DSpace at VNU: Persistent organochlorine residues in estuarine and marine sediments from Ha Long Bay, Hai Phong Bay, and Ba Lat Estuary, Vietnam

DSpace at VNU: Persistent organochlorine residues in estuarine and marine sediments from Ha Long Bay, Hai Phong Bay, and...

Persistent organochlorine residues in estuarine and marine sediments

from Ha Long Bay, Hai Phong Bay, and Ba Lat Estuary, Vietnam

S.H Honga,*, U.H Yima, W.J Shima, J.R Oha, P.H Vietb, P.S Parka

a

South Sea Research Institute, Korea Ocean Research and Development Institute, 391 Jangmok-ri, Jangmok-myon, Geoje-shi 656-834, Republic of Korea

a r t i c l e i n f o

Article history:

Received 18 July 2007

Received in revised form 21 February 2008

Accepted 25 February 2008

Available online 28 April 2008

Keywords:

Organochlorine pesticides

PCBs

Marine sediment

Contamination

Vietnam

a b s t r a c t

To assess the organochlorine contamination in the northeast coastal environment of Vietnam, a total of

41 surface sediments were collected from Ha Long Bay, Hai Phong Bay, and Ba Lat estuary, and analyzed for their organochlorine content Organochlorine compounds (OCs) were widely distributed in the Viet-namese coastal environment Among the OCs measured, DDT compounds predominated with concentra-tions ranging from 0.31 to 274 ng g1 The overall contamination level of DDTs in coastal sediments from northern Vietnam is comparable with those from other Asian countries However, concentrations exceed-ing 100 ng g1are comparable with high concentrations reported from India and China, the largest DDT consumers in the world The overall concentrations of PCBs, HCHs, and chlordanes in surface sediments were in the ranges of 0.04–18.71 ng g1, not detected (n.d.) – 1.00 ng g1, and n.d – 0.75 ng g1, respec-tively Ha Long Bay and Hai Phong Bay were relatively more contaminated with DDTs and PCBs than other regions, respectively In contrast, the distribution of HCHs was relatively homogeneous OCs contamina-tion in the coastal environment of Vietnam is closely related to shipping and industrial activities The lev-els of DDT compounds in harbors and industrial areas exceeded their sediment quality guideline values suggested by Environment Canada [CCME (Canadian Council of Ministers of the Environment), 2002 Canadian sediment quality guidelines for the protection of aquatic life In: Canadian Environmental Qual-ity Guidelines Canadian Council of Ministers of the Environment, Winnipeg, MB] and Australian and New Zealand [ANZECC and ARMCANZ, 2000 National water quality management strategy Paper No 4, Aus-tralian and New Zealand Guidelines for Fresh and Marine Water Quality, vol 1, The Guidelines Australia Document:http://www.deh.gov.au/water/quality/nwqms/volume1.html], indicating that adverse effects may occur to marine species in that areas

Ó 2008 Elsevier Ltd All rights reserved

1 Introduction

Persistent organic pollutants (POPs) such as polychlorinated

bipenyls (PCBs) and organochlorine pesticides have been

recog-nized as one of the most problematic groups of anthropogenic

chemicals for the last few decades A number of studies have

re-ported their harmful effects on reproduction, development, and

immunological function in humans and wildlife (Fry and Toone,

1981; Podreka et al., 1998; Vallack et al., 1998) POPs are

semi-volatile and can therefore travel long distances through the

atmosphere as gases or aerosols, eventually accumulating in

low-temperature regions following condensation and deposition

Increasing evidence indicates that pristine polar regions are widely

contaminated with POPs which probably come from low- and

mid-latitudes (Pacyna, 1995; Oehme et al., 1996; Bard, 1999) Industrial

organic chemicals such as PCBs have been mainly consumed in and

emitted from; mid-latitudinal regions of the Northern hemisphere because many developed countries are located in this region ( Brei-vik et al., 2002) In the case of organochlorine pesticides, most glo-bal emissions are sourced in tropical and sub-tropical developing countries, where they are used for agricultural and malaria control purposes; emissions are lower from developed countries following

a ban on these pesticides in the 1970s Recent investigations reveal that global emissions of a-HCH and b-HCH have undergone a southward trend for the last 20 years as more northern countries have banned the use of technical HCH (Li et al., 2000, 2003) Vietnam is a developing country located in a tropical region Agriculture, which employs approximately 80% of its inhabitants,

is the most important economic sector in Vietnam (Hung and Thie-mann, 2002) By virtue of their low cost and high insecticidal effi-cacy, large amounts of organochlorine pesticides have been applied

to agriculture in order to increase crop yields (Hung and Thiemann,

2002) Additionally, by virtue of suitable climatic conditions, Viet-nam had the world’s fifth-highest malaria incidence outside of Africa until 1992 (Tenenbaum, 1996) Hence, a huge quantity of

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Contents lists available atScienceDirect

Chemosphere

j o u r n a l h o m e p a g e : w w w e l s e v i e r c o m / l o c a t e / c h e m o s p h e r e

insecticides has been widely sprayed in the Vietnamese

environ-ment for malaria vector control

Application of such chemicals in the Vietnamese environment

can influence global pollution as Vietnam is located in a

high-tem-perature region.Li et al (2000, 2003)proposed that Vietnam has

been a dominant contributor to the global emission of a-HCH

and b-HCH since China banned the use of technical HCH in 1983

Thus, understanding the POPs contamination in Vietnam is

impor-tant for understanding global pollution by POPs Monitoring

stud-ies have already been conducted to assess the contamination

status of POPs in Vietnam (Nhan et al., 1998, 1999, 2001; Hung

and Thiemann, 2002; Minh et al., 2002, 2004) Although the use

of DDT was officially banned in Vietnam in 1995, based on high

levels of DDTs found in humans and wildlife, other researchers

have suggested that DDTs are still in use (Nhan et al., 1998; Minh

et al., 2002, 2004) Although many approaches have been tried to

assess POPs pollution in Vietnam more recently, the earlier studies

were limited in extent, particularly for the marine environment,

with only a few sampling stations In this investigation, we have

undertaken intensive sediment sampling in three northeast coastal

regions of Vietnam, including one industrialized bay (Hai Phong Bay), one World Heritage site (Ha Long Bay) and a large river mouth (Ba Lat estuary) to evaluate contamination status and char-acteristics of organochlorine pesticides and PCBs

2 Materials and methods

2.1 Study areas and sampling strategy

Ha Long Bay has been recognized by UNESCO as a World Heri-tage Area for its universal values of landscape, geology and geo-morphology As the surrounding cities of the bay are rapidly developing due to the expansion of tourism and ports, the author-ities have had increasing management difficulties, especially in environmental protection

The sea territories of Hai Phong are part of the north-eastern water area of Gulf of Tonkin Hai Phong has a dense network of riv-ers with an average density of 0.6–0.8 km of river per 1 km2 Re-cently, industrial activities like coal mining, ship-building and ship-repairing have caused geological and environmental changes

Table 1

dry wt) of PCBs and organochlorine pesticides in sediments from Ha Long Bay, Hai Phong Bay, and Ba Lat Estuary

Ha Long Bay

Hai Phong Bay

Ba Lat Estuary

in this region In addition, coastal water quality has degraded due

to pesticide use and the discharge of domestic and industrial waste

water Ba Lat estuary (Red River mouth) is one of the biggest river

estuaries and is a unique Ramsar site in Vietnam The estuary area

is well-known as being the wetland site with the highest

biodiver-sity in the country, and the Red River has a high turbidity,

espe-cially during the rainy season There is only limited data on the

water quality from the flooded area of the Ba Lat estuary

Surface sediment samples were collected from Ha Long Bay, Hai

Phong Bay and Ba Lat estuary in May 2003 and March 2004 A total

of 41 surface sediment samples were taken using a Van veen grab

on a ship (Table 1andFig 1) In Ha Long Bay, sampling sites

in-cluded a coastal area where pollution is problematic, and a

rela-tively pristine area close to the open sea In Hai Phong Bay,

sampling was conducted along the Cam River from the main

stream to its estuary In Ba Lat estuary, samples were collected at

the Red River mouth In each case approximately 2 cm of sediment

was removed from the surface, and stored at 20 °C until later

analysis

2.2 Analytical procedure

Chemical analysis of OCs followed the method previously de-scribed byHong et al (2003, 2006) Briefly, 20 g sediment samples were homogenized with anhydrous Na2SO4 and extracted in a Soxhlet apparatus with dichloromethane Activated copper gran-ules were used to remove elemental sulfur Copper treated extracts were cleaned using 20 g of 5% deactivated silica gel and 10 g of 1% deactivated alumina in a multilayer column The samples were then fractionated using high pressure liquid chromatography (HPLC) with a exclusion column (250  22.5 mm i.d., size-exclusion column packing with Phenogel 100 Å, Phenomenex Co.) The OC fractions were concentrated and solvent-exchanged with n-hexane Finally, quantitative analysis of OCs was carried out using a Hewlett-Packard 5890 gas chromatograph (GC) with

a l-electron capture detector (ECD) A fused silica capillary column (DB-5, 30 m  0.25 mm i.d with 0.25 lm film thickness) (J&W Sci-entific, California, USA) was used Helium and argon:methane (95:5) were used as carrier and make-up gasses, respectively The

Gia Luan

Dong Vang

Lang Bang

Hon 1

2 3 4 5

6

7 8

9 10

11 12 13

14 15 16

Dong Vang

Lang Bang

Hon 1

2 3 4 5

6

7 8

9 10

11 12 13

14 15 16

Hai Phong

Thuy U 1 2

8 9

10 11

12 13

14

15

'

Hai Phong

Thuy U 1 2

8 9

10 11

12 13

14

15

Nghoung Nhan

1

7 8 10 9

Nghoung Nhan

1

7 8 10 9

Hanoi

(a) Ha Long Bay

(b) Hai Phong Bay (c) Ba Lat Estuary

Vietnam

º

temperature program during the run was as follows: 100 °C for

1 min, 100 °C to 140 °C at 5 °C min1, 140 °C for 1 min, 140 °C to

250 °C at 1.5 °C min1, 250 °C for 1 min, 250 °C to 300 °C at 10 °C

min1, and 300 °C for 5 min Injector and detector temperatures

were maintained at 275 °C and 300 °C, respectively

A mixture of dibromooctafluorobiphenyl, PCB103, and PCB198

was added to all samples as a surrogate standard before extraction

Tetrachloro-m-xylene was added to all samples prior to GC

analy-sis The calibration standard consisted of 22 individual PCB

cong-eners (IUPAC No 8, 18, 28, 29, 44, 52, 66, 87, 101, 105, 110, 118,

128, 138, 153, 170, 180, 187, 195, 200, 206, and 209) and

organo-chlorine pesticides (DDT compounds, HCH compounds, chlordane

compounds, aldrin, dieldrin, endrin, and mirex; Ultra Scientific

Co.) The concentration of analytes was adjusted with the surrogate

standard recovery

Recoveries of three surrogate standards (n = 41) were 72 ± 6%,

85 ± 10%, and 95 ± 14% for DBOFB, PCB103, and PCB198,

respec-tively If the recovery of surrogate standards was outside of the

60 to 130% ranges, the sample was reanalyzed A procedural blank

was run with every set of 14 samples to check for secondary

con-tamination Quality assurance for the analysis was confirmed by

analysis of certified reference materials, EC-4, 1941a, and

IAEA-417, provided by Environment Canada, the National Institute of

Standards and Technology (NIST), and the International Atomic

En-ergy Agency, respectively All analytical values were within the

certified ranges The detailed results of the certified reference

material analysis have been reported elsewhere (Hong et al.,

2003) The method detection limit of organochlorine

com-pounds are in the ranges of 0.005–0.02 ng g1for PCB congeners,

0.005–0.02 ng g1for DDT compounds, 0.01–0.03 ng g1for HCH

compounds, 0.005–0.02 ng g1 for chlordane compounds, and

0.005–0.04 ng g1for the other organochlorine pesticides

All concentration data are based on dry weight Total PCB

con-centrations were calculated by summing the 22 individual

congen-ers listed above Total DDT concentrations (DDTs) are the sum of

o,p0-DDE, p,p0-DDE, o,p0-DDD, p,p0-DDD, o,p0-DDT, and p,p0-DDT

Total HCH concentrations (HCHs) are the sum of a-HCH, b-HCH,

c-HCH, and d-HCH Total chlordane concentrations are the sum of

a-chlordane, c-chlordane, cis-nonachlor, and trans-nonachlor

For measurement of total organic carbon (TOC), the

sub-sam-ples of sediments were freeze-dried (LABCONCO, Model 77545)

and ground on a mortar The samples were acidified with 10% (v/

v) hydrochloric acid and dried again at 50 °C in an oven Organic

carbon was measured on a CHNS analyzer (Flash EA1112) at

com-bustion temperature of 900 °C Grain-size analysis was carried out

using standard sieving methods for particles larger than 64 lm and

by pipetting for particles smaller than 64 lm (Carver, 1971)

3 Results and discussion

Organochlorine compounds were shown to be ubiquitously

dis-tributed in the northeast coastal environment of Vietnam PCB,

DDT, and HCH compounds were detected in most sediment

sam-ples Chlordanes were detected in about half of the samples, while

aldrin, endrin, dieldrin, and mirex were detected in less than 30% of

the samples Among the target organochlorine pesticides measured,

DDT compounds were the predominant contaminant with

concen-trations ranging from 0.31 to 274 ng g1(Table 1andFig 2) PCBs

were in the concentration range of 0.04–18.71 ng g1 HCHs,

chlordanes, dieldrin, aldrin, endrin, and mirex were present at

rel-atively low concentrations, in the ranges: n.d.–1.00 ng g1, n.d.–

0.75 ng g1, n.d.–1.05 ng g1, n.d.–0.03 ng g1, n.d.–0.01 ng g1,

and n.d.–0.66 ng g1, respectively

DDTs: The dominance of DDT compounds found in estuarine

and marine environment has also been observed in inland Vietnam

such as in freshwater canals and rivers (Nhan et al., 2001; Hung and Thiemann, 2002; Hung et al., 2004).Minh et al (2002, 2004)

also observed high levels of DDTs in human breast milk and resi-dent bird tissues, which they suspect is due to recent usage of DDT in Vietnam Judging by results of POPs monitoring conducted

in Vietnam to date, DDT is predominant POP in the Vietnamese environment DDT has been used as the main insecticide for

malar-ia control in Vietnam It is estimated that 24,042 tons of DDT were used for malaria-vector control from 1957 to 1994 in Vietnam (Hung and Thiemann, 2002) Following the Vietnamese govern-ment’s adoption of a DDT-free malarial control program in 1991 (WHO, 2000), DDT usage has sharply decreased However, it is still suspected that DDTs are used for crop protection and insect control (Hung and Thiemann, 2002) Agricultural application has been an-other major contributor to DDT contamination in Vietnam, which

is one of the biggest rice exporters in the world (Tenenbaum,

1996)

In Asia, DDT is a ubiquitous contaminant through various envi-ronmental matrices In particular, the dominance of DDT com-pounds among POP chemicals is common in developing Asian countries including Vietnam, China, Thailand, and India (Hong

et al., 1999; Monirith et al., 2003) However, a different situation

is found in industrialized Asian countries such as Japan, Singapore and South Korea (Monirith et al., 2003; Wurl and Obbard, 2005; Hong et al., 2006), where industry-related chemicals such as PCBs are present at high levels The Asian Mussel Watch initiative by

Monirith et al (2003)revealed that Vietnam, along with Hong Kong and China, is one of the three countries having the highest DDT con-centrations among 12 Asia-Pacific countries.Minh et al (2002)also reported that resident birds accumulated large quantities of DDTs

in comparison to migrants in Vietnam DDT levels in human breast milk from Vietnam ranked the highest among those reported from Asian countries (Minh et al., 2004) All these studies indicate that Vietnam is one of the more strongly DDT contaminated countries

in Asia To see whether this characteristic is observed in the marine and estuarine sediment as well, we compared DDT concentrations determined in this study with those reported from other Asian countries inFig 3 China and India, the world’s third and the sixth largest consumers of DDT for agriculture, respectively (Li and Mac-donald, 2005), showed the highest DDT concentrations among the nine Asian countries The overall level of DDTs in Vietnam is lower than those in China and India However, the highest DDT concentra-tions in Ha Long Bay and Hai Phong Bay exceed 100 ng g1and are comparable with the high concentrations reported from those two countries (Hong et al., 1995; Pandit et al., 2001; Mai et al., 2002) Except for these contaminated sites, general DDT levels in Vietnam are comparable to those of Hong Kong, Taiwan, and Singapore (Richardson and Zheng, 1999; Doong et al., 2002; Wurl and Obbard,

2005) The level of DDTs in the coastal sediment of Vietnam is

high-er than those of South Korea (Hong et al., 2006) and Japan (Iwata

et al., 1994) Although United States (US) had been the world’s larg-est consumer of DDT (Li and Macdonald, 2005), the level of DDTs in the US coastal sediments (http://www.epa.gov/emap/nca/html/ data/index.html) is relatively lower than those in tropical Asian countries, which could be due to the early restriction of DDT in

US compared to tropical Asian countries Meanwhile, Mediterra-nean coasts of France showed elevated levels of DDTs (Wafo et al., 2006; Gómez-Gutiérrez et al., 2007) even though their early ban

of DDT

The spatial distribution of DDTs indicates that DDT contamina-tion is closely related to human activities Coastal regions including residential, industrial, and harbor areas showed high DDT concen-trations compared with offshore sites (Table 1andFig 2) Interest-ingly, two top ranked sites, HL15 and HP5, are located in harbor regions The high DDT concentration in harbor regions could be linked to the emission of DDTs by ships DDT is known to have

been used as a biocide in antifoulants in the past Recently, UNEP

reported that China is still using DDT as an active ingredient for

antifouling ship paint (

http://www.gefweb.org/Whats_New/docu-ments/Antifouling_Paint_Final.pdf) The enhanced level of DDTs

around harbor regions has also been found elsewhere (Lee et al.,

2001; Barakat et al., 2002; Hong et al., 2006) Therefore, this

sug-gests that the shipping industry may be a source of DDTs in the

Vietnamese coastal environment, along with agricultural and

dis-ease control activities Among the sites surveyed, coastal regions

of Ha Long Bay showed the highest level of DDTs (Table 1 and

Fig 2) Numerous shipping and port facilities for tourism, fishery,

and cargo transport seem to be a local source of DDTs in the Ha Long Bay On the other hand, in the relatively pristine Ba Lat estu-ary, levels of DDTs were much lower than those reported in Hanoi, which reaches levels of 7.4–80.5 ng g1(Nhan et al., 2001) Concentrations of DDT and its metabolites, DDD and DDE, were in the ranges of 0.07–143 ng g1, 0.30–98.8 ng g1 and 0.05–37.7 ng g1, respectively DDD showed the highest mean concentration (6.68 ± 0.12 ng g1) and was followed by DDT (4.44 ± 0.13 ng g1) and DDE (1.96 ± 0.05 ng g1) Metabolites account for 78 ± 13% of total DDTs (Fig 4a), implying that degrada-tion of the parent compound occurs in the Vietnamese marine

Site

HL1 HL2 HL3 HL4 HL5 HL6 HL7 HL8 HL9

HL10 HL11 HL12 HL13 HL14 HL15 HL16 HP

HP10 HP11 HP12 HP13 HP14 HP15 BL

0 10 20 30 100 200 300

Site

HL1 HL2 HL3 HL4 HL5 HL6 HL7 HL8 HL9

HL10 HL11 HL12 HL13 HL14 HL15 HL16 HP

HP10 HP11 HP12 HP13 HP14 HP15 BL

0.0 0.5 1.0 1.5 2.0 2.5

-1 TOC)

0 50 100 150 200

-1 TOC)

0 200 400 600 800 5000 10000 15000

Site

HL1 HL2 HL3 HL4 HL5 HL6 HL7 HL8 HL9

HL10 HL11 HL12 HL13 HL14 HL15 HL16 HP1 HP2 HP3 HP4 HP5 HP6 HP7 HP8 HP9 HP10 HP11 HP12 HP13 HP14 HP15 BL1 BL2 BL3 BL4 BL5 BL6 BL7 BL8 BL9 BL10

0 5 10 15 20

-1 TOC)

0 200 400 1000 1200 1400 1600 1800

Site

HL1 HL2 HL3 HL4 HL5 HL6 HL7 HL8 HL9

HL10 HL11 HL12 HL13 HL14 HL15 HL16 HP

HP10 HP11 HP12 HP13 HP14 HP15 BL

0 1 2 3 4 5 6 7

0 20 40 60 80 100 120

γ-HCH/Total HCHs

a

b

c

d

Fig 2 Spatial distribution of organochlorine compounds and sediment parameters in surface sediments from Ha Long Bay, Hai Phong Bay, and Ba Lat Estuary (a) PCBs, (b) DDTs, (c) HCHs, and (d) TOC content and particle size of sediment.

USA (655)

Mediterranean coast (44)

Hong Kong (21)

Taiwan (19) Singapore (13) Japan (3)

-1 dw)

0.01 0.1 1 10 100 1000 10000

Other Countries Vietnam

(This study)

Location

USA (655)

Mediterranean coast (39)

Hong Kong (21)

Taiwan (19) Singapore (13) Japan (3)

-1 dw)

0.001 0.01 0.1 1 10 100 1000 10000

Other Countries Vietnam

(This study)

Median;

n.d.

a

b

Fig 3 Comparison of the concentrations of (a) DDTs and (b) HCHs in coastal sediments from Vietnam and other countries The number of data for each country is presented

in parentheses In the box plots, the horizontal lines denote the 25th, 50th, and 75th percentile values The error bars denote the 10th and 90th percentile values The dotted

environment However, relatively elevated composition of DDT

(above 50%) found in station HL15 indicates that there still exists

fresh input of DDT in this region

HCHs: HCH compounds are one of the most widely distributed

organochlorine pesticides in the Vietnamese marine sediment

The concentration of HCHs in Ha Long Bay, Hai Phong Bay, and

Ba Lat estuary were in the ranges of n.d.–0.85 ng g1, 0.15–

1.00 ng g1, and 0.03–0.26 ng g1, respectively (Table 1 and

Fig 2) Compared to DDTs and PCBs, their distribution showed a

little spatial variation due to their physico-chemical properties

like high vapor pressure and low particle affinity (Loganathan

and Kannan, 1994), which cause them easier to diffuse via

atmo-sphere and water than DDTs and PCBs The HCH level observed in

this northern part of Vietnam is slightly higher than those

reported from the Mekong River delta located in the southern part (Minh et al., 2007) Among the HCH compounds, a-HCH is the dominant isomer in both Ha Long Bay and Hai Phong Bay with a mean composition of 49%, followed by b-HCH and c-HCH (Fig 4b) Because the a-isomer is the most volatile of the HCH isomers in this subtropical region (ATSDR, 2005), the abundance

of a-HCH means that a technical HCH has been most recently used in these regions c-HCH was not detected in offshore sta-tions but in estuarine and coastal stasta-tions All stasta-tions in Ba Lat Estuary are located within estuary, resulting in increase of com-position of c-HCH in this region

The major regional contribution of a-HCH and b-HCH changed from the Northern Hemisphere mid-latitudes to the Northern Hemisphere tropics after China banned the use of technical HCH

Percent composition (%)

Ha Long Bay Hai Phong Bay

Ba Lat Estuary

o,p'-DDE p,p'-DDE o,p'-DDD p,p'-DDD o,p'-DD T p,p'-DD T

Percent composition (%)

Ha Long Bay Hai Phong Bay

Ba Lat Estuary

α-HCH β-HCH γ-HCH δ-HCH

Percent composition (%)

Ha Long Bay Hai Phong Bay

Ba Lat Estuary

Di Tri Tetra Penta Hexa Hepta Octa Nona Deca

a

b

c

Fig 4 Relative composition of (a) DDTs, (b) HCHs, and (c) PCBs in sediment from Ha Long Bay, Hai Phong Bay, and Ba Lat estuary, Vietnam.

in 1983 (Li et al., 2000, 2003) According to recent investigations by

Li et al (2000, 2003), Vietnam is classified along with India and

Malaysia as being the region having the highest annual emission

per area for both HCH isomers However, levels of total HCHs in

the Vietnamese marine/estuarine sediment are relatively lower

than other Asian countries (Fig 3) The highest HCH concentration

has been observed in India and followed by China, Hong Kong,

Tai-wan, and Japan > Korea > Vietnam United States (US) and

Mediter-ranean countries showed relatively low level of HCHs compared

with Asian countries Previous international monitoring studies

using mussels and residential birds also reported similar

distribu-tions between the Asian countries (Kunisue et al., 2003; Monirith

et al., 2003) The relatively lower accumulation of HCHs in the

Viet-namese environment might be related to rapid evaporation of HCH

isomers after use due to its high volatility in regions with high

temperatures

PCBs: The concentration of PCBs in Ha Long Bay, Hai Phong Bay,

and Ba Lat estuary were in the ranges of 0.11–10.1 ng g1, 0.45–

18.7 ng g1, and 0.04–0.26 ng g1, respectively (Table 1 and

Fig 2) Hai Phong Bay is more contaminated with PCBs than Ha

Long Bay and Ba Lat estuary Considering PCBs originate in

indus-trial activities, relatively high levels of PCBs in Hai Phong Bay

re-flect its relatively high degree of industrialization among the

three study regions Ha Long Bay showed an intermediate

contam-ination level and Ba Lat estuary showed the lowest Similar to DDT

compounds, the PCB level determined in sediment from Ba Lat

estuary is much lower than those reported from its upstream

Red River (Iwata et al., 1994; Nhan et al., 1998; Nhan et al.,

2001) Long residence times of contaminants in the water column

in natural trapping systems such as mangrove forests seem to be

the reason for lower levels of contaminants in the lower reaches

of the Red River The highest concentration of PCBs was found at

station HP5 where shipbuilding industry is located, and followed

by stations HP14, and HP2 In Ha Long Bay, residential and

partic-ularly harbor regions showed relatively high PCB levels The overall

PCB levels in sediments from the Vietnamese coastal environment

is much lower that those reported from industrialized temperate

regions such as USA (Daskalakis and O’Connor, 1995),

Mediterra-nean sea (Wafo et al., 2006; Gómez-Gutiérrez et al., 2007), and

South Korea (Hong et al., 2006)

To see regional differences in PCB patterns, percent

composi-tions of PCB congeners in sediment samples from three regions

are presented in Fig 4c Mid-chlorinated congeners (penta-,

hexa-, and hepta-PCBs) are significantly abundant in sediment

samples from Hai Phong Bay in comparison with those of Ha Long

Bay (Student t-test, p < 0.005) and Ba Lat estuary (Student t-test,

p < 0.001) On the other hand, low-chlorinated congeners (di-,

tri-, and tetra-PCBs) are relatively abundant in samples from Ha

Long Bay and Ba Lat estuary The percent composition of low- and

mid-chlorinated PCBs in these three regions are as follows:

21 ± 12%:78 ± 12% for Hai Phong Bay, 38 ± 18%:58 ± 19% for Ha

Long Bay, and 47 ± 11%:40 ± 13% for Ba Lat estuary In a previous

study, we observed an enhanced signal of higher chlorinated

cong-eners close to shipyards and harbor regions (Hong et al., 2005),

where penta- to hepta-chlorinated congeners comprised 74% of

to-tal PCBs Hai Phong has been long viewed as a center of the

Viet-namese ship building industry, which accounts for about 50% of

the whole country’s capacity (http://www.marinelink.com/Story/

Haiphong,+Shipbuilding+Center+of+Vietnam-205521.html) Along

the river of the bay, various scales of ship repair/construction

faci-lities are located and shipping activities are very active throughout

the bay These intensive industrial activities result in rather

dis-tinct PCB signatures in this bay compared to other regions By

con-trast, the congener patterns in Ba Lat estuary are similar to those

observed in the regions having no typical local contamination

sources in a Korean nationwide monitoring study (Hong et al.,

2006), where di- to tetra-CBs and penta- to hepta-CBs comprised

47 ± 16% and 42 ± 16% of total PCBs, respectively

Chlordanes, aldrin, endrin, dieldrin, and mirex compounds were rarely detected in the samples and were only present at low con-centrations (Table 1) However, the spatial distribution of chlord-anes is similar to the DDT compounds, showing relatively high levels along the coastline of Ha Long Bay Among the chlordane compounds, trans-nonachlor is relatively abundant, which might

be due to its relatively high persistence property (Strandberg

et al., 1998)

3.1 Relationship between organic pollutants, TOC, and sediment particle size

InTable 1andFig 2, data on total organic carbon (TOC) and par-ticle size in surface sediments are presented The TOC content in sediments collected from Ha Long Bay, Hai Phong Bay, and Ba Lat Estuary were in the ranges of 1.01–6.38%, 0.71–1.63%, and 0.34– 1.2%, respectively Average TOC content was highest in Ha Long Bay, where coastal stations (from HL11 to HL16) showed more ele-vated levels of TOC contents than offshore stations Silt and clay contents showed a little spatial fluctuation

In Ha Long Bay, there was a significant correlation between TOC and PCBs (r2= 0.51, p < 0.001) When station HL15 was not consid-ered, better correlations between TOC and PCBs (r2= 0.92 p < 0.001) was found and there also appeared correlation between TOC and DDTs (r2= 0.47, p < 0.005) Station HL15 showed the ele-vated OCs concentration compared with its TOC content, implying that there exists localized input source, and proximity to source is governing factor in this station Meanwhile, no significant relation-ship (p > 0.05) between OCs and sedimentary parameters (TOC and particle size) in Hai Phong and Ba Lat Estuary were observed Region with spatially limited pollution sources and relatively homogenous environmental conditions, Ha Long Bay, showed sig-nificant correlation between TOC and OCs While, Hai Phong Bay which has spatially scattered pollution sources and heterogeneous dynamic environmental conditions did not show any governing sedimentary parameters over distribution of OCs The concept that TOC and other sedimentary parameters are the main factor domi-nating the sorption of OCs to sediment has been intensively stud-ied (Edgar et al., 2003; Hung et al., 2007and references therein) Good correlation between OCs and TOC can result from either post-depositional sorption or co-emission (Hung et al., 2006) Rel-atively homogeneous environmental conditions like offshore (Kyeonggi Bay, Lee et al., 2001), continental shelf (Yellow Sea,

Zhang et al., 2007) provides TOC dependent post-depositional sorption environment Spatially limited or defined sources could give localized enrichment and gradient of TOC and OCs (Hung

et al., 2006, 2007) Some studies show a lack of correlation between OCs and TOC or particle size, but state that it is the origin of the or-ganic matter that is most important in determining the partition-ing to sediment (Edgar et al., 2003; Secco et al., 2005)

3.2 Ecotoxicological concern

To roughly evaluate the ecotoxicological significance of OC con-tamination in Vietnamese coastal sediments, the data were com-pared with the Canadian environmental quality guideline for marine sediment (CCME, 2002) inFig 5 This guideline specifies the ‘‘interim sediment quality guideline” (ISQG) and the ‘‘probable effect level” (PEL) The ISQG represents the chemical concentration below which an adverse effect would rarely be observed, whereas the PEL represents the concentration above which adverse effect would frequently occur

To compare the data with the guidelines, our sums of 18 PCB congeners (IUPAC Nos 8, 18, 28, 44, 52, 66, 101, 105, 118, 128,

138, 153, 170, 180, 187, 195, 206, and 209) were multiplied by a

factor of 2 (2  18 PCBs), following the method adopted by

Daskal-akis and O’Connor (1995)andO’Connor (1996) PCB concentrations

in this study exceeded the ISQG value (21.5 ng g1) at two sites, but

all are below the PEL value (189 ng g1) All sites above the ISQG

value of PCBs are located in Hai Phong Bay (station HL5 and

HL14) This suggests that PCBs are of concern in Hai Phong Bay

and it is probably necessary to continue monitoring the possible

sources and levels of PCBs in this region Concentrations of p,p0

-DDT, p,p0-DDD, and p,p0-DDE exceeded the ISQG values at 10 sites,

17 sites and 4 sites, respectively, among which 2 sites for p,p0-DDT

and 3 sites for p,p0-DDD also exceeded the PEL values Among the

chemicals investigated in this study, only DDT compounds

ex-ceeded their respective PEL values This result indicates that DDT

is still the chemical of most concern in Vietnam, although

concen-trations are decreasing (Minh et al., 2007) The levels of lindane

(c-HCH) and dieldrin compounds are over their ISQG values at one

site but below the PEL values For chlordane and endrin, all of

the sites showed lower levels than the ISQG values Comparison

of the OC concentrations in Vietnamese coastal sediments with

the Australian and New Zealand Guideline (ANZECC and

ARM-CANZ, 2000) also showed similar results Based on these results,

it is concluded that DDTs are the main compound of concern in

the Vietnamese environment and that the overall concentration

levels of organochlorines, except for DDTs, in sediments from the

northeast coast of Vietnam are relatively low from an

ecotoxicolog-ical aspect for benthic organisms However, they could cause

prob-lems for fish and wildlife through trophic transfer Therefore,

further follow-up studies on POPs contamination in fish and wild-life from the bays are needed

Acknowledgments The authors wish to acknowledge Tran Lieu Thi, Ho Dung My, Le Tuyen Huu for their assistance in collection and processing of sam-ples, and Dr Dhong Il Lim for providing the particle size analysis This work was supported by Grants-in-aid from International Cooperative Research Project of Ministry of Science and Technol-ogy, Korea (Grant No BSPN50300-1640-4) and Ecotechnopia-21 Program of Ministry of Environment, Korea (Grant No 120010032)

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