J. Nig. Soc. Phys. Sci. 4 (2022) 699 Journal of the Nigerian Society of Physical Sciences Assessing the need for radiation protection measures in artisanal and small scale mining of tantalite in Oke-Ogun, Oyo State, Nigeria A. E. Ajetunmobia,∗, A. O. Musthaphab, I. C. Okeyodeb, A. M. Gbadeboc, D. Al-Azmid, T. W. Davida a Department of Physics, Olabisi Onabanjo, Ago-Iwoye, Ogun State, P M B 2002, Ago-Iwoye, Ogun State. b Department of Physics, Federal University of Agriculture, Abeokuta, P M B 2240, Abeokuta, Nigeria c Department of Environmental Management and Toxicology, Federal University of Agriculture, Abeokuta, P M B 2240, Abeokuta, Nigeria d Department of Applied Sciences, College of Technological Studies, Public Authority for Applied Education and Training, Shuwaikh, P O Box 42325, Code 70654, Kuwait Abstract There is concern that work scenarios on the tantalite mining sites in Oke-Ogun, Oyo State, Nigeria may cause occupational radiation exposure of workers due to enhanced concentrations of naturally occurring radionuclides in some process materials. A prior radiological assessment of the mining activities was carried out to determine if and which exposure scenarios may require radiation protection measures. Samples of the materials involved, comprising tantalite (tantalum ores), soil and waste rock were collected and analyzed for activity concentrations of 40K, 226Ra, 238U and 232Th using a hyper pure germanium detector gamma-ray spectrometer. Radon concentrations in the mines were also measured using a continuous radon monitor – Radon-Scout Plus (Sarad, GmbH). Activity concentrations of 40K are below 10 Bqg−1 in all the samples but all the tantalite samples contain more than 1 Bqg−1 of 226Ra and 238U. Hence tantalite is regarded as naturally occurring radioactive material (NORM) and the mining activity as a practice. The requirements for planned exposure situations apply to all the mining sites but, on the basis of graded approach, the optimum radiation protection measures vary from one mine to another, ranging from exemption to authorization. Exposures to radon in the underground mines pose the greatest radiological risks and portend the greatest need for regulatory control in the mining operations. The results further underscore the need to integrate radiation protection with the other health and safety measures in the mining sector. DOI:10.46481/jnsps.2022.699 Keywords: Radiation protection, tantalite, germanium detector Article History : Received: 7 March 2022 Received in revised form: 27 April 2022 Accepted for publication: 29 April 2022 Published: 16 August 2022 c© 2022 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 articleâs title, journal citation, and DOI. Communicated by: W. A. Yahya ∗Corresponding author tel. no: +2348158593532 Email address: abayomi.ajetunmobi@oouagoiwoye.edu.ng (A. E. Ajetunmobi ) 1. Introduction Minerals and raw materials normally contain moderate to elevated concentrations of naturally occurring radionuclides, mainly 40K and those in the decay series of 238U and 232Th [1- 6]. Radiation safety regulations are well established in uranium 1 A. E. Ajetunmobi et al. / J. Nig. Soc. Phys. Sci. 4 (2022) 699 2 mining and processing where uranium ores contain up to sev- eral thousand Bqg−1 of radionuclides in the 238U and 232Th de- cay series [2]. There are many other industrial activities where uranium is not the main product but a contaminant or a sec- ondary mineral [2]. The radiological hazards in such industrial activities may be significantly reduced and the need for regula- tory control may not be clear. The International Atomic Energy Agency (IAEA) has provided some Guidance but the decision on which of the industrial activities to regulate is normally left for the regulatory body [2, 4, 5]. This includes establishing activity concentrations of the relevant radionuclides in the ma- terials involved, determination of doses and appropriately des- ignating exposure situations based on the graded approach and other requirements of the Basic Safety Standards [4]. The effective dose received by a worker exposed to natu- rally occurring radioactive material is reliably assessed by con- ducting a properly developed monitoring programme in the rel- evant workplaces [5, 6]. It can also be derived from model calculations using appropriate operational quantities and dose coefficients [3]. However, if the work scenarios and the activ- ity concentration of radionuclides in relevant process materials are well known, it is possible to obtain, in advance, a broad indication of the expected dose to workers from exposure to gamma radiation and exposure due to airborne dust. The latter approach is described in the IAEA Safety Series Report No. 49 [2] as a prioritization tool for identifying the types of industrial operations and scenarios having the greatest need for radiation protection measures. This approach was adopted in the present study. Artisanal and small-scale Mining (ASM) have been prac- ticed over several decades in many parts of Nigeria, including Oke-Ogun, south western Nigeria. It is an informal mining sec- tor where rudimentary techniques or machinery with small de- gree of mechanization are used to exploit small and shallow mineral resources. Although ASM provides livelihood alter- native for some people, it contributes very little to Nigeria’s economy and it has been associated with various environmental degradation and health hazards. Formalization and reform of the ASM are now being carried to improve the mining sector as part of the national policy to diversify from the oil and gas sec- tor in Nigeria [7]. The formalization is expected to institution- alize best practices including those that address the associated environmental and health hazards, both radiological and non- radiological. In this regard, it is anticipated that the outcome of is study will provide some insights into the potential radiolog- ical exposures associated with ASM operations in general and tantalite mining operations in particular. The report will also serve as practical guide on how to determine the need for ra- diation protection measures in industrial activities that involve naturally occurring radioactive materials (NORM) based on the graded approach. 2. Materials and methods 2.1. Geographic and geological features of the study area The mines are located in Komu, Sepeteri, Gbedu and Eluku villages in Itesiwaju, Saki East, Iwajowa and Saki Local Gov- ernment areas respectively, all in Oke-Ogun, Oyo State, south- west of Nigeria. Oke-Ogun spans over latitudes 80 00’ – 80 39’ N and Longitudes 20 56’ – 30 46’ E, and it is averagely at an elevation of 188m above the sea level. It has a population of about 1.4 million people according to the latest population cen- sus. The main occupations of residents in the area are artisanal mining and farming. The area is well drained by Rivers Oyan, Ofiki, Olori and many other tributaries of Ogun River, forming dendritic drainage patterns in many parts of the area (figure 1). The major geological formations in the area include undif- ferentiated schist and gneiss that are widely distributed around Sepeteri in north eastern and Gbedu in south western regions. Alternate layers of granitic gneiss, biotite hornblende granite, migmatite, migmatic granite gneiss, amphibole schist and por- phyroblastic gneiss run parallel from northwest to southeast, with discontinuities occasioned by minor geological formations including porphyritic granite in the southwest, quartz veins in the east, pegmatite occurrence around Sepeteri, Komu, Gbedu and Iwere-ile in the south and southwest, and syenite and py- roxene diorite in the north. Parts of Komu in the west and Eluku in the northwest are also both underlain by granitic gneiss and biotite hornblende granite, respectively. Oke-Ogun is endowed with a variety of minerals and precious stones, including tanta- lite and iron ore, marble, talc, beryl, etc. (figure 2). 2.2. Determination of activity concentrations of radionuclides in process materials 2.2.1. Types of operations and processes involved The study covered eight mining sites, comprising one each in Gbedu and Sepeteri, two in Eluku and four in Komu. The four mines in Komu are underground while the rest are open pit mines. The entire mining operations were divided into two broad types, namely artisanal mining operations which involve digging manually and blasting to extract ore-bearing rocks, and processing of tantalum ore (tantalite) involving work scenarios such as crushing (dry or wet) and grinding to separate the ore- bearing rock from waste rock, physical separation of tantalite from other metallic ores using gravity, electrostatic or electro- magnetic processes, and working or staying close to stock-piles of tantalite. These two types of operations are among those that have earlier been identified as being likely to require regulatory control [2]. 2.2.2. Types of materials involved and sample preparation The three involved materials considered are residual soil, waste rock and tantalite or tantalum ore. Forty samples, com- prising twelve ores, seventeen soils and eleven waste rocks were collected from all the selected mining sites. The samples were air dried, pulverized and homogenized. Aliquots were sealed in 500 ml cylindrical plastic containers for a month to ensure secular equilibrium between 226Ra and its decay products. 2.2.3. Gamma-ray spectrometry The samples were analyzed using a hyper pure germa- nium (HPGe) detector gamma-ray spectrometer at the National Institute of Radiation Protection and Research, University of 2 A. E. Ajetunmobi et al. / J. Nig. Soc. Phys. Sci. 4 (2022) 699 3 Figure 1: Maps of Nigeria, Oyo State and Oke-Ogun showing the selected mining areas Ibadan, Nigeria. A multi-radionuclides standard source was used for energy and efficiency calibrations. The radionuclides of interest are 40K, 226Ra 232Th and 238U, and the gamma-ray energies used to estimate the activity concentrations are 609.3 keV of 214Bi for 226Ra; 911 keV of 228Ac for 232Th; 1001 keV of 234mPa for 238U; and 1460 keV for 40K. 3 A. E. Ajetunmobi et al. / J. Nig. Soc. Phys. Sci. 4 (2022) 699 4 Figure 2: Map of Oke-Ogun in Oyo State Nigeria showing major geological and mineral deposits 2.3. Measurement of radon concentration The health effect as a result of exposure to 222Ra is radiation induced [8], hence the need to measure radon concentration in the study. Radon concentrations were measured in the open pit and underground mines using a continuous radon monitoring device: Radon Scout Plus (Sarad, GmbH). It is portable (of di- mension 175 × 135 × 55 mm3), battery operated and capable of continuous cyclic data logging of radon concentration, air tem- perature, relative humidity and atmospheric pressure after every predetermined period. During the measurement, the instrument was held above the floor and away from the walls in under- ground mines. The sampling time varied depending mainly on the time permitted by the mine operators. The logged data were assessed by connecting the radon monitor to a personal com- puter through a USB connector for graphical display and fur- ther data analysis through the dedicated software - Sarad Radon vision 4.0.7 [9]. 4 A. E. Ajetunmobi et al. / J. Nig. Soc. Phys. Sci. 4 (2022) 699 5 Table 1: Relationship between dose and activity concentration for occupational exposure to gamma radiation and to dust [2] Category of material Broad estimate of annual ef- fective dose per unit activ- ity concentration (mSv/y per Bq/g) Individual radionu- clide activity concen- tration above which the expected dose may exceed 10% of the dose limit (Bq/g) Minimum Maximum Large quantity, e.g. ore body, large stockpile 0.02 0.4 5 Small quantity, e.g. min- eral concentrate, scale, sludge 0.008 0.04 50 Volatilized: furnace fume and precipitator dust 0.0006 0.003 500a aThis value refers to the activity concentration in the precipitator dust with exposure to fume having been accounted for by assuming an equivalent dust loading of 1 mg/m3 at the same activity concen- tration (i.e. a concentration of 0.05 Bq/m3 in fume) and an activity media aerodynamic diameter (AMAD) of 1 µm. 2.4. Exposure scenarios and pathways Many work scenarios are involved in the two operations as mentioned in section 2.2.1. Each of these work scenarios may constitute an exposure scenario, but in this screening radiolog- ical assessment the exposure pathways considered for workers effective dose are: i. External exposure due to whole body irradiation by gamma-rays emitted by materials associated with the work, ii. Internal exposure due to intake (ingestion and inhalation) of radionuclides in dust of the materials, iii. Inhalation of radon released into air from the surrounding materials 2.5. Assessment of effective doses to artisans The effective dose to workers due to exposure to gamma ra- diation and to airborne dust was calculated from the measured activity concentration of radionuclides in 238U and 232Th decay series, and dose coefficients, i.e. indicative relationships be- tween dose and activity concentration in the IAEA Safety Se- ries Report 49 [2], (table 1). The annual effective dose (E) from exposure to 222Rn in the mine was estimated from the measured 222Rn concentrations (CRn) using the conventional equation [1]: E = CRn × F × T × D, (1) where F is an equilibrium factor between 222Rn and its decay products (0.4 for indoor/underground and 0.6 for outdoor), T is hours in a year (hy−1) spent by miners at the site and D is the dose conversion factor (9.0 × 10−6 mSv per Bq h m−3), which is the effective dose received by an adult per unit 222Rn exposure. 3. Results and discussion 3.1. Activity concentration of radionuclides in process materi- als The ranges of activity concentrations of 40K, 226Ra, 232Th and 238U in the Tantalite, Soil and rock samples are( 0.003- 1.183) Bq/g, (1.231-140.982) Bq/g, (0.753-4.808) Bq/g and (2.314-173.827) Bq/g; (0.003-1.139) Bq/g, (0.008-0.369) Bq/g, (0.003-0.253) Bq/g and (0.003-0.761) Bq/g; and ( 0.071-1.709) Bq/g, (0.003-0.261) Bq/g, (0.003-0.318) Bq/g and (0.003- 0.297) Bq/g1, respectively (table 2). All the materials contain less than 10 Bqg−1 of 40K and all soil and rock samples contain less than 1 Bqg−1 of 226Ra, 232Th and 238U. Concentrations of 226Ra and 238U exceed 1 Bq/g in all the tantalite samples, while those of 232Th exceed 1 Bqg−1 in about 75% of the tantalite samples. The implication of these results is that tantalite qualifies to be regarded as NORM, its mining in all the mine sites is re- garded as a practice and the requirements for planned exposure situations apply as stated in the IAEA GSR-3 [4]. On the other hand, soil and rock in the mine sites do not require further ra- diological considerations unless there are possibilities of being used as building materials. The results also show disequilibrium between 238U and 226Ra in all the tantalite samples, but only in a few soil and rock samples. This was also reported by [3] in columbite-tantalite from the Democratic republic of Congo and by [10] in niobium ore from Brazil. The disequilibrium between 238U and 226Ra in the tantalum ores may indicate mobilization into other materi- als not considered in this study, such as waste water, and this may have radiological environmental impact around the mines as discussed by [3]. 5 A. E. Ajetunmobi et al. / J. Nig. Soc. Phys. Sci. 4 (2022) 699 6 Table 2: Activity concentration of radionuclides in samples of materials involved in the mining operations and 222Rn concentration in the mine air Location and material Range of activity concentrations (Bq/g) Average 222Rn con- centration (Bqm−3) 40K 226Ra 232Th 238U Eluku I 92 Tantalite 0.113 20.821 1.473 23.979 Rock 0.262 0.047 0.005 BDL Soil 0.071 0.029 0.009 BDL Eluku II 55.5 Tantalite 0.13 44.674 1.489 51.01 Rock 0.296 0.062 0.007 BDL Soil 0.13 0.032 0.024 BDL Gbedu 56 Tantalite 0.162 24.277 2.786 27.867 Rock 1.111 0.01 BDL BDL Soil 0.676 0.188 0.107 0.249 Komu I 180335.3 Tantalite BDL 127.048 1.583 155.724 Rock BDL 0.17 0.008 0.23 Soil 1.709 0.035 0.003 BDL Komu II 228.4 Tantalite 0.171 95.663 2.917 118.903 Rock BDL 0.178 0.008 0.259 Soil 1.638 BDL BDL BDL Komu III 4387.6 Tantalite 0.006 95.327 1.509 123.56 Rock 0.621 369 0.253 0.761 Soil 1.652 0.035 0.003 BDL Komu IV 2565.8 Tantalite BDL 140.982 2.056 173.827 Rock 0.213 0.239 0.09 0.417 Soil 1.666 BDL BDL BDL Sepeteri 55 Tantalite 0.743 18.254 1.966 55.783 Rock 0.812 0.023 0.007 0.021 Soil 0.656 0.073 0.016 0.152 BDL=Below Detection Limit; Detection limits are 3.1, 2.8, 2.9 and 2.9 (10−3 Bq/g) for 40K, 226Ra, 232Th and 238U activity concentrations, respectively. 3.2. Radon concentration in the mines The mean 222Rn concentrations vary widely from 55 to 180335 Bqm−3 (table 2). The values recorded in the open pit mines are higher than the global average outdoor value (10 Bqm−3) but within the global range (1-100 Bqm−3) [1]. The values recorded in the underground mines are all significantly higher than the action level for workplaces, which is 1000 Bqm−3 annual average [4, 5]. The operations in underground mines are further subject to the requirements for planned expo- sure situations on account of significantly high 222Rn concentra- tions. This decision is based on the assumption that the average radon concentration during the short-term monitoring is repre- sentative of the annual average, which could be more or less, subject to atmospheric, diurnal and seasonal variations. Unfor- tunately, long term or repeated measurements were not allowed by the mine owners. Presently, they seem unaware of occupa- tion exposure to radiation or the needs for radiation protection in their industry. 3.3. Determination of optimum regulatory control options us- ing the graded approach A graded approach to regulation, as embodied in the IAEA Basic Safety Standards [4], states that the application of the requirements in planned exposure situations “shall be commen- surate with characteristics of the practice or the source within a practice, and with the magnitude and likelihood of the expo- sures”. In the case of exposure to NORM, it will involve more than just establishing that the activity values of the relevant ra- dionuclides are exceeded, but the particular types of operation, process and material will also be considered in more detail, in- cluding screening dose assessments. The outcome will deter- mine the optimum regulatory option. 6 A. E. Ajetunmobi et al. / J. Nig. Soc. Phys. Sci. 4 (2022) 699 7 Table 3: Expected effective dose to workers, operation/scenario with the greatest need for radiation protection and recommended measure based on the graded approach Mine loca- tion Mine type Workers dose (mSv/y) Operation/scenario with greatest need for radiation protection measure Recommended radia- tion protection mea- sure Exposure to 222Rn Exposure to gamma radiation and dust Eluku I Open pit 0.73 2.040 Tantalite processing Exemption Eluku II Open pit 0.44 0.959 Tantalite processing Exemption Gbedu Open pit 0.22 1.115 Tantalite processing Exemption Komu I Underground 5690.0 2.231 Underground mining Authorization Komu II Underground 7.20 6.229 Underground mining Notification Komu III Underground 80.71 4.756 Underground mining Authorization Komu IV Underground 94.40 4.942 Underground mining Authorization Sepeteri Open pit 0.11 6.953 Tantalite processing Notification The two types of operations considered in the study are min- ing of tantalite and processing of tantalite, and tantalite (tanta- lum ore) is the NORM involved in both operations, i.e. material in which concentrations of 226Ra and 238U exceed 1 Bq/g (ta- ble 2). Tantalite processing involves exposure scenarios, e.g. magnetic separation of tantalite from other metallic ores, where workers come in contact with small quantities of materials. Therefore, the expected effective doses due to workers exposed to gamma radiation and to airborne dust of tantalite were esti- mated using the published annual effective dose per unit activity concentration for small quantities of materials (table 1). The es- timated values range from about 1 to about 7 mSv/y as shown in table 3. According to the graded approach to regulation, the operation could be exempted if the effective dose received by a worker from this pathway does not exceed 1 – 2 mSv/y. There- fore the operations in the mines in Eluku I, Eluku II and Gbedu could be considered for exemption, meaning there is no need to impose any regulatory requirements on them. After exemption the next level in the graded approach is no- tification, which is the requirement for the legal person (which in this case is the mine owner) to submit a formal notification to the regulatory body informing it of the operation. Notification alone could be sufficient provided the exposures do not exceed a small fraction of the relevant limits. Consequently, the open pit mine in Sepeteri and one of the underground mines in Komu (Komu II) could be considered for Notification. Authorization is the next to notification when there is need to place higher obligations on the legal person. According to the graded approach, authorization may take the form of regis- tration or licensing, depending on how stringent the regulation is required to be. Registration is the less stringent of the two and it places only limited obligations on the legal person, but “it may provide sufficient level of control in many operations involving significant, but nevertheless moderate exposures to NORM and/or radon”. Licensing is the highest level in the graded approach to regulation. It is the more appropriate au- thorization where optimized protection can only be achieved through the enforcement of specific exposure control measures. In this regard, the high exposures to radon in the remaining three underground mines in Komu may require authorization. While registration may provide sufficient level of control for the operations in Komu III and Komu IV, licensing may be more appropriate for the operation in Komu I where workers may experience significant exposures to radon. Specific control measures such as installation of ventilation system and other remedial actions to drastically reduce exposure to radon would be required, considering that any situation that may result in a annual dose greater than 100 mSv is unacceptable, except un- der emergency exposure situation [4]. There may also be need to establish suitable radiation protection programmes that entail monitoring and dose assessments. 4. Conclusion An assessment was carried out to evaluate the need for ra- diation protection measures in artisanal and small scale mining of tantalite in Oke-Ogun, southwest, Nigeria. The results gen- erally indicate there is need for radiation protection measures in the mining operations. Two types of operations were con- sidered, namely tantalite mining in both open pit and under- ground mines and tantalite processing. Three of the materials involved in the operations, namely soil, rock and tantalite, were 7 A. E. Ajetunmobi et al. / J. Nig. Soc. Phys. Sci. 4 (2022) 699 8 considered but only tantalite (tantalum ore) contains more than 1 Bq/g of 226Ra and 238U and qualifies as NORM. High con- centrations of 222Rn were measured in mine air, particularly in the underground mines. Doses to workers due to exposures to gamma radiation and due to dust, and exposure to 222Rn show that the mining operations are services and the requirements for planned exposure situations apply. The graded approach to reg- ulation was applied to optimize the regulatory options for each of the mines. The optimized regulatory options range from ex- emption to licensing of the operations. But the greatest need for radiation protection measures in the tantalite mining opera- tions is workers exposure to radon in underground mines. It is recommended that the regulatory body should liaise with other relevant stakeholders and seize the opportunity of the ongoing formalization and reform of the ASM sector in Nigeria to inte- grate radiation protection with the general OHS measures in the mining industry. References [1] UNSCEAR, “Dose assessment methodologies”, New York: United Na- tions Scientific Committee on the Effect of Atomic Radiation (2000). Re- port to the General Assembly UNSCEAR) [2] IAEA, “Assessing the need for Radiation Protection measures in work involving minerals and raw materials”, Safety Report Series No. 49 (2006),(Vienna: IAEA). [3] A.O. Mustapha, P. Mbuzukongira , & M. Mangala, “Occupational Ra- diation Exposure of Artisanal Mining of Columbite-tantalite in the East- ern Democratic Republic of Congo”, Journal Radiological Protection 27 (2007) 187. [4] IAEA. “Radiation Protection and Safety of Radiation Sources”. (Inter- national Atomic Energy Agency) International Basic Safety Standards, General Safety Requirements Part 3, No. GSR (2004) (Vienna). [5] IAEA, “Occupational Radiation Protection”, General Safety Guide No. GSG-7 (2018) (Vienna). [6] IAEA, “Occupational Radiation Protection in the Uranium Mining and Processing Industry”, Safety Report Series No. 100(2020) (Vienna: IAEA) [7] The World Bank, Nigeria, “Mineral Sector Support for Economic Diver- sification Project (MinDiver)”, Implementation Status and Results Report (2019). [8] O. A. Ndubisi, B. K. M. Apaemi, S. F. Barikpe & I. T. Ari”, Analysis of Indoor Radon Level and its Health Risks Parameters in three selected towns in Port Harcourt, Rivers State, Nigeria”, J. Nig. Soc. Phys. Sci. 3 (2021) 181. [9] Sarad, “User manual, Radon Scout, version 10/2009, SARAD GmbH”, Wiesbadener Strabe 10. (2009) D-01159 Dresden. [10] D. O. Pires, M. A. Rio, E. C. S. Amaral, H. M. Fernandes & E. R. R. Rochedo, “Environmental radiological impact associated with non- uranium mining industries: A Proposal for screening criteria”, J. Environ. Radioact. 59 (2002) 1. 8