䉷 2006 SETAC Printed in the USA 0730-7268/06 $12.00 ⫹ .00 CONTAMINATION BY POLYBROMINATED DIPHENYL ETHERS AND PERSISTENT ORGANOCHLORINES IN CATFISH AND FEED FROM MEKONG RIVER DELTA, VIET
Trang 1䉷 2006 SETAC Printed in the USA 0730-7268/06 $12.00 ⫹ 00
CONTAMINATION BY POLYBROMINATED DIPHENYL ETHERS AND PERSISTENT
ORGANOCHLORINES IN CATFISH AND FEED FROM
MEKONG RIVER DELTA, VIETNAM
NGUYEN HUNG MINH,† TU BINHMINH,† NATSUKO KAJIWARA,† TATSUYAKUNISUE,† HISATO IWATA,†
PHAMHUNGVIET,‡ NGUYENPHUC CAMTU,§ BUICACH TUYEN, 㛳 and SHINSUKETANABE*†
†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 㛳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 bi-phenyls (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 (⬍0.01–8.2 ng/g), PBDEs (0.12–3.7 ng/g), HCHs (⬍0.03–5.1 ng/g), and HCB (⬍0.07–3.2 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 con-taminants 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
INTRODUCTION
Persistent organochlorines (OCs) are large groups of
chem-icals that were widely used for various applications in
agri-culture and industry during the past several decades Because
these chemicals are persistent, semivolatile, and highly
bioac-cumulative, they distribute ubiquitously in the global
envi-ronment and can be detected at all levels of food chains,
in-cluding humans Several OCs are classified as persistent
or-ganic 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]
Rec-ognition of these consequences has led to international efforts
toward reducing emissions and banning 12 relevant POPs,
in-cluding polychlorinated dibenzo-p-dioxins, polychlorinated
dibenzofurans, polychlorinated biphenyls (PCBs), DDT and
its metabolites (DDTs), chlordane-related compounds (CHLs),
hexachlorobenzene (HCB), and so on ([3]; http://www.pops
int/documents/convtext/convtext㛮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
(shinsuke@agr.ehime-u.ac.jp)
continued until 1995, when its application was officially banned Despite this fact, several monitoring studies have in-dicated 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), ap-pear 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 plas-tics, 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 re-vealed their concentrations were doubled every four to six years [9] Public concerns seem to be increasing as more tox-icological studies of animals show damage to nervous and reproductive systems, as well as endocrine disruption and can-cer 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 consump-tion [13] Most of the scientific publicaconsump-tions regarding con-tamination, potential sources, and pathways of PBDEs in Asia
Trang 2PBDEs and persistent organochlorines in catfish from Vietnam Environ Toxicol Chem 25, 2006 2701 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
coun-tries are situated
The Mekong River Delta (MRD) in southern Vietnam is
one of the most densely populated areas in the world
Ap-proximately, 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];
http://www.eco-web.com/register/02769.html) In addition,
household solid wastes and electronic appliances are
aban-doned 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
redis-tribute such contaminants into the environment Thus,
eval-uating 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
eco-nomic sector Production of catfish has doubled every two
years since 1995, reaching 120,000 tons in 2001 [17]
Un-derstanding contamination status in the catfish is thus
impor-tant 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
col-lected 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⫺20⬚C until chemical analysis
Analytical methods
Organochlorines were analyzed following the procedure de-scribed by Kajiwara et al [18] Briefly, 15 g of sample (skinned muscle or homogenized feed) were ground with Na2SO4and 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 con-taining 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 pes-ticides A procedural blank was run for every batch of five samples to verify cross-contamination Polychlorinated biphe-nyls, 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, 0.25m) The column oven temperature was programmed as follows: 60⬚C for 1 min, in-creased to 160⬚C at a rate of 20⬚C/min, held for 10 min, then increased to 260⬚C at a rate of 2⬚C/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 re-solved 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 deter-mined 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 chro-matographic fraction containing organohalogens was concen-trated and passed through a column packed with 1.5 g of activated Wako-gel S-1 for cleanup and fractionation Poly-brominated 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-selec-tive detection Quantification was performed using a gas chro-matograph (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 mass-selective detector (GC-Mate II; Jeol, Tokyo, Japan) for deca-BDE Recovery of13C-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 concen-tration of PBDEs The detection limit was calculated as three-fold the procedural blank (0.02 ng/g for mono- to di-BDEs,
Trang 3Table 1 Concentrations (ng/g lipid wt) of polybrominated diphenyl ethers (PBDEs) and persistent organochlorines in catfish and aquaculture
feeds from Vietnama
Body length
Lipid
Catfish
Common catfish
(n⫽ 20)
Dumpsite catfish
(n⫽ 5)
30 (29–32) 28 (25–30)
3.8 (0.6–7.2) 3.6 (3.2–4.1)
0.77**
(0.12–1.4) 2.7**
(1.4–3.7)
7.2**
(0.91–27) 50**
(37–77)
59**
(7.9–150) 390**
(330–700)
0.62**
(⬍0.01–2.6) 5.7**
(4.2–8.2)
0.47*
(⬍0.03–1.5) 2.2*
(0.86–5.1)
0.73** (⬍0.07–1.8) 2.6** (2.4–3.2) Aquaculture feed
Feed A (Vietnam)
Feed B (Vietnam)
Feed C (Vietnam)
Feed D (foreign country)
Feed E (foreign country)
Mean (all feeds)
—
—
—
—
—
—
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
22 6.9 47 40 36 30
1.7 0.27 2.3 5.2 2.6 2.4
0.46 5.7 3.5 25 7.7 8.5
0.38 1.0 1.3 2.4 1.2 1.3
aPCBs⫽ polychlorinated biphenyls; DDTs ⫽ DDT and its metabolites; CHLs ⫽ chlordane-related compounds; HCHs ⫽ hexachlorocyclohexane isomers; HCB⫽ hexachlorobenzene ⌺DDTs ⫽ p,p-dichlorodiphenyldichloroethylene ⫹ p,p⬘-dichlorodiphenyldichlorethane ⫹
p,p⬘-dichloro-diphenyltrichloroethane;⌺CHLs ⫽ trans-chlordane ⫹ cis-chlordane ⫹ trans-nonachlor ⫹ cis-nonachlor; ⌺HCHs ⫽ ␣-HCH ⫹ -HCH ⫹ ␥-HCH Values in parentheses represent the range Asterisks indicate a significant difference between two fish categories (* p ⬍ 0.05, ** p ⬍
0.01)
0.1 ng/g for tetra-BDE, 0.05 ng/g for tri- and penta- to
hepta-BDEs, 0.06 ng/g for octa- to nona-hepta-BDEs, and 4 ng/g for
deca-BDE) The same solutions used for PBDE analysis also
un-derwent gas chromatography–mass spectrometry for
deter-mination 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⬍ 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
di-phenyl ethers were found in most of the catfish and feed
sam-ples, 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
octa-to 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
dump-site 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
cat-fish, suggesting additional exposure of the dumpsite catfish to
PBDEs It is noteworthy that the dumpsite catfish were
col-lected from ponds located in the vicinity of the Can Tho
dump-ing site In this dumpdump-ing site, municipal wastes, includdump-ing
household goods and small electrical appliances, which may
contain PBDEs as flame retardants, were dumped Under
am-bient 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 coun-tries 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 con-founded 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, approx-imately 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 contam-ination 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 prod-ucts, 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⬎ PCBs ⬎ CHLs ⬎ HCB ⬎ HCHs However, OC con-centrations generally were higher in the dumpsite catfish com-pared to those in the farmed catfish (Table 1) The pattern in the present study clearly demonstrates DDTs and PCBs as two
Trang 4PBDEs and persistent organochlorines in catfish from Vietnam Environ Toxicol Chem 25, 2006 2703 Table 2 Geographical comparison of polybrominated diphenyl ether (PDDE) concentrations (ng/g lipid wt) in fish species and
aquaculture feedsa
BDE 100
BDE 153
BDE
154 ⌺PBDEs Reference 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
24 227 59 6.6 0.22 0.76
4.63 68.8 45.5 461 0.07 0.18
1.21 32.9 14.7 24.4 0.03 0.43
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 Marine fish
Bay of Bengal
East China Sea
Japan Sea
Off-Indonesia
Skipjack tuna Skipjack tuna Skipjack tuna Skipjack tuna
1998 1997 1997 1999
0.88 12 8.0 1.1
— 3.6 2.0
—
0.21 3.9 2.9 0.41
0.25 2.0 1.5 0.43
0.32 5.8 5.1 1.1
1.7 27 20 3.0
[19]
[19]
[19]
[19]
Off-Philippines
Off-Taiwan
South China Sea
North Sea
Skipjack tuna Skipjack tuna Skipjack tuna Several species
1997 1998 2001 1999
5.9 18 7.9 48
2.1 4.7 3.0 11
1.5 9.2 2.1 14
0.90 4.2 1.7 1.2
2.4 16 5.7 3.4
13 52 20 77
[19]
[19]
[19]
[36]
Aquaculture feed
Can Tho, Vietnam
Vancouver, Canada
Europe
Aquaculture feed Aquaculture feed Aquaculture feed
2004 1999–2000 1999
1.1 3.3 9.5
1.0 0.69 1.6
0.24 0.53 1.5
0.17 0.38
—
0.13 0.18
—
2.7 5.1 12
Present study [37]
[23]
aBDE⫽ brominated diphenyl ether; — ⫽ data not available
Table 3 Geographical comparison of organochlorine concentrations (ng/g lipid wt) in fish species and aquaculture feedsa
Freshwater fish
Cambodia
Cambodia
China (Shanghai)
India
Japan (Lake Biwa)
Several species Several species Several species Several species Several species
1998 1998 2000 1989–1993 1993
Whole body Whole body Whole body Muscle Whole body
10 7.5 180 150 3,700
290 100 1,000 630 1,900
1.5 1.7 68 1,200 240
[38]
[38]
[39]
[20]
[40]
Thailand
Vietnam, 1995
Vietnam, 2002
Vietnam, 2004
Vietnam, 2004
Several species Several species Several species Farmed catfish Dumpsite catfish
1989–1993 1989–1993 1997 2004 2004
Muscle Muscle Whole body Muscle Muscle
30 530 110 7.2 50
120 1,400 4,200 59 390
15 95 120 0.47 2.2
[20]
[20]
[6]
Present study Present study 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
1,600 86 340 81 145–460
650 930 191 77 5–250
10 24
—
— ND–23
[20]
[20]
[37]
[37]
[23]
Aquaculture feed
Can Tho, Vietnam
Vancouver, Canada
Europe
Aquaculture feed Aquaculture feed Aquaculture feed
2004 1999–2000 1999
Feed Feed Feed
3.3–25 70–560 76–1,200
6.9–40 60–320 34–52
0.46–25 2.9–13.3 2.4–46.8
Present study [37]
[23]
aPCBs⫽ polychlorinated biphenyls; DDTs ⫽ DDT and its metabolites; HCHs ⫽ hexachlorocyclohexane isomers; ND ⫽ not detected; — ⫽ 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 dem-onstrates 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 dump-ing sites, suggestdump-ing that they are important sources of OCs Bearing in mind that these catfish were collected from ponds
Trang 5Fig 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)
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
con-taminants 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
pol-lutants 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
do-mestic 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
rea-sons for their lower accumulation in fish compared with OCs,
such as DDTs and PCBs [22,24] In the geographical
com-parison, 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
lo-cations (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
con-gener, 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
Al-ternatively, no quantifiable level of BDE 209, the
represen-tative 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-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 dump-site 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 There-fore, 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 neigh-boring 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 dump-site catfish The relative lower abundance of tetra- and pen-tachlorinated biphenyls in the farmed catfish compared to the feeds may result from a stronger bioaccumulative ability of
Trang 6PBDEs 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)
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-Cat-fish)
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,p⬘-DDT to be slightly higher in the dumpsite catfish.
On the other hand, the composition in feeds is somewhat
dif-ferent, showing the proportion of p,p⬘-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
Be-sides, Minh et al [21] reported the proportion of p,p⬘-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,p⬘-DDT between the farmed
cat-fish and the dumpsite catcat-fish 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 Mex-ico in 1996 [29]
Correlation among contaminants
Correlations among PBDEs and major OCs, including PCBs and DDTs, were examined to further understand sources
of pollution to catfish Significant correlations (p⬍ 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
Trang 7Fig 4 Correlation coefficients observed for polychlorinated biphenyls
(PCBs) and DDT and its metabolites (DDTs; line A), DDTs and
po-lybrominated diphenyl ethers (PBDEs; line B), and PCBs and PBDEs
(line C)
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⫽ chlordane-related compounds; DDTs ⫽ DDT and its metabolites; HCB ⫽ hexachlorobenzene; HCHs ⫽ hexachloro-cyclohexane isomers; PCBs⫽ polychlorinated biphenyls
dumpsite catfish analyzed during the present study (n⫽ 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
influ-encing gender- and age-dependant levels of POPs in fish
John-ston 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,
interpre-tation using means adjusted for age may give somewhat
dif-ferent results compared to interpretation with means adjusted
for body length because of the different growth rates at
ferent life stages Considering these factors, the lack of
dif-ference 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
fish were caught during their early life stages (age, three to four months)
Toxicological risk assessment
Production of the farmed catfish from large-scale culture accounts for the major part of total catfish production in Vi-etnam Alternatively, the production from ponds located near municipal dumping sites is only very minor and entirely con-sumed by the local people Nevertheless, the present results demonstrate significantly higher levels of POPs in these dump-site pond–cultured catfish and, thus, may raise concern re-garding 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 con-sumers of aquatic biota recommend a tolerance limit of 14 ng/g wet weight for total DDTs ([31]; http://www.ccme.ca/ 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 Or-ganization (FAO) ([32]; http://faostat.fao.org/faostat/form? collection⫽FBS&Domain⫽FBS&servlet⫽1&hasbulk⫽ 0&version⫽ext&language⫽EN) estimated that total fish con-sumption 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 con-sumption 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 con-taminant groups, such as heavy metals and dioxin-related com-pounds [15,16] These results suggest that assessment of hu-man 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
Trang 8PBDEs and persistent organochlorines in catfish from Vietnam Environ Toxicol Chem 25, 2006 2707 contaminants, such as PBDEs, CHLs, HCHs, and HCB, had
relatively low contamination levels, suggesting their
insignif-icant contamination Intake of OCs in Vietnam via fish
con-sumption 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
sur-rounding 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
dump-ing sites in Vietnam as well as in other developdump-ing Asian
countries Our investigation of several commercial feeds
sug-gested that some of them may contain higher residues of
PBDEs, depending on the country of origin This may be
an-other source of PBDEs to aquaculture
Acknowledgement—This study was supported by the Research
Rev-olution 2002 Project (RR 2002) for Sustainable Coexistence of
Hu-man, 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
Sci-ence and National Center for Natural SciSci-ence and Technology,
Vi-etnam, 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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