DSpace at VNU: Persistent organochlorine residues and their bioaccumulation profiles in resident and migratory birds from North Vietnam

DSpace at VNU: Persistent organochlorine residues and their bioaccumulation profiles in resident and migratory birds fro...

q 2002 SETAC Printed in the USA 0730-7268/02 $9.00 1 00

PERSISTENT ORGANOCHLORINE RESIDUES AND THEIR BIOACCUMULATION PROFILES IN RESIDENT AND MIGRATORY BIRDS FROM NORTH VIETNAM

TU BINH MINH,† TATSUYA KUNISUE,† NGUYEN THI HONG YEN,† MAFUMI WATANABE,† SHINSUKE TANABE,*†

NGUYEN DUC HUE,‡ and VO QUI§

†Center for Marine Environmental Studies, Ehime University, Tarumi 3-5-7, Matsuyama 790-8566, Japan

‡Faculty of Chemistry, Hanoi National University, 19 Le Thanh Tong Street, Hanoi, Vietnam

§Center for Natural Resources and Environmental Studies, Hanoi National University, 19 Le Thanh Tong Street, Hanoi, Vietnam

(Received 23 July 2001; Accepted 8 March 2002)

Abstract—Concentrations of persistent organochlorines (OCs), such as polychlorinated biphenyls (PCBs),

1,1,1-trichloro-2,2-bis(p-chlorophenyl)ethane (DDT) and its metabolites (DDTs), hexachlorocyclohexane isomers (HCHs), hexachlorobenzene (HCB), and chlordane compounds (CHLs), were determined in whole-body homogenates of resident and migratory birds collected from the Red River estuary, North Vietnam, during March and October 1997 Contamination pattern was in the order of DDTs PCBs

HCHs CHLs HCB in both resident and migratory birds Residue concentrations, according to the feeding habit, showed little

variability, which may reflect relatively similar trophic levels of the bird species analyzed Resident birds accumulated greater concentrations of DDTs as compared to migrants In contrast, HCH residues were greater in migratory species Higher proportions

ofp,p9-DDT to total DDT concentrations were found in many species of residents and migrants, indicating recent exposure to

technical DDT in northern Vietnam Congener-specific PCB analysis showed the predominance of penta- and hexachlorobiphenyls

in all the species analyzed Estimation of hepatic microsomal enzyme activities suggested higher metabolic capacity for PCB congeners in shore birds from Vietnam as compared to higher-trophic predator birds and marine mammals Comparison of OC residues in avian species in Asia-Pacific revealed that DDT residues in resident birds in North Vietnam are among the highest values reported for the countries surveyed, suggesting recent usage of DDT in Vietnam Available data for birds, fish, and bivalves from the recent Asia-Pacific Mussel Watch Program suggested that Vietnam might be a potential source of DDT contamination in Asian developing countries To our knowledge, this is the first study of the OC accumulation in avian species from Vietnam

Keywords—Persistent organochlorines Birds Vietnam DDTs Pollution source

INTRODUCTION

Organochlorine compounds, such as DDTs, HCHs, and

PCBs, are among the most widely known groups of

contam-inants because of their ubiquity, high bioaccumulation

poten-tial, and harmful biological effects [1] A large number of

studies have focused on the accumulation of persistent OCs

in various species of flora and fauna around the world Eggshell

thinning, reproductive failure, and mortality of embryo and

chicks in avifauna have been observed A possible link

be-tween these abnormalities and a high degree of exposure to

OCs, particularly DDTs and PCBs, has been suggested [2–5]

Despite this fact, some OCs are still being used in tropical

and subtropical Asian regions, particularly in developing

coun-tries for agricultural purposes and vector-borne disease

erad-ication programs Our recent comprehensive monitoring

sur-veys in Asia-Pacific have also suggested the role of this region

as one of the major sources of OC contamination in a global

perspective, particularly for pristine areas, such as the Arctic

and the Antarctic [6–8]

Vietnam, a developing country, is located in the tropical

region Agricultural chemicals including DDTs and HCHs have

been used in the country until very recently [9] Despite the

continuing usage of OC pesticides in Vietnam, little

infor-mation has been reported regarding OC exposure in

higher-trophic animals, such as birds living and wintering in this

country It is well known that birds have been widely used as

* To whom correspondence may be addressed

(shinsuke@agr.ehime-u.ac.jp)

bioindicators for environmental pollution, particularly by per-sistent OCs, which have been considered as potential endo-crine-disrupting chemicals in wildlife [10] Earlier studies have indicated widespread occurrence of persistent OCs in abiotic and biotic samples including air, water, soils, sediments, food-stuffs, and human breast milk collected from various locations

in Vietnam [7,8,11–13] From the environmental health point

of view, an understanding of OC exposure in higher-trophic animals is of importance because organochlorines have high bioaccumulation potential and can cause adverse effects in these animals However, no investigation of OC pollution in avian species in Vietnam has been conducted in recent years Therefore, accumulation patterns as well as possible toxic im-pacts of persistent OCs to avian species from Vietnam have not been characterized The magnitude of exposure to OCs in birds from Vietnam is of concern

In the present study, we carried out an extensive sampling survey to collect different species of birds living and wintering

in the Red River estuary, North Vietnam, during March and October 1997 and determined the concentrations of persistent OCs, such as PCBs, DDT and its metabolites (DDTs), HCHs, HCB, and CHLs Residue levels and bioaccumulation profiles

of OC insecticides and PCB congeners are discussed Residue concentrations according to the feeding habit and migratory behavior of birds were also examined Further, OC residues

in fish and bivalves from the present study and those reported

in our recent Mussel Watch Program in the Asia-Pacific region were compiled and analyzed to understand the magnitude of

OC contamination in Vietnamese biota Based on this analysis,

Fig 1 Map showing sampling location in the Red River delta, North

Vietnam

Table 1 Biometric data of resident, migratory birds, and diet analyzed in the present study Species

Body weight (g)

Standard length (cm) Resident

Black-capped kingfisher (Halcyon pileata)

Common kingfisher (Alcedo atthis)

Common moorhen (Gallinula chloropus)

Cinnamon bittern (Ixobrychus cinnamomeus)

Slaty-breasted rail (Rallus striatus)

White-breasted waterhen (Amaurornis phoenicurus)

White-throated kingfisher (Halcyon smyrnensis)

2 5 1 1 2 3 1

2F (3M, 2F) 1F 1F 2F (2M, 1F) 1M

100 (99–101)

16 (14–18) 134 120

133 (120–146)

156 (120–198) 106

28 (27–30)

27 (23–29) 28 39

25 (24–26)

27 (27–28) 28 Migrant

Common redshank (Tringa totanus) (S)b

Common redshank (Tringa totanus) (A)b

Kentish plover (Charadrius alexandrinus)

Gull-billed tern (Sterna nilotica)

Little tern (Sterna albifrons)

10 5 10 1 1

(6M, 4F) (2M, 3F) (7M, 3F) 1M 1F

122 (103–141)

108 (102–114)

20 (16–23) 184 71

31 (29–33)

25 (23–26)

67 (55–85) 33 25 Long-billed Mongolian plover (Charadrius mongolus;

subspeciesC atrifrons) (S)

Long-billed Mongolian plover (Charadrius mongolus) (A)

Whimbrel (Numenius phaeopus)

Whiskered tern (Sterna hybrida) (S)

Whiskered tern (Sterna hybrida) (A)

(Bar-tailed godwit (Limosa lapponica)

2 2 1 2 2 1

2M 2M 1M 2F 2M 1F

79 (78–80)

83 (81–85) 348

76 (74–77)

72 (69–75) 294

20 (20–20)

21 (20–21) 39

27 (26–28)

24 (24–24) 39 Dunlin (Calidris alpnia) (S)

Dunlin (Calidris alpnia) (A)

Great knot (Calidris tenuirostris) (S)

Great knot (Calidris tenuirostris) (A)

Grey plover (Pluvialis squatarola)

Marsh sandpiper (Tringa stagnatilis) (S)

Marsh sandpiper (Tringa stagnalitis) (A)

Red knot (Calidris canutus)

Rufous-necked stint (Calidris ruficollis)

4 4 2 2 3 10 4 5 5

(1M, 3F) (2M, 2F) 2M (1M, 1F) 3M (7M, 3F) 4M 5M (3M, 2F)

58 (53–63)

55 (46–62)

234 (214–261)

200 (181–223)

210 (195–236)

24 (22–26)

24 (24–25)

130 (100–165)

24 (22–26)

20 (19–21)

21 (20–22)

26 (25–28)

29 (28–29)

29 (28–30)

66 (60–73)

61 (56–65)

25 (23–28)

15 (14–16) Short-billed Mongolian plover (Charadrius mongolus;

subspeciesC schaeferi) (S)

Short-billed Mongolian plover (Charadrius mongolus) (A)

Spotted redshank (Tringa erythropus)

Terek sandpiper (Xenus cinereus)

3 2 1 2

(2M, 1F) 2M 1M 2M

62 (60–64)

60 (59–60) 117

65 (64–65)

19 (18–19)

20 (19–20) 29

24 (23–24) Diets

Fish species

aM5 male, F 5 female Figures indicate number of sample

bS, A5 samples collected in spring and autumn, respectively

we also suggest the role of Vietnamese environment among Southeast Asian countries as a source of pollution

MATERIALS AND METHODS

Sampling

Resident and migratory birds (n5 101) were collected from the wetland (Con Lu Island) in the outer estuary system of the main Red River estuary during March and November 1997 (Fig 1) Diet samples that comprised small fish and shrimp were also collected at the same locations for bird samples Bird and diet samples were iced immediately after collection, transported to laboratory, and shipped to Japan with dry ice The data of biological characteristics and ecological infor-mation on birds and diets are shown in Table 1 The entire body, except the feathers, was homogenized and stored at 2208C until analysis

According to ecological studies by de Hoyo et al [14], most of the bird species analyzed in this study were classified into two main groups: residents and migrants Resident species live in the same region throughout their entire life span, while migrants may have their breeding grounds located in other

locations in east and central Asia, Russia, Siberia, and

Aus-tralia Ecological studies have shown that most of the

migra-tory birds that winter in Vietnam originate from east Asian

countries, such as Korea, Japan, Hong Kong and the

Philip-pines, central Russia, and the Russian Arctic [14,15] Some

species, such as the common redshank, kentish plover,

gull-billed tern, little tern, long-gull-billed Mongolian plover,

short-billed Mongolian plover, whimbrel, and whiskered tern, have

breeding grounds mainly in China, Korea, and Japan Other

species, including bar-tailed godwit, dunlin, great knot, grey

plover, marsh sandpiper, rufous-necked stint, spotted redshank,

red knot, and terek sandpiper, breed chiefly in eastern Russia,

Siberia, and the Russian Arctic In addition, these migratory

species have stopover sites in the Indian subcontinent and

Southeast Asian region

Chemical analysis

Chemical analyses of OCs followed the method previously

described [16] Briefly, 10 to 15 g whole-body homogenates

were mixed with anhydrous Na2SO4and extracted in a Soxhlet

apparatus (Millville, NJ, USA) with a mixture of hexane and

diethyl ether The fat content was gravimetrically determined

from an aliquot of the extract The extract was then added into

a dry Florisil column (Supelco, Oakville, ON, Canada) to

re-move fat Organochlorines were eluted with 150 ml of 20%

water in acetonitrile to a separatory funnel containing hexane

and water After partitioning, the hexane layer was

concen-trated and then passed through a 12-g activated Florisil column

for fractionation The first fraction eluted with hexane

con-tained HCB, PCBs, p,p9-dichlorodiphenyldichloroethylene

(DDE),trans-nonachlor; the second fraction eluted with 20%

dichloromethane in hexane containedp,p

9-dichlorodiphenyldi-chloroethane (DDD), p,p9-DDT, HCH isomers (a, b, and g

isomers), CHL compounds (cis-chlordane, trans-chlordane,

cis-nonachlor, and oxychlordane) Each fraction was

concen-trated and injected into a gas chromatograph equipped with

an electron capture detector (GC-ECD) for quantification

Organochlorines were quantified by a Hewlett-Packard

5890 series II GC-ECD (Wilmington, DE, USA) equipped with

a moving needle–type injection port The GC column

em-ployed was DB-1 fused silica capillary column (0.25 mm3

30 m; J & W Scientific, Folsom, CA, USA) coated with 100%

dimethylpolysiloxane at 0.25-mm film thickness The column

oven temperature was programmed from 60 to 1608C, held for

10 min, then increased to 2608C at a rate of 28C/min and held

for 20 min Injector and detector temperatures were set at 260

and 2808C, respectively Helium and nitrogen were used as

carrier and makeup gases, respectively The OC concentrations

were calculated from the peak area of the sample to the

cor-responding external standard The PCB standard used for

quan-tification was an equivalent mixture of Kanechlor preparations

(KC-300, KC-400, KC-500, and KC-600; Kanebuchi

Chem-ical, Osaka, Japan) with known PCB composition and content

Concentrations of individual PCB congeners were summed to

obtain total PCB concentrations Recoveries of target

contam-inants through this analytical method ranged from 95 to 105%

Concentrations were not corrected for recovery rates A

pro-cedural blank was analyzed with every set of six samples to

check for interfering compounds and to correct samples values,

if necessary The DDTs represent the sum ofp,p 9-DDT,

p,p9-DDD, and p,p 9-DDE, while CHLs include cis-chlordane,

trans-chlordane, cis-nonachlor, trans-nonachlor, and

oxychlor-dane The HCHs includea, b, and g-isomers

Isomer-specific analysis of PCBs was similar to that de-scribed previously [17] Briefly, 10 to 15 g of whole-body homogenates was refluxed in 1 N potassium hydroxide (KOH)

in ethanol for 1 h, and the solution was then transferred to a separatory funnel containing hexane and hexane-washed water After partitioning, the hexane layer was concentrated and cleaned up on 1.5 g of silica gel (Wako-gel S-1, Wako Chem-ical, Japan) packed in a glass column The PCB congeners were eluted with 200 ml hexane The hexane was then con-centrated, treated with 5% fuming sulfuric acid, and rinsed with hexane-washed water The final solution was microcon-centrated and injected into a gas chromatograph with a mass selective detector (GC-MSD) for quantification

Quantification of PCB congeners was carried out using a Hewlett-Packard 5890 Series II GC-MSD coupled with a Hew-lett-Packard 5972 Series MS having an electron impact (EI) at

70 eV The GC column employed was DB-1 fused silica cap-illary column (0.25 mm3 30 m; J & W Scientific) coated with 100% dimethylpolysiloxane at 0.25mm film thickness The col-umn oven temperature was programmed from 70 to 1608C, held for 20 min, then increased to 2608C at a rate of 28C/min and held for 30 min Injector and ion source temperatures were kept

at 250 and 2808C, respectively An equivalent mixture of Ka-nechlors 300, 400, 500, and 600 was used as a standard for quantification Concentrations of individual PCBs were quan-tified from the peak area of the sample to that of the corre-sponding external standard The PCB homologues were deter-mined by selective ion monitoring Data were acquired by a Hewlett-Packard 5972C data system in which cluster ions were monitored atm/z 254 and 256, 290 and 292, 324 and 326, 358

and 360, 392 and 394, and 428 and 430 for tri-, tetra-, penta-, hexa-, hepta-, and octachlorobiphenyls, respectively

Recoveries of total PCBs were examined by spiking 3.0mg

of Kanechlor standard to corn oil The recoveries ranged from

using their International Union of Pure and Applied Chemistry (IUPAC) number throughout the manuscript

For quality assurance and quality control, our laboratory participated in the Intercomparison Exercise for Persistent Or-ganochlorine Contaminants in Marine Mammal Blubber or-ganized by the National Institute of Standards and Technology (Gaithersburg, MD, USA) and Marine Mammal Health and Stranding Response Program of the National Oceanic and At-mospheric Administration’s National Marine Fisheries Service (Silver Spring, MD, USA) Standard reference material SRM

1945 was analyzed for selected PCB congeners and persistent OCs Our data were in good agreement with those of other participating laboratories and the certified values

Statistical analysis

Statistical analysis was performed using Mann–WhitneyU

test (p , 0.05) for testing the differences in OC residues between resident and migratory birds

RESULTS AND DISCUSSION

Residue levels and specific accumulation according to the feeding habit and migratory behavior

Organochlorines were detected in all resident and migratory birds in both spring and autumn seasons (Table 2) Residue concentrations in most species of resident and migratory birds analyzed followed the order of DDTs PCBs HCHs

content (%)

Resident Black-capped

(5.8–24) 16

(0.13–1.8) 1.7

Migrant Common

(3.6–8.8) 6.6

(18–36) 89

(18–96) 66

(6.5–88) 6.3

(0.63–1.5) 8.3

(0.62–8.0) 1.2

(0.37–2.5) 2.5

(6.3–17) 10

(18–36) 18

(8.2–71) 16

Fig 2 Organochlorine concentrations in birds according to the feeding habit Residents: Piscivore/insectivore (black-capped kingfisher, cmon kingfisher, cinnacmon bittern, and white-throated kingfisher), om-nivore (common moorhen), and insectivore/graom-nivore (white-breasted waterhen and slaty-breasted rail) Migrants: Piscivore/insectivore (common redshank, little tern, short- and long-billed Mongolian plo-ver, whiskered tern, spotted redshank, and marsh sandpiper), omnivore (gull-billed tern), insectivore/molluscivore (kentish plover, bar-tailed godwit, dunlin, terek sandpiper, and red knot), and insectivore/gran-ivore (rufous-necked stint, grey plover, whimbrel, and great knot) See text for further details

shrimp diet, with elevated concentrations of DDTs (up to 170

ng/g wet wt) The DDT concentrations in resident and

migra-tory species were approximately one order of magnitude

great-er than those of PCBs and HCHs These results indicated high

degree of exposure to DDTs in biota from Vietnam and

ex-tensive usage of this insecticide in tropical Asian countries,

including Vietnam This accumulation pattern is different from

that found in resident and migratory birds collected from south

India and Lake Baikal, Russia, which showed HCHs and PCBs

as predominant contaminants, respectively [16,18] Technical

HCH is still being used in India in large quantities for

agri-cultural purposes, and elevated contamination with HCHs has

been common in most environmental samples collected from

India [7,8,16,19] In the Lake Baikal region, pulp and paper

mill industries and a chlor-alkali plant are located in the Angara

River valley, near the southeastern region of the lake These

are suggested as the main source of PCBs in the lake

[17,20,21] Thus, residue patterns of OC accumulation

ob-served in resident birds from Vietnam, India, and Lake Baikal

reflect the status of OC usage in these areas in recent years

Among residents, higher OC concentrations were found in

black-capped kingfisher, cinnamon bittern, and white-breasted

waterhen In particular, an individual sample of white-breasted

waterhen carried elevated concentrations of DDTs (9,000 ng/

g wet wt), and mean DDT concentration of this species was

3,100 ng/g wet weight, at least five times greater than those

in other species (Table 2) Higher concentration residues of

PCBs and HCHs were found in common and black-capped

kingfisher, while the lowest levels were recorded in

slaty-breasted rail Kingfisher and cinnamon bittern, piscivorous

species that feed mainly on small fish and insects, contained

the highest concentrations of OCs Slaty-breasted rail, an

gra-nivorous species, accumulated lower residues White-breasted

waterhen eats small insects and plants but accumulated high

concentrations of DDTs Ecological studies indicated that this

species often occurs close to human habitation, such as village

ponds and sewage ponds, in addition to agricultural areas, such

as rice fields and sugarcane [14] This is probably a plausible

explanation for elevated OC accumulation in white-breasted

waterhen From an ecotoxicological viewpoint, this species

may experience harmful effect due to DDT accumulation

As-suming a transfer rate of OCs from mother to eggs to be 20%

and the weight of eggs to be 20% of the body mass, residues

in whole body may reflect concentrations in eggs [16] Based

on this, an individual of white-breasted waterhen analyzed in

this study contained a mean DDT level of 9.0mg/g wet weight

in the eggs, which exceeded the level associated with reduced

breeding success (3 mg/g wet wt) as suggested by Newton

[22]

As for migratory birds, residue levels were variable among

species Greater concentrations of DDTs and PCBs were

ob-served in some piscivorous species, such as Mongolian plover,

whiskered tern, and common redshank Whiskered terns breed

in northeastern China and southwest and central Europe, which

may explain noticeable DDT and PCB concentrations in

sam-ples collected in autumn (mean concentrations: 190 and 550

ng/g wet wt, respectively) Great knot (Calidris tenuirostris)

contained relatively high levels of HCHs in both spring and

autumn, which could be due to the migratory behavior along

coastlines of India and Australia [14] Accumulation in

stop-over sites in India may elevate HCH concentrations in this

species Concentrations of CHLs and HCB were uniformly

low in all the species examined, indicating minimal exposure

to these chemicals in resident and migratory birds from Vi-etnam In general, except for a few species, concentrations of OCs in migratory birds from North Vietnam were lower than those observed in birds from India A possible reason is that birds collected for this study probably migrate and winter in stopover sites in Southeast Asia, where OC contamination is deemed to be less than in other countries, such as India, Japan, and China Details regarding comparative assessment of OC pollution in Asian developing countries are discussed later in this paper

To further understand bioaccumulation characteristics of

OC in birds from North Vietnam, we attempted to assess res-idue levels in birds according to their feeding habit, habitat, and migratory behavior It should be noted that feeding habits

of these shore birds were relatively similar Ecological studies regarding food and feeding habit by de Hoyo et al [14] in-dicated that most of the species employed in this study feed

on small insects and other lower-trophic organisms, such as invertebrates, mollusks, crustaceans, and so on A few species also include small fish in their diets (kingfishers, cinnamon bittern, redshanks, terns, Mongolian plovers, and marsh sand-piper), while other species feed extensively on small insects and mollusks (kentish plover, bar-tailed godwit, dunlin, terek sandpiper, and red knot) White-breasted waterhen, slaty-breasted rail, rufous-necked stint, grey plover, whimbrel, and great knot feed mainly on insects and plants and are considered

as insectivore/granivore Two species that have relatively more opportunistic feeding habit were classified as omnivores (com-mon moorhen and gull-billed tern) Bioaccumulation patterns

of OCs in these birds are described in Figure 2 Among res-idents, PCBs and HCHs residues were higher in piscivores than those in omnivores and granivores, which is somewhat similar to those observed in birds from India [16,23] An ex-ception was observed in white-breasted waterhen, which ac-cumulated elevated DDT residues As discussed earlier, habitat areas close to human activities and agricultural fields of this species may explain the observed result In general, piscivo-rous and omnivopiscivo-rous migratory birds accumulated higher lev-els of OCs than insectivores and granivores, but no notable trend was found It has been pointed out in earlier studies that fish-eating birds are capable of accumulating elevated OC con-centrations [16,23,24] The high capacity to accumulate

per-Fig 3 Comparison of organochlorine concentrations in resident and

migratory birds from North Vietnam

Fig 4 Compositions of hexachlorocyclohexane isomers (HCHs) and DDT compounds found in resident and migratory birds from North Vietnam Data for diet are mean values of fish and shrimp

sistent OCs in fish-eating birds was related to their low hepatic

microsomal monooxygenase activities, which are responsible

for metabolism/detoxification of xenobiotics [25,26] Looking

at the accumulation pattern of OCs in birds according to their

feeding habit in this study, it can be said that variations in OC

residues were not so significant This may partly reflect similar

trophic levels of the species examined

Differences in OC accumulation between resident and

mi-gratory birds were more apparent (Fig 3) Concentrations of

DDTs in resident birds were significantly higher than those in

migrants, suggesting recent exposure to DDTs in North

Vi-etnam Earlier studies have also suggested recent input of

DDTs in coastal areas and rivers of the northern region as well

as in the industrial urban city [27–29] Interestingly,

accu-mulation of HCHs revealed a contrasting pattern, showing

apparently greater concentrations in migratory birds This

could be due to accumulation in stopover sites during

migra-tion in some polluted areas, such as India, southern China, and

Japan The role of these countries as a potential source of HCH

accumulation in wintering migrant birds breeding in Lake

Bai-kal has been also suggested in our recent study [18] In general,

mean concentrations of PCBs were similar in residents and

migratory species However, PCB accumulation in birds from

Vietnam was low, indicating smaller sources of PCBs in North

Vietnam in recent years Nhan et al [29] also reported

rela-tively low PCB residues in sediments and mollusks collected

from the freshwater canals of the Hanoi region, which is

sit-uated at the upper end of the Red River delta of northern

Vietnam

Composition of HCHs and DDTs

With regard to HCH composition, some species, such as

common kingfisher, Mongolian plover, dunlin, and great knot,

contained a relatively higher proportion of a-HCH than the

other species, probably reflecting accumulation pattern in their

fish diet or recent exposure in stopover sites during migration

(Fig 4)

The proportion ofp,p9-DDE was highest among DDT

com-pounds, indicating greater ability of birds to transformp,p

9-DDT top,p9-DDE (Fig 4) Interestingly, some residents and

migrants, such as white-breasted waterhen, common

kingfish-er, kentish plovkingfish-er, long-billed Mongolian plovkingfish-er, great knot,

and red knot, contained a relatively larger proportion ofp,p

9-DDT than those in other species examined This result suggests

recent exposure to DDTs in Vietnam Particularly,

white-breasted waterhen contained the greatest proportion ofp,p

9-DDT, about 50% of total DDT concentrations Given that

white-breasted waterhen also accumulated elevated DDT

res-idues (Table 2), we suggest that this species may have low capacity to metabolize DDT compounds Composition of DDT compounds in related species collected from south India ex-hibited a different pattern, in whichp,p9-DDT comprised only

a minor proportion of total DDT concentrations [16] Despite the efficient capacity of birds to transformp,p 9-DDT to

p,p9-DDE, high composition ofp,p9-DDT was found in many res-ident and migrant species collected from North Vietnam, in-dicating recent exposure to technical DDT used in the Red River watershed Recent studies dealing with other biological samples, such as fish and mollusks collected from various locations in the Red River delta, have also revealed relatively high proportions of p,p 9-DDT and o,p9-DDT, suggesting

on-going application of DDT in the river valley [27,29] From an ecotoxicological point of view, this observation is a matter of concern since avian species living and wintering in Vietnam may experience harmful effects, such as eggshell thinning and population decline as observed in some highly industrialized areas in North America and western Europe

Isomer-specific accumulation profile and metabolic capacity of PCBs

Isomer-specific analysis revealed the presence of about 50 chlorobiphenyl (CB) congeners The PCB isomers and con-gener patterns in some representative species of resident and migratory birds and their diet are shown in Figure 5 Penta-and hexachlorobiphenyls, particularly CB-99, 105, 118, 138,

153, and 180, were predominant congeners

In general, congener CB-153 was abundant in all species, which further supported the observations regarding the pref-erential persistence of this congener in birds Similar results were also observed in other studies analyzing aquatic birds [30–32] Among migrants, most of the birds showed similar patterns A specific pattern was observed in rufous-necked stint, showing congener CB-138 and CB-118 as predominant congeners In addition, higher chlorinated congeners (hexa-and heptachlorobiphenyls) also accounted for a relatively high proportion in this species This may be due to the specific accumulation of this species In general, accumulation of PCB

Fig 5 Polychlorinated biphenyl (PCB) isomer and congener

com-positions of some species of resident and migratory birds and their

diet collected from North Vietnam Black-capped kingfisher: Resident

Whiskered tern and rufous-necked stint: Migrants Vertical bars

rep-resent concentrations of individual congeners relative to the most

abundant congeners (CB-153), which were treated as 1.0 Data for

diet are mean values of fish and shrimp IUPAC5 International Union

of Pure and Applied Chemistry

Fig 6 Comparison of estimated phenobarbital (PB)- and 3-methyl-cholanthrene (MC)-type enzyme activities in higher-trophic animals

by metabolic indices of chlorobiphenyl (CB)-52 and -66 Black bars represent enzyme activities of Vietnamese birds Data for other ani-mals are cited from Tanabe et al [33], Nakata et al [17], and Guruge and Tanabe [31]

isomers in birds from Vietnam was somewhat similar to that

observed in related species from south India [32]

To further understand the degradation capacity and explain

the specific isomer pattern of shore birds analyzed in this study,

we attempted to estimate the capacity of metabolism using the

metabolic index proposed by Tanabe et al [33]:

where the metabolic index (MI)iis the metabolic index of PCB

isomeri, CR180is the concentration ratio of CB-180 in the bird

and the diet, and CRiis the concentration ratio of the congener

i Details regarding this concept were described in our previous

study [33]

The metabolism of PCB congeners is mediated by

cyto-chrome P450–dependent mixed-function oxygenase enzymes

Congeners possess vicinal nonchlorinatedmeta-para carbons,

andortho-meta ones are metabolized by phenobarbital

(PB)-and 3-methylcholanthrene (MC)-type enzymes, respectively

Both CB-52 and 66, having two adjacent nonchlorinated

meta-para carbons and ortho-meta carbons, respectively, were

se-lected for calculation of MI The MI values of these two

con-geners can be used to estimate the extent of activities of

PB-and MC-type enzymes [33] Accordingly, estimated PB- PB-and

MC-type enzyme activities of birds from Vietnam in

compar-ison to other high-trophic waterbirds and animals are described

in Figure 6 Since the diet of these species comprises a variety

of items and only small fishes and shrimps were obtained, we

estimated MI values for only some representative species also

having small fish as their main diet, such as black-capped

kingfisher, whiskered tern, long-billed Mongolian plover, and

common redshank Interestingly, estimated PB-type enzyme

activities of some species, such as black-capped kingfisher and

whiskered tern, were comparable to those in common cor-morant but higher than those in other higher-trophic species, such as kite, puffin, and gull, while MC-type enzyme activities seem comparable or slightly higher in these species Although

MI values were estimated on the assumption that fish comprise 100% of bird diet, higher PB- and to some extent MC-type enzyme activities in shorebirds from Vietnam suggest that these species may have a higher capacity to metabolize PCB congeners This result may explain relatively low levels of PCBs and other OCs in shorebirds as compared to high-trophic top predator species

The estimated enzyme activities can be considered to fur-ther clarify the specific isomer pattern observed in rufous-necked stint, which have a specific pattern with CB-118 and CB-138 as predominant congeners Ecological studies have indicated that rufous-necked stint feeds not on fish but on small insects, plants, and crustaceans [14] Therefore, we used data for small shrimps to estimate enzyme activities for this species Based on this assumption, the estimated MI values represent-ing PB- and MC-type enzyme activity would be 0.62 and 0.51, respectively These values were apparently lower than those

in other species, indicating weaker ability to metabolize PCB congeners in this species Metabolism of CB-138 and -118 involves induction of both PB- and MC-type enzymes, while CB-153 is metabolized by PB-type enzymes [34] The pre-dominance of CB-118 and -138 over CB-153 observed in ru-fous-necked stint can be supported by the less active MC-type enzyme in this species It has been reported that in aquatic mammals, such as the Ganger river dolphin, with inactive MC-and PB-type enzymes, higher abundance of CB-138 was also observed [19]

International comparison and the role of the Southeast Asian region as an emission source of contamination

To understand the magnitude of contamination in avian species from Vietnam, OC residues in birds reported for coun-tries in Asia-Pacific were compared (Table 3) Since data were reported for different tissue, we used lipid-normalized con-centrations for comparison The PCB concon-centrations in resi-dent birds from North Vietnam were in the range of those reported for Indian birds but lower than those in birds from

Resident House

2,700 840 3,900 (42–17,000)

Resident Carrion

1991–1993 1991–1993 1991–1993

6,400 2,100

1,900 340

–2,400) 530

5,300 (6–26,000) 11,000 (86–58,000)

13,000 (190

Resident European

1986 1980s

3,700 5,100

Muscle Whole

1998 1998

Muscle Whole

Fish Green

1998 1998

Fish Green

Muscle Whole

Fish Green

Muscle Whole

Lake Baikal, Russia, and Japan Extent of PCB contamination

in each location is consistent with known current status of

usage Accordingly, lesser usage of PCBs in developing

coun-tries is a reason for the lower degree of exposure [8,16] Local

sources in eastern Siberia and historically heavy usage in Japan

are plausible explanations for higher PCB contamination in

Lake Baikal and Japanese birds, respectively The HCH

con-centrations in Vietnamese birds were similar to those reported

for Lake Baikal and Japanese birds but several orders of

mag-nitude lower than those in Indian birds Interestingly,

Viet-namese resident birds accumulated elevated DDT residues

comparable to those in birds from India and apparently greater

than those in Lake Baikal and Japanese resident birds

Al-though DDT levels in migratory birds were still lower than

those in India and Lake Baikal, elevated levels found in

res-ident species indicate recent usage of DDT in Vietnam The

DDT concentrations in birds from Vietnam were even

com-parable or higher than those in avian species recently reported

in some locations in the United States and western Europe,

which are known as heavily polluted areas because of the huge

historical production and usage [35,36] For example, migrant

passerine species from Illinois (USA) collected in 1996

ac-cumulated p,p9-DDE levels in the range of 1.4 to 390 ng/g

wet weight, which were less than those in Vietnamese birds

[35] Little tern collected from the Baltic Sea in 1995 to 1996

contained a mean p,p9-DDE level of 400 ng/g wet weight,

which was in the range of that reported for birds from North

Vietnam [36] These data indicate that recent DDT

contami-nation in birds from developing countries located in tropical

regions, such as Vietnam, may continue to be elevated This

result could be due to current application of this insecticide

for malaria eradication programs as well as agricultural

pur-poses in Asian developing countries

The present pattern of accumulation of OCs in birds

sug-gests that developing countries in the Southeast Asian region

may serve as an emission source of pollution in recent years

To provide further evidence for the role of this region as a

pollution source, we compiled data for fish and mussels

col-lected from the Asia-Pacific Mussel Watch Program in Asian

developing countries This is a comprehensive monitoring

sur-vey conducted in our laboratory (Table 4) Concentrations of

PCBs in Vietnamese fish and mussels were lower than those

reported for developed nations in this region but comparable

to those from India and the Philippines Nevertheless, these

levels were higher than those reported for other developing

countries in Southeast Asia, such as Cambodia, Thailand,

In-donesia, and Malaysia, indicating a greater source of PCB in

Vietnam, probably due to the release from weapons used

dur-ing the Indochina war [13] Interestdur-ingly, as for HCHs and

DDTs, concentrations of these compounds in fish and mussels

from Vietnamese coastal waters are among the highest values

reported for the countries surveyed The HCH residues were

the highest in India, a main HCH user in the world, followed

by Vietnam Likewise, Vietnamese fish and mussels contained

the greatest DDT concentrations Surveys conducted during

1989 to 1993 and recent years have also indicated elevated

DDT concentrations in atmospheric, hydrospheric, and biotic

samples from both North and South Vietnam [7,8,13,28] From

the temporal point of view, DDT residues in fish analyzed in

the present study were higher than those observed in 1989

(Table 4) Nhan et al [29] found high levels of DDTs in

sed-iments and mollusks in Hanoi and suggested recent usage of

DDT for mosquito eradication Information regarding DDT

usage in Vietnam is rather limited According to the domestic

statistical data, approximately 25,000 tons of DDT was

im-ported and used in Vietnam during 1957–1995 [37,38] As for

comparison, cumulative production of DDT in India until 1995

was estimated at about 500,000 tons [8] In fact, residues in

birds and river dolphins from India did not appear to have

declined until recently [16,19] Thus, monitoring studies based

on both spatial and temporal scales were consistent with the

statistical data of usage, and this fact suggests that besides

India, Vietnam has been a potential source of DDT pollution

in the Southeast Asian region

Conclusion and recommendation for future research

Recent monitoring surveys of birds and the Mussel Watch

Program conducted in our laboratory have revealed that

con-tamination by OC insecticides, particularly DDTs, was

appar-ent in the Vietnamese environmappar-ent Results from this study

also indicated that the status of OC contamination in

devel-oping countries seems to become more serious in future

Fur-ther comprehensive investigations regarding the temporal trend

of OC contamination in Asian developing environments are

therefore needed to trace the source and assess possible

long-term impacts of OCs in tropical ecosystems Ecotoxicological

studies on adverse effects of insecticide, particularly DDE, a

potential contaminant causing eggshell thinning in avian

spe-cies, are also required, considering the fact that very little

information from tropical countries is available

Acknowledgement—We thank the staff of the Center for Natural

Re-sources and Environmental Studies, Hanoi National University,

Vi-etnam, for collection of bird samples We also thank K Kannan for

the critical reading of this manuscript Helpful comments and

dis-cussion of E.Y Kim and K Senthilkumar are also appreciated This

study was supported by a Grant-in-Aid from the Scientific Research

Programs of the Ministry of Education, Culture, Sports, Science and

Technology of Japan (Projects 12308030 and 13027101) and by the

Sumitomo Foundation and the Core University Program between the

Japan Society for the Promotion of Science (JSPS) and the National

Center for Natural Science and Technology The award of the JSPS

Postdoctoral Fellowship for Foreign Researchers in Japan to T.B Minh

(P00323) is acknowledged

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