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]; http://www.pops 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 (shinsuke@agr.ehime-u.ac.jp) 2700 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]; http://www.eco-web.com/register/02769.html) 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 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 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 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 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 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 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 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 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 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 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 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 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 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 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 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 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 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]; 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 Organization (FAO) ([32]; http://faostat.fao.org/faostat/form? 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 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 REFERENCES Colborn T, vom Saal FS, Soto AM 1993 Developmental effects of endocrine-disrupting chemicals in wildlife and humans Environ Health Perspect 101:378–384 Cheek AO, Kow K, Chen J, McLachlan JA 1999 Potential mechanisms of thyroid disruption in humans: Interaction of organochlorine compounds with thyroid receptor, transthyretin, and thyroid-binding globulin Environ Health Perspect 107:273–278 Stockholm Convention on Persistent Organic Pollutants 2001 Report May 22 Geneva, Switzerland Sinh NN, Thuy LTB, Kinh NK, Thang LB 1999 The persistent organic pollutants and their management in Vietnam Proceedings, Regional Workshop on the Management of Persistent Organic Pollutants—POPs United Nations Environment Program, Hanoi, Vietnam, March 16–19, pp 385–406 Nhan DD, Carvalho FP, Am NM, Tuan NQ, Yen NTH, Villeneuve JP, Cattini C 2001 Chlorinated pesticides and PCBs in sediments and mollusks from freshwater canals in Hanoi, Vietnam Environ Pollut 112:311–320 Minh TB, Kunisue T, Yen NTH, Watanabe M, Tanabe S, Hue ND, Qui V 2002 Persistent organochlorine residues and their bioaccumulation profiles in resident and migratory birds from North Vietnam Environ Toxicol Chem 21:2108–2118 Minh NH, Someya M, Minh TB, Kunisue T, Watanabe M, Tanabe S, Viet PH, Tuyen BC 2004 Persistent organochlorine residues in human breast milk from Hanoi and Ho Chi Minh City, Vietnam: Contamination, accumulation kinetics, and risk assessment for infants Environ Pollut 129:431–441 Bignert A, Olsson M, Persson W, Jensen S, Zakrisson S, Litze´n K, Eriksson U, Haăggberg L, Alsberg T 1998 Temporal trends of organochlorines in Northern Europe, 1967–1995 Relation to global fractionation, leakage from sediments, and international measures Environ Pollut 99:177–198 Hites RA 2004 Polybrominated diphenyl ethers in the environment and in people: A meta-analysis of concentrations Environ Sci Technol 38:945–956 10 Hale RC, Guardia MJL, Harvey EP, Gaylor MO, Mainor TM, Duff WH 2001 Persistent pollutants in land-applied sludges Nature 412:140–141 Environ Toxicol Chem 25, 2006 2707 11 Darnerud PO 2003 Toxic effects of brominated flame retardants in man and in wildlife Environ Int 29:841–853 12 Hakk H, Letcher RJ 2003 Metabolism in the toxicokinetics and fate of brominated flame retardants—A review Environ Int 29: 801–828 13 Watanabe I, Sakai S 2003 Environmental release and behavior of brominated flame retardants Environ Int 29:665–682 14 Mekong River Commission 2005 Mekong River Commission Environmental Training Kit Vientiane, Laos 15 Agusa T, Kunito T, Nakashima E, Minh TB, Tanabe S, Subramanian A, Viet PH 2003 Preliminary on trace element contamination in dumping sites of municipal wastes in India and Vietnam Journal de Physique (IV) 107:21–24 16 Minh NH, Minh TB, Watanabe M, Kunisue T, Monirith I, Tanabe S, Sakai S, Subramanian A, Sasikumar K, Viet PH, Tuyen BC, Tana T, Prudenteo M 2003 Open dumping site in Asian developing countries: A potential source of polychlorinated dibenzop-dioxins and polychlorinated dibenzofurans Environ Sci Technol 37:1493–1502 17 Andriesz P 2000 Aquaculture in Vietnam Global Aquaculture Advocate 3:36–38 18 Kajiwara N, Ueno D, Monirith I, Tanabe S, Pourkazemi M, Aubrey DG 2003 Contamination by organochlorine compounds in sturgeons from Caspian Sea during 2001 and 2002 Mar Pollut Bull 46:741–747 19 Ueno D, Kajiwara N, Tanaka H, Subramanian A, Fillmann G, Lam PKS, Zheng GJ, Muchitar M, Razak H, Prudente M, Chung KH, Tanabe S 2004 Global pollution monitoring of polybrominated diphenyl ethers using skipjack tuna as a bioindicator Environ Sci Technol 8:2312–2316 20 Kannan K, Tanabe S, Tatsukawa R 1995 Geographical distribution and accumulation features of organochlorines residues in fishes from tropical Asia and Oceania Environ Sci Technol 29: 2673–2683 21 Minh NH, Minh TB, Kajiwara N, Kunisue T, Subramanian A, Iwata H, Tanabe S, Tana TS, Baburajendran R, Karuppiah S, Viet PH, Tuyen BC 2006 Contamination by persistent organic pollutants in dumping sites of Asian developing countries: Implication of emerging pollution sources Arch Environ Contam Toxicol 50:474–481 22 Iwata H, Tanabe S, Sakai N, Nishimura A, Tatsukawa R 1994 Geographical distribution of persistent organochlorines in air, water, and sediments from Asia and Oceania and their implications for global redistribution from lower latitudes Environ Pollut 85: 15–33 23 Jacobs MN, Covaci A, Schepens P 2002 Investigation of selected persistent organic pollutants in farmed Atlantic salmon (Salmo salar), salmon aquaculture feed, and fish oil components of the feed Environ Sci Technol 36:2797–2805 24 Ramesh A, Tanabe S, Kannan K, Subramanian AN, Kumaran PL, Tatsukawa R 1992 Characteristic trend of persistent organochlorine contamination in wildlife from a tropical agricultural watershed, South India Arch Environ Contam Toxicol 23:26–36 25 Dodder NG, Strandberg B, Hites RA 2002 Concentrations and spatial variations of polybrominated diphenyl ethers and several organochlorine compounds in fishes from the Northeastern United States Environ Sci Technol 36:146–151 26 Oliver BG, Niimi AJ 1998 Trophodynamic analysis of polychlorinated biphenyl congeners and other chlorinated hydrocarbons in the lake Ontario ecosystem Environ Sci Technol 22:388– 397 27 Moon JW, Kim YB, Lee SI, Song H, Choi K, Jeong GH 2006 Distribution characteristics of polychlorinated biphenyls in crucian carp (Carassius auratus) from major rivers in Korea Chemosphere 62:430–439 28 Das B, Khan YSA, Das P, Shaheen SM 2002 Organochlorine pesticide residues in catfish, Tachysurus thalassinus (Ruppell, 1835), from the south patches of the Bay of Bengal Environ Pollut 120:255–259 29 Norena-Barroso E, Sima-Alvarez R, Gold-Bouchot G, ZapataPe´rez O 2004 Persistent organic pollutants and histological lesions in Mayan catfish Ariopsis assimilis from the Bay of Chetumal, Mexico Mar Pollut Bull 48:263–269 30 Johnston TA, Fisk AT, Whittle DM, Muir DCG 2002 Variation in organochlorine bioaccumulation by a predatory fish; gender, geography, and data analysis methods Environ Sci Technol 20: 4238–4244 2708 Environ Toxicol Chem 25, 2006 31 Canadian Council of Minister of the Environment 2003 Canadian quality guidelines for the protection of aquatic life Winnipeg, MB, Canada 32 Food and Agriculture Organization of The United Nations 2006 Food Balance sheet Statistic Division, Rome, Italy 33 Kannan K, Tanabe S, Quynh HT, Hue ND, Tatsukawa R 1992 Residue pattern and dietary intake of persistent organochlorine compounds in foodstuff from Vietnam Arch Environ Contam Toxicol 22:367–374 34 Zennegg M, Kohler M, Gerecke AC, Schmid P 2002 Polybrominated diphenyl ethers in whitefish from Swiss lakes and farmed rainbow trout Chemosphere 51:545–553 35 Rayne S, Ikonomou MG, Antcliffe B 2003 Rapidly increasing polybrominated diphenyl ether concentrations in the Columbia River system from 1992 to 2000 Environ Sci Technol 37:2847– 2854 36 Boon JP, Lewis WE, Tjoen-A-Choy MR, Allchin CR, Law RJ, de Boer J, Hallers-Tjabbes CC, Zegers BN 2002 Levels of po- N.H Minh et al 37 38 39 40 lybrominated diphenyl ether (PBDE) flame retardants in animals representing different trophic levels of the North Sea food web Environ Sci Technol 36:4025–4032 Easton MDL, Luszniak D, Geest ED 2002 Preliminary examination of contaminant loadings in farmed salmon, wild salmon, and commercial salmon feed Chemosphere 46:1053–1074 Monirith I, Nakata H, Tanabe S, Tana TS 1998 Persistent organochlorine residues in marine and freshwater fish in Cambodia Mar Pollut Bull 38:604–612 Nakata H, Hirakawa Y, Kawazoe M, Nakabo T, Arizono K, Abe Sh, Kitano T, Shimada H, Watanabe I, Li W, Ding X 2005 Concentrations and compositions of organochlorine contaminants in sediments, soils, crustaceans, fishes and birds collected from Lake Tai, Hangzhou Bay and Shanghai city region, China Environ Pollut 133:415–429 Guruge KS, Tanabe S, Fukuda M, Yamagishi S, Tatsukawa R 1997 Accumulation pattern of persistent organochlorine residues in common cormorants (Phalacrocorax carbo) from Japan Mar Pollut Bull 34:186–193  ... 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... N.H Minh et al Table Concentrations (ng/g lipid wt) of polybrominated diphenyl ethers (PBDEs) and persistent organochlorines in catfish and aquaculture feeds from Vietnama Body length Catfish. .. 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