DSpace at VNU: Contamination by polybrominated diphenyl ethers and persistent organochlorines in catfish and feed from Mekong River Delta, Vietnam

Environmental Toxicology and Chemistry, Vol. 25, No. 10, pp. 2700–2709, 2006
᭧ 2006 SETAC
Printed in the USA
0730-7268/06 $12.00 ϩ .00

CONTAMINATION BY POLYBROMINATED DIPHENYL ETHERS AND PERSISTENT
ORGANOCHLORINES IN CATFISH AND FEED FROM
MEKONG RIVER DELTA, VIETNAM
NGUYEN HUNG MINH,† TU BINH MINH,† NATSUKO KAJIWARA,† TATSUYA KUNISUE,† HISATO IWATA,†
PHAM HUNG VIET,‡ NGUYEN PHUC CAM TU,§ BUI CACH TUYEN,࿣ and SHINSUKE TANABE*†
†Center for Marine Environmental Studies, Ehime University, Bunkyo-cho 2-5, Matsuyama 790-8577, Japan
‡Hanoi National University, 334 Nguyen Trai Str., Thanh Xuan District, Hanoi, Vietnam
§Faculty of Agriculture, Ehime University, Tarumi 3-5-7, Matsuyama 790-8566, Japan
࿣Nong Lam University, Thu Duc District, Ho Chi Minh City, Vietnam
( Received 23 October 2005; Accepted 20 March 2006)
Abstract—Commercial feeds for aquaculture and catfish samples were collected from the Mekong River Delta, Vietnam, for
determination of polybrominated diphenyl ethers (PBDEs) and selected persistent organochlorines, including polychlorinated biphenyls (PCBs), DDT and its metabolites (DDTs), chlordane-related compounds (CHLs), hexachlorocyclohexane isomers (HCHs),
and hexachlorobenzene (HCB). The most abundant contaminants were DDTs, with concentrations ranging from 10 to 700 ng/g
lipid weight, followed by PCBs (1.0–80 ng/g), CHLs (Ͻ0.01–8.2 ng/g), PBDEs (0.12–3.7 ng/g), HCHs (Ͻ0.03–5.1 ng/g), and
HCB (Ͻ0.07–3.2 ng/g). Polybrominated diphenyl ethers were detected in all samples, suggesting their widespread contamination
in the region. However, PBDE contamination levels in the present catfish specimens were low in comparison to levels worldwide.
Interestingly, residue levels of all the contaminants were significantly higher in catfish collected near a municipal dumping site
compared to farmed catfish. This suggests that runoffs from the dumping site during floods and rains may have brought pollutants
to the surrounding areas. Contamination pattern in aquaculture feeds revealed elevated levels of PCBs and PBDEs in samples from
foreign companies, perhaps implying their higher residues in some imported ingredients. Congener profiles of PBDEs and PCBs
demonstrated similarity between the farmed catfish and the aquaculture feeds, suggesting these feeds as a major source of pollution
to the farmed catfish. On the other hand, the PBDE and PCB profiles in the dumpsite catfish are clearly different from those of
the farmed catfish, revealing their exposure to different sources. Risk assessment showed significantly higher intake of the contaminants by people who eat catfish cultured near the dumping areas. Further investigation regarding fate and occurrence of the
contaminants in dumping sites is necessary.
Keywords—Polybrominated diphenyl ethers

Organochlorines

Fish

Aquaculture feed

Dumping site

continued until 1995, when its application was officially
banned. Despite this fact, several monitoring studies have indicated that contamination by such chemicals in Vietnam has
been continuing until recently [5–7]. Therefore, it is important
to continue monitoring the trend of OC contamination in the
environment as well as to identify their possible pollution
sources so that better management would be achieved.
Whereas levels of OCs in the environment seem to decrease
in some regions [8], the group of organobromine contaminants,
especially the polybrominated diphenyl ethers (PBDEs), appear to build up their residues in the environment and food
chains [9]. Polybrominated diphenyl ethers are used in a wide
variety of commercial and household products, such as plastics, textiles, and electronic appliances, including computers,
televisions, and so on. Moreover, experimental studies show
that PBDEs can be emitted from these products [10]. Research
concerning their temporal trend in humans and wildlife revealed their concentrations were doubled every four to six
years [9]. Public concerns seem to be increasing as more toxicological studies of animals show damage to nervous and
reproductive systems, as well as endocrine disruption and cancer induction, following exposure to high doses of PBDEs
[11,12]. In Asia, use of PBDEs was approximately 25,000 tons
in the year 2001, accounting for 40% of the global consumption [13]. Most of the scientific publications regarding contamination, potential sources, and pathways of PBDEs in Asia

INTRODUCTION

Persistent organochlorines (OCs) are large groups of chemicals that were widely used for various applications in agriculture and industry during the past several decades. Because

these chemicals are persistent, semivolatile, and highly bioaccumulative, they distribute ubiquitously in the global environment and can be detected at all levels of food chains, including humans. Several OCs are classified as persistent organic pollutants (POPs) and also are a matter of public concern
because of their ability to alter normal functions of endocrine
and reproductive systems in humans and wildlife [1,2]. Recognition of these consequences has led to international efforts
toward reducing emissions and banning 12 relevant POPs, including polychlorinated dibenzo-p-dioxins, polychlorinated
dibenzofurans, polychlorinated biphenyls (PCBs), DDT and
its metabolites (DDTs), chlordane-related compounds (CHLs),
hexachlorobenzene (HCB), and so on ([3]; s.
int/documents/convtext/convtext࿞en.pdf).
In Vietnam, OC pesticides were used for more than 30 years
to protect agricultural crops as well as to fight malaria. Sinh
et al. [4] reported that before 1985, approximately 6,000 to
9,000 tons per year of OC pesticides were used in Vietnam
for agriculture. In addition, use of DDT for vector control
* To whom corresponding may be addressed
().
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Environ. Toxicol. Chem. 25, 2006

PBDEs and persistent organochlorines in catfish from Vietnam

have been limited to some East Asian countries. Very few
studies have been carried out in other parts of Asia, including
southeastern Asia, where a number of rapidly developing countries are situated.
The Mekong River Delta (MRD) in southern Vietnam is
one of the most densely populated areas in the world. Approximately, 20 million people live in municipal areas and
industrial zones along the Mekong River. In this region, most
of the sewage is discharged directly into the environment ([14];
In addition,

household solid wastes and electronic appliances are abandoned in open dumping sites with very poor management.
Several studies have suggested such discharges as potential
sources of various anthropogenic pollutants, including OCs
and PBDEs, to the environment [10,15,16]. Lack of proper
waste management in many open dumping sites may redistribute such contaminants into the environment. Thus, evaluating the possible influence of such open dumping sites to
the surrounding environment is necessary.
Catfish aquaculture is a very common practice in the MRD,
which has rapidly developed and become an important economic sector. Production of catfish has doubled every two
years since 1995, reaching 120,000 tons in 2001 [17]. Understanding contamination status in the catfish is thus important to assess the possible health risk to catfish consumers. In
addition, because of the wide distribution of catfish in the
region, examining their contamination profile could provide
information regarding pollution sources and accumulation
characteristics in aquatic biota. In the present study, we collected catfish from the MRD for analysis of PBDEs as well
as some OCs, such as PCBs, DDTs, CHLs, HCB, and HCHs.
The catfish samples included farmed catfish as well as catfish
from ponds located near an open dumping site of Can Tho
City, Vietnam. We anticipated that runoffs from that site might
have brought contaminants to the surrounding environment;
thus, analyzing catfish near the dumping site would provide
information for further assessments. Our primary objectives
were to elucidate contamination status and sources of PBDEs
and selected OCs in fish as well as to assess their potential
risk to aquatic biota and humans.
MATERIALS AND METHODS

Sample collection
Twenty farmed catfish (Pangasianodon hypophthalmus)
were collected from the Can Tho and Cao Lanh provinces of
Vietnam during May 2004. The farmed catfish are reared in
large cages submerged in the river or in ponds near the river

and fed with formulated diets. We also collected five catfish
(Clarias sp.) in ponds located near a municipal dumping site
(referred to hereafter as dumpsite catfish) in Can Tho City.
These ponds were suspected to receive leachate and runoff
from the dumping site during floods and rain events. In general,
the dumpsite catfish were slightly smaller than the farmed
catfish.
Five samples of commercial feeds also were collected from
the local markets for the present study. Of these, three were
produced by domestic companies (feeds A, B, and C) and two
by foreign companies. More details regarding the feed samples
are given in Results and Discussion. All the catfish and feed
samples were kept in polyethylene bags and preserved with
dry ice during transport to our laboratory, where they were
stored at Ϫ20ЊC until chemical analysis.

2701

Analytical methods
Organochlorines were analyzed following the procedure described by Kajiwara et al. [18]. Briefly, 15 g of sample (skinned
muscle or homogenized feed) were ground with Na2SO4 and
extracted using a Soxhlet apparatus with a mixture of diethyl
ether and hexane (3:1). The aliquot of extract was concentrated
to 10 ml, and a 2-ml portion was used for determination of
fat content using a gravimetric method. The remaining volume
was evaporated under a gentle nitrogen stream down to 5 ml,
and dichloromethane (5 ml) was added before the sample was
subjected to gel permeation chromatography for fat removal.
The first fraction, containing lipids and eluted with 120 ml of
solvent, was discarded, and the following 100-ml eluate containing the OCs was collected and concentrated to 3 ml. The

concentrate was then added to a glass column packed with 12
g of activated Florisil (Wako-gel S-1; Wako Pure Chemical
Industries, Osaka, Japan) for separation of PCBs and OC pesticides. A procedural blank was run for every batch of five
samples to verify cross-contamination. Polychlorinated biphenyls, DDTs, HCHs, CHLs, and HCB were quantified using a
gas chromatograph with an electron-capture detector (Agilent
6890N; Agilent Technologies, Wilmington, DE, USA) using
a DB-1 fused silica capillary column (length, 30 m; inner
diameter, 0.25 mm; film thickness, 0.25 ␮m). The column oven
temperature was programmed as follows: 60ЊC for 1 min, increased to 160ЊC at a rate of 20ЊC/min, held for 10 min, then
increased to 260ЊC at a rate of 2ЊC/min and held for 20 min.
The PCB standard used for quantification was a mixture of 62
PCB congeners obtained from Wellington Laboratories
(Guelph, ON, Canada). Concentrations of individually resolved peaks of PCB isomers and congeners were summed to
obtain total PCB concentrations. Recovery rates of the target
chemicals through this analytical method were between 80 to
110%. Concentrations were not corrected for recovery rates
and expressed as ng/g on a lipid-weight basis unless specified
otherwise.
Polybrominated diphenyl ethers were analyzed following
the method described by Ueno et al. [19]. Fish muscle and
feed (15 g) were extracted by a Soxhlet apparatus and determined for lipid content as explained above. The aliquot (5 ml),
before being subjected to gel permeation chromatography, was
spiked with 5 ng of [13C]brominated diphenyl ether (BDE)
congeners (including BDEs 3, 15, 28, 47, 99, 153, 154, 183,
197, 207, and 209 as surrogates). The gel permeation chromatographic fraction containing organohalogens was concentrated and passed through a column packed with 1.5 g of
activated Wako-gel S-1 for cleanup and fractionation. Polybrominated diphenyl ethers and PCBs were eluted with 80 ml
of 5% dichloromethane in hexane. Isotope congener [13C]BDE
139 was added to the final solution as an internal standard
before quantification by gas chromatography with mass-selective detection. Quantification was performed using a gas chromatograph (Agilent 6890N) equipped with a mass-selective
detector (Agilent 5973) for mono- to hepta-BDEs and using

a gas chromatograph (Agilent 6890N) coupled with a massselective detector (GC-Mate II; Jeol, Tokyo, Japan) for decaBDE. Recovery of 13C-labeled BDEs ranged between 60 and
120%. Concentrations of major PBDE congeners, including
BDEs 3, 15, 28, 47, 99, 100, 138, 153, 154, 183, 196, 197,
206, 207, and 209, were summed to obtain the total concentration of PBDEs. The detection limit was calculated as threefold the procedural blank (0.02 ng/g for mono- to di-BDEs,


2702

Environ. Toxicol. Chem. 25, 2006

N.H. Minh et al.

Table 1. Concentrations (ng/g lipid wt) of polybrominated diphenyl ethers (PBDEs) and persistent organochlorines in catfish and aquaculture
feeds from Vietnama
Body
length
Catfish
Common catfish
(n ϭ 20)
Dumpsite catfish
(n ϭ 5)
Aquaculture feed
Feed A (Vietnam)
Feed B (Vietnam)
Feed C (Vietnam)
Feed D (foreign country)
Feed E (foreign country)
Mean (all feeds)
a

30
(29–32)
28
(25–30)
—
—
—
—
—
—

Lipid
(%)

⌺PBDEs

⌺PCBs

3.8
0.77**
7.2**
(0.6–7.2) (0.12–1.4) (0.91–27)
3.6
2.7**
50**
(3.2–4.1) (1.4–3.7)
(37–77)
3.4
3.7
3.3

3.4
3.3
3.4

0.35
0.94
1.5
3.7
7.0
2.7

6.3
3.3
12
20
25
13

⌺DDTs

⌺CHLs

59**
0.62**
(7.9–150) (Ͻ0.01–2.6)
5.7**
390**
(4.2–8.2)
(330–700)
22

6.9
47
40
36
30

1.7
0.27
2.3
5.2
2.6
2.4

⌺HCHs

0.47*
(Ͻ0.03–1.5)
2.2*
(0.86–5.1)
0.46
5.7
3.5
25
7.7
8.5

HCB

0.73**
(Ͻ0.07–1.8)

2.6**
(2.4–3.2)
0.38
1.0
1.3
2.4
1.2
1.3

PCBs ϭ polychlorinated biphenyls; DDTs ϭ DDT and its metabolites; CHLs ϭ chlordane-related compounds; HCHs ϭ hexachlorocyclohexane
isomers; HCB ϭ hexachlorobenzene. ⌺DDTs ϭ p,p-dichlorodiphenyldichloroethylene ϩ p,pЈ-dichlorodiphenyldichlorethane ϩ p,pЈ-dichlorodiphenyltrichloroethane; ⌺CHLs ϭ trans-chlordane ϩ cis-chlordane ϩ trans-nonachlor ϩ cis-nonachlor; ⌺HCHs ϭ ␣-HCH ϩ ␤-HCH ϩ ␥HCH. Values in parentheses represent the range. Asterisks indicate a significant difference between two fish categories (* p Ͻ 0.05, ** p Ͻ
0.01).

0.1 ng/g for tetra-BDE, 0.05 ng/g for tri- and penta- to heptaBDEs, 0.06 ng/g for octa- to nona-BDEs, and 4 ng/g for decaBDE). The same solutions used for PBDE analysis also underwent gas chromatography–mass spectrometry for determination of specific PCB congeners according to the procedure
described by Minh et al. [6].

Statistical analysis
Statistical analysis was performed with StatView software
(Ver 5; SAS Institute, Cary, NC, USA). The Mann–Whitney
U test was used to examine statistical differences between
groups (p Ͻ 0.05). Spearman’s rank correlation test was used
to examine significance of correlations between residue levels
of the contaminants.
RESULTS AND DISCUSSION

Contamination by PBDEs in catfish and aquaculture feeds
In the present study, residue levels of all contaminants did
not significantly correlate with gender and body size of fish
(data not shown). Therefore, data of all the male and female
fish were pooled for the interpretation. Polybrominated diphenyl ethers were found in most of the catfish and feed samples, suggesting their widespread contamination in the aquatic

environment. Total concentration of PBDEs was the sum of
six major congeners, including BDEs 47, 99, 100, 153, 154,
and 183. Other congeners, from mono- to tri-BDEs and octato deca-BDEs, could not be quantified in most of the samples
(see Analytical methods for details of detection limits). Mean
concentrations of PBDEs in the farmed catfish and the dumpsite catfish were 0.77 and 2.7 ng/g, respectively (Table 1).
Interestingly, concentrations of PBDEs in the dumpsite catfish
were statistically higher compared to those in the farmed catfish, suggesting additional exposure of the dumpsite catfish to
PBDEs. It is noteworthy that the dumpsite catfish were collected from ponds located in the vicinity of the Can Tho dumping site. In this dumping site, municipal wastes, including
household goods and small electrical appliances, which may
contain PBDEs as flame retardants, were dumped. Under ambient conditions, PBDEs may be emitted from such materials
and contaminate dumping-site soil. Therefore, it is anticipated
that runoff and leachate from the dumping site during flood

and rains, in turn, may have carried PBDEs to the vicinity,
causing higher contamination in the catfish.
Polybrominated diphenyl ether residue levels in the feed
samples were relatively variable. For example, three feeds
from Vietnamese companies (feeds A, B, and C) contained
residues of PBDEs below 1.5 ng/g, whereas feeds D and E
from foreign companies contained 3.7 and 7.0 ng/g of PBDEs,
respectively. Worldwide data regarding contamination by
PBDEs seemingly demonstrates that PBDE levels in North
America are one to two orders of magnitude higher compared
to levels in Japan and Europe [9]. Some ingredients used for
feeds D and E were imported from foreign industrialized countries and, hence, might have contained more PBDEs residues
and, potentially, caused higher PBDE concentrations in the
ultimate products (the feeds).
Geographical comparison of PBDEs in various fish species
is given in Table 2. Although differences in fish species confounded the comparison because of variations in age, habitat,
food, and metabolic capacity, PBDE levels in our fish samples

were approximately two to three orders of magnitude lower
compared to levels in the United States and Europe, approximately one order of magnitude lower compared to levels in
Japan and the East China Sea, and comparable to those levels
near Indonesia and in the Bay of Bengal. This result probably
is in agreement with the observation suggesting less contamination by these brominated contaminants in southeast Asian
countries compared to other countries around the East China
Sea, such as China, Hong Kong, Taiwan, and Japan [19]. The
reason for the lower contamination of PBDEs in Southeast
Asia may be fewer emission sources of these chemicals, such
as release from manufacture and consumption of PBDE products, in the region [19].

Contamination by OCs in catfish and aquaculture feeds
Organochlorines were detected in all the samples, including
the farmed catfish, the dumpsite catfish, and the commercial
feeds. The contamination pattern was consistently as follows:
DDTs Ͼ PCBs Ͼ CHLs Ͼ HCB Ͼ HCHs. However, OC concentrations generally were higher in the dumpsite catfish compared to those in the farmed catfish (Table 1). The pattern in
the present study clearly demonstrates DDTs and PCBs as two


Environ. Toxicol. Chem. 25, 2006

PBDEs and persistent organochlorines in catfish from Vietnam

2703

Table 2. Geographical comparison of polybrominated diphenyl ether (PDDE) concentrations (ng/g lipid wt) in fish species and
aquaculture feedsa
Location

Species

Year

BDE 47

BDE 99

24
227
59
6.6
0.22
0.76

Freshwater fish
Switzerland
Columbia River, USA
Great Lakes,
North America
Kootenay River, USA
Can Tho, Vietnam
Can Tho, Vietnam

Whitefish
Whitefish
Several species
Suckers
Farmed catfish
Dumping site catfish

2002
2000
1999
2000
2004
2004

44.3
179
208
2,110
0.36
0.65

Marine fish
Bay of Bengal
East China Sea
Japan Sea
Off-Indonesia
Off-Philippines
Off-Taiwan
South China Sea
North Sea

Skipjack tuna
Skipjack tuna
Skipjack tuna
Skipjack tuna
Skipjack tuna
Skipjack tuna

Skipjack tuna
Several species

1998
1997
1997
1999
1997
1998
2001
1999

0.88
12
8.0
1.1
5.9
18
7.9
48

Aquaculture feed
Can Tho, Vietnam
Vancouver, Canada
Europe

Aquaculture feed
Aquaculture feed
Aquaculture feed

2004
1999–2000
1999

a

—
3.6
2.0
—
2.1
4.7
3.0
11

1.1
3.3
9.5

1.0
0.69
1.6

BDE
100

BDE
153

4.63 1.21

68.8 32.9
45.5 14.7
24.4
461
0.07 0.03
0.18 0.43

BDE
154

⌺PBDEs

Reference

1.52
20
40.4
168
0.04
0.19

75.6
527
368
2,770
0.77
2.7

[34]
[35]

[25]
[35]
Present study
Present study

0.21
3.9
2.9
0.41
1.5
9.2
2.1
14

0.25
2.0
1.5
0.43
0.90
4.2
1.7
1.2

0.32
5.8
5.1
1.1
2.4
16
5.7

3.4

1.7
27
20
3.0
13
52
20
77

[19]
[19]
[19]
[19]
[19]
[19]
[19]
[36]

0.24
0.53
1.5

0.17
0.38
—

0.13
0.18

—

2.7
5.1
12

Present study
[37]
[23]

BDE ϭ brominated diphenyl ether; — ϭ data not available.

abundant contaminant groups in the environment. In fact, this
observation agrees with those in previous studies of water,
sediments, mussels, birds, and human breast milk collected
from Vietnam [5–7]. However, concentrations of DDTs and
PCBs in the farmed catfish of the MRD were, perhaps, one to
two orders of magnitude lower compared to concentrations in
fish collected during the early 1990s from the coast of Vietnam
[20] and in 1997 from the Red River Delta in northern Vietnam
[6]. This result supports the previous assumption that input of
DDT and PCBs to the environment of Vietnam has consistently
decreased over the last decade [7].

Geographical comparison of DDTs and PCBs in fish demonstrates that their levels in the dumpsite catfish are in the
middle range, whereas those in the farmed catfish are low
(Table 3). It is noteworthy that in this comparison, many fish
samples collected during the early 1990s, when DDT was still
in use, had levels of DDTs and PCBs comparable to those in
the dumpsite catfish. This may suggest very recent exposure

of the dumpsite catfish to the pollutants. Recently, Minh et al.
[21] reported high residue levels of OCs in several open dumping sites, suggesting that they are important sources of OCs.
Bearing in mind that these catfish were collected from ponds

Table 3. Geographical comparison of organochlorine concentrations (ng/g lipid wt) in fish species and aquaculture feedsa
Location

Species

Year

Tissue

Freshwater fish
Cambodia
Cambodia
China (Shanghai)
India
Japan (Lake Biwa)
Thailand
Vietnam, 1995
Vietnam, 2002
Vietnam, 2004
Vietnam, 2004

Several species
Several species
Several species
Several species
Several species

Several species
Several species
Several species
Farmed catfish
Dumpsite catfish

1998
1998
2000
1989–1993
1993
1989–1993
1989–1993
1997
2004
2004

Whole body
Whole body
Whole body
Muscle
Whole body
Muscle
Muscle
Whole body
Muscle
Muscle

Marine fish
Australia

Indonesia
North America
North America
Europe

Several species
Several species
Farmed salmon
Wild salmon
Farmed salmon

1989–1993
1989–1993
1999–2000
1999–2000
1999–2001

Muscle
Muscle
Muscle
Muscle
Muscle

Aquaculture feed
Can Tho, Vietnam
Vancouver, Canada
Europe

Aquaculture feed
Aquaculture feed

Aquaculture feed

2004
1999–2000
1999

Feed
Feed
Feed

a

PCBs

10
7.5
180
150
3,700
30
530
110
7.2
50
1,600
86
340
81
145–460
3.3–25

70–560
76–1,200

DDTs

HCHs

290
100
1,000
630
1,900
120
1,400
4,200
59
390

1.5
1.7
68
1,200
240
15
95
120
0.47
2.2

650

930
191
77
5–250
6.9–40
60–320
34–52

10
24
—
—
ND–23
0.46–25
2.9–13.3
2.4–46.8

Reference

[38]
[38]
[39]
[20]
[40]
[20]
[20]
[6]
Present study
Present study
[20]

[20]
[37]
[37]
[23]
Present study
[37]
[23]

PCBs ϭ polychlorinated biphenyls; DDTs ϭ DDT and its metabolites; HCHs ϭ hexachlorocyclohexane isomers; ND ϭ not detected; — ϭ
data not available.


2704

Environ. Toxicol. Chem. 25, 2006

located in the vicinity of the Can Tho dumping site, we could
assume that runoff and leachate from the dumping site may
have carried OC residues to these vicinities and, consequently,
caused additional exposure of fish to the pollutants.
Concentrations of HCHs, CHLs, and HCB were lower than
10 ng/g (Table 1), suggesting that they are not significant contaminants in the MRD. Compared to their levels during the
early 1990s [22], residues of such pollutants in the present fish
samples were approximately one to two orders of magnitude
lower. The trend showing higher contamination by these pollutants in the dumpsite catfish than in the farmed catfish also
was observed, implying similar influence of the dumping site
for these chemicals, as in the case of DDTs and PCBs. The
geographical comparison shows that concentrations of HCHs
in our catfish are relatively low (Table 3). These facts suggest
less input of such pollutants to the environment during recent

years.
The five commercial feeds in the present study showed
relatively similar levels of OCs. These levels are comparable
to those in the farmed catfish but much lower than those in
the dumpsite catfish. This result, perhaps, supports our earlier
finding that the dumpsite catfish may be exposed to pollution
sources in addition to aquaculture feeds. Interestingly, feeds
with different origins show somewhat different residue levels
of OCs. For instance, feeds D and E from foreign companies
contained levels of PCBs higher than those in feeds from domestic companies (Table 1). Perhaps higher PCBs residues in
the ingredients imported from foreign countries for production
of these feeds have caused the phenomenon. Although HCHs
showed moderate levels in feeds, less accumulation of these
contaminants was observed in the farmed catfish. Jacobs et al.
[23] found a similar phenomenon, with higher HCH levels in
aquaculture feeds than in farmed salmon in Europe. Lower
hydrophobicity and higher volatility of HCHs may be the reasons for their lower accumulation in fish compared with OCs,
such as DDTs and PCBs [22,24]. In the geographical comparison, residues of DDTs in the feeds of the present study
are comparable to those in Europe and slightly lower than
those in North America (Table 3). On the other hand, PCBs
residues seem to be lower in Vietnam than at the above locations (Table 3).

Composition of the contaminants
Congener profiles of six major PBDEs found in catfish and
feeds of the present study are shown in Figure 1. Generally,
in the dumpsite catfish, BDE 99 was the most abundant congener, accounting for 29%, followed by BDEs 47, 153, and
183. On the other hand, BDE 47 had the highest contribution
(46%) in the farmed catfish, followed by BDEs 99, 100, and
154. Some congeners, such as BDEs 153, 154, and 183, were
slightly lower in the farmed catfish compared to the dumpsite

catfish. To clarify the usage pattern of PBDEs in Vietnam, the
composition of PBDEs in all the catfish from Vietnam were
compared with those in commercial products, such penta-,
octa-, and deca-BDE products. The result showed the presence
of all representative congeners for penta-product (BDEs 47,
99, and 100) as well as those for octa-product (BDE 183) [9],
hence suggesting the usage of these products in Vietnam. Alternatively, no quantifiable level of BDE 209, the representative congener for deca-product, was found. Therefore, it is
not yet clear to what extent deca-product has been used in
Vietnam. Nevertheless, it should be noted that because of low
bioaccumulative ability, BDE 209 often is not found in bio-

N.H. Minh et al.

Fig. 1. Polybrominated diphenyl ether congener profiles in dumpsite
catfish (DS-Catfish), farmed catfish (C-Catfish), and commercial feeds
(feeds B and C were from Vietnam, and feeds D and E were imported
from other countries).

logical samples [18,19]. In this context, other environmental
matrices, such as soil and sediment, should be investigated to
elucidate the presence of deca-product in Vietnam.
Interestingly, differences between the profiles in the dumpsite catfish and in the farmed catfish were observed, with higher
contributions of less volatile congeners, such as BDEs 99, 153,
and 183, in the dumpsite catfish. Dodder et al. [25] pointed
out that fish collected near sources of PBDEs contained higher
proportions of the less volatile congeners compared with fish
from remote areas, which were considered as background fish.
This phenomenon probably results from lower mobility of the
less volatile and heavier congeners in the environment. Therefore, the higher abundance of heavier congeners, such as BDEs
99, 153, and 183, in the dumpsite catfish, may be caused by

their proximity to PBDEs pollution sources from the neighboring dumping site. In contrast, the highest abundance of
BDE 47 in the farmed catfish may reflect that their exposure
is close to background levels [25].
Figure 2 demonstrated congener profiles of PCBs in three
sample groups. In these profiles, the relative abundance of each
congener was normalized to that of PCB 153 for comparison.
The profile of the farmed catfish is similar to those of the
feeds, except that it shows less accumulation of tetra- and
pentachlorinated biphenyls in the farmed catfish. In contrast,
the PCB profile in the dumpsite catfish was different compared
to those in the feeds and the farmed catfish. This represents
important evidence that the aquaculture feed is the major
source of PCBs to the farmed catfish, whereas other sources
have a strong influence on the PCB contamination in the dumpsite catfish. The relative lower abundance of tetra- and pentachlorinated biphenyls in the farmed catfish compared to the
feeds may result from a stronger bioaccumulative ability of


PBDEs and persistent organochlorines in catfish from Vietnam

Environ. Toxicol. Chem. 25, 2006

2705

Fig. 2. Polychlorinated biphenyl congener profiles in commercial feeds, farmed catfish, and dumpsite catfish (Number 4Cl–10Cl indicate degrees
of chlorination from tetra- to decachlorinated biphenyls; numbers under the x axis indicate the International Union of Pure and Applied Chemistry
numbers of polychlorinated biphenyl congeners).

higher-chlorinated congeners, such as PCBs 138 and 153, in
fish [26]. On the other hand, specific profile in the dumpsite
catfish with low contributions of tetra- and pentachlorinated

biphenyls could be the result of the characteristics of pollution
sources [27], which were suspected in the present study to be
runoff from the nearby dumping site as well as from human
habitat.
Patterns of DDTs in the farmed catfish, the dumpsite catfish,
and the feeds are shown in Figure 3. The composition of DDTs

appears to be slightly different in the two categories of catfish,
showing p,pЈ-DDT to be slightly higher in the dumpsite catfish.
On the other hand, the composition in feeds is somewhat different, showing the proportion of p,pЈ-DDT as being up to
40% in one sample from Vietnam. This result thus indicates
that some feeds might contain relatively high residues of DDT,
making them a pollution source to the aquaculture fish. Besides, Minh et al. [21] reported the proportion of p,pЈ-DDT as
ranging from 15 to 40% in dumping-site soils collected from
cities in Vietnam. This range is only comparable to those in
the commercial feeds. These facts may explain the relatively
comparable proportion of p,pЈ-DDT between the farmed catfish and the dumpsite catfish. The composition of DDTs in
catfish of the present study is somewhat similar to those in
catfish collected from Bangladesh in 1997 [28] and from Mexico in 1996 [29].

Correlation among contaminants

Fig. 3. Composition of DDTs in commercial feeds (feeds A, B, and
C are from Vietnam, and feeds D and E were imported from other
countries), dumpsite catfish (DS-Catfish), and farmed catfish (C-Catfish).

Correlations among PBDEs and major OCs, including
PCBs and DDTs, were examined to further understand sources
of pollution to catfish. Significant correlations (p Ͻ 0.05) for
PCBs and DDTs, PBDEs and PCBs, and PBDEs and DDTs

were observed in the farmed catfish group (Fig. 4) but not for
the dumpsite catfish group (data not shown). Good correlations
among the contaminants in the farmed catfish may indicate
their exposure to the same pollution sources (perhaps mainly
via aquaculture feeds), but lack of correlations in the dumpsite
catfish group may imply their exposure to multiple pollution
sources [23]. In addition, the poor correlations in the dumpsite
group may be a result, in part, of the small sample size of the


2706

Environ. Toxicol. Chem. 25, 2006

N.H. Minh et al.

fish were caught during their early life stages (age, three to
four months).

Fig. 4. Correlation coefficients observed for polychlorinated biphenyls
(PCBs) and DDT and its metabolites (DDTs; line A), DDTs and polybrominated diphenyl ethers (PBDEs; line B), and PCBs and PBDEs
(line C).

dumpsite catfish analyzed during the present study (n ϭ 5).
Similarly, the correlations among aquaculture feeds showed
no significance among PBDEs, PCBs, and DDTs.

Influence of gender and age/body size of fish on
contamination levels
Fairly complex relationships exist among the factors influencing gender- and age-dependant levels of POPs in fish. Johnston et al. [30] suggested that male fish apparently had a higher

burden of contaminants than female fish at large body sizes
but not at small body sizes, probably because maturity of
female fish occurs at certain body sizes. Likewise, interpretation using means adjusted for age may give somewhat different results compared to interpretation with means adjusted
for body length because of the different growth rates at different life stages. Considering these factors, the lack of difference between male and female catfish as well as the poor
correlation between POP concentrations and catfish body size
in the present study probably resulted from their relatively
narrow range (29–36 cm for the farmed catfish), because these

Toxicological risk assessment
Production of the farmed catfish from large-scale culture
accounts for the major part of total catfish production in Vietnam. Alternatively, the production from ponds located near
municipal dumping sites is only very minor and entirely consumed by the local people. Nevertheless, the present results
demonstrate significantly higher levels of POPs in these dumpsite pond–cultured catfish and, thus, may raise concern regarding possible health risk for the local people who consume
these fish.
Concentrations of DDTs on a wet-weight basis ranged from
1.0 to 5.1 ng/g in the farmed catfish and from 3.2 to 29 ng/g
in the dumpsite catfish. Canadian guidelines to protect consumers of aquatic biota recommend a tolerance limit of 14
ng/g wet weight for total DDTs ([31]; />publications). In comparison to this guideline, only one sample
among the five dumpsite catfish exceeded the tolerance limit,
whereas all the farmed catfish samples had levels of DDTs
below this limit. This fact suggests a possible higher risk for
consumers of the dumpsite catfish but not for those who eat
the farmed catfish. Recently, the Food and Agriculture Organization (FAO) ([32]; />collection ϭ FBS&Domain ϭ FBS&ser vlet ϭ 1&hasbulk ϭ
0&versionϭext&languageϭEN) estimated that total fish consumption of the Vietnamese is approximately 50 g/person/d
for all kinds of fish (more than threefold higher than during
the early 1990s [33]). Using the recent consumption data with
an approach similar to that described previously by Kannan
et al. [33], intake of POPs by the Vietnamese via fish consumption was assessed. In general, the intake via dumpsite
catfish consumption was one order of magnitude higher than
that via the farmed catfish (Fig. 5). However, the intake of

OCs via these catfish was one to two orders of magnitude
lower compared to the estimated intake during the early 1990s
[33]. This result revealed decreasing intake of OCs in Vietnam
during the last decade. However, consumption of the dumpsite
catfish may cause additional exposure to various other contaminant groups, such as heavy metals and dioxin-related compounds [15,16]. These results suggest that assessment of human health risk caused by exposure to various pollutants from
an open dumpsite should be given more attention.
CONCLUSION

The present study demonstrated DDTs and PCBs as two
major groups of OCs in catfish cultured in the MRD. The other

Fig. 5. Comparison for intake of the contaminants via catfish consumption in two groups of people eating dumpsite catfish (exposed) and farmed
catfish (general). CHLs ϭ chlordane-related compounds; DDTs ϭ DDT and its metabolites; HCB ϭ hexachlorobenzene; HCHs ϭ hexachlorocyclohexane isomers; PCBs ϭ polychlorinated biphenyls.


PBDEs and persistent organochlorines in catfish from Vietnam

contaminants, such as PBDEs, CHLs, HCHs, and HCB, had
relatively low contamination levels, suggesting their insignificant contamination. Intake of OCs in Vietnam via fish consumption decreased during the last decade, probably by one
to two orders of magnitude. Interestingly, the contamination
pattern in fish also suggested the existence of local sources of
PBDEs and OCs, such as municipal dumping sites in the surrounding environment. To our knowledge, the present study
is the first comprehensive report of contamination by PBDEs
in the environment of Vietnam. Municipal dumping sites seem
to act as pollution sources for these chemicals to the ambient
environment; therefore, it is important to pay more attention
on the ecological impacts of enormous numbers of such dumping sites in Vietnam as well as in other developing Asian
countries. Our investigation of several commercial feeds suggested that some of them may contain higher residues of
PBDEs, depending on the country of origin. This may be another source of PBDEs to aquaculture.
Acknowledgement—This study was supported by the Research Revolution 2002 Project (RR 2002) for Sustainable Coexistence of Human, Nature, and the Earth of the Ministry of Education, Science,

Sports, Culture, and Technology, Japan (MEXT), and by Scientific
Research (project 16201014) of the Japan Society for the Promotion
of Science (JSPS). Financial assistance also was provided by the Core
University Program between Japan Society for the Promotion of Science and National Center for Natural Science and Technology, Vietnam, and 21st Century COE Program from MEXT and JSPS. The
authors also wish to thank A. Subramanian (Ehime University) for
the critical reading of this manuscript and the staff of Nong Lam
University (Ho Chi Minh City, Vietnam) for their valuable support
during our sampling surveys.
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