40K natural radionuclides have been measured. Then the dose calculations, dose rates, activities, and the risks have been calculated based on these measurements.

The radioactivity measurements and dose calculations have been measured as 10,000 s for each ophiolite sample after making the energy and efficiency calibrations. The external contributions have been removed by making background measurements (Table 1) at the same period to determine net peak area. Activity calculations have been made as shown in Eq. (1).

$$ A = {N \mathord{\left/ {\vphantom {N {\left( {\varepsilon \times P \times T \times m} \right)}}} \right. \kern-0pt} {\left( {\varepsilon \times P \times T \times m} \right)}} $$
(1)

where N is the net peak area, ε is the efficiency, P is the Probability of releasing gamma by the relevant nucleotide, t is the counting time, m is the mass (kg).

Table 1 Measurable minimum activity values for the measurement period of 10,000 s
Full size table

The peaks with the energy of 214Bi-609 keV, 228Ac-911 keV, and 40K-1460 keV have been used to calculate the activities of 238U (226Ra), 232Th (228Ac), and 40K radionuclides [15, 16]. We have used the IAEA quality assurance reference materials (226Ra, 232Th and 40K) to perform the efficiency calibration of the detector [17, 18]. The minimum values which can be measured by gamma spectroscopy system for 1 kg of the 226Ra, 232Th, and 40K radionuclide samples for 10,000 s counting time are given in Table 1.

Absorbed dose rate in the air (D)

If natural radionuclides are equally distributed, the absorbed dose rates (nGy/h) are evaluated by using the activity concentrations. The calculation is shown in Eq. (2) [19].

$$ D = 0.0417A_{\text{K}} + 0.462A_{\text{Ra}} + 0.621A_{\text{Th}} $$
(2)

As seen in the above equation, AK, AU, and ATh are the notation of the 40K, 226Ra, and 232Th radionuclides in Bq/kg. It is stated that the recommended mean value for the world should be between 10 and 200 nGy/h [19].

Annual effective dose rate (AED)

The annual effective dose rate is determined to reveal the effects on human health. The annual effective dose in the open air has been revealed to be (0.7 Sv/Gy) and it can be predicted by the conversion factor between absorbed dose and effective dose [20]. Using it in outdoor areas means that 20% of the time passes in the outdoor areas. The annual effective dose rate (AED) can be calculated as shown in Eq. (3) [19].

$$ {\text{AED }} = {\text{ D}}\left( {\text{nGy/h}} \right) \times 8 7 60\left( {\text{h/y}} \right) \times \, 0. 2\times \, 0. 7\left( {\text{Sv/Gy}} \right) \times 10^{ - 3} $$
(3)

The International Commission on Radiological Protection [20] recommends annual effective dose of 1 and 20 mSv/year for the people and the radiation workers respectively.

Radium equivalent activity (Raeq)

Radium equivalent activity, which is a common method, is used to examine the radiological risk of the samples. Raeq has been used to compare 40K, 226Ra, and 232Th radioactivity values. Raeq is calculated as shown in Eq. (4) [5].

$$ {\text{Raeq}} = \left( {A_{K} \times \, 0.077} \right) + \left( {A_{\text{U}} } \right) + \left( {A_{\text{Th}} \times \, 1.43} \right) $$
(4)

As seen in the above equation, AK, AU, and ATh are the notation of the 40K, 226Ra, and 232Th radionuclides in Bq/kg. The average Radium Equivalent Activity rate in construction materials is 370 Bq/kg. The people can be exposed to dose of 1.5 mSv annually [21].

External radiation hazard index (Hex)

External radiation risk (Hex) is the external radiation hazard index which is based on the emitted gamma rays. It is calculated as shown in Eq. (5) [22].

$$ {\text{Hex }} = \, \left( {A_{\text{U}} /370} \right) + \, \left( {A_{\text{Th}} /259} \right) + \, \left( {A_{\text{K}} /4810} \right) $$
(5)

Radionuclides are expressed in Bq/kg. The external radiation hazard index (Hex) must be less than 1. This value depends on the upper limit of radium equivalent activity rate (370 Bq/kg).

Internal radiation hazard index (Hin)

Radon and short-lived products are harmful to the respiratory system. Therefore, the internal radiation hazard index (Hin) of radon and short-lived products must be examined. The internal radiation hazard index (Hin) is calculated as shown in Eq. (6) [21].

$$ {\text{Hin }} = \, \left( {A_{\text{U}} /185} \right) + \, \left( {A_{\text{Th}} /259} \right) + \, \left( {A_{\text{K}} /4810} \right) $$
(6)

Radionuclides are expressed in Bq/kg and the internal radiation hazard index (Hin) must be less than 1.

Annual gonadal dose equivalent (AGDE)

The activities at bone marrow and cells at the bone surface are regarded as important organs for health [22]. For this reason, the AGDE is calculated due to specific activities of 226Ra, 232Th, and 40K by using Eq. (7) [23, 24].

$$ {\text{AGDE }}\left( {\mu {\text{Sv}}/{\text{year}}} \right) \, = \, 3.09 \, A_{\text{Ra}} + \, 4.18 \, A_{\text{Th}} + \, 0.314 \, A_{\text{K}} $$
(7)

Excess lifetime cancer risk (ELCR)

ELCR is calculated by using Eq. (8).

$$ {\text{ELCR }} = {\text{ AEDE }} \times {\text{ DL }} \times {\text{ RF}} $$
(8)

where DL is the duration of life (70) and RF is the annual risk factor (Sv−1). This rate expresses the fatal cancer risk per Sievert. For stochastic effects, RF value is assumed to be 0.05 [24, 25].

Results and discussion

50 samples have been collected from Tekirova, Kemer, and Kumluca regions and their dose values have been determined, then activity values have been calculated and thus risk analyzes have been made based on these values. 40K, 238U (Ra), and 232Th activity values have been determined at 15 ophiolite samples collected from Tekirova region in Antalya province (Table 2). The highest values for ophiolite samples from Tekirova have been observed at 40K data and the lowest values have been observed at 238U (Ra) data. 40K exists in the rocks more than the others, with the minimum value of 56 Bq/kg and the maximum value of 925 Bq/kg. The minimum value for 238U (Ra) activity is 2 Bq/kg and the maximum value is 126 Bq/kg. The minimum value for 232Th activity is 5 Bq/kg while the maximum value is 101 Bq/kg.

Table 2 238U, 232Th, 40K, D (nGy/h), Raeq (Bq/kg), Hin, Hex, AED (mSv/year), AGDE (µSv/year), ELCR × 10−4 values for Tekirova Region
Full size table

Since the values of ophiolite samples of Tekirova S19, Tekirova S20, Tekirova S23, Tekirova S25, Tekirova S30, Tekirova S31, Tekirova S38, Tekirova S39, Tekirova S46a and S46b from Tekirova, are higher than the world averages (50 Bq/kg for 238U and 232Th), they can pose radiation risk for human health. The rock samples of Tekirova S25, Tekirova S30, and Tekirova S31, which have higher values than the world average (40K: 500 Bq/kg), may also a pose radiation risk for the same reasons.

Total absorbed dose rates of ophiolite samples from Tekirova have been determined to be in the range of normal values between 9 and 122 nGy/h. The minimum value of Raeq has been observed as 19 Bq/kg at Tekirova S27 sample, while the maximum value has been 265 Bq/kg for Tekirova S39 sample. At the end of the study, the maximum Raeq value of all ophiolite samples collected from Tekirova have been determined to be 370 Bq/kg which is less than 370–740 Bq/kg, the limit for industrial products. The Hex and Hin values, which are based on the upper limit of Raeq (370 Bq/kg), have been determined to be less than 1. The AED value is less than 460 Bq/kg. Annual gonadal dose equivalence (AGDE) values range between 65 and 859 μSv/year and the excess lifetime cancer risk (ELCR) ranges between 0.08 and 1.14 and does not pose a risk for human health.

40K, 238U (Ra) and 232Th activity results of 16 ophiolite samples from Kemer region have been determined (Table 3). The highest values for the ophiolite samples from Kemer have been obtained for 40K and the lowest values have been obtained for 238U (Ra). The minimum value for 40Kactivity in Kemer region is 56 Bq/kg and the maximum value is 986 Bq/kg. The minimum value for 238U (Ra) activity is 3 Bq/kg, while the maximum value is 212 Bq/kg. The minimum value for 232Th activity is 3 Bq/kg while the maximum value is 104 Bq/kg.

Table 3 238U, 232Th, 40K, D (nGy/h), Raeq (Bq/kg), Hin, Hex, AED (mSv/year), AGDE (µSv/year, ELCR × 10−4 values for Kemer Region
Full size table

Since the values of ophiolite samples of Kemer S33, Kemer S34, Kemer S35, Kemer S37, Kemer S40, Kemer S41, Kemer S42, Kemer S44, Kemer S45 ile Kemer S33, Kemer S34, Kemer S35, Kemer S40, Kemer S45, Kemer S47b are higher than the world averages (238U–232Th: 50 Bq/kg), they may pose risk for human health. The values of Kemer S33, Kemer S35, Kemer S37, Kemer S40, and Kemer S47b rock samples are higher than the world average (500 Bq/kg for 40K), therefore they may also pose radiation risk.

The total absorbed dose rates for the ophiolite samples from Kemer are between 8 nGy/h and 127 nGy/h and they have been determined to be in the normal range. The minimum value of Raeq has been found to be 16 Bq/kg for the sample from Kemer S36, while the maximum value has been 272 Bq/kg for the sample from Kemer S33. Hex and Hin values are less than 1 and the AED value is below 460 Bq/kg. Annual Gonadal Dose Equivalence (AGDE) values vary between 54 and 920 μSv/year and the calculated value of Excess Lifetime Cancer Risk (ELCR) ranges between 0.07 and 1.17 and it does not pose a risk for human health.

40K, 238U (Ra) and 232Th activity results of 19 ophiolite samples from Kumluca region have been determined (Table 4). The highest values have been obtained for 40K while the lowest values have been obtained for 238U (Ra). The minimum value of 40K activity in Kumluca region is 29 Bq/kg. The maximum value is 924 Bq/kg. The minimum value for 238U (Ra) activity is 0 Bq/kg, while the maximum value is 115 Bq/kg. The minimum value of 232Th activity is 1 Bq/kg and the maximum value is 90 Bq/kg.

Table 4 40K, 238U (Ra), 232Th, D (nGy/h), Raeq (Bq/kg), Hin, Hex, AED (mSv/year), AGDE (µSv/year ELCR × 10−4 values for Kumluca Region
Full size table

The values of Kumluca S4, Kumluca S28, Kumluca S29, Kumluca S4, Kumluca S28 and Kumluca S29 rock samples are higher than the world averages (238U and 232Th: 50 Bq/kg) therefore they may cause radiation risk for human health. Kumluca S4, Kumluca S10, Kumluca S12 and Kumluca S29 rock samples, whose values are higher than the world average (40K: 500 Bq/kg). May also cause radiation risk.

The total absorbed dose rates of ophiolite samples from Kumluca have been determined to range between 5 and 133 nGy/h and to be within the normal limit values. The minimum Raeq value has been observed as 5 Bq/kg at Kumluca S7 sample, while the maximum value has been 283 Bq/kg at Kumluca S29 sample. At the end of the study, the maximum Raeq value (370 Bq/kg) of the ophiolite samples collected from Kumluca region seems to be less than the accepted limit values for industrial products (370–740 Bq/kg). The Hex and Hin values of the ophiolite samples from Kumluca region have been found to be smaller than 1 which is the limit value. The obtained AED values have been found to be between 12 and 347 μSv/year. Annual gonadal dose equivalence (AGDE) values range between 31 and 960 μSv/year and the excess lifetime cancer risk (ELCR) have been found to be between 0.04 and 1.21 and it does not pose a risk for human health.

The mean values of 40K, 238U(Ra), 232Th, D (nGy/h), Raeq (Bq/kg), Hin, Hex, AED (mSv/year), AGDE (µSv/year). ELCR × 10−4 activities in the study area are given at Table 5.

Table 5 The mean values for 40K, 238U(Ra), 232Th, D (nGy/h), Raeq (Bq/kg), Hin, Hex, AED (mSv/year), AGDE (µSv/year), ELCR × 10−4 for the entire study area
Full size table

At the end of the calculations carried out in all the regions, the mean absorbed dose rates of the ophiolite samples have been determined to be between of 38 and 74 nGy/h which are within the normal limit values. The minimum mean Raeq value has been determined for Kumluca region as 80 Bq/kg while the maximum value has been determined as 158 Bq/kg for Kemer region. The minimum value for AED has been obtained for Kumluca region as 98 mSv/year while the maximum value has been calculated as 194 mSv/year for Kemer region.

The Hex and Hin values of the ophiolite samples from all the regions have been determined to be less than 1 which is the limit value. The highest mean value for the Annual Gonadal Dose Equivalence (AGDE) has been found to be 544 μSv/year for Kemer region. The maximum mean value for the Excess Lifetime Cancer Risk (ELCR) has been determined for Kemer region and it has been calculated as 0.68 × 10−4 which is below the world average (2.9 × 10−4).

The findings of the study have been compared to the values for Turkey and world published in the literature (Table 6) and the mean 226Ra (Bq/kg) value has been determined to be above the world average and 232Th and 40K activity values have been determined to be below the world averages [26, 27].

Table 6 Comparison of measured activity values [27]
Full size table

Results

Considering the mean values of the results obtained from ophiolite samples from Tekirova, Kemer and Kumluca regions (Fig. 2). The highest values have been observed for 40K activity while the lowest values have been observed for 232Th activity. It has been determined that 40K activity concentration has varied between 29 and 986 Bq/kg while the minimum mean value has been calculated as 289 Bq/kg for Kumluca region. The maximum mean value has been calculated as 388 Bq/kg for Kemer region. The maximum 40K activity concentration has been observed as 986 Bq/kg at Kemer S35 sample. The potassium value of the station number S35 in Kemer region, is 2.5 times higher than that of world average which is 400 Bq/kg [27]. The health control of the people living in the region should be taken into consideration.

Fig. 2
figure 2

Ophiolites posing radiation risk to all the regions

Full size image

While the 238U (Ra) activity concentration has varied between 0 and 212 Bq/kg. the minimum mean value has been measured in the Kumluca region as 30 Bq/kg and the maximum mean value has been observed as 69 Bq/kg in Kemer region. The maximum 238U activity concentration has been observed as 212 Bq/kg at Kemer S41 sample. Uranium values of Kumluca region are lower than those of world average. The average uranium value in Kemer region, is about two times higher than that of world average which is 35 Bq/kg [27]. Moreover, the average uranium value in the station number S41 is six times higher than it. Therefore Health control is needed also in the vicinity of this station.

While 232Th activity concentration has been observed to be between 1 and 104 Bq/kg. The minimum mean value has been calculated as 21 Bq/kg for Kumluca region and the maximum mean value has been calculated as 50 Bq/kg for Kemer region. The maximum 232Th activity concentration has been measured as 104 Bq/kg at the Kemer S47 sample. Considering the values of 50 Bq/kg for 226Ra. 50 Bq/kg for 232Th and 500 Bq/kg for 40K [26]. The values of Tekirova S25, Tekirova S30, Tekirova S31, Kemer S33, Kemer S35, Kemer S40, Kumluca S4 and Kumluca S29 samples have been determined to be above the acceptable dose level for the three activity values. The people living in the specified areas are under threat of radiation (Fig. 2).

The mean 226Ra value in Tekirova, Kemer and Kumluca regions has been determined to be 55.70 Bq/kg which is higher than the world average [26, 27]. The mean values for 232Th and 40K in three locations have been determined as 36 Bq/kg and 339 Bq/kg respectively which are below the world average. The mean value of D (Total Dose Rate) for Tekirova. Kemer and Kumluca regions has been calculated as 38–73 Gy/h.

Since the range of world average is between 10 and 200 nGy/h. These figures do not cause a threat in terms of world radiation. The range of AED (Annual Effective Dose Rate) is between 98 and 194 mSv/year and it is less than the accepted limit value which is 460 mSv/year therefore. It does not pose a risk in terms of radiation. The range of Raeq (Radium Equivalent Activity Index) is between 80 and 158 Bq/kg and it is less than the accepted limit value which is 370 Bq/kg. Hex (External Radiation Hazard Index) and Hin (Internal Radiation Hazard Index) values are less than 1 therefore. It does not pose hazard in terms of radiation. Since the values of Excess Lifetime Cancer Risk (ELCR) are below the world average (2.9 × 10−4) for all regions. It does not pose any hazard to human health.

Furthermore, the average value of the study area is very high comparing to the average values of the gabbro and serpentinized peridotite of Bonassola of Bracco-Levanto Ophiolite in Italia [37] and the Troodos Ophiolite Complex in Cyprus [38], considering Antalya region which is one of the most important tourism centers in Turkey. The study is quite important in terms of beginning new to the literature. The study will gain more importance when such studies are made for the other touristic regions in Turkey in the future.