The Role of Radon in Some Drinking Water Pollute on in Bukan (North West Iran)
1Geological Survey
of Canada, Canada
2Shiraz University, Shiraz, Iran
*Corresponding author: Jamal Rasouli, Geological Survey of Canada, Canada. Tel: +12896971400; Email: jamal.rasouli1362@gmail.com
Received
Date:
04 January, 2018; Accepted Date: 18
January, 2018; Published Date: 24 January,
2018
Citation: Rasouli J, Mamkhosravi S (2018) The Role of Radon in Some Drinking Water Pollute on in Bukan (North West Iran). Arch Pet Environ Biotechnol: APEB-126. DOI: 10.29011/ 2574-7614. 100026
1. Abstract
In the present study was carried out in Bukan shown which is located in the West Azarbaijan Province of Iran. Evidence suggests that it is possible contaminated drinking water by radon in Bukan. In the present study an electronic solid state Radon monitor, which is the most sophisticated and versatile measuring device has been used for estimating the Radon content in some drinking water samples taken from Bukan (North West Iran). The Radon concentration in water samples has been found to vary from 0.79±0.18 Bql-1 11.87±1.43 Bql-1. The values of Radon concentration in these samples were found below the recommended limit and slightly unhealthy for drinking. The values of annual effective dose were also calculated for these water samples and ranged from 1.27 µSvy-1 to 32.67 µSvy-1. These values lie within the infrequency safe limit. The objective of the study was to assess the radiological risk to human health due to consumption of contaminated drinking water.
2. Keywords: Bukan; Drinking Water Pollution; RAD7; Radon Concentration
1. Introduction
Radon has been measured in water in many parts of the world, mostly for the risk assessments due to consumption of drinking water [1-2]. Radon gas is odourless, tasteless and colourless, and therefore cannot be detected by the human senses [3]. It is an inert and noble gas, with atomic number 86, has highest density 9.73 kgm-3 among all noble gases. Because it is denser than air, Radon gas in the environment tends to settle in lower areas where the air is still and can concentrate in poorly vented rooms and basements. Radon is the only alpha-emitting radio-active gas. It is produced after the alpha decay of radium, which is further the decay product of U-238. This means the concentration of Radon depends on the concentration of U-238 in any source. When radium decays, it produces an alpha particle with 4.78MeV energy and recoiling Radon -222 with recoil energy of 86KeV [4]. Radon has three isotopes i.e. (i) Radon-219 or “actinon” is a part of U-235 decay chain. It is never encountered in indoor air due to its short half-life (3.4 sec). (ii) Radon-220 or “thoron” is a part of Thorium-232 decay chain. Its half-life is more than actinon but less than 1 min (54 sec). Due to this half-life, it found in indoor air, particularly near Radon entry points and more often in soil gas. (iii) Radon-222 or familiar “Radon” is a part of the U-238 decay chain. Its half-life is 3.8 days. Due to this half-life, it is detected in indoor air, outdoor air and soil gas. Radon is also soluble in water. This means that Radon exists in three states of matter i.e. solid (in soil grain), gas (in atmospheric air) and liquid (in drinking water). As Radon decays, it produces a new radioactive element called Radon daughters or decay products i.e. Po-218 (3.05 min), Pb-214(26.8 min), Bi-214(19.9min), Po-214 (164µs) and Pb-210 (22 yrs).
Unlike the gaseous Radon itself, Radon daughters
are solids and stick to the surface. When Radon undergoes alpha decay, Po-218
with alpha particle has energy 5.49 MeV produces. This produced alpha particle
has 39 µm alpha range in water and 4.08 cm alpha
range in air [5]. The mean distance travelled [6] by Radon-222 over its half-life (3.8 days) in different
medium is shown in (Table 1) and shows Radon in water moves slower than Radon in
air. The distance that Radon moves before most of it decays is less than 1 inch
in water-saturated rocks or soils, but it can be more than 6 feet, and
sometimes tens of feet, through dry rocks or soils. Because water also tends to
flow much more slowly through soil pores and rock fractures than air does, Radon
travels shorter distances in wet soils than in dry soils before it decays. Most
of the radionuclides present in drinking water are from natural sources.
Naturally occurring radionuclides are created in the upper atmosphere and are
found in the earth’s crust. They are found in certain types of rocks that
contain trace amounts of the radioactive isotopes (forms) of uranium, thorium
and actinium. As these rocks destroy, the resulting clays and other materials may
transmit radionuclides into drinking water. Higher levels of radionuclides tend
to be found more often in groundwater, such as wells, than in surface water,
such as lakes and streams. Drinking water containing Radon also presents a risk
of developing internal organ cancers, primarily stomach cancer. Based on national
and worldwide investigations, several agencies have concluded that Radon is a
known cancer causing agent in humans and is the second most common cause of lung,
skin and leukaemia cancers afters smoking [7]. However,
this risk is smaller than the risk of developing lung cancer from Radon released
into air from tap water. Based on a National Academy of Science report, EPA
estimates that Radon in drinking water causes about 168 cancer deaths per year:
89% from lung cancer caused by breathing Radon released into the indoor air
from water and 11% from stomach cancer caused by consuming water containing Radon
[8]. In this paper, we are interested in finding
the Radon concentration in water by using RAD7. The limit of Radon concentration
in water samples is 300pCi/l or 11Bq/l as recommended by US Environmental
Protection Agency [9]. The UNSCEAR has suggested
a value of Radon concentration in water for human consumption between 4 to 40
Bql-1 [10].
· Study Area: The present study was carried out in Bukan Shown in (Figure 1). Bukan is located south of Lake Urmia about 1,300 metres above sea level and lies between 36° 31’ 19” north latitude and 46° 12 40” east longitude. It lies in the West Azarbaijan Province of Iran. The town is situated on the eastern bank of the Simineh River, known locally as Čōmī Bukan, on the road between Saqqez and Miandoab. Bukan is inhabited by Kurds, who speak the Sorani, or central, dialect of Kurdish. The rural population is engaged in farming, gardening, and animal husbandry. Environmentally and climatically, Bukan is a highland with snow-capped mountains which looks like as beauty queen of Kurdistan. As regard to the history of the area, according to the archaeological findings, it should be said that from the earliest time the district of Bukan had been populated by ancient tribes, who were inhabited in the foothills of Zagros mountain chain
2. Methodology
Water samples were collected from different sources such as hand pumps and submersible pump of Bukan state. These water samples were taken 20 hours before calculating Radon concentration. They were stored in 250 ml vial properly and fully so that no air particles remain in vial. This makes it possible to calculate Radon concentration only due to water rather than combination of air and water. These water samples were analysed by using RAD7 (Durridge Company) which is an online Radon monitor for calculating the Radon concentration (Durridge company). RAD7 is a continuous Radon gas monitor. It is based on Solid State Silicon Detector. It contains a hemisphere dome in the middle of device, called internal cell [11]. The volume of internal cell is 0.7 litres. At the centre of hemisphere, Silicon Alpha Detector is placed. It is a sophisticated and versatile measuring device capable of complex measurements of Radon in soil, air and water. It is simplest, easiest and portable computer driven electronic instrument to use. The task of RAD7 is divided into two categories:
a) Purging of RAD7: Before using RAD7, the first step is to do purging which means to remove undesired moisture and humidity from measurement chamber. This can be done by connecting gas purifier GAS PURIFIER to RAD7 instrument with tubes. The DRIERITE Gas Purifier is an all-purpose drying unit for the efficient and rapid drying of air. It is used to maintain a dry atmosphere in storage spaces, vaults and commercial packages. In the present study, we are using INDICATING DRIERITE. Indicated Drierite is impregnated with cobalt chloride. It is blue when dry and changes to pink upon absorption of moisture. The need of purging is only to obtain relative humidity less than 10%, so that we can collect accurate result. Purging can be simply done by just connecting the inlet of RAD7 at bottom of dessicant drying unit and outlet of RAD7 at the top of dessicant drying unit as shown in (Figure 2a). If relative humidity becomes less than10% which implies that RAD7 is now ready for use [12].
b)
Determination
of Radon Concentration: Radon concentration was calculated by
using RAD7 (Figure 2b) [13,14]. Set RAD7 at wat
250 modes for finding Radon in water samples. The RAD7’s pump will run for five
minutes. During the five minutes of pumping, more than 95% of the available Radon
is removed from the water. This removed Radon gas is sucked through filter into
the inlet and reaches the measurement chamber. The voltage of 2000 to 2500 V is
applied between detector and hemisphere, creating an electric field throughout
the volume of cell. This electric field drifts the positively charged particles
onto the detector. Inside the chamber, Radon-222 decays into a positively
ionized polonium-218. This positively ionized Po-218 will be accelerated
towards the detector. The produced Po-218 has half-life of 3 minutes. When the
short lived Po-218 nucleus decays upon the detector’s active surface, its alpha-particle
(6MeV) energy have 50% probability of entering the detector and producing an
electrical signal proportional in strength to the energy of alpha particle.
This signal is amplified electronically and transformed into a digital signal. This signal further processed by a microprocessor and helps to produce the spectrum. The Radon concentration in internal cell of RAD7 can be calculated by following differential equations [15]: (1)
dCPo (t)/dC =λPo C (t) - λPo CPo (t) (2)
Where C (t) is the Radon concentration in the internal cell of RAD7, λ is the density constant of Radon, CPo (t) is Po-218 concentration and λPo is Po-218 decay constant and equals to 0.00379 s-1. After certain duration of pumping, the Radon concentration in internal cell of RAD7 equals to that of the environment C0. Equation (2) becomes as:
dCPo (t) dt =λPoC0- λPo CPo (t) (3)
The initial condition is C Po (0) = 0 (4)
The solution of equation (3) is CPo (t) = C0 (1-e- λPot) (5)
If the time is much longer than the
half-life of Po-218, equation (5) becomes
CPo (t) = C0 (6)
Radon concentration can be calculated from
equation (6) and this is the measurement principle of RAD7.
4.1 Evaluation of Mean Annual Effective Dose: The dose due to Radon can be divided into two parts. first is dose from ingestion and second is dose from inhalation. The annual mean effective dose for ingestion and inhalation were calculated according to parameters introduced by UNSCEAR report is calculated as [10]:
Ingestion Dose (mSv) = Rn222conc.(Bql-1)×60ly-1×10-3m3l-1×3.5nSvBq-1 (7)
Inhalation Dose (mSv = Rn222conc.(Bql-1)×10ˉ4×7000hy-1×0.4×9nSv(Bqhmˉ3)ˉ1 (8)
3. Results and Discussion
The results of Radon concentration in
water samples taken from 17 locations of Bukan are shown in (Table 2). The results show that the higher activity
of Radon was 11.87±1.40 Bql-1 in sample no. 14 and low activity was 0.79±0.18 Bql-1 in sample number 11 with mean value
03.75 Bql-1. (Figure 3) shows
the bar chart of mean Radon concentration in the studied dwellings. The US
Environment Protection Agency has suggested that the maximum allowed
concentration level of Radon concentration in water is11Bq l-1 [15]. The
United Nations Scientific Committee on the effects of Atomic Radiation has
given range of 4 to 40 Bq l-1 [16]. The recommended limit of the protection of the
public against exposure to Radon in drinking water supplies (2001/928/Euratom),
which recommends action level of 100 Bq l-1
for public water supplies and 100011 Bq l-1
for private water supplies as recommended by European Commission [17]. The values of Radon concentration obtained in
groundwater were compared with regions of other districts of Bukan. The value
of Radon concentration in groundwater samples of Bukan varies from 1.9 - 5.3 Bql-1 and 1.23 - 4.24 Bq l-1. A few values of Bukan are higher than other
districts as reported in (Table 3). The high value of Radon concentration in Bukan
may be due to high value of uranium content in drinking water samples. All
values of Bukan were well within the permissible limit suggested by UNSCEAR and
USEPA. The Radon concentration values were also compared with the European Commission
limit; all values were found to be well below the level and hence slightly unhealthy
for drinking purposes. The reason for variation in Radon concentration in some
areas may be due to the depth of water sources.
The annual effective dose in the stomach and lungs per person was also evaluated in this study. The values of the annual effective dose per person caused by different water samples in this study are in (Table 2). The average annual effective dose from ingestion of Radon in drinking water was 0.79 µSvyˉ1 and that of inhalation of water-borne Radon was 9.45 µSvyˉ1. So the annual effective dose due to inhalation of water-borne Radon was higher than those from Radon ingestion from water. It is concluded that not the ingestion of Radon in drinking water but inhalation of Radon escaping from water is a substantial part of radiological hazard. The estimated total annual effective dose ranged from 1.27µSvyˉ1 to 32.67µSvyˉ1. The measured values of annual effective dose per person were found to well below the recommended limit of 100 µSvyˉ1 [18,19].
4. Conclusion
·
The results of the Radon concentration in
drinking water samples in Bukan area were below the safe limits recommended by
USEPA and UNSCEAR. The water of these locations is slightly hazardous for us.
·
The variation of Radon concentration may
be due to the depth of the water source, geological structure of the studied
area and may be due to high value of uranium content in drinking water.
·
The value of average annual effective dose
from ingestion of water and inhalation of water-borne Radon was 0.79 µSvyˉ1 and 9.45
µSvyˉ1.
It is concluded that not the ingestion of Radon in drinking water but
inhalation of Radon escaping from water is a substantial part of radiological
hazard.
·
The estimated total annual effective dose
also lies within the safe limits as recommended by the WHO and EU.
Figure 1:
Simplified map of the studied area.
Figures 2(a-b): a) Showing the
purging process of RAD7, b) Schematic diagram of RAD H2O assembly.
Figure 3: Mean
Radon concentration in water samples.
Medium |
Mean Distance Rn222 (cm) |
Air |
220 |
Water |
2.2 |
Porous soil |
155 |
Saturated porous soil |
1.55 |
Table 1: Mean Diffusion distances of Radon in different media.
Sample No. |
Radon concentration in water samples (Bq lˉ 1 ) |
Annual effective dose (µSv/y) |
|||||
Min. |
Max. |
Mean |
S.D. |
Lungs |
Stomach |
Total |
|
1 |
08.65 |
10.69 |
09.44 |
00.88 |
23.78 |
01.98 |
25.76 |
2 |
05.88 |
09.39 |
07.84 |
10.52 |
19.77 |
01.65 |
21.42 |
3 |
04.20 |
07.03 |
05.50 |
10.22 |
13.86 |
01.15 |
15.01 |
4 |
02.58 |
03.15 |
02.80 |
00.24 |
07.06 |
00.59 |
07.64 |
5 |
04.10 |
05.40 |
04.80 |
00.58 |
12.09 |
01.01 |
13.10 |
6 |
01.80 |
02.87 |
08.20 |
01.40 |
05.54 |
00.46 |
06.00 |
7 |
02.73 |
03.44 |
08.09 |
00.31 |
07.79 |
00.65 |
08.44 |
8 |
02.05 |
02.86 |
09.43 |
00.37 |
06.12 |
00.51 |
06.63 |
9 |
07.51 |
09.28 |
08.87 |
00.37 |
04.71 |
00.39 |
05.10 |
10 |
00.66 |
09.94 |
00.96 |
00.12 |
01.97 |
00.16 |
02.13 |
11 |
00.37 |
00.64 |
00.79 |
00.11 |
01.34 |
00.11 |
01.45 |
12 |
01.27 |
01.71 |
01.50 |
00.24 |
03.78 |
00.32 |
04.10 |
13 |
01.51 |
02.01 |
01.70 |
00.23 |
04.28 |
00.36 |
04.64 |
14 |
09.90 |
12.69 |
11.87 |
01.40 |
28.22 |
02.35 |
30.57 |
15 |
02.08 |
02.43 |
02.25 |
00.15 |
05.67 |
00.47 |
06.14 |
16 |
02.06 |
03.49 |
02.75 |
00.21 |
05.67 |
00.47 |
06.14 |
17 |
02.98 |
03.51 |
03.15 |
00.24 |
07.94 |
00.66 |
08.60 |
Average |
03.19 |
04.91 |
03.75 |
01.62 |
09.45 |
00.79 |
10.24 |
Table 2: Radon concentration and annual effective dose in water samples at different locations.
Other regions of some districts |
Radon concentration in water (Bql-1) |
|
Range |
Mean value |
|
Saqqez |
00.40-04.90 |
3.68 |
Mahabad |
00.40-05.10 |
2.63 |
Miyandoab |
00.23-02.10 |
0.88 |
Shahindej |
00.56-07.75 |
2.14 |
Bukan |
00.79-11.87 |
5.73 |
Table 3: Comparison of Radon concentration in groundwater with surrounding cities.
7.
Alghamdi, AS, Aleissa KA (2014)
Influences on Indoor Radon Concentrations in Riyadh, Saudi Arabia. Radiation
measurements 62: 35-40.
8.
United States Environmental
Protection Agency (1999) Federal Register, Washington. 64: 9559-9599.
9.
USEPA (1991) National primary drinking
water regulations for radio nuclides US, Government printing office
EPA/570/9-91/700.
16.
Duggal V, Mehra R, Rani A (2013)
Determination of Rn222 level in groundwater using a RAD7 detector in the
Bathinda district of Punjab, India. Radiation Protection Dosimetry 156: 1-7.
18.
WHO (2003) Guidelines for drinking water
quality. Health criteria and other information.
European
Commission (2005) Commission directive of defining requirements for the
parameters of radioactivity for monitoring the quality of water for the council
directive 98/83 of 3 Nov 1998 on the quality of water intended for human
consumption, draft V3.0 29/11/