Assessment of Radiological Parameters of Soil in Kogi State, Nigeria

Environmental Forensics

ISSN: 1527-5922 (Print) 1527-5930 (Online) Journal homepage: http://www.tandfonline.com/loi/uenf20

Assessment of radiological parameters of soil in Kogi State, Nigeria

M. R. Usikalu, I. A. Fuwape, S. S. Jatto, O. F. Awe, A. B. Rabiu & J. A. Achuka

To cite this article: M. R. Usikalu, I. A. Fuwape, S. S. Jatto, O. F. Awe, A. B. Rabiu & J. A. Achuka (2017) Assessment of radiological parameters of soil in Kogi State, Nigeria, Environmental Forensics, 18:1, 1-14, DOI: 10.1080/15275922.2016.1263898

To link to this article: http://dx.doi.org/10.1080/15275922.2016.1263898

Published online: 26 Jan 2017.

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Download by: [80.248.0.226] Date: 27 January 2017, At: 00:09 ENVIRONMENTAL FORENSICS 2017, VOL. 18, NO. 1, 1–14 http://dx.doi.org/10.1080/15275922.2016.1263898

SCIENTIFIC COMMUNICATION Assessment of radiological parameters of soil in Kogi State, Nigeria

M. R. Usikalua, I. A. Fuwapeb, S. S. Jattoc, O. F. Awec, A. B. Rabiuc, and J. A. Achukaa aDepartment of Physics, Covenant University, Ota, Ogun State, Nigeria; bDepartment of Physics, Federal University of Technology, Akure, Ondo State, Nigeria; cCentre of Atmospheric Research, National Space Research and Development Agency, Ayimgba, Nigeria

ABSTRACT KEYWORDS The natural radioactivity levels of soil samples collected from four local government areas in Kogi Radioactivity; radiological State, Nigeria were measured using a hyper-pure germanium detector, and the radiological hazard hazard indices; soil; Kogi parameters associated with them were estimated. The measured concentration ranged from 7.82 § State 0.63 to 82.22 § 1.99 Bq kg¡1 for 238U, 11.05 § 1.10 to 114.86 § 4.72 Bq kg¡1 for 232Th, and 3.38 § 0.50 to 1272.20 § 23.36 Bq kg¡1 for 40K. Omala local government was found to have the highest concentrations of 238U (44.31 Bq kg¡1) and 232Th (52.13 Bq kg¡1), while Ajaokuta has the highest concentration of 40K (711.72 Bq kg¡1). The lowest activity concentrations of 238U and 232Th were measured from soil samples collected from Ankpa local government area and 40K from Dekina local government area. It was noted that the activity concentrations of 40K were generally low for all the areas investigated except for Ajaokuta areas. The radium equivalents calculated for all the locations were observed to be lower than the radiation protection regulatory body reference value of 370 Bq kg¡1. The radiological parameters estimated for most of the locations compared well with world average values, except for Odogba-okaba, Salem University, Forest, Nepa, Gerugu, Niger Bridge, Igaliwu, Ijeke-ogane, Bagana, and Abegikolo villages, whose values exceeded the recommended limit. This may suggest that those living or working in these areas may be exposed to higher radiation burden from the natural radionuclides.

Introduction in the soil (Muhammad et al., 2011;Alharbi,2013). Terrestrial radiation exposure in form of gamma radia- Human exposure to radiation is mainly from topsoil, tion is due to primordial radionuclides of the 238U, and the concentration varies with soil types or from 232Th series, and 40Kintheearth’s crust (United the parent rock it originates from; studies have Nations Scientific Committee on the Effects of Atomic revealed high concentrations of uranium in phosphate Radiation [UNSCEAR], 2000). These radionuclides rocks and granite rocks (Sentikumar et al., 2010;Lar, and their progenies are one of the major contributors 2013; Sahu et al., 2014). It is practically impossible to to background radiation in an environment; their pres- do away with the primordial radionuclides as nearly ence in the earth’s crust has made it impossible for the all building materials are direct or finished products of soil around us to be free of radiation due to their long soil and rock. Even when it is not so, the building will half-lives. The concentration of radionuclides in an eventually be constructed on soil where radon gas environment varies from one location to another (progeny of U- and Th-decay series) can diffuse easily because of their variable composition in rock and soil out of the soil into the building. These radionuclides in different regions. Coupled with artificial activities are also ingested through food and drinking water or that release ionizing radiation to the environment, the inhaled, thereby causing internal radiation exposure. radioactivity of surface soil can sometimes be very Knowledge of their concentrations in soil is useful in high depending on the parent material. It was reported the assessment of any possible radiological hazard that that mining of uranium automatically increase its con- may arise with the use of the soil. The measurement of centration in the surface soil (Najat and Mazunga, radioactivity in soil cannot be overemphasized. Hence, 2013). Also, the presence of 238U, 232Th, and 40Kin the importance of this study as it seeks to measure the fertilizers that are applied to the soil for optimal crop activity concentrations in soils collected from Kogi yield has been reported to increase their concentration State and thereby provide baseline data for the

CONTACT M. R. Usikalu [email protected] Department of Physics, Covenant University, P.M.B. 1023, Ota, Ogun State, Nigeria. Color versions of one or more of the ﬁgures in the article can be found online at www.tandfonline.com/uenf. © 2017 Taylor & Francis 2 M. R. USIKALU ET AL.

UNSCEAR databank and estimate the radiological rocks along with sediments weathered from these rocks. hazard indices emanating from the soils. Results from Ankpa is located within 7.30.57N, 7.43.29E, with an area this work would also be useful to policymakers. of 1,200 km2 and a population of 266,176 as of the 2006 census. It falls within the Anambra Basin, whose genesis has been linked with the development of the Niger Delta Materials and method Miogeosyncline and the opening of the Benue Trough Study area (Murat, 1972). The stratigraphy comprises a cyclic sedimentary sequence that started in the early Cretaceous Samples were collected from four local government areas (Reyment, 1965). Marine and ﬂuviatile sediments com- (LGAs) in Kogi State, Nigeria: Dekina, Omala, Ajaokuta, prising friable to poorly cemented sands, shales, clays, and Ankpa. Dekina, which is located within 7.41.41N and limestone were deposited, with occasional coal, peat, and 7.01.20E, has an area of 2,461 km2 and a population and thin discontinuous seams of lignite (Chukwu et al., of 260,312 at the 2006 census (NPC, 2006). Geologically, 2008). The study area is typical of the Ajali formation or the area belongs to the upper Cretaceous formation of the false bedded sandstone and the Mamu formation. the Anambra Basin with a stratigraphic succession of The Ajali consists of thick, friable, poorly sorted sand- false bedded sandstone, lower coal measures, and Enugu stone, typically white in color but sometimes iron- shale. The coal outcrops occur at the bank of the Eniji stained. Ajalim sand is often overlain by a considerable River. Omala is located within 7.43N and 7.33E; it has an thickness of red earthy sands, formed by the weathering area of 1,667 km2 and a population of 108,402 at the and feruginization of the formation. The Mamu consists 2006 census. The geology of the area is more of the base- mainly of sandstone, carbonaceous shales, sandy shales, ment complex rocks of Nigeria. Reyment (1965) reported and some coal seams. that Anambra Basin is a platform that is only thinly cov- ered by older sediment during the Albian-Santonian epoch of the Cretaceous. Ajaokuta is located within Sample preparation and radioactivity counting 6.40.11N and 8.48.19E; it has an area of 1,362 km2 and a population of 122,321 at the 2006 census. This area is Five soil samples were collected from different strategic

part of the basement complex of Nigeria and is underlain points at each location (LGA) for better representative mainly by schists and intrusive granitic and pegmatitic sampling (see Figure 1). Samples were kept in Ziploc

Figure 1. Map showing the sampling locations. ENVIRONMENTAL FORENSICS 3

Table 1. Activity concentrations measured in the locations.

Sample code Location No. of samples 238U (Bq kg¡1) 232Th (Bq kg¡1) 40K (Bq kg¡1)

DK 1 Okura 5 7.94 § 0.59 13.26 § 1.23 5.15 § 0.45 DK2 Oje 5 49.70 § 2.43 48.58 § 3.42 20.78 § 1.35 DK 3 Ijale 5 8.92 § 0.99 14.02 § 1.30 7.02 § 0.50 DK 4 Ologba 5 43.62 § 2.35 56.90 § 3.16 BDL DK 5 Odu 5 9.38 § 0.71 15.87 § 1.38 9.40 § 0.64 DK 6 Dekina 5 12.51 § 1.24 21.16 § 1.78 10.35 § 0.74 DK 7 Ajiyolo 5 13.91 § 1.04 17.62 § 1.39 3.85 § 0.45 DK 8 Abocho 5 26.41 § 1.47 34.74 § 2.34 26.89 § 1.38 DK 9 Ajagum 5 15.10 § 1.29 19.45 § 1.63 19.44 § 1.01 DK 10 KSU Campus 5 22.30 § 1.29 31.71 § 2.75 BDL AK 1 Emekutu 5 17.14 § 1.55 19.95 § 1.57 8.10 § 0.61 AK 2 Ogodo 5 9.74 § 0.91 15.06 § 1.47 13.42 § 0.79 AK 3 Ankpa 5 11.62 § 1.04 19.01 § 1.79 13.90 § 0.78 AK 4 Ajobe 5 7.82 § 0.63 11.05 § 1.10 BDL AK 5 Odogba Okaba 5 73.89 § 2.69 73.29 § 4.34 251.62 § 5.90 AK 6 Ejegbo 5 16.01 § 1.21 20.53 § 1.88 18.97 § 1.13 AK 7 Anabo 5 9.91 § 1.01 12.45 § 1.08 19.62 § 1.03 AK 8 Ofugo 5 11.65 § 0.73 12.26 § 1.15 BDL AK 9 Inye 5 20.56 § 0.86 12.75 § 0.90 19.62 § 1.03 AK 10 Ejeke 5 11.54 § 0.97 14.75 § 1.63 BDL AJ 1 Salem University 5 59.23 § 1.51 63.46 § 4.75 1272.20 § 23.36 AJ 2 Prime Polytechnic 5 15.12 § 1.07 26.76 § 2.14 700.64 § 13.52 AJ 3 Forest 5 46.25 § 2.95 77.90 § 4.65 1241.89 § 22.83 AJ 4 Steel Complex 5 30.81 § 1.30 14.82 § 1.23 48.54 § 1.60 AJ 5 Ajaokuta 5 12.03 § 0.98 14.14 § 0.95 553.42 § 10.91 AJ 6 Nepa 5 44.24 § 2.85 33.04 § 3.38 1090.3 § 20.4 AJ 7 Adogo 5 23.53 § 1.49 16.99 § 1.33 869.51 § 16.42 AJ 8 Forest Reserve 5 21.70 § 1.29 36.96 § 2.58 BDL AJ 9 Gerugu 5 26.06 § 1.92 35.31 § 3.03 648.68 § 12.56 AJ 10 Niger Brigde 5 34.59 § 2.78 41.72 § 3.41 691.98 § 13.33 OM 1 Ogodu 5 11.87 § 0.97 17.93 § 1.35 3.38 § 0.50 OM 2 Olokwu 5 9.02 § 0.65 12.32 § 1.25 6.89 § 0.48 OM 3 Igaliwu 5 82.22 § 1.99 114.86 § 4.72 349.04 § 7.87 OM 4 Ijeke-Ogane 5 82.22 § 1.99 96.90 § 4.11 349.04 § 7.88

OM 5 Icheke-Ajokpachi 5 41.48 § 1.64 51.06 § 3.93 BDL OM 6 Ibado 5 20.56 § 1.71 32.83 § 2.30 BDL OM 7 Iga 5 43.51 § 2.56 39.38 § 3.15 25.16 § 1.01 OM 8 Bagana 5 52.74 § 1.62 68.23 § 3.28 BDL OM 9 Abegikolo 5 64.89 § 1.78 50.21 § 3.51 73.22 § 2.73 OM 10 Ihiame 5 34.61 § 2.14 37.55 § 3.00 33.38 § 1.61 Minimum 7.82 § 0.63 11.05 § 1.10 3.38 § 0.50 Maximum 82.22 § 1.99 114.86 § 4.72 1272.20 § 23.36 Mean 28.91 § 1.50 34.17 § 2.38 210.14 § 4.37

BDL: below detection limit. bags and labeled accordingly; there was a total of 200 Protection and Research, University of Ibadan, Nigeria soil samples from all locations. At each point the five using a hyper-pure germanium detector (Canberra, samples were obtained by digging a 1-m square and model GC8023). It was coupled to a Canberra series taking samples at the four vertices and the center at a multichannel analyzer (model 13000742) through a depth of between 3 and 8 cm to obtain samples free preamplifier base. The detector has an efficiency of from debris and vegetation. The samples from each 80% and resolution of 2.4 keV (FWHM) at 1330 keV site were thoroughly mixed together to form a single of 60Co line for the measurement of 40K, 238U, and sample. The samples were processed following stan- 232Th. The detector was properly shielded with lead dard procedures (Volchok and de Planque, 1983). to prevent external background radiation from the These samples were oven dried at 60Ctoattaina environment. The electronics of the system was set constant weight, then ground and sieved with a fine up to cover a photon energy range of about 2.0 MeV mesh, packed in a 1-kg mass, and properly sealed up with 4K channels. The detector was calibrated using in a Marinelli beaker. These were left for 30 days the IAEA-certified multi-gamma ray standard soil ref- before measurement so that the 238Uand232Th would erence (MGS6M315) with densities similar to those of attain secular equilibrium with their respective daugh- the pulverized prepared samples to be measured. ter progenies. Radioactivity measurement in this work Photo peak regions of 1460 keV for 40K, 1760 keV was carried out at the National Institute of Radiation for 214Bi, and 2615 keV for 208Tl were used to 4 M. R. USIKALU ET AL. determine the activity concentration of 40K, 238U, and 232Th respectively with Genie 2000 software according to Equation 1. Each sample was counted for 36,000 s (10 hr) for good statistics.

¡ . ¡ 1/ D Cnet Cb : Ac Bqkg e (1) ggims where eg is the detector efﬁciency at energy of interest, Cnet is the count per second of the sample, Cb is the count per second for background spectrum, ms is the Figure 3. Image map of 232Th activity concentration for the study mass of the sample, and g is the intensity of gamma i area. ray at the particular energy being counted.

Results and discussion ¡ 232Th (52.13 Bq kg 1), while Ajaokuta had the highest ¡ The mean activity concentrations of natural radionu- concentration of 40K (711.72 Bq kg 1). The lowest clides of 238U, 232Th, and 40K in the soil samples collected activity concentrations of 238Uand232Th were mea- from the 40 selected villages in Kogi State are presented sured from soil samples collected from Ankpa LGA in Table 1. The concentration of 238U series ranged and the lowest 40K from Dekina LGA. The low con- ¡ between 7.82 § 0.63 and 82.22 § 1.99 Bq kg 1, with a centrations of 40K obtained in the samples from ¡ mean value of 28.91 § 1.50 Bq kg 1. The results of 232Th Dekina could be as a result of lignitic sub-bituminous ¡ series ranged from 11.05 § 1.10 Bq kg 1 to 114.86 § and non-coking coal deposits in the area. Generally, ¡ 4.72 Bq kg 1, with a mean value of 34.17 § 2.38 Bq the activity concentrations of 40Kwereverylow ¡ kg 1, and 40K activity ranged from 3.38 § 0.50 to except for Ajaokuta, which had highest concentration ¡ 1272.20 § 23.36 Bq kg 1, with a mean value of 42.82 § of 40K(Figure 2). This may be attributed to the pres- ¡ 2.20 Bq kg 1. The mean activity concentrations for all ence of silica in the soil parent Precambrian meta-

the villages are lower than the UNSCEAR reference value morphoric rock underlying the territory and also the ¡ ¡ of 35 Bq kg 1 for 238U and 232Th and 420 Bq kg 1 for 40K application of phosphate-rich fertilizer to the soil by (UNSCEAR, 2000). The distribution of the radionuclides farmers to increase farm yield. We also note that the measured in the area localized for each soil sample with highest activity concentrations for all the nuclides their geographical coordinates are presented in Figures 2, were obtained in rocky areas. The measured concen- 3, and 4 using Gnuplot software. Figures 5(a–c), 6(a–c), trations of 238Uand232Th in Oje, Odogba-Okaba, 7(a–c), and 8(a–c) show the spatial maps and the coordi- Salem Univesity, Forest, Igaliwu, Ijeke-ogane, Bagana, nates of the concentration distributions of the radionu- and Abegikolo were higher than the UNSCEAR refer- clides in all the LGAs using Surfer software. ence value, which may be due to the geology and geo- It was observed that the Omala areas had the high- graphical conditions of these locations; from the ¡ est mean concentrations of 238U (44.31 Bq kg 1)and geology of these locations they belong to the

238 Figure 2. Image map of 40K activity concentration for the study Figure 4. Image map of U activity concentration for the study area. area. ENVIRONMENTAL FORENSICS 5 basement complex, which is associated with igneous mountain belts and continental shield areas, which rock. It may also be as a result of limestone- and occur in great batholiths. They are associated with coal-mining activities in the locations. Igneous rocks quartz,monzonite,diorite,granodiorite,andgabbro such as granite are associated with higher levels of consist mainly of potassium feldspar, coarse quartz, radiation than sedimentary rocks (UNSCEAR, 2000). and sodium feldspar. Granites are associated with nat- Granites are the most abundant plutonic rocks of ural radioactivity and exhibit elevated elemental

Figure 5. Spatial maps of radiological parameters at Dekina LGA. 6 M. R. USIKALU ET AL.

Figure 5. (continued). concentrations of U and Th compared to the low Regression analysis technique was used in drawing a abundance created in the course of partial melting trend line between the points. The regression result was and fractional crystallization of magma, which allows high, positive, and linear. U and Th to concentrate in the liquid phase and The absorbed dose rates in the air at 1 m above the incorporate into more silica-rich products. In other ground surface was estimated using Equation 2 words, igneous rocks of granite origin are highly (UNSCEAR, 2000; Alharbi, 2013). enriched in U and Th when compared to basalt-ori- . ¡ 1/ D : C : C : gin rocks. D nGyh 0 461QU 0 623QTh 0 0414QK (2) ¡ 1 where D.nGyh / is the dose rate, and QU , QTh, and QK are the activity concentrations of 238U, 232Th, and 40K Radiation hazard indices ¡ (Bq kg 1) respectively. The conversion factors used in Radiation hazard indices are used to assess the effects of the estimation are given by UNSCEAR (2000). The radiation on the health of people exposed to the radia- spatial maps with coordinates of the absorbed dose tion and the environment. rate and annual effective dose calculated for all the Table 2 presents the estimated absorbed dose rate LGAs are shown in Figures 5(d and e), 6(d and e), 7

(D), annual effective dose (HE), radium equivalent (d and e), and 8(d and e). The estimated absorbed ¡ 1 activity (Raeq), annual gonadal equivalent dose, repre- dose rates ranged between 11.89 and 122.02 nGyh . sentative gamma index, excess lifetime cancer risk (EL), The calculated absorbed dose rates for Odogba-okaba and percentage risk associated with the exposure. (88.97 nGyh ¡ 1), Salem University (119.13 nGyh ¡ 1), Figure 9 shows the correlation of 238Uwiththeradium Forest (120.58 nGyh ¡ 1), Nepa (86.19 nGyh ¡ 1), Gerugu equivalent activity within the the study areas. (60.61 nGyh ¡ 1), Niger Bridge (70.24 nGyh ¡ 1), Igaliwu ENVIRONMENTAL FORENSICS 7

Figure 6. Spatial maps of radiological parameters at Omala LGA. 8 M. R. USIKALU ET AL.

Figure 6. (Continued).

(122.02 nGyh ¡ 1), Ijeke-ogane (111.17 nGyh ¡ 1), Bagana 10% of villages in Ajaokuta, Omala, and Ankpa areas (65.58 nGyh ¡ 1), and Abegikola (63.38 nGyh ¡ 1)were respectively had higher outdoor annual effective doses found to be higher than the world average (60 than the recommended limit of 70 mSvy ¡ 1 (UNSCEAR, nGyh ¡ 1). The high absorbed dose was due to the high 2000). level of thorium and uranium in the soil from these In order to assess the hazards associated with locations, which may be attributed to the fact that the materials that contain 238U, 232Th, and 40K, radium ¡ 1 soils originated from igneous rock. The annual effective equivalent activity Raeq.Bqkg / was calculated using ¡ 1 dose, HE.mSvy /, was calculated using Equation 3 Equation 4: (UNSCEAR, 2000): . ¡ 1/ D C : C : ¡ 1 Raeq Bqkg QU 1 43QTh 0 077QK (4) HE.mSvy / D D £ Of £Cc £ 8760 (3) where D is the absorbed dose rate, Of is the outdoor where QU , QTh,andQK are the activity concentrations 238 232 40 ¡ 1 occupancy factor taken as 0.2, and Cc is the conversion of U, Th, and K respectively in .Bq kg /. coefﬁcient from absorbed dose rate to effective dose Figures 5(f), 6(f), 7(f), and 8(f) display the maps and received by an adult taken as 0.7 (UNSCEAR, 2000). coordinates of the calculated radium equivalent for The calculated annual effective dose ranged from 14.58 the four LGAs. The present study observed that all the to 149.65 mSvy ¡ 1. It was found that 60%, 40%, and villages have lower radium equivalent activities than ENVIRONMENTAL FORENSICS 9

Figure 7. Spatial maps of radiological parameters at Ankpa LGA.

¡ the 370 Bq kg 1 recommendedastheworldaverage in the speciﬁc material under investigation. It is used as permissible limit. a screening tool in order to identify materials that might Representative gamma index (Ig) is used to assess pose health challenges when used for construction and the gamma radiation hazard due to the natural nuclide building. It was calculated using Equation 5 (Tufail 10 M. R. USIKALU ET AL.

Figure 7. (Continued).

et al., 2007): The annual gonadal equivalent dose (AG)isusedto assess the effect of radiation on the sensitive body cells D 6 C 6 C 6 Ig QU 150 QTh 100 QK 1500 (5) such as bone marrow, gonads, skin, etc. AG was calculated using Equation 6 (Tufail et al., 2007). Figures 5 238 QU , QTh,andQK are the activity concentrations of U, (h), 6(h), 7(h), and 8(h) present the spatial maps and ¡ 232Th, and 40K respectively in .Bq kg 1/ . The spatial coordinates of the annual gonadal equivalent dose cal- maps and coordinates of the estimated gamma index culated for the four LGAs using Surfer software. The are shown in Figures 5(g), 6(g), 7(g), and 8(g) using estimated annual gonadal equivalent dose ranged from Surfer software. The calculated gamma index in this 70.35 to 858.49 Svy ¡ 1, with a mean value of work ranged between 0.16 and 1.93. Samples from 381.19Svy ¡ 1. The annual gonadal equivalent dose Odogba-okaba (1.39), Salem University (1.88), Forest found in this work is higher than the 300 Svy ¡ 1 rec- (1.91), Nepa (1.35), Niger Bridge (1.11), Igaliwu ommended permissible limit (UNSCEAR, 2000). Nearly

(1.93), and Ijeke-ogene (1.75) were found to show all the villages have AG values higher than the recom- higher gamma index level than unity (1), the recommended limit, with highest value obtained in Igaliwu mended permissible limit (UNSCEAR, 2000), which Omala area. The high concentration may be as a result suggests that the soil samples from these areas may of the presence of monazite in the area and exploitation not be suitable for construction of buildings for of coal and limestone in the area. This could pose a dwellings. threat to sensitive cells like gonads and bone marrow in ENVIRONMENTAL FORENSICS 11

Figure 8. Spatial maps of radiological parameters at Ajaokuta LGA.

the dwellers and workers in these areas. developing cancer over a lifetime at a given exposure level using Equation 7 (Taskin et al., 2009): ¡ 1 AG.Svy / D 3:09QU C 4:18QTh C 0:314QK (6) ¡ 1 EL.Svy / D HE £T £RF (7) where QU , QTh,andQK are the activity concentrations where HE istheannualeffectivedoseequivalent,T is ¡ of 238U, 232Th, and 40K respectively in .Bq kg 1/ . the average duration of life for humans, being taken as

The excess lifetime cancer risk (EL) and percentage risk 70, and RF is the risk factor, which is fatal cancer risk were estimated in order to obtain the probability of per Sievert, taken as 0.05 for the public (International 12 M. R. USIKALU ET AL.

Figure 8. (Continued).

CommissiononRadiological Protection, 2012). The (Taskin et al., 2009). percentage risk associated with EL is evaluated using Calculated E ¡ Standard E £ ¡3 D L L £ Equation 8, and the standard EL is given as 0.29 10 % Risk 100 (8) Standard EL Figures 5(i and j), 6(i and j), 7(i and j), and 8(i and j) show the spatial maps and coordinates of the excess lifetime cancer risk and percentage risk for the four LGAs. The estimated average excess lifetime cancer risk ranged between 0:044 £10 ¡ 3 and 0:55£10 ¡ 3 mSv y ¡ 1 with percentage risk between ¡84.77 and 80.61. The mean excess lifetime cancer estimated for all the locations is 0:18£10 ¡ 3 mSvy ¡ 1, which is less than the standard 0:29£10 ¡ 3 mSvy ¡ 1, and the mean percentage risk is found to be ¡36.62, which is below the risk level when considering the radiation burden from all the locations put together. However, there is need to pay close attention to soil from Odogba-okaba, Salem Uni- versity, Forest, Nepa, Gerugu, Niger Bridge, Igaliwu, Ijeke-ogane, Bagana, and Abegikola as their estimated excess lifetime cancer and its associated risk were higher Figure 9. Correlation of 238U with the radium equivalent activity. than the recommended limit, which suggests that those ENVIRONMENTAL FORENSICS 13

Table 2. Estimated radiological parameters for the locations.

¡1 ¡1 ¡1 ¡ 1 ¡1 Sample code D (nGy h ) HE (mSv y ) Raeq (Bq kg ) Ig AG (Svy ) EL (mSv y ) % Risk

DK 1 11.89 14.58 27.30 0.19 81.58 0.051 ¡82.40 DK2 53.18 65.22 120.77 0.83 363.16 0.228 ¡21.29 DK 3 12.88 15.80 29.51 0.20 88.37 0.055 ¡80.93 DK 4 54.52 66.86 124.99 0.86 372.63 0.234 ¡19.31 DK 5 14.31 17.55 32.80 0.23 98.27 0.061 ¡78.82 DK 6 18.99 23.29 43.57 0.30 130.35 0.083 ¡71.89 DK 7 17.23 21.13 39.40 0.27 117.84 0.074 ¡74.50 DK 8 34.31 42.08 78.16 0.54 235.26 0.147 ¡49.21 DK 9 19.54 23.96 44.41 0.31 134.06 0.084 ¡71.08 DK 10 29.46 36.13 67.65 0.47 201.45 0.126 ¡56.39 AK 1 20.31 24.91 46.29 0.32 138.90 0.087 ¡69.94 AK 2 14.16 17.37 32.31 0.22 97.26 0.061 ¡79.04 AK 3 17.43 21.38 39.87 0.28 119.73 0.075 ¡74.20 AK 4 10.29 12.62 23.62 0.16 70.35 0.044 ¡84.77 AK 5 88.97 109.11 198.07 1.39 613.68 0.382 31.68 AK 6 20.59 25.25 46.83 0.32 141.24 0.088 ¡69.53 AK 7 12.91 15.83 29.22 0.20 88.82 0.055 ¡80.89 AK 8 12.79 15.69 29.18 0.20 87.24 0.055 ¡81.06 AK 9 18.02 22.10 40.30 0.28 122.99 0.077 ¡73.33 AK 10 14.24 17.46 32.63 0.22 97.31 0.061 ¡78.93 AJ 1 119.13 146.10 247.94 1.88 847.75 0.511 76.33 AJ 2 52.58 64.48 107.34 0.84 378.58 0.226 ¡22.18 AJ 3 120.58 147.88 253.27 1.91 858.49 0.518 78.48 AJ 4 25.22 30.93 55.74 0.39 172.39 0.108 ¡62.67 AJ 5 37.34 45.79 74.86 0.59 270.05 0.160 ¡44.74 AJ 6 86.19 105.70 175.44 1.35 617.16 0.370 27.57 AJ 7 57.65 70.70 114.78 0.91 416.75 0.247 ¡14.67 AJ 8 32.35 39.67 74.55 0.51 221.55 0.139 ¡52.12 AJ 9 60.61 74.33 126.50 0.96 431.81 0.260 ¡10.29 AJ 10 70.24 86.14 147.53 1.11 498.55 0.301 3.96 OM 1 16.46 20.19 37.77 0.26 112.69 0.071 ¡75.63 OM 2 11.90 14.59 27.17 0.19 81.53 0.051 ¡82.39 OM 3 122.02 149.65 273.35 1.93 843.77 0.524 80.61 OM 4 111.17 136.34 247.66 1.75 768.70 0.477 64.55

OM 5 50.00 61.32 114.50 0.79 341.60 0.215 ¡25.99 OM 6 29.33 35.97 67.51 0.47 200.76 0.126 ¡56.59 OM 7 44.94 55.11 101.76 0.70 306.95 0.193 ¡33.49 OM 8 65.58 80.43 150.31 1.03 448.17 0.282 ¡2.93 OM 9 63.38 77.73 142.33 0.98 433.38 0.272 ¡6.19 OM 10 40.07 49.14 90.88 0.42 274.39 0.172 ¡40.69 Mean 42.82 52.51 93.95 0.67 381.19 0.184 ¡36.62

D: absorbed dose rate, HE: annual effective dose, Raeq: radium equivalent, Ig: gamma index, AG: annual gonadal equivalent dose, EL: excess lifetime cancer risk.

living or working in these areas may be exposed to high annual gonadal equivalent dose for Odogba-okaba, radiation burden from the natural radionuclides. Salem University, Forest, Nepa, Gerugu, Niger Bridge, Igaliwu, Ijeke-ogane, Bagana, and Abegikolo villages were higher than the recommended limit, which sug- Conclusions gests that less of these soils should be used for construc- A gamma spectrometer was used to measure the con- tion of habitation purposes. The study showed that the centration of natural radionuclides and estimate the health burden due to natural radioactivity is low, with radiological hazard indices of soil samples collected little or no radiation hazard, except for Odogba-okaba, from 40 locations spread across four LGAs in Kogi Salem University, Forest, Nepa, Gerugu, Niger Bridge, State, Nigeria. This is to serve as baseline data for future Igaliwu, Ijeke-ogane, Bagana, and Abegikolo villages. radiological study in the area. The study showed that the three radionuclides were not uniformly distributed in the soils. It was observed that Igaliwu has the highest Funding concentration of 238U and 232Th, while Ajobe has the lowest. It also showed that the activity concentrations of The Centre for Atmospheric Research, CAR, National Space 40 Research and Development Agency, funded this research K were generally low in all the LGAs except for Ajao- under the Atmospheric Chemistry and Environmental kuta. The estimated values of absorbed dose rate, Research Project. Mr. Daniel Alfa of CAR helped in collection annual effective dose, representative gamma level, and of samples. 14 M. R. USIKALU ET AL.

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