Measurement of Radionuclides Concentration and Radiological Health Assessment of Some Selected Table Waters in Ilorin

In order to ensure radiation monitoring and protection, an investigation and assessment of radiological risks that may be associated with the consumption of table waters commonly consumed in Ilorin, Nigeria, was carried out. The activity concentration level of 238 U, 232 Th, and 40 K was determined using thallium activated 3˝×3˝ [NaI(TI)] detector connected to ORTEC 456 amplifier. The radiological risks due to the consumption of the samples were then estimated. The highest annual effective dose (AED) values were obtained from VW and the minimum was obtained from UW water. The AED decreases in the order VW>HW>IW>MW>DW>UW. This implies that VW water constitutes more radiation exposure followed by HW, IW, MW, DW, and then UW Water. The values estimated for MW, DW, and UW water were all lower than the world average value of 1 mSv/y and hence pose no serious radiation hazard. While the values estimated for VW, IW, and HW waters were slightly higher than the recommended threshold value, suggesting a possible risk of radiation exposure to customers. The Excess Lifetime Cancer Risks corroborated the findings of the AED, implying that the probability of developing cancer is high for most of the water samples. Since the values of the estimated hazard parameters were mostly higher than the recommended limits for all age groups, it is recommended that public water system should be monitored and efforts should be made to educate and enlighten the public on radiation exposure, its health effects, and remedial actions necessary to reduce radionuclides concentration in drinking water.

Nevertheless, owing to persistent human and industrial activities, constant environmental monitoring needed to be put in place to ensure consumer products like table waters are safe for drinking. This work then focus on investigation and assessment of radiological risks that may be associated with the consumption of table waters commonly consumed in Ilorin, Kwara State in order to ensure radiation monitoring and mitigation.

The Study Area
Ilorin the area of the study lies entirely within the basement rocks in the western part of The study area falls within the North -central, a semi-arid region of Nigeria. The major river in Ilorin is Asa, which flows North-South direction dividing the plain into two namely: Western and Eastern parts. The eastern part is generally steeper than the western part with height ranging from 900 -1200 feet in some part and peaking at isolated landforms. Ilorin city is one of the fastest growing cities in Nigeria with a tropical wet and dry climate with mean annual rainfall of 1,200mm (Orosun et al., 2020;Ajibola et al., 2022). Its average annual temperature is 26.2 ºC; it peaks at about 30 ºC in March which marks the hottest month. Wet season is experienced from April to October and dry season from November to March. Figure 1 shows the map of Nigeria indicating the study area "Ilorin".
The study area consists of Precambrian basement of south-western Nigeria. The soils are formed from metamorphic and igneous rocks which are about 95%. The metamorphic rocks consist of quartzite, augite gneiss, granitic gneiss, biotite gneiss and banded gneiss (Orosun, 2021). The assortment of basement complex rocks bring about large number of ferruginous groups of soils. Therefore, ferrallitic soil type (generally deep red in colour with high clay content) is the major type of soil in Ilorin (Oyegun, 1985). Orosun et al., (MEJS)

Sample Collection and Preparation
Three (3) water samples each were collected from six table water production factories namely VW, IW, HW, MW, DW, and UW water in Ilorin, Kwara state, Nigeria. The samples making a total of 18 samples were collected using clean 1 liter plastic bottles.
The samples were acidified with 11 M HCl at a rate of 10 ml per liter to prevent adsorption of water with the wall of the containers. 200 ml of each sample were then sealed with adhesive tape and kept for at least 28 days (Ajibola et al., 2022;Olomo et al., 1994). This was done in order to allow for radium and its short-lived progenies to reach secular radioactive equilibrium prior to gamma spectroscopy (Olomo et al., 1994;Augustine, 2015). Secular equilibrium is reached when the half-lives of the daughter radionuclide is equivalent to one half-life of the parent radionuclide. After secular equilibrium had been attained, gamma counting was then carried out.

Gamma Counting
The experiments for radioactivity measurement of the water samples were carried out at the National Institute of Radiation Protection and Research (NIRPR) University of Orosun et al., (MEJS)  sides and 10cm thick on top. The energy resolution of 2.0kev and relative efficiency of 33% at 1.33Mev was achieved in the system with the counting time of 27000 seconds.
The standard International Atomic Energy Agency (IAEA) sources were used for calibration. From the counting spectra, the activity concentrations of 238 U, 232 Th and 40 K was determined using computer program. The peak that corresponds to 1460 keV ( 40 K) for 40 K, 1764.5 keV (Bi-214) for 238 U and 2614.5 keV (Ti-208) for 232 Th were considered in arriving at the activity levels (BqL -1 ). The activity concentration (C) of the radionuclide was calculated using equation (1) after subtracting the background peak area from the sample peak areas.
Where, Cs = Activity concentration in the Sample, Na = Net peak area (sample peak area background peak area), ε γ = Efficiency of the detector for a γ-energy of interest, Vs = volume of the water sample, tc = total counting time, P γ = gamma yield and is the mass of the given sample.

Radiological Impact Parameters
These are parameters used to determining the radiation hazards that could be incurred from the consumption of the selected water. Calculating the effective dose is usually the first major step for evaluating the health risk. With regard to biological effects, the radiological and clinical effects are directly related to the absorbed dose rate (Orosun et al., 2018;Ramasamy et al., 2011).

Annual effective dose (AED)
Effective Dose takes into account the type of radiation and the nature of each organ or tissue being irradiated, and enables summation of organ doses due to varying levels and types of radiation. Theannual effective dose for ingested radionuclidefrom water was calculated using equation (2) given by UNSCEAR (UNSCEAR, 2008).
Where, Ci is the activity concentration of of 40 K, 238 U and 232 Th, Iis the daily intakes of water which was assumed to be 2L d -1 for adults, 1 l d -1 for lower ages and 0.5 L d -1 for infants (WHO, 2011) andDi is the ingestion dose coefficient of 40 K, 238 U and 232 Th.

Excess lifetime cancer risk (ELCR)
The Excess Lifetime cancer risk was calculated using equation (3) (Avwiri et al., 2014): Where, AED is the Annual Equivalent Dose Equivalent, DL is the average duration of life (estimated to be 70 years), and RF is the Risk Factor (Sv -1 ), i.e. fatal cancer risk per Sievert. For stochastic effects, ICRP uses RF as 0.05 for public (Avwiri et al., 2014).

RESULTS AND DISCUSSION
The results of the gamma-ray analysis of eighteen  These results shows that some of the table waters have concentration of the radionuclides higher than the world average value of 10, 10 and 1 Bq/l for 40 K, 238 U and 232 Th, respectively (UNSCEAR, 2000). This may be due to the local geology of the factory site and production processes. The mean annual effective dose (AED) estimated for adults is 1.889, 1.583, 1.711, 0.875, 0.837 and 0.616 mSv/y for VW, IW, HW, MW, DW and UW Water, respectively ( Table 2). The highest was obtained in VW and the minimum in UW water. The AED decreases is in the order VW > HW > IW > MW > DW > UW. This implies that VW water constitutes more radiation exposure followed by HW, IW, MW, DW, and then UW Water. The values estimated for MW, DW and UW water were all lower than the world average value of 1 mSv/y (UNSCEAR, 2000) and hence poses no serious radiation hazard. While, the values estimated for VW, IW and HW water were slightly higher than the world average value and suggests a possible risk.  6.2x10 -9 232 Th 1.405x10 1 1.6x10 -6 4.5x10 -7 3.5x10 -7 2.9x10 -7 2.5x10 -7 2.3x10 -7 238 U 4.468x10 9 1.4x10 -7 1.2x10 -7 8.0x10 -8 6.8x10 -8 6.7x10 -8 4.5x10 -8 Most of the AED values for the different age groups were higher than the acceptable limits of 1 msv/y for the public. Although it should be noted that daily intake of water per person of 2 ld -1 for adults, 1 ld -1 for lower ages and 0.5 ld -1 for infants was used as against the 1 liter per day for adults used by Nwankwo (2013) in his determination of natural radioactivity of groundwater in Tanke -Ilorin, Kwara State. The results suggest that infants (˂1year) are unsurprisingly more susceptible to radiation hazards drinking the table waters followed by children 1yr (˂5years) then, Adults (> 15 years), 5years (˂10years), 10years (˂15years) and 15years (˂adult age) respectively. It should be noted that the estimated mean AED was <1mSv/yr across all the age groups for UW. It is obvious that UW water will constitutes less radiation hazard and safest to drink.