DSpace at VNU: Pollution sources and occurrences of selected persistent organic pollutants (POPs) in sediments of the Mekong River delta, South Vietnam

Chemosphere 67 (2007) 1794–1801
www.elsevier.com/locate/chemosphere

Pollution sources and occurrences of selected persistent
organic pollutants (POPs) in sediments of the Mekong River
delta, South Vietnam
Nguyen Hung Minh a, Tu Binh Minh a, Natsuko Kajiwara a, Tatsuya Kunisue a,
Hisato Iwata a, Pham Hung Viet b, Nguyen Phuc Cam Tu c,
Bui Cach Tuyen d, Shinsuke Tanabe a,*
a

Center for Marine Environmental Studies, Ehime University, Bunkyo-cho 2-5, Matsuyama 790-8577, Japan
b
Hanoi National University, 334 Nguyen Trai Str., Thanh Xuan Distr., Hanoi, Viet Nam
c
Faculty of Agriculture, Ehime University, Tarumi 3-5-7, Matsuyama 790-8566, Japan
d
Nong Lam University, Thu Duc Distr., Hochiminh, Viet Nam
Accepted 26 May 2006
Available online 16 January 2007

Abstract
The Mekong River delta is one of the largest agricultural land in the Southeast Asia. It plays a very important role for agriculture and
fisheries in South Vietnam. However, comprehensive studies on the environmental pollution of persistent organic pollutants (POPs) in
Mekong River delta have not been carried out in recent years. In this study, we collected sediment samples from the Mekong River to
evaluate the contamination and ecological risks caused by several POPs. The contamination pattern of POPs was DDT > PCBs >
CHLs > HCHs > HCB. DDTs are the most abundant pollutants, their concentration ranging from 0.01 to 110 ng/g dry wt, followed
by PCBs (0.039–9.2 ng/g dry wt). DDTs and PCBs concentrations were higher in sediment from adjacent to urban areas than those from
rural and agricultural sites, suggesting urban areas as important point sources of DDTs and PCBs to the river. Ratio of p,p 0 -DDT/p,p 0 DDE was lower compared to those previously reported. However, some samples still had the ratio higher than 0.5, indicating recent
input of DDT into the aquatic environments. This result shows that although the magnitude of contamination decreased over time,
recent inputs of DDTs to the river still occur. Some sediment samples had concentrations of DDT compounds higher than the standards

from the Canadian Environmental Quality Guideline, suggesting continuous monitoring for POPs contamination in the Mekong River is
necessary.
Ó 2006 Elsevier Ltd. All rights reserved.
Keywords: Vietnam; Mekong River; POPs; Sediment; Pollution source

1. Introduction
The Mekong River is the longest river in southeastern
Asia, which flows a distance of almost 4800 km from China
through Myanmar, Thailand, Laos, Cambodia and Vietnam. The Mekong River basin with an area of nearly 800
thousand square kilometers is an important habitat for
*

Corresponding author. Tel./fax: +81 89 927 8171.
E-mail address: (S. Tanabe).

0045-6535/$ - see front matter Ó 2006 Elsevier Ltd. All rights reserved.
doi:10.1016/j.chemosphere.2006.05.144

approximately 60 million people. The Mekong River delta
(MRD) in South Vietnam, which is inhabited by about 20
million people, is one of the most highly productive agriculture areas in the world (MRC, 2002). Rice production is a
major agronomic activity in MRD contributing half of the
rice production in Vietnam. On the other hand, economic
development in MRD also raised concerns over the environment and biodiversity. For example, intensive use of
persistent organic pollutants (POPs) including organochlorine pesticides (OCPs) and polychlorinated biphenyls


N.H. Minh et al. / Chemosphere 67 (2007) 1794–1801

(PCBs) may have led to their considerable residues in soil,

water and sediment. Moreover, relative persistence of such
chemicals together with natural processes like evaporation
and runoffs might enhance their ubiquitous distribution in
the environment and food chains. Several of these chemicals are believed to alter normal function of the endocrine
and the reproductive systems in humans and wildlife (Colborn et al., 1993; Kelce, 1995; Cheek et al., 1999; Vos et al.,
2000).
In Vietnam, despite an official ban on the use of OCPs
since 1995 (Sinh et al., 1999), there has been continuous
evidence on their use throughout the country, particularly
for dichlorodiphenyltrichloroethane (DDT). Moreover,
recent studies carried out in Hanoi and Hochiminh city
showed high levels of DDTs in birds, mussels and human
breast milk (Minh et al., 2002; Monirith et al., 2003; Minh
et al., 2004), suggesting relevant contamination by DDTs
in the local environment. High contamination by POPs in
MRD may be expected due to high population density
and the intensive agronomic activities in this region.
Despite this fact, no comprehensive study to evaluate the
contamination status caused by POPs in this region has
been carried out recently.
Generally, POPs are hydrophobic and therefore, readily
bind to the particle fraction in lake and river waters. Subsequently, via sedimentation processes, these chemicals are
deposited to the bottom. They remain very long in sediment
due to their long half-life times (Rawn et al., 2001). From
sediment, they can be taken up and retained in benthic
organisms and consequently biomagnified through aquatic
food chains to higher trophic levels. Humans, through
ingestion of contaminated fish and shellfish, may be
exposed to elevated levels of POPs (Ross and Birnbaum,
2003). Examination of POPs levels in sediment may give

basic information on the contamination status, sources

1795

and ecological risks of POPs in the aquatic environments.
In this study, we collected sediments from different locations along the Mekong River and determined the concentrations of several POPs such as PCBs, DDTs, HCHs
(hexachlorocyclohexane isomers), CHLs (chlordane compounds) and HCB (hexachlorobenzene) in order to elucidate their recent contamination status, their usage pattern
as well as to decide possible potential pollution sources of
these chemicals to the river.
2. Materials and methods
2.1. Sample collection
Sediment samples were collected in September 2003 and
May 2004 from the Hau River – the biggest branch of the
Mekong River, which crosses South Vietnam and empties
into the East Sea. Sampling points were selected along
the Hau River from Chau Doc town to Can Tho city
and Tranh De estuary (Fig. 1). Sediments named as CC
and NKSE were collected near Can Tho city and those
named as Hau were collected at other points along Hau
River (Table 1). At each site, a grab of 5 cm surface sediment was collected by using Ekman dredge. The sediment
was well mixed in an aluminum tray and a portion about
200–300 g was put in a clean polyethylene bag and transported to our laboratory in boxes packed with gel ice. In
the laboratory, sediments were dried in room temperature,
ground and sieved for a particle fraction of less than 2 mm
size, which was used for the chemical analysis.
2.2. Analytical methods
POPs in sediment were analyzed following the
method described by Iwata et al. (1994) with some slight

Fig. 1. Sampling locations in Mekong River, South Vietnam (2003–2004).

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N.H. Minh et al. / Chemosphere 67 (2007) 1794–1801

Table 1
Sampling positions and total organic carbon content of sediments from
the Hau River
Longtitude

TOC (%)

about 20 times the original volume, if necessary, prior to
the quantification by GC/ECD. Good recovery rates
(85%–110%) were obtained for all compounds. The results
were not corrected for recovery rates.

Sample ID

Latitude

2003 September
CC-1
CC-4
CC-7
NK-SE
Hau-1
Hau-2
Hau-3

Hau-4
Hau-5
Hau-6
Hau-7
Hau-8

N
N
N
N
N
N
N
N
N
N
N
N

10°02 0 19.800
10°02 0 34.300
10°01 0 16.000
10°02 0 08.700
09°44 0 37.300
09°50 0 36.600
09°55 0 53.900
10°02 0 53.100
10°23 0 15.000
10°20 0 17.200
10°11 0 23.200

10°08 0 22.500

E
E
E
E
E
E
E
E
E
E
E
E

105°46 0 10.800
105°47 0 06.600
105°46 0 25.100
105°47 0 25.200
106°04 0 11.700
105°59 0 13.100
105°53 0 52.900
105°47 0 46.800
105°26 0 50.500
105°28 0 44.400
105°36 0 43.800
105°40 0 05.600

1.8
1.3

0.55
1.5
1.0
1.4
1.4
1.3
0.82
1.6
0.86
1.5

2.3. Statistical analysis

2004 May
CC-7
Hau-1
Hau-2
Hau-3
Hau-4
Hau-5
Hau-6
Hau-7
Hau-11
Hau-12

N
N
N
N
N

N
N
N
N
N

10°01 0 12.900
09°55 0 51.300
09°50 0 39.400
09°44 0 35.000
10°02 0 21.900
10°23 0 11.800
10°20 0 21.500
10°11 0 23.300
10°42 0 29.700
10°32 0 52.300

E
E
E
E
E
E
E
E
E
E

105°46 0 24.000
105°53 0 47.800

105°59 0 10.700
106°04 0 10.200
105°48 0 12.200
105°26 0 55.800
105°28 0 45.200
105°36 0 43.900
105°07 0 43.100
105°17 0 51.800

n.a.
n.a.
n.a.
n.a.
n.a.
n.a.
n.a.
n.a.
n.a.
n.a.

In general, the residue pattern of POPs in sediment from
the Hau River followed the order: DDTs > PCBs >
CHLs P HCHs P HCB. However, their concentrations
varied among the sampling sites, showing higher concentrations in sediments close to urban areas such as Can
Tho city. The pattern found in this study was similar to
those recently observed in human breast milk samples from
Hochiminh city (Minh et al., 2004), suggesting widespread
and dominant contamination by DDTs and PCBs in the
environment as well as throughout the food chains. The
abundance of DDTs and PCBs in Vietnam may be due

to their larger usage as well as higher persistency and bioaccumulation over the other contaminants. In this study,
correlation between POPs levels and organic carbon content in the sediment (Table 1) was not observed, probably
due to the vast areas investigated and also due to large distance from pollution sources (Iwata et al., 1995). In general, levels of PCBs and DDTs were higher in the rainy
season than those in the dry season (Table 2), perhaps
because more residues of such pollutants are transported
from lands into the river by stormwater in rains.
Concentration of PCBs varied between 0.039 and
9.2 ng/g dry wt. Interestingly, PCBs levels in sediments collected near urban areas such as Can Tho, Chau Doc and
Long Xuyen were higher than those in sites away from
urban areas, indicating metropolitan areas as sources of
PCBs pollution to the river. However, PCB levels in the
present study were approximately five times lower than
those in sediments collected in the early 1990s from South
Vietnam (Table 3), indicating a decreasing temporal trend
in the environment. In fact, Minh et al. (2004) found a
decreasing trend of PCBs in human breast milk in South
Vietnam with half-life ranging from 10 to 18 years for
various PCB congeners. Approximately 30 000 tons of
PCB-contaminated industrial oils were imported to Vietnam until 1985 (Sinh et al., 1999). In addition, electrical
equipments like transformers containing PCB-contaminated oils were also imported until the mid 1980s (Kannan
et al., 1995). Those materials are parts of PCBs sources to
the environment, besides releases from heavy weapons used
during the Indochina War (Thao et al., 1993).

n.a.: not analyzed.

modifications. Approximately 15 g of air-dried sediment
sample were placed in a conical flask containing 15 ml
water. 100 ml acetone was then added and the flask was
shaken vigorously for 60 min using an electric shaker

(SR-2W model, Taitec Co. Ltd.). The soil solution was filtered into a separating funnel containing 600 ml hexanewashed water and 100 ml hexane. The funnel was shaken
vigorously for 15 min and then kept for at least 8 h to separate entirely the aqueous and the hexane layers. The aqueous layer was discarded and the hexane layer was washed
three times with 100 ml water. Volume of hexane in the
final solution was measured for calculating the recovery
from initial 100 ml (this recovery value was used as the
correction factor during calculation). The solution was
concentrated to about 10 ml by Kuderna–Danish (KD)
apparatus and further to 5 ml under gentle nitrogen
stream. An equal volume of concentrated H2 SO4 was
added to this solution to remove pigment, humic acids
and other organic interferences. This step was repeated several times until the hexane layer became transparent. The
solution was further washed three times by hexane-washed
water. 4 ml of this solution was taken for GPC cleanup,
followed by Florisil column chromatography as described
previously (Minh et al., 2004). The final solution was treated with activated copper to remove sulfur-containing substances. For this step, several strings of copper wires
activated by HCl were put into the solution and kept for
an hour until no black sulfur soot appeared on the copper
strings. The final solution was further concentrated up to

The statistical analysis was performed with the StatView
statistical software package (SAS Inc., 1998, Version 5) and
the Mann–Whitney U test was used to examine statistical
differences between groups ðp < 0:05Þ.
3. Results and discussion
3.1. Residue levels and contamination pattern


N.H. Minh et al. / Chemosphere 67 (2007) 1794–1801

1797

Table 2
Concentration of OCs (ng/g dry wt.) in sediment collected from the Mekong River, South Vietnam
Sample ID

PCBs

DDTs compounds
0

0

0

RCHLs

RHCHs

HCB

p,p -DDE

p,p -DDD

p,p -DDT

RDDTs

2003 September (dry season)
CC-1

3.7
CC-4
2.4
CC-7
0.12
NK-SE
0.80
Hau-1
0.12
Hau-2
0.18
Hau-3
0.54
Hau-4
0.60
Hau-5
0.18
Hau-6
0.13
Hau-7
0.15
Hau-8
0.17

1.9
2.1
0.69
0.79
0.022
0.086

0.51
1.3
0.46
0.89
0.53
0.89

0.79
1.9
0.75
0.49
0.011
0.081
0.36
0.32
0.20
0.42
0.32
0.23

0.54
0.98
0.43
0.56
0.011
0.016
0.29
0.22
0.51
0.56

0.15
0.027

3.2
4.3
1.9
1.8
0.043
0.19
1.2
1.9
1.2
1.9
1.0
1.2

0.12
0.18
0.35
0.16
0.025
0.032
0.13
0.049
0.034
0.070
0.056
0.075

0.032

<0.02
0.11
<0.02
<0.02
<0.02
<0.02
<0.02
<0.02
<0.02
<0.02
0.044

0.080
0.022
<0.006
0.059
< 0.006
<0.006
0.0079
0.010
0.020
0.016
0.0076
<0.006

2004 May (rainy season)
CC-7
9.2
Hau-1
0.30

Hau-2
0.13
Hau-3
0.089
Hau-4
0.039
Hau-5
0.28
Hau-6
0.29
Hau-7
0.067
Hau-11
0.14
Hau-12
0.045

15
0.31
<0.01
0.094
0.13
0.57
0.72
0.11
1.5
0.54

46
0.47

<0.01
0.074
0.12
0.28
0.47
0.098
0.41
0.36

44
5.8
<0.01
0.012
0.028
0.051
0.21
<0.01
0.23
0.36

110
6.6
<0.01
0.18
0.28
0.90
1.4
0.21
2.1
1.3

1.9
<0.004
0.0081
<0.004
0.037
0.050
0.048
0.066
0.022
<0.004

0.21
0.078
<0.02
<0.02
<0.02
<0.02
<0.02
<0.02
<0.02
1.3

<0.006
0.0075
<0.006
0.018
<0.006
0.012
0.0077

0.0091
0.016
<0.006

Summary
Mean
Median
Range

1.3
0.56
<0.01–15

2.5
0.34
<0.01–46

2.5
0.23
<0.01–44

6.5
1.3
<0.01–110

0.93
0.050
<0.004–19

0.10

0.020
<0.02–1.3

0.016
0.0078
<0.006–0.080

0.89
0.18
0.039–9.2

RDDTs ¼ p;p0 -DDE þ p;p0 -DDD þ p;p0 -DDT; RCHLs ¼ trans-chlor þ cis-chlor þ trans-nona þ cis-nona; RHCHs ¼ aHCH þ bHCH þ cHCH (when results were less than quantification limits, the limits were insterted to calculate means).

DDTs residue levels were highly variable among sampling sites, ranging from less than 0.01 to 110 ng/g dry
wt. Similar to the distribution of PCBs, concentrations
were higher at sampling sites close to urban areas (e.g.
NK-SE, CC-1, CC-4, CC-7) and decreased downstream.
DDTs levels from sampling sites near Long Xuyen town
and Can Tho city were one to two orders of magnitude
higher than those from their respective downstream sites,
except the sediment at Hau-1 site in 2004. Sediment collected at this site showed very high DDTs level in the rainy
season of 2004 compared to those in the dry season of 2003
(Table 2). In addition, this sample had particularly high
proportion of p,p 0 -DDT (Fig. 2) that may suggests recent
input of DDT to the river. Stormwater might have carried
DDTs from several sources such as agricultural lands or
municipal areas which are sprayed for hygiene purposes
and vector control, into the river.
Comparison of DDTs levels in Hau River sediment
with those in previous studies in Vietnam demonstrated a

decreasing trend. Although the mean concentration (arithmetic mean) of DDT in Hau River was 5.4 ng/g dry wt, the
median concentration (geometric mean) was only 1.5 ng/g
dry wt. In fact, rather high DDTs residues in samples such
as CC-7 and Hau-1 have strong influence on the mean

value. Therefore, the median concentration and the range
of DDTs was used for evaluating their contamination trend
in sediments from Vietnam. The range of DDTs in the
Mekong River sediments was several times lower than sediments collected in 1990 from mangroves of Duyen Hai and
Ho Chi Minh, South Vietnam (Iwata et al., 1994). This fact
suggests consistent decreasing input of DDTs to the aquatic environments of Vietnam.
HCHs, CHLs and HCB in the present study were 10–20
times lower compared to DDTs and PCBs, implying less
contamination by such chemicals in the Hau River. Among
those, CHLs levels were slightly higher than HCHs and
HCB, ranging from 0.004 to 1.9 ng/g dry wt. The present
range of CHLs was lower than those found in the sediments collected in 1990 (Iwata et al., 1994) and comparable
to those in the sediments recently collected in Hanoi (Nhan
et al., 2001). All studies, however, revealed no clear differences in the levels between rural and urban areas. Our
results probably indicated relatively low contamination
by CHLs in MRD.
HCH concentrations in this study were slightly lower
compared to those recently found in the sediments of the
Red River, North Vietnam (Table 3). Higher levels of
HCHs in the North Vietnam were observed in human


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N.H. Minh et al. / Chemosphere 67 (2007) 1794–1801

Table 3
Comparison of organochlorines in surface sediments from various locations in the worlda
Country

Year

n

PCBs

DDTs

HCHs

Reference

A – Vietnam
Can Tho (Mekong River)
Duyen Hai (Mangroves)
Hochiminh (Urban areas)
Hanoi (Urban areas)
Hanoi (Outskirt)
North coast

2003–2004
1990
1990
1997
1995–1996

1995–1996

22
9
4
12
2
4

0.039–9.2
2.1–9.7
7.6–630
0.67–40b
2.2–11b
1.0–3.3b

<0.01–110
1.1–19
46–430
7.3–73
7.0–14
3.0–7.3

<0.02–1.3
0.45–2.3
0.97–7.5
0.07–3.1
–
–

Present study
Iwata et al. (1994)
Iwata et al. (1994)
Nhan et al. (2001)
Nhan et al. (1998)
Nhan et al. (1998)

B – World
Brazil (Amazon region)
Canada (7 lakes)
China (Pearl River Estuary)
China (Minjiang River)
China (Daya Bay)
China (Lingding Bay)
China (Macao Harbor)
Egypt (Alexandria harbor)
Korea (Masan Bay)
Lake Baikal
Taiwan (Wu-Shi River)
Taiwan (Da-han & Erh-Jen)
Ukraine (Black Sea)
Ukraine (Coastline)
Ukraine (Danube River)

1997
1992–1995
1996–1997
1999
1999
1997

1997
1998
1997
1992
1997–1998
1997–1998
1995
1995
1995

7
7
20
9
14
6
1
23
20
6
19
20
2
2
2

–
nd-33.5
0.18–1.82
15.1–57.9

0.85–27
10–12
340
0.9–1210
1.2–41
0.08–6.1
–
–
5.7–6.8
nd-0.4
1.4–2.7

3.2–62
0.08–114
1.36–8.99
1.5–13
0.14–20
2.6–115
1630
<0.25–885
0.28–89
0.014–2.7
0.53–11.4
0.21–8.81
35–65
0.06–0.6
9.2–43

–
nd-1.37

0.28–1.23
2.9–16
0.32–4.1
nd-2.6
2.4
<0.25–2.1
nd-1.03
0.019–0.12
0.99–14.5
0.57–14.1
1.3–2.3
0.02–0.2
1.3–2

Torres et al. (2002)
Rawn et al. (2001)
Hong et al. (1999)
Zhang et al. (2003)
Zhou et al. (2001)
Fu et al. (2003)
Fu et al. (2003)
Barakat et al. (2002)
Hong et al. (2003)
Iwata et al. (1995)
Doong et al. (2002a)
Doong et al. (2002b)
Fillmann et al. (2002)
Fillmann et al. (2002)
Fillmann et al. (2002)

‘‘–’’: Data is not available.
a
Concentration in ng/g dry wt.
b
As alochlor 1254 mixture.

pp'-DDE

Sep. 2003

pp'-DDD

pp'-DDT

Hau-5
NK-SE
Hau-6
Hau-1
Hau-3
CC-4
CC-7
CC-1
Hau-7
Hau-4
Hau-2
Hau-8

May 2004
Hau-1
CC-7

Hau-12
Hau-6
Hau-11
Hau-4
Hau-3
Hau-5

0

20
0

40

60

80

100

DDTs composition (%)
Fig. 2. DDTs composition in sediments collected from the Mekong River, South Vietnam in September 2003 and May 2004.

breast milk (Minh et al., 2004), suggesting more usage of
HCHs in the North compared to South Vietnam. Rather
low levels of HCHs and HCB in sediments in Vietnam
could be due to high average temperature in the region as
well as lower K ow values of such compounds that may
enhance their distribution in aqueous and air phase rather
than in sediments and biota (Iwata et al., 1994).

3.2. Geographical comparison of POPs in sediment
Generally, PCBs levels in Mekong river sediments are
relatively low compared to sediments from other locations
around the world (Table 3). The levels in the Mekong River
were comparable with those in some parts of the Pearl
River estuary, China (Hong et al., 1999) and Ukraine


N.H. Minh et al. / Chemosphere 67 (2007) 1794–1801

3.3. Composition of OCs in sediment samples
Fig. 2 demonstrates the contribution of three major DDT
compounds including p,p 0 -DDT, p,p 0 -DDD and p,p 0 -DDE
(abbreviated to DDT, DDD and DDE, respectively). Except
the sediment Hau-1 collected in 2004, DDE was the most
abundant compound followed by DDT and DDD. Interestingly, proportion of DDT was higher in sediments collected
near urban areas than those in downstream sites (Fig. 2).
Moreover, in sediment Hau-1, DDT composition was as
high as 80%, clearly indicating fresh residues of DDT to
the river.
Ratios of DDT and its metabolites such as DDT/DDE
could be useful to evaluate degradation features of the parent compound in land as well as in sediment (Strandberg
et al., 1998). During the last decade, some studies examined
DDTs residues in sediments from various locations of Vietnam. For an appropriate evaluation of the temporal trend
of DDT in sediments from Vietnam, ratios of DDT and
DDE were compared in Fig. 3. Strandberg et al. (1998)
suggested that in sediments, DDT/ DDE ratios lower than
0.33 could be the result of aged DDTs mixtures in the environment, while those higher than 0.5 might indicate recent
inputs. More than half of the sediments collected in 1990

and 1996 (Iwata et al., 1994; Phuong et al., 1998) from various locations of South Vietnam had the ratio above 0.5
(Fig. 3). In the present study, some sediment samples like
CC-4, CC-7, NK-SE, Hau-5 Hau-6 and Hau-1 also had a
ratio above 0.5, perhaps also indicating contribution from
recent usage of DDT in MRD. However, it should also be

14

6.
6.8

5

DDT/DDE
Ratio of DDT/DDE

coastal areas (Fillmann et al., 2002). However, the levels in
the Mekong River were lower than several other areas in
the Pearl River delta (e.g. Daya Bay and Minjiang River,
Table 3) as well as other locations of prominent industrial
activities like the Black Sea, the Yukon Lake in Canada
and the Alexandria harbour in Egypt (Table 3). Data on
recent PCBs residues in sediments throughout the South
East Asian region are rather scarce. The only comprehensive monitoring of sediments in this region was made during 1989–1990 by Iwata et al. (1994). In this study,
relatively higher levels of PCBs in sediments from Vietnam
compared to other Asian developing countries could be
seen. The similar trend was observed in other studies examining biological samples such as fish, mussels, birds and
human milk (Kannan et al., 1995; Minh et al., 2002; Monirith et al., 2003; Minh et al., 2004).
In the global comparison, while DDT residue levels in
the sediment from the Hau River are comparable to those

in several locations of the Pearl River delta such as the
Minjiang River and the Lingding Bay, concentrations were
higher than in sediments from most rivers and lakes of Taiwan, Korea and Canada (Table 3). However, sediments
from relatively contaminated areas such as the Alexandria
harbour (Egypt), the Macao harbour (China) and the
Black Sea (Ukraine) have higher DDTs levels than the
present study.

1799

4

3

2

1

0
S-VN’04

S-VN’90

S-VN’96

N-VN’96

N-VN’97

Fig. 3. Ratios of DDT/DDE in sediments collected in various locations in

Vietnam from 1990 to 2004. S-VN’04 denotes samples from South
Vietnam in 2004 (present study); S-VN’90: South Vietnam in 1990 (Iwata
et al., 1994); S-VN’96: South Vietnam in 1996 (Phuong et al., 1998);
N-VN’96: North Vietnam in 1996 (Nhan et al., 1998); N-VN’97: North
Vietnam in 1997 (Nhan et al., 2001).

noted that the ratio is influence not only by the transformation kinetic but also by the loss of the substances from the
system (e.g. through offsite transport) relative to new
inputs. Besides, in this study, relative contributions of the
inputs from recent usage and from old residues in agricultural lands have not been elucidated yet. Further study
examining residues of chiral pesticides such as o,p 0 -DDD
in the soil and air samples may be useful to distinguish
the recent and old sources of DDTs in the environment
(Bidleman et al., 1998).
3.4. Toxicological assessment
The risk assessment was carried out based on the standard of Canadian Environmental Quality Guideline for
freshwater sediments (CCME, 1999). Accordingly, criteria
such as the interim sediment quality guideline (ISQG) and
the probable effect level (PEL) for DDT compounds and
PCBs were compared with their respective concentrations
in sediments from the Mekong River as well as sediments
previously collected from South Vietnam (Iwata et al.,
1994; Phuong et al., 1998). Compared to the criteria for
DDE, DDD and DDT (ISQG: 1.42, 3.54, 1.19; PEL: 6.75,
8.51, 4.77 in ng/g dry wt, respectively), five sediments in
the present study exceed the ISQG value for DDE and two
had levels over the PEL for all three compounds (Fig. 4).
On the other hand, more than half of the sediments collected
from 1990 to 1996 had levels beyond the guidelines for all
compounds. Regardless of such a difference between sampling locations in such surveys, this result probably demonstrates the decreasing levels and less toxicological stress of

DDTs on aquatic biota of the Mekong River. Nevertheless,
it is probably necessary to continue monitoring the levels of
DDTs as some sediment samples had levels exceeding the
ISQG values. The ISQG and PEL for total PCBs are 34.1


1800

N.H. Minh et al. / Chemosphere 67 (2007) 1794–1801

Concentration (ng/g dry wt)

500

10
8
6

(PEL)
(PEL
4
2

(ISQG)

0
S-VN’04 S-VN’90 S-VN’96

S-VN’04 S-VN’90 S-VN’96

S-VN’04 S-VN’90 S-VN’96

pp'-DDE

pp'-DDD

pp'-DDT

Fig. 4. Comparison of DDT compounds in various sediments from South Vietnam with standard guidelines issued by Canadian Council of Minister of
the Environment (CCME, 1999; see text for more details). S-VN’04 denotes samples from South Vietnam in 2004 (present study); S-VN’90: South Vietnam
in 1990 (Iwata et al., 1994); S-VN’96: South Vietnam in 1996 (Phuong et al., 1998).

and 277 ng/g dry wt, respectively. Those guidelines for total
PCBs are much higher than the concentrations observed in
this study, suggesting rather lower toxicological effect
caused by PCBs contamination in the sediment of Mekong
River. Besides, considering the fact that so far, no treatment
facility for municipal and industrial discharges is available in
MRD, there should be concerns toward potential pollution
of several other organic contaminants such as antibiotics
and surfactants which are also present in these discharges.
Therefore, further studies toward possible adverse effects
of total organic pollutants in the Mekong River sediments
using toxicity tests (Lan et al., 2000; Chapman et al., 2002)
may be necessary to provide more comprehensive risk
assessment.

4. Conclusions
This study has demonstrated DDTs and PCBs as two
major organochlorine contaminants in the Mekong River

in South Vietnam. Furthermore, urban areas along the river
are apparent major pollution sources of such chemicals to
the aquatic environment. Although DDT was officially
phased out in Vietnam, the results provided evidence for
recent inputs of DDTs into the river sediment. Toxicological assessment suggests that in general, the concentrations
of PCBs are below the Canadian guidelines, while concentrations of DDTs in some sediments exceed those levels.
More comprehensive studies would be needed in order to
clarify the pathways of inputs of DDT to the aquatic
environment as well as to investigate further contamination by other organic pollutant groups such as dioxinrelated compounds, polybrominated diphenyl ethers and
surfactants.

Acknowledgements
This study was supported by a Grant-in-Aid from
the Scientific Research on Priority Areas (Project No.
13027101) of the Japanese Ministry of Education, Science,
Sports, Culture and Technology and by Scientific Research
(Project No. 12308030) of Japan Society for the Promotion
of Science (JSPS). Financial assistance was also provided
by Research Revolution 2002 (RR 2002) project for Sustainable Coexistence of Human, Nature and the Earth
(FY 2002) of the MEXT of the Japanese Government;
the Core University Program between Japan Society for
the Promotion of Science (JSPS) and National Center for
Natural Science and Technology, Vietnam (NCST) and
‘‘21st Century COE Program’’ from the Japanese Ministry
of Education, Science, Sports, Culture and Technology.
The authors also wish to thank Dr. A. Subramanian
(Ehime University) for the critical reading of this manuscript and to thank the staff of Nong Lam University,
Hochiminh City, Vietnam for their valuable support during our sampling surveys.
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