Author’s Accepted Manuscript
Radon and radium Concentrations in drinkable
water supplies of the Thu Duc region in Ho Chi
Minh city, Vietnam
Le Cong Hao, Huynh Nguyen Phong Thu, Nguyen
Van Thang, Le Quoc Bao
PII: S0969-8043(15)30174-3
DOI: />Reference: ARI7122
To appear in:
Applied Radiation and Isotopes
Received date: 12 May 2015
Revised date: 13 August 2015
Accepted date: 24 August 2015
Cite this article as: Le Cong Hao, Huynh Nguyen Phong Thu, Nguyen Van
Thang and Le Quoc Bao, Radon and radium Concentrations in drinkable water
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1
Radon and Radium Concentrations in Drinkable Water Supplies of the Thu Duc Region
in Ho Chi Minh City, Vietnam
Names of the authors: Le Cong Hao, Huynh Nguyen Phong Thu, Nguyen Van Thang,
and Le Quoc Bao
Title: Radon and Radium Concentrations in Drinkable Water Supplies of the Thu Duc
Region in Ho Chi Minh City, Vietnam

226
Ra were found to be 0.11 ± 0.01
Bq.l
-1
and 0.11 ± 0.02 Bq.l
-1
in 14 drinking water samples. They are 0.12 ± 0.01 Bq.l
-1

and 0.10 ± 0.02 Bq.l
-1
in 15 tap water samples, respectively. The mean
222
Rn
concentration of 1.40 ± 0.03 Bq.l
-1
in the 20 groundwater samples of this study is also
lower than the WHO advised level of 100 Bq.l
-1
. Fifty percent of groundwater samples
analysed have
226
Ra levels in excess of the USEPA recommended maximum contaminant
level of 0.185 Bq.l
-1
. The occurrence of elevated concentrations of
226
Ra in groundwater
samples was explained by pH and alkaline conditions.
Keywords

Ra and
222
Rn are essentially soluble in water, thus enter groundwater by the
dissolution of materials in water layers, removal of rock or soil surfaces and expulsion
from minerals by radioactive decay (Sahin et al, 2013).
226
Ra has a long half-life of 1600
years and behaves as calcium, tracing the calcium path in the body partially deposited in
the bone tissue. The alpha-particle emission of radium makes it a carcinogen, with the
continual accumulation of
226
Ra in the bone tissue being a known cause of bone cancer
(Porntepkasemsan and Srisuksawad, 2008).
222
Rn a decay product of
226
Ra has a half-life
of 3.82 days and is a tasteless radioactive gas, inert, colourless, and odourless. Therefore,
human beings are exposed to
222
Rn in two ways, either through inhalation or ingestion
(Khattak et al, 2011). When radon decays after being inhaled or ingested, it releases
energy that can damage parts of living tissue, which may lead to the unnatural
reproduction of a cell and an increased risk of getting cancer.
It is well known that the different radionuclides are not in radioactive equilibrium
with each other due to differences in mobilisation from the rock and water chemistry. So,
for example, radon activities can be three to five orders of magnitude higher than U or Ra
activities, probably due to absorption of the U and Ra into the host rock, while the
gaseous Rn diffuses along microcrystalline imperfections into the interstitial waters
(Wallner et al, 2007). High levels of radon in drinking water represents a potential health

District 2 and water from the Hoa An water intake station on the Dong Nai River is
pumped to the Thu Duc water treatment plant with a capacity of 650,000 m
3
/day. HCMC
also has the following five aquifers, namely, (i) Holocene, (ii) Pleistocene, (iii) Upper
Pliocene, (iv) Lower Pliocene and (v) Mesozoic. Over 150,000 wells/boreholes were
exploited in HCMC. Three of the five aquifers play an important role in terms of water
supply for HCMC: the Pleistocene aquifer (20–50 m), the upper Pliocene aquifer (50–100
m) and the lower Pliocene aquifer (100–140 m) (Institute for Global Environmental
Strategies (IGES), 2007).
Water sampling
In this study, a total of 49 water samples were collected using the techniques
proposed by the manufacturer (RAD7 RAD H
2
O). All water samples (without bubbles)
were collected in dedicated 250-ml glass bottles. 14 drinking water samples were
collected from universities and dormitories (in the University Village), while 35 drinking
water samples were collected from the source drilled wells (tube wells) and water taps.
During sampling a water, the water source flowed for 10 minutes before taking the

5
sample (RAD7 RAD H
2
O), in order to let out the water from a possibly stagnant pipe
section and to obtain parameters characteristic of the fresh water. pH values are an
important indicator of water quality because water with a low pH can damage the piping
of the distribution system, leading to contamination (Sahin et al, 2013). The pH
measurements for each sample/location were done by using a portable “OAKTON pH
TESTER 30” device.
222


6
as a radon-free water sample. The background sample was measured using the same
protocol. The minimum detectable activity (MDA) was estimated to be 0.073 Bq.l
-1
226
Ra Activity Concentration Measurements
After the latest results of radon activity in water, the bottles were tightly closed to
allow the concentration of radon from radium in the samples to increase. The same
experimental method as was used for the radon measurements was followed to measure
the radium content of the samples. The evaluation of the concentration of soluble radium
salts in water was performed after 10 days. Considering that after that time the radon
concentration was reaching the secular equilibrium, the radioactivity of radium (
226
Ra)
soluble compounds and radon (
222
Rn) could be calculated from equation (1):

Rn
C
t
Rn
e
C
k
Ra
C



C
was determined by using a Standard Reference Material (SRM) capsule of
NIST. The SRM capsule contained
226
Ra with an activity of approximately 5 Bq. The
SMS capsule was stored in 250 ml of distilled water for 10 days. Equation (2) presents
the correction factor

Rn
NISTRn
C
C
)(
C
k 
(2)
where C
Rn(NIST)
is the activity of radon calculated from NIST, and C
Rn
is the measured
radioactivity of
222
Rn from RAD-W. The evaluation of the correction factor was found to
be 1.250.03. 7
Dose assessment
The annual effective doses for ingestion and inhalation were estimated according to

was assumed

for a ‘standard adult’ drinking the same water directly from the
source point (Galán López et al, 2004, Somlai et al, 2007, Todorovic et al, 2012) and C
w

(Bq.l
-1
) is the radon or radium concentration in water.
Results and discussion
Table 1 summarises the concentration results of radon and radium in the 14 drinking
water samples collected from the University Village. The highest radon concentration
was measured in TDTT to be 0.36 ± 0.06 Bq.l
-1
. Mean concentrations of
222
Rn in these
water samples were calculated to be 0.11 ± 0.01 Bq.l
-1
. Following that, the highest
radium concentration was found to be 0.18 ± 0.08 Bq.l
-1
in the QT and the mean
concentration of
226
Ra was calculated to be 0.11 ± 0.02 Bq.l
-1
.
The annual effective dose contributions from radon and from radium in the drinking
water samples are also given in Table 1. It was found that the mean annual effective dose

-1
. It has been observed
that these average values obtained are also under UNSCEAR safety limits.
Table 3 summarises the concentration results of radon and radium in the groundwater
samples collected from different drilled wells (tube wells). The recorded
222
Rn activities
in 20 groundwater samples were found to vary from 0.44 ± 0.07 to 4.16 ± 0.20 Bq.l
-1
with
an average value of 1.40 ± 0.03 Bq.l
-1
consequently the average annual effective dose for
ingestion was found to be 9.97 ± 0.20 µSv.y
-1
. The radium concentration was found to
range from 0.08 ± 0.06 to 0.54 ± 0.12 Bq.l
-1
, with an average value of 0.18 ± 0.02 Bq.l
-1

then the mean annual dose resulting directly from water intake was 36.66 ± 3.74 µSv.y
-1
.
In groundwater, findings suggested that the concentration of radium was consistently
controlled by the geochemical properties of the aquifer systems, with the highest
concentrations most likely to be present where, as a consequence of the geochemical
environment, adsorption of the radium was slightly decreased (Szabo et al, 2012). The
three water-chemistry groups defined by low pH, low dissolved oxygen (DO)
concentrations, or by the combination of both factors were supported to explain the

-1
was
associated with acidic water (pH = 5.17) in the G1 sample. This result may be explained
by the fact that the Pleistocene aquifer is widely located under the whole area and is
exposed in Thu Duc district and some others. The high iron concentrations of
groundwater in HCMC and low pH levels of most surveyed wells are the dominant
reasons for high concentrations of
226
Ra in these groundwater samples. This means that
under low pH values and (or) anoxic conditions, the iron compounds can dissolve and
decrease the likelihood of the adsorption of radium onto aquifer materials enhancing the
mobility of radium into groundwater. Thus, low pH value is the most important water
parameter linked to high radium concentration (Almeida et al, 2004).
With two exceptions in the cases of samples from G12 and G16 (pH was larger than
7.5),
226
Ra concentrations were found to be in excess of 0.185 Bq.l
-1
with a frequency of
10%. These two values indicate that the occurrence of elevated concentrations of
226
Ra in
the groundwater samples was not only dependent on low pH levels but also on some
other parameters (Szabo et al, 2012). In fact,
226
Ra is chemically reactive and reacts
similarly to other divalent alkaline earth cations such as Ca and Sr and is most similar to
Ba. Thus, under high pH (pH>7.5) values, there is an increase of the mineral surface or
increasing stability of inorganic complexes such as chlorides so that the increase in
226

play a key role in accelerating the rate of increase of
222
Rn concentrations in these 20
groundwater samples.
Conclusions
From the results for the 14 drinking water samples, and 15 tap water samples, it can be
concluded that these drinkable sources of water are low health risk from the standpoint of
the concentrations of radon (100 Bq.l
-1
) and radium (0.185 Bq.l
-1
) in them.
It was found that none of the radon concentrations of the twenty groundwater samples
are higher than the advised limit set by the WHO of 100 Bq.l
-1
(World Health
Organisation (WHO), 2008). The relationship between radon and radium levels was weak
and
222
Rn may have originated from differences in the physical-geographic characteristics
of underground sources of water.
Concentrations of
226
Ra were greater than 0.185 Bq.l
-1
in 10 (50%) of the 20 samples
analysed for this isotope. Typically, for 40% of the 20 samples the pH of the water was
lower than 6.3 and for 10% of these samples the pH of the water was greater than 7.5.
The occurrence of elevated concentrations of radium in these waters was explained by pH
and alkaline conditions.

Radioanalytical and Nuclear Chemistry, doi: 10.1007/s10967-010-0573-x
7. Institute for Global Environmental Strategies (IGES), 2007. Final research report,
Sustainable Groundwater Management In Asian Cities, IGES (Hayama, Japan)
8. RAD7 RAD H
2
O, User manual, Radon in water accessory, Durridge co.
9. United Nations Scientific Committee on the Effects of Atomic Radiation
(UNSCEAR) (2006) Annex E: Sources-to-effects assessment for radon in homes and
workplaces. New York
10. Galán López, M., Martín Sánchez, A. and Gómez Escobar, V. (2004) Estimates of the
dose due to
222
Rn concentrations in water, Radiation Protection Dosimetry,
doi:10.1093/rpd/nch350

12
11. Somlai, K., Tokonami, S., Ishikawa, T., Vancsura, P., Gáspár, M., Jobbágy, V.,
Somlai, J., and Kovács, T. (2007)
222
Rn concentration of water in the Balaton
Highland and in the southern part of Hungary and the assessment of the resulting
dose. Radiation Measurements, doi:10.1016/j.radmeas.2006.11.005
12. Todorovic, N., Nikolov, J., Forkapic, S., Bikit, I., Mrdja, D., Krmar, M., and
Veskovic, M. (2012) Public exposure to radon in drinking water in Serbia. Applied
Radiation and Isotopes, doi: 10.1016/j.apradiso.2011.11.045
13. United Nations Scientific Committee on the Effects of Atomic Radiation
(UNSCEAR) (2000) Annex E: Sources-to-effects assessment for radon in homes and
workplaces. New York
14. Szabo, Z., dePaul, V. T., Fischer, J. M., Kraemer, T. F., and Jacolsen, E. (2012)
Occurrence and geochemistry of radium in water from principal drinking-water

13

Drinking water
Tap water
Drilled well
water 15

Figure 2: Diagrammatic illustrations of the radon-monitor with RAD-W.
16

Figure 3: Relationship of concentrations of
226
Ra with pH for twenty groundwater
samples.
Ra concentration in drilled well water samples and the annual
effective doses.

17
concentration
(Bq.L
-1
)
226
Ra
concentration
(Bq.L
-1
)
Annual effective dose
due to ingestion (Sv.y
-1
)
222
Rn
226
Ra
KHTN
10°52'33"
0.090.03
0.110.07
0.690.25
22.6213.68

18
106°47'57"
CNTT
10°52'12"
106°48'13"

0.970.29
21.4013.68
NH
10°51'27"
106°45'49"
0.170.04
0.110.07
1.230.31
21.4013.68
KTL
10°50'58"
106°45'13"
0.090.04
0.170.08
0.680.26
34.2415.81
NL
10°52'20"
106°47'34"
0.080.03
0.100.06
0.560.24
19.9613.08
ANND
10°52'24"
106°48'20"
0.070.03
0.110.07
0.540.23
22.0113.98


Table 2.
222
Rn and
226
Ra concentration in tap water samples and the annual effective
doses

19

Sample
Coordinates
222
Rn
concentration
(Bq.L
-1
)

106°45'27’’
0.190.05
0.170.08
1.400.34
35.1616.11
M4
10°51'2"
106°46'52’’
0.140.04
0.150.07
1.010.29
29.9615.20
M5
10°52'8"
106°46'42’’
0.170.05
0.090.07
1.270.34
19.0214.28
M6
10°51'10"
106°45'52’’
0.060.03
0.060.06
0.410.22
11.7112.18
M7
10°52'6"
106°44'9’’
0.190.05

13.4512.78
M12
10°52'13"
106°46'25’’
0.170.04
0.150.08
1.250.31
29.6617.01
M13
10°50'53"
106°45'58’’
0.100.04
0.070.06
0.700.28
14.6212.48
M14
10°51'2"
106°45'44’’
0.090.04
0.110.07
0.640.26
22.6213.68
M15
10°51'9"
106°45'10’’
0.180.04
0.070.06
1.290.32
14.5212.78


Rn
226
Ra
G1
10°50'41"
106°46'2’’
5.17
4.160.20
0.540.12
30.371.47
111.2924.74
G2
10°52'40"
106°45'9’’
4.13
2.390.17
0.260.09
17.451.25
52.5918.55
G3
10°51'34"
106°47'18’’
6.27
2.400.15
0.430.12
17.551.11
87.4424.68
G4
10°51'6"
106°45'47’’

10°52'18"
106°44'5’’
4.91
2.960.19
0.080.06
21.591.41
16.1413.38
G9
10°51'23"
106°45'39’’
6.04
1.420.12
0.170.08
10.350.89
34.8617.02
G10
10°51'38"
106°46'3’’
6.92
1.080.11
0.180.08
7.850.79
36.9916.42
G11
10°51'55"
106°48'2’’
4.30
1.370.11
0.100.06
9.990.82

0.090.06
3.220.49
17.7013.38
G16
10°52'24"
106°47'59’’
7.90
1.460.12
0.230.09
10.680.92
46.4718.54
G17
10°52'32"
106°46'2’’
4.15
1.030.11
0.320.11
7.500.82
65.4321.60
G18
10°51'9"
106°47'16’’
6.94
3.790.20
0.110.07
27.651.45
23.2414.59
G19
10°50'41"
106°44'2’’

explained by pH and alkaline conditions.