Evaluation of Gross Alpha and Gross Beta Radioactivity in Crude Oil Polluted Soil, Sediment and Water in the Niger Delta Region of Nigeria

The evaluation of gross alpha and beta activities in crude oil contaminated soil, sediment and water samples was conducted in ten oil polluted environment of Delta State using Gas-flow proportional counter. Samples were collected from the oil polluted environment in each oil field and samples were prepared and analyzed following standard procedures. The mean gross alpha and beta activities obtained are 331.4 ± 24.5 Bq kg−1 and 11,335 ± 112 Bq kg−1 respectively for soil, 259.2 ± 17.6 Bq kg−1 and 4508 ± 96 Bq kg−1 respectively for sediment, and 1.00 ± 0.09 Bq kg−1 and 20.3 ± 1.7 Bq kg−1 respectively for water. The estimated average values of the total annual effective dose equivalent (AEDET(α,β)), the total annual gonadal dose equivalent (AGDET(α,β)), and the total excess lifetime cancer risk (ELCRT(α,β)) are 10.64 mSv y−1, 0.037 μSv y−1 and 0.037 μSv y−1 respectively. The gross alpha and beta activities values obtained in soil and sediment were relatively high compared to values reported in some parts of the country and other regions and countries of the world. The radiological risk parameters examined show that AEDET(α,β) and AGDET(α,β) are above recommended permissible limits while ELCRT(α,β) is within the recommended permissible limit. The overall results obtained in this study indicate that the environmental samples have been radiologically impaired due to the crude oil spillage. An appropriate remediation technique was therefore recommended to remediate the polluted soil, sediment, and water to their near original state. How to cite this paper: Agbalagba, E.O., Egarievwe, S.U., Odesiri-Eruteyan, E.A. and Drabo, M.L. (2021) Evaluation of Gross Alpha and Gross Beta Radioactivity in Crude Oil Polluted Soil, Sediment and Water in the Niger Delta Region of Nigeria. Journal of Environmental Protection, 12, 526-546. https://doi.org/10.4236/jep.2021.128033 Received: June 18, 2021 Accepted: August 7, 2021 Published: August 10, 2021 Copyright © 2021 by author(s) and Scientific Research Publishing Inc. This work is licensed under the Creative Commons Attribution International License (CC BY 4.0). http://creativecommons.org/licenses/by/4.0/ Open Access E. O. Agbalagba et al. DOI: 10.4236/jep.2021.128033 527 Journal of Environmental Protection


Introduction
The radiological contamination of the human environment always results in the elevation of natural background ionizing radiation. The radiological hazards to man and the environment from radioactive contamination depend on the nature of the radioactive contaminants, the degree of contamination and the level of the spread of the contamination [1]. Human activities such as mining, milling and processing of uranium ores, and mineral sands, smelting of metalliferous ores, manufacture of fertilizers, drilling of oil and gas, transportation, processing and burning of fossil fuels have raised the concentration of naturally occurring radioactive materials in the environment [1] [2] [3] [4]. Researchers in recent time have focused on the assessment of gross activities in soil, sediments and water, to ensure that the Reference Dose Level (RDL) of 1.0 mSv y −1 for soil and sediments and the committed effective dose of 0.1 mSv y −1 for consumption of drinking water is not exceeded in an environment [5] [6]. For water, the RDL of 0.1 mSv is equal to 10% of the dose limit for members of the public as recommended by the International Commission for Radiological Protection (ICRP) [7] and the International Basic Safety Standard by IAEA [8], and is acceptable to most World Health Organization (WHO) member States, European Commission, Food and Agriculture Organization [9] [10].
Gross alpha activity concentration in soil and sediment samples is defined as the total radioactivity of all alpha emitters in the samples. The value of gross activity originating from these alpha emitters in soil and sediment depends on the geological formation of the area, the concentration of mineral component and the nature of human activities in the area [1]. Alpha emitters mixed with ground or surface water percolating through soil and sediment samples have contributed to the increased concentrations of gross alpha in drinking water samples [10]. The presence of gross beta radioactivity in soil and sediment is due to the natural long-lived isotopes 40 K, 210 Pb and 228 Ra [11] [12]. Alpha and beta radiations are less penetrating unlike γ-ray that has the highest penetrating power, but the effects of alpha and beta particles within the body either through inhalation or ingestion are far more detrimental because of their ionizing power [1].
Crude oil, being particulate in nature, when spilled into the environment, can settle on farmlands, farm crops and in the communities' sources of water and can as well be inhaled continuously. Crops grown in such an oil spilled environment could absorb the radioactive content from the crude oil in the soil or through the leaves, while sea foods/aquatic organisms or drinkable water could also be radioactive to a level that could be harmful to man. When these contaminated crops and aquatic animals are eaten by man, radioactive elements get into the body and could attain a detrimental level depending on the type of radionuclides involved, the rate of consumption and the extent to which the food/water has been contaminated. These have manifested in the organs of man as kidney or lung cancer, cataract, leukemia, and other radioactive induced sicknesses. This, no doubt, is a major environmental challenge in the oil producing communities of the Niger Delta region, especially now that a new set of militant groups has resurfaced in the region, destroying pipes carrying crude oil and gas and causing great oil spillage on land and water. Petroleum, a naturally occurring liquid mineral resource, is deposited beneath the earth surface, and its occurrence is sometimes accompanied with the existence of natural gas. The oil, gas and associated gas are generally contaminated with radionuclide in the earth crust. All these provide the source of radiation of α, β and γ often found in the petroleum matrix [13] [14] [15]. High concentrations of naturally occurring radionuclide materials (NORMs) in water, sediment and soil can be harmful to land and marine animals and plants, and they can upset delicate ecological balances and contaminate food sources [16]. These occur as a result of oil spillage into land, failure in underground crude or gas pipelines, vandalizing of crude oil pipes, and road accident by crude oil transporting trucks or vehicles. Studies have shown that almost all the elements in the periodic table including heavy metals (radioisotopes) are found in the crude oil matrix [14] [16] [17]. Thus, the release of gas through flaring, oil spillage on land and water bodies and its derivative may have serious radiological and hazardous effects on man and direct impact on the soil and water [18].
The removal of radioactivity from soil, sediment and water when present above ambient level is gamine to environmental sustainability and human health protection. Natural processes that result in the removal of crude oil from the natural environment include evaporation, oxidation and biodegradation [19]. Evaporation, oxidation and biodegradation are some known methods that can naturally remediate crude oil polluted water, soil and sediment [20] [21] [22]. These constitute the natural remediation web that can reduce the toxic (radioactive) content of crude oil spill into any ecosystem. Thus, the natural remediation processes with the passage of time on the study area will be examined.
The main objective of this study is to evaluate the gross alpha and beta activity concentration in soil, sediment and water in crude oil spilled environment and its natural remediation effect with passage of time on the gross alpha and beta radioactivity concentration in spilled/environment. This is to ascertain the safety of drinking water, the suitability of soil for farming and sediments for optimal use as building material in the study area. The health implications of living and of drinking water in the environment and working within the study locations will be examined.

Experimental Methods
within Delta State of Nigeria. This is well above the four years of study in previous research. This is to give round for wider range of study time and for comprehensive data acquisition for good inference. Ten crude oil polluted sites were identified, and samples of soil, sediment/sludge and water were each collected from the ten locations (oil producing field). The study area lies within latitude 5˚18"N and 5˚68"N and longitude 5˚33"E and 6˚40"E Mid-West of the Niger Delta region of Nigeria. The geology of the study area has been reported elsewhere [23].

Sample Collection and Preparation Techniques
Twelve samples each were collected for soil, sediment/sludge and water in each of the ten crude oil polluted environment (oil fields). Collection of samples was carried out twice a year (wet and dry season) in all the sampling sites for the period of six years. One sample each of soil, sediment/sludge and water from non-oil polluted site from the same environment was collected as control sample.
The bulk soil samples (stones, vegetation and organic debris removed) were collected each in a black polythene bag at a depth between 0 to 15 cm (topsoil), which represent the soil permeability to crude oil spillage and particle settlement depth. Sediment samples were collected at the bottom of waste pit (sludge) and water beds (sediment) of crude oil polluted water bodies, using a steel hand geological auger. The geological auger was first cleaned with acid, detergent and rinsed with tap water. Samples were collected into new aluminum foil labeled and placed in black polythene bags, while the water content in sediment samples was separated from samples by decantation and filtration. Samples were later kept in a slow-air flow, low temperature (50˚C) drying cabinet to help accelerate the drying process without loss of radionuclides from the samples [8]. The dried samples were grinded with mortar and pestle and then allowed to pass through a 100-mesh sieve. The prepared samples were then sent for pelleting into counting planchet geometry using the hydraulic compressor machine. Pelleted samples were then kept in desiccators and stored in the laboratory before counting.
The water samples were collected in oil polluted rivers/streams and drinking water in the host communities, using the grab sampling techniques. Samples were collected into 2-liters plastic containers after rinsing containers thrice with sample water to minimize contamination, and about 1% air space left for thermal expansion [6]. The water samples collected were acidified at point of collection with 20 ml ± 1 ml of nitric acid per liter to minimize the absorption of radionuclides into the walls of the containers {International Standard Organization (ISO), 9697 & 9698} [24]. The samples were then tightly covered with container lids and kept in the laboratory until analysis. At the laboratory samples were slowly evaporated (avoid boiling) in a furnace temperature at 60˚C down to a 50 ml volume. The residues were transferred quantitatively to stainless-steel planchet and dried. Samples were then allowed to equilibrate with ambient tem-perature and then weighed.
The counting or screening time of samples was 30,000 s for gross alpha and beta activities. Further detailed procedures for the actual counting technique to determine the gross alpha and beta radioactivity in the samples are as reported by Avwiri and Agbalagba [6], which are in accordance with ISO, 9697 & 9698(E) guidelines [24].

Counting Equipment
The counting system employed in the analysis was the gas-flow proportional counter {Eurisys Measure IN20 low-background multiple (eight) channel coun-ter} at Centre for Energy Research and Training (CERT) Material Laboratory, Ahmadu Bello University Zaria (ABU) Nigeria. Each channel of the counter has a 450 µg·cm −3 window thickness and is 60 mm of diameter. The chambers were covered with lead whose thickness can be varied. The detectors were operated within a background radiation environment of <101 µrad h −1 . The system was connected to a microprocessor loaded with a spreadsheet program (Quarttro-Pro) and graphic program (Multiplan). The system was operated at a bias voltage (~1100 V with P10 gas: argon-methane of 10%) where only alpha particles were detected, which is commonly referred to as "alpha-only" mode. But when the bias voltage was increased to ~1650 V with same gas, the counter responded to both alpha and beta particles simultaneously. Operation at this higher voltage was referred to as "simultaneous" or "alpha+ beta" mode [9].

Detector Calibration
The alpha standard was 239 Pu with half-life of 24,110 years, while the beta standard was 90 Sr with half-life of 28 years. These standards were certified by CERCA LEA Laboratories in France with certification numbers CT 001/1285/001920-1927 and CT 1271/00/1778-1783, respectively.
Plateau test was run with the manufacturer's calibration standards ( 239 Pu and 90 Sr) whose activities ranged from 133.29 to 185 51 Bq and 92.31 to 103.68 Bq respectively in all the three operating modes which was run for 1800 s for five cycles. The result of the efficiency calibration indicated an average channel efficiency of 35.5% for the alpha counts in the alpha-only mode, 40.0% for the beta counts in beta-only mode, while the average efficiency in alpha/beta was 22.8%.
The alpha-only and beta-only mode of counting was more efficient and therefore was employed in the final counting stage.
The background radioactivity counting procedure for the counting of water, soil and sediment samples followed as reported elsewhere [6] [9] [25]. The results of background activity indicated reproducibility in the channels of the counter. The results also gave an average background radiation activity of 0.17 Bq for alpha in alpha-only mode, and 1.13 Bq for beta in beta-only mode. The results gave an average efficiency value greater than 30%. The guidance level by WHO for drinking water is 0.5 Bq l −1 for gross alpha activity and that for gross beta activity is 1 Bq l −1 [26]. These values obtained are good representative of the environment and could therefore be employed in the subsequent measurement of the soil, sediment and water samples.

Counting of Samples
The counting equipment was automated; the procedure involved entering the present time, number of cycles and the counting (operational) voltage. Also, the counter characteristics (channel efficiency and background count rate), volume of sample used, and sample efficiency were entered. The sample efficiency was calculated as: where M T is the mass of pelleted sample gotten from sample preparation and 0.1A (mg) is the expected mass in the planchet.

Gross Alpha Counting
For gross alpha counting, the high voltage was set at 1650 V and samples were counted for 13 cycles of 180secs per cycle. The results were displayed as raw counts; count rate (count/min), activity and standard deviation. The data were acquired for alpha only mode and the alpha count rate R α as well as alpha activity A α was calculated using the formula: where unit coefficient is multiplication coefficient making it possible to obtain the results expressed in the units used by the operator. The alpha activity is expressed as activity concentration C α , in Becquerel per liter or (Bq kg −1 ) for water and soil/sediment respectively. The activity concentration C α is calculated using the formula ISO 9696:1992 (E) [24].
where R b is the observed sample count rate (s −1 ), R 0 is the background count rate (s −1 ), R s is the observed standard count rate (s −1 ), a s is the specific activity of the alpha standard, V is the volume of the sample soil used.

Gross Beta Counting
The high voltage for gross beta counting was set at 1700 V and samples were counted for 25 cycles of 180 seconds per cycle in beta only mode. The count rate and the activity were calculated using the formula.

Raw count Count time
The gross beta activity is expressed as activity concentration C β in Bq kg −1 and where 14.4/1000 represents the specific activity of 40 K. All other terms have their usual meaning. The standard deviation σ associated with the activity of the samples collected for background was calculated using ISO 9697:1992 (E) [27] ( )

Gross Alpha and Gross Beta Activity in Soil Sediment
The results of the analysis for gross alpha activity concentration in the soil, sediment and water samples are presented in Table 1, while Ra, in the spilled crude oil samples on the soil. It may also be attributed to non-cleanup of the spilled crude oil observed throughout the study period in these sampling sites. This is an indication that the crude oil from these locations will be of high leaded Brent crude from the reported beta activities. The relatively high alpha activity level in sediment samples in Uzere, Ewreni and Ughelli West study locations may be attributed to the transport phenomena of the affected river waters and the settlement and accumulation of the crude particles in these rivers water beds and bottom pits. It was observed that all the sediment sample sites with high alpha activities are unperturbed sites while the sites with relative human activities are low in alpha activities. The elevated beta activity level sites of: Uzere, Agharha and Ughelli West (Ekakpamre) were crude oil waste pits sludge. The results obtained in both wet and dry seasons for the six years of the study showed no significant variation in gross alpha and gross beta activity concentration with time.
A comparison of the average activity concentration values obtained in the soil and sediment samples with those obtained at the control, revealed that the crude oil spillage into the soil has elevated the gross alpha activity levels of the soil in the order of 7.7 times magnitude while beta activity is 6.8 times magnitude higher than the value of the control site. In the sediment samples, the alpha activity levels is 8.6 times magnitude and beta activity is 9.6 times magnitude higher than the control samples result for sediment. The result shows that the crude oil spilled environment (soil) has been polluted radiologically. These mean alpha activities values obtained in soil and sediment in this study compare favorably with the alpha activity value of 530 ± 20 Bq kg −1 obtained in similar crude oil polluted environment of Imirigin oil field in Bayelsa State and the   Figure 1 and Figure 2 show the comparison of the alpha and beta activity concentration of soil and sediment in the different locations investigated. A comparison of the alpha activity concentration in soil and sediments in the various locations indicate a clear variation from location to location as shown in Figure 1, which indicates that additional factors may also be responsible for the   elevation of alpha activity levels in these crude-oil-spilled environments. Similarly, the same trend is also observed in the comparison of gross beta activity in soil and sediment as shown in Figure 2. This pattern of variation however confirmed that there is a radiological pollution of the soil and sediment samples through the crude oil spillage on the environment. Figure 3 shows the comparison of gross alpha and beta activity in water samples.
There is a weak correlation of the alpha and beta activities in the soil samples as shown in Figure 4(a) with a regression value of R 2 = 0.473, while a poor correlation was recorded between alpha and beta activities in sediment samples as shown in Figure 4(b), with a regression value of R 2 = 0.0249. The correlation of gross alpha and beta activity in water sample is also poor, as shown in Figure  4(c). The poor to weak correlations observed can be attributed to the different

Gross Alpha and Gross Beta Activity in Water Samples
The results of the gross alpha and gross beta activities in the water samples analyzed are presented in columns 5 of Table 1 and Table 2 40], and ground water in Western Anatolia, Turkey [41], Rio Gande do Norte, Brazil [42] and Tekirdag˘, Turkey [43]. There exists a slight strong correlation of the alpha and beta activities in the water samples as shown in Figure 4(c) with a regression value of R 2 = 0.5107.

Estimation of Radiological Risk Parameters
The following radiological risk parameters were further used to quantify the health impacts associated with the exposure to environmental radiation in water from the gross alpha and gross beta activities.

Annual Effective Dose Equivalent (AEDE)
The annual alpha and beta effective dose equivalent due to intake of water was determined by averaging the individual annual committed effective doses contributed by the major alpha and beta emitters in the 238 U and 232 Th naturally occurring radionuclides series respectively [1] [44]. The Annual Effective Dose Equivalent (AEDE) is the quantity of ionizing radiation a person may receive in a year according to protection guidelines. The formula for computation of AEDE for gross alpha or gross beta radiation received is given as [44] [45] The sum of AEDE for gross alpha and gross beta radiation is given as where ( ) , A α β is the average activity concentrations of alpha or beta in Bq l −1 , W C is the water consumed by an adult in a year (It is assumed that standard water consumption for a normal adult is approximately 2 liters a day which approximates to 730 liters in a year) and ( ) , DCF α β is the ingestion dose conversion factor for individual natural radionuclides for an adult extracted from UNSEAR report [44]. In line with the procedure by Damla et al., (2006) [32] and Ogundare and Adekoya (2015) [1], it is considered that about 50% or more of the annual dose from the intake of water corresponds to radium (gross alpha radium) [1].
This was adopted in this work, since the machine used could not determine the component radionuclides.    obtained is thrice the RDL, thus both the polluted water and the control water from the environment are not suitable for drinking radiologically. Thus, the surface water of the oil producing areas where these oil spillages occurred needed to be treated before drinking. Table 4 and Table 5  yearly reduction in gross activity with the fourth year witnessing the greatest reduction or decline in activity concentration. This reduction/decay process fits in fairly into the exponential decay curve for both gross alpha analyses. However, gross beta exponential curve was more of rapid decay curve compared to alpha activity. This can be attributed to the shorter half-life of beta emitter radionuclides in the samples compared to those of alpha emitter.
The gradual reduction in the gross alpha and beta activities may be attributed to natural (bio) remediation due to growing plants and microorganisms' activities that have taken place over time in the environment under investigation.

Annual Gonadal Dose Equivalent (AGDE)
Annual Gonadal Dose Equivalent (AGDE) measures the dose of gross alpha and gross beta received by the bone marrow and the bone surface cells as a result of exposure to radiation [51]. The computation of AGDE for gross alpha or gross beta is given by the formula [45].
The sum of AGDE for gross alpha and gross beta radiation is given as where, RWF is the radiation weighting factor and TWF is the tissue weighting factor; RWF for α activity is 20, and for β activity it is given as 1. For gonads, TWF is 0.20 for α-activity and β-activity.

Excess Lifetime Cancer Risk (ELCR)
Excess Lifetime Cancer Risk (ELCR) is the probability of developing cancer over a lifetime at a given exposure level [45]. In this work, 70 years was considered as the average duration of life for humans [53] [54]. ELCR for gross alpha or gross beta was calculated using the formula (Mangset et al. 2014) [45].
where DL is the average life span of man (estimated to be 70 years), and RF is Risk Factor (Sv −1 ), which is fatal cancer risk per Sievert. For stochastic effects, the International Commission on Radiological Protection (ICRP) recommended RF as 0.05 Sv −1 equivalent to 5.0 × 10 −5 (mSv −1 ) for the public [55].
The results of the computed total Excess Lifetime Cancer Risk (

( )
, T ELCR α β ) from gross alpha and gross beta activities are presented in Table 3. The  [54]. This indicates that the chance of contracting cancer from the reported contamination is low despite the degree of crude oil pollution of the water bodies. The overall results of the gross alpha and beta activity concentration in water of the study area show that the water bodies have been impaired radiologically by the crude oil spillage, which contain radioactive content in crude oil [17].

Conclusions
An analytical approach to the assessment of gross alpha and beta activities in soil, sediment and water samples from oil spilled environment in Delta State oil bearing areas has been carried out. The results obtained show a significant elevation of the gross alpha and beta activities due to the crude oil spillage into the soil and sediment environments and the crude contamination of both surface and subsurface water body. The elevation of the gross alpha and beta activity concentration observed in the oil fields is attributed to the radioactivity content in the crude oil that have spilled into and impacted the polluted soil and water in the study locations. A clear evidence of radiological contamination of the study areas was established with some field locations more impacted than others. The average gross activities in water obtained exceeded the practical screening levels recommended by World Health Organization (WHO). The estimation of the ra-E. O. Agbalagba et al. diological risk parameters indicates that the mean annual effect equivalent dose and annual gonadal dose equivalent were far higher than the international recommended limit and higher than values reported in some parts of the world, but the excess lifetime cancers risk factor mean value for water is within the recommendation permissible limits.
It is recommended that clean-up be done on all oil polluted environments and proper treatment of water sources be carried out before use, while further research study on specific radioactivity should be conducted.