Abstract

In the current research, water samples were collected from selected sites in the Tigris River. The water samples were collected monthly started from September 2017 to January 2018.The results demonstrate that the total average values of radon activity level for the 5 months for site 1, site 2, site 3 and site 4 were 36.6, 28.5, 46.2 and 37.2 Bq.m−3, respectively. The average radon concentration value of the four sites during the 5 months was 37.1 Bq.m−3. Dissolved radon concentrations for the study samples were also calculated and their average values were 1.242, 0.930, 1.510 and 0.930 Bq.L−1 for site 1, site 2, site 3 and site 4, respectively. The overall average calculated radon surface exhalation rate for the water samples was 0.363 Bq.m−2.h−1. Annual effective doses due to water consumption for adults, children and babies were also calculated. The obtained values of radon concentrations in the study water samples were found to be lower than the maximum permissible concentrations in water as recommended by the US Environmental Protection Agency (EPA). Also, the results reveal that the radon activity level has its lowest value during November but that there are no considerable variations with different times of the year.

INTRODUCTION

Radon and its progenies are known as the main sources of human radiation exposure by natural radioactivity. It is considered as the second cause of lung cancer (UNSCEAR 2000). High concentrations of radon can be hazardous to individuals and can cause lung cancer (Folger et al. 1994; Khan 2000). During the past decades, many studies of radon levels in water sources have been conducted (Yu et al. 1994; Al-Bataina et al. 1997; Vásárhelyi et al. 1997; Otwoma & Mustapha 1998; Tayyeb et al. 1998; Horváth et al. 2000; Al-Kazwini & Hasan 2003; Moussa & El Arabi 2003; Segovia et al. 2003; Erees et al. 2006; Schubert et al. 2006).

The three naturally occurring radioactive isotopes of radon are Actinon (219Rn), Thoron (220Rn) and Radon (222Rn) which are the progenies of the 235U, 232Th and 238U decay series, respectively (UNSCEAR 2000). The 222Rn isotope is the one of concern in human radiation exposure due to its longer half-life of 3.82 days, while the other radon isotopes (219Rn and 220Rn) are considered unimportant sources of human exposure, due to their short half-lives of 3.96 s and 55.6 s, respectively. Radon is a noble, tasteless, odorless and colorless gas. The solubility of 222Rn in water is 510 cm3.L−1 at 0 °C and it decreases with increasing water temperature (Zakari et al. 2015).

Radon, which is soluble in water, is dissolved and transported with water during water movement through soil and rocks that contain radon. The possibility of radon absorption depends on the radium and uranium concentrations in the soil and rocks. Hence, as the concentrations of radium and uranium in soil and rocks increase, the absorption of radon increases.

Since the Tigris River is the household water supply in Baghdad, the knowledge of the radon level in Tigris river water is important for public protection from the consequences of severe exposure to radiation, which is considered a risk for lung cancer specifically. The aim of this study is to measure radon levels in water samples collected from four selected points from the Tigris River for a period of five successive months (September 2017 to January 2018). Radon was measured using solid-state nuclear track detector CR-39.

MATERIALS AND METHODS

Study area

The river Tigris is 1,850 km long, ascending in the Taurus Mountains of eastern Turkey. The waterway streams for around 400 km through Turkey before entering Iraq. The aggregate length of the stream in Iraq is 1,418 km. A few urban areas have been based on the banks of the Tigris since the beginning of urban development. Among these is Baghdad, the capital city of Iraq with a populace of around 8,765,000, making it the greatest city in Iraq.

The City of Baghdad is divided into two substantial areas (Al-Karch and Al-Rusafa) by the river Tigris. Al-Karch and Al-Rusafa are connected by 12 bridges, which disturb the flow of the waters (Ali et al. 2012). The Tigris River is the main source of household water supplies for Baghdad inhabitants.

The water samples were collected monthly (from September 2017 to January 2018) from four selected sites along the Tigris River. The coordinates of the selected sites are given in Table 1. The survey area was extended from Al-Muthana Bridge in the north of Baghdad through Al-Sarrafia Bridge and Al-Shuhadaa Bridge then Al-Dora Bridge in the south of Baghdad, shown in Figure 1. Site 1 is near Baghdad Tourism Island (i.e. heavy human activities), site 2 is near Baghdad Medical Hospital (a congregation of many educational hospitals in Bab Al-Moatham, Baghdad, Iraq), site 3 is near Al Mutanabi Street (one of the oldest and best-known streets in Baghdad i.e. heavy human activities), and site 4 is near the Vegetable Oil Factory and Al-Rasheed Gas Power Plant. In addition, the Tigris River experiences growth and accumulation of plants such as water hyacinth (Eichhornia crassipes), vascular plants of reeds and papyrus, and hornwort (ceratophyllum demersum).

Table 1

Coordinates of the selected sites on the Tigris River

Site no. Location Longitude Latitude 
Site 1 Al-Muthana Bridge 44°34′55.50″E 33°42′83.22″N 
Site 2 Al-Sarrafia Bridge 44°37′36.01″E 33°35′37.53″N 
Site 3 Al-Shuhadaa Bridge 44°38′79.03″E 33°33′79.59″N 
Site 4 Al-Dora Bridge 44°45′02.84″E 33°28′96.82″N 
Site no. Location Longitude Latitude 
Site 1 Al-Muthana Bridge 44°34′55.50″E 33°42′83.22″N 
Site 2 Al-Sarrafia Bridge 44°37′36.01″E 33°35′37.53″N 
Site 3 Al-Shuhadaa Bridge 44°38′79.03″E 33°33′79.59″N 
Site 4 Al-Dora Bridge 44°45′02.84″E 33°28′96.82″N 
Figure 1

Map of the selected sites on the Tigris River.

Figure 1

Map of the selected sites on the Tigris River.

Water sample preparation

An amount of 250 mL of each water sample was put in a sealed glass container. A piece of CR-39 detector was stuck on the bottom side of the container cover about 12 cm above the water sample. Figure 2 shows a schematic diagram of the set-up technique used. Three repetitions of each water sample were made. After an exposure period of 60 days, the detectors were etched in 6.25 N NaOH solution at 70 °C for 5 hours in order to reveal α-tracks caused by the α-particles emitted by radon that reached the CR-39 detector under an angle smaller than its critical angle of etching. After etching, the detectors were washed with tap water, then with distilled water and finally with alcohol solution. Eventually, α-tracks were counted using an optical microscope with a magnification of 400×.

Figure 2

Set-up of the sealed can.

Figure 2

Set-up of the sealed can.

Calculations

The track densities (ρ) in the samples were calculated using Equation (1) (Tawfiq et al. 2015): 
formula
(1)
Radon concentration (CRn) in (Bq/L) in the wastewater samples was calculated by the following equation (Sarma 2013): 
formula
(2)
where ρ = the density of the measured α-track (track.cm−2), T= time of exposure and CF= the calibration factor, which is calculated using Equation (3) (Hussein et al. 2013): 
formula
(3)
where R = the radius of the container (cm), θc = CR-39 critical angle, which is equal to 35°, and Rα = the range of α-particles emitted from 222Rn in CR-39 and equal to 4.15 cm. The calculated value was CF = 0.04891 track.cm−2.d−1/Bq.L−1.
Equations (4) and (5) were used to calculate the dissolved radon concentration (Cdis) in wastewater samples in units of Bq.L−1 and radon surface exhalation rates (RERS) in Bq.m−2.h−1, respectively (Tawfiq et al. 2015): 
formula
(4)
 
formula
(5)
where CRn = the radon concentration in the sample (Bq.L−1), λ = 222Rn decay constant (h−1), h = the water surface to detector distance (m), T = time of exposure (h), L = the height of the sample (m), C = the total radon concentration (Bq.L−1.h), V = the volume of air in the cup (L) and A = the surface area of the water sample (m2).
Equation (6) was used to calculate the annual effective dose (AED) (Ajayi & Achuka 2009): 
formula
(6)
where Win is the intake of water (730, 330 and 230 L.y−1 for adults, children and babies, respectively) (WHO 1988) and Cf represents dose conversion factors for radon (3.5, 5.9 and 23 nSv.y −1 for adults, children and babies, respectively) (UNSCEAR 2000).

RESULTS AND DISCUSSION

Table 2 displays the obtained results of average radon activity levels in the study water samples for the survey period of 5 months. Figure 3 shows the radon activity levels/month for the study sites with their average values. The lowest calculated radon activity levels were observed during November (moderate weather) with values of 36.07, 17.97, 31.90 and 23.92 Bq.m−3 for sites 1, 2, 3 and 4, respectively. The total average radon activity level value during November was 27.47 Bq.m−3, which was many times below the mean value.

Table 2

Average radon levels for the study sites during the period of survey

Radon activity levels Bq.m−3
 
Collection time Site 1 Site 2 Site 3 Site 4 Average/month 
September-17 30.31 35.31 54.55 49.691 42.47 
October-17 29.74 31.14 47.46 42.02 37.59 
November-17 36.07 17.97 31.90 23.92 27.47 
December-17 53.29 21.01 55.44 35.57 41.33 
January-18 33.04 36.96 41.90 35.57 36.86 
Average/site 38.03 28.48 46.25 34.27 36.76 
Radon activity levels Bq.m−3
 
Collection time Site 1 Site 2 Site 3 Site 4 Average/month 
September-17 30.31 35.31 54.55 49.691 42.47 
October-17 29.74 31.14 47.46 42.02 37.59 
November-17 36.07 17.97 31.90 23.92 27.47 
December-17 53.29 21.01 55.44 35.57 41.33 
January-18 33.04 36.96 41.90 35.57 36.86 
Average/site 38.03 28.48 46.25 34.27 36.76 
Figure 3

Radon activity levels for the study sites during the period of survey and average values for each site.

Figure 3

Radon activity levels for the study sites during the period of survey and average values for each site.

Site 3 shows the highest radon activity levels during the 5 months of the survey with an average value of 46.25 Bq.m−3. Average radon activity levels/month are given in Figure 4. However, values of radon activity in the study water samples are lower than the world permissible limit, which is equal to 555 Bq.m−3 (USEPA 2012).

Figure 4

Average radon activity level/month and its mean value for the study sites.

Figure 4

Average radon activity level/month and its mean value for the study sites.

Figure 5 shows the average concentration of the dissolved radon in the study water samples. The results show that the highest average value of dissolved radon concentration in the water samples was at site 3, which was equal to 1.510 Bq.L−1, while its lowest value was at sites 2 and 4, which was 0.830 Bq.L−1. The variation in dissolved radon concentrations may be due to human activities which vary from site to site that affect the ecosystem of the Tigris River and increase the pollutants discharged into the Tigris River (Hassan et al. 2018). The general average dissolved radon concentration was 1.153 Bq.L−1, which is below the permissible value of 11.1 Bq.L−1 recommended by USEPA (2012) and the 10 Bq.L−1 recommended by UNSCEAR (2000) and WHO (2011).

Figure 5

Average dissolved radon concentration for study sites during the period of survey.

Figure 5

Average dissolved radon concentration for study sites during the period of survey.

The surface exhalation rates of radon (RERS) for the study water samples are presented in Table 3. The obtained overall average value of the surface exhalation rate of radon was found to be 0.36 Bq.m−2.h−1. The highest and the lowest RERS values were 0.55 Bq.m−2.h−1 at site 3 during December and 0.18 Bq.m−2.h−1 at site 2 during November, respectively.

Table 3

Radon surface exhalation rate for the study sites during the period of survey

Month Radon exhalation rate (Bq.m−2.h−1)
 
Site 1 Site 2 Site 3 Site 4 Mean/Month 
September-17 0.30 0.35 0.54 0.49 0.42 
October-17 0.29 0.31 0.47 0.42 0.37 
November-17 0.36 0.18 0.32 0.24 0.27 
December-17 0.53 0.21 0.55 0.35 0.41 
January-18 0.33 0.37 0.41 0.35 0.36 
Mean/site 0.38 0.28 0.46 0.34 0.36 
Month Radon exhalation rate (Bq.m−2.h−1)
 
Site 1 Site 2 Site 3 Site 4 Mean/Month 
September-17 0.30 0.35 0.54 0.49 0.42 
October-17 0.29 0.31 0.47 0.42 0.37 
November-17 0.36 0.18 0.32 0.24 0.27 
December-17 0.53 0.21 0.55 0.35 0.41 
January-18 0.33 0.37 0.41 0.35 0.36 
Mean/site 0.38 0.28 0.46 0.34 0.36 

The annual effective doses were also calculated using Equation (6) and are tabulated in Table 4. The average values during the time of study were 2.913, 2.220 and 6.032 μSv.y−1 for adults, children and babies, respectively. The average values are well below the world permissible value recommended by UNSCEAR (2000).

Table 4

Annual effective doses (μSv.y−1) for adults, children and babies due to consumption of water

Annual effective dose (AED) μSv.y−1
 
Location Adults Children Babies 
Site 1 3.044 2.319 6.302 
Site 2 2.375 1.810 4.919 
Site 3 3.858 2.940 7.988 
Site 4 2.375 1.810 4.919 
Average value 2.913 2.220 6.032 
World permissible value (UNSCEAR 2000100 μSv.y−1 
Annual effective dose (AED) μSv.y−1
 
Location Adults Children Babies 
Site 1 3.044 2.319 6.302 
Site 2 2.375 1.810 4.919 
Site 3 3.858 2.940 7.988 
Site 4 2.375 1.810 4.919 
Average value 2.913 2.220 6.032 
World permissible value (UNSCEAR 2000100 μSv.y−1 

CONCLUSIONS

The obtained results reveal that radon activity levels in the study samples were below the permissible value given by the USEPA. The lowest radon level was found during November at moderate weather temperature. The variation in the dissolved radon concentrations may be due to human activities that vary from site to site and the increase of the pollutants discharged to the Tigris River. The annual effective doses are below the permissible value, thus it is clear that the water samples do not show any considerable source of radiation risk and are not harmful as far as radon concentration is concerned.

REFERENCES

REFERENCES
Al-Bataina
B. A.
,
Ismail
A. M.
,
Kullab
M. K.
,
Abumurad
K. M.
&
Mustafa
H.
1997
Radon measurements in different types of natural waters in Jordan
.
Radiation Measurements
28
,
591
594
.
Ali
A. A.
,
Al-Ansari
N. A.
&
Knutsson
S.
2012
Morphology of Tigris river within Baghdad city
.
Hydrology and Earth System Sciences
16
,
3783
3790
.
Al-Kazwini
A. T.
&
Hasan
M. A.
2003
Radon concentration in Jordanian drinking water and hot springs
.
Journal of Radiological Protection
23
,
439
448
.
Erees
F. S.
,
Yener
G.
,
Salk
M.
&
Özbal
Ö.
2006
Measurements of radon content in soil gas and in the thermal waters in Western Turkey
.
Radiation Measurements
41
,
354
361
.
Horváth
Á.
,
Bohus
L. O.
,
Urbani
F.
,
Marx
G.
,
Piróth
A.
&
Greaves
E. D.
2000
Radon concentration in hot springs waters in northern Venezuela
.
Journal of Environmental Radioactivity
47
,
127
133
.
Hussein
Z. A.
,
Jaafar
M. S.
&
Ismail
A. H.
2013
Measurement of radium content and radon exhalation rates in building material samples using passive and active detecting techniques
.
International Journal of Scientific and Engineering Research
4
(
9
),
1827
1831
.
Otwoma
D.
&
Mustapha
A. O.
1998
Measurement of Rn-222 concentration in Kenyan groundwater
.
Health Physics
74
(
1
),
91
95
.
Sarma
H. K.
2013
Radon activity and radon exhalation rates from some soil samples by using SSNTD
.
International Journal of Advanced Research in Electrical, Electronics and Instrumentation Engineering
2
(
10
),
5024
5029
.
Segovia
N.
,
Armienta
M. A.
,
Valdes
C.
,
Mena
M.
,
Seidel
J. L.
,
Monnin
M.
,
Peña
P.
,
Lopez
M. B. E.
&
Reyes
A. V.
2003
Volcanic monitoring for radon and chemical species in the soil and in spring water samples
.
Radiation Measurements
36
,
379
383
.
Tawfiq
N. F.
,
Mansour
H. L.
&
Karim
M. S.
2015
Measurement of radon gas concentrations in tap water for Baghdad Governorate by using nuclear track detector (CR-39)
.
International Journal of Physics
3
(
6
),
233
238
.
Available online at http://pubs.sciepub.com/ijp/3/6/2. doi:10.12691/ijp-3-6-2
Tayyeb
Z. A.
,
Kinsara
A. R.
&
Farid
S. M.
1998
A study on the radon concentrations in water in Jeddah (Saudi Arabia) and the associated health effects
.
Journal of Environmental Radioactivity
38
,
97
104
.
UNSCEAR
2000
Sources and Effects of Ionizing Radiation: Report to the General Assembly with Scientific Annexes
.
United Nations
,
New York, USA
.
USEPA
2012
2012 Edition of the Drinking Water Standards and Health Advisories
.
Office of Water, USEPA, Washington, DC, USA
.
Vásárhelyi
A.
,
Csige
I.
,
Hakl
J.
&
Hunyadi
I.
1997
Spatial distribution of radon content of soil-gas and well-waters measured with etched track radon monitors
.
Radiation Measurements
28
,
685
690
.
WHO
1988
The Challenge of Implementation: District Health Systems for Primary Health Care. Part A pp. 7–11 and Part C pp. 65–67
.
World Health Organisation, Geneva, Switzerland
.
WHO
2011
Guidelines for Drinking-Water Quality
,
4th edn
.
World Health Organisation, Geneva, Switzerland. http://www.whqlibdoc.who.int/publications/2011/9789241548151_eng.pdf (accessed 15 January 2011).
Zakari
Y. I.
,
Nasiru
R.
,
Ahmed
Y. A.
&
Abdullahi
M. A.
2015
Measurement of radon concentration in water sources around Ririwai Artisanal Tin Mine Kano State, Nigeria
.
Journal of Natural Sciences Research
5
(
24
),
49
55
.