Introduction

Daily homo life routines cannot exist separated from radiation exposure, especially natural radiation exposure. The radioactive elements in the earth'southward crust that atomic number 82 to human exposure are potassium (40K), uranium (238U), thorium (232Thursday), and their radioactive decay products, e.g., radium (226Ra) and radon (222Rn)1,ii,iii. Residents in some areas are exposed to radiation doses that are higher than the global annual mean radiation dose (around two.4 mSv) past one to 2 orders, and a few regions are loftier natural background radiation areas (HNBRAs) with potential annual effective doses which are even higher than the 20 mSv dose limit for radiations workers4,five.

UNSCEAR reported4 that measurements in HNBRAs were important for radiation protection of their residents and for environmental radiations protection. Health studies of populations living in HNBRAs are a potential source of information on the effects of chronic depression-dose-charge per unit exposures. Although the studies of diminutive bomb survivors provide potent evidence of health effects such as cancer and non-cancer diseases associated with single acute exposure to moderate to high doses of ionizing radiations, the upshot of low dose-rates on wellness and cancer risks afterward exposure to ionizing radiation is, as yet, unclear. Based on these circumstances, it is necessary to brand a comprehensive ecology assessment of the existing exposure situation in a HNBRA to become scientific show of health effects due to chronic low-dose-charge per unit radiation exposure.

Some studies on HNBRAs of Brazil, Mainland china, India, and Iran have been made in recent years4,six,seven,eight,nine. High radiation exposure levels can cause radiation-induced diseases such equally cancer10. Additionally, it is important to note that the incidence of non-cancer diseases such as cerebrovascular diseases, tuberculosis, and digestive system diseases that was found in Yangjiang, Cathay had a meaning impact from the HNBRAiii,eleven. Likewise as radiation exposure doses due to natural radionuclides, such contaminants as toxic heavy metals are important. Heavy metallic pollution has been discussed in areas with high natural radionuclides in the soil, such as areas around uranium mines and HNBRAs12.

In 2015, the Un established the Sustainability Development Goals (SDGs) program for the sustainable evolution of human being benefits including good wellness and well-being, clean water and proper sanitation every bit well every bit responsible consumption and product13. Natural radiations and heavy metals in the environment can be viewed equally natural pollution. They can be nowadays in the human trunk from both internal and external sources, and they tin affect human Deoxyribonucleic acid. In addition, natural radiation and heavy metals also enter the ecosystem (h2o, air, soil, plants and animals) naturally and by human activities and then that the quality of life and the health of residents in HNBRAs are affected. This becomes a challenge for coming together the SDGs.

According to the ambient dose equivalent rate map of Republic of indonesia, as shown in Supplementary Figure S1fourteen, the ambience dose equivalent rate in Mamuju is quite high when compared to other regions. For example Takandeang Village had measured rates betwixt 100 and 2800 nSv h−1 xv. This paper presents the first study that comprehensively explains exposure assessments for the whole Mamuju region from the viewpoints of health and human activities. We measured all parameters that contribute to external and internal radiation exposures caused past radionuclides, especially heavy metal radionuclides and including label exposure. Our goals were (one) characterizing exposure of the whole Mamuju region as for a HNBRA; (2) assessing the existing exposure to assure radiations protection of the public; and (3) providing the main input for an epidemiological written report. This study is unlike previous studies that looked at several specific areas and had limited telescopic such as: the preliminary survey on Botteng Village, Mamuju16; the preliminary study on cytogenetics biomarkers17; radon (222Rn) and thoron (220Rn) measurements in Takandeang Village18; radioactivity measurements in soil samples and ambient dose equivalent charge per unit in Northern Botteng Villagexix,20; radium measurements in drinking water21; and radioactive mineral explorations in Mamuju22,23. The limitation of this paper is that the dose contribution of 210Po has not been determined.

Results

Lifestyle and consumption behaviors

Generally, daily life in Mamuju is dependent on nature. Almost residents work outdoors and swallow food that is mainly locally grown or produced or that comes from traditional markets. The drinking water sources for almost 86% of the residents are wells and springs, and merely a small percentage buy bottled drinking water. The drinking water addiction is consuming it directly without boiling. Hence, the Mamuju residents are vulnerable to becoming contaminated by natural radionuclides and heavy metals, so it is important to measure the quality of drinking water, following the SDGs mandates to ensure cleanliness of drinking water and feasibility of sanitation. From our questionnaire, we establish that the average consumption of drinking water per mean solar day was 1.6 Fifty.

Natural radionuclide activity concentration in soil samples

The concentration of natural radionuclides in soil samples in the Mamuju region is very high. The average activity concentrations of 238U, 232Th and 40K were 1387 Bq kg−1, 1468 Bq kg−1, and 301 Bq kg−1, respectively. The 238U activeness concentration ranged from 570 to 3456 Bq kg−1, 232Thursday activity concentration ranged from 819 to 3577 Bq kg−1 and twoscoreM activity concentration ranged from 121 to 555 Bq kg−ane. Detailed information near the natural radionuclide activity concentration in soil samples tin be found in Supplementary Figure S2 and Table S1.

Drinking water quality and heavy metal chemical element content

In full general, drinking h2o quality in Mamuju is nonetheless below the reference level set by the Ministry of Wellness of Indonesia or the recommendation by WHO24,25. From the 30 samples nosotros measured (Tabular array i), i sample had an electroconductivity above i.5 mS cm−one. Drinking water samples had a pH range of 6.vi–7.4; and electroconductivity ranged from 0.04 to 0.83 mS cm−1. For total hardness, chloride, sodium, sulfate, fluor and nitrate concentrations had ranges from 15 to 244 mg L−1, 0.02 to vi.87 mg L−1, 2.07 to 26.94 mg L−i, 0.08 to 8.46 mg L−one, 0.02 to one.12 mg L−one, and 0.01 to 1.52 mg L−one, respectively. Nearly natural drinking h2o samples in Mamuju contained higher heavy metal concentrations than bottled drinking h2o did (Table two).

Table i Drinking h2o quality measurement results of samples.

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Table 2 Heavy metallic measurement results of drinking water samples given in Table one.

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Radiation exposure measurements

Indoor-to-outdoor dose-rate ratio

The measurement results of ambience dose equivalent rates in the HNBRA (Fig. 1a) for residential houses indoors had a geometric mean of 551 nSv h−1 with a range of 250–1653 nSv h−i; the rates outdoors had a geometric mean of 613 nSv h−one with a range of 200–2300 nSv h−1. The measurement results of ambient dose equivalent rates in the normal background radiation expanse (NBRA) or the command expanse (Fig. 1b) for indoors had a geometric mean of 81 nSv h−one with a range of 38–127 nSv h−1; the rates outdoors had a geometric mean of 71 nSv h−1 with a range of 39–116 nSv h−1. Figure 1c is the ambient dose equivalent charge per unit map in Mamuju fatigued using the collected outdoor ambient gamma doses. The distribution of radiation exposure in the Mamuju HNBRA is wide with several high exposure hotspots (outliers) found. Indoor-to-outdoor dose-rate ratio in the HNBRA had the range of 0.57–1.51 with geometric mean 0.90 and for command surface area had the range of 0.66–2.02 with geometric mean 1.thirteen.

Effigy 1
figure 1

Indoor and outdoor ambient dose equivalent rate distributions in the: (a) HNBRA and (b) the NBRA. (c) Ambient dose equivalent dose-rate map of Mamuju region. Maps were created in MAPINFO PROFESSIONAL version x.five (https://www.precisely.com/product/precisely-mapinfo/mapinfo-pro) using map data derived from the National Mapping Bureau of Indonesia (https://tanahair.indonesia.become.id/portal-web).

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Action concentrations from foodstuffs, drinking water, radon and thoron

The respective average activity concentrations for 226Ra, 232Th and twoscoreK in foodstuffs were: rice, 0.iv Bq kg−one, 6.2 Bq kg−1, and 87.9 Bq kg−i; meat/fish/vegetables, 36 Bq kg−1, 57.1 Bq kg−1, and 971.v Bq kg−one; fruits, vii.iv Bq kg−1, 7.4 Bq kg−one, and 390.viii Bq kg−1. Details regarding radioactivity in foodstuffs tin be found in Supplementary Table S2.

From radioactive decay measurements in drinking water samples, the 226Ra concentration ranged from xiv to 238 mBq Fifty−i (Fig. 2a). The highest drinking h2o concentration of 226Ra was obtained in Botteng Village. For the control expanse and also for bottled water, the observed concentrations were minor, around 14 mBq Fifty−1. The measured radon concentrations in drinking h2o (Fig. 2b) ranged from i to 1141 Bq Fifty−1 in the dry out season and one–652 Bq Fifty−1 in the rainy flavor. Figure 2c shows the radon concentration in water after a boiling process.

Effigy ii
figure 2

(a) Radium and radon activeness concentration measurement results in drinking h2o; and ambient dose equivalent charge per unit measurements. (b) Radon measurement results in drinking water for rainy and dry seasons. (c) Radon measurement results in drinking water after humid. The graphs in (a) include results of the present enquiry and the literature21. NBRA refer to the normal groundwork radiation expanse or command area.

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Radon concentrations in the HNBRA had a geometric hateful of 270 Bq yard−3 with a range of ninety–1644 Bq thou−three while 220Rn concentrations had a geometric mean of 210 Bq m−3 with a range of 46–2244 Bq m−3 (Fig. 3a). The 222Rn and 220Rn concentrations in the NBRA (control area) are plotted in Fig. 3b. Figure 3c,d show the radon concentrations and thoron concentrations in each village of the HNBRA and the NBRA. The equilibrium equivalent thoron concentration (EETC) in the HNBRA obtained with the thoron progeny monitor had a range of 2–42 Bq grand−3 with the geometric hateful of 11 Bq thousand−3. For the NBRA the EETC had a range of 0.4–4 Bq thousand−iii with geometric hateful of i.9 Bq one thousand−three.

Figure 3
figure 3

Almanac boilerplate radon and thoron concentrations in houses. (a) Distributions of 222Rn and 220Rn in the HNBRA. (b) Distributions of 222Rn and 220Rn in the NBRA. (c) Annual boilerplate 222Rn concentration in the study villages and control area. (d) Annual average 220Rn concentration in the study villages and control area. In (c,d) the horizontal black lines are the uncertainties. WHO26 and ICRP27 reference levels for indoor 222Rn activity concentration are 100 and 300 Bq 1000−3, respectively.

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Give-and-take

Feature exposure and source identification

The presently accepted worldwide average activity concentrations of twoscoreK, 238U, and 232Th nuclides are 412, 32, and 45 Bq kg−i, respectivelyii. We compared our obtained average activity concentrations with these worldwide boilerplate values. The concentrations of natural radionuclides in soil samples in the Mamuju region are very high, as shown in Supplementary Effigy S2 and Tabular array S1. The concentration of 238U is 23–30 times greater than the globe average, and that of 232Th is 27–60 times greater. The Mamuju region is unique because information technology has a high concentration of both 238U and 232Th natural radionuclides.

From the soil radioactive decay results (Supplementary Figure S2), we can identify several characteristics of this HNBRA: dominant areas for 238U include Botteng and Taan Villages; and ascendant areas for 232Th include Takandeang, Northern Botteng, and Ahu. The main sources of external radiation are uranium and thorium. Supplementary Figure S3 shows the correlation analysis between radioactivity (238U, 232Th and 40K) in the soil with the ambient dose-charge per unit. The negative relationship of 401000 occurs because the 238U and 232Th contents are loftier and then that the potassium concentration is not significant. These results reinforce the results of a previous written report using a scintillation detector16.

The external exposure predicted from the indoor-to-outdoor dose-rate ratio (range 0.57–1.51; geometric mean 0.90) in the HNBRA is college than that indoors. This indicates that the radiation originates from outside the house considering inside, at that place is a shielding effect. Most houses in the HNBRA take wood walls and coated cement floors. In a low radiations surface area, the radiation exposure within the firm is slightly higher than outdoors where the indoor-to-outdoor dose-rate ratio ranges between 0.66 and 2.02 (geometric mean, one.xiii). This may be the influence of the building materials used. In Topoyo Village (NBRA) and Salugatta Hamlet (a medium radiation area), the houses are made with brick walls and ceramic floors. This deviation in edifice types from the HNBRA occurs because Salugatta and Topoyo are transmigration areas, and then they have a slightly different lifestyle betwixt other villages studied in the HNBRA. The indoor-to-outdoor dose-rate ratio in Mamuju is slightly more homogeneous comparison with a study in Kerala, India where the ratio ranged between 0.08 and 1.xx7.

Annual hateful effective dose interpretation

The annual effective dose is determined from the accumulated external and internal doses received by the public. For external dose contribution, nosotros note that the estimated dose excludes external exposure due to cosmic radiation. External radiation measurements tin can exist made using a personal dosimeter or measuring indoor and outdoor ambience dose with a survey meter. Measurement of indoor-to-outdoor dose-rate with a survey meter has limitations because it must be multiplied past the occupancy cistron, while residents oft change places. Based on this fact we used a personal dosimeter to decide external exposure, referred to in UNSCEARtwo equally personal dose equivalent. The personal dosimeter measures the integration of external radiation so no conversion factors are required.

The individual external effective dose obtained using the personal dosimeter in the high radiation area ranges from one.ix to xiv.3 mSv year−1 with a geometric mean of 4.vii mSv year−1. For the NBRA (control area), the individual external effective dose ranges from 0.3 to 0.9 mSv year−ane with a geometric hateful of 0.five mSv yr−1. For the medium radiation expanse in the HNBRA, the private external effective dose ranges from 0.5 to ane.0 mSv year−1 with geometric mean of 0.75 mSv year−1.

Virtually Mamuju residents consume natural drinking water and foods they have grown or produced themselves. Well-nigh all foodstuffs in Mamuju have a concentration activity that exceeds the reference value of the IAEA, although they do non exceed a value of nigh one mSv annually. The reference values for meat, fruits and leafy vegetables respectively are 0.015 Bq kg−one, 0.030 Bq kg−1, and 0.050 Bq kg−1 for 226Ra and 0.001 Bq kg−1, 0.001 Bq kg−one, 0.015 Bq kg−1 for 232Thursday28. Contributions of rice, meat + vegetables and fruits to annual constructive dose, respectively, are 0.01–0.xiv mSv (geometric mean, 0.04 mSv), 0.01–2.51 mSv (geometric hateful 0.54 mSv) and 0.01–0.ane mSv (geometric hateful 0.05 mSv). Among the radioactivity results obtained in foodstuffs, spinach is peculiarly high. The presence of radionuclides in food may be a consequence of root uptake from the soil, direct deposition from the atmosphere onto crops or transfer through aquatic pathways. Regarding this, it is necessary to behave out further research on the transfer of factors from soil to these foodstuffs.

The results obtained from the measurement of radioactivity in drinking h2o in Mamuju are shown in Fig. 2a. Samples from the HNBRA accept higher activity concentration than those from the NBRA. The highest radon activity concentration in drinking water is 1141 Bq L−1, and in the rainy season the values are smaller than in the dry season (summertime) (Fig. 2b). The almanac effective doses from radon in drinking h2o are betwixt 0.01 and 2.33 mSv (geometric mean 0.02 mSv). Several drinking water samples have radon concentrations exceeding 100 Bq L−ane. The United states of america Environmental Protection Agency (USEPA) proposed a maximum contaminant level (MCL) for radon in drinking water of 11 Bq L−1 and an alternative maximum contaminant level (AMCL) of 148 Bq L−one 29,30. On the other paw, the European Marriage (Eu) recommended that the reference level for 222Rn in drinking water is 100 Bq L−1 31. Additionally, remedial action without further consideration is justified in all EU countries if radon concentration in drinking water exceeds 1000 Bq Fifty−1 31. However, the radon concentration in drinking water will decrease after humid, as shown in Fig. 2c. For this reason, radon released when boiling h2o must exist considered, equally it will increment the concentration of radon in the air. This released atmospheric radon poses a larger public health adventure than radon that enters through ingestion. The radium contribution in drinking water to the annual effective dose is small and information technology ranges from 0.01 to 0.04 mSv (geometric mean 0.01 mSv).

For heavy metals in drinking water, some samples have values to a higher place the allowable limit according to the Indonesian Ministry building of Wellness regulations33 and WHO guidelines for water quality24,25,32. Near drinking water in Mamuju contains higher concentrations of heavy metals than bottled drinking water. Heavy metal contents might exist due to environmental influences such as being in a HNBRA, which has loftier radioactivity in soil. The natural decay procedure of radionuclides tin lead to heavy metals, in detail Atomic number 82.

The WHO proposed a reference level of 100 Bq one thousand−3 to minimize health hazards due to indoor radon exposure26. Additionally, the report stated that if the reference level of 100 Bq m−three cannot exist reached, the called reference level should not exceed 300 Bq grand−3 according to ICRP recommendations27. Around 99% of the houses in the HNBRA have 222Rn activity concentrations exceeding the WHO reference level and 40% of the houses exceed the ICRP recommendations. The highest 222Rn and 220Rn concentrations are in Tande-Tande and Northern Botteng Villages, with a concentration of 1644 Bq g−3 (presented later on in Fig. 5). Almanac effective doses from radon in the HNBRA are between four and 78 mSv (geometric hateful thirteen mSv). This value is extremely loftier and correlates with concentrations of 238U and 232Th in soil samples in the area, which are parents of 222Rn and 220Rn.

According to the backdrop of 220Rn, which has a curt half-life of nearly 56 southward, this tin crusade a problem for the measurement because the 220Rn concentration volition depend on the distance from the radionuclide source to the detector. To solve this problem, the thoron progeny concentration was directly measured. The thoron progeny monitor was used to obtain the EETC. Figure 4 shows the correlation between EETC and thoron concentration. Annual effective doses from thoron are betwixt 3 and thirty mSv (geometric mean 9 mSv).

Effigy iv
figure 4

Correlation betwixt thoron concentration and EETC.

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In the instance of radiation exposure from groundwork radiation and technologically enhanced naturally occurring radioactive material (TENORM), the ICRP has classified it as the "existing exposure" situation33. In the radiological protection system, the ICRP stated that the reference level used in conjunction with the optimization of protection to restrict individual dose due to "existing exposure" is betwixt 1 and 20 mSv.

The estimated annual effective dose in Mamuju HNBRA is shown in Fig. 5. The annual effective dose (geometric mean) from Topoyo, Salugatta, Botteng, Northern Botteng, Takandeang, Ahu, and Taan villages respectively are two–5 (three.half-dozen) mSv, 5–10 (7.v) mSv, 25–75 (33.nine) mSv, 17–115 (41.half dozen) mSv, twenty–41 (27) mSv, 16–27 (xx.1) mSv, and xiii–24 (18.5) mSv. For the whole HNBRA, the average almanac effective dose is 32 mSv and the geometric mean is 29.vii mSv. This value exceeds the global mean of 2.4 mSv and also the highest value exceeds the upper value of the reference level for existing exposure situations. The largest contribution to the annual constructive dose comes from radon and thoron gases. Radon gas contributes 48% to the annual constructive dose, while thoron gas, external dose, foodstuffs and drinking water contribute 33.2%, 15.eight%, 1%, and 2%, respectively.

Figure 5
figure 5

Comparison of (a) annual internal effective dose and (b) annual external effective dose in the study villages and control expanse to the annual effective dose. (c) The almanac constructive dose. (d) Pie chart showing the contribution of each dose to the almanac constructive dose.

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Dose data from the present written report HNBRA and other HNBRAs in the world are listed in Table 3. We note that the estimated annual effective dose of radon and thoron in this study used the dose coefficient of ICRP 137, which is slightly higher than the previous ICRP publication. Nosotros tin can come across that Mamuju is a unique HNBRA because it has big external and internal doses. Besides that, the landscape in Mamuju is all the same natural and there is no mining; the radiation exposure distribution is broad and there are many residents.

Table 3 A comparison of doses and dose coefficients of radon and thoron between the present report of the Mamuju HNBRA and other previously studied HNBRAs.

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The implication of the HNBRA to homo health and its use as an epidemiological study area related to chronic low-dose-rate radiation from ecology sources

Residents in Mamuju are completely dependent on nature for their daily activities which include working in vegetable and fruit gardens and fetching water for drinking from wells. Almost all of their time is spent in a loftier radiation area. The HNBRA can lead to ecology pollution caused by radiation and heavy metals from radionuclide decay that eventually enter the human torso. The activity concentration information presented in this newspaper have high values, even exceeding the values for radiations workers, and they are of particular business concern from the viewpoint of public wellness.

Radon and thoron gas are the radionuclides which make the nearly meaning contribution to the annual dose received by humans, especially in the HNBRA. Based on the radioactivity characteristics from soil samples in Mamuju that have 238U and 232Th radionuclides, measurements of 222Rn, 220Rn, and their progeny are essential. The monitoring results of 222Rn and 220Rn are also influenced past the characteristics of the expanse, which shows that the dose contribution comes from NORM contained in the area soil. Many factors affect the concentration of radon and thoron in residential dwellings. The nearly influential factor is air ventilation35. Radon gas diffuses easily and disappears from dwellings that take proper air ventilation, simply based on the characteristics of natural exposure and radioactive decay in the soil of the Mamuju HNBRA, it will be challenging to reduce the 222Rn and 220Rn concentration there.

The high internal doses of radon can cause human health bug, especially in the respiratory tract. Moreover, combined exposure to radon and tobacco smoke may further increase lung cancer chance. The alpha particles emitted by radon and its progeny can directly assail genomic Deoxyribonucleic acid and cause mainly double-strand breaks in Deoxyribonucleic acid36,37,38. As well, overproduction of reactive oxygen species in the lungs acquired by persistent radon exposure may cause oxidative stress, leading to inflammation of pulmonary, tissue impairment, and eventually to chronic diseases of the lung such equally chronic obstructive pulmonary disease (COPD), pulmonary fibrosis, and lung cancer36. Strong and complementary risk bear witness for lung cancer from cumulative exposure to radon and its progeny through inhalation has been determined from studies of occupational exposures of uranium miners and residential exposures of the public4. According to the WHO Handbook26, the risk of lung cancer increases past sixteen% per 100 Bq m−3 increase in radon concentration. Zhang et al.39 reported on a meta-analysis of case–control studies on residential radon and lung cancer chance that showed for every 100 Bq m−iii, an increase in radon exposure was associated with a meaning 7% increase in lung cancer take a chance. Li et al.xl reported radon exposure was associated with risk increases in lung cancer, small-cell lung carcinoma and adenocarcinoma past 11%, 19% and 13%, respectively. Therefore, the dose–response relationship is linear, i.e., the risk of lung cancer is proportional to radon exposure. As well, several heavy metals tin induce cancer (e.g., arsenic, As) or non-cancer disease (e.g., mercury, Hg) risks in humans12.

Conducting nested case–control studies, with dose assessment on an private level and collection of individual information on known likewise as other possible risk factors for the diseases of interest, will exist a useful tool for the evaluation of any potential health risks from low-level chronic radiation exposuresfour. From public health data, upper respiratory tract infection, gastritis, and hypertension are the dominant illnesses in Mamuju (see Fig. 7). If we consider the internal dose received past the population of Mamuju, it is necessary to written report the state of affairs farther epidemiologically.

Epidemiological studies of populations in HNBRAs exposed to radiations delivered at low dose-rates over long periods leading to cumulative doses upwardly to several hundred millisieverts offer an opportunity to investigate the health effects associated with chronic low-dose-charge per unit radiation exposure. The epidemiological studies of populations exposed to ecology sources of radiation offer an opportunity to obtain risk estimates for the induction of cancer from depression-dose-rate radiation exposure upwardly to a cumulative dose of 0.5 Sv or more4,41. The lifetime cumulative dose is calculated by multiplying 70 years by the almanac effective dose. Based on the information presented in this paper, the lifetime cumulative dose adding suggests that the residents in Mamuju could be exposed to 2.2 Sv on average (range one.two–eight.1 Sv) which is much higher than the boilerplate doses for atomic bomb survivors (boilerplate dose: 200 mSv) and for almost other exposed populations. In the instance of the atomic bombs survivors, they were received astute exposure, whereas residents in the HNBRA have existence exposed to chronic radiation. Therefore, we demand to continue studies on the differences in homo effects due to acute and chronic exposures. Epidemiological studies in several regions of the earth (Ramsar, Yangjiang, Kerala and Guarapari) reported no correlation between radiation exposures in the HNBRA and cancer rate or mortality42,43,44,45. The same description was found in the 2017 UNSCEAR reportfour, i.e. the effect of low dose-rates on wellness and cancer risks after exposure to ionizing radiations is, as yet, unclear. Based on this state of affairs, Mamuju is a potential area for epidemiological study of health risks (cancer and non-cancerous) due to the chronic low-dose-rate radiations from environmental sources.

Material and methods

Study area and population

We used a cross-exclusive report method with cluster sampling areas. For natural radioactivity measurements, soil and food samples were analysed in the National Nuclear Energy Agency of Indonesia, Center for Technology of Radiation Safety and Metrology, National Environmental Safety Laboratory, which is accredited to ISO17025 and a member of the IAEA-Analytical Laboratories for the Measurement of Environmental Radioactivity (ALMERA network laboratories). Other analyses were performed at Hirosaki University, Institute of Radiations Emergency Medicine, Japan. Table 4 summarizes the radionuclides and elements analysed and the analytical techniques used for their conclusion.

Tabular array 4 Summary of methods.

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The study involved villages in the two cities of Mamuju and Mamuju Tengah, located in West Sulawesi Province on Sulawesi Island. Location maps of the island and the villages are shown in Fig. half dozen. This study was conducted from November 2018 to March 2020. West Sulawesi Province had a population of 432,000 people in 2018 on an area of 5406 km2. The Mamuju region has a tropical climate with ii seasons, the dry season from April to September and the rainy flavor from October to March. The landscape is still natural, with rivers and mount topography beyond well-nigh all sub-districts and there is no mining activity46. Mamuju Metropolis had 286,389 people in the agronomical sector working as farmers, representing 62.2% of the population; and the principal agricultural product is cacao, which is exported to strange countries. Almost of the houses in Mamuju City are of wood (effectually 57.six%); but twoscore.8% take brick walls amongst which 39.7% have a cement floor and 31.vi% a wooden flooring. The nearly mutual diseases suffered by residents (Fig. 7) are upper respiratory tract infectionsURI, with 21,070 cases and gastritis with 18,177 cases46 and life expectancy is effectually 67.2 years.

Figure half-dozen
figure 6

Location maps. (a) Sulawesi Island, including Mamuju region which was the written report HNBRA and Topoyo Hamlet which was the written report NBRA. (b) Villages of the study in Mamuju region. HNBRA refer to the high natural background radiation surface area and command area (CA) refers to the normal background radiation area (NBRA) or control area. Maps were created in MAPINFO PROFESSIONAL version x.v (https://www.precisely.com/product/precisely-mapinfo/mapinfo-pro) using map information derived from the National Mapping Bureau of Indonesia (https://tanahair.republic of indonesia.get.id/portal-web).

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Figure 7
figure 7

Pie chart summarizing the primary diseases suffered by Mamuju region residents46. URI stands for upper respiratory tract infection.

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Lifestyle and consumption behavior questionnaire survey

We conducted a short questionnaire survey of residents to decide their lifestyle and consumption behaviors. All questionnaire surveys were performed in accordance with relevant guidelines and regulations; 408 families roofing the whole study area were surveyed and we confirmed that informed consent was obtained from all subjects and/or their legal guardians. The report itself was approved by the Committee of Medical Ethics of Hirosaki University Graduate School of Medicine (2018-089, Hirosaki, Japan).

Based on previous results of the car-borne survey16, it was found that several areas in Mamuju have meaning gamma exposure, including Northern Botteng, Botteng, Takandeang, Ahu and Taan Villages (loftier radiation surface area villages). For the written report control expanse, a NBRA was selected, Topoyo Village in Mamuju Tengah City well-nigh 120 km from Mamuju Urban center. Between the high radiation area villages and NBRA control area, Salugatta Village was a medium area having an ambient dose-rate ranging from 100 to 200 nSv h−ane. The residential populations and the surveyed populations of each hamlet are shown in Tabular array five.

Tabular array 5 Resident populations and surveyed populations in the written report area.

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Natural radionuclide activity concentrations in soil samples

A full of 30 soil samples of 1 kg each were collected from xxx locations including 24 samples in the HNBRA and 6 samples in the control surface area. The location of sample selection was carried out randomly past because the number of hamlets in a village and the presence of residents in the hamlet because some hamlets were no longer inhabited. Detailed information on the location is shown in the Supplementary information. The soil samples were crushed and sieved, and placed in sealed standard Marinelli beakers. Their disuse products were allowed to reach secular equilibrium (30 days) and then they were measured using a high purity germanium (HPGe) detector.

The HPGe detector was calibrated using a standard source (NIST, USA) with the same geometry as the Marinelli beakers for samples. A p-type HPGe detector (GEM sixty-5, ORTEC, USA) with the relative efficiency of 35% and resolution of 1.81 keV at 1.33 MeV and ultra-depression background shielding with old lead content (ISuS, Sweden) was used for measurement of 238U, 232Thursday, and 40M. The detector was enclosed in a 10 cm thick compact lead shield. The counting of the samples was obtained by analyzing the spectrum acquired from a multi-channel analyzer (MCA) on a PC with associated software Gamma vision (ORTEC, Us) with eighty,000 s counting fourth dimension.

The total energy absorbed peaks of 351 keV for 214Lead and 609 keV for 214Bi were identified for calculations of 238U activity concentration. The full energy absorbed peaks of 238 keV for 212Pb, 581 keV for 208Tl, and 911 keV for 228Ac were used for 232Thursday, and a single peak of 1460 keV was used for 401000. The minimum detectable concentrations (MDCs) of 238U, 232Thursday, 235U, and fortyOne thousand for this measurement were 5.ii × ten−3, five.ii × 10−3, iii.4 × ten−iii, and 1.v × 10−3 Bq kg−1, respectively47. We used Eqs. (one) and (2) to calculate activeness concentrations from these measurements.

$$A=\frac{n}{E Y Due west{f}_{c}},$$

(i)

$${L}_{D}={L}_{C}+Yard{\sigma }_{D},$$

(2)

Here north is net count rate (cps), E is the counting efficiency, Y is the photon emission probability, Due west is the sample weight (kg), and f c is the correction cistron (including summing-in, summing-out, decay factor, recovery factor, attenuation factor, branching ratio, and growth factor), L D is the detection limit, 50 C is the decision threshold, \({\sigma }_{D}\) is the standard divergence, and K is the error probability23,48,49.

Drinking water quality measurements and identification of heavy metal elements

We collected drinking water samples and measured their temperature, pH and electroconductivity (Laquatwin, Horiba, Nippon). Moreover, we measured the ambient dose equivalent rates (PDR-111, Hitachi, Nippon) around the collection location. The drinking water samples were acidified to 3% using nitric acid. Furthermore, a triple quadrupole inductively coupled plasma mass spectrometry (ICP-MS-QQQ) instrument (8800, Agilent, USA) was used for determining concentrations of major and heavy metal elements (Cu, Cr, Cd, Mn, Co, Equally, Se, Ba, 206Lead, 207Atomic number 82, 208Pb) and a Dionex ion chromatography system (ICS-210, Thermo Scientific, U.s.a.) was used for determining concentrations of ions (F−, Cl−, NOiii −, Na+, and Ca2+).

Radiation exposure assessment

Indoor-to-outdoor dose-rate ratio

The measurements of indoor and outdoor ambient dose equivalent rates (H*(10)) were fabricated using a pocket survey meter (PDR-111, Hitachi, Ltd., Nippon). This was done for the high radiations area, and the normal radiation (control) and medium surface area. GPS was used to locate the measurement points. A full of 450 houses were surveyed: 100 in the control area, 100 in the medium radiation area, and 250 houses in the high radiation area. Around 50 houses were selected from each hamlet in the high radiation area. Indoor and outdoor dose measurements were conducted randomly at the hamlets in a village where people were living at the time of the study. The measurements were taken at the height of 1 m above the ground surface and 2 m from the wall. The pocket survey meter was calibrated annually using a standard source of 137Cs with a correction cistron (CF) of 0.998. The dose-rate can exist estimated using Eq. (3).

$${H}^{*}(x)={N}_{read} \times CF$$

(3)

Here H * (10) is ambient dose equivalent rates (nSv h−1), N read is the value of the ambience dose equivalent rate obtained from the survey meter, and CF is the correction gene.

External annual constructive dose estimation

The ambient dose equivalent is an operational quantity for area monitoring. However, for the assessment of the residence dose, an individual dose received by the residents is required, and then we conducted individual measurements of the personal dose equivalent H p (10) using optically stimulated brilliance dosimeters (OSLDs, Nagase Landauer, Ltd., Japan). In the loftier radiations expanse, eighty dosimeters were used by adults, 20 dosimeters were used in the medium surface area and 20 dosimeters were used in the control surface area. The dosimeters were used for a full year, and every user wore information technology in the daytime, and at night it was placed near the bedside. The detector has been calibrated using the 137Cs source with the detector positioned on a phantom.

Internal radiation dose measurements: ingestion

Nosotros nerveless about 30 food samples of 2 kg each. All samples were foodstuffs ordinarily consumed daily by residents such as rice, fish, meat, and vegetables. Well-nigh of the population in Mamuju consumes mainly locally grown or produced food which comes from traditional markets. Based on these facts, we adamant the location and type of food samples commonly and daily consumed after taking into account availability of these foodstuffs. The samples were dried using a freeze dryer (Labconco, Us) at − seventy °C and 10 Pa until dryness (around 3–4 days) then sieved using a 180 µm mesh filter. The samples were transferred into a standard Marinelli chalice and kept for 30 days to achieve a secular equilibrium before being analyzed using the HPGe detector50.

Furthermore, we likewise measured 226Ra and 222Rn in drinking water; determination of 226Ra was done by a liquid scintillation counting method21 , a total of 18 drinking h2o samples of ane 50 each and 12 samples from the literature21 were collected using PET bottles, filtered using a 0.45 µm pore membrane and adjusted to pH 2 with the improver of 65% nitric acid. After that, a 200 g sample was weighed out and evaporated at around 60 °C until the sample weight was approximately xx thou. From this a sample of approximately 10 mL was transferred into a loftier-operation glass vial (PerkinElmer, The states) and accurately weighed. Subsequently that, a x mL aliquot of scintillation cocktail (Ultima Gilt uLLT, PerkinElmer, USA) was added and the solution was immune to stand for 30 days to reach equilibrium with the progeny isotopes.

For 222Rn concentration measurement in drinking water, a total of 30 drinking h2o samples of 250 mL each were collected using a glass bottle and measured with an electrostatic collection type radon monitor (RAD7, Durridge Co., United states) continued to a water analysis accessory (RAD-H2O, Durridge Co., USA). We measured the water samples on days in two seasons, rainy (November 8, 2018) and dry (July 8, 2019). The RAD7 detector was continued to a bubbling kit, for degassing of radon in the water sample into the air in a airtight loop. A water sample was put into a radon-tight reagent bottle (250 mL) connected to the closed loop to detect blastoff activity. Earlier the radon gas reached the detector it was stale with desiccant (CaSO4, Drierite, Due west A Hammond, United states of america) to blot the wet. Air was so circulated in the closed loop for a 5 min bike in five recycle times until the radon was uniformly mixed with the air. The measured alpha activity was recorded, from which the radon concentration was obtained directly.

Internal radiation dose measurements: inhalation

We conducted inhalation exposure measurements by measuring radon, thoron and thoron progeny. The measurements of 222Rn and 220Rn concentrations used the RADUET monitor (Radosys, Ltd, Hungary)51. The RADUET had solid-country nuclear rail detectors (SSNTDs) fabricated from CR-39 and also a thoron progeny monitor. The radon, thoron and thoron progeny measurements were carried out in the same location together with the measurement of the indoor and outdoor ambient dose-charge per unit. However, those data could not exist retrieved from 42 houses because the house owners were no longer living. They were installed in 408 houses: 100 houses in the NBRA, 100 houses in the medium radiation surface area and 208 houses in the high radiation area. They were placed in the center of the living room of each business firm or at least 2 m from the wall for a 1-year measurement period in which the monitor were replaced at three-month intervals. Every house was well ventilated and had a window in every room. Later the exposure, the CR-39 was chemically etched for 24 h in a half dozen Thou NaOH solution at 60 °C, and alpha tracks were counted with an optical microscopesixteen,52. The radon and thoron activity concentrations were calculated using the track densities for each of two pieces of CR-39 and the conversion factors for radon and thoron. To measure thoron progeny, we used the stainless steel plate with CR-39 and aluminized film53,54.

A RADUET contains paired detection chambers, a low-diffusion chamber, and a high-diffusion sleeping accommodation. In principle, the rail densities in the low-diffusion chamber (d L) and high-diffusion bedroom (d H) depend on both radon and thoron concentrations in the air. For calculating radon and thoron concentrations, the obtained total runway densities are replaced into Eqs. (iv) and (v)

$${C}_{Rn}=\left({d}_{L}-\overline{b }\correct)\times \frac{{f}_{Tn2}}{t.\left({f}_{Rn1}.{f}_{Tn2}-{f}_{Rn2}.{f}_{Tn1}\right)}-({d}_{H}-\overline{b })\frac{{f}_{Tn1}}{t.\left({f}_{Rn1}.{f}_{Tn2}-{f}_{Rn2}.{f}_{Tn1}\right)}$$

(four)

$${C}_{Tn}=\left({d}_{H}-\overline{b }\right)\times \frac{{f}_{Rn1}}{t.\left({f}_{Rn1}.{f}_{Tn2}-{f}_{Rn2}.{f}_{Tn1}\right)}-({d}_{L}-\overline{b })\frac{{f}_{Rn2}}{t.\left({f}_{Rn1}.{f}_{Tn2}-{f}_{Rn2}.{f}_{Tn1}\correct)}$$

(5)

$$N_{{{\text{TnP}}}} = EETC \times CF_{{{\text{TnP}}}} \times T + b_{{2}}$$

(half dozen)

Here C Rn and C Tn are the hateful concentrations of radon and thoron during the exposure period in Bq grand−three. d L and d H are the total alpha track densities (rail grand−2) taken from the CR-39 detectors of depression and high air-exchange charge per unit chambers. f Rn1 and f Tn1 are the radon and thoron calibration coefficients for the low air-exchange rate chamber in tracks 1000−2 kBq−i m3 h−1. f Rn2 and f Tn2 are the radon and thoron calibration coefficients for the high air-exchange charge per unit chamber in tracks grand−two kBq−1 m3 h−1. t is the exposure time in hours and \(\overline{b }\) is the background track density of the CR-39 detector in tracks m−2 52. The low-diffusion bedroom limits the improvidence of thoron into the bedroom; therefore,c eleven≫c 12. The high-improvidence chamber is designed such that both radon and thoron can diffuse into the bedchamber easily, andc 21 ≈c 22. Due north TnP is the track density of CR-39 in the thoron progeny deposition detector, EETC is the equilibrium equivalent thoron concentration, and CF TnP is the conversion factor for thoron progeny which was 6.9 × 10–2 (Bq thou−3 h)−i 55. Furthermore, for quality control, the radon and thoron monitor must be calibrated. The calibration was carried out in the Institute of Radiations Emergency Medicine, Hirosaki University56.

Estimation of almanac effective dose

For quantification of the effective dose, the effective dose was calculated as the accumulation of the dose received from external and internal exposure. We note that the estimated almanac constructive doses were calculated for adults. External exposure comes from exposure to ecology gamma radiation, while internal exposure tin occur through digestion and breathing. Internal exposure through digestion tin occur due to the ingestion of food/drink into the body, while internal exposure through animate tin can occur due to inhalation of gas containing radioactive substances. An constructive dose calculation methodology tin can apply the following equation past UNSCEAR2:

$${E}_{\mathrm{T}} = {H}_{\mathrm{p}}(d) + \sum_{j}{due east}_{j,\mathrm{ing}}{I}_{j,\mathrm{ing}}+ \sum_{j}{east}_{j,\mathrm{inh}}.{I}_{j,\mathrm{inh}}$$

(ix)

where East T is an effective dose (Sv), H p(d) is the personal dose equivalent due to external exposure obtained by personal dosimeter (Sv) at a depth of ten mm for penetrating radiation (Hp(x)), \({e}_{j,\mathrm{ing}}\) is the committed effective dose per unit activeness intake by ingestion (Sv Bq−1) for radionuclide (j) by historic period group (one thousand), \({e}_{j,\mathrm{inh}}\) the dose coefficient of inhalation dose (Sv Bq−1) per unit of respiratory input for radionuclides (j) by the historic period grouping (g), I j,ing I j,inh is the ingestion and inhalation intake (Bq).

$${D}_{\mathrm{Rn}}={C}_{\mathrm{Rn}}\times F\times {DCF}_{\mathrm{TnP}}\times OF$$

(x)

$${D}_{\mathrm{Tn}}=EETC\times {DCF}_{\mathrm{TnP}}\times OF$$

(11)

To calculate input through digestion (I j,ing) derived from nutrient, the population consumption data for food types whose radionuclide concentrations are known were based on consumption pattern data in which the rice, meat + vegetable and fruit daily consumptions were 270.iv, 64.6 and 36.8 k with i year equal to 365 days57. On the other hand, respiratory input (Ij,inh) is the average of calculated radon and thoron concentrations for one-year measurement. To avoid the effect or influence of season, ventillation and so on, the average of radon thoron concentration for one year was used to calculate effective dose with the dose conversion factor for radon of 1.7 × 10–five mSv (Bq h m−three)−1 and the dose coefficient for thoron of 1.07 × ten–iv mSv (Bq h m−3)−one** 58,59.

Calculation of external exposure dose causeless that the population received external exposure for 8 h outside the home (from eight am to 4 pm), because that almost all residents who lived in the HNBRA are farmers with a total of 7000 h for radon occupancy factor in houses34,60. For ingestion, the daily consumption of water was ane.half-dozen L d−1 based on the questionnaire survey, and the dose conversion factors for adults are reported as 2.8 × 10–7 Sv Bq−1 for 226Ra, iv.5 × x–8 Sv Bq−i for 238U and 2.3 × ten–seven Sv Bq−ane for 232Th61.

Statistical analysis and map creation

We used ORIGIN PRO 2020b (educatee version, OriginLab Corp, USA) to evaluate significant relationships between the distribution coefficients of radionuclides for characterization exposure. We conducted a Pearson and Spearman rank correlation analysis, and nosotros also calculated the values of correlation coefficients with a two-tailed significance test (p value at 0.05). Furthermore, nosotros as well compared the results of the dose assessment betwixt the HNBRA and command expanse using a 2-sided pupil's t test. Nosotros used MAPINFO Professional (version 10.5, Precisely, USA) to create maps and dose distribution maps.

Ethical approval

The study itself was canonical by the Committee of Medical Ethics of Hirosaki Academy Graduate School of Medicine (2018-089, Hirosaki, Japan).