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Assessment of Radon Exposure in Erbil Drinking Water Resources

Article History: Received: 01/06/2017 Accepted: 05/08/2017 Published: 20/12/2017 In present study radon activity concentration in drinking water samples were carried out from Erbil-governorate (Kurdistan region-Iraq) by using a permeable cup provided with CR-39 alpha nuclear track detector as a passive method. The results show that the range of radon (Rn) concentration values vary from (0.081±0.002 to 14.742±0.262) Bq/l . The obtained values in this study are below the maximum contamination level (MCL) 11.1 Bq/l as recommended by US-EPA, except sample no. (S12), from Barsaleen region. The total annual effective dose due to ingestion and inhalation of radon from drinking water samples for adults, children and infants were determined. The maximum values found in (S12)were (0.09489±0.0007, 0.10920±0.0009 and 0.233±0.0024) mSv/y respectively, while the minimum values recorded in the (S20) from Koyea were (0.00043±0.0001, 0.00049±0.0001and 0.001±0.0004) mSv/y respectively. The results of this study well indicate that 32% and 4%, from the total annual effective doses in well and spring drinking water samples which intake by infants and children respectively in Erbil are higher than the maximum contaminate levels of 0.1mSv/y proposed in the WHO for the intake of radionuclide in drinking water.


INTRODUCTION
Radiation is a natural part of the environment in which we live in. All people are exposed to naturally occurring radioactivity in soil, water, air and food. The largest fraction of the natural radiation exposure we receive comes from a radioactive gas, radon ( 222 Rn) (Rafat M. A., 2013). Radon is the decay product of radium ( 226 Ra) in the naturally occurring uranium ( 238 U) series. As an inert gas, radon can move freely through the soil and water from its source to a distance which is determined by many factors such as rate of diffusion, effective permeability of the medium and its own half-life. Being a natural alpha emitter, radon can be detected by an alpha sensitive detector. It has been established that radon is a causative agent of lung cancer when present in higher concentrations (V. E. Archer and et.al, 1976). The World Health Organization (WHO) suggests that radon causes up to 15%of lung cancers worldwide (R. L. Fleischer, 1982). In 2012, Environmental Protection Agency (EPA) proposed a Maximum Contaminant Level (MCL) for radon of 11.1Bq/L (about 300 PCi/L) in drinking water (R. L. Fleischer, 1980). Monitoring drinking water quality is an important aspect of public health studies. Radon estimation is one among the public health studies, as it describes the extent of population exposure to radiation as well as the influencing sources water. Hence, an attempt has been made in this present research work for estimation of radon in drinking water resources from Erbil-Governorate -Iraqi Kurdistan region using CR-39 nuclear track detectors.

2.1Geographical Location
Hawler (Erbil) is the capital of the Iraqi Kurdistan Region, located between latitudes 35˚ 40′ and 36˚ 30′ N, and longitudes 43˚ 20′ and 44˚ 20′ E as shown in Fig. (1). The area is bordered by two major rivers, the upper Zab River in the North West and the lower Zab River in the southeast side. Precipitation, snow melting in winter and spring sources in the summer season are the main sources of these two rivers. The two rivers flow at a much lower elevation than the general topographic level of the area, thus the ground water is the most important source for irrigation and drinking purposes (R.H. Haddad andP.B. Smoor, 1973) and(Z. Stevanovic, andA. Iurkiewicz, 2009).
In the present work, twenty-one types of widely-used drinking bottled water samples which are available in the market of Iraqi Kurdistan Region were collected and analyzed by using passive (SSNTDs) and active (RAD-H 2 O) methods. For each type about 2 liters of bottled water, have been taken. Pieces of CR-39 track detectors (1×1 cm 2 area) were fixed under the cover of plastic Can, which contain the water samples.

Field work preparation
The sample of the drinking water in Erbil governorate was collected according to two factors, one of them is the geological difference formation and the second is population density in the area of study. Erbil possesses a population of approximately1.9 million, 1.007million of which live in the capital. Erbil is the fourth largest city in Iraq after Baghdad, Basra, and Mosul. According to the last survey by the NCCI in 2012 [8], Erbil's population distribution by district is as follows, 11.1% in Shaqlawa, 2.7% in Choman, 3.7% in Makhmur, 13.4% in Soran, 6% in Koisnjaq, 3.7% in Mergasur, and 59.4% in Erbil. The geographic distribution in rural and urban areas is 24% and 76% respectively. The total area of Erbil is 14,417 Km2. (3.5% of Iraq). Water samples collected from the surface, spring and ground wells were used as drinking water. The sample's position was fixed on the map by using GPS systems as shown in Table (

Water sampling and sample preparation
Twenty-five water samples from different water resources, twelve from underground wells, five from spring source and eight of surface sources were collected from the study areas in Erbil Governorate and analyzed as shown in Table (1). Samples were collected in (1.5) liters capacity polyethylene containers, saved in cool box and transferred to our laboratory in Erbil City and kept in a room temperature for preservation. About 250mL, were prepared for radon activity concentration measurement by using a permeable cup provide with CR-39 plastic track detectors.

Radon Activity Concentration Measurement
A closed permeable cup of 3.55 cm in radius and 8 cm in height was provided with CR-39 nuclear track detectors and a sponge filter, was calibrated previously (Samal, S.F, 2011) and has been used as a passive method for measuring radon activity concentration in water samples. This cup is covered by a cover containing many holes for air exchange, the holes are covered by a piece of sponge as a diffusion barrier with a thickness of (0.5cm) as shown in Figures (3) that discriminates short-lived thoron by delaying the entry of gases into the cup, and blocks the entry of radon progeny and to diminish the evaporation of the water samples.
In order to find the relationship between the track density recorded by a CR-39 alpha track detector and the emitted radon from water samples, we fixed the permeable cup tightly on the water container which is of the same dimensions in diameter and length with the permeable cup, (250) mL of water sample from each source were placed in a container and sealed by different techniques for 60 days so as to attain the equilibrium and although to collect a good quantity of radon gas. Then the detectors can record alpha particles resulting from the decay of radon. Then the exposed detectors were etched in 6.25NaOH solution at 70 o C for 6 hours using a constant temperature bath [9] . The tracks were counted using an optical microscope at 40X magnification. A total of 20 fields to a maximum 22 fields of the detector were counted. The number of alpha-particle tracks per field is averaged over the number of fields counted after subtracting the background (which equal to 127 tracks/cm 2 ). The standard deviation of the average was obtained and the track density (tracks/cm 2 ) on each detector was calculated, subsequently the radon activity concentration in each water samples have been determined by using (Durrani. S.A., 1997) where C Rn is radon activity concentration in the air volume of cup which is removed from water samples, is track density and K is calibration factor (0.141 Tracks.cm -2 d - Where T eff is the effective time (54.47 days), which is the correction time needed only for closed system and can be calculated by (Duggala. V. and et.al 2012) where T is the exposure time (60 days) and = 0.181 days -1 The radon concentration in the water samples can be measured by (somogyi. Gand L.Lenart, (1986).
where t is the lab water temperature (20±2) ºC

Radon Dose
The radiation dose received from radon present in drinking water can be divided into two components, namely, (a) the dose received from radon ingested and (b) the dose received from radon inhaled. In case of ingestion, radon and its progenies present in the drinking water can impart a radiation dose mainly to the stomach. However, radon gas present in the drinking water can also escape into the indoor air during showering and other domestic uses and can cause a significant increase in the risk of lung cancer due to the radon inhaled.
The annual effective dose (µSv/y) due to ingestion of the drinking water were calculated by taking into account the activity concentration of radon (Bq/l), the dose conversion factor DCF (Sv/Bq) and the annual water consumption (l/y) according to equation (Ali. N, and et.al, 2010).
The annual effect dose due to inhalation of the drinking water was calculated by using the following equation: A.E.D inh =C RnW ×R×F×O×DCF (6) R is the ratio of radon in air to the radon in water (10 -4 ), F is the equilibrium factor between radon and its progeny (0.4), O is the average indoor occupancy time per individual (7,000 h. y -1 ) and DCF is the dose conversion factor for radon exposure [9 nSv/(Bq h m -3 )]( Khattak, N and eat.al, 2011).

Results and Discussion
The results for radon activity concentrations in water samples belong to the area of the Erbil governorate by this method was reported in Table (  It is clear that the radon concentration in water samples changed from location to another. This variation may be due to the type of water, the geological formation and the difference of geochemical distribution of areas under the study (Oliveiraa. Jand et.al. (2001). On the other hand, Table (2) shows that the rate of radon activity concentration in the sample (S24) is higher than of the sample (S23), which was taken from the well and tank and both were originate from the same resource. This indicates that the radon activity in well is higher than that of tank. Thus, before it is used in public networks, it is necessary to use drinking water from groundwater or wells after being stored for the purpose of purification and treatment. When water storage before its usage, will reduce the concentration of radon and its progenies.
Tables (3) (4) and (5) show that the minimum average value of radon concentration was found in surface water (S20) while the maximum average value was found in well water (S12). It is clear from Tables (3, 4 and 5) that the average radon concentration in the well is higher than spring and surface waters. This is because the ground water may contain high amounts of natural radioactive isotopes mainly associated with uranium and thorium-rich soils and rocks, while surface water usually contains lower amounts of radon than spring and ground waters (Duenas. C and et.al,1999). The reason of high radon concentration in the water samples (S12) of the Barsaleen may be due to its site, which is located in uranium rich black shell bedrocks. This fact also reported by the refs. (Asad. H., 2004). Also, the high radon concentration in water samples (S3,S8&S6) of Debaga, SH. Mamodian and Hojran may be due to foundation of petroleum in that place which is an indicator of uranium presence. These uranium rich geological formations may have played a major role in contributing high radon contents to the water sources within the region. Since there is no specific national regulation of radioactivity concentration in drinking water in the Iraqi Kurdistan region, the results have been compared with the maximum contaminant level (11.1) Bq/l for radon in public drinking water, suggested by the US-EPA (Mustapha. A.O, 2002 ) . The obtained results are listed in Tables (3,4-5) for radon concentration values in surface, spring and well water samples which are below this normal level, except for Barsaleen (S12). The range measurement of radon activity concentration in surface, spring and drilling well drinking water samples in this study were found to be in agreement with those reported by other references as shown in Table (6).   It is found that the values are the same for all age groups. More ever, Table (7) shows the total annual effective dose due to ingestion and inhalation of radon from drinking water samples for infants, children and adults. The maximum values found in (S12) were (0.09489±0.0007, 0.10920±0.0009 and 0.233±0.0024) mSv/y respectively, while the minimum values recorded in the (S20) were (0.00043±0.0001, 0.00049±0.0001and 0.001±0.0004) mSv/y respectively. Children and infant show increased vulnerability due to a combination of changes in dose conversion factor and water intake with age as shown in Fig. (6).
The results of this study indicate that 32% and 4% of the total annual effective doses intake by infants and children in Erbil are higher than the maximum contaminant levels of 0.1mSv/y proposed in the WHO for intake of radionuclide in drinking water (Moldovan, M and et.al, 2014).
The mean total annual effective dose due to drinking water samples in this study was found to be in a good agreement with those values reported in other references as shown in Table (11). Figure 6. Annual effective dose due to ingestion of radon in drinking water samples for difference groups age as a function of their radon activity concentration.

4-Conclusions
In this research, the following points have been concluded: 1-The well water samples are characterized by the highest average of radon levels, while the surface water is characterized by the lowest one. The overall average of radon levels in Erbil public drinking water samples is about 36.8% of the internationally acceptable radon level in drinking water.
2-The results of this study indicate that 32% and 4% of the total annual effective doses intake by infants and children in Erbil are higher than the maximum contaminant levels of 0.1mSv/y proposed in the WHO for intake of radionuclide in drinking water.
3-The obtained values show that surface water in Erbil governorate is safe for drinking without exceeding the proposed radioactivity criterion level.