Spatial Distribution of Gamma Dose Rates and Radioactivity Levels in Some Parts of Iju Community in Ado-Odo Ota, Ogun State

This study investigates the background dose rates and radiological risk exposure to Iju community in Ado-Odo Ota. Using a hand-held calibrated gamma detector (RS-125 Gamma-Spec), the study area’s outdoor gamma dose rates and radionuclide activity concentrations of 40K, 238-U, and 32-Th were measured in situ. The results showed differing activities of the primordial radionuclides (40-K, 238-U, and 232-Th) with average values lying within the recommended limits, with the exception of 40K, which geologically can be caused by regional subsidence while on marine transgression. Based on statistical analysis, the correlation results verified that 40K, 238-U, and 232-Th were the primary causes of the elevated outdoor dose rates at Iju community. The International Commission on Radiological Protection (ICRP) specified allowable limits for radiation exposure, and the estimated mean hazard indices for the increased lifetime cancer risk in the research area exceeded these limitations. In order to ensure sufficient radiation protection, the research area needs attention right away.


Introduction
Natural sources of ionizing radiation are an inevitable aspect of life as we know it.The primary natural source of ionizing radiation exposure for humans, aside from cosmic radiation, which bombards the globe from space, is terrestrial radiation, which is largely emitted by radionuclides in the decay series of uranium and thorium as well as the non-series potassium-40 [1].Because natural radionuclides have the potential to cause cancer, exposure to them by humans has raised concerns in recent decades.The level of radioactivity in soil and sediments in the environment needs to be assessed in order to safeguard human health and prevent negative consequences [2], [3].Radioactivity in the marine environment may come from anthropogenic sources connected to crude oil mining or from naturally occurring crustal particles arising in terrestrial ecosystems [4], [5].The detection of radioactivity is a sign of anthropogenic threats to the marine environment, such as industrial operations and mining [6], [2].Important data on environmental radioactivity, mining, industrial development, agricultural production, offshore gas, and oil exploration are lacking in the coastal region of West Africa; however, this may be due to the environment's radiation level [6], [7].
The occupants of Iju community are not aware of the background radiation or the risk from ionizing radiation.In terms of the health effects in human, all kind/forms of ionizing radiation can damage or destroy DNA in cells.High amount dosage of ionizing radiation have been shown to cause mutations in radiation victims' descendants [8].Due to the facts above, assessment of Iju community is necessary to evaluate the level of exposure to the public in the region.With the IAEA's concern, it's critical to urgently investigate natural radioactivity levels and background dose distributions among the Iju community.After comparing the level of risk exposure to the residents with the International Reference Level (IRL) proposed by the International Atomic Energy Agency (IAEA), World Health Organization (WHO), and International Commission for Radiological Protection (ICRP), this will help understand the level of risk exposure to the residents (ICRP).The aim/purpose of this study is to assess the level of radioactivity and the corresponding radiological risk exposure to the inhabitants of Iju community in Ado-odo Ota.

Study Location
Iju is a forefront local area arranged in Ado-Odo Ota nearby government territory, Ogun State in southwestern Nigeria.Iju is arranged between latitude 6o 36' 38.6'' N and longitude 3o 5'8.5''E. The people group lies at the connective course of Nigeria and the republic of Benin, it straightforwardly connections to Sango-Ota.The total population according to the population Census carried out in 2006 was viewed at approximately 50 000 plus.The local geology of the study area is shown in Figure 1.

Material and Methods
The Super SPEC RS-125 hand-held gamma detector, coated with a 2.0 cm x 2.0 cm NaI crystal, was used to measure the activity concentration of 40 K, 232-Th, and 238-U in-situ at a height of approximately one meter above the ground.The method of [7] was used in order to measure the radioactive levels in the sediment samples with accuracy.Canadian Geophysical Inc. offers a handheld user-friendly radiation detector (Super-SPEC RS-125).With the RS-125 Super SPEC measurement, test concentrations in K (%), U (ppm), and Th (ppm) are instantly available.For flawless testing, it also includes user-selectable sample energy.Utility software is available for downloading memory information with the RS-125 Super SPEC.All memory data is sent to the PC (personal computer) RS-Analyst via Bluetooth or USB.This can gather spectrum over 1024 channels, measure data, or output data in addition to GPS.Additionally, the application provides numerical and graphical information perspectives.It is also possible to resend the data as the content document's enemy.The radiation identifier was used one meter off the ground for every estimating purpose, readings were obtained several times at each station sequentially, and their normal established to assure precision.Thirteen (13) stations were calculated across the inquiry territory.As advised by the manufacturer, the instrument is given a 15-minute to stabilize and balance out before starting the estimating portion of the research to ensure accurate results [7], [9].Every station's GPS ranges, or coordinates, were noted.There were about twelve meters separating the two stations.There was a 90-second reading break in between each session.Parts per million (ppm) data collected by the equipment are converted to Becquerel per kilogram (Bqkg-1) in accordance with [8].Using ArcGIS version 10.8, the measured gamma dose rate data that were saved in an Excel file with the correct coordinates were processed, geospatially referenced, and interpolated to create a map of the spatial distribution analysis.

Activity concentrations of 238-U, 232-Th and 40-K in the study areas
The radionuclide activity concentrations of 238

Geospatial map indicating High and Low Risk zones
ArcGIS (version 10.8) spatial analysis was used to analyze, georeference, and interpolate the base map, as shown in Figure 2. The data from the gamma dose rates in Table 2 were used as the input data for the spatial distribution map in Figure 2. The station highlighted in red colour circles represents points stations 1 and 7, with the highest background gamma dose rates.Figure 3 and 4, respectively gives a clear depiction of this information as it shows the area that could be dangerous to the community's health by displaying the spatial distribution of the background gamma radiation rate.

The Combined Activity Concentrations of 238U, 232Th and 40K in the Study Area
The combined activity concentrations of 238 U, 232-Th and 40-K is presented in Figure 4.All the radionuclides in the study area are randomly distributed except 232-Th that shows increasing order from station 1.The activity concentration of 238U from the graph shows that the activity level ranges from 6.175 to 30.875 Bq/Kq.The highest value 30.875 was in station 9 while the lowest value 6.175 was located at station 3. The value gotten from the study area were randomly distributed and did not exceed the standard value which is 32 Bq/Kq suggested by [1] activity levels in the study area were randomly distributed and it can be shown that station 1, 4 and 7, respectively, exceeded the standard reference level of 420 Bq/Kq, suggested by [1].This research revealed that the AEDR for outdoor values at the study area has a mean value of 0.36 mSv y−1, which is considerably higher than the 0.07 mSv y−1 recommended by [1].The estimated Excess Lifetime Cancer Risk at the area of study was found to have a mean risk value of 1.29 exposure to the public that reside in the area.Overall, the study shows that the AEDR and the Excess Lifetime Cancer Risk values are distinctly highr than the world accepted range according to [10], [1] and [8].Radiologically, the study area may be a potential stochastic radiological risk zone to humans in Iju community due to the high 40K activity level that exceeds the IRS, which pose a threat to human.In addition, this study may serve as a guideline for future assessment and estimation of neighbouring communities for potential exposures.This study has recommended adequate background check in the zone by the authority to avert the long-term exposure to public in the community.

Figure 1 :
Figure 1: Geological map of Ogun State (Source: Nigerian Geological Survey Agency)

Figure 2 :Figure 3 :
Figure 2: Base map Indicating Highest (hotspots) and Lowest Dose Rate StationsFigure3presents the spatial distribution analysis map generated from the field data measured in the study/research area.The background gamma dose rate reported higher at stations 7 and 1, respectively.The implication here is that the zone is a spot where the majority of the community gather for different purposes daily.The values of the gamma dose rate for these hot spots are comparable with the values obtained by[7] and [9], respectively.The values are slightly above the recommended values according to[4],[10]-[11].

Figure 4 - 4 . 4
Figure 4-The Activity values of 238 U, 232 Th and 40 K combined in the Study Area

Figure 5 -
Figure 5-Comparing the Highest Activity Values of 238 U, 232 Th & 40 K in Study Area with International Reference Standard (IRS)

Table 1 -
U, 232-Th and 40-K were determined from the measured concentrations in parts per million (ppm) from gamma scintillation detector.Conversion Factors for 238-U, 232-Th, 40-K [8] are displayed in Table 1.The converted field data acquired are presented in Tables 2 and also presented in Table 2 are the activity concentrations of naturally occurring radionuclides, dose rates, longitudes, latitudes and elevation acquired from Iju community.The results of 238 U, 232-Th and 40-K activity levels are discussed in different Figures below and compared with the International standard levels [1], [9].Conversion Factor

Table 2 -
The acquired Field Data (In-situ measurements of 238-U, 232-Th and 40-K activities) ,[7].It can be observed that the activity level ranges from 17.86 to 30.45 Bq/Kq, with the highest value of 30.45 recorded at both stations 5 and 10, whereas the lowest value 17.86 was recorded at station 3. The values from the graph were randomly distributed and did not exceed the standard reference level of 45 Bq/Kq, suggested by[7].A consistent decrease in activity levels can be observed after the highest activity concentration noted in station 10, which can be found in stations 11,12 and 13, respectively.The activity concentration of 40-K in the study area range between 31.3 and 876.4 Bq/Kq.The highest value of 876.4 recorded at station 7, whereas the lowest value 31.3 was recorded at station 2. The values of the