J. Nig. Soc. Phys. Sci. 5 (2023) 896 Journal of the Nigerian Society of Physical Sciences Annual Effective Dose and Excess Lifetime Cancer Risk due to Ingestion and Inhalation of Radon in Groundwater of Bosso Community Minna, North-Central Nigeria Matthew Tikpangi Koloa,∗, Oyeleke Olarinoyea, Simon Olonkwoh Salihub, Hyginus Anayo Ugwuanyia, Paul Onuchea, Opeyemi Faladea, Nwachukwu Chibuezea aDepartment of Physics, Federal University of Technology, Minna, Niger State, Nigeria bDepartment of Chemistry, Federal University of Technology, Minna, Niger State, Nigeria Abstract Radon in potable water has become an issue of public health concern, especially when consumed or used directly from source for domestic purposes without any pre-treatment. In this study, 222Rn concentration in 22 water samples collected from 2 groundwater sources (open wells, 12 samples and boreholes, 10 samples) in Bosso town, North central Nigeria were measured using Durridge RAD-7 radon detector with RAD-H2O accessories. 222Rn concentrations in open wells varied from 2.1±0.7 to 27.9±2.5 Bq L−1 with a mean of 10.2±1.5 Bq L−1, while that in boreholes ranged from 2.8±1.1 to 39.2±1.5 Bq L−1 with a mean value of 14.3±1.7 Bq L−1. These values are lower than the 100 Bq L−1 upper limit proposed by the European Union Commission, above which any practical intervention may be necessary. Mean annual committed effective dose to adults, children and infants from ingestion of water were 74.64, 71.58 and 53.17 µSv y−1 respectively for the open wells and 104.24, 99.96 and 74.26 µSv y−1 respectively for borehole water samples. Mean whole body dose due to ingestion and inhalation of waterborne radon from open wells and boreholes are 27.56 and 38.48 µSv y−1 respectively, which are below the reference level of 0.1 mSv y−1 for potable water recommended by the World Health Organization for public safety. The excess lifetime cancer risk were 0.10 × 10−3 for the open wells and 0.13 × 10−3 for the boreholes, which are lower than the world safety limit 0.29 × 10−3. Water from the two groundwater sources investigated is therefore fit for consumption and other domestic usage from the point of view of radiation protection. DOI:10.46481/jnsps.2023.896 Keywords: 222Rn concentration, groundwater, Bosso community, RAD-7 radon detector, Committed effective dose, ELCR, Nigeria Article History : Received: 28 June 2022 Received in revised form: 07 January 2023 Accepted for publication: 07 January 2023 Published: 19 April 2023 c© 2023 The Author(s). Published by the Nigerian Society of Physical Sciences under the terms of the Creative Commons Attribution 4.0 International license (https://creativecommons.org/licenses/by/4.0). Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI. Communicated by: M. Orosun 1. Introduction The daily influx of human population coupled with rapid ur- banization of Bosso community of Minna, north-central Nige- ∗Corresponding author tel. no: +234 8105168992 Email address: matthewkolo@futminna.edu.ng (Matthew Tikpangi Kolo) ria has put increased pressure on the existing epileptic potable water supply within the community. To effectively combat this growing challenge therefore, residents of the community have turned their attention to open wells and drilled boreholes. Ground- water has thus, become the primary source of potable water for majority of the population in the community. Groundwa- ter, which is the World’s largest reservoir of fresh water [1], 1 Kolo et al. / J. Nig. Soc. Phys. Sci. 5 (2023) 896 2 derives its radioactivity from the underlying rocks, soil forma- tions, dissolved radioactive and mineral substances. Dissolved radon (222Rn) in groundwater arises from the decay of naturally occurring uranium and radium (226Ra) deposits present in soil and reservoir rocks over which the water bodies move, cou- pled with the emanation coefficient of the reservoir rocks [2-4]. Other factors that control the distribution of 222Rn in ground- water includes the type of rocks, host rock mineralogy, shear zones, degree of weathering, frequency of fractures, permeabil- ity of host rock, secondary porosity, physiochemical, and na- ture of the geological aquifers, depths of wells and duration of water storage times [3, 5, 6]. 222Rn often finds its way out of the earth’s crust and underlying bedrocks through cracks, crevices and other openings in the foundation floor and walls, into human homes, thereby enhancing the level of human expo- sure. Additionally, human exposure to waterborne radon occur through daily use of groundwater for bathing, laundries, cook- ing and other domestic purposes [7].Most often, human expo- sure occur through direct ingestion of water containing radon and inhalation of radon gas in indoor air. Waterborne radon monitoring and mitigation has been a sub- ject of great concern and research in many countries of the world, owing to its hazardous effects [2]. World Health Organi- zation (WHO) [8] reported that about 1-7% of deaths from lung cancer is attributed to increased levels of waterborne radon. Various studies have also shown that direct inhalation and in- gestion of waterborne radon over long period of time can lead to pathological effects such as the respiratory functional changes, and DNA damage in sensitive lung tissues leading to lung can- cer (, stomach and gastrointestinal cancer [1, 2, 5, 9]. Epidemi- ological studies have also shown that ingestion of 222Rn over a considerable length of time can be responsible for stomach and gastrointestinal cancer [10]. Levels of 222Rn in water should therefore be measured, checked and controlled consis- tently in order to protect the human population from internal exposure that may arise from inhalation and ingestion of water- borne radon Isinkaye et al [11],underscores the importance of water to human existence and an expressive indices for radiological, ge- ological and environmental studies. Hence, its purity, acces- sibility and quality cannot be jeopardized especially from the point of view of human health and protection. The first campus of Federal University of Technology, Minna is located in Bosso community. The challenge of insufficient hostel accommodation within the campus has pushed major- ity of the students to rented apartments within Bosso. Bosso community is also the readily available home for local farm- ers who have been displaced from their respective communi- ties due to the nefarious activities of bandits and herdsmen. As a result of the growing population, the community has re- sulted into drilling open wells and boreholes to meet the in- creasing demand for potable water supply. Locally built apart- ments available for rent within the community are semi en suite and poorly ventilated, resulting in high probability of popu- lation exposure to accumulated radon from groundwater used for laundry, bathing, dishwashing and other domestic activi- ties. Moreover, radon concentration in groundwater sources in Figure 1: Map of Niger State showing the study area Bosso community have not so far been examined or reported in literature. This study is therefore a pioneering work aimed at measuring 222Rn concentrations in groundwater sourced from open wells and boreholes in Bosso community and to evalu- ate the level of exposure to radiation dose from the daily usage of groundwater within the community. Results from this study will help in raising awareness on the likelihood of radiation in- cidence that may occur from daily exposure, through inhalation and ingestion, to waterborne radon within the community. 2. Materials and Method 2.1. Location and Geology of the Study Area Bosso, a community in Niger State, north central Nigeria (Fig. 1), with average area of 1592 km2, is geographically located within the Guinea Savanna ecological zone of Nigeria. It lies between latitudes 090 40 ′ N to 090 42 ′ N and longitudes 060 30 ′ E to 060 36 ′ E. The community falls within the regional Base- ment Complex of Nigeria, which according to Okanlawon et al [12], is underlain by two geologic episodes viz igneous and metamorphic orogeneses. The community is underlain by un- differentiated granitic rocks which are believed to be part of the Older Granitic suites of Nigeria and various metamorphic rocks [13, 14, 15]. The metamorphic terrain is made up of gneisses, schists, quartzites and some migmatites [16]. In hand specimens, the granitic rocks constitute feldspars (mostly pla- gioclase), quartz, micas and some few ferromagnesian minerals like pyroxenes, amphiboles and hornblendes. The metamor- phic rocks are mostly made of biotites, amphiboles, staurolites and asbestos. Structurally, most of the rocks are non-deformed to slightly deformed [17]. Secondary structures such as faults, folds, foliations and lineations are obvious on the insitu rocks. The community is marked by two distinct seasons, the raining season which lasts from the month of April to October, and the dry season which lasts from November to March/April. Annual rainfall values ranges between 900 mm to 1,000 mm, with mean temperature of around 32◦C. 2 Kolo et al. / J. Nig. Soc. Phys. Sci. 5 (2023) 896 3 2.2. Sample Collection 12 groundwater samples from open wells and 10 groundwa- ter samples from drilled boreholes within the community were collected and analysed for 222Rn concentration. Empty 75cl water bottles which were used for collection of water samples were purchased from commercial shops. The sample bottles were thoroughly washed with distilled water and with dilute 0.1M HCl after purchase. They were then allowed to dry be- fore sample collection. Fresh water sample from open wells were collected using bailers. Clean sample bottles were gently filled with water samples by submerging them into the bailers and immediately sealed tightly with a cap underwater to avoid any formation of air bubbles. Fresh water from boreholes were collected into the samples bottles directly from the borehole tap heads after they were turned on and allowed to run freely for about five minutes. This was necessary to purge out all trapped air and to ensure that the temperature of the water is stable be- fore collection. All samples bottles were well labelled and care- fully filled to prevent agitations that could lead to the escape of radon gas. 2.3. Sample Analysis All the samples were analysed at Radioanalytical Research Laboratory, Ekiti State University, Ado Ekiti, Nigeria, using RAD-7 radon analyzer (Durridge Co., USA) coupled to RAD- H2O accessories. In the RAD-7 detector setup shown in Fig. 2, required portion of water sample was transferred into the 250 mL vial, from which radon gas was expelled using bubbling kit. The expelled gas was passed via air circulation into the hemisphere chamber where it decayed into its daughter nuclei, polonium (Po). A silicon solid-state detector which was main- tained at high electric field, collected the Po nuclei which were finally counted by an in-built software to give an estimation of radon concentration in the water sample. Each water sample was automatically analyzed by the detector in four cycles of 5 min each, with an initial aeration time of 5 min. This was neces- sary for quality control purposes and to guarantee reliability of analytical methods [11, 18]. Since the counting was not imme- diately done at the sample collection point, radon concentration in the samples must have reduced due to radioactive decay. The results of the analysis were therefore decay-corrected back to the original concentration values at the time of sample collec- tion, following the correction procedure outlined in Durridge [19]. RAD-7 is a sophisticated, active radon detector that uses a computer-driven electronic detector with pre-programmed se- tups. The detector is able to give the result of analysis within 30 minutes, which makes it a comparatively faster analysis pro- cedure. 2.4. Annual Effective Dose Estimation Exposure to waterborne radon by human and animal popu- lation occur on daily basis as a result of water consumption and other various domestic use, which results in the annual commit- ted effective dose (ACED) incurred. ACED to different ICRP Figure 2: Schematic diagram of RAD-H20 set for measurement of waterborne radon age groups due to ingestion of waterborne radon was computed from the equation ACED = CRn × WCR × DCF (1) where CRn is the radon concentration in groundwater measured in Bq L−1, WCR is the water consumption rate per year (L yr−1) and DCF is the dose conversion factor expressed in Sv Bq−1. WCR and DCF values adopted in this study are given in Table 1. The contribution of radon in the different sources of water to indoor radon was determined using equation [21]: χRn = CRn × w × ω v ×λc (2) where χRn is the fractional contribution of waterborne radon to radon in indoor air, CRn is the radon concentration in water, w is the water consumption rate per person (0.01 m3 h−1), ω (0.5) is the coefficient to indoor air, v is the bulk volume of indoor air per person taken to be 20 m3, and λc (0.7 h−1) is the air exchange rate [22, 23]. 3. Results and Discussion 3.1. Radon Concentration The measured 222Rn concentration in groundwater, fractional contribution of waterborne radon to radon in indoor and the as- sociated health hazard within the study area are presented in Table 2 As shown in Table 2, 222Rn concentrations in LW varied be- tween 2.1±0.7 to 27.9±2.5 Bq l−1 with a mean value of 10.2±1.5 Bq l−1. Similarly, 222Rn concentrations in BH ranged from 2.8±1.1 to 39.2±1.5 Bq l−1 with a mean value of 14.3±1.7 Bq l−1. According to Kalip, Haque and Gaiya [24], and Suresh et al [25], observed differences in radon concentrations in LW and BH may be due to the depth of water sources, hydrogeo- logical state of the source location and the prevailing climatic conditions. Although 33% of water samples from both LW and BH have 222Rn concentration values above the USEPA safety threshold of 11.1 Bq l−1 as seen in Figure 3, 222Rn concentra- tion in two groundwater sources were within the safety range 3 Kolo et al. / J. Nig. Soc. Phys. Sci. 5 (2023) 896 4 Table 1: WCR and DCF for respective ICRP age groups [20] Water consumption Age group Age range(yrs) (L/day) WCR (L/yr) DCF (Sv/Bq) 3 months 0 - 1 0.55 200 1 yr (infants) 1 - 2 0.71 260 2 × 10−8 3 yrs 2 - 7 0.82 300 10 yrs (children) 7 - 12 0.96 350 2 × 10−8 15 yrs 12 - 17 1.64 600 Adults > 17 2.00 730 1 × 10−8 Table 2: 222Rn concentration in groundwater, fractional contribution of waterborne radon to radon in indoor and the associated health hazard within the study area ACED (µSv y−1) to ICRP age groups Sample ID 222Rn(Bq l−1) χRn (mBq l−1) Adults Children Infants Open wells LW 01 2.1±0.7 0.75 15.33 14.70 10.92 LW 02 27.9±2.5 9.96 203.67 195.30 145.08 LW 03 24.9±2.5 8.89 181.77 174.30 129.48 LW 04 10.2±1.6 3.64 74.46 71.40 53.04 LW 05 2.9±0.8 1.04 21.17 20.30 15.08 LW 06 4.5±1.1 1.61 32.85 31.50 23.40 LW 07 8.8±1.4 3.14 64.24 61.60 45.76 LW 08 2.4±0.8 0.86 17.52 16.80 12.48 LW 09 4.4±1.1 1.57 32.12 30.80 22.88 LW 10 3.1±2.0 1.11 22.63 21.70 16.12 LW 11 16.0±2.8 5.71 116.80 112.00 83.20 LW 12 15.5±0.8 5.53 113.15 108.50 80.60 Min 2.1±0.7 0.75 15.33 14.70 10.92 Max 27.9±2.5 9.96 203.67 195.30 145.08 Mean 10.2±1.5 3.65 74.64 71.58 53.17 Boreholes BH 01 28.7±3.1 10.25 209.51 200.90 149.24 BH 02 10.1±1.5 3.61 73.73 70.70 52.52 BH 03 22.2±1.0 7.93 162.06 155.40 115.44 BH 04 2.8±1.1 1.00 20.44 19.60 14.56 BH 05 39.2±1.5 13.99 286.16 274.40 203.84 BH 06 9.9±2.0 3.53 72.27 69.30 51.48 BH 07 12.3±4.5 4.39 89.79 86.10 63.96 BH 08 10.5±0.2 3.75 76.65 73.50 54.60 BH 09 3.7±0.8 1.32 27.01 25.90 19.24 BH 10 3.4±1.3 1.21 24.82 23.80 17.68 Min 2.8±1.1 1.00 20.44 19.60 14.56 Max 39.2±1.5 13.99 286.16 274.40 203.84 Mean 14.3±1.7 5.10 104.24 99.96 74.26 of 4 – 40 Bq l−1 recommended by the United Nations Scien- tific Committee on Effects of Atomic Radiation (UNSCEAR). According to the recommendations of European Union com- mission, no remedial action should be required if the concen- tration of radon in drinking water is less than 100 Bq l−1 [26, 27]. Results of this study does not therefore suggest any imme- diate implimentation of whichever practical radon programme in Bosso community. The contribution of waterborne radon to radon in indoor air varies from 0.75 to 9.96 mBq l−1 for LW wa- ter sources and from 1.00 to 13.99 mBq l−1 for the BH water. These values are lower than the estimated mean indoor radon level of 1.3 pCi/l (48.1 mBq l−1), thereby indicating the paltry contribution of waterborne radon within the community to total radon in indoor air. Table 2 also shows the computed annual effective dose (ACED) to the adults, children and infants due to 222Rn concentration in the two groundwater sources (LW and BH) of the studied com- munity. ACED due to ingestion of water from LW source by 4 Kolo et al. / J. Nig. Soc. Phys. Sci. 5 (2023) 896 5 Figure 3: 222Rn concentration in LW and BH sources together with the USEPA threshold Figure 4: ACED received by different ICRP age groups due to waterborne radon from LW groundwater sources adult population ranged from 15.33 to 203.67 µSv y−1 with an average value of 74.64 µSv y−1, from 14.70 to 195.30 µSv y−1 with a mean value of 71.58 µSv y−1 for the children, while in- fants recorded ACED values between 10.92 to 145.08 µSv y−1, with a mean value of 53.17 µSv y−1. Similarly, average ACED due to ingestion of water from BH source by adult, children and infants population of the stud- ied community are 104.24, 99.96 and 74.26 µSv y−1 respec- tively. The results shows that ACED increases with mean radon concentration, rate of water consumption and age; thus, in- fants suffer least radon exposure compared to the children and adults. This agrees with the results obtained for similar stud- ies by Kalip et al [24] and Ravikumar and Somashekar [10]. Furthermore, the highest ACED due to groundwater consump- tion from LW and BH sources among the ICRP age groups is 0.204 mSv y−1 and 0.274 mSv y−1 respectively. These values are below the 1mSv y−1 safety threshold recommended by UN- SCEAR and WHO. The infants, children and adult population of Bosso community are therefore not under any immediate health threat from waterborne radon. Variations of ACED re- ceived by different ICRP age groups due to ingestion of wa- terborne radon from LW and BH groundwater sources in the studied community are shown in Figures 4 and 5. Table 3 shows the comparison of the results of this inves- tigation with those of similar studies from different parts of Figure 5: ACED received by different ICRP age groups due to waterborne radon from BH groundwater sources Nigeria. Mean radon concentration for open wells within the community (10.2 Bq l−1) is higher than that reported by Kalip et al [24] for Kaduna (1.8 Bq l−1). Additionally, average value obtained for the boreholes within the community (14.3 Bq l−1) is about 54% lower than the one reported by Isinkaye and Aji- boye [28] for Ekiti State. This may be due to variations in local geology of the respective sampling areas and depth of sampling. Judging from the Table generally, the range of radon concentra- tion values obtained for the two groundwater sources in Bosso community is comparable to those reported in literature from other parts of Nigeria. 3.2. Evaluation of Excess Lifetime Cancer Risk and Annual Ef- fective Dose Due to Inhalation and Ingestion Radiation dose to the internal organs of human population from waterborne radon has been identified as a highly potent human health threat. Human exposure to waterborne radon is principally through direct ingestion of radon-contaminated wa- ter and inhalation of radon-saturated indoor air. Direct inges- tion results in radiation dose delivery to the human stomach while inhalation pathway delivers dose to the lungs and respira- tory track. Annual committed effective dose (ACED) to human stomach from direct ingestion of radon-contaminated water in the studied community was calculated from the equation [11, 35]: ACEDing ( mS v y−1 ) = CRn × WCR × DCFing (3) where CRn is the concentration of radon in water, WCR the an- nual water consumption for adults (730 L y−1) and DCFing is the effective dose conversion factor for ingestion (3.5 nSv Bq−1). Since radon is comparatively insoluble in water, continuous domestic utilization of water can result in consistent liberation of radon gas into the indoor air, thereby enhancing the average committed dose incurred via inhalation pathway [9, 35]. ACED due to inhalation of waterborne radon was computed from the equation [8, 36]: ACEDinh ( mS v y−1 ) = CRn×RAW ×EF×OF×DCFinh(4) where CRn is the concentration of radon in water, RAW is the ratio of radon-in-air to radon-in-water (10−4), EF is the equilib- rium factor between radon and its progeny for indoor environ- ment (0.4), OF is the average global indoor occupancy factor 5 Kolo et al. / J. Nig. Soc. Phys. Sci. 5 (2023) 896 6 Table 3: Comparison of radon concentrations in groundwater obtained in this study with other locations within Nigeria Location Source of water 222Rn Conc (Bq l−1) References Ekiti State, Nigeria borehole 30.9 Isinkaye and Ajoboye [28] well 19.5 Ogbomosho, SW Nigeria borehole 0.60 - 2.64 (1.86) Oni et al. [29] Ekiti State University, Nigeria Hand pumped boreholes 7.0 - 41.5 (23.3) Isinkaye et al. [11] hand dug wells 0.6 - 36.2 (13.33) Motorized boreholes 0.6 - 27.4 (7.4) Gadau, Bauchi State, Nigeria well 4.92 - 82.89 (38.3) Shu’abu et al. [30] Ibadan, Nigeria well 2.18 - 76.75 Ademola and Oyeleke [31] Kaduna, Nigeria well 0.85 - 2.57 (1.8) Kalip et al. [24] borehole 0.35 - 085 (0.57) Ogun State, Nigeria borehole 1.23 - 12.68 Fatoki and Ademola [32] Zaria, Nigeria borehole 7.41 Garba et al. [33] well 7.18 Sabon Gari, Kaduna, Nigeria borehole 14.9 Jibril et al. [34] Bosso, north-central Nigeria borehole 14.3 Present study Open well 10.2 Mean values are in parenthesis. (7000 h y−1) and DCFinh is the dose conversion factor for expo- sure to radon in air (9 nSv Bq−1 h−1 m3). Computed values for committed annual effective dose (ACED) received by internal organs (stomach and lungs) due to inges- tion and inhalation of waterborne radon in Bosso community and presented in Table 4. Also presented in Table 4 is the calculated excess lifetime cancer risk (ELCR) due to water- borne radon in the studied community. ACED delivered to the stomach as a result of ingestion of waterborne radon from LW sources varied from 0.37 to 4.88 µSv y−1, with a mean value of 1.79 µSv y−1, while the ACED range to the lungs via inhalation is 5.29 to 70.31 µSv y−1 with an average value of 25.77 µSv y−1. Similarly, the range of ACED from BH sources delivered to the stomach via the ingestion pathway is 0.49 to 6.86 µSv y−1 with a mean of 2.50 µSv y−1 and to the lungs via inhalation route is 7.06 to 98.78 µSv y−1 with an average value of 35.99 µSv y−1. With reference to the US National Academy of Sciences re- port of 1999, UNSCEAR [37] computed mean dose from radon in drinking water to be 0.002 mSv y−1 and 0.025 mSv y−1 for ingestion and inhalation pathways respectively. The results fur- ther show that the highest percentage of whole body dose comes through the inhalation pathway, hence, the lung cells and res- piratory track in general are more prone to cancer incidences compared to the walls of the stomach. The total annual effec- tive doses due to ingestion and inhalation (whole body dose) incurred from waterborne radon in Bosso community ranged from 5.66×10−3 to 0.075 mSv y−1 for LW groundwater sources and from 7.55×10−3 to 0.106 mSv y−1 for BH groundwater sources, with mean values of 0.0276 and 0.0385 mSv y−1 in se- quence. These values are below the threshold value of 0.1 mSv y−1 recommended by UNSCEAR and WHO for public safety. The probability of cancer incidence was evaluated in order to assess any possible potential carcinogenic effects to human population for a specific lifetime of exposure to waterborne radon. Excess lifetime cancer risk (ELCR), which shows the extra risk of occurrence of cancer due to exposure to water- borne radon in the studied community was computed using the equation [38, 39]: ELCR = W BD × RF × DL (5) where WBD is the whole body dose in µSv y−1, RF is the risk factor taken to be 0.05 Sv−1 for stochastic effects [40] and DL is the lifetime duration of 70 years. Computed ELCR values which gives an indication of extra risk of cancer incidence due to exposure to waterborne radon among the studied community are presented in Table 4. Aver- age ELCR values for LW and BH groundwater sources in Bosso community are 0.10 × 10−3 and 0.13 × 10−3 respectively, which are below the world mean value of 0.29 × 10−3. The likelihood of any cancer incidence among the population of the studied community is therefore insignificant. Hence water from the two groundwater sources investigated is fit for consumption and for other domestic usage from the point of view of radiation pro- tection. 4. Conclusion Water samples from two major groundwater sources (open wells and boreholes) in Bosso community were collected and analysed for their radon (222Rn) concentration using Durridge RAD-7 radon detector. The results showed that, although 222Rn concentration values in about 33% of water samples from the two groundwater sources were above the USEPA safety thresh- old, all values were within the safety range of 4 – 40 Bq l−1 recommended by the United Nations Scientific Committee on Effects of Atomic Radiation. The results also indicated that about 94% of whole body dose comes through the inhalation pathway, which shows that inhalation of radon escaping from water is a considerable 6 Kolo et al. / J. Nig. Soc. Phys. Sci. 5 (2023) 896 7 Table 4: Radon concentration, ACED to internal organs and ELCR in LW and BH water samples ACED (µSv/y) to internal organs ELCR (10−3) Sample ID 222Rn (Bq/l) Ingestion (Stomach) Inhalation (lungs) Whole body Open wells LW 01 2.1±0.7 0.37 5.29 5.66 0.02 LW 02 27.9±2.5 4.88 70.31 75.19 0.26 LW 03 24.9±2.5 4.36 62.75 67.11 0.23 LW 04 10.2±1.6 1.79 25.70 27.49 0.10 LW 05 2.9±0.8 0.51 7.31 7.82 0.03 LW 06 4.5±1.1 0.79 11.34 12.13 0.04 LW 07 8.8±1.4 1.54 22.18 23.72 0.08 LW 08 2.4±0.8 0.42 6.05 6.47 0.02 LW 09 4.4±1.1 0.77 11.09 11.86 0.04 LW 10 3.1±2.0 0.54 7.81 8.35 0.03 LW 11 16.0±2.8 2.80 40.32 43.12 0.15 LW 12 15.5±0.8 2.71 39.06 41.77 0.15 Min 2.1±0.7 0.37 5.29 5.66 0.02 Max 27.9±2.5 4.88 70.31 75.19 0.26 Mean 10.2±1.5 1.79 25.77 27.56 0.10 Boreholes BH 01 28.7±3.1 5.02 72.32 77.35 0.27 BH 02 10.1±1.5 1.77 25.45 27.22 0.10 BH 03 22.2±1.0 3.89 55.94 59.83 0.21 BH 04 2.8±1.1 0.49 7.06 7.55 0.03 BH 05 39.2±1.5 6.86 98.78 105.64 0.37 BH 06 9.9±2.0 1.73 24.95 26.68 0.09 BH 07 12.3±4.5 2.15 31.00 33.15 0.12 BH 08 10.5±0.2 1.84 26.46 28.30 0.10 BH 09 3.7±0.8 0.65 9.32 9.97 0.03 BH 10 3.4±1.3 0.60 8.57 9.16 0.03 Min 2.8±1.1 0.49 7.06 7.55 0.03 Max 39.2±1.5 6.86 98.78 105.64 0.37 Mean 14.3±1.7 2.50 35.99 38.48 0.13 influence on the radiological hazard of the population. 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