Measurement of NORM in Building Materials to Assess Radiological Hazards to Human Health and Develop the Standard Guidelines for Residents in Thailand: Case Study in Sand Samples Collected from Seven Northeastern Thailand Provinces

: A total of 223 sand samples collected from seven provinces in Northeastern Thailand were analyzed for their gamma radioactivity from naturally occurring radioactive materials (NORMs), and the data were used to calculate the concentrations of Ra-226, Th-232, and K-40. Radiological safety indicators such as the indoor external dose rates ( D in ), the annual indoor effective dose ( E in ), the activity concentration index ( I ), the radium equivalent activity ( Ra eq ), the external hazard index ( H ex ), the internal haphazard index ( H in ), and the excess lifetime cancer risk ( ELCR ) were calculated. The activity concentrations were found to be 36 ± 10 Bq/kg for Ra-226, 2.64 ± 0.58 Bq/kg for Th-232, and 323 ± 168 Bq/kg for K-40. D in is 62 ± 23 nGy/h. The E in is 0.30 ± 0.11 mSv/y. The activity concentrations and other indicators were reported by each province and compared with the safety standards and are found to be within the safe limits in this study. The results can be used to develop the standard guideline levels for choosing building materials in Thailand. These results can be used to develop the standard guideline levels for choosing


Introduction
Building materials such as rock, soil and sand are formed from the earth's crust, enriched with naturally occurring radioactive materials (NORMs). The main radionuclides in NORMs are long-lived radionuclides such as uranium-238 (U-238), thorium-232 (Th-232), radium-226 (Ra-226), and potassium-40 (K-40), etc. These radioisotopes are the main external source of irradiation that enters the human body [1]. Klepeis et al. (2001) investigated how humans might be impacted by pollutants in our various indoor and outdoor environments by assessing the time humans spend in various locations. This study found that normally human beings spend nearly 90% of their time indoors [2]. Therefore, their exposure to radiation in the residence is strongly related to the radioactivity from building materials [3]. The health risk concern when they are exposed to NORMs is regarded as the potential for developing cancer, because the emitted ionizing radiation is a known carcinogen [3]. Thus, an increase in exposure to ionizing radiation results in an increased risk of developing cancer. So far, several reported activity concentrations are relatively low compared with NORMs from the mineral industry; even though the ICRP 1990 reported that the chronic exposure of low doses from ionizing radiation can increase the risk of health damage to individuals, which may occur decades after exposure [4]. The annual effective dose of public exposure does not exceed the dose limit (1 mSv/y) recommended from ICRP publication 103 [5]. Building materials have been recommended by several organizations to have their radioactivity measured before being put on the market, especially by the EU Basic Safety Standards (EU-BSS), Standard GB 6566-2001 (limits of radionuclides in building materials) and other national standards. The EU-BSS requires the determination of activity concentration (Ra-226, Th-232 and K-40) in building materials and the index (I) value to be less than one [6,7]. The index value of one can be used as a conservative screening tool for identifying materials that during their use would cause doses exceeding the reference level (1 mSv/y excess in addition to outdoor exposure) in the case of a bulk amount inbuilt [7]. Furthermore, the IAEA Specific Safety Guide No. SSG-32 proposes the use of an activity concentration index as a screening tool for identifying building materials that may need to be subject to restrictions. The limit values of the index (I) depend on the dose criterion adopted and the use of the material ( Table 1). Table 1. Limit values for the index (I) [8].

Does Criterion
0.3 mSv/y 1 mSv/y Materials used in bulk amounts, e.g., concrete I ≤ 0.5 I ≤ 1 Superficial and other materials with restricted use: tiles, boards, etc.
The building materials on sale in Thailand consist of raw materials from both local production and abroad. The radionuclide concentrations in building materials in Thailand were reported to be within a wide range. There are currently no standard or safety limits of radionuclides in building materials to control production or the importing of building materials into the country. Sand is a component of many building materials in Thailand such as cement, concrete, block bricks, brick, sandstone tiles, land reclamation, etc. Many researchers worldwide reported the different levels of NORMs in the sand samples of their country. Xinwei and Xiaolan (2006) [9] reported levels of the natural radioactivity from the Baoji Weihe Sand Park, China; the radioactivity concentration of the sand ranges from 10 to 38 Bq/kg for Ra-226, 27 to 48 Bq/kg for Th-232 and 635 to 1127 Bq/kg for K-40. Vasconcelos et al. (2011) [10] reported that the activity concentrations of Ra-226, Th-232 and K-40 in beach sand ranged from 8 to 8300 Bq/kg, from 21 to 18,450 Bq/kg, and from 3 to 3110 Bq/kg, respectively. Malain et al. (2010) [11] reported that the levels of the activity concentrations of Ra-226, Th-232, and K-40 in beach sand samples along the Andaman coast of Thailand were found to lie in the range of 3 ± 0.1 to 24 ± 0.1, 3 ± 0.1 to 35 ± 1, 11 ± 1 to 654 ± 22 Bq/kg, respectively. Most studies reported the levels of radionuclides in beach sand, whereas only a small number of papers reported the radionuclides in sand from building materials. Although the database of activity concentrations of radionuclides in sand for construction and the estimations of the haphazard index are more beneficial in terms of human health, because several reports indicated that the building materials are the main external and internal source of indoor irradiation.
The aim of this research is to determine the natural radionuclides levels in sand samples which are used in Thailand. These samples were collected from seven Northeastern Thailand provinces to analyze the activity concentration of major NORM isotopes, Ra-226, Th-232, and K-40, and to use these values to calculate the indoor external dose rates (D in ), the annual indoor effective dose (E in ), the activity concentration index (I) and the radium equivalent activity (Ra eq ) for the gamma radiation emitted by the building materials and to assess the health hazard indices such as the external hazard index (H ex ), the internal haphazard index (H in ), and the excess lifetime cancer risk (ELRCA). The determination of Ra-226, Th-232, and K-40 values and other indicators of each province were estimated. These results can be used to develop the standard guideline levels for choosing building materials in Thailand.

Study Area
This study is part of a research project which aims to measure the radioactivity of building materials used in Thailand. The database can be used to develop the standard guideline levels in Thailand. In this study, all sand samples were collected from Loei, Nong Bua Lam Phu, Khon Kaen, Nakhon Ratchasima, Nong Khai, Bueng Kan, and Sakhon Nakhon provinces in Northeastern Thailand. The studied area can be divided into four zones: the upper northeast province group 1 (Loei, Nong Bua Lam Phu, Nong Khai, Bueng Kan), the upper northeast province group 2 (Sakon Nakhon), the central northeast province (Khon Kaen), and the lower northeast province group 1 (Nakhon Ratchasima). The fifth zone, lower northeast province group 2, was planned but due to the COVID-19 situation, we were not able to obtain samples from this zone. Khon Kaen, Nakhon Ratchasima and Sakhon Nakhon are large cities and trade centers including the building material center of the northeast. The sand samples were collected by random sampling to determine the natural radionuclide levels in sand samples from each zone in Northeastern Thailand. The study areas are shown in Figure 1.
These results can be used to develop the standard guideline levels for choosing building materials in Thailand.

Study Area
This study is part of a research project which aims to measure the radioactivity o building materials used in Thailand. The database can be used to develop the standard guideline levels in Thailand. In this study, all sand samples were collected from Loei Nong Bua Lam Phu, Khon Kaen, Nakhon Ratchasima, Nong Khai, Bueng Kan, and Sakhon Nakhon provinces in Northeastern Thailand. The studied area can be divided into four zones: the upper northeast province group 1 (Loei, Nong Bua Lam Phu, Nong Khai Bueng Kan), the upper northeast province group 2 (Sakon Nakhon), the central northeas province (Khon Kaen), and the lower northeast province group 1 (Nakhon Ratchasima) The fifth zone, lower northeast province group 2, was planned but due to the COVID-1 situation, we were not able to obtain samples from this zone. Khon Kaen, Nakhon Ratchasima and Sakhon Nakhon are large cities and trade centers including the building material center of the northeast. The sand samples were collected by random sampling to determine the natural radionuclide levels in sand samples from each zone in Northeastern Thailand. The study areas are shown in Figure 1.

Sample Collection and Preparation
The sand samples were obtained from local residents of each province, weighing about 2 kg per sample. The samples were bought from local building material stores. Sand samples were kept in plastic bags and labelled by the sample code and province along with the geographical coordinate of each sampling point by global positioning system (GPSmap 78 s, Garmin). Sand samples (shown in Figure 2) were sifted out from the rubble and dried in an oven at 105 • C for 24 h, then the dried samples were packed in fully cylindrical plastic containers which were sealed with silicone glue and PVC tape, dry weighed and kept for one month.

Sample Collection and Preparation
The sand samples were obtained from local residents of each province, weighing about 2 kg per sample. The samples were bought from local building material stores. Sand samples were kept in plastic bags and labelled by the sample code and province along with the geographical coordinate of each sampling point by global positioning system (GPSmap 78 s, Garmin). Sand samples (shown in Figure 2) were sifted out from the rubble and dried in an oven at 105 °C for 24 h, then the dried samples were packed in fully cylindrical plastic containers which were sealed with silicone glue and PVC tape, dry weighed and kept for one month.

Gamma-Ray Detector and Calibration
Natural radioactivity was measured using a high-purity germanium (HPGe) gammaray detector (Oxford, USA) with a relative efficiency of 30%. The energy resolution (FWHM) of the detector is 2 keV at 1332 keV of a Co-60 source. The energy and efficiency calibration of the detector were carried out using certified reference materials IAEA-RGU-1 and IAEA-RGTh-1. The detector was shielded with 10 cm of lead to reduce gamma radiation from the environment and interferences with the radiation metering system.

Radioactivity Measurement, Dose and Hazard Index Calculation
Samples in Marinelli containers were counted for their gamma radioactivity for 80,000 s per sample. Background radiation counts were obtained with a blank Marinelli container under the same conditions before the measurement of samples. The average of the background counts was subtracted from the sample spectrum. The gamma-ray photo peaks corresponding to 186 keV, 911 keV, 1460 keV corresponded to the emitted gamma from Ra-226, Th-232, K-40, respectively. The activity concentration ( ) in the sand samples was calculated using the following equation [12]: where is the net gamma count rate (count per second), ε is the detector efficiency of a specific gamma ray, is the intensity of the gamma line in radionuclides, and is the mass of the sand sample in kilograms. We assumed that in this case these sand samples

Gamma-Ray Detector and Calibration
Natural radioactivity was measured using a high-purity germanium (HPGe) gammaray detector (Oxford, USA) with a relative efficiency of 30%. The energy resolution (FWHM) of the detector is 2 keV at 1332 keV of a Co-60 source. The energy and efficiency calibration of the detector were carried out using certified reference materials IAEA-RGU-1 and IAEA-RGTh-1. The detector was shielded with 10 cm of lead to reduce gamma radiation from the environment and interferences with the radiation metering system.

Radioactivity Measurement, Dose and Hazard Index Calculation
Samples in Marinelli containers were counted for their gamma radioactivity for 80,000 s per sample. Background radiation counts were obtained with a blank Marinelli container under the same conditions before the measurement of samples. The average of the background counts was subtracted from the sample spectrum. The gamma-ray photo peaks corresponding to 186 keV, 911 keV, 1460 keV corresponded to the emitted gamma from Ra-226, Th-232, K-40, respectively. The activity concentration (C) in the sand samples was calculated using the following equation [12]: where C a is the net gamma count rate (count per second), ε is the detector efficiency of a specific gamma ray, I e f f is the intensity of the gamma line in radionuclides, and M s is the mass of the sand sample in kilograms. We assumed that in this case these sand samples will be used as a component of building materials. Thus, the indoor external dose and the annual indoor effective dose were used to calculate the other indicators in this study. The indoor external dose rates (D in ) in (nGy/h) could be obtained from the following equation (UNSCEAR, 2000) [3]: where A Ra , A Th , and A K are the activity concentration of Ra-226, Th-232 and K-40 in (Bq/kg), respectively. The annual indoor effective dose (E in ) in (mSv/y) is determined as follows (UNSCEAR, 2000) [3]: where D in is the indoor external dose rate in (nGy/h), 8760 is the number of hours in a year, 0.7 (Sv/Gy) is the conversion factor, which convert the absorbed dose rate in the air to the human effective dose, and 0.8 is the indoor occupancy factor. The E in value should be <1 mSv/y. The European Commission (EC) proposed an index called the gamma index (I) to verify whether the guidelines of the EC for building materials usage are met. I is calculated using the following formula (EC, 1999) [13]: The radium equivalent activity (Ra eq ) is an evaluation index of the radiation hazard associated with the building materials used. Assuming that all of the decay products of Ra-226 and Th-232 are in radioactive equilibrium with their precursors, Ra eq is calculated from the formula below [14]. The Ra eq value should be ≤370 Bq/kg.
The external hazard index (H ex ), is an assessment of the excess gamma radiation from the building materials. H ex was calculated using the following Equation [14]: The value of H in should be below 1 to ensure the safe use of building materials, which corresponds to the upper limit of Ra eq (370 Bq/kg).
The internal haphazard index (H in ) is an assessment of the excess radiation due to radon from the building materials. H in can be used for considering the excess internal radiation due to the inhalation of Rn-222 and its short-lived decay products from building materials, which is determined as [15]: where A Ra , A Th , and A K in Equations (2) and (4)-(7) are the activity concentration of Ra-226, Th-232 and K-40 in (Bq/kg), respectively. The value of H in should be ≤1. The excess lifetime cancer risk (ELCR) due to radioactive exposure form spending a lifetime in residences with these sand mixtures was calculated using the following equation [16,17]: The ELCR values do not indicate a level that safe or acceptable.
where AEDE is the annual effective dose equivalent (mSv/y), DL is an average duration of life (70 y), and RF is a risk factor (Sv −1 ), the fatal cancer risk per Sievert. For stochastic effects, ICRP60 uses the value of 0.05 for the public [4].

Results and Discussion
The activity concentrations of Ra-226, Th-232, and K-40 in sand samples are shown as a box distribution (Figure 3). Loei has only two samples. For Loei, Th-232 values are quite different.

Results and Discussion
The activity concentrations of Ra-226, Th-232, and K-40 in sand samples are shown as a box distribution (Figure 3). Loei has only two samples. For Loei, Th-232 values are quite different.  The activity concentrations of Ra-226, Th-232, and K-40 are reported in map format to report the level of NORM concentration in sand samples used in building construction in different provinces (Figure 4). This map with the data of radionuclides from every province of Thailand will be complete in 2022. The map will be useful for selecting building materials in Thailand in the future.  The activity concentrations of Ra-226, Th-232, and K-40 are reported in map format to report the level of NORM concentration in sand samples used in building construction in different provinces (Figure 4). This map with the data of radionuclides from every province of Thailand will be complete in 2022. The map will be useful for selecting building materials in Thailand in the future.  The average results of the activity concentrations of Ra-226, Th-232, and K-40 (C) are shown in Table 2 and the indoor external dose rates (D in ), the annual indoor effective dose (E in ), the activity concentration index (I) the radium equivalent activity (Ra eq ), the external hazard index (H ex ), the internal haphazard index (H in ), and the excess lifetime cancer risk (ELCR) are shown in Table 3.
The average results of this study were compared with reports of Ra-226, Th-232, and K-40 concentrations and D in , E in , I, Ra eq , H ex and H in values from sand samples in the different countries, the world averages, and the guideline levels (Table 4).  Atmosphere 2021, 12, 1024 9 of 12 The lowest activity concentrations of Ra-226 and K-40 were 2, 0.31, and 9 Bq/kg, respectively, found at Khon Kaen; the lowest activity concentrations were found at Nakhon Ratchasima for Th-232 (0.31 Bq/kg). The highest activity concentrations of Ra-226, Th-232, and K-40 were found at Bueng Kan (89 Bq/kg), Loei (20 Bq/kg), and Nakhon Ratchasima (814 Bq/kg), respectively. Sand samples for building materials brought from Khon Kaen were found to have low activity concentrations of Ra-226, Th-232, and K-40. The lowest and highest values of E in , I, Ra eq , H ex , H in , and ELCR are consistent with the D in value.
The lowest values of D in , E in , I, Ra eq , H ex , H in , and ELCR were 23 ± 13 nGy/h, 0.11 ± 0.07 mSv/y, 0.09 ± 0.05, 25 ± 14 Bq/kg, 0.07 ± 0.04, 0.12 ± 0.07, and 0.40 ± 0.23, respectively, found at Khon Kaen. The highest values of D in , E in , I, Ra eq , H ex , H in , and ELCR were 84 ± 9 nGy/h, 0.41 ± 0.05 mSv/y, 0.33 ± 0.03, 87 ± 10 Bq/kg, 0.24 ± 0.03, 0.32 ± 0.05, and 1.44 × 10 −3 respectively, found at Nong Bua Lum Phu. The four measured quantities (activity concentrations of Ra-226, Th-232, and K-40, and the annual indoor effective dose) are used to cluster the data from each province (excluding Loei due to low number of measurements) into two dimensions by principal component analysis (PCA) (see Figure 5). Because the values from the provinces are not that different, the province clusters are not clearly separated. The PCA diagram shows that radioactive (Ra-226, Th-232, K-40, and E in ) levels in sand samples collected from the neighboring provinces are in the same range, with Sakon Nakhon results being perhaps the most different from others. The lowest activity concentrations of Ra-226 and K-40 were 2, 0.31, and 9 Bq/kg, respectively, found at Khon Kaen; the lowest activity concentrations were found at Nakhon Ratchasima for Th-232 (0.31 Bq/kg). The highest activity concentrations of Ra-226, Th-232, and K-40 were found at Bueng Kan (89 Bq/kg), Loei (20 Bq/kg), and Nakhon Ratchasima (814 Bq/kg), respectively. Sand samples for building materials brought from Khon Kaen were found to have low activity concentrations of Ra-226, Th-232, and K-40. The lowest and highest values of , , , , , and ELCR are consistent with the value. The lowest values of , , , , , , and ELCR were 23 ± 13 nGy/h, 0.11 ± 0.07 mSv/y, 0.09 ± 0.05, 25 ± 14 Bq/kg, 0.07 ± 0.04, 0.12 ± 0.07, and 0.40 ± 0.23, respectively, found at Khon Kaen. The highest values of , , , , , , and ELCR were 84 ± 9 nGy/h, 0.41 ± 0.05 mSv/y, 0.33 ± 0.03, 87 ± 10 Bq/kg, 0.24 ± 0.03, 0.32 ± 0.05, and 1.44 × 10 −3 respectively, found at Nong Bua Lum Phu. The four measured quantities (activity concentrations of Ra-226, Th-232, and K-40, and the annual indoor effective dose) are used to cluster the data from each province (excluding Loei due to low number of measurements) into two dimensions by principal component analysis (PCA) (see Figure 5). Because the values from the provinces are not that different, the province clusters are not clearly separated. The PCA diagram shows that radioactive (Ra-226, Th-232, K-40, and ) levels in sand samples collected from the neighboring provinces are in the same range, with Sakon Nakhon results being perhaps the most different from others. The mean values of activity concentrations from seven province in Northeastern Thailand ( ) were 36 ± 10, 2.64 ± 0.58, and 323 ± 168 Bq/kg for Ra-226, Th-232, and K-40, The mean values of activity concentrations from seven province in Northeastern Thailand (C) were 36 ± 10, 2.64 ± 0.58, and 323 ± 168 Bq/kg for Ra-226, Th-232, and K-40, respectively. The mean indoor external dose rates value (D in ) is 62 ± 23 nGy/h. The world averages are 35, 30, and 400 Bq/kg, and 51 nGy/h for Ra-226, Th-232, K-40, and the absorbed dose rates, respectively, as reported by the United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR, 2000) [3]. The mean values of Ra-226 and K-40 in the sand samples are close to the world averages; whereas, the mean value of Th-232 in sand samples is much lower than the world average.
The average indoor annual effective dose (E in ) is 0.30 ± 0.11 mSv/y which is lower than the dose limit of 1 mSv/y recommended by the International Commission on Radio-logical Protection (ICRP) (ICRP, 2007) [5]. The index (I) was found to be 0.24 ± 0.09. These results were within the guideline levels of the EU-BSS: I ≤ 1 for materials used in bulk, and I ≤ 6 for superficial materials (Council of the European Union, 2013). An I lower than 1 indicates that the annual effective dose is less than 1 mSv. The radium equivalent activity (Ra eq ) was 64 ± 23 Bq/kg which does not exceed the limit of 370 Bq/kg recommended by UNSCEAR, 2000. The external hazard index and the internal haphazard index values are 0.17 ± 0.06 and 0.26 ± 0.08. The value of the index H ex should be ≤1, the maximum level of H ex corresponds to the upper limit of Ra eq (370 Bq/kg) to hold the radiation hazard as insignificant. The value of the index H in should be ≤1 to keep the radon and its daughter concentrations safe enough for human respiratory organs. The excess lifetime cancer risk (ELCR) was found to be 1.06 × 10 −3 . The world average value of ELCR was 0.29 × 10 −3 reported by UNSCEAR, 2000 [3].
The results can be used to develop the standard guideline levels for choosing building materials in Thailand.

Conclusions
Sand samples collected from Loei, Nong Bua Lam Phu, Khon Kaen, Nakhon Ratchasima, Nong Khai, Bueng Kan, and Sakon Nakhon provinces of Northeastern Thailand were measured using an HPGe gamma-ray detector to determine the activity concentrations, dose and hazard index values. The average activity concentrations are found to be 36 ± 10 Bq/kg for Ra-226, 2.64 ± 0.58 Bq/kg for Th-232, and 323 ± 168 Bq/kg for K-40. The indoor external dose rate (D in ) is 62 ± 23 nGy/h. The world averages are 40, 40, and 370 Bq/kg and 51 nGy/h for Ra-226, Th-232, and K-40 concentrations, and the absorbed dose rates, respectively (UNSCEAR2000). The average indoor annual effective dose (E in ) is 0.30 ± 0.11 mSv/y which is lower than the dose limit of 1 mSv/y recommended by ICRP. The index (I) and radium equivalent activity (Ra eq ) were 0.24 ± 0.09 Bq/kg and 64 ± 23 Bq/kg, respectively. The results showed that the index (I) is lower than the standard levels of the EU-BSS: I ≤ 1, indicating the radium equivalent activity (Ra eq ) does not exceed 370 Bq/kg as recommended by UNSCEAR 2000. The results of radiation hazard indices H ex , H in are 0.17 ± 0.06, and 0.26 ± 0.08, respectively. The values of the indices H ex and H in are within the guideline level of 1 recommended by EU. The excess lifetime cancer risk (ELCR) if the sand is used indoor was found to be 1.06 × 10 −3 which is higher than the world average value of ELCR (0.29 × 10 −3 ). It can be implied from the results that using sand in a large quantity in a closed room may increase the risk of lung cancer and mitigation measures should be applied. The project will collect more samples to measure and add to the database. The results will be used to develop the standard guideline levels for choosing building materials in Thailand.
Author Contributions: P.S. is responsible for measurement the naturally occurring radioactive materials in this research, as well as designing the experiment, calculating, interpreting the data and wrote the manuscript. R.P. is responsible for data analysis, visualization, and manuscript revision. S.T. and C.K. (Chutima Kranrod) designed, reviewed, and made recommendations on this manuscript. U.I. and C.K. (Chunyapuk Kukusamude) are responsible for sample preparation and measurement of naturally occurring radioactive materials and calculated the net count of radionuclides from all samples in this research. All authors have read and agreed to the published version of the manuscript.

Funding:
The research funding was supported by the Thailand Institute of Nuclear Technology (Public Organization) or TINT under the Ministry of Higher Education, Science, Research and Innovation, Thailand.

Data Availability Statement:
The measurement data is available upon request, an email phachi-rarats@tint.or.th.