PCBs in central vietnam coastal lagoons levels and trends in dynamic environments

Marine Pollution Bulletin 62 (2011) 1013–1024

Contents lists available at ScienceDirect

Marine Pollution Bulletin
journal homepage: www.elsevier.com/locate/marpolbul

PCBs in Central Vietnam coastal lagoons: Levels and trends
in dynamic environments
Silvia Giuliani a,⇑, Rossano Piazza b,c, Luca Giorgio Bellucci a, Nguyen Huu Cu d, Marco Vecchiato b,c,
Stefania Romano a, Cristian Mugnai a, Dang Hoai Nhon d, Mauro Frignani a
a

CNR-Istituto di Scienze Marine, Via Gobetti 101, 40129 Bologna, Italy
Dipartimento di Scienze Ambientali, Università di Venezia, Dorsoduro 2137, 30123 Venice, Italy
CNR-Istituto per la Dinamica dei Processi Ambientali, Dorsoduro 2137, 30123 Venice, Italy
d
Institute of Marine Environment and Resources, 246 Da Nang Street, Haiphong City, Vietnam
b
c

a r t i c l e

i n f o

Keywords:
Polychlorinated biphenyls
Sediments
Historical trends
Coastal lagoons
Central Vietnam

a b s t r a c t
PCBs were analysed in surficial sediments and selected sediment cores collected between 2002 and 2008
in Central Vietnam coastal lagoons. The aim was to determine contamination levels and trends, and to
evaluate the effects of anthropogenic pressures and natural events. Samples were mostly fine-grained
with low total PCB concentrations (0.367–44.7 lg kgÀ1). Atmospheric transport and post depositional
processes modify to some degree the fingerprint of PCB inputs to the environment favouring the predominance of 3, 4 and 5 chlorinated congeners. The similarity of congener distributions in contemporary surficial samples also suggests the presence of a unique source over the entire study area, probably
connected to mobilisation and long range transports from land-based stocks. The removal of consistent
sediment layers is hypothesised based on repeated samplings of the same area. Natural meteorological
events (such as typhoons) are suspected to be responsible for these sediment losses.
Ó 2011 Elsevier Ltd. All rights reserved.

1. Introduction
Polychlorinated biphenyls (PCBs) are compounds with a wide
range of properties. Commercially PCBs were marketed as mixtures
with a degree of chlorination from 21% to 68%. The most commonly
used were those with a chlorine content between 42% and 54%, such
as Aroclor 1242 and 1254 (Barbalace, 2003). Starting from their first
commercialisation in 1929, these mixtures were used in many open
(e.g., as lubricants, softeners for plastics and glues, laminating
agents in paper production, impregnating agents, fire retardants,
printing inks, oils, paints, self-copying paper, cement plaster and
casting agents, insecticides, etc.) and closed systems (e.g., insulation
liquid in capacitors, insulation and cooling liquid in transformers,
hydraulic oils, heat exchangers), but their danger was soon
acknowledged and the production was first regulated and then
banned in the late 1970s (Erickson, 2001). Despite these efforts,
PCBs have become ubiquitous pollutants, due to many factors: (1)
the multiplicity of PCB sources and transport mechanisms; (2) the
fact that their use is still allowed in enclosed transformers and

capacitors, and (3) the presence of PCB in old ships as hydraulic
liquids and covers of electric cables (Hutzinger et al., 1974; Atlas
et al., 1986). In addition, landfills are now considered a major source,
⇑ Corresponding author. Address: Consiglio Nazionale delle Ricerche Istituto di
Scienze Marine, Sede di Bologna, Via Gobetti 101, 40129 Bologna, Italy. Tel.: +39
051 6398864; fax: +39 051 6398940.
E-mail address: (S. Giuliani).
0025-326X/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved.
doi:10.1016/j.marpolbul.2011.02.035

due to their release from rubbish and wastes (Breivik et al., 2002). As
a consequence, PCBs still constitute a worldwide environmental
problem, and the knowledge of their concentrations in the environment is needed to understand present contamination levels and
trends, to assess the risk, and to plan management strategies. In this
context, the assessment of sediment contamination is considered a
fundamental indicator of the overall health of the systems (e.g. Nhan
et al., 2001; Colombo et al., 2005; Kuzyk et al., 2005; Sundberg et al.,
2005; Denton et al., 2006).
The information about PCB sources and levels in Vietnam is limited. However, it is likely that environmental levels have been
exacerbated by the long periods of conflict and subsequent rapid
industrialization/economic development. Frignani et al. (2007)
described the PCB distribution in cores and surficial samples from
Tam Giang-Cau Hai (TG-CH) system, but nothing was known about
the contamination of the other coastal lagoons in Central Vietnam.
We aimed to fill this gap by assessing present PCB levels through
the analysis of surficial samples. Additionally, trends and controlling factors were examined at five selected sites (four lagoons)
through the study of sediment cores and the repeated sampling
of the same locations in different years.
2. Study sites
The studied lagoons are all located in the central part of the country, between 11°N and 16°N (Fig. 1), and belong to the coastal

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S. Giuliani et al. / Marine Pollution Bulletin 62 (2011) 1013–1024

provinces of Thua Thien Hué, Quang Nam, Quang Ngai, Binh Dinh,
Phu Yen, Khanh Hoa and Ninh Thuan. They are diverse in scale, shape,
size, stability of inlets, water features and geological and geomorphological distribution (Cu, 1995), and can be rated into four categories: very small (less than 10 km2, as Nuoc Man, NM, and Dam Nai,
DN), small (10–20 km2 as Lang Co, LC, Nuoc Ngot, NN, and O Loan,
OL), medium (20–50 km2 as Truong Giang, TG, and Thuy Trieu, here
referred to as Cam Ranh, CR), and large (more than 50 km2 as TG-CH,
and Thi Nai, TN). These valuable and diverse ecosystems, important
as tourist attractions and useful for fishing and aquaculture activities, are key sites for the development of the Vietnamese economy.
However, ongoing problems with anthropogenic pollution, such as
high concentrations of oil, nitrate and coliforms in water (Dieu,
2006; Thom, 2006) are believed to be deeply affecting the environmental quality of these sites over time. Although the concentrations
of persistent organic pollutants such as PCBs and PAHs (Frignani
et al., 2007; Giuliani et al., 2008) are believed to be low, these are also
expected to increase over time as economic development continues.
3. Materials and methods
Sampling locations in Central Vietnam coastal lagoons are shown
in Fig. 1. Sediment cores were sampled multiple times from 2002 to

2008, using a manual piston corer (6 cm i.d.) that preserved undisturbed sediment–water interfaces. Collection dates and core lengths
of the 2004–2008 samplings are reported in Table 1, in addition to
sampling details of the TG-CH cores collected in 2002 and already
described by Frignani et al. (2007). After collection, the cores were
extruded and sectioned at intervals of 1–4 cm, with higher resolution at the top. Sediment slabs, cleaned at the edges to avoid the
effects of smearing, were then put in polyethylene vessels and stored

in a refrigerator at 0 °C until arrival at the lab. Afterwards, they were
conserved at À18 °C until analysis.
Grain size analyses were carried out by wet sieving, to separate sands, after a pre-treatment with H2O2. Silt and clay fractions were determined with a X-ray Micrometric SediGraph.
Organic carbon (OC) content was obtained through a CHN analyser after elimination of carbonates by treatment with HCl in
a silver capsule.
210
Pb activities were determined through acid extraction and
alpha counting of the daughter 210Po spontaneously deposited onto
silver disks. 209Po was used as an internal standard to account for
methodological and counting efficiencies. 137Cs determinations
were obtained by gamma counting of dry samples in standard
vessels of suitable geometries. Radiotracer analyses were described
in detail by Bellucci et al. (2007).

Fig. 1. Sample locations in Central Vietnam coastal lagoons.


Table 1
Collection dates and results of the analysed parameters (core length, porosity,% content of fines, i.e. silt plus clay, 210Pb activity, total and fine-normalised PCB concentrations,% contribution of each PCB congener class, from 1 to 10 Cl
substitutes) for all surficial samples of the cores collected from 2002 and 2008.
Collection
date

Core length
(cm)

Porosity

Fines
(%)a

210
Pb
activity
(Bq kgÀ1)

PCBs
(lg
kgÀ1)

Norm
PCBs
(lg kgÀ1)

CB-1
(%)

CB-2
(%)

CB-3
(%)

CB-4
(%)

CB-5
(%)

CB-6

(%)

CB-7
(%)

CB-8
(%)

CB-9
(%)

CB-10
(%)

TG-CH 02

08/12/02
23/06/04
27/06/07
11/12/02
22/06/04
27/06/07
22/06/04
27/01/08
07/06/05
08/06/05
26/01/08
08/06/05
25/01/08
09/06/05

25/01/08
10/06/05
23/01/08
11/06/05
21/01/08
11/06/05
21/01/08

74
81
51
50
37
51
87
79
73
69
59
57
59
29
99
77
71
73
95
49
75

0.74
0.63
0.66
0.70
0.61
0.73
0.74
0.77
0.70
0.69
0.59
0.70
0.57
0.62
0.59
0.78
0.74
0.94
0.73
0.60
0.45

93
91
82
88
80
95
92
92

40
85
77
76
51
1.0b
40
96
96
81
54
1.0b
18

174
152
95
240
196
106
445
196
85
78
64
84
44
109
70
94

74
60
37
36
28

22.9
5.04
6.39
24.5
5.29
1.40
4.39
4.35
2.55
1.99
5.80
2.12
5.04
44.7
3.36
2.34
4.15
2.32
5.38
1.32
4.50

24.6
5.53

7.83
27.8
6.64
1.48
4.77
4.73
6.30
2.33
7.52
2.79
9.94
4470b
8.42
2.44
4.34c
2.86
9.91c
132b
25.4c

n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.

n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.

n.d
17
n.d
n.d
14
n.d
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.

n.d.
n.d.
n.d.

47
28
21
55
28
30
25
36
26
19
25
24
31
2.7
38
23
40
19
37
37
31

37
30
32
35

34
16
26
48
14
27
50
11
54
4.7
45
40
46
40
47
23
50

12
17
36
8.0
16
23
41
13
40
33
12
30

11
25
12
32
12
34
12
37
15

3.5
5.1
9.2
2.2
4.6
26
5.4
2.6
9.6
11
4.8
22
3.0
46
3.2
5.2
2.0
6.7
2.8
3.2

3.4

0.64
1.7
1.5
0.39
1.0
5.2
3.3
1.0
6.7
7.8
2.7
8.8
1.2
20
1.4
n.d.
n.d.
n.d.
1.5
n.d.
n.d.

n.d
n.d.
n.d
n.d
1.3
n.d

n.d.
n.d.
3.8
2.1
5.0
4.2
n.d.
2.0
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.

n.d
0.89
n.d
n.d
0.70
n.d
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.

n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.

n.d
0.58
n.d
n.d
0.51
n.d
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.

TG-CH 10

LC
TG
NM
NN
TN
OL
CR
DN

S. Giuliani et al. / Marine Pollution Bulletin 62 (2011) 1013–1024

Lagoon

n.d. = Not detected.
a
Grain sizes are calculated considering only the fraction <2 mm.
b
The sediment is entirely sandy; a silt plus clay value of 1% was assumed for normalisation.
c
Samples from OL, CR and DN contain 21.5%, 6.3% and 6.3% of shell fragments and small gravels, respectively; normalising with respect to the real content of fines would give PCB concentrations of 5.52, 10.6 and 27.1 lg kgÀ1.

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S. Giuliani et al. / Marine Pollution Bulletin 62 (2011) 1013–1024

PCBs were extracted from 1 to 3.5 ± 0.01 g of lyophilised sediment by means of a Pressurized Solvent Extractor (PSE oneÒ,
Applied Separations, LabService Analytica) using dichloromethane/acetone (1:1 v/v) in presence of anhydrous sodium sulphate,
diatomaceous earth and activated metallic copper. The clean-up
procedure was performed by means of a Power-PrepÒ System (Dioxin Prep, Fluid Management System, Inc., LabService Analytica)
using a column of neutral silica and elution with n-hexane and
then n-hexane/dichloromethane (1:1 v/v). PCBs were determined
by High Resolution Gas Chromatography-Low Resolution Mass
Spectrometry (HRGC-LRMS) with a Hewlett Packard Model 6890
Gas-chromatograph coupled with a Hewlett Packard model 5973
Mass Selective Detector (mass analyzer: quadrupole) according
to Moret et al. (2005). Analytical details are fully described in Moret et al. (2001) and Piazza et al. (2009). High-Resolution Mass Spectrometry (MAT 95 XP, Thermo Finnigan, Bremen, Germany) was
also used for the identification of PCB congeners. For the quantification, six 13C labelled PCBs (EC-4058 mixture, Cambridge Isotope
Laboratories, Andover, Massachusetts, USA) were added to the
samples as internal standards before extractions. 13C-PCB28 was
used for the quantification of 1-, 2- and 3-CB congeners, 13CPCB52 for 4-CBs, 13C-PCB101 for 5-CBs, 13C-PCB153 for 6-CBs,
13
C-PCB180 for 7- and 8-CBs, and 13C-PCB209 for 9-CBs and 10CB. Crude concentration values were corrected with congener-specific instrumental response factors obtained by measuring four PCB
standard solutions (C-CS01, C-CS02, C-CS03 and C-CS05 by AccuStandard, Inc., New Haven, USA), for a total of 122 congeners. Only
those peaks with heights equivalent to at least three times the
background value were considered for identification and subsequent quantification. GC–MS detection limits were 1 pg for all
congeners, whereas at 0.6 pg level, 80% of them were detectable.
Eighty-three chromatographic peaks, representing 101 PCBs congeners (14 as double and 2 as triple peaks), were detected: two 2CBs (PCBs 12 and 15), nine 3-CBs (PCBs 18, 17, 24 + 27, 16 + 32,
26, 25, 28 + 31, 20 + 33 and 22), 14 4-CBs (PCBs 45, 46, 52, 49,
47 + 48, 44, 42 + 59, 41 + 64 + 71, 40, 74, 70, 66, 56 + 60 and 77),
16 5-CBs (PCBs 93 + 95, 91, 92, 84 + 90 + 101, 99, 97, 87 + 115,
83, 85, 110, 82, 109, 119, 123, 118 and 105), 18 6-CBs (PCBs 136,
151, 135 + 144, 147, 149, 134, 131, 146, 153, 132, 141, 137,
138 + 164, 128 + 167, 156, 158, 129 and 157), 16 7-CBs (PCBs
179, 176, 187, 178, 183, 174, 185, 177, 171, 172, 173, 180, 193,
191, 170 + 190 and 189s), six 8-CBs (PCBs 196 + 203, 197, 201,

195, 194 and 205), one 9-CB (PCB 207) and PCB209 (the sole 10CB). All solvents used were pesticide grade (Labscan Ltd., Dublin,
Ireland). Accuracy was checked at the time of analysis using a certified standard sediment (NIST, Standard Reference Material
1941b). The observed concentrations fell within the 95% confidential intervals reported in the certificate of analysis. Reproducibility,
based on six analyses of the same certified standard, was 4% for the
sum of congeners, and between 0% and 9% for each individual
congener.
All surficial samples (0–1 cm) were analysed, together with selected samples from cores collected in 2004 and 2007 from TG-CH
Lagoon (just core 10 in 2004), in 2005 from TN and in 2008 from
LC, TN and OL. PCB concentrations of the TG-CH 2002 cores are
those reported in Frignani et al. (2007).

at CR, DN, and NN, probably linked to grain size variations (see
below).
Most surficial samples are fine grained (clayey silt or silty clay)
with sands prevailing only at TG, TN and DN (Table 1). When comparing the samples over time, a shift to a coarser composition is
observed at CR and NN, with a doubling in the contribution of sand
from 2005 to 2008, and the presence of shells and small gravels up
to 6.3% in 2008. The grain size composition remains unvaried at LC
and OL, while there is a decrease of the sandy fraction in the 2008
samples from TN and DN. The samples from TG-CH 10 showed an
increase in the sandy fraction from 2002 to 2004 and a subsequent
decrease to values finer than the original sample in the period
2004–2007 (Table 1).
Surficial 210Pb values range from a maximum of 445 Bq kgÀ1 (LC
in 2004) to a minimum of 28 Bq kgÀ1 (DN in 2008) and are consistently higher in the first samplings. A general decreasing trend is
observed from the northernmost locations (TG-CH and LC) towards
the south, likely linked to the natural enrichment of 238U, 210Pb
being one of its decay products, in the Thua Thien-Hué region
(where the two lagoons are located). The natural enrichment of
238

U is due to the presence of mineralised zircon sands from the
Quang Nam deposit near Hué (Kušnír, 2000).

4. Results

4.1.2. PCB concentrations and compositions
Total PCB concentrations in surficial samples from the 2002–
2008 campaigns are listed in Table 1 and range from 1.32 lg kgÀ1
(DN in 2005) to 44.7 lg kgÀ1 (TN in 2005). In general, values from
the most recent samples are higher that the previous ones (from 2
to 3 times, as observed at OL and DN, respectively) or roughly constant (LC). In contrast, TG-CH 02, TG-CH 10 and TN present total
PCB concentrations in the earlier samples (2002 and 2005, respectively) that are considerably higher than subsequent measurements
(up to 13 times in the case of TN). The decreasing trend continues at
TG-CH 10 from 2004 to 2007, while in the same period a slight increase (from 5.05 to 6.39, Table 1) is observed at TG-CH 02.
In order to compare surficial concentrations without the effects
of sediment grain size composition, PCB values were normalised to
the content of silt plus clay, thus determining what PCB concentrations would be expected if the sediments were entirely fine
grained (Table 1). This effect is minimal in the majority of samples
classified as clayey silt or silty clay but becomes more apparent
with the increasing content of sand. This is the case for TG in
2005 and NN, TN, TT and DN in 2008, and gets to its greatest extent
in TN and DN in 2005, where the normalisation enhances PCB concentrations up to two orders of magnitude due to the completely
sandy composition of the surficial sediments (Table 1).
The PCB homologue composition of 2002–2008 surficial
samples is reported in Table 1 as percent contribution to the total
concentration. In general, 3, 4 and 5-CBs together account for the
greatest portion of PCBs, averaging 91% and being less than 70%
in only two samples: the first, NN (0–1) from 2005, shows a significant contribution of 6-CBs, and a smaller content of 4-CBs,
whereas the other, TN (0–1) from 2005, has practically no 3 and
4-CBs and is composed almost exclusively of heavier 5, 6 and

7-CBs. As for the TG-CH cores, the 2002 samples contain almost
entirely 3, 4 and 5-CBs, whereas the later samples showed a slight
increasing presence of both lighter (2-CBs) and heavier (6, 7-CBs)
congeners. Additionally, in the 2004 TG-CH 10 core, some 8, 9,
and 10-CBs were detected.

4.1. Surficial samples

4.2. Sediment cores

4.1.1. Porosity, grain size and 210Pb
Porosity values of surficial samples collected in the period
2002–2008 range from 0.45 to 0.94 and remain quite constant
between repeated samplings. The highest differences are observed

4.2.1. Profiles of porosity, grain size and 210Pb
Results from cores collected in 2002 from TG-CH and in 2004–
2005 from the eight minor lagoons have been already described by
Frignani et al. (2007) and Giuliani et al. (2008), respectively.


S. Giuliani et al. / Marine Pollution Bulletin 62 (2011) 1013–1024

However, they are here briefly summarized in Fig. 2, together with
new data from the 2004, 2007 and 2008 campaigns.
Core sample porosity ranges from 0.51 (TG-CH 10 in 2004) to
0.78 (OL in 2005) and is generally higher at surface, follows a
decreasing trend in the intermediate layers, then remains quite

1017

constant down to the core bottom. TG-CH 02 in 2007 and TN in
2005 differ slightly from this pattern, in that they have deep sediment values that are higher than surface ones. In addition, porosities of TN in 2008 constantly increase with depth and the value
measured at surface is among the lowest. Despite these limited

Fig. 2. Depth distributions of porosity, contents of sand and fines, 210Pb and total PCBs in sediment cores collected from TG-CH, LC, TN and OL coastal lagoons during different
sampling campaigns (2002–2008). PCB homologue patterns at selected depths are also shown.


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S. Giuliani et al. / Marine Pollution Bulletin 62 (2011) 1013–1024

differences, in general profiles are quite similar between repeated
samplings.
The prevalence of fine sediments shown by surficial values (see
above) is also confirmed by core profiles: the sand content is significantly below 50% in most cores, with fine particles accounting for
more than 75% of the total. The sole exception is TN where both
samples have surface and subsurface sand percentages above
50%. Surface sediments have already been discussed in the relative
section (see above), but grain size profiles show that the sandy
fraction remains significant down to 20 and 30 cm depth (in the
2005 and 2008 core, respectively), below which the content of fine
grains is similar to those of the other lagoons.
210
Pb profiles follow semi-logaritmic downcore trends, with no
evidence of post-depositional reworking, such as bioturbation processes. Unsupported background values (i.e. those produced by
in situ decay of 226Ra) of ca. 25 Bq kgÀ1 are reached at variable
depths, from 5 cm (TN in 2008) to 30 cm (LC and TG-CH 02 in
2002). The use of 210Pb profiles for the determination of reliable

core chronologies is weakened in these environments because of
the absence of useful 137Cs signals (Giuliani et al., 2008).
4.2.2. Profiles of PCB concentrations and compositions
Sediment core values of total PCBs range from 0.367 lg kgÀ1
(TG-CH 10 in 2007 at 7 cm depth) to 44.7 lg kgÀ1 (TN in 2005 at
0.5 cm depth). Trends are quite constant or increase significantly
near surface (this is the case for TG-CH 02 and 10 in 2002 and
TN in 2005). As for TG-CH Lagoon, the 2002 values are generally
higher than the corresponding layers from the later campaigns.
Congener composition is variable not only between sites, but
also within core repetitions and along the same sedimentary record. While the 3, 4 and 5-CBs (with a minor contribution from
6-CB) account for the majority of PCBs as observed in surficial
samples, their relative importance differs between layers (Fig. 2).
The presence of other PCB congeners (i.e. 2-CBs and from 7 to
10-CBs) occurs only in TG-CH 02 and 10 in 2004. In general, the
comparison of repeated samples shows that OL remains constant

Fig. 3. Worldwide distribution of average PCB levels in surficial sediments compared to Central Vietnam coastal lagoons. Values are grouped into three major sections:
contaminated sites (Van Bavel et al., 1995; Camacho-Ibar and McEvoy, 1996; Sundberg et al., 2005), Coastal and industrial areas (Tolosa et al., 1997; Khim et al., 1999; Laane
et al., 1999; Müller et al., 1999; Nhan et al., 1999, 2001; Pettersen et al., 1999; Frignani et al., 2001; Lee et al., 2001; Ma et al., 2001; Santschi et al., 2001; Barakat et al., 2002;
Fillman et al., 2002; Bertolotto et al., 2004; Frignani et al., 2004; Saponizhnikova et al., 2004; Colombo et al., 2005; Kuzyk et al., 2005; Denton et al., 2006; Hung et al., 2006)
and Lagoons (Frignani et al., 2001, 2004; Konat and Kowalewska, 2001; Menone et al., 2001; Moret et al., 2001; Fillman et al., 2002; Secco et al., 2005). Maximum and
minimum range bar for Central Vietnam lagoons is also shown. International sediment quality guidelines are indicated as horizontal continuous (ERM) or dotted (ERL) lines.


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S. Giuliani et al. / Marine Pollution Bulletin 62 (2011) 1013–1024

from 2005 to 2008 (with the predominance of 4-CBs in both samplings), while LC and TN display a shift over time to lower Clsubstituted congeners (from 5 and 6-CBs to 4-CBs). A similar
temporal pattern can also be observed for TG-CH 10, where the
proportion of 3-CBs increases from 2002 to 2007. TG-CH 02 is completely different, with 3-CBs present only in 2002 and at depth in
2007. In this latter core, 5-CBs are predominant at the surface
and at 6–8 cm depth.

5. Discussion
5.1. PCBs in Vietnamese coastal lagoons and their potential threat to
the environment
The average surficial sediment concentration found in this
study (7.60 lg kgÀ1, considering all samples) is similar to those
of low impacted coastal and lagoon areas reported in the literature
for globally distributed environments (Fig. 3), and is up to three orders of magnitude lower than those observed in the most contaminated sites. The highest value measured in the TN Lagoon in 2005
(44.7 lg kgÀ1) is higher than the NOAA ERL guideline (22.7 lg kgÀ1
as reported by Burton, 2002; Fig. 3) but well below the upper level
of most sediment quality guidelines used around the world, above
which adverse effects to biota are expected (e.g., NOAA ERM guideline of 180 lg kgÀ1; Burton, 2002, Fig. 3). It therefore follows that
present PCB sediment concentrations of Central Vietnam coastal
lagoons do not constitute a threat to the environment. Even in case
of resuspension of deep sediment layers (which can happen during
dredging, floods, or storms), the risk of contamination is absent
since downcore PCB values, in most cases, are lower than at the
surface (Fig. 2). Nevertheless, increasing values found in some of
the minor lagoons by the repeated samplings (Table 1 and Fig. 2)
might be an indicator of enhanced recent human pressure that suggests the need for a monitoring plan to prevent the possible
dangerous worsening in the near future.
5.2. PCBs sources, transport mechanisms and natural degradation
processes
In order to evaluate the origin of the PCB patterns found in surficial samples from all sampling campaigns, the homologue composition was compared with that of the principal commercial
mixtures. Aroclor 1016, 1242, 1254, 1260 and 1268 were considered, and their compositions were normalized with respect to

the list of congeners found in samples. Autoscaled data were
processed by a cluster analysis (Ward’s method as aggregative

clustering, using the Euclidean distance as similarity measure),
and the results are shown in Fig. 4. Two main clusters, and a smaller one, are well distinguished, with each essentially containing
samples collected in the same period. Starting from the right of
Fig. 4, the first group (‘‘a’’, with the highest similarity) is composed
of all 2008 samples from the minor lagoons plus those from TG-GH
in 2002 and is not associated with any of the commercial Aroclor
mixtures (as defined by EPA, 2008) considered. The second group
(‘‘b’’, Fig. 4) is composed of the 2004–2005 samples of the minor
lagoons (with the exception of TN) and the 2007 repetitions at
TG-CH, with the predominance of 4- and 5-CBs, resembling Aroclor
1248 and 1254, respectively (EPA, 2008). Moreover, the 2004 samples collected from TG-CH define a smaller cluster (‘‘c’’, Fig. 4) not
strictly linked to any of the commercial mixtures that we considered. The finding that contemporary samples present similar PCB
compositions suggests a unique source type over the entire study
area which should be connectable to mobilisation processes from
land-based stocks, such as evaporation from products and contaminated soils, spills or leakages from landfills or incinerators, or improper disposal of equipments still containing PCBs. These
processes may be further enhanced in tropical and subtropical regions by the prevailing climatic conditions. These latter favour the
remobilisation and volatilisation of PCBs into the atmosphere
(Iwata et al., 1994) also from remote locations, as confirmed by
the fact that PCB fluxes through atmospheric currents are the largest reaching marine environments (Zarfl and Matthies, 2010). Indeed, the low PCB values in the studied sediments could imply
their atmospheric transport from very distant zone with respect
to more localised point sources, as happens, for example, in much
more polluted areas where local sources are predominant over
long-range atmospheric inputs (e.g. the Venice Lagoon;
Sommerfreund et al., 2010). However, the discrimination between
local and remote sources is impeded by the lack of information relative to the composition of PCB mixtures present over the territory.
In addition, the differences observed among repeated samples of
the same area are most likely linked to structural modifications

of PCB compositions due to post-depositional processes, instead
of a change in sources. Indeed, there is no evidence that could justify such source variation, with the exception of the TN Lagoon
where the 2005 surficial sample is by itself on the left side (‘‘d’’)
of Fig. 4 and is somewhat related to Aroclor 1260. This is not surprising since the TN-05 congener composition presents practically
no 3- or 4-CBs, as it is composed almost exclusively of the heavier
5-, 6-, and 7-CBs as in the above mentioned commercial mixture
(EPA, 2008). This particular sample is completely different from
the lower layers and the samples collected in 2008 at the same site,
with both groups resembling the general 3-, 4-, and 5-CB predom-

Ward`s method - Euclidean distances
20

Linkage Distance

15

10

5

b

a

d
1268
1260
TN-05
1242

1016
10-04
02-04
1254
10-07
NN-05
1248
CR-05
OL-05
DN-05
TG-05
NM-05
02-07
LC-04
NM-08
NN-08
DN-08
CR-08
LC-08
OL-08
TN-08
10-02
02-02

c
0

Fig. 4. Cluster analysis (Ward’s method as aggregative clustering, using the Euclidean distance) comparing the composition of PCBs in surficial samples from Central Vietnam
coastal lagoons with the most common Aroclor commercial mixtures. Main clusters (a–d) are indicated.

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S. Giuliani et al. / Marine Pollution Bulletin 62 (2011) 1013–1024

inant composition. Additionally, this sample shows the highest PCB
concentration of the entire dataset and is the only one in the sediment core composed entirely of sand (Table 1; Fig. 2). The presence of a relatively high PCB concentration in a completely sandy
sediment (not suited to interact with and store contaminants) is
very unusual. These evidences, together with the contemporary
observation of a different congener distribution, account for the effect of external point sources, most likely linked to the activities

carried out in the nearby Phuong Mai peninsula in the framework
of the Nhon Hoi Economic Zone (NEZ) development plan. Indeed,
the NEZ is a new urban centre (120 km2 wide) east of Quy Nhon
City in the Binh Dinh province where the TN Lagoon is located. It
was completed in 2010 and includes residential areas, an industrial
park (14 km2), a deep water port, and a resort (BDEZ, 2010). The
NEZ is connected to Quy Nhon’s city centre by the Thi Nai Bridge
that was under construction in 2005, just when the TN core was

Fig. 5. 210Pb activity-depth profiles from repeated samplings in the TG-CH, LC, TN and OL lagoons. Two subsequent campaigns are compared (2002–2004 and 2004–2007 for
TG-CH 02 and TG-CH-10, 2004–2008 for LC and 2005–2008 for TN and OL), the values of the older ones being corrected for 210Pb natural decay. Depths relative to one sample
are shifted downward (as specified in the relative legend) to provide a satisfying superposition of the two profiles. Grey areas identify the hypothesized thicknesses of
removed sediments.


1021

S. Giuliani et al. / Marine Pollution Bulletin 62 (2011) 1013–1024

5.3. Influence of natural and anthropogenic events as revealed by
repeated sedimentary sequences
The research strategy that combines the study of temporal records from cores and repeated sampling is suited for the identification of processes that control and modify the sedimentary
sequence and the presence of contaminants in the environment.
In this case we can rely on both records and can observe some
interesting features that could be in accordance with the effects
of natural and anthropogenic events.
An attentive look at 210Pb activity profiles of repeated cores
shows that trends are similar, just shifted slightly in depth (Fig. 2).
Under the assumption of constant 210Pb supply, the superposition
of the profiles becomes quite good when they are decay corrected
and transposed downward (Fig. 5). As an example, a highly significant linear relationship (R2 = 0.72; p < 0.01) was found at TG-CH
02 between 210Pb values of the 2002 and 2004 samplings. Highly significant correlations (R2 ranging from 0.79 to 0.90 with p < 0.01) can
be defined also for the other profiles in Fig. 5. On the one hand, this
accounts for the representativeness of the second and third samplings, lateral inhomogeneities of 210Pb depth profiles being absent
or unable to disguise the basic information. On the other hand, it
indicates that there are major changes over time, interesting especially the topmost sediments. For example, the 2004 210Pb profile
of TG-CH 02 almost ovelaps that obtained in 2002 (once corrected
for 210Pb natural decay during the period encompassed between
the two samplings) if it is shifted of about 7 cm downward. This results by comparing the intercept (a) and the angular coefficients (m)
of the equations (in the general form y = mx + a) representing the linear section of the profiles in Fig. 5 (Fig. 6): if m are similar, the lines
are almost parallel and the shift is given by the difference (7) between the intercepts (a): 19.6 and 12.6 cm for 2002 and 2004
210
Pb activity profiles, respectively (Fig. 6) This may imply that a sediment layer of at least 7 cm (when further sedimentation is not considered) has been removed from the site of core TG-CH 02 at some
point between 2002 and 2004, and was displaced elsewhere. Similar
conclusions can be drawn for the first two samples of the other lagoons, with varying thicknesses of the removed layer (from 3 cm
at TG-CH 10 to 8 cm at TN from 2005 to 2008, Fig. 5). As a further confirmation, the shifts in the second samples, attributed to sediment
losses, produce a certain superposition of observed trends when applied to other sedimentary parameters (i.e. porosity and grain size
composition Fig. 7), especially in the topmost sections. Some discrepancies can be noticed in sand profiles, in particular at TN, due

TG-CH 02
0

Bq kg
100

-1

200

300

0

5

depth (cm)

collected. As none of the analysed sediment layers of the core
collected in 2008 present either the PCB levels measured at the
surface or its congener composition in 2005 suggests a recent
recovery which can be attributed to both degradation and removal
processes (see the following section), or lateral inhomogeneity.
If the changes in PCB homologue profiles in surficial samples
can be explained based on sediment dynamics, it is then difficult
to explain the observed differences downcore. However, in most
cases the composition remains constant, or nearly constant,
throughout the core (e.g., LC, 2008; TG-CH 02, 2002; TG-CH 10,
2007; TN, 2008; OL 2008), but at certain places the PCB pattern
has changed over time. However, at some locations the PCB

composition is only slightly different (e.g., TG-CH 10, 2002), and
in almost all cases different sediment levels were analysed in cores
taken in different years.
As for the differences among repeated samplings of the other lagoons, the congener patterns define a general trend towards the
enrichment of lower Cl-substituted classes (3- and 4-CBs) in the
second samples (Table 1 and Fig. 2). The physical properties that
control the behaviour of PCBs in the environment favour the
mobility of the more volatile congeners, i.e. those with lower chlorination degree (Gevao et al., 1998), so that sediments from several
marine coastal locations generally present congener patterns in
which 5-, 6-, 7-, or 8-CBs contribute to a greater proportion to
the total (Khim et al., 1999). In spite of that, not only lighter congeners dominate in sediments of Vietnamese lagoons but their relevance also increases with time. This situation might not be so
unusual, as Piazza et al. (2008, 2009) also found that 3-, 4-, and
5-CB dominated patterns in Mexican and Moroccan aquatic sediments. Coastal marine settings may be different due to the use of
lower chlorinated PCB mixtures in these countries, or, most likely,
to easier long range transport and incorporation of less chlorinated
PCBs in these sediments. Indeed, PCB fractionation along horizontal gradients is driven by the atmospheric persistence of individual
congeners that is higher for the lighter, less chlorinated PCBs
(Schuster et al., 2010). Therefore the predominance of 3- and 4CBs in the studied sediments can be explained by the prevalence
of atmospheric-derived inputs from distant anthropogenic locations, following predominant wind directions. These blow from
southwest during the hot-rainy season (May–October) and from
northeast during the cold–dry season (November–April; Pham
et al., 2010), indicating the urbanized areas of Southern Vietnam
and South-western China as potential source areas for PCB
contamination.
Finally, biologically mediated degradation processes can also
modify the PCB composition under both aerobic and anaerobic
conditions. The former mineralises the pollutants to its constituent
elements (CO2 and Cl2), whereas the latter (occurring principally in
soils and sediments, as reported by Borja et al. (2005) removes
chlorine atoms from highly chlorinated PCBs (Lake et al., 1992;

Borja et al., 2005), namely the flanked ones followed by those in
meta positions (Karcher et al., 2007). In sewage sludges and under
strict methanogenic conditions, PCB removals have been estimated
as about 40% for all congeners, while strong aerating actions enhanced the removal of the lightest PCBs up to 100% (Patureau
and Trably, 2006). However, biotic PCB degradation may be slowed
down in natural environments due to binding of PCBs to sediment
surfaces (Strand, 1990) and is also strongly limited by PCB bioavailability (Patureau and Trably, 2006). In synthesis, anaerobic processes active in our sediment cores might have increased the
presence of lower chlorinated PCBs (3- and 4-CBs of the minor lagoons and 2-CBs in TG-CH in 2004) in the 2004–2008 samples,
while mineralisation might explain the disappearance of 2-CBs
from TG-CH sediments in 2007. However, a correct assessment of
the importance of these processes requires further dedicated
research.

10

y = -0.0826x + 12.60
R2 = 0.9853

y = -0.0637x + 19.60
R2 = 0.8166

15

decay corrected from 2002
20

measured in 2004

Fig. 6. Linear regression of the upper portion of 2002 and 2004 210Pb activity-depth
profiles at TG-CH 02. Assuming the similarity of the angular coefficients, the lines

almost superimpose themselves if they are shifted of 19.6–12.6 = 7 cm.


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S. Giuliani et al. / Marine Pollution Bulletin 62 (2011) 1013–1024

Fig. 7. Profiles of porosity and sand content modified according to the depth shifts shown in Fig. 5. As for TG-CH Lagoon, only the first two sampling campaigns (2002 and
2004) are considered here.


S. Giuliani et al. / Marine Pollution Bulletin 62 (2011) 1013–1024

to the significantly coarser grain size at surface, and at depth in the
other lagoons. Such differences might be determined by lateral inhomogeneities that affect sand content to a higher degree with respect
to 210Pb, but also by different analytical resolutions (e.g. just five levels were analysed for sand content at OL in 2005, whereas their number doubled in 2008). Additionally, the removal of surficial
sediments in TG-CH and TN would explain the consistent decrease
in PCBs observed from the first and second samplings (Fig. 2): a significant negative correlation (R2 = 0.3; p < 0.05) between total PCBs
and the clay content has been observed. The causes for such removal
can be natural (floods and typhoons) or anthropogenic (such as
dredging). The only evidence of heavy human impacts during those
periods can be found in TN Lagoon, with the above mentioned activities for the NEZ development plan, while natural events must be
used to explain changes in the other lagoons. For example, the
typhoon Nepartak struck over the Vietnamese coast in November
2003 (NMFC/JTWC, 2003), with maximum sustained winds of ca.
140 km hÀ1 (EO-NASA, 2003). Its impact over Central Vietnam was
presumably strong enough to cause the sediment losses found by
the comparison of TG-CH cores from 2002 to 2004. Other similar
events (like the typhoon Xangsane that hit Central Vietnam at the
end of September 2006 with maximum sustained winds ca.

230 km hÀ1; EORC-JAXA, 2010) may explain what was observed at
LC and OL in the following years.
The cores collected in the TG-CH Lagoon in the period 2004–
2007 do not indicate any evidence of the above mentioned sediment losses, on the contrary, a sedimentation rate of ca. 1 cm yÀ1
can be assumed (Fig. 5). However, it must be noted that the
210
Pb surficial signal appears to be diluted at both sites. Under
the assumption of constant 210Pb supply this would imply a higher
than usual sediment delivery to the lagoon, as can happen during
floods caused by heavy rains. Indeed, in the period between 2004
and 2007, the Thua Thien Hue province was hit repeatedly by
typhoons and tropical storms, causing destructive floods and the
erosion of approximately 70,000 m3 of soils and terrains from
dikes, reservoirs, and roads over the mainland (CCFSC, 2010).
6. Conclusions
The following conclusions can be drawn:
(1) Presently, PCB contamination in coastal lagoon sediments of
Central Vietnam appears not to be particularly worrisome.
Recent contamination increases, if any, can be attributed to
slightly higher fluxes from enhanced anthropogenic pressure. The relatively high PCB level in the coarse sediment
at the top of the TN core in 2005 was likely originated from
the use of contaminated sand during the development of the
Phuong Mai peninsula;
(2) The cluster analysis showed a strong similarity between
contemporary samples, thus suggesting the presence of a
unique source type (i.e. the mobilisation from stocks located
on land widespread over the entire study area that superimposes to the most likely higher contribution from remote
regions through the atmospheric transport);
(3) PCBs with 3, 4 and 5 chlorine atoms largely prevail in lagoon
samples, with few exceptions. This is a rather peculiar situation as lighter congeners are more mobile that higher ones.

Even if the role of microbial dechlorination cannot be
excluded in some cases, it is possible that the accumulation
of these PCBs is due to their preferential atmospheric long
distance transport;
(4) Results from repeated sampling suggest that the surficial
sediment was removed in a number of sites in the time
encompassed between the first and second samplings.
Particularly evident were the cases of both the TG-CH

1023

Lagoon (between 2002 and 2004) and the TN Lagoon
(between 2005 and 2008). In the first case the entire
contaminated surficial level was removed and probably
this surficial sediment erosion can be caused by major
typhoons.

Acknowledgements
Funds for this work were provided by the Italian Ministry of
Foreign Affairs – Directorate General for Cultural Cooperation
and Promotion (MAE-DGCCP), the Vietnamese Ministry of Science
and Technology (MOST) and the Italian scientific institutions
involved in the research, in the framework of a bilateral project.
We are greatly indebted with S. Csiszar, L. Melymuk, and
M. Robson for their help in language revision. This is contribution
No. 1711 from the Istituto di Scienze Marine, Bologna (Italy).
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