Introduction

Industrialization can be beneficial and detrimental to man and his environment. The Earth’s crust possesses some natural resources that enhance industrialization which tends to develop the human race. These resources are commonly explored to a great level by spontaneous and artificial activities, which tend to degrade the environment frequently (Lone et al. 2008). The environment is subjected to degradation due to pollution as a result of anthropogenic activities that deteriorate the quality of air, soil, and water, posing a great risk to human health (McGrath et al. 2001). Natural radionuclides are spontaneous in nature and are readily available in our environment. These radionuclides can be technically enhanced by human activities such as industrialization and agricultural activities. The widespread of radionuclides in the environment exists in numerous geological formations (water, soils, air, plants, rocks, and earth crust) (Unscear 2000). Soil radionuclide activity concentration is one of the main factors of the naturally occurring radiation.

Soil radionuclides can be influenced by human activities, in addition to natural sources. The concentration of radionuclides in the soil is studied to have an in-depth understanding of their spatial distribution. Long-term exposure to radionuclides such as thorium and radium through inhalation and direct exposure is of severe health and environmental concerns today in the world (Bickerstaff and Walker 2001). Linkages between serious health effects like chronic diseases and respiratory-related ones that could induce high mortality and exposure to radionuclides have been established by previous studies (Lü et al. 2015). Health challenges like acute leucopenia, anemia, necrosis of the mouth, and chronic lung diseases are associated with long-term exposure to thorium (Agency 1991; Taskin et al. 2009), while radium causes weakening of the bone, cranial, and nasal tumors. Other diseases as a result of radionuclide exposure include leukemia, cataracts, sterility, atrophy of the kidney, cancer of skin, lungs, pancreas, kidney, and bone (Oke et al. 2020; Taskin et al. 2009).

The radiation of radionuclide emanating from the soil contributed some percentage to background radiation which increases the level of human exposure and health risk. Also, the contribution of cosmic rays to background radiation is not left out as 90% of human exposure arises from a natural source of radiation (Oladele et al. 2018). Geiger Muller (GM) counter is one of the suitable devices for background radiation measurement due to its ability to detect and measure radiation instantaneously; however, it cannot differentiate sources of radiation. A high dose of background radiation is detrimental to various organs of the human body. Ionizing radiation is highly energetic particles with high penetrating power. Cell structures are altered when ionizing radiation passed through biological cells (Emelue 2014). High-level gamma radiation exposure causes cancers and mutation (Saad-El-Din et al. 2014) in humans and other kinds of diseases (Taskin et al. 2009). Therefore, the knowledge of background radiation in a particular environment enables one to understand the level of radiation and radiological health hazards associated with exposure.

Table 1 Sample locations, point names, point codes, coordinates, radionuclide activity concentrations, and background equivalent dose rates
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Several researchers have reported high and low dose rates of a different environment, particularly in industrial areas in Nigeria. Agbalagba (2017) evaluated the dose rate of background radiation in the industrial area of Warri. His result indicated a higher level of radiation dose in the area (Agbalagba 2017). James et al. (2013) carried out their work at Idu industrial area (James et al. 2013). Their work shows that the area is not of great concern. Agbalagba et al. (2016) studied the level of radiation in Ughelli metropolis owing to industrial activities in the environment and reported a high level of radiation dose in the area (Agbalagba et al. 2016). Ramli et al. (2014) also studied the levels of radiation in Keffi and Akwanga towns and found that the radiation dose rate is below the recommended limit (Ramli et al. 2014).

Despite the efforts in carrying out researches in industrial areas of Nigeria, no data have been recorded on the assessment of background radiation in Agbara industrial estate, which makes its selection of interest and necessity. This work was conducted to ascertain the safety of the dwellers and industrial workers of the study area due to exposure to background radiation as a result of industrial activities, which has never been considered nor evaluated. It is therefore of interest to provide knowledge on the ionizing radiation exposure levels in Agbara Industrial Estate, owing to industrial activities to evaluate possible health hazards to safeguard the environment. The data obtained in this study will be documented for future purposes.

Materials and methods

Study area

Agbara estate is situated in Ado-odo otta LGA between 3° 00′ and 3° 15′ latitude and 6° 15′ and 63° 5′ longitude of Ogun State, Nigeria. The estate comprises three phases which are recreational, residential, and commercial (industries) areas. The industrial areas are located on a 188.289 ha of land, which is 41.55% of the total 454.1 ha of Agbara estate. The industries found in this area are multinational companies, which produce most of the consumables in the country. Some of these companies are Nestle Nig PLC, Beta Glass Nigeria PLC, Pharma Deko (Nig.) PLC, Vitamalt PLC, Reckitt Benckiser Nigeria Ltd., Lotus Plastic, Evans Medical Nigeria PLC, DIL/Maltex (Nig.) PLC, Henley Industries, Cometstar Cables Ltd, Pace Factory, Glaxo-Smith-kline Nigeria PLC, etc. Most of these companies belong to the pharmaceutical, food, and beverages group. The estate also comprises of three phases of residential areas. The residential phase one presently accommodates over five thousand dwellers, while more than fifty thousand people come to the various companies for daily businesses and transactions or the other. The other phases (two and three) are yet to be developed which was estimated to accommodate over fifteen thousand dwellers each. The wastes from both the commercial and residential areas are linked into a sewage treatment plant through sewage pipes, which treats both industrial and domestic wastes, respectively before liquidating the treated waste into the Ologe Lagoon through a stream (Bodunrin and Ajayi 2017). The map of Nigeria, Ogun State, and Ado-odo Ota LGA showing the study area is depicted in Fig. 1.

Fig. 1
figure 1

Map of Nigeria, Ogun State, and Ado-odo Ota LGA showing the study area (Agbara)

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Sample collection

Fifty-five (55) soil samples were taken from the study area. Twenty-five were from residential, fifteen from industrial, ten from dumpsites, and five from the sewage area of the study area. Each point in which samples were collected was marked 1.0 m × 1.0 m and carefully cleared of unwanted particles to a depth of few centimeters. Afterward, the samples were collected randomly from several points and thoroughly homogenized to obtain a composite soil sample of the same location. The soil samples were packed into Polyethylene bags, tightly sealed, and were labeled accordingly. The information on the labeled soil samples includes location, point name, and point code. The soil samples were air-dried, pulverize, and sieved with a 2-mm standard net. The samples were placed in Marinelli beaker containers and weighed to 200 g. The containers were covered, sealed with PVC tape, and kept for a month to establish secular equilibrium among 226Ra (long-lived parent nuclides) and 232Th (short-lived daughters) (Oke et al. 2020) before analysis with the high-purity germanium detector (HPGe).

The in situ background radiation measurement was taken at each point where soil samples were collected using a Geiger Muller (GM) counter (Kindenoo blue Geiger PG-15) and a Global Positioning System (GPS) to determine the equivalent dose rate (EDR) and coordinate of each point, respectively. The measurements were taken at about 1 m above the ground level at 55 points where soil samples were taken. Three (3) readings were taken at each point at intervals of 2 min, making a total of 165 readings and the average value of each point was recorded.

The information on the soil samples and coordinates are presented in Table 1.

Table 2 Gamma ray emission lines of radionuclide
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HPGe analysis of radionuclide

HPGe computerized system with a resolution of 1.8 keV at 1.33 MeV of 60Co was utilized to measure the activities of 40K, 232Th, and 226Ra in the soil samples. Relative efficiency of 40% was utilized, and a multichannel analyzer and gamma spectrometer were connected to the detector. The efficiency and energy of the system were calibrated prior to sample measurement. The calibration ensures both qualitative and quantitative analysis of the measured samples. A standard calibration of mixed radionuclide in a 1.0-L container, a density of 1.0 g cm−3, and a volume of 1000 mL with serial number NW 146 were utilized (Deutscher Kalibrierdienst (DKD-3), QSA Global GmBH, Germany). For energy calibration, a combination of channel number and the standard calibration spectrum were used in observing the principal gamma-ray peaks. The efficiency calibration was also accomplished by attaining a typical spectrum to calculate the total absorption count rate with a statistical uncertainly of less than 1% at 95% assurance. The counting rate was then determined by the energies at the photo peaks for estimating the efficiency. The efficiency at other peaks was then calculated by deducing its values from a plotted graph of each energy efficiency against peak energies.

Afterward, the soil samples were inserted into the detector, inside a cylindrical Lead shield of thickness, internal diameter, and height of 5 cm, 24 cm, and 60 cm, respectively. MAESTRO 32 software was used to study the data. The concentration of the radionuclide was determined using the gamma emission lines presented in Table 2. A counting time of 10 h was utilized to obtain a spectrum for each sample. The theoretical determination of these radionuclides and the uncertainties associated with measurements can be found elsewhere (Nguyen and Zsigrai 2006; Zsigrai et al. 2015).

The activity concentrations of radionuclides in soil samples were examined using Eq. 1 (Tzortzis et al. 2003):

$$ {A}_c={N}_{\mathrm{sam}}/M\times {P}_E\times {T}_c\times \varepsilon $$
(1)

where Ac is activity concentration, Nsam is radionuclide net counts, M is mass of the sample, PE is gamma-ray emission probability, Tc is sample counting time, and ε is detector efficiency.

MapInfo 6.0 software was adopted for the spatial distribution of activity concentration of radionuclide as depicted in Fig. 2.

Fig. 2
figure 2

Spatial distribution of a 40K, b 232Th, and c 226Ra in the study area

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GM counter measurement of radiation

The in situ background radiation measurement was performed using a PG-15 Kindenoo GM counter with version and serial number 38.0 and 0018B2012589, respectively. The range of its measurement is 0.05–300 μSv/h with maximum radiation and time measurement of 250 mSv and 10 years, respectively. The detector was calibrated at the National Institute of Radiation Protection and Research, a secondary standard laboratory certified by the International Atomic Energy Agency (IAEA) and a division of the Nigerian Nuclear Regulatory Authority (NNRA). The characteristic features of this instrument are small size, flexibility of operation, and superior measurement performance which is provided by the use of low power technology.

The sievert (Sv) is the International System of Units (SI) derived unit of equivalent radiation dose, effective dose, and committed dose. One sievert is the amount of radiation needed to produce the same effect on living tissue as one gray (Gy) of high-penetration x-rays. Quantities that are measured in sieverts are designed to represent the biological effects of ionizing radiation (Cember 1969). The conversion of Gy to Sv is presented below:

$$ 1\ \mathrm{gray}\ \left(\mathrm{Gy}\right)=1\ \mathrm{sievert}\ \left(\mathrm{Sv}\right) $$
(2)

Outdoor terrestrial dose assessment

Absorb dose rate (ADR) is the amount of radiation emanating from radionuclide in the soil per unit time in the air. This is direct exposure of humans to activity concentration of radionuclide. The ADR in the air at 1 m above the ground surface for 40K, 226Ra, and 232Th (Bq/kg) in soil samples was evaluated using the equation below (Suleiman et al. 2018). The dose coefficients in units of nGyh−1 per Bqkg−1 were taken from the United Nations Scientific Committee on the Effects of Atomic Radiation report (Unscear 2000).

$$ \mathrm{ADR}\ \left(\mathrm{nGy}/\mathrm{h}\right)=0.462{A}_{\mathrm{Ra}}+0.604{A}_{\mathrm{Th}}+0.0417{A}_{\mathrm{K}} $$
(3)

where ADR is absorbed dose rate and AK, ARa, and ATh are the activity concentrations of 40K, 226Ra, and 232Th, respectively.

The annual effective dose equivalent (AEDE) is the accumulated dose rate in a year and was assessed using an outdoor occupancy factor and a conversion factor of 20% and 0.7 Sv/Gy, respectively. The equation below was used to determine the AEDE:

$$ \mathrm{AEDE}\ \left(\mathrm{mSv}/\mathrm{year}\right)=\mathrm{ADR}\ \left(\mathrm{nGy}/\mathrm{h}\right)\times 8760\ \left(\mathrm{h}/\mathrm{year}\right)\ 0.7\times \left({10}^3\ \mathrm{mSv}/\mathrm{nGy}\ {10}^9\right)\times 0.2 $$
(4)

where ADR is the absorbed dose rate and 0.2 is the outdoor occupancy factor

The maximum permissible value recommended by ICRP is 1.0 mSv/year (ICRP 1991) for radiological, epidemiological, and somatic health effects to be insignificant for the public and industrial worker as well.

Outdoor background radiation dose assessment

The equivalent dose rate (EDR) is an in situ approach of measuring ambient radiation to enable samples to maintain their original environmental features. A radiation monitor, GM counter (Kindenoo blue Geiger PG-15), was used. The GM counter detects radiations such as alpha, beta, gamma, and x-rays.

The EDR was measured with the GM counter in μSv/h. The spatial distribution of EDR using MapInfo 6.0 software is displayed in Fig. 5.

The annual equivalent dose rate (AEDR) measures the quantity of energy absorbed by the human body in a year. Equation 4 below was used to calculate the AEDR received outdoor in mSv/year (Pourfallah et al. 2012). A 20% outdoor occupancy factor was considered translating to an occupancy factor of 0.2.

$$ \mathrm{AEDR}\ \left(\mathrm{mSv}/\mathrm{year}\right)=\mathrm{EDR}\ \left(\upmu \mathrm{Sv}/\mathrm{h}\right)\times 8760\ \left(\mathrm{h}/\mathrm{year}\right)\times 0.2\times 0.001\ \left(\upmu \mathrm{Sv}/\mathrm{mSv}\right) $$
(5)

where EDR is the equivalent dose rate and 0.2 is the occupancy factor.

The effective dose (EDorgans) to various organs of the body evaluates the quantity of intake radiation dose to several organs of the body and tissues. The EDorgan of the body due to inhalation was calculated using the equation below (Agbalagba et al. 2016; Ugbede and Benson 2018):

$$ {\mathrm{ED}}_{\mathrm{organs}}\ \left(\mathrm{mSv}/\mathrm{year}\right)=\mathrm{AEDR}\times {F}_{\mathrm{risk}} $$
(6)

where Frisk is the risk factor of organ dose from air dose. The Frisk for each organ of the body is presented in Table 5.

Excess lifetime cancer risk (ELCR)

ELCR reveals the possibility of having cancer over a period of time at a given level of exposure. The ELCR was assessed using the equation given below (Faromika et al. 2016):

$$ \mathrm{ELCR}=\mathrm{AEDR}\left(\mathrm{AEDE}\right)\times \mathrm{DL}\times \mathrm{RF} $$
(7)

where DL is the duration of life (70 years) and RF is the risk factor (0.05 Sv−1). These values were recommended for the public by ICRP (ICRP 1991).

Results and discussions

Activity concentration of radionuclide in the study area

The spatial distributions of 40K, 232Th, and 226Ra in soils of several locations (industrial, residential, dumpsite, and sewage) of the study area are displayed in Fig. 2a, b, and c, respectively. In the figures, each point with the same color falls within the same range as depicted in the legend beside each figure. Considering Fig. 2a, more than a few points are found within the color range of 58.04–127.24 Bq/kg and are distributed across all the studied locations. A point with the highest value is found within the color of 532.89–666.5 Bq/kg and is found in the residential area. In Fig. 2b, many points are found within the color range 2.90–5.72 Bq/kg and are distributed across residential, sewage, and industrial locations. The lowest points are found in dumpsite and industrial within the color range of 8.49–9.34 Bq/kg. Figure 2c shows multiple points within the color range of 1.56–3.01 Bq/kg and is distributed across residential, sewage, and industrial locations. The lowest points fall within 3.80–4.37 Bq/kg color range and are found at the residential location.

The mean activity concentration of these radionuclides in soils of several locations has been assessed due to industrial activities and are presented and depicted in Table 3 and Fig. 3, respectively. 40K is radioactive among natural potassium (39K, 40K, and 41K) owing to its decay process which gives rise to 40Ca and 40Ar (progenies) isotopes. The occurrence of 40Ca and 40Ar isotopes was said to be from the emissions of beta and gamma radiation, respectively, which are detrimental to human health and their environment (Ramola et al. 2008). The concentrations of 40K ranged from 57.88 to 340.67 Bq/kg, and the mean is found to be 147.03 Bq/kg for industrial, 61.23–667.55 Bq/kg, and the mean is found to be 230.74 Bq/kg for residential, 68.10–139.75 Bq/kg, and the mean is found to be 100.46 Bq/kg for dumpsite and 72.14–113.88 Bq/kg, and the mean is found to be 88.98 Bq/kg for sewage area.

Table 3 Mean activity concentration of radionuclide in soil
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Fig. 3
figure 3

Mean activity concentration of 40K, 232Th, and 226Ra at each location

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226Ra diffuses from 238U, the radioactive equilibrium is well-known among the parent 238U, and it progenies in the decay chain at a rate of the progeny half-life, and at the level of the parent decay rate. The decay process goes through 226Ra → 222Rn down to 206Pb at a rate consistent with the parent. 220Rn also diffuses from 232Th, 222Rn, and 220Rn can be formed in the air due to their gaseous nature. These radionuclides get into the atmosphere and groundwater by its presence and that of their progenies and are among the most toxic elements (Choppin et al. 2002). Thus, exposure to 232Th and 226Ra radiation emanating from the soil is associated with several ailments such as chronic hepatic cancers, lung cancer, acute leucopenia, anemia, leukemia, pancreas, kidney, and bone damage when their activity concentration exceeds the recommended dose (Agency 1991; Oke et al. 2020). The concentrations of 232Th in soil of the study area range within 5.15–15.10 Bq/kg and the mean is found to be 10.15 Bq/kg for industrial, 2.89–17.73 Bq/kg, and the mean is found to be 7.67 Bq/kg for residential, 5.01–16.72 Bq/kg, and the mean is found to be 11.34 Bq/kg for dumpsite and 5.51–12.83 Bq/kg, and the mean is found to be 8.77 Bq/kg for sewage location. The concentrations of 226Ra range within 1.53–8.85 Bq/kg, and the mean is found to be 5.17 Bq/kg for industrial, 1.76–9.83 Bq/kg, and the mean is found to be 4.58 Bq/kg for residential, 3.34–7.48 Bq/kg, and the mean is found to be 5.60 Bq/kg for dumpsite, 1.61–9.39 Bq/kg, and the mean is found to be 5.97 Bq/kg for sewage location. The overall activity concentration of the study area ranged from 57.88 to 667.55, 2.89 to 17.73, and 1.53 to 9.83 Bq/kg, and the mean is found to be 171.33, 9.11, and 5.05 Bq/kg for 40K, 232Th, and 226Ra, respectively.

From Fig. 3, the concentrations of 40K in all sampling locations are higher than that of 232Th and 226Ra. The variation in the concentrations of the studied radionuclides can be attributed to the geological conditions due to the rock formation and transport processes in the soils of the area (Oke et al. 2020; Ramola et al. 2008). From the same figure, we also observed that the concentration of 40K is very high at the residential location, followed by the overall mean than other locations. This observation can be associated with agricultural activities that is been practice by the dwellers of the study area, which may involve the use of fertilizers as a nutrient to enhance the growth of plants and has been reported elsewhere (Faisal et al. 2015). Actually, the soil contains 0.012% of natural potassium and can be enhanced by anthropogenic activities (Ramola et al. 2008). The concentrations of 232Th and 226Ra at industrial, dumpsite, and sewage locations are higher than that of residential. This may be due to several industrial activities in which residues contain either 238U or 232Th series. We also observed that the overall mean of the radionuclides is higher than in some locations as seen in the figure. Therefore, it can be said that the increase in the concentration of 40K in the residential, 232Th in the dumpsite, and 226Ra in sewage locations are major contributors to the overall mean values for 40K, 232Th, and 226Ra in Agbara estate. The studied radionuclides at all points in each location of the study area are below the standard values of 400, 30, and 35 (Unscear 2000) for 40K, 232Th, and 226Ra, respectively, except points L13 (Area 8b) and L17 (Area 1) with higher concentrations of 40K in the residential location (see Table 1).

Assessment of outdoor terrestrial dose

The mean values of radionuclide ADR and AEDE at each location in the study area are presented in Table 4. The ADR at each location within the study area ranged from 9.02 to 22.50 nGy/h, and the mean is found to be 14.43 nGy/h for industrial, 8.21–24.57 nGy/h, and the mean is found to be 16.18 nGy/h for residential, 8.05–17.49 nGy/h, and the mean is found to be 13.39 nGy/h for dumpsite, 7.40–15.45 nGy/h, and the mean is found to be 11.52 nGy/h for sewage area. The values of ADR in the study area ranged within 7.40–34.68 nGy/h with an overall mean of 14.77 nGy/h. The highest (24.57 nGy/h) and lowest (7.40 nGy/h) value corresponding to L3 (Unilever PLC 1) and L38 (Sewage 3) points are found in residential and sewage areas, respectively, of the study area. All the measured ADR in soil samples were found to be lower than the world average value (54 nGy/h) (Unscear 2000) (see Table 1).

Table 4 Mean dose rate from radionuclide and background radiation
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The lower value of ADR in the study area led to the evaluation of AEDE to have in-depth knowledge about the annual implication of ADR in Agbara estate due to industrial activities. Therefore, AEDE is dependent on ADR. For radiological, epidemiological, and somatic health effects to be insignificant for the public and industrial worker as well, ICRP set the maximum permissible limit as 1.0 mSv/year (ICRP 1991). The values of AEDE in the study area ranged within 0.01–0.04 mSv/year and an overall mean to be 0.02 mSv/year (see Table 4). In comparison with ICRP acceptable limit, the annual dose levels of all locations were below the limit set for both the industrial workers and the public.

Figure 4a and b shows the mean dose rate of radionuclide (ADR and AEDE, respectively) at each location in the study area. Figure 4 a shows a higher mean value of ADR at residential followed by industrial, dumpsite, and sewage locations. It was also confirmed that the mean value of ADR at residential location is higher than the overall mean, while others are lower. The higher ADR was due to the higher values of 40K at each point in the residential area, which contributed more to the overall mean for ADR in Agbara estate as a result of agricultural activities. From Fig. 4b, the same mean values were obtained for AEDE at residential, industrial, and dumpsite locations. The overall mean value is also the same with these locations, while the mean value at the sewage location is lower. The dwellers of these locations of higher dose rates will be more exposed to radiation than the locations with lower dose rates.

Fig. 4
figure 4

Mean of radionuclide. a Absorb dose rate and b annual effective dose equivalent at each location

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Assessment of outdoor background radiation dose

A total of 165 measurements were taken across the 55 points in the study area, translating to three readings per point, and the average of each point was recorded. Generally, the average EDR for each point ranged from 0.09 to 0.35 μSv/h. The average value for Eko supreme (L44) shows the highest EDR, while that of Kurogboji (L23) was the lowest (see Table 1). Figure 5 shows the spatial distribution of EDR. From the figure, several points are distributed across residential, sewage, and industrial locations within the color range of 0.095–0.124 μSv/h as seen in the legend beside the figure. The lowest points are found within 0.153–0.180 μSv/h color range and are found across residential, sewage, and industrial locations.

Fig. 5
figure 5

Spatial distribution of background EDR in the study area

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The data for the background radiation dose rate (EDR) from several points in Agbara estate are presented in Table 1, and the calculated mean of several locations is presented in Table 4. From Table 4, the EDR at each location within the study area ranged within of 0.16–0.35 μSv/h and mean is found to be of 0.27 μSv/h for industrial, 0.09–0.24 μSv/h, and the mean is found to be 0.16 μSv/h for residential, 0.19–0.27 μSv/h, and the mean is found to be 0.23 μSv/h for dumpsite, 0.23–0.23 μSv/h, and the mean is found to be 0.23 μSv/h for sewage area. The values of EDR in all the 55 points ranged between 0.09 and 0.35, and the overall mean is found to be 0.22 μSv/h. The mean values of all locations in the study area are higher than 0.13 μSv/h recommended by ICRP (James et al. 2013). Comparing the levels of EDR with the standard value of 0.13 μSv/h and values of each point, the result shows that only four points in two locations, Area 8d (L15), Kurogboji 2 (L23), Kurogboji 3 (L24), and Kurogboji 4 (L25) (see Table 1) have EDR lower than the value of the standard background radiation. The EDR of other locations were above the standard value. The four points that have lower EDR than the standard value were located in the residential location of the study area.

The AEDR was considered based on higher values of EDR measured at each location in the study area. The AEDR mean values of several locations are presented in Table 4. AEDR is the measure of the quantity of energy absorbed by the human body annually. The mean AEDR at each location ranged from 0.28 to 0.58 mSv/year, and the mean is found to be 0.46 mSv/year for industrial, 0.16 to 0.42 mSv/year, and the mean is found to be 0.29 mSv/year for residential, 0.33–0.47 mSv/year, and the mean is found to be 0.40 mSv/year for dumpsite, 0.40–0.40 mSv/year, and the mean is found to be 0.40 mSv/year for sewage location. The AEDR of all locations ranged within 0.16–0.61 mSv/year and an overall mean of 0.39 mSv/year . The obtained values are higher than the world average of 0.07 mSv/year (Unscear 2000). The AEDR follows the same trend as observed in EDR at different locations.

Figure 6a and b shows the mean plots of background EDR and AEDR, respectively, at each location in the study area. From the same figures, it was observed that the highest EDR and AEDR are found in the industrial, followed by dumpsite and sewage, and residential is the least. Thus, the increased dose rate in the industrial location contributed more to the overall mean values for EDR in Agbara estate. The workers and dwellers around these areas of increased EDR will be more exposed than those areas with lower EDR of background radiation. The highest mean values in these locations are mainly due to industrial activities. Although, all the measured mean values of EDR for several locations in the study area are not significantly different due to the geographical nature of the area (see Fig. 6). An extra-terrestrial source such as cosmic rays also contributes to EDR but depending on the function of altitude and latitude. The increase in altitude increases the exposure levels to cosmic rays due to a decrease in shielding effects of the atmosphere. Based on the deflection of high-velocity charged constituent particles of the radiation across the Earth’s magnetic field, the shielding effects decrease with an increase in the latitude of north and south of the equator (Cember 1969). Taking the above and the values of EDR into consideration, cosmic radiation contributed little or no effect due to the geographical location of the Agbara industrial estate. Cosmic radiation constituent could have been completely attenuated before attaining the maximum altitude of the study area. The report of Unscear (2000) on exposure to natural radiation confirmed that the level of cosmic radiations constituent rapidly decreases from the altitude of 10–20 km to small or nothing at the sea level (Oladele et al. 2018).

Fig. 6
figure 6

Mean of background. a Equivalent dose rate and b annual equivalent dose rate at each location

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EDorgans helps to evaluate the amount of radiation that affects a particular organ. To calculate the effect on some organs of the body that absorbs radiation, an effective radiation dose and the risk factor for different organs are used (see Table 5), because the increase in the risk of cancer is different for different organs, even if the amount of radiation absorbed is the same. The EDorgans for various organs of the body were evaluated and are presented in Table 5. The values of EDorgans for liver, kidney, testes, ovaries, lungs, bone marrow, and bone marrow are 0.1794, 0.2418, 0.3198, 0.2262, 0.2496, 0.2691, and 0.2652 mSv/year , respectively. The calculated results are within the acceptable value of 1.0 mSv/year (Agbalagba et al. 2016; Ugbede and Benson 2018) and do not pose any instant hazard to the dwellers and workers of the study area. Figure 7 shows the percentage distribution of EDorgans for various organs of the body due to background radiation exposure in the area. The results show that testes and ovaries are most and least sensible to radiation with the percentages of 18.26% and 10.24%, respectively.

Table 5 Frisk and EDorgans values for organs of the body
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Fig. 7
figure 7

Percentage distribution of EDorgans to various organs of the body owing to background radiation exposure

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Excess lifetime cancer risk (ELCR)

ELCR was evaluated due to low exposure risk to predict if there is a possibility of developing cancer over a lifetime. The ELCR was calculated using overall mean AEDE and AEDR owing to exposure to radionuclide and background radiation, respectively. The overall value for ELCR ranged within 0.04 × 10−3–0.14 × 10−3 with a mean of 0.07 × 10−3 for radionuclide and ranged within 0.56 × 10−3–2.03 × 10−3 with a mean of 1.37 × 10−3 for background radiation. The obtained mean value of ELCR for background radiation is higher than the world average of 0.29 × 10−3 (Unscear 2000), indicating there are possibilities of developing cancer by the dwellers and workers who intend to live all their life in the study area.

Comparison of dose rates

Figure 8a represents the comparison of mean ADR and EDR at each location. As seen in the figure, the ADR was converted from nGy/h to μSv/h in order to make the comparison easier. The EDR was evaluated using GM counter to measure the background radiation at each point in the study area. While ADR was evaluated by adding the multiplications of mean activity concentration of each radionuclide and its conversion factor (see Eq. 3). Considering the same figure, EDR ≫ ADR at all locations. This observation is due to the fact that Geiger Muller counter measures all radiation detectable irrespective of their source, while ADR was calculated due to radiation from radionuclide in the soil. The comparison of mean AEDE and AEDR at each location in the study area is also depicted in Fig. 8b. The mean values of AEDR ≫ AEDE at each location, as a result of several sources of radiation. Also, AEDR and AEDE followed a similar trend with EDR and ADR. This was due to the fact that AEDR and AEDE were calculated putting into consideration EDR and ADR, which means that AEDR and AEDE depend on EDR and ADR, respectively. The percentage contribution of radionuclides in the air was calculated taking into consideration the overall mean value of ADR to that of EDR of ambient radiation. The percentage contribution of radionuclides in the air was calculated to be 6.7% for ADR to background radiation.

Fig. 8
figure 8

Comparison of mean. a Dose rates of radionuclide and background radiation. b Annual effective doses of radionuclide and background radiation at each location

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The obtained results owing to background radiation showed a significant increase in radiation levels at Agbara industrial estate when compared with those of other locations of the world (see Table 6). The increased levels of background radiation should be of great concern as the majority of these industrial workers and people transacting businesses in the study area spends more than eight hours per day outdoors. Predictably, continual exposure to these high levels of radiation may cause lung cancer and other forms of cancers in the future. Furthermore, the industrial workers and dwellers of this area can have several diseases associated with long-term exposure owing to the condensation of radioactive elements as rain and underground water constituent, as these serve as drinking water and source of water for agriculture purposes.

Table 6 Comparison of present study area with other location of the world
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Conclusion

We have assessed the dose rates of natural radionuclides and background radiation using calculated ADR and GM counter, respectively. The mean values of ADR and AEDE of radionuclides in the soil samples were within the world average. The mean values of EDR and AEDR of ambient radiation were found higher than the world average values at all locations. The comparison of dose rates reveals that ADR of radionuclide in the soils contributed 6.7% to background radiation in the area. The result from EDorgans for various organs of the body does not pose any immediate human health hazard. The ELCR owing to background radiation exposure indicates that the dwellers and industrial workers in the study area may develop cancer over a lifetime.

The following needs to be considered to safeguard the environment due to the long-term exposure to background radiation, which has been predicted to have a future effect on the industrial workers and dwellers of the study area.

  1. 1

    Operators of companies should liaise with the government to develop a procedure to reduce the radionuclide concentrations to prevent an increase in background radiation.

  2. 2

    Proper monitoring exercise should be carried out by the operating companies, and government agencies to checkmate the possible rise in the background radiation of the study area.

  3. 3

    Further research on both natural and artificial radionuclides in drinking water, plants and animals, effluent, and sediment should be conducted to evaluate their levels of contamination in the environment.