Introduction

Radiation is emitted due to spontaneous transformation of an unstable nucleus. Radiation dose released from natural sources is higher than that of anthropogenic sources, which were received by mankind. Therefore exposure due to natural radiation has special significance [1, 2]. Naturally radioactivity arises from primordial radioactive materials that mainly consisting uranium (238U, 235U), thorium (232Th), potassium (40K) and 226Ra [3,4,5]. The artificial radioactivity is due to various human-artificial activities [6,7,8]. Naturally background radiation is due to cosmic and terrestrial sources [9,10,11]. The variation in the value of terrestrial radiation is generally greater than the cosmic rays [12]. Cosmic radiation comes from the sun and galaxies through the earth’s atmosphere. The worldwide annual average cosmic radiation dose at sea level is 0.39 mSv/y [1, 13]. Terrestrial radiation comes from the radioactive nuclides present in the Earth’s crust, from the atmosphere and from building materials (derived from rocks and soils) [14]. Average annual outdoor terrestrial radiation dose is 0.07 mSv/y and for indoor 0.41 mSv/y [1, 13]. The health impact due to an exposure to radionuclides, inhalation by human beings within the indoor environment is a major public concern worldwide [15, 16]. Avoiding natural radionuclides is not possible since as it is present since the formation of the earth [17]. Few researchers studied the risk assessment of the gamma radiation dose rate for outdoor and indoor environment [3,4,5, 14, 18,19,20,21]. The main objective of this study is to determine the risk arises from the gamma dose rate for Balod District. The result of this study will serve as baseline data for future gamma radiation effect in Chhattisgarh region.

Material and methodology

Selection of the measurement sites

Balod city is situated on the bank of Tandula River, which has District Headquarter from 1st January 2012. This District is situated on an average 324 meters (1063 feet) above sea level. The total areas of District Balod which situated in Chhattisgarh centre is 352,700 ha, where 74,911 ha covered by forest and remain are part of the land. This District is endowed with natural resources like water, forest and mineral resources [22]. Outdoor and Indoor gamma dose rates were measured in 52 study locations from Balod District, Chhattisgarh India, where total population is 78,764 [23]; that is mentioned in Table 1. All study locations are shown in Fig. 1. Six square kilometre grid have been taken as per Board of Research in Nuclear Sciences, Department of Atomic Energy.

Table 1 Outdoor and indoor gamma dose rate and AEDE values for Balod District of Chhattisgarh
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Fig. 1
figure 1

Grid map of study areas Balod District, Chhattisgarh India

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Gamma dose rate measurement

Outdoor and Indoor gamma dose rates were measured by using Geiger–Muller based dosimeter (Polimaster PM-1405) for study locations. Reading was recorded in nSv/h. This apparatus record both the cosmic and the terrestrial radiation at 1 m height above the ground surface. The energy range of this device for gamma radiation is 0.05–3 MeV and measurement range for dose rate is 0.01 µSv/h to 100 mSv/h [20]. The Latitude (N) and Longitude (E) of all study locations were determined by the GPS (GARMIN OREGON-650) coordination device.

Calculation of Annual Effective Dose Equivalent (AEDE)

Annual effective dose equivalent (AEDE) value of outdoor and indoor from study locations were calculated by using outdoor and indoor gamma dose rates respectively. The biological effects on humans due to radiations are evaluated on the basis of AEDE [24]. AEDE was estimated by using the following equation:

$$\begin{aligned} & {\text{AEDE}}({\text{indoor/outdoor}}) \\ & \quad = D({\text{indoor/outdoor}}) \times {\text{conversion}}\;{\text{coefficient}} \times T \\ & \quad \quad \times \,{\text{occupancy}}\;{\text{factor}} \\ \end{aligned}$$
(1)

where: D(indoor) = Absorbed gamma dose rate in indoor (nGy/h), D(outdoor) = Absorbed gamma dose rate in outdoor (nGy/h), T = Time (h).

The value of occupancy factor reported by UNSCEAR for indoor and outdoor was 0.8 and 0.2, respectively; and the conversion coefficient for an adult was reported 0.7 [1]. The values are about 10 and 30% higher for children and infants [1].

Therefore above formula become as:

$${\text{AEDE}}({\text{indoor}}) = {\text{D}}({\text{indoor}}) \times 0.7 \times 8760 \times 0.8$$
(2)
$${\text{AEDE}}({\text{outdoor}}) = {\text{D}}({\text{outdoor}}) \times 0.7 \times 8760 \times 0.2$$
(3)

Equation (2) and (3) were used for calculation of AEDE indoor and outdoor respectively. Total AEDE was calculated by adding indoor and outdoor AEDE values.

$${\text{Total}}\;{\text{AEDE}} = {\text{AEDE}}({\text{indoor}}) + {\text{AEDE}}({\text{outdoor}})$$
(4)

Risk assessment

Lifetime effective dose

Lifetime effective dose calculated by total AEDE values and duration of life.

$${\text{Lifetime}}\;{\text{effective}}\;{\text{dose}} = {\text{Total AEDE}} \times {\text{duration}}\;{\text{of}}\;{\text{life}}$$
(5)

where total AEDE value calculated by Eq. (4) and take duration of life 70 year [3, 20].

Calculation of Excess Lifetime Cancer Risk (ELCR)

Excess lifetime cancer risk was calculated by using lifetime effective dose (from Eq. (5)) and risk factor. For public, value of risk factor was 0.05 used by ICRP 60 [3, 20]. The value of cancer risk calculated only for those locations where lifetime effective dose crosses the 100 mSv [25].

$${\text{ELCR}} = {\text{Lifetime}}\;{\text{effective}}\;{\text{dose}} \times {\text{risk}}\;{\text{factor}}$$
(6)

Results and discussion

Results of outdoor gamma dose rate, indoor gamma dose rate, AEDE and lifetime effective dose from Balod District of Chhattisgarh are presented in Table 1. In the present investigation, the value of outdoor and indoor gamma dose rate range was found to be extending from 103.0 ± 3.1 to 201.0 ± 6.0 and 132.0 ± 4.0 to 260.0 ± 7.8 nSv/h, respectively. The values of the Indoor and outdoor gamma dose rate are shown in Figs. 2 and 3. Arithmetic average values for outdoor and indoor gamma dose rate was 143.6 ± 4.3 and 194.7 ± 5.8 nSv/h. The maximum value of indoor gamma dose rate was observed 260.0 nSv/h in Bohara area; however UNSCEAR reported gamma dose rate varies from 20 to 200 nSv/h. In this study indoor gamma dose rate from area code B-3, B-7, B-12, B-19, B-24, B-27, B-28, B-29, B-31, B-40, B-44, B-47, B-48 and B-49 were found to be more than 200 nSv/h.

Fig. 2
figure 2

Indoor gamma dose rate from Balod District Chhattisgarh

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Fig. 3
figure 3

Outdoor gamma dose rate from Balod District Chhattisgarh

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Annual Effective Dose Equivalent (AEDE)

Annual Effective Dose Equivalent values for outdoor and indoor are shown in Fig. 4. The value of outdoor and indoor AEDE was found to be in the range from 0.13 to 0.25 and 0.65 to 1.28 mSv/y, respectively. In this study Indoor AEDE value found to be higher than the outdoor AEDE because people spend more time inside as compare to outside. Arithmetic average value of indoor AEDE was found to be 0.95 mSv/y and arithmetic average value of outdoor annual dose was found to be 0.18 mSv/y. Total AEDE was found to be 1.13 mSv/y; however the world population weighted average value reported for AEDE was 0.87 mSv/y [1]. The values of total AEDE and their comparison with world population weighed average value are shown in Fig. 5. This study indicates the values of AEDE from Balod District to be slightly higher than the above mentioned world average. The data reported in this study will seem as useful baseline data for this region.

Fig. 4
figure 4

Indoor and outdoor annual effective dose equivalent values from Balod District Chhattisgarh

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Fig. 5
figure 5

Values of total annual effective dose equivalent and their comparison with world population weighed average value

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Indoor and outdoor gamma dose rate ratio

The range of indoor to outdoor gamma dose ratios was found to be 0.90–1.92, with an arithmetic average value 1.37. This ratio value is slightly lower than the world population weighted average 1.4 [1]. Only in two study location (B-9 and B-34) indoor gamma dose rate values recorded lower than the outdoor gamma dose rate.

Overall Statistical data of gamma dose rates for Balod District of Chhattisgarh and their comparison with world population weighted average are shown in Table 2.

Table 2 Statistical data of gamma dose rates for Balod District of Chhattisgarh and their comparison with world population weighted average
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Excess Lifetime Cancer Risk (ELCR)

The probability of the incidence of cancer and the potentially carcinogenic effects of gamma dose rates during a specific lifetime is evaluated by ELCR [19]. In this study calculated ELCR values with their location are shown in Table 3. The values of ELCR from gamma dose rate in different locations (country/city) of the world are shown in Table 4. The highest value of ELCR found to be 5.2 × 10−3 in Marram Kheda. Present study showed that the ELCR range varies from 5.0 × 10−3 to 5.2 × 10−3; which are higher than the reported values from Jhelum valley Northwest Himalayas, Pakistan; Ondo State, Nigeria; Alapuzha Kerala; Ebonyi State and Turkey [3,4,5, 14, 18,19,20,21]. Previous study was also reported high uranium in water sample from Deur Tarai [26] and in this area ELCR found to be 5.0 × 10−3 due gamma dose rate.

Table 3 Values of Excess Lifetime Cancer Risk (ELCR)
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Table 4 Values of Excess lifetime cancer risk from gamma dose rate in different location (country/city) of world
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Conclusions

The mean value (arithmetic and geometric) of AEDE for Balod district was slightly higher than the world population weighted average value. The maximum value of AEDE was found to be 1.49 mSv/y in Marram Kheda area. Lifetime effective dose was varies from 54.2 to 104.2 mSv. Only in five area lifetime effective dose more than the 100 mSv. ELCR values were found to be 5.2 × 10−3, 5.0 × 10−3, 5.0 × 10−3, 5.2 × 10−3 and 5.1 × 10−3 in areas Bohara, Deur Tarai, Parregura, Marram Kheda and Pandel, respectively. The population of five areas of Balod district: Bohra, Deor Tarai, Paraguara, Marram Kheda and Pandel was 1011, 583, 746, 217 and 805, respectively; where the ELCR was calculated. This study will be helpful for a preventive measure towards cancer risk. As per Indian scenario we generally lives in concrete structure. So here all most all indoor data were effective the radiation. It seems that our data represent the authentic proof for indoor to outdoor ratios values.