Trace elements in anadara spp (mollusca bivalva) collected along the coast of vietnam, with emphasis on regional differences and human health risk assessment

Fish Sci (2011) 77:1033–1043
DOI 10.1007/s12562-011-0410-3

Environment

ORIGINAL ARTICLE

Trace elements in Anadara spp. (Mollusca: Bivalva) collected
along the coast of Vietnam, with emphasis on regional differences
and human health risk assessment
Nguyen Phuc Cam Tu • Nguyen Ngoc Ha • Tetsuro Agusa
Tokutaka Ikemoto • Bui Cach Tuyen • Shinsuke Tanabe •
Ichiro Takeuchi

•

Received: 23 March 2011 / Accepted: 30 August 2011 / Published online: 4 October 2011
Ó The Japanese Society of Fisheries Science 2011

Abstract This study measured concentrations of 21 trace
elements in whole soft tissue of the blood cockle Anadara
spp., which is a common food for local people, collected
along the coast of Vietnam. Results showed that concentrations of As, Sr, Mo, Sn, and Pb in cockles collected from
Khanh Hoa Province in the Central Coastal Zone (CCZ)
had higher values than those from the other regions, while
cockles collected from the Mekong River Delta (MRD)
showed the highest concentrations of Hg. Regional differences in trace element concentrations of the cockle may be
due to differences in human activities, i.e., shipyards in the
CCZ and agriculture in the MRD. Trace element concentrations measured in the soft tissues of blood cockles
investigated here were within safe levels for human consumption following criteria by the European Commission
(EC) and the United States Food and Drug Agency, but

several specimens had Cd levels exceeding the EC

N. P. C. Tu Á T. Ikemoto Á I. Takeuchi (&)
Department of Life Environment Conservation,
Faculty of Agriculture, Ehime University,
Tarumi 3-5-7, Matsuyama, Ehime 790-8566, Japan
e-mail:
N. N. Ha Á T. Agusa Á S. Tanabe
Center for Marine Environmental Studies (CMES),
Ehime University, Bunkyo-cho 2-5, Matsuyama,
Ehime 790-8577, Japan
T. Agusa
Department of Legal Medicine, Faculty of Medicine,
Shimane University, Enya 89-1, Izumo,
Shimane 693-8501, Japan
B. C. Tuyen
Research Institute for Biotechnology and Environment (RIBE),
Nong Lam University, Thu Duc District,
Hochiminh City, Vietnam

guidelines of 1 lg/g wet weight. The estimated target
hazard quotients for trace elements via consuming bivalves
were \1, indicating that the cumulative noncarcinogenic
risk was completely insignificant. However, the estimated
target cancer risk values by assumed inorganic As concentrations seem to implicate consumption of these cockles
as posing potential human health concerns.
Keywords Blood cockle Á Anadara spp. Á Cadmium Á
Human health risk Á Trace elements Á Vietnam

Introduction

At present, nearly a quarter of Vietnam’s population lives
in the coastal provinces, and there is an increasing migration into this region where there are many large cities (e.g.,
Hochiminh City) in addition to coastal economic and
centralized industrial zones. These activities have created
increased pollution, most likely in hotspots such as the
major estuaries and the coastline, which receive different
kinds of wastes produced by inland industrial and population centers [1]. The aquaculture industry in Vietnam has
encountered serious issues in recent years, including poor
water quality, disease outbreaks, and food safety problems
in products for export and local consumption, particularly
from contaminated filter feeding bivalve mollusks [2].
Besides the lyrate hard clam Meretrix lyrata, the blood
cockle Anadara spp. (Mollusca: Bivalva: Arcidae) are
favored species of edible shellfish in Vietnam. Among the
blood cockle species, Anadara granosa is one of the most
popular cultured species in brackish-water areas, particularly in southern Vietnam, whereas A. nodifera is found
more in the northern and central coast [2]. These bivalves
are cultured mostly on muddy tidal flats. Cockles can also

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be cultured in nutrient-rich ponds and have a high capacity
for removing nutrient-derived primary production from
black tiger shrimp ponds between crops [2]. Because
Anadara spp. are filter feeding organisms, trace element
contaminants in the mudflats or shrimp pond beds tend to
accumulate in their tissues. These cockles may act as the

main environmental sink of trace elements and therefore
may be an effective bioindicator of coastal pollution. It is
well known that no single species of bivalve is present on
all coasts and, therefore, environmental monitoring programs often need to utilize multiple species. Studies
comparing trace element profiles from several taxa taken at
the same locations permit an assessment of the relative
bioavailabilities of trace elements to different species
[3, 4]. Thus, the different species studied in this work
would be proposed as sentinel biomonitors to assess the
contamination status by trace element in the coastal zone.
A number of studies on bivalve mollusks associated with
trace element pollution have been performed, but few
studies have been published related to Anadara spp. [5–7].
According to our previous study, concentrations of trace
elements in hard clam Meretrix spp. from the Vietnam
coast were typically high, particularly in samples collected
from the central coast, and estimation of cancer risk based
on As concentration indicated that hard clams pose a high
potential risk to local residents [8].
The objective of this study was to determine regional
differences in trace element concentrations of Anadara spp.
collected along Vietnam’s coastal waters. Furthermore, our
previously reported data on the hard clam Meretrix spp. [8]
were compared with the present study in order to clearly
understand the contamination status of trace elements in
Vietnamese coastal environment. The potential health risks
associated with consuming trace element levels in cockles
were also estimated.

Materials and methods

Sample collection and preparation
Anadara spp. were collected from extensive bivalve production areas or were purchased from small stalls near
culture sites along the coast of Vietnam between 2003 and
2007. Anadara granosa was taken from Hochiminh City
(HCMC), Ba Ria Vung Tau (BRVT), Long An (LA), and
Tien Giang (TG) Provinces in the South Key Economic
Zone (SKEZ), and from Ben Tre (BT), Tra Vinh (TV), Soc
Trang (ST), Bac Lieu (BL), Ca Mau (CM), and Kien Giang
(KG) Provinces in the Mekong River Delta (MRD).
Anadara nodifera was sampled in Khanh Hoa (KH)

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Fish Sci (2011) 77:1033–1043

Province in the Central Coastal Zone (CCZ) (Fig. 1). Both
species are likely to be found on intertidal and marginally
subtidal muddy substrates in areas where there is an estuarine influence and feed on a mixture of detritus (or
microorganisms attached to detritus) and benthic microalgae from the sediment [9]. Cockles were not purified
because we were interested in estimating human health
risks. Samples were frozen in plastic bags and transported
to Ehime University, Japan, and maintained in a freezer
below -20°C until dissection and trace element analysis
could take place.
Blood cockles from sampling sites (six individuals per
site) were cleansed of mud by washing thoroughly with
deionized water (Millipore, Milford, MA, USA). Cockles
were measured for shell length and whole body weight,
after which soft tissue was carefully removed using a clean
stainless steel scalpel blade, then dried at 80°C for 12 h, and

finally ground to a fine powder using a mortar and pestle in
preparation for analysis. Biometry and water content of
cockles are shown in Table 1. Trace element concentrations
in blood cockle tissue were measured based on dry weight
(wt) but were also converted to wet wt by use of the
respective conversion factors given in Table 1 to allow for
comparison with values from other studies and guidelines
and to estimate potential health risk on a wet wt basis.
Trace element analyses
We used previously described methods for analyzing trace
elements [8, 10, 11]. Briefly, dried soft tissue was digested
with concentrated nitric acid in a microwave system (Ethos
D, Milestone, Sorisole, BG, Italy). Mercury was determined using a cold vapor-atomic absorption spectrometer
(AAS) (AA680, Shimadzu, Kyoto, Japan; Model HG-3000
cold vapor system, Sanso, Tsukuba, Japan). The concentrations of 19 trace elements (V, Cr, Mn, Co, Cu, Zn, Rb,
Sr, Mo, Ag, Cd, In, Sn, Sb, Cs, Ba, Tl, Pb, and Bi) were
determined using an inductively coupled plasma-mass
spectrometer (HP-4500, Hewlett-Packard, Avondale, PA,
USA) with yttrium as an internal standard. For As analysis,
samples were digested with an acid mixture (HNO3:H2SO4:HClO4 = 1:1:2) and determined using a hydride
generation-AAS (HVG-1 hydride system, Shimadzu,
Kyoto, Japan). Accuracies of the methods were assessed
using a certified reference material DOLT-3 (National
Research Council of Canada) in triplicate, and recovery of
the elements ranged from 83 to 100% of the certified values. All data are expressed on a dry weight basis (lg/g dry
wt). Detection limits for most trace elements were
0.001 lg/g dry wt, except for As, Sb, and Cs (0.01 lg/g
dry wt), and Hg (0.05 lg/g dry wt).

Fish Sci (2011) 77:1033–1043

1035

Fig. 1 Map of sampling
locations for blood cockles
Anadara spp. For abbreviations,
refer to Table 1

Table 1 Biometry of the blood cockle Anadara spp. collected from the coast of Vietnam
Species

Region

Location

Anadara
granosa

SKEZ

HCMC

MRD

Anadara
nodifera

CCZ

Latitude

Longitude

Number

Whole
body
wt. (g)a

Shell
length
(mm)a

Water
content
(%)b

Can Gio,
Hochiminh City

10°23.2020 N

106°55.4460 E

6

15.5 ± 3.3

36.6 ± 2.3

85.2

6.84

BRVT

Tan Thanh, Ba
Ria Vung Tau

10°27.4130 N

107°05.4460 E

6

11.5 ± 0.8

34.0 ± 1.4

88.6

9.05

LA

Can Giuoc,
Long An

10°36.2160 N

106°40.2660 E

6

9.9 ± 0.5

31.5 ± 0.6

87.6

8.15

TG

Go Cong Dong,
Tien Giang

10°17.2770 N

106°46.4610 E

6

9.3 ± 0.3

29.8 ± 1.1

89.9

BT

Binh Dai, Ben Tre

10°11.1170 N

106°41.3750 E

6

19.3 ± 1.3

37.1 ± 0.6

83.7

6.17

TV

Duyen Hai,
Tra Vinh

09°37.5850 N

106°29.5410 E

6

11.8 ± 2.5

32.1 ± 1.4

87.8

8.43

ST

Vinh Chau,
Soc Trang

09°19.6300 N

105°58.8670 E

6

12.8 ± 1.2

32.7 ± 1.2

85.6

6.98

BL

Nha Mat, Bac Lieu

09°12.3390 N

105°44.3210 E

Conversion
factor
(dry:wet)b

10.0

6

9.0 ± 0.5

30.7 ± 1.5

86.5

7.45

CM

Ward 7 Market,
Ca Mau

09°10.376 N

105°08.5010 E

6

12.7 ± 1.5

34.0 ± 0.8

84.5

6.61

KG

Rach Soi,
Kien Giang

09°57.1580 N

105°07.1410 E

6

14.5 ± 1.5

34.4 ± 0.3

87.9

8.35

KH

Nha Phu Bay,
Khanh Hoa

12°20.5560 N

109°12.3360 E

6

14.1 ± 1.3

35.4 ± 0.5

84.0

6.62

a

Mean and standard deviation

b

Mean

0

Potential human health risk assessments
Noncarcinogenic effects were evaluated by comparing the
trace element exposure level over a specified time period

with a reference dose (RfD), otherwise known as the target
hazard quotient (THQ). A THQ value of \1 indicates that

exposures are not likely to be associated with adverse
noncarcinogenic effects. The sum of all THQ values for
multiple trace elements for a particular sampling site is
represented by the hazard index (HI) [12]. Likewise, target
cancer risk (TR) was estimated as the incremental probability of an individual developing cancer over a lifetime as

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a result of exposures to potential carcinogen (i.e., inorganic
As in the present study). This risk was calculated using
average lifetime exposure values that were multiplied by
the oral slope factor for inorganic As [12]. Estimation of
THQ and TR at each location followed the United State
Environmental Protection Agency (US EPA) Region 3
Risk-based Concentration (RBC) Table (US EPA Region
III website: />pdf/NOVEMBER_2010_FISH.pdf; accessed 09 Dec 2010).
The methodology for estimating THQ and TR is described
in detail by Tu et al. [8]. RfDs were obtained from the RBC
table, except for Cr, Rb, In, Cs, Hg, Pb, and Bi. Total Cr
was not available on the RBC table, the US EPA assumes
that the ratio of Cr(VI) to total Cr was 1:7 in fish tissue, and
offers the RfD for Cr(VI). Thus, we divided our total Cr
data by 7 to estimate the THQ for Cr. Because most Hg in
shellfish tissue is present primarily as methyl mercury

(MeHg) [12], the conservative assumption was made that
total Hg is present as MeHg as recommended by the US
EPA [12]. Lead was not listed on the RBC table; a provisional tolerable weekly intake of 25 lg/kg body wt/week
(equal to 3.57 lg/kg body wt/day) was used [13]. For
calculation of THQ and TR for inorganic As, we assumed
that inorganic As accounted for 10% of total As [14–16].
The bivalve consumption rate of 2.85 g/Vietnamese
person/day (FAO website: />DesktopDefault.aspx?PageID=368#ancor; accessed 04 Jan
2011) was used for these estimations.
Statistical analyses
One half of the value of the respective limit of detection
(LOD) was substituted for those values below the LOD and
used in statistical analysis and risk assessment. Statistical
analyses were performed using the SPSS version 15 for
Windows (SPSS, Chicago, IL, USA). All data were tested
for goodness-of-fit to a normal distribution with Kolmogorov-Smirnov’s one sample test. Because most of the
variables were not normally distributed, the data were
logarithmically transformed and subjected to parametric
statistics. Pearson correlation analyses were performed for
shell length and trace element concentrations to determine
size effects in blood cockles. Regional differences in trace
element concentrations in blood cockles were tested by
analysis of variance (ANOVA) or analysis of covariance
(ANCOVA) with shell length as the covariate wherever
practicable. Prior to the use of ANCOVA, assumption of
equality (homogeneity) of regression slopes of dependent
(trace element concentration)-covariate (shell length)
relationships was tested by fitting a model containing
covariate-by-factor interaction. If the homogeneity of
regression assumption was not rejected, ANCOVA was

applied to test differences between regions. To compare

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Fish Sci (2011) 77:1033–1043

regional differences of trace element concentrations
between blood cockles and hard clams, a two-independentsamples t test was used. A p value of \0.05 indicated
statistical significance.

Results
Trace element concentrations
Means and standard deviations of trace element concentrations of Anadara spp. samples are shown in Table 2.
Concentration of Zn was the highest among the trace elements analyzed, followed by Mn, Sr, As, Cu, Cd, and Rb.
The mean concentrations of Zn and Mn in Anadara spp.
ranged from 51.3 to 113 lg/g and from 11.3 to 63.9 lg/g
(Table 2), respectively. Moreover, the mean concentrations
of Cd and As were present at relatively high levels in the
tissues of blood cockles, ranging from 2.15 to 9.61 lg/g,
and from 3.5 to 26 lg/g, respectively (Table 2). Similar
mean concentrations of Cu (ranged from 5.37 to 9.89 lg/g),
Rb (ranged from 2.57 to 4.52 lg/g), and Sr (ranged from
21.0 to 40.7 lg/g) were observed in blood cockles from
the sampling locations (Table 2). The lowest concentration in cockle tissues was In (ranged from 0.001 to
0.005 lg/g).
For all the blood cockles analyzed, concentrations of Cr
(Pearson correlation, r = -0.28, p \ 0.05), Mn (r = -0.53,
p \ 0.001), Co (r = -0.47, p \ 0.001), Cu (r = -0.30,
p \ 0.05), Sr (r = -0.31, p \ 0.05), Cd (r = -0.27, p \
0.05), Sb (r = -0.41, p \ 0.001), Ba (r = -0.52,

p \ 0.001), and Hg (r = -0.34, p \ 0.01) were negatively
correlated with shell length, whereas no correlations were
found between concentrations of the others and shell length
(p [ 0.05).
Regional differences in trace element concentrations
For regional comparisons, the cockle sampling sites were
pooled into three regions: SKEZ, MRD, and CCZ. Because
of the significant correlations between shell length and
tissue concentration of Cr, Mn, Co, Cu, Sr, Cd, Sb, Ba, and
Hg, a comparison among regions was conducted using
ANCOVA with shell length as the covariate. In contrast,
ANOVA was used for assessment of variations between
regions for trace elements that had no significant relationship with shell length.
Results of regional differences in trace element concentrations with statistical significance are shown in Fig. 2.
Among analyzed trace elements, concentrations of As, Sr,
Mo, Sn, and Pb in cockles from the CCZ and Hg concentrations in cockles collected from the MRD were significantly higher than those from the other regions


Region
SKEZ

MRD

Location

V

Cr

Mn

Co

HCMC

0.19 ± 0.02

BRVT

0.52 ± 0.09

Cu

0.86 ± 0.40

15.9 ± 7.3

0.81 ± 0.14

1.5 ± 0.9

21.4 ± 6.3

1.3 ± 0.2

Zn

As

Rb

Sr

Mo

Ag

6.83 ± 1.08

82.5 ± 10.3

5.6 ± 0.6

3.32 ± 0.21

24.3 ± 1.9

0.664 ± 0.094

0.73 ± 0.44

7.26 ± 0.80

51.7 ± 2.8

12 ± 1

3.61 ± 0.61

38.3 ± 12.0

0.591 ± 0.077

0.051 ± 0.013

LA

0.81 ± 0.22

1.1 ± 0.3

63.9 ± 31.9

2.1 ± 0.3

5.37 ± 0.34

73.3 ± 7.3

5.4 ± 1.0

4.39 ± 0.36

31.8 ± 2.6

0.512 ± 0.079

0.087 ± 0.107

TG

0.48 ± 0.32

2.1 ± 1.1

36.8 ± 11.6

1.7 ± 0.2

9.55 ± 1.57

113 ± 10

8.2 ± 0.2

4.43 ± 0.66

35.2 ± 14.7

0.725 ± 0.050

1.4 ± 1.1

BT

0.44 ± 0.05

0.58 ± 0.10

29.1 ± 6.6

1.2 ± 0.1

6.87 ± 1.49

90.1 ± 16.4

3.5 ± 0.4

3.78 ± 0.36

21.0 ± 4.0

0.534 ± 0.052

0.19 ± 0.11

TV

0.43 ± 0.08

0.51 ± 0.03

30.3 ± 3.9

2.6 ± 0.8

8.96 ± 1.06

86.1 ± 14.3

4.9 ± 0.5

2.57 ± 0.28

29.1 ± 4.2

0.541 ± 0.054

0.11 ± 0.08
0.084 ± 0.034

ST

1.0 ± 1.6

1.3 ± 1.4

26.3 ± 13.0

1.1 ± 0.3

7.90 ± 0.30

81.7 ± 9.5

4.8 ± 0.5

3.65 ± 2.23

35.9 ± 5.4

0.621 ± 0.052

BL

0.41 ± 0.16

0.84 ± 0.26

56.5 ± 27.2

1.4 ± 0.3

9.89 ± 2.52

107 ± 10

7.0 ± 0.4

4.00 ± 0.34

30.7 ± 2.9

0.701 ± 0.087

0.99 ± 0.47

CM

0.73 ± 0.30

0.78 ± 0.33

33.1 ± 6.4

1.6 ± 0.5

5.97 ± 0.42

92.8 ± 20.2

3.7 ± 0.8

4.52 ± 0.63

21.8 ± 3.9

0.465 ± 0.053

0.085 ± 0.139

KG

0.43 ± 0.27

1.1 ± 0.3

27.5 ± 11.9

1.4 ± 0.4

8.73 ± 2.54

111 ± 11

7.0 ± 1.6

4.31 ± 0.48

26.0 ± 3.6

0.623 ± 0.044

0.64 ± 0.36

CCZ

KH

0.62 ± 0.21

0.85 ± 0.31

11.3 ± 3.8

0.77 ± 0.16

6.90 ± 1.34

96.6 ± 5.5

26 ± 5

3.93 ± 0.45

40.7 ± 6.7

1.59 ± 0.64

0.24 ± 0.32

Region

Location

Cd

In

SKEZ

MRD

CCZ

Sn

Sb

Cs

Ba

Hg

Tl

Pb

Fish Sci (2011) 77:1033–1043

Table 2 Trace element concentrations (mean ± standard deviation; lg/g dry wt) in the blood cockle Anadara spp. collected from the coast of Vietnam

Bi

HCMC

3.83 ± 0.26

0.003 ± 0.001

0.067 ± 0.010

0.02 ± 0.00

0.01 ± 0.00

0.72 ± 0.29

\0.05

0.004 ± 0.001

0.153 ± 0.019

0.011 ± 0.001

BRVT

2.68 ± 0.70

0.005 ± 0.002

0.068 ± 0.014

0.02 ± 0.00

0.03 ± 0.01

0.76 ± 0.31

\0.05

0.007 ± 0.002

0.208 ± 0.050

0.018 ± 0.003

LA

5.57 ± 1.15

0.005 ± 0.006

0.064 ± 0.025

0.02 ± 0.01

0.09 ± 0.03

3.0 ± 1.0

0.13 ± 0.04

0.012 ± 0.008

0.625 ± 0.139

0.118 ± 0.028

TG

8.19 ± 1.23

0.002 ± 0.000

0.028 ± 0.008

0.04 ± 0.01

0.05 ± 0.04

2.8 ± 1.6

0.13 ± 0.05

0.006 ± 0.003

0.509 ± 0.144

0.026 ± 0.002

BT

8.97 ± 0.78

0.001 ± 0.000

0.029 ± 0.013

0.02 ± 0.00

0.02 ± 0.00

1.4 ± 0.3

0.12 ± 0.04

0.006 ± 0.002

0.227 ± 0.034

0.024 ± 0.005
0.047 ± 0.005

TV

9.06 ± 1.00

0.002 ± 0.000

0.047 ± 0.020

0.03 ± 0.00

0.01 ± 0.01

1.9 ± 0.6

0.11 ± 0.02

0.003 ± 0.001

0.401 ± 0.077

ST

9.61 ± 1.63

0.003 ± 0.004

0.073 ± 0.050

0.04 ± 0.02

0.10 ± 0.19

4.4 ± 5.2

0.09 ± 0.01

0.009 ± 0.015

0.763 ± 0.501

0.021 ± 0.010

BL

7.12 ± 0.85

0.002 ± 0.001

0.033 ± 0.006

0.03 ± 0.01

0.03 ± 0.02

2.3 ± 0.6

0.11 ± 0.02

0.006 ± 0.002

0.422 ± 0.103

0.023 ± 0.002

CM

2.15 ± 0.60

0.003 ± 0.001

0.033 ± 0.009

0.02 ± 0.01

0.06 ± 0.04

1.4 ± 0.8

0.08 ± 0.04

0.005 ± 0.002

0.530 ± 0.230

0.064 ± 0.046

KG

7.67 ± 1.52

0.001 ± 0.000

0.219 ± 0.535

0.02 ± 0.01

0.04 ± 0.03

2.0 ± 1.1

0.11 ± 0.05

0.004 ± 0.002

0.500 ± 0.166

0.029 ± 0.011

KH

5.26 ± 1.91

0.004 ± 0.002

0.568 ± 0.471

0.02 ± 0.01

0.02 ± 0.01

0.80 ± 0.50

\0.05

0.005 ± 0.002

2.71 ± 0.73

0.055 ± 0.012

1037

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1038

Fig. 2 Regional differences in trace element concentrations in blood
cockle Anadara spp. All trace elements with significantly different
(p \ 0.05) concentrations between regions are represented in this

Fish Sci (2011) 77:1033–1043

figure. Data represent the mean and standard deviation of the trace
element concentrations (log transformed). *p \ 0.05, **p \ 0.01, and
***p \ 0.001. For abbreviations, refer to Table 1

(ANOVA or ANCOVA, p \ 0.05). Concentrations of Mn
and Co in the CCZ cockles, Zn in the SKEZ cockles, and In
in the MRD cockles were the lowest among regions
(p \ 0.05). Chromium levels in the SKEZ blood cockles
were greater than those in the MRD animals (p \ 0.001),
though neither zone was significantly different from the
CCZ measurement (p [ 0.05). Cadmium concentrations in
the SKEZ cockles were lower than those from the MRD
animals (p \ 0.01), but there were no significant differences between Cd values in cockles from the SKEZ and
CCZ, or between those values from the MRD and CCZ
(p [ 0.05). Barium concentration in the MRD cockles was
higher than those from the CCZ (p \ 0.05), but there were
no significant differences in Ba concentration between the
SKEZ and the other two regions (p [ 0.05). The concentration of V, Cu, Rb, Ag, Sb, Cs, Tl, and Bi did not differ
significantly among regions (p [ 0.05).
In comparison with our previous results for trace elements in hard clam Meretrix spp. [8], concentrations of Cr,
Mn, Cu, Mo, Ag, Cd, Sb, Hg, Pb, and Bi in the SKEZ
cockles, Mn, Zn, Mo, Ag, Cd, Sb, Hg, Pb, and Bi in the
MRD cockles, and As, Cd, Pb, and Bi in the CCZ cockles
were higher (two-independent-samples t test, p \ 0.05;
Fig. 3). In contrast, concentrations of Co, Sr, and Cs in the
SKEZ clams, Co, As, Sr, In, Cs, Ba, and Tl in the MRD
clams, and V, Co, Cu, Rb, Sr, Mo, Cs, Ba, and Tl in the
CCZ clams were elevated (p \ 0.05; Fig. 3).
Estimation of potential human health risk
As shown in Fig. 4 and represented by the THQ and HIs,

the noncarcinogenic risks associated with the consumption
of blood cockle were \1. Considering the composition of
the relative contribution to THQ by trace elements, the
highest risk contribution of trace elements for consumers is
from Cd (range of 20–55%), followed by Co (range of
14–49%) and inorganic As (range of 7–46%). The contribution of Cd to the HIs showed a high value for consumers

123

Fig. 3 Species-specific differences in trace element concentrations
between blood cockle Anadara spp. and hard clam Meretrix spp. [8].
Selected trace elements with significantly different (p \ 0.05) concentrations between two species in all three regions are represented in
this figure. Data represent the mean and standard deviation of the
trace element concentrations (log transformed). *p \ 0.05,
**p \ 0.01, and ***p \ 0.001. For abbreviations, refer to Table 1

from the MRD, particularly in ST (55%), while Co constituted the majority of the risk and contributed to nearly
half of the total HIs for CM consumers. The THQ for


Fish Sci (2011) 77:1033–1043

1039

Fig. 4 Mean hazard indices
(HIs) of individual trace
elements from consuming blood
cockle Anadara spp. collected
from different sites. For
abbreviations, refer to Table 1

inorganic As had a larger percentage contribution 46% of
HIs from KH in the CCZ.
Conversely, the target cancer risk estimates for inorganic As through consuming blood cockles from different
locations along the coast of Vietnam were higher than 10-6
(range of 4.8 9 10-6 to 3.3 9 10-5) (Fig. 5). The highest
risk for inorganic As was 3.3 9 10-5 for consumption of
cockles by KH residents in the CCZ.

Discussion
Trace element concentrations in blood cockle
Bivalves are often used as a measure of contamination in
estuarine waters because they usually accumulate high
concentrations of trace elements [17]. Among trace elements, Zn is an essential element that is present in all
organisms, and concentrations of Zn in tissues of several
bivalve species including scallops, clams, oysters, and
mussels are on the order of 100–1,000 lg/g, with little
variation among species [17]. Zinc is not limiting to normal
molluscan life processes in the marine environment and
filter-feeding mollusks accumulated the highest concentrations of Zn in soft tissues [17]. In the present study, the
mean concentrations of Zn in blood cockle differed slightly
among the sampling sites. These results showed that blood
cockle could regulate its soft tissue levels of Zn. Phillips
and Rainbow [4] reported that several bivalve species are
known to possess this ability.
In several studies, trends of decreasing trace element
concentrations with increasing shell length have been

Fig. 5 Mean estimated target cancer risks for assumed inorganic As
through consuming blood cockle Anadara spp. collected from

different sites. For abbreviations, refer to Table 1

reported and were attributed primarily to increased metabolic rates in smaller organisms, which corresponded to a
so-called growth dilution effect [8, 18–21]. Boyden [18]
reported similar size-concentration relationships for Cu,
Zn, and Pb in the limpet Patella vulgate collected from
Portishead, Severn Estuary. Joiris and Azokwu [20]
observed the same results with Cd and Pb in the West
African bloody cockle Anadara (Senilia) selinis collected
from Bonny River estuary in the Niger Delta area of
Nigeria. In a previous study of hard clams from Vietnam
[8], we also found an inverse relationship of decreasing

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concentrations of Zn, As, Mo, Sn, and Bi with increasing
shell size.
Regional differences in trace element concentrations
The estimated human population density of Khanh Hoa
Province (CCZ) is 220/km2, in contrast with 510/km2 and
428/km2 for the SKEZ and MRD, respectively (General
Statistics Office of Vietnam website: .
vn/default.aspx?tabid=387&idmid=3&ItemID=9865; accessed 21 Dec 2010), indicating that human activities in the
CCZ are lower than in the others. However, the blood
cockles in the CCZ showed the highest mean concentrations of As (26 lg/g), Sr (40.7 lg/g), Mo (1.59 lg/g), Sn
(0.568 lg/g), and Pb (2.71 lg/g). We observed similar
results in a previous study in which concentrations of As,

Mo, Sn, and Pb were highest in hard clam Meretrix spp.
collected from the CCZ [8]. These results suggest that
some point sources of trace element contamination are
present in the CCZ, in spite of the relatively lower human
activity. Contaminants likely originated from industrial
waste from large shipyards near the sampling site. As
compared to a more distant site, elevated levels of Cr, Cu,
Zn, Cd, and Pb were reported in water, sediment, and the
oyster Saccostrea cucullata collected from the vicinity of a
shipyard in Khanh Hoa Province [22]. The shipyard used
copper slag as a blasting abrasive for the removal of rust,
paint chips, and marine deposits on the surfaces of ship
hulls. The slag contained high levels of Cr (336 lg/g), Cu
(8,549 lg/g), Zn (7,275 lg/g), and Pb (113 lg/g) [22]. In
fact, the CCZ was reported as one of the hot spots for trace
element contamination in Vietnam [1].
In contrast, concentrations of Hg were found to be the
highest in the MRD cockles. Moreover, accumulated Cd
concentrations were greater in blood cockles from this
region, particularly sampling sites close to the mouth of the
Mekong River such as TV (9.06 lg/g) and ST (9.61 lg/g),
when compared with those in cockles collected from the
other sites. Our previous studies also reported relatively
high levels of Cd and Hg in the giant river prawn Macrobrachium rosenbergii and black tiger shrimp Penaeus
monodon, and Cd in the hard clam Meretrix lyrata collected from the MRD [8, 10, 11], suggesting that sources of
Hg and Cd contamination in the MRD may be agricultural
use of mineral fertilizers. As stated by the Agency for
Toxic Substances and Disease Registry (ATSDR), Hg is
released to cultivated soils through the direct application of
inorganic and organic fertilizers (e.g., sewage sludge and

compost), lime, and fungicides containing Hg (ATSDR
toxicological profile for mercury website: http://www.
atsdr.cdc.gov/ToxProfiles/tp46.pdf; accessed 25 May
2011). Furthermore, because of intensive crop cultivation
on alluvial soils, some soils in the MRD receive large

123

Fish Sci (2011) 77:1033–1043

amounts of fertilizer, particularly phosphates containing Cd
levels ranging from 0.02 to 2.76 mg/kg [23]. In addition,
the high accumulation of Cd in the MRD cockles may be
due to Cd bioavailability in the low salinity environment.
As mentioned above, salinity is a natural factor influencing
metal uptake, and it is well known that there is an increased
net uptake of Cd by bivalves at low salinities [19, 24–26].
According to Debenay and Luan [27], HCMC and its
surroundings were the most affected by marine waters,
whereas TV and its vicinity were exposed to the strongest
freshwater influence.
The species-specific variations between blood cockle
and hard clam could be due to differences in their habitats
and feeding habits. Blood cockles live on the muddy bottom in the intertidal zone and can be affected by freshwater, whereas hard clams occur in sand and/or muddy
sand flats in large estuarine areas with greater marine
influence [2, 28]. Several studies have been conducted to
evaluate the influence of salinity or sediment type on trace
element uptake in bivalve species. Sarkar et al. [29]
reported that a high organic carbon value together with
high clay concentration in sediment enhances elevated

concentration of Cd, Zn, and Hg by cockle Anadara
granosa from Jharkhali (India). Moreover, most studies
suggest an increased net uptake of Hg, Pb, and in particular
Cd by bivalves at lower salinities [19, 24, 25]. Furthermore, the assimilation efficiencies of Ag and Cd in
bivalves were higher from organic-rich sediments than
those from organic-poor sediments [30].
Comparison with published data and the guidelines
Our data were compared with measurements made elsewhere in Asia (Table 3). Chromium concentrations in
cockles from Vietnam were found to be similar to or higher
than those reported from Juru and Jejawi, Malaysia [5]. This
study shows that the average concentrations of Cu, Zn, and
Cd in Anadara spp. collected from Vietnam were comparable to or higher than those in this species from Perak and
Sabah, Malaysia, and from Zhejiang, China, but exceeded
the mean Cu, Zn, and Cd in cockles from Juru and Jejawi,
Malaysia [3, 5, 7]. Arsenic concentrations in Anadara spp.
found in the SKEZ and MRD were similar to those in
cockles from Juru and Jejawi, Malaysia [5]. However, As
levels in this species obtained from the CCZ were higher
than those in cockles from Juru and Jejawi, Malaysia [5].
Comparing the mean Pb concentrations in cockles found in
this work from the SKEZ and MRD with those from other
countries shows that the levels from Vietnam were comparable to those in cockles from Juru and Jejawi, Malaysia,
and from Zhejiang, China, yet lower than those in cockles
from Perak and Sabah, Malaysia [3, 5, 7, 31]. However, Pb
levels in this species obtained from the CCZ were higher


Fish Sci (2011) 77:1033–1043

1041

Table 3 Comparison of mean concentrations of trace elements (lg/g dry wt) in the blood cockle Anadara spp. with those from other Asian
countries and human consumption guidelines
Region

Species

Cr

Cu

Zn

SKEZ, Vietnam

Anadara granosa

1.4

7.25

80.2

MRD, Vietnam

A. granosa

0.85

8.05

94.8

CCZ, Vietnam

A. nodifera

0.85

6.90

96.6

Zhejiang, China

Tegillarca granosaa

1.61

5.56

Juru, Malaysia

A. granosab

0.17

0.19

0.22

2.67

0.17

0.19

0.20

2.69

nd

6.3
6.89

Jejawi, Malaysia
Perak, Malaysia
Sabah, Malaysia

A. granosa
A. granosa

As

Cd

Hg

References

0.374

This study

7.7

5.07

5.1

7.43

0.10

0.474

This study

5.26

\0.05

2.71

This study

2.42

\0.05

0.060

[3]

0.89

1.33

0.11

[5]

0.87

1.36

0.12

[5]

1.8
4.74

[6]
[31]
[32]

26

64
96.0

0.08

Pb

6.1
0.630

Vietnamese guidelineb

2.0

0.5

1.5

EC guidelineb

1.0

0.5

1.5

[33]

1.7

[34]

US FDA guidelineb

13

86

4

nd Not detected. For region abbreviations, see Table 1
a

Synonym of A. granosa

b

Based on wet wt

than those in cockles from Juru and Jejawi, Malaysia, and
from Zhejiang, China, which were comparable to those of
cockles from Perak and Sabah, Malaysia [3, 5, 7, 31]. The
concentrations of Hg reported in this work were lower than
those in blood cockles studied previously [3, 5].
The concentrations of most trace elements in Anadara
spp. were below the reference values for human consumption set by the European Commission (EC), the US
Food and Drug Agency (US FDA), and the Vietnamese
Ministry of Agriculture and Rural Development (MARD)
[32–34]. However, over 30% (21/66) of cockle samples
had Cd levels exceeding the EC guideline of 1 lg/g wet wt

(Fig. 6). In particular, most specimens from BT, TV, and
ST were above the EC limit (Fig. 6). Recently, the
sanitation monitoring program for the bivalve mollusk
production area in 2010 conducted by the National AgroForestry-Fisheries Quality Assurance Department, MARD
also found Cd concentrations in BT cockle ranging from
1.7 to 2.1 lg/g wet wt [35], exceeding the current Vietnamese safety guideline of 2 lg/g wet wt for bivalve
mollusks as set by the MARD [32]. Therefore, to wholly
meet the European Union (EU) requirements for an EUapproved better management production area, the authority
recommends that these aquaculture areas open for harvesting under the condition that the bivalves go through
purification (relaying) before consumption and proposes a
sampling frequency of once per week when harvesting is
being done [35].
Estimation of human health risks
In the present study, there were no estimated THQs and HIs
for all trace elements[1, suggesting that non-cancer health
effects from consuming blood cockles were insignificant.

Fig. 6 Comparison of Cd concentrations (lg/g wet wt) in blood
cockle Anadara spp. with European Commission (EC) guidelines for
human consumption [33]. For abbreviations, refer to Table 1

Concerning the relative contribution of each trace element
to THQs, the potential health risks of Cd were highest in
comparison to other trace elements investigated. Because
Cd is a cumulative toxin and has a very long half-life (from
several months up to several years) in the body, exposure
of children to even low amounts may have long-term
adverse consequences. The exposure to Cd is associated
with renal dysfunction, increased calciuria, osteoporosis,
and a risk of fractures (ATSDR toxicological profile for

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1042

cadmium website: />tp5.pdf; accessed 25 May 2011). Using the US EPA RfD
of 1 lg/kg/day for estimating noncarcinogenic risk associated with Cd, our results indicate that the consumption of
cockles at the current rate was not harmful to consumers.
Yet, Satarug and Moore [36] reported that Cd-linked bone
and kidney toxicities have been observed in people whose
dietary Cd intakes were well within 1 lg/kg/day limits.
Satarug et al. [37] believed that the recommended Cd
intake of 1 lg/kg/day was shown to be too high to ensure
that renal dysfunction does not occur as a result of dietary
Cd intake. As stated by Widmeyer and Bendell-Young
[38], there is little to no safety margin between Cd exposure in the normal diet and exposure that could produce
deleterious effects, particularly in persons consuming
bivalves on a regular basis. Cadmium toxicity via consuming bivalves should be considered, particularly for high
risk groups, including women with low iron stores, people
with renal impairment, smokers, children, and indigenous
people as suggested by Cheng and Gobas [39].
On the other hand, the TR values of inorganic As due to
consumption of this cockle indicated that human health risk
might be of concern. However, caution must be taken
because this estimation of risk was based on the assumptions
of the ratio of inorganic As to total As due to the lack of
information on the contamination status of As compounds in
Vietnamese bivalves. The assumption of 10% inorganic As
from the total As concentration has often been used to estimate health risk [14–16]. However, use of this ratio may have

overestimated the true risk levels for As exposure. For
example, in two studies from the same location for consumption of oyster Crassostrea gigas in Taiwan, Liu et al.
[40] measured the inorganic As fraction in oysters at 1.64%
of total As, and estimated TR nearly 10 times less than Han
et al. [14] who assumed 10% as inorganic As in this oyster
[41]. Clearly, more studies are needed regarding the concentration and speciation of As in bivalves and the biogeochemical cycling of As in aquatic environments of Vietnam.
Based on the results of this study, it may be concluded
that the significant differences in trace element concentrations in blood cockles Anadara spp. among regions may
be explained by differences in human activities, i.e., shipyards in the CCZ and agriculture in the MRD. It can also be
concluded that levels of Cd and As in blood cockles in
Vietnam may be a public health concern. Further research
on understanding the distribution and accumulation profiles
of potential toxic trace elements in different marine
organisms from these regions is clearly warranted. Also, it
is essential that ongoing environmental monitoring programs should be developed and implemented to ensure that
bivalves are grown from areas with acceptable levels of
chemical pollution.

123

Fish Sci (2011) 77:1033–1043
Acknowledgments We express our sincere thanks to Dr. Todd
Miller, Center for Marine Environmental Studies (CMES), Ehime
University, for critical review of the manuscript. This study was
partially supported by a grant from the Research Revolution 2002
(RR2002) of the Project for Sustainable Coexistence of Humans,
Nature, and the Earth (FY2002) from the Ministry of Education,
Culture, Sports, Science, and Technology (MEXT) of Japan, and
Global COE Program from MEXT. The Grants-in-Aid for Scientific
Research for Postdoctoral Fellows by the Japan Society for the Promotion of Science (No. 2109237 to NPCT, and No. 207871 to TA) are

also acknowledged.

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