A preliminary study on 226Ra, 232Th, 40K and 137Cs activity concentrations in vegetables and fruits frequently consumed by inhabitants of Elazığ Region, Turkey

Determining radioactivity levels in foodstuffs is of great importance for the protection of human health. In addition, the literature includes few studies related to this subject in Turkey. In this study, gamma spectroscopic system was used in order to measure 226Ra, 232Th, 40K and 137Cs activity concentrations in vegetables and fruits produced in Elazığ Region. The average activity concentrations in vegetables was calculated as 0.64 ± 0.26 Bq kg−1 for 226Ra, 0.65 ± 0.14 Bq kg−1 for 232Th, 13.98 ± 1.22 Bq kg−1 for 40K, and 0.54 ± 0.04 Bq kg−1 for 137Cs. The average activity concentrations in fruits were 1.52 ± 0.34, 0.98 ± 0.23, 18.66 ± 1.13 and 0.59 ± 0.16 Bq kg−1, respectively for 226Ra, 232Th, 40K and 137Cs. Total committed effective dose value was determined as 20 and 30.55 μSv y−1, respectively for vegetables and fruits. The findings were compared with previous data reported for Turkey and other regions of the world.


Introduction
Natural radionuclide concentrations in environmental samples varies according to geographical and geological factors [1]. Natural sources of radioactivity in the environment are called naturally occurring radioactive materials, and are categorized as being of terrestrial or cosmic origin [2]. Humans are exposed to both internal and external radiation from these natural sources. Internal exposure occurs through the intake of terrestrial radionuclides through inhalation or ingestion. Inhalation exposure dose results from the existence of dust particles in air, including radionuclides from 238 U and 232 Th decay series. The biggest contribution to inhalation exposure comes from short half-life decay products of radon. Ingestion exposure dose mostly results from 238 U and 232 Th series radionuclides and 40 K in drinking water and foodstuff. In addition, 137 Cs is the most important fission product released to the environment as a result of nuclear activities, because this radionuclide rapidly passes to foodstuffs and creates a dose effect [3]. The literature includes this type of studies [4][5][6][7][8][9][10]. The aim of this study is to determine the exposure dose of 226 Ra, 232 Th, 40 K and 137 Cs radionuclide concentrations in fruits and vegetables produced in the Elazıg Region of Turkey, which are frequently consumed by local residents. The significance of the study is that it is the first study to determine the background radiation levels in such food products in this region and will provide data for future studies and in case of a nuclear accident (as in Chernobyl nuclear accident) or nuclear fallout, to determine level of contamination.
The province of Elazıg is located in the Eastern Anatolian Region, between longitude 38°30 0 -40°21 0 E and latitude 38°17 0 -39°11 0 N. Its surface area is 9,151 km 2 and the average altitude is 1,067 m. The region is divided into 11 administrative regions, with a total population of 540,000 ( Fig. 1). Approximately 50 % of the province consists of grasslands, 28 % is agricultural land, 12 % forest, and 10 % is dams and lakes. A continental climate prevails; winters are cold and snowy, and summers are hot and arid. The province is rich in mineral resources, and mining activities include copper, fluoride, chalcopyrite, zinc, lead, chrome, manganese, molybdenum, iron and wolfram [11].

Radioactivity measurements in vegetable and fruit samples
Samples of fruits and vegetables produced and frequently consumed in the region were provided from a public market. Any soil or foreign materials on the samples were removed so that they were suitable for consumption, divided into small pieces, and washed under distilled water. They were kept at room temperature for 3 months without allowing any contamination and then totally oven-dried at 105°C. Afterwards, incineration was applied, which was realized through dry ashing. The temperature of the oven was increased to 250°C and was continued until the samples were reduced to ash. The ashed samples were then homogenized and transferred into a plastic container (5 cm height 9 5 cm diameter). Finally, the samples were sealed and stored for a period of about 1 month before counting, in order to allow equilibrium between 226 Ra and its short-lived decay products.
The activity concentrations of 226 Ra, 232 Th, 40 K and 137 Cs radionuclides in vegetable and fruit samples were determined using a gamma spectroscopic system, comprising a 2 00 9 2 00 NaI(Tl) well-type detector and a detector surrounded by a cylindrical lead shield (thickness, diameter and length approximately 3.5, 13.7 and 15.5 cm, respectively). The detector window was made of aluminum of 0.50 mm thickness. Energy calibration of detector was performed by using 60 Co (37 kBq) and 226 Ra (370 kBq) point sources. Photopeak efficiency was 24 %. 226 Ra, 232 Th, 40 K and 137 Cs activity concentrations in vegetable and fruit were based on the detection of 609.3, 583, 1461 and 662 keV energy gamma rays transmitted by 214 Bi, 208 Tl, 40 K and 137 Cs, respectively. The activity concentrations in vegetable and fruit samples were calculated using Eq. (1) where C is the gamma ray count (number per second), e is the detector efficiency of the specific gamma ray, P c is the absolute transition probability of gamma decay and M s is the mass of the sample (kg) [12].

Dose estimation
Ingestion dose occurring through the intake of radionuclides depends on the consumption rate of foodstuff and the concentration of the radionuclide involved. Ingestion dose is calculated with the Eq. (2) where i is foodstuff group, U i and C i r are annual consumption rate (kg) and radionuclide activity concentration (Bq kg -1 ), respectively for their coefficients, and g T;r is dose conversion coefficient for r radionuclide (Sv Bq -1 ). Dose conversion coefficients of 226 Ra, 232 Th, 40 K and 137 Cs radionuclides for the adult members of society are 4.5 9 10 -8 , 2.3 9 10 -7 , 6.2 9 10 -9 and 1.3 9 10 -8 Sv Bq -1 , respectively [13,15,16].
Results and discussion Table 1 shows the natural and manmade radionuclide activity concentrations measured in samples of vegetables and fruits frequently consumed in Elazıg and its surrounding region. Minimum detectable activity values for vegetable and fruit samples were calculated as 0.02 Bq for Effective dose values exposed due to radionuclides taken into body through the consumption of fruit and vegetable samples are shown in Table 2. Primarily, average activity concentration (Bq kg -1 ) for each radionuclide was multiplied by food consumption rate, and annual activity intake value was determined in Bq unit. Food consumption rate was taken as 73 kg a -1 for both fruits and vegetables. This value represents the average consumption for Turkey [17]. The effective dose value was then determined by multiplying annual activity intake value by effective dose coefficient. Effective dose values of fruit samples for all radionuclides ( 226 Ra, 232 Th, 40 K and 137 Cs) were higher than those for vegetable samples. Average effective exposure dose through the consumption of vegetable samples were 2.12 lSv y -1 (SD: 0.86), 11.04 lSv y -1 (SD: 2.3), 6.33 lSv y -1 (SD: 0.55) and 0.51 lSv y -1 (SD: 0.04), respectively for 226 Ra, 232 Th, 40 Table 3 shows committed effective dose values reported for some countries and regions [3,[18][19][20][21]. Total adult  K and 137 Cs radionuclides were calculated as 20 lSv y -1 (SD:3.75) and 30.55 lSv y -1 (SD:5.72), respectively. In summary, this study found that adults living in the study region intake a radiation dose of approximately 50.55 lSv y -1 from fruit and vegetable consumption. This radiation dose (50.55 lSv y -1 ) is lower than the world average value (290 lSv y -1 ) and presents no risk to public health [3]. Dose values obtained in this present study reflect other reported values in general.
Conclusion 226 Ra, 232 Th, 40 K and 137 Cs radionuclide concentrations in vegetables and fruits that are produced and frequently consumed in the Elazıg Region of Turkey were determined in this study. It was found that the radiation dose due to consumption of vegetables and fruits was less than the world average, and poses no threat to public health. The results were lower than the committed effective dose values reported for various regions and countries.