Radioactivity of some natural and artificial radionuclides in coastal seawater at Ninh Thuan, Ba Ria

Nuclear Science and Technology, Vol.10, No. 2 (2020), pp. 44-51

Radioactivity of some natural and artificial radionuclides

in coastal seawater at Ninh Thuan, Ba Ria - Vung Tau

and Ca Mau provinces in 2018

Nguyen Dinh Tung, Le Nhu Sieu, Nguyen Van Phuc, Nguyen Van Phu, Tran Dinh Khoa,

Vuong Thi Thu Hang, Nguyen Thi Thanh Nga, Le Thi Minh Tuyen

Nuclear Research Institute

01 Nguyen Tu Luc Str., Dalat City, Lamdong Province, Vietnam

Email: ndtung79@gmail.com

arch 2020

Abstract: Radioactivities of some natural (Ra-226, Th-232, U-238, Po-210) and artificial (Cs-137, Sr-

90 and Pu-239,240) radionuclides in coastal seawater at monitoring points of Ninh Thuan, Ba Ria -

Vung Tau and Ca Mau provinces were analyzed quarterly in the year of 2018. Radioactivities of Ra-

226, Th-232, U-238, and Cs-137 had been determined by simultaneous precipitation method and

measured on low-level background gamma spectrometer; the radioactivities of Po-210 and Pu-

239,240 had been analyzed by radiochemical separation method and measured on alpha spectrometer;

the radioactivity of Sr-90 had been analyzed by radiochemical separation method and measured on

low-level background beta counting system. The ranges of radioactivities of Ra-226, Th-232, U-238,

Po-210, Cs-137, Sr-90, and Pu-239,240 were 2.71 ÷ 15.91, 3.45 ÷ 35.93, 3.02 ÷ 21.47, 1.51÷ 6.74,

0.88 ÷ 1.68, 1.08 ÷ 1.86 and 0.0026 ÷ 0.0062 mBq/L, with the average values of 6.37, 12.67, 8.34,

3.29, 1.36, 1.46 and 0.0043 mBq/L, respectively. The results shown that the radioactivities of the

above-mentioned radionuclides varied between the seawaters at Ninh Thuan, Ba Ria - Vung Tau and

Ca Mau seawater. Additionally, physicochemical parameters in seawater were also surveyed to assess

their impact on the fluctuations of the above radionuclides.

Keywords: Natural radionuclide, artificial radionuclide, radioactivity in coastal seawate.

nuclear weapon tests in the atmosphere and

water, routine releases of under-controlled

low-level radioactive wastes of nuclear

facilities (nuclear power plants, fuel

reprocessing facilities, etc.) [1, 2, 3],

radioactive waste dumping under the sea in

the year 60s of last century, and nuclear

incidents/accidents of nuclear power plants,

nuclear submarines, incidents occurring

during the receiving, using, and transporting

of radioactive materials [1, 4, 5, 6,].

I. INTRODUCTION

Natural and artificial radionuclides are

always present in the soil, water, and the air.

Natural radionuclides are sourced from the

Earth's crust, the most common being K-40,

the radioactive chains of U-238, U-235, Th-

232, and some of the less common

radionuclides such as V-50, Rb-87, Cd-113,

In-115, Te-123, La-138, Ce-142, etc. In

addition, cosmogenic radionuclides are

formed continually in the atmosphere due to

cosmic radiation from outer space as H-3,

Be-7 and C-14 are some important

cosmogenic ones. Artificial radionuclides

have been formed from the products of

The principal objectives of the

environmental marine radioactivity monitoring

programme are: (1) survey and obtain the

environmental quality changes for major

NGUYEN DINH TUNG et al.

radionuclides in coastal seawater at Ninh

Thuan, Ba Ria - Vung Tau and Ca Mau in the

year of 2018; (2) detect and issue monitoring

about abnormal radioactive fluctuations of

industrial activities as well as the use of

nuclear energy of countries in the region that

may affect Vietnam's marine environment.

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].

II. MATERIAL AND METHOD

Coastal seawater samples were collected

in February, May, August and November in the

year of 2018 at three monitoring points (Ninh

Thuan, Ba Ria - Vung Tau and Ca Mau

provinces) and shown on Fig. 1. The samples

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

radionuclides were enriched by selective

precipitation, using the radiochemical

Po-210

and

Pu-239,240

45

RADIOACTIVITY OF SOME NATURAL AND ARTIFICIAL RADIONUCLIDES

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

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.

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

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

Radionuclide

Pu-

239,240,

µBq/L

Lab. code

Ra-226,

mBq/L

Th-232,

mBq/L

U-238,

mBq/L

Po-210,

mBq/L

Cs-137,

mBq/L

Sr-90,

mBq/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

CM 08-18 6.61 ± 1.01 18.72± 2.94

7.88± 1.78 4.23 ± 0.20 1.20 ± 0.41 1.58 ± 0.24 2.6 ± 0.6

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

46

NGUYEN DINH TUNG et al.

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

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.

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

47

RADIOACTIVITY OF SOME NATURAL AND ARTIFICIAL RADIONUCLIDES

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

Conductivity

(mS/cm)

Salinity

Monitoring point

Lab. code

pH

TSS (mg/L)

NT 02-18

NT 05-18

NT 08-18

NT 11-18

VT 02-18

VT 05-18

VT 08-18

VT 11-18

CM 02-18

CM 05-18

CM 08-18

CM 11-18

7.55

7.41

7.62

7.75

7.78

7.97

7.54

7.52

7.45

7.54

7.44

7.32

1.62

3.00

47.8

48.3

47.8

46.4

48.2

45.7

44.7

47.9

36.8

43.5

42.0

41.4

33.4

34.2

33.8

32.5

34.0

32.3

31.4

33.4

25.2

30.6

29.3

28.5

Ninh Thuan

2.36

2.10

8.08

10.50

21.02

36.66

513.26

56.80

90.54

481.34

Ba Ria Vung Tau

Ca Mau

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.

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 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 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

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

48

NGUYEN DINH TUNG et al.

Tau was the same level as in Ninh Thuan.

210 was the same as the radioactivities of

Ra-226, Th-232 and U-238.

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-

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.

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.

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

49

RADIOACTIVITY OF SOME NATURAL AND ARTIFICIAL RADIONUCLIDES

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

Ba Ria - Vung

Tau

Asia - Pacific

region [12]

Radionuclide

Ninh Thuan

Ca Mau

Ra-226 (mBq/L)

Th-232 (mBq/L)

U-238 (mBq/L)

Po-210 (mBq/L)

Cs-137 (mBq/L)

Sr-90 (mBq/L)

3.58 ÷ 4.14

3.45 ÷ 5.75

3.24 ÷ 6.37

1.51 ÷ 1.87

0.88 ÷ 1.57

1.08 ÷ 1.38

3.7 ÷ 5.3

2.71 ÷ 6.00

5.04 ÷ 9.07

3.02 ÷ 6.98

1.61 ÷ 2.53

1.18 ÷ 1.86

1.16 ÷ 1.68

3.2 ÷ 5.4

5.06 ÷ 15.91

15.77 ÷ 35.93

7.88 ÷ 21.47

4.23 ÷ 7.64

1.20 ÷ 1.70

1.27 ÷ 1.77

2.6 ÷ 6.2

0.50 ÷ 4.14

5.27

1.00 ÷ 5.29

0.20 ÷ 1.84

0.13 ÷ 2.95

0.67 ÷ 2.01

5.3

Pu-239,240 (µBq/L)

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.

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.

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