RADIOLOGICAL IMPLICATIONS OF ARTISANAL GOLD MINING ACTIVITIES IN GABABIYU, MINNA METROPOLIS, NIGERIA

ABSTRACT

Radiological contaminations of the human environment due to anthropogenic activities have been associated with significant human health challenges. Forty surface soil samples collected at random from Gababiyu artisanal gold mining site in Minna were assessed for their radiological contents using gamma spectrometric technique which employs NaI (Tl) detector. Radiological hazard parameters were also computed from the measured activity concentrations in order to assess the level of exposure of the miners and the public to ionising radiation. Specific activities of 226Ra, 232Th and 40K ranged from 10.27±2.88 to 152.60±3.80 Bq.kg-1, 32.67±1.93 to 185.90±6.06 Bq.kg-1  and 35.18±1.45 to 947.50±7.51 Bq.kg-1 respectively, with mean values of 65.06±4.20, 87.63±2.89 and 267.94±4.29 Bq.kg-1 in sequence. The mean values for 226Ra and 232Th were above the UNSCEAR stipulated global averages. Thus, indicating that the soil bears significant concentrations of 226Ra and 232Th. Computed average absorbed dose rate at 1 m above ground was 94.16 nGy.h-1 with corresponding mean annual dose equivalent of 0.22 mSv.y-1  and average excess lifetime cancer risk of 0.76×10-3. These values were all below respective safety limits set by UNSCEAR. The results of this investigation therefore indicated minimal radiological risk associated with artisanal gold mining activities in the studied area.

CHAPTER ONE

1.0 INTRODUCTION

1.1 Background of the Study

For survival and development, mankind requires natural resources which are randomly distributed on earth (Candeias et al., 2018). Mining and mineral extraction occurs wherever natural resources (metallic, non-metallic minerals and fossils) are present and economically viable  (Ako  et  al.,  2014).  One  of  the  most  precious  and  economically  viable  natural resource that has continuously attracted the attention of miners is gold. On a large scale, gold-mining yields foreign exchange and economic development. However, Several gold- rich rural areas in Nigeria have been dominated by artisanal miners who are ill-equipped, uneducated and have little appreciation of the environment (Sabo et al., 2018). Artisanal or small-scale mining circumscribes informal, small, medium, legal and illegal mining activities  involving the  use of  unsophisticated  tools  and  techniques  to  extract  mineral resources (Sabo et al., 2018). In developing countries (particularly in West Africa), the environmental  consequence  of  artisanal  gold  mining  has  been   assessed  and  well documented (Hilson, 2002; Lacerda and Salomons, 1998; Meech et al., 1998; Hollaway, 1993  and  Mireku-Gyimah  and  Suglo,  1993).  Mining processes  incite  depletion  of the environment such as land degradation, de-vegetation, air and water pollutions and loss of aquatic organisms (Ako et al., 2014).

Nigeria is a gold-rich country. Gold deposits are found in Northern Nigeria and Iperindo, Osun State (Okere, 2018). Nigeria has gold deposits averaging 21370 kg from 2000 to 2018. This number attained an all-time high of 21400 kg in the first quarter of 2018 (Okere,

2018). However, poor attention from the government towards exploiting this mineral, unemployment and extreme poverty have driven large number of people into the local mining occupation. These occupational artisanal miners are from socially and economically marginalised communities (Pure Earth, 2008). They are also uninformed of the implications of mining activities to the environment and human health.

United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR) (2000) identified mining as a potential cause of exposure to naturally occurring radioactive materials (NORM) (Faanu et al., 2016). Mining activities propagate NORM and other Potentially Hazardous Trace Elements (PHTE) within the human environment. Wherever these NORM and PHTE are present at levels above the prescribed safety limits by UNSCEAR (2000), they become detrimental to humans and the environment in general. Exposure to the ionising radiation emitted by NORM pose radiological risk to humans and the environment (Alharbi, 2016). The probability and nature of effects induced in humans depend on the radiation dose received by an individual. Such effects may be somatic, occurring only in the exposed individual or genetic, occurring in the descendants of the exposed individual (New York State Department of Health (NYSDH), 2007).

For decades, Gababiyu area in Minna Metropolis has been known for artisanal gold mining activities.  Most  recently,  the  area  have  been  marked  as  proposed  site  for  El-Amin University.  Consequently,  the  population  of  the  proposed  University  will  occupy  a degraded environment. Furthermore, there is a likelihood of NORM and PHTE propagation within the mining environment. It has therefore become necessary that the radiation load on the miners and the public as a result of this anthropogenic activity be evaluated to check the level of radiation exposure.

In Nigeria, there is a general lack of information regarding concentration of NORM and associated radiological parameters from local mining areas. Thus, this work seeks to assess the radiological implications of artisanal mining in Gababiyu artisanal gold mine in Minna Metropolis, Nigeria.

1.2 Statement of the Research Problem

Associated with mining and mineral processing are potential adverse health risks that are more significant to occupationally exposed individuals. Artisanal mining is associated with the generation of significant mining wastes (tailings) which are indiscriminately disposed off  in  the  surrounding  environment.  Additionally,  natural  processes  like  rainfall  and leaching processes wash NORM to river bodies, thereby radiologically contaminating the water bodies. The tailings are also used as aggregates of building materials, which thus enhances radiation concentration in human dwellings. The human food chain is also contaminated as crops cultivated around the study area absorb NORM from the soil. More artisanal mines have been surveyed in Ghana and Nigeria due to their huge gold deposits. Poverty has also driven more rural dweller into the mining occupation in these two countries. Furthermore, artisanal miners ignore necessary safety procedures while mining for gold as they are unaware of the radiological implications of exposure to NORM. All these processes potentially increase human exposure to radiations, some to levels that seem detrimental to human health as well as the environment.  Thus, this work is aimed at determining the level of exposure of miners and the environment to NORM.

1.3 Aim and Objectives of the Study

This study is aimed at quantifying the radiation dose to miners and the environment from artisanal mining activities around Gababiyu pre-industrial goldmine, in Minna Metropolis through gamma spectrometry.

The objectives are to:

i.      determine the specific activity concentration of naturally occurring radionuclides (226Ra, 232Th and 40K) in soil around Gababiyu pre-industrial  gold mining site, Minna.

ii.      compute radiological parameters and assess the radiological health risk related to mining in the area.

1.4 Scope of the Study

The cynosure of this research is to assess the radiological health risk associated with small- scale  gold  mining  in  Gababiyu,  Minna  Metropolis.  Through  the  determination  of  the activity concentration of naturally occurring radionuclides in 40 soil samples collected from Gababiyu artisanal gold mine. Using identification and quantification of radionuclides by examining  the  gamma-ray  energy  spectrum  produced  in  a  Sodium  Iodide  Thalium- activated (NaI[Tl]) gamma-ray spectrometer in the department of radiation biophysics of the Centre for Energy Research and Training (CERT), Zaria.

Natural radionuclides detection in this study is limited to gamma energy peaks (channels) of 1460.0, 2614.5 and 1764.0 KeV analysing for 40K, 232Th and 226Ra respectively. They exhibit photon intensity sufficient for gamma-ray spectrometry and contribute significantly to the doses dispersed in the environment and received by human populace. From the determined activity concentration,  radiological parameters are computed and compared with globally recommended thresholds for occupational exposure to radiation. Determined values above the stipulated threshold will indicate significant radiological contamination and associated health risks while values below the threshold will indicate minimal radiological risks.

1.5 Significance of the Study

Understanding the behaviour of radionuclides in the environment provides information of related parameter values for radiological assessments. These assessments are relevant for monitoring environmental radioactivity levels and remediation.

It is essential to determine the activity concentration of NORM in Gababiyu pre-industrial gold mine as the area under study and its immediate environs may be at risk of exposure to radiation dose(s) resulting from the artisanal gold mining activities. Upon comparison with global screening level for occupational radiation exposure, the estimated dose rate from this study will establish the radiological safety for artisanal mining in the region. The outcome of this study will enlighten the miners who are occupationally exposed to NORM on the need  for radiological  protection  during  their routine mining processes.  Results  of this research will serve as baseline data for the region upon which future determination can be compared with. The baseline data will be relevant for evaluating potential radiological health risk to the populace of the proposed El-Amin University.  Also, there are no defined guidelines by the Nigerian Nuclear Regulatory body for existing mining areas in Nigeria. Therefore, there is need for radioactivity measurements in artisanal gold mining communities in Nigeria to establish baseline data for safety and future comparison. This will enable the assessment of the variations of NORM concentration due to mining and evaluation of contamination levels. Also, government environmental and health regulatory agencies will find the result of this study valuable for policy making as regards to safeguarding environmental and human health. This is achievable by expanding future determinations to other gold mining communities and immediate environs.

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