Radioactivity of some natural and artificial radionuclides in coastal seawater at Ninh Thuan, Ba Ria - Vung Tau and Ca Mau provinces in 2018

 at three monitoring points (Ninh 
Thuan, Ba Ria - Vung Tau and Ca Mau 
provinces) and shown on Fig. 1. The samples 
were collectted at about 2-5 km from the coast 
with a volume of 200 L to analyze 
radionuclides of Ra-226, Th-232, U-238, Cs-
137 [7]; 100 L for Po-210 analysis [8]; 100 L 
for Sr-90 analysis [9]; and 400 L for Pu-
239,240 analysis [10]. The obtained samples 
were pretreated in the field and transferred to 
the laboratory to determine the radioactivity of 
natural and artificial radionuclides according to 
the procedures established by Center for 
Environment Research and Monitoring, 
Nuclear Research Institute that have been 
evaluated and accredited to be conformable to 
the ISO/IEC 17025:2017 with the national 
code of VILAS 525 [7-10].
Fig. 1. Three sampling monitoring points for coastal seawater at Ninh Thuan, Ba Ria-Vung Tau, 
and Ca Mau provinces of Vietnam
The radionuclides of Ra-226, Th-232, 
U-238, Cs-137 were enriched by simultaneous 
precipitation method, with recovery efficiency 
from 90 to 95%. They were then determined 
on the low-level background gamma 
spectrometer with the HpGe detector model 
GX3019, which had a relative efficiency of 
30%, and an energy resolution of 1.90 keV at 
1333 keV and a peak-to-Compton ratio of 
56:1. Computer software MAESTRO-32 was 
used to process obtained spectrums [7].
The Po-210 and Pu-239,240
radionuclides were enriched by selective 
precipitation, using the radiochemical 
RADIOACTIVITY OF SOME NATURAL AND ARTIFICIAL RADIONUCLIDES
46
separation method and then deposited on silver 
or stainlesssteel discs by electrolysis technique. 
The recovery efficiency for Po-210 was from 
85 to 90% determined by the Po-209 yield 
tracer, and for Pu-239,240 from 75 to 80% 
determined by the Pu-242 yield tracer. The 
enriched samples were measured on alpha 
spectrometer having a energy resolution of
25 keV, a counting efficiency of
background in the energy range greater than 3 
MeV of [8, 9].
The Sr-90 radionuclide was analyzed 
by radiochemical separation method to 
enrich, remove influencing elements, wait for 
14 days (to reach the radioactive equilibrium
between Sr-90 and Y-90), separate the 
radionulide of Y-90, and then measure on a 
low-level background beta counter. The 
recovery efficiency of the separation process 
was about 75%. The low-level background 
alpha/beta counting system (MPC 9300) with 
gas - flow proportional detector has beta 
background of 0.02 counts/s, beta counting 
efficiency of 37% for mixed standard source 
Sr-90/Y-90 [10].
Quality control programme for the 
measurements was conducted by using the 
IAEA standard reference materials (SRM) 
samples, and by IAEA proficiency tests to
determine Cs-134, Cs-137, Sr-90, Po-210 and 
Pu-239,240 radionuclides.
III. RESULTS AND DISCUSSION
Results of radioactivities in coastal 
seawater at monitoring points of Ninh Thuan
(NT), Vung Tau (VT) and Ca Mau (CM) 
provinces during the survey in the year of 
2018 are presented in Table I and shown on 
Figs. 2 and 3.
Table I. The radioactivities of radionuclides in coastal seawater at monitoring points of Ninh Thuan, Vung 
Tau and Ca Mau provinces during the survey in the year of 2018
Lab. code
Radionuclide
Ra-226, 
mBq/L
Th-232, 
mBq/L
U-238,
mBq/L
Po-210, 
mBq/L
Cs-137, 
mBq/L
Sr-90, 
mBq/L
Pu-
239,240, 
µBq/L
NT 02-18 3.58 ± 0.64 5.75 ± 2.80 6.37 ± 2.48 1.51 ± 0.08 1.57 ± 0.42 1.31 ± 0.33 3.7± 0.6
NT 05-18 3.60 ± 0.49 3.45 ± 0.71 3.24 ± 0.72 1.87 ± 0.12 1.05 ± 0.37 1.38 ± 0.25 4.4 ± 0.7
NT 08-18 4.14 ± 0.76 4.78 ± 1.55 5.29 ± 0.69 1.53 ± 0.03 1.36 ± 0.40 1.32 ± 0.33 5.3 ± 1.1
NT 11-18 3.71 ± 0.65 5.98 ± 0.64 4.36 ± 0.65 1.86 ± 0.10 0.88 ± 0.27 1.08 ± 0.27 4.5 ± 1.0
VT 02-18 2.71 ± 0.94 5.04 ± 1.28 3.02 ± 0.45 2.20 ± 0.11 1.41 ± 0.37 1.18 ± 0.28 5.4 ± 0.9
VT 05-18 5.08 ± 1.18 6.63 ± 0.94 5.36 ± 1.00 2.53 ± 0.12 1.16 ± 0.19 1.45 ± 0.44 3.4 ± 0.8
VT 08-18 6.00 ± 1.37 8.50 ± 2.36 6.98 ± 1.48 1.61 ± 0.05 1.68 ± 0.38 1.86 ± 0.55 3.2 ± 0.7
VT 11-18 5.30 ± 0.70 9.07 ± 1.06 6.00 ± 0.70 2.46 ± 0.13 1.29 ± 0.33 1.63 ± 0.30 4.8 ± 1.0
CM 02-18 15.91 ± 2.39 35.93± 5.17 20.93± 2.74 7.64 ± 0.23 1.70 ± 0.44 1.65 ± 0.37 6.2 ± 0.9
CM 05-18 5.06 ± 1.02 15.77± 3.10 7.88± 1.78 4.23 ± 0.20 1.20 ± 0.41 1.58 ± 0.24 2.6 ± 0.6
CM 08-18 6.61 ± 1.01 18.72± 2.94 9.18± 1.89 5.30 ± 0.21 1.37 ± 0.19 1.27 ± 0.30 3.2 ± 0.8
CM 11-18 14.73 ± 2.31 33.47± 3.76 21.47± 2.18 6.74 ± 0.23 1.68 ± 0.44 1.77 ± 0.37 5.1 ± 0.9
NGUYEN DINH TUNG et al.
47
Fig. 2. Variability of radioactivity of Ra-226, Th-232, U-238 and Po-210 in coastal seawater 
at monitoring points of Ninh Thuan, Vung Tau and Ca Mau provinces
Fig. 3. Variability of radioactivity of Cs-137, Sr-90 and Pu-239,240 in coastal seawater at monitoring points 
of Ninh Thuan, Vung Tau and Ca Mau provinces
Some physicochemical parameters such 
as pH, total suspended solids (TSS), 
conductivity, etc., were measured along with 
the radioactivity of radionuclides in coastal 
seawater samples. The results of 
physicochemical parameters in coastal 
seawater at monitoring points of Ninh Thuan, 
Vung Tau and Ca Mau in the year of 2018 are 
presented in Table II.
The obtained data at monitoring point of 
Ninh Thuan show that the physicochemical 
parameters such as pH, TSS, conductivity, and 
salinity of seawater were not much changed in 
2018. At monitoring point of Vung Tau, the 
TSS parameter was a tendency to increase 
from February to November. At monitoring 
point of Ca Mau, the TSS parameter exceeded 
the permissible limit about 10 times in 
February and November (QCVN 10-MT: 
2015/BTNMT) and had a wide range of 
fluctuations. Other indicators at the both 
monitoring points of Vung Tau and Ca Mau 
had not much fluctuation range.
RADIOACTIVITY OF SOME NATURAL AND ARTIFICIAL RADIONUCLIDES
48
Table II. The results of physicochemical parameters in coastal seawater at monitoring points of Ninh Thuan, 
Vung Tau and Ca Mau provinces during the survey in the year of 2018
Monitoring point Lab. code pH TSS (mg/L)
Conductivity 
(mS/cm)
Salinity 
Ninh Thuan
NT 02-18 7.55 1.62 47.8 33.4
NT 05-18 7.41 3.00 48.3 34.2
NT 08-18 7.62 2.36 47.8 33.8
NT 11-18 7.75 2.10 46.4 32.5
Ba Ria Vung Tau
VT 02-18 7.78 8.08 48.2 34.0
VT 05-18 7.97 10.50 45.7 32.3
VT 08-18 7.54 21.02 44.7 31.4
VT 11-18 7.52 36.66 47.9 33.4
Ca Mau
CM 02-18 7.45 513.26 36.8 25.2
CM 05-18 7.54 56.80 43.5 30.6
CM 08-18 7.44 90.54 42.0 29.3
CM 11-18 7.32 481.34 41.4 28.5
At the monitoring point of Ninh Thuan, 
the radioactivity of Ra-226 did not have any 
significant changes, and the average 
radioactivity of Ra-226 in seawater was of 3.76 
mBq/L. Meanwhile, the average radioactivity 
of Ra-226 in seawater in Ca Mau was of 10.58 
mBq/L, and larger than in Ninh Thuan (4.77 
mBq/L) and Vung Tau (3.76 mBq/L) about 2.8 
and 2.2 times, respectively.
The average radioactivity of Th-232 at 
the monitoring point of Ninh Thuan was of 
4.74 mBq/L. After 4 monitoring periods, it was 
found that the radioactivity of Th-232 tended 
to increase slightly from February to 
November. The average radioactivity value of 
Th-232 at the monitoring point of Ca Mau was 
of 25.97 mBq/L, which about 7 times higher 
than the monitoring points of Ninh Thuan and 
Vung Tau in February, November (dry season) 
and 4 times in May, August (rainy season). 
The average radioactivity of U-238 was 
of 4.82 mBq/L at the monitoring point of Ninh 
Thuan and it had no significant change in 
comparison of previous surveys (from the year 
of 2014 to 2017) [11]. For the monitoring point 
of Vung Tau, the average radioactivity of U-
238 was of 5.34 mBq/L and the range was of 
3.02 ÷ 6.98 mBq/L. For the monitoring point 
of Ca Mau, the radioactivity of U-238 was
quite wide, ranging from 7.88 to 21.47 mBq/L 
with the maximum value falling in February 
and November. For the monitoring point of Ca 
Mau, the radioactivity of U-238 was about 
from 3 to 7 times higher than those in Ninh 
Thuan and Vung Tau in February and 
November, and about from 2 to 3 times in May 
and August.
The radioactivity of Po-210 in coastal 
seawater at the monitoring point of Ninh 
Thuan shown that there was no significant 
change among the observations, and the 
range of radioactivity was within of 0.16 ÷ 
2.05 mBq/L that was in correspondence with 
the value range of previously surveys from 
2014 to 2017 [11]. The radioactivity of Po-
210 in seawater at monitoring point of Vung 
NGUYEN DINH TUNG et al.
49
Tau was the same level as in Ninh Thuan. 
Particularly, the radioactivity of Po-210 in 
coastal seawater at the monitoring point of 
Ca Mau ranged from 4.23 ÷ 7.64 mBq/L that 
was higher than about 2 to 4 times in 
comparison of those of Vung Tau and Ninh 
Thuan. The variability of radioactivity of Po-
210 was the same as the radioactivities of 
Ra-226, Th-232 and U-238.
The relationship between the 
radioactivities of Ra-226, Th-232, U-238, Po-
210 and TSS in coastal seawater at monitoring 
points of Ninh Thuan, Vung Tau and Ca Mau 
were shown on Fig. 4.
Fig. 4. The relationship between the radioactivities of Ra-226, Th-232, U-238, Po-210 and total suspended 
solids in coastal seawater at the monitoring points of Ninh Thuan, Vung Tau and Ca Mau
The average radioactivity of Cs-137 in 
coastal seawater at the monitoring point of 
Ninh Thuan was of 1.22 mBq/L and it had no 
significant change in comparison with the 
previous surveys [11]. The radioactivities of 
Cs-137 at monitoring points of Vung Tau
and Ca Mau were the same level in 
comparison with those of the monitoring 
point of Ninh Thuan.
According to the monitoring results, the 
radioactivity of Sr-90 in coastal seawater at the 
monitoring point of Ninh Thuan was no change 
among observations and in correspondence
with the value of previous surveys (from 2014 
to 2017) [11]. The radioactivities of Sr-90 in 
coastal seawater at the monitoring points of 
Vung Tau and Ca Mau were the same level in 
comparerison of the monitoring point of Ninh 
Thuan, and the range of radioactivity of Sr-90 
was of 1.08 ÷ 1.86 mBq/L.
The radioactivity of Pu-239,240 in 
coastal seawater at the monitoring point of 
Ninh Thuan was an average value of 0.0045 
mBq/L. It was found that there was no 
significant change in comparison with the
previous surveys (from 2014 to 2017) [11]. At 
the monitoring points of Vung Tau and Ca 
Mau, the levels of radioactivity of Pu-239,240
did not have significant fluctuations among
the observations.
RADIOACTIVITY OF SOME NATURAL AND ARTIFICIAL RADIONUCLIDES
50
By analyzing the correlation between 
the radioactivity of natural radionuclides and 
TSS, it is shown that the higher of TSS in 
coastal seawater tended to the higher of 
radioctivities of Ra-226, Th-232, U-238 and 
Po-210 (Fig. 4). This explains that the 
radioactivity of Ra-226, Th-232, U-238 and 
Po-210 in coastal seawater at the monitoring 
point of Ca Mau was higher than at other 
monitoring points (Table I) [11, 12]. 
The ranges of radioactivity of natural 
and artificial radionuclides in coastal seawater 
at monitoring points of Ninh Thuan, Vung 
Tau and Ca Mau provinces and the data of 
Asia - Pacific region in 2018 were presented 
in Table III.
Table III. Ranges of radioactivity of natural and artificial radionuclides in coastal seawater at monitoring 
points of Ninh Thuan, Vung Tau and Ca Mau provinces and the data of Asia - Pacific region in 2018
Radionuclide Ninh Thuan
Ba Ria - Vung 
Tau
Ca Mau
Asia - Pacific 
region [12]
Ra-226 (mBq/L) 3.58 ÷ 4.14 2.71 ÷ 6.00 5.06 ÷ 15.91 0.50 ÷ 4.14
Th-232 (mBq/L) 3.45 ÷ 5.75 5.04 ÷ 9.07 15.77 ÷ 35.93 5.27
U-238 (mBq/L) 3.24 ÷ 6.37 3.02 ÷ 6.98 7.88 ÷ 21.47 1.00 ÷ 5.29
Po-210 (mBq/L) 1.51 ÷ 1.87 1.61 ÷ 2.53 4.23 ÷ 7.64 0.20 ÷ 1.84
Cs-137 (mBq/L) 0.88 ÷ 1.57 1.18 ÷ 1.86 1.20 ÷ 1.70 0.13 ÷ 2.95
Sr-90 (mBq/L) 1.08 ÷ 1.38 1.16 ÷ 1.68 1.27 ÷ 1.77 0.67 ÷ 2.01
Pu-239,240 (µBq/L) 3.7 ÷ 5.3 3.2 ÷ 5.4 2.6 ÷ 6.2 5.3
The obtained results shown that the 
radioactivities of the above-mentioned 
radionuclides in coastal seawater at monitoring 
points of Ninh Thuan and Vung Tau was
similar to those in the Asia-Pacific region. At 
monitoring points of Ca Mau, the 
radioactivities of natural radionuclides were
higher in comparison with the published levels 
in the Asia-Pacific region, especially for Th-
232 and U-238 due to the high TSS. 
IV. CONCLUSIONS
The average value of radioactivity of 
concerned natural and artificial radionuclides
in coastal seawater at the monitoring points of 
Ninh Thuan and Vung Tau was within the 
value of the Asia Pacific region. At the 
monitoring point of Ca Mau, the average 
radioactivities of the natural radionuclides was 
higher than the values at the monitoring points
of Ninh Thuan and Vung Tau from 1.0 to 5.5 
times. For artificial radionuclides, the 
variations of radioactivity were not significant 
among the monitoring observations as well as 
the monitoring points.
REFERENCES
[1]. Ryan, T.P., Nuclear fallout in the Irish 
terrestrial environment , Ph.D. Thesis, Dublin: 
University College Dublin, 1992.
[2]. Ryan, T.P., Mitchell, P.I., Sanchez-Cabeza, 
J.A., Smith, V and Vives i Batlle, J., 
throughout Ireland. In: Science, Green Issues
and the Environment: Ireland and the Global 
p. 276-283, 1993.
[3]. UNSCEAR, Sources, effects and risks of ionizing 
radiation, New York: United Nations, 2008.
NGUYEN DINH TUNG et al.
51
[4]. Cunningham, J.D., MacNeill, G., Pollard, D.,
Chernobyl. Its effect on Ireland . Dublin: 
Nuclear Energy Board, 1987.
[5].
for Environmental Radioactivity. Reference of 
report: IE-07/03, 2008.
[6]. McAulay, I.R. and Moran, D., Radiocaesium 
fallout in Ireland from the Chernobyl accident , 
Journal of Radiological Protection, Vol. 9, (1), 
p. 29-32, 1989.
[7]. Laboratory of Environmental Analyses (VILAS 
525), Center for Environment Research and 
Monitoring, Nuclear Research Institute, TCCS-
NN-13: 2017.
[8]. Laboratory of Environmental Analyses (VILAS 
525), Center for Environment Research and 
Monitoring, Nuclear Research Institute, TCCS-
N-24:2017.
[9]. Laboratory of Environmental Analyses(VILAS 
525), Center for Environment Research and 
Monitoring, Nuclear Research Institute, TCCS-
NB-26:2014.
[10]. Laboratory of Environmental 
Analyses(VILAS 525), Center for Environment 
Research and Monitoring, Nuclear Research 
Institute, TCCS-NB-16:2017.
[11]. Station of Chemical and Radioactive 
Environment Monitoring and Analysis No. 3, 
Nuclear Research Institute, Report on the 
implementation of Annually National 
Projects:Monitoring and analyzing sea 
environmental radioactivity in Ninh Thuan 
Province (2014 2017).
[12]. IAEA/RCA/UNDP Project, Asia-Pacific 
marine radioactivity database (ASPAMARD), 
 2018.