DSpace at VNU: Historical profiles of trace element concentrations in Mangrove sediments from the Ba Lat Estuary, Red River, Vietnam

Water Air Soil Pollut (2012) 223:1315–1330
DOI 10.1007/s11270-011-0947-x

Historical Profiles of Trace Element Concentrations
in Mangrove Sediments from the Ba Lat Estuary,
Red River, Vietnam
Nguyen Tai Tue & Tran Dang Quy &
Atsuko Amano & Hideki Hamaoka &
Shinsuke Tanabe & Mai Trong Nhuan & Koji Omori

Received: 2 May 2011 / Accepted: 1 September 2011 / Published online: 15 September 2011
# Springer Science+Business Media B.V. 2011

Abstract Historical profiles of trace element concentrations were reconstructed from two mangrove
sediment cores collected within the Ba Lat Estuary
(BLE), Red River, Vietnam. Chronologies of sediment cores were determined by the 210Pb method,
which showed that each respective sediment core
from the south and north entrances of BLE provided a
record of sediment accumulation spanning approximately 100 and 60 years. The profiles of Pb, Zn, Cu,
Cr, V, Co, Sb, and Sn concentrations markedly
increased from the years of the 1920s–1950s, and
leveled out from 1950s–1980s, and then gradually
decreased from 1980s to present. The profiles of Cd
N. T. Tue (*) : H. Hamaoka : S. Tanabe : K. Omori
Center for Marine Environmental Studies,
Ehime University,
2-5 Bunkyo-cho,
Matsuyama, Japan
e-mail:
N. T. Tue
e-mail:

T. D. Quy : M. T. Nhuan
Faculty of Geology, Hanoi University of Science,
334 Nguyen Trai, Thanh Xuan,
Hanoi, Vietnam
A. Amano
Geological Survey of Japan, National Institute
of Advanced Industrial Science and Technology,
1-1-1 Higashi,
Tsukuba 305-8567, Japan

and Ag concentrations increased from 1920s–1940s,
and then decreased from 1940s to present. The profile
of Mo concentrations progressively increased from
1920s–1980s, then decreased to present. The Mn
concentrations failed to show a clear trend in both
sediment cores. Results from contamination factors,
Pearson’s correlation, and hierarchical cluster analysis
suggest that the trace elements were likely attributed
to discharge of untreated effluents from industry,
domestic sewage, as well as non-point sources.
Pollution Load Index (PLI) revealed levels higher
than other mangrove sediment studies, and the longterm variations in PLI matched significant socioeconomic shifts and population growth in Vietnam.
Geoaccumulation Index showed that mangrove sediments were moderately polluted by Pb and Ag, and
from unpolluted to moderately polluted by Zn, Cu,
and Sb. The concentrations of Pb, Zn, Cu, Cr, and Cd
exceeded the threshold effect levels and effect range low
concentrations of sediment quality guidelines, implying
that the sediments may be occasionally associated with
adverse biological effects to benthic organisms.
Keywords Historical profiles . Trace element .

Mangrove sediment . Ba Lat Estuary . Vietnam

1 Introduction
Mangrove ecosystems act as natural filters for retaining
sediments and pollutants that originate from land-


1316

derived materials and river outflows prior to entering the
ocean (Harbison 1986; Lacerda et al. 1991; Tam and
Wong 1995; Clark et al. 1998). The high density of
root systems and trees reduce tidal flows, which
preferentially accumulate suspended clay and silt
particles. As much as 80% of suspended sediments
can be retained within mangrove forests from
coastal waters during periods of spring tides
(Furukawa et al. 1997).
Mangrove sediments are generally homogeneous
in texture and rich in organic matter, therefore, they
act as effective sinks of pollutants, particularly in the
case of trace elements. As a result they have a high
capacity to retain trace elements from tidal and river
outflows. Trace elements can be retained within
mangrove sediments by mechanisms of direct adsorption, forming a complex with organic matter and
through the formation of insoluble sulfides (Clark et
al. 1998). Trace elements however are also very
reactive to geochemical conditions, where factors of
pH and salinity can influence their mobility within
mangrove sediments (Liang and Wong 2003). Thus,

trace elements have a high potential for release from
the sediment–water interface when any oxidizing
processes occur, such as in flooding or dredging
activities. From mangrove sediments, trace elements
can also move by being directly absorbed into plants
(MacFarlane et al. 2003) and benthic organisms (Saha
et al. 2006; Amin et al. 2009), subsequently transferring into higher trophic levels of local food webs
(Jara-Marini et al. 2009).
In recent decades, land-use changes have resulted
in high soil erosion rates and have increased pollutant
yields to coastal environments (Owen and Lee 2004),
and these pollutants can be subsequently retained in
estuarine mangrove ecosystems of the (sub)tropical
coastline. However, historical concentrations of trace
elements within mangrove ecosystems are poorly
known, especially in developing countries. Therefore,
study on the historical profiles of trace element
concentrations in mangrove sediments is important
for not only tracing anthropogenic disturbances to the
estuarine environment but also essential to sediment
quality assessment.
The Red River (RR) is the largest river in northern
Vietnam, draining a total area of 78,695 km2 (Le et al.
2007), with the Red River Delta (RRD) being one of
the largest deltas in Southeast Asia (Tanabe et al.
2003). The total human population of the RRD is

Water Air Soil Pollut (2012) 223:1315–1330

approximately 19.6×106 people (.

vn), which is the most populous region of Vietnam.
As a result, the RRD drains a very large area
consisting of high urban and industrial development,
trade villages, agriculture, and ventures in aquaculture. However, very little in terms of effluent
treatment occur within this vast and complex
system (Marcussen et al. 2008), with runoff from
urban, industrial, and agricultural activities being
directly discharged into surface-flowing channels
and rivers. The RRD has therefore been considered
as one of the top environmental hotspots of Vietnam
(), yet there still remains a
major deficiency of information on pollutant concentrations (e.g., trace elements) from the region (i.e.,
estuaries and coastal ecosystems).
The purpose of this study was to examine the
historical profiles of 12 trace element concentrations
(Pb, Zn, Cu, Cr, V, Mn, Cd, Co, Sb, Sn, Ag, and Mo)
in age-dated sediment cores, in order to understand
the temporal variations of these trace element concentrations, and to assess sediment quality of mangrove
ecosystems from the Ba Lat Estuary (BLE). Our results
provide information on trace element concentrations in
mangrove sediments in the context of anthropogenic
disturbances to the system, both during the past and in
forecasting future risk. This study presents the first
record of historical profiles of trace element concentrations in the mangrove ecosystems from the BLE. The
trace element concentrations reported in this work are
highly valuable as baselines for comparison in future
sediment quality studies.

2 Materials and Methods
2.1 Study Area

The BLE is the largest estuary of the RR system,
consisting of two major mangrove wetland sites
(Xuan Thuy National Park and Tien Hai Nature
Reserve; Fig. 1). The mangrove forests are dominated
by trees of Sonneratia caseolaris, Bruguiera gymnorhiza, Kandelia candel, Aegiceras corniculatum, and
Acanthus ilicifolius, which play important roles in the
filtering and containment of terrestrial-derived materials
and various pollutants, and act as a physical buffer
against erosion and surge from major storm events.
Moreover, the BLE is of great regional importance as a


Water Air Soil Pollut (2012) 223:1315–1330

1317

Fig. 1 Sampling sites
showing location of cores
R2 and R4 within mangrove
forests from the Ba Lat
Estuary, Vietnam

major breeding and stopover for migratory birds along
the East-Asian and Australian flyways, and locally as
essential habitat for a diversity of benthic organisms
and vertebrate animals and other wildlife.
The BLE is located within a distinct monsoon
climate zone with a rainy season from May to
October and a dry season from November to April.
The temperature and rainfall annually vary from 15.9

to 29°C and from 1,300 to 1,800 mm, respectively.
Tides at the BLE are diurnal with a mesotidal regime
and a tidal range from 2.5 m at spring tide to 0.5 m at
the neap tide. Waves approach the BLE from the
south in the rainy season and from the northeast in the
dry season.
2.2 Sample Collection and Storage
Sampling was conducted from 28 January to 10
February, 2008 during low tide from two dense
natural mangrove forests, one adjacent to the south
entrance (Xuan Thuy National Park, core R2) and one
to the north entrance (Tien Hai Nature Reserve, core
R4) of the BLE (Fig. 1). Cores R2 and R4 were

located in the high and low intertidal zone, respectively. Core R4 was located approximately 200 m
from a tidal creek. Cores were taken by hand corer
with a PVC inner tube (1.5 m in length and 10 cm in
diameter), with lengths of cores R2 and R4 being 68
and 75 cm, respectively. Immediately following
collection, cores were capped and stored in an upright
position and maintained cool. Cores were processed
within 12 h of collection by first removing the outer
layers (0.5 cm in thickness) and then slicing by a
plastic knife into 1 cm intervals. Sediment samples
were packed in labeled polyethylene bags for
further analysis. Sections of the sediment slices
were also placed in plastic cubes (1 cm3) for
porosity analysis. Samples were immediately stored
in iceboxes and transported to the laboratory where
they were frozen at −20°C until further processing

and analysis.
2.3 Analytical Methods
Sediment samples were dried at 60°C for 48 h in an
electric oven and subsequently pulverized using a


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Water Air Soil Pollut (2012) 223:1315–1330

mortar and pestle. For 210Pb analysis, approximately
20 g of the pulverized sample was sealed in a plastic
jar and equilibrated with 226Ra, 222Rn, and 214Pb for
30 days. Based on characteristics of the gamma peaks,
the activities of 210 Pb (46.5 KeV) and 214 Pb
(351.9 KeV) were measured using a Ge detector
(GXM25P, ORTEC Co.). 210Pb excess (210Pbex) was
calculated by subtracting 214Pb activity from 210Pb
activity. During the 210Pb analysis process, 137Cs
activity was simultaneously analyzed. However, the
137
Cs activities ranged from undetectable to very low
in sediment cores. Thus, 137Cs activities were not
used to confirm the chronologies of sediment cores.
Based on 210Pbex activities, the constant initial
concentration (CIC) model was used to calculate
sedimentation rates. The CIC model has been successfully applied in other studies of estuaries (e.g.,
Bonotto and de Lima 2006), intertidal mudflats
(e.g., Andersen et al. 2000), and mangrove ecosystems
(e.g., Sanders et al. 2010). Ages of sediment cores

were calculated with the assumption of a constant
sedimentation rate (Appleby and Oldfield 1978). For
the CIC model, the 210Pbex activity (Cx) at any
sediment layer (x) with age (t) is simply expressed as:
Cx ¼ Co»eÀlt ¼ Co»eÀlx=So ;

ð1Þ

in which Co presents the 210Pbex at the sediment–
water interface, 1 is the radioactive decay constant for
210
Pb (0.03114 year−1), and So is the sedimentation
rate at the sediment–water interface (cm year−1). From
Eq. 1, the sedimentation rate (So) was determined by
the slope of 210Pbex profiles using least squares
regression. However, a number of studies have shown
that the effect of compaction on sediment layers may
cause an incorrect depth (x) (e.g., Lu 2007). An
alternative method, which expresses 210Pbex as a
function of the cumulative weight of sediment
(w: g cm−2) removes the compaction effect (Lu
2007). The Eq. 1 can be rewritten as:
Cm ¼ Co»eÀlt ¼ Co»eÀlðw=rÞ ;

ð2Þ

where w is the cumulative dry weight (g cm−2) at the
sediment layer with bulk weight (m: g cm−3), r is the
sediment accumulation rate (g cm−2 year−1), Cm is
the 210Pbex at the sediment layer (m), and Co is the

210
Pbex at the sediment–water interface layer. From
Eq. 2, the sediment accumulation rate (r) was
determined by the slope of 210Pbex profiles using

least squares regression. The ages of sediments
(year) was calculated based on the equation:
t ¼ w=r:

ð3Þ

Finally, the 210Pb chronologies of both methods
were compared to derive the final chronologies. The
results of both methods were agreed, thus the
compaction effects did not show significantly in
the 210Pb chronologies in the both sediment cores.
Therefore, the results of sediment chronologies were
unique and reported by the least squares regression
from the Eq. 1.
Sediment grain size was measured by using a laser
diffraction particle size analyzer (SALD-2100, Shimadzu Co.) according to the procedure described by
Amano et al. (2006). Sediment grain size was assigned
to the median diameter based on the 8 scale (Md8). To
examine water content and porosity of sediment, the
wet sediment in a plastic cube (1 cm3) was weighed
and dried in an electric oven at 40°C until obtaining a
constant weight. The relative water content was
determined after drying. Sediment porosity was calculated based on a sediment density of 2.65 gcm−3, the
sample cube volume (1 cm3) and the bulk dry sediment
weight (Baskaran and Naidu 1995; Bonotto and de

Lima 2006).
For total organic carbon (TOC) analysis, a total of
3 g of pulverized sediment sample was placed in a
glass tube and approximately 4 ml of 2 N HCl was
added and thoroughly mixed using a vibrating mixer,
and then left at room temperature for 24 h to remove
carbonates. After acid treatment, the samples were
thoroughly rinsed with MILLI-Q water (Millipore),
and then dried at 60°C for 48 h in an electric oven.
Total organic carbon was analyzed with an element
analyzer CN corder Yanaco, MT-700. Hippuric acid
(C6H5CONHCH2COOH; for the CN coder, Co. Ltd
Kishida chemicals) was used as the certified reference
material for calibration of the organic carbon.
For trace element analysis, 0.2 g of pulverized
sample was treated in a microwave Teflon vessel with
an acid mixture (5 ml HNO3, and 1 ml HF). The
mixture was heated in a microwave system (Ethos D,
Milestone S.r.l., Sorisole, BG, Italy) with the following programs: 2, 3, 5, 5, 5, and 5 min under 250, 0,
250, 400, 500, and 400 W power, respectively; this
was followed by ventilation for 5 min. To remove HF,
digested sample solutions were evaporated by heat-


Water Air Soil Pollut (2012) 223:1315–1330

1319

ing. After digestion and cooling, the samples were
diluted with ultrapure MILLI-Q water to 50 ml for

further analysis. Concentrations of 12 trace elements
(Pb, Zn, Cu, Cr, V, Mn, Cd, Co, Sb, Sn, Ag, and Mo)
were analyzed with an inductively coupled plasmamass spectrometer (ICP-MS, HP-4,500, Avondale,
PA, USA) with rhodium as the internal standard.
Accuracy and precision of the methods were assessed
using the certified marine sediment reference material
PACS-2 (National Research Council Canada), and
recoveries of all the trace elements ranged from 89.3%
to 111.6% of the certified values (Table 1). In addition,
triplicate analyses were applied for each sediment
sample, and the concentrations of trace elements were
displayed by the average values. One half of the value
of the respective limits was substituted for those values
below the limit of detection.

3 Results and Discussion
3.1

210

Pbex Geochronology

The plots of 210Pbex and depth for both cores R2 and
R4 are shown in Fig. 2. The 210Pbex increased from
the core bottom to the depth of 11 and 18 cm, and
then decreased to surface sediments in cores R2 and
R4, respectively. The decrease in 210Pbex activities at
the surface sediments may have resulted from
perturbation processes (Farmer 1991). In mangrove
ecosystems of the BLE, there are high densities of

crabs and mollusks that can cause significant remixing of sediments (Smoak and Patchineelam 1999).
In addition, during operation of the hand corer, the
mechanical mixing and subsequent diffusion of 210Pb
may occur in the first layers of the sediment cores
(Bonotto and de Lima 2006). Thus, the 210Pbex
activities at these depths were not used in the least
squares regressions for calculating sedimentation rates
(Fig. 2). The results showed that the sedimentation
rate for core R2 was 0.78 cm year−1, suggesting core
R2 provided a record of sediment accumulation
spanning approximately 100 years. The sedimentation
rate for core R4 was 1.2 cm year−1, nearly twice that
of core R2, providing a record of sediment accumulation approximately 60 years. These sedimentation
rates were consistent with those of a previous study
(range 0.81 to 1.46 cm year−1) within mangrove
forests from the BLE (Van Santen et al. 2007). The
sedimentation rates were also confirmed from our
observation of a distinctive, very thin layer of bivalve
shells, and a fine sand layer from 29 to 30 cm of
depth in core R2, which was likely formed during a
major storm and flooding event that occurred in 1971
in the RRD (van Maren 2007). The chronologies of
the sediment cores therefore provided reliable histories of sediment accumulation in the mangrove
ecosystems of the BLE.

2.4 Statistical Analysis
The representative average concentrations of trace
elements were log transformed prior to statistical
analysis to meet assumptions of a normal distribution.
Pearson’s correlation was used to examine correlations among trace elements and sediment parameters

(TOC, porosity, and sediment grain size (Md8)).
Hierarchical cluster analysis is a multivariate technique, which is used to classify the variables into
categories based on their similarity. The objective of
the hierarchical cluster analysis is to find an optimal
grouping for which the variables with each cluster are
similar, but the clusters are dissimilar to each other.
Hierarchical cluster analysis was applied to the
representative mean concentrations of trace elements
and sedimentary parameters (TOC, porosity, and
Mdφ). The distance metric was based on the
Euclidean distance completed linkage method. All
statistical analyses were performed using a SPSS
statistical software package 17 (SPSS 17.0).

Table 1 Marine sediment reference material (PACS-2) for trace element values, analytical values, and recovery (n=16)
Elements

Pb

Zn

Cu

Cr

V

Mn

Cd

Co

Sb

Sn

Ag

Mo

Analytical value
(μg/g dry wt.)
PACS-2 reference
value (μg/g dry wt.)
Recovery (%)

187±9

393±18

323±13

81.0±4.0

140±6.0

417±20.0

2.35±0.21

12.0±0.6

12.5±0.5

21.3±0.6

1.28±0.12

6.06±0.60

183±8

364±23

310±12

90.7±4.6

133±5.0

440±19.0

2.11±0.15

11.5±0.3

11.3±2.6

19.8±2.5

1.22±0.14

5.43±0.28

102.19

107.97

104.19

89.31

105.26

94.77

111.37

104.35

110.62

107.58

105

111.6

The trace element concentrations are shown by the mean ± 1SD

1320

Water Air Soil Pollut (2012) 223:1315–1330

markedly increased from 0.23% to 2.65% between the
core bottom and 26 cm of depth. The TOC content
remained high to15 cm of depth, and then decreased
to 1.2% at the surface sediment.
For core R4, the Md8 decreased from 29.85 to
10.6 μm between the core bottom and 61 cm of depth.
The Md8 was then invariant from 61 cm of depth to
the surface sediment. The porosity showed a progressive increase from the bottom of core to the surface
sediment. The TOC content varied from 0.61% to
1.43%, with a mean of 0.93%. The TOC content
showed a progressive increase from core bottom to
surface sediment.
3.3 Historical Profiles of Trace Element
Concentrations

Fig. 2 Plots of 210Pbex activity with depth in the sediment
cores used to determine sedimentation rates in this study. Error
bars denote the standard error of mean 210Pbex. Shaded areas
indicate parts of the cores that were affected by perturbation
processes. Data from filled squares were therefore not
included in least squares regressions for calculating sedimentation rates (see text for detail). Top figure: Core R2, bottom
figure: Core R4

3.2 Sediment Characteristics

For both cores, the sediment characteristics were
homogeneous, muddy, and rich in organic matter.
The sediment colors changed from light olivinebrown to dark grayish brown, indicating the dominant
reducing conditions. Sediment grain sizes (Mdφ),
porosity, and TOC contents (%) of both cores R2 and
R4 are shown in Fig. 3. According to the Mdφ values,
the sediments of both cores R2 and R4 were mainly
composed of very fine grain sizes (<29.85 μm). For
core R2, the Mdφ varied from 4.6 to 13.2 μm, with a
mean of 6.2 μm. The Md8 was invariant from the
core bottom to 8 cm of depth, and it reached a
maximum value of 13.2 μm at 5.5 cm of depth, and
then decreased to 6.6 μm at the surface sediment. The
porosity increased from 0.5 to 0.7 between the core
bottom and 31 cm of depth, and was invariant to
15 cm of depth. The porosity subsequently decreased
to 0.6 at the surface sediment. The TOC content

The ranges of trace element concentrations (Pb,
Zn, Cu, Cr, V, Mn, Cd, Co, Sb, Sn, Ag, and Mo;
average ± SD, μg/g dry wt.) are summarized in
Tables 2 and 3. In order to understand levels of trace
element concentrations, a contamination factor (CF)
was calculated by the ratio of trace element concentration to the average in world shale (Hakanson
1980; Chatterjee et al. 2009). In the present study,
average values of trace element concentrations
in world shale were reported by Turekian and
Wedepohl (1961) (Table 2). According to the CF
scale proposed by Hakanson (1980), 12 trace
elements in both cores R2 and R4 were classified

into four groups of contamination factors. The
percentage of sediment samples in which trace
elements were observed in the group of values with
a low contamination factor (CF < 1) were 13% (Zn),
6% (Cu), 100% (Cr), 3% (Co), 29% (Cd), 39% (V),
19% (Mn), 100% (Mo), and 58% (Sn); in the group
with values of a moderate contamination factor (1 ≤
CF < 3) were 3% (Pb), 87% (Zn), 94% (Cu), 100%
(Sb), 97% (Co), 81% (Cd), 61% (V), 81% (Mn), 3%
(Ag), and 42% (Sn); in the group of values with a
considerable contamination factor (3 ≤ CF < 6) were
97% (Pb), and 87% (Ag); and in the group of values
with a high contamination factor (CF ≥ 6) contained
10% (Ag). In the RRD the major industrial sectors,
including mechanical, chemical, and textile industries have been initiated since 1950s. The industries
have discharge consistent with trace element-rich
(Pb, Cu, Zn, and Cd) sewage sludge and wastewater
which are commonly disposed untreated and to the


Water Air Soil Pollut (2012) 223:1315–1330

1321

Fig. 3 Sedimentary parameters for mangrove sediment
cores R2 (top) and R4
\(bottom) from the BLE,
Vietnam

local soil and water environments (Huong et al.

2007). In addition, Phuong et al. (2010) observed
high concentrations of trace elements (Pb, Cu, Zn) in
the top layers of rice paddy soils near smelting and
recycling Pb and Zn factories. Moreover, they also
showed that the intensive utilization of N-P-K
fertilizer in agriculture, which often includes Zn,
Cu, B, Mo, Co, and other trace elements, likely
attributed to the high trace element concentrations in
the soil environment. Subsequently, a substantial
quantity of these trace elements in the RRD
watershed can be annually transported from the
main waterway of the RR to coastal areas. The high
concentrations of trace elements (Ag, Pb, Zn, Cu, V,
Mn, Co, Cd, Sb, and Sn) in the mangrove sediments
can therefore most likely be attributed to the
discharge of untreated effluent from industrial activities (e.g., mechanical, chemical, zinc smelt, and steel
works), and drainage from agriculture in the RRD
(Huong et al. 2007; Phuong et al. 2010).
Because the variation in sediment grain size will
directly influence the levels of trace elements (Grant
and Middleton 1998), such as the finer sediment grain
sizes can provide greater reactive surface areas, and

generally contain higher trace element concentrations.
Therefore, the trace element concentrations should be
normalized to remove the effects of varying sediment
grain sizes. Thus, for some trace elements the
normalized trace element profiles will more accurately illustrate the effects of increased loading over time
(Grant and Middleton. 1998). In this study, the trace
element concentrations were normalized by calculating the ratios of trace element concentrations to

sediment grain sizes (Mdφ). The normalized trace
element profiles are shown in Fig. 4. The results
showed that concentrations of trace elements (Pb, Zn,
Cu, Cr, V, Co, Sb, and Sn) markedly increased
between years of 1920s and 1950s. The concentrations of these elements leveled out from 1950s to
1980s, after which concentrations decreased from
1980s to the present. The concentrations of Cd and
Ag increased from the 1920s to 1940s, after which
they decreased to the present. The Mo concentration
progressively increased from 1920s to 1980s, after
which it decreased to the present. The Mn concentration failed to show a clear trend in both sediment
cores R2 and R4. In this study, the marked increase in
trace element concentrations between 1920s and


2008

2001

1995

1989

1982

1976

1970

1963

1957

1950

1944

1937

1931

1925

1918

0–1

5–6

10–11

15–16

20–21

25–26

30–31

35–36

40–41

45–46

50–51

55–56

60–61

65–66

67–68

20

53.0±3.8

62.3±6.7

81.2±5.5

101.0±12.7

89.9±11.7

98.7±11.2

105.0±11.4

97.7±16.3

93.0±6.0

81.0±9.3

85.1±10.9

74.3±26.7

83.9±10.1

71.9±8.0

66.2±21.9

Pb

95

79.8±5.1

104.0±16.0

118.0±8.4

150.0±26.3

130.0±19.9

153.0±24.7

164.0±2.4

150.0±29.6

146.0±15.3

145.0±15.3

144.0±22.0

132.0±27.7

159.0±24.3

143.0±21.3

127.0±33.4

Zn

45

31.8±1.4

42.3±6.0

58.6±7.9

70.6±13.4

65.9±10.5

68.3±8.7

93.1±14.2

75.5±12.4

78.4±12.1

77.3±12.9

78.4±13.2

72.0±20.6

84.0±10.7

77.9±16.9

70.2±21.9

Cu

90

54±7.9

57±10

66±9.7

60±6.4

67±9.5

65±6.2

71±7.3

65±14

71±13

69±16

70±18

56±17

76±12

71±15

63±20

Cr

130

81±1.2

100±1.6

120±1.8

130±2.0

130±2.3

130±1.6

140±1.8

130±2.3

150±2.5

140±2.4

140±2.6

130±3.9

140±2.1

130±2.3

110±3.7

V

850

628±10.1

843±15.2

854±24.6

634±15.9

592±14.7

393±54.2

686±18.2

462±10.7

655±12.7

539±10.7

493±11.3

447±13.8

583±89.4

801±24.5

1,040±43.8

Mn

0.3

0.235±0.024

0.124±0.024

0.299±0.040

0.631±0.041

0.511±0.077

0.359±0.021

0.626±0.072

0.345±0.029

0.258±0.054

0.266±0.015

0.419±0.012

0.264±0.010

0.315±0.016

0.254±0.023

0.286±0.093

Cd

Average shale indicates the average concentrations of trace elements in world shale (Turekian and Wedepohl 1961)

Average shale

Year

Depth (cm)

19

13±1.6

15±2.2

17±2.1

17±3.0

17±2.9

17±2.0

20±0.7

18±2.3

18±2.4

17±2.7

18±2.9

16±4.9

18±2.2

18±3.0

16±5.1

Co

Table 2 Concentrations of trace elements (μg/g dry wt.) in core R2 from Xuan Thuy National Park of the BLE, Vietnam

1.5

1.95±0.33

2.23±0.20

2.71±0.13

3.56±0.80

3.22±0.38

3.47±0.28

3.46±0.18

3.54±0.63

3.23±0.24

3.70±0.16

3.86±0.10

3.43±0.86

3.72±0.36

3.56±0.45

2.83±0.78

Sb

6

3.62±0.18

4.32±0.62

5.92±0.59

6.01±0.33

6.17±0.76

5.93±0.05

6.88±0.47

7.18±0.98

6.47±0.60

5.72±0.59

6.61±1.00

5.50±0.68

7.12±0.18

6.05±0.86

5.32±0.79

Sn

0.07

0.28±0.12

0.19±0.04

0.22±0.16

0.27±0.15

0.47±0.16

0.26±0.08

0.36±0.07

0.25±0.07

0.27±0.02

0.28±0.07

0.31±0.10

0.28±0.09

0.32±0.11

0.32±0.11

0.27±0.93

Ag

2.6

0.82±0.50

0.56±0.08

0.85±0.12

1.37±0.79

1.12±0.20

1.28±0.15

1.43±0.18

1.68±0.06

1.60±0.22

1.48±0.33

1.61±0.13

1.18±0.43

1.50±0.31

1.12±0.08

0.91±0.29

Mo

1322
Water Air Soil Pollut (2012) 223:1315–1330


2008

2004

2000

1996

1991

1987

1983

1979

1975

1971

1966

1962

1958

1954

1950

1946

0–1

5–6

10–11

15–16

20–21

25–26

30–31

35–36

40–41

45–46

50–51

55–56

60–61

65–66

70–71

74–75

20

78.4±2.2

70.7±0.3

74.3±2.2

72.2±5.0

71.7±3.8

80.2±5.8

76.1±2.6

84.1±1.8

80.8±0.7

95.6±4.8

82.9±5.4

82.3±2.0

75.9±3.9

90.2±2.7

83.1±0.3

85.1±1.3

Pb

95

94.1±35.2

76.5±32.5

87.9±35.7

126.0±9.5

135.0±1.6

158.0±3.1

143.0±8.9

127.0±21.2

170.0±38.8

132.0±26.5

139.0±46.7

124.0±23.8

123.0±22.8

133.0±24.9

199.0±85.4

149.0±3.0

Zn

45

64.9±1.5

60.0±1.2

65.2±1.4

71.1±6.4

75.3±3.7

86.1±7.1

71.5±2.0

78.8±3.2

78.7±3.4

80.1±1.5

81.5±5.6

81.4±1.2

74.4±3.1

93.6±3.3

90.7±7.2

84.1±0.7

Cu

90

68±3.8

65±4.5

65±2.5

69±7.9

68±3.1

79±5.9

65±3.5

75±2.7

69±2.4

71±3.4

72±1.1

67±3.0

65±3.6

68±1.0

65±2.8

66±0.5

Cr

130

110±2.5

100±0.6

100±6.7

110±14

120±7.0

140±8.6

120±4.0

130±1.5

130±3.8

130±7.0

130±2.6

120±2.2

120±1.0

130±1.6

120±5.6

130±2.6

V

850

725±16.2

637±7.2

668±27.3

726±82.6

760±40.5

1180±21.2

777±32.4

870±2.0

842±16.7

1040±14.5

759±11.7

708±2.4

708±21.3

720±18.0

643±20.8

915±4.1

Mn

0.3

0.225±0.093

0.496±0.041

0.469±0.078

0.349±0.037

0.638±0.039

0.417±0.017

0.336±0.088

0.514±0.089

0.708±0.056

0.195±0.015

0.513±0.062

0.38±0.029

0.339±0.083

0.391±0.014

0.754±0.064

0.383±0.047

Cd

19

17±0.2

16±0.6

16±0.9

17±0.9

18±1.0

20±1.1

18±0.7

19±0.5

18±0.5

18±0.5

18±0.6

18±0.3

17±0.6

19±0.6

18±0.4

18±0.1

Co

Average Shale indicates the average concentrations of trace elements in world shale (Turekian and Wedepohl 1961)

Average shale

Year

Depth (cm)

Table 3 Concentrations of trace elements (μg/g dry wt.) in core R4 from Tien Hai Nature Reserve of the BLE, Vietnam

1.5

3.04±0.21

2.79±0.11

3.43±0.24

2.97±0.28

3.50±0.81

4.03±0.41

4.10±0.16

3.77±0.14

4.70±0.32

3.90±0.25

4.08±0.20

4.06±0.18

3.92±0.19

4.29±0.17

4.17±0.50

4.27±0.16

Sb

6

4.09±0.50

4.00±0.60

4.50±1.10

5.74±0.54

5.72±0.89

6.08±0.78

5.32±0.05

6.05±0.93

6.26±0.43

5.18±0.57

5.30±0.69

4.57±0.91

5.35±0.54

5.70±0.93

6.80±1.17

6.13±0.37

Sn

0.07

0.30±0.07

0.24±0.08

0.31±0.07

0.28±0.03

0.39±0.06

0.41±0.04

0.29±0.07

0.43±0.01

0.48±0.23

0.32±0.08

0.41±0.06

0.36±0.09

0.38±0.09

0.37±0.04

0.36±0.07

0.34±0.08

Ag

2.6

0.88±0.14

0.87±0.22

0.70±0.08

0.85±0.02

1.00±0.16

1.31±0.62

1.45±0.43

1.02±0.14

1.85±0.71

1.54±0.10

2.05±0.63

1.18±0.05

1.38±0.31

1.65±0.16

1.69±0.36

1.61±0.05

Mo

Water Air Soil Pollut (2012) 223:1315–1330
1323


1324

Water Air Soil Pollut (2012) 223:1315–1330

Fig. 4 Historical profiles of trace element concentrations (μg/g
dry wt.) in mangrove sediment cores from the BLE, Vietnam.
Filled and open circles denote cores R2 and R4, respectively.

The dotted line traces population growth of Vietnam
(×1,000,000 people) ()

1950s was likely in response to the rapid increase in
population in Vietnam (Fig. 4). Therefore, human

activities could be a major contributor of these trace
elements to the mangrove sediments. Moreover, the
decrease in trace element concentrations from the
1990s to present may partially be in response to
regulatory measures that have been implemented to
control municipal and industrial waste and pollution, including air quality in Vietnam (http://www.
nea.gov.vn), i.e., the banning of lead gasoline in
2001. Despite presence of the regulatory measures,
the concentrations of trace elements in the nearsurface sediments were declined due to simultaneous
disturbances by the biological mixing (e.g., crab
activities) and particularly during operation of the
hand corer.

and Mo) were positively and highly correlated with
each other, suggesting that the trace elements likely
originated from similar sources (Callaway et al.
1998). In the upper RR and throughout the RRD,
there are numerous centers of high-density urban and
industrial development. The correlation of these
trace elements, particularly Pb, Cu, Zn, Co, and Sn
likely reflected similar urban and industrial origins.
The high correlation of Pb and Cd likely occurred
from the manufacture of batteries (Huong et al.
2007) and combustion of coal (Bac and Hien 2009)
within the RRD. In addition, the significant correlations between Pb and Zn in both cores suggested that
these trace elements may have originated more from
atmospheric fallout (Bac and Hien 2009) or urban
and agriculture surface runoff (Brack and Stevens
2001). Silver (Ag) has been used in recent years as a
tracer of municipal effluents because of its low

abundance in the crust and the fact that there are
numerous anthropogenic sources (e.g., dentistry,
photoprocessing) which are often added to wastewater discharge (Feng et al. 1998; Hornberger et al.
1999). Therefore, the high significant correlations of

3.4 Inter-element Relationship
The correlation coefficients among the 12 trace
elements and sedimentary parameters (TOC, Mdφ,
and porosity) for both cores are shown in Table 4. As
seen, trace elements (Pb, Zn, Cu, Cr, V, Co, Sb, Sn,


Water Air Soil Pollut (2012) 223:1315–1330

1325

Table 4 Correlation matrices of inter-element in the mangrove sediment cores from BLE
Pb
Pb
Zn
Cu

Zn

Cu

Cr

Co

0.83

a

0.69

a

1.00
a

0.94

0.77

0.79

1.00

0.63

a
a

0.72

0.77

1.00

0.71

0.82a

0.94a

0.94a

0.82a

1.00

Cd

0.74

a

b

Sb

0.68a

0.91a

0.88a

0.66a

0.84a

Sn

0.80

a

a

a

0.80

a

a

0.72

a

0.62

b

0.73

a

0.80

a

Cr

Mo

a

a

b

0.80

0.59
0.88

a

0.78

0.73

0.75

a

0.89

a

0.69

a

0.71

a

0.90

a

0.91

−0.55

a

0.90

TOC

0.67a

0.53b

0.58

0.80

0.71

0.57

0.68

b
b

a

a

a

0.51

0.65

0.63a

0.91a 0.67a

b

b

0.51
0.83

a

0.84

a

0.90

a

−0.52

b

0.69a
0.63b

a

0.83a

0.70a

0.76a

1.00

0.53

0.60

0.66

0.52

0.70

1.00

0.72a

a

0.81

a

0.89

0.77

Mdφ

Porosity
0.50b

−0.69

a

0.71a

−0.71

a

0.61b

a

−0.55b

0.50

0.62a

b

b
b

1.00
0.84

a

−0.62

b

0.64b
−0.53

b

0.62b

Mn

0.62b 0.64a
1.00

0.75

0.54b 0.66a

TOC
Porosity

0.77

a

0.55b
a

V

0.59b

a

1.00

a

Mn
Mdφ

Ag

b

0.93

Ag
V

Mo

a

0.53
0.89

Sn

0.59b

a

Co

a

Sb

0.55b

0.7a

1.00

Cd

a

1.00

0.73a

0.82a

−0.73

a

0.54b

0.60

−0.61

b

0.78a

0.64a

−0.64a

0.55b

b

1.00
0.70a

b

0.62b

0.53b −0.70a

a

0.57

0.69a

0.67a

1.00
b

1.00
0.94a

−0.82a
1.00

Values of core R4 are in italic and bold italic
a

Pearson correlation significance at the 0.01 level (two-tailed)

b

Pearson correlation significance at the 0.05 level (two-tailed)

Ag with all trace elements (with the exception of Pb)
in core R4, suggests that local untreated urban and
industrial effluents have probably been a long-term
occurrence to the Tien Hai mangrove area (see Fig. 1).
The correlation analysis results showed that
trace elements were positively correlated with
TOC and porosity, and they were negatively
correlated with sediment grain size (Mdφ). This is

consistent with classical geochemical studies that
TOC acts as a trace element carrier (Harbison 1986;
Bernardello et al. 2006), and that the contaminant
concentrations usually show an inverse correlation
with sediment grain size (Grant and Middleton.
1998). In addition, the porosity of sediments
depends on several factors, including the grain size,
shape, degree of sorting, and degree of cementation.
Therefore, in this study, the positive correlation
between porosity and trace elements was likely to
vary with sediment grain size. Overall, given the
high levels of TOC and very fine sediment grain
size, it is likely that this was the main mechanism of
absorption of trace elements into mangrove sediments of the BLE.

Fig. 5 Hierarchical cluster analysis for cores R2 (top) and R4
(bottom) mangrove sediment cores from the BLE, Vietnam.
Distance metrics were based on the Euclidean distance
completed linkage method


1326

3.5 Hierarchical Cluster Analysis
Hierarchical cluster analysis resulted in three clusters of
trace elements for each core (Fig. 5). The first cluster
consisted of trace elements (Pb, Cu, Cr, Zn, V, and Mn).
These trace elements originated primarily from the
combustion of fossil fuels, such as from automobiles,
manufacture of glassware and ceramics, and erosion

from the watershed (Bac and Hien 2009, Callaway et al.
1998; Feng et al. 1998; Huong et al. 2007). The second
cluster of trace elements (Cd, Ag, Mo, and Sn) was
highly correlated with sediment porosity. As previously
discussed, porosity is strongly associated with sediment
grain size, which could affect trace element concentrations in mangrove sediments. The origins of trace
elements in this cluster were primarily derived from the
untreated effluents of the urban and industrial sources
(e.g., manufacture of batteries, and urban effluents) from
upper estuary (Feng et al. 1998). The third cluster of
trace elements (Sb and Co) closely correlated with TOC
and Mdφ. This pattern demonstrated that TOC and
Mdφ were important carriers of these trace elements to
mangrove sediments (Tam and Wong 2000). The
origins of these trace elements may be mainly derived
from metallurgical sources in the RRD.
3.6 Comparison of Trace Element Concentrations
in Mangrove Sediments of the BLE
with Other Studies
This study is the first to measure the trace element
concentrations in bulk mangrove sediments from the
BLE. To understand the status of trace element concentrations in mangrove sediments, the concentration levels
of selected trace elements were compared with other
studies in Vietnam and with mangrove and estuarine
sediments throughout the world (Table 5). The results
showed that the concentrations of Pb, Zn, Cu, Cr, and
Co were higher than those within mangrove sediments
of the Brisbane River (Mackey and Hodgkinson 1995),
Godavari Estuarine (Ray et al. 2006), Sunderban
(Chatterjee et al. 2009), and Mai Po marshes Nature

Reserve (Liang and Wong 2003) mangrove ecosystems,
and in the estuarine sediments of the Pearl River
Estuary (Ip et al. 2007). Moreover, the concentrations
of Pb, Cu, Cr, and Cd were generally 1.8–5.7 times
higher than those in sediments from the municipal Nha
Be and Sai Gon Rivers (Thuy et al. 2007), and Mekong
River Estuary (Cenci and Martin 2004). However, these

Water Air Soil Pollut (2012) 223:1315–1330

trace element concentrations were lower than those in
sediments from other more heavily polluted rivers (To
Lich and Kim Nguu Rivers) (Marcussen et al. 2008).
These comparisons indicated that trace element concentrations in the mangrove sediment cores from BLE
were relatively high and moderately contaminated,
likely as a result of expansive economic development
to the region and unregulated flow into the RR and
RRD over a period of decades.
3.7 Sediment Quality Assessment
In this study the Pollution Load Index (PLI) and
Geoaccumulation Index (Igeo) were used to assess
sediment quality, and two sets of sediment quality
guidelines (SQGs) were applied to assess the potential
ecotoxicological effects associated with the trace
element concentrations.
Tomlinson et al. (1980) proposed the PLI for
detecting environmental pollution levels, which permits comparisons of pollution levels between sites
and different times. The PLI is calculated by the Eq. 4
as follows:
PLI ¼

pffi
½nŠCF1»CF2»CF3»:::»CFn

ð4Þ

where CFn is the contamination factor of trace
element n.
For core R2, PLI values ranged from 0.76 to
\1.36. The PLI profile increased between the years
of 1920 to the 1950s, and peaked around the
1960s, and then decreased slightly from the 1960s
to present. For core R4, PLI values ranged from
1.13 to 1.67, the PLI profile markedly increased
between the years of 1940 to the 1960s, and then
the PLI profile showed invariance from the 1960s
to the present (Fig. 6). The present results showed
that the PLI values were high in comparison with
other mangrove sediment studies (i.e., Chatterjee et
al. 2009). It is striking that the long-term variations
in PLI corresponded well with socioeconomic shifts
and population growth of Vietnam (.
gov.vn; Fig. 6). The first stage of industrial development in Vietnam occurred during the 1950s to
1960s, which largely consisted of heavy industry in
the production of batteries, chemicals, and machinery (Huong et al. 2007). Therefore, the PLI values
increased between the years of 1920s and the 1950s,
reflecting an increase in population growth and


Water Air Soil Pollut (2012) 223:1315–1330

1327

Table 5 Comparison of trace element concentrations (μg/g dry wt.): range (average) in the mangrove sediment cores from the BLE
and other studies
Sites

Pb

Zn

Cu

Cr

Cd

Co

Ag

Methods of
extraction

52.95–105.12
(82.95)
70.72–95.62
(80.22)

79.85–164.47

(136.47)
76.53–199.44
(132.29)

31.79–93.07
(69.62)
60.04–93.59
(77.35)

53.65–75.59
(65.32)
64.94–78.73
(68.58)

0.12–0.63
(0.35)
0.20–0.75
(0.44)

12.72–19.76
(17.0)
15.66–2.18
(17.83)

0.19–0.47
(0.29)
0.24–0.48
(0.35)

HNO3 + HF

NA

NA

HCl + HNO3

The present study
Core R2
Core R4

HNO3 + HF

Vietnam’s coastal sediment
Nha Be River (municipal
2.59–28.6
68.5–256
channels, southern Vietnam)a
(14.5)
(137)
Sai Gon River (municipal
3.31–63.1 (23.8) 79.8–237 (157)
a
channels, southern Vietnam)
Mekong River Estuary
44
166
(sediment core)b

11.9–25.1

18.9–32.6
(16.8)
(26.6)
14.3–58.8 (31.6) 19.5–41.5
(28)
50
75

0.07–0.09
(0.08)
0.03–0.24
(0.1)
0.4

NA

NA

HCl + HNO3

NA

NA

HNO3 + HF +
HClO4

To Lich River (0–10 cm)
168±64
1240±779

(municipal
c
channels, northern Vietnam)
97.4±36.1
687±100
Kim Nguu River (0–10 cm)
(municipal
c
channels, northern Vietnam)
Mangrove sediments and coastal sediments elsewhere

97.2±31.2

179±67

427±306

11.3±0.8

NA

HNO3 + HF

128±22

157±40

2.1±0.9

10.2±0.9

NA

HNO3 + HF

Brisbane River mangrove,
Australiad
Godavari Estuarine mangrove,
Indiae

7.7–84.7

40.8–144

3.1–34.1

7.6–116.8

ND–2.0

NA

ND–2.8

HNO3 + HCl

16–95 (55.8)

NA

34–58 (47.8)

1.45–2.7 (2.2)

6–17 (10.9)

21–44 (28.8)

NA

HF + HCl +
HNO3

Sunderban mangrove, Indiaf

16.8–34.1

27.6–108

8.63–58.5

26.5–87.2

0.117–0.209 5.43–15.1

NA

HCl + HNO3 +
HF

Mai Po Marshes Nature
Reserve, Hong Kongh

17.1–90.7
(52±12.2)

55.6–328
(149±53.6)

18.8–86.6
(42.8±16.7)

10.5–46.1
(22.4±7.86)

NA

NA

HNO3 + H2SO4

16–96.3
(47.9±13.7)
Marine sediment quality guideline

55.1–268
(140±42)

6.2–100
(46.8±17)

33.8–135
(87.6±22)

ND–3.46
(1.05±
0.823)
NA

7.4–24
(14.6±3.4)

NA

HNO3 +HClO4

TEL (Threshold Effect Level)i

30.2

124

18.7

52.3

0.68

NA

0.73

PEL (Probable Effect Level)i

112

271

108

160

4.21

NA

1.77

ERLj

46.7

150

34

81

1.2

NA

1

ERMj

218

410

270

370

9.6

NA

3.7

Pearl River Estuary, Chinai

NA not available
a

Thuy et al. (2007)

b

Cenci and Martin (2004)

c

Marcussen et al. (2008)

d

Mackey and Hodgkinson (1995)

e

Ray et al. (2006)

f

Chatterjee et al. (2009)

g

Liang and Wong (2003)

h

Ip et al. (2007)

i

Macdonald et al. (1996)

j

Long et al. (1995)

relatively little industrial impact on the environment
(pre-1950s), whereas the highest PLI values probably reflected industrial expansion (post-1950s).
From 1960s to the present, the PLI values have
remained relatively high. This pattern could be
hypothesized that some trace element concentrations

have decreased due to the regulatory measures and
the perturbation processes (as shown in Fig. 4),
however, the PLI values have not decreased as stated.
The Igeo was proposed by Muller (1979), and has
since been used as a reference to study trace element
pollution in mangrove sediments (Praveena et al.


1328

Water Air Soil Pollut (2012) 223:1315–1330

Fig. 6 Pollution Load Index (PLI) for both sediment cores R2
(filled) and R4 (open) from the BLE, Vietnam. Dotted line
traces population growth of Vietnam ()

2008; Chatterjee et al. 2009); Igeo is calculated by the
Eq. 5 as follows:
Igeo ¼ log2

Cn

1:5Bn

ð5Þ

Where Cn is the measured concentration of examined element n in the sediment; Bn is the geochemical
background concentration of element n; and the
coefficient of 1.5 is the background matrix correction
factor due to lithogenic effect. In this study, the
geochemical background concentrations of trace elements were used from reported values for world shale
(Turekian and Wedepohl 1961). Based on Muller’s
(1979) Igeo scale, the Igeo values of 12 trace elements
in the present study were classified into three classes:
class 0 (unpolluted) consisted of elements Cr, Co, Cd,
V, Mn, Mo, and Sn, class 1 (from unpolluted to
moderately polluted) consisted of elements Cu, Zn, and
Sb, and class 2 (moderately polluted) consisted of
elements Pb and Ag. The high Igeo values of elements
Pb, Ag, Cu, Zn, and Sb in mangrove sediments from
the BLE inferred that the mangrove ecosystems have
been potentially impacted by the pollutants from
industrial sources (e.g., manufacture of batteries,
glassware and ceramics, plastics, rubber, and steel
works) and other non-point sources.
Sediment quality guidelines have been established
to provide a standard of known environmental quality
based on quantitative data to protect organisms from
adverse biological effects (Long et al. 1995; MacDonald
et al. 2000; Bjørgesæter and Gray 2008). Unfortunately,
the SQGs are unavailable for marine sediments of
Vietnam, therefore, two sets of SQGs consisting of the

threshold effect level (TEL) and probable effect level

(PEL) (MacDonald et al. 1996), and the effect range
low (ERL) and effect range median (ERM) (Long et al.
1995) were used to assess the ecotoxicological risks
from the selected trace elements in the mangrove
sediments (Table 5). The ratios of Pb, Zn, Cu, Cr, Cd,
and Ag concentration/TEL ranged 1.7–3.5, 0.6–1.3,
1.7–4.9, 1.0–1.4, 0.2–0.9, and 0.3–0.6 respectively, for
core R2; and 2.3–3.2, 0.6–1.6, 3.2–5.0, 1.2–1.5, 0.3–
1.1, and 0.3–0.7 respectively, for core R4. In addition,
the ratios of Pb, Zn, Cu, Cr, Cd, and Ag concentration/
ERL ranged 1.1–2.2, 0.5–1.1, 0.9–2.7, 0.7–0.9, 0.1–0.5,
and 0.2–0.5 for core R2 respectively; and 1.5–2.0,
0.5–1.3, 1.8–2.8, 0.8–0.97, 0.2–0.6, and 0.2–0.5
for core R4, respectively (Table 5). These comparisons illustrated that the Pb, Zn, Cu, and Cr
concentrations from both cores and Cd concentration from core R4 exceeded the TEL values. In
addition, the Pb, Zn, and Cu concentrations from
both cores exceed the ERL values. However, the
trace element concentrations were lower than the
PEL and ERM (Table 5). These patterns suggested
that the Pb, Zn, Cu, Cr, and Cd concentrations in
sediments may be occasionally associated with
adverse biological effects to aquatic organisms, in
particular to benthic organisms (MacDonald et al.
1996, Long et al. 1995). Therefore, a general conclusion can be inferred that mangrove sediments have
been significantly contaminated by selected trace
elements, which was predominantly due to anthropogenic sources.

4 Conclusions

This study presents the first record of historical profiles
of 12 trace element concentrations (Pb, Zn, Cu, Cr, V,
Mn, Cd, Co, Sb, Sn, Ag, and Mo) in the mangrove
sediments from the Ba Lat Estuary, Red River, Vietnam.
The chronologies of sediment cores were determined by
the 210Pbex method. Results showed that cores from
south and north entrances of the BLE provided records
of sediment accumulation spanning approximately 100
and 60 years, respectively. The historical profiles of
trace element concentrations were classified into four
groups: group 1 consisted of trace elements Pb, Zn,
Cu, Cr, V, Co, Sb, and Sn which markedly increased in
concentrations from the 1920s to the 1950s, and then
leveled out from the 1950s to 1980s, and decreased
from the 1980s to the present; group 2 consisted of Cd


Water Air Soil Pollut (2012) 223:1315–1330

and Ag which increased concentrations from the 1920s
to 1940s, and these concentrations decreased from the
1940s to the present; group 3 consisted of only Mo that
progressively increased from the 1920s to the 1980s,
then decreased from 1980s to the present; group 4
consisted of only Mn, the concentrations of which
failed to show a clear temporal trend in both sediment
cores. The PLI revealed levels higher than those
reported from other mangrove sediment studies, and
the long-term variations in PLI matched significant
socioeconomic shifts and population growth in Vietnam. The Igeo values demonstrated that mangrove

sediments were moderately polluted by the elements
Pb and Ag, and from unpolluted to moderately polluted
by elements Zn, Cu, and Sb. The mean concentrations
of trace elements Pb, Zn, Cu, Cr, and Cd exceeded
TEL and ERL values, suggesting that the sediments
may have occasionally been associated with adverse
biological effects to local aquatic organisms, in
particular to benthic organisms in mangrove ecosystems. Therefore, future studies should focus on the
assessment of trace element concentrations in
surface sediments and bioaccumulation of these
trace elements in benthic organisms, as well as
higher trophic level organisms from the mangrove
ecosystems of the BLE. The results from this study
indicated that mangrove sediment cores can be an
alternative approach to monitoring environmental
change in developing countries such as Vietnam
that usually lack such data.
Acknowledgments The authors are grateful to the staff of
Xuan Thuy National Park, Vietnam for their help with
sampling. We express our sincere thanks to Dr. Todd W. Miller
and anonymous reviewers for their critical reviews and comments which significantly improved this manuscript. This work
was supported by the “Global COE Program” from the Ministry
of Education, Culture, Sports, Science, and Technology, Japan.

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