163 transport and bioaccumulation

Hundreds of samples including soil, sediment and fish were collected at the Bien Hoa Agent Orange hotspot for assessment of the environmental contamination caused by dibenzo-p-dioxins an

12TH IHPA FORUM AND SELECTED STUDIES ON POPS

Transport and bioaccumulation of polychlorinated

Orange hotspot in Vietnam

Nguyen Hung Minh

Received: 13 August 2014 / Accepted: 2 December 2014 / Published online: 17 December 2014

# Springer-Verlag Berlin Heidelberg 2014

Abstract The Bien Hoa airbase (south of Vietnam) is known

as one of the Agent Orange hotspots which have been

seri-ously contaminated by Agent Orange/dioxin during the

Viet-nam War Hundreds of samples including soil, sediment and

fish were collected at the Bien Hoa Agent Orange hotspot for

assessment of the environmental contamination caused by

dibenzo-p-dioxins and polychlorinated dibenzofurans

(PCDD/Fs) The toxicity equivalency quotient (TEQ)

concen-tration of PCDD/Fs in soil and sediment varied from 7.6 to

962,000 and 17 to 4860 pg/g dry wt, respectively, implying

very high contamination of PCDD/Fs in several areas

PCDD/F levels in fish ranged between 1.8 and 288 pg/g

TEQ wet wt and was generally higher than advisory

guide-lines for food consumption 2,3,7,8-Tetrachlorinated

dibenzo-p-dioxins (2,3,7,8-TCDD) contributed 66–99 % of TEQ for

most of the samples, suggesting 2,4,5-trichlorophenoxyacetic

acid (2,4,5-T) from Agent Orange as the major source of the

contamination The vertical transport of PCDD/Fs was ob-served in soil column with high TEQ levels above 1000 pg/g dry wt (Vietnamese limit for necessary remediation

vertical transport of PCDD/Fs has probably mainly taken

to the leaks and spills of phenoxy herbicides and solvents The congener patterns suggest that transports of PCDD/Fs by weathering processes have led to their redistribution in the low-land areas Also, an estimate for the total volume of contaminated soil requiring remediation to meet Vietnamese regulatory limits is provided

Keywords Dioxin Contaminated site 2,3,7,8-TCDD Agent Orange 2,4,5-T Fish

Introduction

Bien Hoa is a city of the Dong Nai province and located about

35 km east of Ho Chi Minh City The area of Bien Hoa city is

people in 2012 During the Vietnam War, Bien Hoa airbase was one of the most important military facilities of the United States (US) army in Vietnam From 1961 to 1972, under the Operation Ranch Hand carried out by the US Army, about 74 million litres of defoliants were sprayed to destroy forest canopies and crops belonging to the North Liberty Army

chlori-nated phenoxy herbicides 2,4,5-trichlorophenoxyacetic acid (2,4,5-T)- and 2,4-dichlorophenoxyacetic acid (2,4-D) as ac-tive ingredients in different concentrations in the formulations labelled as Agent Orange, Agent Purple and Agent White with Agent Orange nearly contributing half of total defoliant

Responsible editor: Roland Kallenborn

This article belongs to the series “Dioxin and POP Contaminated Sites”

(Weber et al 2008 ) edited by Roland Weber, Mats Tysklind and Caroline

Gaus.

N Van Thuong:N X Hung:N T Mo:N M Thang:P Q Huy:

H Van Binh:V D Nam:L K Son:N H Minh ( *)

Dioxin Laboratory Project, Vietnam Environment Administration

(VEA), Nr 556 Nguyen Van Cu, Long Bien, Hanoi, Vietnam

e-mail: lab.dioxin@gmail.com

N Van Thuy

Center for Environmental Monitoring (CEM), Vietnam Environment

Administration (VEA), Nr 556 Nguyen Van Cu, Long Bien, Hanoi,

Vietnam

L K Son

Office of the National Steering Committee 33, Ministry of Natural

Resources and Environment (MONRE), Nr 83 Nguyen Chi Thanh

Street, Dong Da, Hanoi, Vietnam

DOI 10.1007/s11356-014-3946-9

volume (Stellman et al.2003) More importantly, most of the

defoliants contained the extremely toxic by-products

dibenzo-p-dioxins and polychlorinated dibenzofurans (PCDD/Fs),

es-pecially the most toxic isomer 2,3,7,8-Tetrachlorinated

dibenzo-p-dioxins (2,3,7,8-TCDD) The total amount of

PCDD/F sprayed during Vietnam war was between 366 and

1223 kg toxicity equivalency quotient (TEQ) (Stellman et al

inven-tory of approximately 140 kg/year considering average per

TEQ kilogramme scales is related with deposits of single

former pesticide productions producing 2,4,5-T (Götz et al

historic use of pesticides in Japan (approx 450 kg TEQ) or

wood preservatives in Sweden (250 kg TEQ) demonstrating

the historic overall relevance of pesticide use for global dioxin

PCDD/Fs are known as one of the most toxic man-made

chemicals belonging to the group of persistent organic

pollut-ants (POPs) listed in the Stockholm Convention The

expo-sures of humans and animals to PCDD/Fs at low levels have

been linked with negative health effects such as the

develop-ment of cancer, reproductive problems, immune alterations,

It is estimated that during the Ranch Hand operation,

between 2.1 and 4.8 millions of Vietnamese people were

possibly exposed to dioxins by means of the Agent Orange

effects and health consequences from the AO spraying are

observed in Vietnam until today Great efforts from the

Viet-namese Government and international communities have been

made to overcome the consequences of AO/dioxin in the

It was estimated that approximately 33 million litres of the

defoliants (45 % of total defoliant used) were transported to

Bien Hoa airbase for the Ranch Hand missions Among those,

AO was accounted for about 60 % (approximately 20.4

mil-lion litres or 98,000 drums, each of 208 l) The improper

handlings of the chemicals and accidental spills were the main

reasons leading to the extremely high contamination of

di-oxins found in the airbase For example, from December 1969

to March 1970, four major accidental spills occurred at Bien

Hoa airbase Two spills were associated with the 28,000-l

tanks of AO and two others with the 28,000-l tanks of Agent

White (AW) The spills and leakages have caused extremely

high levels of AO-related dioxin (AO/dioxin) pollution at

certain areas in the airbase making the airbase well known

as one of the AO/dioxin hotspots in Vietnam (Dwernychuk

of AO/dioxin contamination to the local environment and

human health, the Government of Vietnam had implemented

a 3-year project starting from 2006, in order to contain the highest dioxin-contaminated areas commonly known as the Z1 site (area of 4 ha) by a secure landfill However, the airbase has been used for various military purposes, making the site assessment for environmental investigation much limited In

2007, a seminar between the US Department of Defense and the Vietnam Ministry of Defense in Hanoi for sharing infor-mation on the historical usage of the herbicides has unveiled

an operation coded as Pacer Ivy which revoked and returned

This has raised more concern about potential AO/dioxin-contaminated sites which have not been noticed before by environmental investigators Furthermore, the existing AO/ dioxin contamination could be widely dispersed to larger areas because the contaminated soil was washed out by floods and

implement a comprehensive assessment of the area including possibly affected fish to understand the present distribution and transport of the AO/dioxin contamination in Bien Hoa airbase and its vicinities The results will help to identify the extension and scale of the contamination and thus provide useful information for subsequent environmental remediation steps

Materials and methods

Sampling locations

Topographical surveys

In order to record basic features for the designing of the sampling campaign, the topographical survey for the Western contaminated area (Pacer Ivy area) and ponds and lake down-stream of the most heavily contaminated area (namely Z1) of

the Western contaminated area is completely rough and

divid-ed by internal roads, ponds and lakes The slope of the Western contaminated area is downward to the west part with the elevation in the east part, and the lowest land is the bed of ponds system Rainwater from Pacer Ivy contaminated site may contain dioxins/toxicants that flows into ponds and lower land in the West, then into Dong Nai River through the sewer

low-land areas near Pacer Ivy site have been identified for the

Previous sampling survey primarily focused on the assess-ment and mitigation of dioxin impacts in the Z1 area, the southwest area of the airbase and the southwest corner of the

terrain with a slight slope to the south Therefore, rainwater may carry the contaminated soil from the southwest area to

lakes and ponds nearby (Fig.1) The Z1 contaminated area

located on the south of the airbase includes the a former

storage area and washing area used for the Ranch Hand

Operation Over the years, the natural influences and human

activities have caused surrounding land of Z1 to considerably

change its topographic feature Human activities included the

digging of drainage channel, concrete capping and planting

and cutting of trees caused the mobilization of contaminated

soil from Z1 area to lower land in the south of the site In

addition, the erosion by rain and floods can result in the

accumulation of dioxin-contaminated soil which is washed

out from the site The slope of the Z1 area and the surrounding

land is downward from highly contaminated site towards the

lake and low land of the South Basing on the field surveys,

we identified suspect contaminated ponds and lakes impacted

by drain water from the Z1 area including Z1 Lake, G2 Lake

Sampling of soil, sediment and biological samples

In this study, 106 samples (surface and sub-surface soil down

to a depth of 2.4 m) were collected in the Pacer Ivy

contam-inated area and vicinities based on topographic surveys The

The whole area was divided into many lots (50×50 m), and

each surface soil samples consisted of five sub-samples

com-posites The sampling procedure followed strictly those used

in previous studies implemented by Hatfield Consultants

developed by us in order to take soil samples down to 2.4 m in

depth Surface sediment samples were collected by Ekman

dredge from surface to depth of 10 cm underwater sediment

bed Besides, sediment core were collected by a core sampler and divided into several segments of 5 cm which were then considered sub-samples

Tilapias (Oreochromis niloticus) were collected in ponds and lakes, and also, muscles were taken for analysis of PCDD/Fs A duck sample (muscle tissue) was also collected

transferred into pre-cleaned glass jars and transported to the laboratory All soils or sediments and biological samples were

respectively

Analysis of PCDD/F

All samples were analyzed for 17 2,3,7,8-substitute PCDD/Fs and TEF values given by WHO; 2005 was used to calculate TEQ concentration Soil and sediment samples were expressed

on a dry weight basis, while biological samples were on a fresh weight basis The analytical procedure followed the US EPA

PCDD/Fs by isotopic dilution with gas chromatography and high-resolution mass spectrometer HRGC/HRMS (Micromass Auto Spec Ultima system [Waters, UK] with Agilent 7890A gas chromatograph [Agilent, USA]) The method was accord-ing to US EPA Method 1613 with minor modifications consid-ering available recent advanced techniques All modifications were adequately validated prior to regular usage

The soil samples were dried at room temperature, crushed and sieved to less than 1 mm Briefly, 2 g of sample was then

pres-surized liquid extraction in 60 min with DCM:hexane (10:90, v/v) at 120 °C and 1700 psi Cleanup steps were performed by

Fig 1 Map showing Bien Hoa airbase and relevant sampling sites (2011 –2013)

the Fluid Management Systems (FMS, USA) following the

recommended procedure by the manufacturer (FMS, 2008)

and were validated in our laboratory Basically, pre-packed

silica column (Silica #PCBS-ABN-STD, FMS), alumina

col-umn (Alumina #PCBA-BAS-011, FMS) and carbon colcol-umn

(Carbon #PCBC-CCE-034) were used for cleanup and

stan-dards were added to the concentrated aliquot of the sample

prior to quantification

Separation and quantification was conducted using a

thickness, J & W Scientific Inc., Folsom, CA) The oven

temperature program was as follows: 140 to 220 °C at

5 °C/min, kept at 220 °C for 16 min, increased from 220 to

235 °C at 5 °C /min, kept at 235 °C for 7 min, increased from

235 to 330 °C at 5 °C/min and kept at 330 °C for 4 min The

injector and interface temperatures were set at 290 and 250 °C,

respectively The mass spectrometer was operated with a

resolution greater than 10,000 and positive electron impact

(EI) conditions Data were obtained in the selected ion record

All of the sediment and biological samples were analyzed

at the Eurofins Laboratory in Hamburg, Germany and the

Laboratory of Organic Analytical in Wadsworth Center,

USA The standard method for analysis of PCDD/F in the

Eurofins Laboratory and Laboratory of Organic Analytical in

Wadsworth Center was followed by EN:1948 and US EPA

1613, respectively These analytical methods have previously

Quality control

To ensure free cross contamination during field sampling, all utensils used were thoroughly washed and rinsed three times

by acetone, followed by hexane before sampling Solvent rinses were also collected and analyzed as control samples for clean degree of samplers and utensils Besides, quality control (QC) data was carried out in order to meet require-ments of the analytical method QC data included laboratory blank, laboratory duplicate and surrogate analysis for each batch of 20 samples Moreover, 30 soil samples conducted

in 2011 were cross-check analyzed by an international

standards for soil or sediment and biological samples was ranged from 50 to 150 % For soil or sediment samples, the method detection limits were 0.5 and 3.33 ng/kg for tetra-CDD/Fs and penta- to octa-CDD/F congeners, respectively The detection limits of the method for tissues samples were 0.1, 0.5 and 1.0 ng/kg for tetra-CDD/Fs, penta- to hepta-CDD/

Fs and octa-CDD/Fs congeners, respectively

Results and discussion

PCDD/F contamination status

The PCDD/F contamination in vicinities of the Z1 site

Although the most contaminated site namely Z1 was

Table 1 General information of the sampling locations in Bien Hoa airbase

Sampling location/

sample kind

Location area (ha)

Number of sample

Year of sampling Z1 Lake

G2 Lake

Bien Hung Lake

Pacer Ivy area

its existence in over 30 years has caused the transport and

distribution of the dioxin contamination in the wider vicinity

due to the runoff of the contaminated soil in weathering

processes such as flood, rain, wind, etc In this study, sediment

samples were collected in two low land areas (named as Lake

Z1 and Lake G2) which could serve as reservoirs for the

of PCDD/F and TEQ levels in sediment samples from these

concen-tration on mass basis is 2720 pg/g dry wt (560–5330 pg/g dry

wt) in Lake Z1 and 5680 pg/g dry wt (2600–9900 pg/g dry wt)

in Lake G2 The mean TEQ concentration is 503 pg TEQ/g

dry wt (147–1030 pg TEQ/g dry wt) and 317 pg TEQ/g dry wt

(219–472 pg TEQ/g dry wt) in Lake Z1 and Lake G2,

respec-tively These sediment contamination levels were higher

com-pared to the allowance level of PCDD/Fs in bottom sediment

set by the Vietnamese authorities (150 pg TEQ/g dry wt;

elevated contamination of PCDD/Fs in the bottom sediment of

lakes close to the Z1 site which is the major original AO/

dioxin contamination source The elevated PCDD/F

contam-ination in the low land areas can be understood considering

that runoffs from the Z1 site are being received by these lakes

for more than 30 years until the present time The

2,3,7,8-TCDD contribution to TEQ in all sediment samples from

these two lakes was very high (95 and 92 % in Lake Z1 and

G2, respectively) This congener pattern shows that the source

of the PCDD/F contamination in the lakes is derived from the

AO/dioxin contamination resulting from 2,4-D and 2,4,5-T

In the present study, sediment samples were also collected

from three other lakes which distribute further to the north of

Currently, there is no direct input of the runoff from Z1 site to

these lakes, and thus, it is interesting to compare the PCDD/F

accumulation in these lakes with those in Lake Z1 and G2 On

average, the mass concentrations of PCDD/Fs in the sediment

of Lake Bien Hung, Lake 4A and Lake 4B were 8590, 1270

and 8930 pg/g dry wt, respectively with TEQ concentrations

of 70, 53 and 42 pg TEQ/g The results revealed that all the

sediment samples has lower PCDD/F TEQ contamination in

comparison to the Vietnamese sediment standard (150 pg

TEQ/g, REF) The TEQ levels in these three lakes were about

4.5- to 12-folds lower compared to those in Lake Z1 and G2,

suggesting significantly less influence of the contamination

from Z1 site to the three lakes However, it should be noted

that the contribution of TCDD to the TEQ for these three lakes

still vary in a relatively high range (73–91 %) Kishida et al

TEQ for sediment collected at Can Gio, Hue and Ha Noi were

PCDD/Fs and dioxin-like polychlorinated biphenyls

could be considered as general TEQ background levels in lake

ponds near Bien Hoa airbase have higher TEQ levels com-pared to the general range in Vietnam

The TEQ concentrations in Lake Bien Hung, Lake 4A and Lake 4B were significantly lower than those in Lake Z1 and

octachlordibenzodioxin (OCDD) was higher in the earlier

phenomenon perhaps implies that there were inputs of PCDD/Fs which are dominated by OCDD to Lake Bien Hung, Lake 4A and Lake 4B These lakes might have received PCDD/Fs mainly from other sources such as

which also largely originate from PCP (Baker and Hites

con-tribution stems from 2,3,7,8-TCDD, and therefore, dioxin toxicity stems largely from the AO/dioxin with high TEQ

PCDD/F contamination in the Pacer Ivy site

Analytical results from 59 surface soil samples showed very high TEQ concentrations of PCDD/Fs at the Pacer Ivy site The TEQ levels range from 7.6 to 962,000 pg TEQ/g with the mean concentration of 18,260 pg TEQ/g dry wt Furthermore, the 2,3,7,8-TCDD TEQ contribution for these samples were

elevated concentrations were found at the southwest corner of the site which is close to a taxiway of airplanes The mean and the highest TEQ concentrations in this site are hundred folds higher compared to those found in the A Luoi former airbase

in the North Central Coast region of Vietnam (Dwernychuk

From 1970 to 1972, the Pacer Ivy operation was launched

to revoke the unused defoliant barrels for transport back to the

barrels were recovered or emptied to soil, and therefore, these sites could be contaminated seriously by AO/dioxins leaking from these activities The extremely high concentration of

support this hypothesis In the present study, it is estimated that the elevated contamination of AO/dioxin covered an area

In the current study, 10 soil column samples were collected

in the Pacer Ivy site, and totally 48 samples at various depths were determined for PCDD/F residue levels The soil columns were segmented in 30-cm samples, and each soil segment was

% TCD

L Sediment

– 1,271,000

homologized for a representative sample The depth of the soil

columns depended on the hydrological conditions at each

point In most cases, the column could reach to the shallow

water table when soil became wet and could not be drawn up

collected at 180–210 cm The analytical results are shown in

observed that the highest mean concentration (130,000 pg

g at the depth of 180–210 cm It is important to note that at the

above the allowance of PCDD/F levels recommended for

necessary remediation actions in Vietnam (1000 pg TEQ/g,

and depth profile of PCDD/Fs changed among the soil

col-umns, this result demonstrates a large amount of the AO/

dioxin-contaminated soil to be remediated at the site in the

future The high levels of PCDD/Fs were also found in the

contaminated sites where it produced chlorinated pesticide,

PCB and the related contaminants all over the world (Weber

the high concentration of PCDD/F contaminated from the site

caused by AO/dioxin storage and usage at Bien Hoa airbase

during the war

Also, in all these samples, the same unique PCDD/F

pat-tern with the high 2,3,7,8-TCDD TEQ contribution (89–99 %)

was observed, proving AO/dioxin as the dominant

Fs showed an increase as the depth of soil increases (75–91 %,

data not showed), while those of OCDD/∑PCDD/Fs was

PCDD/F residues in the deeper layers may have existed there

at the early time of the contamination occurrence rather than

being the results of the vertical movements of PCDD/Fs over

40 years since the contamination occurred Perhaps, at the time when AO/dioxin leakage and spill occurred, solvents which were used to dissolve the defoliants (Alvin L Young

PCDD/Fs downward

Sediment samples collected from ponds in this area had very high PCDD/F and TEQ concentration (6540 pg/g and

TEQ concentration is about 3- to 30-folds higher compared to those in Lake Z1 and other lakes outside of the airbase The contamination in Pacer Ivy ponds is extremely high when compared to the maximum concentration required for sedi-ment remediation (150 pg TEQ/g, TCVN) Consequently, tilapia and duck muscle tissue samples collected in this area also contained very high PCDD/F levels (respectively 182 and

36 pg TEQ/g wet wt, on average) Also here, very high contribution of 2,3,7,8-TCDD to total TEQ in fish and duck was found (96–99 %), suggesting that the AOA/dioxin con-tamination accumulates in the aquatic animals Although the Vietnamese authorities have not set PCDD/F standards for food, the concentration observed in fish samples of this study

is several folder higher than the allowable level issued by Health Canada (20 pg TEQ/g wet wt, Health Canada…) or

impose significant health risk to people who might have consumed or consume such local food items

PCDD/F homologue profiles

basis) in different soil layers from 0 to 150 cm The profiles consistently revealed very low concentration of PCDFs and the dominance of TCDD (75–92 % in the total mass concentration) The 2,3,7,8-TCDD contribution slightly in-creased from the surface layer (75 %) to the deeper layers (92 %) More interestingly, the results might also imply that the movement of PCDD/Fs to the deeper soil in the past might occur relatively fast when the initial concentration of

Fig 2 Distribution of PCDD/Fs

in deep soil in Bien Hoa airbase

TCDD was much higher than other congeners This is

evidence supporting our previous consideration that solvent

mixtures which were used to dilute the herbicides might

play as a mean to transport the chemicals to deeper soils If this is the fact, the contamination at deeper soil would be expected to vary largely as it is in the surface, and thus, the estimation of the contaminated soil may face considerable variation

The PCDD/F homologue profiles on mass basis are

different sites in and around the airbase Even though TCDD is the most abundant congener contributing to

showed higher levels of OCDD compare to TCDD It is also known that from tetrachlorinated to octachlorinated CDDs, the water solubility decreases by about 4 orders of magnitude and thus favouring the accumulation of OCDD

in the atmosphere and in the lake sediment and reported the significant enhancement of OCDD in sediment compared to all other congeners

In the present study, we found that sediment samples collected in ponds/lakes close to the original contaminated sites (e.g Pacer Ivy and Z1 sites) contained much higher

other hand, the proportion of OCDD showed a reverse trend

erosions in the contaminated sites by weathering processes (rains, floods, winds, etc.) had brought the contaminated soil/sediment to the farther ponds/lakes where the

contaminat-ed soil/scontaminat-ediment was mixcontaminat-ed with the existing scontaminat-ediment and therefore decreasing both the concentration and the proportion

of TCDD This observation might be relevant for the assess-ment of monitoring data in the search of unknown AO/dioxin contamination sites

duck samples which were collected from the same area were presented It is interesting to observe the large variation of the profiles among these samples The TCDD contribution is higher in the profile of biota samples (fish and duck) com-pared to those in abiotic matrices (soil and sediment) Vice versa, the heptachlordibenzodioxin (HpCDD) and OCDD show a higher contribution in abiotic matrices It is suggested that in an aquatic environment, hydrophobic compounds such

effec-tively bioaccumulated than those compounds with lower log

making them less bioavailable to organisms (Loonen et al

bioaccumula-tion potential of 2,3,7,8-TCDD compared to the higher chlo-rinated congeners

In other geographical areas, the contribution of TCDD congener to PCDD/F mass concentrations in fish samples

is quite low compared to other congeners such as OCDD,

Fig 3 PCDD/F congener profiles (on mass basis) in different soil layers

at the Paver Ivy site (a –e)

HpCDDs and HxCDDs (Lirong et al 2014;

hand, in this study, TCDD was found as the highest

congener in the fish showing ongoing contamination of

TCDD contamination in fish at the Agent Orange hotspots

also today

Furthermore, the high TCDD levels in Bin Hoa airport

and also in fish collected from A Luoi area at another AO/

dioxin hotspot in Vietnam ranging from 21 to 51 pg/g (all

contamination levels when comparing to other geographical

concen-tration from 0.1 to 0.92 pg/g TEQ (PCDD/F) in six fish

species from Dongting (China) In Germany, Stachel et al

in eels and white fish in the Elbe River also impacted by

dioxin contamination but from industrial sources (Götz

con-centrations varied from 0.17 to 13.6 pg/g in the

Mediterranean Sea (Javier et al 2013) and 0.03–0.31 pg/g

river is also impacted by a former HCH production

levels in fish are much higher than the above locations, demonstrating the high PCDD/F contamination in the fish near the Bien Hoa hotspot (and A Luoi area)

At the present, there is no regulation in Vietnam for the allowable level of PCDD/Fs in fish However, the evalu-ation of the fish TEQ levels in this study can rely upon the European Commission (EC) Regulation No 466/2001/

EC which recommends 3.5 pg/g TEQ (w/w) as the per-mitted maximum level of PCDD/Fs in fish muscle tissue

It is recognized that the levels found in this study are far exceeding this EC Regulation Therefore, since

2012, the local authorities have put restriction on the accessibility and bans on the aquaculture and the con-sumption of fish and related food items in the contam-inated ponds

Fig 4 PCDD/F congeners profiles (on mass basis) in sediment samples from different areas in and around Bien Hoa airbase (a –f)

This study demonstrates elevated contamination of PCDD/Fs

in the Bien Hoa airbase as well as transport of the

contamina-tion to the surrounding areas due to weathering processes The

congener fingerprint with 2,3,7,8-TCDD as a marker

conge-ner shows that the contamination of PCDD/Fs is derived from

uses and handlings of Agent Orange by the US Army during

the wartime in Vietnam As a consequence, several lakes and

ponds located in and near the Bien Hoa airbase have become

sinks for dioxin’s residues over time These dioxin reservoirs

in sediments and soils serve as a source for PCDD/F

contam-ination in aquatic biota such as fish by bioaccumulation and

thus also as exposure risk to human consumers Despite the

ban of catching fish by local authorities, it is suspected that a

portion of the local population may consume fish and other

local foods and be exposed to dioxins through other

environ-mental exposure pathways with associated health risk

Basing on available results, it is estimated that a

may need remediation actions to meet the Vietnamese

guide-line (1000 ng TEQ/kg for soil and 150 ng TEQ/kg for

sedi-ment) The complex vertical distributions of dioxin

contami-nation have been observed, and high concentrations (i.e

above 1000 ng TEQ/kg) might distribute in a depth from 0

to 1.8 m in the investigated sites However, at certain places

with particular spills, it might reach deeper soil layers Future

studies are needed for further assessment on the PCDD/Fs

exposure pathways and the human health risks in the

sur-rounding communities

Acknowledgments This study was jointly implemented under the frameworks of the project “Establishment of Dioxin Laboratory in Viet-nam ” (AP-16657 and BMGF-50799), the Research Grant KHCN-33.01/ 11-15 from the Vietnam National Science and Technology Research Program KHCN-33/11-15 (Research and overcoming long-term conse-quences of Agent Orange/Dioxin on the environment and the human health in Vietnam) The authors would like to express sincerest thanks to

Dr Roland Weber (POPs Environmental Consulting, Germany) for crit-ical reading and comments to the manuscript.

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Fig 5 PCDD/F congener profiles (on mass basis) in abiota (soil and sediment) and biota (fish and duck) collected at the Paver Ivy site (a –d)