Review of the status of radioactivity profile in the oil and gas producing areas of the Niger delta region of Nigeria

Journal of Environmental Radioactivity 202 (2019) 66–73

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Review of the status of radioactivity profile in the oil and gas producing areas of the Niger delta region of Nigeria

T

B.B. Babatundea,b,∗, F.D. Sikokia,b, G.O. Avwiric, Y.E. Chad-Umorehc a

Department of Animal and Environmental Biology, Faculty of Science, University of Port Harcourt, P.M.B. 5323, Choba, Port Harcourt, Rivers State, Nigeria National Coordination Centre, FG_IAEA RAF07015 Project, University of Port Harcourt, P.M.B. 5323, Choba, Port Harcourt, Rivers State, Nigeria c Department of Physics, University of Port Harcourt, Rivers State, Nigeria b

A R T I C LE I N FO

A B S T R A C T

Keywords: Radioactivity Oil producing region Human health implications Radiation hazard indices

There is widespread degradation of the environment of the Niger Delta region of Nigeria such that the United Nations Environment Program described it as an ecological wasteland. The contamination is due mainly to unregulated oil and gas production activities leading to oil spills and illegal disposal of contaminated materials, indiscriminate industrial and domestic discharges into water bodies. This widespread contamination includes naturally occurring radioactive materials (NORM) and technologically enhanced radioactive materials (TENORM). NORMs are naturally associated with every mineral in the earth crust, thus the exploitation of such minerals may transport NORM to the surface as TENORM. If uncontrolled by operators and unregulated by government agencies, NORM can find its way into surface and ground water, seafood and even crops consumed by humans. The Niger Delta region is the hub of oil and gas activities providing huge employment and socioeconomic benefits to its indigenes and accounting for more than 90% of foreign exchange earnings for the country. However, uncontrolled spills and discharges from these activities have left the land desolate, degrading most of its aquifers and surface waters, leaving the indigenes with a Hobson choice, eating and drinking contaminated substances everyday of their lives. It is expedient that attention be drawn to this area as radionuclides such as Po-210, Pb-210 and Ra-226 have been confirmed as radiotoxic and may be responsible for several new cases of health challenges reported in the study area over the years.

1. Introduction The Niger Delta in the South-South geopolitical zone of Nigeria is an important region to Nigeria because of its oil and gas reserves which earns the country more than 90% of its foreign exchange revenue. Apart from the mineral resources, the Niger Delta ecosystem contains one of the highest concentrations of biodiversity on the planet and in addition to supporting abundant flora and fauna, its arable terrain and water resources can sustain a wide variety of crops, lumbar and agricultural trees and more species of freshwater fisheries than any other wetland in West Africa. This incredible ecosystem is however, vulnerable to destruction by petroleum and its products due to oil industry activities within the area (Ajao and Anurigwo, 2002). The exploitation and exploration of crude oil and gas may bring economic benefits to a country but its activities are destructive to the environment even at the safest and best operating practices and such unsafe acts may include the redistribution of naturally occurring radioactive materials (NORM).

The earth crust was originally incorporated with 238U (T1/ 232 Th (T1/2 = 1.405E+10 years) isotopes 2 = 4.468E+9 years) and which formed the primary natural decay series giving rise to daughter nuclides also radioactive such as 234Pa, 226Ra, 222Rn, 210Pb, 210Po and, 228 Ac, 212Pb, 208Tl for 238U and 232Th respectively. These isotopes are widely distributed in the earth's environment occurring in trace amount (ppm/ppb) in sediments, seafood, air, soil, foodstuff, surface and groundwater (Pates and Mullinger, 2007). The extent of distribution depends on the geological features of the area, industrial application of radionuclides and the chemical and biochemical distribution of Uranium and Thorium and their progenies. Also widely distributed is 40K, a natural radioactive isotope occurring in high background levels in biological systems and earth minerals such as rocks, clay, shale, limestone and granite. During the processes of crude oil and gas recovery from the earth crust, naturally occurring radioactive materials (NORM) associated with the minerals in the earth crust are brought to the surface and distributed widely in the environment with potential

∗ Corresponding author. Department of Animal and Environmental Biology, Faculty of Science, University of Port Harcourt, P.M.B. 5323, Choba, Port Harcourt, Rivers State, Nigeria. E-mail address: [email protected] (B.B. Babatunde).

https://doi.org/10.1016/j.jenvrad.2019.01.015 Received 15 November 2018; Received in revised form 25 January 2019; Accepted 25 January 2019 0265-931X/ © 2019 Elsevier Ltd. All rights reserved.

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Fig. 1. The origins of NORM, indicating where NORM may accumulate in the recovery process. Source (OGP, 2008).

adequate regulatory framework to control the distribution of such waste into the environment (De-Paula-Costa, 2018). In the oil and gas industries, a good example of literature compilation of radionuclides associated with oil and gas production is given in Jonkers et al. (1997) and OGP, 2008 which reported global average of concentrations of radionuclides in formation water and crude oil Tables 1 and 2. Other reviews of global distribution of NORM in oil and gas producing regions of the world exist, for example in the USA, Smith (1992) gave a good account of the most common radionuclide associated with oil and gas production and concentrations ranges in well heads, formation water and other waste materials. According to Smith (1992), elevated NORM concentrations have been detected in produced water, scale, sludge, and oil and gas production and processing equipment in many geographic regions. The primary radionuclides of concern in oil and gas NORM are radium-226 and radium-228. These isotopes are the decay products of uranium and thorium isotopes that are present in subsurface formations from which hydrocarbons are produced. While uranium and thorium are largely immobile, radium is slightly more soluble and may become mobilized in the fluid phases of the formation. Other radionuclides of concern, particularly in gas processing equipment, are

consequences of contaminating food and water sources consumed by humans. According to Jonkers et al., (1997) and International Association of Oil and Gas Producers (OGP, 2008), during the production process, NORM now referred to as TENORM (Technologically Enhanced Natural Occurring Radioactive Materials) flows with the oil, gas and water mixture and accumulates in scale, sludge and scrapings. It can also form a thin film on the interior surfaces of gas processing equipment and vessels. The level of NORM accumulation can vary substantially from one facility to another depending on geological formation, operational and other factors. Fig. 1 indicates where NORM may accumulate, eg at wellheads in the form of scale; at Gas/Oil Separation Plants (GOSP) in the form of sludge; and at gas plants the formation of thin films as the result of radon gas decay. This is supported by the report of (El Afifi and Awwad, 2005) which states that NORM occurs by precipitation or in-corporation of these materials in the oil sludge, pipe cleaning, in scales inside pipes, vessels, heat exchanger, pieces of pumps, and others. To determine whether or not a facility has NORM contamination, NORM survey, sampling and analysis needs to be conducted. Although the sources of NORM are well delineated and reported in literature around oil and gas production activities (Jonkers et al., 1997; Pates and Mullinger, 2007; OGP, 2008), issues bothering around lack of access to facilities for sampling, lack of adequate regulatory framework and lack of appropriate equipment and human capacity have limited scientific studies on this topic in the Niger Delta where oil and gas production are prolific in Nigeria. In Brazil also (De-Paula-Costa, 2018), lamented lack of appropriate regulatory framework to combat NORM in oil and gas waste. The importance of naturally occurring radioactive materials (NORM) in the environment as a source of ionization radiation dose to man has been studied for many years (McDonald et al., 1996; Arogunjo et al., 2004). The present of NORM in oil and gas waste has raised concerns in the last few decades and more worrisome is the absence of

Table 1 Activity concentration of and232Th,228Ra,224Rain production water. (Source: Jonkers et al.,(1997)) Radionuclide

Reported Range (Bq/I)

238

0.0003–0.1 0.002–1200 0.05–190 0.0003–0.001 0.3–180 0.5–40

U Ra 210 Pb 232 Th 228 Ra 224 Ra 226

67

238U,226Ra,210Pb

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UNSCEAR, 2000). Yet at the present, most of the data available on radionuclide concentration in environmental media such as sediment, drinking water sources and some well relished fish species from this oil and gas producing region are baseline information. This is because application of nuclear analytical techniques for pollution and environmental monitoring is still relatively elementary in Nigeria due to equipment cost and low human capacity to deploy the techniques as well as gross inadequate regulatory framework. In addition, radioecology which evaluates the sources, distribution and interaction of ionization radiation in the environment is totally alien to Nigeria but it is a powerful tool for the determination of effects of ionization radiation on biota of the study area as it affects the food chain and energy transfer along the tropic levels. It is useful for using results of the activity concentration of radionuclides in seafood samples to estimated internal dose of ionization radiation received by the inhabitants through ingestion of fish meal per year. This information can be useful in determining health risk to the population due to ionization radiation through ingestion of fish resources. The aim of this review is provide account of the present status of environmental radioactivity in the oil producing areas of the Niger Delta region with the message to encourage more work in this area to generate scientific data required to convince opinion leaders of the looming danger of consuming radioactivity in water and seafood in the region.

Table 2 Activity concentration of 238U,226Ra, 210Po and 232Th in crude oil. Radionuclide

Reported Range (Bq/I)

238

0.0000001–0.01 0.0001–0.04 0–0.01 0.00003–0.002

U Ra 210 Po 232 Th 226

lead-210 and radon-222, which is sometimes present in natural gas. The amount of radioactivity that accumulates in oil and gas wastes depends on a variety of factors, including the amount of uranium and thorium present in the subsurface formation, the formation fluid chemistry, extraction and treatment processes, and the age of the production well. In Oman, Al-Farsi, 2008 evaluated NORM in sludge from separation tanks, sludge farming, scaling in oil tubulars, NORM storage, scaling in gas production and sedimentation in produced water evaporation ponds and report that all radionuclides of concern (RA-226, Ra-228, Pb-210 and Po-210) concentrations were above stipulated limit and can pose serious human health challenges because of the reported absorbed doses. In Nigeria, the Niger Delta in particular, data on NORM associated with oil and gas production is scarce due to lack of expertise, specialised equipment and inadequate regulatory concerns. However, NORM have been reported in sediments and soils around oil and gas production areas (Meindinyo and Agbalagba, 2012; Avwiri and Agbalagba, 2012), in sediments and water from a flood plain lake near oil and gas activities (Agablagba and Onoja, 2011), in crude oil (Ajayi et al., 2009), in foodstuffs harvested around oil and gas production activities (Akinloye and Olomo, 2000; Jibril et al., 2007), in bedrocks and soils around a cement factory also near oil and gas activities (Gbadebo and Amos, 2010). Radionuclides have also been reported in drinking water sold to the public (Ajayi and Adesida, 2009) and in medicinal plants (Oni et al., 2011), all in the oil and gas producing area of the Niger Delta. Some of the studies have also presented the corresponding radiation exposure and equivalent dose to humans living in the areas believed to be contaminated by ionization radiation from oil and gas activities (Akram et al., 2006; Jibiri et al., 2007; Agbalagba and Onoja, 2011). Awareness of the health implication of ionization radiation is increasing and the most dreadful being the damage radionuclides can cause to the gene pool (Sankaranarayanan, 1990). Apart from physical exposure to cosmic radiation and gamma and beta emitting radionuclides, humans are exposed to ionization radiation through inhalation of 238U daughter nuclide, 222Rn in air (UNCEAR, 2000), ingestion of its progenies, 210Pb and 210Po in water, seafood and foodstuff (Chen et al., 2001). 226Ra and its daughter nuclides, 210Pb, 210Po are said to be of considerable threat to biological systems, they have been reported as the most radiotoxic naturally occurring radioisotopes (AL-Masri et al., 2004a; Akhtar et al., 2005). According to Stepnoski and Skwarzec, (2001b), 210Pb and 210Po have been known to contribute the highest internal dose from ionization radiation in marine organisms and humans. They also bioaccumulate in the tissues of marine organisms and are thus transferrable up the food chain with potential health consequences at the higher trophic levels (Tahir and Alaamar, 2008; Fowler, 2011). In Nigeria, especially in rural and fishing communities such as the study area, fish constitute about 75% of animal protein consumed (Edun et al., 2010). Fish is consumed either freshly prepared or smoked, shell fish especially periwinkle is used largely as condiment in most meals eaten in the Niger Delta (Gomna and Rana, 2007). Given the review of literature (Mathew et al., 2007; Avwiri and Agbalagba, 2012; Jibiri et al., 2007; Agbalagba and Onoja, 2011; Babatunde et al., 2015), it is obvious that the people of the Niger Delta region are exposed to levels of radiation above regulated limits by (WHO/FAO, 2012;

1.1. Justification of the problem The widespread contamination of the environment of the Niger Delta may not have been adequately reported as holistic scientific investigations are limited in scope and may not include important contaminants such as radionuclides which have been reported elsewhere to cause cancer and other genetic disorders. This review collated data on radioactivity in the oil and gas rich Niger Delta which can be useful in holistic evaluation of contamination and public health effects to humans in the region. Furthermore, more robust and elaborate research designs can be derived based on the available data collated here for more comprehensive data sets required for policy redress and holistic regulation of oil and gas activities in the environment of the Niger Delta. 1.2. The Niger delta The fan-shaped Niger Delta represent about 7.5% of Nigeria's total landmass and is the third largest delta in the world after the Mississippi and Pantanal (S/W Brazil). It lies between latitude 4° and 6oNorth of the equator and longitudes 5° and 9° east of the Greenwich Meridian and was formed primarily by sediment deposit at the mouth of River Niger/ River Benue course (Akpomuvie, 2011). The South-North extent of 4-6° North of the equator is expressly defined by the Great Atlantic Ocean in the South to Aboh (Delta State) in the North where River Niger forks into River Nun and River Forcados at a village called Obotor. The EastWest extension is from the boundary of the Bonny River to Sapele River, Delta State. This implies that the East-West extent of approximately 440 km is two times the North-South extent of approximately 220 km. Thus, the states covered by the actual geographical Niger Delta defined by the natural boundaries described earlier are: Delta, Bayelsa and Rivers with about 25, 640 km2 (Ashton-Jones, 1998). However, NDDC (2004) defined the Niger Delta to include nine oil producing states in the South (Delta, Bayelsa and Rivers, Edo, Ondo, Akwa Ibom, Cross River, Abia and Imo States) with an extended 70,000 km2. The hydrology of the Niger Delta comprises a huge network of Rivers (Ramos, Sengana, Nun, St. Nicholas, Santa Barbara, San Bartholomew, Sombreiro, New Calabar, Bonny, Andoni, Warri and Imo), some running parallel to River Niger and discharging into the Atlantic Ocean (Plate 1). The Niger Delta has the largest wetland and maintains the third-largest drainage basin in Africa (Moffat and Linden, 68

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Plate 1. Satellite image of the Niger Delta showing a network of rivers and estuaries emptying into the Atlantic Ocean (Google Earth, 2009).

(Cercopithecus sclateri), sitatunga (Tragelaphusspekei), white throated monkey (Cercopithecus erythrogaster) just to name a few. The Niger Delta is also rich in fishery resources; it provides breeding grounds for numerous species of finfish, prawns and as habitats for crabs and mollusks (IPIECA, 1993). Available records show that the delta has more freshwater fish species (197) than any other ecosystem in West Africa (Moffat and Linden, 1995). Beyond these, the extensive mangrove forest provides nesting sites for sea and shore birds; stabilizes and protect the Nigerian coastline, and filters and traps water borne pollutants. In addition, plants products are obtained from the forest such as logs, fuel wood, charcoal, building materials, stakes for fish traps, paper pulp, railway sleepers etc (Semesi and Howell, 1992; IPIECA, 1993; IUCN, 1993). Other products of medicinal and agricultural values are also got from mangrove forests (Semesi and Howell, 1992; Mills et al., 1999). The mangrove swamps have sustainably supported the economics of the local populace for decades before the advent of oil mining. This valuable ecosystem is however vulnerable to destruction by petroleum and its products due to unregulated oil industry operational activities within the area (Ekweozor, 2004). Hydrocarbon exploration started in the Niger Delta in 1937, but it was not until 1956 that the first oil well was struck, other discoveries followed and two years after Nigeria made her first batch of oil export. Nigeria became an independent country in 1960, and soon became an important member of the organization of petroleum exporting countries (OPEC). Nigeria is currently rated as the sixth largest producer and the eighth largest exporter of petroleum with a daily crude oil production rate of 2.4 million barrels. As at today, the country's crude oil and gas

1995). The lithology of the Niger Delta comprises an upper sandy Benin Formation, an intervening unit of alternating sandstone and shale named the Agbada Formation, and a lower shaly Akata Formation. These three units extend across the whole delta. Detailed geology of the study area is described elsewhere (Taiwo and Tse, 2009). The Delta's environment can be broken down into four ecological zones: coastal barrier islands, mangrove swamp forests, freshwater swamps, and lowland rainforests. This incredibly well-endowed ecosystem contains one of the highest concentrations of biodiversity on the planet, in addition to supporting abundant flora and fauna, arable terrain that can sustain a wide variety of crops, plantation, and more species of freshwater fish than any ecosystem in West Africa. In addition to petroleum resources, the Niger Delta has been reported to be highly diverse and rich in biological resources (ERML, 1997). Being the largest wetland in Africa, the biological diversity of the Niger Delta is of both regional and global importance (Moffat and Linden, 1995). For instance the Delta hosts a number of endangered species listed in the 1996 IUCN (Note: Give the full meaning of the initials) red list including the pygmy hippopotamus (Choeropsisliberiensis), manatees (Trichechus senegalensis), maritime hippopotamus (Hippopotamus amphibious) and all species of crocodiles, including the Nile (Crocodylusniloticus), slender nosed (C. cataphractus) and dwarf (Osteolaemustetraspis) (Moffat and Linden, 1995; World Bank, 1995). Other wildlife of conservation interests include the Cape clawless otter (Aonyxcapensis), African palm nut vulture (Gypohieraxangolensis), Cuviers fire footed squirrel (Funisciuruspyrropus), Hammerkop (Scopus umbretta), African fish eagle (Haliaetusvocifer), Sclater's guenon 69

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reserve stands at over 20 million bbl and 3.4 trillion cubic meters respectively (Imevbore, 2001).

Table 3 shows typical activity concentrations of three radionuclides reported around the world.

1.3. Contamination in the Niger delta environment

1.5. Radioactivity in the Niger delta environment

Despite the socio-economic, ecologic and biodiversity value of these wetlands, they are being threatened by anthropogenic influences, outstanding among these are the discharges from oil and gas production activities, dredging and the concomitant disposal of dredge spoil. The Niger Delta is laden with environmental contaminants including ionization radiation as a consequence of oil and gas exploitation and exploration, industrial activities and urbanization which have devastated its environment for many years (Akpomuvie, 2011). Large scale oil and gas production, industrialization and urbanization characterised the neighbourhood of the Niger Delta with reported devastation of its environment by oil spills, gas flare, industrial discharges, agricultural run offs and domestic effluents and leachates which may lead to human exposure to contaminants including ionization radiation. The estuarine areas also support marine transportation by heavy vessels conveying goods and services to and from petroleum tank farms, flow stations and other oil terminals among others in addition to heavy traffic of fast speed boats for communal transportation doting every nook and cranny. The oil spillages ongoing for several decades have characterised the area by contaminating rivers, stream and forest. Approximately 3 million barrels of oil has been spilled within the Niger Delta region over the span of several decades, most of which was partially cleaned or not cleaned totally, making some areas complete wastelands. The Nigerian National Petroleum Corporation places the quantity of petroleum jettisoned into the environment yearly at 2300 cubic metres with an average of 300 individual spills annually. However, because this amount does not take into account "minor" spills, the World Bank argues that the true quantity of petroleum spilled into the environment could be as much as ten times the officially claimed amount (Moffat and Linden, 1995; Zabbey and Babatunde, 2011). As of 2006, there were eleven (11) oil companies operating one hundred and fifty-nine (159) oil fields and one thousand four hundred and eighty-one (1,481) wells in the Niger Delta in Nigeria. Human activities and those of oil exploration and exploitation raise a number of issues such as depletion of biodiversity, coastal and riverbank erosion, flooding, oil spillage, gas flaring, noise pollution, sewage and wastewater pollution, land degradation and soil fertility loss and deforestation, which are all major environmental issues (Chindah et al., 2009). It has had disastrous impacts on the environment in the region and has adversely affected people inhabiting that region. (Chindah et al., 2004; Davies and Abowei, 2009).

There is growing need to understand the potential effect of low dose or environmentally occurring ionization radiation on man through all sources of exposure. Studies on naturally occurring radioactive materials (NORM) as important source of ionization radiation dose to man has been studied for more than four decades now (McDonald et al., 1996; Sohrhabi, 1998). The measurement of environmental radioactivity in Nigeria and the Niger Delta is a more recent effort by some scientists spanning the last one decade with reports on radioactivity in soils (Jibiri and Okusanya, 2008; Agbalagba et al., 2012), sediments (Agbalagba and Onoja, 2011), surface waters (Meindinyo and Agbalagba, 2012), drinking water (Ajayi and Adesida, 2009), grasses (Akinloye and Olomo, 2005; Jibiri and Ajao, 2005), medicinal plants (Oni et al., 2011), foodstuffs (Jibiri et al., 2007; Jibiri and Okeyode, 2011), building materials (Gbadebo and Amos, 2010), bitumen (Balogun et al., 2003; Fasasi et al., 2003) and even crude oil (Ajayi et al., 2009). Most of the studies reported radioactivity levels of NORM to be within natural background levels and reported averages by (UNSCEAR, 2000). However, these studies may have been limited in scope as the equipment for measuring radioactivity in environmental samples are generally scarce in the country. For instance, few data exist on alpha emitting radionuclides such as 210 Po (Babatunde et al., 2015) which is reported elsewhere to contribute more than 80% of effective dose to humans (UNSCEAR, 2000). However, the reports of the various authors can be useful as baseline data for further research on radiological hazard to humans in the Niger Delta. Agbalagba et al. (2012) measured naturally occurring radionuclides (226Ra, 232Th and 40K) for use in the assessment of radiation hazard indices in soil samples collected from oil and gas field environment of Delta state in the Niger Delta region of Nigeria. The activity concentration of the samples was reported to range from 19.2 ± 5.6 Bqkg−1 to 94.2 ± 7.7 Bqkg−1 with mean value of 41.0 ± 5.0 Bqkg−1 for 226Ra, 17.1 ± 3.0 Bqkg−1 to 47.5 ± 5.3 Bqkg−1 with mean value of 29.7 ± 4 Bqkg−1 for 232Th and 107.0 ± 10.2 Bqkg−1 to 712.4 ± 38.9 Bqkg−1 with a mean value of 412.5 ± 20.0 Bqkg−1 for 40 K. These values obtained were reported to be well within the world range and values reported elsewhere in other countries, but are little above some countries reported average values and some part of Nigeria Agbalagba et al. (2012). The study also examined some radiation hazard indices, the mean values obtained are, 98.5 ± 12.3 Bqkg−1, 0.8 Bqkg−1, 54.6 h ƞGyh−1, 0.07 μSvy−1, 0.3 and 0.4 for Radium equivalent activity (Raeq), Representative level index (Ig), Absorbed Dose rates (D), Annual Effective Dose Rates (Eff Dose), External Hazard Index (Hex) and Internal Hazard Index (Hin) respectively. These calculated hazard indices to estimate the potential radiological health risk in soil and the dose rate associated with it are well below their permissible limit. The soil and sediments from the study area provide no excessive exposures for inhabitants and can be used as construction materials without posing any immediate radiological threat to the public. However, oil workers in the fields and host communities are cautioned against excess exposure to avoid future accumulative dose of these radiations from sludge and sediment of this area. Tchokossa et al. (2012) also measured radioactivity concentrations in soils around the oil and gas producing areas in Delta State of Nigeria to determine the suitability of the soil for use as building material. Soil samples were collected from 20 locations from the study area and analysed. The radionuclides detected are traceable to the primordial series of 238U and 232Th as well as 40K and traces of globally released 137 Cs. The specific activity values ranged between 7 and 60 Bqkg−1 with a mean of 24 + 2 Bqkg−1 for 238U; while for 232Th the range was 7–73 Bqkg−1 with a mean of 29 ± 3 Bqkg−1. Relatively higher specific

1.4. Radioactivity in the environment Radioisotopes like other elements, have found applications in nearly every facet of human endeavour being used for military, energy generation, medical, agriculture, industrial and research purposes. Consequently, their background levels in the environment can be enhanced or concentrated by these uses. In addition, processes associated with recovery of minerals from the bedrocks such as oil and gas, limestone and industrial productions of inorganic fertilizer and building materials are capable of increasing environmental concentration of ionization radiation. These enhanced NORM, often known as TENORM (Technologically-Enhanced Naturally Occurring Radioactive Materials) are usually redistributed in the environment by biogeochemical processes with radioecological consequences for biological systems including humans (Agbalagba et al., 2012; Carvalho et al., 2011). In Africa, more reports are from the east African countries bordering the Mediterranean and Red Seas such as Egypt, Morocco, Tunisia, Algeria and Sudan (Adam et al., 1998; Azouazi et al., 2001; Belafrites, 2008; ElGamal et al., 2007; Radi Dar and El-Saharty, 2012; Tayibi et al., 2009). 70

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Table 3 Activity concentrations (Bqkg−1) of226Ra,232Th and40K reported worldwide. Country/Region

226

Alexandria, Egypt France Zacatecas (Mexico) Malaysian Cyprus Sudan Punjab, Pakistan South India Spain South west Nigeria Kenya China Louisiana (USA) Niger Delta, Nigeria World's average UNSCEAR, 2000

16.7 ± 2.7 9–62 23 20.9 ± 4.1 7.1 ± 0.6 28.31 35 ± 7 35 46 16.2 ± 3.7 28.7 ± 3.6 42.7 ± 15 4.3 ± 96 41 ± 5 35

Ra

232

40

19.4 ± 5.0 1.6–56 19 33.8 ± 2.9 5.0 ± 0.7 20.12 41 ± 8 29.8 49 24.4 ± 4.7 73.3 ± 9.1 46.3 ± 12 5 ± 191 29.7 ± 4 30

262 ± 82 120–1026 530 125.9 ± 21.1 105 ± 95 280.29 615 ± 143 117.5 650 234.8 ± 20.4 255.7 ± 38.5 578 ± 164 43.729 412.5 ± 20 400

Th

activity values were recorded in 40K with a range of 15–696 Bqkg−1, while the mean was 256 ± 37 Bqkg−1. However, a relatively lowspecific radioactivity was obtained from 137Cs with a range of 1–25 Bqkg−1 and a mean of 7 ± 1 Bqkg−1. The estimated dose equivalent obtainable per year from these levels of radioactivity is < 5% of the recommended safe level of 1 mSv per annum. Therefore, the area and the use of the soils as building materials may be considered safe. Also, an environmental radiation survey was carried out by Avwiri and Agbalagba (2012) around oil fields in communities in Ughelli, Delta State and reported that the radiation within the study area was far above natural background levels of 0.013 mR h−1 but the average dose equivalent obtained were within safe radiation limit of 0.02 mSv/week recommended by UNSCEAR. Agbalagba and Meindinyo (2010) also reported similar results from the Niger Delta and said results obtained will not pose any immediate radiological health hazard to the communities nor the workers within the environment. In Bayelsa State, Meindinyo and Agbalagba, (2011) measured gross alpha and beta activity concentrations in soils and water samples in and around Imirigin oil field and reported that the mean values for alpha and beta activity in soil were above reported values in similar environment while mean values obtained in water samples were above WHO recommended maximum permissible limit for drinking water. According to the study, these values obtained showed that drinking water from sampled locations may pose some long term health hazards to the public users though soil from the area is still safe as construction material for buildings. One of the pivotal states in the Niger delta region of Nigeria is Rivers State. Chad-Umoren and Briggs-Kamara (2010) studied the environmental ionizing radiation distribution in this important State on the assumption that the state-wide distribution of oil and gas operations will result in a homogeneous ionizing radiation environment. The state was split into three sub environments as follows: an upland school environment, a rural riverine environment and an industrial environment. The ionizing radiation was found to be distributed as follows: Their work gave a mean dose equivalent of 0.745±0.085 mSv/yr (upland campus environment), 0.690±0.170 mSv/yr (rural riverine communities) and 1.270±0.087 mSv/yr (industrial zone) indicating an inhomogeneous radiation profile. The study therefore indicates that industrial operations, which included oil and gas activities, had an impact on the radiation profile of the state. Agbalagba and Onoja (2011) reported a baseline study undertaken to evaluate the natural radioactivity levels in soil, sediment and water samples in four flood plain lakes around oil and gas producing areas of the Niger Delta. The activity profile of radionuclides showed low activity across the study area. The mean activity level of the natural radionuclides 226Ra, 232Th and 40K is 20 ± 3, 20 ± 3 and 180 ± 50 Bq kg−1, respectively. These values are well within values reported

K

Reference Saleh et al. (2007) Lambrechts et al. (1992) Noordin (1999) Masitah et al. (2008) Zortzis et al. (2004) Sam et al. (1997) Tahir et al. (2005) Narayana et al. (2001) Baeza et al. (1992) Arogunjo et al. (2004) Mustapha et al. (1999) Ziqiang et al. (1988) Delaune et al. (1986) Agbalagba and Onoja, 2011 UNSCEAR (2000)

elsewhere in the country and in other countries with similar environments. The study also examined some radiation hazard indices. The mean values obtained were, 76 ± 14 Bq kg−1, 30 ± 5.5 ƞGy h−1, 37 ± 6.8 mSv y−1, 0.17 and 0.23 for Radium Equivalent Activity (Raeq), Absorbed Dose Rates (D), Annual Effective Dose Rates (Eff Dose), External Hazard Index (Hex) and Internal Hazard Index (Hin) respectively. All the health hazard indices were well below their recommended limits. The soil and sediments from the study area provided no excessive exposures for inhabitants and can be used as construction materials without posing any significant radiological threat to the population. The water is radiologically safe for domestic and industrial use. The paper recommends further studies to estimate internal and external doses from other suspected radiological sources to the population of the Biseni kingdom in Bayelsa State, Niger Delta, Nigeria. In a similar study, natural radionuclide concentrations in soil samples collected within and around crude oil flow and gas compression stations in the Niger Delta, Nigeria, were determined. The mean activity concentrations of 40K, 238U and 232Th varied from 30.1 ± 3.0 to 59.0 ± 17.1, BDL to 8.8 ± 2.3 and 7.9 ± 3.7 to 10.9 ± 1.9 Bq.kg-1, respectively. The 40K, 238U and 232Th contents of the soil samples are very low compared with the world average for natural background area. The absorbed dose rate and effective dose ranged from 6.9 to 11.1 nGy.h-1 and 8.5–13.6 μSv.y-1, respectively. The annual gonadal dose equivalent rate ranged from 48.9 to 77.5 μSv.y-1, which is lower than the world average of 0.30 mSv.y-1. The radium equivalent activity and the external hazard index of the soil samples were below the recommended limits of 370 Bq.kg-1 and unity, respectively. The results obtained reveal that there is no significant radiation hazard due to natural radionuclides of the soil samples in the studied areas Ademola and Atare (2010). To determine natural radioactivity content in crude oil, Ajayi et al. (2009) collected crude oil samples from six different fields in the central Niger Delta with the aim of assessing the radiological health implications and environmental health hazard and also to provide natural radioactivity baseline data that could be used for more comprehensive future study in this respect. The radionuclides identified with reliable regularity belong to the decay series of naturally occurring radionuclides headed by 238U and 232Th along with the non-decay series radionuclide, 40K. The averaged activity concentrations obtained were 10.52 ± 0.03 Bq kg−1, 0.80 ± 0.37 Bq kg−1 and 0.17 ± 0.09 Bq kg−1 for 40K, 238U and 232Th, respectively. The equivalent doses were very low, ranging from 0.0028 to 0.012 mSv year−1 with a mean value of 0.0070 mSv year−1. The results obtained were low, and hence, the radioactivity content from the crude oils in the Niger delta oil province of Nigeria do not constitute any health hazard to occupationally exposed workers, the public and the end user. A study was carried out by Chad-Umoren and Ohwekevwo (2013) to

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alpha emitters and are poorly studied in this oil and gas rich region, efforts must therefore be concentrated on analysing these radionuclides in associated oil and gas activities to determine their extent of contamination in the Niger Delta.

investigate the impact of oil spillage on the ionizing radiation profile of some communities in the Niger Delta region. For the purpose, five water samples were collected from each community making a total of 15 water samples and 5 soil samples were also collected from each community, also making a total of 15. These were analysed using the Gamma Scout γ-spectrometer and Na (TI) detector. The study found that all radiation parameters for both water and soil, such as the minimum dose rates for the three communities, exceeded acceptable international regulatory standards for the general public. The study therefore suggested that oil spill had resulted in the elevation of the radiation levels of the affected communities and that suitable steps needed to be taken to protect those living in the study area from radiation hazards. Babatunde et al. (2015) reported radioactivity profiles in the sediment and seafood from the Bonny estuary, one of the most environmentally stressed estuary systems in the Niger Delta. Radionuclides such as U-238, Ra-226 and Pb-210 decreased with depth indicating more contamination in later years of oil exploitation corresponding to heightened oil and gas activities in the region. Effective dose due to consumption of seafood in the region was higher than stipulated safe limits by WHO/UNSCEAR for some of the biota particularly Ergeria radiata. They opined that 210Po, an alpha emitter, was responsible for the highest dose received by consumers.

Appendix A. Supplementary data Supplementary data to this article can be found online at https:// doi.org/10.1016/j.jenvrad.2019.01.015. References Adam, K.S., Ahamed, M.M.O., El Khangi, F.A., El Nigumi, Y.O., Holm, E., 1998. Radioactivity levels in the Red Sea coastal environment of Sudan. Mar. Pollut. Bull. 36, 19–26. Ademola, J.A., Atare, E.E., 2010. Radiological assessment of natural radionuclides in soil within and around crude oil flow and gas compression stations in the Niger Delta, Nigeria. Radioprotection 45 (2), 219–227. Agbalagba, E.O., Meindinyo, R.K., 2010. Radiological impact of oil spilled environment: a case study of the Eriemu well 13 and 19 oil spillage in Ughelli region of Delta Sate, Nigeria. Indi. J. Sci. Technol. 3 (9), 10011005. Agbalagba, E.O., Onoja, R.A., 2011. Evaluation of natural radioactivity in soil, sediment and water samples of Niger Delta (Biseni) flood plain lakes, Nigeria. J. Environ. Radioact. 102, 667–671. Agbalagba, E.O., Avwiri, G.O., Chad-Umoreh, Y.E., 2012. Gamma spectroscopy measurement of natural radioactivity and assessment of radiation hazard indices in soil samples from oil fields environment of Delta State, Nigeria. J. Environ. Radioact. 109, 64–70 2012. Ajao, E.A., Anurigwo, Sam, 2002. Land-based sources of pollution in the Niger delta, Nigeria. AMBIO A J. Hum. Environ. 442–445. Ajayi, O.S., Adesida, G., 2009. Radioactivity in some sachet drinking water samples produced in Nigeria Iran. J. Radiat. Res. 7 (3), 151–158. Ajayi, T.R., Torto, N., Chokossa, P.T., Akinlua, A., 2009. Natural radioactivity and trace metals in crude oil:implication for health. Environ. Geochem. Health 31, 61–69. Akhtar, N., Tufail, M., Ashraf, M., Iqbal, M.M., 2005. Measurement of environmental radioactivity for estimation of radiation exposure from saline soil of Lahore, Pakistan. Radiat. Meas. 39 (1), 11–14. Akinloye, M.K., Olomo, J.B., 2000. The measurement of the natural radioactivity in some tubers cultivated in farmlands within the Obafemi Awolowo University, Ile-Ife, Nigeria. Niger. J. Phys. 12, 60–63. Akpomuvie, O.B., 2011. Tragedy of commons: analysis of oil spillage, gas flaring and sustainable development of the Niger Delta of Nigeria. J. Sustain. Dev. 4, 200–210. Akram, M., Qureshi, R.M., Ahmad, N., Solaija, T.J., Mashiatullah, A., Afzal, M., Faruq, M.U., Zeb, L., 2006. Concentration of naatural and artificial radionuclides in bottom sediments of Karachi Harbour/Manora channel, Pakistan coast (Arabian sea). J. Chem.Soc.Pak 28, 306–312. AL-Masri, M.S., Nashawati, A., Amin, Y., AL-Akel, B., 2004. Determination of Po-210 in tea, mate and their infusions and its annual intake by Syrians. J. Radioanal. Nucl. Chem. 260, 27–34. Arogunjo, A.M., Farai, I.P., Fuwape, I.A., 2004. Dose rate assessment of terrestrial gamma radiation in the Delta region of Nigeria. Radiat. Protect. Dosim. 108, 73–77. Ashton-Jones, N., 1998. The Human Ecosystems of the Niger Delta. Ibadan; Krat books, Ltd Lagos, Nigeria. Avwiri, G.O., Agbalagba, E.O., 2012. Studies on radiological impact of oil and gas activities in oil mineral lease 30 (Om130) oil fields in Delta State, Nigeria. J. Petrol Environ. Biotechnol. 3, 1–8. Azouazi, M., Ouahidi, Y., Fakhi, S., Andres, Y., Abbe, J.Ch, Benmansour, M., 2001. Natural radioactivity in phosphates, phosphogypsum and natural waters in Morocco. J. Environ. Radioact. 54, 231–242. Babatunde, B.B., Sikoki, F.D., Ibitoruh, Hart, 2015. Human health impact of natural and artificial radioactivity levels in the sediments and fish of Bonny estuary, Niger delta, Nigeria. Challenges 6, 244–257. https://doi.org/10.3390/challe6020244. Balogun, F.A., Mokobia, C.E., Fasasi, M.K., Ogundare, F.O., 2003. Natural radioactivity associated with bituminous coal mining in Nigeria. Nucl. Instrum. Methods Phys. Res. Sect. A Accel. Spectrom. Detect. Assoc. Equip. 505, 444–448. Beaza, A., del Rio, M., Mir, C., Paniagua, J.M., 1992. Natural radioactivity in soils of the province of caceres (Spain). Radiat. Protect. Dosim. 45, 261–263. Belafrites, A., 2008. Natural radioactivity in geological samples from Algeria by SSNTD and γ-ray spectrometry. In: Radiation Physics & Protection Conference, 15-19 November 2008, Nasr City - Cairo, Egypt. Carvalho, P. Fernando, Joan, M. Oliveira, Margarida, Malta, 2011. Radionuclides in deepsea fish and other organisms from the North Atlantic Ocean. Ices J. Marine Sci. 68 (2), 333–340. Chad-Umoren, Y.E., Briggs-Kamara, M.A., 2010. Environmental ionizing radiation distribution in rivers state, Nigeria. J. Environ. Eng. Landsc. Manag. 18 (2), 154–161. Chad-Umoren, Y.E., Ohwekevwo, E., 2013. Influence of crude oil spillage on γ-radiation status of water and soil in ogba/egbema/ndoni area, Nigeria. Energy Environ. Res. 3 (2), 45–52. Chen, Q.J., Hou, X.L., Dahlgaard, H., Nielsen, S.P., Aarkrog, A., 2001. 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2. Conclusion The studies on radioactivity concentrations associated with oil and gas production and environmental mediafrom the Niger Delta are limited in scope and approach due to a number of factors bothering on non-availability of expertise, specialised equipment and inadequate regulatory framework to facilitate research in this area. Most researches seem to report NORM levels of only gamma emitting radionuclides which are said to be within natural background levels and within reported global averages by UNSCEAR and the absorbed doses as well as effective doses within recommended levels byICRP (2012) and UNSCEAR. However, few reports for example, Babatunde et al. (2015) exist on alpha emitting radionuclides such as 210Pb and 210Po which have been reported elsewhere to be among the most radiotoxic naturally occurring radionuclides. Indeed, 210Po is considered to be one of the most toxic naturally occurring radionuclides (AL-Masri et al., 2004), and one of the most important environmental radionuclides due to its wide distribution and potential for human radiation exposure through ingestion and inhalation (Momoshima et al., 2002). It has been widely reported that 210Po is concentrated in many marine organisms, particularly in the digestive glands of molluscs and crustaceans (Theng et al., 2004), and is the largest contributor to the radiation dose received by marine organisms (Stepnowski and Skwarzec, 2000). Others such as have also reported gross alpha and gross beta level in environmental samples in the Niger Delta region. Of the natural radioactivity of human foodstuffs, 210Po is by far the major contributor, with the average dietary fish-product component containing 2Bq kg−1210Po (UNSCEAR, 2000). Through the ingestion pathway, 210Pb and 210Po deliver about 83% of the annual effective dose to humans (UNSCEAR, 2000), comprising 43 mSv y−1, including 11 mSv y−1 from 210Po (22% of total). For humans, 210Po and 210Pb enter the body through ingestion of food and water, and inhalation, with ingestion of seafood being the most significant route (Chen et al., 2001). These alpha emitting radionuclides must therefore be of priority in the estimation of effective doses to humans in the Niger Delta. The complete dearth of information on these elements in environmental samples in the Niger Delta may be as a result of lack of technical expertise in their radiochemistry and lack of equipment such as the alpha spectrometer needed for their measurement. Considering the reports reviewed here, the most important radionuclides of interest associated with oil and gas such as Ra-226 and Ra-228, Pb-21- and Po-210 are 72

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