ESEARCH ARTICLE R ScienceAsia 47S (2021): 120–129 doi: 10.2306/scienceasia1513-1874.2021.S016 Measurement of radionuclides in surface soil and beach sand samples from Rayong Province (Thailand) and the evaluation of excess lifetime cancer risk a, a b Prasong Kessaratikoon ∗, Ruthairat Boonkrongcheep , Sitthipong Polthum a Nuclear and Material Physics Research Unit, Department of Basic Science and Mathematics, Faculty of Science, Thaksin University, Songkhla 90000 Thailand b Thailand Institute of Nuclear Technology (Public Organization), Ongkharak, Nakhon Nayok 26120 Thailand ∗Corresponding author, e-mail: [email protected] Received 11 Nov 2020 Accepted 18 Jun 2021 ABSTRACT: Specific activities of natural (40K, 226Ra, and 232Th) and anthropogenic (137Cs) radionuclides in 230 surface soil and beach sand samples collected from the densely populated areas of industrial activities in Rayong Province, Thailand, were analyzed. Experimental results were obtained using a high-purity germanium detector and gamma spectrometric analysis system. The frequency distributions of the four radionuclides were investigated and calculated as suitable medium values of all distributions. According to asymmetrical distribution, medium values of the specific activities of all required radionuclides should be median values. Furthermore, the median values of the three natural radionuclides were also used to evaluate absorbed dose rates in the air (D), radium equivalent (Raeq), external hazard index (Hex), annual effective dose rate (AEDout), and excess lifetime cancer risk (ELCR) in the studied areas. The results were compared with data obtained from the annual report of Thailand’s Office of Atoms for Peace, the global radioactivity measurements, and the evaluations and recommended values proposed by the United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR). It was found that most of the results were significantly lower than the recommended values of UNSCEAR except for the median value of specific activity of 226Ra. Moreover, the radioactive contour map for the investigated areas was constructed. KEYWORDS: radionuclides, high-purity germanium detector, gamma-ray spectrometry, radiological hazard index, excess lifetime cancer risk INTRODUCTION Product (GDP). Moreover, Rayong Province has been recently selected as one of the three provinces, Rayong Province, located in Eastern Thailand, has besides Chonburi and Chachoengsao, promoted for played an important role as part of the Eastern industrial progress in the Eastern Economic Corridor Seaboard Development Project since 1982. It is (EEC) Project. As a result, Rayong Province is an a gateway for the Northeast region to send prod- area of continuous industrial development, and a ucts to foreign countries without passing through significant increase in number of factories in parallel Bangkok. The Thai government has prepared a with an increase in accidents in this area is foreseen. complete basic utility system and designated Map There are seven refineries for crude oil refining Ta Phut, Mueang District, Rayong Province as a industry in Thailand. Almost all are located in location of the industrial estate. The primary in- the eastern part of the country. Oil refinery is dustries in Rayong Province are natural gas sepa- classified as one of fourteen types of high-polluting ration plants, petrochemical industry, and chemical plants according to the Notification of the Ministry fertilizer industry. Hence, the province comprises of Industry in the year 2002 [3]. Although oil industrial estates jointly operated with many private refining provides enormous benefits to humans, it individuals, industrial areas, industrial communi- also causes many environmental pollutants and, in ties, and industrial parks, thus having a high po- particular, an increase or build-up of radioactive tential for industrial investment and rapid industrial materials in the environment. The existence of development [1,2 ]. It creates a total annual value radioactive materials coincides with the creation of of almost one-third of Thailand’s Gross Domestic the Earth. Therefore, rocks and sand on the Earth’s www.scienceasia.org ScienceAsia 47S (2021) 121 surface and crude oil, caused by the deposition of neighboring Chonburi Province to the north-west, fossil in the shale beneath the Earth’s surface for mil- Chanthaburi Province to the north-east, and the Gulf lions years, are composed of radioactive substances of Thailand to the south. The province is divided [4,5 ]. Measuring the amount of radioactivity in the into eight districts: Mueang, Ban Chang, Nikhom area where the manufacturing industry is located Phatthana, Pluak Daeng, Ban Khai, Wang Chan, has been a point of interest worldwide, especially Khao Chamao, and Klaeng Districts. The population to monitor the concentration of natural and ar- of Rayong Province was 723,316 in 2018. tificial radionuclides in the environment 6–10 . [ ] Surface soil and beach sand sample collection In the United States, State and Federal regulatory and preparation agencies have developed guidelines for controlling naturally occurring radioactive materials that will Two hundred surface soil samples (yellow color) adequately protect health of the public and the en- were collected from populated areas in the eight vironment [11]. The European Union (EU) has also districts (Fig. 1). At the same time, 30 beach sand focused on the survey and measurement of radioac- samples (blue color) were collected from Mae Ram tive substances from oil and gas productions among Phueng Beach located in the south of Mueang Dis- the the EU member states [12]. In addition, the trict of the studied area. The collected surface soil Safety Report Series 34 of the International Atomic samples were ground and homogenized and air- Energy Agency (IAEA) also provides information on dried for several days. In the meantime, the beach the naturally occurring radioactive substances in oil sand samples were taken to dry in the ambient and gas productions [13]. environment for 2–3 days. Both the surface soil Generally, the geology of Rayong Province is not and the beach sand samples were placed in an oven quite intricate. Two principal rock types, namely at 100 °C for at least 3 h to eliminate any traces sedimentary rocks and igneous rocks, are found of water and, then, were sieved through a 2 mm in the area. Granitic rock, which is one type of mesh-sized. Approximately 420 g of each meshed igneous rock mainly Triassic in age, underlines ap- surface soil and beach sand sample was removed to proximately 20% of the area. Hence, some natural a PVC (8.2 cm 7.5 cm) cylindrical container. The radionuclides such as 226Ra, 232Th, and 40K might container was sealed× hermetically and externally us- be accumulated in this area. The distribution of ing cellophane tape and left for about four weeks to these radionuclides has proved to be important in ensure equilibrium between 226Ra and its daughters 228 estimating the level of natural background radiation and Ra and its daughters [15]. to which humans are exposed 14 . [ ] Measurement, analysis, and frequency For this reason, we were interested in the mea- distribution of specific activities surement and analysis of background radioactivity of Rayong Province. The aim was to measure The specific activities of natural (226Ra, 232Th, and and analyze specific activities of natural radioactive 40K) and anthropogenic (137Cs) radionuclides in nuclides (226Ra, 232Th, and 40K) and man-made ra- 230 surface soil and beach sand samples were de- dioactive nuclides (137Cs) in surface soil and beach termined using a high-purity germanium detector sand samples collected from eight districts in Ray- (HPGe, EG&G ORTEC Model GEM 20 P4) and ong Province. The frequency distribution and some gamma spectrometric analysis system at the Thai- medium values of all measured specific activities land Institute of Nuclear Technology (Public Or- were investigated. Then, some interesting radio- ganization) (TINT). The detector was enclosed in logical hazard indices and ELCR value were also a massive 10-cm thick lead shielding. The con- evaluated using the suitable medium values from tainer’s geometric efficiency for soil matrices was the frequency distribution values. Moreover, the determined by the IAEA Soil-375 reference mate- radioactive contour maps (RCM) of all radioactive rials (International Atomic Energy Agency IAEA, nuclides were created. Vienna, Austria). Gamma-ray energies of 214Pb (351.9 keV), 214Bi (609.3, 1764.5 keV), and 226Ra MATERIALS AND METHODS (185.99 keV) were used to estimate the specific 226 activities of Ra [16]. Evaluation of specific ac- Studied areas tivities of 232Th was from gamma-lines of 212Pb Rayong Province, one of the seven provinces in (238.6 keV) and 228Ac (338.4, 911.07, 968.90 keV). 40 137 Eastern Thailand, is located at 12°40051.400 N lat- The specific activities of K and Cs in all samples itude and 101°15028.700 E longitude (Fig. 1) with were evaluated from gamma energies 1460.8 and www.scienceasia.org 122 ScienceAsia 47S (2021) Fig. 1 Geographical map of Rayong Province and sampling locations. 212Pb (283.6 keV) 228Ac (338.4 keV) 208Tl (583.2 keV) 214Pb (351.9 keV) 214 226 Bi (609.3 keV) Ra (185.99 keV) 228Ac (911.07 keV) 40 137Cs (661.7 keV) K (1460.8 keV) 214Bi (1764.5 keV) 228Ac (968.90 keV) Counts Energy (keV) Fig. 2 The gamma-ray energy spectrum of surface soil sample collected from Klang District, Rayong Province. www.scienceasia.org ScienceAsia 47S (2021) 123 661.7 keV of themselves, respectively (Fig. 2). The (AEDout (mSv/y)) [17] could be determined by SPSS computer program was employed to analyze Eq. (5): the frequency distribution of specific activities of 226 232 40 137 6 Ra, Th, K, and Cs radionuclides. The re- AEDout = D 8760 0.2 0.7 10− . (5) sults were compared with existing data in Thailand × × × × and global measurement and evaluation. Then the excess lifetime cancer risk (ELCR) (out- door) [21] was also evaluated for the investigated Evaluation of radiological hazard indices and area as shown in Eq.